Refine GC_calloc_typed_descr_s to support pointers larger than words

Issue #627 (bdwgc).

* include/gc/gc_typed.h (GC_CALLOC_TYPED_DESCR_PTRS): New macro.
* include/gc/gc_typed.h (GC_CALLOC_TYPED_DESCR_WORDS): Add comment
(that the value is the number of both "normal" and "pointer-sized"
words).
* include/gc/gc_typed.h [!GC_BUILD] (GC_calloc_typed_descr_s.opaque_p):
New field.
* include/gc/gc_typed.h [!GC_BUILD] (GC_calloc_typed_descr_s.opaque):
Change elements count from GC_CALLOC_TYPED_DESCR_WORDS to
GC_CALLOC_TYPED_DESCR_WORDS-GC_CALLOC_TYPED_DESCR_PTRS.
* typd_mlc.c (GC_calloc_typed_descr_s): Move complex_d field upper to
be the first field.
* typd_mlc.c (GC_calloc_prepare_explicitly_typed): Update static assert
about size of GC_calloc_typed_descr_s to use both
GC_CALLOC_TYPED_DESCR_WORDS and GC_CALLOC_TYPED_DESCR_PTRS.

include/gc/gc_typed.h

@@ -117,13 +117,15 @@ GC_API GC_ATTR_MALLOC GC_ATTR_CALLOC_SIZE(1, 2) void * GC_CALL
         /* bitmap of d multiplied by the size of a pointer.     */
         /* Returned object is cleared.                          */
 
-#define GC_CALLOC_TYPED_DESCR_WORDS 8
+#define GC_CALLOC_TYPED_DESCR_PTRS 1
+#define GC_CALLOC_TYPED_DESCR_WORDS 8 /* includes space for pointers */
 
 #ifdef GC_BUILD
   struct GC_calloc_typed_descr_s;
 #else
   struct GC_calloc_typed_descr_s {
-    GC_word opaque[GC_CALLOC_TYPED_DESCR_WORDS];
+    GC_uintptr_t opaque_p[GC_CALLOC_TYPED_DESCR_PTRS];
+    GC_word opaque[GC_CALLOC_TYPED_DESCR_WORDS - GC_CALLOC_TYPED_DESCR_PTRS];
   };
 #endif
 

typd_mlc.c

@@ -467,9 +467,9 @@ STATIC int GC_make_array_descriptor(size_t nelements, size_t size,
 }
 
 struct GC_calloc_typed_descr_s {
+  complex_descriptor *complex_d; /* the first field, the only pointer */
   struct LeafDescriptor leaf;
   GC_descr simple_d;
-  complex_descriptor *complex_d;
   word alloc_lb; /* size_t actually */
   signed_word descr_type; /* int actually */
 };
@@ -480,7 +480,9 @@ GC_API int GC_CALL GC_calloc_prepare_explicitly_typed(
                                 size_t n, size_t lb, GC_descr d)
 {
     GC_STATIC_ASSERT(sizeof(struct GC_calloc_typed_descr_s)
-                        == GC_CALLOC_TYPED_DESCR_WORDS * sizeof(word));
+        == GC_CALLOC_TYPED_DESCR_PTRS * sizeof(ptr_t)
+            + (GC_CALLOC_TYPED_DESCR_WORDS - GC_CALLOC_TYPED_DESCR_PTRS)
+                * sizeof(word));
     GC_ASSERT(GC_explicit_typing_initialized);
     GC_ASSERT(sizeof(struct GC_calloc_typed_descr_s) == ctd_sz);
     (void)ctd_sz; /* unused currently */