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,
137 struct TransformVisitor<'a, 'tcx: 'a> {
138 tcx: TyCtxt<'a, 'tcx, 'tcx>,
139 state_adt_ref: &'tcx AdtDef,
140 state_substs: &'tcx Substs<'tcx>,
142 // The index of the generator state in the generator struct
145 // Mapping from Local to (type of local, generator struct index)
146 remap: HashMap<Local, (Ty<'tcx>, usize)>,
148 // A map from a suspension point in a block to the locals which have live storage at that point
149 storage_liveness: HashMap<BasicBlock, liveness::LocalSet>,
151 // A list of suspension points, generated during the transform
152 suspension_points: Vec<SuspensionPoint>,
154 // The original RETURN_POINTER local
155 new_ret_local: Local,
158 impl<'a, 'tcx> TransformVisitor<'a, 'tcx> {
159 // Make a GeneratorState rvalue
160 fn make_state(&self, idx: usize, val: Operand<'tcx>) -> Rvalue<'tcx> {
161 let adt = AggregateKind::Adt(self.state_adt_ref, idx, self.state_substs, None);
162 Rvalue::Aggregate(box adt, vec![val])
165 // Create a Lvalue referencing a generator struct field
166 fn make_field(&self, idx: usize, ty: Ty<'tcx>) -> Lvalue<'tcx> {
167 let base = Lvalue::Local(self_arg());
168 let field = Projection {
170 elem: ProjectionElem::Field(Field::new(idx), ty),
172 Lvalue::Projection(Box::new(field))
175 // Create a statement which changes the generator state
176 fn set_state(&self, state_disc: u32, source_info: SourceInfo) -> Statement<'tcx> {
177 let state = self.make_field(self.state_field, self.tcx.types.u32);
178 let val = Operand::Constant(box Constant {
179 span: source_info.span,
180 ty: self.tcx.types.u32,
181 literal: Literal::Value {
182 value: self.tcx.mk_const(ty::Const {
183 val: ConstVal::Integral(ConstInt::U32(state_disc)),
184 ty: self.tcx.types.u32
190 kind: StatementKind::Assign(state, Rvalue::Use(val)),
195 impl<'a, 'tcx> MutVisitor<'tcx> for TransformVisitor<'a, 'tcx> {
196 fn visit_local(&mut self,
198 _: LvalueContext<'tcx>,
200 assert_eq!(self.remap.get(local), None);
203 fn visit_lvalue(&mut self,
204 lvalue: &mut Lvalue<'tcx>,
205 context: LvalueContext<'tcx>,
206 location: Location) {
207 if let Lvalue::Local(l) = *lvalue {
208 // Replace an Local in the remap with a generator struct access
209 if let Some(&(ty, idx)) = self.remap.get(&l) {
210 *lvalue = self.make_field(idx, ty);
213 self.super_lvalue(lvalue, context, location);
217 fn visit_basic_block_data(&mut self,
219 data: &mut BasicBlockData<'tcx>) {
220 // Remove StorageLive and StorageDead statements for remapped locals
221 data.retain_statements(|s| {
223 StatementKind::StorageLive(l) | StatementKind::StorageDead(l) => {
224 !self.remap.contains_key(&l)
230 let ret_val = match data.terminator().kind {
231 TerminatorKind::Return => Some((1,
233 Operand::Consume(Lvalue::Local(self.new_ret_local)),
235 TerminatorKind::Yield { ref value, resume, drop } => Some((0,
242 if let Some((state_idx, resume, v, drop)) = ret_val {
243 let source_info = data.terminator().source_info;
244 // We must assign the value first in case it gets declared dead below
245 data.statements.push(Statement {
247 kind: StatementKind::Assign(Lvalue::Local(RETURN_POINTER),
248 self.make_state(state_idx, v)),
250 let state = if let Some(resume) = resume { // Yield
251 let state = 3 + self.suspension_points.len() as u32;
253 self.suspension_points.push(SuspensionPoint {
257 storage_liveness: self.storage_liveness.get(&block).unwrap().clone(),
262 1 // state for returned
264 data.statements.push(self.set_state(state, source_info));
265 data.terminator.as_mut().unwrap().kind = TerminatorKind::Return;
268 self.super_basic_block_data(block, data);
272 fn make_generator_state_argument_indirect<'a, 'tcx>(
273 tcx: TyCtxt<'a, 'tcx, 'tcx>,
275 mir: &mut Mir<'tcx>) {
276 let gen_ty = mir.local_decls.raw[1].ty;
278 let region = ty::ReFree(ty::FreeRegion {
280 bound_region: ty::BoundRegion::BrEnv,
283 let region = tcx.mk_region(region);
285 let ref_gen_ty = tcx.mk_ref(region, ty::TypeAndMut {
287 mutbl: hir::MutMutable
