add codegen test for rust-lang#74938

Author: tesuji

tests/codegen/issues/issue-74938-array-split-at.rs

@@ -0,0 +1,15 @@
+//@ compile-flags: -O
+
+#![crate_type = "lib"]
+
+const N: usize = 3;
+pub type T = u8;
+
+#[no_mangle]
+// CHECK-LABEL: @split_mutiple
+// CHECK-NOT: unreachable
+pub fn split_mutiple(slice: &[T]) -> (&[T], &[T]) {
+    let len = slice.len() / N;
+    slice.split_at(len * N)
+}
+