https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121740
Bug ID: 121740
Summary: missed load fre/pre with std::optional
Product: gcc
Version: 16.0
Status: UNCONFIRMED
Keywords: missed-optimization, needs-reduction
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: pinskia at gcc dot gnu.org
Target Milestone: ---
Take:
```
#include <optional>
#include <vector>
#include <string>
struct O
{
std::optional <int> i;
std::optional <std::string> s;
};
std::vector <O> a;
O a1;
void f0 ()
{
for (auto &i: a)
i = { };
}
void f1 ()
{
a1 = {};
}
```
In f0, in .optimized we still have:
```
D.58046 = {};
SR.83_44->i = {};
_34 = (void *) ivtmp.132_94;
_17 = MEM[(bool *)_34 + 16B];
pretmp_41 = MEM[(struct _Optional_payload_base &)&D.58046 + 8]._M_engaged;
```
That is pretmp_41 should be 0 here as far as I can tell. In fre3 we have:
```
D.58030 = {};
SR.84_7->i = {};
_11 = &MEM[(struct _Optional_payload *)SR.84_7 + 8B].D.55976;
_17 = MEM[(struct _Optional_payload_base *)SR.84_7 + 8B]._M_engaged;
if (_17 != 0)
goto <bb 4>; [50.00%]
else
goto <bb 16>; [50.00%]
<bb 4> [local count: 477815112]:
_18 = MEM[(struct _Optional_payload_base &)&D.58030 + 8]._M_engaged;
```
The store to `SR.84_7->i` should not alias with the other optional field so the
load from `MEM[(struct _Optional_payload_base &)&D.58030 + 8]._M_engaged` in
<bb 4> is still 0 (well and the store to SR.84_7->i is zeros anyways.
f1 has a similar issue but pre is able to figure out later on.
