[PATCH] PR17473: Disallow LSR to perform non-invertible normalization

[Eric Christopher]

> As we discussed, once you have finished running the test-suite with a check
> to find out if any important cases are no longer normalized as expected,
> then I think you can commit. I know you've already verified performance, so
> this is just an extra sanity check.
>

Any interesting results?

-eric

> Thanks.
>
> -Andy
>
>
> Thanks,
> Michael
>
> Thanks,
> Arnold
>
> On Mar 10, 2014, at 2:56 PM, Michael Zolotukhin <mzolotukhin at apple.com>
> wrote:
>
> Hi,
>
> This is a fix for PR17473. The issue is that LSR performs normalization of
> detected IV users and sometimes wants to denormalize it back hoping to get
> the original expression. But normalization isn't always invertible, and the
> new expression might be not equivalent to the original one. In the test
> case, we were losing sign-extension in such transformation. The patch simply
> adds a check, if the transformation is invertible.
>
> <pr17473.patch>
>
> Ok for trunk?
>
> Thanks,
> Michael
>
>
>
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