[PATCH] Fix PR71824

[Sebastian Pop]

Resend as plain text to please gcc-patches@

On Tue, Jan 31, 2017 at 8:39 AM, Sebastian Pop <sebpop@gmail.com> wrote:
>
>
> On Tue, Jan 31, 2017 at 7:49 AM, Richard Biener <rguenther@suse.de> wrote:
>>
>>
>> The following fixes an ICE that happens because instantiate_scev
>> doesn't really work as expected for SESE regions (a FIXME comment
>> hints at this already).  So instead of asserting all goes well
>> just bail out (add_loop_constraints seems to add constraints not
>> required for correctness?).
>
>
> The conditions under which a loop is executed are required for correctness.
> There is a similar check in scop_detection::can_represent_loop_1
>
>     && (niter = number_of_latch_executions (loop))
>     && !chrec_contains_undetermined (niter)
>
> that is supposed to filter out all these loops where this assert does not
> hold.
> The question is: why scop detection has not rejected this loop?
>
> Well, I see that we do not check that niter can be analyzed in the region:
> so we would need another check like this:
>
> diff --git a/gcc/graphite-scop-detection.c b/gcc/graphite-scop-detection.c
> index 3860693..8e14412 100644
> --- a/gcc/graphite-scop-detection.c
> +++ b/gcc/graphite-scop-detection.c
> @@ -931,6 +931,7 @@ scop_detection::can_represent_loop_1 (loop_p loop,
> sese_l scop)
>      && niter_desc.control.no_overflow
>      && (niter = number_of_latch_executions (loop))
>      && !chrec_contains_undetermined (niter)
> +    && !chrec_contains_undetermined (scalar_evolution_in_region (scop,
> loop, niter))
>      && graphite_can_represent_expr (scop, loop, niter);
>  }
>
> Could you please try this patch and see whether it fixes the problem?
>
> Thanks,
> Sebastian
>