1200 lines
44 KiB
Rust
1200 lines
44 KiB
Rust
//! This is the implementation of the pass which transforms generators into state machines.
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//!
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//! MIR generation for generators creates a function which has a self argument which
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//! passes by value. This argument is effectively a generator type which only contains upvars and
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//! is only used for this argument inside the MIR for the generator.
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//! It is passed by value to enable upvars to be moved out of it. Drop elaboration runs on that
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//! MIR before this pass and creates drop flags for MIR locals.
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//! It will also drop the generator argument (which only consists of upvars) if any of the upvars
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//! are moved out of. This pass elaborates the drops of upvars / generator argument in the case
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//! that none of the upvars were moved out of. This is because we cannot have any drops of this
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//! generator in the MIR, since it is used to create the drop glue for the generator. We'd get
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//! infinite recursion otherwise.
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//!
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//! This pass creates the implementation for the Generator::resume function and the drop shim
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//! for the generator based on the MIR input. It converts the generator argument from Self to
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//! &mut Self adding derefs in the MIR as needed. It computes the final layout of the generator
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//! struct which looks like this:
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//! First upvars are stored
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//! It is followed by the generator state field.
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//! Then finally the MIR locals which are live across a suspension point are stored.
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//!
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//! struct Generator {
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//! upvars...,
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//! state: u32,
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//! mir_locals...,
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//! }
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//!
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//! This pass computes the meaning of the state field and the MIR locals which are live
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//! across a suspension point. There are however three hardcoded generator states:
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//! 0 - Generator have not been resumed yet
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//! 1 - Generator has returned / is completed
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//! 2 - Generator has been poisoned
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//!
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//! It also rewrites `return x` and `yield y` as setting a new generator state and returning
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//! GeneratorState::Complete(x) and GeneratorState::Yielded(y) respectively.
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//! MIR locals which are live across a suspension point are moved to the generator struct
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//! with references to them being updated with references to the generator struct.
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//!
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//! The pass creates two functions which have a switch on the generator state giving
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//! the action to take.
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//!
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//! One of them is the implementation of Generator::resume.
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//! For generators with state 0 (unresumed) it starts the execution of the generator.
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//! For generators with state 1 (returned) and state 2 (poisoned) it panics.
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//! Otherwise it continues the execution from the last suspension point.
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//!
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//! The other function is the drop glue for the generator.
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//! For generators with state 0 (unresumed) it drops the upvars of the generator.
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//! For generators with state 1 (returned) and state 2 (poisoned) it does nothing.
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//! Otherwise it drops all the values in scope at the last suspension point.
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use crate::dataflow::{do_dataflow, DataflowResultsCursor, DebugFormatted};
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use crate::dataflow::{DataflowResults, DataflowResultsConsumer, FlowAtLocation};
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use crate::dataflow::{HaveBeenBorrowedLocals, MaybeStorageLive, RequiresStorage};
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use crate::transform::no_landing_pads::no_landing_pads;
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use crate::transform::simplify;
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use crate::transform::{MirPass, MirSource};
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use crate::util::dump_mir;
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use crate::util::liveness;
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use rustc::hir;
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use rustc::hir::def_id::DefId;
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use rustc::mir::visit::{MutVisitor, PlaceContext, Visitor};
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use rustc::mir::*;
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use rustc::ty::layout::VariantIdx;
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use rustc::ty::subst::SubstsRef;
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use rustc::ty::GeneratorSubsts;
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use rustc::ty::{self, AdtDef, Ty, TyCtxt};
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use rustc_data_structures::fx::FxHashMap;
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use rustc_index::bit_set::{BitMatrix, BitSet};
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use rustc_index::vec::{Idx, IndexVec};
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use std::borrow::Cow;
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use std::iter;
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pub struct StateTransform;
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struct RenameLocalVisitor<'tcx> {
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from: Local,
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to: Local,
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tcx: TyCtxt<'tcx>,
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}
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impl<'tcx> MutVisitor<'tcx> for RenameLocalVisitor<'tcx> {
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fn tcx(&self) -> TyCtxt<'tcx> {
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self.tcx
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}
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fn visit_local(&mut self, local: &mut Local, _: PlaceContext, _: Location) {
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if *local == self.from {
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*local = self.to;
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}
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}
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fn process_projection_elem(&mut self, elem: &PlaceElem<'tcx>) -> Option<PlaceElem<'tcx>> {
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match elem {
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PlaceElem::Index(local) if *local == self.from => Some(PlaceElem::Index(self.to)),
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_ => None,
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}
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}
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}
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struct DerefArgVisitor<'tcx> {
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tcx: TyCtxt<'tcx>,
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}
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impl<'tcx> MutVisitor<'tcx> for DerefArgVisitor<'tcx> {
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fn tcx(&self) -> TyCtxt<'tcx> {
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self.tcx
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}
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fn visit_local(&mut self, local: &mut Local, _: PlaceContext, _: Location) {
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assert_ne!(*local, self_arg());
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}
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fn visit_place(&mut self, place: &mut Place<'tcx>, context: PlaceContext, location: Location) {
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if place.base == PlaceBase::Local(self_arg()) {
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replace_base(
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place,
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Place {
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base: PlaceBase::Local(self_arg()),
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projection: self.tcx().intern_place_elems(&vec![ProjectionElem::Deref]),
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},
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self.tcx,
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);
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} else {
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self.visit_place_base(&mut place.base, context, location);
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for elem in place.projection.iter() {
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if let PlaceElem::Index(local) = elem {
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assert_ne!(*local, self_arg());
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}
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}
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}
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}
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}
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struct PinArgVisitor<'tcx> {
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ref_gen_ty: Ty<'tcx>,
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tcx: TyCtxt<'tcx>,
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}
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impl<'tcx> MutVisitor<'tcx> for PinArgVisitor<'tcx> {
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fn tcx(&self) -> TyCtxt<'tcx> {
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self.tcx
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}
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fn visit_local(&mut self, local: &mut Local, _: PlaceContext, _: Location) {
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assert_ne!(*local, self_arg());
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}
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fn visit_place(&mut self, place: &mut Place<'tcx>, context: PlaceContext, location: Location) {
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if place.base == PlaceBase::Local(self_arg()) {
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replace_base(
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place,
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Place {
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base: PlaceBase::Local(self_arg()),
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projection: self.tcx().intern_place_elems(&vec![ProjectionElem::Field(
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Field::new(0),
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self.ref_gen_ty,
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)]),
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},
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self.tcx,
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);
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} else {
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self.visit_place_base(&mut place.base, context, location);
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for elem in place.projection.iter() {
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if let PlaceElem::Index(local) = elem {
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assert_ne!(*local, self_arg());
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}
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}
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}
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}
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}
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fn replace_base<'tcx>(place: &mut Place<'tcx>, new_base: Place<'tcx>, tcx: TyCtxt<'tcx>) {
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place.base = new_base.base;
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let mut new_projection = new_base.projection.to_vec();
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new_projection.append(&mut place.projection.to_vec());
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place.projection = tcx.intern_place_elems(&new_projection);
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}
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fn self_arg() -> Local {
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Local::new(1)
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}
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/// Generator have not been resumed yet
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const UNRESUMED: usize = GeneratorSubsts::UNRESUMED;
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/// Generator has returned / is completed
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const RETURNED: usize = GeneratorSubsts::RETURNED;
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/// Generator has been poisoned
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const POISONED: usize = GeneratorSubsts::POISONED;
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struct SuspensionPoint {
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state: usize,
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resume: BasicBlock,
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drop: Option<BasicBlock>,
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storage_liveness: liveness::LiveVarSet,
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}
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struct TransformVisitor<'tcx> {
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tcx: TyCtxt<'tcx>,
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state_adt_ref: &'tcx AdtDef,
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state_substs: SubstsRef<'tcx>,
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// The type of the discriminant in the generator struct
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discr_ty: Ty<'tcx>,
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// Mapping from Local to (type of local, generator struct index)
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// FIXME(eddyb) This should use `IndexVec<Local, Option<_>>`.
