diff --git a/auto_update_tests.py b/auto_update_tests.py
index 6f86bc1fec4..0a42d8357b1 100755
--- a/auto_update_tests.py
+++ b/auto_update_tests.py
@@ -67,7 +67,8 @@
   if t.endswith('.wast'):
     print '..', t
     passname = os.path.basename(t).replace('.wast', '')
-    cmd = [os.path.join('bin', 'binaryen-shell'), ('--' + passname if passname != 'O' else '-O'), os.path.join('test', 'passes', t), '--print']
+    opts = ['-O'] if passname == 'O' else ['--' + p for p in passname.split('_')]
+    cmd = [os.path.join('bin', 'binaryen-shell')] + opts + [os.path.join('test', 'passes', t), '--print']
     print '    ', ' '.join(cmd)
     actual, err = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE).communicate()
     open(os.path.join('test', 'passes', passname + '.txt'), 'w').write(actual)
diff --git a/check.py b/check.py
index c0733cb6c90..722371f2a35 100755
--- a/check.py
+++ b/check.py
@@ -276,8 +276,8 @@ def minify_check(wast, verify_final_result=True):
   if t.endswith('.wast'):
     print '..', t
     passname = os.path.basename(t).replace('.wast', '')
-    opt = '-O' if passname == 'O' else '--' + passname
-    cmd = [os.path.join('bin', 'binaryen-shell'), opt, os.path.join('test', 'passes', t), '--print']
+    opts = ['-O'] if passname == 'O' else ['--' + p for p in passname.split('_')]
+    cmd = [os.path.join('bin', 'binaryen-shell')] + opts + [os.path.join('test', 'passes', t), '--print']
     actual = run_command(cmd)
     fail_if_not_identical(actual, open(os.path.join('test', 'passes', passname + '.txt')).read())
 
diff --git a/src/passes/MergeBlocks.cpp b/src/passes/MergeBlocks.cpp
index 5794e1379ca..7b9723b0bb5 100644
--- a/src/passes/MergeBlocks.cpp
+++ b/src/passes/MergeBlocks.cpp
@@ -100,7 +100,7 @@ struct MergeBlocks : public WalkerPass<PostWalker<MergeBlocks, Visitor<MergeBloc
     if (dependency1 && *dependency1 && EffectAnalyzer(*dependency1).hasSideEffects()) return outer;
     if (dependency2 && *dependency2 && EffectAnalyzer(*dependency2).hasSideEffects()) return outer;
     if (auto* block = child->dynCast<Block>()) {
-      if (block->list.size() >= 2) {
+      if (!block->name.is() && block->list.size() >= 2) {
         child = block->list.back();
         if (outer == nullptr) {
           // reuse the block, move it out
diff --git a/test/passes/merge-blocks.txt b/test/passes/merge-blocks.txt
deleted file mode 100644
index f5d772c7495..00000000000
--- a/test/passes/merge-blocks.txt
+++ /dev/null
@@ -1,537 +0,0 @@
-(module
-  (memory 256 256)
-  (type $i (func (param i32)))
-  (type $ii (func (param i32 i32)))
-  (type $iii (func (param i32 i32 i32)))
-  (table $call-i)
-  (func $call-i (param $0 i32)
-    (nop)
-  )
-  (func $call-ii (param $0 i32) (param $1 i32)
-    (nop)
-  )
-  (func $call-iii (param $0 i32) (param $1 i32) (param $2 i32)
-    (nop)
-  )
-  (func $b0-yes (param $i1 i32)
-    (block $topmost
-      (block $block0
-        (i32.const 10)
-      )
-    )
-  )
-  (func $b1-yes (param $i1 i32)
-    (block $topmost
-      (block $block0
-        (block $block1
-          (i32.const 10)
-        )
-      )
-    )
-  )
-  (func $b2-yes (param $i1 i32)
-    (block $topmost
-      (i32.const 5)
-      (block $block0
-        (i32.const 10)
-      )
-      (i32.const 15)
-    )
-  )
-  (func $b3-yes (param $i1 i32)
-    (block $topmost
-      (i32.const 3)
-      (block $block0
-        (i32.const 6)
-        (block $block1
-          (i32.const 10)
-        )
-        (i32.const 15)
