First step toward an optimizing compiler:

runtime/vm/stub_code_x64.cc

 // Copyright (c) 2012, 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/assembler_macros.h"
 #include "vm/code_generator.h"
@@ skipping 563 matching lines @@
   __ popq(RAX);
   __ popq(RAX);  // Get result into RAX.
 
   // Remove the stub frame as we are about to return.
   __ LeaveFrame();
   __ ret();
 }
 
 
 void StubCode::GenerateDeoptimizeStub(Assembler* assembler) {
-  __ Untested("Deoptimize stub");
   AssemblerMacros::EnterStubFrame(assembler);
   // RAX: deoptimization reason id.
   // Stack at this point:
   // TOS + 0: PC marker => RawInstruction object.
   // TOS + 1: Saved EBP of function frame that will be deoptimized. <== EBP
   // TOS + 2: Deoptimization point (return address), will be patched.
   // TOS + 3: top-of-stack at deoptimization point (all arguments on stack).
   __ pushq(RAX);
   __ CallRuntime(kDeoptimizeRuntimeEntry);
   __ popq(RAX);
@@ skipping 1261 matching lines @@
 // TOS + 2: instance.
 // TOS + 3: cache array.
 // Result in RCX: null -> not found, otherwise result (true or false).
 void StubCode::GenerateSubtype3TestCacheStub(Assembler* assembler) {
   GenerateSubtypeNTestCacheStub(assembler, 3);
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64