Eliminatable CheckMaps replaced with if(true) or if(false).

src/hydrogen.cc

Index: src/hydrogen.cc
diff --git a/src/hydrogen.cc b/src/hydrogen.cc
index 4377b420705755d36223b319fc2119ab40bfcd42..f924307993a2835b3aadf6f2da06fe9b0b4e5c8e 100644
--- a/src/hydrogen.cc
+++ b/src/hydrogen.cc
@@ -313,6 +313,30 @@ int HBasicBlock::LoopNestingDepth() const {
 }
 
 
+void HBasicBlock::ReplaceControlWithGotoSuccessor(int succ) {
+  ASSERT(IsFinished());
+  ASSERT(end()->SuccessorCount() == 2);  // Only this case is supported yet.
+  ASSERT(succ < end()->SuccessorCount());
+
+  int unreachable_succ = 1 - succ;
+
+  // Replace control instruction with if (true) {succ} else {unreachable_succ}.
+  HBranch* new_branch = HBranch::New(
+      zone(),
+      NULL,
+      graph()->GetConstantTrue(),
+      ToBooleanStub::Types(ToBooleanStub::BOOLEAN),
+      end()->SuccessorAt(succ),
+      end()->SuccessorAt(unreachable_succ));
+
+  MarkSuccEdgeUnreachable(unreachable_succ);
+
+  end()->DeleteAndReplaceWith(end()->ActualValue());

[Jakob Kummerow, 2014/01/15 10:30:19]

As discussed offline, this is a bug.

Some instructions define dependencies on control instructions (such as
HCheckMaps) because they must be scheduled after the check (i.e. must not be
hoisted past it). Replacing the control node input to such an instruction with
the check's input value is hence invalid, as doing so removes the explicit
scheduling dependency.
(At least, I think that's the reason why this CL is causing test failures.)

+  new_branch->InsertAfter(last());
+  end_ = new_branch;
+}
+
+
 void HBasicBlock::PostProcessLoopHeader(IterationStatement* stmt) {
   ASSERT(IsLoopHeader());
 
@@ -331,6 +355,15 @@ void HBasicBlock::PostProcessLoopHeader(IterationStatement* stmt) {
 }
 
 
+void HBasicBlock::MarkSuccEdgeUnreachable(int succ) {
+  ASSERT(IsFinished());
+  HBasicBlock* succ_block = end()->SuccessorAt(succ);
+
+  ASSERT(succ_block->predecessors()->length() == 1);
+  succ_block->MarkUnreachable();
+}
+
+
 void HBasicBlock::RegisterPredecessor(HBasicBlock* pred) {
   if (HasPredecessor()) {
     // Only loop header blocks can have a predecessor added after