https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89230
Martin Sebor <msebor at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |alias
CC| |msebor at gcc dot gnu.org
Depends on| |81776
--- Comment #4 from Martin Sebor <msebor at gcc dot gnu.org> ---
Making GCC aware that printf doesn't modify memory (at least not without %n in
the format string, or without addresses in its argument list) is the subject of
pr81776.
It's hard to tell for sure without more context but a similar (if not the same)
problem can be reproduced in the following test case. Uncommenting the
attribute makes the warning go away because it tells GCC that the pointer
returned from f() and assigned to q does not alias any object in memory, so
printf cannot clobber what it points to. With the test case below, I could
confirm this bug as a dependency of pr81776. But if your case is different
then as Andrew requests, please try to reduce it to a small reproducible test
case to show us what's going on there.
$ cat z.c && gcc -O2 -S -Wall z.c
struct S { int i, j; };
/* attribute__ ((malloc)) */ struct S* f (void);
int g (void)
{
struct S *p = f (), *q;
if (p->i || !(q = f ()) || p->j != q->i)
{
__builtin_printf ("%i", p->i);
if (p->i)
return 1;
if (!q)
return 2;
}
return 0;
}
z.c: In function ‘g’:
z.c:16:9: warning: ‘q’ may be used uninitialized in this function
[-Wmaybe-uninitialized]
16 | if (!q)
| ^
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81776
[Bug 81776] missing sprintf optimization due to pointer escape analysis
