Fix bug with clang + directory_files_internal + GC.

* src/dired.c (directory_files_internal): Use a volatile variable
to prevent the compiler from optimizing away all copies of a local.
I wonder how many other GC-related bugs like this lurk elsewhere?

Fixes: debbugs:16986

2 files changed, 12 insertions, 0 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index b85aee0d35a..93c27a6e565 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,5 +1,10 @@
 2014-08-02  Paul Eggert  <eggert@cs.ucla.edu>
 
+        Fix bug with clang + directory_files_internal + GC (Bug#16986).
+        * dired.c (directory_files_internal): Use a volatile variable
+        to prevent the compiler from optimizing away all copies of a local.
+        I wonder how many other GC-related bugs like this lurk elsewhere?
+
         Avoid 100% CPU utilization on ssh session exit (Bug#17691).
         * xterm.h (struct x_display_info): New member 'connection'.
         * xterm.c (x_term_init, x_delete_terminal): Set and use it,
diff --git a/src/dired.c b/src/dired.c
index 55b2f6658c7..c2db1f02782 100644
--- a/src/dired.c
+++ b/src/dired.c
@@ -150,6 +150,12 @@ directory_files_internal (Lisp_Object directory, Lisp_Object full,
   Lisp_Object w32_save = Qnil;
 #endif
 
+  /* Don't let the compiler optimize away all copies of DIRECTORY,
+     which would break GC; see Bug#16986.  Although this is required
+     only in the common case where GC_MARK_STACK == GC_MAKE_GCPROS_NOOPS,
+     it shouldn't break anything in the other cases.  */
+  Lisp_Object volatile directory_volatile = directory;
+
   /* Because of file name handlers, these functions might call
      Ffuncall, and cause a GC.  */
   list = encoded_directory = dirfilename = Qnil;
@@ -325,6 +331,7 @@ directory_files_internal (Lisp_Object directory, Lisp_Object full,
     list = Fsort (Fnreverse (list),
                   attrs ? Qfile_attributes_lessp : Qstring_lessp);
 
+  (void) directory_volatile;
   RETURN_UNGCPRO (list);
 }