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;
64 use rustc::middle::const_val::ConstVal;
66 use rustc::mir::transform::{MirPass, MirSource};
67 use rustc::mir::visit::{LvalueContext, Visitor, MutVisitor};
68 use rustc::ty::{self, TyCtxt, AdtDef, Ty, GeneratorInterior};
69 use rustc::ty::subst::{Kind, Substs};
72 use rustc_const_math::ConstInt;
73 use rustc_data_structures::indexed_vec::Idx;
74 use rustc_data_structures::indexed_set::IdxSetBuf;
75 use std::collections::HashMap;
79 use transform::simplify;
80 use transform::no_landing_pads::no_landing_pads;
81 use dataflow::{self, MaybeStorageLive, state_for_location};
83 pub struct StateTransform;
85 struct RenameLocalVisitor {
90 impl<'tcx> MutVisitor<'tcx> for RenameLocalVisitor {
91 fn visit_local(&mut self,
93 _: LvalueContext<'tcx>,
95 if *local == self.from {
101 struct DerefArgVisitor;
103 impl<'tcx> MutVisitor<'tcx> for DerefArgVisitor {
104 fn visit_local(&mut self,
106 _: LvalueContext<'tcx>,
108 assert_ne!(*local, self_arg());
111 fn visit_lvalue(&mut self,
112 lvalue: &mut Lvalue<'tcx>,
113 context: LvalueContext<'tcx>,
114 location: Location) {
115 if *lvalue == Lvalue::Local(self_arg()) {
116 *lvalue = Lvalue::Projection(Box::new(Projection {
117 base: lvalue.clone(),
118 elem: ProjectionElem::Deref,
121 self.super_lvalue(lvalue, context, location);
126 fn self_arg() -> Local {
130 struct SuspensionPoint {
133 drop: Option<BasicBlock>,
134 storage_liveness: liveness::LocalSet,
135 storage_live: Option<BasicBlock>,
138 struct TransformVisitor<'a, 'tcx: 'a> {
139 tcx: TyCtxt<'a, 'tcx, 'tcx>,
140 state_adt_ref: &'tcx AdtDef,
141 state_substs: &'tcx Substs<'tcx>,
143 // The index of the generator state in the generator struct
146 // Mapping from Local to (type of local, generator struct index)
147 remap: HashMap<Local, (Ty<'tcx>, usize)>,
149 mir_local_count: usize,
151 // A map from a suspension point in a block to the locals which have live storage at that point
152 storage_liveness: HashMap<BasicBlock, liveness::LocalSet>,
154 // A list of suspension points, generated during the transform
155 suspension_points: Vec<SuspensionPoint>,
157 // The original RETURN_POINTER local
158 new_ret_local: Local,
161 impl<'a, 'tcx> TransformVisitor<'a, 'tcx> {
162 // Make a GeneratorState rvalue
163 fn make_state(&self, idx: usize, val: Operand<'tcx>) -> Rvalue<'tcx> {
164 let adt = AggregateKind::Adt(self.state_adt_ref, idx, self.state_substs, None);
165 Rvalue::Aggregate(box adt, vec![val])
168 // Create a Lvalue referencing a generator struct field
169 fn make_field(&self, idx: usize, ty: Ty<'tcx>) -> Lvalue<'tcx> {
170 let base = Lvalue::Local(self_arg());
171 let field = Projection {
173 elem: ProjectionElem::Field(Field::new(idx), ty),
175 Lvalue::Projection(Box::new(field))
178 // Create a statement which changes the generator state
179 fn set_state(&self, state_disc: u32, source_info: SourceInfo) -> Statement<'tcx> {
180 let state = self.make_field(self.state_field, self.tcx.types.u32);
181 let val = Operand::Constant(box Constant {
182 span: source_info.span,
183 ty: self.tcx.types.u32,
184 literal: Literal::Value {
185 value: self.tcx.mk_const(ty::Const {
186 val: ConstVal::Integral(ConstInt::U32(state_disc)),
187 ty: self.tcx.types.u32
