Add an "else" argument to IFN_COND_* functions

Add an "else" argument to IFN_COND_* functions

As suggested by Richard B, this patch changes the IFN_COND_*
functions so that they take the else value of the ?: operation
as a final argument, rather than always using argument 1.

All current callers will still use the equivalent of argument 1,
so this patch makes the SVE code assert that for now.  Later patches
add the general case.

2018-05-25  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	* doc/md.texi: Update the documentation of the cond_* optabs
	to mention the new final operand.  Fix GET_MODE_NUNITS call.
	Describe the scalar case too.
	* internal-fn.def (IFN_EXTRACT_LAST): Change type to fold_left.
	* internal-fn.c (expand_cond_unary_optab_fn): Expect 3 operands
	instead of 2.
	(expand_cond_binary_optab_fn): Expect 4 operands instead of 3.
	(get_conditional_internal_fn): Update comment.
	* tree-vect-loop.c (vectorizable_reduction): Pass the original
	accumulator value as a final argument to conditional functions.
	* config/aarch64/aarch64-sve.md (cond_<optab><mode>): Turn into
	a define_expand and add an "else" operand.  Assert for now that
	the else operand is equal to operand 2.  Use SVE_INT_BINARY and
	SVE_COND_FP_BINARY instead of SVE_COND_INT_OP and SVE_COND_FP_OP.
	(*cond_<optab><mode>): New patterns.
	* config/aarch64/iterators.md (UNSPEC_COND_SMAX, UNSPEC_COND_UMAX)
	(UNSPEC_COND_SMIN, UNSPEC_COND_UMIN, UNSPEC_COND_AND, UNSPEC_COND_ORR)
	(UNSPEC_COND_EOR): Delete.
	(optab): Remove associated mappings.
	(SVE_INT_BINARY): New code iterator.
	(sve_int_op): Remove int attribute and add "minus" to the code
	attribute.
	(SVE_COND_INT_OP): Delete.
	(SVE_COND_FP_OP): Rename to...
	(SVE_COND_FP_BINARY): ...this.

From-SVN: r260707