Port optimization of comparison with a trivial LHS from ia32 to x64.

src/x64/codegen-x64.cc

 // Copyright 2010 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 3818 matching lines @@
       cc = greater;
       break;
     case Token::LTE:
       cc = less_equal;
       break;
     case Token::GTE:
       cc = greater_equal;
       break;
     case Token::IN: {
       Load(left);
       Load(right);

[Lasse Reichstein, 2010/06/24 08:59:48]

The optimization is likely to apply here too, because left is almost certainly a
literal string.

[William Hesse, 2010/06/24 14:43:53]

But since we are going to a builtin, it will be spilled anyway.

       Result answer = frame_->InvokeBuiltin(Builtins::IN, CALL_FUNCTION, 2);
       frame_->Push(&answer);  // push the result
       return;
     }
     case Token::INSTANCEOF: {
       Load(left);
       Load(right);

[Lasse Reichstein, 2010/06/24 08:59:48]

... but it's probably not worth it here, since left should be an object.

       InstanceofStub stub;
       Result answer = frame_->CallStub(&stub, 2);
       answer.ToRegister();
       __ testq(answer.reg(), answer.reg());
       answer.Unuse();
       destination()->Split(zero);
       return;
     }
     default:
       UNREACHABLE();
   }
-  Load(left);
-  Load(right);
+
+  if (left->IsTrivial()) {
+    Load(right);
+    Result right_result = frame_->Pop();
+    frame_->Push(left);
+    frame_->Push(&right_result);

[Lasse Reichstein, 2010/06/24 08:59:48]

Could we reverse the comparison instead, and keep left on top of the stack?

[William Hesse, 2010/06/24 14:43:53]

I don't think so, because the ToNumber calls inside comparison have to happen in
a certain order.

+  } else {
+    Load(left);
+    Load(right);
+  }
+
   Comparison(node, cc, strict, destination());
 }
 
 
 void CodeGenerator::VisitThisFunction(ThisFunction* node) {
   frame_->PushFunction();
 }
 
 
 void CodeGenerator::GenerateArguments(ZoneList<Expression*>* args) {
@@ skipping 8024 matching lines @@
 }
 
 #endif
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64