This patch replaces the existing tree_code widen_plus and widen_minus
patterns with internal_fn versions.

DEF_INTERNAL_OPTAB_HILO_FN is like DEF_INTERNAL_OPTAB_FN except it 
provides convenience wrappers for defining conversions that require a 
hi/lo split, like widening and narrowing operations.  Each definition 
for <NAME> will require an optab named <OPTAB> and two other optabs that 
you specify for signed and unsigned. The hi/lo pair is necessary because 
the widening operations take n narrow elements as inputs and return n/2 
wide elements as outputs. The 'lo' operation operates on the first n/2 
elements of input. The 'hi' operation operates on the second n/2 
elements of input. Defining an internal_fn along with hi/lo variations 
allows a single internal function to be returned from a vect_recog 
function that will later be expanded to hi/lo.

DEF_INTERNAL_OPTAB_HILO_FN is used in internal-fn.def to register a 
widening internal_fn. It is defined differently in different places and 
internal-fn.def is sourced from those places so the parameters given can 
be reused.
   internal-fn.c: defined to expand to hi/lo signed/unsigned optabs, 
later defined to generate the  'expand_' functions for the hi/lo 
versions of the fn.
   internal-fn.def: defined to invoke DEF_INTERNAL_OPTAB_FN for the 
original and hi/lo variants of the internal_fn

  For example:
  IFN_VEC_WIDEN_PLUS -> IFN_VEC_WIDEN_PLUS_HI, IFN_VEC_WIDEN_PLUS_LO
for aarch64: IFN_VEC_WIDEN_PLUS_HI   -> vec_widen_<su>addl_hi_<mode> -> 
(u/s)addl2
                        IFN_VEC_WIDEN_PLUS_LO  -> 
vec_widen_<su>addl_lo_<mode> -> (u/s)addl

This gives the same functionality as the previous WIDEN_PLUS/WIDEN_MINUS 
tree codes which are expanded into VEC_WIDEN_PLUS_LO, VEC_WIDEN_PLUS_HI.

gcc/ChangeLog:

2023-04-28  Andre Vieira  <andre.simoesdiasvieira@arm.com>
             Joel Hutton  <joel.hutton@arm.com>
             Tamar Christina  <tamar.christina@arm.com>

	* internal-fn.cc (INCLUDE_MAP): Include maps for use in optab
     lookup.
	(DEF_INTERNAL_OPTAB_HILO_FN): Macro to define an internal_fn that
     expands into multiple internal_fns (for widening).
	(ifn_cmp): Function to compare ifn's for sorting/searching.
	(lookup_hilo_ifn_optab): Add lookup function.
	(lookup_hilo_internal_fn): Add lookup function.
	(commutative_binary_fn_p): Add widen_plus fn's.
	(widening_fn_p): New function.
	(decomposes_to_hilo_fn_p): New function.
	* internal-fn.def (DEF_INTERNAL_OPTAB_HILO_FN): Define widening
     plus,minus functions.
	(VEC_WIDEN_PLUS): Replacement for VEC_WIDEN_PLUS tree code.
	(VEC_WIDEN_MINUS): Replacement for VEC_WIDEN_MINUS tree code.
	* internal-fn.h (GCC_INTERNAL_FN_H): Add headers.
	(lookup_hilo_ifn_optab): Add prototype.
	(lookup_hilo_internal_fn): Likewise.
	(widening_fn_p): Likewise.
	(decomposes_to_hilo_fn_p): Likewise.
	* optabs.cc (commutative_optab_p): Add widening plus, minus optabs.
	* optabs.def (OPTAB_CD): widen add, sub optabs
	* tree-vect-patterns.cc (vect_recog_widen_op_pattern): Support
     patterns with a hi/lo split.
	(vect_recog_widen_plus_pattern): Refactor to return
     IFN_VECT_WIDEN_PLUS.
	(vect_recog_widen_minus_pattern): Refactor to return new
     IFN_VEC_WIDEN_MINUS.
	* tree-vect-stmts.cc (vectorizable_conversion): Add widen plus/minus
     ifn
     support.
	(supportable_widening_operation): Add widen plus/minus ifn support.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/vect-widen-add.c: Test that new
     IFN_VEC_WIDEN_PLUS is being used.
	* gcc.target/aarch64/vect-widen-sub.c: Test that new
     IFN_VEC_WIDEN_MINUS is being used.