Make CTX allocatable by the register allocator.

runtime/vm/exceptions.cc

 // Copyright (c) 2011, 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/exceptions.h"
 
 #include "vm/dart_api_impl.h"
 #include "vm/dart_entry.h"
 #include "vm/debugger.h"
 #include "vm/flags.h"
@@ skipping 262 matching lines @@
                                    uword stack_pointer,
                                    uword frame_pointer,
                                    const Object& exception_object,
                                    const Object& stacktrace_object) {
   // The no_gc StackResource is unwound through the tear down of
   // stack resources below.
   NoGCScope no_gc;
   RawObject* raw_exception = exception_object.raw();
   RawObject* raw_stacktrace = stacktrace_object.raw();
 
-  // The following operation is part of the 'epilogue' of the CallToRuntime,
-  // CallBootstrapCFunction, and CallNativeCFunction stubs. In the case of an
-  // exception, we skip the epilogues and must set the correct state here.
-  // The other operations performed as part of the 'epilogue' are handled
-  // by the simulator's Longjmp or the JumpToExceptionHandler stub.
-  isolate->set_top_context(Context::null());
-
 #if defined(USING_SIMULATOR)
   // Unwinding of the C++ frames and destroying of their stack resources is done
   // by the simulator, because the target stack_pointer is a simulated stack
   // pointer and not the C++ stack pointer.
 
   // Continue simulating at the given pc in the given frame after setting up the
   // exception object in the kExceptionObjectReg register and the stacktrace
   // object (may be raw null) in the kStackTraceObjectReg register.
 
   Simulator::Current()->Longjmp(program_counter, stack_pointer, frame_pointer,
@@ skipping 478 matching lines @@
 
 // Throw JavascriptCompatibilityError exception.
 void Exceptions::ThrowJavascriptCompatibilityError(const char* msg) {
   const Array& exc_args = Array::Handle(Array::New(1));
   const String& msg_str = String::Handle(String::New(msg));
   exc_args.SetAt(0, msg_str);
   Exceptions::ThrowByType(Exceptions::kJavascriptCompatibilityError, exc_args);
 }
 
 }  // namespace dart