RTL alias analysis (nonoverlapping_component_refs_p) with a quadratic loop
finds that c->a1.i and b->a1.j cannot alias based on a offset test on the
common sub-reference base a1. The tree based alias oracle only does two
linear searches for the base type *c in b->a1.j and for *b in c->a1.i.
This is related to PR13146 where even that is not enough, but a
(non-conservative?) answer based on not finding a common base needs to be
given.
/* { dg-do compile } */
/* { dg-options "-O -fstrict-aliasing -fdump-tree-optimized" } */
struct A {
int i;
int j;
};
struct B {
struct A a1;
struct A a2;
};
struct C {
struct A a1;
struct B b;
};
int foo(struct C *c, struct B *b)
{
c->a1.i = 1;
b->a1.j = 0;
return c->a1.i;
}
/* { dg-final { scan-tree-dump "return 1;" "optimized" } } */
/* { dg-final { cleanup-tree-dump "optimized" } } */
--
Summary: missed type-based disambiguation
Product: gcc
Version: 4.4.0
Status: UNCONFIRMED
Keywords: missed-optimization, alias, TREE
Severity: enhancement
Priority: P3
Component: tree-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: rguenth at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38895