-      )
-      (i32.const 20)
-    )
-  )
-  (func $b4 (param $i1 i32)
-    (block $topmost
-      (block $inner
-        (i32.const 10)
-        (br $inner)
-      )
-    )
-  )
-  (func $b5 (param $i1 i32)
-    (block $topmost
-      (block $middle
-        (block $inner
-          (i32.const 10)
-          (br $inner)
-        )
-        (br $middle)
-      )
-    )
-  )
-  (func $b6 (param $i1 i32)
-    (block $topmost
-      (i32.const 5)
-      (block $inner
-        (i32.const 10)
-        (br $inner)
-      )
-      (i32.const 15)
-    )
-  )
-  (func $b7 (param $i1 i32)
-    (block $topmost
-      (i32.const 3)
-      (block $middle
-        (i32.const 6)
-        (block $inner
-          (i32.const 10)
-          (br $inner)
-        )
-        (i32.const 15)
-        (br $middle)
-      )
-      (i32.const 20)
-    )
-  )
-  (func $unary
-    (local $x i32)
-    (i32.eqz
-      (block $block0
-        (i32.const 10)
-      )
-    )
-    (block $block1
-      (i32.const 10)
-      (i32.eqz
-        (i32.const 20)
-      )
-    )
-    (block $block2
-      (i32.const 10)
-      (i32.const 20)
-      (i32.eqz
-        (i32.const 30)
-      )
-    )
-    (block $block3
-      (i32.const 10)
-      (set_local $x
-        (i32.const 20)
-      )
-    )
-    (block $block4
-      (i32.const 10)
-      (i32.load
-        (i32.const 20)
-      )
-    )
-    (block $block5
-      (i32.const 10)
-      (return
-        (unreachable)
-      )
-    )
-  )
-  (func $binary
-    (i32.add
-      (block $block0
-        (i32.const 10)
-      )
-      (i32.const 20)
-    )
-    (block $block1
-      (i32.const 10)
-      (i32.add
-        (i32.const 20)
-        (i32.const 30)
-      )
-    )
-    (block $block2
-      (i32.const 10)
-      (i32.const 20)
-      (i32.add
-        (i32.const 30)
-        (i32.const 40)
-      )
-    )
-    (i32.add
-      (i32.const 10)
-      (block $block3
-        (i32.const 20)
-      )
-    )
-    (block $block4
-      (i32.const 20)
-      (i32.add
-        (i32.const 10)
-        (i32.const 30)
-      )
-    )
-    (block $block5
-      (i32.const 20)
-      (i32.const 30)
-      (i32.add
-        (i32.const 10)
-        (i32.const 40)
-      )
-    )
-    (i32.add
-      (block $block6
-        (i32.const 10)
-      )
-      (block $block7
-        (i32.const 20)
-      )
-    )
-    (block $block8
-      (i32.const 10)
-      (i32.const 30)
-      (i32.add
-        (i32.const 20)
-        (i32.const 40)
-      )
-    )
-    (block $block10
-      (i32.const 10)
-      (i32.const 20)
-      (i32.const 40)
-      (i32.const 50)
-      (i32.add
-        (i32.const 30)
-        (i32.const 60)
-      )
-    )
-    (block $block12
-      (i32.const 20)
-      (i32.store
-        (i32.const 10)
-        (i32.const 30)
-      )
-    )
-    (block $block13
-      (i32.const 10)
-      (i32.store
-        (i32.const 20)
-        (i32.const 30)
-      )
-    )
-    (i32.add
-      (unreachable)
-      (block $block14
-        (i32.const 10)
-        (i32.const 20)
-      )
-    )
-    (block $block15
-      (unreachable)
-      (i32.const 20)
-      (i32.add
-        (i32.const 10)
-        (i32.const 30)
-      )
-    )
-  )
-  (func $trinary
-    (block $block0
-      (i32.const 10)
-      (i32.const 30)
-      (i32.const 50)
-      (select
-        (i32.const 20)
-        (i32.const 40)
-        (i32.const 60)
-      )
-    )
-    (block $block4
-      (i32.const 20)
-      (i32.const 40)
