re PR tree-optimization/42438 (Fix for PR38819 is too conservative)

2010-01-03  Richard Guenther  <rguenther@suse.de>

	PR tree-optimization/42438
	* tree-ssa-pre.c (struct bb_bitmap_sets): Add
	contains_may_not_return_call flag.
	(BB_MAY_NOTRETURN): New.
	(valid_in_sets): Trapping nary operations are not valid
	in blocks that may not return.
	(insert_into_preds_of_block): Remove check for trapping
	expressions.
	(compute_avail): Compute also BB_MAY_NOTRETURN.

	* gcc.dg/tree-ssa/ssa-pre-27.c: New testcase.

From-SVN: r155584