diff --git a/.github/workflows/annocheck.yml b/.github/workflows/annocheck.yml
index bc5b81a9b99b2c..f3f496c29ac593 100644
--- a/.github/workflows/annocheck.yml
+++ b/.github/workflows/annocheck.yml
@@ -74,7 +74,7 @@ jobs:
           builddir: build
           makeup: true
 
-      - uses: ruby/setup-ruby@5f19ec79cedfadb78ab837f95b87734d0003c899 # v1.173.0
+      - uses: ruby/setup-ruby@6bd3d993c602f6b675728ebaecb2b569ff86e99b # v1.174.0
         with:
           ruby-version: '3.0'
           bundler: none
diff --git a/.github/workflows/baseruby.yml b/.github/workflows/baseruby.yml
index 2bc1e39e0c807a..50ff7014fff342 100644
--- a/.github/workflows/baseruby.yml
+++ b/.github/workflows/baseruby.yml
@@ -51,7 +51,7 @@ jobs:
           - ruby-3.3
 
     steps:
-      - uses: ruby/setup-ruby@5f19ec79cedfadb78ab837f95b87734d0003c899 # v1.173.0
+      - uses: ruby/setup-ruby@6bd3d993c602f6b675728ebaecb2b569ff86e99b # v1.174.0
         with:
           ruby-version: ${{ matrix.ruby }}
           bundler: none
diff --git a/.github/workflows/check_dependencies.yml b/.github/workflows/check_dependencies.yml
index 5187138be97c8e..a5e491d7a44cec 100644
--- a/.github/workflows/check_dependencies.yml
+++ b/.github/workflows/check_dependencies.yml
@@ -55,7 +55,7 @@ jobs:
 
       - uses: ./.github/actions/setup/directories
 
-      - uses: ruby/setup-ruby@5f19ec79cedfadb78ab837f95b87734d0003c899 # v1.173.0
+      - uses: ruby/setup-ruby@6bd3d993c602f6b675728ebaecb2b569ff86e99b # v1.174.0
         with:
           ruby-version: '3.0'
           bundler: none
diff --git a/.github/workflows/codeql-analysis.yml b/.github/workflows/codeql-analysis.yml
index 38148d4f667ce6..f0dab96550c7ac 100644
--- a/.github/workflows/codeql-analysis.yml
+++ b/.github/workflows/codeql-analysis.yml
@@ -80,15 +80,15 @@ jobs:
         run: sudo rm /usr/lib/ruby/vendor_ruby/rubygems/defaults/operating_system.rb
 
       - name: Initialize CodeQL
-        uses: github/codeql-action/init@4355270be187e1b672a7a1c7c7bae5afdc1ab94a # v3.24.10
+        uses: github/codeql-action/init@df5a14dc28094dc936e103b37d749c6628682b60 # v3.25.0
         with:
           languages: ${{ matrix.language }}
 
       - name: Autobuild
-        uses: github/codeql-action/autobuild@4355270be187e1b672a7a1c7c7bae5afdc1ab94a # v3.24.10
+        uses: github/codeql-action/autobuild@df5a14dc28094dc936e103b37d749c6628682b60 # v3.25.0
 
       - name: Perform CodeQL Analysis
-        uses: github/codeql-action/analyze@4355270be187e1b672a7a1c7c7bae5afdc1ab94a # v3.24.10
+        uses: github/codeql-action/analyze@df5a14dc28094dc936e103b37d749c6628682b60 # v3.25.0
         with:
           category: '/language:${{ matrix.language }}'
           upload: False
@@ -118,7 +118,7 @@ jobs:
         continue-on-error: true
 
       - name: Upload SARIF
-        uses: github/codeql-action/upload-sarif@4355270be187e1b672a7a1c7c7bae5afdc1ab94a # v3.24.10
+        uses: github/codeql-action/upload-sarif@df5a14dc28094dc936e103b37d749c6628682b60 # v3.25.0
         with:
           sarif_file: sarif-results/${{ matrix.language }}.sarif
         continue-on-error: true
diff --git a/.github/workflows/mingw.yml b/.github/workflows/mingw.yml
index 1ed83de53521a3..d8c075fc7a64ab 100644
--- a/.github/workflows/mingw.yml
+++ b/.github/workflows/mingw.yml
@@ -66,7 +66,7 @@ jobs:
 
     steps:
       - name: Set up Ruby & MSYS2
-        uses: ruby/setup-ruby@5f19ec79cedfadb78ab837f95b87734d0003c899 # v1.173.0
+        uses: ruby/setup-ruby@6bd3d993c602f6b675728ebaecb2b569ff86e99b # v1.174.0
         with:
           ruby-version: ${{ matrix.baseruby }}
 
diff --git a/.github/workflows/rjit-bindgen.yml b/.github/workflows/rjit-bindgen.yml
index 65f7b080a3d678..b77d79e83ab2e4 100644
--- a/.github/workflows/rjit-bindgen.yml
+++ b/.github/workflows/rjit-bindgen.yml
@@ -47,7 +47,7 @@ jobs:
 
     steps:
       - name: Set up Ruby
-        uses: ruby/setup-ruby@5f19ec79cedfadb78ab837f95b87734d0003c899 # v1.173.0
+        uses: ruby/setup-ruby@6bd3d993c602f6b675728ebaecb2b569ff86e99b # v1.174.0
         with:
           ruby-version: '3.1'
 
diff --git a/.github/workflows/scorecards.yml b/.github/workflows/scorecards.yml
index 69b31e6b698783..99f85235ad6f04 100644
--- a/.github/workflows/scorecards.yml
+++ b/.github/workflows/scorecards.yml
@@ -67,6 +67,6 @@ jobs:
 
       # Upload the results to GitHub's code scanning dashboard.
       - name: 'Upload to code-scanning'
-        uses: github/codeql-action/upload-sarif@4355270be187e1b672a7a1c7c7bae5afdc1ab94a # v2.1.27
+        uses: github/codeql-action/upload-sarif@df5a14dc28094dc936e103b37d749c6628682b60 # v2.1.27
         with:
           sarif_file: results.sarif
diff --git a/.github/workflows/spec_guards.yml b/.github/workflows/spec_guards.yml
index f4d8c378373eb0..bb4bf8441f85e5 100644
--- a/.github/workflows/spec_guards.yml
+++ b/.github/workflows/spec_guards.yml
@@ -47,7 +47,7 @@ jobs:
     steps:
       - uses: actions/checkout@9bb56186c3b09b4f86b1c65136769dd318469633 # v4.1.2
 
-      - uses: ruby/setup-ruby@5f19ec79cedfadb78ab837f95b87734d0003c899 # v1.173.0
+      - uses: ruby/setup-ruby@6bd3d993c602f6b675728ebaecb2b569ff86e99b # v1.174.0
         with:
           ruby-version: ${{ matrix.ruby }}
           bundler: none
diff --git a/.github/workflows/ubuntu.yml b/.github/workflows/ubuntu.yml
index 42b485700d3838..8f70fcfaaf6d35 100644
--- a/.github/workflows/ubuntu.yml
+++ b/.github/workflows/ubuntu.yml
@@ -67,7 +67,7 @@ jobs:
         with:
           arch: ${{ matrix.arch }}
 
-      - uses: ruby/setup-ruby@5f19ec79cedfadb78ab837f95b87734d0003c899 # v1.173.0
+      - uses: ruby/setup-ruby@6bd3d993c602f6b675728ebaecb2b569ff86e99b # v1.174.0
         with:
           ruby-version: '3.0'
           bundler: none
diff --git a/.github/workflows/wasm.yml b/.github/workflows/wasm.yml
index 5ec4bfafaed22e..1e0a0574bea660 100644
--- a/.github/workflows/wasm.yml
+++ b/.github/workflows/wasm.yml
@@ -100,7 +100,7 @@ jobs:
         run: |
           echo "WASI_SDK_PATH=/opt/wasi-sdk" >> $GITHUB_ENV
 
-      - uses: ruby/setup-ruby@5f19ec79cedfadb78ab837f95b87734d0003c899 # v1.173.0
+      - uses: ruby/setup-ruby@6bd3d993c602f6b675728ebaecb2b569ff86e99b # v1.174.0
         with:
           ruby-version: '3.0'
           bundler: none
diff --git a/.github/workflows/windows.yml b/.github/workflows/windows.yml
index 56e2711b5b9d5d..e1a18297551bd9 100644
--- a/.github/workflows/windows.yml
+++ b/.github/workflows/windows.yml
@@ -91,7 +91,7 @@ jobs:
             ${{ steps.find-tools.outputs.needs }}
         if: ${{ steps.find-tools.outputs.needs != '' }}
 
-      - uses: ruby/setup-ruby@5f19ec79cedfadb78ab837f95b87734d0003c899 # v1.173.0
+      - uses: ruby/setup-ruby@6bd3d993c602f6b675728ebaecb2b569ff86e99b # v1.174.0
         with:
           ruby-version: '3.0'
           bundler: none
diff --git a/.github/workflows/yjit-ubuntu.yml b/.github/workflows/yjit-ubuntu.yml
index 92ff9eadaed607..dcf7e1874af78f 100644
--- a/.github/workflows/yjit-ubuntu.yml
+++ b/.github/workflows/yjit-ubuntu.yml
@@ -145,7 +145,7 @@ jobs:
         if: ${{ matrix.rust_version }}
         run: rustup install ${{ matrix.rust_version }} --profile minimal
 
-      - uses: ruby/setup-ruby@5f19ec79cedfadb78ab837f95b87734d0003c899 # v1.173.0
+      - uses: ruby/setup-ruby@6bd3d993c602f6b675728ebaecb2b569ff86e99b # v1.174.0
         with:
           ruby-version: '3.0'
           bundler: none
diff --git a/NEWS.md b/NEWS.md
index 34fa51ce9d051a..f3368421a9a10e 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -32,6 +32,10 @@ Note: We're only listing outstanding class updates.
   * Exception#set_backtrace now accepts arrays of `Thread::Backtrace::Location`.
     `Kernel#raise`, `Thread#raise` and `Fiber#raise` also accept this new format. [[Feature #13557]]
 
+* Range
+
+  * Range#size now raises TypeError if the range is not iterable. [[Misc #18984]]
+
 ## Stdlib updates
 
 The following default gems are updated.
@@ -47,7 +51,7 @@ The following default gems are updated.
 * optparse 0.5.0
 * prism 0.25.0
 * rdoc 6.6.3.1
-* reline 0.5.1
+* reline 0.5.2
 * resolv 0.4.0
 * stringio 3.1.1
 * strscan 3.1.1
@@ -118,11 +122,17 @@ See GitHub releases like [GitHub Releases of Logger](https://github.com/ruby/log
   a warning on verbose mode (`-w`).
   [[Feature #15554]]
 
+* Redefining some core methods that are specially optimized by the interpeter
+  and JIT like `String.freeze` or `Integer#+` now emits a performance class
+  warning (`-W:performance` or `Warning[:performance] = true`).
+  [[Feature #20429]]
+
 [Feature #13557]: https://bugs.ruby-lang.org/issues/13557
 [Feature #15554]: https://bugs.ruby-lang.org/issues/15554
 [Feature #16495]: https://bugs.ruby-lang.org/issues/16495
 [Feature #18290]: https://bugs.ruby-lang.org/issues/18290
 [Feature #18980]: https://bugs.ruby-lang.org/issues/18980
+[Misc #18984]:    https://bugs.ruby-lang.org/issues/18984
 [Feature #19117]: https://bugs.ruby-lang.org/issues/19117
 [Bug #19918]:     https://bugs.ruby-lang.org/issues/19918
 [Bug #20064]:     https://bugs.ruby-lang.org/issues/20064
diff --git a/class.c b/class.c
index ada95dde1a57d5..36736a6091dcff 100644
--- a/class.c
+++ b/class.c
@@ -2335,7 +2335,7 @@ rb_freeze_singleton_class(VALUE x)
         VALUE klass = RBASIC_CLASS(x);
         if (klass && // no class when hidden from ObjectSpace
             FL_TEST(klass, (FL_SINGLETON|FL_FREEZE)) == FL_SINGLETON) {
-            OBJ_FREEZE_RAW(klass);
+            OBJ_FREEZE(klass);
         }
     }
 }
diff --git a/common.mk b/common.mk
index 3fce9df761bf80..77aa8b04ffee8b 100644
--- a/common.mk
+++ b/common.mk
@@ -105,7 +105,6 @@ PRISM_FILES = prism/api_node.$(OBJEXT) \
 		prism/util/pm_list.$(OBJEXT) \
 		prism/util/pm_memchr.$(OBJEXT) \
 		prism/util/pm_newline_list.$(OBJEXT) \
-		prism/util/pm_state_stack.$(OBJEXT) \
 		prism/util/pm_string.$(OBJEXT) \
 		prism/util/pm_string_list.$(OBJEXT) \
 		prism/util/pm_strncasecmp.$(OBJEXT) \
@@ -227,6 +226,11 @@ srcs: $(srcdir)/lib/prism/node.rb
 $(srcdir)/lib/prism/node.rb: $(PRISM_SRCDIR)/config.yml $(PRISM_SRCDIR)/templates/template.rb $(PRISM_SRCDIR)/templates/lib/prism/node.rb.erb
 	$(Q) $(BASERUBY) $(PRISM_SRCDIR)/templates/template.rb lib/prism/node.rb $(srcdir)/lib/prism/node.rb
 
+main: $(srcdir)/lib/prism/reflection.rb
+srcs: $(srcdir)/lib/prism/reflection.rb
+$(srcdir)/lib/prism/reflection.rb: $(PRISM_SRCDIR)/config.yml $(PRISM_SRCDIR)/templates/template.rb $(PRISM_SRCDIR)/templates/lib/prism/reflection.rb.erb
+	$(Q) $(BASERUBY) $(PRISM_SRCDIR)/templates/template.rb lib/prism/reflection.rb $(srcdir)/lib/prism/reflection.rb
+
 main: $(srcdir)/lib/prism/serialize.rb
 srcs: $(srcdir)/lib/prism/serialize.rb
 $(srcdir)/lib/prism/serialize.rb: $(PRISM_SRCDIR)/config.yml $(PRISM_SRCDIR)/templates/template.rb $(PRISM_SRCDIR)/templates/lib/prism/serialize.rb.erb
@@ -337,7 +341,7 @@ YJIT_RUSTC_ARGS = --crate-name=yjit \
 	'--out-dir=$(CARGO_TARGET_DIR)/release/' \
 	$(top_srcdir)/yjit/src/lib.rs
 
-all: $(SHOWFLAGS) main docs
+all: $(SHOWFLAGS) main
 
 main: $(SHOWFLAGS) exts $(ENCSTATIC:static=lib)encs
 	@$(NULLCMD)
@@ -479,7 +483,7 @@ docs: srcs-doc $(DOCTARGETS)
 pkgconfig-data: $(ruby_pc)
 $(ruby_pc): $(srcdir)/template/ruby.pc.in config.status
 
-install-all: docs pre-install-all do-install-all post-install-all
+install-all: pre-install-all docs do-install-all post-install-all
 pre-install-all:: all pre-install-local pre-install-ext pre-install-gem pre-install-doc
 do-install-all: pre-install-all
 	$(INSTRUBY) --make="$(MAKE)" $(INSTRUBY_ARGS) --install=all $(INSTALL_DOC_OPTS)
@@ -2267,7 +2271,6 @@ ast.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 ast.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 ast.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.h
 ast.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-ast.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 ast.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 ast.$(OBJEXT): $(top_srcdir)/prism/util/pm_string_list.h
 ast.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
@@ -2704,7 +2707,6 @@ builtin.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 builtin.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 builtin.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.h
 builtin.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-builtin.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 builtin.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 builtin.$(OBJEXT): $(top_srcdir)/prism/util/pm_string_list.h
 builtin.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
@@ -3339,7 +3341,6 @@ compile.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 compile.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 compile.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.h
 compile.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-compile.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 compile.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 compile.$(OBJEXT): $(top_srcdir)/prism/util/pm_string_list.h
 compile.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
@@ -3804,7 +3805,6 @@ cont.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 cont.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 cont.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.h
 cont.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-cont.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 cont.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 cont.$(OBJEXT): $(top_srcdir)/prism/util/pm_string_list.h
 cont.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
@@ -6779,7 +6779,6 @@ eval.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 eval.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 eval.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.h
 eval.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-eval.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 eval.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 eval.$(OBJEXT): $(top_srcdir)/prism/util/pm_string_list.h
 eval.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
@@ -7260,7 +7259,6 @@ gc.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 gc.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 gc.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.h
 gc.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-gc.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 gc.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 gc.$(OBJEXT): $(top_srcdir)/prism/util/pm_string_list.h
 gc.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
@@ -7517,7 +7515,6 @@ goruby.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 goruby.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 goruby.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.h
 goruby.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-goruby.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 goruby.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 goruby.$(OBJEXT): $(top_srcdir)/prism/util/pm_string_list.h
 goruby.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
@@ -7761,7 +7758,6 @@ hash.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 hash.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 hash.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.h
 hash.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-hash.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 hash.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 hash.$(OBJEXT): $(top_srcdir)/prism/util/pm_string_list.h
 hash.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
@@ -8800,7 +8796,6 @@ iseq.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 iseq.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 iseq.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.h
 iseq.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-iseq.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 iseq.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 iseq.$(OBJEXT): $(top_srcdir)/prism/util/pm_string_list.h
 iseq.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
@@ -9057,7 +9052,6 @@ load.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 load.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 load.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.h
 load.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-load.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 load.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 load.$(OBJEXT): $(top_srcdir)/prism/util/pm_string_list.h
 load.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
@@ -10388,7 +10382,6 @@ miniinit.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 miniinit.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 miniinit.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.h
 miniinit.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-miniinit.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 miniinit.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 miniinit.$(OBJEXT): $(top_srcdir)/prism/util/pm_string_list.h
 miniinit.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
@@ -11976,7 +11969,6 @@ prism/api_node.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 prism/api_node.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 prism/api_node.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.h
 prism/api_node.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-prism/api_node.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 prism/api_node.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 prism/api_node.$(OBJEXT): $(top_srcdir)/prism/util/pm_string_list.h
 prism/api_node.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
@@ -12172,7 +12164,6 @@ prism/api_pack.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 prism/api_pack.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 prism/api_pack.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.h
 prism/api_pack.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-prism/api_pack.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 prism/api_pack.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 prism/api_pack.$(OBJEXT): $(top_srcdir)/prism/util/pm_string_list.h
 prism/api_pack.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
@@ -12382,7 +12373,6 @@ prism/extension.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 prism/extension.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 prism/extension.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.h
 prism/extension.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-prism/extension.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 prism/extension.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 prism/extension.$(OBJEXT): $(top_srcdir)/prism/util/pm_string_list.h
 prism/extension.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
@@ -12570,7 +12560,6 @@ prism/node.$(OBJEXT): $(top_srcdir)/prism/util/pm_constant_pool.h
 prism/node.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 prism/node.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 prism/node.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-prism/node.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 prism/node.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 prism/node.$(OBJEXT): $(top_srcdir)/prism/util/pm_string_list.h
 prism/node.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
@@ -12596,7 +12585,6 @@ prism/prettyprint.$(OBJEXT): $(top_srcdir)/prism/util/pm_constant_pool.h
 prism/prettyprint.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 prism/prettyprint.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 prism/prettyprint.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-prism/prettyprint.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 prism/prettyprint.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 prism/prettyprint.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
 prism/prettyprint.$(OBJEXT): {$(VPATH)}prism/ast.h
@@ -12619,7 +12607,6 @@ prism/prism.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 prism/prism.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 prism/prism.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.h
 prism/prism.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-prism/prism.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 prism/prism.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 prism/prism.$(OBJEXT): $(top_srcdir)/prism/util/pm_string_list.h
 prism/prism.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
@@ -12641,7 +12628,6 @@ prism/regexp.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 prism/regexp.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 prism/regexp.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.h
 prism/regexp.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-prism/regexp.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 prism/regexp.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 prism/regexp.$(OBJEXT): $(top_srcdir)/prism/util/pm_string_list.h
 prism/regexp.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
@@ -12663,7 +12649,6 @@ prism/serialize.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 prism/serialize.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 prism/serialize.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.h
 prism/serialize.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-prism/serialize.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 prism/serialize.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 prism/serialize.$(OBJEXT): $(top_srcdir)/prism/util/pm_string_list.h
 prism/serialize.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
@@ -12685,7 +12670,6 @@ prism/static_literals.$(OBJEXT): $(top_srcdir)/prism/util/pm_constant_pool.h
 prism/static_literals.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 prism/static_literals.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 prism/static_literals.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-prism/static_literals.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 prism/static_literals.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 prism/static_literals.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
 prism/static_literals.$(OBJEXT): {$(VPATH)}prism/ast.h
@@ -12727,16 +12711,12 @@ prism/util/pm_memchr.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 prism/util/pm_memchr.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.c
 prism/util/pm_memchr.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.h
 prism/util/pm_memchr.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-prism/util/pm_memchr.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 prism/util/pm_memchr.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 prism/util/pm_memchr.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
 prism/util/pm_memchr.$(OBJEXT): {$(VPATH)}prism/ast.h
 prism/util/pm_newline_list.$(OBJEXT): $(top_srcdir)/prism/defines.h
 prism/util/pm_newline_list.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.c
 prism/util/pm_newline_list.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-prism/util/pm_state_stack.$(OBJEXT): $(top_srcdir)/prism/defines.h
-prism/util/pm_state_stack.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.c
-prism/util/pm_state_stack.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 prism/util/pm_string.$(OBJEXT): $(top_srcdir)/prism/defines.h
 prism/util/pm_string.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.c
 prism/util/pm_string.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
@@ -12757,7 +12737,6 @@ prism/util/pm_strpbrk.$(OBJEXT): $(top_srcdir)/prism/util/pm_constant_pool.h
 prism/util/pm_strpbrk.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 prism/util/pm_strpbrk.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 prism/util/pm_strpbrk.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-prism/util/pm_strpbrk.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 prism/util/pm_strpbrk.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 prism/util/pm_strpbrk.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
 prism/util/pm_strpbrk.$(OBJEXT): $(top_srcdir)/prism/util/pm_strpbrk.c
@@ -12784,7 +12763,6 @@ prism_init.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 prism_init.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 prism_init.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.h
 prism_init.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-prism_init.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 prism_init.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 prism_init.$(OBJEXT): $(top_srcdir)/prism/util/pm_string_list.h
 prism_init.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
@@ -13001,7 +12979,6 @@ proc.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 proc.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 proc.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.h
 proc.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-proc.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 proc.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 proc.$(OBJEXT): $(top_srcdir)/prism/util/pm_string_list.h
 proc.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
@@ -15485,7 +15462,6 @@ rjit.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 rjit.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 rjit.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.h
 rjit.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-rjit.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 rjit.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 rjit.$(OBJEXT): $(top_srcdir)/prism/util/pm_string_list.h
 rjit.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
@@ -15739,7 +15715,6 @@ rjit_c.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 rjit_c.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 rjit_c.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.h
 rjit_c.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-rjit_c.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 rjit_c.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 rjit_c.$(OBJEXT): $(top_srcdir)/prism/util/pm_string_list.h
 rjit_c.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
@@ -16019,7 +15994,6 @@ ruby.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 ruby.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 ruby.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.h
 ruby.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-ruby.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 ruby.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 ruby.$(OBJEXT): $(top_srcdir)/prism/util/pm_string_list.h
 ruby.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
@@ -18461,7 +18435,6 @@ thread.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 thread.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 thread.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.h
 thread.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-thread.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 thread.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 thread.$(OBJEXT): $(top_srcdir)/prism/util/pm_string_list.h
 thread.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
@@ -19723,7 +19696,6 @@ vm.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 vm.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 vm.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.h
 vm.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-vm.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 vm.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 vm.$(OBJEXT): $(top_srcdir)/prism/util/pm_string_list.h
 vm.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
@@ -19982,7 +19954,6 @@ vm_backtrace.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 vm_backtrace.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 vm_backtrace.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.h
 vm_backtrace.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-vm_backtrace.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 vm_backtrace.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 vm_backtrace.$(OBJEXT): $(top_srcdir)/prism/util/pm_string_list.h
 vm_backtrace.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
@@ -20213,7 +20184,6 @@ vm_dump.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 vm_dump.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 vm_dump.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.h
 vm_dump.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-vm_dump.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 vm_dump.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 vm_dump.$(OBJEXT): $(top_srcdir)/prism/util/pm_string_list.h
 vm_dump.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
@@ -20655,7 +20625,6 @@ vm_trace.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 vm_trace.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 vm_trace.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.h
 vm_trace.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-vm_trace.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 vm_trace.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 vm_trace.$(OBJEXT): $(top_srcdir)/prism/util/pm_string_list.h
 vm_trace.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
@@ -21097,7 +21066,6 @@ yjit.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
 yjit.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
 yjit.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.h
 yjit.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
-yjit.$(OBJEXT): $(top_srcdir)/prism/util/pm_state_stack.h
 yjit.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 yjit.$(OBJEXT): $(top_srcdir)/prism/util/pm_string_list.h
 yjit.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
diff --git a/compile.c b/compile.c
index 791620aaa25578..2a4eb70122d912 100644
--- a/compile.c
+++ b/compile.c
@@ -1999,6 +1999,19 @@ iseq_set_arguments_keywords(rb_iseq_t *iseq, LINK_ANCHOR *const optargs,
     return arg_size;
 }
 
