Check elimination improvement: propagation of state through phis is supported, CheckMap narrowing i…

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 284 matching lines @@
 bool HBasicBlock::Dominates(HBasicBlock* other) const {
   HBasicBlock* current = other->dominator();
   while (current != NULL) {
     if (current == this) return true;
     current = current->dominator();
   }
   return false;
 }
 
 
+bool HBasicBlock::EqualToOrDominates(HBasicBlock* other) const {
+  if (this == other) return true;
+  return Dominates(other);
+}
+
+
 int HBasicBlock::LoopNestingDepth() const {
   const HBasicBlock* current = this;
   int result  = (current->IsLoopHeader()) ? 1 : 0;
   while (current->parent_loop_header() != NULL) {
     current = current->parent_loop_header();
     result++;
   }
   return result;
 }
 
@@ skipping 3593 matching lines @@
 
 #ifdef DEBUG
     for (int i = 0; i < block->phis()->length(); i++) {
       HPhi* phi = block->phis()->at(i);
       ASSERT(phi->ActualValue() == phi);
     }
 #endif
 
     for (HInstructionIterator it(block); !it.Done(); it.Advance()) {
       HInstruction* instruction = it.Current();
-      if (instruction->ActualValue() != instruction) {
+      if (instruction->CheckFlag(HValue::kIsDead)) {
+        // The instruction was marked as deleted but left in the graph
+        // as a control flow dependency point for subsequent
+        // instructions.
+        instruction->DeleteAndReplaceWith(instruction->ActualValue());
+
+      } else if (instruction->ActualValue() != instruction) {
         ASSERT(instruction->IsInformativeDefinition());
         if (instruction->IsPurelyInformativeDefinition()) {
           instruction->DeleteAndReplaceWith(instruction->RedefinedOperand());
         } else {
           instruction->ReplaceAllUsesWith(instruction->ActualValue());
         }
       }
     }
   }
 }
@@ skipping 7077 matching lines @@
   if (ShouldProduceTraceOutput()) {
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 } }  // namespace v8::internal