[gcc r12-8205] tree-optimization/104912 - ensure cost model is checked first

[gcc r12-8205] tree-optimization/104912 - ensure cost model is checked first

[Richard Biener]

https://gcc.gnu.org/g:4d4eaa77a7d27bf7b220c3be79615410c873fcf1

commit r12-8205-g4d4eaa77a7d27bf7b220c3be79615410c873fcf1
Author: Richard Biener <rguenther@suse.de>
Date:   Mon Mar 21 14:08:25 2022 +0100

    tree-optimization/104912 - ensure cost model is checked first
    
    The following makes sure that when we build the versioning condition
    for vectorization including the cost model check, we check for the
    cost model and branch over other versioning checks.  That is what
    the cost modeling assumes, since the cost model check is the only
    one accounted for in the scalar outside cost.  Currently we emit
    all checks as straight-line code combined with bitwise ops which
    can result in surprising ordering of checks in the final assembly.
    
    Since loop_version accepts only a single versioning condition
    the splitting is done after the fact.
    
    The result is a 1.5% speedup of 416.gamess on x86_64 when compiling
    with -Ofast and tuning for generic or skylake.  That's not enough
    to recover from the slowdown when vectorizing but it now cuts off
    the expensive alias versioning test.
    
    2022-03-21  Richard Biener  <rguenther@suse.de>
    
            PR tree-optimization/104912
            * tree-vect-loop-manip.cc (vect_loop_versioning): Split
            the cost model check to a separate BB to make sure it is
            checked first and not combined with other version checks.

Diff:
---
 gcc/tree-vect-loop-manip.cc | 60 ++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 57 insertions(+), 3 deletions(-)

diff --git a/gcc/tree-vect-loop-manip.cc b/gcc/tree-vect-loop-manip.cc
index 63fb6f669a0..e4381eb7079 100644
--- a/gcc/tree-vect-loop-manip.cc
+++ b/gcc/tree-vect-loop-manip.cc
@@ -3445,13 +3445,34 @@ vect_loop_versioning (loop_vec_info loop_vinfo,
 	cond_expr = expr;
     }
 
+  tree cost_name = NULL_TREE;
+  profile_probability prob2 = profile_probability::uninitialized ();
+  if (cond_expr
+      && !integer_truep (cond_expr)
+      && (version_niter
+	  || version_align
+	  || version_alias
+	  || version_simd_if_cond))
+    {
+      cost_name = cond_expr = force_gimple_operand_1 (unshare_expr (cond_expr),
+						      &cond_expr_stmt_list,
+						      is_gimple_val, NULL_TREE);
+      /* Split prob () into two so that the overall probability of passing
+	 both the cost-model and versioning checks is the orig prob.  */
+      prob2 = prob.split (prob);
+    }
+
   if (version_niter)
     vect_create_cond_for_niters_checks (loop_vinfo, &cond_expr);
 
   if (cond_expr)
-    cond_expr = force_gimple_operand_1 (unshare_expr (cond_expr),
-					&cond_expr_stmt_list,
-					is_gimple_condexpr, NULL_TREE);
+    {
+      gimple_seq tem = NULL;
+      cond_expr = force_gimple_operand_1 (unshare_expr (cond_expr),
+					  &tem,
+					  is_gimple_condexpr, NULL_TREE);
+      gimple_seq_add_seq (&cond_expr_stmt_list, tem);
+    }
 
   if (version_align)
     vect_create_cond_for_align_checks (loop_vinfo, &cond_expr,
@@ -3655,6 +3676,39 @@ vect_loop_versioning (loop_vec_info loop_vinfo,
       update_ssa (TODO_update_ssa);
     }
 
+  /* Split the cost model check off to a separate BB.  Costing assumes
+     this is the only thing we perform when we enter the scalar loop
+     from a failed cost decision.  */
+  if (cost_name && TREE_CODE (cost_name) == SSA_NAME)
+    {
+      gimple *def = SSA_NAME_DEF_STMT (cost_name);
+      /* All uses of the cost check are 'true' after the check we
+	 are going to insert.  */
+      replace_uses_by (cost_name, boolean_true_node);
+      /* And we're going to build the new single use of it.  */
+      gcond *cond = gimple_build_cond (NE_EXPR, cost_name, boolean_false_node,
+				       NULL_TREE, NULL_TREE);
+      edge e = split_block (gimple_bb (def), def);
+      gimple_stmt_iterator gsi = gsi_for_stmt (def);
+      gsi_insert_after (&gsi, cond, GSI_NEW_STMT);
+      edge true_e, false_e;
+      extract_true_false_edges_from_block (e->dest, &true_e, &false_e);
+      e->flags &= ~EDGE_FALLTHRU;
+      e->flags |= EDGE_TRUE_VALUE;
+      edge e2 = make_edge (e->src, false_e->dest, EDGE_FALSE_VALUE);
+      e->probability = prob2;
+      e2->probability = prob2.invert ();
+      set_immediate_dominator (CDI_DOMINATORS, false_e->dest, e->src);
+      auto_vec<basic_block, 3> adj;
+      for (basic_block son = first_dom_son (CDI_DOMINATORS, e->dest);
+	   son;
+	   son = next_dom_son (CDI_DOMINATORS, son))
+	if (EDGE_COUNT (son->preds) > 1)
+	  adj.safe_push (son);
+      for (auto son : adj)
+	set_immediate_dominator (CDI_DOMINATORS, son, e->src);
+    }
+
   if (version_niter)
     {
       /* The versioned loop could be infinite, we need to clear existing