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Re: [PATCH] Fix PR78413
- From: Richard Biener <richard dot guenther at gmail dot com>
- To: Bill Schmidt <wschmidt at linux dot vnet dot ibm dot com>
- Cc: GCC Patches <gcc-patches at gcc dot gnu dot org>
- Date: Mon, 21 Nov 2016 10:51:00 +0100
- Subject: Re: [PATCH] Fix PR78413
- Authentication-results: sourceware.org; auth=none
- References: <87911474-3353-c0dc-4d8f-b2ac15e8db12@linux.vnet.ibm.com>
On Fri, Nov 18, 2016 at 5:27 PM, Bill Schmidt
<wschmidt@linux.vnet.ibm.com> wrote:
> Hi,
>
> The if-conversion patch for PR77848 missed a case where an outer loop
> should not be versioned for vectorization; this was caught by an assert
> in tests recorded in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78413.
> This patch fixes the problem by ensuring that both inner and outer loop
> latches have a single predecessor before versioning an outer loop.
>
> Bootstrapped and tested on powerpc64le-unknown-linux-gnu with no
> regressions. Is this ok for trunk?
Ok (with the suggested testcase adjustment).
Maybe as a followup we can factor out a common predicate usable by the
vectorizer and if-conversion. I'll see if I can do that.
Thanks,
Richard.
> Thanks,
> Bill
>
>
> [gcc]
>
> 2016-11-18 Bill Schmidt <wschmidt@linux.vnet.ibm.com>
>
> PR tree-optimization/78413
> * tree-if-conv.c (versionable_outer_loop_p): Require that both
> inner and outer loop latches have single predecessors.
>
> [gcc/testsuite]
>
> 2016-11-18 Bill Schmidt <wschmidt@linux.vnet.ibm.com>
>
> PR tree-optimization/78413
> * gcc.dg/tree-ssa/pr78413.c: New test.
>
>
> Index: gcc/testsuite/gcc.dg/tree-ssa/pr78413.c
> ===================================================================
> --- gcc/testsuite/gcc.dg/tree-ssa/pr78413.c (revision 0)
> +++ gcc/testsuite/gcc.dg/tree-ssa/pr78413.c (working copy)
> @@ -0,0 +1,35 @@
> +/* PR78413. These previously failed in tree if-conversion due to a loop
> + latch with multiple predecessors that the code did not anticipate. */
> +/* { dg-do compile } */
> +/* { dg-options "-O3 -ffast-math" } */
> +
> +extern long long int llrint(double x);
> +int a;
> +double b;
> +__attribute__((cold)) void decode_init() {
> + int c, d = 0;
> + for (; d < 12; d++) {
> + if (d)
> + b = 0;
> + c = 0;
> + for (; c < 6; c++)
> + a = b ? llrint(b) : 0;
> + }
> +}
> +
> +struct S {
> + _Bool bo;
> +};
> +int a, bb, c, d;
> +void fn1() {
> + do
> + do
> + do {
> + struct S *e = (struct S *)1;
> + do
> + bb = a / (e->bo ? 2 : 1);
> + while (bb);
> + } while (0);
> + while (d);
> + while (c);
> +}
> Index: gcc/tree-if-conv.c
> ===================================================================
> --- gcc/tree-if-conv.c (revision 242551)
> +++ gcc/tree-if-conv.c (working copy)
> @@ -2575,6 +2575,8 @@ version_loop_for_if_conversion (struct loop *loop)
> - The loop has a single exit.
> - The loop header has a single successor, which is the inner
> loop header.
> + - Each of the inner and outer loop latches have a single
> + predecessor.
> - The loop exit block has a single predecessor, which is the
> inner loop's exit block. */
>
> @@ -2586,7 +2588,9 @@ versionable_outer_loop_p (struct loop *loop)
> || loop->inner->next
> || !single_exit (loop)
> || !single_succ_p (loop->header)
> - || single_succ (loop->header) != loop->inner->header)
> + || single_succ (loop->header) != loop->inner->header
> + || !single_pred_p (loop->latch)
> + || !single_pred_p (loop->inner->latch))
> return false;
>
> basic_block outer_exit = single_pred (loop->latch);
>