From 6f386152ccfe727a9deda68ca67856e33fc33508 Mon Sep 17 00:00:00 2001
From: Aaron Patterson <aaron.patterson@gmail.com>
Date: Mon, 26 Nov 2018 16:40:46 -0800
Subject: [PATCH] Use a shared array for the `duparray` instruction

In this example code:

```ruby
def foo
  [1, 2, 3, 4]
end
```

The array literal uses a `duparray` instruction. Before this patch,
`rb_ary_resurrect` would malloc and memcpy a new array buffer.  This
patch changes `rb_ary_resurrect` to use `ary_make_partial` so that the
new array object shares the underlying buffer with the array stored in
the instruction sequences.

Before this patch, the new array object is not shared:

```
$ ruby -r objspace -e'p ObjectSpace.dump([1, 2, 3, 4])'
"{\"address\":\"0x7fa2718372d0\", \"type\":\"ARRAY\", \"class\":\"0x7fa26f8b0010\", \"length\":4, \"memsize\":72, \"flags\":{\"wb_protected\":true}}\n"
```

After this patch:

```
$ ./ruby -r objspace -e'p ObjectSpace.dump([1, 2, 3, 4])'
"{\"address\":\"0x7f9a76883638\", \"type\":\"ARRAY\", \"class\":\"0x7f9a758af900\", \"length\":4, \"shared\":true, \"references\":[\"0x7f9a768837c8\"], \"memsize\":40, \"flags\":{\"wb_protected\":true}}\n"
```
---
 array.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/array.c b/array.c
index f74ceab04e..38ed1753bd 100644
--- a/array.c
+++ b/array.c
@@ -2191,7 +2191,7 @@ rb_ary_dup(VALUE ary)
 VALUE
 rb_ary_resurrect(VALUE ary)
 {
-    return rb_ary_new4(RARRAY_LEN(ary), RARRAY_CONST_PTR_TRANSIENT(ary));
+    return ary_make_partial(ary, rb_cArray, 0, RARRAY_LEN(ary));
 }
 
 extern VALUE rb_output_fs;
-- 
2.17.0