Suppress some unhelpful warnings when using clang.

* configure.ac: With clang, check for and use -Wno-switch,
-Wno-tautological-constant-out-of-range-compare and -Wno-pointer-sign.

* conf_post.h(assume): Use __builtin_unreachable for clang.

* src/filelock.c (lock_file_1): Rearrange to remove compiler warning
about excess arguments to snprintf.

ChangeLog

@@ -1,3 +1,8 @@
+2013-09-23  Jan Djärv  <jan.h.d@swipnet.se>
+
+	* configure.ac: With clang, check for and use -Wno-switch,
+	-Wno-tautological-constant-out-of-range-compare and -Wno-pointer-sign.
+
 2013-09-23  Daniel Colascione  <dancol@dancol.org>
 
 	* configure.ac: Check for valgrind headers.

configure.ac

@@ -787,10 +787,28 @@ AC_DEFUN([gl_GCC_VERSION_IFELSE],
   ]
 )
 
+# clang is unduly picky about some things.
+AC_CACHE_CHECK([whether the compiler is clang], [emacs_cv_clang],
+  [AC_COMPILE_IFELSE(
+     [AC_LANG_PROGRAM([[
+	  #ifndef __clang__
+	    #error "not clang"
+	  #endif
+        ]])],
+     [emacs_cv_clang=yes],
+     [emacs_cv_clang=no])])
+
 # When compiling with GCC, prefer -isystem to -I when including system
 # include files, to avoid generating useless diagnostics for the files.
 if test "$gl_gcc_warnings" != yes; then
   isystem='-I'
+  if test "$emacs_cv_clang" = yes
+  then
+     # Turn off some warnings if supported.
+     gl_WARN_ADD([-Wno-switch])
+     gl_WARN_ADD([-Wno-tautological-constant-out-of-range-compare])
+     gl_WARN_ADD([-Wno-pointer-sign])
+  fi
 else
   isystem='-isystem '
 
@@ -840,16 +858,6 @@ else
   nw="$nw -Wtype-limits"
   nw="$nw -Wunused-parameter"
 
-  # clang is unduly picky about some things.
-  AC_CACHE_CHECK([whether the compiler is clang], [emacs_cv_clang],
-    [AC_COMPILE_IFELSE(
-       [AC_LANG_PROGRAM([[
-	    #ifndef __clang__
-	      #error "not clang"
-	    #endif
-          ]])],
-       [emacs_cv_clang=yes],
-       [emacs_cv_clang=no])])
   if test $emacs_cv_clang = yes; then
     nw="$nw -Wcast-align"
   fi

src/ChangeLog

@@ -1,3 +1,10 @@
+2013-09-23  Jan Djärv  <jan.h.d@swipnet.se>
+
+	* filelock.c (lock_file_1): Rearrange to remove compiler warning
+	about excess arguments to snprintf.
+
+	* conf_post.h(assume): Use __builtin_unreachable for clang.
+
 2013-09-23  Juanma Barranquero  <lekktu@gmail.com>
 
 	* w32console.c (initialize_w32_display): Remove unused variable hlinfo.

src/conf_post.h

@@ -248,12 +248,20 @@ extern void _DebPrint (const char *fmt, ...);
 # define FLEXIBLE_ARRAY_MEMBER 1
 #endif
 
+#ifdef __clang__
+# ifndef __has_builtin
+#  define __has_builtin(x) 0
+# endif
+#endif
+
 /* assume(cond) tells the compiler (and lint) that a certain condition
  * will always hold, and that it should optimize (or check) accordingly. */
 #if defined lint
 # define assume(cond) ((cond) ? (void) 0 : abort ())
 #elif (__GNUC__ == 4 && __GNUC_MINOR__ >= 5) || __GNUC__ > 4
 # define assume(cond) ((cond) || (__builtin_unreachable(), 0))
+#elif defined (__clang__) && __has_builtin (__builtin_unreachable)
+# define assume(cond) ((cond) || (__builtin_unreachable(), 0))
 #elif defined __MSC_VER
 # define assume(cond) __assume ((cond))
 #else

src/filelock.c

@@ -459,10 +459,18 @@ lock_file_1 (char *lfname, bool force)
   char lock_info_str[MAX_LFINFO + 1];
   printmax_t pid = getpid ();
 
-  if (sizeof lock_info_str
-      <= snprintf (lock_info_str, sizeof lock_info_str,
-		   boot ? "%s@%s.%"pMd":%"pMd : "%s@%s.%"pMd,
-		   user_name, host_name, pid, boot))
+  if (boot)
+    {
+      if (sizeof lock_info_str
+          <= snprintf (lock_info_str, sizeof lock_info_str,
+                       "%s@%s.%"pMd":%"pMd,
+                       user_name, host_name, pid, boot))
+        return ENAMETOOLONG;
+    }
+  else if (sizeof lock_info_str
+           <= snprintf (lock_info_str, sizeof lock_info_str,
+                        "%s@%s.%"pMd,
+                        user_name, host_name, pid))
     return ENAMETOOLONG;
 
   return create_lock_file (lfname, lock_info_str, force);