1 files changed, 42 insertions, 3 deletions

diff --git a/include/ruby/internal/core/robject.h b/include/ruby/internal/core/robject.h
index f2028063a6..7823061d8f 100644
--- a/include/ruby/internal/core/robject.h
+++ b/include/ruby/internal/core/robject.h
@@ -75,6 +75,7 @@ enum ruby_robject_flags {
     ROBJECT_EMBED = RUBY_FL_USER1
 };
 
+#if !USE_RVARGC
 /**
  * This is an enum because GDB wants it (rather than a macro).  People need not
  * bother.
@@ -83,6 +84,7 @@ enum ruby_robject_consts {
     /** Max possible number of instance variables that can be embedded. */
     ROBJECT_EMBED_LEN_MAX = RBIMPL_EMBED_LEN_MAX_OF(VALUE)
 };
+#endif
 
 struct st_table;
 
@@ -95,6 +97,14 @@ struct RObject {
     /** Basic part, including flags and class. */
     struct RBasic basic;
 
+#if USE_RVARGC
+    /**
+    * Number of instance variables.  This is per object; objects might
+    * differ in this field even if they have the identical classes.
+    */
+    uint32_t numiv;
+#endif
+
     /** Object's specific fields. */
     union {
 
@@ -103,12 +113,13 @@ struct RObject {
          * this pattern.
          */
         struct {
-
+#if !USE_RVARGC
             /**
              * Number of instance variables.  This is per object; objects might
              * differ in this field even if they have the identical classes.
              */
             uint32_t numiv;
+#endif
 
             /** Pointer to a C array that holds instance variables. */
             VALUE *ivptr;
@@ -124,14 +135,38 @@ struct RObject {
             struct st_table *iv_index_tbl;
         } heap;
 
-        /**
-         * Embedded instance  variables.  When  an object  is small  enough, it
+#if USE_RVARGC
+        /* Embedded instance variables. When an object is small enough, it
          * uses this area to store the instance variables.
+         *
+         * 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
          */
+        VALUE ary[1];
+#else
+        /**
+        * Embedded instance  variables.  When  an object  is small  enough, it
+        * uses this area to store the instance variables.
+        */
         VALUE ary[ROBJECT_EMBED_LEN_MAX];
+#endif
     } as;
 };
 
+/* Offsets for YJIT */
+#ifndef __cplusplus
+# if USE_RVARGC
+static const int32_t ROBJECT_OFFSET_NUMIV = offsetof(struct RObject, numiv);
+# else
+static const int32_t ROBJECT_OFFSET_NUMIV = offsetof(struct RObject, as.heap.numiv);
+# endif
+static const int32_t ROBJECT_OFFSET_AS_HEAP_IVPTR = offsetof(struct RObject, as.heap.ivptr);
+static const int32_t ROBJECT_OFFSET_AS_HEAP_IV_INDEX_TBL = offsetof(struct RObject, as.heap.iv_index_tbl);
+static const int32_t ROBJECT_OFFSET_AS_ARY = offsetof(struct RObject, as.ary);
+#endif
+
 RBIMPL_ATTR_PURE_UNLESS_DEBUG()
 RBIMPL_ATTR_ARTIFICIAL()
 /**
@@ -146,12 +181,16 @@ ROBJECT_NUMIV(VALUE obj)
 {
     RBIMPL_ASSERT_TYPE(obj, RUBY_T_OBJECT);
 
+#if USE_RVARGC
+    return ROBJECT(obj)->numiv;
+#else
     if (RB_FL_ANY_RAW(obj, ROBJECT_EMBED)) {
         return ROBJECT_EMBED_LEN_MAX;
     }
     else {
         return ROBJECT(obj)->as.heap.numiv;
     }
+#endif
 }
 
 RBIMPL_ATTR_PURE_UNLESS_DEBUG()