[gcc r12-4606] Revert the avoid threading circular paths commit.

[gcc r12-4606] Revert the avoid threading circular paths commit.

[Aldy Hernandez]

https://gcc.gnu.org/g:d6a3c0cfb852dbeee4255e3588e9a1f52e376042

commit r12-4606-gd6a3c0cfb852dbeee4255e3588e9a1f52e376042
Author: Aldy Hernandez <aldyh@redhat.com>
Date:   Thu Oct 21 13:18:49 2021 +0200

    Revert the avoid threading circular paths commit.
    
    I've tested this patch on the wrong tree, and picked up the test changes
    in a pending patch, without which this patch is no longer obvious.
    Plus, it causes a regression in an invalid test I've recommended we remove.
    
    I'm reverting this patch until the dependencies are reviewed.
    
    Sorry for the noise.
    
    gcc/ChangeLog:
    
            * tree-ssa-threadbackward.c
            (back_threader::maybe_register_path): Remove circular paths check.

Diff:
---
 gcc/tree-ssa-threadbackward.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/gcc/tree-ssa-threadbackward.c b/gcc/tree-ssa-threadbackward.c
index 38913b06717..d94e3b962db 100644
--- a/gcc/tree-ssa-threadbackward.c
+++ b/gcc/tree-ssa-threadbackward.c
@@ -140,10 +140,6 @@ back_threader::maybe_register_path ()
 
   if (taken_edge && taken_edge != UNREACHABLE_EDGE)
     {
-      // Avoid circular paths.
-      if (m_visited_bbs.contains (taken_edge->dest))
-	return UNREACHABLE_EDGE;
-
       bool irreducible = false;
       bool profitable
 	= m_profit.profitable_path_p (m_path, m_name, taken_edge, &irreducible);