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remap: FxHashMap<Local, (Ty<'tcx>, VariantIdx, usize)>,
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// A map from a suspension point in a block to the locals which have live storage at that point
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// FIXME(eddyb) This should use `IndexVec<BasicBlock, Option<_>>`.
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storage_liveness: FxHashMap<BasicBlock, liveness::LiveVarSet>,
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// A list of suspension points, generated during the transform
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suspension_points: Vec<SuspensionPoint>,
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// The original RETURN_PLACE local
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new_ret_local: Local,
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}
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impl TransformVisitor<'tcx> {
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// Make a GeneratorState rvalue
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fn make_state(&self, idx: VariantIdx, val: Operand<'tcx>) -> Rvalue<'tcx> {
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let adt = AggregateKind::Adt(self.state_adt_ref, idx, self.state_substs, None, None);
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Rvalue::Aggregate(box adt, vec![val])
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}
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// Create a Place referencing a generator struct field
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fn make_field(&self, variant_index: VariantIdx, idx: usize, ty: Ty<'tcx>) -> Place<'tcx> {
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let self_place = Place::from(self_arg());
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let base = self.tcx.mk_place_downcast_unnamed(self_place, variant_index);
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let mut projection = base.projection.to_vec();
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projection.push(ProjectionElem::Field(Field::new(idx), ty));
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Place { base: base.base, projection: self.tcx.intern_place_elems(&projection) }
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}
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// Create a statement which changes the discriminant
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fn set_discr(&self, state_disc: VariantIdx, source_info: SourceInfo) -> Statement<'tcx> {
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let self_place = Place::from(self_arg());
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Statement {
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source_info,
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kind: StatementKind::SetDiscriminant {
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place: box self_place,
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variant_index: state_disc,
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},
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}
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}
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// Create a statement which reads the discriminant into a temporary
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fn get_discr(&self, body: &mut Body<'tcx>) -> (Statement<'tcx>, Place<'tcx>) {
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let temp_decl = LocalDecl::new_internal(self.tcx.types.isize, body.span);
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let local_decls_len = body.local_decls.push(temp_decl);
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let temp = Place::from(local_decls_len);
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let self_place = Place::from(self_arg());
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let assign = Statement {
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source_info: source_info(body),
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kind: StatementKind::Assign(box (temp.clone(), Rvalue::Discriminant(self_place))),
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};
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(assign, temp)
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}
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}
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impl MutVisitor<'tcx> for TransformVisitor<'tcx> {
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fn tcx(&self) -> TyCtxt<'tcx> {
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self.tcx
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}
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fn visit_local(&mut self, local: &mut Local, _: PlaceContext, _: Location) {
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assert_eq!(self.remap.get(local), None);
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}
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fn visit_place(&mut self, place: &mut Place<'tcx>, context: PlaceContext, location: Location) {
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if let PlaceBase::Local(l) = place.base {
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// Replace an Local in the remap with a generator struct access
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if let Some(&(ty, variant_index, idx)) = self.remap.get(&l) {
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replace_base(place, self.make_field(variant_index, idx, ty), self.tcx);
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}
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} else {
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self.visit_place_base(&mut place.base, context, location);
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for elem in place.projection.iter() {
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if let PlaceElem::Index(local) = elem {
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assert_ne!(*local, self_arg());
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}
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}
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}
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}
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fn visit_basic_block_data(&mut self, block: BasicBlock, data: &mut BasicBlockData<'tcx>) {
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// Remove StorageLive and StorageDead statements for remapped locals
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data.retain_statements(|s| match s.kind {
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StatementKind::StorageLive(l) | StatementKind::StorageDead(l) => {
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!self.remap.contains_key(&l)
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}
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_ => true,
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});
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let ret_val = match data.terminator().kind {
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TerminatorKind::Return => Some((
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VariantIdx::new(1),
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None,
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Operand::Move(Place::from(self.new_ret_local)),
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None,
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)),
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TerminatorKind::Yield { ref value, resume, drop } => {
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Some((VariantIdx::new(0), Some(resume), value.clone(), drop))
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}
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_ => None,
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};
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if let Some((state_idx, resume, v, drop)) = ret_val {
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let source_info = data.terminator().source_info;
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// We must assign the value first in case it gets declared dead below
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data.statements.push(Statement {
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source_info,
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kind: StatementKind::Assign(box (
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Place::return_place(),
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self.make_state(state_idx, v),
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)),
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});
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let state = if let Some(resume) = resume {
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// Yield
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let state = 3 + self.suspension_points.len();
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self.suspension_points.push(SuspensionPoint {
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state,
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resume,
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drop,
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storage_liveness: self.storage_liveness.get(&block).unwrap().clone(),
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});
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VariantIdx::new(state)
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} else {
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// Return
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VariantIdx::new(RETURNED) // state for returned
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};
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data.statements.push(self.set_discr(state, source_info));
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data.terminator_mut().kind = TerminatorKind::Return;
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}
