pub use super::*;
-use crate::dataflow::{BitDenotation, GenKillSet};
+use crate::dataflow::generic::{AnalysisDomain, GenKill, GenKillAnalysis};
use rustc::mir::visit::Visitor;
use rustc::mir::*;
+use rustc::ty::{ParamEnv, TyCtxt};
+use rustc_span::DUMMY_SP;
+
+pub type MaybeMutBorrowedLocals<'mir, 'tcx> = MaybeBorrowedLocals<MutBorrow<'mir, 'tcx>>;
+
+/// A dataflow analysis that tracks whether a pointer or reference could possibly exist that points
+/// to a given local.
+///
+/// The `K` parameter determines what kind of borrows are tracked. By default,
+/// `MaybeBorrowedLocals` looks for *any* borrow of a local. If you are only interested in borrows
+/// that might allow mutation, use the `MaybeMutBorrowedLocals` type alias instead.
+///
+/// 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. `MaybeMutBorrowedLocals` is used during const checking to prove that a
+/// local has not been mutated via indirect assignment (e.g., `*p = 42`), the side-effects of a
+/// function call or inline assembly.
+pub struct MaybeBorrowedLocals<K = AnyBorrow> {
+ kind: K,
+}
-/// This calculates if any part of a MIR local could have previously been borrowed.
-/// This means that once a local has been borrowed, its bit will be set
-/// from that point and onwards, until we see a StorageDead statement for the local,
-/// at which points there is no memory associated with the local, so it cannot be borrowed.
-/// This is used to compute which locals are live during a yield expression for
-/// immovable generators.
-#[derive(Copy, Clone)]
-pub struct HaveBeenBorrowedLocals<'a, 'tcx> {
- body: &'a Body<'tcx>,
+impl MaybeBorrowedLocals {
+ /// A dataflow analysis that records whether a pointer or reference exists that may alias the
+ /// given local.
+ pub fn new() -> Self {
+ MaybeBorrowedLocals { kind: AnyBorrow }
+ }
}
-impl<'a, 'tcx> HaveBeenBorrowedLocals<'a, 'tcx> {
- pub fn new(body: &'a Body<'tcx>) -> Self {
- HaveBeenBorrowedLocals { body }
+impl MaybeMutBorrowedLocals<'mir, 'tcx> {
+ /// A dataflow analysis that records whether a pointer or reference exists that may *mutably*
+ /// alias the given local.
+ pub fn new_mut_only(
+ tcx: TyCtxt<'tcx>,
+ body: &'mir mir::Body<'tcx>,
+ param_env: ParamEnv<'tcx>,
+ ) -> Self {
+ MaybeBorrowedLocals { kind: MutBorrow { body, tcx, param_env } }
}
+}
- pub fn body(&self) -> &Body<'tcx> {
- self.body
+impl<K> MaybeBorrowedLocals<K> {
+ fn transfer_function<'a, T>(&'a self, trans: &'a mut T) -> TransferFunction<'a, T, K> {
+ TransferFunction { kind: &self.kind, trans }
}
}
-impl<'a, 'tcx> BitDenotation<'tcx> for HaveBeenBorrowedLocals<'a, 'tcx> {
+impl<K> AnalysisDomain<'tcx> for MaybeBorrowedLocals<K>
+where
+ K: BorrowAnalysisKind<'tcx>,
+{
type Idx = Local;
- fn name() -> &'static str {
- "has_been_borrowed_locals"
+
+ const NAME: &'static str = K::ANALYSIS_NAME;
+
+ fn bits_per_block(&self, body: &mir::Body<'tcx>) -> usize {
+ body.local_decls().len()
+ }
+
+ fn initialize_start_block(&self, _: &mir::Body<'tcx>, _: &mut BitSet<Self::Idx>) {
+ // No locals are aliased on function entry
+ }
+}
+
+impl<K> GenKillAnalysis<'tcx> for MaybeBorrowedLocals<K>
+where
+ K: BorrowAnalysisKind<'tcx>,
+{
+ 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 bits_per_block(&self) -> usize {
- self.body.local_decls.len()
+
+ 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 start_block_effect(&self, _on_entry: &mut BitSet<Local>) {
- // Nothing is borrowed on function entry
+ fn call_return_effect(
+ &self,
+ _trans: &mut impl GenKill<Self::Idx>,
+ _block: mir::BasicBlock,
+ _func: &mir::Operand<'tcx>,
+ _args: &[mir::Operand<'tcx>],
+ _dest_place: &mir::Place<'tcx>,
+ ) {
}
+}
- fn statement_effect(&self, trans: &mut GenKillSet<Local>, loc: Location) {
- let stmt = &self.body[loc.block].statements[loc.statement_index];
+impl<K> BottomValue for MaybeBorrowedLocals<K> {
+ // bottom = unborrowed
+ const BOTTOM_VALUE: bool = false;
+}
- BorrowedLocalsVisitor { trans }.visit_statement(stmt, loc);
+/// A `Visitor` that defines the transfer function for `MaybeBorrowedLocals`.