193 kind: StatementKind::Assign(state, Rvalue::Use(val)),
198 impl<'a, 'tcx> MutVisitor<'tcx> for TransformVisitor<'a, 'tcx> {
199 fn visit_local(&mut self,
201 _: LvalueContext<'tcx>,
203 assert_eq!(self.remap.get(local), None);
206 fn visit_lvalue(&mut self,
207 lvalue: &mut Lvalue<'tcx>,
208 context: LvalueContext<'tcx>,
209 location: Location) {
210 if let Lvalue::Local(l) = *lvalue {
211 // Replace an Local in the remap with a generator struct access
212 if let Some(&(ty, idx)) = self.remap.get(&l) {
213 *lvalue = self.make_field(idx, ty);
216 self.super_lvalue(lvalue, context, location);
220 fn visit_basic_block_data(&mut self,
222 data: &mut BasicBlockData<'tcx>) {
223 // Remove StorageLive and StorageDead statements for remapped locals
224 data.retain_statements(|s| {
226 StatementKind::StorageLive(l) | StatementKind::StorageDead(l) => {
227 !self.remap.contains_key(&l)
233 let ret_val = match data.terminator().kind {
234 TerminatorKind::Return => Some((1,
236 Operand::Consume(Lvalue::Local(self.new_ret_local)),
238 TerminatorKind::Yield { ref value, resume, drop } => Some((0,
245 if let Some((state_idx, resume, v, drop)) = ret_val {
246 let source_info = data.terminator().source_info;
247 // We must assign the value first in case it gets declared dead below
248 data.statements.push(Statement {
250 kind: StatementKind::Assign(Lvalue::Local(RETURN_POINTER),
251 self.make_state(state_idx, v)),
253 let state = if let Some(resume) = resume { // Yield
254 let state = 3 + self.suspension_points.len() as u32;
256 let liveness = self.storage_liveness.get(&block).unwrap();
258 for i in 0..(self.mir_local_count) {
259 let l = Local::new(i);
260 if liveness.contains(&l) && !self.remap.contains_key(&l) {
261 data.statements.push(Statement {
263 kind: StatementKind::StorageDead(l),
268 self.suspension_points.push(SuspensionPoint {
272 storage_liveness: liveness.clone(),
278 1 // state for returned
280 data.statements.push(self.set_state(state, source_info));
281 data.terminator.as_mut().unwrap().kind = TerminatorKind::Return;
284 self.super_basic_block_data(block, data);
288 fn make_generator_state_argument_indirect<'a, 'tcx>(
289 tcx: TyCtxt<'a, 'tcx, 'tcx>,
291 mir: &mut Mir<'tcx>) {
292 let gen_ty = mir.local_decls.raw[1].ty;
294 let region = ty::ReFree(ty::FreeRegion {
296 bound_region: ty::BoundRegion::BrEnv,
299 let region = tcx.mk_region(region);
301 let ref_gen_ty = tcx.mk_ref(region, ty::TypeAndMut {
303 mutbl: hir::MutMutable
306 // Replace the by value generator argument
307 mir.local_decls.raw[1].ty = ref_gen_ty;
309 // Add a deref to accesses of the generator state
310 DerefArgVisitor.visit_mir(mir);
313 fn replace_result_variable<'tcx>(ret_ty: Ty<'tcx>,
314 mir: &mut Mir<'tcx>) -> Local {
315 let new_ret = LocalDecl {
316 mutability: Mutability::Mut,
319 source_info: source_info(mir),
321 is_user_variable: false,
323 let new_ret_local = Local::new(mir.local_decls.len());
324 mir.local_decls.push(new_ret);
325 mir.local_decls.swap(0, new_ret_local.index());
328 from: RETURN_POINTER,
335 struct StorageIgnored(liveness::LocalSet);
337 impl<'tcx> Visitor<'tcx> for StorageIgnored {
338 fn visit_statement(&mut self,
340 statement: &Statement<'tcx>,
341 _location: Location) {
342 match statement.kind {
343 StatementKind::StorageLive(l) |