+static void
+iseq_set_use_block(rb_iseq_t *iseq)
+{
+    struct rb_iseq_constant_body *const body = ISEQ_BODY(iseq);
+    if (!body->param.flags.use_block) {
+        body->param.flags.use_block = 1;
+
+        rb_vm_t *vm = GET_VM();
+        st_data_t key = (st_data_t)rb_intern_str(body->location.label); // String -> ID
+        st_insert(vm->unused_block_warning_table, key, 1);
+    }
+}
+
 static int
 iseq_set_arguments(rb_iseq_t *iseq, LINK_ANCHOR *const optargs, const NODE *const node_args)
 {
@@ -2100,7 +2113,7 @@ iseq_set_arguments(rb_iseq_t *iseq, LINK_ANCHOR *const optargs, const NODE *cons
         if (block_id) {
             body->param.block_start = arg_size++;
             body->param.flags.has_block = TRUE;
-            body->param.flags.use_block = 1;
+            iseq_set_use_block(iseq);
         }
 
         iseq_calc_param_size(iseq);
@@ -5921,7 +5934,7 @@ defined_expr0(rb_iseq_t *iseq, LINK_ANCHOR *const ret,
         ADD_INSN(ret, line_node, putnil);
         ADD_INSN3(ret, line_node, defined, INT2FIX(DEFINED_YIELD), 0,
                   PUSH_VAL(DEFINED_YIELD));
-        ISEQ_BODY(ISEQ_BODY(iseq)->local_iseq)->param.flags.use_block = 1;
+        iseq_set_use_block(ISEQ_BODY(iseq)->local_iseq);
         return;
 
       case NODE_BACK_REF:
@@ -8637,7 +8650,7 @@ compile_builtin_attr(rb_iseq_t *iseq, const NODE *node)
             ISEQ_BODY(iseq)->builtin_attrs |= BUILTIN_ATTR_INLINE_BLOCK;
         }
         else if (strcmp(RSTRING_PTR(string), "use_block") == 0) {
-            ISEQ_BODY(iseq)->param.flags.use_block = 1;
+            iseq_set_use_block(iseq);
         }
         else {
             goto unknown_arg;
@@ -9486,7 +9499,7 @@ compile_super(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const node, i
     }
 
     if (use_block && parent_block == NULL) {
-        ISEQ_BODY(ISEQ_BODY(iseq)->local_iseq)->param.flags.use_block = 1;
+        iseq_set_use_block(ISEQ_BODY(iseq)->local_iseq);
     }
 
     flag |= VM_CALL_SUPER | VM_CALL_FCALL;
@@ -9532,7 +9545,7 @@ compile_yield(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const node, i
 
     ADD_SEQ(ret, args);
     ADD_INSN1(ret, node, invokeblock, new_callinfo(iseq, 0, FIX2INT(argc), flag, keywords, FALSE));
-    ISEQ_BODY(ISEQ_BODY(iseq)->local_iseq)->param.flags.use_block = 1;
+    iseq_set_use_block(ISEQ_BODY(iseq)->local_iseq);
 
     if (popped) {
         ADD_INSN(ret, node, pop);
@@ -10014,7 +10027,7 @@ compile_shareable_literal_constant(rb_iseq_t *iseq, LINK_ANCHOR *ret, enum rb_pa
 
       case NODE_ZLIST:{
         VALUE lit = rb_ary_new();
-        OBJ_FREEZE_RAW(lit);
+        OBJ_FREEZE(lit);
         ADD_INSN1(ret, node, putobject, lit);
         RB_OBJ_WRITTEN(iseq, Qundef, lit);
         *value_p = lit;
@@ -11766,6 +11779,10 @@ rb_iseq_build_from_ary(rb_iseq_t *iseq, VALUE misc, VALUE locals, VALUE params,
         ISEQ_BODY(iseq)->param.flags.ambiguous_param0 = TRUE;
     }
 
+    if (Qtrue == rb_hash_aref(params, SYM(use_block))) {
+        ISEQ_BODY(iseq)->param.flags.use_block = TRUE;
+    }
+
     if (int_param(&i, params, SYM(kwrest))) {
         struct rb_iseq_param_keyword *keyword = (struct rb_iseq_param_keyword *)ISEQ_BODY(iseq)->param.keyword;
         if (keyword == NULL) {
diff --git a/complex.c b/complex.c
index 4e2bff5df427aa..ff278f80fae3a6 100644
--- a/complex.c
+++ b/complex.c
@@ -397,7 +397,7 @@ nucomp_s_new_internal(VALUE klass, VALUE real, VALUE imag)
 
     RCOMPLEX_SET_REAL(obj, real);
     RCOMPLEX_SET_IMAG(obj, imag);
-    OBJ_FREEZE_RAW((VALUE)obj);
+    OBJ_FREEZE((VALUE)obj);
 
     return (VALUE)obj;
 }
@@ -1717,7 +1717,7 @@ nucomp_loader(VALUE self, VALUE a)
 
     RCOMPLEX_SET_REAL(dat, rb_ivar_get(a, id_i_real));
     RCOMPLEX_SET_IMAG(dat, rb_ivar_get(a, id_i_imag));
-    OBJ_FREEZE_RAW(self);
+    OBJ_FREEZE(self);
 
     return self;
 }
diff --git a/cont.c b/cont.c
index f7a4863f2cd270..2cbabba48900fc 100644
--- a/cont.c
+++ b/cont.c
@@ -3227,7 +3227,13 @@ rb_fiber_s_yield(int argc, VALUE *argv, VALUE klass)
 static VALUE
 fiber_raise(rb_fiber_t *fiber, VALUE exception)
 {
-    if (FIBER_SUSPENDED_P(fiber) && !fiber->yielding) {
+    if (fiber == fiber_current()) {
+        rb_exc_raise(exception);
+    }
+    else if (fiber->resuming_fiber) {
+        return fiber_raise(fiber->resuming_fiber, exception);
+    }
+    else if (FIBER_SUSPENDED_P(fiber) && !fiber->yielding) {
         return fiber_transfer_kw(fiber, -1, &exception, RB_NO_KEYWORDS);
     }
     else {
diff --git a/defs/gmake.mk b/defs/gmake.mk
index 40a4750c733e5f..e502b9f83e19c3 100644
--- a/defs/gmake.mk
+++ b/defs/gmake.mk
@@ -193,7 +193,7 @@ $(SCRIPTBINDIR):
 	$(Q) mkdir $@
 
 .PHONY: commit
-COMMIT_PREPARE := $(filter-out commit do-commit,$(MAKECMDGOALS)) up
+COMMIT_PREPARE := $(subst :,\:,$(filter-out commit do-commit,$(MAKECMDGOALS))) up
 
 commit: pre-commit $(DOT_WAIT) do-commit $(DOT_WAIT) post_commit
 pre-commit: $(COMMIT_PREPARE)
diff --git a/doc/contributing/building_ruby.md b/doc/contributing/building_ruby.md
index 2991385b94a6e6..4dabaca840e47f 100644
--- a/doc/contributing/building_ruby.md
+++ b/doc/contributing/building_ruby.md
@@ -96,11 +96,20 @@
 5. Build Ruby:
 
     ``` shell
-    make install
+    make
     ```
 
 6. [Run tests](testing_ruby.md) to confirm your build succeeded.
 
+7. Install Ruby:
+
+    ``` shell
+    make install
+    ```
+
+    - If you need to run `make install` with `sudo` and want to avoid document generation with different permissions, you can use
+    `make SUDO=sudo install`.
+
 ### Unexplainable Build Errors
 
 If you are having unexplainable build errors, after saving all your work, try running `git clean -xfd` in the source root to remove all git ignored local files. If you are working from a source directory that's been updated several times, you may have temporary build artifacts from previous releases which can cause build failures.
diff --git a/enumerator.c b/enumerator.c
index 989fdb34263d0f..193a865dbc5536 100644
--- a/enumerator.c
+++ b/enumerator.c
@@ -3536,10 +3536,19 @@ static VALUE
 enum_product_total_size(VALUE enums)
 {
     VALUE total = INT2FIX(1);
+    VALUE sizes = rb_ary_hidden_new(RARRAY_LEN(enums));
     long i;
 
     for (i = 0; i < RARRAY_LEN(enums); i++) {
         VALUE size = enum_size(RARRAY_AREF(enums, i));
+        if (size == INT2FIX(0)) {
+            rb_ary_resize(sizes, 0);
+            return size;
+        }
+        rb_ary_push(sizes, size);
+    }
+    for (i = 0; i < RARRAY_LEN(sizes); i++) {
+        VALUE size = RARRAY_AREF(sizes, i);
 
         if (NIL_P(size) || (RB_TYPE_P(size, T_FLOAT) && isinf(NUM2DBL(size)))) {
             return size;
diff --git a/ext/pathname/extconf.rb b/ext/pathname/extconf.rb
index 84e68277aae84e..b4e1617b9e6b7f 100644
--- a/ext/pathname/extconf.rb
+++ b/ext/pathname/extconf.rb
@@ -1,4 +1,3 @@
 # frozen_string_literal: false
 require 'mkmf'
-have_func("rb_file_s_birthtime")
 create_makefile('pathname')
diff --git a/ext/pathname/pathname.c b/ext/pathname/pathname.c
index 878f216fb5cad7..cdecb3f897ee68 100644
--- a/ext/pathname/pathname.c
+++ b/ext/pathname/pathname.c
@@ -479,7 +479,6 @@ path_atime(VALUE self)
     return rb_funcall(rb_cFile, id_atime, 1, get_strpath(self));
 }
 
-#if defined(HAVE_RB_FILE_S_BIRTHTIME)
 /*
  * call-seq:
  *   pathname.birthtime	-> time
@@ -494,10 +493,6 @@ path_birthtime(VALUE self)
 {
     return rb_funcall(rb_cFile, id_birthtime, 1, get_strpath(self));
 }
-#else
-/* check at compilation time for `respond_to?` */
-# define path_birthtime rb_f_notimplement
-#endif
 
 /*
  * call-seq:
diff --git a/ext/stringio/stringio.c b/ext/stringio/stringio.c
index f0e5ee4e85ff09..820b8228a31fb7 100644
--- a/ext/stringio/stringio.c
+++ b/ext/stringio/stringio.c
@@ -1623,10 +1623,9 @@ strio_read(int argc, VALUE *argv, VALUE self)
 	if (len > rest) len = rest;
 	rb_str_resize(str, len);
 	MEMCPY(RSTRING_PTR(str), RSTRING_PTR(ptr->string) + ptr->pos, char, len);
-	if (binary)
-	    rb_enc_associate(str, rb_ascii8bit_encoding());
-	else
+	if (!binary) {
 	    rb_enc_copy(str, ptr->string);
+	}
     }
     ptr->pos += RSTRING_LEN(str);
     return str;
diff --git a/gc.c b/gc.c
index 6655d62fa89855..4bf80ff3361cdd 100644
--- a/gc.c
+++ b/gc.c
@@ -21,8 +21,6 @@
 
 #include <signal.h>
 
-#define sighandler_t ruby_sighandler_t
-
 #ifndef _WIN32
 #include <unistd.h>
 #include <sys/mman.h>
@@ -800,7 +798,7 @@ enum gc_mode {
 };
 
 typedef struct rb_global_space {
-    VALUE next_object_id;
+    unsigned long long next_object_id;
 
     rb_ractor_t *prev_id_assigner;
     rb_nativethread_lock_t next_object_id_lock;
@@ -1659,6 +1657,7 @@ total_freed_objects(rb_objspace_t *objspace)
 
 #define gc_mode(objspace)                gc_mode_verify((enum gc_mode)(objspace)->flags.mode)
 #define gc_mode_set(objspace, m)         ((objspace)->flags.mode = (unsigned int)gc_mode_verify(m))
+#define gc_needs_major_flags             objspace->rgengc.need_major_gc
 
 #define is_marking(objspace)             (gc_mode(objspace) == gc_mode_marking)
 #define is_sweeping(objspace)            (gc_mode(objspace) == gc_mode_sweeping)
@@ -3489,7 +3488,7 @@ heap_prepare(rb_objspace_t *objspace, rb_size_pool_t *size_pool, rb_heap_t *heap
              * sweeping and still don't have a free page, then
              * gc_sweep_finish_size_pool should allow us to create a new page. */
             if (heap->free_pages == NULL && !heap_increment(objspace, size_pool, heap)) {
-                if (objspace->rgengc.need_major_gc == GPR_FLAG_NONE) {
+                if (gc_needs_major_flags == GPR_FLAG_NONE) {
                     rb_bug("cannot create a new page after GC");
                 }
                 else { // Major GC is required, which will allow us to create new page
@@ -5233,7 +5232,7 @@ rb_global_space_t *
 rb_global_space_init(void)
 {
     rb_global_space_t *global_space = calloc1(sizeof(rb_global_space_t));
-    global_space->next_object_id = INT2FIX(OBJ_ID_INITIAL);
+    global_space->next_object_id = OBJ_ID_INITIAL;
     global_space->prev_id_assigner = NULL;
     rb_nativethread_lock_initialize(&global_space->next_object_id_lock);
     rb_nativethread_lock_initialize(&global_space->absorbed_thread_tbl_lock);
@@ -6492,7 +6491,7 @@ id2ref(VALUE objid)
 
     rb_global_space_t *global_space = &rb_global_space;
     rb_native_mutex_lock(&global_space->next_object_id_lock);
-    VALUE not_id_value = rb_int_ge(objid, global_space->next_object_id);
+    VALUE not_id_value = rb_int_ge(objid, ULL2NUM(global_space->next_object_id));
     rb_native_mutex_unlock(&global_space->next_object_id_lock);
 
     if (not_id_value) {
@@ -6540,8 +6539,8 @@ cached_object_id(VALUE obj)
 
 	    rb_global_space_t *global_space = &rb_global_space;
 	    rb_native_mutex_lock(&global_space->next_object_id_lock);
-	    id = global_space->next_object_id;
-	    global_space->next_object_id = rb_int_plus(id, INT2FIX(OBJ_ID_INCREMENT));
+	    id = ULL2NUM(global_space->next_object_id);
+	    global_space->next_object_id += OBJ_ID_INCREMENT;
 	    global_space->prev_id_assigner = rb_current_allocating_ractor();
 	    rb_native_mutex_unlock(&global_space->next_object_id_lock);
 
@@ -7415,10 +7414,7 @@ gc_sweep_page(rb_objspace_t *objspace, rb_heap_t *heap, struct gc_sweep_context
     sweep_page->size_pool->total_freed_objects += ctx->freed_slots;
 
     if (heap_pages_deferred_final && !finalizing) {
-        rb_thread_t *th = GET_THREAD();
-        if (th) {
-            gc_finalize_deferred_register(objspace);
-        }
+        gc_finalize_deferred_register(objspace);
     }
 
 #if RGENGC_CHECK_MODE
@@ -7593,7 +7589,7 @@ gc_sweep_finish_size_pool(rb_objspace_t *objspace, rb_size_pool_t *size_pool)
                 grow_heap = TRUE;
             }
             else if (is_growth_heap) { /* Only growth heaps are allowed to start a major GC. */
-                objspace->rgengc.need_major_gc |= GPR_FLAG_MAJOR_BY_NOFREE;
+                gc_needs_major_flags |= GPR_FLAG_MAJOR_BY_NOFREE;
                 size_pool->force_major_gc_count++;
             }
         }
@@ -9750,11 +9746,6 @@ gc_mark_roots(rb_objspace_t *objspace, const char **categoryp)
     rb_global_space_t *global_space = &rb_global_space;
 
     MARK_CHECKPOINT("object_id");
-    rb_native_mutex_lock(&global_space->next_object_id_lock);
-    if (global_space->prev_id_assigner == objspace->ractor) {
-	rb_gc_mark(global_space->next_object_id);
-    }
-    rb_native_mutex_unlock(&global_space->next_object_id_lock);
     rb_native_mutex_lock(&objspace->obj_id_lock);
     mark_tbl_no_pin(objspace, objspace->obj_to_id_tbl); /* Only mark ids */
     rb_native_mutex_unlock(&objspace->obj_id_lock);
@@ -10671,7 +10662,7 @@ gc_marks_finish(rb_objspace_t *objspace)
                 }
                 else {
                     gc_report(1, objspace, "gc_marks_finish: next is full GC!!)\n");
-                    objspace->rgengc.need_major_gc |= GPR_FLAG_MAJOR_BY_NOFREE;
+                    gc_needs_major_flags |= GPR_FLAG_MAJOR_BY_NOFREE;
                 }
             }
         }
@@ -10696,20 +10687,20 @@ gc_marks_finish(rb_objspace_t *objspace)
 	}
 
         if (objspace->rgengc.uncollectible_wb_unprotected_objects > objspace->rgengc.uncollectible_wb_unprotected_objects_limit) {
-            objspace->rgengc.need_major_gc |= GPR_FLAG_MAJOR_BY_SHADY;
+            gc_needs_major_flags |= GPR_FLAG_MAJOR_BY_SHADY;
         }
         if (objspace->rgengc.old_objects > objspace->rgengc.old_objects_limit) {
-            objspace->rgengc.need_major_gc |= GPR_FLAG_MAJOR_BY_OLDGEN;
+            gc_needs_major_flags |= GPR_FLAG_MAJOR_BY_OLDGEN;
         }
         if (RGENGC_FORCE_MAJOR_GC) {
-            objspace->rgengc.need_major_gc = GPR_FLAG_MAJOR_BY_FORCE;
+            gc_needs_major_flags = GPR_FLAG_MAJOR_BY_FORCE;
         }
 
 	const char *next_gc;
 	if (global_space->rglobalgc.need_global_gc) {
 	    next_gc = "global";
 	}
-	else if (objspace->rgengc.need_major_gc) {
+	else if (gc_needs_major_flags) {
 	    next_gc = "major";
 	}
 	else {
@@ -11747,7 +11738,7 @@ gc_reset_malloc_info(rb_objspace_t *objspace, bool full_mark)
 #if RGENGC_ESTIMATE_OLDMALLOC
     if (!full_mark) {
         if (objspace->rgengc.oldmalloc_increase > objspace->rgengc.oldmalloc_increase_limit) {
-            objspace->rgengc.need_major_gc |= GPR_FLAG_MAJOR_BY_OLDMALLOC;
+            gc_needs_major_flags |= GPR_FLAG_MAJOR_BY_OLDMALLOC;
             objspace->rgengc.oldmalloc_increase_limit =
               (size_t)(objspace->rgengc.oldmalloc_increase_limit * gc_params.oldmalloc_limit_growth_factor);
 
@@ -11758,7 +11749,7 @@ gc_reset_malloc_info(rb_objspace_t *objspace, bool full_mark)
 
         if (0) fprintf(stderr, "%"PRIdSIZE"\t%d\t%"PRIuSIZE"\t%"PRIuSIZE"\t%"PRIdSIZE"\n",
                        rb_gc_count(),
-                       objspace->rgengc.need_major_gc,
+                       gc_needs_major_flags,
                        objspace->rgengc.oldmalloc_increase,
                        objspace->rgengc.oldmalloc_increase_limit,
                        gc_params.oldmalloc_limit_max);
@@ -11919,8 +11910,8 @@ gc_set_flags_finish(rb_objspace_t *objspace, unsigned int reason, unsigned int *
         objspace->flags.immediate_sweep = !(flag & (1<<gc_stress_no_immediate_sweep));
     }
 
-    if (objspace->rgengc.need_major_gc) {
-        reason |= objspace->rgengc.need_major_gc;
+    if (gc_needs_major_flags) {
+        reason |= gc_needs_major_flags;
         *do_full_mark = TRUE;
     }
     else if (RGENGC_FORCE_MAJOR_GC) {
@@ -11928,7 +11919,7 @@ gc_set_flags_finish(rb_objspace_t *objspace, unsigned int reason, unsigned int *
         *do_full_mark = TRUE;
     }
 
-    objspace->rgengc.need_major_gc = GPR_FLAG_NONE;
+    gc_needs_major_flags = GPR_FLAG_NONE;
 
     if (*do_full_mark && (reason & GPR_FLAG_MAJOR_MASK) == 0) {
         reason |= GPR_FLAG_MAJOR_BY_FORCE; /* GC by CAPI, METHOD, and so on. */
@@ -12074,10 +12065,8 @@ gc_start(rb_objspace_t *objspace, unsigned int reason)
 static void
 gc_rest(rb_objspace_t *objspace)
 {
-    int marking = is_incremental_marking(objspace);
-    int sweeping = is_lazy_sweeping(objspace);
-
-    if (marking || sweeping) {
+    if (is_incremental_marking(objspace) || is_lazy_sweeping(objspace)) {
+        unsigned int lock_lev;
 	LOCAL_GC_BEGIN(objspace);
 	{
 	    gc_enter(objspace, gc_enter_event_rest);
@@ -12572,12 +12561,11 @@ gc_is_moveable_obj(rb_objspace_t *objspace, VALUE obj)
 
     switch (BUILTIN_TYPE(obj)) {
       case T_NONE:
-      case T_NIL:
       case T_MOVED:
       case T_ZOMBIE:
         return FALSE;
       case T_SYMBOL:
-        if (DYNAMIC_SYM_P(obj) && (RSYMBOL(obj)->id & ~ID_SCOPE_MASK)) {
+        if (RSYMBOL(obj)->id & ~ID_SCOPE_MASK) {
             return FALSE;
         }
         /* fall through */
@@ -13884,7 +13872,7 @@ gc_info_decode(rb_objspace_t *objspace, const VALUE hash_or_key, const unsigned
     SET(major_by, major_by);
 
     if (orig_flags == 0) { /* set need_major_by only if flags not set explicitly */
-        unsigned int need_major_flags = objspace->rgengc.need_major_gc;
+        unsigned int need_major_flags = gc_needs_major_flags;
         need_major_by =
             (need_major_flags & GPR_FLAG_MAJOR_BY_NOFREE) ? sym_nofree :
             (need_major_flags & GPR_FLAG_MAJOR_BY_OLDGEN) ? sym_oldgen :
diff --git a/include/ruby/internal/fl_type.h b/include/ruby/internal/fl_type.h
index eb212db7dc9555..0a05166784b4e0 100644
--- a/include/ruby/internal/fl_type.h
+++ b/include/ruby/internal/fl_type.h
@@ -905,6 +905,10 @@ RB_OBJ_FROZEN(VALUE obj)
     }
 }
 
