Re: [PATCH] Fix endless recursion in decide_alg (PR target/69888)

[Uros Bizjak <ubizjak at gmail dot com>]

On Mon, Feb 22, 2016 at 10:16 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> Hi!
>
> On the following testcase, we ICE due to infinite recursion in decide_alg
> - max is 0, and expected_size is the same (2048) in the second and following
> recursive calls.
>
> Fixed by avoiding recursing with the same arguments as before.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> 2016-02-22  Jakub Jelinek  <jakub@redhat.com>
>
>         PR target/69888
>         * config/i386/i386.c (decide_alg): Ensure we don't recurse with
>         identical arguments.  Formatting and spelling fixes.
>
>         * gcc.target/i386/pr69888.c: New test.

OK with a nit below.

Thanks,
Uros.

>
> --- gcc/config/i386/i386.c.jj   2016-02-12 00:50:55.000000000 +0100
> +++ gcc/config/i386/i386.c      2016-02-22 10:25:53.564338145 +0100
> @@ -26032,11 +26032,12 @@ decide_alg (HOST_WIDE_INT count, HOST_WI
>             bool memset, bool zero_memset, bool have_as,
>             int *dynamic_check, bool *noalign)
>  {
> -  const struct stringop_algs * algs;
> +  const struct stringop_algs *algs;
>    bool optimize_for_speed;
>    int max = 0;
>    const struct processor_costs *cost;
>    int i;
> +  HOST_WIDE_INT orig_expected_size = expected_size;
>    bool any_alg_usable_p = false;
>
>    *noalign = false;
> @@ -26066,7 +26067,7 @@ decide_alg (HOST_WIDE_INT count, HOST_WI
>        any_alg_usable_p |= usable;
>
>        if (candidate != libcall && candidate && usable)
> -         max = algs->size[i].max;
> +       max = algs->size[i].max;
>      }
>
>    /* If expected size is not known but max size is small enough
> @@ -26076,7 +26077,7 @@ decide_alg (HOST_WIDE_INT count, HOST_WI
>        && expected_size == -1)
>      expected_size = min_size / 2 + max_size / 2;
>
> -  /* If user specified the algorithm, honnor it if possible.  */
> +  /* If user specified the algorithm, honor it if possible.  */
>    if (ix86_stringop_alg != no_stringop
>        && alg_usable_p (ix86_stringop_alg, memset, have_as))
>      return ix86_stringop_alg;
> @@ -26152,20 +26153,20 @@ decide_alg (HOST_WIDE_INT count, HOST_WI
>           || !alg_usable_p (algs->unknown_size, memset, have_as)))
>      {
>        enum stringop_alg alg;
> +      HOST_WIDE_INT new_expected_size = (max > 0 ? max : 4096) / 2;

      HOST_WIDE_INT new_expected_size = max > 0 ? max / 2 : 2048;

> -      /* If there aren't any usable algorithms, then recursing on
> -         smaller sizes isn't going to find anything.  Just return the
> -         simple byte-at-a-time copy loop.  */
> -      if (!any_alg_usable_p)
> +      /* If there aren't any usable algorithms or if recursing with the
> +        same arguments as before, then recursing on smaller sizes or
> +        same size isn't going to find anything.  Just return the simple
> +        byte-at-a-time copy loop.  */
> +      if (!any_alg_usable_p || orig_expected_size == new_expected_size)
>          {
>            /* Pick something reasonable.  */
>            if (TARGET_INLINE_STRINGOPS_DYNAMICALLY)
>              *dynamic_check = 128;
>            return loop_1_byte;
>          }
> -      if (max <= 0)
> -       max = 4096;
> -      alg = decide_alg (count, max / 2, min_size, max_size, memset,
> +      alg = decide_alg (count, new_expected_size, min_size, max_size, memset,
>                         zero_memset, have_as, dynamic_check, noalign);
>        gcc_assert (*dynamic_check == -1);
>        if (TARGET_INLINE_STRINGOPS_DYNAMICALLY)
> --- gcc/testsuite/gcc.target/i386/pr69888.c.jj  2016-02-22 10:31:52.529401396 +0100
> +++ gcc/testsuite/gcc.target/i386/pr69888.c     2016-02-22 10:34:10.852502628 +0100
> @@ -0,0 +1,10 @@
> +/* PR target/69888 */
> +/* { dg-do compile } */
> +/* { dg-options "-minline-all-stringops -mmemset-strategy=no_stringop:-1:noalign" } */
> +/* { dg-additional-options "-march=geode" { target ia32 } } */
> +
> +void
> +foo (char *p)
> +{
> +  __builtin_memset (p, 0, 32);
> +}
>
>         Jakub