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Fix an ICE when attempting to transmute an uninhabited type
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varkor committed May 17, 2018
1 parent dbd10f8 commit 05067cf
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Showing 2 changed files with 46 additions and 3 deletions.
16 changes: 13 additions & 3 deletions src/librustc_codegen_llvm/mir/block.rs
Expand Up @@ -428,9 +428,19 @@ impl<'a, 'tcx> FunctionCx<'a, 'tcx> {
let intrinsic = intrinsic.as_ref().map(|s| &s[..]);

if intrinsic == Some("transmute") {
let &(ref dest, target) = destination.as_ref().unwrap();
self.codegen_transmute(&bx, &args[0], dest);
funclet_br(self, bx, target);
if let Some(destination_ref) = destination.as_ref() {
let &(ref dest, target) = destination_ref;
self.trans_transmute(&bx, &args[0], dest);
funclet_br(self, bx, target);
} else {
// If we are trying to transmute to an uninhabited type,
// it is likely there is no allotted destination. In fact,
// transmuting to an uninhabited type is UB, which means
// we can do what we like. Here, we declare that transmuting
// into an uninhabited type is impossible, so anything following
// it must be unreachable.
bx.unreachable();
}
return;
}

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33 changes: 33 additions & 0 deletions src/test/compile-fail/never_transmute_never.rs
@@ -0,0 +1,33 @@
// 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.

// compile-pass

#![crate_type="lib"]

#![feature(never_type)]
#![allow(dead_code)]
#![allow(unreachable_code)]
#![allow(unused_variables)]

struct Foo;

pub fn f(x: !) -> ! {
x
}

pub fn ub() {
// This is completely undefined behaviour,
// but we still want to make sure it compiles.
let x: ! = unsafe {
std::mem::transmute::<Foo, !>(Foo)
};
f(x)
}

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