gh-90536: Add support for the BOLT post-link binary optimizer

Doc/using/configure.rst

@@ -191,7 +191,8 @@ Performance options
 -------------------
 
 Configuring Python using ``--enable-optimizations --with-lto`` (PGO + LTO) is
-recommended for best performance.
+recommended for best performance. The experimental ``--enable-bolt`` flag can
+also be used to improve performance.
 
 .. cmdoption:: --enable-optimizations
 
@@ -231,6 +232,24 @@ recommended for best performance.
    .. versionadded:: 3.11
       To use ThinLTO feature, use ``--with-lto=thin`` on Clang.
 
+.. cmdoption:: --enable-bolt
+
+   Enable usage of the `BOLT post-link binary optimizer
+   <https://github.com/llvm/llvm-project/tree/main/bolt>` (disabled by
+   default).
+
+   BOLT is part of the LLVM project but is not always included in their binary
+   distributions. This flag requires that ``llvm-bolt`` and ``merge-fdata``
+   are available.
+
+   BOLT is still a fairly new project so this flag should be considered
+   experimental for now. Because this tool operates on machine code its success
+   is dependent on a combination of the build environment + the other
+   optimization configure args + the CPU architecture, and not all combinations
+   are supported.
+
+   .. versionadded:: 3.12
+
 .. cmdoption:: --with-computed-gotos
 
    Enable computed gotos in evaluation loop (enabled by default on supported

Doc/whatsnew/3.12.rst

@@ -133,6 +133,10 @@ Optimizations
   It reduces object size by 8 or 16 bytes on 64bit platform. (:pep:`623`)
   (Contributed by Inada Naoki in :gh:`92536`.)
 
+* Added experimental support for using the BOLT binary optimizer in the build
+  process, which improves performance by 1-5%.
+  (Contributed by Kevin Modzelewski in :gh:`90536`.)
+
 
 CPython bytecode changes
 ========================

Makefile.pre.in

@@ -640,6 +640,16 @@ profile-opt: profile-run-stamp
 	-rm -f profile-clean-stamp
 	$(MAKE) @DEF_MAKE_RULE@ CFLAGS_NODIST="$(CFLAGS_NODIST) $(PGO_PROF_USE_FLAG)" LDFLAGS_NODIST="$(LDFLAGS_NODIST)"
 
+bolt-opt: @PREBOLT_RULE@
+	rm -f *.fdata
+	@LLVM_BOLT@ ./$(BUILDPYTHON) -instrument -instrumentation-file-append-pid -instrumentation-file=$(abspath $(BUILDPYTHON).bolt) -o $(BUILDPYTHON).bolt_inst
+	./$(BUILDPYTHON).bolt_inst $(PROFILE_TASK) || true
+	@MERGE_FDATA@ $(BUILDPYTHON).*.fdata > $(BUILDPYTHON).fdata
+	@LLVM_BOLT@ ./$(BUILDPYTHON) -o $(BUILDPYTHON).bolt -data=$(BUILDPYTHON).fdata -update-debug-sections -reorder-blocks=ext-tsp -reorder-functions=hfsort+ -split-functions=3 -icf=1 -inline-all -split-eh -reorder-functions-use-hot-size -peepholes=all -jump-tables=aggressive -inline-ap -indirect-call-promotion=all -dyno-stats -use-gnu-stack -frame-opt=hot
+	rm -f *.fdata
+	rm -f $(BUILDPYTHON).bolt_inst
+	mv $(BUILDPYTHON).bolt $(BUILDPYTHON)
+
 # Compile and run with gcov
 .PHONY=coverage coverage-lcov coverage-report
 coverage:

Misc/ACKS

@@ -1212,6 +1212,7 @@ Gideon Mitchell
 Tim Mitchell
 Zubin Mithra
 Florian Mladitsch
+Kevin Modzelewski
 Doug Moen
 Jakub Molinski
 Juliette Monsel

Misc/NEWS.d/next/Build/2022-08-12-13-06-03.gh-issue-90536.qMpF6p.rst

@@ -0,0 +1,2 @@
+Use the BOLT post-link optimizer to improve performance, particularly on
+medium-to-large applications.