-      (select
-        (block $block3
-          (i32.const 10)
-        )
-        (i32.const 30)
-        (i32.const 50)
-      )
-    )
-    (block $block6
-      (i32.const 10)
-      (i32.const 40)
-      (select
-        (i32.const 20)
-        (block $block7
-          (i32.const 30)
-        )
-        (i32.const 50)
-      )
-    )
-    (block $block9
-      (i32.const 10)
-      (i32.const 30)
-      (select
-        (i32.const 20)
-        (i32.const 40)
-        (block $block11
-          (i32.const 50)
-        )
-      )
-    )
-    (block $block14
-      (i32.const 30)
-      (select
-        (block $block12
-          (i32.const 10)
-        )
-        (block $block13
-          (i32.const 20)
-        )
-        (i32.const 40)
-      )
-    )
-    (block $block16
-      (i32.const 20)
-      (select
-        (block $block15
-          (i32.const 10)
-        )
-        (i32.const 30)
-        (block $block17
-          (i32.const 40)
-        )
-      )
-    )
-    (block $block18
-      (i32.const 10)
-      (select
-        (i32.const 20)
-        (block $block19
-          (i32.const 30)
-        )
-        (block $block20
-          (i32.const 40)
-        )
-      )
-    )
-    (block $block21
-      (unreachable)
-      (i32.const 30)
-      (i32.const 50)
-      (select
-        (i32.const 20)
-        (i32.const 40)
-        (i32.const 60)
-      )
-    )
-    (block $block24
-      (i32.const 10)
-      (select
-        (unreachable)
-        (block $block25
-          (i32.const 30)
-          (i32.const 40)
-        )
-        (block $block26
-          (i32.const 50)
-          (i32.const 60)
-        )
-      )
-    )
-    (block $block27
-      (i32.const 10)
-      (unreachable)
-      (i32.const 50)
-      (select
-        (i32.const 20)
-        (i32.const 40)
-        (i32.const 60)
-      )
-    )
-    (block $block30
-      (i32.const 10)
-      (i32.const 30)
-      (select
-        (i32.const 20)
-        (unreachable)
-        (block $block32
-          (i32.const 50)
-          (i32.const 60)
-        )
-      )
-    )
-    (block $block33
-      (i32.const 10)
-      (i32.const 30)
-      (unreachable)
-      (select
-        (i32.const 20)
-        (i32.const 40)
-        (i32.const 60)
-      )
-    )
-    (block $block36
-      (i32.const 10)
-      (i32.const 30)
-      (i32.const 50)
-      (select
-        (i32.const 20)
-        (i32.const 40)
-        (unreachable)
-      )
-    )
-  )
-  (func $breaks
-    (block $out
-      (block $block0
-        (i32.const 10)
-        (br $out
-          (i32.const 20)
-        )
-      )
-      (block $block1
-        (i32.const 10)
-        (br_if $out
-          (i32.const 20)
-        )
-      )
-      (block $block2
-        (i32.const 10)
-        (i32.const 30)
-        (br_if $out
-          (i32.const 20)
-          (i32.const 40)
-        )
-      )
-      (block $block4
-        (i32.const 10)
-        (br_table $out $out
-          (i32.const 20)
-        )
-      )
-      (block $block5
-        (i32.const 10)
-        (i32.const 30)
-        (br_table $out $out
-          (i32.const 20)
-          (i32.const 40)
-        )
-      )
-    )
-  )
-  (func $calls
-    (call $call-i
-      (block $block0
-        (i32.const 10)
-      )
-    )
-    (block $block1
-      (i32.const 10)
-      (call $call-i
-        (i32.const 20)
-      )
-    )
-    (block $block2
-      (i32.const 10)
-      (i32.const 20)
