* data.c: Work around bogus GCC diagnostic about shift count.

Reported by Eli Zaretskii in
<http://lists.gnu.org/archive/html/emacs-devel/2013-11/msg00489.html>.
(pre_value): New function.
(count_trailing_zero_bits): Use it.

2 files changed, 20 insertions, 1 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 14de1e793b5..f92eb7b85fc 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,11 @@
+2013-11-15  Paul Eggert  <eggert@cs.ucla.edu>
+
+        * data.c: Work around bogus GCC diagnostic about shift count.
+        Reported by Eli Zaretskii in
+        <http://lists.gnu.org/archive/html/emacs-devel/2013-11/msg00489.html>.
+        (pre_value): New function.
+        (count_trailing_zero_bits): Use it.
+
 2013-11-15  Eli Zaretskii  <eliz@gnu.org>
 
         * lisp.h (DEBUGGER_SEES_C_MACROS) [GCC < v3.5]: Pessimistically
diff --git a/src/data.c b/src/data.c
index 7ff7ac6b130..d0171b5d758 100644
--- a/src/data.c
+++ b/src/data.c
@@ -3078,6 +3078,16 @@ bool_vector_binop_driver (Lisp_Object op1,
   return changed ? dest : Qnil;
 }
 
+/* PRECONDITION must be true.  Return VALUE.  This odd construction
+   works around a bogus GCC diagnostic "shift count >= width of type".  */
+
+static int
+pre_value (bool precondition, int value)
+{
+  eassume (precondition);
+  return precondition ? value : 0;
+}
+
 /* Compute the number of trailing zero bits in val.  If val is zero,
    return the number of bits in val.  */
 static int
@@ -3111,7 +3121,8 @@ count_trailing_zero_bits (bits_word val)
 
       if (BITS_PER_BITS_WORD % BITS_PER_ULL != 0
           && BITS_WORD_MAX == (bits_word) -1)
-        val |= (bits_word) 1 << (BITS_PER_BITS_WORD % BITS_PER_ULL);
+        val |= (bits_word) 1 << pre_value (ULONG_MAX < BITS_WORD_MAX,
+                                           BITS_PER_BITS_WORD % BITS_PER_ULL);
       return count + count_trailing_zeros_ll (val);
     }
 }