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

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

> -----Original Message-----
> From: Andre Vieira (lists) <andre.simoesdiasvieira@arm.com>
> Sent: Monday, January 30, 2023 4:39 PM
> To: Kyrylo Tkachov <Kyrylo.Tkachov@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]
> 
> Here's a new version with a more robust test.
> 
> OK for trunk?

Ok.
Thanks,
Kyrill

> 
> On 27/01/2023 09:56, Kyrylo Tkachov wrote:
> 
> >
> >
> >> -----Original Message-----
> >> From: Andre Vieira (lists) <andre.simoesdiasvieira@arm.com>
> >> Sent: Friday, January 27, 2023 9:54 AM
> >> To: Kyrylo Tkachov <Kyrylo.Tkachov@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]
> >>
> >>
> >>
> >> On 26/01/2023 15:02, Kyrylo Tkachov wrote:
> >>> 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?
> >> No not really, as it's not unsigned everywhere, only in its intermediate
> >> representation between intrinsics. GCC is aware that mve_pred16_t is an
> >> unsigned short, so as soon as you try to use the value on its own or
> >> pass it as an argument or return, there is an implicit cast.
> >>
> >> I could make this particular test-case more robust by not checking
> >> specific registers. Though the sequence of loads-cmp-add-store will
> >> always be the same as it's data-dependent.
> >
> > Yeah, I suspected as such. Ok, let's abstract the registers away (I think
> check-function-bodies can use regex capturing to record particular registers)
> then.
> > Thanks,
> > Kyrill
> >