-      (call $call-i
-        (i32.const 30)
-      )
-    )
-    (block $block3
-      (i32.const 10)
-      (i32.const 30)
-      (call $call-ii
-        (i32.const 20)
-        (i32.const 40)
-      )
-    )
-    (block $block5
-      (unreachable)
-      (i32.const 20)
-      (call $call-ii
-        (i32.const 10)
-        (i32.const 30)
-      )
-    )
-    (block $block7
-      (i32.const 10)
-      (call $call-ii
-        (unreachable)
-        (block $block8
-          (i32.const 20)
-          (i32.const 30)
-        )
-      )
-    )
-    (block $block9
-      (i32.const 10)
-      (unreachable)
-      (call $call-ii
-        (i32.const 20)
-        (i32.const 30)
-      )
-    )
-    (block $block11
-      (i32.const 10)
-      (i32.const 30)
-      (call $call-ii
-        (i32.const 20)
-        (unreachable)
-      )
-    )
-    (block $block13
-      (i32.const 10)
-      (i32.const 30)
-      (i32.const 50)
-      (call $call-iii
-        (i32.const 20)
-        (i32.const 40)
-        (i32.const 60)
-      )
-    )
-    (block $block16
-      (i32.const 10)
-      (i32.const 40)
-      (call $call-iii
-        (i32.const 20)
-        (i32.const 30)
-        (i32.const 50)
-      )
-    )
-    (block $block18
-      (i32.const 10)
-      (i32.const 30)
-      (i32.const 50)
-      (call_indirect $ii
-        (i32.const 20)
-        (i32.const 40)
-        (i32.const 60)
-      )
-    )
-    (call_indirect $ii
-      (unreachable)
-      (block $block21
-        (i32.const 30)
-        (i32.const 40)
-      )
-      (block $block22
-        (i32.const 50)
-        (i32.const 60)
-      )
-    )
-  )
-  (func $block-type-change
-    (local $0 f64)
-    (local $1 f64)
-    (if
-      (block $block0
-        (nop)
-        (f64.gt
-          (get_local $0)
-          (get_local $1)
-        )
-      )
-      (nop)
-    )
-  )
-)
diff --git a/test/passes/remove-unused-names_merge-blocks.txt b/test/passes/remove-unused-names_merge-blocks.txt
new file mode 100644
index 00000000000..a0ed7ea326a
--- /dev/null
+++ b/test/passes/remove-unused-names_merge-blocks.txt
@@ -0,0 +1,438 @@
+(module
+  (memory 256 256)
+  (type $i (func (param i32)))
+  (type $ii (func (param i32 i32)))
+  (type $iii (func (param i32 i32 i32)))
+  (table $call-i)
+  (func $call-i (param $0 i32)
+    (nop)
+  )
+  (func $call-ii (param $0 i32) (param $1 i32)
+    (nop)
+  )
+  (func $call-iii (param $0 i32) (param $1 i32) (param $2 i32)
+    (nop)
+  )
+  (func $b0-yes (param $i1 i32)
+    (i32.const 10)
+  )
+  (func $b0-no (param $i1 i32)
+    (block $topmost
+      (block $block0
+        (br $block0)
+      )
+      (br $topmost)
+    )
+  )
+  (func $b0-br-but-ok (param $i1 i32)
+    (block $topmost
+      (br $topmost)
+    )
+  )
+  (func $b1-yes (param $i1 i32)
+    (i32.const 10)
+  )
+  (func $b2-yes (param $i1 i32)
+    (i32.const 5)
+    (i32.const 10)
+    (i32.const 15)
+  )
+  (func $b3-yes (param $i1 i32)
+    (i32.const 3)
+    (i32.const 6)
+    (i32.const 10)
+    (i32.const 15)
+    (i32.const 20)
+  )
+  (func $b4 (param $i1 i32)
+    (block $inner
+      (i32.const 10)
+      (br $inner)
+    )
+  )
+  (func $b5 (param $i1 i32)
+    (block $middle
+      (block $inner
+        (i32.const 10)
+        (br $inner)
+      )
+      (br $middle)
+    )
+  )
+  (func $b6 (param $i1 i32)
+    (i32.const 5)
+    (block $inner
+      (i32.const 10)
+      (br $inner)
+    )
+    (i32.const 15)
+  )
+  (func $b7 (param $i1 i32)
+    (i32.const 3)
