On Fri, 19 Apr 2024, Jakub Jelinek wrote:
> Hi!
>
> On the following testcase, combine propagates the mem/v load into mem store
> with the same address and then removes it, because noop_move_p says it is a
> no-op move. If it was the other way around, i.e. mem/v store and mem load,
> or both would be mem/v, it would be kept.
> The problem is that rtx_equal_p never checks any kind of flags on the rtxes
> (and I think it would be quite dangerous to change it at this point), and
> set_noop_p checks side_effects_p on just one of the operands, not both.
> In the MEM <- MEM set, it only checks it on the destination, in
> store to ZERO_EXTRACT only checks it on the source.
>
> The following patch adds the missing side_effects_p checks.
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
OK.
Thanks,
Richard.
> 2024-04-19 Jakub Jelinek <ja...@redhat.com>
>
> PR rtl-optimization/114768
> * rtlanal.cc (set_noop_p): Don't return true for MEM <- MEM
> sets if src has side-effects or for stores into ZERO_EXTRACT
> if ZERO_EXTRACT operand has side-effects.
>
> * gcc.dg/pr114768.c: New test.
>
> --- gcc/rtlanal.cc.jj 2024-02-24 12:45:28.674249100 +0100
> +++ gcc/rtlanal.cc 2024-04-18 15:09:55.199499083 +0200
> @@ -1637,12 +1637,15 @@ set_noop_p (const_rtx set)
> return true;
>
> if (MEM_P (dst) && MEM_P (src))
> - return rtx_equal_p (dst, src) && !side_effects_p (dst);
> + return (rtx_equal_p (dst, src)
> + && !side_effects_p (dst)
> + && !side_effects_p (src));
>
> if (GET_CODE (dst) == ZERO_EXTRACT)
> - return rtx_equal_p (XEXP (dst, 0), src)
> - && !BITS_BIG_ENDIAN && XEXP (dst, 2) == const0_rtx
> - && !side_effects_p (src);
> + return (rtx_equal_p (XEXP (dst, 0), src)
> + && !BITS_BIG_ENDIAN && XEXP (dst, 2) == const0_rtx
> + && !side_effects_p (src)
> + && !side_effects_p (XEXP (dst, 0)));
>
> if (GET_CODE (dst) == STRICT_LOW_PART)
> dst = XEXP (dst, 0);
> --- gcc/testsuite/gcc.dg/pr114768.c.jj 2024-04-18 15:37:49.139433678
> +0200
> +++ gcc/testsuite/gcc.dg/pr114768.c 2024-04-18 15:43:30.389730365 +0200
> @@ -0,0 +1,10 @@
> +/* PR rtl-optimization/114768 */
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-rtl-final" } */
> +/* { dg-final { scan-rtl-dump "\\\(mem/v:" "final" { target { ! { nvptx*-*-*
> } } } } } */
> +
> +void
> +foo (int *p)
> +{
> + *p = *(volatile int *) p;
> +}
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
