Modify verify.h to pacify gcc -Wredundant_decls.

* lib/verify.h (GL_CONCAT, GL_CONCAT0, GL_GENSYM): New macros.
These use the prefix "GL_" since they're likely to be useful elsewhere.
We may need to break them out into a different .h file.
(__COUNTER__): Define to 0 if the compiler doesn't support it.
(verify) [!defined __cplusplus]: Use them to avoid duplicate decls
of verify_function__.

diff --git a/ChangeLog b/ChangeLog
index b1bd09d113d0343324becdb384590448f754bed3..1709a974cae619f8742e8e9d519b47ccea0e6eb3 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2010-05-05  Paul Eggert  <eggert@cs.ucla.edu>
+
+       Modify verify.h to pacify gcc -Wredundant_decls.
+       * lib/verify.h (GL_CONCAT, GL_CONCAT0, GL_GENSYM): New macros.
+       These use the prefix "GL_" since they're likely to be useful elsewhere.
+       We may need to break them out into a different .h file.
+       (__COUNTER__): Define to 0 if the compiler doesn't support it.
+       (verify) [!defined __cplusplus]: Use them to avoid duplicate decls
+       of verify_function__.
+
 2010-05-05  Peter O'Gorman  <pogma@thewrittenword.com>
 
        Tests for module pwrite.

diff --git a/lib/verify.h b/lib/verify.h
index bcd3f5a09dceebb70a7d97f726297f315dbf60a1..dbca35c817d3a6e3f1dedae491eb21f967d2f874 100644 (file)
--- a/lib/verify.h
+++ b/lib/verify.h
@@ -75,7 +75,8 @@
 
      But this has the problem that two invocations of verify from
      within the same macro would collide, since the __LINE__ value
-     would be the same for both invocations.
+     would be the same for both invocations.  (The GCC __COUNTER__
+     macro solves this problem, but is not portable.)
 
      A solution is to use the sizeof operator.  It yields a number,
      getting rid of the identity of the type.  Declarations like
@@ -103,20 +104,38 @@
 
        extern int (*dummy (void)) [sizeof (struct {...})];
 
+   * GCC warns about duplicate declarations of the dummy function if
+     -Wredundant_decls is used.  GCC 4.3 and later have a builtin
+     __COUNTER__ macro that can let us generate unique identifiers for
+     each dummy function, to suppress this warning.
+
    * This implementation exploits the fact that GCC does not warn about
      the last declaration mentioned above.  If a future version of GCC
      introduces a warning for this, the problem could be worked around
-     by using code specialized to GCC, e.g.,:
+     by using code specialized to GCC, just as __COUNTER__ is already
+     being used if available.
 
        #if 4 <= __GNUC__
-       # define verify(R) \
-           extern int (* verify_function__ (void)) \
-                      [__builtin_constant_p (R) && (R) ? 1 : -1]
+       # define verify(R) [another version to keep GCC happy]
        #endif
 
    * In C++, any struct definition inside sizeof is invalid.
      Use a template type to work around the problem.  */
 
+/* Concatenate two preprocessor tokens.  */
+# define GL_CONCAT(x, y) GL_CONCAT0 (x, y)
+# define GL_CONCAT0(x, y) x##y
+
+/* __COUNTER__ evaluates to 0, 1, 2,..., adding one one each time the
+   preprocessor uses it.  If the preprocessor doesn't support this
+   builtin macro, define it to 0.  */
+# ifndef __COUNTER__
+#  define __COUNTER__ 0
+# endif
+
+/* Generate a symbol with the given prefix, making it unique if
+   possible.  */
+# define GL_GENSYM(prefix) GL_CONCAT(prefix, __COUNTER__)
 
 /* Verify requirement R at compile-time, as an integer constant expression.
    Return 1.  */
@@ -135,6 +154,7 @@ template <int w>
 /* Verify requirement R at compile-time, as a declaration without a
    trailing ';'.  */
 
-# define verify(R) extern int (* verify_function__ (void)) [verify_true (R)]
+# define verify(R) \
+    extern int (* GL_GENSYM(verify_function) (void)) [verify_true (R)]
 
 #endif