On Mon, 1 Jul 2024, Tamar Christina wrote:
> Hi All,
>
> wide_int_constant_multiple_p tries to check if for two tree expressions a and
> b
> that there is a multiplier which makes a == b * c.
>
> This code however seems to think that there's no c where a=0 and b=0 are equal
> which is of course wrong.
>
> This fixes it and also fixes the comment.
>
> Bootstrapped Regtested on aarch64-none-linux-gnu,
> x86_64-pc-linux-gnu -m32, -m64 and no issues.
>
> Ok for master?
>
> Thanks,
> Tamar
>
> gcc/ChangeLog:
>
> PR tree-optimization/114932
> * tree-affine.cc (wide_int_constant_multiple_p): Support 0 and 0 being
> multiples.
>
> ---
> diff --git a/gcc/tree-affine.cc b/gcc/tree-affine.cc
> index
> d6309c4390362b680f0aa97a41fac3281ade66fd..bfea0fe826a6affa0ace154e3ca38c9ef632fcba
> 100644
> --- a/gcc/tree-affine.cc
> +++ b/gcc/tree-affine.cc
> @@ -880,11 +880,10 @@ free_affine_expand_cache (hash_map<tree, name_expansion
> *> **cache)
> *cache = NULL;
> }
>
> -/* If VAL != CST * DIV for any constant CST, returns false.
> - Otherwise, if *MULT_SET is true, additionally compares CST and MULT,
> - and if they are different, returns false. Finally, if neither of these
> - two cases occur, true is returned, and CST is stored to MULT and MULT_SET
> - is set to true. */
> +/* If VAL == CST * DIV for any constant CST, returns true.
> + and if *MULT_SET is true, additionally compares CST and MULT
> + and if they are different, returns false. If true is returned, CST is
> + stored to MULT and MULT_SET is set to true. */
>
> static bool
> wide_int_constant_multiple_p (const poly_widest_int &val,
> @@ -895,6 +894,12 @@ wide_int_constant_multiple_p (const poly_widest_int &val,
>
> if (known_eq (val, 0))
> {
> + if (maybe_eq (div, 0))
shouldn't that be known_eq as well?
> + {
> + *mult = 1;
and this looks wrong - it shouldn't update *mult if already set,
*mult could be 4 (constrained by other sub-expressions). I think
it also shouldn't set *mult_set to true.
The function comment should mention this exceptional case 0 == CST * O,
maybe as "If VAL and DIV are zero then any constant CST satisfies the
equality. In this case neither *MUL nor *MULT_SET are updated and
the function returns true."
OK with that changes.
Richard.
> + return true;
> + }
> +
> if (*mult_set && maybe_ne (*mult, 0))
> return false;
> *mult_set = true;
>
>
>
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
