Use FL_USER0 for ELTS_SHARED

This makes space in RString for two bits for chilled strings.

array.c

@@ -42,12 +42,12 @@ VALUE rb_cArray_empty_frozen;
 
 /* Flags of RArray
  *
+ * 0:   RARRAY_SHARED_FLAG (equal to ELTS_SHARED)
+ *          The array is shared. The buffer this array points to is owned by
+ *          another array (the shared root).
  * 1:   RARRAY_EMBED_FLAG
  *          The array is embedded (its contents follow the header, rather than
  *          being on a separately allocated buffer).
- * 2:   RARRAY_SHARED_FLAG (equal to ELTS_SHARED)
- *          The array is shared. The buffer this array points to is owned by
- *          another array (the shared root).
  * 3-9: RARRAY_EMBED_LEN
  *          The length of the array when RARRAY_EMBED_FLAG is set.
  * 12:  RARRAY_SHARED_ROOT_FLAG

include/ruby/internal/core/rarray.h

@@ -80,6 +80,8 @@
  * here is at least incomplete.
  */
 enum ruby_rarray_flags {
+    /* RUBY_FL_USER0 is for ELTS_SHARED */
+
     /**
      * This flag  has something to do  with memory footprint.  If  the array is
      * "small"  enough, ruby  tries to  be creative  to abuse  padding bits  of
@@ -99,8 +101,6 @@ enum ruby_rarray_flags {
      */
     RARRAY_EMBED_FLAG      = RUBY_FL_USER1,
 
-    /* RUBY_FL_USER2 is for ELTS_SHARED */
-
     /**
      * When an array employs embedded strategy (see ::RARRAY_EMBED_FLAG), these
      * bits  are used  to store  the number  of elements  actually filled  into

include/ruby/internal/fl_type.h

@@ -370,7 +370,7 @@ ruby_fl_type {
      * 3rd parties.  It must be an implementation detail that they should never
      * know.  Might better be hidden.
      */
-    RUBY_ELTS_SHARED  = RUBY_FL_USER2,
+    RUBY_ELTS_SHARED  = RUBY_FL_USER0,
 
     /**
      * This flag has something to do with an object's class.  There are kind of

internal/string.h

@@ -15,8 +15,8 @@
 #include "ruby/encoding.h"      /* for rb_encoding */
 #include "ruby/ruby.h"          /* for VALUE */
 
+#define STR_SHARED       FL_USER0 /* = ELTS_SHARED */
 #define STR_NOEMBED      FL_USER1
-#define STR_SHARED       FL_USER2 /* = ELTS_SHARED */
 #define STR_CHILLED      FL_USER3
 
 enum ruby_rstring_private_flags {

string.c

@@ -80,13 +80,13 @@ VALUE rb_cSymbol;
 
 /* Flags of RString
  *
+ * 0:     STR_SHARED (equal to ELTS_SHARED)
+ *            The string is shared. The buffer this string points to is owned by
+ *            another string (the shared root).
  * 1:     RSTRING_NOEMBED
  *            The string is not embedded. When a string is embedded, the contents
  *            follow the header. When a string is not embedded, the contents is
  *            on a separately allocated buffer.
- * 2:     STR_SHARED (equal to ELTS_SHARED)
- *            The string is shared. The buffer this string points to is owned by
- *            another string (the shared root).
  * 3:     STR_CHILLED (will be frozen in a future version)
  *            The string appears frozen but can be mutated with a warning.
  * 4:     STR_PRECOMPUTED_HASH

yjit/src/cruby_bindings.inc.rs

@@ -251,7 +251,7 @@ pub const RUBY_FL_USER16: ruby_fl_type = 268435456;
 pub const RUBY_FL_USER17: ruby_fl_type = 536870912;
 pub const RUBY_FL_USER18: ruby_fl_type = 1073741824;
 pub const RUBY_FL_USER19: ruby_fl_type = -2147483648;
-pub const RUBY_ELTS_SHARED: ruby_fl_type = 16384;
+pub const RUBY_ELTS_SHARED: ruby_fl_type = 4096;
 pub const RUBY_FL_SINGLETON: ruby_fl_type = 8192;
 pub type ruby_fl_type = i32;
 pub const RSTRING_NOEMBED: ruby_rstring_flags = 8192;