https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104547
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed| |2022-02-15
CC| |aldyh at gcc dot gnu.org,
| |amacleod at redhat dot com,
| |jakub at gcc dot gnu.org
Ever confirmed|0 |1
Status|UNCONFIRMED |NEW
--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
If you mean with -O3 on the
#include <vector>
void shrink(std::vector<int>& v, unsigned n) {
if (v.size() < n)
__builtin_unreachable();
v.resize(v.size() - n);
}
testcase (with -O2 _M_default_append isn't nlined), then I think it is
something that ideally ranger's symbolic handling should figure out but
doesn't.
We have:
long unsigned int _1;
...
long unsigned int _11;
...
if (_1 > _11)
goto <bb 3>; [0.00%]
else
goto <bb 4>; [100.00%]
<bb 3> [count: 0]:
__builtin_unreachable ();
<bb 4> [local count: 1073741824]:
# RANGE ~[2305843009213693952, 16140901060200890368]
_2 = _11 - _1;
if (_2 > _11)
and we don't figure out that _2 > _11 is always false, because we earlier
assert that _1 <= _11 and so _11 - _1 will not wrap around and so the result _2
<= _11.
