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976 lines
38 KiB
Rust
976 lines
38 KiB
Rust
//! A pass that promotes borrows of constant rvalues.
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//!
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//! The rvalues considered constant are trees of temps,
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//! each with exactly one initialization, and holding
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//! a constant value with no interior mutability.
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//! They are placed into a new MIR constant body in
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//! `promoted` and the borrow rvalue is replaced with
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//! a `Literal::Promoted` using the index into `promoted`
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//! of that constant MIR.
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//!
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//! This pass assumes that every use is dominated by an
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//! initialization and can otherwise silence errors, if
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//! move analysis runs after promotion on broken MIR.
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use either::{Left, Right};
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use rustc_hir as hir;
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use rustc_middle::mir;
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use rustc_middle::mir::visit::{MutVisitor, MutatingUseContext, PlaceContext, Visitor};
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use rustc_middle::mir::*;
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use rustc_middle::ty::GenericArgs;
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use rustc_middle::ty::{self, List, Ty, TyCtxt, TypeVisitableExt};
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use rustc_span::Span;
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use rustc_index::{Idx, IndexSlice, IndexVec};
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use rustc_span::source_map::Spanned;
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use std::assert_matches::assert_matches;
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use std::cell::Cell;
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use std::{cmp, iter, mem};
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use rustc_const_eval::transform::check_consts::{qualifs, ConstCx};
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/// A `MirPass` for promotion.
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///
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/// Promotion is the extraction of promotable temps into separate MIR bodies so they can have
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/// `'static` lifetime.
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///
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/// After this pass is run, `promoted_fragments` will hold the MIR body corresponding to each
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/// newly created `Constant`.
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#[derive(Default)]
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pub struct PromoteTemps<'tcx> {
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pub promoted_fragments: Cell<IndexVec<Promoted, Body<'tcx>>>,
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}
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impl<'tcx> MirPass<'tcx> for PromoteTemps<'tcx> {
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fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
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// There's not really any point in promoting errorful MIR.
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//
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// This does not include MIR that failed const-checking, which we still try to promote.
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if let Err(_) = body.return_ty().error_reported() {
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debug!("PromoteTemps: MIR had errors");
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return;
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}
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if body.source.promoted.is_some() {
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return;
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}
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let ccx = ConstCx::new(tcx, body);
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let (mut temps, all_candidates) = collect_temps_and_candidates(&ccx);
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let promotable_candidates = validate_candidates(&ccx, &mut temps, &all_candidates);
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let promoted = promote_candidates(body, tcx, temps, promotable_candidates);
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self.promoted_fragments.set(promoted);
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}
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}
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/// State of a temporary during collection and promotion.
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#[derive(Copy, Clone, PartialEq, Eq, Debug)]
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enum TempState {
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/// No references to this temp.
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Undefined,
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/// One direct assignment and any number of direct uses.
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/// A borrow of this temp is promotable if the assigned
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/// value is qualified as constant.
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Defined { location: Location, uses: usize, valid: Result<(), ()> },
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/// Any other combination of assignments/uses.
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Unpromotable,
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/// This temp was part of an rvalue which got extracted
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/// during promotion and needs cleanup.
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PromotedOut,
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}
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/// A "root candidate" for promotion, which will become the
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/// returned value in a promoted MIR, unless it's a subset
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/// of a larger candidate.
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#[derive(Copy, Clone, PartialEq, Eq, Debug)]
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struct Candidate {
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location: Location,
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}
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struct Collector<'a, 'tcx> {
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ccx: &'a ConstCx<'a, 'tcx>,
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temps: IndexVec<Local, TempState>,
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candidates: Vec<Candidate>,
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}
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impl<'tcx> Visitor<'tcx> for Collector<'_, 'tcx> {
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fn visit_local(&mut self, index: Local, context: PlaceContext, location: Location) {
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debug!("visit_local: index={:?} context={:?} location={:?}", index, context, location);
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// We're only interested in temporaries and the return place
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match self.ccx.body.local_kind(index) {
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LocalKind::Arg => return,
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LocalKind::Temp if self.ccx.body.local_decls[index].is_user_variable() => return,
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LocalKind::ReturnPointer | LocalKind::Temp => {}
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}
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// Ignore drops, if the temp gets promoted,
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// then it's constant and thus drop is noop.
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// Non-uses are also irrelevant.
