Use register allocator for context on x64.

src/x64/code-stubs-x64.cc

 // Copyright 2013 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 1118 matching lines @@
     __ movsd(xmm0, double_base);
     ASSERT(double_exponent.is(xmm1));
     {
       AllowExternalCallThatCantCauseGC scope(masm);
       __ PrepareCallCFunction(2);
       __ CallCFunction(
           ExternalReference::power_double_double_function(masm->isolate()), 2);
     }
     // Return value is in xmm0.
     __ movsd(double_result, xmm0);
-    // Restore context register.
-    __ movq(rsi, Operand(rbp, StandardFrameConstants::kContextOffset));
 
     __ bind(&done);
     __ IncrementCounter(counters->math_pow(), 1);
     __ ret(0);
   }
 }
 
 
 void FunctionPrototypeStub::Generate(MacroAssembler* masm) {
   Label miss;
@@ skipping 4664 matching lines @@
   __ bind(&fast_elements_case);
   GenerateCase(masm, FAST_ELEMENTS);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64