PR c++/33799 - destroy return value, take 2.

This patch differs from the reverted patch for 33799 in that it adds the
CLEANUP_STMT for the return value at the end of the function, and only if
we've seen a cleanup that might throw, so it should not affect most C++11
code.

	* cp-tree.h (current_retval_sentinel): New macro.
	(struct language_function): Add throwing_cleanup bitfield.
	* decl.c (cxx_maybe_build_cleanup): Set it.
	* except.c (maybe_set_retval_sentinel)
	(maybe_splice_retval_cleanup): New functions.
	* parser.c (cp_parser_compound_statement): Call
	maybe_splice_retval_cleanup.
	* typeck.c (check_return_expr): Call maybe_set_retval_sentinel.

1 files changed, 72 insertions, 0 deletions

diff --git a/gcc/cp/except.c b/gcc/cp/except.c
index 55b4b6a..0b40234 100644
--- a/gcc/cp/except.c
+++ b/gcc/cp/except.c
@@ -1325,4 +1325,76 @@ build_noexcept_spec (tree expr, tsubst_flags_t complain)
     }
 }
 
+/* If the current function has a cleanup that might throw, and the return value
+   has a non-trivial destructor, return a MODIFY_EXPR to set
+   current_retval_sentinel so that we know that the return value needs to be
+   destroyed on throw.  Otherwise, returns NULL_TREE.  */
+
+tree
+maybe_set_retval_sentinel ()
+{
+  if (processing_template_decl)
+    return NULL_TREE;
+  tree retval = DECL_RESULT (current_function_decl);
+  if (!TYPE_HAS_NONTRIVIAL_DESTRUCTOR (TREE_TYPE (retval)))
+    return NULL_TREE;
+  if (!cp_function_chain->throwing_cleanup)
+    return NULL_TREE;
+
+  if (!current_retval_sentinel)
+    {
+      /* Just create the temporary now, maybe_splice_retval_cleanup
+	 will do the rest.  */
+      current_retval_sentinel = create_temporary_var (boolean_type_node);
+      DECL_INITIAL (current_retval_sentinel) = boolean_false_node;
+      pushdecl_outermost_localscope (current_retval_sentinel);
+    }
+
+  return build2 (MODIFY_EXPR, boolean_type_node,
+		 current_retval_sentinel, boolean_true_node);
+}
+
+/* COMPOUND_STMT is the STATEMENT_LIST for the current function body.  If
+   current_retval_sentinel was set in this function, wrap the body in a
+   CLEANUP_STMT to destroy the return value on throw.  */
+
+void
+maybe_splice_retval_cleanup (tree compound_stmt)
+{
+  /* If need_retval_cleanup set current_retval_sentinel, wrap the function body
+     in a CLEANUP_STMT to handle destroying the return value.  */
+  if (!DECL_CONSTRUCTOR_P (current_function_decl)
+      && !DECL_DESTRUCTOR_P (current_function_decl)
+      && current_retval_sentinel)
+    {
+      location_t loc = DECL_SOURCE_LOCATION (current_function_decl);
+
+      /* Add a DECL_EXPR for current_retval_sentinel.  */
+      tree_stmt_iterator iter = tsi_start (compound_stmt);
+      tree retval = DECL_RESULT (current_function_decl);
+      tree decl_expr = build_stmt (loc, DECL_EXPR, current_retval_sentinel);
+      tsi_link_before (&iter, decl_expr, TSI_SAME_STMT);
+
+      /* Skip past other decls, they can't contain a return.  */
+      while (TREE_CODE (tsi_stmt (iter)) == DECL_EXPR)
+	tsi_next (&iter);
+      gcc_assert (!tsi_end_p (iter));
+
+      /* Wrap the rest of the STATEMENT_LIST in a CLEANUP_STMT.  */
+      tree stmts = NULL_TREE;
+      while (!tsi_end_p (iter))
+	{
+	  append_to_statement_list_force (tsi_stmt (iter), &stmts);
+	  tsi_delink (&iter);
+	}
+      tree dtor = build_cleanup (retval);
+      tree cond = build3 (COND_EXPR, void_type_node, current_retval_sentinel,
+			  dtor, void_node);
+      tree cleanup = build_stmt (loc, CLEANUP_STMT,
+				 stmts, cond, retval);
+      CLEANUP_EH_ONLY (cleanup) = true;
+      append_to_statement_list_force (cleanup, &compound_stmt);
+    }
+}
+
 #include "gt-cp-except.h"