RE: [PATCH 1/3] arm: Fix sign of MVE predicate mve_pred16_t [PR 107674]

[Kyrylo Tkachov <Kyrylo.Tkachov@arm.com>]

> -----Original Message-----
> From: Kyrylo Tkachov
> Sent: Thursday, January 26, 2023 3:02 PM
> To: Andre Vieira (lists) <andre.simoesdiasvieira@arm.com>; gcc-
> patches@gcc.gnu.org
> Cc: Richard Earnshaw <Richard.Earnshaw@arm.com>
> Subject: RE: [PATCH 1/3] arm: Fix sign of MVE predicate mve_pred16_t [PR
> 107674]
> 
> Hi Andre,
> 
> > -----Original Message-----
> > From: Andre Vieira (lists) <andre.simoesdiasvieira@arm.com>
> > Sent: Tuesday, January 24, 2023 1:41 PM
> > To: gcc-patches@gcc.gnu.org
> > Cc: Kyrylo Tkachov <Kyrylo.Tkachov@arm.com>; Richard Earnshaw
> > <Richard.Earnshaw@arm.com>
> > Subject: [PATCH 1/3] arm: Fix sign of MVE predicate mve_pred16_t [PR
> > 107674]
> >
> > Hi,
> >
> > The ACLE defines mve_pred16_t as an unsigned short.  This patch makes
> > sure GCC treats the predicate as an unsigned type, rather than signed.
> >
> > Bootstrapped on aarch64-none-eabi and regression tested on arm-none-
> eabi
> > and armeb-none-eabi for armv8.1-m.main+mve.fp.
> >
> > OK for trunk?
> >
> > gcc/ChangeLog:
> >
> > 	PR target/107674
> > 	* config/arm/arm-builtins.cc (arm_simd_builtin_type): Rewrite to
> > use
> > 	new qualifiers parameter and use unsigned short type for MVE
> > predicate.
> > 	(arm_init_builtin): Call arm_simd_builtin_type with qualifiers
> > 	parameter.
> > 	(arm_init_crypto_builtins): Likewise.
> >
> > gcc/testsuite/ChangeLog:
> >
> > 	PR target/107674
> > 	* gcc.target/arm/mve/mve_vpt.c: New test.
> 
> diff --git a/gcc/config/arm/arm-builtins.cc b/gcc/config/arm/arm-builtins.cc
> index
> 11d7478d9df69139802a9d42c09dd0de7480b60e..6c67cec93ff76a4b42f3a0b3
> 05f697142e88fcd9 100644
> --- a/gcc/config/arm/arm-builtins.cc
> +++ b/gcc/config/arm/arm-builtins.cc
> @@ -1489,12 +1489,14 @@ arm_lookup_simd_builtin_type (machine_mode
> mode,
>  }
> 
>  static tree
> -arm_simd_builtin_type (machine_mode mode, bool unsigned_p, bool
> poly_p)
> +arm_simd_builtin_type (machine_mode mode, enum arm_type_qualifiers
> qualifiers)
>  {
> 
> I think in C++ now we can leave out the "enum" here.
> 
> diff --git a/gcc/testsuite/gcc.target/arm/mve/mve_vpt.c
> b/gcc/testsuite/gcc.target/arm/mve/mve_vpt.c
> new file mode 100644
> index
> 0000000000000000000000000000000000000000..26a565b79dd1348e361b3a
> a23a1d6e6d13bffce8
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/arm/mve/mve_vpt.c
> @@ -0,0 +1,27 @@
> +/* { dg-options "-O2" } */
> +/* { dg-require-effective-target arm_v8_1m_mve_ok } */
> +/* { dg-add-options arm_v8_1m_mve } */
> +/* { dg-final { check-function-bodies "**" "" } } */
> +#include <arm_mve.h>
> +void test0 (uint8_t *a, uint8_t *b, uint8_t *c)
> +{
> +    uint8x16_t va = vldrbq_u8 (a);
> +    uint8x16_t vb = vldrbq_u8 (b);
> +    mve_pred16_t p = vcmpeqq_u8 (va, vb);
> +    uint8x16_t vc = vaddq_x_u8 (va, vb, p);
> +    vstrbq_p_u8 (c, vc, p);
> +}
> +/*
> +** test0:
> +**	vldrb.8	q2, \[r0\]
> +**	vldrb.8	q1, \[r1\]
> +**	vcmp.i8	eq, q2, q1
> +**	vmrs	r3, p0	@ movhi
> +**	uxth	r3, r3
> +**	vmsr	p0, r3	@ movhi
> +**	vpst
> +**	vaddt.i8	q3, q2, q1
> +**	vpst
> +**	vstrbt.8	q3, \[r2\]
> +**	bx	lr
> +*/
> 
> This explicit assembly matching looks quite fragile and sensitive to future
> scheduling and RA changes.
> Is there something more targeted we could scan for to check that the
> predicate is unsigned now?

The patch looks fine to me btw. With a more robust testcase and the cosmetic fix above it can go in.
Thanks,
Kyrill

> 
> Thanks,
> Kyrill