https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120817
--- Comment #13 from Richard Biener <rguenth at gcc dot gnu.org> --- (In reply to Tamar Christina from comment #12) > Looks like the problem is that during ao_ref_init_from_ptr_and_range when > initializing vectp_target.14_54 = &targetD.4595 + _55; > > we don't enter the block splitting apart POINTER_PLUS_EXPR. > > So it ends up creating a ref with the base being MEM_REF <&targetD.4595 + > _55> > > later on when checking of &targetD.4595 and MEM_REF <&targetD.4595 + _55> > could alias in refs_may_alias_p it doesn't think these two can alias, even > though > > # _38 = PHI <niters_vector_mult_vf.6_33(6), 0(3)> > # RANGE [irange] sizetype [0, 0][32, 4294967264] MASK 0xffffffe0 VALUE 0x0 > _55 = (sizetype) _38; > > > so clearly they can alias. Need to look into how tree-ssa-alias normally > handles PHI offsets. The problem is that _55 is negative. But the alias oracle does not consider negative offsets but only the 8B positive offset which makes the access clearly out of bounds of &targetD.4595. Do not use POINTER_PLUS_EXPR to "advance" a pointer to sth outside of [&object, &object + sizeof(object)], since such a pointer is UB.
