[gcc r12-4420] Minor cleanups to backward threader.

[Aldy Hernandez <aldyh@gcc.gnu.org>]

https://gcc.gnu.org/g:d71e1be7c3a3e2058d1243e6a090e421c9fd7f85

commit r12-4420-gd71e1be7c3a3e2058d1243e6a090e421c9fd7f85
Author: Aldy Hernandez <aldyh@redhat.com>
Date:   Thu Oct 14 16:14:34 2021 +0200

    Minor cleanups to backward threader.
    
    Tested on x86-64 Linux.
    
    gcc/ChangeLog:
    
            * tree-ssa-threadbackward.c (class back_threader): Make m_imports
            an auto_bitmap.
            (back_threader::~back_threader): Do not release m_path.

Diff:
---
 gcc/tree-ssa-threadbackward.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/gcc/tree-ssa-threadbackward.c b/gcc/tree-ssa-threadbackward.c
index 496b68e0a82..1999ccf4834 100644
--- a/gcc/tree-ssa-threadbackward.c
+++ b/gcc/tree-ssa-threadbackward.c
@@ -105,7 +105,7 @@ private:
   hash_set<basic_block> m_visited_bbs;
   // The set of SSA names, any of which could potentially change the
   // value of the final conditional in a path.
-  bitmap m_imports;
+  auto_bitmap m_imports;
   // The last statement in the path.
   gimple *m_last_stmt;
   // This is a bit of a wart.  It's used to pass the LHS SSA name to
@@ -125,13 +125,10 @@ back_threader::back_threader (bool speed_p)
     m_solver (m_ranger, /*resolve=*/false)
 {
   m_last_stmt = NULL;
-  m_imports = BITMAP_ALLOC (NULL);
 }
 
 back_threader::~back_threader ()
 {
-  m_path.release ();
-  BITMAP_FREE (m_imports);
 }
 
 // Register the current path for jump threading if it's profitable to