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if context.is_drop() || !context.is_use() {
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debug!(
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"visit_local: context.is_drop={:?} context.is_use={:?}",
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context.is_drop(),
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context.is_use(),
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);
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return;
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}
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let temp = &mut self.temps[index];
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debug!("visit_local: temp={:?}", temp);
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*temp = match *temp {
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TempState::Undefined => match context {
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PlaceContext::MutatingUse(MutatingUseContext::Store)
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| PlaceContext::MutatingUse(MutatingUseContext::Call) => {
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TempState::Defined { location, uses: 0, valid: Err(()) }
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}
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_ => TempState::Unpromotable,
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},
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TempState::Defined { ref mut uses, .. } => {
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// We always allow borrows, even mutable ones, as we need
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// to promote mutable borrows of some ZSTs e.g., `&mut []`.
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let allowed_use = match context {
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PlaceContext::MutatingUse(MutatingUseContext::Borrow)
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| PlaceContext::NonMutatingUse(_) => true,
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PlaceContext::MutatingUse(_) | PlaceContext::NonUse(_) => false,
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};
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debug!("visit_local: allowed_use={:?}", allowed_use);
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if allowed_use {
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*uses += 1;
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return;
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}
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TempState::Unpromotable
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}
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TempState::Unpromotable | TempState::PromotedOut => TempState::Unpromotable,
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};
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}
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fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
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self.super_rvalue(rvalue, location);
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if let Rvalue::Ref(..) = *rvalue {
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self.candidates.push(Candidate { location });
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}
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}
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}
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fn collect_temps_and_candidates<'tcx>(
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ccx: &ConstCx<'_, 'tcx>,
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) -> (IndexVec<Local, TempState>, Vec<Candidate>) {
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let mut collector = Collector {
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temps: IndexVec::from_elem(TempState::Undefined, &ccx.body.local_decls),
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candidates: vec![],
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ccx,
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};
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for (bb, data) in traversal::reverse_postorder(ccx.body) {
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collector.visit_basic_block_data(bb, data);
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}
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(collector.temps, collector.candidates)
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}
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/// Checks whether locals that appear in a promotion context (`Candidate`) are actually promotable.
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///
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/// This wraps an `Item`, and has access to all fields of that `Item` via `Deref` coercion.
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struct Validator<'a, 'tcx> {
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ccx: &'a ConstCx<'a, 'tcx>,
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temps: &'a mut IndexSlice<Local, TempState>,
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}
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impl<'a, 'tcx> std::ops::Deref for Validator<'a, 'tcx> {
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type Target = ConstCx<'a, 'tcx>;
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fn deref(&self) -> &Self::Target {
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self.ccx
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}
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}
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struct Unpromotable;
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impl<'tcx> Validator<'_, 'tcx> {
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fn validate_candidate(&mut self, candidate: Candidate) -> Result<(), Unpromotable> {
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let Left(statement) = self.body.stmt_at(candidate.location) else { bug!() };
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let Some((_, Rvalue::Ref(_, kind, place))) = statement.kind.as_assign() else { bug!() };
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// We can only promote interior borrows of promotable temps (non-temps
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// don't get promoted anyway).
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self.validate_local(place.local)?;
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// The reference operation itself must be promotable.
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// (Needs to come after `validate_local` to avoid ICEs.)
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self.validate_ref(*kind, place)?;
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// We do not check all the projections (they do not get promoted anyway),
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// but we do stay away from promoting anything involving a dereference.
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if place.projection.contains(&ProjectionElem::Deref) {
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return Err(Unpromotable);
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}
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Ok(())
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}
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// FIXME(eddyb) maybe cache this?
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fn qualif_local<Q: qualifs::Qualif>(&mut self, local: Local) -> bool {
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let TempState::Defined { location: loc, .. } = self.temps[local] else {
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return false;
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};
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let stmt_or_term = self.body.stmt_at(loc);
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match stmt_or_term {
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Left(statement) => {
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let Some((_, rhs)) = statement.kind.as_assign() else {
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span_bug!(statement.source_info.span, "{:?} is not an assignment", statement)
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};
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qualifs::in_rvalue::<Q, _>(self.ccx, &mut |l| self.qualif_local::<Q>(l), rhs)
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}
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Right(terminator) => {
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assert_matches!(terminator.kind, TerminatorKind::Call { .. });
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let return_ty = self.body.local_decls[local].ty;
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Q::in_any_value_of_ty(self.ccx, return_ty)
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}
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}
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}
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fn validate_local(&mut self, local: Local) -> Result<(), Unpromotable> {
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let TempState::Defined { location: loc, uses, valid } = self.temps[local] else {
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return Err(Unpromotable);
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};
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// We cannot promote things that need dropping, since the promoted value would not get
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// dropped.
