target/111600 - avoid deep recursion in access diagnostics

pass_waccess::check_dangling_stores uses recursion to traverse the CFG.
The following changes this to use a heap allocated worklist to avoid
blowing the stack.

Instead of using a better iteration order it tries hard to preserve
the current iteration order to avoid new false positives to pop up
since the set of stores we keep track isn't properly modeling flow,
so what is diagnosed and what not is quite random.  We are also
lacking the ideal RPO compute on the inverted graph that would just
ignore reverse unreachable code (as the current iteration scheme does).

Bootstrapped and tested on x86_64-unknown-linux-gnu, with this
8MB of stack are now enough to build riscv insn-opinit.cc.

Pushed.

	PR target/111600
	* gimple-ssa-warn-access.cc (pass_waccess::check_dangling_stores):
	Use a heap allocated worklist for CFG traversal instead of
	recursion.

gcc/gimple-ssa-warn-access.cc

@@ -2141,7 +2141,7 @@ class pass_waccess : public gimple_opt_pass
   void check_dangling_uses (tree, tree, bool = false, bool = false);
   void check_dangling_uses ();
   void check_dangling_stores ();
-  void check_dangling_stores (basic_block, hash_set<tree> &, auto_bitmap &);
+  bool check_dangling_stores (basic_block, hash_set<tree> &);
 
   void warn_invalid_pointer (tree, gimple *, gimple *, tree, bool, bool = false);
 
@@ -4524,17 +4524,13 @@ pass_waccess::check_dangling_uses (tree var, tree decl, bool maybe /* = false */
 
 /* Diagnose stores in BB and (recursively) its predecessors of the addresses
    of local variables into nonlocal pointers that are left dangling after
-   the function returns.  BBS is a bitmap of basic blocks visited.  */
+   the function returns.  Returns true when we can continue walking
+   the CFG to predecessors.  */
 
-void
+bool
 pass_waccess::check_dangling_stores (basic_block bb,
-				     hash_set<tree> &stores,
-				     auto_bitmap &bbs)
+				     hash_set<tree> &stores)
 {
-  if (!bitmap_set_bit (bbs, bb->index))
-    /* Avoid cycles. */
-    return;
-
   /* Iterate backwards over the statements looking for a store of
      the address of a local variable into a nonlocal pointer.  */
   for (auto gsi = gsi_last_nondebug_bb (bb); ; gsi_prev_nondebug (&gsi))
@@ -4550,7 +4546,7 @@ pass_waccess::check_dangling_stores (basic_block bb,
 	  && !(gimple_call_flags (stmt) & (ECF_CONST | ECF_PURE)))
 	/* Avoid looking before nonconst, nonpure calls since those might
 	   use the escaped locals.  */
-	return;
+	return false;
 
       if (!is_gimple_assign (stmt) || gimple_clobber_p (stmt)
 	  || !gimple_store_p (stmt))
@@ -4576,7 +4572,7 @@ pass_waccess::check_dangling_stores (basic_block bb,
 	  gimple *def_stmt = SSA_NAME_DEF_STMT (lhs_ref.ref);
 	  if (!gimple_nop_p (def_stmt))
 	    /* Avoid looking at or before stores into unknown objects.  */
-	    return;
+	    return false;
 
 	  lhs_ref.ref = SSA_NAME_VAR (lhs_ref.ref);
 	}
@@ -4620,13 +4616,7 @@ pass_waccess::check_dangling_stores (basic_block bb,
 	}
     }
 
-  edge e;
-  edge_iterator ei;
-  FOR_EACH_EDGE (e, ei, bb->preds)
-    {
-      basic_block pred = e->src;
-      check_dangling_stores (pred, stores, bbs);
-    }
+  return true;
 }
 
 /* Diagnose stores of the addresses of local variables into nonlocal
@@ -4635,9 +4625,32 @@ pass_waccess::check_dangling_stores (basic_block bb,
 void
 pass_waccess::check_dangling_stores ()
 {
+  if (EDGE_COUNT (EXIT_BLOCK_PTR_FOR_FN (m_func)->preds) == 0)
+    return;
+
   auto_bitmap bbs;
   hash_set<tree> stores;
-  check_dangling_stores (EXIT_BLOCK_PTR_FOR_FN (m_func), stores, bbs);
+  auto_vec<edge_iterator, 8> worklist (n_basic_blocks_for_fn (cfun) + 1);
+  worklist.quick_push (ei_start (EXIT_BLOCK_PTR_FOR_FN (m_func)->preds));
+  do
+    {
+      edge_iterator ei = worklist.last ();
+      basic_block src = ei_edge (ei)->src;
+      if (bitmap_set_bit (bbs, src->index))
+	{
+	  if (check_dangling_stores (src, stores)
+	      && EDGE_COUNT (src->preds) > 0)
+	    worklist.quick_push (ei_start (src->preds));
+	}
+      else
+	{
+	  if (ei_one_before_end_p (ei))
+	    worklist.pop ();
+	  else
+	    ei_next (&worklist.last ());
+	}
+    }
+  while (!worklist.is_empty ());
 }
 
 /* Check for and diagnose uses of dangling pointers to auto objects