PR mudflap/19319, c++/19317

        * gimplify.c (gimplify_modify_expr_rhs) [CALL_EXPR]: Make return
        slot explicit.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@95150 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 63 insertions, 0 deletions

diff --git a/gcc/gimplify.c b/gcc/gimplify.c
index d461d776ee8..89fd5c7e4f4 100644
--- a/gcc/gimplify.c
+++ b/gcc/gimplify.c
@@ -2913,6 +2913,69 @@ gimplify_modify_expr_rhs (tree *expr_p, tree *from_p, tree *to_p, tree *pre_p,
 	  ret = GS_UNHANDLED;
 	break;
 
+      case CALL_EXPR:
+	/* For calls that return in memory, give *to_p as the CALL_EXPR's
+	   return slot so that we don't generate a temporary.  */
+	if (aggregate_value_p (*from_p, *from_p))
+	  {
+	    tree init = *from_p;
+	    tree fn = TREE_OPERAND (init, 0);
+	    tree args = TREE_OPERAND (init, 1);
+	    tree rettype = TREE_TYPE (TREE_TYPE (TREE_TYPE (fn)));
+	    tree arg = *to_p;
+	    tree type;
+
+	    /* Only use the original target if *to_p isn't already
+	       addressable; if its address escapes, and the called function
+	       uses the NRV optimization, a conforming program could see
+	       *to_p change before the called function returns.  This is
+	       c++/19317.  */
+	    bool use_temp = !is_gimple_non_addressable (*to_p);
+
+	    /* A CALL_EXPR with an explicit return slot argument should
+	       never appear on the RHS of a MODIFY_EXPR.  */
+	    if (CALL_EXPR_HAS_RETURN_SLOT_ADDR (*from_p))
+	      abort ();
+
+	    if (use_temp)
+	      {
+		arg = create_tmp_var (rettype, "ret");
+		*from_p = arg;
+	      }
+
+	    type = TREE_TYPE (arg);
+	    /* FIXME: Mark the address as not escaping.  */
+	    lang_hooks.mark_addressable (arg);
+	    arg = build1 (ADDR_EXPR, build_pointer_type (type), arg);
+	    /* The return type might have different cv-quals from arg.  */
+	    arg = convert (build_pointer_type (rettype), arg);
+	    args = tree_cons (NULL_TREE, arg, args);
+	    init = build3 (CALL_EXPR, rettype, fn, args, NULL_TREE);
+	    CALL_EXPR_HAS_RETURN_SLOT_ADDR (init) = 1;
+	    TREE_USED (init) = 1;
+
+	    if (use_temp)
+	      {
+		gimplify_and_add (init, pre_p);
+		ret = GS_OK;
+		break;
+	      }
+	    else if (want_value)
+	      {
+		gimplify_and_add (init, pre_p);
+		*expr_p = *to_p;
+		return GS_OK;
+	      }
+	    else
+	      {
+		*expr_p = init;
+		return GS_OK;
+	      }
+	  }
+	else
+	  ret = GS_UNHANDLED;
+	break;
+
       default:
 	ret = GS_UNHANDLED;
 	break;