Machine Description: Add LEN_MASK_{GATHER_LOAD, SCATTER_STORE} pattern

Hi, Richi and Richard.

Base one the review comments from Richard:
https://gcc.gnu.org/pipermail/gcc-patches/2023-July/623405.html

I change len_mask_gather_load/len_mask_scatter_store order into:
{len,bias,mask}

We adjust adding len and mask using using add_len_and_mask_args
which is same as partial_load/parial_store.

Now, the codes become more reasonable and easier maintain.

This patch is adding LEN_MASK_{GATHER_LOAD,SCATTER_STORE} to allow targets
handle flow control by mask and loop control by length on gather/scatter memory
operations. Consider this following case:

void
f (uint8_t *restrict a,
   uint8_t *restrict b, int n,
   int base, int step,
   int *restrict cond)
{
  for (int i = 0; i < n; ++i)
    {
      if (cond[i])
        a[i * step + base] = b[i * step + base];
    }
}

We hope RVV can vectorize such case into following IR:

loop_len = SELECT_VL
control_mask = comparison
v = LEN_MASK_GATHER_LOAD (.., loop_len, bias, control_mask)
LEN_SCATTER_STORE (... v, ..., loop_len, bias, control_mask)

This patch doesn't apply such patterns into vectorizer, just add patterns
and update the documents.

Will send patch which apply such patterns into vectorizer soon after this
patch is approved.

Ok for trunk?

gcc/ChangeLog:

	* doc/md.texi: Add len_mask_gather_load/len_mask_scatter_store.
	* internal-fn.cc (expand_scatter_store_optab_fn): Ditto.
	(expand_gather_load_optab_fn): Ditto.
	(internal_load_fn_p): Ditto.
	(internal_store_fn_p): Ditto.
	(internal_gather_scatter_fn_p): Ditto.
	(internal_fn_len_index): Ditto.
	(internal_fn_mask_index): Ditto.
	(internal_fn_stored_value_index): Ditto.
	* internal-fn.def (LEN_MASK_GATHER_LOAD): Ditto.
	(LEN_MASK_SCATTER_STORE): Ditto.
	* optabs.def (OPTAB_CD): Ditto.

1 files changed, 17 insertions, 0 deletions

diff --git a/gcc/doc/md.texi b/gcc/doc/md.texi
index 5e54822..f14dd32 100644
--- a/gcc/doc/md.texi
+++ b/gcc/doc/md.texi
@@ -5040,6 +5040,15 @@ operand 5.  Bit @var{i} of the mask is set if element @var{i}
 of the result should be loaded from memory and clear if element @var{i}
 of the result should be set to zero.
 
+@cindex @code{len_mask_gather_load@var{m}@var{n}} instruction pattern
+@item @samp{len_mask_gather_load@var{m}@var{n}}
+Like @samp{gather_load@var{m}@var{n}}, but takes an extra length operand (operand 5),
+a bias operand (operand 6) as well as a mask operand (operand 7).  Similar to len_maskload,
+the instruction loads at most (operand 5 + operand 6) elements from memory.
+Bit @var{i} of the mask is set if element @var{i} of the result should
+be loaded from memory and clear if element @var{i} of the result should be undefined.
+Mask elements @var{i} with @var{i} > (operand 5 + operand 6) are ignored.
+
 @cindex @code{scatter_store@var{m}@var{n}} instruction pattern
 @item @samp{scatter_store@var{m}@var{n}}
 Store a vector of mode @var{m} into several distinct memory locations.
@@ -5069,6 +5078,14 @@ Like @samp{scatter_store@var{m}@var{n}}, but takes an extra mask operand as
 operand 5.  Bit @var{i} of the mask is set if element @var{i}
 of the result should be stored to memory.
 
+@cindex @code{len_mask_scatter_store@var{m}@var{n}} instruction pattern
+@item @samp{len_mask_scatter_store@var{m}@var{n}}
+Like @samp{scatter_store@var{m}@var{n}}, but takes an extra length operand (operand 5),
+a bias operand (operand 6) as well as a mask operand (operand 7).  The instruction stores
+at most (operand 5 + operand 6) elements of (operand 4) to memory.
+Bit @var{i} of the mask is set if element @var{i} of (operand 4) should be stored.
+Mask elements @var{i} with @var{i} > (operand 5 + operand 6) are ignored.
+
 @cindex @code{vec_set@var{m}} instruction pattern
 @item @samp{vec_set@var{m}}
 Set given field in the vector value.  Operand 0 is the vector to modify,