cpplib.h (struct cpp_options): Add new boolean flag warn_builtin_macro_redefined.

* include/cpplib.h (struct cpp_options): Add new boolean flag
	warn_builtin_macro_redefined.
	* init.c (cpp_create_reader): Initialize warn_builtin_macro_redefined.
	* (struct builtin_operator): Split out from previous struct builtin,
	enhance extra const correctness.
	* (struct builtin_macro): Split out from previous struct builtin, add
	new always_warn_if_redefined flag, enhance const correctness.
	* (mark_named_operators): Use struct builtin_operator.
	* (cpp_init_special_builtins): Use struct builtin_macro, add NODE_WARN
	to builtins selectively.
	* macro.c (warn_of_redefinition): Return false if a builtin macro
	is not flagged with NODE_WARN.

	* c-opts.c (c_common_handle_option): Add handling for
	-Wbuiltin-macro-redefined command line option.
	* c.opt: Added builtin-macro-redefined option.
	* doc/invoke.texi (Warning Options): Add -Wbuiltin-macro-redefined
	documentation.

	* gcc.dg/builtin-redefine.c: New.

From-SVN: r140461

libcpp/ChangeLog

@@ -1,3 +1,18 @@
+2008-09-18  Simon Baldwin  <simonb@google.com>
+
+	* include/cpplib.h (struct cpp_options): Add new boolean flag
+	warn_builtin_macro_redefined.
+	* init.c (cpp_create_reader): Initialize warn_builtin_macro_redefined.
+	* (struct builtin_operator): Split out from previous struct builtin,
+	enhance extra const correctness.
+	* (struct builtin_macro): Split out from previous struct builtin, add
+	new always_warn_if_redefined flag, enhance const correctness.
+	* (mark_named_operators): Use struct builtin_operator.
+	* (cpp_init_special_builtins): Use struct builtin_macro, add NODE_WARN
+	to builtins selectively.
+	* macro.c (warn_of_redefinition): Return false if a builtin macro
+	is not flagged with NODE_WARN.
+
 2008-07-31  Jakub Jelinek  <jakub@redhat.com>
 
 	PR preprocessor/36649

libcpp/include/cpplib.h

@@ -349,6 +349,10 @@ struct cpp_options
      Presumably the usage is protected by the appropriate #ifdef.  */
   unsigned char warn_variadic_macros;
 
+  /* Nonzero means warn about builtin macros that are redefined or
+     explicitly undefined.  */
+  unsigned char warn_builtin_macro_redefined;
+
   /* Nonzero means turn warnings into errors.  */
   unsigned char warnings_are_errors;
 

libcpp/init.c

@@ -163,6 +163,7 @@ cpp_create_reader (enum c_lang lang, hash_table *table,
   CPP_OPTION (pfile, dollars_in_ident) = 1;
   CPP_OPTION (pfile, warn_dollars) = 1;
   CPP_OPTION (pfile, warn_variadic_macros) = 1;
+  CPP_OPTION (pfile, warn_builtin_macro_redefined) = 1;
   CPP_OPTION (pfile, warn_normalize) = normalized_C;
 
   /* Default CPP arithmetic to something sensible for the host for the
@@ -303,31 +304,41 @@ cpp_destroy (cpp_reader *pfile)
    altered through #define, and #if recognizes them as operators.  In
    C, these are not entered into the hash table at all (but see
    <iso646.h>).  The value is a token-type enumerator.  */
-struct builtin
+struct builtin_macro
 {
-  const uchar *name;
-  unsigned short len;
-  unsigned short value;
+  const uchar *const name;
+  const unsigned short len;
+  const unsigned short value;
+  const bool always_warn_if_redefined;
+};
+
+#define B(n, t, f)    { DSC(n), t, f }
+static const struct builtin_macro builtin_array[] =
+{
+  B("__TIMESTAMP__",	 BT_TIMESTAMP,     false),
+  B("__TIME__",		 BT_TIME,          false),
+  B("__DATE__",		 BT_DATE,          false),
+  B("__FILE__",		 BT_FILE,          false),
+  B("__BASE_FILE__",	 BT_BASE_FILE,     false),
+  B("__LINE__",		 BT_SPECLINE,      true),
+  B("__INCLUDE_LEVEL__", BT_INCLUDE_LEVEL, true),
+  B("__COUNTER__",	 BT_COUNTER,       true),
+  /* Keep builtins not used for -traditional-cpp at the end, and
+     update init_builtins() if any more are added.  */
+  B("_Pragma",		 BT_PRAGMA,        true),
+  B("__STDC__",		 BT_STDC,          true),
+};
+#undef B
+
+struct builtin_operator
+{
+  const uchar *const name;
+  const unsigned short len;
+  const unsigned short value;
 };
 
 #define B(n, t)    { DSC(n), t }
-static const struct builtin builtin_array[] =
-{
-  B("__TIMESTAMP__",	 BT_TIMESTAMP),
-  B("__TIME__",		 BT_TIME),
-  B("__DATE__",		 BT_DATE),
-  B("__FILE__",		 BT_FILE),
-  B("__BASE_FILE__",	 BT_BASE_FILE),
-  B("__LINE__",		 BT_SPECLINE),
-  B("__INCLUDE_LEVEL__", BT_INCLUDE_LEVEL),
-  B("__COUNTER__",	 BT_COUNTER),
-  /* Keep builtins not used for -traditional-cpp at the end, and
-     update init_builtins() if any more are added.  */
-  B("_Pragma",		 BT_PRAGMA),
-  B("__STDC__",		 BT_STDC),
-};
-
-static const struct builtin operator_array[] =
+static const struct builtin_operator operator_array[] =
 {
   B("and",	CPP_AND_AND),
   B("and_eq",	CPP_AND_EQ),
@@ -347,7 +358,7 @@ static const struct builtin operator_array[] =
 static void
 mark_named_operators (cpp_reader *pfile)
 {
-  const struct builtin *b;
+  const struct builtin_operator *b;
 
   for (b = operator_array;
        b < (operator_array + ARRAY_SIZE (operator_array));
@@ -363,7 +374,7 @@ mark_named_operators (cpp_reader *pfile)
 void
 cpp_init_special_builtins (cpp_reader *pfile)
 {
-  const struct builtin *b;
+  const struct builtin_macro *b;
   size_t n = ARRAY_SIZE (builtin_array);
 
   if (CPP_OPTION (pfile, traditional))
@@ -376,7 +387,10 @@ cpp_init_special_builtins (cpp_reader *pfile)
     {
       cpp_hashnode *hp = cpp_lookup (pfile, b->name, b->len);
       hp->type = NT_MACRO;
-      hp->flags |= NODE_BUILTIN | NODE_WARN;
+      hp->flags |= NODE_BUILTIN;
+      if (b->always_warn_if_redefined
+          || CPP_OPTION (pfile, warn_builtin_macro_redefined))
+	hp->flags |= NODE_WARN;
       hp->value.builtin = (enum builtin_type) b->value;
     }
 }

libcpp/macro.c

@@ -1392,6 +1392,10 @@ warn_of_redefinition (cpp_reader *pfile, const cpp_hashnode *node,
   if (node->flags & NODE_WARN)
     return true;
 
+  /* Suppress warnings for builtins that lack the NODE_WARN flag.  */
+  if (node->flags & NODE_BUILTIN)
+    return false;
+
   /* Redefinitions of conditional (context-sensitive) macros, on
      the other hand, must be allowed silently.  */
   if (node->flags & NODE_CONDITIONAL)