+    (block $middle
+      (i32.const 6)
+      (block $inner
+        (i32.const 10)
+        (br $inner)
+      )
+      (i32.const 15)
+      (br $middle)
+    )
+    (i32.const 20)
+  )
+  (func $unary
+    (local $x i32)
+    (i32.eqz
+      (block
+        (i32.const 10)
+      )
+    )
+    (i32.const 10)
+    (i32.eqz
+      (i32.const 20)
+    )
+    (i32.const 10)
+    (i32.const 20)
+    (i32.eqz
+      (i32.const 30)
+    )
+    (i32.const 10)
+    (set_local $x
+      (i32.const 20)
+    )
+    (i32.const 10)
+    (i32.load
+      (i32.const 20)
+    )
+    (i32.const 10)
+    (return
+      (unreachable)
+    )
+  )
+  (func $binary
+    (i32.add
+      (block
+        (i32.const 10)
+      )
+      (i32.const 20)
+    )
+    (i32.const 10)
+    (i32.add
+      (i32.const 20)
+      (i32.const 30)
+    )
+    (i32.const 10)
+    (i32.const 20)
+    (i32.add
+      (i32.const 30)
+      (i32.const 40)
+    )
+    (i32.add
+      (i32.const 10)
+      (block
+        (i32.const 20)
+      )
+    )
+    (i32.const 20)
+    (i32.add
+      (i32.const 10)
+      (i32.const 30)
+    )
+    (i32.const 20)
+    (i32.const 30)
+    (i32.add
+      (i32.const 10)
+      (i32.const 40)
+    )
+    (i32.add
+      (block
+        (i32.const 10)
+      )
+      (block
+        (i32.const 20)
+      )
+    )
+    (i32.const 10)
+    (i32.const 30)
+    (i32.add
+      (i32.const 20)
+      (i32.const 40)
+    )
+    (i32.const 10)
+    (i32.const 20)
+    (i32.const 40)
+    (i32.const 50)
+    (i32.add
+      (i32.const 30)
+      (i32.const 60)
+    )
+    (i32.const 20)
+    (i32.store
+      (i32.const 10)
+      (i32.const 30)
+    )
+    (i32.const 10)
+    (i32.store
+      (i32.const 20)
+      (i32.const 30)
+    )
+    (i32.add
+      (unreachable)
+      (block
+        (i32.const 10)
+        (i32.const 20)
+      )
+    )
+    (unreachable)
+    (i32.const 20)
+    (i32.add
+      (i32.const 10)
+      (i32.const 30)
+    )
+  )
+  (func $trinary
+    (i32.const 10)
+    (i32.const 30)
+    (i32.const 50)
+    (select
+      (i32.const 20)
+      (i32.const 40)
+      (i32.const 60)
+    )
+    (i32.const 20)
+    (i32.const 40)
+    (select
+      (block
+        (i32.const 10)
+      )
+      (i32.const 30)
+      (i32.const 50)
+    )
+    (i32.const 10)
+    (i32.const 40)
+    (select
+      (i32.const 20)
+      (block
+        (i32.const 30)
+      )
+      (i32.const 50)
+    )
+    (i32.const 10)
+    (i32.const 30)
+    (select
+      (i32.const 20)
+      (i32.const 40)
+      (block
+        (i32.const 50)
+      )
+    )
+    (i32.const 30)
+    (select
+      (block
+        (i32.const 10)
+      )
+      (block
+        (i32.const 20)
+      )
+      (i32.const 40)
+    )
+    (i32.const 20)
+    (select
+      (block
+        (i32.const 10)
+      )
+      (i32.const 30)
+      (block
+        (i32.const 40)
+      )
+    )
+    (i32.const 10)
+    (select
+      (i32.const 20)
+      (block
+        (i32.const 30)
+      )
+      (block
+        (i32.const 40)
+      )
+    )
+    (unreachable)
+    (i32.const 30)
+    (i32.const 50)
+    (select
+      (i32.const 20)
+      (i32.const 40)
+      (i32.const 60)
+    )
+    (i32.const 10)
+    (select
+      (unreachable)
+      (block
+        (i32.const 30)
+        (i32.const 40)
+      )
+      (block
+        (i32.const 50)
+        (i32.const 60)
+      )
+    )
+    (i32.const 10)
+    (unreachable)
+    (i32.const 50)
