Re: [PATCH] strlen: Fix up !si->full_string_p handling in count_nonzero_bytes_addr [PR115152]

[Richard Biener <rguenther@suse.de>]

On Tue, 21 May 2024, Jakub Jelinek wrote:

> Hi!
> 
> The following testcase is miscompiled because
> strlen_pass::count_nonzero_bytes_addr doesn't handle correctly
> the !si->full_string_p case.
> If si->full_string_p, it correctly computes minlen and maxlen as
> minimum and maximum length of the '\0' terminated stgring and
> clears *nulterm (ie. makes sure !full_string_p in the ultimate
> caller) if minlen is equal or larger than nbytes and so
> '\0' isn't guaranteed to be among those bytes.
> But in the !si->full_string_p case, all we know is that there
> are [minlen,maxlen] non-zero bytes followed by unknown bytes,
> so effectively the maxlen is infinite (but caller cares about only
> the first nbytes bytes) and furthermore, we never know if there is
> any '\0' char among those, so *nulterm needs to be always cleared.
> 
> Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux,
> ok for trunk and affected release branches?

OK.

Richard.

> 2024-05-21  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR tree-optimization/115152
> 	* tree-ssa-strlen.cc (strlen_pass::count_nonzero_bytes_addr): If
> 	!si->full_string_p, clear *nulterm and set maxlen to nbytes.
> 
> 	* gcc.dg/pr115152.c: New test.
> 
> --- gcc/tree-ssa-strlen.cc.jj	2024-04-29 11:00:45.000000000 +0200
> +++ gcc/tree-ssa-strlen.cc	2024-05-21 13:43:31.031208000 +0200
> @@ -4829,7 +4829,7 @@ strlen_pass::count_nonzero_bytes_addr (t
>        if (maxlen + 1 < nbytes)
>  	return false;
>  
> -      if (nbytes <= minlen)
> +      if (nbytes <= minlen || !si->full_string_p)
>  	*nulterm = false;
>  
>        if (nbytes < minlen)
> @@ -4839,6 +4839,9 @@ strlen_pass::count_nonzero_bytes_addr (t
>  	    maxlen = nbytes;
>  	}
>  
> +      if (!si->full_string_p)
> +	maxlen = nbytes;
> +
>        if (minlen < lenrange[0])
>  	lenrange[0] = minlen;
>        if (lenrange[1] < maxlen)
> --- gcc/testsuite/gcc.dg/pr115152.c.jj	2024-05-21 13:46:02.793214348 +0200
> +++ gcc/testsuite/gcc.dg/pr115152.c	2024-05-21 12:49:38.791626073 +0200
> @@ -0,0 +1,17 @@
> +/* PR tree-optimization/115152 */
> +/* { dg-do run } */
> +/* { dg-options "-O3 -fno-tree-fre -fno-tree-dominator-opts -fno-tree-loop-im" } */
> +
> +int a, b, c, d;
> +signed char e[1] = { 1 };
> +
> +int
> +main ()
> +{
> +  for (a = 0; a < 3; a++)
> +    for (b = 0; b < 2; b++)
> +      c = e[0] = e[0] ^ d;
> +  if (!c)
> +    __builtin_abort ();
> +  return 0;
> +}
> 
> 	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)