[gcc r12-9256] middle-end/108500 - replace recursive domtree DFS traversal

[gcc r12-9256] middle-end/108500 - replace recursive domtree DFS traversal

[Richard Biener]

https://gcc.gnu.org/g:b955080a5ab8690902f7cc99a770f9c3da171d6f

commit r12-9256-gb955080a5ab8690902f7cc99a770f9c3da171d6f
Author: Richard Biener <rguenther@suse.de>
Date:   Tue Jan 31 15:45:43 2023 +0100

    middle-end/108500 - replace recursive domtree DFS traversal
    
    The following replaces the recursive DFS traversal of the dominator
    tree in assign_dfs_numbers with a tree traversal using the fact
    that we have recorded parents.
    
    Bootstrapped and tested on x86_64-unknown-linux-gnu.
    
    This makes r13-5325 somewhat obsolete, though not computing the
    DFS numbers at all is beneficial in the cases where we perform
    immediate CFG manipulations.
    
    OK for trunk and later branch(es)?
    
    Thanks,
    Richard.
    
            PR middle-end/108500
            * dominance.cc (assign_dfs_numbers): Replace recursive DFS
            with tree traversal algorithm.
    
    (cherry picked from commit 97258480438db77e52f4b3947fa2c075b09d3fe1)

Diff:
---
 gcc/dominance.cc | 27 +++++++++++++++++----------
 1 file changed, 17 insertions(+), 10 deletions(-)

diff --git a/gcc/dominance.cc b/gcc/dominance.cc
index 09d12d0f618..60b19637935 100644
--- a/gcc/dominance.cc
+++ b/gcc/dominance.cc
@@ -639,18 +639,25 @@ dom_info::calc_idoms ()
 static void
 assign_dfs_numbers (struct et_node *node, int *num)
 {
-  struct et_node *son;
-
-  node->dfs_num_in = (*num)++;
-
-  if (node->son)
+  et_node *n = node;
+  while (1)
     {
-      assign_dfs_numbers (node->son, num);
-      for (son = node->son->right; son != node->son; son = son->right)
-	assign_dfs_numbers (son, num);
+      n->dfs_num_in = (*num)++;
+      if (n->son)
+	n = n->son;
+      else
+	{
+	  while (!n->right || n->right == n->father->son)
+	    {
+	      n->dfs_num_out = (*num)++;
+	      if (n == node)
+		return;
+	      n = n->father;
+	    }
+	  n->dfs_num_out = (*num)++;
+	  n = n->right;
+	}
     }
-
-  node->dfs_num_out = (*num)++;
 }
 
 /* Compute the data necessary for fast resolving of dominator queries in a