[11a/n] Avoid retrying with the same vector modes

[Richard Sandiford <richard.sandiford@arm.com>]

Patch 12/n makes the AArch64 port add four entries to
autovectorize_vector_modes.  Each entry describes a different
vector mode assignment for vector code that mixes 8-bit, 16-bit,
32-bit and 64-bit elements.  But if (as usual) the vector code has
fewer element sizes than that, we could end up trying the same
combination of vector modes multiple times.  This patch adds a
check to prevent that.

As before: each patch tested individually on aarch64-linux-gnu and the
series as a whole on x86_64-linux-gnu.


2019-11-04  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* tree-vectorizer.h (vec_info::mode_set): New typedef.
	(vec_info::used_vector_mode): New member variable.
	(vect_chooses_same_modes_p): Declare.
	* tree-vect-stmts.c (get_vectype_for_scalar_type): Record each
	chosen vector mode in vec_info::used_vector_mode.
	(vect_chooses_same_modes_p): New function.
	* tree-vect-loop.c (vect_analyze_loop): Use it to avoid trying
	the same vector statements multiple times.
	* tree-vect-slp.c (vect_slp_bb_region): Likewise.

Index: gcc/tree-vectorizer.h
===================================================================
--- gcc/tree-vectorizer.h	2019-11-05 10:48:11.246092351 +0000
+++ gcc/tree-vectorizer.h	2019-11-05 10:57:41.662071145 +0000
@@ -298,6 +298,7 @@ typedef std::pair<tree, tree> vec_object
 /* Vectorizer state common between loop and basic-block vectorization.  */
 class vec_info {
 public:
+  typedef hash_set<int_hash<machine_mode, E_VOIDmode, E_BLKmode> > mode_set;
   enum vec_kind { bb, loop };
 
   vec_info (vec_kind, void *, vec_info_shared *);
@@ -335,6 +336,9 @@ typedef std::pair<tree, tree> vec_object
   /* Cost data used by the target cost model.  */
   void *target_cost_data;
 
+  /* The set of vector modes used in the vectorized region.  */
+  mode_set used_vector_modes;
+
   /* The argument we should pass to related_vector_mode when looking up
      the vector mode for a scalar mode, or VOIDmode if we haven't yet
      made any decisions about which vector modes to use.  */
@@ -1615,6 +1619,7 @@ extern tree get_related_vectype_for_scal
 extern tree get_vectype_for_scalar_type (vec_info *, tree);
 extern tree get_mask_type_for_scalar_type (vec_info *, tree);
 extern tree get_same_sized_vectype (tree, tree);
+extern bool vect_chooses_same_modes_p (vec_info *, machine_mode);
 extern bool vect_get_loop_mask_type (loop_vec_info);
 extern bool vect_is_simple_use (tree, vec_info *, enum vect_def_type *,
 				stmt_vec_info * = NULL, gimple ** = NULL);
Index: gcc/tree-vect-stmts.c
===================================================================
--- gcc/tree-vect-stmts.c	2019-11-05 10:48:11.242092379 +0000
+++ gcc/tree-vect-stmts.c	2019-11-05 10:57:41.662071145 +0000
@@ -11235,6 +11235,10 @@ get_vectype_for_scalar_type (vec_info *v
 						      scalar_type);
   if (vectype && vinfo->vector_mode == VOIDmode)
     vinfo->vector_mode = TYPE_MODE (vectype);
+
+  if (vectype)
+    vinfo->used_vector_modes.add (TYPE_MODE (vectype));
+
   return vectype;
 }
 
@@ -11274,6 +11278,20 @@ get_same_sized_vectype (tree scalar_type
 					      scalar_type, nunits);
 }
 
+/* Return true if replacing LOOP_VINFO->vector_mode with VECTOR_MODE
+   would not change the chosen vector modes.  */
+
+bool
+vect_chooses_same_modes_p (vec_info *vinfo, machine_mode vector_mode)
+{
+  for (vec_info::mode_set::iterator i = vinfo->used_vector_modes.begin ();
+       i != vinfo->used_vector_modes.end (); ++i)
+    if (!VECTOR_MODE_P (*i)
+	|| related_vector_mode (vector_mode, GET_MODE_INNER (*i), 0) != *i)
+      return false;
+  return true;
+}
+
 /* Function vect_is_simple_use.
 
    Input:
Index: gcc/tree-vect-loop.c
===================================================================
--- gcc/tree-vect-loop.c	2019-11-05 10:48:11.238092407 +0000
+++ gcc/tree-vect-loop.c	2019-11-05 10:57:41.658071173 +0000
@@ -2430,6 +2430,19 @@ vect_analyze_loop (class loop *loop, vec
 	}
 
       loop->aux = NULL;
+
+      if (!fatal)
+	while (mode_i < vector_modes.length ()
+	       && vect_chooses_same_modes_p (loop_vinfo, vector_modes[mode_i]))
+	  {
+	    if (dump_enabled_p ())
+	      dump_printf_loc (MSG_NOTE, vect_location,
+			       "***** The result for vector mode %s would"
+			       " be the same\n",
+			       GET_MODE_NAME (vector_modes[mode_i]));
+	    mode_i += 1;
+	  }
+
       if (res)
 	{
 	  LOOP_VINFO_VECTORIZABLE_P (loop_vinfo) = 1;
Index: gcc/tree-vect-slp.c
===================================================================
--- gcc/tree-vect-slp.c	2019-11-05 10:48:11.242092379 +0000
+++ gcc/tree-vect-slp.c	2019-11-05 10:57:41.662071145 +0000
@@ -3238,6 +3238,18 @@ vect_slp_bb_region (gimple_stmt_iterator
       if (mode_i == 0)
 	autodetected_vector_mode = bb_vinfo->vector_mode;
 
+      if (!fatal)
+	while (mode_i < vector_modes.length ()
+	       && vect_chooses_same_modes_p (bb_vinfo, vector_modes[mode_i]))
+	  {
+	    if (dump_enabled_p ())
+	      dump_printf_loc (MSG_NOTE, vect_location,
+			       "***** The result for vector mode %s would"
+			       " be the same\n",
+			       GET_MODE_NAME (vector_modes[mode_i]));
+	    mode_i += 1;
+	  }
+
       delete bb_vinfo;
 
       if (mode_i < vector_modes.length ()