Fix reductions for fully-masked loops

Fix reductions for fully-masked loops

Now that vectorizable_operation vectorises most loop stmts involved
in a reduction, it needs to be aware of reductions in fully-masked loops.
The LOOP_VINFO_CAN_FULLY_MASK_P parts of vectorizable_reduction now only
apply to cases that use vect_transform_reduction.

This new way of doing things is definitely an improvement for SVE though,
since it means we can lift the old restriction of not using fully-masked
loops for reduction chains.

2019-10-25  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* tree-vect-loop.c (vectorizable_reduction): Restrict the
	LOOP_VINFO_CAN_FULLY_MASK_P handling to cases that will be
	handled by vect_transform_reduction.  Allow fully-masked loops
	to be used with reduction chains.
	* tree-vect-stmts.c (vectorizable_operation): Handle reduction
	operations in fully-masked loops.
	(vectorizable_condition): Reject EXTRACT_LAST_REDUCTION
	operations in fully-masked loops.

gcc/testsuite/
	* gcc.dg/vect/pr65947-1.c: No longer expect doubled dump lines
	for FOLD_EXTRACT_LAST reductions.
	* gcc.dg/vect/pr65947-2.c: Likewise.
	* gcc.dg/vect/pr65947-3.c: Likewise.
	* gcc.dg/vect/pr65947-4.c: Likewise.
	* gcc.dg/vect/pr65947-5.c: Likewise.
	* gcc.dg/vect/pr65947-6.c: Likewise.
	* gcc.dg/vect/pr65947-9.c: Likewise.
	* gcc.dg/vect/pr65947-10.c: Likewise.
	* gcc.dg/vect/pr65947-12.c: Likewise.
	* gcc.dg/vect/pr65947-13.c: Likewise.
	* gcc.dg/vect/pr65947-14.c: Likewise.
	* gcc.dg/vect/pr80631-1.c: Likewise.
	* gcc.dg/vect/pr80631-2.c: Likewise.
	* gcc.dg/vect/vect-cond-reduc-3.c: Likewise.
	* gcc.dg/vect/vect-cond-reduc-4.c: Likewise.

From-SVN: r277438