344 StatementKind::StorageDead(l) => { self.0.remove(&l); }
350 fn locals_live_across_suspend_points<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
352 source: MirSource) ->
354 HashMap<BasicBlock, liveness::LocalSet>) {
355 let dead_unwinds = IdxSetBuf::new_empty(mir.basic_blocks().len());
356 let node_id = source.item_id();
357 let analysis = MaybeStorageLive::new(mir);
359 dataflow::do_dataflow(tcx, mir, node_id, &[], &dead_unwinds, analysis,
360 |bd, p| &bd.mir().local_decls[p]);
362 let mut ignored = StorageIgnored(IdxSetBuf::new_filled(mir.basic_blocks().len()));
363 ignored.visit_mir(mir);
365 let mut set = liveness::LocalSet::new_empty(mir.local_decls.len());
366 let result = liveness::liveness_of_locals(mir);
367 liveness::dump_mir(tcx, "generator_liveness", source, mir, &result);
369 let mut storage_liveness_map = HashMap::new();
371 for (block, data) in mir.basic_blocks().iter_enumerated() {
372 if let TerminatorKind::Yield { .. } = data.terminator().kind {
375 statement_index: data.statements.len(),
378 let mut storage_liveness = state_for_location(loc, &analysis, &storage_live);
380 storage_liveness_map.insert(block, storage_liveness.clone());
382 // Mark locals without storage statements as always live
383 storage_liveness.union(&ignored.0);
385 // Locals live are live at this point only if they are used across suspension points
386 // and their storage is live
387 storage_liveness.intersect(&result.outs[block]);
389 // Add the locals life at this suspension point to the set of locals which live across
390 // any suspension points
391 set.union(&storage_liveness);
395 // The generator argument is ignored
396 set.remove(&self_arg());
398 (set, storage_liveness_map)
401 fn compute_layout<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
403 interior: GeneratorInterior<'tcx>,
405 -> (HashMap<Local, (Ty<'tcx>, usize)>,
406 GeneratorLayout<'tcx>,
407 HashMap<BasicBlock, liveness::LocalSet>)
409 // Use a liveness analysis to compute locals which are live across a suspension point
410 let (live_locals, storage_liveness) = locals_live_across_suspend_points(tcx, mir, source);
412 // Erase regions from the types passed in from typeck so we can compare them with
414 let allowed = tcx.erase_regions(&interior.as_slice());
416 for (local, decl) in mir.local_decls.iter_enumerated() {
417 // Ignore locals which are internal or not live
418 if !live_locals.contains(&local) || decl.internal {
422 // Sanity check that typeck knows about the type of locals which are
423 // live across a suspension point
424 if !allowed.contains(&decl.ty) {
426 "Broken MIR: generator contains type {} in MIR, \
427 but typeck only knows about {}",
433 let upvar_len = mir.upvar_decls.len();
434 let dummy_local = LocalDecl::new_internal(tcx.mk_nil(), mir.span);
436 // Gather live locals and their indices replacing values in mir.local_decls with a dummy
437 // to avoid changing local indices
438 let live_decls = live_locals.iter().map(|local| {
439 let var = mem::replace(&mut mir.local_decls[local], dummy_local.clone());
443 // Create a map from local indices to generator struct indices.
444 // These are offset by (upvar_len + 1) because of fields which comes before locals.
445 // We also create a vector of the LocalDecls of these locals.
