re PR c++/9993 (destructor not called for local object created within and…

re PR c++/9993 (destructor not called for local object created within and returned from infinite loop)

        PR c++/9993
        * decl.c (finish_function): Only allow the NRVO to use variables
        declared at function scope.

From-SVN: r64488

gcc/cp/ChangeLog

+2003-03-16  Jason Merrill  <jason@redhat.com>
+
+	PR c++/9993
+	* decl.c (finish_function): Only allow the NRVO to use variables
+	declared at function scope.
+
 2003-03-17  Andreas Jaeger  <aj@suse.de>
 
 	* Make-lang.in (cp/TAGS): Remove.

gcc/cp/decl.c

@@ -14092,11 +14092,21 @@ finish_function (int flags)
   if (current_function_return_value)
     {
       tree r = current_function_return_value;
-      /* This is only worth doing for fns that return in memory--and
-	 simpler, since we don't have to worry about promoted modes.  */
+      tree outer;
+
       if (r != error_mark_node
-	  && aggregate_value_p (TREE_TYPE (TREE_TYPE (fndecl))))
+	  /* This is only worth doing for fns that return in memory--and
+	     simpler, since we don't have to worry about promoted modes.  */
+	  && aggregate_value_p (TREE_TYPE (TREE_TYPE (fndecl)))
+	  /* Only allow this for variables declared in the outer scope of
+	     the function so we know that their lifetime always ends with a
+	     return; see g++.dg/opt/nrv6.C.  We could be more flexible if
+	     we were to do this optimization in tree-ssa.  */
+	  /* Skip the artificial function body block.  */
+	  && (outer = BLOCK_SUBBLOCKS (BLOCK_SUBBLOCKS (DECL_INITIAL (fndecl))),
+	      chain_member (r, BLOCK_VARS (outer))))
 	{
+	  
 	  DECL_ALIGN (r) = DECL_ALIGN (DECL_RESULT (fndecl));
 	  walk_tree_without_duplicates (&DECL_SAVED_TREE (fndecl),
 					nullify_returns_r, r);

gcc/testsuite/g++.dg/opt/nrv6.C

+// PR c++/9993
+// Bug: We were failing to destroy b.
+
+// { dg-do run }
+
+int c, d;
+
+struct Object {
+  Object()                      { ++c; }
+  Object(const Object&)         { ++c; }
+  ~Object()                     { ++d; }
+};
+
+Object function() {
+  int i = 0;
+  do {
+    Object b;
+    if (i++ == 2)
+      return b;
+  } while (1);
+}
+
+int main() {
+  function();
+  return c != d;
+}