https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105319
Bug ID: 105319
Summary: Unexpected warning with zero-length sized array using
-std=gnu99 and -O2
Product: gcc
Version: 10.3.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: piannetta at kalrayinc dot com
Target Milestone: ---
// main.c
#define LEN 0
static volatile int tab[LEN];
int main (int argc, char * argv[]) {
tab[argc] = 0;
}
The code above builds fine with:
gcc -Wall -std=gnu99
but reports a warning when compiled with -O2:
gcc -Wall -std=gnu99 -O2
main.c: In function ‘main’:
main.c:4:12: warning: array subscript argc is outside array bounds of ‘volatile
int[0]’ [-Warray-bounds]
4 | tab[argc] = 0;
| ~~~^~~~~~
main.c:2:21: note: while referencing ‘tab’
2 | static volatile int tab[LEN];
| ^~~
I've observed this behavior on gcc 10.3.1 and on gcc 12.0.1 (I have not tested
other versions).
I would have expected that the snippet would compile the same way in both cases
and not produce a warning since gnu99 supports zero-length arrays.
