Replace REDUC_*_EXPRs with internal functions.

Replace REDUC_*_EXPRs with internal functions.

This patch replaces the REDUC_*_EXPR tree codes with internal functions.
This is needed so that the upcoming in-order reductions can also use
internal functions without too much complication.

2017-11-22  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	* tree.def (REDUC_MAX_EXPR, REDUC_MIN_EXPR, REDUC_PLUS_EXPR): Delete.
	* cfgexpand.c (expand_debug_expr): Remove handling for them.
	* expr.c (expand_expr_real_2): Likewise.
	* fold-const.c (const_unop): Likewise.
	* optabs-tree.c (optab_for_tree_code): Likewise.
	* tree-cfg.c (verify_gimple_assign_unary): Likewise.
	* tree-inline.c (estimate_operator_cost): Likewise.
	* tree-pretty-print.c (dump_generic_node): Likewise.
	(op_code_prio): Likewise.
	(op_symbol_code): Likewise.
	* internal-fn.def (DEF_INTERNAL_SIGNED_OPTAB_FN): Define.
	(IFN_REDUC_PLUS, IFN_REDUC_MAX, IFN_REDUC_MIN): New internal functions.
	* internal-fn.c (direct_internal_fn_optab): New function.
	(direct_internal_fn_array, direct_internal_fn_supported_p
	(internal_fn_expanders): Handle DEF_INTERNAL_SIGNED_OPTAB_FN.
	* fold-const-call.c (fold_const_reduction): New function.
	(fold_const_call): Handle CFN_REDUC_PLUS, CFN_REDUC_MAX and
	CFN_REDUC_MIN.
	* tree-vect-loop.c: Include internal-fn.h.
	(reduction_code_for_scalar_code): Rename to...
	(reduction_fn_for_scalar_code): ...this and return an internal
	function.
	(vect_model_reduction_cost): Take an internal_fn rather than
	a tree_code.
	(vect_create_epilog_for_reduction): Likewise.  Build calls rather
	than assignments.
	(vectorizable_reduction): Use internal functions rather than tree
	codes for the reduction operation.  Update calls to the functions
	above.
	* config/aarch64/aarch64-builtins.c (aarch64_gimple_fold_builtin):
	Use calls to internal functions rather than REDUC tree codes.
	* config/aarch64/aarch64-simd.md: Update comment accordingly.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@255073 138bc75d-0d04-0410-961f-82ee72b054a4