[Feature #18634] Implement Arrays on Variable Width Allocation

This commit implements arrays on Variable Width Allocation. This allows
longer arrays to be embedded (i.e. contents directly follow the object
header) which improves performance through better cache locality.

2 files changed, 21 insertions, 2 deletions

diff --git a/include/ruby/internal/abi.h b/include/ruby/internal/abi.h
index 7a6caa6e2e..98a63927c5 100644
--- a/include/ruby/internal/abi.h
+++ b/include/ruby/internal/abi.h
@@ -22,7 +22,7 @@
  * In released versions of Ruby, this number should not be changed since teeny
  * versions of Ruby should guarantee ABI compatibility.
  */
-#define RUBY_ABI_VERSION 0
+#define RUBY_ABI_VERSION 1
 
 /* Windows does not support weak symbols so ruby_abi_version will not exist
  * in the shared library. */
diff --git a/include/ruby/internal/core/rarray.h b/include/ruby/internal/core/rarray.h
index 9f1d0509ea..d9e08839cb 100644
--- a/include/ruby/internal/core/rarray.h
+++ b/include/ruby/internal/core/rarray.h
@@ -130,7 +130,13 @@ enum ruby_rarray_flags {
      * 3rd parties must  not be aware that  there even is more than  one way to
      * store array elements.  It was a bad idea to expose this to them.
      */
+#if USE_RVARGC
+    RARRAY_EMBED_LEN_MASK  = RUBY_FL_USER8 | RUBY_FL_USER7 | RUBY_FL_USER6 |
+                                 RUBY_FL_USER5 | RUBY_FL_USER4 | RUBY_FL_USER3
+#else
     RARRAY_EMBED_LEN_MASK  = RUBY_FL_USER4 | RUBY_FL_USER3
+#endif
+
 #if USE_TRANSIENT_HEAP
     ,
 
@@ -156,10 +162,14 @@ enum ruby_rarray_flags {
  */
 enum ruby_rarray_consts {
     /** Where ::RARRAY_EMBED_LEN_MASK resides. */
-    RARRAY_EMBED_LEN_SHIFT = RUBY_FL_USHIFT + 3,
+    RARRAY_EMBED_LEN_SHIFT = RUBY_FL_USHIFT + 3
+
+#if !USE_RVARGC
+    ,
 
     /** Max possible number elements that can be embedded. */
     RARRAY_EMBED_LEN_MAX   = RBIMPL_EMBED_LEN_MAX_OF(VALUE)
+#endif
 };
 
 /** Ruby's array. */
@@ -218,7 +228,16 @@ struct RArray {
          * to store its elements.  In this  case the length is encoded into the
          * flags.
          */
+#if USE_RVARGC
+        /* This is a length 1 array because:
+         *   1. GCC has a bug that does not optimize C flexible array members
+         *      (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102452)
+         *   2. Zero length arrays are not supported by all compilers
+         */
+        const VALUE ary[1];
+#else
         const VALUE ary[RARRAY_EMBED_LEN_MAX];
+#endif
     } as;
 };