+struct TransferFunction<'a, T, K> {
+ trans: &'a mut T,
+ kind: &'a K,
+}
- // StorageDead invalidates all borrows and raw pointers to a local
- match stmt.kind {
- StatementKind::StorageDead(l) => trans.kill(l),
- _ => (),
+impl<T, K> Visitor<'tcx> for TransferFunction<'a, T, K>
+where
+ T: GenKill<Local>,
+ K: BorrowAnalysisKind<'tcx>,
+{
+ 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 terminator_effect(&self, trans: &mut GenKillSet<Local>, loc: Location) {
- let terminator = self.body[loc.block].terminator();
- BorrowedLocalsVisitor { trans }.visit_terminator(terminator, loc);
- match &terminator.kind {
- // Drop terminators borrows the location
- TerminatorKind::Drop { location, .. }
- | TerminatorKind::DropAndReplace { location, .. } => {
- if let Some(local) = find_local(location) {
- trans.gen(local);
+ fn visit_rvalue(&mut self, rvalue: &mir::Rvalue<'tcx>, location: Location) {
+ self.super_rvalue(rvalue, location);
+
+ match rvalue {
+ mir::Rvalue::AddressOf(mt, borrowed_place) => {
+ if !borrowed_place.is_indirect() && self.kind.in_address_of(*mt, borrowed_place) {
+ self.trans.gen(borrowed_place.local);
}
}
- _ => (),
+
+ mir::Rvalue::Ref(_, kind, borrowed_place) => {
+ if !borrowed_place.is_indirect() && self.kind.in_ref(*kind, borrowed_place) {
+ self.trans.gen(borrowed_place.local);
+ }
+ }
+
+ mir::Rvalue::Cast(..)
+ | mir::Rvalue::Use(..)
+ | mir::Rvalue::Repeat(..)
+ | mir::Rvalue::Len(..)
+ | mir::Rvalue::BinaryOp(..)
+ | mir::Rvalue::CheckedBinaryOp(..)
+ | mir::Rvalue::NullaryOp(..)
+ | mir::Rvalue::UnaryOp(..)
+ | mir::Rvalue::Discriminant(..)