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self.super_basic_block_data(block, data);
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}
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}
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fn make_generator_state_argument_indirect<'tcx>(
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tcx: TyCtxt<'tcx>,
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def_id: DefId,
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body: &mut BodyAndCache<'tcx>,
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) {
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let gen_ty = body.local_decls.raw[1].ty;
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let region = ty::ReFree(ty::FreeRegion { scope: def_id, bound_region: ty::BoundRegion::BrEnv });
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let region = tcx.mk_region(region);
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let ref_gen_ty = tcx.mk_ref(region, ty::TypeAndMut { ty: gen_ty, mutbl: hir::Mutability::Mut });
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// Replace the by value generator argument
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body.local_decls.raw[1].ty = ref_gen_ty;
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// Add a deref to accesses of the generator state
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DerefArgVisitor { tcx }.visit_body(body);
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}
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fn make_generator_state_argument_pinned<'tcx>(tcx: TyCtxt<'tcx>, body: &mut BodyAndCache<'tcx>) {
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let ref_gen_ty = body.local_decls.raw[1].ty;
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let pin_did = tcx.lang_items().pin_type().unwrap();
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let pin_adt_ref = tcx.adt_def(pin_did);
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let substs = tcx.intern_substs(&[ref_gen_ty.into()]);
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let pin_ref_gen_ty = tcx.mk_adt(pin_adt_ref, substs);
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// Replace the by ref generator argument
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body.local_decls.raw[1].ty = pin_ref_gen_ty;
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// Add the Pin field access to accesses of the generator state
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PinArgVisitor { ref_gen_ty, tcx }.visit_body(body);
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}
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fn replace_result_variable<'tcx>(
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ret_ty: Ty<'tcx>,
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body: &mut BodyAndCache<'tcx>,
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tcx: TyCtxt<'tcx>,
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) -> Local {
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let source_info = source_info(body);
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let new_ret = LocalDecl {
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mutability: Mutability::Mut,
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ty: ret_ty,
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user_ty: UserTypeProjections::none(),
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source_info,
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internal: false,
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is_block_tail: None,
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local_info: LocalInfo::Other,
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};
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let new_ret_local = Local::new(body.local_decls.len());
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body.local_decls.push(new_ret);
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body.local_decls.swap(RETURN_PLACE, new_ret_local);
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RenameLocalVisitor { from: RETURN_PLACE, to: new_ret_local, tcx }.visit_body(body);
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new_ret_local
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}
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struct StorageIgnored(liveness::LiveVarSet);
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impl<'tcx> Visitor<'tcx> for StorageIgnored {
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fn visit_statement(&mut self, statement: &Statement<'tcx>, _location: Location) {
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match statement.kind {
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StatementKind::StorageLive(l) | StatementKind::StorageDead(l) => {
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self.0.remove(l);
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}
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_ => (),
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}
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}
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}
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struct LivenessInfo {
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/// Which locals are live across any suspension point.
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///
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/// GeneratorSavedLocal is indexed in terms of the elements in this set;
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/// i.e. GeneratorSavedLocal::new(1) corresponds to the second local
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/// included in this set.
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live_locals: liveness::LiveVarSet,
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/// The set of saved locals live at each suspension point.
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live_locals_at_suspension_points: Vec<BitSet<GeneratorSavedLocal>>,
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/// For every saved local, the set of other saved locals that are
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/// storage-live at the same time as this local. We cannot overlap locals in
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/// the layout which have conflicting storage.
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storage_conflicts: BitMatrix<GeneratorSavedLocal, GeneratorSavedLocal>,
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/// For every suspending block, the locals which are storage-live across
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/// that suspension point.
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storage_liveness: FxHashMap<BasicBlock, liveness::LiveVarSet>,
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}
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fn locals_live_across_suspend_points(
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tcx: TyCtxt<'tcx>,
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body: ReadOnlyBodyAndCache<'_, 'tcx>,
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source: MirSource<'tcx>,
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movable: bool,
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) -> LivenessInfo {
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let dead_unwinds = BitSet::new_empty(body.basic_blocks().len());
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let def_id = source.def_id();
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let body_ref: &Body<'_> = &body;
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// Calculate when MIR locals have live storage. This gives us an upper bound of their
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// lifetimes.
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let storage_live_analysis = MaybeStorageLive::new(body_ref);
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let storage_live_results =
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do_dataflow(tcx, body_ref, def_id, &[], &dead_unwinds, storage_live_analysis, |bd, p| {
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DebugFormatted::new(&bd.body().local_decls[p])
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});
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let mut storage_live_cursor = DataflowResultsCursor::new(&storage_live_results, body_ref);
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// Find the MIR locals which do not use StorageLive/StorageDead statements.
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// The storage of these locals are always live.
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let mut ignored = StorageIgnored(BitSet::new_filled(body.local_decls.len()));
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ignored.visit_body(body);
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// Calculate the MIR locals which have been previously
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// borrowed (even if they are still active).
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let borrowed_locals_analysis = HaveBeenBorrowedLocals::new(body_ref);
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let borrowed_locals_results = do_dataflow(
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tcx,
|
|
body_ref,
|
|
def_id,
|
|
&[],
|
|
&dead_unwinds,
|
|
borrowed_locals_analysis,
|
|
|bd, p| DebugFormatted::new(&bd.body().local_decls[p]),
|
|
);
|
|
let mut borrowed_locals_cursor = DataflowResultsCursor::new(&borrowed_locals_results, body_ref);
|
|
|
|
// Calculate the MIR locals that we actually need to keep storage around
|
|
// for.
|
|
let requires_storage_analysis = RequiresStorage::new(body, &borrowed_locals_results);
|
|
let requires_storage_results = do_dataflow(
|
|
tcx,
|
|
body_ref,
|
|
def_id,
|
|
&[],
|
|
&dead_unwinds,
|
|
requires_storage_analysis,
|
|
|bd, p| DebugFormatted::new(&bd.body().local_decls[p]),
|
|
);
|
|
let mut requires_storage_cursor =
|
|
DataflowResultsCursor::new(&requires_storage_results, body_ref);
|
|
|
|
// Calculate the liveness of MIR locals ignoring borrows.
