[PATCH] vec: Revert "dead code removal in tree-vect-loop.c" and add a comment.

[Andrea Corallo]

Hi Richard,

this reverts the discussed patch and adds what was suggested as a
comment.

Apologies for the inconvenience, okay for trunk?

Thanks

  Andrea


>From 84dfa2d461692f445f45b3c3498f9bedba5c3848 Mon Sep 17 00:00:00 2001
From: Andrea Corallo <andrea.cora...@arm.com>
Date: Mon, 7 Sep 2020 13:45:47 +0100
Subject: [PATCH] vec: Revert "dead code removal in tree-vect-loop.c" and add a
 comment.

gcc/ChangeLog

2020-09-07  Andrea Corallo  <andrea.cora...@arm.com>

        * tree-vect-loop.c (vect_estimate_min_profitable_iters): Revert
        dead-code removal introduced by 09fa6acd8d9 + add a comment to
        clarify.
---
 gcc/tree-vect-loop.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/gcc/tree-vect-loop.c b/gcc/tree-vect-loop.c
index 9a82573604b..5ba4e594df9 100644
--- a/gcc/tree-vect-loop.c
+++ b/gcc/tree-vect-loop.c
@@ -4103,6 +4103,8 @@ vect_estimate_min_profitable_iters (loop_vec_info 
loop_vinfo,
 
   if (vec_outside_cost <= 0)
     min_profitable_estimate = 0;
+  /* ??? This "else if" arm is written to handle all cases; see below for
+     what we would do for !LOOP_VINFO_USING_PARTIAL_VECTORS_P.  */
   else if (LOOP_VINFO_USING_PARTIAL_VECTORS_P (loop_vinfo))
     {
       /* This is a repeat of the code above, but with + SOC rather
@@ -4115,10 +4117,17 @@ vect_estimate_min_profitable_iters (loop_vec_info 
loop_vinfo,
       if (outside_overhead > 0)
        min_vec_niters = outside_overhead / saving_per_viter + 1;
 
-      int threshold = (vec_inside_cost * min_vec_niters
-                      + vec_outside_cost
-                      + scalar_outside_cost);
-      min_profitable_estimate = threshold / scalar_single_iter_cost + 1;
+      if (LOOP_VINFO_USING_PARTIAL_VECTORS_P (loop_vinfo))
+       {
+         int threshold = (vec_inside_cost * min_vec_niters
+                          + vec_outside_cost
+                          + scalar_outside_cost);
+         min_profitable_estimate = threshold / scalar_single_iter_cost + 1;
+       }
+      else
+       min_profitable_estimate = (min_vec_niters * assumed_vf
+                                  + peel_iters_prologue
+                                  + peel_iters_epilogue);
     }
   else
     {
-- 
2.17.1