1 // Copyright 2016 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! This is the implementation of the pass which transforms generators into state machines.
13 //! MIR generation for generators creates a function which has a self argument which
14 //! passes by value. This argument is effectively a generator type which only contains upvars and
15 //! is only used for this argument inside the MIR for the generator.
16 //! It is passed by value to enable upvars to be moved out of it. Drop elaboration runs on that
17 //! MIR before this pass and creates drop flags for MIR locals.
18 //! It will also drop the generator argument (which only consists of upvars) if any of the upvars
19 //! are moved out of. This pass elaborates the drops of upvars / generator argument in the case
20 //! that none of the upvars were moved out of. This is because we cannot have any drops of this
21 //! generator in the MIR, since it is used to create the drop glue for the generator. We'd get
22 //! infinite recursion otherwise.
24 //! This pass creates the implementation for the Generator::resume function and the drop shim
25 //! for the generator based on the MIR input. It converts the generator argument from Self to
26 //! &mut Self adding derefs in the MIR as needed. It computes the final layout of the generator
27 //! struct which looks like this:
28 //! First upvars are stored
29 //! It is followed by the generator state field.
30 //! Then finally the MIR locals which are live across a suspension point are stored.
32 //! struct Generator {
38 //! This pass computes the meaning of the state field and the MIR locals which are live
39 //! across a suspension point. There are however two hardcoded generator states:
40 //! 0 - Generator have not been resumed yet
41 //! 1 - Generator has returned / is completed
42 //! 2 - Generator has been poisoned
44 //! It also rewrites `return x` and `yield y` as setting a new generator state and returning
45 //! GeneratorState::Complete(x) and GeneratorState::Yielded(y) respectively.
46 //! MIR locals which are live across a suspension point are moved to the generator struct
47 //! with references to them being updated with references to the generator struct.
49 //! The pass creates two functions which have a switch on the generator state giving
50 //! the action to take.
52 //! One of them is the implementation of Generator::resume.
53 //! For generators with state 0 (unresumed) it starts the execution of the generator.
54 //! For generators with state 1 (returned) and state 2 (poisoned) it panics.
55 //! Otherwise it continues the execution from the last suspension point.
57 //! The other function is the drop glue for the generator.
58 //! For generators with state 0 (unresumed) it drops the upvars of the generator.
59 //! For generators with state 1 (returned) and state 2 (poisoned) it does nothing.
60 //! Otherwise it drops all the values in scope at the last suspension point.
63 use rustc::hir::def_id::DefId;
65 use rustc::mir::visit::{PlaceContext, Visitor, MutVisitor};
66 use rustc::ty::{self, TyCtxt, AdtDef, Ty};
67 use rustc::ty::subst::Substs;
69 use util::liveness::{self, IdentityMap, LivenessMode};
70 use rustc_data_structures::indexed_vec::Idx;
71 use rustc_data_structures::indexed_set::IdxSetBuf;
72 use std::collections::HashMap;
76 use transform::{MirPass, MirSource};
77 use transform::simplify;
78 use transform::no_landing_pads::no_landing_pads;
79 use dataflow::{do_dataflow, DebugFormatted, state_for_location};
80 use dataflow::{MaybeStorageLive, HaveBeenBorrowedLocals};
82 pub struct StateTransform;
84 struct RenameLocalVisitor {
