[Patch] Improving jump-thread pass for PR 54742

[Sebastian Pop]

Jeff Law wrote:
> I'm a bit worried about compile-time impacts of the all the
> recursion

I will also restrict the recursion to the loop in which we look for the FSM
thread, like this:

diff --git a/gcc/tree-ssa-threadedge.c b/gcc/tree-ssa-threadedge.c
index a6fb361..9a153bb 100644
--- a/gcc/tree-ssa-threadedge.c
+++ b/gcc/tree-ssa-threadedge.c
@@ -959,13 +959,17 @@ thread_around_empty_blocks (edge taken_edge,
 
 /* Return true if the CFG contains at least one path from START_BB to END_BB.
    When a path is found, record in PATH the blocks from END_BB to START_BB.
-   VISITED_BBS is used to make sure we don't fall into an infinite loop.  */
+   VISITED_BBS is used to make sure we don't fall into an infinite loop.  Bound
+   the recursion to basic blocks belonging to LOOP.  */
 
 static bool
 fsm_find_thread_path (basic_block start_bb, basic_block end_bb,
                      vec<basic_block, va_gc> *&path,
-                     hash_set<basic_block> *visited_bbs, int n_insns)
+                     hash_set<basic_block> *visited_bbs, loop_p loop)
 {
+  if (loop != start_bb->loop_father)
+    return false;
+
   if (start_bb == end_bb)
     {
       vec_safe_push (path, start_bb);
@@ -977,7 +981,7 @@ fsm_find_thread_path (basic_block start_bb, basic_block end_bb,
       edge e;
       edge_iterator ei;
       FOR_EACH_EDGE (e, ei, start_bb->succs)
-       if (fsm_find_thread_path (e->dest, end_bb, path, visited_bbs, n_insns))
+       if (fsm_find_thread_path (e->dest, end_bb, path, visited_bbs, loop))
          {
            vec_safe_push (path, start_bb);
            return true;
@@ -1035,7 +1039,8 @@ fsm_find_control_statement_thread_paths (tree expr,
        {
          hash_set<basic_block> *visited_bbs = new hash_set<basic_block>;
 
-         if (fsm_find_thread_path (var_bb, e->src, next_path, visited_bbs, 0))
+         if (fsm_find_thread_path (var_bb, e->src, next_path, visited_bbs,
+                                   e->src->loop_father))
            ++e_count;
 
          delete visited_bbs;