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[rustc.git] / src / test / run-fail / overflowing-lsh-4.rs
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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
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11// ignore-pretty : (#23623) problems when ending with // comments
12
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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
b039eaaf 19#![warn(exceeding_bitshifts)]
c34b1796 20
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21#![feature(rustc_attrs)]
22#[rustc_no_mir] // FIXME #29769 MIR overflow checking is TBD.
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23fn main() {
24 // this signals overflow when checking is on
b039eaaf 25 let x = 1_i8 << 17;
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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}