do not premote non-ZST mutable references ever

This commit is contained in:
Ralf Jung 2020-08-16 11:08:29 +02:00
parent 6c6003a7ad
commit 720293b640
2 changed files with 19 additions and 16 deletions

View file

@ -364,15 +364,7 @@ impl<'tcx> Validator<'_, 'tcx> {
// In theory, any zero-sized value could be borrowed
// mutably without consequences. However, only &mut []
// is allowed right now, and only in functions.
if self.const_kind
== Some(hir::ConstContext::Static(hir::Mutability::Mut))
{
// Inside a `static mut`, &mut [...] is also allowed.
match ty.kind() {
ty::Array(..) | ty::Slice(_) => {}
_ => return Err(Unpromotable),
}
} else if let ty::Array(_, len) = ty.kind() {
if let ty::Array(_, len) = ty.kind() {
// FIXME(eddyb) the `self.is_non_const_fn` condition
// seems unnecessary, given that this is merely a ZST.
match len.try_eval_usize(self.tcx, self.param_env) {
@ -673,13 +665,7 @@ impl<'tcx> Validator<'_, 'tcx> {
// In theory, any zero-sized value could be borrowed
// mutably without consequences. However, only &mut []
// is allowed right now, and only in functions.
if self.const_kind == Some(hir::ConstContext::Static(hir::Mutability::Mut)) {
// Inside a `static mut`, &mut [...] is also allowed.
match ty.kind() {
ty::Array(..) | ty::Slice(_) => {}
_ => return Err(Unpromotable),
}
} else if let ty::Array(_, len) = ty.kind() {
if let ty::Array(_, len) = ty.kind() {
// FIXME(eddyb): We only return `Unpromotable` for `&mut []` inside a
// const context which seems unnecessary given that this is merely a ZST.
match len.try_eval_usize(self.tcx, self.param_env) {

View file

@ -0,0 +1,17 @@
// run-pass
#![feature(const_mut_refs)]
static mut TEST: i32 = {
// We cannot promote this, as CTFE needs to be able to mutate it later.
let x = &mut [1,2,3];
x[0] += 1;
x[0]
};
// This still works -- it's not done via promotion.
#[allow(unused)]
static mut TEST2: &'static mut [i32] = &mut [0,1,2];
fn main() {
assert_eq!(unsafe { TEST }, 2);
}