https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92417
Bug ID: 92417
Summary: gcc generates wrong debug information at -O2
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: debug
Assignee: unassigned at gcc dot gnu.org
Reporter: qrzhang at gatech dot edu
Target Milestone: ---
It happens at O2 only. "-O1" and "-O3" works fine. It's a recent regression
since "gcc-9 -O2" also works.
The expected value of l_1162[0][0][0] should be 61344 or opt-out. However, with
"-O2", gdb outputs "l_1162[0][0][0]=3".
$ gcc-trunk -v
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 10.0.0 20191107 (experimental) [trunk revision 277920] (GCC)
#expected output
$ gcc-trunk -O1 -g abc.c
$ gdb-trunk -x cmds -batch a.out
Breakpoint 1 at 0x400576: file abc.c, line 23.
Breakpoint 1, n () at abc.c:23
23 if (b) // optimize_me_not()
$1 = 61344
#wrong output at O2
$ gcc-trunk -O2 -g abc.c
$ gdb-trunk -x cmds -batch a.out
Breakpoint 1 at 0x400616: file abc.c, line 23.
Breakpoint 1, n () at abc.c:23
23 if (b) // optimize_me_not()
$1 = 3
$ cat abc.c
int a, d, e, f, h, l;
short b, g, i, m;
char c;
void n() {
char o;
int p = 0, j, k;
int q[70] = {0};
for (; i <= 1; i++) {
unsigned short l_1162[6][2][2];
l = 0;
for (; l < 6; l++) {
j = 0;
for (; j < 2; j++) {
k = 0;
for (; k < 2; k++)
l_1162[l][j][k] = 61344;
}
}
for (; f <= 1; f++)
if (d)
for (; p >= 0; p--)
d = q[f];
if (b) // optimize_me_not()
h = l_1162[4][1][0];
for (; e; e++)
g = l_1162[5][0][1] <= o;
c = a ? c : 0;
q[1] = m;
}
}
int main() {
n();
printf("%X\n");
}
$ cat cmds
b abc.c:23
r
p l_1162[0][0][0]
kill
q