89 impl<'tcx> MutVisitor<'tcx> for RenameLocalVisitor {
90 fn visit_local(&mut self,
92 _: PlaceContext<'tcx>,
94 if *local == self.from {
100 struct DerefArgVisitor;
102 impl<'tcx> MutVisitor<'tcx> for DerefArgVisitor {
103 fn visit_local(&mut self,
105 _: PlaceContext<'tcx>,
107 assert_ne!(*local, self_arg());
110 fn visit_place(&mut self,
111 place: &mut Place<'tcx>,
112 context: PlaceContext<'tcx>,
113 location: Location) {
114 if *place == Place::Local(self_arg()) {
115 *place = Place::Projection(Box::new(Projection {
117 elem: ProjectionElem::Deref,
120 self.super_place(place, context, location);
125 fn self_arg() -> Local {
129 struct SuspensionPoint {
132 drop: Option<BasicBlock>,
133 storage_liveness: liveness::LocalSet<Local>,
136 struct TransformVisitor<'a, 'tcx: 'a> {
137 tcx: TyCtxt<'a, 'tcx, 'tcx>,
138 state_adt_ref: &'tcx AdtDef,
139 state_substs: &'tcx Substs<'tcx>,
141 // The index of the generator state in the generator struct
144 // Mapping from Local to (type of local, generator struct index)
145 remap: HashMap<Local, (Ty<'tcx>, usize)>,
147 // A map from a suspension point in a block to the locals which have live storage at that point
148 storage_liveness: HashMap<BasicBlock, liveness::LocalSet<Local>>,
150 // A list of suspension points, generated during the transform
151 suspension_points: Vec<SuspensionPoint>,
153 // The original RETURN_PLACE local
154 new_ret_local: Local,
157 impl<'a, 'tcx> TransformVisitor<'a, 'tcx> {
158 // Make a GeneratorState rvalue
159 fn make_state(&self, idx: usize, val: Operand<'tcx>) -> Rvalue<'tcx> {
160 let adt = AggregateKind::Adt(self.state_adt_ref, idx, self.state_substs, None);
161 Rvalue::Aggregate(box adt, vec![val])
164 // Create a Place referencing a generator struct field
165 fn make_field(&self, idx: usize, ty: Ty<'tcx>) -> Place<'tcx> {
166 let base = Place::Local(self_arg());
167 let field = Projection {
169 elem: ProjectionElem::Field(Field::new(idx), ty),
171 Place::Projection(Box::new(field))
174 // Create a statement which changes the generator state
175 fn set_state(&self, state_disc: u32, source_info: SourceInfo) -> Statement<'tcx> {
176 let state = self.make_field(self.state_field, self.tcx.types.u32);
177 let val = Operand::Constant(box Constant {
178 span: source_info.span,
179 ty: self.tcx.types.u32,
180 literal: Literal::Value {
181 value: ty::Const::from_bits(
184 ty::ParamEnv::empty().and(self.tcx.types.u32)),
189 kind: StatementKind::Assign(state, Rvalue::Use(val)),
194 impl<'a, 'tcx> MutVisitor<'tcx> for TransformVisitor<'a, 'tcx> {
195 fn visit_local(&mut self,
197 _: PlaceContext<'tcx>,
199 assert_eq!(self.remap.get(local), None);
202 fn visit_place(&mut self,
203 place: &mut Place<'tcx>,
204 context: PlaceContext<'tcx>,
205 location: Location) {
206 if let Place::Local(l) = *place {
207 // Replace an Local in the remap with a generator struct access
208 if let Some(&(ty, idx)) = self.remap.get(&l) {
209 *place = self.make_field(idx, ty);
212 self.super_place(place, context, location);
216 fn visit_basic_block_data(&mut self,
218 data: &mut BasicBlockData<'tcx>) {
219 // Remove StorageLive and StorageDead statements for remapped locals
220 data.retain_statements(|s| {
222 StatementKind::StorageLive(l) | StatementKind::StorageDead(l) => {
223 !self.remap.contains_key(&l)
229 let ret_val = match data.terminator().kind {
230 TerminatorKind::Return => Some((1,
232 Operand::Move(Place::Local(self.new_ret_local)),
234 TerminatorKind::Yield { ref value, resume, drop } => Some((0,
241 if let Some((state_idx, resume, v, drop)) = ret_val {
242 let source_info = data.terminator().source_info;