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if self.qualif_local::<qualifs::NeedsDrop>(local) {
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return Err(Unpromotable);
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}
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if valid.is_ok() {
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return Ok(());
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}
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let ok = {
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let stmt_or_term = self.body.stmt_at(loc);
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match stmt_or_term {
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Left(statement) => {
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let Some((_, rhs)) = statement.kind.as_assign() else {
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span_bug!(
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statement.source_info.span,
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"{:?} is not an assignment",
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statement
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)
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};
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self.validate_rvalue(rhs)
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}
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Right(terminator) => match &terminator.kind {
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TerminatorKind::Call { func, args, .. } => self.validate_call(func, args),
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TerminatorKind::Yield { .. } => Err(Unpromotable),
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kind => {
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span_bug!(terminator.source_info.span, "{:?} not promotable", kind);
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}
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},
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}
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};
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self.temps[local] = match ok {
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Ok(()) => TempState::Defined { location: loc, uses, valid: Ok(()) },
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Err(_) => TempState::Unpromotable,
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};
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ok
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}
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fn validate_place(&mut self, place: PlaceRef<'tcx>) -> Result<(), Unpromotable> {
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let Some((place_base, elem)) = place.last_projection() else {
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return self.validate_local(place.local);
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};
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// Validate topmost projection, then recurse.
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match elem {
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// Recurse directly.
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ProjectionElem::ConstantIndex { .. }
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| ProjectionElem::Subtype(_)
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| ProjectionElem::Subslice { .. } => {}
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// Never recurse.
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ProjectionElem::OpaqueCast(..) | ProjectionElem::Downcast(..) => {
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return Err(Unpromotable);
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}
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ProjectionElem::Deref => {
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// When a static is used by-value, that gets desugared to `*STATIC_ADDR`,
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// and we need to be able to promote this. So check if this deref matches
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// that specific pattern.
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// We need to make sure this is a `Deref` of a local with no further projections.
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// Discussion can be found at
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// https://github.com/rust-lang/rust/pull/74945#discussion_r463063247
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if let Some(local) = place_base.as_local()
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&& let TempState::Defined { location, .. } = self.temps[local]
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&& let Left(def_stmt) = self.body.stmt_at(location)
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&& let Some((_, Rvalue::Use(Operand::Constant(c)))) = def_stmt.kind.as_assign()
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&& let Some(did) = c.check_static_ptr(self.tcx)
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// Evaluating a promoted may not read statics except if it got
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// promoted from a static (this is a CTFE check). So we
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// can only promote static accesses inside statics.
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&& let Some(hir::ConstContext::Static(..)) = self.const_kind
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&& !self.tcx.is_thread_local_static(did)
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{
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// Recurse.
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} else {
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return Err(Unpromotable);
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}
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}
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ProjectionElem::Index(local) => {
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// Only accept if we can predict the index and are indexing an array.
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if let TempState::Defined { location: loc, .. } = self.temps[local]
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&& let Left(statement) = self.body.stmt_at(loc)
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&& let Some((_, Rvalue::Use(Operand::Constant(c)))) = statement.kind.as_assign()
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&& let Some(idx) = c.const_.try_eval_target_usize(self.tcx, self.param_env)
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// Determine the type of the thing we are indexing.
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&& let ty::Array(_, len) = place_base.ty(self.body, self.tcx).ty.kind()
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// It's an array; determine its length.
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&& let Some(len) = len.try_eval_target_usize(self.tcx, self.param_env)
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// If the index is in-bounds, go ahead.
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&& idx < len
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{
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self.validate_local(local)?;
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// Recurse.
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} else {
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return Err(Unpromotable);
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}
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}
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ProjectionElem::Field(..) => {
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let base_ty = place_base.ty(self.body, self.tcx).ty;
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if base_ty.is_union() {
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// No promotion of union field accesses.
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return Err(Unpromotable);
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}
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}
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}
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self.validate_place(place_base)
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}
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fn validate_operand(&mut self, operand: &Operand<'tcx>) -> Result<(), Unpromotable> {
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match operand {
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Operand::Copy(place) | Operand::Move(place) => self.validate_place(place.as_ref()),
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// The qualifs for a constant (e.g. `HasMutInterior`) are checked in
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// `validate_rvalue` upon access.
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Operand::Constant(c) => {
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if let Some(def_id) = c.check_static_ptr(self.tcx) {
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// Only allow statics (not consts) to refer to other statics.
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// FIXME(eddyb) does this matter at all for promotion?
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// FIXME(RalfJung) it makes little sense to not promote this in `fn`/`const fn`,
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// and in `const` this cannot occur anyway. The only concern is that we might
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// promote even `let x = &STATIC` which would be useless, but this applies to
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// promotion inside statics as well.
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let is_static = matches!(self.const_kind, Some(hir::ConstContext::Static(_)));
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if !is_static {
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return Err(Unpromotable);
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}
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let is_thread_local = self.tcx.is_thread_local_static(def_id);
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if is_thread_local {
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return Err(Unpromotable);
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}
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}
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Ok(())
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}
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}
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}
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fn validate_ref(&mut self, kind: BorrowKind, place: &Place<'tcx>) -> Result<(), Unpromotable> {
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match kind {
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// Reject these borrow types just to be safe.
