[Emacs-diffs] /srv/bzr/emacs/trunk r110868: Another tweak to vectorlike_header change.

[Paul Eggert]

------------------------------------------------------------
revno: 110868
committer: Paul Eggert <address@hidden>
branch nick: trunk
timestamp: Sun 2012-11-11 17:09:34 -0800
message:
  Another tweak to vectorlike_header change.
  
  * alloc.c (struct Lisp_Vectorlike_Free, NEXT_IN_FREE_LIST):
  Remove, and replace all uses with ...
  (next_in_free_list, set_next_in_free_list):
  New functions, which respect C's aliasing rules better.
modified:
  src/ChangeLog
  src/alloc.c

=== modified file 'src/ChangeLog'
--- a/src/ChangeLog     2012-11-11 18:39:29 +0000
+++ b/src/ChangeLog     2012-11-12 01:09:34 +0000
@@ -1,3 +1,11 @@
+2012-11-12  Paul Eggert  <address@hidden>
+
+       Another tweak to vectorlike_header change.
+       * alloc.c (struct Lisp_Vectorlike_Free, NEXT_IN_FREE_LIST):
+       Remove, and replace all uses with ...
+       (next_in_free_list, set_next_in_free_list):
+       New functions, which respect C's aliasing rules better.
+
 2012-11-11  Paul Eggert  <address@hidden>
 
        * window.c (list4i): Rename from 'quad'.  All uses changed.

=== modified file 'src/alloc.c'
--- a/src/alloc.c       2012-11-09 11:38:31 +0000
+++ b/src/alloc.c       2012-11-12 01:09:34 +0000
@@ -2611,18 +2611,21 @@
 
 #define VINDEX(nbytes) (((nbytes) - VBLOCK_BYTES_MIN) / roundup_size)
 
-/* This special type is used to represent any block-allocated vectorlike
-   object on the free list.  */
-
-struct Lisp_Vectorlike_Free
-{
-  struct vectorlike_header header;
-  struct Lisp_Vector *next;
-};
-
-/* When V is on the free list, it's always treated as Lisp_Vectorlike_Free.  */
-
-#define NEXT_IN_FREE_LIST(v) ((struct Lisp_Vectorlike_Free *) v)->next
+/* Get and set the next field in block-allocated vectorlike objects on
+   the free list.  Doing it this way respects C's aliasing rules.
+   We could instead make 'contents' a union, but that would mean
+   changes everywhere that the code uses 'contents'.  */
+static struct Lisp_Vector *
+next_in_free_list (struct Lisp_Vector *v)
+{
+  intptr_t i = XLI (v->contents[0]);
+  return (struct Lisp_Vector *) i;
+}
+static void
+set_next_in_free_list (struct Lisp_Vector *v, struct Lisp_Vector *next)
+{
+  v->contents[0] = XIL ((intptr_t) next);
+}
 
 /* Common shortcut to setup vector on a free list.  */
 
@@ -2633,7 +2636,7 @@
     eassert ((nbytes) % roundup_size == 0);            \
     (tmp) = VINDEX (nbytes);                           \
     eassert ((tmp) < VECTOR_MAX_FREE_LIST_INDEX);      \
-    NEXT_IN_FREE_LIST (v) = vector_free_lists[tmp];    \
+    set_next_in_free_list (v, vector_free_lists[tmp]); \
     vector_free_lists[tmp] = (v);                      \
     total_free_vector_slots += (nbytes) / word_size;   \
   } while (0)
@@ -2730,7 +2733,7 @@
   if (vector_free_lists[index])
     {
       vector = vector_free_lists[index];
-      vector_free_lists[index] = NEXT_IN_FREE_LIST (vector);
+      vector_free_lists[index] = next_in_free_list (vector);
       total_free_vector_slots -= nbytes / word_size;
       return vector;
     }
@@ -2744,7 +2747,7 @@
       {
        /* This vector is larger than requested.  */
        vector = vector_free_lists[index];
-       vector_free_lists[index] = NEXT_IN_FREE_LIST (vector);
+       vector_free_lists[index] = next_in_free_list (vector);
        total_free_vector_slots -= nbytes / word_size;
 
        /* Excess bytes are used for the smaller vector,