Simplify some code related to x64 calling convention.

src/x64/builtins-x64.cc

 // Copyright 2012 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 630 matching lines @@
   // For now, we are relying on the fact that make_code_young doesn't do any
   // garbage collection which allows us to save/restore the registers without
   // worrying about which of them contain pointers. We also don't build an
   // internal frame to make the code faster, since we shouldn't have to do stack
   // crawls in MakeCodeYoung. This seems a bit fragile.
 
   // Re-execute the code that was patched back to the young age when
   // the stub returns.
   __ subq(Operand(rsp, 0), Immediate(5));
   __ Pushad();
-#ifdef _WIN64
-  __ movq(rcx, Operand(rsp, kNumSafepointRegisters * kPointerSize));
-#else
-  __ movq(rdi, Operand(rsp, kNumSafepointRegisters * kPointerSize));
-#endif
+  __ movq(arg_reg_1, Operand(rsp, kNumSafepointRegisters * kPointerSize));
   {  // NOLINT
     FrameScope scope(masm, StackFrame::MANUAL);
     __ PrepareCallCFunction(1);
     __ CallCFunction(
         ExternalReference::get_make_code_young_function(masm->isolate()), 1);
   }
   __ Popad();
   __ ret(0);
 }
 
@@ skipping 1198 matching lines @@
   Deoptimizer::EntryGenerator generator(masm, Deoptimizer::OSR);
   generator.Generate();
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64