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// FIXME(RalfJung): could we allow them? Should we? No point in it until we have a usecase.
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BorrowKind::Fake | BorrowKind::Mut { kind: MutBorrowKind::ClosureCapture } => {
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return Err(Unpromotable);
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}
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BorrowKind::Shared => {
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let has_mut_interior = self.qualif_local::<qualifs::HasMutInterior>(place.local);
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if has_mut_interior {
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return Err(Unpromotable);
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}
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}
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// FIXME: consider changing this to only promote &mut [] for default borrows,
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// also forbidding two phase borrows
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BorrowKind::Mut { kind: MutBorrowKind::Default | MutBorrowKind::TwoPhaseBorrow } => {
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let ty = place.ty(self.body, self.tcx).ty;
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// In theory, any zero-sized value could be borrowed
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// mutably without consequences. However, only &mut []
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// is allowed right now.
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if let ty::Array(_, len) = ty.kind() {
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match len.try_eval_target_usize(self.tcx, self.param_env) {
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Some(0) => {}
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_ => return Err(Unpromotable),
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}
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} else {
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return Err(Unpromotable);
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}
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}
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}
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Ok(())
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}
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fn validate_rvalue(&mut self, rvalue: &Rvalue<'tcx>) -> Result<(), Unpromotable> {
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match rvalue {
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Rvalue::Use(operand) | Rvalue::Repeat(operand, _) => {
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self.validate_operand(operand)?;
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}
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Rvalue::CopyForDeref(place) => {
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let op = &Operand::Copy(*place);
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self.validate_operand(op)?
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}
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Rvalue::Discriminant(place) | Rvalue::Len(place) => {
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self.validate_place(place.as_ref())?
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}
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Rvalue::ThreadLocalRef(_) => return Err(Unpromotable),
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// ptr-to-int casts are not possible in consts and thus not promotable
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Rvalue::Cast(CastKind::PointerExposeProvenance, _, _) => return Err(Unpromotable),
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// all other casts including int-to-ptr casts are fine, they just use the integer value
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// at pointer type.
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Rvalue::Cast(_, operand, _) => {
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self.validate_operand(operand)?;
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}
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Rvalue::NullaryOp(op, _) => match op {
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NullOp::SizeOf => {}
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NullOp::AlignOf => {}
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NullOp::OffsetOf(_) => {}
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NullOp::UbChecks => {}
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},
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Rvalue::ShallowInitBox(_, _) => return Err(Unpromotable),
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Rvalue::UnaryOp(op, operand) => {
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match op {
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// These operations can never fail.
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UnOp::Neg | UnOp::Not => {}
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}
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self.validate_operand(operand)?;
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}
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Rvalue::BinaryOp(op, box (lhs, rhs)) | Rvalue::CheckedBinaryOp(op, box (lhs, rhs)) => {
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let op = *op;
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let lhs_ty = lhs.ty(self.body, self.tcx);
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if let ty::RawPtr(_, _) | ty::FnPtr(..) = lhs_ty.kind() {
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// Raw and fn pointer operations are not allowed inside consts and thus not promotable.
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assert!(matches!(
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op,
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BinOp::Eq
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| BinOp::Ne
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| BinOp::Le
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|
| BinOp::Lt
|
|
| BinOp::Ge
|
|
| BinOp::Gt
|
|
| BinOp::Offset
|
|
));
|
|
return Err(Unpromotable);
|
|
}
|
|
|
|
match op {
|
|
BinOp::Div | BinOp::Rem => {
|
|
if lhs_ty.is_integral() {
|
|
let sz = lhs_ty.primitive_size(self.tcx);
|
|
// Integer division: the RHS must be a non-zero const.
|
|
let rhs_val = match rhs {
|
|
Operand::Constant(c) => {
|
|
c.const_.try_eval_scalar_int(self.tcx, self.param_env)
|
|
}
|
|
_ => None,
|
|
};
|
|
match rhs_val.map(|x| x.try_to_uint(sz).unwrap()) {
|
|
// for the zero test, int vs uint does not matter
|
|
Some(x) if x != 0 => {} // okay
|
|
_ => return Err(Unpromotable), // value not known or 0 -- not okay
|
|
}
|
|
// Furthermore, for signed divison, we also have to exclude `int::MIN / -1`.
|
|
if lhs_ty.is_signed() {
|
|
match rhs_val.map(|x| x.try_to_int(sz).unwrap()) {
|
|
Some(-1) | None => {
|
|
// The RHS is -1 or unknown, so we have to be careful.
|
|
// But is the LHS int::MIN?
