https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97135
Bug ID: 97135
Summary: [11 Regression] Wrong code at -Os since
r11-408-g84935c98221
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: acoplan at gcc dot gnu.org
Target Milestone: ---
For the following testcase:
long c;
long *d = &c;
int a, e, f;
int main(void) {
for (; f <= 5; f++) {
e = 0;
for (; e <= 5; e++) {
a = 1;
for (; a <= 5; a++);
*d = 0;
if (f)
break;
}
}
return a;
}
Compiling with -O{0,1,2,3} (for both gcc and clang), as expected, the program
returns 6.
Compiling with -Os, the program returns 1 (since
r11-408-g84935c9822183ce403bb361c5f405711b9a808c6).
I've reproduced this on both x86 and aarch64. Interestingly, compiling with -Os
-fno-strict-aliasing, we no longer see the wrong code bug (the program returns
6). However, I believe this program is free of strict aliasing violations.
To reproduce:
$ bin/gcc wrong_code.c
$ ./a.out || echo $?
6
$ bin/gcc wrong_code.c -Os
$ ./a.out || echo $?
1
$ bin/gcc wrong_code.c -Os -fno-strict-aliasing
$ ./a.out || echo $?
6
