VECT: Add LEN_FOLD_EXTRACT_LAST pattern

Hi, Richard and Richi.

This is the last autovec pattern I want to add for RVV (length loop control).

This patch is supposed to handled this following case:

int __attribute__ ((noinline, noclone))
condition_reduction (int *a, int min_v, int n)
{
  int last = 66; /* High start value.  */

  for (int i = 0; i < n; i++)
    if (a[i] < min_v)
      last = i;

  return last;
}

ARM SVE IR:

  ...
  mask__7.11_39 = vect__4.10_37 < vect_cst__38;
  _40 = loop_mask_36 & mask__7.11_39;
  last_5 = .FOLD_EXTRACT_LAST (last_15, _40, vect_vec_iv_.7_32);
  ...

RVV IR, we want to see:
 ...
 loop_len = SELECT_VL
 mask__7.11_39 = vect__4.10_37 < vect_cst__38;
 last_5 = .LEN_FOLD_EXTRACT_LAST (last_15, _40, vect_vec_iv_.7_32, loop_len, bias);
 ...

gcc/ChangeLog:

	* doc/md.texi: Add LEN_FOLD_EXTRACT_LAST pattern.
	* internal-fn.cc (fold_len_extract_direct): Ditto.
	(expand_fold_len_extract_optab_fn): Ditto.
	(direct_fold_len_extract_optab_supported_p): Ditto.
	* internal-fn.def (LEN_FOLD_EXTRACT_LAST): Ditto.
	* optabs.def (OPTAB_D): Ditto.

gcc/doc/md.texi

@@ -5636,6 +5636,12 @@ has mode @var{m} and operands 0 and 1 have the mode appropriate for
 one element of @var{m}.  Operand 2 has the usual mask mode for vectors
 of mode @var{m}; see @code{TARGET_VECTORIZE_GET_MASK_MODE}.
 
+@cindex @code{len_fold_extract_last_@var{m}} instruction pattern
+@item @code{len_fold_extract_last_@var{m}}
+Like @samp{fold_extract_last_@var{m}}, but takes an extra length operand as
+operand 4 and an extra bias operand as operand 5.  The last associated element
+is extracted should have the index i < len (operand 4) + bias (operand 5).
+
 @cindex @code{fold_left_plus_@var{m}} instruction pattern
 @item @code{fold_left_plus_@var{m}}
 Take scalar operand 1 and successively add each element from vector

gcc/internal-fn.cc

@@ -188,6 +188,7 @@ init_internal_fns ()
 #define cond_len_ternary_direct { 1, 1, true }
 #define while_direct { 0, 2, false }
 #define fold_extract_direct { 2, 2, false }
+#define fold_len_extract_direct { 2, 2, false }
 #define fold_left_direct { 1, 1, false }
 #define mask_fold_left_direct { 1, 1, false }
 #define mask_len_fold_left_direct { 1, 1, false }
@@ -3863,6 +3864,9 @@ expand_convert_optab_fn (internal_fn fn, gcall *stmt, convert_optab optab,
 #define expand_fold_extract_optab_fn(FN, STMT, OPTAB) \
   expand_direct_optab_fn (FN, STMT, OPTAB, 3)
 
+#define expand_fold_len_extract_optab_fn(FN, STMT, OPTAB) \
+  expand_direct_optab_fn (FN, STMT, OPTAB, 5)
+
 #define expand_fold_left_optab_fn(FN, STMT, OPTAB) \
   expand_direct_optab_fn (FN, STMT, OPTAB, 2)
 
@@ -3980,6 +3984,7 @@ multi_vector_optab_supported_p (convert_optab optab, tree_pair types,
 #define direct_mask_len_store_optab_supported_p convert_optab_supported_p
 #define direct_while_optab_supported_p convert_optab_supported_p
 #define direct_fold_extract_optab_supported_p direct_optab_supported_p
+#define direct_fold_len_extract_optab_supported_p direct_optab_supported_p
 #define direct_fold_left_optab_supported_p direct_optab_supported_p
 #define direct_mask_fold_left_optab_supported_p direct_optab_supported_p
 #define direct_mask_len_fold_left_optab_supported_p direct_optab_supported_p

gcc/internal-fn.def

@@ -312,6 +312,9 @@ DEF_INTERNAL_OPTAB_FN (EXTRACT_LAST, ECF_CONST | ECF_NOTHROW,
 DEF_INTERNAL_OPTAB_FN (FOLD_EXTRACT_LAST, ECF_CONST | ECF_NOTHROW,
 		       fold_extract_last, fold_extract)
 
+DEF_INTERNAL_OPTAB_FN (LEN_FOLD_EXTRACT_LAST, ECF_CONST | ECF_NOTHROW,
+		       len_fold_extract_last, fold_len_extract)
+
 DEF_INTERNAL_OPTAB_FN (FOLD_LEFT_PLUS, ECF_CONST | ECF_NOTHROW,
 		       fold_left_plus, fold_left)
 

gcc/optabs.def

@@ -393,6 +393,7 @@ OPTAB_D (mask_len_fold_left_plus_optab, "mask_len_fold_left_plus_$a")
 
 OPTAB_D (extract_last_optab, "extract_last_$a")
 OPTAB_D (fold_extract_last_optab, "fold_extract_last_$a")
+OPTAB_D (len_fold_extract_last_optab, "len_fold_extract_last_$a")
 
 OPTAB_D (uabd_optab, "uabd$a3")
 OPTAB_D (sabd_optab, "sabd$a3")