Re: [PATCH 1/2] target/113255 - avoid REG_POINTER on a pointer difference

Re: [PATCH 1/2] target/113255 - avoid REG_POINTER on a pointer difference

[Uros Bizjak]

On Thu, Feb 1, 2024 at 3:18 PM Richard Biener <rguenther@suse.de> wrote:
>
> The following avoids re-using a register holding a pointer (and
> thus might be REG_POINTER) for the result of a pointer difference
> computation.  That might confuse heuristics in (broken) RTL alias
> analysis which relies on REG_POINTER indicating that we're
> dealing with one.
>
> This alone doesn't fix anything.
>
> Bootstrapped and tested on x86_64-unknown-linux-gnu, OK for trunk
> and branches (as necessary)?

LGTM, also for branches.

Thanks,
Uros.

>
> Thanks,
> Richard.
>
>         PR target/113255
>         * config/i386/i386-expand.cc
>         (expand_set_or_cpymem_prologue_epilogue_by_misaligned_moves):
>         Use a new pseudo for the skipped number of bytes.
> ---
>  gcc/config/i386/i386-expand.cc | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/gcc/config/i386/i386-expand.cc b/gcc/config/i386/i386-expand.cc
> index 0d817fc3f3b..26c48e8b0c8 100644
> --- a/gcc/config/i386/i386-expand.cc
> +++ b/gcc/config/i386/i386-expand.cc
> @@ -8090,7 +8090,7 @@ expand_set_or_cpymem_prologue_epilogue_by_misaligned_moves (rtx destmem, rtx src
>        /* See how many bytes we skipped.  */
>        saveddest = expand_simple_binop (GET_MODE (*destptr), MINUS, saveddest,
>                                        *destptr,
> -                                      saveddest, 1, OPTAB_DIRECT);
> +                                      NULL_RTX, 1, OPTAB_DIRECT);
>        /* Adjust srcptr and count.  */
>        if (!issetmem)
>         *srcptr = expand_simple_binop (GET_MODE (*srcptr), MINUS, *srcptr,
> --
> 2.35.3
>

[PATCH 1/2] target/113255 - avoid REG_POINTER on a pointer difference

[Richard Biener]

The following avoids re-using a register holding a pointer (and
thus might be REG_POINTER) for the result of a pointer difference
computation.  That might confuse heuristics in (broken) RTL alias
analysis which relies on REG_POINTER indicating that we're
dealing with one.

This alone doesn't fix anything.

Bootstrapped and tested on x86_64-unknown-linux-gnu, OK for trunk
and branches (as necessary)?

Thanks,
Richard.

	PR target/113255
	* config/i386/i386-expand.cc
	(expand_set_or_cpymem_prologue_epilogue_by_misaligned_moves):
	Use a new pseudo for the skipped number of bytes.
---
 gcc/config/i386/i386-expand.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/gcc/config/i386/i386-expand.cc b/gcc/config/i386/i386-expand.cc
index 0d817fc3f3b..26c48e8b0c8 100644
--- a/gcc/config/i386/i386-expand.cc
+++ b/gcc/config/i386/i386-expand.cc
@@ -8090,7 +8090,7 @@ expand_set_or_cpymem_prologue_epilogue_by_misaligned_moves (rtx destmem, rtx src
       /* See how many bytes we skipped.  */
       saveddest = expand_simple_binop (GET_MODE (*destptr), MINUS, saveddest,
 				       *destptr,
-				       saveddest, 1, OPTAB_DIRECT);
+				       NULL_RTX, 1, OPTAB_DIRECT);
       /* Adjust srcptr and count.  */
       if (!issetmem)
 	*srcptr = expand_simple_binop (GET_MODE (*srcptr), MINUS, *srcptr,
-- 
2.35.3