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.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>

From-SVN: r256633