Define GC_CAST_AWAY_CONST_PVOID() public macro

Issue #627 (bdwgc).

* dbg_mlc.c (GC_debug_ptr_store_and_dirty): Use
GC_CAST_AWAY_CONST_PVOID() instead of explicit cast to word and then
to void*.
* include/gc/gc.h (GC_GENERAL_REGISTER_DISAPPEARING_LINK_SAFE,
GC_REGISTER_LONG_LINK_SAFE): Likewise.
* include/private/gc_priv.h (GC_base_C): Likewise.
* specific.c (GC_key_create_inner): Likewise.
* include/gc/gc.h (include/gc/gc.h): New public macro.

dbg_mlc.c

@@ -611,8 +611,8 @@ GC_API void GC_CALL GC_debug_end_stubborn_change(const void *p)
 
 GC_API void GC_CALL GC_debug_ptr_store_and_dirty(void *p, const void *q)
 {
-    *(void **)GC_is_visible(p) = GC_is_valid_displacement(
-                                        (/* no const */ void *)(word)q);
+    *(void **)GC_is_visible(p)
+                = GC_is_valid_displacement(GC_CAST_AWAY_CONST_PVOID(q));
     GC_debug_end_stubborn_change(p);
     REACHABLE_AFTER_DIRTY(q);
 }

include/gc/gc.h

@@ -1098,15 +1098,16 @@ GC_API /* 'realloc' attr */ GC_ATTR_ALLOC_SIZE(2) void * GC_CALL
         GC_debug_realloc_replacement(void * /* object_addr */,
                                      size_t /* size_in_bytes */);
 
+#define GC_CAST_AWAY_CONST_PVOID(p) ((/* no const */ void *)(GC_uintptr_t)(p))
+
 /* Convenient macros for disappearing links registration working both   */
 /* for debug and non-debug allocated objects, and accepting interior    */
 /* pointers to object.                                                  */
 #define GC_GENERAL_REGISTER_DISAPPEARING_LINK_SAFE(link, obj) \
       GC_general_register_disappearing_link(link, \
-                        GC_base((/* no const */ void *)(GC_word)(obj)))
+                                        GC_base(GC_CAST_AWAY_CONST_PVOID(obj)))
 #define GC_REGISTER_LONG_LINK_SAFE(link, obj) \
-      GC_register_long_link(link, \
-                            GC_base((/* no const */ void *)(GC_word)(obj)))
+      GC_register_long_link(link, GC_base(GC_CAST_AWAY_CONST_PVOID(obj)))
 
 #ifdef GC_DEBUG_REPLACEMENT
 # define GC_MALLOC(sz) GC_debug_malloc_replacement(sz)

include/private/gc_priv.h

@@ -2705,7 +2705,7 @@ GC_EXTERN GC_bool GC_print_back_height;
 #endif
 
 /* Same as GC_base but excepts and returns a pointer to const object.   */
-#define GC_base_C(p) ((const void *)GC_base((/* no const */ void *)(word)(p)))
+#define GC_base_C(p) ((const void *)GC_base(GC_CAST_AWAY_CONST_PVOID(p)))
 
 /* Debugging print routines: */
 void GC_print_block_list(void);

specific.c

@@ -34,10 +34,10 @@ GC_INNER int GC_key_create_inner(tsd ** key_ptr)
     GC_ASSERT(ADDR(&invalid_tse.next) % sizeof(tse *) == 0);
     result = (tsd *)MALLOC_CLEAR(sizeof(tsd));
     if (NULL == result) return ENOMEM;
-    ret = pthread_mutex_init(&result->lock, NULL);
+    ret = pthread_mutex_init(&(result -> lock), NULL);
     if (ret != 0) return ret;
     for (i = 0; i < TS_CACHE_SIZE; ++i) {
-      result -> cache[i] = (/* no const */ tse *)(word)(&invalid_tse);
+      result -> cache[i] = (tse *)GC_CAST_AWAY_CONST_PVOID(&invalid_tse);
     }
 #   ifdef GC_ASSERTIONS
       for (i = 0; i < TS_HASH_SIZE; ++i) {