+RUBY_SYMBOL_EXPORT_BEGIN
+void rb_obj_freeze_inline(VALUE obj);
+RUBY_SYMBOL_EXPORT_END
+
 RBIMPL_ATTR_ARTIFICIAL()
 /**
  * This is an  implementation detail of RB_OBJ_FREEZE().  3rd  parties need not
@@ -915,14 +919,7 @@ RBIMPL_ATTR_ARTIFICIAL()
 static inline void
 RB_OBJ_FREEZE_RAW(VALUE obj)
 {
-    RB_FL_SET_RAW(obj, RUBY_FL_FREEZE);
-    if (TYPE(obj) == T_STRING) {
-        RB_FL_UNSET_RAW(obj, FL_USER3); // STR_CHILLED
-    }
+    rb_obj_freeze_inline(obj);
 }
 
-RUBY_SYMBOL_EXPORT_BEGIN
-void rb_obj_freeze_inline(VALUE obj);
-RUBY_SYMBOL_EXPORT_END
-
 #endif /* RBIMPL_FL_TYPE_H */
diff --git a/iseq.c b/iseq.c
index 7b3fc1a3743d7e..9bc8fb6c61cbcc 100644
--- a/iseq.c
+++ b/iseq.c
@@ -3204,6 +3204,7 @@ iseq_data_to_ary(const rb_iseq_t *iseq)
         }
         if (iseq_body->param.flags.has_kwrest) rb_hash_aset(params, ID2SYM(rb_intern("kwrest")), INT2FIX(keyword->rest_start));
         if (iseq_body->param.flags.ambiguous_param0) rb_hash_aset(params, ID2SYM(rb_intern("ambiguous_param0")), Qtrue);
+        if (iseq_body->param.flags.use_block) rb_hash_aset(params, ID2SYM(rb_intern("use_block")), Qtrue);
     }
 
     /* body */
diff --git a/lib/bundled_gems.rb b/lib/bundled_gems.rb
index e61c1ad231b297..a340463c9844e5 100644
--- a/lib/bundled_gems.rb
+++ b/lib/bundled_gems.rb
@@ -143,18 +143,8 @@ def self.build_message(gem)
       # Additionally, we need to skip Bootsnap and Zeitwerk if present, these
       # gems decorate Kernel#require, so they are not really the ones issuing
       # the require call users should be warned about. Those are upwards.
-      frames_to_skip = 2
-      location = nil
-      Thread.each_caller_location do |cl|
-        if frames_to_skip >= 1
-          frames_to_skip -= 1
-          next
-        end
-
-        if cl.base_label != "require"
-          location = cl.path
-          break
-        end
+      location = Thread.each_caller_location(2) do |cl|
+        break cl.path unless cl.base_label == "require"
       end
 
       if location && File.file?(location) && !location.start_with?(Gem::BUNDLED_GEMS::LIBDIR)
diff --git a/lib/bundler/spec_set.rb b/lib/bundler/spec_set.rb
index 96e1403bf7f1da..2933d284500668 100644
--- a/lib/bundler/spec_set.rb
+++ b/lib/bundler/spec_set.rb
@@ -65,7 +65,7 @@ def add_extra_platforms!(platforms)
 
       platforms.concat(new_platforms)
 
-      less_specific_platform = new_platforms.find {|platform| platform != Gem::Platform::RUBY && Bundler.local_platform === platform }
+      less_specific_platform = new_platforms.find {|platform| platform != Gem::Platform::RUBY && Bundler.local_platform === platform && platform === Bundler.local_platform }
       platforms.delete(Bundler.local_platform) if less_specific_platform
 
       platforms
diff --git a/lib/irb/command/base.rb b/lib/irb/command/base.rb
index ff74b5fb35438b..b078b482375711 100644
--- a/lib/irb/command/base.rb
+++ b/lib/irb/command/base.rb
@@ -50,25 +50,6 @@ def initialize(irb_context)
 
       attr_reader :irb_context
 
-      def unwrap_string_literal(str)
-        return if str.empty?
-
-        sexp = Ripper.sexp(str)
-        if sexp && sexp.size == 2 && sexp.last&.first&.first == :string_literal
-          @irb_context.workspace.binding.eval(str).to_s
-        else
-          str
-        end
-      end
-
-      def ruby_args(arg)
-        # Use throw and catch to handle arg that includes `;`
-        # For example: "1, kw: (2; 3); 4" will be parsed to [[1], { kw: 3 }]
-        catch(:EXTRACT_RUBY_ARGS) do
-          @irb_context.workspace.binding.eval "IRB::Command.extract_ruby_args #{arg}"
-        end || [[], {}]
-      end
-
       def execute(arg)
         #nop
       end
diff --git a/lib/irb/command/edit.rb b/lib/irb/command/edit.rb
index 3c4a54e5e2fa64..cb7e0c4873b3a3 100644
--- a/lib/irb/command/edit.rb
+++ b/lib/irb/command/edit.rb
@@ -8,6 +8,8 @@ module IRB
 
   module Command
     class Edit < Base
+      include RubyArgsExtractor
+
       category "Misc"
       description 'Open a file or source location.'
       help_message <<~HELP_MESSAGE
diff --git a/lib/irb/command/internal_helpers.rb b/lib/irb/command/internal_helpers.rb
new file mode 100644
index 00000000000000..249b5cdedeb080
--- /dev/null
+++ b/lib/irb/command/internal_helpers.rb
@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+module IRB
+  module Command
+    # Internal use only, for default command's backward compatibility.
+    module RubyArgsExtractor # :nodoc:
+      def unwrap_string_literal(str)
+        return if str.empty?
+
+        sexp = Ripper.sexp(str)
+        if sexp && sexp.size == 2 && sexp.last&.first&.first == :string_literal
+          @irb_context.workspace.binding.eval(str).to_s
+        else
+          str
+        end
+      end
+
+      def ruby_args(arg)
+        # Use throw and catch to handle arg that includes `;`
+        # For example: "1, kw: (2; 3); 4" will be parsed to [[1], { kw: 3 }]
+        catch(:EXTRACT_RUBY_ARGS) do
+          @irb_context.workspace.binding.eval "IRB::Command.extract_ruby_args #{arg}"
+        end || [[], {}]
+      end
+    end
+  end
+end
diff --git a/lib/irb/command/load.rb b/lib/irb/command/load.rb
index 33e327f4a93838..1cd3f279d1003e 100644
--- a/lib/irb/command/load.rb
+++ b/lib/irb/command/load.rb
@@ -10,6 +10,7 @@ module IRB
 
   module Command
     class LoaderCommand < Base
+      include RubyArgsExtractor
       include IrbLoader
 
       def raise_cmd_argument_error
diff --git a/lib/irb/command/ls.rb b/lib/irb/command/ls.rb
index f6b19648640489..cbd9998bc4e601 100644
--- a/lib/irb/command/ls.rb
+++ b/lib/irb/command/ls.rb
@@ -11,6 +11,8 @@ module IRB
 
   module Command
     class Ls < Base
+      include RubyArgsExtractor
+
       category "Context"
       description "Show methods, constants, and variables."
 
diff --git a/lib/irb/command/measure.rb b/lib/irb/command/measure.rb
index 70dc69cdec5ef5..f96be20de86bbd 100644
--- a/lib/irb/command/measure.rb
+++ b/lib/irb/command/measure.rb
@@ -3,6 +3,8 @@ module IRB
 
   module Command
     class Measure < Base
+      include RubyArgsExtractor
+
       category "Misc"
       description "`measure` enables the mode to measure processing time. `measure :off` disables it."
 
diff --git a/lib/irb/command/show_doc.rb b/lib/irb/command/show_doc.rb
index f9393cd3b5cab9..8a2188e4ebc365 100644
--- a/lib/irb/command/show_doc.rb
+++ b/lib/irb/command/show_doc.rb
@@ -3,6 +3,8 @@
 module IRB
   module Command
     class ShowDoc < Base
+      include RubyArgsExtractor
+
       category "Context"
       description "Look up documentation with RI."
 
diff --git a/lib/irb/command/show_source.rb b/lib/irb/command/show_source.rb
index c4c8fc004121c2..f4c6f104a2d577 100644
--- a/lib/irb/command/show_source.rb
+++ b/lib/irb/command/show_source.rb
@@ -7,6 +7,8 @@
 module IRB
   module Command
     class ShowSource < Base
+      include RubyArgsExtractor
+
       category "Context"
       description "Show the source code of a given method, class/module, or constant."
 
diff --git a/lib/irb/command/subirb.rb b/lib/irb/command/subirb.rb
index 24428a5c130ed7..138d61c9307228 100644
--- a/lib/irb/command/subirb.rb
+++ b/lib/irb/command/subirb.rb
@@ -9,6 +9,8 @@ module IRB
 
   module Command
     class MultiIRBCommand < Base
+      include RubyArgsExtractor
+
       private
 
       def print_deprecated_warning
diff --git a/lib/irb/default_commands.rb b/lib/irb/default_commands.rb
index 6025b0547da0be..d680655feed9f0 100644
--- a/lib/irb/default_commands.rb
+++ b/lib/irb/default_commands.rb
@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require_relative "command"
+require_relative "command/internal_helpers"
 require_relative "command/context"
 require_relative "command/exit"
 require_relative "command/force_exit"
diff --git a/lib/prism.rb b/lib/prism.rb
index 23a72fa49a334b..c512cb40158359 100644
--- a/lib/prism.rb
+++ b/lib/prism.rb
@@ -24,6 +24,7 @@ module Prism
   autoload :NodeInspector, "prism/node_inspector"
   autoload :Pack, "prism/pack"
   autoload :Pattern, "prism/pattern"
+  autoload :Reflection, "prism/reflection"
   autoload :Serialize, "prism/serialize"
   autoload :Translation, "prism/translation"
   autoload :Visitor, "prism/visitor"
@@ -64,22 +65,6 @@ def self.lex_ripper(source)
   def self.load(source, serialized)
     Serialize.load(source, serialized)
   end
-
-  # :call-seq:
-  #   Prism::parse_failure?(source, **options) -> bool
-  #
-  # Returns true if the source parses with errors.
-  def self.parse_failure?(source, **options)
-    !parse_success?(source, **options)
-  end
-
-  # :call-seq:
-  #   Prism::parse_file_failure?(filepath, **options) -> bool
-  #
-  # Returns true if the file at filepath parses with errors.
-  def self.parse_file_failure?(filepath, **options)
-    !parse_file_success?(filepath, **options)
-  end
 end
 
 require_relative "prism/node"
diff --git a/lib/prism/ffi.rb b/lib/prism/ffi.rb
index 0a064a5c941850..1fd053f9020448 100644
--- a/lib/prism/ffi.rb
+++ b/lib/prism/ffi.rb
@@ -286,12 +286,22 @@ def parse_success?(code, **options)
       LibRubyParser::PrismString.with_string(code) { |string| parse_file_success_common(string, options) }
     end
 
+    # Mirror the Prism.parse_failure? API by using the serialization API.
+    def parse_failure?(code, **options)
+      !parse_success?(code, **options)
+    end
+
     # Mirror the Prism.parse_file_success? API by using the serialization API.
     def parse_file_success?(filepath, **options)
       options[:filepath] = filepath
       LibRubyParser::PrismString.with_file(filepath) { |string| parse_file_success_common(string, options) }
     end
 
+    # Mirror the Prism.parse_file_failure? API by using the serialization API.
+    def parse_file_failure?(filepath, **options)
+      !parse_file_success?(filepath, **options)
+    end
+
     private
 
     def dump_common(string, options) # :nodoc:
diff --git a/lib/prism/prism.gemspec b/lib/prism/prism.gemspec
index 6cf28460c2d5af..e55cac6df6d21b 100644
--- a/lib/prism/prism.gemspec
+++ b/lib/prism/prism.gemspec
@@ -63,7 +63,6 @@ Gem::Specification.new do |spec|
     "include/prism/util/pm_list.h",
     "include/prism/util/pm_memchr.h",
     "include/prism/util/pm_newline_list.h",
-    "include/prism/util/pm_state_stack.h",
     "include/prism/util/pm_strncasecmp.h",
     "include/prism/util/pm_string.h",
     "include/prism/util/pm_string_list.h",
@@ -88,6 +87,7 @@ Gem::Specification.new do |spec|
     "lib/prism/parse_result/newlines.rb",
     "lib/prism/pattern.rb",
     "lib/prism/polyfill/string.rb",
+    "lib/prism/reflection.rb",
     "lib/prism/serialize.rb",
     "lib/prism/translation.rb",
     "lib/prism/translation/parser.rb",
@@ -117,7 +117,6 @@ Gem::Specification.new do |spec|
     "src/util/pm_list.c",
     "src/util/pm_memchr.c",
     "src/util/pm_newline_list.c",
-    "src/util/pm_state_stack.c",
     "src/util/pm_string.c",
     "src/util/pm_string_list.c",
     "src/util/pm_strncasecmp.c",
@@ -136,6 +135,7 @@ Gem::Specification.new do |spec|
     "sig/prism/pack.rbs",
     "sig/prism/parse_result.rbs",
     "sig/prism/pattern.rbs",
+    "sig/prism/reflection.rbs",
     "sig/prism/serialize.rbs",
     "sig/prism/visitor.rbs",
     "rbi/prism.rbi",
@@ -145,7 +145,11 @@ Gem::Specification.new do |spec|
     "rbi/prism/node_ext.rbi",
     "rbi/prism/node.rbi",
     "rbi/prism/parse_result.rbi",
+    "rbi/prism/reflection.rbi",
+    "rbi/prism/translation/parser.rbi",
     "rbi/prism/translation/parser/compiler.rbi",
+    "rbi/prism/translation/parser33.rbi",
+    "rbi/prism/translation/parser34.rbi",
     "rbi/prism/translation/ripper.rbi",
     "rbi/prism/translation/ripper/ripper_compiler.rbi",
     "rbi/prism/translation/ruby_parser.rbi",
diff --git a/lib/reline/line_editor.rb b/lib/reline/line_editor.rb
index e4d7ecf1a29189..6e5ef11bc000d1 100644
--- a/lib/reline/line_editor.rb
+++ b/lib/reline/line_editor.rb
@@ -112,7 +112,11 @@ def set_pasting_state(in_pasting)
     else
       prompt = @prompt
     end
-    if @prompt_proc
+    if !@is_multiline
+      mode_string = check_mode_string
+      prompt = mode_string + prompt if mode_string
+      [prompt] + [''] * (buffer.size - 1)
+    elsif @prompt_proc
       prompt_list = @prompt_proc.(buffer).map { |pr| pr.gsub("\n", "\\n") }
       prompt_list.map!{ prompt } if @vi_arg or @searching_prompt
       prompt_list = [prompt] if prompt_list.empty?
@@ -1220,7 +1224,7 @@ def call_completion_proc_with_checking_args(pre, target, post)
   end
 
   def line()
-    current_line unless eof?
+    @buffer_of_lines.join("\n") unless eof?
   end
 
   def current_line
@@ -1304,14 +1308,12 @@ def retrieve_completion_block(set_completion_quote_character = false)
       end
       target = before
     end
-    if @is_multiline
-      lines = whole_lines
-      if @line_index > 0
-        preposing = lines[0..(@line_index - 1)].join("\n") + "\n" + preposing
-      end
-      if (lines.size - 1) > @line_index
-        postposing = postposing + "\n" + lines[(@line_index + 1)..-1].join("\n")
-      end
+    lines = whole_lines
+    if @line_index > 0
+      preposing = lines[0..(@line_index - 1)].join("\n") + "\n" + preposing
+    end
+    if (lines.size - 1) > @line_index
+      postposing = postposing + "\n" + lines[(@line_index + 1)..-1].join("\n")
     end
     [preposing.encode(@encoding), target.encode(@encoding), postposing.encode(@encoding)]
   end
@@ -1333,20 +1335,16 @@ def insert_text(text)
 
   def delete_text(start = nil, length = nil)
     if start.nil? and length.nil?
-      if @is_multiline
-        if @buffer_of_lines.size == 1
-          @buffer_of_lines[@line_index] = ''
-          @byte_pointer = 0
-        elsif @line_index == (@buffer_of_lines.size - 1) and @line_index > 0
-          @buffer_of_lines.pop
-          @line_index -= 1
-          @byte_pointer = 0
-        elsif @line_index < (@buffer_of_lines.size - 1)
-          @buffer_of_lines.delete_at(@line_index)
-          @byte_pointer = 0
-        end
-      else
-        set_current_line('', 0)
+      if @buffer_of_lines.size == 1
+        @buffer_of_lines[@line_index] = ''
+        @byte_pointer = 0
+      elsif @line_index == (@buffer_of_lines.size - 1) and @line_index > 0
+        @buffer_of_lines.pop
+        @line_index -= 1
+        @byte_pointer = 0
+      elsif @line_index < (@buffer_of_lines.size - 1)
+        @buffer_of_lines.delete_at(@line_index)
+        @byte_pointer = 0
       end
     elsif not start.nil? and not length.nil?
       if current_line
@@ -1502,7 +1500,7 @@ def finish
     byte_size = Reline::Unicode.get_next_mbchar_size(current_line, @byte_pointer)
     if (@byte_pointer < current_line.bytesize)
       @byte_pointer += byte_size
-    elsif @is_multiline and @config.editing_mode_is?(:emacs) and @byte_pointer == current_line.bytesize and @line_index < @buffer_of_lines.size - 1
+    elsif @config.editing_mode_is?(:emacs) and @byte_pointer == current_line.bytesize and @line_index < @buffer_of_lines.size - 1
       @byte_pointer = 0
       @line_index += 1
     end
@@ -1515,7 +1513,7 @@ def finish
     if @byte_pointer > 0
       byte_size = Reline::Unicode.get_prev_mbchar_size(current_line, @byte_pointer)
       @byte_pointer -= byte_size
-    elsif @is_multiline and @config.editing_mode_is?(:emacs) and @byte_pointer == 0 and @line_index > 0
+    elsif @config.editing_mode_is?(:emacs) and @byte_pointer == 0 and @line_index > 0
       @line_index -= 1
       @byte_pointer = current_line.bytesize
     end
@@ -1543,131 +1541,95 @@ def finish
   end
   alias_method :end_of_line, :ed_move_to_end
 
-  private def generate_searcher
-    Fiber.new do |first_key|
-      prev_search_key = first_key
-      search_word = String.new(encoding: @encoding)
-      multibyte_buf = String.new(encoding: 'ASCII-8BIT')
-      last_hit = nil
-      case first_key
-      when "\C-r".ord
-        prompt_name = 'reverse-i-search'
-      when "\C-s".ord
-        prompt_name = 'i-search'
+  private def generate_searcher(search_key)
+    search_word = String.new(encoding: @encoding)
+    multibyte_buf = String.new(encoding: 'ASCII-8BIT')
+    hit_pointer = nil
+    lambda do |key|
+      search_again = false
+      case key
+      when "\C-h".ord, "\C-?".ord
+        grapheme_clusters = search_word.grapheme_clusters
+        if grapheme_clusters.size > 0
+          grapheme_clusters.pop
+          search_word = grapheme_clusters.join
+        end
+      when "\C-r".ord, "\C-s".ord
+        search_again = true if search_key == key
+        search_key = key
+      else
+        multibyte_buf << key
+        if multibyte_buf.dup.force_encoding(@encoding).valid_encoding?
+          search_word << multibyte_buf.dup.force_encoding(@encoding)
+          multibyte_buf.clear
+        end
       end
-      loop do
-        key = Fiber.yield(search_word)
-        search_again = false
-        case key
-        when -1 # determined
-          Reline.last_incremental_search = search_word
-          break
-        when "\C-h".ord, "\C-?".ord
-          grapheme_clusters = search_word.grapheme_clusters
-          if grapheme_clusters.size > 0
-            grapheme_clusters.pop
-            search_word = grapheme_clusters.join
-          end
-        when "\C-r".ord, "\C-s".ord
-          search_again = true if prev_search_key == key
-          prev_search_key = key
-        else
-          multibyte_buf << key
-          if multibyte_buf.dup.force_encoding(@encoding).valid_encoding?
-            search_word << multibyte_buf.dup.force_encoding(@encoding)
-            multibyte_buf.clear
+      hit = nil
+      if not search_word.empty? and @line_backup_in_history&.include?(search_word)
+        hit_pointer = Reline::HISTORY.size
+        hit = @line_backup_in_history
+      else
+        if search_again
+          if search_word.empty? and Reline.last_incremental_search
+            search_word = Reline.last_incremental_search
           end
-        end
-        hit = nil
-        if not search_word.empty? and @line_backup_in_history&.include?(search_word)
-          @history_pointer = nil
-          hit = @line_backup_in_history
-        else
-          if search_again
-            if search_word.empty? and Reline.last_incremental_search
-              search_word = Reline.last_incremental_search
-            end
-            if @history_pointer
-              case prev_search_key
-              when "\C-r".ord
-                history_pointer_base = 0
-                history = Reline::HISTORY[0..(@history_pointer - 1)]
-              when "\C-s".ord
-                history_pointer_base = @history_pointer + 1
-                history = Reline::HISTORY[(@history_pointer + 1)..-1]
-              end
-            else
-              history_pointer_base = 0
-              history = Reline::HISTORY
-            end
-          elsif @history_pointer
-            case prev_search_key
+          if @history_pointer
+            case search_key
             when "\C-r".ord
               history_pointer_base = 0
-              history = Reline::HISTORY[0..@history_pointer]
+              history = Reline::HISTORY[0..(@history_pointer - 1)]
             when "\C-s".ord
-              history_pointer_base = @history_pointer
-              history = Reline::HISTORY[@history_pointer..-1]
+              history_pointer_base = @history_pointer + 1
+              history = Reline::HISTORY[(@history_pointer + 1)..-1]
             end
           else
             history_pointer_base = 0
             history = Reline::HISTORY
           end
-          case prev_search_key
+        elsif @history_pointer
+          case search_key
           when "\C-r".ord
-            hit_index = history.rindex { |item|
-              item.include?(search_word)
-            }
+            history_pointer_base = 0
+            history = Reline::HISTORY[0..@history_pointer]
           when "\C-s".ord
-            hit_index = history.index { |item|
-              item.include?(search_word)
-            }
-          end
-          if hit_index
-            @history_pointer = history_pointer_base + hit_index
-            hit = Reline::HISTORY[@history_pointer]
+            history_pointer_base = @history_pointer
+            history = Reline::HISTORY[@history_pointer..-1]
           end
+        else
+          history_pointer_base = 0
+          history = Reline::HISTORY
         end
-        case prev_search_key
+        case search_key
         when "\C-r".ord
-          prompt_name = 'reverse-i-search'
+          hit_index = history.rindex { |item|
+            item.include?(search_word)
+          }
         when "\C-s".ord
-          prompt_name = 'i-search'
+          hit_index = history.index { |item|
+            item.include?(search_word)
+          }
         end
-        if hit
-          if @is_multiline
-            @buffer_of_lines = hit.split("\n")
-            @buffer_of_lines = [String.new(encoding: @encoding)] if @buffer_of_lines.empty?
-            @line_index = @buffer_of_lines.size - 1
-            @byte_pointer = current_line.bytesize
-            @searching_prompt = "(%s)`%s'" % [prompt_name, search_word]
-          else
-            @buffer_of_lines = [hit]
-            @byte_pointer = hit.bytesize
-            @searching_prompt = "(%s)`%s': %s" % [prompt_name, search_word, hit]
-          end
-          last_hit = hit
-        else
-          if @is_multiline
-            @searching_prompt = "(failed %s)`%s'" % [prompt_name, search_word]
-          else
-            @searching_prompt = "(failed %s)`%s': %s" % [prompt_name, search_word, last_hit]
-          end
+        if hit_index
+          hit_pointer = history_pointer_base + hit_index
+          hit = Reline::HISTORY[hit_pointer]
         end
       end
+      case search_key
+      when "\C-r".ord
+        prompt_name = 'reverse-i-search'
+      when "\C-s".ord
+        prompt_name = 'i-search'
+      end
+      prompt_name = "failed #{prompt_name}" unless hit
+      [search_word, prompt_name, hit_pointer]
     end
   end
 
