Fold VEC_COND_EXPRs to IFN_COND_* where possible

Fold VEC_COND_EXPRs to IFN_COND_* where possible

This patch adds the folds:

  (vec_cond COND (foo A B) C) -> (IFN_COND_FOO COND A B C)
  (vec_cond COND C (foo A B)) -> (IFN_COND_FOO (!COND) A B C)

with the usual implicit restriction that the target must support
the produced IFN_COND_FOO.

The results of these folds don't have identical semantics, since
the reverse transform would be invalid if (FOO A[i] B[i]) faults when
COND[i] is false.  But this direction is OK since we're simply dropping
faults for operations whose results aren't needed.

The new gimple_resimplify4 doesn't try to do any constant folding
on the IFN_COND_*s.  This is because a later patch will handle it
by folding the associated unconditional operation.

Doing this in gimple is better than doing it in .md patterns,
since the second form (with the inverted condition) is much more
common than the first, and it's better to fold away the inversion
in gimple and optimise the result before entering expand.

2018-05-24  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	* doc/sourcebuild.texi (vect_double_cond_arith: Document.
	* gimple-match.h (gimple_match_op::MAX_NUM_OPS): Bump to 4.
	(gimple_match_op::gimple_match_op): Add an overload for 4 operands.
	(gimple_match_op::set_op): Likewise.
	(gimple_resimplify4): Declare.
	* genmatch.c (get_operand_type): Handle CFN_COND_* functions.
	(expr::gen_transform): Likewise.
	(decision_tree::gen): Generate a simplification routine for 4 operands.
	* gimple-match-head.c (gimple_simplify): Add an overload for
	4 operands.  In the top-level function, handle up to 4 call
	arguments and call gimple_resimplify4.
	(gimple_resimplify4): New function.
	(build_call_internal): Pass a fourth operand.
	(maybe_push_to_seq): Likewise.
	* match.pd (UNCOND_BINARY, COND_BINARY): New operator lists.
	Fold VEC_COND_EXPRs of an operation and a default value into
	an IFN_COND_* function if possible.
	* config/aarch64/iterators.md (UNSPEC_COND_MAX, UNSPEC_COND_MIN):
	New unspecs.
	(SVE_COND_FP_BINARY): Include them.
	(optab, sve_fp_op): Handle them.
	(SVE_INT_BINARY_REV): New code iterator.
	(SVE_COND_FP_BINARY_REV): New int iterator.
	(commutative): New int attribute.
	* config/aarch64/aarch64-protos.h (aarch64_sve_prepare_conditional_op):
	Declare.
	* config/aarch64/aarch64.c (aarch64_sve_prepare_conditional_op): New
	function.
	* config/aarch64/aarch64-sve.md (cond_<optab><mode>): Use it.
	(*cond_<optab><mode>): New patterns for reversed operands.

gcc/testsuite/
	* lib/target-supports.exp
	(check_effective_target_vect_double_cond_arith): New proc.
	* gcc.dg/vect/vect-cond-arith-1.c: New test.
	* gcc.target/aarch64/sve/vcond_8.c: Likewise.
	* gcc.target/aarch64/sve/vcond_8_run.c: Likewise.
	* gcc.target/aarch64/sve/vcond_9.c: Likewise.
	* gcc.target/aarch64/sve/vcond_9_run.c: Likewise.
	* gcc.target/aarch64/sve/vcond_12.c: Likewise.
	* gcc.target/aarch64/sve/vcond_12_run.c: Likewise.

From-SVN: r260710