|
|
let mut live_locals = liveness::LiveVarSet::new_empty(body.local_decls.len());
|
|
let mut liveness = liveness::liveness_of_locals(body);
|
|
liveness::dump_mir(tcx, "generator_liveness", source, body_ref, &liveness);
|
|
|
|
let mut storage_liveness_map = FxHashMap::default();
|
|
let mut live_locals_at_suspension_points = Vec::new();
|
|
|
|
for (block, data) in body.basic_blocks().iter_enumerated() {
|
|
if let TerminatorKind::Yield { .. } = data.terminator().kind {
|
|
let loc = Location { block: block, statement_index: data.statements.len() };
|
|
|
|
if !movable {
|
|
// The `liveness` variable contains the liveness of MIR locals ignoring borrows.
|
|
// This is correct for movable generators since borrows cannot live across
|
|
// suspension points. However for immovable generators we need to account for
|
|
// borrows, so we conseratively assume that all borrowed locals are live until
|
|
// we find a StorageDead statement referencing the locals.
|
|
// To do this we just union our `liveness` result with `borrowed_locals`, which
|
|
// contains all the locals which has been borrowed before this suspension point.
|
|
// If a borrow is converted to a raw reference, we must also assume that it lives
|
|
// forever. Note that the final liveness is still bounded by the storage liveness
|
|
// of the local, which happens using the `intersect` operation below.
|
|
borrowed_locals_cursor.seek(loc);
|
|
liveness.outs[block].union(borrowed_locals_cursor.get());
|
|
}
|
|
|
|
storage_live_cursor.seek(loc);
|
|
let storage_liveness = storage_live_cursor.get();
|
|
|
|
// Store the storage liveness for later use so we can restore the state
|
|
// after a suspension point
|
|
storage_liveness_map.insert(block, storage_liveness.clone());
|
|
|
|
requires_storage_cursor.seek(loc);
|
|
let storage_required = requires_storage_cursor.get().clone();
|
|
|
|
// Locals live are live at this point only if they are used across
|
|
// suspension points (the `liveness` variable)
|
|
// and their storage is required (the `storage_required` variable)
|
|
let mut live_locals_here = storage_required;
|
|
live_locals_here.intersect(&liveness.outs[block]);
|
|
|
|
// The generator argument is ignored
|
|
live_locals_here.remove(self_arg());
|
|
|
|
debug!("loc = {:?}, live_locals_here = {:?}", loc, live_locals_here);
|
|
|
|
// Add the locals live at this suspension point to the set of locals which live across
|
|
// any suspension points
|
|
live_locals.union(&live_locals_here);
|
|
|
|
live_locals_at_suspension_points.push(live_locals_here);
|
|
}
|
|
}
|
|
debug!("live_locals = {:?}", live_locals);
|
|
|
|
// Renumber our liveness_map bitsets to include only the locals we are
|
|
// saving.
|
|
let live_locals_at_suspension_points = live_locals_at_suspension_points
|
|
.iter()
|
|
.map(|live_here| renumber_bitset(&live_here, &live_locals))
|
|
.collect();
|
|
|
|
let storage_conflicts =
|
|
compute_storage_conflicts(body_ref, &live_locals, &ignored, requires_storage_results);
|
|
|
|
LivenessInfo {
|
|
live_locals,
|
|
live_locals_at_suspension_points,
|
|
storage_conflicts,
|
|
storage_liveness: storage_liveness_map,
|
|
}
|
|
}
|
|
|
|
/// Renumbers the items present in `stored_locals` and applies the renumbering
|
|
/// to 'input`.
|
|
///
|
|
/// For example, if `stored_locals = [1, 3, 5]`, this would be renumbered to
|
|
/// `[0, 1, 2]`. Thus, if `input = [3, 5]` we would return `[1, 2]`.
|
|
fn renumber_bitset(
|
|
input: &BitSet<Local>,
|
|
stored_locals: &liveness::LiveVarSet,
|
|
) -> BitSet<GeneratorSavedLocal> {
|
|
assert!(stored_locals.superset(&input), "{:?} not a superset of {:?}", stored_locals, input);
|
|
let mut out = BitSet::new_empty(stored_locals.count());
|
|
for (idx, local) in stored_locals.iter().enumerate() {
|
|
let saved_local = GeneratorSavedLocal::from(idx);
|
|
if input.contains(local) {
|
|
out.insert(saved_local);
|
|
}
|
|
}
|
|
debug!("renumber_bitset({:?}, {:?}) => {:?}", input, stored_locals, out);
|
|
out
|
|
}
|
|
|
|
/// For every saved local, looks for which locals are StorageLive at the same
|
|
/// time. Generates a bitset for every local of all the other locals that may be
|
|
/// StorageLive simultaneously with that local. This is used in the layout
|
|
/// computation; see `GeneratorLayout` for more.
|
|
fn compute_storage_conflicts(
|
|
body: &'mir Body<'tcx>,
|
|
stored_locals: &liveness::LiveVarSet,
|
|
ignored: &StorageIgnored,
|
|
requires_storage: DataflowResults<'tcx, RequiresStorage<'mir, 'tcx>>,
|
|
) -> BitMatrix<GeneratorSavedLocal, GeneratorSavedLocal> {
|
|
assert_eq!(body.local_decls.len(), ignored.0.domain_size());
|
|
assert_eq!(body.local_decls.len(), stored_locals.domain_size());
|
|
debug!("compute_storage_conflicts({:?})", body.span);
|
|
debug!("ignored = {:?}", ignored.0);
|
|
|
|
// Storage ignored locals are not eligible for overlap, since their storage
|
|
// is always live.
|
|
let mut ineligible_locals = ignored.0.clone();
|
|
ineligible_locals.intersect(&stored_locals);
|
|
|
|
// Compute the storage conflicts for all eligible locals.
