Improve ClampDoubleToUint8 on ia32/x64

src/ia32/lithium-ia32.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 1761 matching lines @@
   LCheckMaps* result = new(zone()) LCheckMaps(value);
   return AssignEnvironment(result);
 }
 
 
 LInstruction* LChunkBuilder::DoClampToUint8(HClampToUint8* instr) {
   HValue* value = instr->value();
   Representation input_rep = value->representation();
   if (input_rep.IsDouble()) {
     LOperand* reg = UseRegister(value);
-    return DefineAsRegister(new(zone()) LClampDToUint8(reg));
+    return DefineFixed(new(zone()) LClampDToUint8(reg), eax);

[Yang, 2012/10/19 09:29:45]

I assume that you have to use EAX because SETcc needs to access the least
significant byte, ruling out ESI and EDI?

   } else if (input_rep.IsInteger32()) {
     LOperand* reg = UseFixed(value, eax);
     return DefineFixed(new(zone()) LClampIToUint8(reg), eax);
   } else {
     ASSERT(input_rep.IsTagged());
     LOperand* reg = UseFixed(value, eax);
     // Register allocator doesn't (yet) support allocation of double
     // temps. Reserve xmm1 explicitly.
     LOperand* temp = FixedTemp(xmm1);
     LClampTToUint8* result = new(zone()) LClampTToUint8(reg, temp);
@@ skipping 638 matching lines @@
 LInstruction* LChunkBuilder::DoLoadFieldByIndex(HLoadFieldByIndex* instr) {
   LOperand* object = UseRegister(instr->object());
   LOperand* index = UseTempRegister(instr->index());
   return DefineSameAsFirst(new(zone()) LLoadFieldByIndex(object, index));
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32