On Wed, 30 Nov 2022, Jakub Jelinek wrote:
> Hi!
>
> r13-254-gdd3c7873a61019e9 added an optimization for {a, +, a} (x-1),
> but as can be seen on the following testcase, the way it is written
> where chrec_fold_multiply is called with type doesn't work for pointers:
> res = build_int_cst (TREE_TYPE (x), 1);
> res = chrec_fold_plus (TREE_TYPE (x), x, res);
> res = chrec_convert_rhs (type, res, NULL);
> res = chrec_fold_multiply (type, chrecr, res);
> while what we were doing before and what is still used if the condition
> doesn't match is fine:
> res = chrec_convert_rhs (TREE_TYPE (chrecr), x, NULL);
> res = chrec_fold_multiply (TREE_TYPE (chrecr), chrecr, res);
> res = chrec_fold_plus (type, CHREC_LEFT (chrec), res);
> because it performs chrec_fold_multiply on TREE_TYPE (chrecr) and converts
> only afterwards.
>
> I think the easiest fix is to ignore the new path for pointer types.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
OK.
Thanks,
Richard.
> 2022-11-30 Jakub Jelinek <ja...@redhat.com>
>
> PR tree-optimization/107835
> * tree-chrec.cc (chrec_apply): Don't handle "{a, +, a} (x-1)"
> as "a*x" if type is a pointer type.
>
> * gcc.c-torture/compile/pr107835.c: New test.
>
> --- gcc/tree-chrec.cc.jj 2022-05-10 18:33:14.641029951 +0200
> +++ gcc/tree-chrec.cc 2022-11-29 15:24:41.810400368 +0100
> @@ -622,7 +622,8 @@ chrec_apply (unsigned var,
> /* "{a, +, b} (x)" -> "a + b*x". */
> else if (operand_equal_p (CHREC_LEFT (chrec), chrecr)
> && TREE_CODE (x) == PLUS_EXPR
> - && integer_all_onesp (TREE_OPERAND (x, 1)))
> + && integer_all_onesp (TREE_OPERAND (x, 1))
> + && !POINTER_TYPE_P (type))
> {
> /* We know the number of iterations can't be negative.
> So {a, +, a} (x-1) -> "a*x". */
> --- gcc/testsuite/gcc.c-torture/compile/pr107835.c.jj 2022-11-29
> 15:31:32.565382590 +0100
> +++ gcc/testsuite/gcc.c-torture/compile/pr107835.c 2022-11-29
> 15:31:15.795628304 +0100
> @@ -0,0 +1,11 @@
> +/* PR tree-optimization/107835 */
> +
> +int *
> +foo (void)
> +{
> + int *x = 0;
> + unsigned n = n;
> + for (; n; --n, ++x)
> + ;
> + return x;
> +}
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg,
Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
HRB 36809 (AG Nuernberg)
