Make breakpoints on == fire reliably

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 1667 matching lines @@
 }
 
 
 // Megamorphic call is currently implemented as IC call but through a stub
 // that does not check/count function invocations.
 void StubCode::GenerateMegamorphicCallStub(Assembler* assembler) {
   GenerateNArgsCheckInlineCacheStub(assembler, 1);
 }
 
 
+//  RBX: ICData.
+//  TOS(0): return address (Dart code).
+void StubCode::GenerateBreakpointEqNullStub(Assembler* assembler) {
+  __ EnterStubFrame();
+  __ pushq(RBX);  // Preserve ICData.
+  __ CallRuntime(kBreakpointClosureHandlerRuntimeEntry);
+  __ popq(RBX);  // Restore arguments descriptor.
+  __ LeaveFrame();
+  __ jmp(&StubCode::EqualityWithNullArgLabel());
+}
+
+
 //  R10: Arguments descriptor array.
 //  TOS(0): return address (Dart code).
 void StubCode::GenerateBreakpointClosureStub(Assembler* assembler) {
   __ EnterStubFrame();
   __ pushq(R10);       // Preserve arguments descriptor.
   __ CallRuntime(kBreakpointClosureHandlerRuntimeEntry);
   __ popq(R10);  // Restore arguments descriptor.
   __ LeaveFrame();
   __ jmp(&StubCode::CallClosureFunctionLabel());
 }
@@ skipping 394 matching lines @@
   __ cmpq(left, right);
   __ Bind(&done);
   __ popq(right);
   __ popq(left);
   __ ret();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64