+ | mir::Rvalue::Aggregate(..) => {}
}
}
- fn propagate_call_return(
- &self,
- _in_out: &mut BitSet<Local>,
- _call_bb: mir::BasicBlock,
- _dest_bb: mir::BasicBlock,
- _dest_place: &mir::Place<'tcx>,
- ) {
- // Nothing to do when a call returns successfully
+ fn visit_terminator(&mut self, terminator: &mir::Terminator<'tcx>, location: Location) {
+ self.super_terminator(terminator, location);
+
+ match terminator.kind {
+ // Drop terminators may call custom drop glue (`Drop::drop`), which takes `&mut self`
+ // as a parameter. Hypothetically, 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
+ mir::TerminatorKind::Drop { location: dropped_place, .. }
+ | mir::TerminatorKind::DropAndReplace { location: dropped_place, .. } => {
+ self.trans.gen(dropped_place.local);
+ }
+
+ TerminatorKind::Abort
+ | TerminatorKind::Assert { .. }
+ | TerminatorKind::Call { .. }
+ | TerminatorKind::FalseEdges { .. }
+ | TerminatorKind::FalseUnwind { .. }
+ | TerminatorKind::GeneratorDrop
+ | TerminatorKind::Goto { .. }
+ | TerminatorKind::Resume
+ | TerminatorKind::Return
+ | TerminatorKind::SwitchInt { .. }
+ | TerminatorKind::Unreachable
+ | TerminatorKind::Yield { .. } => {}
+ }
}
}
-impl<'a, 'tcx> BottomValue for HaveBeenBorrowedLocals<'a, 'tcx> {
- // bottom = unborrowed
- const BOTTOM_VALUE: bool = false;
+pub struct AnyBorrow;
+
+pub struct MutBorrow<'mir, 'tcx> {
+ tcx: TyCtxt<'tcx>,
+ body: &'mir Body<'tcx>,
+ param_env: ParamEnv<'tcx>,
}
-struct BorrowedLocalsVisitor<'gk> {
- trans: &'gk mut GenKillSet<Local>,
+impl MutBorrow<'mir, 'tcx> {
+ // `&` and `&raw` only allow mutation if the borrowed place is `!Freeze`.
+ //
+ // This assumes that it is UB to take the address of a struct field whose type is
+ // `Freeze`, then use pointer arithmetic to derive a pointer to a *different* field of
+ // that same struct whose type is `!Freeze`. If we decide that this is not UB, we will
+ // have to check the type of the borrowed **local** instead of the borrowed **place**
+ // below. See [rust-lang/unsafe-code-guidelines#134].
+ //
+ // [rust-lang/unsafe-code-guidelines#134]: https://github.com/rust-lang/unsafe-code-guidelines/issues/134
+ fn shared_borrow_allows_mutation(&self, place: &Place<'tcx>) -> bool {
+ !place.ty(self.body, self.tcx).ty.is_freeze(self.tcx, self.param_env, DUMMY_SP)
+ }
}
-fn find_local(place: &Place<'_>) -> Option<Local> {
- if !place.is_indirect() { Some(place.local) } else { None }
+pub trait BorrowAnalysisKind<'tcx> {
+ const ANALYSIS_NAME: &'static str;
+
+ fn in_address_of(&self, mt: Mutability, place: &Place<'tcx>) -> bool;
+ fn in_ref(&self, kind: mir::BorrowKind, place: &Place<'tcx>) -> bool;
}
-impl<'tcx> Visitor<'tcx> for BorrowedLocalsVisitor<'_> {
- fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
- if let Rvalue::Ref(_, _, ref place) = *rvalue {
- if let Some(local) = find_local(place) {
- self.trans.gen(local);
+impl BorrowAnalysisKind<'tcx> for AnyBorrow {
+ const ANALYSIS_NAME: &'static str = "maybe_borrowed_locals";
+
+ fn in_ref(&self, _: mir::BorrowKind, _: &Place<'_>) -> bool {
+ true
+ }
+ fn in_address_of(&self, _: Mutability, _: &Place<'_>) -> bool {
+ true
+ }
+}
+
+impl BorrowAnalysisKind<'tcx> for MutBorrow<'mir, 'tcx> {
+ const ANALYSIS_NAME: &'static str = "maybe_mut_borrowed_locals";
+
+ fn in_ref(&self, kind: mir::BorrowKind, place: &Place<'tcx>) -> bool {
+ match kind {
+ mir::BorrowKind::Mut { .. } => true,
+ mir::BorrowKind::Shared | mir::BorrowKind::Shallow | mir::BorrowKind::Unique => {
+ self.shared_borrow_allows_mutation(place)
}
}
+ }
- self.super_rvalue(rvalue, location)
+ fn in_address_of(&self, mt: Mutability, place: &Place<'tcx>) -> bool {
+ match mt {
+ Mutability::Mut => true,
+ Mutability::Not => self.shared_borrow_allows_mutation(place),
+ }
}
}
projects / rust.git / commitdiff