|
|
let lhs_val = match lhs {
|
|
Operand::Constant(c) => c
|
|
.const_
|
|
.try_eval_scalar_int(self.tcx, self.param_env),
|
|
_ => None,
|
|
};
|
|
let lhs_min = sz.signed_int_min();
|
|
match lhs_val.map(|x| x.try_to_int(sz).unwrap()) {
|
|
Some(x) if x != lhs_min => {} // okay
|
|
_ => return Err(Unpromotable), // value not known or int::MIN -- not okay
|
|
}
|
|
}
|
|
_ => {}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
// The remaining operations can never fail.
|
|
BinOp::Eq
|
|
| BinOp::Ne
|
|
| BinOp::Le
|
|
| BinOp::Lt
|
|
| BinOp::Ge
|
|
| BinOp::Gt
|
|
| BinOp::Cmp
|
|
| BinOp::Offset
|
|
| BinOp::Add
|
|
| BinOp::AddUnchecked
|
|
| BinOp::Sub
|
|
| BinOp::SubUnchecked
|
|
| BinOp::Mul
|
|
| BinOp::MulUnchecked
|
|
| BinOp::BitXor
|
|
| BinOp::BitAnd
|
|
| BinOp::BitOr
|
|
| BinOp::Shl
|
|
| BinOp::ShlUnchecked
|
|
| BinOp::Shr
|
|
| BinOp::ShrUnchecked => {}
|
|
}
|
|
|
|
self.validate_operand(lhs)?;
|
|
self.validate_operand(rhs)?;
|
|
}
|
|
|
|
Rvalue::AddressOf(_, place) => {
|
|
// We accept `&raw *`, i.e., raw reborrows -- creating a raw pointer is
|
|
// no problem, only using it is.
|
|
if let Some((place_base, ProjectionElem::Deref)) = place.as_ref().last_projection()
|
|
{
|
|
let base_ty = place_base.ty(self.body, self.tcx).ty;
|
|
if let ty::Ref(..) = base_ty.kind() {
|
|
return self.validate_place(place_base);
|
|
}
|
|
}
|
|
return Err(Unpromotable);
|
|
}
|
|
|
|
Rvalue::Ref(_, kind, place) => {
|
|
// Special-case reborrows to be more like a copy of the reference.
|
|
let mut place_simplified = place.as_ref();
|
|
if let Some((place_base, ProjectionElem::Deref)) =
|
|
place_simplified.last_projection()
|
|
{
|
|
let base_ty = place_base.ty(self.body, self.tcx).ty;
|
|
if let ty::Ref(..) = base_ty.kind() {
|
|
place_simplified = place_base;
|
|
}
|
|
}
|
|
|
|
self.validate_place(place_simplified)?;
|
|
|
|
// Check that the reference is fine (using the original place!).
|
|
// (Needs to come after `validate_place` to avoid ICEs.)
|
|
self.validate_ref(*kind, place)?;
|
|
}
|
|
|
|
Rvalue::Aggregate(_, operands) => {
|
|
for o in operands {
|
|
self.validate_operand(o)?;
|
|
}
|
|
}
|
|
}
|
|
|
|
Ok(())
|
|
}
|
|
|
|
fn validate_call(
|
|
&mut self,
|
|
callee: &Operand<'tcx>,
|
|
args: &[Spanned<Operand<'tcx>>],
|
|
) -> Result<(), Unpromotable> {
|
|
let fn_ty = callee.ty(self.body, self.tcx);
|
|
|
|
// Inside const/static items, we promote all (eligible) function calls.
|
|
// Everywhere else, we require `#[rustc_promotable]` on the callee.
|
|
let promote_all_const_fn = matches!(
|
|
self.const_kind,
|
|
Some(hir::ConstContext::Static(_) | hir::ConstContext::Const { inline: false })
|
|
);
|
|
if !promote_all_const_fn {
|
|
if let ty::FnDef(def_id, _) = *fn_ty.kind() {
|
|
// Never promote runtime `const fn` calls of
|
|
// functions without `#[rustc_promotable]`.
|
|
if !self.tcx.is_promotable_const_fn(def_id) {
|
|
return Err(Unpromotable);
|
|
}
|
|
}
|
|
}
|
|
|
|
let is_const_fn = match *fn_ty.kind() {
|
|
ty::FnDef(def_id, _) => self.tcx.is_const_fn_raw(def_id),
|
|
_ => false,
|
|
};
|
|
if !is_const_fn {
|
|
return Err(Unpromotable);
|
|
}
|
|
|
|
self.validate_operand(callee)?;
|
|
for arg in args {
|
|
self.validate_operand(&arg.node)?;
|
|
}
|
|
|
|
Ok(())
|
|
}
|
|
}
|
|
|
|
// FIXME(eddyb) remove the differences for promotability in `static`, `const`, `const fn`.
