re PR tree-optimization/14287 ([tree-ssa] does not remove unnecessary extensions)

re PR tree-optimization/14287 ([tree-ssa] does not remove unnecessary extensions)

2006-05-04  Richard Guenther  <rguenther@suse.de>

	PR tree-optimization/14287
	PR tree-optimization/14844
	PR tree-optimization/19792
	PR tree-optimization/21608
	PR tree-optimization/27090
	* tree-ssa-pre.c (try_combine_conversion): New function.
	(compute_avail): After constructing the value-handle
	expression, use try_combine_conversion to combine NOP_EXPRs
	with previous value-handle expressions and use the result if it
	is available.

	* gcc.dg/tree-ssa/ssa-fre-1.c: New testcase.
	* gcc.dg/tree-ssa/ssa-fre-2.c: Likewise.
	* gcc.dg/tree-ssa/ssa-fre-3.c: Likewise.
	* gcc.dg/tree-ssa/ssa-fre-4.c: Likewise.
	* gcc.dg/tree-ssa/ssa-fre-5.c: Likewise.

From-SVN: r113527