Implement the Named Return Value optimization.

        * c-common.h (RETURN_NULLIFIED_P): New macro.
        * c-semantics.c (genrtl_return_stmt): Check it.
        * cp-tree.h (struct cp_language_function): Add x_return_value.
        (current_function_return_value): Now a macro.
        * decl.c: Don't define it.
        (define_label, finish_case_label): Don't clear it.
        (init_decl_processing): Don't register it with GC.
        * semantics.c (genrtl_finish_function): Don't check it for
        no_return_label.  Copy the RTL from the return value to
        current_function_return_value and walk, calling...
        (nullify_returns_r): ...this new fn.
        * typeck.c (check_return_expr): Set current_function_return_value.

        * expr.c (clear_storage): Set TREE_NOTHROW on the decl for memset.
        (emit_block_move): Likewise.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@43445 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 36 insertions, 1 deletions

diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
index 9dddf230ddd..0dc392a9a89 100644
--- a/gcc/cp/semantics.c
+++ b/gcc/cp/semantics.c
@@ -49,6 +49,7 @@
 
 static tree maybe_convert_cond PARAMS ((tree));
 static tree simplify_aggr_init_exprs_r PARAMS ((tree *, int *, void *));
+static tree nullify_returns_r PARAMS ((tree *, int *, void *));
 static void deferred_type_access_control PARAMS ((void));
 static void emit_associated_thunks PARAMS ((tree));
 static void genrtl_try_block PARAMS ((tree));
@@ -2464,6 +2465,25 @@ expand_body (fn)
   timevar_pop (TV_EXPAND);
 }
 
+/* Helper function for walk_tree, used by genrtl_start_function to override
+   all the RETURN_STMTs for the named return value optimization.  */
+
+static tree
+nullify_returns_r (tp, walk_subtrees, data)
+     tree *tp;
+     int *walk_subtrees;
+     void *data ATTRIBUTE_UNUSED;
+{
+  /* No need to walk into types.  */
+  if (TYPE_P (*tp))
+    *walk_subtrees = 0;
+  else if (TREE_CODE (*tp) == RETURN_STMT)
+    RETURN_NULLIFIED_P (*tp) = 1;
+
+  /* Keep iterating.  */
+  return NULL_TREE;
+}
+
 /* Start generating the RTL for FN.  */
 
 static void
@@ -2541,6 +2561,22 @@ genrtl_start_function (fn)
   /* Create a binding contour which can be used to catch
      cleanup-generated temporaries.  */
   expand_start_bindings (2);
+
+  /* Set up the named return value optimization, if we can.  */
+  if (current_function_return_value
+      && current_function_return_value != error_mark_node)
+    {
+      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.  */
+      if (aggregate_value_p (TREE_TYPE (TREE_TYPE (fn))))
+	{
+	  COPY_DECL_RTL (DECL_RESULT (fn), r);
+	  DECL_ALIGN (r) = DECL_ALIGN (DECL_RESULT (fn));
+	  walk_tree_without_duplicates (&DECL_SAVED_TREE (fn),
+					nullify_returns_r, NULL_TREE);
+	}
+    }
 }
 
 /* Finish generating the RTL for FN.  */
@@ -2579,7 +2615,6 @@ genrtl_finish_function (fn)
 
   if (!dtor_label && !DECL_CONSTRUCTOR_P (fn)
       && return_label != NULL_RTX
-      && current_function_return_value == NULL_TREE
       && ! DECL_NAME (DECL_RESULT (current_function_decl)))
     no_return_label = build_decl (LABEL_DECL, NULL_TREE, NULL_TREE);