|
|
let mut visitor = StorageConflictVisitor {
|
|
body,
|
|
stored_locals: &stored_locals,
|
|
local_conflicts: BitMatrix::from_row_n(&ineligible_locals, body.local_decls.len()),
|
|
};
|
|
let mut state = FlowAtLocation::new(requires_storage);
|
|
visitor.analyze_results(&mut state);
|
|
let local_conflicts = visitor.local_conflicts;
|
|
|
|
// Compress the matrix using only stored locals (Local -> GeneratorSavedLocal).
|
|
//
|
|
// NOTE: Today we store a full conflict bitset for every local. Technically
|
|
// this is twice as many bits as we need, since the relation is symmetric.
|
|
// However, in practice these bitsets are not usually large. The layout code
|
|
// also needs to keep track of how many conflicts each local has, so it's
|
|
// simpler to keep it this way for now.
|
|
let mut storage_conflicts = BitMatrix::new(stored_locals.count(), stored_locals.count());
|
|
for (idx_a, local_a) in stored_locals.iter().enumerate() {
|
|
let saved_local_a = GeneratorSavedLocal::new(idx_a);
|
|
if ineligible_locals.contains(local_a) {
|
|
// Conflicts with everything.
|
|
storage_conflicts.insert_all_into_row(saved_local_a);
|
|
} else {
|
|
// Keep overlap information only for stored locals.
|
|
for (idx_b, local_b) in stored_locals.iter().enumerate() {
|
|
let saved_local_b = GeneratorSavedLocal::new(idx_b);
|
|
if local_conflicts.contains(local_a, local_b) {
|
|
storage_conflicts.insert(saved_local_a, saved_local_b);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
storage_conflicts
|
|
}
|
|
|
|
struct StorageConflictVisitor<'body, 'tcx, 's> {
|
|
body: &'body Body<'tcx>,
|
|
stored_locals: &'s liveness::LiveVarSet,
|
|
// FIXME(tmandry): Consider using sparse bitsets here once we have good
|
|
// benchmarks for generators.
|
|
local_conflicts: BitMatrix<Local, Local>,
|
|
}
|
|
|
|
impl<'body, 'tcx, 's> DataflowResultsConsumer<'body, 'tcx>
|
|
for StorageConflictVisitor<'body, 'tcx, 's>
|
|
{
|
|
type FlowState = FlowAtLocation<'tcx, RequiresStorage<'body, 'tcx>>;
|
|
|
|
fn body(&self) -> &'body Body<'tcx> {
|
|
self.body
|
|
}
|
|
|
|
fn visit_block_entry(&mut self, block: BasicBlock, flow_state: &Self::FlowState) {
|
|
// statement_index is only used for logging, so this is fine.
|
|
self.apply_state(flow_state, Location { block, statement_index: 0 });
|
|
}
|
|
|
|
fn visit_statement_entry(
|
|
&mut self,
|
|
loc: Location,
|
|
_stmt: &Statement<'tcx>,
|
|
flow_state: &Self::FlowState,
|
|
) {
|
|
self.apply_state(flow_state, loc);
|
|
}
|
|
|
|
fn visit_terminator_entry(
|
|
&mut self,
|
|
loc: Location,
|
|
_term: &Terminator<'tcx>,
|
|
flow_state: &Self::FlowState,
|
|
) {
|
|
self.apply_state(flow_state, loc);
|
|
}
|
|
}
|
|
|
|
impl<'body, 'tcx, 's> StorageConflictVisitor<'body, 'tcx, 's> {
|
|
fn apply_state(
|
|
&mut self,
|
|
flow_state: &FlowAtLocation<'tcx, RequiresStorage<'body, 'tcx>>,
|
|
loc: Location,
|
|
) {
|
|
// Ignore unreachable blocks.
|
|
match self.body.basic_blocks()[loc.block].terminator().kind {
|
|
TerminatorKind::Unreachable => return,
|
|
_ => (),
|
|
};
|
|
|
|
let mut eligible_storage_live = flow_state.as_dense().clone();
|
|
eligible_storage_live.intersect(&self.stored_locals);
|
|
|
|
for local in eligible_storage_live.iter() {
|
|
self.local_conflicts.union_row_with(&eligible_storage_live, local);
|
|
}
|
|
|
|
if eligible_storage_live.count() > 1 {
|
|
trace!("at {:?}, eligible_storage_live={:?}", loc, eligible_storage_live);
|
|
}
|
|
}
|
|
}
|
|
|
|
fn compute_layout<'tcx>(
|
|
tcx: TyCtxt<'tcx>,
|
|
source: MirSource<'tcx>,
|
|
upvars: &Vec<Ty<'tcx>>,
|
|
interior: Ty<'tcx>,
|
|
movable: bool,
|
|
body: &mut BodyAndCache<'tcx>,
|
|
) -> (
|
|
FxHashMap<Local, (Ty<'tcx>, VariantIdx, usize)>,
|
|
GeneratorLayout<'tcx>,
|
|
FxHashMap<BasicBlock, liveness::LiveVarSet>,
|
|
) {
|
|
// Use a liveness analysis to compute locals which are live across a suspension point
|
|
let LivenessInfo {
|
|
live_locals,
|
|
live_locals_at_suspension_points,
|
|
storage_conflicts,
|
|
storage_liveness,
|
|
} = locals_live_across_suspend_points(tcx, read_only!(body), source, movable);
|
|
|
|
// Erase regions from the types passed in from typeck so we can compare them with
|
|
// MIR types
|
|
let allowed_upvars = tcx.erase_regions(upvars);
|
|
let allowed = match interior.kind {
|
|
ty::GeneratorWitness(s) => tcx.erase_late_bound_regions(&s),
|
|
_ => bug!(),
|
|
};
|
|
|
|
for (local, decl) in body.local_decls.iter_enumerated() {
|
|
// Ignore locals which are internal or not live
|
|
if !live_locals.contains(local) || decl.internal {
|
|
continue;
|
|
}
|
|
|
|
// Sanity check that typeck knows about the type of locals which are
|
|
// live across a suspension point
|
|
if !allowed.contains(&decl.ty) && !allowed_upvars.contains(&decl.ty) {
|
|
span_bug!(
|
|
body.span,
|
|
"Broken MIR: generator contains type {} in MIR, \
|
|
but typeck only knows about {}",
|
|
decl.ty,
|
|
interior
|
|
);
|
|
}
|
|
}
|
|
|
|
// Gather live local types and their indices.
