Improve and simplify removal of unreachable code

src/hydrogen-instructions.cc

 // Copyright 2012 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 491 matching lines @@
   switch (opcode()) {
 #define MAKE_CASE(type) case k##type: return #type;
     HYDROGEN_CONCRETE_INSTRUCTION_LIST(MAKE_CASE)
 #undef MAKE_CASE
     case kPhi: return "Phi";
     default: return "";
   }
 }
 
 
+bool HValue::CanReplaceWithDummyUses() {
+  return FLAG_unreachable_code_elimination &&
+      !(block()->IsReachable() ||
+        IsBlockEntry() ||
+        IsControlInstruction() ||
+        IsSimulate() ||
+        IsEnterInlined() ||
+        IsLeaveInlined());
+}
+
+
 bool HValue::IsInteger32Constant() {
   return IsConstant() && HConstant::cast(this)->HasInteger32Value();
 }
 
 
 int32_t HValue::GetInteger32Constant() {
   return HConstant::cast(this)->Integer32Value();
 }
 
 
@@ skipping 521 matching lines @@
   if (expected_input_types_.Contains(ToBooleanStub::HEAP_NUMBER)) {
     return Representation::Double();
   }
   if (expected_input_types_.Contains(ToBooleanStub::SMI)) {
     return Representation::Smi();
   }
   return Representation::None();
 }
 
 
+bool HBranch::KnownSuccessorBlock(HBasicBlock** block) {
+  HValue* value = this->value();
+  if (value->EmitAtUses()) {
+    ASSERT(value->IsConstant());
+    ASSERT(!value->representation().IsDouble());
+    *block = HConstant::cast(value)->BooleanValue()
+        ? FirstSuccessor()
+        : SecondSuccessor();
+    return true;
+  }
+  *block = NULL;
+  return false;
+}
+
+
 void HCompareMap::PrintDataTo(StringStream* stream) {
   value()->PrintNameTo(stream);
   stream->Add(" (%p)", *map().handle());
   HControlInstruction::PrintDataTo(stream);
 }
 
 
 const char* HUnaryMathOperation::OpName() const {
   switch (op()) {
     case kMathFloor: return "floor";
@@ skipping 1787 matching lines @@
 
 
 void HCompareObjectEqAndBranch::PrintDataTo(StringStream* stream) {
   left()->PrintNameTo(stream);
   stream->Add(" ");
   right()->PrintNameTo(stream);
   HControlInstruction::PrintDataTo(stream);
 }
 
 
+bool HCompareObjectEqAndBranch::KnownSuccessorBlock(HBasicBlock** block) {
+  if (left()->IsConstant() && right()->IsConstant()) {
+    bool comparison_result =
+        HConstant::cast(left())->DataEquals(HConstant::cast(right()));

[Michael Starzinger, 2013/10/01 11:17:47]

suggestion: We could use Equals() instead of DataEquals() here. Admittedly that
performs some redundant checks, but would allow us to keep
HConstant::DataEquals() protected and not break abstraction. I am fine either
way, your choice.

[danno, 2013/10/23 11:46:51]

Done.

+    *block = comparison_result
+        ? FirstSuccessor()
+        : SecondSuccessor();
+    return true;
+  }
+  *block = NULL;
+  return false;
+}
+
+
 void HCompareHoleAndBranch::InferRepresentation(
     HInferRepresentationPhase* h_infer) {
   ChangeRepresentation(value()->representation());
 }
 
 
 void HGoto::PrintDataTo(StringStream* stream) {
   stream->Add("B%d", SuccessorAt(0)->block_id());
 }
 
@@ skipping 1355 matching lines @@
       break;
     case kExternalMemory:
       stream->Add("[external-memory]");
       break;
   }
 
   stream->Add("@%d", offset());
 }
 
 } }  // namespace v8::internal