446 let (remap, vars) = live_decls.enumerate().map(|(idx, (local, var))| {
447 ((local, (var.ty, upvar_len + 1 + idx)), var)
450 let layout = GeneratorLayout {
454 (remap, layout, storage_liveness)
457 fn insert_switch<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
459 cases: Vec<(u32, BasicBlock)>,
460 transform: &TransformVisitor<'a, 'tcx>) {
461 let return_block = insert_return_block(mir);
463 let switch = TerminatorKind::SwitchInt {
464 discr: Operand::Consume(transform.make_field(transform.state_field, tcx.types.u32)),
465 switch_ty: tcx.types.u32,
466 values: Cow::from(cases.iter().map(|&(i, _)| ConstInt::U32(i)).collect::<Vec<_>>()),
467 targets: cases.iter().map(|&(_, d)| d).chain(once(return_block)).collect(),
470 let source_info = source_info(mir);
471 mir.basic_blocks_mut().raw.insert(0, BasicBlockData {
472 statements: Vec::new(),
473 terminator: Some(Terminator {
480 let blocks = mir.basic_blocks_mut().iter_mut();
482 for target in blocks.flat_map(|b| b.terminator_mut().successors_mut()) {
483 *target = BasicBlock::new(target.index() + 1);
487 fn elaborate_generator_drops<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
489 mir: &mut Mir<'tcx>) {
490 use util::elaborate_drops::{elaborate_drop, Unwind};
491 use util::patch::MirPatch;
492 use shim::DropShimElaborator;
494 // Note that `elaborate_drops` only drops the upvars of a generator, and
495 // this is ok because `open_drop` can only be reached within that own
496 // generator's resume function.
498 let param_env = tcx.param_env(def_id);
499 let gen = self_arg();
501 for block in mir.basic_blocks().indices() {
502 let (target, unwind, source_info) = match mir.basic_blocks()[block].terminator() {
505 kind: TerminatorKind::Drop {
506 location: Lvalue::Local(local),
510 } if local == gen => (target, unwind, source_info),
513 let unwind = if let Some(unwind) = unwind {
519 let mut elaborator = DropShimElaborator {
521 patch: MirPatch::new(mir),
540 fn create_generator_drop_shim<'a, 'tcx>(
541 tcx: TyCtxt<'a, 'tcx, 'tcx>,
542 transform: &TransformVisitor<'a, 'tcx>,
547 drop_clean: BasicBlock) -> Mir<'tcx> {
548 let mut mir = mir.clone();
550 let source_info = source_info(&mir);
552 let mut cases: Vec<_> = transform.suspension_points.iter().filter_map(|point| {
553 point.drop.map(|drop| {
554 // Make the point's storage live block goto the drop block
555 let block = point.storage_live.unwrap();
556 let term = Terminator {
558 kind: TerminatorKind::Goto {
562 mir.basic_blocks_mut()[block].terminator = Some(term);
567 cases.insert(0, (0, drop_clean));
569 // The returned state 1 and the poisoned state 2 falls through to
570 // the default case which is just to return
572 insert_switch(tcx, &mut mir, cases, &transform);
574 for block in mir.basic_blocks_mut() {
575 let kind = &mut block.terminator_mut().kind;
576 if let TerminatorKind::GeneratorDrop = *kind {
577 *kind = TerminatorKind::Return;
581 // Replace the return variable
582 mir.return_ty = tcx.mk_nil();
583 mir.local_decls[RETURN_POINTER] = LocalDecl {
584 mutability: Mutability::Mut,
589 is_user_variable: false,
592 make_generator_state_argument_indirect(tcx, def_id, &mut mir);
