Remove reference counting for all frozen arrays

The RARRAY_LITERAL_FLAG was added in commit
5871ecf956711fcacad7c03f2aef95115ed25bc4 to improve CoW performance for
array literals by not keeping track of reference counts.

This commit reverts that commit and has an alternate implementation that
is more generic for all frozen arrays. Since frozen arrays cannot be
modified, we don't need to set the RARRAY_SHARED_ROOT_FLAG and we don't
need to do reference counting.

1 files changed, 17 insertions, 28 deletions

diff --git a/array.c b/array.c
index f398ac8e52..b0c4cee0bf 100644
--- a/array.c
+++ b/array.c
@@ -55,19 +55,19 @@ VALUE rb_cArray;
  *          The length of the array when RARRAY_EMBED_FLAG is set.
  * endif
  * 12:  RARRAY_SHARED_ROOT_FLAG
- *          The array is a shared root. The buffer this array points to is
- *          owned by this array but may be pointed to by other arrays.
+ *          The array is a shared root that does reference counting. The buffer
+ *          this array points to is owned by this array but may be pointed to
+ *          by other arrays.
+ *          Note: Frozen arrays may be a shared root without this flag being
+ *                set. Frozen arrays do not have reference counting because
+ *                they cannot be modified. Not updating the reference count
+ *                improves copy-on-write performance. Their reference count is
+ *                assumed to be infinity.
  * 13:  RARRAY_TRANSIENT_FLAG
  *          The buffer of the array is allocated on the transient heap.
  * 14:  RARRAY_PTR_IN_USE_FLAG
  *          The buffer of the array is in use. This is only used during
  *          debugging.
- * 15:  RARRAY_LITERAL_FLAG
- *          The array is a shared root for array literals. This differs from
- *          RARRAY_SHARED_ROOT_FLAG in that this does not keep track of the
- *          reference count (it assumes that the reference count is infinity).
- *          This is used to improve copy-on-write performance since updating
- *          reference counts could cause system page invalidation.
  */
 
 /* for OPTIMIZED_CMP: */
@@ -166,18 +166,20 @@ should_be_T_ARRAY(VALUE ary)
     const VALUE _value_ = (value); \
     assert(!ARY_EMBED_P(_ary_)); \
     assert(ARY_SHARED_P(_ary_)); \
-    assert(!ARY_LITERAL_P(_ary_)); \
-    assert(ARY_SHARED_ROOT_P(_value_) || ARY_LITERAL_P(_value_)); \
+    assert(!OBJ_FROZEN(_ary_)); \
+    assert(ARY_SHARED_ROOT_P(_value_) || OBJ_FROZEN(_value_)); \
     RB_OBJ_WRITE(_ary_, &RARRAY(_ary_)->as.heap.aux.shared_root, _value_); \
 } while (0)
 
-#define ARY_SHARED_ROOT_OCCUPIED(ary) (!ARY_LITERAL_P(ary) && ARY_SHARED_ROOT_REFCNT(ary) == 1)
+#define ARY_SHARED_ROOT_OCCUPIED(ary) (!OBJ_FROZEN(ary) && ARY_SHARED_ROOT_REFCNT(ary) == 1)
 #define ARY_SET_SHARED_ROOT_REFCNT(ary, value) do { \
     assert(ARY_SHARED_ROOT_P(ary)); \
+    assert(!OBJ_FROZEN(ary)); \
     assert((value) >= 0); \
     RARRAY(ary)->as.heap.aux.capa = (value); \
 } while (0)
 #define FL_SET_SHARED_ROOT(ary) do { \
+    assert(!OBJ_FROZEN(ary)); \
     assert(!ARY_EMBED_P(ary)); \
     assert(!RARRAY_TRANSIENT_P(ary)); \
     FL_SET((ary), RARRAY_SHARED_ROOT_FLAG); \
@@ -259,7 +261,7 @@ ary_verify_(VALUE ary, const char *file, int line)
         const VALUE *ptr = ARY_HEAP_PTR(ary);
         const VALUE *root_ptr = RARRAY_CONST_PTR_TRANSIENT(root);
         long len = ARY_HEAP_LEN(ary), root_len = RARRAY_LEN(root);
-        assert(ARY_SHARED_ROOT_P(root) || ARY_LITERAL_P(root));
+        assert(ARY_SHARED_ROOT_P(root) || OBJ_FROZEN(root));
         assert(root_ptr <= ptr && ptr + len <= root_ptr + root_len);
         ary_verify(root);
     }
@@ -588,7 +590,7 @@ ary_double_capa(VALUE ary, long min)
 static void
 rb_ary_decrement_share(VALUE shared_root)
 {
-    if (!ARY_LITERAL_P(shared_root)) {
+    if (!OBJ_FROZEN(shared_root)) {
         long num = ARY_SHARED_ROOT_REFCNT(shared_root);
         ARY_SET_SHARED_ROOT_REFCNT(shared_root, num - 1);
     }
@@ -619,7 +621,7 @@ rb_ary_reset(VALUE ary)
 static VALUE
 rb_ary_increment_share(VALUE shared_root)
 {
-    if (!ARY_LITERAL_P(shared_root)) {
+    if (!OBJ_FROZEN(shared_root)) {
         long num = ARY_SHARED_ROOT_REFCNT(shared_root);
         assert(num >= 0);
         ARY_SET_SHARED_ROOT_REFCNT(shared_root, num + 1);
@@ -982,15 +984,6 @@ rb_ary_tmp_new_fill(long capa)
     return ary;
 }
 
-VALUE
-rb_ary_literal_new(long capa)
-{
-    VALUE ary = ary_new(0, capa);
-    rb_ary_transient_heap_evacuate(ary, TRUE);
-    FL_SET(ary, RARRAY_LITERAL_FLAG);
-    return ary;
-}
-
 void
 rb_ary_free(VALUE ary)
 {
@@ -1044,7 +1037,6 @@ static VALUE
 ary_make_shared(VALUE ary)
 {
     assert(!ARY_EMBED_P(ary));
-    assert(!ARY_LITERAL_P(ary));
     ary_verify(ary);
 
     if (ARY_SHARED_P(ary)) {
@@ -1056,8 +1048,6 @@ ary_make_shared(VALUE ary)
     else if (OBJ_FROZEN(ary)) {
         rb_ary_transient_heap_evacuate(ary, TRUE);
         ary_shrink_capa(ary);
-        FL_SET_SHARED_ROOT(ary);
-        ARY_SET_SHARED_ROOT_REFCNT(ary, 1);
         return ary;
     }
     else {
@@ -1077,7 +1067,6 @@ ary_make_shared(VALUE ary)
         FL_SET_SHARED(ary);
         RB_DEBUG_COUNTER_INC(obj_ary_shared_create);
         ARY_SET_SHARED(ary, shared);
-        OBJ_FREEZE(shared);
 
         ary_verify(shared);
         ary_verify(ary);
@@ -1348,7 +1337,7 @@ ary_make_partial(VALUE ary, VALUE klass, long offset, long len)
         VALUE result = ary_alloc_heap(klass);
         assert(!ARY_EMBED_P(result));
 
-        VALUE shared = ARY_LITERAL_P(ary) ? ary : ary_make_shared(ary);
+        VALUE shared = ary_make_shared(ary);
 
         ARY_SET_PTR(result, RARRAY_CONST_PTR_TRANSIENT(ary));
         ARY_SET_LEN(result, RARRAY_LEN(ary));