[gcc r12-3921] reassoc: Do not bias loop-carried PHIs early

[Ilya Leoshkevich]

https://gcc.gnu.org/g:99c106e695bd8f1de580c4ff0b1d3fe59c9a4f1e

commit r12-3921-g99c106e695bd8f1de580c4ff0b1d3fe59c9a4f1e
Author: Ilya Leoshkevich <iii@linux.ibm.com>
Date:   Tue Sep 14 20:41:18 2021 +0200

    reassoc: Do not bias loop-carried PHIs early
    
    Biasing loop-carried PHIs during the 1st reassociation pass interferes
    with reduction chains and does not bring measurable benefits, so do it
    only during the 2nd reassociation pass.
    
    gcc/ChangeLog:
    
            * passes.def (pass_reassoc): Rename parameter to early_p.
            * tree-ssa-reassoc.c (reassoc_bias_loop_carried_phi_ranks_p):
            New variable.
            (phi_rank): Don't bias loop-carried phi ranks
            before vectorization pass.
            (execute_reassoc): Add bias_loop_carried_phi_ranks_p parameter.
            (pass_reassoc::pass_reassoc): Add bias_loop_carried_phi_ranks_p
            initializer.
            (pass_reassoc::set_param): Set bias_loop_carried_phi_ranks_p
            value.
            (pass_reassoc::execute): Pass bias_loop_carried_phi_ranks_p to
            execute_reassoc.
            (pass_reassoc::bias_loop_carried_phi_ranks_p): New member.

Diff:
---
 gcc/passes.def         |  4 ++--
 gcc/tree-ssa-reassoc.c | 16 ++++++++++++++--
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/gcc/passes.def b/gcc/passes.def
index 9115da7beb6..c11c237f6d2 100644
--- a/gcc/passes.def
+++ b/gcc/passes.def
@@ -243,7 +243,7 @@ along with GCC; see the file COPYING3.  If not see
       /* Identify paths that should never be executed in a conforming
 	 program and isolate those paths.  */
       NEXT_PASS (pass_isolate_erroneous_paths);
-      NEXT_PASS (pass_reassoc, true /* insert_powi_p */);
+      NEXT_PASS (pass_reassoc, true /* early_p */);
       NEXT_PASS (pass_dce);
       NEXT_PASS (pass_forwprop);
       NEXT_PASS (pass_phiopt, false /* early_p */);
@@ -326,7 +326,7 @@ along with GCC; see the file COPYING3.  If not see
       NEXT_PASS (pass_lower_vector_ssa);
       NEXT_PASS (pass_lower_switch);
       NEXT_PASS (pass_cse_reciprocals);
-      NEXT_PASS (pass_reassoc, false /* insert_powi_p */);
+      NEXT_PASS (pass_reassoc, false /* early_p */);
       NEXT_PASS (pass_strength_reduction);
       NEXT_PASS (pass_split_paths);
       NEXT_PASS (pass_tracer);
diff --git a/gcc/tree-ssa-reassoc.c b/gcc/tree-ssa-reassoc.c
index 8498cfc7aa8..420c14e8cf5 100644
--- a/gcc/tree-ssa-reassoc.c
+++ b/gcc/tree-ssa-reassoc.c
@@ -180,6 +180,10 @@ along with GCC; see the file COPYING3.  If not see
    point 3a in the pass header comment.  */
 static bool reassoc_insert_powi_p;
 
+/* Enable biasing ranks of loop accumulators.  We don't want this before
+   vectorization, since it interferes with reduction chains.  */
+static bool reassoc_bias_loop_carried_phi_ranks_p;
+
 /* Statistics */
 static struct
 {
@@ -269,6 +273,9 @@ phi_rank (gimple *stmt)
   use_operand_p use;
   gimple *use_stmt;
 
+  if (!reassoc_bias_loop_carried_phi_ranks_p)
+    return bb_rank[bb->index];
+
   /* We only care about real loops (those with a latch).  */
   if (!father->latch)
     return bb_rank[bb->index];
@@ -6940,9 +6947,10 @@ fini_reassoc (void)
    optimization of a gimple conditional.  Otherwise returns zero.  */
 
 static unsigned int
-execute_reassoc (bool insert_powi_p)
+execute_reassoc (bool insert_powi_p, bool bias_loop_carried_phi_ranks_p)
 {
   reassoc_insert_powi_p = insert_powi_p;
+  reassoc_bias_loop_carried_phi_ranks_p = bias_loop_carried_phi_ranks_p;
 
   init_reassoc ();
 
@@ -6983,15 +6991,19 @@ public:
     {
       gcc_assert (n == 0);
       insert_powi_p = param;
+      bias_loop_carried_phi_ranks_p = !param;
     }
   virtual bool gate (function *) { return flag_tree_reassoc != 0; }
   virtual unsigned int execute (function *)
-    { return execute_reassoc (insert_powi_p); }
+  {
+    return execute_reassoc (insert_powi_p, bias_loop_carried_phi_ranks_p);
+  }
 
  private:
   /* Enable insertion of __builtin_powi calls during execute_reassoc.  See
      point 3a in the pass header comment.  */
   bool insert_powi_p;
+  bool bias_loop_carried_phi_ranks_p;
 }; // class pass_reassoc
 
 } // anon namespace