594 // Change the generator argument from &mut to *mut
595 mir.local_decls[self_arg()] = LocalDecl {
596 mutability: Mutability::Mut,
597 ty: tcx.mk_ptr(ty::TypeAndMut {
599 mutbl: hir::Mutability::MutMutable,
604 is_user_variable: false,
607 no_landing_pads(tcx, &mut mir);
609 // Make sure we remove dead blocks to remove
610 // unrelated code from the resume part of the function
611 simplify::remove_dead_blocks(&mut mir);
613 dump_mir(tcx, None, "generator_drop", &0, source, &mut mir);
618 fn insert_return_block<'tcx>(mir: &mut Mir<'tcx>) -> BasicBlock {
619 let return_block = BasicBlock::new(mir.basic_blocks().len());
620 let source_info = source_info(mir);
621 mir.basic_blocks_mut().push(BasicBlockData {
622 statements: Vec::new(),
623 terminator: Some(Terminator {
625 kind: TerminatorKind::Return,
632 fn insert_panic_block<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
634 message: AssertMessage<'tcx>) -> BasicBlock {
635 let assert_block = BasicBlock::new(mir.basic_blocks().len());
636 let term = TerminatorKind::Assert {
637 cond: Operand::Constant(box Constant {
640 literal: Literal::Value {
641 value: tcx.mk_const(ty::Const {
642 val: ConstVal::Bool(false),
649 target: assert_block,
653 let source_info = source_info(mir);
654 mir.basic_blocks_mut().push(BasicBlockData {
655 statements: Vec::new(),
656 terminator: Some(Terminator {
666 fn create_generator_resume_function<'a, 'tcx>(
667 tcx: TyCtxt<'a, 'tcx, 'tcx>,
668 transform: TransformVisitor<'a, 'tcx>,
671 mir: &mut Mir<'tcx>) {
672 // Poison the generator when it unwinds
673 for block in mir.basic_blocks_mut() {
674 let source_info = block.terminator().source_info;
675 if let &TerminatorKind::Resume = &block.terminator().kind {
676 block.statements.push(transform.set_state(1, source_info));
680 let mut cases: Vec<_> = transform.suspension_points.iter().map(|point| {
681 // Make the point's storage live block goto the resume block
682 let block = point.storage_live.unwrap();
683 let term = Terminator {
684 source_info: source_info(mir),
685 kind: TerminatorKind::Goto {
686 target: point.resume,
689 mir.basic_blocks_mut()[block].terminator = Some(term);
693 // Jump to the entry point on the 0 state
694 cases.insert(0, (0, BasicBlock::new(0)));
695 // Panic when resumed on the returned (1) state
696 cases.insert(1, (1, insert_panic_block(tcx, mir, AssertMessage::GeneratorResumedAfterReturn)));
697 // Panic when resumed on the poisoned (2) state
698 cases.insert(2, (2, insert_panic_block(tcx, mir, AssertMessage::GeneratorResumedAfterPanic)));
700 insert_switch(tcx, mir, cases, &transform);
702 make_generator_state_argument_indirect(tcx, def_id, mir);
704 no_landing_pads(tcx, mir);
706 // Make sure we remove dead blocks to remove
707 // unrelated code from the drop part of the function
708 simplify::remove_dead_blocks(mir);
710 dump_mir(tcx, None, "generator_resume", &0, source, mir);
713 fn source_info<'a, 'tcx>(mir: &Mir<'tcx>) -> SourceInfo {
716 scope: ARGUMENT_VISIBILITY_SCOPE,
720 fn insert_clean_drop<'a, 'tcx>(mir: &mut Mir<'tcx>) -> BasicBlock {
721 let return_block = insert_return_block(mir);
723 // Create a block to destroy an unresumed generators. This can only destroy upvars.