   private def incremental_search_history(key)
     unless @history_pointer
-      if @is_multiline
-        @line_backup_in_history = whole_buffer
-      else
-        @line_backup_in_history = current_line
-      end
+      @line_backup_in_history = whole_buffer
     end
-    searcher = generate_searcher
-    searcher.resume(key)
+    searcher = generate_searcher(key)
     @searching_prompt = "(reverse-i-search)`': "
     termination_keys = ["\C-j".ord]
     termination_keys.concat(@config.isearch_terminators&.chars&.map(&:ord)) if @config.isearch_terminators
@@ -1679,53 +1641,41 @@ def finish
         else
           buffer = @line_backup_in_history
         end
-        if @is_multiline
-          @buffer_of_lines = buffer.split("\n")
-          @buffer_of_lines = [String.new(encoding: @encoding)] if @buffer_of_lines.empty?
-          @line_index = @buffer_of_lines.size - 1
-        else
-          @buffer_of_lines = [buffer]
-        end
+        @buffer_of_lines = buffer.split("\n")
+        @buffer_of_lines = [String.new(encoding: @encoding)] if @buffer_of_lines.empty?
+        @line_index = @buffer_of_lines.size - 1
         @searching_prompt = nil
         @waiting_proc = nil
         @byte_pointer = 0
-        searcher.resume(-1)
       when "\C-g".ord
-        if @is_multiline
-          @buffer_of_lines = @line_backup_in_history.split("\n")
-          @buffer_of_lines = [String.new(encoding: @encoding)] if @buffer_of_lines.empty?
-          @line_index = @buffer_of_lines.size - 1
-        else
-          @buffer_of_lines = [@line_backup_in_history]
-        end
-        @history_pointer = nil
+        @buffer_of_lines = @line_backup_in_history.split("\n")
+        @buffer_of_lines = [String.new(encoding: @encoding)] if @buffer_of_lines.empty?
+        @line_index = @buffer_of_lines.size - 1
+        move_history(nil, line: :end, cursor: :end, save_buffer: false)
         @searching_prompt = nil
         @waiting_proc = nil
-        @line_backup_in_history = nil
         @byte_pointer = 0
       else
         chr = k.is_a?(String) ? k : k.chr(Encoding::ASCII_8BIT)
         if chr.match?(/[[:print:]]/) or k == "\C-h".ord or k == "\C-?".ord or k == "\C-r".ord or k == "\C-s".ord
-          searcher.resume(k)
+          search_word, prompt_name, hit_pointer = searcher.call(k)
+          Reline.last_incremental_search = search_word
+          @searching_prompt = "(%s)`%s'" % [prompt_name, search_word]
+          @searching_prompt += ': ' unless @is_multiline
+          move_history(hit_pointer, line: :end, cursor: :end, save_buffer: false) if hit_pointer
         else
           if @history_pointer
             line = Reline::HISTORY[@history_pointer]
           else
             line = @line_backup_in_history
           end
-          if @is_multiline
-            @line_backup_in_history = whole_buffer
-            @buffer_of_lines = line.split("\n")
-            @buffer_of_lines = [String.new(encoding: @encoding)] if @buffer_of_lines.empty?
-            @line_index = @buffer_of_lines.size - 1
-          else
-            @line_backup_in_history = current_line
-            @buffer_of_lines = [line]
-          end
+          @line_backup_in_history = whole_buffer
+          @buffer_of_lines = line.split("\n")
+          @buffer_of_lines = [String.new(encoding: @encoding)] if @buffer_of_lines.empty?
+          @line_index = @buffer_of_lines.size - 1
           @searching_prompt = nil
           @waiting_proc = nil
           @byte_pointer = 0
-          searcher.resume(-1)
         end
       end
     }
@@ -1741,191 +1691,96 @@ def finish
   end
   alias_method :forward_search_history, :vi_search_next
 
-  private def ed_search_prev_history(key, arg: 1)
-    history = nil
-    h_pointer = nil
-    line_no = nil
-    substr = current_line.slice(0, @byte_pointer)
-    if @history_pointer.nil?
-      return if not current_line.empty? and substr.empty?
-      history = Reline::HISTORY
-    elsif @history_pointer.zero?
-      history = nil
-      h_pointer = nil
-    else
-      history = Reline::HISTORY.slice(0, @history_pointer)
-    end
-    return if history.nil?
-    if @is_multiline
-      h_pointer = history.rindex { |h|
-        h.split("\n").each_with_index { |l, i|
-          if l.start_with?(substr)
-            line_no = i
-            break
-          end
-        }
-        not line_no.nil?
-      }
-    else
-      h_pointer = history.rindex { |l|
-        l.start_with?(substr)
-      }
-    end
-    return if h_pointer.nil?
-    @history_pointer = h_pointer
-    cursor = current_byte_pointer_cursor
-    if @is_multiline
-      @buffer_of_lines = Reline::HISTORY[@history_pointer].split("\n")
-      @buffer_of_lines = [String.new(encoding: @encoding)] if @buffer_of_lines.empty?
-      @line_index = line_no
-      calculate_nearest_cursor(cursor)
-    else
-      @buffer_of_lines = [Reline::HISTORY[@history_pointer]]
-      calculate_nearest_cursor(cursor)
+  private def search_history(prefix, pointer_range)
+    pointer_range.each do |pointer|
+      lines = Reline::HISTORY[pointer].split("\n")
+      lines.each_with_index do |line, index|
+        return [pointer, index] if line.start_with?(prefix)
+      end
     end
+    nil
+  end
+
+  private def ed_search_prev_history(key, arg: 1)
+    substr = current_line.byteslice(0, @byte_pointer)
+    return if @history_pointer == 0
+    return if @history_pointer.nil? && substr.empty? && !current_line.empty?
+
+    history_range = 0...(@history_pointer || Reline::HISTORY.size)
+    h_pointer, line_index = search_history(substr, history_range.reverse_each)
+    return unless h_pointer
+    move_history(h_pointer, line: line_index || :start, cursor: @byte_pointer)
     arg -= 1
     ed_search_prev_history(key, arg: arg) if arg > 0
   end
   alias_method :history_search_backward, :ed_search_prev_history
 
   private def ed_search_next_history(key, arg: 1)
-    substr = current_line.slice(0, @byte_pointer)
-    if @history_pointer.nil?
-      return
-    elsif @history_pointer == (Reline::HISTORY.size - 1) and not substr.empty?
-      return
-    end
+    substr = current_line.byteslice(0, @byte_pointer)
+    return if @history_pointer.nil?
+
+    history_range = @history_pointer + 1...Reline::HISTORY.size
     history = Reline::HISTORY.slice((@history_pointer + 1)..-1)
-    h_pointer = nil
-    line_no = nil
-    if @is_multiline
-      h_pointer = history.index { |h|
-        h.split("\n").each_with_index { |l, i|
-          if l.start_with?(substr)
-            line_no = i
-            break
-          end
-        }
-        not line_no.nil?
-      }
-    else
-      h_pointer = history.index { |l|
-        l.start_with?(substr)
-      }
-    end
-    h_pointer += @history_pointer + 1 if h_pointer and @history_pointer
+    h_pointer, line_index = search_history(substr, history_range)
     return if h_pointer.nil? and not substr.empty?
-    @history_pointer = h_pointer
-    if @is_multiline
-      if @history_pointer.nil? and substr.empty?
-        @buffer_of_lines = []
-        @line_index = 0
-        @byte_pointer = 0
-      else
-        cursor = current_byte_pointer_cursor
-        @buffer_of_lines = Reline::HISTORY[@history_pointer].split("\n")
-        @line_index = line_no
-        calculate_nearest_cursor(cursor)
-      end
-      @buffer_of_lines = [String.new(encoding: @encoding)] if @buffer_of_lines.empty?
-    else
-      if @history_pointer.nil? and substr.empty?
-        set_current_line('', 0)
-      else
-        set_current_line(Reline::HISTORY[@history_pointer])
-      end
-    end
+
+    move_history(h_pointer, line: line_index || :start, cursor: @byte_pointer)
     arg -= 1
     ed_search_next_history(key, arg: arg) if arg > 0
   end
   alias_method :history_search_forward, :ed_search_next_history
 
+  private def move_history(history_pointer, line:, cursor:, save_buffer: true)
+    history_pointer ||= Reline::HISTORY.size
+    return if history_pointer < 0 || history_pointer > Reline::HISTORY.size
+    old_history_pointer = @history_pointer || Reline::HISTORY.size
+    if old_history_pointer == Reline::HISTORY.size
+      @line_backup_in_history = save_buffer ? whole_buffer : ''
+    else
+      Reline::HISTORY[old_history_pointer] = whole_buffer if save_buffer
+    end
+    if history_pointer == Reline::HISTORY.size
+      buf = @line_backup_in_history
+      @history_pointer = @line_backup_in_history = nil
+    else
+      buf = Reline::HISTORY[history_pointer]
+      @history_pointer = history_pointer
+    end
+    @buffer_of_lines = buf.split("\n")
+    @buffer_of_lines = [String.new(encoding: @encoding)] if @buffer_of_lines.empty?
+    @line_index = line == :start ? 0 : line == :end ? @buffer_of_lines.size - 1 : line
+    @byte_pointer = cursor == :start ? 0 : cursor == :end ? current_line.bytesize : cursor
+  end
+
   private def ed_prev_history(key, arg: 1)
-    if @is_multiline and @line_index > 0
+    if @line_index > 0
       cursor = current_byte_pointer_cursor
       @line_index -= 1
       calculate_nearest_cursor(cursor)
       return
     end
-    if Reline::HISTORY.empty?
-      return
-    end
-    if @history_pointer.nil?
-      @history_pointer = Reline::HISTORY.size - 1
-      cursor = current_byte_pointer_cursor
-      if @is_multiline
-        @line_backup_in_history = whole_buffer
-        @buffer_of_lines = Reline::HISTORY[@history_pointer].split("\n")
-        @buffer_of_lines = [String.new(encoding: @encoding)] if @buffer_of_lines.empty?
-        @line_index = @buffer_of_lines.size - 1
-        calculate_nearest_cursor(cursor)
-      else
-        @line_backup_in_history = whole_buffer
-        @buffer_of_lines = [Reline::HISTORY[@history_pointer]]
-        calculate_nearest_cursor(cursor)
-      end
-    elsif @history_pointer.zero?
-      return
-    else
-      if @is_multiline
-        Reline::HISTORY[@history_pointer] = whole_buffer
-        @history_pointer -= 1
-        @buffer_of_lines = Reline::HISTORY[@history_pointer].split("\n")
-        @buffer_of_lines = [String.new(encoding: @encoding)] if @buffer_of_lines.empty?
-        @line_index = @buffer_of_lines.size - 1
-      else
-        Reline::HISTORY[@history_pointer] = whole_buffer
-        @history_pointer -= 1
-        @buffer_of_lines = [Reline::HISTORY[@history_pointer]]
-      end
-    end
-    if @config.editing_mode_is?(:emacs, :vi_insert)
-      @byte_pointer = current_line.bytesize
-    elsif @config.editing_mode_is?(:vi_command)
-      @byte_pointer = 0
-    end
+    move_history(
+      (@history_pointer || Reline::HISTORY.size) - 1,
+      line: :end,
+      cursor: @config.editing_mode_is?(:vi_command) ? :start : :end,
+    )
     arg -= 1
     ed_prev_history(key, arg: arg) if arg > 0
   end
   alias_method :previous_history, :ed_prev_history
 
   private def ed_next_history(key, arg: 1)
-    if @is_multiline and @line_index < (@buffer_of_lines.size - 1)
+    if @line_index < (@buffer_of_lines.size - 1)
       cursor = current_byte_pointer_cursor
       @line_index += 1
       calculate_nearest_cursor(cursor)
       return
     end
-    if @history_pointer.nil?
-      return
-    elsif @history_pointer == (Reline::HISTORY.size - 1)
-      if @is_multiline
-        @history_pointer = nil
-        @buffer_of_lines = @line_backup_in_history.split("\n")
-        @buffer_of_lines = [String.new(encoding: @encoding)] if @buffer_of_lines.empty?
-        @line_index = 0
-      else
-        @history_pointer = nil
-        @buffer_of_lines = [@line_backup_in_history]
-      end
-    else
-      if @is_multiline
-        Reline::HISTORY[@history_pointer] = whole_buffer
-        @history_pointer += 1
-        @buffer_of_lines = Reline::HISTORY[@history_pointer].split("\n")
-        @buffer_of_lines = [String.new(encoding: @encoding)] if @buffer_of_lines.empty?
-        @line_index = 0
-      else
-        Reline::HISTORY[@history_pointer] = whole_buffer
-        @history_pointer += 1
-        @buffer_of_lines = [Reline::HISTORY[@history_pointer]]
-      end
-    end
-    if @config.editing_mode_is?(:emacs, :vi_insert)
-      @byte_pointer = current_line.bytesize
-    elsif @config.editing_mode_is?(:vi_command)
-      @byte_pointer = 0
-    end
+    move_history(
+      (@history_pointer || Reline::HISTORY.size) + 1,
+      line: :start,
+      cursor: @config.editing_mode_is?(:vi_command) ? :start : :end,
+    )
     arg -= 1
     ed_next_history(key, arg: arg) if arg > 0
   end
@@ -1956,17 +1811,13 @@ def finish
         end
       end
     else
-      if @history_pointer
-        Reline::HISTORY[@history_pointer] = whole_buffer
-        @history_pointer = nil
-      end
       finish
     end
   end
 
   private def em_delete_prev_char(key, arg: 1)
     arg.times do
-      if @is_multiline and @byte_pointer == 0 and @line_index > 0
+      if @byte_pointer == 0 and @line_index > 0
         @byte_pointer = @buffer_of_lines[@line_index - 1].bytesize
         @buffer_of_lines[@line_index - 1] += @buffer_of_lines.delete_at(@line_index)
         @line_index -= 1
@@ -1990,7 +1841,7 @@ def finish
       line, deleted = byteslice!(current_line, @byte_pointer, current_line.bytesize - @byte_pointer)
       set_current_line(line, line.bytesize)
       @kill_ring.append(deleted)
-    elsif @is_multiline and @byte_pointer == current_line.bytesize and @buffer_of_lines.size > @line_index + 1
+    elsif @byte_pointer == current_line.bytesize and @buffer_of_lines.size > @line_index + 1
       set_current_line(current_line + @buffer_of_lines.delete_at(@line_index + 1), current_line.bytesize)
     end
   end
@@ -2030,7 +1881,7 @@ def finish
   alias_method :kill_whole_line, :em_kill_line
 
   private def em_delete(key)
-    if current_line.empty? and (not @is_multiline or @buffer_of_lines.size == 1) and key == "\C-d".ord
+    if current_line.empty? and @buffer_of_lines.size == 1 and key == "\C-d".ord
       @eof = true
       finish
     elsif @byte_pointer < current_line.bytesize
@@ -2038,7 +1889,7 @@ def finish
       mbchar = splitted_last.grapheme_clusters.first
       line, = byteslice!(current_line, @byte_pointer, mbchar.bytesize)
       set_current_line(line)
-    elsif @is_multiline and @byte_pointer == current_line.bytesize and @buffer_of_lines.size > @line_index + 1
+    elsif @byte_pointer == current_line.bytesize and @buffer_of_lines.size > @line_index + 1
       set_current_line(current_line + @buffer_of_lines.delete_at(@line_index + 1), current_line.bytesize)
     end
   end
@@ -2281,7 +2132,7 @@ def finish
   end
 
   private def vi_delete_prev_char(key)
-    if @is_multiline and @byte_pointer == 0 and @line_index > 0
+    if @byte_pointer == 0 and @line_index > 0
       @byte_pointer = @buffer_of_lines[@line_index - 1].bytesize
       @buffer_of_lines[@line_index - 1] += @buffer_of_lines.delete_at(@line_index)
       @line_index -= 1
@@ -2378,7 +2229,7 @@ def finish
   end
 
   private def vi_list_or_eof(key)
-    if (not @is_multiline and current_line.empty?) or (@is_multiline and current_line.empty? and @buffer_of_lines.size == 1)
+    if current_line.empty? and @buffer_of_lines.size == 1
       set_current_line('', 0)
       @eof = true
       finish
@@ -2409,36 +2260,18 @@ def finish
     if Reline::HISTORY.empty?
       return
     end
-    if @history_pointer.nil?
-      @history_pointer = 0
-      @line_backup_in_history = current_line
-      set_current_line(Reline::HISTORY[@history_pointer], 0)
-    elsif @history_pointer.zero?
-      return
-    else
-      Reline::HISTORY[@history_pointer] = current_line
-      @history_pointer = 0
-      set_current_line(Reline::HISTORY[@history_pointer], 0)
-    end
+    move_history(0, line: :start, cursor: :start)
   end
 
   private def vi_histedit(key)
     path = Tempfile.open { |fp|
-      if @is_multiline
-        fp.write whole_lines.join("\n")
-      else
-        fp.write current_line
-      end
+      fp.write whole_lines.join("\n")
       fp.path
     }
     system("#{ENV['EDITOR']} #{path}")
-    if @is_multiline
-      @buffer_of_lines = File.read(path).split("\n")
-      @buffer_of_lines = [String.new(encoding: @encoding)] if @buffer_of_lines.empty?
-      @line_index = 0
-    else
-      @buffer_of_lines = File.read(path).split("\n")
-    end
+    @buffer_of_lines = File.read(path).split("\n")
+    @buffer_of_lines = [String.new(encoding: @encoding)] if @buffer_of_lines.empty?
+    @line_index = 0
     finish
   end
 
@@ -2610,7 +2443,7 @@ def finish
   end
 
   private def vi_join_lines(key, arg: 1)
-    if @is_multiline and @buffer_of_lines.size > @line_index + 1
+    if @buffer_of_lines.size > @line_index + 1
       next_line = @buffer_of_lines.delete_at(@line_index + 1).lstrip
       set_current_line(current_line + ' ' + next_line, current_line.bytesize)
     end
@@ -2630,4 +2463,12 @@ def finish
     @mark_pointer = new_pointer
   end
   alias_method :exchange_point_and_mark, :em_exchange_mark
+
+  private def emacs_editing_mode(key)
+    @config.editing_mode = :emacs
+  end
+
+  private def vi_editing_mode(key)
+    @config.editing_mode = :vi_insert
+  end
 end
diff --git a/lib/reline/version.rb b/lib/reline/version.rb
index acb5e279b8cc77..e6f370c6ec1438 100644
--- a/lib/reline/version.rb
+++ b/lib/reline/version.rb
@@ -1,3 +1,3 @@
 module Reline
-  VERSION = '0.5.1'
+  VERSION = '0.5.2'
 end
diff --git a/node.c b/node.c
index 8a6b55b0b5808a..7706f71fdaeb44 100644
--- a/node.c
+++ b/node.c
@@ -81,7 +81,6 @@ rb_node_buffer_new(void)
 #define xfree ast->node_buffer->config->free
 #define rb_xmalloc_mul_add ast->node_buffer->config->xmalloc_mul_add
 #define ruby_xrealloc(var,size) (ast->node_buffer->config->realloc_n((void *)var, 1, size))
-#define rb_gc_mark_and_move ast->node_buffer->config->gc_mark_and_move
 #endif
 
 typedef void node_itr_t(rb_ast_t *ast, void *ctx, NODE *node);
diff --git a/prism/config.yml b/prism/config.yml
index a0abb98ef7e3a8..8551c95b1f6c23 100644
--- a/prism/config.yml
+++ b/prism/config.yml
@@ -104,6 +104,14 @@ errors:
   - EXPECT_STRING_CONTENT
   - EXPECT_WHEN_DELIMITER
   - EXPRESSION_BARE_HASH
+  - EXPRESSION_NOT_WRITABLE
+  - EXPRESSION_NOT_WRITABLE_ENCODING
+  - EXPRESSION_NOT_WRITABLE_FALSE
+  - EXPRESSION_NOT_WRITABLE_FILE
+  - EXPRESSION_NOT_WRITABLE_LINE
+  - EXPRESSION_NOT_WRITABLE_NIL
+  - EXPRESSION_NOT_WRITABLE_SELF
+  - EXPRESSION_NOT_WRITABLE_TRUE
   - FLOAT_PARSE
   - FOR_COLLECTION
   - FOR_IN
diff --git a/prism/extension.c b/prism/extension.c
index 27e799a8da645e..807c8f69dc2da9 100644
--- a/prism/extension.c
+++ b/prism/extension.c
@@ -969,7 +969,7 @@ parse_input_success_p(pm_string_t *input, const pm_options_t *options) {
 
 /**
  * call-seq:
- *   Prism::parse_success?(source, **options) -> Array
+ *   Prism::parse_success?(source, **options) -> bool
  *
  * Parse the given string and return true if it parses without errors. For
  * supported options, see Prism::parse.
@@ -989,7 +989,19 @@ parse_success_p(int argc, VALUE *argv, VALUE self) {
 
 /**
  * call-seq:
- *   Prism::parse_file_success?(filepath, **options) -> Array
+ *   Prism::parse_failure?(source, **options) -> bool
+ *
+ * Parse the given string and return true if it parses with errors. For
+ * supported options, see Prism::parse.
+ */
+static VALUE
+parse_failure_p(int argc, VALUE *argv, VALUE self) {
+    return RTEST(parse_success_p(argc, argv, self)) ? Qfalse : Qtrue;
+}
+
+/**
+ * call-seq:
+ *   Prism::parse_file_success?(filepath, **options) -> bool
  *
  * Parse the given file and return true if it parses without errors. For
  * supported options, see Prism::parse.
@@ -1008,6 +1020,18 @@ parse_file_success_p(int argc, VALUE *argv, VALUE self) {
     return result;
 }
 
+/**
+ * call-seq:
+ *   Prism::parse_file_failure?(filepath, **options) -> bool
+ *
+ * Parse the given file and return true if it parses with errors. For
+ * supported options, see Prism::parse.
+ */
+static VALUE
+parse_file_failure_p(int argc, VALUE *argv, VALUE self) {
+    return RTEST(parse_file_success_p(argc, argv, self)) ? Qfalse : Qtrue;
+}
+
 /******************************************************************************/
 /* Utility functions exposed to make testing easier                           */
 /******************************************************************************/
@@ -1366,7 +1390,9 @@ Init_prism(void) {
     rb_define_singleton_method(rb_cPrism, "parse_lex", parse_lex, -1);
     rb_define_singleton_method(rb_cPrism, "parse_lex_file", parse_lex_file, -1);
     rb_define_singleton_method(rb_cPrism, "parse_success?", parse_success_p, -1);
+    rb_define_singleton_method(rb_cPrism, "parse_failure?", parse_failure_p, -1);
     rb_define_singleton_method(rb_cPrism, "parse_file_success?", parse_file_success_p, -1);
+    rb_define_singleton_method(rb_cPrism, "parse_file_failure?", parse_file_failure_p, -1);
 
