http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50067
--- Comment #13 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-08-22 08:39:18 UTC --- *sigh*, and when we fix it like http://gcc.gnu.org/ml/gcc-patches/2011-08/msg01582.html then gcc.dg/torture/pr44913.c is vectorized bogously because dr_may_alias_p returns false for a[1] and a[-1] (and we don't compute any difference vector). I suppose dr_may_alias_p is completely wrong and does not want to know whether /* Returns false if we can prove that data references A and B do not alias, true otherwise. */ but instead whether the data references may refer to the same base object (plus, I guess, whether the references may alias using TBAA - though as soon as we'd start to do strided stores that will break as well for struct { int i; float f; } a[]). But of course DR_BASE_OBJECT is not what we should adjust to "fix" the dr_may_alias_p answer, but we need to adjust dr_may_alias_p instead (and hope all users do mean to get the same kind of answer... other than ddr init it is graphite that calls it, I will simply ignore that).
