[gcc r12-3362] tree-optimization/102176 - locally compute participating SLP stmts

[Richard Biener <rguenth@gcc.gnu.org>]

https://gcc.gnu.org/g:a3fb781d4b341c0d50ef1b92cd3e8734e673ef18

commit r12-3362-ga3fb781d4b341c0d50ef1b92cd3e8734e673ef18
Author: Richard Biener <rguenther@suse.de>
Date:   Thu Sep 2 14:48:10 2021 +0200

    tree-optimization/102176 - locally compute participating SLP stmts
    
    This performs local re-computation of participating scalar stmts
    in BB vectorization subgraphs to allow precise computation of
    liveness of scalar stmts after vectorization and thus precise
    costing.  This treats all extern defs as live but continues
    to optimistically handle scalar defs that we think we can handle
    by lane-extraction even though that can still fail late during
    code-generation.
    
    2021-09-02  Richard Biener  <rguenther@suse.de>
    
            PR tree-optimization/102176
            * tree-vect-slp.c (vect_slp_gather_vectorized_scalar_stmts):
            New function.
            (vect_bb_slp_scalar_cost): Use the computed set of
            vectorized scalar stmts instead of relying on the out-of-date
            and not accurate PURE_SLP_STMT.
            (vect_bb_vectorization_profitable_p): Compute the set
            of vectorized scalar stmts.

Diff:
---
 gcc/tree-vect-slp.c | 69 +++++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 64 insertions(+), 5 deletions(-)

diff --git a/gcc/tree-vect-slp.c b/gcc/tree-vect-slp.c
index fa3566f3d06..024a1c38a23 100644
--- a/gcc/tree-vect-slp.c
+++ b/gcc/tree-vect-slp.c
@@ -5104,6 +5104,42 @@ vect_bb_partition_graph (bb_vec_info bb_vinfo)
     }
 }
 
+/* Compute the set of scalar stmts participating in internal and external
+   nodes.  */
+
+static void
+vect_slp_gather_vectorized_scalar_stmts (vec_info *vinfo, slp_tree node,
+					 hash_set<slp_tree> &visited,
+					 hash_set<stmt_vec_info> &vstmts,
+					 hash_set<stmt_vec_info> &estmts)
+{
+  int i;
+  stmt_vec_info stmt_info;
+  slp_tree child;
+
+  if (visited.add (node))
+    return;
+
+  if (SLP_TREE_DEF_TYPE (node) == vect_internal_def)
+    {
+      FOR_EACH_VEC_ELT (SLP_TREE_SCALAR_STMTS (node), i, stmt_info)
+	vstmts.add (stmt_info);
+
+      FOR_EACH_VEC_ELT (SLP_TREE_CHILDREN (node), i, child)
+	if (child)
+	  vect_slp_gather_vectorized_scalar_stmts (vinfo, child, visited,
+						   vstmts, estmts);
+    }
+  else
+    for (tree def : SLP_TREE_SCALAR_OPS (node))
+      {
+	stmt_vec_info def_stmt = vinfo->lookup_def (def);
+	if (def_stmt)
+	  estmts.add (def_stmt);
+      }
+}
+
+
 /* Compute the scalar cost of the SLP node NODE and its children
    and return it.  Do not account defs that are marked in LIFE and
    update LIFE according to uses of NODE.  */
@@ -5112,6 +5148,7 @@ static void
 vect_bb_slp_scalar_cost (vec_info *vinfo,
 			 slp_tree node, vec<bool, va_heap> *life,
 			 stmt_vector_for_cost *cost_vec,
+			 hash_set<stmt_vec_info> &vectorized_scalar_stmts,
 			 hash_set<slp_tree> &visited)
 {
   unsigned i;
@@ -5148,8 +5185,7 @@ vect_bb_slp_scalar_cost (vec_info *vinfo,
 		  {
 		    stmt_vec_info use_stmt_info = vinfo->lookup_stmt (use_stmt);
 		    if (!use_stmt_info
-			|| !PURE_SLP_STMT
-			      (vect_stmt_to_vectorize (use_stmt_info)))
+			|| !vectorized_scalar_stmts.contains (use_stmt_info))
 		      {
 			(*life)[i] = true;
 			break;
@@ -5212,7 +5248,7 @@ vect_bb_slp_scalar_cost (vec_info *vinfo,
 	      subtree_life.safe_splice (*life);
 	    }
 	  vect_bb_slp_scalar_cost (vinfo, child, &subtree_life, cost_vec,
-				   visited);
+				   vectorized_scalar_stmts, visited);
 	  subtree_life.truncate (0);
 	}
     }
@@ -5254,11 +5290,33 @@ vect_bb_vectorization_profitable_p (bb_vec_info bb_vinfo,
 			      SLP_INSTANCE_TREE (instance), visited);
     }
 
+  /* Compute the set of scalar stmts we know will go away 'locally' when
+     vectorizing.  This used to be tracked with just PURE_SLP_STMT but that's
+     not accurate for nodes promoted extern late or for scalar stmts that
+     are used both in extern defs and in vectorized defs.  */
+  hash_set<stmt_vec_info> vectorized_scalar_stmts;
+  hash_set<stmt_vec_info> scalar_stmts_in_externs;
+  hash_set<slp_tree> visited;
+  FOR_EACH_VEC_ELT (slp_instances, i, instance)
+    {
+      vect_slp_gather_vectorized_scalar_stmts (bb_vinfo,
+					       SLP_INSTANCE_TREE (instance),
+					       visited,
+					       vectorized_scalar_stmts,
+					       scalar_stmts_in_externs);
+      for (stmt_vec_info rstmt : SLP_INSTANCE_ROOT_STMTS (instance))
+	vectorized_scalar_stmts.add (rstmt);
+    }
+  /* Scalar stmts used as defs in external nodes need to be preseved, so
+     remove them from vectorized_scalar_stmts.  */
+  for (stmt_vec_info stmt : scalar_stmts_in_externs)
+    vectorized_scalar_stmts.remove (stmt);
+
   /* Calculate scalar cost and sum the cost for the vector stmts
      previously collected.  */
   stmt_vector_for_cost scalar_costs = vNULL;
   stmt_vector_for_cost vector_costs = vNULL;
-  hash_set<slp_tree> visited;
+  visited.empty ();
   FOR_EACH_VEC_ELT (slp_instances, i, instance)
     {
       auto_vec<bool, 20> life;
@@ -5271,7 +5329,8 @@ vect_bb_vectorization_profitable_p (bb_vec_info bb_vinfo,
 			  SLP_INSTANCE_ROOT_STMTS (instance)[0], 0, vect_body);
       vect_bb_slp_scalar_cost (bb_vinfo,
 			       SLP_INSTANCE_TREE (instance),
-			       &life, &scalar_costs, visited);
+			       &life, &scalar_costs, vectorized_scalar_stmts,
+			       visited);
       vector_costs.safe_splice (instance->cost_vec);
       instance->cost_vec.release ();
     }