Add support for reductions in fully-masked loops

Add support for reductions in fully-masked loops

This patch removes the restriction that fully-masked loops cannot
have reductions.  The key thing here is to make sure that the
reduction accumulator doesn't include any values associated with
inactive lanes; the patch adds a bunch of conditional binary
operations for doing that.

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 (cond_add@var{mode}, cond_sub@var{mode})
	(cond_and@var{mode}, cond_ior@var{mode}, cond_xor@var{mode})
	(cond_smin@var{mode}, cond_smax@var{mode}, cond_umin@var{mode})
	(cond_umax@var{mode}): Document.
	* optabs.def (cond_add_optab, cond_sub_optab, cond_and_optab)
	(cond_ior_optab, cond_xor_optab, cond_smin_optab, cond_smax_optab)
	(cond_umin_optab, cond_umax_optab): New optabs.
	* internal-fn.def (COND_ADD, COND_SUB, COND_MIN, COND_MAX, COND_AND)
	(COND_IOR, COND_XOR): New internal functions.
	* internal-fn.h (get_conditional_internal_fn): Declare.
	* internal-fn.c (cond_binary_direct): New macro.
	(expand_cond_binary_optab_fn): Likewise.
	(direct_cond_binary_optab_supported_p): Likewise.
	(get_conditional_internal_fn): New function.
	* tree-vect-loop.c (vectorizable_reduction): Handle fully-masked loops.
	Cope with reduction statements that are vectorized as calls rather
	than assignments.
	* config/aarch64/aarch64-sve.md (cond_<optab><mode>): New insns.
	* config/aarch64/iterators.md (UNSPEC_COND_ADD, UNSPEC_COND_SUB)
	(UNSPEC_COND_SMAX, UNSPEC_COND_UMAX, UNSPEC_COND_SMIN)
	(UNSPEC_COND_UMIN, UNSPEC_COND_AND, UNSPEC_COND_ORR)
	(UNSPEC_COND_EOR): New unspecs.
	(optab): Add mappings for them.
	(SVE_COND_INT_OP, SVE_COND_FP_OP): New int iterators.
	(sve_int_op, sve_fp_op): New int attributes.

gcc/testsuite/
	* gcc.dg/vect/pr60482.c: Remove XFAIL for variable-length vectors.
	* gcc.target/aarch64/sve/reduc_1.c: Expect the loop operations
	to be predicated.
	* gcc.target/aarch64/sve/slp_5.c: Check for a fully-masked loop.
	* gcc.target/aarch64/sve/slp_7.c: Likewise.
	* gcc.target/aarch64/sve/reduc_5.c: New test.
	* gcc.target/aarch64/sve/slp_13.c: Likewise.
	* gcc.target/aarch64/sve/slp_13_run.c: Likewise.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@256626 138bc75d-0d04-0410-961f-82ee72b054a4