https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108817
Martin Liška <marxin at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |INVALID
Status|UNCONFIRMED |RESOLVED
--- Comment #1 from Martin Liška <marxin at gcc dot gnu.org> ---
Here we prove that 'return c' only depends on the last execution of 'c =
b[a+1];' which is going to happen with a == 0 and thus we optimize out that.
$ gcc pr108817.C -fsanitize=address -O3 -fdump-tree-optimized=/dev/stdout
int main ()
{
signed char _4;
unsigned long _8;
int _12;
unsigned long _15;
bool _16;
unsigned long _18;
int _19;
char _20;
bool _21;
signed char _22;
signed char _23;
unsigned long _25;
signed char * _27;
bool _38;
<bb 2> [local count: 26541933]:
a = 2;
_15 = (unsigned long) &MEM <int> [(void *)&b + 4B];
(checking if &b + 4 is valid in shadow memory)
if (_16 != 0)
goto <bb 3>; [0.05%]
else
goto <bb 4>; [99.95%]
<bb 3> [local count: 13271]:
__builtin___asan_report_load4 (_15);
<bb 4> [local count: 26541933]:
_19 = b[1]; <- here we use it as the future value
_20 = (char) _19;
c = _20;
a = -1;
_12 = (int) _20;
return _12;
}
Final note: note clang does not report the issue even with -O1.
