RE: [PATCH] aarch64: Specify that FEAT_MOPS sequences clobber CC

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

> -----Original Message-----
> From: Kyrylo Tkachov
> Sent: Wednesday, November 30, 2022 5:40 PM
> To: gcc-patches@gcc.gnu.org
> Subject: [PATCH] aarch64: Specify that FEAT_MOPS sequences clobber CC
> 
> Hi all,
> 
> According to the architecture pseudocode the FEAT_MOPS sequences
> overwrite the NZCV flags
> as part of their operation, so GCC needs to model that in the relevant RTL
> patterns.
> For the testcase:
> void g();
> void foo (int a, size_t N, char *__restrict__ in,
>          char *__restrict__ out)
> {
>   if (a != 3)
>     __builtin_memcpy (out, in, N);
>   if (a > 3)
>     g ();
> }
> 
> we will currently generate:
> foo:
>         cmp     w0, 3
>         bne     .L6
> .L1:
>         ret
> .L6:
>         cpyfp   [x3]!, [x2]!, x1!
>         cpyfm   [x3]!, [x2]!, x1!
>         cpyfe   [x3]!, [x2]!, x1!
>         ble     .L1 // Flags reused after CPYF* sequence
>         b       g
> 
> This is wrong as the result of cmp needs to be recalculated after the MOPS
> sequence.
> With this patch we'll insert a "cmp w0, 3" before the ble, like what clang
> does.
> 
> Bootstrapped and tested on aarch64-none-linux-gnu.
> Pushing to trunk and to the GCC 12 branch after some baking time.

Pushed to releases/gcc-12 now.

Thanks,
Kyrill

> 
> Thanks,
> Kyrill
> 
> gcc/ChangeLog:
> 
> 	* config/aarch64/aarch64.md (aarch64_cpymemdi): Specify clobber
> of CC reg.
> 	(*aarch64_cpymemdi): Likewise.
> 	(aarch64_movmemdi): Likewise.
> 	(aarch64_setmemdi): Likewise.
> 	(*aarch64_setmemdi): Likewise.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* gcc.target/aarch64/mops_5.c: New test.
> 	* gcc.target/aarch64/mops_6.c: Likewise.
> 	* gcc.target/aarch64/mops_7.c: Likewise.