Re: [PATCH] rtlanal: Fix set_noop_p for volatile loads or stores [PR114768]

[Richard Biener <rguenther@suse.de>]

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  <jakub@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 <rguenther@suse.de>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)