add codegen test

The test confirms that when val < base, we do not divide or multiply.

tests/codegen/checked_ilog.rs

@@ -0,0 +1,20 @@
+//@ compile-flags: -O
+
+#![crate_type = "lib"]
+
+// Ensure that when val < base, we do not divide or multiply.
+
+// CHECK-LABEL: @checked_ilog
+// CHECK-SAME: (i16 noundef %val, i16 noundef %base)
+#[no_mangle]
+pub fn checked_ilog(val: u16, base: u16) -> Option<u32> {
+    // CHECK-NOT: udiv
+    // CHECK-NOT: mul
+    // CHECK: %[[IS_LESS:.+]] = icmp ult i16 %val, %base
+    // CHECK: br i1 %[[IS_LESS]], label %[[TRUE:.+]], label %[[FALSE:.+]]
+    // CHECK: [[TRUE]]:
+    // CHECK-NOT: udiv
+    // CHECK-NOT: mul
+    // CHECK: ret { i32, i32 }
+    val.checked_ilog(base)
+}