https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78035
Bug ID: 78035
Summary: Inconsistency between address comparison and alias
analysis
Product: gcc
Version: 7.0
Status: UNCONFIRMED
Keywords: missed-optimization, wrong-code
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: rguenth at gcc dot gnu.org
CC: hubicka at gcc dot gnu.org
Target Milestone: ---
Consider
extern int a;
extern int b;
extern int c;
int foo(int choose_a)
{
int *p;
if (choose_a)
p = &a;
else
p = &b;
return p != &c;
}
int bar ()
{
return &a != &c;
}
where trunk optimizes foo to return 1 while leaving the address comparison
in bar alone. This is because for bar we end up invoking
symtab_node::equal_address_to which considers symbol interposition while
for simplifying foo we look at alias info (points-to) which considers
a, b and c distinct objects.
Either we are being too conservative in bar or we have a possible wrong-code
issue in foo considering the very same points-to information is also used
for alias analysis (and obviously direct accesses to a and b are not considered
aliasing either).
