src/test/run-fail/overflowing-lsh-4.rs

   1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 // ignore-pretty : (#23623) problems when  ending with // comments
  12
  13 // error-pattern:thread '<main>' panicked at 'shift operation overflowed'
  14 // compile-flags: -C debug-assertions
  15
  16 // This function is checking that our automatic truncation does not
  17 // sidestep the overflow checking.
  18
  19 #![warn(exceeding_bitshifts)]
  20
  21 #![feature(rustc_attrs)]
  22 #[rustc_no_mir] // FIXME #29769 MIR overflow checking is TBD.
  23 fn main() {
  24     // this signals overflow when checking is on
  25     let x = 1_i8 << 17;
  26
  27     // ... but when checking is off, the fallback will truncate the
  28     // input to its lower three bits (= 1). Note that this is *not*
  29     // the behavior of the x86 processor for 8- and 16-bit types,
  30     // but it is necessary to avoid undefined behavior from LLVM.
  31     //
  32     // We check that here, by ensuring the result has only been
  33     // shifted by one place; if overflow checking is turned off, then
  34     // this assertion will pass (and the compiletest driver will
  35     // report that the test did not produce the error expected above).
  36     assert_eq!(x, 2_i8);
  37 }