[gcc r10-9756] remove write-only array in rev_post_order_and_mark_dfs_back_seme

[gcc r10-9756] remove write-only array in rev_post_order_and_mark_dfs_back_seme

[Richard Biener]

https://gcc.gnu.org/g:9db2c895fe2cb2aba61f6ef006c6f6c46ef07521

commit r10-9756-g9db2c895fe2cb2aba61f6ef006c6f6c46ef07521
Author: Richard Biener <rguenther@suse.de>
Date:   Mon Jul 20 15:58:19 2020 +0200

    remove write-only array in rev_post_order_and_mark_dfs_back_seme
    
    This removes a write-only array in
    rev_post_order_and_mark_dfs_back_seme.
    
    2020-07-20  Richard Biener  <rguenther@suse.de>
    
            * cfganal.c (rev_post_order_and_mark_dfs_back_seme): Remove
            write-only post array.
    
    (cherry picked from commit 57d4771b7c15db139043bf41a03b8abe01e11f18)

Diff:
---
 gcc/cfganal.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/gcc/cfganal.c b/gcc/cfganal.c
index 395b810262a..5c85ebe3c1a 100644
--- a/gcc/cfganal.c
+++ b/gcc/cfganal.c
@@ -1079,13 +1079,12 @@ rev_post_order_and_mark_dfs_back_seme (struct function *fn, edge entry,
      a need to re-allocate.  */
   auto_vec<edge, 20> stack (2 * n_basic_blocks_for_fn (fn));
 
-  int *pre = XNEWVEC (int, 2 * last_basic_block_for_fn (fn));
-  int *post = pre + last_basic_block_for_fn (fn);
+  int *pre = XNEWVEC (int, last_basic_block_for_fn (fn));
 
   /* BB flag to track nodes that have been visited.  */
   auto_bb_flag visited (fn);
-  /* BB flag to track which nodes have post[] assigned to avoid
-     zeroing post.  */
+  /* BB flag to track which nodes have postorder visting completed.  Used
+     for backedge marking.  */
   auto_bb_flag post_assigned (fn);
 
   /* Push the first edge on to the stack.  */
@@ -1133,7 +1132,6 @@ rev_post_order_and_mark_dfs_back_seme (struct function *fn, edge entry,
 	    {
 	      /* There are no successors for the DEST node so assign
 		 its reverse completion number.  */
-	      post[dest->index] = rev_post_order_num;
 	      dest->flags |= post_assigned;
 	      rev_post_order[rev_post_order_num] = dest->index;
 	      rev_post_order_num++;
@@ -1142,16 +1140,15 @@ rev_post_order_and_mark_dfs_back_seme (struct function *fn, edge entry,
       else
 	{
 	  if (dest->flags & visited
+	      && !(dest->flags & post_assigned)
 	      && src != entry->src
-	      && pre[src->index] >= pre[dest->index]
-	      && !(dest->flags & post_assigned))
+	      && pre[src->index] >= pre[dest->index])
 	    e->flags |= EDGE_DFS_BACK;
 
 	  if (idx != 0 && stack[idx - 1]->src != src)
 	    {
 	      /* There are no more successors for the SRC node
 		 so assign its reverse completion number.  */
-	      post[src->index] = rev_post_order_num;
 	      src->flags |= post_assigned;
 	      rev_post_order[rev_post_order_num] = src->index;
 	      rev_post_order_num++;