Use a fixed input register where we require a byte register.

src/x64/lithium-x64.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
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 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
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@@ skipping 1855 matching lines @@
 LInstruction* LChunkBuilder::DoStoreKeyedSpecializedArrayElement(
     HStoreKeyedSpecializedArrayElement* instr) {
   Representation representation(instr->value()->representation());
   ExternalArrayType array_type = instr->array_type();
   ASSERT((representation.IsInteger32() && array_type != kExternalFloatArray) ||
          (representation.IsDouble() && array_type == kExternalFloatArray));
   ASSERT(instr->external_pointer()->representation().IsExternal());
   ASSERT(instr->key()->representation().IsInteger32());
 
   LOperand* external_pointer = UseRegister(instr->external_pointer());
-  bool val_is_temp_register = array_type == kExternalPixelArray ||
-      array_type == kExternalFloatArray;
-  LOperand* val = val_is_temp_register
-      ? UseTempRegister(instr->value())
-      : UseRegister(instr->key());
+  LOperand* val = NULL;
+  switch (array_type) {
+    case kExternalPixelArray:

[danno, 2011/03/29 14:25:34]

Doesn't pixel array still need to be a temp, since the clamping code overwrites
rax and you don't want to accidentally use it later expecting the contents to
still be val. 

[fschneider, 2011/03/29 14:43:58]

That would be ok, since UseFixed is always a fixed writable input register. The
naming of UseFixed is however not ideal.

+    case kExternalByteArray:
+    case kExternalUnsignedByteArray:
+      // We need a byte register in these cases.
+      val = UseFixed(instr->value(), rax);

[danno, 2011/03/29 14:25:34]

Do you really need to use rax? On 64 bit the byte store should work for any
register with the REX prefix that's handled by the assembler?

[fschneider, 2011/03/29 14:43:58]

You're right. I didn't realize x64 allows that. I don't need to change anything
on x64 then.

+      break;
+    case kExternalFloatArray:
+      // We need a writable register here.
+      val = UseTempRegister(instr->value());
+      break;
+    default:
+      val = UseRegister(instr->value());
+      break;
+  }
   LOperand* key = UseRegister(instr->key());
 
   return new LStoreKeyedSpecializedArrayElement(external_pointer,
                                                 key,
                                                 val);
 }
 
 
 LInstruction* LChunkBuilder::DoStoreKeyedGeneric(HStoreKeyedGeneric* instr) {
   LOperand* object = UseFixed(instr->object(), rdx);
@@ skipping 204 matching lines @@
 
 LInstruction* LChunkBuilder::DoLeaveInlined(HLeaveInlined* instr) {
   HEnvironment* outer = current_block_->last_environment()->outer();
   current_block_->UpdateEnvironment(outer);
   return NULL;
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64