re PR middle-end/88963 (gcc generates terrible code for vectors of 64+ length which are not natively supported)

2019-05-03  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/88963
	* tree-ssa-forwprop.c (pass_forwprop::execute): Rewrite
	vector loads feeding only BIT_FIELD_REFs to component
	loads.  Rewrite stores fed by CONSTRUCTORs to component
	stores.

	* gcc.dg/tree-ssa/ssa-fre-31.c: Disable forwprop.
	* gcc.target/i386/pr88963-1.c: New testcase.
	* gcc.target/i386/pr88963-2.c: Likewise.

From-SVN: r270844