290 // Replace the by value generator argument
291 mir.local_decls.raw[1].ty = ref_gen_ty;
293 // Add a deref to accesses of the generator state
294 DerefArgVisitor.visit_mir(mir);
297 fn replace_result_variable<'tcx>(ret_ty: Ty<'tcx>,
298 mir: &mut Mir<'tcx>) -> Local {
299 let new_ret = LocalDecl {
300 mutability: Mutability::Mut,
303 source_info: source_info(mir),
305 is_user_variable: false,
307 let new_ret_local = Local::new(mir.local_decls.len());
308 mir.local_decls.push(new_ret);
309 mir.local_decls.swap(0, new_ret_local.index());
312 from: RETURN_POINTER,
319 struct StorageIgnored(liveness::LocalSet);
321 impl<'tcx> Visitor<'tcx> for StorageIgnored {
322 fn visit_statement(&mut self,
324 statement: &Statement<'tcx>,
325 _location: Location) {
326 match statement.kind {
327 StatementKind::StorageLive(l) |
328 StatementKind::StorageDead(l) => { self.0.remove(&l); }
334 fn locals_live_across_suspend_points<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
336 source: MirSource) ->
338 HashMap<BasicBlock, liveness::LocalSet>) {
339 let dead_unwinds = IdxSetBuf::new_empty(mir.basic_blocks().len());
340 let node_id = source.item_id();
341 let analysis = MaybeStorageLive::new(mir);
343 dataflow::do_dataflow(tcx, mir, node_id, &[], &dead_unwinds, analysis,
344 |bd, p| &bd.mir().local_decls[p]);
346 let mut ignored = StorageIgnored(IdxSetBuf::new_filled(mir.local_decls.len()));
347 ignored.visit_mir(mir);
349 let mut set = liveness::LocalSet::new_empty(mir.local_decls.len());
350 let liveness = liveness::liveness_of_locals(mir);
351 liveness::dump_mir(tcx, "generator_liveness", source, mir, &liveness);
353 let mut storage_liveness_map = HashMap::new();
355 for (block, data) in mir.basic_blocks().iter_enumerated() {
356 if let TerminatorKind::Yield { .. } = data.terminator().kind {
359 statement_index: data.statements.len(),
362 let storage_liveness = state_for_location(loc, &analysis, &storage_live);
364 storage_liveness_map.insert(block, storage_liveness.clone());
366 let mut live_locals = storage_liveness;
368 // Mark locals without storage statements as always having live storage
369 live_locals.union(&ignored.0);
371 // Locals live are live at this point only if they are used across suspension points
372 // and their storage is live
373 live_locals.intersect(&liveness.outs[block]);
375 // Add the locals life at this suspension point to the set of locals which live across
376 // any suspension points
377 set.union(&live_locals);
381 // The generator argument is ignored
382 set.remove(&self_arg());
384 (set, storage_liveness_map)
387 fn compute_layout<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
389 interior: GeneratorInterior<'tcx>,
391 -> (HashMap<Local, (Ty<'tcx>, usize)>,
392 GeneratorLayout<'tcx>,
393 HashMap<BasicBlock, liveness::LocalSet>)
395 // Use a liveness analysis to compute locals which are live across a suspension point
396 let (live_locals, storage_liveness) = locals_live_across_suspend_points(tcx, mir, source);
398 // Erase regions from the types passed in from typeck so we can compare them with
400 let allowed = tcx.erase_regions(&interior.as_slice());
402 for (local, decl) in mir.local_decls.iter_enumerated() {
403 // Ignore locals which are internal or not live
404 if !live_locals.contains(&local) || decl.internal {
408 // Sanity check that typeck knows about the type of locals which are
409 // live across a suspension point
410 if !allowed.contains(&decl.ty) {
412 "Broken MIR: generator contains type {} in MIR, \
413 but typeck only knows about {}",
419 let upvar_len = mir.upvar_decls.len();
420 let dummy_local = LocalDecl::new_internal(tcx.mk_nil(), mir.span);
422 // Gather live locals and their indices replacing values in mir.local_decls with a dummy
423 // to avoid changing local indices
424 let live_decls = live_locals.iter().map(|local| {
425 let var = mem::replace(&mut mir.local_decls[local], dummy_local.clone());
429 // Create a map from local indices to generator struct indices.
