[PATCH] [CodeGen] Annotate signed shift lefts with NUW

[Richard Smith]

On Wed, Apr 8, 2015 at 11:42 AM, Chandler Carruth <chandlerc at gmail.com>
wrote:

> Before we go here, I think we should seriously ask whether we want to undo
> that restriction on shift left.
>
> I can see arguments both for and against it.
>
> Does GCC already do this optimization?


I've not found any evidence that GCC optimizes on the assumption that the
LHS of a signed left shift is not negative.
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