Flatten bitmap when there is only one element

We can avoid allocating a bitmap when the number of elements in the iseq
is fewer than the size of an iseq_bits_t

1 files changed, 4 insertions, 1 deletions

diff --git a/vm_core.h b/vm_core.h
index 5a6643674a..b7d980e0ec 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -465,7 +465,10 @@ struct rb_iseq_constant_body {
     unsigned int ivc_size; // Number of IVC and ICVARC caches
     unsigned int ci_size;
     unsigned int stack_max; /* for stack overflow check */
-    iseq_bits_t * mark_offset_bits; /* Find references for GC */
+    union {
+        iseq_bits_t * list; /* Find references for GC */
+        iseq_bits_t single;
+    } mark_bits;
 
     char catch_except_p; /* If a frame of this ISeq may catch exception, set TRUE */
     // If true, this ISeq is leaf *and* backtraces are not used, for example,