https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93891
Bug ID: 93891
Summary: CSE where clobber writes the same value
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: glisse at gcc dot gnu.org
Target Milestone: ---
void f(int**p,int**q){
++**p;
*q=*p;
--**p;
}
produces
_1 = *p_8(D);
_2 = *_1;
_3 = _2 + 1;
*_1 = _3;
*q_10(D) = _1;
_4 = *p_8(D);
etc
where we do not CSE _4 -> _1. We do have code in vn_reference_lookup_3 to
handle this kind of thing, look past a potential clobber, and ignore it if we
find the same value. But for this test, vn_reference_lookup_2 returns 0 and we
never look further than *q=1 when we valueize *p for _4. If we did, I expect we
would skip *_1=3 using TBAA and eventually find _1=*p, which matches the
potential clobber.
(this comes from the same code as PR 93745 but should not have the same issue)
