Instrument function exit with __builtin_unreachable in C++

2017-11-06  Martin Liska  <mliska@suse.cz>

	PR middle-end/82404
	* c-opts.c (c_common_post_options): Set -Wreturn-type for C++
	FE.
	* c.opt: Set default value of warn_return_type.
2017-11-06  Martin Liska  <mliska@suse.cz>

	PR middle-end/82404
	* constexpr.c (cxx_eval_builtin_function_call): Handle
	__builtin_unreachable call.
	(get_function_named_in_call): Declare function earlier.
	(constexpr_fn_retval): Skip __builtin_unreachable.
	* cp-gimplify.c (cp_ubsan_maybe_instrument_return): Rename to
	...
	(cp_maybe_instrument_return): ... this.
	(cp_genericize): Call the function unconditionally.
2017-11-06  Martin Liska  <mliska@suse.cz>

	PR middle-end/82404
	* options.c (gfc_post_options): Set default value of
	-Wreturn-type to false.

From-SVN: r254437

1 files changed, 35 insertions, 17 deletions

diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 483f731..670aae2 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -628,6 +628,20 @@ build_constexpr_constructor_member_initializers (tree type, tree body)
     return error_mark_node;
 }
 
+/* We have an expression tree T that represents a call, either CALL_EXPR
+   or AGGR_INIT_EXPR.  If the call is lexically to a named function,
+   retrun the _DECL for that function.  */
+
+static tree
+get_function_named_in_call (tree t)
+{
+  tree fun = cp_get_callee (t);
+  if (fun && TREE_CODE (fun) == ADDR_EXPR
+      && TREE_CODE (TREE_OPERAND (fun, 0)) == FUNCTION_DECL)
+    fun = TREE_OPERAND (fun, 0);
+  return fun;
+}
+
 /* Subroutine of register_constexpr_fundef.  BODY is the body of a function
    declared to be constexpr, or a sub-statement thereof.  Returns the
    return value if suitable, error_mark_node for a statement not allowed in
@@ -682,6 +696,15 @@ constexpr_fn_retval (tree body)
     case USING_STMT:
       return NULL_TREE;
 
+    case CALL_EXPR:
+	{
+	  tree fun = get_function_named_in_call (body);
+	  if (fun != NULL_TREE
+	      && DECL_FUNCTION_CODE (fun) == BUILT_IN_UNREACHABLE)
+	    return NULL_TREE;
+	}
+      /* Fallthru.  */
+
     default:
       return error_mark_node;
     }
@@ -1098,20 +1121,6 @@ save_fundef_copy (tree fun, tree copy)
 }
 
 /* We have an expression tree T that represents a call, either CALL_EXPR
-   or AGGR_INIT_EXPR.  If the call is lexically to a named function,
-   retrun the _DECL for that function.  */
-
-static tree
-get_function_named_in_call (tree t)
-{
-  tree fun = cp_get_callee (t);
-  if (fun && TREE_CODE (fun) == ADDR_EXPR
-      && TREE_CODE (TREE_OPERAND (fun, 0)) == FUNCTION_DECL)
-    fun = TREE_OPERAND (fun, 0);
-  return fun;
-}
-
-/* We have an expression tree T that represents a call, either CALL_EXPR
    or AGGR_INIT_EXPR.  Return the Nth argument.  */
 
 static inline tree
@@ -1180,9 +1189,18 @@ cxx_eval_builtin_function_call (const constexpr_ctx *ctx, tree t, tree fun,
     {
       if (!*non_constant_p && !ctx->quiet)
 	{
-	  new_call = build_call_array_loc (EXPR_LOCATION (t), TREE_TYPE (t),
-					   CALL_EXPR_FN (t), nargs, args);
-	  error ("%q+E is not a constant expression", new_call);
+	  /* Do not allow__builtin_unreachable in constexpr function.
+	     The __builtin_unreachable call with BUILTINS_LOCATION
+	     comes from cp_maybe_instrument_return.  */
+	  if (DECL_FUNCTION_CODE (fun) == BUILT_IN_UNREACHABLE
+	      && EXPR_LOCATION (t) == BUILTINS_LOCATION)
+	    error ("constexpr call flows off the end of the function");
+	  else
+	    {
+	      new_call = build_call_array_loc (EXPR_LOCATION (t), TREE_TYPE (t),
+					       CALL_EXPR_FN (t), nargs, args);
+	      error ("%q+E is not a constant expression", new_call);
+	    }
 	}
       *non_constant_p = true;
       return t;