https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92468
Bug ID: 92468
Summary: gcc generates wrong debug information at -O2 and -O3
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 affects the trunk and both 8 and 9 releases. Gcc-7 works fine.
The expected output is k=0 or opt-out. With O2 and O3, gdb outputs k=1.
$ gcc-trunk -v
gcc version 10.0.0 20191111 (experimental) [trunk revision 278048] (GCC)
#expected output
$ gcc-trunk -g abc.c
$ gdb-trunk -x cmds -batch a.out
Breakpoint 1 at 0x40054c: file abc.c, line 20.
Breakpoint 1, main () at abc.c:20
20 if (g) printf("index = %d%d%d\n", b, f, k); //
optimize_me_not()
$1 = 0
#wrong output
$ gcc-trunk -g abc.c -O3
$ gdb-trunk -x cmds -batch a.out
Breakpoint 1 at 0x4003c0: file abc.c, line 20.
Breakpoint 1, main () at abc.c:20
20 if (g) printf("index = %d%d%d\n", b, f, k); //
optimize_me_not()
$1 = 1
$ cat abc.c
int a, b ;
short c[5][16] ;
void
d (e) {
a =
a ^ e;
}
int main ()
{
int f, k, g = 0;
for (; b < 5; b++)
{
f = 0;
for (; f < 4; f++)
{
k = 0;
for (; k < 4; k++)
{
d (c[b][f] & c[b][f*4+k] & 5);
if (g) printf("index = %d%d%d\n", b, f, k); //
optimize_me_not()
}
}
}
}
$ cat cmds
b abc.c:20
r
p k
kill
q
