re PR tree-optimization/70497 (Missed CSE of subregs on GIMPLE)

re PR tree-optimization/70497 (Missed CSE of subregs on GIMPLE)

2016-05-10  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/70497
	PR tree-optimization/28367
	* tree-ssa-sccvn.c (vn_nary_build_or_lookup): New function
	split out from ...
	(visit_reference_op_load): ... here.
	(vn_reference_lookup_3): Use it to handle subreg-like accesses
	with simplified BIT_FIELD_REFs.
	* tree-ssa-pre.c (eliminate_insert): Handle inserting BIT_FIELD_REFs.
	* tree-complex.c (extract_component): Handle BIT_FIELD_REFs
	correctly.

	* gcc.dg/torture/20160404-1.c: New testcase.
	* gcc.dg/tree-ssa/ssa-fre-54.c: Likewise.
	* gcc.dg/tree-ssa/ssa-fre-55.c: Likewise.

From-SVN: r236066