[llvm] r367941 - Add a note to the release not about a potentially breaking optimization

[Hans Wennborg via llvm-commits]

I've moved this to the release_90 branch in r367997.

On Tue, Aug 6, 2019 at 12:34 AM Philip Reames via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
>
> Author: reames
> Date: Mon Aug  5 15:34:59 2019
> New Revision: 367941
>
> URL: http://llvm.org/viewvc/llvm-project?rev=367941&view=rev
> Log:
> Add a note to the release not about a potentially breaking optimization
>
> This has come up twice already (once in pr42763 and once in the commit thread), so give warning of a new way in which UB can result in unexpected program behavior.
>
>
> Modified:
>     llvm/trunk/docs/ReleaseNotes.rst
>
> Modified: llvm/trunk/docs/ReleaseNotes.rst
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/ReleaseNotes.rst?rev=367941&r1=367940&r2=367941&view=diff
> ==============================================================================
> --- llvm/trunk/docs/ReleaseNotes.rst (original)
> +++ llvm/trunk/docs/ReleaseNotes.rst Mon Aug  5 15:34:59 2019
> @@ -50,6 +50,19 @@ Non-comprehensive list of changes in thi
>
>     Makes programs 10x faster by doing Special New Thing.
>
> +Noteworthy optimizations
> +------------------------
> +
> +* LLVM will now remove stores to constant memory (since this is a
> +  contradiction) under the assumption the code in question must be dead.  This
> +  has proven to be problematic for some C/C++ code bases which expect to be
> +  able to cast away 'const'.  This is (and has always been) undefined
> +  behavior, but up until now had not been actively utilized for optimization
> +  purposes in this exact way.  For more information, please see:
> +  `bug 42763 <https://bugs.llvm.org/show_bug.cgi?id=42763>_` and
> +  `post commit discussion <http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20190422/646945.html>_`.
> +
> +
>  Changes to the LLVM IR
>  ----------------------
>
>
>
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