 #ifndef PRISM_EXCLUDE_SERIALIZATION
     rb_define_singleton_method(rb_cPrism, "dump", dump, -1);
diff --git a/prism/options.c b/prism/options.c
index 2854b765b9323b..4d0d6dbc49a70c 100644
--- a/prism/options.c
+++ b/prism/options.c
@@ -47,29 +47,40 @@ pm_options_command_line_set(pm_options_t *options, uint8_t command_line) {
  */
 PRISM_EXPORTED_FUNCTION bool
 pm_options_version_set(pm_options_t *options, const char *version, size_t length) {
-    if (version == NULL && length == 0) {
-        options->version = PM_OPTIONS_VERSION_LATEST;
-        return true;
-    }
+    switch (length) {
+        case 0:
+            if (version == NULL) {
+                options->version = PM_OPTIONS_VERSION_LATEST;
+                return true;
+            }
 
-    if (length == 5) {
-        if (strncmp(version, "3.3.0", length) == 0) {
-            options->version = PM_OPTIONS_VERSION_CRUBY_3_3_0;
-            return true;
-        }
+            return false;
+        case 5:
+            assert(version != NULL);
 
-        if (strncmp(version, "3.4.0", length) == 0) {
-            options->version = PM_OPTIONS_VERSION_LATEST;
-            return true;
-        }
-    }
+            if (strncmp(version, "3.3.0", length) == 0) {
+                options->version = PM_OPTIONS_VERSION_CRUBY_3_3_0;
+                return true;
+            }
 
-    if (length == 6 && strncmp(version, "latest", length) == 0) {
-        options->version = PM_OPTIONS_VERSION_LATEST;
-        return true;
-    }
+            if (strncmp(version, "3.4.0", length) == 0) {
+                options->version = PM_OPTIONS_VERSION_LATEST;
+                return true;
+            }
+
+            return false;
+        case 6:
+            assert(version != NULL);
 
-    return false;
+            if (strncmp(version, "latest", length) == 0) {
+                options->version = PM_OPTIONS_VERSION_LATEST;
+                return true;
+            }
+
+            return false;
+        default:
+            return false;
+    }
 }
 
 // For some reason, GCC analyzer thinks we're leaking allocated scopes and
diff --git a/prism/parser.h b/prism/parser.h
index b0ff2f38fcf38d..b35026e6a25900 100644
--- a/prism/parser.h
+++ b/prism/parser.h
@@ -13,7 +13,6 @@
 #include "prism/util/pm_constant_pool.h"
 #include "prism/util/pm_list.h"
 #include "prism/util/pm_newline_list.h"
-#include "prism/util/pm_state_stack.h"
 #include "prism/util/pm_string.h"
 
 #include <stdbool.h>
@@ -612,6 +611,11 @@ static const uint8_t PM_SCOPE_PARAMETERS_FORWARDING_ALL = 0x40;
 static const int8_t PM_SCOPE_NUMBERED_PARAMETERS_DISALLOWED = -1;
 static const int8_t PM_SCOPE_NUMBERED_PARAMETERS_NONE = 0;
 
+/**
+ * A struct that represents a stack of boolean values.
+ */
+typedef uint32_t pm_state_stack_t;
+
 /**
  * This struct represents the overall parser. It contains a reference to the
  * source file, as well as pointers that indicate where in the source it's
diff --git a/prism/prism.c b/prism/prism.c
index 91d27f566d4e00..18675b994a9c24 100644
--- a/prism/prism.c
+++ b/prism/prism.c
@@ -2774,6 +2774,7 @@ pm_call_node_not_create(pm_parser_t *parser, pm_node_t *receiver, pm_token_t *me
     if (arguments->closing_loc.start != NULL) {
         node->base.location.end = arguments->closing_loc.end;
     } else {
+        assert(receiver != NULL);
         node->base.location.end = receiver->location.end;
     }
 
@@ -7631,6 +7632,30 @@ pm_parser_scope_pop(pm_parser_t *parser) {
 /* Stack helpers                                                              */
 /******************************************************************************/
 
+/**
+ * Pushes a value onto the stack.
+ */
+static inline void
+pm_state_stack_push(pm_state_stack_t *stack, bool value) {
+    *stack = (*stack << 1) | (value & 1);
+}
+
+/**
+ * Pops a value off the stack.
+ */
+static inline void
+pm_state_stack_pop(pm_state_stack_t *stack) {
+    *stack >>= 1;
+}
+
+/**
+ * Returns the value at the top of the stack.
+ */
+static inline bool
+pm_state_stack_p(const pm_state_stack_t *stack) {
+    return *stack & 1;
+}
+
 static inline void
 pm_accepts_block_stack_push(pm_parser_t *parser, bool value) {
     // Use the negation of the value to prevent stack overflow.
@@ -12945,6 +12970,32 @@ parse_write(pm_parser_t *parser, pm_node_t *target, pm_token_t *operator, pm_nod
     }
 }
 
+/**
+ * Certain expressions are not writable, but in order to provide a better
+ * experience we give a specific error message. In order to maintain as much
+ * information in the tree as possible, we replace them with local variable
+ * writes.
+ */
+static pm_node_t *
+parse_unwriteable_write(pm_parser_t *parser, pm_node_t *target, const pm_token_t *equals, pm_node_t *value) {
+    switch (PM_NODE_TYPE(target)) {
+        case PM_SOURCE_ENCODING_NODE: pm_parser_err_token(parser, equals, PM_ERR_EXPRESSION_NOT_WRITABLE_ENCODING); break;
+        case PM_FALSE_NODE: pm_parser_err_token(parser, equals, PM_ERR_EXPRESSION_NOT_WRITABLE_FALSE); break;
+        case PM_SOURCE_FILE_NODE: pm_parser_err_token(parser, equals, PM_ERR_EXPRESSION_NOT_WRITABLE_FILE); break;
+        case PM_SOURCE_LINE_NODE: pm_parser_err_token(parser, equals, PM_ERR_EXPRESSION_NOT_WRITABLE_LINE); break;
+        case PM_NIL_NODE: pm_parser_err_token(parser, equals, PM_ERR_EXPRESSION_NOT_WRITABLE_NIL); break;
+        case PM_SELF_NODE: pm_parser_err_token(parser, equals, PM_ERR_EXPRESSION_NOT_WRITABLE_SELF); break;
+        case PM_TRUE_NODE: pm_parser_err_token(parser, equals, PM_ERR_EXPRESSION_NOT_WRITABLE_TRUE); break;
+        default: break;
+    }
+
+    pm_constant_id_t name = pm_parser_constant_id_location(parser, target->location.start, target->location.end);
+    pm_local_variable_write_node_t *result = pm_local_variable_write_node_create(parser, name, 0, value, &target->location, equals);
+
+    pm_node_destroy(parser, target);
+    return (pm_node_t *) result;
+}
+
 /**
  * Parse a list of targets for assignment. This is used in the case of a for
  * loop or a multi-assignment. For example, in the following code:
@@ -19357,13 +19408,25 @@ parse_expression_infix(pm_parser_t *parser, pm_node_t *node, pm_binding_power_t
                     pm_node_t *value = parse_assignment_values(parser, previous_binding_power, PM_BINDING_POWER_MULTI_ASSIGNMENT + 1, accepts_command_call, PM_ERR_EXPECT_EXPRESSION_AFTER_EQUAL);
                     return parse_write(parser, (pm_node_t *) multi_target, &token, value);
                 }
+                case PM_SOURCE_ENCODING_NODE:
+                case PM_FALSE_NODE:
+                case PM_SOURCE_FILE_NODE:
+                case PM_SOURCE_LINE_NODE:
+                case PM_NIL_NODE:
+                case PM_SELF_NODE:
+                case PM_TRUE_NODE: {
+                    // In these special cases, we have specific error messages
+                    // and we will replace them with local variable writes.
+                    parser_lex(parser);
+                    pm_node_t *value = parse_assignment_values(parser, previous_binding_power, binding_power, accepts_command_call, PM_ERR_EXPECT_EXPRESSION_AFTER_EQUAL);
+                    return parse_unwriteable_write(parser, node, &token, value);
+                }
                 default:
+                    // In this case we have an = sign, but we don't know what
+                    // it's for. We need to treat it as an error. We'll mark it
+                    // as an error and skip past it.
                     parser_lex(parser);
-
-                    // In this case we have an = sign, but we don't know what it's for. We
-                    // need to treat it as an error. For now, we'll mark it as an error
-                    // and just skip right past it.
-                    pm_parser_err_token(parser, &token, PM_ERR_EXPECT_EXPRESSION_AFTER_EQUAL);
+                    pm_parser_err_token(parser, &token, PM_ERR_EXPRESSION_NOT_WRITABLE);
                     return node;
             }
         }
@@ -21191,6 +21254,8 @@ pm_parser_errors_format(const pm_parser_t *parser, const pm_list_t *error_list,
 
         if (inline_messages) {
             pm_buffer_append_byte(buffer, ' ');
+            assert(error->error != NULL);
+
             const char *message = error->error->message;
             pm_buffer_append_string(buffer, message, strlen(message));
         }
diff --git a/prism/templates/lib/prism/node.rb.erb b/prism/templates/lib/prism/node.rb.erb
index 12a984e5a28bb4..6b5a28531585fe 100644
--- a/prism/templates/lib/prism/node.rb.erb
+++ b/prism/templates/lib/prism/node.rb.erb
@@ -60,6 +60,17 @@ module Prism
       DotVisitor.new.tap { |visitor| accept(visitor) }.to_dot
     end
 
+    # Returns a list of the fields that exist for this node class. Fields
+    # describe the structure of the node. This kind of reflection is useful for
+    # things like recursively visiting each node _and_ field in the tree.
+    def self.fields
+      # This method should only be called on subclasses of Node, not Node
+      # itself.
+      raise NoMethodError, "undefined method `fields' for #{inspect}" if self == Node
+
+      Reflection.fields_for(self)
+    end
+
     # --------------------------------------------------------------------------
     # :section: Node interface
     # These methods are effectively abstract methods that must be implemented by
@@ -102,6 +113,11 @@ module Prism
     def inspect(inspector = NodeInspector.new)
       raise NoMethodError, "undefined method `inspect' for #{inspect}"
     end
+
+    # Returns the type of the node as a symbol.
+    def self.type
+      raise NoMethodError, "undefined method `type' for #{inspect}"
+    end
   end
   <%- nodes.each do |node| -%>
 
diff --git a/prism/templates/lib/prism/reflection.rb.erb b/prism/templates/lib/prism/reflection.rb.erb
new file mode 100644
index 00000000000000..13d1da33e874ff
--- /dev/null
+++ b/prism/templates/lib/prism/reflection.rb.erb
@@ -0,0 +1,151 @@
+module Prism
+  # The Reflection module provides the ability to reflect on the structure of
+  # the syntax tree itself, as opposed to looking at a single syntax tree. This
+  # is useful in metaprogramming contexts.
+  module Reflection
+    # A field represents a single piece of data on a node. It is the base class
+    # for all other field types.
+    class Field
+      # The name of the field.
+      attr_reader :name
+
+      # Initializes the field with the given name.
+      def initialize(name)
+        @name = name
+      end
+    end
+
+    # A node field represents a single child node in the syntax tree. It
+    # resolves to a Prism::Node in Ruby.
+    class NodeField < Field
+    end
+
+    # An optional node field represents a single child node in the syntax tree
+    # that may or may not be present. It resolves to either a Prism::Node or nil
+    # in Ruby.
+    class OptionalNodeField < Field
+    end
+
+    # A node list field represents a list of child nodes in the syntax tree. It
+    # resolves to an array of Prism::Node instances in Ruby.
+    class NodeListField < Field
+    end
+
+    # A constant field represents a constant value on a node. Effectively, it
+    # represents an identifier found within the source. It resolves to a symbol
+    # in Ruby.
+    class ConstantField < Field
+    end
+
+    # An optional constant field represents a constant value on a node that may
+    # or may not be present. It resolves to either a symbol or nil in Ruby.
+    class OptionalConstantField < Field
+    end
+
+    # A constant list field represents a list of constant values on a node. It
+    # resolves to an array of symbols in Ruby.
+    class ConstantListField < Field
+    end
+
+    # A string field represents a string value on a node. It almost always
+    # represents the unescaped value of a string-like literal. It resolves to a
+    # string in Ruby.
+    class StringField < Field
+    end
+
+    # A location field represents the location of some part of the node in the
+    # source code. For example, the location of a keyword or an operator. It
+    # resolves to a Prism::Location in Ruby.
+    class LocationField < Field
+    end
+
+    # An optional location field represents the location of some part of the
+    # node in the source code that may or may not be present. It resolves to
+    # either a Prism::Location or nil in Ruby.
+    class OptionalLocationField < Field
+    end
+
+    # A uint8 field represents an unsigned 8-bit integer value on a node. It
+    # resolves to an Integer in Ruby.
+    class UInt8Field < Field
+    end
+
+    # A uint32 field represents an unsigned 32-bit integer value on a node. It
+    # resolves to an Integer in Ruby.
+    class UInt32Field < Field
+    end
+
+    # A flags field represents a bitset of flags on a node. It resolves to an
+    # integer in Ruby. Note that the flags cannot be accessed directly on the
+    # node because the integer is kept private. Instead, the various flags in
+    # the bitset should be accessed through their query methods.
+    class FlagsField < Field
+      # The names of the flags in the bitset.
+      attr_reader :flags
+
+      # Initializes the flags field with the given name and flags.
+      def initialize(name, flags)
+        super(name)
+        @flags = flags
+      end
+    end
+
+    # An integer field represents an arbitrarily-sized integer value. It is used
+    # exclusively to represent the value of an integer literal. It resolves to
+    # an Integer in Ruby.
+    class IntegerField < Field
+    end
+
+    # A double field represents a double-precision floating point value. It is
+    # used exclusively to represent the value of a floating point literal. It
+    # resolves to a Float in Ruby.
+    class DoubleField < Field
+    end
+
+    # Returns the fields for the given node.
+    def self.fields_for(node)
+      case node.type
+      <%- nodes.each do |node| -%>
+      when :<%= node.human %>
+        [<%= node.fields.map { |field|
+          case field
+          when Prism::Template::NodeField
+            "NodeField.new(:#{field.name})"
+          when Prism::Template::OptionalNodeField
+            "OptionalNodeField.new(:#{field.name})"
+          when Prism::Template::NodeListField
+            "NodeListField.new(:#{field.name})"
+          when Prism::Template::ConstantField
+            "ConstantField.new(:#{field.name})"
+          when Prism::Template::OptionalConstantField
+            "OptionalConstantField.new(:#{field.name})"
+          when Prism::Template::ConstantListField
+            "ConstantListField.new(:#{field.name})"
+          when Prism::Template::StringField
+            "StringField.new(:#{field.name})"
+          when Prism::Template::LocationField
+            "LocationField.new(:#{field.name})"
+          when Prism::Template::OptionalLocationField
+            "OptionalLocationField.new(:#{field.name})"
+          when Prism::Template::UInt8Field
+            "UInt8Field.new(:#{field.name})"
+          when Prism::Template::UInt32Field
+            "UInt32Field.new(:#{field.name})"
+          when Prism::Template::FlagsField
+            found = flags.find { |flag| flag.name == field.kind }.tap { |found| raise "Expected to find #{field.kind}" unless found }
+            "FlagsField.new(:#{field.name}, [#{found.values.map { |value| ":#{value.name.downcase}?" }.join(", ")}])"
+          when Prism::Template::IntegerField
+            "IntegerField.new(:#{field.name})"
+          when Prism::Template::DoubleField
+            "DoubleField.new(:#{field.name})"
+          else
+            raise field.class.name
+          end
+        }.join(", ") %>]
+      <%- end -%>
+      else
+        raise "Unknown node type: #{node.type.inspect}"
+      end
+    end
+  end
+end
diff --git a/prism/templates/src/diagnostic.c.erb b/prism/templates/src/diagnostic.c.erb
index 97ad451890a2a2..42f802455146ea 100644
--- a/prism/templates/src/diagnostic.c.erb
+++ b/prism/templates/src/diagnostic.c.erb
@@ -188,6 +188,14 @@ static const pm_diagnostic_data_t diagnostic_messages[PM_DIAGNOSTIC_ID_MAX] = {
     [PM_ERR_EXPECT_STRING_CONTENT]              = { "expected string content after opening string delimiter", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_EXPECT_WHEN_DELIMITER]              = { "expected a delimiter after the predicates of a `when` clause", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_EXPRESSION_BARE_HASH]               = { "unexpected bare hash in expression", PM_ERROR_LEVEL_SYNTAX },
+    [PM_ERR_EXPRESSION_NOT_WRITABLE]            = { "unexpected '='; target cannot be written", PM_ERROR_LEVEL_SYNTAX },
+    [PM_ERR_EXPRESSION_NOT_WRITABLE_ENCODING]   = { "Can't assign to __ENCODING__", PM_ERROR_LEVEL_SYNTAX },
+    [PM_ERR_EXPRESSION_NOT_WRITABLE_FALSE]      = { "Can't assign to false", PM_ERROR_LEVEL_SYNTAX },
+    [PM_ERR_EXPRESSION_NOT_WRITABLE_FILE]       = { "Can't assign to __FILE__", PM_ERROR_LEVEL_SYNTAX },
+    [PM_ERR_EXPRESSION_NOT_WRITABLE_LINE]       = { "Can't assign to __LINE__", PM_ERROR_LEVEL_SYNTAX },
+    [PM_ERR_EXPRESSION_NOT_WRITABLE_NIL]        = { "Can't assign to nil", PM_ERROR_LEVEL_SYNTAX },
+    [PM_ERR_EXPRESSION_NOT_WRITABLE_SELF]       = { "Can't change the value of self", PM_ERROR_LEVEL_SYNTAX },
+    [PM_ERR_EXPRESSION_NOT_WRITABLE_TRUE]       = { "Can't assign to true", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_FLOAT_PARSE]                        = { "could not parse the float '%.*s'", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_FOR_COLLECTION]                     = { "expected a collection after the `in` in a `for` statement", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_FOR_INDEX]                          = { "expected an index after `for`", PM_ERROR_LEVEL_SYNTAX },
diff --git a/prism/templates/template.rb b/prism/templates/template.rb
index 31257ef1a150c5..d0ce6c6643755d 100755
--- a/prism/templates/template.rb
+++ b/prism/templates/template.rb
@@ -631,6 +631,7 @@ def locals
       "lib/prism/dsl.rb",
       "lib/prism/mutation_compiler.rb",
       "lib/prism/node.rb",
+      "lib/prism/reflection.rb",
       "lib/prism/serialize.rb",
       "lib/prism/visitor.rb",
       "src/diagnostic.c",
diff --git a/prism/util/pm_integer.c b/prism/util/pm_integer.c
index 8f8b75474df33a..0739662e98037b 100644
--- a/prism/util/pm_integer.c
+++ b/prism/util/pm_integer.c
@@ -172,21 +172,21 @@ karatsuba_multiply(pm_integer_t *destination, pm_integer_t *left, pm_integer_t *
     pm_integer_t y0 = { 0, half, right_values, false };
     pm_integer_t y1 = { 0, right_length - half, right_values + half, false };
 
-    pm_integer_t z0;
+    pm_integer_t z0 = { 0 };
     karatsuba_multiply(&z0, &x0, &y0, base);
 
-    pm_integer_t z2;
+    pm_integer_t z2 = { 0 };
     karatsuba_multiply(&z2, &x1, &y1, base);
 
     // For simplicity to avoid considering negative values,
     // use `z1 = (x0 + x1) * (y0 + y1) - z0 - z2` instead of original karatsuba algorithm.
-    pm_integer_t x01;
+    pm_integer_t x01 = { 0 };
     big_add(&x01, &x0, &x1, base);
 
-    pm_integer_t y01;
+    pm_integer_t y01 = { 0 };
     big_add(&y01, &y0, &y1, base);
 
-    pm_integer_t xy;
+    pm_integer_t xy = { 0 };
     karatsuba_multiply(&xy, &x01, &y01, base);
 
     pm_integer_t z1;
@@ -194,7 +194,11 @@ karatsuba_multiply(pm_integer_t *destination, pm_integer_t *left, pm_integer_t *
 
     size_t length = left_length + right_length;
     uint32_t *values = (uint32_t*) xcalloc(length, sizeof(uint32_t));
+
+    assert(z0.values != NULL);
     memcpy(values, z0.values, sizeof(uint32_t) * z0.length);
+
+    assert(z2.values != NULL);
     memcpy(values + 2 * half, z2.values, sizeof(uint32_t) * z2.length);
 
     uint32_t carry = 0;
@@ -326,6 +330,8 @@ pm_integer_convert_base(pm_integer_t *destination, const pm_integer_t *source, u
     INTEGER_EXTRACT(source, source_length, source_values)
 
     size_t bigints_length = (source_length + 1) / 2;
+    assert(bigints_length > 0);
+
     pm_integer_t *bigints = (pm_integer_t *) xcalloc(bigints_length, sizeof(pm_integer_t));
     if (bigints == NULL) return;
 
@@ -345,13 +351,13 @@ pm_integer_convert_base(pm_integer_t *destination, const pm_integer_t *source, u
         base = next_base;
 
         size_t next_length = (bigints_length + 1) / 2;
-        pm_integer_t *next_bigints = (pm_integer_t *) xmalloc(sizeof(pm_integer_t) * next_length);
+        pm_integer_t *next_bigints = (pm_integer_t *) xcalloc(next_length, sizeof(pm_integer_t));
 
         for (size_t bigints_index = 0; bigints_index < bigints_length; bigints_index += 2) {
             if (bigints_index + 1 == bigints_length) {
                 next_bigints[bigints_index / 2] = bigints[bigints_index];
             } else {
-                pm_integer_t multiplied;
+                pm_integer_t multiplied = { 0 };
                 karatsuba_multiply(&multiplied, &base, &bigints[bigints_index + 1], base_to);
 
                 big_add(&next_bigints[bigints_index / 2], &bigints[bigints_index], &multiplied, base_to);
@@ -584,7 +590,7 @@ pm_integer_string(pm_buffer_t *buffer, const pm_integer_t *integer) {
     }
 
