[Feature #18901] Support size pool movement for Arrays

This commit enables Arrays to move between size pools during compaction.
This can occur if the array is mutated such that it would fit in a
different size pool when embedded.

The move is carried out in two stages:

1. The RVALUE is moved to a destination heap during object movement
   phase of compaction
2. The array data is re-embedded and the original buffer free'd if
   required. This happens during the update references step

1 files changed, 41 insertions, 1 deletions

diff --git a/array.c b/array.c
index 7b3f5bd0b0..dc8c4abe07 100644
--- a/array.c
+++ b/array.c
@@ -107,7 +107,6 @@ should_not_be_shared_and_embedded(VALUE ary)
 #define ARY_SET_EMBED_LEN(ary, n) do { \
     long tmp_n = (n); \
     assert(ARY_EMBED_P(ary)); \
-    assert(!OBJ_FROZEN(ary)); \
     RBASIC(ary)->flags &= ~RARRAY_EMBED_LEN_MASK; \
     RBASIC(ary)->flags |= (tmp_n) << RARRAY_EMBED_LEN_SHIFT; \
 } while (0)
@@ -212,6 +211,30 @@ ary_embeddable_p(long capa)
 #endif
 }
 
+bool
+rb_ary_embeddable_p(VALUE ary)
+{
+    // if the array is shared or a shared root then it's not moveable
+    return !(ARY_SHARED_P(ary) || ARY_SHARED_ROOT_P(ary));
+}
+
+size_t
+rb_ary_size_as_embedded(VALUE ary)
+{
+    size_t real_size;
+
+    if (ARY_EMBED_P(ary)) {
+        real_size = ary_embed_size(ARY_EMBED_LEN(ary));
+    }
+    else if (rb_ary_embeddable_p(ary)) {
+        real_size = ary_embed_size(ARY_HEAP_CAPA(ary));
+    }
+    else {
+        real_size = sizeof(struct RString);
+    }
+    return real_size;
+}
+
 
 #if ARRAY_DEBUG
 #define ary_verify(ary) ary_verify_(ary, __FILE__, __LINE__)
@@ -468,6 +491,23 @@ rb_ary_detransient(VALUE ary)
 }
 #endif
 
+void
+rb_ary_make_embedded(VALUE ary)
+{
+    assert(rb_ary_embeddable_p(ary));
+    if (!ARY_EMBED_P(ary)) {
+        VALUE *buf = RARRAY_PTR(ary);
+        long len = RARRAY_LEN(ary);
+
+        FL_SET_EMBED(ary);
+        ARY_SET_EMBED_LEN(ary, len);
+        RARY_TRANSIENT_UNSET(ary);
+
+        memmove(RARRAY_PTR(ary), buf, len * sizeof(VALUE));
+        ary_heap_free_ptr(ary, buf, len * sizeof(VALUE));
+    }
+}
+
 static void
 ary_resize_capa(VALUE ary, long capacity)
 {