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

3 files changed, 61 insertions, 23 deletions

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 590e322..bb90b5a 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,15 @@
+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.
+
 2017-11-03  Nathan Sidwell  <nathan@acm.org>
 
 	PR c++/82710
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;
diff --git a/gcc/cp/cp-gimplify.c b/gcc/cp/cp-gimplify.c
index 262485a..014c1ee 100644
--- a/gcc/cp/cp-gimplify.c
+++ b/gcc/cp/cp-gimplify.c
@@ -1556,10 +1556,11 @@ cp_genericize_tree (tree* t_p, bool handle_invisiref_parm_p)
 
 /* If a function that should end with a return in non-void
    function doesn't obviously end with return, add ubsan
-   instrumentation code to verify it at runtime.  */
+   instrumentation code to verify it at runtime.  If -fsanitize=return
+   is not enabled, instrument __builtin_unreachable.  */
 
 static void
-cp_ubsan_maybe_instrument_return (tree fndecl)
+cp_maybe_instrument_return (tree fndecl)
 {
   if (VOID_TYPE_P (TREE_TYPE (TREE_TYPE (fndecl)))
       || DECL_CONSTRUCTOR_P (fndecl)
@@ -1600,7 +1601,16 @@ cp_ubsan_maybe_instrument_return (tree fndecl)
   tree *p = &DECL_SAVED_TREE (fndecl);
   if (TREE_CODE (*p) == BIND_EXPR)
     p = &BIND_EXPR_BODY (*p);
-  t = ubsan_instrument_return (DECL_SOURCE_LOCATION (fndecl));
+
+  location_t loc = DECL_SOURCE_LOCATION (fndecl);
+  if (sanitize_flags_p (SANITIZE_RETURN, fndecl))
+    t = ubsan_instrument_return (loc);
+  else
+    {
+      tree fndecl = builtin_decl_explicit (BUILT_IN_UNREACHABLE);
+      t = build_call_expr_loc (BUILTINS_LOCATION, fndecl, 0);
+    }
+
   append_to_statement_list (t, p);
 }
 
@@ -1674,9 +1684,7 @@ cp_genericize (tree fndecl)
      walk_tree's hash functionality.  */
   cp_genericize_tree (&DECL_SAVED_TREE (fndecl), true);
 
-  if (sanitize_flags_p (SANITIZE_RETURN)
-      && current_function_decl != NULL_TREE)
-    cp_ubsan_maybe_instrument_return (fndecl);
+  cp_maybe_instrument_return (fndecl);
 
   /* Do everything else.  */
   c_genericize (fndecl);