GCAwareJITStubRoutineWithExceptionHandler has a stale CodeBlock pointer in its destructor

[Saam Barati]

The problem is that we may regenerate many GCAwareJITStubRoutineWithExceptionHandler stubs per one PolymorphicAccess.
Only the last GCAwareJITStubRoutineWithExceptionHandler stub that was generated will get the CodeBlock's aboutToDie()
notification. All other GCAwareJITStubRoutineWithExceptionHandler stubs will still be holding a stale CodeBlock pointer
that they will use in their destructor. The solution is to have GCAwareJITStubRoutineWithExceptionHandler remove its
exception handler in observeZeroRefCount() instead of its destructor. observeZeroRefCount() will run when a PolymorphicAccess
replaces its m_stubRoutine.

[Saam Barati]

Created attachment 263539 [details]
patch

[Mark Lam]

Comment on attachment 263539 [details]
patch

View in context: https://bugs.webkit.org/attachment.cgi?id=263539&action=review

r=me

> Source/JavaScriptCore/jit/GCAwareJITStubRoutine.cpp:129
> +GCAwareJITStubRoutineWithExceptionHandler::~GCAwareJITStubRoutineWithExceptionHandler()
> +{
>  }

maybe get rid of the destructor now since you don't need it anymore.

> Source/JavaScriptCore/jit/GCAwareJITStubRoutine.h:101
>      ~GCAwareJITStubRoutineWithExceptionHandler() override;

No need to override if we don't need it.

[Saam Barati]

Thanks for the review. I've included your suggestions in the landed patch.

landed in:
http://trac.webkit.org/changeset/191350