Do not generate assumes for plain integer casts

src/test/codegen/no-assumes-on-casts.rs

@@ -0,0 +1,29 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![crate_type = "lib"]
+
+// compile-flags: -Cno-prepopulate-passes
+
+// CHECK-LABEL: fna
+#[no_mangle]
+pub fn fna(a: i16) -> i32 {
+    a as i32
+// CHECK-NOT: assume
+// CHECK: sext
+}
+
+// CHECK-LABEL: fnb
+#[no_mangle]
+pub fn fnb(a: u16) -> u32 {
+    a as u32
+// CHECK-NOT: assume
+// CHECK: zext
+}