On Mon, Mar 7, 2011 at 8:15 PM, Jakub Jelinek <ja...@redhat.com> wrote:
> Hi!
>
> EQ/NE comparisons don't really assume that overflow doesn't happen unlike
>>/>=/etc., so it is strange that we warn about it.
> As the warning happens on simple strcmp uses when using glibc string.h,
> it is extra annoying.
>
> Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux, ok for
> trunk?
Ok.
Thanks,
Richard.
> 2011-03-07 Jakub Jelinek <ja...@redhat.com>
>
> PR tree-optimization/48022
> * fold-const.c (fold_comparison): Don't call fold_overflow_warning
> for EQ/NE_EXPR.
>
> * gcc.dg/pr48022-1.c: New test.
> * gcc.dg/pr48022-2.c: New test.
>
> --- gcc/fold-const.c.jj 2011-03-03 09:11:43.000000000 +0100
> +++ gcc/fold-const.c 2011-03-07 17:44:02.000000000 +0100
> @@ -8572,10 +8572,11 @@ fold_comparison (location_t loc, enum tr
> && (TREE_CODE (lhs) != INTEGER_CST
> || !TREE_OVERFLOW (lhs)))
> {
> - fold_overflow_warning ("assuming signed overflow does not occur "
> - "when changing X +- C1 cmp C2 to "
> - "X cmp C1 +- C2",
> - WARN_STRICT_OVERFLOW_COMPARISON);
> + if (code != EQ_EXPR && code != NE_EXPR)
> + fold_overflow_warning ("assuming signed overflow does not occur "
> + "when changing X +- C1 cmp C2 to "
> + "X cmp C1 +- C2",
> + WARN_STRICT_OVERFLOW_COMPARISON);
> return fold_build2_loc (loc, code, type, variable, lhs);
> }
> }
> --- gcc/testsuite/gcc.dg/pr48022-1.c.jj 2011-03-07 17:46:55.000000000 +0100
> +++ gcc/testsuite/gcc.dg/pr48022-1.c 2011-03-07 17:47:18.000000000 +0100
> @@ -0,0 +1,14 @@
> +/* PR tree-optimization/48022 */
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -Wstrict-overflow" } */
> +
> +int
> +foo (const char *x)
> +{
> + unsigned long l = 1;
> + const unsigned char *s = (const unsigned char *) (const char *) (x);
> + int r = s[0] - ((const unsigned char *) (const char *) ("/"))[0];
> + if (l > 0 && r == 0)
> + r = (s[1] - ((const unsigned char *) (const char *) ("/"))[1]);
> + return r;
> +}
> --- gcc/testsuite/gcc.dg/pr48022-2.c.jj 2011-03-07 17:47:26.000000000 +0100
> +++ gcc/testsuite/gcc.dg/pr48022-2.c 2011-03-07 17:47:45.000000000 +0100
> @@ -0,0 +1,11 @@
> +/* PR tree-optimization/48022 */
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -Wstrict-overflow" } */
> +
> +#include <string.h>
> +
> +int
> +foo (const char *x)
> +{
> + return strcmp (x, "/");
> +}
>
> Jakub
>