430 // These are offset by (upvar_len + 1) because of fields which comes before locals.
431 // We also create a vector of the LocalDecls of these locals.
432 let (remap, vars) = live_decls.enumerate().map(|(idx, (local, var))| {
433 ((local, (var.ty, upvar_len + 1 + idx)), var)
436 let layout = GeneratorLayout {
440 (remap, layout, storage_liveness)
443 fn insert_switch<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
445 cases: Vec<(u32, BasicBlock)>,
446 transform: &TransformVisitor<'a, 'tcx>) {
447 let return_block = insert_return_block(mir);
449 let switch = TerminatorKind::SwitchInt {
450 discr: Operand::Consume(transform.make_field(transform.state_field, tcx.types.u32)),
451 switch_ty: tcx.types.u32,
452 values: Cow::from(cases.iter().map(|&(i, _)| ConstInt::U32(i)).collect::<Vec<_>>()),
453 targets: cases.iter().map(|&(_, d)| d).chain(once(return_block)).collect(),
456 let source_info = source_info(mir);
457 mir.basic_blocks_mut().raw.insert(0, BasicBlockData {
458 statements: Vec::new(),
459 terminator: Some(Terminator {
466 let blocks = mir.basic_blocks_mut().iter_mut();
468 for target in blocks.flat_map(|b| b.terminator_mut().successors_mut()) {
469 *target = BasicBlock::new(target.index() + 1);
473 fn elaborate_generator_drops<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
475 mir: &mut Mir<'tcx>) {
476 use util::elaborate_drops::{elaborate_drop, Unwind};
477 use util::patch::MirPatch;
478 use shim::DropShimElaborator;
480 // Note that `elaborate_drops` only drops the upvars of a generator, and
481 // this is ok because `open_drop` can only be reached within that own
482 // generator's resume function.
484 let param_env = tcx.param_env(def_id);
485 let gen = self_arg();
487 for block in mir.basic_blocks().indices() {
488 let (target, unwind, source_info) = match mir.basic_blocks()[block].terminator() {
491 kind: TerminatorKind::Drop {
492 location: Lvalue::Local(local),
496 } if local == gen => (target, unwind, source_info),
499 let unwind = if let Some(unwind) = unwind {
505 let mut elaborator = DropShimElaborator {
507 patch: MirPatch::new(mir),
526 fn create_generator_drop_shim<'a, 'tcx>(
527 tcx: TyCtxt<'a, 'tcx, 'tcx>,
528 transform: &TransformVisitor<'a, 'tcx>,
533 drop_clean: BasicBlock) -> Mir<'tcx> {
534 let mut mir = mir.clone();
536 let source_info = source_info(&mir);
538 let mut cases = create_cases(&mut mir, transform, |point| point.drop);
540 cases.insert(0, (0, drop_clean));
542 // The returned state (1) and the poisoned state (2) falls through to
543 // the default case which is just to return
545 insert_switch(tcx, &mut mir, cases, &transform);
547 for block in mir.basic_blocks_mut() {
548 let kind = &mut block.terminator_mut().kind;
549 if let TerminatorKind::GeneratorDrop = *kind {
550 *kind = TerminatorKind::Return;
554 // Replace the return variable
555 mir.return_ty = tcx.mk_nil();
556 mir.local_decls[RETURN_POINTER] = LocalDecl {
557 mutability: Mutability::Mut,
562 is_user_variable: false,