|
|
let mut locals = IndexVec::<GeneratorSavedLocal, _>::new();
|
|
let mut tys = IndexVec::<GeneratorSavedLocal, _>::new();
|
|
for (idx, local) in live_locals.iter().enumerate() {
|
|
locals.push(local);
|
|
tys.push(body.local_decls[local].ty);
|
|
debug!("generator saved local {:?} => {:?}", GeneratorSavedLocal::from(idx), local);
|
|
}
|
|
|
|
// Leave empty variants for the UNRESUMED, RETURNED, and POISONED states.
|
|
const RESERVED_VARIANTS: usize = 3;
|
|
|
|
// Build the generator variant field list.
|
|
// Create a map from local indices to generator struct indices.
|
|
let mut variant_fields: IndexVec<VariantIdx, IndexVec<Field, GeneratorSavedLocal>> =
|
|
iter::repeat(IndexVec::new()).take(RESERVED_VARIANTS).collect();
|
|
let mut remap = FxHashMap::default();
|
|
for (suspension_point_idx, live_locals) in live_locals_at_suspension_points.iter().enumerate() {
|
|
let variant_index = VariantIdx::from(RESERVED_VARIANTS + suspension_point_idx);
|
|
let mut fields = IndexVec::new();
|
|
for (idx, saved_local) in live_locals.iter().enumerate() {
|
|
fields.push(saved_local);
|
|
// Note that if a field is included in multiple variants, we will
|
|
// just use the first one here. That's fine; fields do not move
|
|
// around inside generators, so it doesn't matter which variant
|
|
// index we access them by.
|
|
remap.entry(locals[saved_local]).or_insert((tys[saved_local], variant_index, idx));
|
|
}
|
|
variant_fields.push(fields);
|
|
}
|
|
debug!("generator variant_fields = {:?}", variant_fields);
|
|
debug!("generator storage_conflicts = {:#?}", storage_conflicts);
|
|
|
|
let layout = GeneratorLayout { field_tys: tys, variant_fields, storage_conflicts };
|
|
|
|
(remap, layout, storage_liveness)
|
|
}
|
|
|
|
fn insert_switch<'tcx>(
|
|
body: &mut BodyAndCache<'tcx>,
|
|
cases: Vec<(usize, BasicBlock)>,
|
|
transform: &TransformVisitor<'tcx>,
|
|
default: TerminatorKind<'tcx>,
|
|
) {
|
|
let default_block = insert_term_block(body, default);
|
|
let (assign, discr) = transform.get_discr(body);
|
|
let switch = TerminatorKind::SwitchInt {
|
|
discr: Operand::Move(discr),
|
|
switch_ty: transform.discr_ty,
|
|
values: Cow::from(cases.iter().map(|&(i, _)| i as u128).collect::<Vec<_>>()),
|
|
targets: cases.iter().map(|&(_, d)| d).chain(iter::once(default_block)).collect(),
|
|
};
|
|
|
|
let source_info = source_info(body);
|
|
body.basic_blocks_mut().raw.insert(
|
|
0,
|
|
BasicBlockData {
|
|
statements: vec![assign],
|
|
terminator: Some(Terminator { source_info, kind: switch }),
|
|
is_cleanup: false,
|
|
},
|
|
);
|
|
|
|
let blocks = body.basic_blocks_mut().iter_mut();
|
|
|
|
for target in blocks.flat_map(|b| b.terminator_mut().successors_mut()) {
|
|
*target = BasicBlock::new(target.index() + 1);
|
|
}
|
|
}
|
|
|
|
fn elaborate_generator_drops<'tcx>(
|
|
tcx: TyCtxt<'tcx>,
|
|
def_id: DefId,
|
|
body: &mut BodyAndCache<'tcx>,
|
|
) {
|
|
use crate::shim::DropShimElaborator;
|
|
use crate::util::elaborate_drops::{elaborate_drop, Unwind};
|
|
use crate::util::patch::MirPatch;
|
|
|
|
// Note that `elaborate_drops` only drops the upvars of a generator, and
|
|
// this is ok because `open_drop` can only be reached within that own
|
|
// generator's resume function.
|
|
|
|
let param_env = tcx.param_env(def_id);
|
|
let gen = self_arg();
|
|
|
|
let mut elaborator = DropShimElaborator { body, patch: MirPatch::new(body), tcx, param_env };
|
|
|
|
for (block, block_data) in body.basic_blocks().iter_enumerated() {
|
|
let (target, unwind, source_info) = match block_data.terminator() {
|
|
Terminator { source_info, kind: TerminatorKind::Drop { location, target, unwind } } => {
|
|
if let Some(local) = location.as_local() {
|
|
if local == gen {
|
|
(target, unwind, source_info)
|
|
} else {
|
|
continue;
|
|
}
|
|
} else {
|
|
continue;
|
|
}
|
|
}
|
|
_ => continue,
|
|
};
|
|
let unwind = if block_data.is_cleanup {
|
|
Unwind::InCleanup
|
|
} else {
|
|
Unwind::To(unwind.unwrap_or_else(|| elaborator.patch.resume_block()))
|
|
};
|
|
elaborate_drop(
|
|
&mut elaborator,
|
|
*source_info,
|
|
&Place::from(gen),
|
|
(),
|
|
*target,
|
|
unwind,
|
|
block,
|
|
);
|
|
}
|
|
elaborator.patch.apply(body);
|
|
}
|
|
|
|
fn create_generator_drop_shim<'tcx>(
|
|
tcx: TyCtxt<'tcx>,
|
|
transform: &TransformVisitor<'tcx>,
|
|
def_id: DefId,
|
|
source: MirSource<'tcx>,
|
|
gen_ty: Ty<'tcx>,
|
|
body: &mut BodyAndCache<'tcx>,
|
|
drop_clean: BasicBlock,
|
|
) -> BodyAndCache<'tcx> {
|
|
let mut body = body.clone();
|
|
|
|
let source_info = source_info(&body);
|
|
|
|
let mut cases = create_cases(&mut body, transform, |point| point.drop);
|
|
|
|
cases.insert(0, (UNRESUMED, drop_clean));
|
|
|
|
// The returned state and the poisoned state fall through to the default
