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|
use super::*;
use crate::{AnalysisDomain, CallReturnPlaces, GenKill, GenKillAnalysis};
use rustc_middle::mir::visit::Visitor;
use rustc_middle::mir::*;
/// A dataflow analysis that tracks whether a pointer or reference could possibly exist that points
/// to a given local.
///
/// At present, this is used as a very limited form of alias analysis. For example,
/// `MaybeBorrowedLocals` is used to compute which locals are live during a yield expression for
/// immovable generators.
pub struct MaybeBorrowedLocals;
impl MaybeBorrowedLocals {
fn transfer_function<'a, T>(&'a self, trans: &'a mut T) -> TransferFunction<'a, T> {
TransferFunction { trans }
}
}
impl<'tcx> AnalysisDomain<'tcx> for MaybeBorrowedLocals {
type Domain = BitSet<Local>;
const NAME: &'static str = "maybe_borrowed_locals";
fn bottom_value(&self, body: &mir::Body<'tcx>) -> Self::Domain {
// bottom = unborrowed
BitSet::new_empty(body.local_decls().len())
}
fn initialize_start_block(&self, _: &mir::Body<'tcx>, _: &mut Self::Domain) {
// No locals are aliased on function entry
}
}
impl<'tcx> GenKillAnalysis<'tcx> for MaybeBorrowedLocals {
type Idx = Local;
fn statement_effect(
&self,
trans: &mut impl GenKill<Self::Idx>,
statement: &mir::Statement<'tcx>,
location: Location,
) {
self.transfer_function(trans).visit_statement(statement, location);
}
fn terminator_effect(
&self,
trans: &mut impl GenKill<Self::Idx>,
terminator: &mir::Terminator<'tcx>,
location: Location,
) {
self.transfer_function(trans).visit_terminator(terminator, location);
}
fn call_return_effect(
&self,
_trans: &mut impl GenKill<Self::Idx>,
_block: mir::BasicBlock,
_return_places: CallReturnPlaces<'_, 'tcx>,
) {
}
}
/// A `Visitor` that defines the transfer function for `MaybeBorrowedLocals`.
struct TransferFunction<'a, T> {
trans: &'a mut T,
}
impl<'tcx, T> Visitor<'tcx> for TransferFunction<'_, T>
where
T: GenKill<Local>,
{
fn visit_statement(&mut self, stmt: &Statement<'tcx>, location: Location) {
self.super_statement(stmt, location);
// When we reach a `StorageDead` statement, we can assume that any pointers to this memory
// are now invalid.
if let StatementKind::StorageDead(local) = stmt.kind {
self.trans.kill(local);
}
}
fn visit_rvalue(&mut self, rvalue: &mir::Rvalue<'tcx>, location: Location) {
self.super_rvalue(rvalue, location);
match rvalue {
mir::Rvalue::AddressOf(_, borrowed_place) | mir::Rvalue::Ref(_, _, borrowed_place) => {
if !borrowed_place.is_indirect() {
self.trans.gen(borrowed_place.local);
}
}
mir::Rvalue::Cast(..)
| mir::Rvalue::ShallowInitBox(..)
| mir::Rvalue::Use(..)
| mir::Rvalue::ThreadLocalRef(..)
| mir::Rvalue::Repeat(..)
| mir::Rvalue::Len(..)
| mir::Rvalue::BinaryOp(..)
| mir::Rvalue::CheckedBinaryOp(..)
| mir::Rvalue::NullaryOp(..)
| mir::Rvalue::UnaryOp(..)
| mir::Rvalue::Discriminant(..)
| mir::Rvalue::Aggregate(..)
| mir::Rvalue::CopyForDeref(..) => {}
}
}
fn visit_terminator(&mut self, terminator: &mir::Terminator<'tcx>, location: Location) {
self.super_terminator(terminator, location);
match terminator.kind {
mir::TerminatorKind::Drop { place: dropped_place, .. }
| mir::TerminatorKind::DropAndReplace { place: dropped_place, .. } => {
// Drop terminators may call custom drop glue (`Drop::drop`), which takes `&mut
// self` as a parameter. In the general case, a drop impl could launder that
// reference into the surrounding environment through a raw pointer, thus creating
// a valid `*mut` pointing to the dropped local. We are not yet willing to declare
// this particular case UB, so we must treat all dropped locals as mutably borrowed
// for now. See discussion on [#61069].
//
// [#61069]: https://github.com/rust-lang/rust/pull/61069
self.trans.gen(dropped_place.local);
}
TerminatorKind::Abort
| TerminatorKind::Assert { .. }
| TerminatorKind::Call { .. }
| TerminatorKind::FalseEdge { .. }
| TerminatorKind::FalseUnwind { .. }
| TerminatorKind::GeneratorDrop
| TerminatorKind::Goto { .. }
| TerminatorKind::InlineAsm { .. }
| TerminatorKind::Resume
| TerminatorKind::Return
| TerminatorKind::SwitchInt { .. }
| TerminatorKind::Unreachable
| TerminatorKind::Yield { .. } => {}
}
}
}
/// The set of locals that are borrowed at some point in the MIR body.
pub fn borrowed_locals(body: &Body<'_>) -> BitSet<Local> {
struct Borrowed(BitSet<Local>);
impl GenKill<Local> for Borrowed {
#[inline]
fn gen(&mut self, elem: Local) {
self.0.gen(elem)
}
#[inline]
fn kill(&mut self, _: Local) {
// Ignore borrow invalidation.
}
}
let mut borrowed = Borrowed(BitSet::new_empty(body.local_decls.len()));
TransferFunction { trans: &mut borrowed }.visit_body(body);
borrowed.0
}
|
