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remove a hack that seems to only benefit a few very special cases

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This commit is contained in:
Ralf Jung 2020-10-25 18:06:41 +01:00
parent bd837e899b
commit 99a44ed086
3 changed files with 37 additions and 55 deletions
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58
compiler/rustc_mir/src/transform/promote_consts.rs
View file

@ -22,7 +22,7 @@ use rustc_middle::ty::cast::CastTy;
use rustc_middle::ty::subst::InternalSubsts;
use rustc_middle::ty::{self, List, TyCtxt, TypeFoldable};
use rustc_span::symbol::sym;
use rustc_span::{Span, DUMMY_SP};
use rustc_span::Span;
use rustc_index::vec::{Idx, IndexVec};
use rustc_target::spec::abi::Abi;
@ -326,41 +326,16 @@ impl<'tcx> Validator<'_, 'tcx> {
if place.projection.contains(&ProjectionElem::Deref) {
return Err(Unpromotable);
}
let mut has_mut_interior =
self.qualif_local::<qualifs::HasMutInterior>(place.local);
// HACK(eddyb) this should compute the same thing as
// `<HasMutInterior as Qualif>::in_projection` from
// `check_consts::qualifs` but without recursion.
if has_mut_interior {
// This allows borrowing fields which don't have
// `HasMutInterior`, from a type that does, e.g.:
// `let _: &'static _ = &(Cell::new(1), 2).1;`
let mut place_projection = &place.projection[..];
// FIXME(eddyb) use a forward loop instead of a reverse one.
while let &[ref proj_base @ .., elem] = place_projection {
// FIXME(eddyb) this is probably excessive, with
// the exception of `union` member accesses.
let ty =
Place::ty_from(place.local, proj_base, self.body, self.tcx)
.projection_ty(self.tcx, elem)
.ty;
if ty.is_freeze(self.tcx.at(DUMMY_SP), self.param_env) {
has_mut_interior = false;
break;
}
place_projection = proj_base;
}
if self.qualif_local::<qualifs::NeedsDrop>(place.local) {
return Err(Unpromotable);
}
// FIXME(eddyb) this duplicates part of `validate_rvalue`.
let has_mut_interior =
self.qualif_local::<qualifs::HasMutInterior>(place.local);
if has_mut_interior {
return Err(Unpromotable);
}
if self.qualif_local::<qualifs::NeedsDrop>(place.local) {
return Err(Unpromotable);
}
if let BorrowKind::Mut { .. } = kind {
let ty = place.ty(self.body, self.tcx).ty;
@ -692,28 +667,7 @@ impl<'tcx> Validator<'_, 'tcx> {
self.validate_place(place)?;
// HACK(eddyb) this should compute the same thing as
// `<HasMutInterior as Qualif>::in_projection` from
// `check_consts::qualifs` but without recursion.
let mut has_mut_interior =
self.qualif_local::<qualifs::HasMutInterior>(place.local);
if has_mut_interior {
let mut place_projection = place.projection;
// FIXME(eddyb) use a forward loop instead of a reverse one.
while let &[ref proj_base @ .., elem] = place_projection {
// FIXME(eddyb) this is probably excessive, with
// the exception of `union` member accesses.
let ty = Place::ty_from(place.local, proj_base, self.body, self.tcx)
.projection_ty(self.tcx, elem)
.ty;
if ty.is_freeze(self.tcx.at(DUMMY_SP), self.param_env) {
has_mut_interior = false;
break;
}
place_projection = proj_base;
}
}
let has_mut_interior = self.qualif_local::<qualifs::HasMutInterior>(place.local);
if has_mut_interior {
return Err(Unpromotable);
}

9
src/test/ui/consts/promote-not.rs
View file

@ -34,7 +34,14 @@ const TEST_UNION: () = {
let _x: &'static i32 = &unsafe { U { x: 0 }.x }; //~ ERROR temporary value dropped while borrowed
};
// In a `const`, we do not promote things with interior mutability. Not even if we "project it away".
const TEST_INTERIOR_MUT: () = {
// The "0." case is already ruled out by not permitting any interior mutability in `const`.
let _val: &'static _ = &(Cell::new(1), 2).1; //~ ERROR temporary value dropped while borrowed
};
fn main() {
// We must not promote things with interior mutability.
// We must not promote things with interior mutability. Not even if we "project it away".
let _val: &'static _ = &(Cell::new(1), 2).0; //~ ERROR temporary value dropped while borrowed
let _val: &'static _ = &(Cell::new(1), 2).1; //~ ERROR temporary value dropped while borrowed
}

25
src/test/ui/consts/promote-not.stderr
View file

@ -49,15 +49,36 @@ LL | };
| - temporary value is freed at the end of this statement
error[E0716]: temporary value dropped while borrowed
--> $DIR/promote-not.rs:39:29
--> $DIR/promote-not.rs:40:29
|
LL | let _val: &'static _ = &(Cell::new(1), 2).1;
| ---------- ^^^^^^^^^^^^^^^^^ creates a temporary which is freed while still in use
| |
| type annotation requires that borrow lasts for `'static`
LL | };
| - temporary value is freed at the end of this statement
error[E0716]: temporary value dropped while borrowed
--> $DIR/promote-not.rs:45:29
|
LL | let _val: &'static _ = &(Cell::new(1), 2).0;
| ---------- ^^^^^^^^^^^^^^^^^ creates a temporary which is freed while still in use
| |
| type annotation requires that borrow lasts for `'static`
LL | let _val: &'static _ = &(Cell::new(1), 2).1;
LL | }
| - temporary value is freed at the end of this statement
error[E0716]: temporary value dropped while borrowed
--> $DIR/promote-not.rs:46:29
|
LL | let _val: &'static _ = &(Cell::new(1), 2).1;
| ---------- ^^^^^^^^^^^^^^^^^ creates a temporary which is freed while still in use
| |
| type annotation requires that borrow lasts for `'static`
LL | }
| - temporary value is freed at the end of this statement
error: aborting due to 6 previous errors
error: aborting due to 8 previous errors
For more information about this error, try `rustc --explain E0716`.