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Date: Wed, 01 Aug 2012 12:42:00 -0000
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Subject: Re: [PATCH] propagate anti-range to switch in tree-vrp
From: Richard Guenther <richard.guenther@gmail.com>
To: Tom de Vries <Tom_deVries@mentor.com>
Cc: Jakub Jelinek <jakub@redhat.com>, "gcc-patches@gcc.gnu.org" <gcc-patches@gcc.gnu.org>
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On Sat, Jul 21, 2012 at 3:57 PM, Tom de Vries <Tom_deVries@mentor.com> wrote:
> Jakub,
>
> this patch adds propagation of anti-ranges to switches.
>
> The test-case is this:
> ...
> void
> f3 (int s)
> {
>   if (s >> 3 == -2)
>     /* s in range [ -16, -9].  */
>     ;
>   else
>     {
>       /* s in range ~[-16, -9], so none of the case labels can be taken.  */
>       switch (s)
>         {
>         case -16:
>         case -12:
>         case -9:
>           link_error ();
>           break;
>         default:
>           break;
>         }
>     }
> }
> ...
>
> The call to link_error is unreachable but tree-vrp fails to analyze that.
>
> Using the patch, the switch is replaced by the default case.
>
> Bootstrapped and reg-tested (Ada inclusive) on x86_64.
>
> OK for trunk?

Ok.

Thanks,
Richard.

> Thanks,
> - Tom
>
> 2012-07-21  Tom de Vries  <tom@codesourcery.com>
>
>         * tree-vrp.c (find_case_label_ranges): New function.
>         (vrp_visit_switch_stmt, simplify_switch_using_ranges): Use
>         find_case_label_ranges instead of find_case_label_range.  Handle second
>         range.
>
>         * gcc.dg/tree-ssa/vrp72.c: New test.