From 06c7ff06662440a900c06cda5646b7090ab9d8c9 Mon Sep 17 00:00:00 2001
From: "Yukihiro \"Matz\" Matsumoto" <matz@ruby.or.jp>
Date: Fri, 16 Aug 2019 16:36:13 +0900
Subject: Avoid creating unnecessary empty arrays on splat.

But this changes requires `OP_ARYCAT` and `OP_ARYPUSH` to accept `nil`
as their first operand. Alternative VMs (e.g. `mruby/c`) that understand
mruby bytecode need to be updated.
---
 src/vm.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

(limited to 'src')

diff --git a/src/vm.c b/src/vm.c
index 12805a8e4..458b9249e 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -2441,7 +2441,12 @@ RETRY_TRY_BLOCK:
 
     CASE(OP_ARYCAT, B) {
       mrb_value splat = mrb_ary_splat(mrb, regs[a+1]);
-      mrb_ary_concat(mrb, regs[a], splat);
+      if (mrb_nil_p(regs[a])) {
+        regs[a] = splat;
+      }
+      else {
+        mrb_ary_concat(mrb, regs[a], splat);
+      }
       mrb_gc_arena_restore(mrb, ai);
       NEXT;
     }
-- 
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