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rustc_mir: promote references of statics from other statics.

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This commit is contained in:
Eduard-Mihai Burtescu 2017-12-06 01:28:27 +02:00
parent cf30759a84
commit 292c6ac57f
2 changed files with 18 additions and 7 deletions
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23
src/librustc_mir/transform/qualify_consts.rs
View File

@ -41,6 +41,9 @@ use transform::{MirPass, MirSource};
use super::promote_consts::{self, Candidate, TempState};
bitflags! {
// Borrows of temporaries can be promoted only if
// they have none of these qualifications, with
// the exception of `STATIC_REF` (in statics only).
struct Qualif: u8 {
// Constant containing interior mutability (UnsafeCell).
const MUTABLE_INTERIOR = 1 << 0;
@ -65,10 +68,6 @@ bitflags! {
// promote_consts decided they weren't simple enough.
const NOT_PROMOTABLE = 1 << 6;
// Borrows of temporaries can be promoted only
// if they have none of the above qualifications.
const NEVER_PROMOTE = 0b111_1111;
// Const items can only have MUTABLE_INTERIOR
// and NOT_PROMOTABLE without producing an error.
const CONST_ERROR = !Qualif::MUTABLE_INTERIOR.bits &
@ -197,7 +196,17 @@ impl<'a, 'tcx> Qualifier<'a, 'tcx, 'tcx> {
self.add(original);
}
/// Check if an Place with the current qualifications could
/// Check if a Local with the current qualifications is promotable.
fn can_promote(&mut self) -> bool {
// References to statics are allowed, but only in other statics.
if self.mode == Mode::Static || self.mode == Mode::StaticMut {
(self.qualif - Qualif::STATIC_REF).is_empty()
} else {
self.qualif.is_empty()
}
}
/// Check if a Place with the current qualifications could
/// be consumed, by either an operand or a Deref projection.
fn try_consume(&mut self) -> bool {
if self.qualif.intersects(Qualif::STATIC) && self.mode != Mode::Fn {
@ -633,7 +642,7 @@ impl<'a, 'tcx> Visitor<'tcx> for Qualifier<'a, 'tcx, 'tcx> {
// We might have a candidate for promotion.
let candidate = Candidate::Ref(location);
if !self.qualif.intersects(Qualif::NEVER_PROMOTE) {
if self.can_promote() {
// We can only promote direct borrows of temps.
if let Place::Local(local) = *place {
if self.mir.local_kind(local) == LocalKind::Temp {
@ -745,7 +754,7 @@ impl<'a, 'tcx> Visitor<'tcx> for Qualifier<'a, 'tcx, 'tcx> {
this.visit_operand(arg, location);
if is_shuffle && i == 2 && this.mode == Mode::Fn {
let candidate = Candidate::ShuffleIndices(bb);
if !this.qualif.intersects(Qualif::NEVER_PROMOTE) {
if this.can_promote() {
this.promotion_candidates.push(candidate);
} else {
span_err!(this.tcx.sess, this.span, E0526,

2
src/test/run-pass/issue-44373.rs
View File

@ -8,6 +8,8 @@
// option. This file may not be copied, modified, or distributed
// except according to those terms.
// compile-flags: -Z borrowck=compare
struct Foo(bool);
struct Container(&'static [&'static Foo]);