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clean up const checking of mutable references

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This commit is contained in:
Ralf Jung 2024-08-18 01:24:50 +02:00
parent 3175cc2814
commit 9ad5728593
1 changed files with 2 additions and 77 deletions
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79
compiler/rustc_const_eval/src/check_consts/check.rs
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@ -11,11 +11,11 @@ use rustc_hir::{self as hir, LangItem};
use rustc_index::bit_set::BitSet;
use rustc_infer::infer::TyCtxtInferExt;
use rustc_infer::traits::ObligationCause;
use rustc_middle::mir::visit::{MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor};
use rustc_middle::mir::visit::Visitor;
use rustc_middle::mir::*;
use rustc_middle::span_bug;
use rustc_middle::ty::adjustment::PointerCoercion;
use rustc_middle::ty::{self, Instance, InstanceKind, Ty, TyCtxt, TypeVisitableExt};
use rustc_middle::ty::{self, Instance, InstanceKind, Ty, TypeVisitableExt};
use rustc_mir_dataflow::impls::MaybeStorageLive;
use rustc_mir_dataflow::storage::always_storage_live_locals;
use rustc_mir_dataflow::Analysis;
@ -373,47 +373,6 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
trace!("visit_rvalue: rvalue={:?} location={:?}", rvalue, location);
// Special-case reborrows to be more like a copy of a reference.
// FIXME: this does not actually handle all reborrows. It only detects cases where `*` is the outermost
// projection of the borrowed place, it skips deref'ing raw pointers and it skips `static`.
// All those cases are handled below with shared/mutable borrows.
// Once `const_mut_refs` is stable, we should be able to entirely remove this special case.
// (`const_refs_to_cell` is not needed, we already allow all borrows of indirect places anyway.)
match *rvalue {
Rvalue::Ref(_, kind, place) => {
if let Some(reborrowed_place_ref) = place_as_reborrow(self.tcx, self.body, place) {
let ctx = match kind {
BorrowKind::Shared => {
PlaceContext::NonMutatingUse(NonMutatingUseContext::SharedBorrow)
}
BorrowKind::Fake(_) => {
PlaceContext::NonMutatingUse(NonMutatingUseContext::FakeBorrow)
}
BorrowKind::Mut { .. } => {
PlaceContext::MutatingUse(MutatingUseContext::Borrow)
}
};
self.visit_local(reborrowed_place_ref.local, ctx, location);
self.visit_projection(reborrowed_place_ref, ctx, location);
return;
}
}
Rvalue::RawPtr(mutbl, place) => {
if let Some(reborrowed_place_ref) = place_as_reborrow(self.tcx, self.body, place) {
let ctx = match mutbl {
Mutability::Not => {
PlaceContext::NonMutatingUse(NonMutatingUseContext::RawBorrow)
}
Mutability::Mut => PlaceContext::MutatingUse(MutatingUseContext::RawBorrow),
};
self.visit_local(reborrowed_place_ref.local, ctx, location);
self.visit_projection(reborrowed_place_ref, ctx, location);
return;
}
}
_ => {}
}
self.super_rvalue(rvalue, location);
match rvalue {
@ -885,40 +844,6 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
}
}
fn place_as_reborrow<'tcx>(
tcx: TyCtxt<'tcx>,
body: &Body<'tcx>,
place: Place<'tcx>,
) -> Option<PlaceRef<'tcx>> {
match place.as_ref().last_projection() {
Some((place_base, ProjectionElem::Deref)) => {
// FIXME: why do statics and raw pointers get excluded here? This makes
// some code involving mutable pointers unstable, but it is unclear
// why that code is treated differently from mutable references.
// Once TransientMutBorrow and TransientCellBorrow are stable,
// this can probably be cleaned up without any behavioral changes.
// A borrow of a `static` also looks like `&(*_1)` in the MIR, but `_1` is a `const`
// that points to the allocation for the static. Don't treat these as reborrows.
if body.local_decls[place_base.local].is_ref_to_static() {
None
} else {
// Ensure the type being derefed is a reference and not a raw pointer.
// This is sufficient to prevent an access to a `static mut` from being marked as a
// reborrow, even if the check above were to disappear.
let inner_ty = place_base.ty(body, tcx).ty;
if let ty::Ref(..) = inner_ty.kind() {
return Some(place_base);
} else {
return None;
}
}
}
_ => None,
}
}
fn is_int_bool_float_or_char(ty: Ty<'_>) -> bool {
ty.is_bool() || ty.is_integral() || ty.is_char() || ty.is_floating_point()
}