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

src/hydrogen.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 295 matching lines @@
   const HBasicBlock* current = this;
   int result  = (current->IsLoopHeader()) ? 1 : 0;
   while (current->parent_loop_header() != NULL) {
     current = current->parent_loop_header();
     result++;
   }
   return result;
 }
 
 
+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());
 
   SetJoinId(stmt->EntryId());
   if (predecessors()->length() == 1) {
     // This is a degenerated loop.
     DetachLoopInformation();
     return;
   }
 
   // Only the first entry into the loop is from outside the loop. All other
   // entries must be back edges.
   for (int i = 1; i < predecessors()->length(); ++i) {
     loop_information()->RegisterBackEdge(predecessors()->at(i));
   }
 }
 
 
+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
     // instructions have been added to the block (they have phis for all
     // values in the environment, these phis may be eliminated later).
     ASSERT(IsLoopHeader() || first_ == NULL);
     HEnvironment* incoming_env = pred->last_environment();
     if (IsLoopHeader()) {
       ASSERT(phis()->length() == incoming_env->length());
       for (int i = 0; i < phis_.length(); ++i) {
@@ skipping 10631 matching lines @@
   if (ShouldProduceTraceOutput()) {
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 } }  // namespace v8::internal