diff -r 43287eef2fff -r 072f1114ea5d src/compiler/HIR.cpp
--- a/src/compiler/HIR.cpp	Mon Dec 24 02:56:02 2012 -0800
+++ b/src/compiler/HIR.cpp	Mon Dec 24 16:09:13 2012 -0800
@@ -75,11 +75,8 @@
 {
     __ object(hir->array());
 
-    if (!hir->type()->isConst()) {
-        // If the type isn't const, we have to assume a consumer may modify
-        // the array, and therefore we have to duplicate it here.
+    if (hir->duplicate())
         __ duparray(); 
-    }
 }
 
 void
@@ -355,16 +352,30 @@
 HIRTranslator::visitStore(HStore *store)
 {
     store->lval()->bind(this, emitter_);
+
     if (store->kind() == TOK_ASSIGN) {
-        store->rval()->accept(this);
+        // Fixed-length arrays and structs have copy semantics.
+        Local<Type> type(zone_, store->lval()->type());
+        if (type->isArray() && ArrayType::cast(type)->isFixedLength()) {
+            store->lval()->load(emitter_);
+            store->rval()->accept(this);
+            __ copyarray();
+        } else if (type->isStruct()) {
+            store->lval()->load(emitter_);
+            store->rval()->accept(this);
+            __ copystruct();
+        } else {
+            store->rval()->accept(this);
+            store->lval()->store(emitter_);
+        }
     } else {
         // Advanced case: dup the ref, load, op, store.
         store->lval()->hold(emitter_);
         store->lval()->load(emitter_);
         store->rval()->accept(this);
         __ binary(TokenToOpcode(store->kind()));
+        store->lval()->store(emitter_);
     }
-    store->lval()->store(emitter_);
 }
 
 void