Optimize duparray/expandarray -> putobject/expandarray

There's no point in making a copy of an array just to expand it. Saves
an unnecessary array allocation in the multiple assignment case, with
a 35-84% improvement in affected cases in benchmark/masgn.yml.

1 files changed, 14 insertions, 0 deletions

diff --git a/compile.c b/compile.c
index 8879e661fe..484399abc6 100644
--- a/compile.c
+++ b/compile.c
@@ -3396,6 +3396,20 @@ iseq_peephole_optimize(rb_iseq_t *iseq, LINK_ELEMENT *list, const int do_tailcal
         }
     }
 
+    if (IS_INSN_ID(iobj, duparray)) {
+        LINK_ELEMENT *next = iobj->link.next;
+        /*
+         *  duparray obj
+         *  expandarray X, 0
+         * =>
+         *  putobject obj
+         *  expandarray X, 0
+         */
+        if (IS_INSN(next) && IS_INSN_ID(next, expandarray)) {
+            INSN_OF(iobj) = BIN(putobject);
+        }
+    }
+
     if (IS_INSN_ID(iobj, anytostring)) {
         LINK_ELEMENT *next = iobj->link.next;
         /*