     // Otherwise, first we'll convert the base from 1<<32 to 10**9.
-    pm_integer_t converted;
+    pm_integer_t converted = { 0 };
     pm_integer_convert_base(&converted, integer, (uint64_t) 1 << 32, 1000000000);
 
     if (converted.values == NULL) {
diff --git a/prism/util/pm_state_stack.c b/prism/util/pm_state_stack.c
deleted file mode 100644
index 2a424b4c03c296..00000000000000
--- a/prism/util/pm_state_stack.c
+++ /dev/null
@@ -1,25 +0,0 @@
-#include "prism/util/pm_state_stack.h"
-
-/**
- * Pushes a value onto the stack.
- */
-void
-pm_state_stack_push(pm_state_stack_t *stack, bool value) {
-    *stack = (*stack << 1) | (value & 1);
-}
-
-/**
- * Pops a value off the stack.
- */
-void
-pm_state_stack_pop(pm_state_stack_t *stack) {
-    *stack >>= 1;
-}
-
-/**
- * Returns the value at the top of the stack.
- */
-bool
-pm_state_stack_p(pm_state_stack_t *stack) {
-    return *stack & 1;
-}
diff --git a/prism/util/pm_state_stack.h b/prism/util/pm_state_stack.h
deleted file mode 100644
index 1ce57a2209f0c2..00000000000000
--- a/prism/util/pm_state_stack.h
+++ /dev/null
@@ -1,42 +0,0 @@
-/**
- * @file pm_state_stack.h
- *
- * A stack of boolean values.
- */
-#ifndef PRISM_STATE_STACK_H
-#define PRISM_STATE_STACK_H
-
-#include "prism/defines.h"
-
-#include <stdbool.h>
-#include <stdint.h>
-
-/**
- * A struct that represents a stack of boolean values.
- */
-typedef uint32_t pm_state_stack_t;
-
-/**
- * Pushes a value onto the stack.
- *
- * @param stack The stack to push the value onto.
- * @param value The value to push onto the stack.
- */
-void pm_state_stack_push(pm_state_stack_t *stack, bool value);
-
-/**
- * Pops a value off the stack.
- *
- * @param stack The stack to pop the value off of.
- */
-void pm_state_stack_pop(pm_state_stack_t *stack);
-
-/**
- * Returns the value at the top of the stack.
- *
- * @param stack The stack to get the value from.
- * @return The value at the top of the stack.
- */
-bool pm_state_stack_p(pm_state_stack_t *stack);
-
-#endif
diff --git a/rational.c b/rational.c
index 3b82016f323087..014cbb6c6adf87 100644
--- a/rational.c
+++ b/rational.c
@@ -418,7 +418,7 @@ nurat_s_new_internal(VALUE klass, VALUE num, VALUE den)
 
     RATIONAL_SET_NUM((VALUE)obj, num);
     RATIONAL_SET_DEN((VALUE)obj, den);
-    OBJ_FREEZE_RAW((VALUE)obj);
+    OBJ_FREEZE((VALUE)obj);
 
     return (VALUE)obj;
 }
@@ -1847,7 +1847,7 @@ nurat_loader(VALUE self, VALUE a)
     nurat_canonicalize(&num, &den);
     RATIONAL_SET_NUM((VALUE)dat, num);
     RATIONAL_SET_DEN((VALUE)dat, den);
-    OBJ_FREEZE_RAW(self);
+    OBJ_FREEZE(self);
 
     return self;
 }
diff --git a/ruby.c b/ruby.c
index fb60551c3fc050..e939320f1f63d3 100644
--- a/ruby.c
+++ b/ruby.c
@@ -706,11 +706,11 @@ ruby_init_loadpath(void)
             p -= bindir_len;
             archlibdir = rb_str_subseq(sopath, 0, p - libpath);
             rb_str_cat_cstr(archlibdir, libdir);
-            OBJ_FREEZE_RAW(archlibdir);
+            OBJ_FREEZE(archlibdir);
         }
         else if (p - libpath >= libdir_len && !strncmp(p - libdir_len, libdir, libdir_len)) {
             archlibdir = rb_str_subseq(sopath, 0, (p2 ? p2 : p) - libpath);
-            OBJ_FREEZE_RAW(archlibdir);
+            OBJ_FREEZE(archlibdir);
             p -= libdir_len;
         }
 #ifdef ENABLE_MULTIARCH
@@ -741,7 +741,7 @@ ruby_init_loadpath(void)
 #endif
     rb_gc_register_address(&ruby_prefix_path);
     ruby_prefix_path = PREFIX_PATH();
-    OBJ_FREEZE_RAW(ruby_prefix_path);
+    OBJ_FREEZE(ruby_prefix_path);
     if (!archlibdir) archlibdir = ruby_prefix_path;
     rb_gc_register_address(&ruby_archlibdir_path);
     ruby_archlibdir_path = archlibdir;
diff --git a/ruby_parser.c b/ruby_parser.c
index 5d9c6c938f35db..16a868bc6b3707 100644
--- a/ruby_parser.c
+++ b/ruby_parser.c
@@ -309,18 +309,6 @@ syntax_error_new(void)
     return rb_class_new_instance(0, 0, rb_eSyntaxError);
 }
 
-static VALUE
-obj_write(VALUE old, VALUE *slot, VALUE young)
-{
-    return RB_OBJ_WRITE(old, slot, young);
-}
-
-static VALUE
-default_rs(void)
-{
-    return rb_default_rs;
-}
-
 static void *
 memmove2(void *dest, const void *src, size_t t, size_t n)
 {
@@ -429,7 +417,6 @@ static const rb_parser_config_t rb_global_parser_config = {
     .ary_push = rb_ary_push,
     .ary_new_from_args = rb_ary_new_from_args,
     .ary_unshift = rb_ary_unshift,
-    .ary_modify = rb_ary_modify,
     .array_len = rb_array_len,
     .array_aref = RARRAY_AREF,
 
@@ -476,7 +463,6 @@ static const rb_parser_config_t rb_global_parser_config = {
 
     .stderr_tty_p = rb_stderr_tty_p,
     .write_error_str = rb_write_error_str,
-    .default_rs = default_rs,
     .io_write = rb_io_write,
     .io_flush = rb_io_flush,
     .io_puts = rb_io_puts,
@@ -501,7 +487,6 @@ static const rb_parser_config_t rb_global_parser_config = {
     .enc_mbcput = enc_mbcput,
     .enc_find_index = rb_enc_find_index,
     .enc_from_index = enc_from_index,
-    .enc_associate_index = rb_enc_associate_index,
     .enc_isspace = enc_isspace,
     .enc_coderange_7bit = ENC_CODERANGE_7BIT,
     .enc_coderange_unknown = ENC_CODERANGE_UNKNOWN,
@@ -528,10 +513,8 @@ static const rb_parser_config_t rb_global_parser_config = {
 
     .sized_xfree = ruby_sized_xfree,
     .sized_realloc_n = ruby_sized_realloc_n,
-    .obj_write = obj_write,
     .gc_guard = gc_guard,
     .gc_mark = rb_gc_mark,
-    .gc_mark_and_move = rb_gc_mark_and_move,
 
     .reg_compile = rb_reg_compile,
     .reg_check_preprocess = rb_reg_check_preprocess,
diff --git a/rubyparser.h b/rubyparser.h
index d36e8dcede032f..6d346a7ff484a9 100644
--- a/rubyparser.h
+++ b/rubyparser.h
@@ -1264,7 +1264,6 @@ typedef struct rb_parser_config_struct {
     VALUE (*ary_push)(VALUE ary, VALUE elem);
     VALUE (*ary_new_from_args)(long n, ...);
     VALUE (*ary_unshift)(VALUE ary, VALUE item);
-    void (*ary_modify)(VALUE ary);
     long (*array_len)(VALUE a);
     VALUE (*array_aref)(VALUE, long);
 
@@ -1318,7 +1317,6 @@ typedef struct rb_parser_config_struct {
     /* IO */
     int (*stderr_tty_p)(void);
     void (*write_error_str)(VALUE mesg);
-    VALUE (*default_rs)(void);
     VALUE (*io_write)(VALUE io, VALUE str);
     VALUE (*io_flush)(VALUE io);
     VALUE (*io_puts)(int argc, const VALUE *argv, VALUE out);
@@ -1345,7 +1343,6 @@ typedef struct rb_parser_config_struct {
     int (*enc_mbcput)(unsigned int c, void *buf, rb_encoding *enc);
     int (*enc_find_index)(const char *name);
     rb_encoding *(*enc_from_index)(int idx);
-    VALUE (*enc_associate_index)(VALUE obj, int encindex);
     int (*enc_isspace)(OnigCodePoint c, rb_encoding *enc);
     rb_encoding *(*enc_compatible)(VALUE str1, VALUE str2);
     VALUE (*enc_from_encoding)(rb_encoding *enc);
@@ -1378,10 +1375,8 @@ typedef struct rb_parser_config_struct {
     /* GC */
     void (*sized_xfree)(void *x, size_t size);
     void *(*sized_realloc_n)(void *ptr, size_t new_count, size_t element_size, size_t old_count);
-    VALUE (*obj_write)(VALUE, VALUE *, VALUE);
     void (*gc_guard)(VALUE);
     void (*gc_mark)(VALUE);
-    void (*gc_mark_and_move)(VALUE *ptr);
 
     /* Re */
     VALUE (*reg_compile)(VALUE str, int options, const char *sourcefile, int sourceline);
diff --git a/spec/bundler/install/gemfile/specific_platform_spec.rb b/spec/bundler/install/gemfile/specific_platform_spec.rb
index c81c7095b0e74a..5f1b034bfc0de1 100644
--- a/spec/bundler/install/gemfile/specific_platform_spec.rb
+++ b/spec/bundler/install/gemfile/specific_platform_spec.rb
@@ -1262,43 +1262,47 @@
     end
   end
 
-  it "adds current musl platform" do
-    build_repo4 do
-      build_gem "rcee_precompiled", "0.5.0" do |s|
-        s.platform = "x86_64-linux"
-      end
+  ["x86_64-linux", "x86_64-linux-musl"].each do |host_platform|
+    describe "on host platform #{host_platform}" do
+      it "adds current musl platform" do
+        build_repo4 do
+          build_gem "rcee_precompiled", "0.5.0" do |s|
+            s.platform = "x86_64-linux"
+          end
+
+          build_gem "rcee_precompiled", "0.5.0" do |s|
+            s.platform = "x86_64-linux-musl"
+          end
+        end
 
-      build_gem "rcee_precompiled", "0.5.0" do |s|
-        s.platform = "x86_64-linux-musl"
-      end
-    end
+        gemfile <<~G
+          source "#{file_uri_for(gem_repo4)}"
 
-    gemfile <<~G
-      source "#{file_uri_for(gem_repo4)}"
+          gem "rcee_precompiled", "0.5.0"
+        G
 
-      gem "rcee_precompiled", "0.5.0"
-    G
+        simulate_platform host_platform do
+          bundle "lock", artifice: "compact_index", env: { "BUNDLER_SPEC_GEM_REPO" => gem_repo4.to_s }
 
-    simulate_platform "x86_64-linux-musl" do
-      bundle "lock", artifice: "compact_index", env: { "BUNDLER_SPEC_GEM_REPO" => gem_repo4.to_s }
+          expect(lockfile).to eq(<<~L)
+            GEM
+              remote: #{file_uri_for(gem_repo4)}/
+              specs:
+                rcee_precompiled (0.5.0-x86_64-linux)
+                rcee_precompiled (0.5.0-x86_64-linux-musl)
 
-      expect(lockfile).to eq(<<~L)
-        GEM
-          remote: #{file_uri_for(gem_repo4)}/
-          specs:
-            rcee_precompiled (0.5.0-x86_64-linux)
-            rcee_precompiled (0.5.0-x86_64-linux-musl)
+            PLATFORMS
+              x86_64-linux
+              x86_64-linux-musl
 
-        PLATFORMS
-          x86_64-linux
-          x86_64-linux-musl
+            DEPENDENCIES
+              rcee_precompiled (= 0.5.0)
 
-        DEPENDENCIES
-          rcee_precompiled (= 0.5.0)
-
-        BUNDLED WITH
-           #{Bundler::VERSION}
-      L
+            BUNDLED WITH
+               #{Bundler::VERSION}
+          L
+        end
+      end
     end
   end
 
diff --git a/spec/ruby/core/fiber/raise_spec.rb b/spec/ruby/core/fiber/raise_spec.rb
index eb4b39c8be55df..b3e021e6360b7a 100644
--- a/spec/ruby/core/fiber/raise_spec.rb
+++ b/spec/ruby/core/fiber/raise_spec.rb
@@ -91,6 +91,40 @@
 
     fiber_two.resume.should == [:yield_one, :rescued]
   end
+
+  ruby_version_is "3.4" do
+    it "raises on the resumed fiber" do
+      root_fiber = Fiber.current
+      f1 = Fiber.new { root_fiber.transfer }
+      f2 = Fiber.new { f1.resume }
+      f2.transfer
+
+      -> do
+        f2.raise(RuntimeError, "Expected error")
+      end.should raise_error(RuntimeError, "Expected error")
+    end
+
+    it "raises on itself" do
+      -> do
+        Fiber.current.raise(RuntimeError, "Expected error")
+      end.should raise_error(RuntimeError, "Expected error")
+    end
+
+    it "should raise on parent fiber" do
+      f2 = nil
+      f1 = Fiber.new do
+        # This is equivalent to Kernel#raise:
+        f2.raise(RuntimeError, "Expected error")
+      end
+      f2 = Fiber.new do
+        f1.resume
+      end
+
+      -> do
+        f2.resume
+      end.should raise_error(RuntimeError, "Expected error")
+    end
+  end
 end
 
 
diff --git a/spec/ruby/core/thread/each_caller_location_spec.rb b/spec/ruby/core/thread/each_caller_location_spec.rb
index dbece06cd8183e..29c271789b5225 100644
--- a/spec/ruby/core/thread/each_caller_location_spec.rb
+++ b/spec/ruby/core/thread/each_caller_location_spec.rb
@@ -40,10 +40,10 @@
       }.should raise_error(LocalJumpError, "no block given")
     end
 
-    it "doesn't accept positional and keyword arguments" do
+    it "doesn't accept keyword arguments" do
       -> {
         Thread.each_caller_location(12, foo: 10) {}
-      }.should raise_error(ArgumentError, "wrong number of arguments (given 2, expected 0)")
+      }.should raise_error(ArgumentError);
     end
   end
 end
diff --git a/string.c b/string.c
index 98bf0dcbb82d11..b760c4652cc410 100644
--- a/string.c
+++ b/string.c
@@ -380,7 +380,7 @@ fstr_update_callback(st_data_t *key, st_data_t *value, st_data_t data, int exist
                                      RSTRING(str)->len,
                                      ENCODING_GET(str));
             }
-            OBJ_FREEZE_RAW(str);
+            OBJ_FREEZE(str);
         }
         else {
             if (!OBJ_FROZEN(str) || CHILLED_STRING_P(str)) {
@@ -416,7 +416,7 @@ rb_fstring(VALUE str)
     bare = BARE_STRING_P(str);
     if (!bare) {
         if (STR_EMBED_P(str)) {
-            OBJ_FREEZE_RAW(str);
+            OBJ_FREEZE(str);
 	    FL_SET_RAW(str, RUBY_FL_SHAREABLE);
             return str;
         }
@@ -437,7 +437,7 @@ rb_fstring(VALUE str)
 
     if (!bare) {
         str_replace_shared_without_enc(str, fstr);
-        OBJ_FREEZE_RAW(str);
+        OBJ_FREEZE(str);
 	FL_SET_RAW(str, RUBY_FL_SHAREABLE);
         return str;
     }
diff --git a/struct.c b/struct.c
index e82bcc3e032804..544228f76b9582 100644
--- a/struct.c
+++ b/struct.c
@@ -136,7 +136,7 @@ struct_set_members(VALUE klass, VALUE /* frozen hidden array */ members)
                 j = struct_member_pos_probe(j, mask);
             }
         }
-        OBJ_FREEZE_RAW(back);
+        OBJ_FREEZE(back);
     }
     rb_ivar_set(klass, id_members, members);
     rb_ivar_set(klass, id_back_members, back);
@@ -422,7 +422,7 @@ struct_make_members_list(va_list ar)
     }
     ary = rb_hash_keys(list);
     RBASIC_CLEAR_CLASS(ary);
-    OBJ_FREEZE_RAW(ary);
+    OBJ_FREEZE(ary);
     return ary;
 }
 
@@ -682,7 +682,7 @@ rb_struct_s_def(int argc, VALUE *argv, VALUE klass)
     }
     rest = rb_hash_keys(rest);
     RBASIC_CLEAR_CLASS(rest);
-    OBJ_FREEZE_RAW(rest);
+    OBJ_FREEZE(rest);
     if (NIL_P(name)) {
         st = anonymous_struct(klass);
     }
@@ -794,7 +794,7 @@ VALUE
 rb_struct_initialize(VALUE self, VALUE values)
 {
     rb_struct_initialize_m(RARRAY_LENINT(values), RARRAY_CONST_PTR(values), self);
-    if (rb_obj_is_kind_of(self, rb_cData)) OBJ_FREEZE_RAW(self);
+    if (rb_obj_is_kind_of(self, rb_cData)) OBJ_FREEZE(self);
     RB_GC_GUARD(values);
     return Qnil;
 }
@@ -1685,7 +1685,7 @@ rb_data_s_def(int argc, VALUE *argv, VALUE klass)
     }
     rest = rb_hash_keys(rest);
     RBASIC_CLEAR_CLASS(rest);
-    OBJ_FREEZE_RAW(rest);
+    OBJ_FREEZE(rest);
     data_class = anonymous_struct(klass);
     setup_data(data_class, rest);
     if (rb_block_given_p()) {
@@ -1802,7 +1802,7 @@ rb_data_initialize_m(int argc, const VALUE *argv, VALUE self)
     rb_hash_foreach(argv[0], struct_hash_set_i, (VALUE)&arg);
     // Freeze early before potentially raising, so that we don't leave an
     // unfrozen copy on the heap, which could get exposed via ObjectSpace.
-    OBJ_FREEZE_RAW(self);
+    OBJ_FREEZE(self);
     if (arg.unknown_keywords != Qnil) {
         rb_exc_raise(rb_keyword_error_new("unknown", arg.unknown_keywords));
     }
@@ -1814,7 +1814,7 @@ static VALUE
 rb_data_init_copy(VALUE copy, VALUE s)
 {
     copy = rb_struct_init_copy(copy, s);
-    RB_OBJ_FREEZE_RAW(copy);
+    RB_OBJ_FREEZE(copy);
     return copy;
 }
 
diff --git a/test/prism/reflection_test.rb b/test/prism/reflection_test.rb
new file mode 100644
index 00000000000000..869b68b1f8f5cb
--- /dev/null
+++ b/test/prism/reflection_test.rb
@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+require_relative "test_helper"
+
+module Prism
+  class ReflectionTest < TestCase
+    def test_fields_for
+      fields = Reflection.fields_for(CallNode)
+      methods = CallNode.instance_methods(false)
+
+      fields.each do |field|
+        if field.is_a?(Reflection::FlagsField)
+          field.flags.each do |flag|
+            assert_includes methods, flag
+          end
+        else
+          assert_includes methods, field.name
+        end
+      end
+    end
+  end
+end
diff --git a/test/reline/helper.rb b/test/reline/helper.rb
index f2f3421ded0bf4..26fe8344829523 100644
--- a/test/reline/helper.rb
+++ b/test/reline/helper.rb
@@ -131,7 +131,7 @@ def input_raw_keys(input, convert = true)
   def assert_line_around_cursor(before, after)
     before = convert_str(before)
     after = convert_str(after)
-    line = @line_editor.line
+    line = @line_editor.current_line
     byte_pointer = @line_editor.instance_variable_get(:@byte_pointer)
     actual_before = line.byteslice(0, byte_pointer)
     actual_after = line.byteslice(byte_pointer..)
diff --git a/test/reline/test_key_actor_emacs.rb b/test/reline/test_key_actor_emacs.rb
index 8f5676a1d4f170..a9baf9ad3724a6 100644
--- a/test/reline/test_key_actor_emacs.rb
+++ b/test/reline/test_key_actor_emacs.rb
@@ -1436,4 +1436,9 @@ def test_unix_line_discard
     input_keys("\C-f\C-u", false)
     assert_line_around_cursor('', '')
   end
+
+  def test_vi_editing_mode
+    @line_editor.__send__(:vi_editing_mode, nil)
+    assert(@config.editing_mode_is?(:vi_insert))
+  end
 end
diff --git a/test/reline/test_key_actor_vi.rb b/test/reline/test_key_actor_vi.rb
index cf3943ae379bce..4deae2dd8313c1 100644
--- a/test/reline/test_key_actor_vi.rb
+++ b/test/reline/test_key_actor_vi.rb
@@ -911,4 +911,9 @@ def test_vi_motion_operators
       input_keys("test = { foo: bar }\C-[BBBldt}b")
     end
   end
+
+  def test_emacs_editing_mode
+    @line_editor.__send__(:emacs_editing_mode, nil)
+    assert(@config.editing_mode_is?(:emacs))
+  end
 end
diff --git a/test/reline/yamatanooroti/test_rendering.rb b/test/reline/yamatanooroti/test_rendering.rb
index fe0f8842eafa92..09d064934a9c32 100644
--- a/test/reline/yamatanooroti/test_rendering.rb
+++ b/test/reline/yamatanooroti/test_rendering.rb
@@ -309,6 +309,21 @@ def test_prompt_with_escape_sequence_and_autowrap
       EOC
     end
 
+    def test_readline_with_multiline_input
+      start_terminal(5, 50, %W{ruby -I#{@pwd}/lib #{@pwd}/test/reline/yamatanooroti/multiline_repl --dynamic-prompt}, startup_message: 'Multiline REPL.')
+      write("def foo\n  bar\nend\n")
+      write("Reline.readline('prompt> ')\n")
+      write("\C-p\C-p")
+      close
+      assert_screen(<<~EOC)
+        => :foo
+        [0000]> Reline.readline('prompt> ')
+        prompt> def foo
+          bar
+        end
+      EOC
+    end
+
     def test_multiline_and_autowrap
       start_terminal(10, 20, %W{ruby -I#{@pwd}/lib #{@pwd}/test/reline/yamatanooroti/multiline_repl}, startup_message: 'Multiline REPL.')
       write("def aaaaaaaaaa\n  33333333\n           end\C-a\C-pputs\C-e\e\C-m888888888888888")
diff --git a/test/ruby/test_backtrace.rb b/test/ruby/test_backtrace.rb
index cfc65faacb1ab1..fca7b620302680 100644
--- a/test/ruby/test_backtrace.rb
+++ b/test/ruby/test_backtrace.rb
@@ -155,6 +155,10 @@ def test_caller_with_nil_length
   end
 
   def test_each_backtrace_location
+    assert_nil(Thread.each_caller_location {})
+
+    assert_raise(LocalJumpError) {Thread.each_caller_location}
+
     i = 0
     cl = caller_locations(1, 1)[0]; ecl = Thread.each_caller_location{|x| i+=1; break x if i == 1}
     assert_equal(cl.to_s, ecl.to_s)
@@ -181,6 +185,10 @@ def test_each_backtrace_location
     assert_raise(StopIteration) {
       ecl.next
     }
+
+    ary = []
+    cl = caller_locations(1, 2); Thread.each_caller_location(1, 2) {|x| ary << x}
+    assert_equal(cl.map(&:to_s), ary.map(&:to_s))
   end
 
   def test_caller_locations_first_label
diff --git a/test/ruby/test_enumerator.rb b/test/ruby/test_enumerator.rb
index 825c191d874c81..7599d434635d19 100644
--- a/test/ruby/test_enumerator.rb
+++ b/test/ruby/test_enumerator.rb
@@ -953,11 +953,7 @@ def each(&block)
     assert_equal(true, e.is_lambda)
   end
 
-  def test_product
-    ##
-    ## Enumerator::Product
-    ##
-
+  def test_product_new
     # 0-dimensional
     e = Enumerator::Product.new
     assert_instance_of(Enumerator::Product, e)
@@ -994,15 +990,16 @@ def test_product
     e.each { |x,| heads << x }
     assert_equal [1, 1, 2, 2, 3, 3], heads
 
+    # Any enumerable is 0 size
+    assert_equal(0, Enumerator::Product.new([], 1..).size)
+
     # Reject keyword arguments
     assert_raise(ArgumentError) {
       Enumerator::Product.new(1..3, foo: 1, bar: 2)
     }
+  end
 
