https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96457
Bug ID: 96457
Summary: PRE gets confused by punned load handling
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: rguenth at gcc dot gnu.org
Target Milestone: ---
int flag;
union { double f; unsigned long long i; } u;
void foo();
unsigned long long i;
unsigned long long
test ()
{
double f = 0.;
if (flag)
{
foo ();
f = u.f;
}
else
i = u.i;
f = u.f + f;
return f;
}
here we fail to PRE the load of u.f because PHI translation to the else
path fails since we run into
/* If we'd have to convert things we would need to validate
if we can insert the translated expression. So fail
here for now - we cannot insert an alias with a different
type in the VN tables either, as that would assert. */
if (result
&& !useless_type_conversion_p (ref->type, TREE_TYPE (result)))
return NULL;
because we found a value for u.f there, that of u.i (because we value-number
them the same). If one replaces 'i = u.i;' with 'foo ();' we appropriately
insert a load from u.f in the else path and remove the partial redundancy.
