Avoid using a register for constant external array indices.

src/x64/lithium-x64.cc

 // Copyright 2011 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 1833 matching lines @@
     HLoadKeyedSpecializedArrayElement* instr) {
   ExternalArrayType array_type = instr->array_type();
   Representation representation(instr->representation());
   ASSERT(
       (representation.IsInteger32() && (array_type != kExternalFloatArray &&
                                         array_type != kExternalDoubleArray)) ||
       (representation.IsDouble() && (array_type == kExternalFloatArray ||
                                      array_type == kExternalDoubleArray)));
   ASSERT(instr->key()->representation().IsInteger32());
   LOperand* external_pointer = UseRegister(instr->external_pointer());
-  LOperand* key = UseRegister(instr->key());
+  LOperand* key = UseRegisterOrConstant(instr->key());
   LLoadKeyedSpecializedArrayElement* result =
       new LLoadKeyedSpecializedArrayElement(external_pointer, key);
   LInstruction* load_instr = DefineAsRegister(result);
   // An unsigned int array load might overflow and cause a deopt, make sure it
   // has an environment.
   return (array_type == kExternalUnsignedIntArray) ?
       AssignEnvironment(load_instr) : load_instr;
 }
 
 
@@ skipping 36 matching lines @@
                                      array_type == kExternalDoubleArray)));
   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->value());
-  LOperand* key = UseRegister(instr->key());
+  LOperand* key = UseRegisterOrConstant(instr->key());
 
   return new LStoreKeyedSpecializedArrayElement(external_pointer,
                                                 key,
                                                 val);
 }
 
 
 LInstruction* LChunkBuilder::DoStoreKeyedGeneric(HStoreKeyedGeneric* instr) {
   LOperand* object = UseFixed(instr->object(), rdx);
   LOperand* key = UseFixed(instr->key(), rcx);
@@ skipping 219 matching lines @@
   LOperand* key = UseOrConstantAtStart(instr->key());
   LOperand* object = UseOrConstantAtStart(instr->object());
   LIn* result = new LIn(key, object);
   return MarkAsCall(DefineFixed(result, rax), instr);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64