243 // We must assign the value first in case it gets declared dead below
244 data.statements.push(Statement {
246 kind: StatementKind::Assign(Place::Local(RETURN_PLACE),
247 self.make_state(state_idx, v)),
249 let state = if let Some(resume) = resume { // Yield
250 let state = 3 + self.suspension_points.len() as u32;
252 self.suspension_points.push(SuspensionPoint {
256 storage_liveness: self.storage_liveness.get(&block).unwrap().clone(),
261 1 // state for returned
263 data.statements.push(self.set_state(state, source_info));
264 data.terminator.as_mut().unwrap().kind = TerminatorKind::Return;
267 self.super_basic_block_data(block, data);
271 fn make_generator_state_argument_indirect<'a, 'tcx>(
272 tcx: TyCtxt<'a, 'tcx, 'tcx>,
274 mir: &mut Mir<'tcx>) {
275 let gen_ty = mir.local_decls.raw[1].ty;
277 let region = ty::ReFree(ty::FreeRegion {
279 bound_region: ty::BoundRegion::BrEnv,
282 let region = tcx.mk_region(region);
284 let ref_gen_ty = tcx.mk_ref(region, ty::TypeAndMut {
286 mutbl: hir::MutMutable
289 // Replace the by value generator argument
290 mir.local_decls.raw[1].ty = ref_gen_ty;
292 // Add a deref to accesses of the generator state
293 DerefArgVisitor.visit_mir(mir);
296 fn replace_result_variable<'tcx>(ret_ty: Ty<'tcx>,
297 mir: &mut Mir<'tcx>) -> Local {
298 let source_info = source_info(mir);
299 let new_ret = LocalDecl {
300 mutability: Mutability::Mut,
304 visibility_scope: source_info.scope,
306 is_user_variable: None,
308 let new_ret_local = Local::new(mir.local_decls.len());
309 mir.local_decls.push(new_ret);
310 mir.local_decls.swap(0, new_ret_local.index());
320 struct StorageIgnored(liveness::LocalSet<Local>);
322 impl<'tcx> Visitor<'tcx> for StorageIgnored {
323 fn visit_statement(&mut self,
325 statement: &Statement<'tcx>,
326 _location: Location) {
327 match statement.kind {
328 StatementKind::StorageLive(l) |
329 StatementKind::StorageDead(l) => { self.0.remove(&l); }
335 struct BorrowedLocals(liveness::LocalSet<Local>);
337 fn mark_as_borrowed<'tcx>(place: &Place<'tcx>, locals: &mut BorrowedLocals) {
339 Place::Local(l) => { locals.0.add(&l); },
340 Place::Static(..) => (),
341 Place::Projection(ref proj) => {
343 // For derefs we don't look any further.
344 // If it pointed to a Local, it would already be borrowed elsewhere
345 ProjectionElem::Deref => (),
346 _ => mark_as_borrowed(&proj.base, locals)
352 impl<'tcx> Visitor<'tcx> for BorrowedLocals {
353 fn visit_rvalue(&mut self,
354 rvalue: &Rvalue<'tcx>,
355 location: Location) {
356 if let Rvalue::Ref(_, _, ref place) = *rvalue {
357 mark_as_borrowed(place, self);
360 self.super_rvalue(rvalue, location)
364 fn locals_live_across_suspend_points<'a, 'tcx,>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
368 (liveness::LocalSet<Local>,
369 HashMap<BasicBlock, liveness::LocalSet<Local>>) {
370 let dead_unwinds = IdxSetBuf::new_empty(mir.basic_blocks().len());
371 let node_id = tcx.hir.as_local_node_id(source.def_id).unwrap();
373 // Calculate when MIR locals have live storage. This gives us an upper bound of their
375 let storage_live_analysis = MaybeStorageLive::new(mir);
377 do_dataflow(tcx, mir, node_id, &[], &dead_unwinds, storage_live_analysis,
378 |bd, p| DebugFormatted::new(&bd.mir().local_decls[p]));
380 // Find the MIR locals which do not use StorageLive/StorageDead statements.
381 // The storage of these locals are always live.
382 let mut ignored = StorageIgnored(IdxSetBuf::new_filled(mir.local_decls.len()));
383 ignored.visit_mir(mir);
385 // Calculate the MIR locals which have been previously
386 // borrowed (even if they are still active).
387 // This is only used for immovable generators.
