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Use unions for uninhabitedness checking rather than mem::transmute

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This commit is contained in:
varkor 2018-10-18 16:58:10 +01:00
parent 51e1c6437e
commit 6e5e54f735
3 changed files with 18 additions and 26 deletions
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2
src/librustc/ty/layout.rs
View file

@ -557,7 +557,7 @@ impl<'a, 'tcx> LayoutCx<'tcx, TyCtxt<'a, 'tcx, 'tcx>> {
let size = element.size.checked_mul(count, dl)
.ok_or(LayoutError::SizeOverflow(ty))?;
let abi = if size != Size::ZERO && ty.conservative_is_uninhabited(tcx) {
let abi = if count != 0 && ty.conservative_is_uninhabited(tcx) {
Abi::Uninhabited
} else {
Abi::Aggregate { sized: true }

26
src/test/ui/consts/const-eval/ub-uninhabit.rs
View file

@ -1,13 +1,3 @@
// 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.
#![feature(const_transmute)]
#![allow(const_err)] // make sure we cannot allow away the errors tested here
@ -16,14 +6,18 @@ use std::mem;
#[derive(Copy, Clone)]
enum Bar {}
const BAD_BAD_BAD: Bar = unsafe { mem::transmute(()) };
//~^ ERROR it is undefined behavior to use this value
union TransmuteUnion<A: Clone + Copy, B: Clone + Copy> {
a: A,
b: B,
}
const BAD_BAD_BAD: Bar = unsafe { (TransmuteUnion::<(), Bar> { a: () }).b };
//~^ ERROR this constant likely exhibits undefined behavior
const BAD_BAD_REF: &Bar = unsafe { mem::transmute(1usize) };
//~^ ERROR it is undefined behavior to use this value
const BAD_BAD_ARRAY: [Bar; 1] = unsafe { mem::transmute(()) };
//~^ ERROR it is undefined behavior to use this value
const BAD_BAD_ARRAY: [Bar; 1] = unsafe { (TransmuteUnion::<(), [Bar; 1]> { a: () }).b };
//~^ ERROR this constant likely exhibits undefined behavior
fn main() {
}
fn main() {}

16
src/test/ui/consts/const-eval/ub-uninhabit.stderr
View file

@ -1,12 +1,10 @@
error[E0080]: it is undefined behavior to use this value
--> $DIR/ub-uninhabit.rs:19:1
|
LL | const BAD_BAD_BAD: Bar = unsafe { mem::transmute(()) };
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^------------------^^^
| |
| entered unreachable code
LL | const BAD_BAD_BAD: Bar = unsafe { (TransmuteUnion::<(), Bar> { a: () }).b };
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a value of an uninhabited type
|
= note: #[deny(const_err)] on by default
= note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
error[E0080]: it is undefined behavior to use this value
--> $DIR/ub-uninhabit.rs:22:1
@ -19,10 +17,10 @@ LL | const BAD_BAD_REF: &Bar = unsafe { mem::transmute(1usize) };
error[E0080]: it is undefined behavior to use this value
--> $DIR/ub-uninhabit.rs:25:1
|
LL | const BAD_BAD_ARRAY: [Bar; 1] = unsafe { mem::transmute(()) };
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^------------------^^^
| |
| entered unreachable code
LL | const BAD_BAD_ARRAY: [Bar; 1] = unsafe { (TransmuteUnion::<(), [Bar; 1]> { a: () }).b };
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a value of an uninhabited type
|
= note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
error: aborting due to 3 previous errors