|
|
// case which is just to return
|
|
|
|
insert_switch(&mut body, cases, &transform, TerminatorKind::Return);
|
|
|
|
for block in body.basic_blocks_mut() {
|
|
let kind = &mut block.terminator_mut().kind;
|
|
if let TerminatorKind::GeneratorDrop = *kind {
|
|
*kind = TerminatorKind::Return;
|
|
}
|
|
}
|
|
|
|
// Replace the return variable
|
|
body.local_decls[RETURN_PLACE] = LocalDecl {
|
|
mutability: Mutability::Mut,
|
|
ty: tcx.mk_unit(),
|
|
user_ty: UserTypeProjections::none(),
|
|
source_info,
|
|
internal: false,
|
|
is_block_tail: None,
|
|
local_info: LocalInfo::Other,
|
|
};
|
|
|
|
make_generator_state_argument_indirect(tcx, def_id, &mut body);
|
|
|
|
// Change the generator argument from &mut to *mut
|
|
body.local_decls[self_arg()] = LocalDecl {
|
|
mutability: Mutability::Mut,
|
|
ty: tcx.mk_ptr(ty::TypeAndMut { ty: gen_ty, mutbl: hir::Mutability::Mut }),
|
|
user_ty: UserTypeProjections::none(),
|
|
source_info,
|
|
internal: false,
|
|
is_block_tail: None,
|
|
local_info: LocalInfo::Other,
|
|
};
|
|
if tcx.sess.opts.debugging_opts.mir_emit_retag {
|
|
// Alias tracking must know we changed the type
|
|
body.basic_blocks_mut()[START_BLOCK].statements.insert(
|
|
0,
|
|
Statement {
|
|
source_info,
|
|
kind: StatementKind::Retag(RetagKind::Raw, box Place::from(self_arg())),
|
|
},
|
|
)
|
|
}
|
|
|
|
no_landing_pads(tcx, &mut body);
|
|
|
|
// Make sure we remove dead blocks to remove
|
|
// unrelated code from the resume part of the function
|
|
simplify::remove_dead_blocks(&mut body);
|
|
|
|
dump_mir(tcx, None, "generator_drop", &0, source, &mut body, |_, _| Ok(()));
|
|
|
|
body
|
|
}
|
|
|
|
fn insert_term_block<'tcx>(
|
|
body: &mut BodyAndCache<'tcx>,
|
|
kind: TerminatorKind<'tcx>,
|
|
) -> BasicBlock {
|
|
let term_block = BasicBlock::new(body.basic_blocks().len());
|
|
let source_info = source_info(body);
|
|
body.basic_blocks_mut().push(BasicBlockData {
|
|
statements: Vec::new(),
|
|
terminator: Some(Terminator { source_info, kind }),
|
|
is_cleanup: false,
|
|
});
|
|
term_block
|
|
}
|
|
|
|
fn insert_panic_block<'tcx>(
|
|
tcx: TyCtxt<'tcx>,
|
|
body: &mut BodyAndCache<'tcx>,
|
|
message: AssertMessage<'tcx>,
|
|
) -> BasicBlock {
|
|
let assert_block = BasicBlock::new(body.basic_blocks().len());
|
|
let term = TerminatorKind::Assert {
|
|
cond: Operand::Constant(box Constant {
|
|
span: body.span,
|
|
user_ty: None,
|
|
literal: ty::Const::from_bool(tcx, false),
|
|
}),
|
|
expected: true,
|
|
msg: message,
|
|
target: assert_block,
|
|
cleanup: None,
|
|
};
|
|
|
|
let source_info = source_info(body);
|
|
body.basic_blocks_mut().push(BasicBlockData {
|
|
statements: Vec::new(),
|
|
terminator: Some(Terminator { source_info, kind: term }),
|
|
is_cleanup: false,
|
|
});
|
|
|
|
assert_block
|
|
}
|
|
|
|
fn create_generator_resume_function<'tcx>(
|
|
tcx: TyCtxt<'tcx>,
|
|
transform: TransformVisitor<'tcx>,
|
|
def_id: DefId,
|
|
source: MirSource<'tcx>,
|
|
body: &mut BodyAndCache<'tcx>,
|
|
) {
|
|
// Poison the generator when it unwinds
|
|
for block in body.basic_blocks_mut() {
|
|
let source_info = block.terminator().source_info;
|
|
if let &TerminatorKind::Resume = &block.terminator().kind {
|
|
block.statements.push(transform.set_discr(VariantIdx::new(POISONED), source_info));
|
|
}
|
|
}
|
|
|
|
let mut cases = create_cases(body, &transform, |point| Some(point.resume));
|
|
|
|
use rustc::mir::interpret::PanicInfo::{ResumedAfterPanic, ResumedAfterReturn};
|
|
|
|
// Jump to the entry point on the unresumed
|
|
cases.insert(0, (UNRESUMED, BasicBlock::new(0)));
|
|
|
|
// Panic when resumed on the returned or poisoned state
|
|
let generator_kind = body.generator_kind.unwrap();
|
|
cases.insert(1, (RETURNED, insert_panic_block(tcx, body, ResumedAfterReturn(generator_kind))));
|
|
cases.insert(2, (POISONED, insert_panic_block(tcx, body, ResumedAfterPanic(generator_kind))));
|
|
|
|
insert_switch(body, cases, &transform, TerminatorKind::Unreachable);
|
|
|
|
make_generator_state_argument_indirect(tcx, def_id, body);
|
|
make_generator_state_argument_pinned(tcx, body);
|
|
|
|
no_landing_pads(tcx, body);
|
|
|
|
// Make sure we remove dead blocks to remove
|
|
// unrelated code from the drop part of the function
|
|
simplify::remove_dead_blocks(body);
|
|
|
|
dump_mir(tcx, None, "generator_resume", &0, source, body, |_, _| Ok(()));
|
|
}
|
|
|
|
fn source_info(body: &Body<'_>) -> SourceInfo {
|
|
SourceInfo { span: body.span, scope: OUTERMOST_SOURCE_SCOPE }
|
|
}
|
|
|
|
fn insert_clean_drop(body: &mut BodyAndCache<'_>) -> BasicBlock {
|
|
let return_block = insert_term_block(body, TerminatorKind::Return);
|
|
|
|
// Create a block to destroy an unresumed generators. This can only destroy upvars.
