add codegen test for array::repeat

tests/codegen/array-repeat.rs

@@ -0,0 +1,15 @@
+// compile-flags: -O
+
+#![crate_type = "lib"]
+#![feature(array_repeat)]
+
+use std::array::repeat;
+
+// CHECK-LABEL: @byte_repeat
+#[no_mangle]
+fn byte_repeat(b: u8) -> [u8; 1024] {
+    // CHECK-NOT: alloca
+    // CHECK-NOT: store
+    // CHECK: memset
+    repeat(b)
+}