https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101494
Bug ID: 101494
Summary: -Wmaybe-uninitialized false alarm with memrchr of size
0
Product: gcc
Version: 11.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: eggert at cs dot ucla.edu
Target Milestone: ---
I ran into this problem when compiling Gnulib tests on gcc (GCC) 11.1.1
20210531 (Red Hat 11.1.1-3) on x86-64. Here is a stripped down program
illustrating the bug:
void *malloc (unsigned long)
__attribute__((__malloc__)) __attribute__((__alloc_size__ (1)));
void *memrchr (const void *, int, unsigned long)
__attribute__((__access__ (__read_only__, 1, 3)));
int
main (void)
{
char *input = malloc (1);
if (!input)
return 1;
*input = 0;
return !!memrchr (input, 'a', 0);
}
The following command:
gcc -Wmaybe-uninitialized -O2 -S w.i
outputs:
w.i: In function 'main':
w.i:14:12: warning: 'input' may be used uninitialized [-Wmaybe-uninitialized]
14 | return !!memrchr (input, 'a', 0);
| ^~~~~~~~~~~~~~~~~~~~~~~
w.i:4:7: note: in a call to 'memrchr' declared with attribute 'access
(read_onl\
y, 1, 3)' here
4 | void *memrchr (const void *, int, unsigned long)
| ^~~~~~~
This warning is bogus, as 'input' is initialized; and even if "input = 0;" were
removed the call to memrchr would still be valid as the size argument is 0.