|
|
fn validate_candidates(
|
|
ccx: &ConstCx<'_, '_>,
|
|
temps: &mut IndexSlice<Local, TempState>,
|
|
candidates: &[Candidate],
|
|
) -> Vec<Candidate> {
|
|
let mut validator = Validator { ccx, temps };
|
|
|
|
candidates
|
|
.iter()
|
|
.copied()
|
|
.filter(|&candidate| validator.validate_candidate(candidate).is_ok())
|
|
.collect()
|
|
}
|
|
|
|
struct Promoter<'a, 'tcx> {
|
|
tcx: TyCtxt<'tcx>,
|
|
source: &'a mut Body<'tcx>,
|
|
promoted: Body<'tcx>,
|
|
temps: &'a mut IndexVec<Local, TempState>,
|
|
extra_statements: &'a mut Vec<(Location, Statement<'tcx>)>,
|
|
|
|
/// If true, all nested temps are also kept in the
|
|
/// source MIR, not moved to the promoted MIR.
|
|
keep_original: bool,
|
|
}
|
|
|
|
impl<'a, 'tcx> Promoter<'a, 'tcx> {
|
|
fn new_block(&mut self) -> BasicBlock {
|
|
let span = self.promoted.span;
|
|
self.promoted.basic_blocks_mut().push(BasicBlockData {
|
|
statements: vec![],
|
|
terminator: Some(Terminator {
|
|
source_info: SourceInfo::outermost(span),
|
|
kind: TerminatorKind::Return,
|
|
}),
|
|
is_cleanup: false,
|
|
})
|
|
}
|
|
|
|
fn assign(&mut self, dest: Local, rvalue: Rvalue<'tcx>, span: Span) {
|
|
let last = self.promoted.basic_blocks.last_index().unwrap();
|
|
let data = &mut self.promoted[last];
|
|
data.statements.push(Statement {
|
|
source_info: SourceInfo::outermost(span),
|
|
kind: StatementKind::Assign(Box::new((Place::from(dest), rvalue))),
|
|
});
|
|
}
|
|
|
|
fn is_temp_kind(&self, local: Local) -> bool {
|
|
self.source.local_kind(local) == LocalKind::Temp
|
|
}
|
|
|
|
/// Copies the initialization of this temp to the
|
|
/// promoted MIR, recursing through temps.
|
|
fn promote_temp(&mut self, temp: Local) -> Local {
|
|
let old_keep_original = self.keep_original;
|
|
let loc = match self.temps[temp] {
|
|
TempState::Defined { location, uses, .. } if uses > 0 => {
|
|
if uses > 1 {
|
|
self.keep_original = true;
|
|
}
|
|
location
|
|
}
|
|
state => {
|
|
span_bug!(self.promoted.span, "{:?} not promotable: {:?}", temp, state);
|
|
}
|
|
};
|
|
if !self.keep_original {
|
|
self.temps[temp] = TempState::PromotedOut;
|
|
}
|
|
|
|
let num_stmts = self.source[loc.block].statements.len();
|
|
let new_temp = self.promoted.local_decls.push(LocalDecl::new(
|
|
self.source.local_decls[temp].ty,
|
|
self.source.local_decls[temp].source_info.span,
|
|
));
|
|
|
|
debug!("promote({:?} @ {:?}/{:?}, {:?})", temp, loc, num_stmts, self.keep_original);
|
|
|
|
// First, take the Rvalue or Call out of the source MIR,
|
|
// or duplicate it, depending on keep_original.
|
|
if loc.statement_index < num_stmts {
|
|
let (mut rvalue, source_info) = {
|
|
let statement = &mut self.source[loc.block].statements[loc.statement_index];
|
|
let StatementKind::Assign(box (_, rhs)) = &mut statement.kind else {
|
|
span_bug!(statement.source_info.span, "{:?} is not an assignment", statement);
|
|
};
|
|
|
|
(
|
|
if self.keep_original {
|
|
rhs.clone()
|
|
} else {
|
|
let unit = Rvalue::Use(Operand::Constant(Box::new(ConstOperand {
|
|
span: statement.source_info.span,
|
|
user_ty: None,
|
|
const_: Const::zero_sized(self.tcx.types.unit),
|
|
})));
|
|
mem::replace(rhs, unit)
|
|
},
|
|
statement.source_info,
|
|
)
|
|
};
|
|
|
|
self.visit_rvalue(&mut rvalue, loc);
|
|
self.assign(new_temp, rvalue, source_info.span);
|
|
} else {
|
|
let terminator = if self.keep_original {
|
|
self.source[loc.block].terminator().clone()
|
|
} else {
|
|
let terminator = self.source[loc.block].terminator_mut();
|
|
let target = match &terminator.kind {
|
|
TerminatorKind::Call { target: Some(target), .. } => *target,
|
|
kind => {
|
|
span_bug!(terminator.source_info.span, "{:?} not promotable", kind);
|
|
}
|
|
};
|
|
Terminator {
|
|
source_info: terminator.source_info,
|
|
kind: mem::replace(&mut terminator.kind, TerminatorKind::Goto { target }),
|
|
}
|
|
};
|
|
|
|
match terminator.kind {
|
|
TerminatorKind::Call {
|
|
mut func, mut args, call_source: desugar, fn_span, ..
