On Tue, 28 Mar 2023, Jakub Jelinek wrote:
> Hi!
>
> The following testcase ICEs since the sincos and vect pass order has
> been swapped. It is not valid to replace vector sqrt (sqrt (x)) with
> pow (x, 0.25) because build_real on vector type is invalid (could be
> handled by using build_uniform_cst and adjusting type passed to
> build_real) but more importantly because nothing checks if we can
> actually do vector pow.
> While we have pow_optab, apparently no target defines it, so it doesn't
> seem to be worth bothering with for now and the patch just punts on
> non-scalar sqrts.
> I think the other simplifications next to it are fine, as they mostly
> use CBRT which doesn't even have internal function (so is a builtin
> only and therefore always scalar), or have already pow in the IL (which
> doesn't have optab and shouldn't be thus vector either).
> It is true that with <bits/math-vector.h> we do vectorize some calls to
> pow or cbrt (but don't handle others strangely), but those aren't using
> internal functions but simd clones and so match.pd doesn't know anything
> about those (at least for now).
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
Hmm, but canonicalize_math_p () should be false after vectorization?
When we moved the pass we should have made sure to put the
PROP_gimple_opt_math property set to pass_expand_powcabs instead.
Now, the sqrt (sqrt ()) canonicalization to pow (.., 1./4) is
probably invalid anyway, not sure if we can add a user-written
vector sqrt testcase that would trigger during the canonicalization
phase. There are other uses of build_real that have the same
issue - what's your conclusion this is never a problem there?
Thanks,
Richard.
> 2023-03-28 Jakub Jelinek <ja...@redhat.com>
>
> PR tree-optimization/109301
> * match.pd (sqrt (sqrt (x)) -> pow (x, 0.25)): Only simplify for
> scalar floating point types.
>
> * gcc.dg/pr109301.c: New test.
>
> --- gcc/match.pd.jj 2023-03-27 10:25:40.171676370 +0200
> +++ gcc/match.pd 2023-03-27 21:03:38.816171522 +0200
> @@ -6820,7 +6820,8 @@ (define_operator_list SYNC_FETCH_AND_AND
> /* sqrt(sqrt(x)) -> pow(x,1/4). */
> (simplify
> (sqrts (sqrts @0))
> - (pows @0 { build_real (type, dconst_quarter ()); }))
> + (if (SCALAR_FLOAT_TYPE_P (type))
> + (pows @0 { build_real (type, dconst_quarter ()); })))
> /* sqrt(cbrt(x)) -> pow(x,1/6). */
> (simplify
> (sqrts (cbrts @0))
> --- gcc/testsuite/gcc.dg/pr109301.c.jj 2023-03-27 21:06:22.635806234
> +0200
> +++ gcc/testsuite/gcc.dg/pr109301.c 2023-03-27 21:06:05.413054906 +0200
> @@ -0,0 +1,13 @@
> +/* PR tree-optimization/109301 */
> +/* { dg-do compile } */
> +/* { dg-options "-O3 -ffast-math" } */
> +
> +double x[256];
> +
> +void
> +foo (void)
> +{
> + for (int i = 0; i < 256; ++i)
> + for (int j = 0; j < 8; ++j)
> + x[i] = __builtin_pow (x[i], 0.5);
> +}
>
> 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)
