VECT: Add mask_len_fold_left_plus for in-order floating-point reduction

Hi, Richard and Richi.

This patch adds mask_len_fold_left_plus pattern to support in-order floating-point
reduction for target support len loop control.

Consider this following case:
double
foo2 (double *__restrict a,
     double init,
     int *__restrict cond,
     int n)
{
    for (int i = 0; i < n; i++)
      if (cond[i])
        init += a[i];
    return init;
}

ARM SVE:

...
vec_mask_and_60 = loop_mask_54 & mask__23.33_57;
vect__ifc__35.37_64 = .VCOND_MASK (vec_mask_and_60, vect__8.36_61, { 0.0, ... });
_36 = .MASK_FOLD_LEFT_PLUS (init_20, vect__ifc__35.37_64, loop_mask_54);
...

For RVV, we want to see:
...
_36 = .MASK_LEN_FOLD_LEFT_PLUS (init_20, vect__ifc__35.37_64, control_mask, loop_len, bias);
...

gcc/ChangeLog:

	* doc/md.texi: Add mask_len_fold_left_plus.
	* internal-fn.cc (mask_len_fold_left_direct): Ditto.
	(expand_mask_len_fold_left_optab_fn): Ditto.
	(direct_mask_len_fold_left_optab_supported_p): Ditto.
	* internal-fn.def (MASK_LEN_FOLD_LEFT_PLUS): Ditto.
	* optabs.def (OPTAB_D): Ditto.

gcc/doc/md.texi

@@ -5615,6 +5615,19 @@ no reassociation.
 Like @samp{fold_left_plus_@var{m}}, but takes an additional mask operand
 (operand 3) that specifies which elements of the source vector should be added.
 
+@cindex @code{mask_len_fold_left_plus_@var{m}} instruction pattern
+@item @code{mask_len_fold_left_plus_@var{m}}
+Like @samp{fold_left_plus_@var{m}}, but takes an additional mask operand
+(operand 3), len operand (operand 4) and bias operand (operand 5) that
+performs following operations strictly in-order (no reassociation):
+
+@smallexample
+operand0 = operand1;
+for (i = 0; i < LEN + BIAS; i++)
+  if (operand3[i])
+    operand0 += operand2[i];
+@end smallexample
+
 @cindex @code{sdot_prod@var{m}} instruction pattern
 @item @samp{sdot_prod@var{m}}
 

gcc/internal-fn.cc

@@ -190,6 +190,7 @@ init_internal_fns ()
 #define fold_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 }
 #define check_ptrs_direct { 0, 0, false }
 
 const direct_internal_fn_info direct_internal_fn_array[IFN_LAST + 1] = {
@@ -3890,6 +3891,9 @@ expand_convert_optab_fn (internal_fn fn, gcall *stmt, convert_optab optab,
 #define expand_mask_fold_left_optab_fn(FN, STMT, OPTAB) \
   expand_direct_optab_fn (FN, STMT, OPTAB, 3)
 
+#define expand_mask_len_fold_left_optab_fn(FN, STMT, OPTAB) \
+  expand_direct_optab_fn (FN, STMT, OPTAB, 5)
+
 #define expand_check_ptrs_optab_fn(FN, STMT, OPTAB) \
   expand_direct_optab_fn (FN, STMT, OPTAB, 4)
 
@@ -3997,6 +4001,7 @@ multi_vector_optab_supported_p (convert_optab optab, tree_pair types,
 #define direct_fold_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
 #define direct_check_ptrs_optab_supported_p direct_optab_supported_p
 #define direct_vec_set_optab_supported_p direct_optab_supported_p
 #define direct_vec_extract_optab_supported_p direct_optab_supported_p

gcc/internal-fn.def

@@ -319,6 +319,9 @@ DEF_INTERNAL_OPTAB_FN (FOLD_LEFT_PLUS, ECF_CONST | ECF_NOTHROW,
 DEF_INTERNAL_OPTAB_FN (MASK_FOLD_LEFT_PLUS, ECF_CONST | ECF_NOTHROW,
 		       mask_fold_left_plus, mask_fold_left)
 
+DEF_INTERNAL_OPTAB_FN (MASK_LEN_FOLD_LEFT_PLUS, ECF_CONST | ECF_NOTHROW,
+		       mask_len_fold_left_plus, mask_len_fold_left)
+
 /* Unary math functions.  */
 DEF_INTERNAL_FLT_FN (ACOS, ECF_CONST, acos, unary)
 DEF_INTERNAL_FLT_FN (ACOSH, ECF_CONST, acosh, unary)

gcc/optabs.def

@@ -385,6 +385,7 @@ OPTAB_D (reduc_ior_scal_optab,  "reduc_ior_scal_$a")
 OPTAB_D (reduc_xor_scal_optab,  "reduc_xor_scal_$a")
 OPTAB_D (fold_left_plus_optab, "fold_left_plus_$a")
 OPTAB_D (mask_fold_left_plus_optab, "mask_fold_left_plus_$a")
+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")