[gcc r13-1323] Speedup loop splitting SSA update

[gcc r13-1323] Speedup loop splitting SSA update

[Richard Biener]

https://gcc.gnu.org/g:8354d0abeb7646e109b2fb982afbc253644b0925

commit r13-1323-g8354d0abeb7646e109b2fb982afbc253644b0925
Author: Richard Biener <rguenther@suse.de>
Date:   Tue Jun 28 12:07:14 2022 +0200

    Speedup loop splitting SSA update
    
    Since we never process loops with inner loops that have been split
    we can delay SSA update until after the pass is done with the whole
    loop, avoiding the O(function-size) work associated with it.
    
    2022-06-28  Richard Biener  <rguenther@suse.de>
    
            * tree-ssa-loop-split.cc (fix_loop_bb_probability): Do not
            call update_ssa.

Diff:
---
 gcc/tree-ssa-loop-split.cc | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/gcc/tree-ssa-loop-split.cc b/gcc/tree-ssa-loop-split.cc
index d61bad5ba47..bccf621493b 100644
--- a/gcc/tree-ssa-loop-split.cc
+++ b/gcc/tree-ssa-loop-split.cc
@@ -491,8 +491,6 @@ static void
 fix_loop_bb_probability (class loop *loop1, class loop *loop2, edge true_edge,
 			 edge false_edge)
 {
-  update_ssa (TODO_update_ssa);
-
   /* Proportion first loop's bb counts except those dominated by true
      branch to avoid drop 1s down.  */
   basic_block *bbs1, *bbs2;
@@ -1668,7 +1666,8 @@ tree_ssa_split_loops (void)
       if (loop->aux)
 	{
 	  /* If any of our inner loops was split, don't split us,
-	     and mark our containing loop as having had splits as well.  */
+	     and mark our containing loop as having had splits as well.
+	     This allows for delaying SSA update.  */
 	  loop_outer (loop)->aux = loop;
 	  continue;
 	}