|
|
let drop_clean = BasicBlock::new(body.basic_blocks().len());
|
|
let term = TerminatorKind::Drop {
|
|
location: Place::from(self_arg()),
|
|
target: return_block,
|
|
unwind: None,
|
|
};
|
|
let source_info = source_info(body);
|
|
body.basic_blocks_mut().push(BasicBlockData {
|
|
statements: Vec::new(),
|
|
terminator: Some(Terminator { source_info, kind: term }),
|
|
is_cleanup: false,
|
|
});
|
|
|
|
drop_clean
|
|
}
|
|
|
|
fn create_cases<'tcx, F>(
|
|
body: &mut BodyAndCache<'tcx>,
|
|
transform: &TransformVisitor<'tcx>,
|
|
target: F,
|
|
) -> Vec<(usize, BasicBlock)>
|
|
where
|
|
F: Fn(&SuspensionPoint) -> Option<BasicBlock>,
|
|
{
|
|
let source_info = source_info(body);
|
|
|
|
transform
|
|
.suspension_points
|
|
.iter()
|
|
.filter_map(|point| {
|
|
// Find the target for this suspension point, if applicable
|
|
target(point).map(|target| {
|
|
let block = BasicBlock::new(body.basic_blocks().len());
|
|
let mut statements = Vec::new();
|
|
|
|
// Create StorageLive instructions for locals with live storage
|
|
for i in 0..(body.local_decls.len()) {
|
|
let l = Local::new(i);
|
|
if point.storage_liveness.contains(l) && !transform.remap.contains_key(&l) {
|
|
statements
|
|
.push(Statement { source_info, kind: StatementKind::StorageLive(l) });
|
|
}
|
|
}
|
|
|
|
// Then jump to the real target
|
|
body.basic_blocks_mut().push(BasicBlockData {
|
|
statements,
|
|
terminator: Some(Terminator {
|
|
source_info,
|
|
kind: TerminatorKind::Goto { target },
|
|
}),
|
|
is_cleanup: false,
|
|
});
|
|
|
|
(point.state, block)
|
|
})
|
|
})
|
|
.collect()
|
|
}
|
|
|
|
impl<'tcx> MirPass<'tcx> for StateTransform {
|
|
fn run_pass(&self, tcx: TyCtxt<'tcx>, source: MirSource<'tcx>, body: &mut BodyAndCache<'tcx>) {
|
|
let yield_ty = if let Some(yield_ty) = body.yield_ty {
|
|
yield_ty
|
|
} else {
|
|
// This only applies to generators
|
|
return;
|
|
};
|
|
|
|
assert!(body.generator_drop.is_none());
|
|
|
|
let def_id = source.def_id();
|
|
|
|
// The first argument is the generator type passed by value
|
|
let gen_ty = body.local_decls.raw[1].ty;
|
|
|
|
// Get the interior types and substs which typeck computed
|
|
let (upvars, interior, discr_ty, movable) = match gen_ty.kind {
|
|
ty::Generator(_, substs, movability) => {
|
|
let substs = substs.as_generator();
|
|
(
|
|
substs.upvar_tys(def_id, tcx).collect(),
|
|
substs.witness(def_id, tcx),
|
|
substs.discr_ty(tcx),
|
|
movability == hir::Movability::Movable,
|
|
)
|
|
}
|
|
_ => bug!(),
|
|
};
|
|
|
|
// Compute GeneratorState<yield_ty, return_ty>
|
|
let state_did = tcx.lang_items().gen_state().unwrap();
|
|
let state_adt_ref = tcx.adt_def(state_did);
|
|
let state_substs = tcx.intern_substs(&[yield_ty.into(), body.return_ty().into()]);
|
|
let ret_ty = tcx.mk_adt(state_adt_ref, state_substs);
|
|
|
|
// We rename RETURN_PLACE which has type mir.return_ty to new_ret_local
|
|
// RETURN_PLACE then is a fresh unused local with type ret_ty.
|
|
let new_ret_local = replace_result_variable(ret_ty, body, tcx);
|
|
|
|
// Extract locals which are live across suspension point into `layout`
|
|
// `remap` gives a mapping from local indices onto generator struct indices
|
|
// `storage_liveness` tells us which locals have live storage at suspension points
|
|
let (remap, layout, storage_liveness) =
|
|
compute_layout(tcx, source, &upvars, interior, movable, body);
|
|
|
|
// Run the transformation which converts Places from Local to generator struct
|
|
// accesses for locals in `remap`.
|
|
// It also rewrites `return x` and `yield y` as writing a new generator state and returning
|
|
// GeneratorState::Complete(x) and GeneratorState::Yielded(y) respectively.
|
|
let mut transform = TransformVisitor {
|
|
tcx,
|
|
state_adt_ref,
|
|
state_substs,
|
|
remap,
|
|
storage_liveness,
|
|
suspension_points: Vec::new(),
|
|
new_ret_local,
|
|
discr_ty,
|
|
};
|
|
transform.visit_body(body);
|
|
|
|
// Update our MIR struct to reflect the changed we've made
|
|
body.yield_ty = None;
|
|
body.arg_count = 1;
|
|
body.spread_arg = None;
|
|
body.generator_layout = Some(layout);
|
|
|
|
// Insert `drop(generator_struct)` which is used to drop upvars for generators in
|
|
// the unresumed state.
|
|
// This is expanded to a drop ladder in `elaborate_generator_drops`.
|
|
let drop_clean = insert_clean_drop(body);
|
|
|
|
dump_mir(tcx, None, "generator_pre-elab", &0, source, body, |_, _| Ok(()));
|
|
|
|
// Expand `drop(generator_struct)` to a drop ladder which destroys upvars.
|
|
// If any upvars are moved out of, drop elaboration will handle upvar destruction.
|
|
// However we need to also elaborate the code generated by `insert_clean_drop`.
|
|
elaborate_generator_drops(tcx, def_id, body);
|
|
|
|
dump_mir(tcx, None, "generator_post-transform", &0, source, body, |_, _| Ok(()));
|
|
|
|
// Create a copy of our MIR and use it to create the drop shim for the generator
|
|
let drop_shim =
|
|
create_generator_drop_shim(tcx, &transform, def_id, source, gen_ty, body, drop_clean);
|
|
|
|
body.generator_drop = Some(box drop_shim);
|
|
|
|
// Create the Generator::resume function
|
|
create_generator_resume_function(tcx, transform, def_id, source, body);
|
|
}
|
|
}
|