388 let borrowed_locals = if !movable {
389 let analysis = HaveBeenBorrowedLocals::new(mir);
391 do_dataflow(tcx, mir, node_id, &[], &dead_unwinds, analysis,
392 |bd, p| DebugFormatted::new(&bd.mir().local_decls[p]));
393 Some((analysis, result))
398 // Calculate the liveness of MIR locals ignoring borrows.
399 let mut set = liveness::LocalSet::new_empty(mir.local_decls.len());
400 let mut liveness = liveness::liveness_of_locals(
403 include_regular_use: true,
406 &IdentityMap::new(mir),
410 "generator_liveness",
413 &IdentityMap::new(mir),
417 let mut storage_liveness_map = HashMap::new();
419 for (block, data) in mir.basic_blocks().iter_enumerated() {
420 if let TerminatorKind::Yield { .. } = data.terminator().kind {
423 statement_index: data.statements.len(),
426 if let Some((ref analysis, ref result)) = borrowed_locals {
427 let borrowed_locals = state_for_location(loc,
431 // The `liveness` variable contains the liveness of MIR locals ignoring borrows.
432 // This is correct for movable generators since borrows cannot live across
433 // suspension points. However for immovable generators we need to account for
434 // borrows, so we conseratively assume that all borrowed locals live forever.
435 // To do this we just union our `liveness` result with `borrowed_locals`, which
436 // contains all the locals which has been borrowed before this suspension point.
437 // If a borrow is converted to a raw reference, we must also assume that it lives
438 // forever. Note that the final liveness is still bounded by the storage liveness
439 // of the local, which happens using the `intersect` operation below.
440 liveness.outs[block].union(&borrowed_locals);
443 let mut storage_liveness = state_for_location(loc,
444 &storage_live_analysis,
448 // Store the storage liveness for later use so we can restore the state
449 // after a suspension point
450 storage_liveness_map.insert(block, storage_liveness.clone());
452 // Mark locals without storage statements as always having live storage
453 storage_liveness.union(&ignored.0);
455 // Locals live are live at this point only if they are used across
456 // suspension points (the `liveness` variable)
457 // and their storage is live (the `storage_liveness` variable)
458 storage_liveness.intersect(&liveness.outs[block]);
460 let live_locals = storage_liveness;
462 // Add the locals life at this suspension point to the set of locals which live across
463 // any suspension points
464 set.union(&live_locals);
468 // The generator argument is ignored
469 set.remove(&self_arg());
471 (set, storage_liveness_map)
474 fn compute_layout<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
476 upvars: Vec<Ty<'tcx>>,
480 -> (HashMap<Local, (Ty<'tcx>, usize)>,
481 GeneratorLayout<'tcx>,
482 HashMap<BasicBlock, liveness::LocalSet<Local>>)
484 // Use a liveness analysis to compute locals which are live across a suspension point
485 let (live_locals, storage_liveness) = locals_live_across_suspend_points(tcx,
489 // Erase regions from the types passed in from typeck so we can compare them with
491 let allowed_upvars = tcx.erase_regions(&upvars);
492 let allowed = match interior.sty {
493 ty::TyGeneratorWitness(s) => tcx.erase_late_bound_regions(&s),
497 for (local, decl) in mir.local_decls.iter_enumerated() {
498 // Ignore locals which are internal or not live
499 if !live_locals.contains(&local) || decl.internal {
503 // Sanity check that typeck knows about the type of locals which are
504 // live across a suspension point
505 if !allowed.contains(&decl.ty) && !allowed_upvars.contains(&decl.ty) {
507 "Broken MIR: generator contains type {} in MIR, \
508 but typeck only knows about {}",
514 let upvar_len = mir.upvar_decls.len();
515 let dummy_local = LocalDecl::new_internal(tcx.mk_nil(), mir.span);
517 // Gather live locals and their indices replacing values in mir.local_decls with a dummy
518 // to avoid changing local indices
519 let live_decls = live_locals.iter().map(|local| {
520 let var = mem::replace(&mut mir.local_decls[local], dummy_local.clone());
524 // Create a map from local indices to generator struct indices.
