Add support for conditional reductions using SVE CLASTB

Add support for conditional reductions using SVE CLASTB

This patch uses SVE CLASTB to optimise conditional reductions.  It means
that we no longer need to maintain a separate index vector to record
the most recent valid value, and no longer need to worry about overflow
cases.

2018-01-13  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* doc/md.texi (fold_extract_last_@var{m}): Document.
	* doc/sourcebuild.texi (vect_fold_extract_last): Likewise.
	* optabs.def (fold_extract_last_optab): New optab.
	* internal-fn.def (FOLD_EXTRACT_LAST): New internal function.
	* internal-fn.c (fold_extract_direct): New macro.
	(expand_fold_extract_optab_fn): Likewise.
	(direct_fold_extract_optab_supported_p): Likewise.
	* tree-vectorizer.h (EXTRACT_LAST_REDUCTION): New vect_reduction_type.
	* tree-vect-loop.c (vect_model_reduction_cost): Handle
	EXTRACT_LAST_REDUCTION.
	(get_initial_def_for_reduction): Do not create an initial vector
	for EXTRACT_LAST_REDUCTION reductions.
	(vectorizable_reduction): Leave the scalar phi in place for
	EXTRACT_LAST_REDUCTIONs.  Try using EXTRACT_LAST_REDUCTION
	ahead of INTEGER_INDUC_COND_REDUCTION.  Do not check for an
	epilogue code for EXTRACT_LAST_REDUCTION and defer the
	transform phase to vectorizable_condition.
	* tree-vect-stmts.c (vect_finish_stmt_generation_1): New function,
	split out from...
	(vect_finish_stmt_generation): ...here.
	(vect_finish_replace_stmt): New function.
	(vectorizable_condition): Handle EXTRACT_LAST_REDUCTION.
	* config/aarch64/aarch64-sve.md (fold_extract_last_<mode>): New
	pattern.
	* config/aarch64/aarch64.md (UNSPEC_CLASTB): New unspec.

gcc/testsuite/
	* lib/target-supports.exp
	(check_effective_target_vect_fold_extract_last): New proc.
	* gcc.dg/vect/pr65947-1.c: Update dump messages.  Add markup
	for fold_extract_last.
	* 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/pr65947-14.c: Likewise.
	* gcc.dg/vect/pr80631-1.c: Likewise.
	* gcc.target/aarch64/sve/clastb_1.c: New test.
	* gcc.target/aarch64/sve/clastb_1_run.c: Likewise.
	* gcc.target/aarch64/sve/clastb_2.c: Likewise.
	* gcc.target/aarch64/sve/clastb_2_run.c: Likewise.
	* gcc.target/aarch64/sve/clastb_3.c: Likewise.
	* gcc.target/aarch64/sve/clastb_3_run.c: Likewise.
	* gcc.target/aarch64/sve/clastb_4.c: Likewise.
	* gcc.target/aarch64/sve/clastb_4_run.c: Likewise.
	* gcc.target/aarch64/sve/clastb_5.c: Likewise.
	* gcc.target/aarch64/sve/clastb_5_run.c: Likewise.
	* gcc.target/aarch64/sve/clastb_6.c: Likewise.
	* gcc.target/aarch64/sve/clastb_6_run.c: Likewise.
	* gcc.target/aarch64/sve/clastb_7.c: Likewise.
	* gcc.target/aarch64/sve/clastb_7_run.c: Likewise.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@256633 138bc75d-0d04-0410-961f-82ee72b054a4