724 let drop_clean = BasicBlock::new(mir.basic_blocks().len());
725 let term = TerminatorKind::Drop {
726 location: Lvalue::Local(self_arg()),
727 target: return_block,
730 let source_info = source_info(mir);
731 mir.basic_blocks_mut().push(BasicBlockData {
732 statements: Vec::new(),
733 terminator: Some(Terminator {
743 impl MirPass for StateTransform {
744 fn run_pass<'a, 'tcx>(&self,
745 tcx: TyCtxt<'a, 'tcx, 'tcx>,
747 mir: &mut Mir<'tcx>) {
748 let yield_ty = if let Some(yield_ty) = mir.yield_ty {
751 // This only applies to generators
755 assert!(mir.generator_drop.is_none());
757 let node_id = source.item_id();
758 let def_id = tcx.hir.local_def_id(source.item_id());
759 let hir_id = tcx.hir.node_to_hir_id(node_id);
761 // Get the interior types which typeck computed
762 let interior = *tcx.typeck_tables_of(def_id).generator_interiors().get(hir_id).unwrap();
764 // The first argument is the generator type passed by value
765 let gen_ty = mir.local_decls.raw[1].ty;
767 // Compute GeneratorState<yield_ty, return_ty>
768 let state_did = tcx.lang_items().gen_state().unwrap();
769 let state_adt_ref = tcx.adt_def(state_did);
770 let state_substs = tcx.mk_substs([Kind::from(yield_ty),
771 Kind::from(mir.return_ty)].iter());
772 let ret_ty = tcx.mk_adt(state_adt_ref, state_substs);
774 // We rename RETURN_POINTER which has type mir.return_ty to new_ret_local
775 // RETURN_POINTER then is a fresh unused local with type ret_ty.
776 let new_ret_local = replace_result_variable(ret_ty, mir);
778 // Extract locals which are live across suspension point into `layout`
779 // `remap` gives a mapping from local indices onto generator struct indices
780 // `storage_liveness` tells us which locals have live storage at suspension points
781 let (remap, layout, storage_liveness) = compute_layout(tcx, source, interior, mir);
783 let state_field = mir.upvar_decls.len();
785 // Run the transformation which converts Lvalues from Local to generator struct
786 // accesses for locals in `remap`.
787 // It also rewrites `return x` and `yield y` as writing a new generator state and returning
788 // GeneratorState::Complete(x) and GeneratorState::Yielded(y) respectively.
789 let mut transform = TransformVisitor {
795 mir_local_count: mir.local_decls.len(),
796 suspension_points: Vec::new(),
800 transform.visit_mir(mir);
802 // Update our MIR struct to reflect the changed we've made
803 mir.return_ty = ret_ty;
806 mir.spread_arg = None;
807 mir.generator_layout = Some(layout);
809 // Insert `drop(generator_struct)` which is used to drop upvars for generators in
810 // the unresumed (0) state.
811 // This is expanded to a drop ladder in `elaborate_generator_drops`.
812 let drop_clean = insert_clean_drop(mir);
814 dump_mir(tcx, None, "generator_pre-elab", &0, source, mir);
816 // Expand `drop(generator_struct)` to a drop ladder which destroys upvars.
817 // If any upvars are moved out of, drop elaboration will handle upvar destruction.
818 // However we need to also elaborate the code generated by `insert_clean_drop`.
819 elaborate_generator_drops(tcx, def_id, mir);
821 dump_mir(tcx, None, "generator_post-transform", &0, source, mir);
823 // Create StorageLive instruction blocks for suspension points
824 for point in &mut transform.suspension_points {
825 point.storage_live = Some(BasicBlock::new(mir.basic_blocks().len()));
826 let source_info = source_info(mir);
827 let mut statements = Vec::new();
828 for i in 0..(transform.mir_local_count) {
829 let l = Local::new(i);
830 if point.storage_liveness.contains(&l) && !transform.remap.contains_key(&l) {
831 statements.push(Statement {
833 kind: StatementKind::StorageLive(l),
837 mir.basic_blocks_mut().push(BasicBlockData {
839 terminator: Some(Terminator {
841 kind: TerminatorKind::Unreachable,
847 // Create a copy of our MIR and use it to create the drop shim for the generator
848 let drop_shim = create_generator_drop_shim(tcx,
856 mir.generator_drop = Some(box drop_shim);
858 // Create the Generator::resume function
859 create_generator_resume_function(tcx, transform, def_id, source, mir);