VEC_COND_EXPR optimizations v2

Richard Biener richard.guenther@gmail.com
Wed Aug 5 14:24:15 GMT 2020


On Wed, Aug 5, 2020 at 3:33 PM Marc Glisse <marc.glisse@inria.fr> wrote:
>
> New version that passed bootstrap+regtest during the night.
>
> When vector comparisons were forced to use vec_cond_expr, we lost a number of
> optimizations (my fault for not adding enough testcases to prevent that).
> This patch tries to unwrap vec_cond_expr a bit so some optimizations can
> still happen.
>
> I wasn't planning to add all those transformations together, but adding one
> caused a regression, whose fix introduced a second regression, etc.
>
> Restricting to constant folding would not be sufficient, we also need at
> least things like X|0 or X&X. The transformations are quite conservative
> with :s and folding only if everything simplifies, we may want to relax
> this later. And of course we are going to miss things like a?b:c + a?c:b
> -> b+c.
>
> In terms of number of operations, some transformations turning 2
> VEC_COND_EXPR into VEC_COND_EXPR + BIT_IOR_EXPR + BIT_NOT_EXPR might not look
> like a gain... I expect the bit_not disappears in most cases, and
> VEC_COND_EXPR looks more costly than a simpler BIT_IOR_EXPR.
>
> I am a bit confused that with avx512 we get types like "vector(4)
> <signed-boolean:2>" with :2 and not :1 (is it a hack so true is 1 and not
> -1?), but that doesn't matter for this patch.

OK.

Thanks,
Richard.

> 2020-08-05  Marc Glisse  <marc.glisse@inria.fr>
>
>         PR tree-optimization/95906
>         PR target/70314
>         * match.pd ((c ? a : b) op d, (c ? a : b) op (c ? d : e),
>         (v ? w : 0) ? a : b, c1 ? c2 ? a : b : b): New transformations.
>         (op (c ? a : b)): Update to match the new transformations.
>
>         * gcc.dg/tree-ssa/andnot-2.c: New file.
>         * gcc.dg/tree-ssa/pr95906.c: Likewise.
>         * gcc.target/i386/pr70314.c: Likewise.
>
> --
> Marc Glisse


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