+    (select
+      (i32.const 20)
+      (i32.const 40)
+      (i32.const 60)
+    )
+    (i32.const 10)
+    (i32.const 30)
+    (select
+      (i32.const 20)
+      (unreachable)
+      (block
+        (i32.const 50)
+        (i32.const 60)
+      )
+    )
+    (i32.const 10)
+    (i32.const 30)
+    (unreachable)
+    (select
+      (i32.const 20)
+      (i32.const 40)
+      (i32.const 60)
+    )
+    (i32.const 10)
+    (i32.const 30)
+    (i32.const 50)
+    (select
+      (i32.const 20)
+      (i32.const 40)
+      (unreachable)
+    )
+  )
+  (func $breaks
+    (block $out
+      (i32.const 10)
+      (br $out
+        (i32.const 20)
+      )
+      (i32.const 10)
+      (br_if $out
+        (i32.const 20)
+      )
+      (i32.const 10)
+      (i32.const 30)
+      (br_if $out
+        (i32.const 20)
+        (i32.const 40)
+      )
+      (i32.const 10)
+      (br_table $out $out
+        (i32.const 20)
+      )
+      (i32.const 10)
+      (i32.const 30)
+      (br_table $out $out
+        (i32.const 20)
+        (i32.const 40)
+      )
+    )
+  )
+  (func $calls
+    (call $call-i
+      (block
+        (i32.const 10)
+      )
+    )
+    (i32.const 10)
+    (call $call-i
+      (i32.const 20)
+    )
+    (i32.const 10)
+    (i32.const 20)
+    (call $call-i
+      (i32.const 30)
+    )
+    (i32.const 10)
+    (i32.const 30)
+    (call $call-ii
+      (i32.const 20)
+      (i32.const 40)
+    )
+    (unreachable)
+    (i32.const 20)
+    (call $call-ii
+      (i32.const 10)
+      (i32.const 30)
+    )
+    (i32.const 10)
+    (call $call-ii
+      (unreachable)
+      (block
+        (i32.const 20)
+        (i32.const 30)
+      )
+    )
+    (i32.const 10)
+    (unreachable)
+    (call $call-ii
+      (i32.const 20)
+      (i32.const 30)
+    )
+    (i32.const 10)
+    (i32.const 30)
+    (call $call-ii
+      (i32.const 20)
+      (unreachable)
+    )
+    (i32.const 10)
+    (i32.const 30)
+    (i32.const 50)
+    (call $call-iii
+      (i32.const 20)
+      (i32.const 40)
+      (i32.const 60)
+    )
+    (i32.const 10)
+    (i32.const 40)
+    (call $call-iii
+      (i32.const 20)
+      (i32.const 30)
+      (i32.const 50)
+    )
+    (i32.const 10)
+    (i32.const 30)
+    (i32.const 50)
+    (call_indirect $ii
+      (i32.const 20)
+      (i32.const 40)
+      (i32.const 60)
+    )
+    (call_indirect $ii
+      (unreachable)
+      (block
+        (i32.const 30)
+        (i32.const 40)
+      )
+      (block
+        (i32.const 50)
+        (i32.const 60)
+      )
+    )
+  )
+  (func $block-type-change
+    (local $0 f64)
+    (local $1 f64)
+    (if
+      (block
+        (nop)
+        (f64.gt
+          (get_local $0)
+          (get_local $1)
+        )
+      )
+      (nop)
+    )
+  )
+)
diff --git a/test/passes/merge-blocks.wast b/test/passes/remove-unused-names_merge-blocks.wast
similarity index 97%
rename from test/passes/merge-blocks.wast
rename to test/passes/remove-unused-names_merge-blocks.wast
index a4a9873e900..85bb11da62d 100644
--- a/test/passes/merge-blocks.wast
+++ b/test/passes/remove-unused-names_merge-blocks.wast
@@ -17,6 +17,21 @@
       )
     )
   )
+  (func $b0-no (param $i1 i32)
+    (block $topmost
+      (block $block0
+        (br $block0)
+      )
+      (br $topmost)
+    )
+  )
+  (func $b0-br-but-ok (param $i1 i32)
+    (block $topmost
+      (block $block0
+        (br $topmost)
+      )
+    )
+  )
   (func $b1-yes (param $i1 i32)
     (block $topmost
       (block