|
|
} => {
|
|
self.visit_operand(&mut func, loc);
|
|
for arg in &mut args {
|
|
self.visit_operand(&mut arg.node, loc);
|
|
}
|
|
|
|
let last = self.promoted.basic_blocks.last_index().unwrap();
|
|
let new_target = self.new_block();
|
|
|
|
*self.promoted[last].terminator_mut() = Terminator {
|
|
kind: TerminatorKind::Call {
|
|
func,
|
|
args,
|
|
unwind: UnwindAction::Continue,
|
|
destination: Place::from(new_temp),
|
|
target: Some(new_target),
|
|
call_source: desugar,
|
|
fn_span,
|
|
},
|
|
source_info: SourceInfo::outermost(terminator.source_info.span),
|
|
..terminator
|
|
};
|
|
}
|
|
kind => {
|
|
span_bug!(terminator.source_info.span, "{:?} not promotable", kind);
|
|
}
|
|
};
|
|
};
|
|
|
|
self.keep_original = old_keep_original;
|
|
new_temp
|
|
}
|
|
|
|
fn promote_candidate(mut self, candidate: Candidate, next_promoted_id: usize) -> Body<'tcx> {
|
|
let def = self.source.source.def_id();
|
|
let mut rvalue = {
|
|
let promoted = &mut self.promoted;
|
|
let promoted_id = Promoted::new(next_promoted_id);
|
|
let tcx = self.tcx;
|
|
let mut promoted_operand = |ty, span| {
|
|
promoted.span = span;
|
|
promoted.local_decls[RETURN_PLACE] = LocalDecl::new(ty, span);
|
|
let args = tcx.erase_regions(GenericArgs::identity_for_item(tcx, def));
|
|
let uneval = mir::UnevaluatedConst { def, args, promoted: Some(promoted_id) };
|
|
|
|
Operand::Constant(Box::new(ConstOperand {
|
|
span,
|
|
user_ty: None,
|
|
const_: Const::Unevaluated(uneval, ty),
|
|
}))
|
|
};
|
|
|
|
let blocks = self.source.basic_blocks.as_mut();
|
|
let local_decls = &mut self.source.local_decls;
|
|
let loc = candidate.location;
|
|
let statement = &mut blocks[loc.block].statements[loc.statement_index];
|
|
let StatementKind::Assign(box (_, Rvalue::Ref(region, borrow_kind, place))) =
|
|
&mut statement.kind
|
|
else {
|
|
bug!()
|
|
};
|
|
|
|
// Use the underlying local for this (necessarily interior) borrow.
|
|
debug_assert!(region.is_erased());
|
|
let ty = local_decls[place.local].ty;
|
|
let span = statement.source_info.span;
|
|
|
|
let ref_ty =
|
|
Ty::new_ref(tcx, tcx.lifetimes.re_erased, ty, borrow_kind.to_mutbl_lossy());
|
|
|
|
let mut projection = vec![PlaceElem::Deref];
|
|
projection.extend(place.projection);
|
|
place.projection = tcx.mk_place_elems(&projection);
|
|
|
|
// Create a temp to hold the promoted reference.
|
|
// This is because `*r` requires `r` to be a local,
|
|
// otherwise we would use the `promoted` directly.
|
|
let mut promoted_ref = LocalDecl::new(ref_ty, span);
|
|
promoted_ref.source_info = statement.source_info;
|
|
let promoted_ref = local_decls.push(promoted_ref);
|
|
assert_eq!(self.temps.push(TempState::Unpromotable), promoted_ref);
|
|
|
|
let promoted_ref_statement = Statement {
|
|
source_info: statement.source_info,
|
|
kind: StatementKind::Assign(Box::new((
|
|
Place::from(promoted_ref),
|
|
Rvalue::Use(promoted_operand(ref_ty, span)),
|
|
))),
|
|
};
|
|
self.extra_statements.push((loc, promoted_ref_statement));
|
|
|
|
Rvalue::Ref(
|
|
tcx.lifetimes.re_erased,
|
|
*borrow_kind,
|
|
Place {
|
|
local: mem::replace(&mut place.local, promoted_ref),
|
|
projection: List::empty(),
|
|
},
|
|
)
|
|
};
|
|
|
|
assert_eq!(self.new_block(), START_BLOCK);
|
|
self.visit_rvalue(
|
|
&mut rvalue,
|
|
Location { block: START_BLOCK, statement_index: usize::MAX },
|
|
);
|
|
|
|
let span = self.promoted.span;
|
|
self.assign(RETURN_PLACE, rvalue, span);
|
|
self.promoted
|
|
}
|
|
}
|
|
|
|
/// Replaces all temporaries with their promoted counterparts.