565 make_generator_state_argument_indirect(tcx, def_id, &mut mir);
567 // Change the generator argument from &mut to *mut
568 mir.local_decls[self_arg()] = LocalDecl {
569 mutability: Mutability::Mut,
570 ty: tcx.mk_ptr(ty::TypeAndMut {
572 mutbl: hir::Mutability::MutMutable,
577 is_user_variable: false,
580 no_landing_pads(tcx, &mut mir);
582 // Make sure we remove dead blocks to remove
583 // unrelated code from the resume part of the function
584 simplify::remove_dead_blocks(&mut mir);
586 dump_mir(tcx, None, "generator_drop", &0, source, &mut mir);
591 fn insert_return_block<'tcx>(mir: &mut Mir<'tcx>) -> BasicBlock {
592 let return_block = BasicBlock::new(mir.basic_blocks().len());
593 let source_info = source_info(mir);
594 mir.basic_blocks_mut().push(BasicBlockData {
595 statements: Vec::new(),
596 terminator: Some(Terminator {
598 kind: TerminatorKind::Return,
605 fn insert_panic_block<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
607 message: AssertMessage<'tcx>) -> BasicBlock {
608 let assert_block = BasicBlock::new(mir.basic_blocks().len());
609 let term = TerminatorKind::Assert {
610 cond: Operand::Constant(box Constant {
613 literal: Literal::Value {
614 value: tcx.mk_const(ty::Const {
615 val: ConstVal::Bool(false),
622 target: assert_block,
626 let source_info = source_info(mir);
627 mir.basic_blocks_mut().push(BasicBlockData {
628 statements: Vec::new(),
629 terminator: Some(Terminator {
639 fn create_generator_resume_function<'a, 'tcx>(
640 tcx: TyCtxt<'a, 'tcx, 'tcx>,
641 transform: TransformVisitor<'a, 'tcx>,
644 mir: &mut Mir<'tcx>) {
645 // Poison the generator when it unwinds
646 for block in mir.basic_blocks_mut() {
647 let source_info = block.terminator().source_info;
648 if let &TerminatorKind::Resume = &block.terminator().kind {
649 block.statements.push(transform.set_state(1, source_info));
653 let mut cases = create_cases(mir, &transform, |point| Some(point.resume));
655 // Jump to the entry point on the 0 state
656 cases.insert(0, (0, BasicBlock::new(0)));
657 // Panic when resumed on the returned (1) state
658 cases.insert(1, (1, insert_panic_block(tcx, mir, AssertMessage::GeneratorResumedAfterReturn)));
659 // Panic when resumed on the poisoned (2) state
660 cases.insert(2, (2, insert_panic_block(tcx, mir, AssertMessage::GeneratorResumedAfterPanic)));
662 insert_switch(tcx, mir, cases, &transform);
664 make_generator_state_argument_indirect(tcx, def_id, mir);
666 no_landing_pads(tcx, mir);
668 // Make sure we remove dead blocks to remove
669 // unrelated code from the drop part of the function
670 simplify::remove_dead_blocks(mir);
672 dump_mir(tcx, None, "generator_resume", &0, source, mir);
675 fn source_info<'a, 'tcx>(mir: &Mir<'tcx>) -> SourceInfo {
678 scope: ARGUMENT_VISIBILITY_SCOPE,
682 fn insert_clean_drop<'a, 'tcx>(mir: &mut Mir<'tcx>) -> BasicBlock {
683 let return_block = insert_return_block(mir);
685 // Create a block to destroy an unresumed generators. This can only destroy upvars.
