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

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

[Jakub Jelinek]

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?

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

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

[Richard Biener]

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)