Simplify some code related to x64 calling convention.

src/x64/macro-assembler-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 799 matching lines @@
   LoadRoot(rax, Heap::kUndefinedValueRootIndex);
   jmp(&prologue);
 
   bind(&promote_scheduled_exception);
   TailCallRuntime(Runtime::kPromoteScheduledException, 0, 1);
 
   // HandleScope limit has changed. Delete allocated extensions.
   bind(&delete_allocated_handles);
   movq(Operand(base_reg, kLimitOffset), prev_limit_reg);
   movq(prev_limit_reg, rax);
-#ifdef _WIN64
-  LoadAddress(rcx, ExternalReference::isolate_address(isolate()));
-#else
-  LoadAddress(rdi, ExternalReference::isolate_address(isolate()));
-#endif
+  LoadAddress(arg_reg_1, ExternalReference::isolate_address(isolate()));
   LoadAddress(rax,
               ExternalReference::delete_handle_scope_extensions(isolate()));
   call(rax);
   movq(rax, prev_limit_reg);
   jmp(&leave_exit_frame);
 }
 
 
 void MacroAssembler::JumpToExternalReference(const ExternalReference& ext,
                                              int result_size) {
@@ skipping 3802 matching lines @@
   j(greater, &no_info_available);
   CompareRoot(MemOperand(scratch_reg, -AllocationSiteInfo::kSize),
               Heap::kAllocationSiteInfoMapRootIndex);
   bind(&no_info_available);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64