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

src/x64/code-stubs-x64.cc

 // Copyright 2013 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.
 
 #if V8_TARGET_ARCH_X64
 
 #include "src/code-stubs.h"
 #include "src/api-arguments.h"
 #include "src/bootstrapper.h"
 #include "src/codegen.h"
@@ skipping 144 matching lines @@
     Register result_reg = final_result_reg.is(rcx) ? rax : final_result_reg;
     // Save ecx if it isn't the return register and therefore volatile, or if it
     // is the return register, then save the temp register we use in its stead
     // for the result.
     Register save_reg = final_result_reg.is(rcx) ? rax : rcx;
     __ pushq(scratch1);
     __ pushq(save_reg);
 
     bool stash_exponent_copy = !input_reg.is(rsp);
     __ movl(scratch1, mantissa_operand);
-    __ Movsd(xmm0, mantissa_operand);
+    __ Movsd(kScratchDoubleReg, mantissa_operand);
     __ movl(rcx, exponent_operand);
     if (stash_exponent_copy) __ pushq(rcx);
 
     __ andl(rcx, Immediate(HeapNumber::kExponentMask));
     __ shrl(rcx, Immediate(HeapNumber::kExponentShift));
     __ leal(result_reg, MemOperand(rcx, -HeapNumber::kExponentBias));
     __ cmpl(result_reg, Immediate(HeapNumber::kMantissaBits));
     __ j(below, &process_64_bits);
 
     // Result is entirely in lower 32-bits of mantissa
     int delta = HeapNumber::kExponentBias + Double::kPhysicalSignificandSize;
     __ subl(rcx, Immediate(delta));
     __ xorl(result_reg, result_reg);
     __ cmpl(rcx, Immediate(31));
     __ j(above, &done);
     __ shll_cl(scratch1);
     __ jmp(&check_negative);
 
     __ bind(&process_64_bits);
-    __ Cvttsd2siq(result_reg, xmm0);
+    __ Cvttsd2siq(result_reg, kScratchDoubleReg);
     __ jmp(&done, Label::kNear);
 
     // If the double was negative, negate the integer result.
     __ bind(&check_negative);
     __ movl(result_reg, scratch1);
     __ negl(result_reg);
     if (stash_exponent_copy) {
         __ cmpl(MemOperand(rsp, 0), Immediate(0));
     } else {
         __ cmpl(exponent_operand, Immediate(0));
@@ skipping 5247 matching lines @@
                            kStackUnwindSpace, nullptr, return_value_operand,
                            NULL);
 }
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_X64