Add no_sanitize_undefined attribute (PR sanitizer/58411)

--- gcc/c-family/c-common.c.mp2	2013-09-17 15:55:56.417946667 +0200
+++ gcc/c-family/c-common.c	2013-09-17 15:58:55.905513029 +0200
@@ -311,6 +311,8 @@  static tree handle_no_sanitize_address_a
 						  int, bool *);
 static tree handle_no_address_safety_analysis_attribute (tree *, tree, tree,
 							 int, bool *);
+static tree handle_no_sanitize_undefined_attribute (tree *, tree, tree, int,
+						    bool *);
 static tree handle_noinline_attribute (tree *, tree, tree, int, bool *);
 static tree handle_noclone_attribute (tree *, tree, tree, int, bool *);
 static tree handle_leaf_attribute (tree *, tree, tree, int, bool *);
@@ -722,6 +724,9 @@  const struct attribute_spec c_common_att
   { "no_sanitize_address",    0, 0, true, false, false,
 			      handle_no_sanitize_address_attribute,
 			      false },
+  { "no_sanitize_undefined",  0, 0, true, false, false,
+			      handle_no_sanitize_undefined_attribute,
+			      false },
   { "warning",		      1, 1, true,  false, false,
 			      handle_error_attribute, false },
   { "error",		      1, 1, true,  false, false,
@@ -6575,6 +6580,22 @@  handle_no_address_safety_analysis_attrib
   return NULL_TREE;
 }
 
+/* Handle a "no_sanitize_undefined" attribute; arguments as in
+   struct attribute_spec.handler.  */
+
+static tree
+handle_no_sanitize_undefined_attribute (tree *node, tree name, tree, int,
+				      bool *no_add_attrs)
+{
+  if (TREE_CODE (*node) != FUNCTION_DECL)
+    {
+      warning (OPT_Wattributes, "%qE attribute ignored", name);
+      *no_add_attrs = true;
+    }
+
+  return NULL_TREE;
+}
+
 /* Handle a "noinline" attribute; arguments as in
    struct attribute_spec.handler.  */
 
--- gcc/doc/extend.texi.mp2	2013-09-17 15:55:44.250907707 +0200
+++ gcc/doc/extend.texi	2013-09-17 16:06:21.439974916 +0200
@@ -2136,6 +2136,7 @@  attributes are currently defined for fun
 @code{warn_unused_result}, @code{nonnull}, @code{gnu_inline},
 @code{externally_visible}, @code{hot}, @code{cold}, @code{artificial},
 @code{no_sanitize_address}, @code{no_address_safety_analysis},
+@code{no_sanitize_undefined},
 @code{error} and @code{warning}.
 Several other attributes are defined for functions on particular
 target systems.  Other attributes, including @code{section} are
@@ -3500,6 +3501,12 @@  The @code{no_address_safety_analysis} is
 @code{no_sanitize_address} attribute, new code should use
 @code{no_sanitize_address}.
 
+@item no_sanitize_undefined
+@cindex @code{no_sanitize_undefined} function attribute
+The @code{no_sanitize_undefined} attribute on functions is used
+to inform the compiler that it should not check for undefined behavior
+in the function when compiling with the @option{-fsanitize=undefined} option.
+
 @item regparm (@var{number})
 @cindex @code{regparm} attribute
 @cindex functions that are passed arguments in registers on the 386
--- gcc/cp/typeck.c.mp2	2013-09-17 16:10:49.935644344 +0200
+++ gcc/cp/typeck.c	2013-09-17 16:11:20.601743694 +0200
@@ -4887,6 +4887,8 @@  cp_build_binary_op (location_t location,
   if ((flag_sanitize & SANITIZE_UNDEFINED)
       && !processing_template_decl
       && current_function_decl != 0
+      && !lookup_attribute ("no_sanitize_undefined",
+			    DECL_ATTRIBUTES (current_function_decl))
       && (doing_div_or_mod || doing_shift))
     {
       /* OP0 and/or OP1 might have side-effects.  */
--- gcc/c/c-typeck.c.mp2	2013-09-17 16:09:31.423381687 +0200
+++ gcc/c/c-typeck.c	2013-09-17 16:10:00.626476422 +0200
@@ -10498,6 +10498,8 @@  build_binary_op (location_t location, en
 
   if (flag_sanitize & SANITIZE_UNDEFINED
       && current_function_decl != 0
+      && !lookup_attribute ("no_sanitize_undefined",
+			    DECL_ATTRIBUTES (current_function_decl))
       && (doing_div_or_mod || doing_shift))
     {
       /* OP0 and/or OP1 might have side-effects.  */
--- gcc/testsuite/c-c++-common/ubsan/attrib-1.c.mp2	2013-09-17 16:33:46.729660165 +0200
+++ gcc/testsuite/c-c++-common/ubsan/attrib-1.c	2013-09-17 16:43:22.308566840 +0200
@@ -0,0 +1,33 @@ 
+/* PR sanitizer/58411 */
+/* { dg-do compile } */
+/* { dg-options "-fsanitize=undefined -w" } */
+
+__attribute__((no_sanitize_undefined)) int
+f1 (int i)
+{
+  return 16 << i;
+}
+
+int f2 (int i);
+int f2 (int i) __attribute__((no_sanitize_undefined));
+int f2 (int i) __attribute__((no_sanitize_undefined));
+int f2 (int i);
+
+int
+f2 (int i)
+{
+  return 1 / i;
+}
+
+void f3 (void);
+__typeof (f3) f3  __attribute__((__no_sanitize_undefined__));
+
+void
+f3 (void)
+{
+  __builtin_unreachable ();
+}
+
+/* { dg-final { scan-assembler-not "__ubsan_handle_shift_out_of_bounds" } } */
+/* { dg-final { scan-assembler-not "__ubsan_handle_divrem_overflow" } } */
+/* { dg-final { scan-assembler-not "__ubsan_handle_builtin_unreachable" } } */
--- gcc/builtins.c.mp2	2013-09-17 16:13:26.623161281 +0200
+++ gcc/builtins.c	2013-09-17 18:56:20.972164488 +0200
@@ -10313,7 +10313,10 @@  fold_builtin_0 (location_t loc, tree fnd
       return fold_builtin_classify_type (NULL_TREE);
 
     case BUILT_IN_UNREACHABLE:
-      if (flag_sanitize & SANITIZE_UNREACHABLE)
+      if (flag_sanitize & SANITIZE_UNREACHABLE
+	  && (current_function_decl == NULL
+	      || !lookup_attribute ("no_sanitize_undefined",
+				    DECL_ATTRIBUTES (current_function_decl))))
 	return ubsan_instrument_unreachable (loc);
       break;