https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97474
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed| |2020-10-17
Ever confirmed|0 |1
Summary|Regression: optimization |[8/9/10/11 Regression]
|produces wrong code |produces wrong code with
| |references to another field
Component|c++ |tree-optimization
Keywords| |alias
Target Milestone|--- |8.5
Status|UNCONFIRMED |NEW
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #1)
> This feels like an use after something goes out of scope.
It is not, there is some weird aliasing issue.
The IR looks like:
int foo(A) (struct A & restrict a)
{
int _1;
int & _2;
int _3;
int _4;
int & _5;
int _9;
<bb 2> [0.00%]:
_1 = *a_7(D).a;
_2 = *a_7(D).b;
_3 = *_2;
_4 = _1 * _3;
*a_7(D).a = _4;
_5 = *a_7(D).b;
_9 = *_5;
return _9;
}
For some reason we think _5 cannot alias (*a_7(D)).a. Most likely due to the
restict in the IR. The restrict is there because a was passed by value rather
than reference but the way the ABI works, it is passed by a temp struct and we
expose this in the IR. All things go down hill from there.
