VM: Fix identical comparisons with bigints.

runtime/vm/stub_code_x64.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/assembler.h"
 #include "vm/compiler.h"
 #include "vm/dart_entry.h"
@@ skipping 2136 matching lines @@
   const Register left = RAX;
   const Register right = RDX;
 
   __ movq(left, Address(RSP, 2 * kWordSize));
   __ movq(right, Address(RSP, 1 * kWordSize));
   GenerateIdenticalWithNumberCheckStub(assembler, left, right);
   __ ret();
 }
 
 
-// Called from otpimzied code only. Must preserve any registers that are
-// destroyed.
+// Called from optimized code only.
 // TOS + 0: return address
 // TOS + 1: right argument.
 // TOS + 2: left argument.
 // Returns ZF set.
 void StubCode::GenerateOptimizedIdenticalWithNumberCheckStub(
     Assembler* assembler) {
   const Register left = RAX;
   const Register right = RDX;
-  // Preserve left and right.
-  __ pushq(left);
-  __ pushq(right);
-  __ movq(left, Address(RSP, 4 * kWordSize));
-  __ movq(right, Address(RSP, 3 * kWordSize));
+
+  __ movq(left, Address(RSP, 2 * kWordSize));
+  __ movq(right, Address(RSP, 1 * kWordSize));
   GenerateIdenticalWithNumberCheckStub(assembler, left, right);
-  __ popq(right);
-  __ popq(left);
   __ ret();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64