-    ##
-    ## Enumerator.product
-    ##
-
+  def test_s_product
     # without a block
     e = Enumerator.product(1..3, %w[a b])
     assert_instance_of(Enumerator::Product, e)
@@ -1029,6 +1026,8 @@ def test_product
     assert_equal(nil, e.size)
     assert_equal [[1, "a"], [1, "b"], [2, "a"], [2, "b"]], e.take(4)
 
+    assert_equal(0, Enumerator.product([], 1..).size)
+
     # Reject keyword arguments
     assert_raise(ArgumentError) {
       Enumerator.product(1..3, foo: 1, bar: 2)
diff --git a/test/ruby/test_iseq.rb b/test/ruby/test_iseq.rb
index dc84d8bd7c4b51..dbf91fe8c94025 100644
--- a/test/ruby/test_iseq.rb
+++ b/test/ruby/test_iseq.rb
@@ -827,6 +827,24 @@ def test_compile_prism_with_file
     end
   end
 
+  def block_using_method
+    yield
+  end
+
+  def block_unused_method
+  end
+
+  def test_unused_param
+    a = RubyVM::InstructionSequence.of(method(:block_using_method)).to_a
+
+    omit 'TODO: Prism' if a.dig(4, :parser) != :"parse.y"
+
+    assert_equal true, a.dig(11, :use_block)
+
+    b = RubyVM::InstructionSequence.of(method(:block_unused_method)).to_a
+    assert_equal nil, b.dig(11, :use_block)
+  end
+
   def test_compile_prism_with_invalid_object_type
     assert_raise(TypeError) do
       RubyVM::InstructionSequence.compile_prism(Object.new)
diff --git a/test/ruby/test_method.rb b/test/ruby/test_method.rb
index a41704cf069055..5301b51650b3cc 100644
--- a/test/ruby/test_method.rb
+++ b/test/ruby/test_method.rb
@@ -1692,5 +1692,19 @@ def f6 = super{}       # zsuper / unuse
       assert_match(/-:23: warning.+f5/, err.join)
       assert_match(/-:24: warning.+f6/, err.join)
     end
+
+    assert_in_out_err '-w', <<-'RUBY' do |_out, err, _status|
+      class C0
+        def f = yield
+      end
+
+      class C1 < C0
+        def f = nil
+      end
+
+      C1.new.f{} # do not warn on duck typing
+    RUBY
+      assert_equal 0, err.size, err.join("\n")
+    end
   end
 end
diff --git a/test/ruby/test_string.rb b/test/ruby/test_string.rb
index 13261eacdd1f79..ebe85dac826d6e 100644
--- a/test/ruby/test_string.rb
+++ b/test/ruby/test_string.rb
@@ -3358,7 +3358,7 @@ def test_uplus_minus
 
     require 'objspace'
 
-    str = "bar".freeze
+    str = "test_uplus_minus_str".freeze
     assert_includes ObjectSpace.dump(str), '"fstring":true'
 
     assert_predicate(str, :frozen?)
@@ -3368,7 +3368,7 @@ def test_uplus_minus
     assert_not_same(str, +str)
     assert_same(str, -str)
 
-    bar = -%w(b a r).join('')
+    bar = -%w(test uplus minus str).join('_')
     assert_same(str, bar, "uminus deduplicates [Feature #13077] str: #{ObjectSpace.dump(str)} bar: #{ObjectSpace.dump(bar)}")
   end
 
diff --git a/test/rubygems/helper.rb b/test/rubygems/helper.rb
index 82fb50b70492c7..f97306717d1b47 100644
--- a/test/rubygems/helper.rb
+++ b/test/rubygems/helper.rb
@@ -285,9 +285,12 @@ def assert_contains_make_command(target, output, msg = nil)
   def setup
     @orig_hooks = {}
     @orig_env = ENV.to_hash
-    @tmp = File.expand_path("../../tmp", __dir__)
 
-    FileUtils.mkdir_p @tmp
+    top_srcdir = __dir__ + "/../.."
+    @tmp = File.expand_path(ENV.fetch("GEM_TEST_TMPDIR", "tmp"), top_srcdir)
+
+    FileUtils.mkdir_p(@tmp, mode: 0o700) # =rwx
+    @tmp = File.realpath(@tmp)
 
     @tempdir = Dir.mktmpdir("test_rubygems_", @tmp)
 
diff --git a/test/rubygems/test_gem_ext_cargo_builder/custom_name/ext/custom_name_lib/Cargo.lock b/test/rubygems/test_gem_ext_cargo_builder/custom_name/ext/custom_name_lib/Cargo.lock
index 34db31f61c81f4..b9fed0e2b0b46c 100644
--- a/test/rubygems/test_gem_ext_cargo_builder/custom_name/ext/custom_name_lib/Cargo.lock
+++ b/test/rubygems/test_gem_ext_cargo_builder/custom_name/ext/custom_name_lib/Cargo.lock
@@ -152,18 +152,18 @@ dependencies = [
 
 [[package]]
 name = "rb-sys"
-version = "0.9.91"
+version = "0.9.94"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "eb81203e271055178603e243fee397f5f4aac125bcd20036279683fb1445a899"
+checksum = "06dab8dbb0beb0a575a80c4b46355c8ace1f3dc5df60a3109758f205f1061366"
 dependencies = [
  "rb-sys-build",
 ]
 
 [[package]]
 name = "rb-sys-build"
-version = "0.9.91"
+version = "0.9.94"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9de9403a6aac834e7c9534575cb14188b6b5b99bafe475d18d838d44fbc27d31"
+checksum = "164d44950a42f2ba2f94efdcb650e14764270f84d281352aebb261806da0b2ce"
 dependencies = [
  "bindgen",
  "lazy_static",
diff --git a/test/rubygems/test_gem_ext_cargo_builder/custom_name/ext/custom_name_lib/Cargo.toml b/test/rubygems/test_gem_ext_cargo_builder/custom_name/ext/custom_name_lib/Cargo.toml
index 00a48df5d57ddb..9f844b62be54dc 100644
--- a/test/rubygems/test_gem_ext_cargo_builder/custom_name/ext/custom_name_lib/Cargo.toml
+++ b/test/rubygems/test_gem_ext_cargo_builder/custom_name/ext/custom_name_lib/Cargo.toml
@@ -7,4 +7,4 @@ edition = "2021"
 crate-type = ["cdylib"]
 
 [dependencies]
-rb-sys = "0.9.91"
+rb-sys = "0.9.94"
diff --git a/test/rubygems/test_gem_ext_cargo_builder/rust_ruby_example/Cargo.lock b/test/rubygems/test_gem_ext_cargo_builder/rust_ruby_example/Cargo.lock
index f96b1442936e2f..7e1617a663784b 100644
--- a/test/rubygems/test_gem_ext_cargo_builder/rust_ruby_example/Cargo.lock
+++ b/test/rubygems/test_gem_ext_cargo_builder/rust_ruby_example/Cargo.lock
@@ -145,18 +145,18 @@ dependencies = [
 
 [[package]]
 name = "rb-sys"
-version = "0.9.91"
+version = "0.9.94"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "eb81203e271055178603e243fee397f5f4aac125bcd20036279683fb1445a899"
+checksum = "06dab8dbb0beb0a575a80c4b46355c8ace1f3dc5df60a3109758f205f1061366"
 dependencies = [
  "rb-sys-build",
 ]
 
 [[package]]
 name = "rb-sys-build"
-version = "0.9.91"
+version = "0.9.94"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9de9403a6aac834e7c9534575cb14188b6b5b99bafe475d18d838d44fbc27d31"
+checksum = "164d44950a42f2ba2f94efdcb650e14764270f84d281352aebb261806da0b2ce"
 dependencies = [
  "bindgen",
  "lazy_static",
diff --git a/test/rubygems/test_gem_ext_cargo_builder/rust_ruby_example/Cargo.toml b/test/rubygems/test_gem_ext_cargo_builder/rust_ruby_example/Cargo.toml
index dca81463949243..a84cc8aabbf6ca 100644
--- a/test/rubygems/test_gem_ext_cargo_builder/rust_ruby_example/Cargo.toml
+++ b/test/rubygems/test_gem_ext_cargo_builder/rust_ruby_example/Cargo.toml
@@ -7,4 +7,4 @@ edition = "2021"
 crate-type = ["cdylib"]
 
 [dependencies]
-rb-sys = "0.9.91"
+rb-sys = "0.9.94"
diff --git a/test/stringio/test_stringio.rb b/test/stringio/test_stringio.rb
index e17cd0abb11a01..90316505819b8c 100644
--- a/test/stringio/test_stringio.rb
+++ b/test/stringio/test_stringio.rb
@@ -700,6 +700,18 @@ def test_read
     s.force_encoding(Encoding::US_ASCII)
     assert_same(s, f.read(nil, s))
     assert_string("", Encoding::UTF_8, s, bug13806)
+
+    bug20418 = '[Bug #20418] ™€®'.b
+    f = StringIO.new(bug20418)
+    s = ""
+    assert_equal(Encoding::UTF_8, s.encoding, bug20418)
+    f.read(4, s)
+    assert_equal(Encoding::UTF_8, s.encoding, bug20418)
+
+    f.rewind
+    s = ""
+    f.read(nil, s)
+    assert_equal(Encoding::ASCII_8BIT, s.encoding, bug20418)
   end
 
   def test_readpartial
@@ -711,8 +723,8 @@ def test_readpartial
     assert_equal("\u3042\u3044".force_encoding(Encoding::ASCII_8BIT), f.readpartial(f.size))
     f.rewind
     # not empty buffer
-    s = '0123456789'
-    assert_equal("\u3042\u3044".force_encoding(Encoding::ASCII_8BIT), f.readpartial(f.size, s))
+    s = '0123456789'.b
+    assert_equal("\u3042\u3044".b, f.readpartial(f.size, s))
   end
 
   def test_read_nonblock
@@ -736,8 +748,8 @@ def test_read_nonblock_no_exceptions
     assert_equal("\u3042\u3044".force_encoding(Encoding::ASCII_8BIT), f.read_nonblock(f.size))
     f.rewind
     # not empty buffer
-    s = '0123456789'
-    assert_equal("\u3042\u3044".force_encoding(Encoding::ASCII_8BIT), f.read_nonblock(f.size, s))
+    s = '0123456789'.b
+    assert_equal("\u3042\u3044".b, f.read_nonblock(f.size, s))
   end
 
   def test_sysread
diff --git a/thread.c b/thread.c
index 404c009a13c78c..b4edc845670746 100644
--- a/thread.c
+++ b/thread.c
@@ -2300,7 +2300,7 @@ rb_thread_s_handle_interrupt(VALUE self, VALUE mask_arg)
         mask = mask_arg;
     }
     else if (RB_TYPE_P(mask, T_HASH)) {
-        OBJ_FREEZE_RAW(mask);
+        OBJ_FREEZE(mask);
     }
 
     rb_ary_push(th->pending_interrupt_mask_stack, mask);
@@ -5864,7 +5864,7 @@ rb_uninterruptible(VALUE (*b_proc)(VALUE), VALUE data)
     rb_thread_t *cur_th = GET_THREAD();
 
     rb_hash_aset(interrupt_mask, rb_cObject, sym_never);
-    OBJ_FREEZE_RAW(interrupt_mask);
+    OBJ_FREEZE(interrupt_mask);
     rb_ary_push(cur_th->pending_interrupt_mask_stack, interrupt_mask);
 
     VALUE ret = rb_ensure(b_proc, data, uninterruptible_exit, Qnil);
diff --git a/universal_parser.c b/universal_parser.c
index 23a86311a5e039..2055681889ddb1 100644
--- a/universal_parser.c
+++ b/universal_parser.c
@@ -95,7 +95,6 @@
 #undef rb_ary_new_from_args
 #define rb_ary_new_from_args p->config->ary_new_from_args
 #define rb_ary_unshift       p->config->ary_unshift
-#define rb_ary_modify        p->config->ary_modify
 #undef RARRAY_LEN
 #define RARRAY_LEN           p->config->array_len
 #define RARRAY_AREF          p->config->array_aref
@@ -154,7 +153,6 @@
 
 #define rb_stderr_tty_p    p->config->stderr_tty_p
 #define rb_write_error_str p->config->write_error_str
-#define rb_default_rs      p->config->default_rs()
 #define rb_io_write        p->config->io_write
 #define rb_io_flush        p->config->io_flush
 #define rb_io_puts         p->config->io_puts
@@ -179,7 +177,6 @@
 #define rb_enc_mbcput           p->config->enc_mbcput
 #define rb_enc_find_index       p->config->enc_find_index
 #define rb_enc_from_index       p->config->enc_from_index
-#define rb_enc_associate_index  p->config->enc_associate_index
 #define rb_enc_isspace          p->config->enc_isspace
 #define ENC_CODERANGE_7BIT      p->config->enc_coderange_7bit
 #define ENC_CODERANGE_UNKNOWN   p->config->enc_coderange_unknown
@@ -202,8 +199,6 @@
 
 #define ruby_sized_xfree p->config->sized_xfree
 #define SIZED_REALLOC_N(v, T, m, n) ((v) = (T *)p->config->sized_realloc_n((void *)(v), (m), sizeof(T), (n)))
-#undef RB_OBJ_WRITE
-#define RB_OBJ_WRITE(old, slot, young) p->config->obj_write((VALUE)(old), (VALUE *)(slot), (VALUE)(young))
 #undef RB_GC_GUARD
 #define RB_GC_GUARD p->config->gc_guard
 #define rb_gc_mark p->config->gc_mark
diff --git a/variable.c b/variable.c
index 2478d65db2b5b4..983cd76be2e67d 100644
--- a/variable.c
+++ b/variable.c
@@ -1874,7 +1874,10 @@ rb_shape_set_shape_id(VALUE obj, shape_id_t shape_id)
 void rb_obj_freeze_inline(VALUE x)
 {
     if (RB_FL_ABLE(x)) {
-        RB_OBJ_FREEZE_RAW(x);
+        RB_FL_SET_RAW(x, RUBY_FL_FREEZE);
+        if (TYPE(x) == T_STRING) {
+            RB_FL_UNSET_RAW(x, FL_USER3); // STR_CHILLED
+        }
 
         rb_shape_t * next_shape = rb_shape_transition_shape_frozen(x);
 
diff --git a/vm.c b/vm.c
index 329e47fe68de94..917195377881f2 100644
--- a/vm.c
+++ b/vm.c
@@ -1008,6 +1008,11 @@ vm_make_env_each(const rb_execution_context_t * const ec, rb_control_frame_t *co
     }
 #endif
 
+    // Invalidate JIT code that assumes cfp->ep == vm_base_ptr(cfp).
+    if (env->iseq) {
+        rb_yjit_invalidate_ep_is_bp(env->iseq);
+    }
+
     return (VALUE)env;
 }
 
@@ -4300,6 +4305,7 @@ Init_BareVM(void)
     vm->negative_cme_table = rb_id_table_create(16);
     vm->overloaded_cme_table = st_init_numtable();
     vm->constant_cache = rb_id_table_create(0);
+    vm->unused_block_warning_table = st_init_numtable();
 
     rb_native_mutex_initialize(&vm->subclass_list_lock);
     vm->subclass_list_lock_owner = NULL;
diff --git a/vm_args.c b/vm_args.c
index 9df175eaa94a79..1a78e96776d53b 100644
--- a/vm_args.c
+++ b/vm_args.c
@@ -1021,7 +1021,7 @@ vm_caller_setup_arg_block(const rb_execution_context_t *ec, rb_control_frame_t *
                     VALUE callback_arg = rb_ary_hidden_new(2);
                     rb_ary_push(callback_arg, block_code);
                     rb_ary_push(callback_arg, ref);
-                    OBJ_FREEZE_RAW(callback_arg);
+                    OBJ_FREEZE(callback_arg);
                     func = rb_func_lambda_new(refine_sym_proc_call, callback_arg, 1, UNLIMITED_ARGUMENTS);
                     rb_hash_aset(ref, block_code, func);
                 }
diff --git a/vm_backtrace.c b/vm_backtrace.c
index 3fe816930da2de..22b28368d74d77 100644
--- a/vm_backtrace.c
+++ b/vm_backtrace.c
@@ -1170,17 +1170,17 @@ rb_make_backtrace(void)
     return rb_ec_backtrace_str_ary(GET_EC(), BACKTRACE_START, ALL_BACKTRACE_LINES);
 }
 
-static VALUE
-ec_backtrace_to_ary(const rb_execution_context_t *ec, int argc, const VALUE *argv, int lev_default, int lev_plus, int to_str)
+static long
+ec_backtrace_range(const rb_execution_context_t *ec, int argc, const VALUE *argv, int lev_default, int lev_plus, long *len_ptr)
 {
-    VALUE level, vn;
+    VALUE level, vn, opts;
     long lev, n;
-    VALUE btval;
-    VALUE r;
-    int too_large;
 
-    rb_scan_args(argc, argv, "02", &level, &vn);
+    rb_scan_args(argc, argv, "02:", &level, &vn, &opts);
 
+    if (!NIL_P(opts)) {
+        rb_get_kwargs(opts, (ID []){0}, 0, 0, NULL);
+    }
     if (argc == 2 && NIL_P(vn)) argc--;
 
     switch (argc) {
@@ -1201,7 +1201,7 @@ ec_backtrace_to_ary(const rb_execution_context_t *ec, int argc, const VALUE *arg
                 n = ALL_BACKTRACE_LINES;
                 break;
               case Qnil:
-                return Qnil;
+                return -1;
               default:
                 lev = beg + lev_plus;
                 n = len;
@@ -1225,6 +1225,20 @@ ec_backtrace_to_ary(const rb_execution_context_t *ec, int argc, const VALUE *arg
         break;
     }
 
+    *len_ptr = n;
+    return lev;
+}
+
+static VALUE
+ec_backtrace_to_ary(const rb_execution_context_t *ec, int argc, const VALUE *argv, int lev_default, int lev_plus, int to_str)
+{
+    long lev, n;
+    VALUE btval, r;
+    int too_large;
+
+    lev = ec_backtrace_range(ec, argc, argv, lev_default, lev_plus, &n);
+    if (lev < 0) return Qnil;
+
     if (n == 0) {
         return rb_ary_new();
     }
@@ -1354,15 +1368,19 @@ rb_f_caller_locations(int argc, VALUE *argv, VALUE _)
 
 /*
  *  call-seq:
- *     Thread.each_caller_location{ |loc| ... } -> nil
+ *     Thread.each_caller_location(...) { |loc| ... } -> nil
  *
  *  Yields each frame of the current execution stack as a
  *  backtrace location object.
  */
 static VALUE
-each_caller_location(VALUE unused)
+each_caller_location(int argc, VALUE *argv, VALUE _)
 {
-    rb_ec_partial_backtrace_object(GET_EC(), 2, ALL_BACKTRACE_LINES, NULL, FALSE, TRUE);
+    rb_execution_context_t *ec = GET_EC();
+    long n, lev = ec_backtrace_range(ec, argc, argv, 1, 1, &n);
+    if (lev >= 0 && n != 0) {
+        rb_ec_partial_backtrace_object(ec, lev, n, NULL, FALSE, TRUE);
+    }
     return Qnil;
 }
 
@@ -1442,7 +1460,7 @@ Init_vm_backtrace(void)
     rb_define_global_function("caller", rb_f_caller, -1);
     rb_define_global_function("caller_locations", rb_f_caller_locations, -1);
 
-    rb_define_singleton_method(rb_cThread, "each_caller_location", each_caller_location, 0);
+    rb_define_singleton_method(rb_cThread, "each_caller_location", each_caller_location, -1);
 }
 
 /* debugger API */
diff --git a/vm_core.h b/vm_core.h
index 949d912872a1dd..6395ebf759e9cd 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -796,6 +796,7 @@ typedef struct rb_vm_struct {
 
     struct rb_id_table *negative_cme_table;
     st_table *overloaded_cme_table; // cme -> overloaded_cme
+    st_table *unused_block_warning_table;
 
     // This id table contains a mapping from ID to ICs. It does this with ID
     // keys and nested st_tables as values. The nested tables have ICs as keys
diff --git a/vm_insnhelper.c b/vm_insnhelper.c
index 04e7d3714ef288..ccf93fa6b553a4 100644
--- a/vm_insnhelper.c
+++ b/vm_insnhelper.c
@@ -2980,9 +2980,9 @@ VALUE rb_gen_method_name(VALUE owner, VALUE name); // in vm_backtrace.c
 static void
 warn_unused_block(const rb_callable_method_entry_t *cme, const rb_iseq_t *iseq, void *pc)
 {
-    static st_table *dup_check_table = NULL;
+    rb_vm_t *vm = GET_VM();
+    st_table *dup_check_table = vm->unused_block_warning_table;
 
-    st_data_t key = 0;
     union {
         VALUE v;
         unsigned char b[SIZEOF_VALUE];
@@ -2992,6 +2992,14 @@ warn_unused_block(const rb_callable_method_entry_t *cme, const rb_iseq_t *iseq,
         .v = (VALUE)cme->def,
     };
 
+    // relax check
+    st_data_t key = (st_data_t)cme->def->original_id;
+
+    if (st_lookup(dup_check_table, key, NULL)) {
+        return;
+    }
+
+    // strict check
     // make unique key from pc and me->def pointer
     for (int i=0; i<SIZEOF_VALUE; i++) {
         // fprintf(stderr, "k1:%3d k2:%3d\n", k1.b[i], k2.b[SIZEOF_VALUE-1-i]);
@@ -3004,10 +3012,6 @@ warn_unused_block(const rb_callable_method_entry_t *cme, const rb_iseq_t *iseq,
         fprintf(stderr, "key:%p\n", (void *)key);
     }
 
-    if (!dup_check_table) {
-        dup_check_table = st_init_numtable();
-    }
-
     // duplication check
     if (st_insert(dup_check_table, key, 1)) {
         // already shown
@@ -3017,7 +3021,7 @@ warn_unused_block(const rb_callable_method_entry_t *cme, const rb_iseq_t *iseq,
         VALUE name = rb_gen_method_name(cme->defined_class, ISEQ_BODY(iseq)->location.base_label);
 
         if (!NIL_P(m_loc)) {
-            rb_warning("the passed block for '%"PRIsVALUE"' defined at %"PRIsVALUE":%"PRIsVALUE" may be ignored",
+            rb_warning("the block passed to '%"PRIsVALUE"' defined at %"PRIsVALUE":%"PRIsVALUE" may be ignored",
                        name, RARRAY_AREF(m_loc, 0), RARRAY_AREF(m_loc, 1));
         }
         else {
diff --git a/yjit.c b/yjit.c
index ffd180429e4485..8ae010ac40b0b4 100644
--- a/yjit.c
+++ b/yjit.c
@@ -629,6 +629,12 @@ rb_get_iseq_body_stack_max(const rb_iseq_t *iseq)
     return iseq->body->stack_max;
 }
 
+enum rb_iseq_type
+rb_get_iseq_body_type(const rb_iseq_t *iseq)
+{
+    return iseq->body->type;
+}
+
 bool
 rb_get_iseq_flags_has_lead(const rb_iseq_t *iseq)
 {
diff --git a/yjit.h b/yjit.h
index dde9f750aaf72b..baf984eb530808 100644
--- a/yjit.h
+++ b/yjit.h
@@ -48,6 +48,7 @@ void rb_yjit_tracing_invalidate_all(void);
 void rb_yjit_show_usage(int help, int highlight, unsigned int width, int columns);
 void rb_yjit_lazy_push_frame(const VALUE *pc);
 void rb_yjit_invalidate_no_singleton_class(VALUE klass);
+void rb_yjit_invalidate_ep_is_bp(const rb_iseq_t *iseq);
 
