backport: re PR tree-optimization/85257 (wrong code with -O -fno-tree-ccp and reading...

backport: re PR tree-optimization/85257 (wrong code with -O -fno-tree-ccp and reading zeroed vector member)

	Backported from mainline
	2018-04-07  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/85257
	* fold-const.c (native_encode_vector): If not all elts could fit
	and off is -1, return 0 rather than offset.
	* tree-ssa-sccvn.c (vn_reference_lookup_3): Pass
	(offset - offset2) / BITS_PER_UNIT as 4th argument to
	native_encode_expr.  Verify len * BITS_PER_UNIT >= maxsizei.  Don't
	adjust buffer in native_interpret_expr call.

	* gcc.dg/pr85257.c: New test.

From-SVN: r261951