On Mon, 30 Sep 2013, Jakub Jelinek wrote:
> Hi!
>
> Apparently sign_bit_p looks through both sign and zero extensions.
> That is just fine for the single bit test optimization, where we know the
> constant is a power of two, and it is (A & power_of_two) == 0 (or != 0)
> test. sign_bit_p is also used to check for minimum value of some integral
> type, because it is called with the same argument twice, it must be
> INTEGER_CST if non-NULL is returned and thus there is no zero extensions.
> But in the last spot where sign_bit_p is used, sign extensions would be
> fine, ((int) x) < 0 for say signed char or signed short x iff x < 0,
> but if there is a zero extension, it is just a possible missed optimization
> on the comparison.
>
> Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux, ok for
> trunk/4.8?
Ok.
Thanks,
Richard.
> 2013-09-30 Jakub Jelinek <ja...@redhat.com>
>
> PR middle-end/58564
> * fold-const.c (fold_ternary_loc): For A < 0 : <sign bit of A> : 0
> optimization, punt if sign_bit_p looked through any zero extension.
>
> * gcc.c-torture/execute/pr58564.c: New test.
>
> --- gcc/fold-const.c.jj 2013-09-27 15:42:37.000000000 +0200
> +++ gcc/fold-const.c 2013-09-30 11:19:06.333978484 +0200
> @@ -14196,14 +14196,29 @@ fold_ternary_loc (location_t loc, enum t
> && integer_zerop (op2)
> && (tem = sign_bit_p (TREE_OPERAND (arg0, 0), arg1)))
> {
> + /* sign_bit_p looks through both zero and sign extensions,
> + but for this optimization only sign extensions are
> + usable. */
> + tree tem2 = TREE_OPERAND (arg0, 0);
> + while (tem != tem2)
> + {
> + if (TREE_CODE (tem2) != NOP_EXPR
> + || TYPE_UNSIGNED (TREE_TYPE (TREE_OPERAND (tem2, 0))))
> + {
> + tem = NULL_TREE;
> + break;
> + }
> + tem2 = TREE_OPERAND (tem2, 0);
> + }
> /* sign_bit_p only checks ARG1 bits within A's precision.
> If <sign bit of A> has wider type than A, bits outside
> of A's precision in <sign bit of A> need to be checked.
> If they are all 0, this optimization needs to be done
> in unsigned A's type, if they are all 1 in signed A's type,
> otherwise this can't be done. */
> - if (TYPE_PRECISION (TREE_TYPE (tem))
> - < TYPE_PRECISION (TREE_TYPE (arg1))
> + if (tem
> + && TYPE_PRECISION (TREE_TYPE (tem))
> + < TYPE_PRECISION (TREE_TYPE (arg1))
> && TYPE_PRECISION (TREE_TYPE (tem))
> < TYPE_PRECISION (type))
> {
> --- gcc/testsuite/gcc.c-torture/execute/pr58564.c.jj 2013-09-30
> 11:09:38.691122488 +0200
> +++ gcc/testsuite/gcc.c-torture/execute/pr58564.c 2013-09-30
> 11:09:14.000000000 +0200
> @@ -0,0 +1,14 @@
> +/* PR middle-end/58564 */
> +
> +extern void abort (void);
> +int a, b;
> +short *c, **d = &c;
> +
> +int
> +main ()
> +{
> + b = (0, 0 > ((&c == d) & (1 && (a ^ 1)))) | 0U;
> + if (b != 0)
> + abort ();
> + return 0;
> +}
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE / SUSE Labs
SUSE LINUX Products GmbH - Nuernberg - AG Nuernberg - HRB 16746
GF: Jeff Hawn, Jennifer Guild, Felix Imend
