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 --git a/gcc/tree-ssa-loop-split.cc b/gcc/tree-ssa-loop-split.cc
index d61bad5ba47bbbabb6461b3b3b16a4f5c59853ba..bccf621493b00d693fb72c962dd7f09da07e9a1a 100644 (file)
--- 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;
        }