525 // These are offset by (upvar_len + 1) because of fields which comes before locals.
526 // We also create a vector of the LocalDecls of these locals.
527 let (remap, vars) = live_decls.enumerate().map(|(idx, (local, var))| {
528 ((local, (var.ty, upvar_len + 1 + idx)), var)
531 let layout = GeneratorLayout {
535 (remap, layout, storage_liveness)
538 fn insert_switch<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
540 cases: Vec<(u32, BasicBlock)>,
541 transform: &TransformVisitor<'a, 'tcx>,
542 default: TerminatorKind<'tcx>) {
543 let default_block = insert_term_block(mir, default);
545 let switch = TerminatorKind::SwitchInt {
546 discr: Operand::Copy(transform.make_field(transform.state_field, tcx.types.u32)),
547 switch_ty: tcx.types.u32,
548 values: Cow::from(cases.iter().map(|&(i, _)| i.into()).collect::<Vec<_>>()),
549 targets: cases.iter().map(|&(_, d)| d).chain(once(default_block)).collect(),
552 let source_info = source_info(mir);
553 mir.basic_blocks_mut().raw.insert(0, BasicBlockData {
554 statements: Vec::new(),
555 terminator: Some(Terminator {
562 let blocks = mir.basic_blocks_mut().iter_mut();
564 for target in blocks.flat_map(|b| b.terminator_mut().successors_mut()) {
565 *target = BasicBlock::new(target.index() + 1);
569 fn elaborate_generator_drops<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
571 mir: &mut Mir<'tcx>) {
572 use util::elaborate_drops::{elaborate_drop, Unwind};
573 use util::patch::MirPatch;
574 use shim::DropShimElaborator;
576 // Note that `elaborate_drops` only drops the upvars of a generator, and
577 // this is ok because `open_drop` can only be reached within that own
578 // generator's resume function.
580 let param_env = tcx.param_env(def_id);
581 let gen = self_arg();
583 for block in mir.basic_blocks().indices() {
584 let (target, unwind, source_info) = match mir.basic_blocks()[block].terminator() {
587 kind: TerminatorKind::Drop {
588 location: Place::Local(local),
592 } if local == gen => (target, unwind, source_info),
595 let unwind = if let Some(unwind) = unwind {
601 let mut elaborator = DropShimElaborator {
603 patch: MirPatch::new(mir),
622 fn create_generator_drop_shim<'a, 'tcx>(
623 tcx: TyCtxt<'a, 'tcx, 'tcx>,
624 transform: &TransformVisitor<'a, 'tcx>,
629 drop_clean: BasicBlock) -> Mir<'tcx> {
630 let mut mir = mir.clone();
632 let source_info = source_info(&mir);
634 let mut cases = create_cases(&mut mir, transform, |point| point.drop);
636 cases.insert(0, (0, drop_clean));
638 // The returned state (1) and the poisoned state (2) falls through to
639 // the default case which is just to return
641 insert_switch(tcx, &mut mir, cases, &transform, TerminatorKind::Return);
643 for block in mir.basic_blocks_mut() {
644 let kind = &mut block.terminator_mut().kind;
645 if let TerminatorKind::GeneratorDrop = *kind {
646 *kind = TerminatorKind::Return;
650 // Replace the return variable
651 mir.local_decls[RETURN_PLACE] = LocalDecl {
652 mutability: Mutability::Mut,
656 visibility_scope: source_info.scope,
658 is_user_variable: None,
661 make_generator_state_argument_indirect(tcx, def_id, &mut mir);
