2008-05-22  Richard Guenther  <rguenther@suse.de>

	* tree-dfa.c (refs_may_alias_p): Exit early if possible.  Handle
	more cases of offset disambiguation that is possible if
	strict-aliasing rules apply.
	* tree-ssa-loop-im.c (mem_refs_may_alias_p): Use refs_may_alias_p
	for basic offset and type-based disambiguation.

	* gcc.dg/tree-ssa/alias-18.c: New testcase.

From-SVN: r135754