[x64] Make xmm0 allocatable and use xmm15 as scratch register instead.

src/crankshaft/x64/lithium-codegen-x64.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_CRANKSHAFT_X64_LITHIUM_CODEGEN_X64_H_
 #define V8_CRANKSHAFT_X64_LITHIUM_CODEGEN_X64_H_
 
 
 #include "src/ast/scopes.h"
 #include "src/base/logging.h"
@@ skipping 97 matching lines @@
   // Declare methods that deal with the individual node types.
 #define DECLARE_DO(type) void Do##type(L##type* node);
   LITHIUM_CONCRETE_INSTRUCTION_LIST(DECLARE_DO)
 #undef DECLARE_DO
 
  private:
   LPlatformChunk* chunk() const { return chunk_; }
   Scope* scope() const { return scope_; }
   HGraph* graph() const { return chunk()->graph(); }
 
-  XMMRegister double_scratch0() const { return xmm0; }
+  XMMRegister double_scratch0() const { return kScratchDoubleReg; }
 
   void EmitClassOfTest(Label* if_true,
                        Label* if_false,
                        Handle<String> class_name,
                        Register input,
                        Register temporary,
                        Register scratch);
 
   bool HasAllocatedStackSlots() const {
     return chunk()->HasAllocatedStackSlots();
@@ skipping 250 matching lines @@
   Label exit_;
   Label done_;
   Label* external_exit_;
   int instruction_index_;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_CRANKSHAFT_X64_LITHIUM_CODEGEN_X64_H_