This patch is no difference from V2.
Just add PR tree-optimization/109971 as Kewen's suggested.

Already bootstrapped and Regression on X86 no difference.

Ok for trunk ?


juzhe.zhong@rivai.ai
 
From: juzhe.zhong
Date: 2023-06-01 12:36
To: gcc-patches
CC: richard.sandiford; rguenther; linkw; Ju-Zhe Zhong
Subject: [PATCH V3] VECT: Change flow of decrement IV
From: Ju-Zhe Zhong <juzhe.zhong@rivai.ai>
 
Follow Richi's suggestion, I change current decrement IV flow from:
 
do {
   remain -= MIN (vf, remain);
} while (remain != 0);
 
into:
 
do {
   old_remain = remain;
   len = MIN (vf, remain);
   remain -= vf;
} while (old_remain >= vf);
 
to enhance SCEV.
 
Include fixes from kewen.
 
 
This patch will need to wait for Kewen's test feedback.
 
Testing on X86 is on-going
 
Co-Authored by: Kewen Lin  <linkw@linux.ibm.com>
 
  PR tree-optimization/109971
 
gcc/ChangeLog:
 
        * tree-vect-loop-manip.cc (vect_set_loop_controls_directly): Change decrement IV flow.
        (vect_set_loop_condition_partial_vectors): Ditto.
 
---
gcc/tree-vect-loop-manip.cc | 36 +++++++++++++++++++++++++-----------
1 file changed, 25 insertions(+), 11 deletions(-)
 
diff --git a/gcc/tree-vect-loop-manip.cc b/gcc/tree-vect-loop-manip.cc
index acf3642ceb2..3f735945e67 100644
--- a/gcc/tree-vect-loop-manip.cc
+++ b/gcc/tree-vect-loop-manip.cc
@@ -483,7 +483,7 @@ vect_set_loop_controls_directly (class loop *loop, loop_vec_info loop_vinfo,
gimple_stmt_iterator loop_cond_gsi,
rgroup_controls *rgc, tree niters,
tree niters_skip, bool might_wrap_p,
- tree *iv_step)
+ tree *iv_step, tree *compare_step)
{
   tree compare_type = LOOP_VINFO_RGROUP_COMPARE_TYPE (loop_vinfo);
   tree iv_type = LOOP_VINFO_RGROUP_IV_TYPE (loop_vinfo);
@@ -538,9 +538,9 @@ vect_set_loop_controls_directly (class loop *loop, loop_vec_info loop_vinfo,
   ...
   vect__4.8_28 = .LEN_LOAD (_17, 32B, _36, 0);
   ...
-    ivtmp_35 = ivtmp_9 - _36;
+    ivtmp_35 = ivtmp_9 - POLY_INT_CST [4, 4];
   ...
-    if (ivtmp_35 != 0)
+    if (ivtmp_9 > POLY_INT_CST [4, 4])
     goto <bb 4>; [83.33%]
   else
     goto <bb 5>; [16.67%]
@@ -549,13 +549,15 @@ vect_set_loop_controls_directly (class loop *loop, loop_vec_info loop_vinfo,
       tree step = rgc->controls.length () == 1 ? rgc->controls[0]
       : make_ssa_name (iv_type);
       /* Create decrement IV.  */
-      create_iv (nitems_total, MINUS_EXPR, step, NULL_TREE, loop, &incr_gsi,
- insert_after, &index_before_incr, &index_after_incr);
+      create_iv (nitems_total, MINUS_EXPR, nitems_step, NULL_TREE, loop,
+ &incr_gsi, insert_after, &index_before_incr,
+ &index_after_incr);
       gimple_seq_add_stmt (header_seq, gimple_build_assign (step, MIN_EXPR,
    index_before_incr,
    nitems_step));
       *iv_step = step;
-      return index_after_incr;
+      *compare_step = nitems_step;
+      return index_before_incr;
     }
   /* Create increment IV.  */
@@ -825,6 +827,7 @@ vect_set_loop_condition_partial_vectors (class loop *loop,
      arbitrarily pick the last.  */
   tree test_ctrl = NULL_TREE;
   tree iv_step = NULL_TREE;
+  tree compare_step = NULL_TREE;
   rgroup_controls *rgc;
   rgroup_controls *iv_rgc = nullptr;
   unsigned int i;
@@ -861,7 +864,7 @@ vect_set_loop_condition_partial_vectors (class loop *loop,
&preheader_seq, &header_seq,
loop_cond_gsi, rgc, niters,
niters_skip, might_wrap_p,
- &iv_step);
+ &iv_step, &compare_step);
    iv_rgc = rgc;
  }
@@ -884,10 +887,21 @@ vect_set_loop_condition_partial_vectors (class loop *loop,
   /* Get a boolean result that tells us whether to iterate.  */
   edge exit_edge = single_exit (loop);
-  tree_code code = (exit_edge->flags & EDGE_TRUE_VALUE) ? EQ_EXPR : NE_EXPR;
-  tree zero_ctrl = build_zero_cst (TREE_TYPE (test_ctrl));
-  gcond *cond_stmt = gimple_build_cond (code, test_ctrl, zero_ctrl,
- NULL_TREE, NULL_TREE);
+  gcond *cond_stmt;
+  if (LOOP_VINFO_USING_DECREMENTING_IV_P (loop_vinfo))
+    {
+      gcc_assert (compare_step);
+      tree_code code = (exit_edge->flags & EDGE_TRUE_VALUE) ? LE_EXPR : GT_EXPR;
+      cond_stmt = gimple_build_cond (code, test_ctrl, compare_step, NULL_TREE,
+      NULL_TREE);
+    }
+  else
+    {
+      tree_code code = (exit_edge->flags & EDGE_TRUE_VALUE) ? EQ_EXPR : NE_EXPR;
+      tree zero_ctrl = build_zero_cst (TREE_TYPE (test_ctrl));
+      cond_stmt
+ = gimple_build_cond (code, test_ctrl, zero_ctrl, NULL_TREE, NULL_TREE);
+    }
   gsi_insert_before (&loop_cond_gsi, cond_stmt, GSI_SAME_STMT);
   /* The loop iterates (NITERS - 1) / VF + 1 times.
-- 
2.36.3