686 let drop_clean = BasicBlock::new(mir.basic_blocks().len());
687 let term = TerminatorKind::Drop {
688 location: Lvalue::Local(self_arg()),
689 target: return_block,
692 let source_info = source_info(mir);
693 mir.basic_blocks_mut().push(BasicBlockData {
694 statements: Vec::new(),
695 terminator: Some(Terminator {
705 fn create_cases<'a, 'tcx, F>(mir: &mut Mir<'tcx>,
706 transform: &TransformVisitor<'a, 'tcx>,
707 target: F) -> Vec<(u32, BasicBlock)>
708 where F: Fn(&SuspensionPoint) -> Option<BasicBlock> {
709 let source_info = source_info(mir);
711 transform.suspension_points.iter().filter_map(|point| {
712 // Find the target for this suspension point, if applicable
713 target(point).map(|target| {
714 let block = BasicBlock::new(mir.basic_blocks().len());
715 let mut statements = Vec::new();
717 // Create StorageLive instructions for locals with live storage
718 for i in 0..(mir.local_decls.len()) {
719 let l = Local::new(i);
720 if point.storage_liveness.contains(&l) && !transform.remap.contains_key(&l) {
721 statements.push(Statement {
723 kind: StatementKind::StorageLive(l),
728 // Then jump to the real target
729 mir.basic_blocks_mut().push(BasicBlockData {
731 terminator: Some(Terminator {
733 kind: TerminatorKind::Goto {
745 impl MirPass for StateTransform {
746 fn run_pass<'a, 'tcx>(&self,
747 tcx: TyCtxt<'a, 'tcx, 'tcx>,
749 mir: &mut Mir<'tcx>) {
750 let yield_ty = if let Some(yield_ty) = mir.yield_ty {
753 // This only applies to generators
757 assert!(mir.generator_drop.is_none());
759 let node_id = source.item_id();
760 let def_id = tcx.hir.local_def_id(source.item_id());
761 let hir_id = tcx.hir.node_to_hir_id(node_id);
763 // Get the interior types which typeck computed
764 let interior = *tcx.typeck_tables_of(def_id).generator_interiors().get(hir_id).unwrap();
766 // The first argument is the generator type passed by value
767 let gen_ty = mir.local_decls.raw[1].ty;
769 // Compute GeneratorState<yield_ty, return_ty>
770 let state_did = tcx.lang_items().gen_state().unwrap();
771 let state_adt_ref = tcx.adt_def(state_did);
772 let state_substs = tcx.mk_substs([Kind::from(yield_ty),
773 Kind::from(mir.return_ty)].iter());
774 let ret_ty = tcx.mk_adt(state_adt_ref, state_substs);
776 // We rename RETURN_POINTER which has type mir.return_ty to new_ret_local
777 // RETURN_POINTER then is a fresh unused local with type ret_ty.
778 let new_ret_local = replace_result_variable(ret_ty, mir);
780 // Extract locals which are live across suspension point into `layout`
781 // `remap` gives a mapping from local indices onto generator struct indices
782 // `storage_liveness` tells us which locals have live storage at suspension points
783 let (remap, layout, storage_liveness) = compute_layout(tcx, source, interior, mir);
785 let state_field = mir.upvar_decls.len();
787 // Run the transformation which converts Lvalues from Local to generator struct
788 // accesses for locals in `remap`.
789 // It also rewrites `return x` and `yield y` as writing a new generator state and returning
790 // GeneratorState::Complete(x) and GeneratorState::Yielded(y) respectively.
791 let mut transform = TransformVisitor {
797 suspension_points: Vec::new(),
801 transform.visit_mir(mir);
803 // Update our MIR struct to reflect the changed we've made
804 mir.return_ty = ret_ty;
807 mir.spread_arg = None;
808 mir.generator_layout = Some(layout);
810 // Insert `drop(generator_struct)` which is used to drop upvars for generators in
811 // the unresumed (0) state.
812 // This is expanded to a drop ladder in `elaborate_generator_drops`.
813 let drop_clean = insert_clean_drop(mir);
815 dump_mir(tcx, None, "generator_pre-elab", &0, source, mir);
817 // Expand `drop(generator_struct)` to a drop ladder which destroys upvars.
818 // If any upvars are moved out of, drop elaboration will handle upvar destruction.
819 // However we need to also elaborate the code generated by `insert_clean_drop`.
820 elaborate_generator_drops(tcx, def_id, mir);
822 dump_mir(tcx, None, "generator_post-transform", &0, source, mir);
824 // Create a copy of our MIR and use it to create the drop shim for the generator
825 let drop_shim = create_generator_drop_shim(tcx,
833 mir.generator_drop = Some(box drop_shim);
835 // Create the Generator::resume function
836 create_generator_resume_function(tcx, transform, def_id, source, mir);