Eliminate overflow check after integer add and sub if result is truncated to int32.

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 267 matching lines @@
 
 HUseListNode* HUseListNode::tail() {
   // Skip and remove dead items in the use list.
   while (tail_ != NULL && tail_->value()->CheckFlag(HValue::kIsDead)) {
     tail_ = tail_->tail_;
   }
   return tail_;
 }
 
 
+bool HValue::CheckUsesForFlag(Flag f) {
+  for (HUseIterator it(uses()); !it.Done(); it.Advance()) {
+    if (!it.value()->CheckFlag(f)) return false;
+  }
+  return true;
+}
+
+
 HUseIterator::HUseIterator(HUseListNode* head) : next_(head) {
   Advance();
 }
 
 
 void HUseIterator::Advance() {
   current_ = next_;
   if (current_ != NULL) {
     next_ = current_->tail();
     value_ = current_->value();
@@ skipping 526 matching lines @@
 
 
 void HLoadFieldByIndex::PrintDataTo(StringStream* stream) {
   object()->PrintNameTo(stream);
   stream->Add(" ");
   index()->PrintNameTo(stream);
 }
 
 
 HValue* HConstant::Canonicalize() {
-  return HasNoUses() && !IsBlockEntry() ? NULL : this;
+  return HasNoUses() ? NULL : this;
 }
 
 
 HValue* HTypeof::Canonicalize() {
-  return HasNoUses() && !IsBlockEntry() ? NULL : this;
+  return HasNoUses() ? NULL : this;
 }
 
 
 HValue* HBitwise::Canonicalize() {
   if (!representation().IsInteger32()) return this;
   // If x is an int32, then x & -1 == x, x | 0 == x and x ^ 0 == x.
   int32_t nop_constant = (op() == Token::BIT_AND) ? -1 : 0;
   if (left()->IsConstant() &&
       HConstant::cast(left())->HasInteger32Value() &&
       HConstant::cast(left())->Integer32Value() == nop_constant) {
     return right();
   }
   if (right()->IsConstant() &&
       HConstant::cast(right())->HasInteger32Value() &&
       HConstant::cast(right())->Integer32Value() == nop_constant) {
     return left();
   }
   return this;
 }
 
 
+HValue* HAdd::Canonicalize() {
+  if (!representation().IsInteger32()) return this;
+  if (CheckUsesForFlag(kTruncatingToInt32)) ClearFlag(kCanOverflow);
+  return this;
+}
+
+
+HValue* HSub::Canonicalize() {
+  if (!representation().IsInteger32()) return this;
+  if (CheckUsesForFlag(kTruncatingToInt32)) ClearFlag(kCanOverflow);
+  return this;
+}
+
+
 HValue* HChange::Canonicalize() {
   return (from().Equals(to())) ? value() : this;
 }
 
 
 void HTypeof::PrintDataTo(StringStream* stream) {
   value()->PrintNameTo(stream);
 }
 
 
@@ skipping 1379 matching lines @@
 
 
 void HCheckPrototypeMaps::Verify() {
   HInstruction::Verify();
   ASSERT(HasNoUses());
 }
 
 #endif
 
 } }  // namespace v8::internal