Embed small size array elements in the heap.

It reduces the memory consumption and sometimes improve the
performance as well.  For example, the consumed memory size
of `bench/bm_ao_render.rb` is reduced from 1.2GB to 1GB, and
its total execution time become 18.795 sec from 22.229 sec.

1 files changed, 33 insertions, 7 deletions

diff --git a/include/mruby/array.h b/include/mruby/array.h
index e553faf92..bd3124d8c 100644
--- a/include/mruby/array.h
+++ b/include/mruby/array.h
@@ -21,22 +21,48 @@ typedef struct mrb_shared_array {
   mrb_value *ptr;
 } mrb_shared_array;
 
+#define MRB_ARY_EMBED_LEN_MAX ((mrb_int)(sizeof(void*)*3/sizeof(mrb_value)))
 struct RArray {
   MRB_OBJECT_HEADER;
-  mrb_int len;
   union {
-    mrb_int capa;
-    mrb_shared_array *shared;
-  } aux;
-  mrb_value *ptr;
+    struct {
+      mrb_int len;
+      union {
+        mrb_int capa;
+        mrb_shared_array *shared;
+      } aux;
+      mrb_value *ptr;
+    } heap;
+    mrb_value embed[MRB_ARY_EMBED_LEN_MAX];
+  } as;
 };
 
 #define mrb_ary_ptr(v)    ((struct RArray*)(mrb_ptr(v)))
 #define mrb_ary_value(p)  mrb_obj_value((void*)(p))
 #define RARRAY(v)  ((struct RArray*)(mrb_ptr(v)))
 
-#define RARRAY_LEN(a) (RARRAY(a)->len)
-#define RARRAY_PTR(a) ((const mrb_value*)RARRAY(a)->ptr)
+#define MRB_ARY_EMBED       4
+#define MRB_ARY_EMBED_MASK  3
+#define ARY_EMBED_P(a) ((a)->flags & MRB_ARY_EMBED)
+#define ARY_SET_EMBED_FLAG(a) ((a)->flags |= MRB_ARY_EMBED)
+#define ARY_UNSET_EMBED_FLAG(a) ((a)->flags &= ~(MRB_ARY_EMBED|MRB_ARY_EMBED_MASK))
+#define ARY_EMBED_LEN(a) ((a)->flags & MRB_ARY_EMBED_MASK)
+#define ARY_SET_EMBED_LEN(a,len) (a)->flags = ((a)->flags&~MRB_ARY_EMBED_MASK) | ((len)&MRB_ARY_EMBED_MASK);
+#define ARY_EMBED_PTR(a) (&((a)->as.embed[0]))
+
+#define ARY_LEN(a) (ARY_EMBED_P(a)?ARY_EMBED_LEN(a):(a)->as.heap.len)
+#define ARY_PTR(a) (ARY_EMBED_P(a)?ARY_EMBED_PTR(a):(a)->as.heap.ptr)
+#define RARRAY_LEN(a) ARY_LEN(RARRAY(a))
+#define RARRAY_PTR(a) ARY_PTR(RARRAY(a))
+#define ARY_SET_LEN(a,n) do {\
+  if (ARY_EMBED_P(a)) {\
+    mrb_assert((n) <= MRB_ARY_EMBED_LEN_MAX); \
+    ARY_SET_EMBED_LEN(a,n);\
+  }\
+  else\
+    (a)->as.heap.len = (n);\
+} while (0)
+#define ARY_CAPA(a) (ARY_EMBED_P(a)?MRB_ARY_EMBED_LEN_MAX:(a)->as.heap.aux.capa)
 #define MRB_ARY_SHARED      256
 #define ARY_SHARED_P(a) ((a)->flags & MRB_ARY_SHARED)
 #define ARY_SET_SHARED_FLAG(a) ((a)->flags |= MRB_ARY_SHARED)