Re: [PATCH] match.pd: extend the MIN/MAX narrowing through a cast to vectors

On 8/4/2026 3:58 AM, [email protected] wrote:
> From: Kyrylo Tkachov <[email protected]>
>
> The rule folding (type) minmax ((wide_type) a, (wide_type) b) to
> minmax (a, b) is restricted to scalars.  Extension is monotone, so it
> commutes with the comparison and the outer truncation is exact, and the
> argument is lanewise, so it holds for vectors unchanged.
>
> The vector case additionally needs the narrow operation to be available,
> otherwise vector lowering would scalarise what used to be a single wide
> instruction.
>
>    typedef int  v2si __attribute__((vector_size (8)));
>    typedef long v2di __attribute__((vector_size (16)));
>    v2si h (v2si a, v2si b)
>    {
>      v2di x = __builtin_convertvector (a, v2di);
>      v2di y = __builtin_convertvector (b, v2di);
>      return __builtin_convertvector (x < y ? x : y, v2si);
>    }
>
> aarch64 -O3 before:
>
> 	sshll	v0.2d, v0.2s, 0
> 	sshll	v1.2d, v1.2s, 0
> 	cmgt	v2.2d, v1.2d, v0.2d
> 	bsl	v2.16b, v0.16b, v1.16b
> 	xtn	v0.2s, v2.2d
>
> after:
>
> 	smin	v0.2s, v0.2s, v1.2s
>
> Require the wide vector MIN or MAX to have one use.  A shared wide
> result would otherwise gain a second narrow operation.
>
> Bootstrapped and tested on aarch64-none-linux-gnu.
> Ok for trunk?
> Thanks,
> Kyrill
>
> gcc/ChangeLog:
>
> 	* match.pd ((type) minmax ((wide_type) a, (wide_type) b)): Accept
> 	vector types, using element_precision and requiring the narrow
> 	operation to be supported.
>
> gcc/testsuite/ChangeLog:
>
> 	* g++.dg/tree-ssa/vec-narrow-1.C: New test.
> 	* g++.dg/tree-ssa/vec-narrow-minmax-2.C: New test.
OK
jeff