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

For integer bitwise operations we can replace
x & -1 with x,  x | 0 with x and x ^ 0 with x.
Review URL: http://codereview.chromium.org/9177001

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10382 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/hydrogen-instructions.cc

@@ -788,6 +788,24 @@ HValue* HTypeof::Canonicalize() {
 }
 
 
+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;
+}
+
+
 void HTypeof::PrintDataTo(StringStream* stream) {
   value()->PrintNameTo(stream);
 }

src/hydrogen-instructions.h

@@ -3151,6 +3151,8 @@ class HBitwise: public HBitwiseBinaryOperation {
 
   virtual bool IsCommutative() const { return true; }
 
+  virtual HValue* Canonicalize();
+
   static HInstruction* NewHBitwise(Zone* zone,
                                    Token::Value op,
                                    HValue* context,