Re: backwards threader cleanups

[Trevor Saunders <tbsaunde at tbsaunde dot org>]

On Fri, Sep 01, 2017 at 04:18:20PM -0400, Aldy Hernandez wrote:
> Hi.
> 
> Attached are misc cleanups to tree-ssa-threadbackwards.c and friends.
> The main gist of the patch is making the path vectors live in the
> heap, not GC.  But I also cleaned up some comments to reflect reality,
> and renamed VAR_BB which could use a more meaningful name.  Finally, I
> abstracted some common code to
> register_jump_thread_path_if_profitable() in preparation for some
> upcoming work by me :).
> 
> Tested on x86-64 Linux.
> 
> OK?

 check_subpath_and_update_thread_path (basic_block last_bb, basic_block new_bb,
 				      hash_set<basic_block> *visited_bbs,
-				      vec<basic_block, va_gc> *&path,
+				      vec<basic_block> &path,
 				      int *next_path_length)
 {
   edge e;
   int e_count = 0;
   edge_iterator ei;
-  vec<basic_block, va_gc> *next_path;
-  vec_alloc (next_path, 10);
+  vec<basic_block> next_path = vNULL;

I believe all paths out of this scope release next_path, so it can be
said the scope owns this vector and you could use auto_vec here.

@@ -776,9 +786,8 @@ find_jump_threads_backwards (basic_block bb, bool speed_p)
   if (!name || TREE_CODE (name) != SSA_NAME)
     return;
 
-  vec<basic_block, va_gc> *bb_path;
-  vec_alloc (bb_path, 10);
-  vec_safe_push (bb_path, bb);
+  vec<basic_block> bb_path = vNULL;

same holds here I think.

+  bb_path.safe_push (bb);
   hash_set<basic_block> *visited_bbs = new hash_set<basic_block>;

   btw I don't see why this hash table can't be just a hash_table<> and
   live on the stack.

thanks

Trev