------- Comment #6 from rguenth at gcc dot gnu dot org 2010-01-14 16:57 ------- Note that with the current middle-end setup we cannot really ever derive anything about alignment when just seeing a pointer type. We only can ever derive alignment information when having access to the pointed-to decl or when encountering an actual dereference of a pointer (though as with this middle-end problem I'm sure we have bugs where the alignment of the access is not that of the type of the dereferenced pointer).
Thus get_pointer_alignment is overly optimistic. We could establish some C rules in the middle-end namely that pointer function arguments have proper alignment, likewise passing a pointer to a function is as good as a dereference of it. But as other people have noted we simply need to propagate alignment information somewhere and the frontends need a way to communicate constraints to the middle-end. The operand scanner could set a flag in the SSA names pointer information whether it is dereferenced or passed as function argument, points-to information can constrain alignment based on the pointed-to objects (but never can derive larger alignment than the pointed-to types). -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40060