|
|
impl<'a, 'tcx> MutVisitor<'tcx> for Promoter<'a, 'tcx> {
|
|
fn tcx(&self) -> TyCtxt<'tcx> {
|
|
self.tcx
|
|
}
|
|
|
|
fn visit_local(&mut self, local: &mut Local, _: PlaceContext, _: Location) {
|
|
if self.is_temp_kind(*local) {
|
|
*local = self.promote_temp(*local);
|
|
}
|
|
}
|
|
}
|
|
|
|
fn promote_candidates<'tcx>(
|
|
body: &mut Body<'tcx>,
|
|
tcx: TyCtxt<'tcx>,
|
|
mut temps: IndexVec<Local, TempState>,
|
|
candidates: Vec<Candidate>,
|
|
) -> IndexVec<Promoted, Body<'tcx>> {
|
|
// Visit candidates in reverse, in case they're nested.
|
|
debug!("promote_candidates({:?})", candidates);
|
|
|
|
let mut promotions = IndexVec::new();
|
|
|
|
let mut extra_statements = vec![];
|
|
for candidate in candidates.into_iter().rev() {
|
|
let Location { block, statement_index } = candidate.location;
|
|
if let StatementKind::Assign(box (place, _)) = &body[block].statements[statement_index].kind
|
|
{
|
|
if let Some(local) = place.as_local() {
|
|
if temps[local] == TempState::PromotedOut {
|
|
// Already promoted.
|
|
continue;
|
|
}
|
|
}
|
|
}
|
|
|
|
// Declare return place local so that `mir::Body::new` doesn't complain.
|
|
let initial_locals = iter::once(LocalDecl::new(tcx.types.never, body.span)).collect();
|
|
|
|
let mut scope = body.source_scopes[body.source_info(candidate.location).scope].clone();
|
|
scope.parent_scope = None;
|
|
|
|
let mut promoted = Body::new(
|
|
body.source, // `promoted` gets filled in below
|
|
IndexVec::new(),
|
|
IndexVec::from_elem_n(scope, 1),
|
|
initial_locals,
|
|
IndexVec::new(),
|
|
0,
|
|
vec![],
|
|
body.span,
|
|
None,
|
|
body.tainted_by_errors,
|
|
);
|
|
promoted.phase = MirPhase::Analysis(AnalysisPhase::Initial);
|
|
|
|
let promoter = Promoter {
|
|
promoted,
|
|
tcx,
|
|
source: body,
|
|
temps: &mut temps,
|
|
extra_statements: &mut extra_statements,
|
|
keep_original: false,
|
|
};
|
|
|
|
let mut promoted = promoter.promote_candidate(candidate, promotions.len());
|
|
promoted.source.promoted = Some(promotions.next_index());
|
|
promotions.push(promoted);
|
|
}
|
|
|
|
// Insert each of `extra_statements` before its indicated location, which
|
|
// has to be done in reverse location order, to not invalidate the rest.
|
|
extra_statements.sort_by_key(|&(loc, _)| cmp::Reverse(loc));
|
|
for (loc, statement) in extra_statements {
|
|
body[loc.block].statements.insert(loc.statement_index, statement);
|
|
}
|
|
|
|
// Eliminate assignments to, and drops of promoted temps.
|
|
let promoted = |index: Local| temps[index] == TempState::PromotedOut;
|
|
for block in body.basic_blocks_mut() {
|
|
block.statements.retain(|statement| match &statement.kind {
|
|
StatementKind::Assign(box (place, _)) => {
|
|
if let Some(index) = place.as_local() {
|
|
!promoted(index)
|
|
} else {
|
|
true
|
|
}
|
|
}
|
|
StatementKind::StorageLive(index) | StatementKind::StorageDead(index) => {
|
|
!promoted(*index)
|
|
}
|
|
_ => true,
|
|
});
|
|
let terminator = block.terminator_mut();
|
|
if let TerminatorKind::Drop { place, target, .. } = &terminator.kind {
|
|
if let Some(index) = place.as_local() {
|
|
if promoted(index) {
|
|
terminator.kind = TerminatorKind::Goto { target: *target };
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
promotions
|
|
}
|