663 // Change the generator argument from &mut to *mut
664 mir.local_decls[self_arg()] = LocalDecl {
665 mutability: Mutability::Mut,
666 ty: tcx.mk_ptr(ty::TypeAndMut {
668 mutbl: hir::Mutability::MutMutable,
672 visibility_scope: source_info.scope,
674 is_user_variable: None,
677 no_landing_pads(tcx, &mut mir);
679 // Make sure we remove dead blocks to remove
680 // unrelated code from the resume part of the function
681 simplify::remove_dead_blocks(&mut mir);
683 dump_mir(tcx, None, "generator_drop", &0, source, &mut mir, |_, _| Ok(()) );
688 fn insert_term_block<'tcx>(mir: &mut Mir<'tcx>, kind: TerminatorKind<'tcx>) -> BasicBlock {
689 let term_block = BasicBlock::new(mir.basic_blocks().len());
690 let source_info = source_info(mir);
691 mir.basic_blocks_mut().push(BasicBlockData {
692 statements: Vec::new(),
693 terminator: Some(Terminator {
702 fn insert_panic_block<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
704 message: AssertMessage<'tcx>) -> BasicBlock {
705 let assert_block = BasicBlock::new(mir.basic_blocks().len());
706 let term = TerminatorKind::Assert {
707 cond: Operand::Constant(box Constant {
710 literal: Literal::Value {
711 value: ty::Const::from_bool(tcx, false),
716 target: assert_block,
720 let source_info = source_info(mir);
721 mir.basic_blocks_mut().push(BasicBlockData {
722 statements: Vec::new(),
723 terminator: Some(Terminator {
733 fn create_generator_resume_function<'a, 'tcx>(
734 tcx: TyCtxt<'a, 'tcx, 'tcx>,
735 transform: TransformVisitor<'a, 'tcx>,
738 mir: &mut Mir<'tcx>) {
739 // Poison the generator when it unwinds
740 for block in mir.basic_blocks_mut() {
741 let source_info = block.terminator().source_info;
742 if let &TerminatorKind::Resume = &block.terminator().kind {
743 block.statements.push(transform.set_state(1, source_info));
747 let mut cases = create_cases(mir, &transform, |point| Some(point.resume));
749 use rustc::mir::interpret::EvalErrorKind::{
750 GeneratorResumedAfterPanic,
751 GeneratorResumedAfterReturn,
754 // Jump to the entry point on the 0 state
755 cases.insert(0, (0, BasicBlock::new(0)));
756 // Panic when resumed on the returned (1) state
757 cases.insert(1, (1, insert_panic_block(tcx, mir, GeneratorResumedAfterReturn)));
758 // Panic when resumed on the poisoned (2) state
759 cases.insert(2, (2, insert_panic_block(tcx, mir, GeneratorResumedAfterPanic)));
761 insert_switch(tcx, mir, cases, &transform, TerminatorKind::Unreachable);
763 make_generator_state_argument_indirect(tcx, def_id, mir);
765 no_landing_pads(tcx, mir);
767 // Make sure we remove dead blocks to remove
768 // unrelated code from the drop part of the function
769 simplify::remove_dead_blocks(mir);
771 dump_mir(tcx, None, "generator_resume", &0, source, mir, |_, _| Ok(()) );
774 fn source_info<'a, 'tcx>(mir: &Mir<'tcx>) -> SourceInfo {
777 scope: OUTERMOST_SOURCE_SCOPE,
781 fn insert_clean_drop<'a, 'tcx>(mir: &mut Mir<'tcx>) -> BasicBlock {
782 let return_block = insert_term_block(mir, TerminatorKind::Return);
784 // Create a block to destroy an unresumed generators. This can only destroy upvars.
