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

src/hydrogen-instructions.cc

Index: src/hydrogen-instructions.cc
===================================================================
--- src/hydrogen-instructions.cc	(revision 10369)
+++ src/hydrogen-instructions.cc	(working copy)
@@ -788,6 +788,25 @@
 }
 
 
+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);
 }