 #else
 // !USE_YJIT
@@ -71,6 +72,7 @@ static inline void rb_yjit_constant_ic_update(const rb_iseq_t *const iseq, IC ic
 static inline void rb_yjit_tracing_invalidate_all(void) {}
 static inline void rb_yjit_lazy_push_frame(const VALUE *pc) {}
 static inline void rb_yjit_invalidate_no_singleton_class(VALUE klass) {}
+static inline void rb_yjit_invalidate_ep_is_bp(const rb_iseq_t *iseq) {}
 
 #endif // #if USE_YJIT
 
diff --git a/yjit/bindgen/src/main.rs b/yjit/bindgen/src/main.rs
index c58df7c3773b90..d91e330f5e1eb1 100644
--- a/yjit/bindgen/src/main.rs
+++ b/yjit/bindgen/src/main.rs
@@ -298,6 +298,7 @@ fn main() {
         .allowlist_type("ruby_tag_type")
         .allowlist_type("ruby_vm_throw_flags")
         .allowlist_type("vm_check_match_type")
+        .allowlist_type("rb_iseq_type")
 
         // From yjit.c
         .allowlist_function("rb_iseq_(get|set)_yjit_payload")
@@ -415,6 +416,7 @@ fn main() {
         .allowlist_function("rb_get_iseq_body_parent_iseq")
         .allowlist_function("rb_get_iseq_body_iseq_encoded")
         .allowlist_function("rb_get_iseq_body_stack_max")
+        .allowlist_function("rb_get_iseq_body_type")
         .allowlist_function("rb_get_iseq_flags_has_lead")
         .allowlist_function("rb_get_iseq_flags_has_opt")
         .allowlist_function("rb_get_iseq_flags_has_kw")
diff --git a/yjit/src/codegen.rs b/yjit/src/codegen.rs
index d60f4f0ec1029b..9d355b854d3c83 100644
--- a/yjit/src/codegen.rs
+++ b/yjit/src/codegen.rs
@@ -46,7 +46,7 @@ type InsnGenFn = fn(
 /// Represents a [core::Block] while we build it.
 pub struct JITState {
     /// Instruction sequence for the compiling block
-    iseq: IseqPtr,
+    pub iseq: IseqPtr,
 
     /// The iseq index of the first instruction in the block
     starting_insn_idx: IseqIdx,
@@ -101,6 +101,9 @@ pub struct JITState {
     /// A list of classes that are not supposed to have a singleton class.
     pub no_singleton_class_assumptions: Vec<VALUE>,
 
+    /// When true, the block is valid only when base pointer is equal to environment pointer.
+    pub no_ep_escape: bool,
+
     /// When true, the block is valid only when there is a total of one ractor running
     pub block_assumes_single_ractor: bool,
 
@@ -130,6 +133,7 @@ impl JITState {
             bop_assumptions: vec![],
             stable_constant_names_assumption: None,
             no_singleton_class_assumptions: vec![],
+            no_ep_escape: false,
             block_assumes_single_ractor: false,
             perf_map: Rc::default(),
             perf_stack: vec![],
@@ -171,6 +175,23 @@ impl JITState {
         unsafe { *(self.pc.offset(arg_idx + 1)) }
     }
 
+    /// Return true if the current ISEQ could escape an environment.
+    ///
+    /// As of vm_push_frame(), EP is always equal to BP. However, after pushing
+    /// a frame, some ISEQ setups call vm_bind_update_env(), which redirects EP.
+    /// Also, some method calls escape the environment to the heap.
+    fn escapes_ep(&self) -> bool {
+        match unsafe { get_iseq_body_type(self.iseq) } {
+            // <main> frame is always associated to TOPLEVEL_BINDING.
+            ISEQ_TYPE_MAIN |
+            // Kernel#eval uses a heap EP when a Binding argument is not nil.
+            ISEQ_TYPE_EVAL => true,
+            // If this ISEQ has previously escaped EP, give up the optimization.
+            _ if iseq_escapes_ep(self.iseq) => true,
+            _ => false,
+        }
+    }
+
     // Get the index of the next instruction
     fn next_insn_idx(&self) -> u16 {
         self.insn_idx + insn_len(self.get_opcode()) as u16
@@ -250,6 +271,19 @@ impl JITState {
         true
     }
 
+    /// Assume that base pointer is equal to environment pointer in the current ISEQ.
+    /// Return true if it's safe to assume so.
+    fn assume_no_ep_escape(&mut self, asm: &mut Assembler, ocb: &mut OutlinedCb) -> bool {
+        if jit_ensure_block_entry_exit(self, asm, ocb).is_none() {
+            return false; // out of space, give up
+        }
+        if self.escapes_ep() {
+            return false; // EP has been escaped in this ISEQ. disable the optimization to avoid an invalidation loop.
+        }
+        self.no_ep_escape = true;
+        true
+    }
+
     fn get_cfp(&self) -> *mut rb_control_frame_struct {
         unsafe { get_ec_cfp(self.ec) }
     }
@@ -2203,16 +2237,22 @@ fn gen_get_lep(jit: &JITState, asm: &mut Assembler) -> Opnd {
 fn gen_getlocal_generic(
     jit: &mut JITState,
     asm: &mut Assembler,
+    ocb: &mut OutlinedCb,
     ep_offset: u32,
     level: u32,
 ) -> Option<CodegenStatus> {
-    // Load environment pointer EP (level 0) from CFP
-    let ep_opnd = gen_get_ep(asm, level);
+    let local_opnd = if level == 0 && jit.assume_no_ep_escape(asm, ocb) {
+        // Load the local using SP register
+        asm.ctx.ep_opnd(-(ep_offset as i32))
+    } else {
+        // Load environment pointer EP (level 0) from CFP
+        let ep_opnd = gen_get_ep(asm, level);
 
-    // Load the local from the block
-    // val = *(vm_get_ep(GET_EP(), level) - idx);
-    let offs = -(SIZEOF_VALUE_I32 * ep_offset as i32);
-    let local_opnd = Opnd::mem(64, ep_opnd, offs);
+        // Load the local from the block
+        // val = *(vm_get_ep(GET_EP(), level) - idx);
+        let offs = -(SIZEOF_VALUE_I32 * ep_offset as i32);
+        Opnd::mem(64, ep_opnd, offs)
+    };
 
     // Write the local at SP
     let stack_top = if level == 0 {
@@ -2230,29 +2270,29 @@ fn gen_getlocal_generic(
 fn gen_getlocal(
     jit: &mut JITState,
     asm: &mut Assembler,
-    _ocb: &mut OutlinedCb,
+    ocb: &mut OutlinedCb,
 ) -> Option<CodegenStatus> {
     let idx = jit.get_arg(0).as_u32();
     let level = jit.get_arg(1).as_u32();
-    gen_getlocal_generic(jit, asm, idx, level)
+    gen_getlocal_generic(jit, asm, ocb, idx, level)
 }
 
 fn gen_getlocal_wc0(
     jit: &mut JITState,
     asm: &mut Assembler,
-    _ocb: &mut OutlinedCb,
+    ocb: &mut OutlinedCb,
 ) -> Option<CodegenStatus> {
     let idx = jit.get_arg(0).as_u32();
-    gen_getlocal_generic(jit, asm, idx, 0)
+    gen_getlocal_generic(jit, asm, ocb, idx, 0)
 }
 
 fn gen_getlocal_wc1(
     jit: &mut JITState,
     asm: &mut Assembler,
-    _ocb: &mut OutlinedCb,
+    ocb: &mut OutlinedCb,
 ) -> Option<CodegenStatus> {
     let idx = jit.get_arg(0).as_u32();
-    gen_getlocal_generic(jit, asm, idx, 1)
+    gen_getlocal_generic(jit, asm, ocb, idx, 1)
 }
 
 fn gen_setlocal_generic(
@@ -2264,11 +2304,11 @@ fn gen_setlocal_generic(
 ) -> Option<CodegenStatus> {
     let value_type = asm.ctx.get_opnd_type(StackOpnd(0));
 
-    // Load environment pointer EP at level
-    let ep_opnd = gen_get_ep(asm, level);
-
     // Fallback because of write barrier
     if asm.ctx.get_chain_depth() > 0 {
+        // Load environment pointer EP at level
+        let ep_opnd = gen_get_ep(asm, level);
+
         // This function should not yield to the GC.
         // void rb_vm_env_write(const VALUE *ep, int index, VALUE v)
         let index = -(ep_offset as i64);
@@ -2286,16 +2326,27 @@ fn gen_setlocal_generic(
         return Some(KeepCompiling);
     }
 
-    // Write barriers may be required when VM_ENV_FLAG_WB_REQUIRED is set, however write barriers
-    // only affect heap objects being written. If we know an immediate value is being written we
-    // can skip this check.
-    if !value_type.is_imm() {
-        // flags & VM_ENV_FLAG_WB_REQUIRED
+    let (flags_opnd, local_opnd) = if level == 0 && jit.assume_no_ep_escape(asm, ocb) {
+        // Load flags and the local using SP register
+        let local_opnd = asm.ctx.ep_opnd(-(ep_offset as i32));
+        let flags_opnd = asm.ctx.ep_opnd(VM_ENV_DATA_INDEX_FLAGS as i32);
+        (flags_opnd, local_opnd)
+    } else {
+        // Load flags and the local for the level
+        let ep_opnd = gen_get_ep(asm, level);
         let flags_opnd = Opnd::mem(
             64,
             ep_opnd,
             SIZEOF_VALUE_I32 * VM_ENV_DATA_INDEX_FLAGS as i32,
         );
+        (flags_opnd, Opnd::mem(64, ep_opnd, -SIZEOF_VALUE_I32 * ep_offset as i32))
+    };
+
+    // Write barriers may be required when VM_ENV_FLAG_WB_REQUIRED is set, however write barriers
+    // only affect heap objects being written. If we know an immediate value is being written we
+    // can skip this check.
+    if !value_type.is_imm() {
+        // flags & VM_ENV_FLAG_WB_REQUIRED
         asm.test(flags_opnd, VM_ENV_FLAG_WB_REQUIRED.into());
 
         // if (flags & VM_ENV_FLAG_WB_REQUIRED) != 0
@@ -2319,8 +2370,7 @@ fn gen_setlocal_generic(
     let stack_top = asm.stack_pop(1);
 
     // Write the value at the environment pointer
-    let offs = -(SIZEOF_VALUE_I32 * ep_offset as i32);
-    asm.mov(Opnd::mem(64, ep_opnd, offs), stack_top);
+    asm.mov(local_opnd, stack_top);
 
     Some(KeepCompiling)
 }
@@ -8223,6 +8273,7 @@ fn gen_struct_aset(
 fn gen_send_dynamic<F: Fn(&mut Assembler) -> Opnd>(
     jit: &mut JITState,
     asm: &mut Assembler,
+    ocb: &mut OutlinedCb,
     cd: *const rb_call_data,
     sp_pops: usize,
     vm_sendish: F,
@@ -8262,7 +8313,10 @@ fn gen_send_dynamic<F: Fn(&mut Assembler) -> Opnd>(
     gen_counter_incr(asm, Counter::num_send_dynamic);
 
     jit_perf_symbol_pop!(jit, asm, PerfMap::Codegen);
-    Some(KeepCompiling)
+
+    // End the current block for invalidationg and sharing the same successor
+    jump_to_next_insn(jit, asm, ocb);
+    Some(EndBlock)
 }
 
 fn gen_send_general(
@@ -8776,7 +8830,7 @@ fn gen_opt_send_without_block(
     }
 
     // Otherwise, fallback to dynamic dispatch using the interpreter's implementation of send
-    gen_send_dynamic(jit, asm, cd, unsafe { rb_yjit_sendish_sp_pops((*cd).ci) }, |asm| {
+    gen_send_dynamic(jit, asm, ocb, cd, unsafe { rb_yjit_sendish_sp_pops((*cd).ci) }, |asm| {
         extern "C" {
             fn rb_vm_opt_send_without_block(ec: EcPtr, cfp: CfpPtr, cd: VALUE) -> VALUE;
         }
@@ -8801,7 +8855,7 @@ fn gen_send(
 
     // Otherwise, fallback to dynamic dispatch using the interpreter's implementation of send
     let blockiseq = jit.get_arg(1).as_iseq();
-    gen_send_dynamic(jit, asm, cd, unsafe { rb_yjit_sendish_sp_pops((*cd).ci) }, |asm| {
+    gen_send_dynamic(jit, asm, ocb, cd, unsafe { rb_yjit_sendish_sp_pops((*cd).ci) }, |asm| {
         extern "C" {
             fn rb_vm_send(ec: EcPtr, cfp: CfpPtr, cd: VALUE, blockiseq: IseqPtr) -> VALUE;
         }
@@ -8824,7 +8878,7 @@ fn gen_invokeblock(
     }
 
     // Otherwise, fallback to dynamic dispatch using the interpreter's implementation of send
-    gen_send_dynamic(jit, asm, cd, unsafe { rb_yjit_invokeblock_sp_pops((*cd).ci) }, |asm| {
+    gen_send_dynamic(jit, asm, ocb, cd, unsafe { rb_yjit_invokeblock_sp_pops((*cd).ci) }, |asm| {
         extern "C" {
             fn rb_vm_invokeblock(ec: EcPtr, cfp: CfpPtr, cd: VALUE) -> VALUE;
         }
@@ -8984,7 +9038,7 @@ fn gen_invokesuper(
 
     // Otherwise, fallback to dynamic dispatch using the interpreter's implementation of send
     let blockiseq = jit.get_arg(1).as_iseq();
-    gen_send_dynamic(jit, asm, cd, unsafe { rb_yjit_sendish_sp_pops((*cd).ci) }, |asm| {
+    gen_send_dynamic(jit, asm, ocb, cd, unsafe { rb_yjit_sendish_sp_pops((*cd).ci) }, |asm| {
         extern "C" {
             fn rb_vm_invokesuper(ec: EcPtr, cfp: CfpPtr, cd: VALUE, blockiseq: IseqPtr) -> VALUE;
         }
diff --git a/yjit/src/core.rs b/yjit/src/core.rs
index fb7d52cc5d0f61..ccc458fe227b17 100644
--- a/yjit/src/core.rs
+++ b/yjit/src/core.rs
@@ -1657,6 +1657,9 @@ impl JITState {
         for klass in self.no_singleton_class_assumptions {
             track_no_singleton_class_assumption(blockref, klass);
         }
+        if self.no_ep_escape {
+            track_no_ep_escape_assumption(blockref, self.iseq);
+        }
 
         blockref
     }
@@ -1798,6 +1801,13 @@ impl Context {
         return Opnd::mem(64, SP, offset);
     }
 
+    /// Get an operand for the adjusted environment pointer address using SP register.
+    /// This is valid only when a Binding object hasn't been created for the frame.
+    pub fn ep_opnd(&self, offset: i32) -> Opnd {
+        let ep_offset = self.get_stack_size() as i32 + 1;
+        self.sp_opnd(-ep_offset + offset)
+    }
+
     /// Stop using a register for a given stack temp.
     /// This allows us to reuse the register for a value that we know is dead
     /// and will no longer be used (e.g. popped stack temp).
@@ -3124,6 +3134,12 @@ pub fn defer_compilation(
     // Likely a stub due to the increased chain depth
     let target0_address = branch.set_target(0, blockid, &next_ctx, ocb);
 
+    // Pad the block if it has the potential to be invalidated. This must be
+    // done before gen_fn() in case the jump is overwritten by a fallthrough.
+    if jit.block_entry_exit.is_some() {
+        asm.pad_inval_patch();
+    }
+
     // Call the branch generation function
     asm_comment!(asm, "defer_compilation");
     asm.mark_branch_start(&branch);
@@ -3307,9 +3323,10 @@ pub fn invalidate_block_version(blockref: &BlockRef) {
 
             assert!(
                 cb.get_write_ptr() <= block_end,
-                "invalidation wrote past end of block (code_size: {:?}, new_size: {})",
+                "invalidation wrote past end of block (code_size: {:?}, new_size: {}, start_addr: {:?})",
                 block.code_size(),
                 cb.get_write_ptr().as_offset() - block_start.as_offset(),
+                block.start_addr.raw_ptr(cb),
             );
             cb.set_write_ptr(cur_pos);
             cb.set_dropped_bytes(cur_dropped_bytes);
diff --git a/yjit/src/cruby.rs b/yjit/src/cruby.rs
index 9547e3fa2cc67b..d07262ad4ffb2f 100644
--- a/yjit/src/cruby.rs
+++ b/yjit/src/cruby.rs
@@ -170,6 +170,7 @@ pub use rb_iseq_encoded_size as get_iseq_encoded_size;
 pub use rb_get_iseq_body_local_iseq as get_iseq_body_local_iseq;
 pub use rb_get_iseq_body_iseq_encoded as get_iseq_body_iseq_encoded;
 pub use rb_get_iseq_body_stack_max as get_iseq_body_stack_max;
+pub use rb_get_iseq_body_type as get_iseq_body_type;
 pub use rb_get_iseq_flags_has_lead as get_iseq_flags_has_lead;
 pub use rb_get_iseq_flags_has_opt as get_iseq_flags_has_opt;
 pub use rb_get_iseq_flags_has_kw as get_iseq_flags_has_kw;
diff --git a/yjit/src/cruby_bindings.inc.rs b/yjit/src/cruby_bindings.inc.rs
index 359227d60db211..98d380826a69cf 100644
--- a/yjit/src/cruby_bindings.inc.rs
+++ b/yjit/src/cruby_bindings.inc.rs
@@ -478,6 +478,16 @@ pub struct iseq_inline_iv_cache_entry {
 pub struct iseq_inline_cvar_cache_entry {
     pub entry: *mut rb_cvar_class_tbl_entry,
 }
+pub const ISEQ_TYPE_TOP: rb_iseq_type = 0;
+pub const ISEQ_TYPE_METHOD: rb_iseq_type = 1;
+pub const ISEQ_TYPE_BLOCK: rb_iseq_type = 2;
+pub const ISEQ_TYPE_CLASS: rb_iseq_type = 3;
+pub const ISEQ_TYPE_RESCUE: rb_iseq_type = 4;
+pub const ISEQ_TYPE_ENSURE: rb_iseq_type = 5;
+pub const ISEQ_TYPE_EVAL: rb_iseq_type = 6;
+pub const ISEQ_TYPE_MAIN: rb_iseq_type = 7;
+pub const ISEQ_TYPE_PLAIN: rb_iseq_type = 8;
+pub type rb_iseq_type = u32;
 pub const BUILTIN_ATTR_LEAF: rb_builtin_attr = 1;
 pub const BUILTIN_ATTR_SINGLE_NOARG_LEAF: rb_builtin_attr = 2;
 pub const BUILTIN_ATTR_INLINE_BLOCK: rb_builtin_attr = 4;
@@ -1153,6 +1163,7 @@ extern "C" {
     pub fn rb_get_iseq_body_local_table_size(iseq: *const rb_iseq_t) -> ::std::os::raw::c_uint;
     pub fn rb_get_iseq_body_iseq_encoded(iseq: *const rb_iseq_t) -> *mut VALUE;
     pub fn rb_get_iseq_body_stack_max(iseq: *const rb_iseq_t) -> ::std::os::raw::c_uint;
+    pub fn rb_get_iseq_body_type(iseq: *const rb_iseq_t) -> rb_iseq_type;
     pub fn rb_get_iseq_flags_has_lead(iseq: *const rb_iseq_t) -> bool;
     pub fn rb_get_iseq_flags_has_opt(iseq: *const rb_iseq_t) -> bool;
     pub fn rb_get_iseq_flags_has_kw(iseq: *const rb_iseq_t) -> bool;
diff --git a/yjit/src/invariants.rs b/yjit/src/invariants.rs
index e4602934409dac..a5fd6b7ab5fdb0 100644
--- a/yjit/src/invariants.rs
+++ b/yjit/src/invariants.rs
@@ -59,6 +59,11 @@ pub struct Invariants {
     /// there has been a singleton class for the class after boot, so you cannot
     /// assume no singleton class going forward.
     no_singleton_classes: HashMap<VALUE, HashSet<BlockRef>>,
+
+    /// A map from an ISEQ to a set of blocks that assume base pointer is equal
+    /// to environment pointer. When the set is empty, it means that EP has been
+    /// escaped in the ISEQ.
+    no_ep_escape_iseqs: HashMap<IseqPtr, HashSet<BlockRef>>,
 }
 
 /// Private singleton instance of the invariants global struct.
@@ -76,6 +81,7 @@ impl Invariants {
                 constant_state_blocks: HashMap::new(),
                 block_constant_states: HashMap::new(),
                 no_singleton_classes: HashMap::new(),
+                no_ep_escape_iseqs: HashMap::new(),
             });
         }
     }
@@ -154,6 +160,23 @@ pub fn has_singleton_class_of(klass: VALUE) -> bool {
         .map_or(false, |blocks| blocks.is_empty())
 }
 
+/// Track that a block will assume that base pointer is equal to environment pointer.
+pub fn track_no_ep_escape_assumption(uninit_block: BlockRef, iseq: IseqPtr) {
+    Invariants::get_instance()
+        .no_ep_escape_iseqs
+        .entry(iseq)
+        .or_default()
+        .insert(uninit_block);
+}
+
+/// Returns true if a given ISEQ has previously escaped an environment.
+pub fn iseq_escapes_ep(iseq: IseqPtr) -> bool {
+    Invariants::get_instance()
+        .no_ep_escape_iseqs
+        .get(&iseq)
+        .map_or(false, |blocks| blocks.is_empty())
+}
+
 // Checks rb_method_basic_definition_p and registers the current block for invalidation if method
 // lookup changes.
 // A "basic method" is one defined during VM boot, so we can use this to check assumptions based on
@@ -420,6 +443,10 @@ pub fn block_assumptions_free(blockref: BlockRef) {
     for (_, blocks) in invariants.no_singleton_classes.iter_mut() {
         blocks.remove(&blockref);
     }
+    // Remove tracking for blocks assuming EP doesn't escape
+    for (_, blocks) in invariants.no_ep_escape_iseqs.iter_mut() {
+        blocks.remove(&blockref);
+    }
 }
 
 /// Callback from the opt_setinlinecache instruction in the interpreter.
@@ -515,6 +542,34 @@ pub extern "C" fn rb_yjit_invalidate_no_singleton_class(klass: VALUE) {
     }
 }
 
+/// Invalidate blocks for a given ISEQ that assumes environment pointer is
+/// equal to base pointer.
+#[no_mangle]
+pub extern "C" fn rb_yjit_invalidate_ep_is_bp(iseq: IseqPtr) {
+    // Skip tracking EP escapes on boot. We don't need to invalidate anything during boot.
+    if unsafe { INVARIANTS.is_none() } {
+        return;
+    }
+
+    // If an EP escape for this ISEQ is detected for the first time, invalidate all blocks
+    // associated to the ISEQ.
+    let no_ep_escape_iseqs = &mut Invariants::get_instance().no_ep_escape_iseqs;
+    match no_ep_escape_iseqs.get_mut(&iseq) {
+        Some(blocks) => {
+            // Invalidate existing blocks and let jit.ep_is_bp()
+            // return true when they are compiled again
+            for block in mem::take(blocks) {
+                invalidate_block_version(&block);
+                incr_counter!(invalidate_no_singleton_class);
+            }
+        }
+        None => {
+            // Let jit.ep_is_bp() return false for this ISEQ
+            no_ep_escape_iseqs.insert(iseq, HashSet::new());
+        }
+    }
+}
+
 // Invalidate all generated code and patch C method return code to contain
 // logic for firing the c_return TracePoint event. Once rb_vm_barrier()
 // returns, all other ractors are pausing inside RB_VM_LOCK_ENTER(), which