vect: Support gather loads with SLP

This patch adds SLP support for IFN_GATHER_LOAD.  Like the SLP
support for IFN_MASK_LOAD, it works by treating only some of the
arguments as child nodes.  Unlike IFN_MASK_LOAD, it requires the
other arguments (base, scale, and extension type) to be the same
for all calls in the group.  It does not require/expect the loads
to be in a group (which probably wouldn't make sense for gathers).

I was worried about the possible alias effect of moving gathers
around to be part of the same SLP group.  The patch therefore
makes vect_analyze_data_ref_dependence treat gathers and scatters
as a top-level concern, punting if the accesses aren't completely
independent and if the user hasn't told us that a particular
VF is safe.  I think in practice we already punted in the same
circumstances; the idea is just to make it more explicit.

gcc/
	PR tree-optimization/102467
	* doc/sourcebuild.texi (vect_gather_load_ifn): Document.
	* tree-vect-data-refs.c (vect_analyze_data_ref_dependence):
	Commonize safelen handling.  Punt for anything involving
	gathers and scatters unless safelen says otherwise.
	* tree-vect-slp.c (arg1_map): New variable.
	(vect_get_operand_map): Handle IFN_GATHER_LOAD.
	(vect_build_slp_tree_1): Likewise.
	(vect_build_slp_tree_2): Likewise.
	(compatible_calls_p): If vect_get_operand_map returns nonnull,
	check that any skipped arguments are equal.
	(vect_slp_analyze_node_operations_1): Tighten reduction check.
	* tree-vect-stmts.c (check_load_store_for_partial_vectors): Take
	an ncopies argument.
	(vect_get_gather_scatter_ops): Take slp_node and ncopies arguments.
	Handle SLP nodes.
	(vectorizable_store, vectorizable_load): Adjust accordingly.

gcc/testsuite/
	* lib/target-supports.exp
	(check_effective_target_vect_gather_load_ifn): New target test.
	* gcc.dg/vect/vect-gather-1.c: New test.
	* gcc.dg/vect/vect-gather-2.c: Likewise.
	* gcc.target/aarch64/sve/gather_load_11.c: Likewise.

1 files changed, 30 insertions, 34 deletions

diff --git a/gcc/tree-vect-data-refs.c b/gcc/tree-vect-data-refs.c
index 888ad72..12a82cd 100644
--- a/gcc/tree-vect-data-refs.c
+++ b/gcc/tree-vect-data-refs.c
@@ -359,6 +359,20 @@ vect_analyze_data_ref_dependence (struct data_dependence_relation *ddr,
   lambda_vector dist_v;
   unsigned int loop_depth;
 
+  /* If user asserted safelen consecutive iterations can be
+     executed concurrently, assume independence.  */
+  auto apply_safelen = [&]()
+    {
+      if (loop->safelen >= 2)
+	{
+	  if ((unsigned int) loop->safelen < *max_vf)
+	    *max_vf = loop->safelen;
+	  LOOP_VINFO_NO_DATA_DEPENDENCIES (loop_vinfo) = false;
+	  return true;
+	}
+      return false;
+    };
+
   /* In loop analysis all data references should be vectorizable.  */
   if (!STMT_VINFO_VECTORIZABLE (stmtinfo_a)
       || !STMT_VINFO_VECTORIZABLE (stmtinfo_b))
@@ -393,26 +407,23 @@ vect_analyze_data_ref_dependence (struct data_dependence_relation *ddr,
 				 get_alias_set (DR_REF (drb))))
     return opt_result::success ();
 
+  if (STMT_VINFO_GATHER_SCATTER_P (stmtinfo_a)
+      || STMT_VINFO_GATHER_SCATTER_P (stmtinfo_b))
+    {
+      if (apply_safelen ())
+	return opt_result::success ();
+
+      return opt_result::failure_at
+	(stmtinfo_a->stmt,
+	 "possible alias involving gather/scatter between %T and %T\n",
+	 DR_REF (dra), DR_REF (drb));
+    }
+
   /* Unknown data dependence.  */
   if (DDR_ARE_DEPENDENT (ddr) == chrec_dont_know)
     {
-      /* If user asserted safelen consecutive iterations can be
-	 executed concurrently, assume independence.  */
-      if (loop->safelen >= 2)
-	{
-	  if ((unsigned int) loop->safelen < *max_vf)
-	    *max_vf = loop->safelen;
-	  LOOP_VINFO_NO_DATA_DEPENDENCIES (loop_vinfo) = false;
-	  return opt_result::success ();
-	}
-
-      if (STMT_VINFO_GATHER_SCATTER_P (stmtinfo_a)
-	  || STMT_VINFO_GATHER_SCATTER_P (stmtinfo_b))
-	return opt_result::failure_at
-	  (stmtinfo_a->stmt,
-	   "versioning for alias not supported for: "
-	   "can't determine dependence between %T and %T\n",
-	   DR_REF (dra), DR_REF (drb));
+      if (apply_safelen ())
+	return opt_result::success ();
 
       if (dump_enabled_p ())
 	dump_printf_loc (MSG_MISSED_OPTIMIZATION, stmtinfo_a->stmt,
@@ -427,23 +438,8 @@ vect_analyze_data_ref_dependence (struct data_dependence_relation *ddr,
   /* Known data dependence.  */
   if (DDR_NUM_DIST_VECTS (ddr) == 0)
     {
-      /* If user asserted safelen consecutive iterations can be
-	 executed concurrently, assume independence.  */
-      if (loop->safelen >= 2)
-	{
-	  if ((unsigned int) loop->safelen < *max_vf)
-	    *max_vf = loop->safelen;
-	  LOOP_VINFO_NO_DATA_DEPENDENCIES (loop_vinfo) = false;
-	  return opt_result::success ();
-	}
-
-      if (STMT_VINFO_GATHER_SCATTER_P (stmtinfo_a)
-	  || STMT_VINFO_GATHER_SCATTER_P (stmtinfo_b))
-	return opt_result::failure_at
-	  (stmtinfo_a->stmt,
-	   "versioning for alias not supported for: "
-	   "bad dist vector for %T and %T\n",
-	   DR_REF (dra), DR_REF (drb));
+      if (apply_safelen ())
+	return opt_result::success ();
 
       if (dump_enabled_p ())
 	dump_printf_loc (MSG_MISSED_OPTIMIZATION, stmtinfo_a->stmt,