[PATCH PR72817/PR73450]Fix wrong code caused by niter analyzer for NE_EXPR exit cond.

[Richard Biener]

On Thu, Aug 11, 2016 at 6:35 PM, Bin Cheng <Bin.Cheng@arm.com> wrote:
> Hi,
> I made a mistake when improving loop niter analysis for NE_EXPR exit condition.
> It can results in wrong code as reported in PR72817/PR73450.  In previous patch,
> it simplifies below condition:
>             base <= FINAL ; step > 0
>             base >= FINAL ; step < 0
> into:
>             base - step < FINAL ; step > 0 && base - step doesn't underflow
>             base - step > FINAL ; step < 0 && base - step doesn't overflow
> But this is not enough.  Since we adjusted IV.base to "new_base = IV.base - IV.step"
> in the condition, we need to check if |FINAL - new_base| is multiple of |step| for the
> adjusted base.
>
> This patch fixes the issue as well as revises the comment.  Bootstrap and test on
> x86_64.  Is it OK?

Ok.

Thanks,
Richard.

> Thanks,
> bin
>
> 2016-08-11  Bin Cheng  <bin.cheng@arm.com>
>
>         PR tree-optimization/72817
>         PR tree-optimization/73450
>         * tree-ssa-loop-niter.c (number_of_iterations_ne): Check
>         multiple_of_p for adjusted IV.base.
>
> gcc/testsuite/ChangeLog
> 2016-08-11  Bin Cheng  <bin.cheng@arm.com>
>
>         PR tree-optimization/72817
>         PR tree-optimization/73450
>         * gcc.dg/tree-ssa/pr72817.c: New test.
>         * gcc.dg/tree-ssa/pr73450.c: New test.