785 let drop_clean = BasicBlock::new(mir.basic_blocks().len());
786 let term = TerminatorKind::Drop {
787 location: Place::Local(self_arg()),
788 target: return_block,
791 let source_info = source_info(mir);
792 mir.basic_blocks_mut().push(BasicBlockData {
793 statements: Vec::new(),
794 terminator: Some(Terminator {
804 fn create_cases<'a, 'tcx, F>(mir: &mut Mir<'tcx>,
805 transform: &TransformVisitor<'a, 'tcx>,
806 target: F) -> Vec<(u32, BasicBlock)>
807 where F: Fn(&SuspensionPoint) -> Option<BasicBlock> {
808 let source_info = source_info(mir);
810 transform.suspension_points.iter().filter_map(|point| {
811 // Find the target for this suspension point, if applicable
812 target(point).map(|target| {
813 let block = BasicBlock::new(mir.basic_blocks().len());
814 let mut statements = Vec::new();
816 // Create StorageLive instructions for locals with live storage
817 for i in 0..(mir.local_decls.len()) {
818 let l = Local::new(i);
819 if point.storage_liveness.contains(&l) && !transform.remap.contains_key(&l) {
820 statements.push(Statement {
822 kind: StatementKind::StorageLive(l),
827 // Then jump to the real target
828 mir.basic_blocks_mut().push(BasicBlockData {
830 terminator: Some(Terminator {
832 kind: TerminatorKind::Goto {
844 impl MirPass for StateTransform {
845 fn run_pass<'a, 'tcx>(&self,
846 tcx: TyCtxt<'a, 'tcx, 'tcx>,
848 mir: &mut Mir<'tcx>) {
849 let yield_ty = if let Some(yield_ty) = mir.yield_ty {
852 // This only applies to generators
856 assert!(mir.generator_drop.is_none());
858 let def_id = source.def_id;
860 // The first argument is the generator type passed by value
861 let gen_ty = mir.local_decls.raw[1].ty;
863 // Get the interior types and substs which typeck computed
864 let (upvars, interior, movable) = match gen_ty.sty {
865 ty::TyGenerator(_, substs, movability) => {
866 (substs.upvar_tys(def_id, tcx).collect(),
867 substs.witness(def_id, tcx),
868 movability == hir::GeneratorMovability::Movable)
873 // Compute GeneratorState<yield_ty, return_ty>
874 let state_did = tcx.lang_items().gen_state().unwrap();
875 let state_adt_ref = tcx.adt_def(state_did);
876 let state_substs = tcx.intern_substs(&[
878 mir.return_ty().into(),
880 let ret_ty = tcx.mk_adt(state_adt_ref, state_substs);
882 // We rename RETURN_PLACE which has type mir.return_ty to new_ret_local
883 // RETURN_PLACE then is a fresh unused local with type ret_ty.
884 let new_ret_local = replace_result_variable(ret_ty, mir);
886 // Extract locals which are live across suspension point into `layout`
887 // `remap` gives a mapping from local indices onto generator struct indices
888 // `storage_liveness` tells us which locals have live storage at suspension points
889 let (remap, layout, storage_liveness) = compute_layout(
897 let state_field = mir.upvar_decls.len();
899 // Run the transformation which converts Places from Local to generator struct
900 // accesses for locals in `remap`.
901 // It also rewrites `return x` and `yield y` as writing a new generator state and returning
902 // GeneratorState::Complete(x) and GeneratorState::Yielded(y) respectively.
903 let mut transform = TransformVisitor {
909 suspension_points: Vec::new(),
913 transform.visit_mir(mir);
915 // Update our MIR struct to reflect the changed we've made
918 mir.spread_arg = None;
919 mir.generator_layout = Some(layout);
921 // Insert `drop(generator_struct)` which is used to drop upvars for generators in
922 // the unresumed (0) state.
923 // This is expanded to a drop ladder in `elaborate_generator_drops`.
924 let drop_clean = insert_clean_drop(mir);
926 dump_mir(tcx, None, "generator_pre-elab", &0, source, mir, |_, _| Ok(()) );
928 // Expand `drop(generator_struct)` to a drop ladder which destroys upvars.
929 // If any upvars are moved out of, drop elaboration will handle upvar destruction.
930 // However we need to also elaborate the code generated by `insert_clean_drop`.
931 elaborate_generator_drops(tcx, def_id, mir);
933 dump_mir(tcx, None, "generator_post-transform", &0, source, mir, |_, _| Ok(()) );
935 // Create a copy of our MIR and use it to create the drop shim for the generator
936 let drop_shim = create_generator_drop_shim(tcx,
944 mir.generator_drop = Some(box drop_shim);
946 // Create the Generator::resume function
947 create_generator_resume_function(tcx, transform, def_id, source, mir);