[Bug c++/86769] g++ destroys condition variable in for statement too early

["mpolacek at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86769

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mpolacek at gcc dot gnu.org

--- Comment #4 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Unfinished/untested patch:

commit f873acfa7ed1956a58d02cc383b8d709c446f656 (HEAD -> PR86769)
Author: Marek Polacek <polacek@redhat.com>
Date:   Fri Nov 20 16:40:50 2020 -0500

    c++: Condition in for statement destroyed too early [PR86769]

diff --git a/gcc/c-family/c-gimplify.c b/gcc/c-family/c-gimplify.c
index a7c0ec3be0d..f0a19456715 100644
--- a/gcc/c-family/c-gimplify.c
+++ b/gcc/c-family/c-gimplify.c
@@ -205,6 +205,30 @@ expr_loc_or_loc (const_tree expr, location_t or_loc)
   return loc;
 }

+/* TODO */
+
+static bool
+maybe_inject_incr_to_body (tree body, tree incr)
+{
+  if (TREE_CODE (body) == BIND_EXPR)
+    body = BIND_EXPR_BODY (body);
+  if (TREE_CODE (body) == STATEMENT_LIST)
+    {
+      tree_stmt_iterator i = tsi_last (body);
+      tree t = tsi_stmt (i);
+      if (TREE_CODE (t) == TRY_FINALLY_EXPR)
+   {
+     if (TREE_CODE (TREE_OPERAND (t, 0)) == STATEMENT_LIST)
+       {
+         i = tsi_last (TREE_OPERAND (t, 0));
+         tsi_link_after (&i, incr, TSI_CONTINUE_LINKING);
+         return true;
+       }
+   }
+    }
+  return false;
+}
+
 /* Build a generic representation of one of the C loop forms.  COND is the
    loop condition or NULL_TREE.  BODY is the (possibly compound) statement
    controlled by the loop.  INCR is the increment expression of a for-loop,
@@ -291,6 +315,9 @@ genericize_c_loop (tree *stmt_p, location_t start_locus,
tree cond, tree body,
       append_to_statement_list (top, &stmt_list);
     }

+  if (maybe_inject_incr_to_body (body, incr))
+    incr = NULL_TREE;
+
   append_to_statement_list (body, &stmt_list);
   finish_bc_block (&stmt_list, bc_continue, clab);
   if (incr)