2 files changed, 17 insertions, 25 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index b91221ef8f3..010f5fd95dd 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,9 +1,9 @@
 2014-09-18  Paul Eggert  <eggert@cs.ucla.edu>
 
         Port USE_LOCAL_ALLOCATORS code to clang 3.4 x86-64.
-        * lisp.h (ALLOCA_FIXUP): New constant.
-        (LOCAL_ALLOCA): New macro.
-        (local_cons, make_local_vector, make_local_string): Use them.
+        * lisp.h (USE_LOCAL_ALLOCATORS): Define only if __GNUC__ &&
+        !__clang__.  This works with GCC and with clang and is safer for
+        compilers we don't know about.
         (local_cons): Rename parameter to make capture less likely.
 
 2014-09-17  Samuel Bronson  <naesten@gmail.com>
diff --git a/src/lisp.h b/src/lisp.h
index 7a3e0d6a8a3..c5e698cc7c7 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -4599,30 +4599,22 @@ verify (sizeof (struct Lisp_Cons) == sizeof (union Aligned_Cons));
 # define scoped_list3(x, y, z) list3 (x, y, z)
 #endif
 
-#if USE_STACK_LISP_OBJECTS && HAVE_STATEMENT_EXPRESSIONS
-
+/* Local allocators require both statement expressions and a
+   GCALIGNMENT-aligned alloca.  clang's alloca isn't properly aligned
+   in some cases.  In the absence of solid information, play it safe
+   for other non-GCC compilers.  */
+#if (USE_STACK_LISP_OBJECTS && HAVE_STATEMENT_EXPRESSIONS \
+     && __GNUC__ && !__clang__)
 # define USE_LOCAL_ALLOCATORS
+#endif
 
-/* Alignment fixup needed for alloca.  GCC aligns alloca properly already,
-   Clang sometimes doesn't, and play it safe for other random compilers.  */
-# if __GNUC__ && !__clang__
-enum { ALLOCA_FIXUP = 0 };
-# else
-enum { ALLOCA_FIXUP = GCALIGNMENT - 1 };
-# endif
-
-/* Declare a void * variable PTR and set it to a properly-aligned array of
-   N newly allocated bytes with function lifetime.  */
-# define LOCAL_ALLOCA(ptr, n)                           \
-    void *ptr = alloca ((n) + ALLOCA_FIXUP);            \
-    ptr = (void *) ((intptr_t) ptr_ & ~(ALLOCA_FIXUP))
+#ifdef USE_LOCAL_ALLOCATORS
 
 /* Return a function-scoped cons whose car is X and cdr is Y.  */
 
 # define local_cons(x, y)                                               \
     ({                                                                  \
-       LOCAL_ALLOCA (ptr_, sizeof (struct Lisp_Cons));                  \
-       struct Lisp_Cons *c_ = ptr_;                                     \
+       struct Lisp_Cons *c_ = alloca (sizeof (struct Lisp_Cons));       \
        c_->car = (x);                                                   \
        c_->u.cdr = (y);                                                 \
        make_lisp_ptr (c_, Lisp_Cons);                                   \
@@ -4640,9 +4632,9 @@ enum { ALLOCA_FIXUP = GCALIGNMENT - 1 };
        ptrdiff_t size_ = size;                                          \
        Lisp_Object init_ = init;                                        \
        Lisp_Object vec_;                                                \
-       if (size_ <= (MAX_ALLOCA - ALLOCA_FIXUP - header_size) / word_size) \
+       if (size_ <= (MAX_ALLOCA - header_size) / word_size)             \
          {                                                              \
-           LOCAL_ALLOCA (ptr_, size_ * word_size + header_size);        \
+           void *ptr_ = alloca (size_ * word_size + header_size);       \
            vec_ = local_vector_init (ptr_, size_, init_);               \
          }                                                              \
        else                                                             \
@@ -4657,10 +4649,10 @@ enum { ALLOCA_FIXUP = GCALIGNMENT - 1 };
        char const *data_ = data;                                        \
        ptrdiff_t nbytes_ = nbytes;                                      \
        Lisp_Object string_;                                             \
-       if (nbytes_                                                      \
-           <= MAX_ALLOCA - ALLOCA_FIXUP - sizeof (struct Lisp_String) - 1) \
+       if (nbytes_ <= MAX_ALLOCA - sizeof (struct Lisp_String) - 1)     \
          {                                                              \
-           LOCAL_ALLOCA (ptr_, sizeof (struct Lisp_String) + 1 + bytes_); \
+           struct Lisp_String *ptr_                                     \
+             = alloca (sizeof (struct Lisp_String) + 1 + nbytes_);      \
            string_ = local_string_init (ptr_, data_, nbytes_);          \
          }                                                              \
        else                                                             \