Optimize ~~(expr) in optimized code.

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 852 matching lines @@
   }
   if (right()->IsConstant() &&
       HConstant::cast(right())->HasInteger32Value() &&
       HConstant::cast(right())->Integer32Value() == nop_constant) {
     return left();
   }
   return this;
 }
 
 
+HValue* HBitNot::Canonicalize() {
+  // Optimize ~~x, a common pattern used for ToInt32(x).
+  if (value()->IsBitNot()) {
+    HValue* result = HBitNot::cast(value())->value();
+    ASSERT(result->representation().IsInteger32());
+    return result;
+  }
+  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);
@@ skipping 1476 matching lines @@
 
 
 void HCheckPrototypeMaps::Verify() {
   HInstruction::Verify();
   ASSERT(HasNoUses());
 }
 
 #endif
 
 } }  // namespace v8::internal