Optimize simple constant cases for bitwise &, | and ^.

src/hydrogen-instructions.cc

 // Copyright 2011 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 770 matching lines @@
 HValue* HConstant::Canonicalize() {
   return HasNoUses() && !IsBlockEntry() ? NULL : this;
 }
 
 
 HValue* HTypeof::Canonicalize() {
   return HasNoUses() && !IsBlockEntry() ? NULL : this;
 }
 
 
+HValue* HBitwise::Canonicalize() {
+  if (!representation().IsInteger32()) return this;
+  if (op() == Token::BIT_XOR) return this;

[Sven Panne, 2012/01/11 09:54:03]

I don't think we need this special case, because 'x ^ 0 == x', just like 'x | 0
== x'.

[fschneider, 2012/01/11 10:00:30]

Done.

+  // If x is an int32, x & -1 == x and x | 0 == x.
+  int nop_constant = (op() == Token::BIT_AND) ? -1 : 0;

[Sven Panne, 2012/01/11 09:54:03]

Use int32_t, not int.

[fschneider, 2012/01/11 10:00:30]

Done.

+  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;
+}
+
+
 void HTypeof::PrintDataTo(StringStream* stream) {
   value()->PrintNameTo(stream);
 }
 
 
 void HChange::PrintDataTo(StringStream* stream) {
   HUnaryOperation::PrintDataTo(stream);
   stream->Add(" %s to %s", from().Mnemonic(), to().Mnemonic());
 
   if (CanTruncateToInt32()) stream->Add(" truncating-int32");
@@ skipping 1305 matching lines @@
 
 
 void HCheckPrototypeMaps::Verify() {
   HInstruction::Verify();
   ASSERT(HasNoUses());
 }
 
 #endif
 
 } }  // namespace v8::internal