Fix PR47271: only if-convert full writes.

2011-01-25  Sebastian Pop  <sebastian.pop@amd.com>
	    Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/47271
	* tree-if-conv.c (bb_postdominates_preds): New.
	(if_convertible_bb_p): Call bb_postdominates_preds.
	(if_convertible_loop_p_1): Compute CDI_POST_DOMINATORS.
	(predicate_scalar_phi): Call bb_postdominates_preds.

	* gcc.dg/tree-ssa/ifc-pr47271.c: New.

Co-Authored-By: Jakub Jelinek <jakub@redhat.com>

From-SVN: r169233