%X => %_X, %_X => %__X

src/x64/full-codegen-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 3776 matching lines @@
   __ bind(&return_result);
   // Drop temp values from the stack, and restore context register.
   __ addq(rsp, Immediate(3 * kPointerSize));
   __ movq(rsi, Operand(rbp, StandardFrameConstants::kContextOffset));
   context()->Plug(rax);
 }
 
 
 void FullCodeGenerator::VisitCallRuntime(CallRuntime* expr) {
   Handle<String> name = expr->name();
-  if (name->length() > 0 && name->Get(0) == '_') {
+  if (name->length() > 1 && name->Get(0) == '_' && name->Get(1) == '_') {
     Comment cmnt(masm_, "[ InlineRuntimeCall");
     EmitInlineRuntimeCall(expr);
     return;
   }
 
   Comment cmnt(masm_, "[ CallRuntime");
   ZoneList<Expression*>* args = expr->arguments();
 
   if (expr->is_jsruntime()) {
     // Prepare for calling JS runtime function.
@@ skipping 718 matching lines @@
   *context_length = 0;
   return previous_;
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64