2 use rustc::hir::def_id::DefId;
5 use rustc::ty::{self, Ty, TyCtxt, GenericParamDefKind};
6 use rustc::ty::layout::VariantIdx;
7 use rustc::ty::subst::{Subst, Substs};
8 use rustc::ty::query::Providers;
10 use rustc_data_structures::indexed_vec::{IndexVec, Idx};
12 use rustc_target::spec::abi::Abi;
19 use transform::{add_moves_for_packed_drops, add_call_guards};
20 use transform::{remove_noop_landing_pads, no_landing_pads, simplify};
21 use util::elaborate_drops::{self, DropElaborator, DropStyle, DropFlagMode};
22 use util::patch::MirPatch;
24 pub fn provide(providers: &mut Providers) {
25 providers.mir_shims = make_shim;
28 fn make_shim<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
29 instance: ty::InstanceDef<'tcx>)
32 debug!("make_shim({:?})", instance);
34 let mut result = match instance {
35 ty::InstanceDef::Item(..) =>
36 bug!("item {:?} passed to make_shim", instance),
37 ty::InstanceDef::VtableShim(def_id) => {
41 Adjustment::DerefMove,
42 CallKind::Direct(def_id),
46 ty::InstanceDef::FnPtrShim(def_id, ty) => {
47 let trait_ = tcx.trait_of_item(def_id).unwrap();
48 let adjustment = match tcx.lang_items().fn_trait_kind(trait_) {
49 Some(ty::ClosureKind::FnOnce) => Adjustment::Identity,
50 Some(ty::ClosureKind::FnMut) |
51 Some(ty::ClosureKind::Fn) => Adjustment::Deref,
52 None => bug!("fn pointer {:?} is not an fn", ty)
54 // HACK: we need the "real" argument types for the MIR,
55 // but because our substs are (Self, Args), where Args
56 // is a tuple, we must include the *concrete* argument
57 // types in the MIR. They will be substituted again with
58 // the param-substs, but because they are concrete, this
59 // will not do any harm.
60 let sig = tcx.erase_late_bound_regions(&ty.fn_sig(tcx));
61 let arg_tys = sig.inputs();
71 ty::InstanceDef::Virtual(def_id, _) => {
72 // We are generating a call back to our def-id, which the
73 // codegen backend knows to turn to an actual virtual call.
78 CallKind::Direct(def_id),
82 ty::InstanceDef::ClosureOnceShim { call_once } => {
83 let fn_mut = tcx.lang_items().fn_mut_trait().unwrap();
84 let call_mut = tcx.global_tcx()
85 .associated_items(fn_mut)
86 .find(|it| it.kind == ty::AssociatedKind::Method)
93 CallKind::Direct(call_mut),
97 ty::InstanceDef::DropGlue(def_id, ty) => {
98 build_drop_shim(tcx, def_id, ty)
100 ty::InstanceDef::CloneShim(def_id, ty) => {
101 let name = tcx.item_name(def_id);
103 build_clone_shim(tcx, def_id, ty)
104 } else if name == "clone_from" {
105 debug!("make_shim({:?}: using default trait implementation", instance);
106 return tcx.optimized_mir(def_id);
108 bug!("builtin clone shim {:?} not supported", instance)
111 ty::InstanceDef::Intrinsic(_) => {
112 bug!("creating shims from intrinsics ({:?}) is unsupported", instance)
115 debug!("make_shim({:?}) = untransformed {:?}", instance, result);
116 add_moves_for_packed_drops::add_moves_for_packed_drops(
117 tcx, &mut result, instance.def_id());
118 no_landing_pads::no_landing_pads(tcx, &mut result);
119 remove_noop_landing_pads::remove_noop_landing_pads(tcx, &mut result);
120 simplify::simplify_cfg(&mut result);
121 add_call_guards::CriticalCallEdges.add_call_guards(&mut result);
122 debug!("make_shim({:?}) = {:?}", instance, result);
124 tcx.alloc_mir(result)
127 #[derive(Copy, Clone, Debug, PartialEq)]
135 #[derive(Copy, Clone, Debug, PartialEq)]
141 fn temp_decl(mutability: Mutability, ty: Ty, span: Span) -> LocalDecl {
142 let source_info = SourceInfo { scope: OUTERMOST_SOURCE_SCOPE, span };
146 user_ty: UserTypeProjections::none(),
149 visibility_scope: source_info.scope,
151 is_user_variable: None,
156 fn local_decls_for_sig<'tcx>(sig: &ty::FnSig<'tcx>, span: Span)
157 -> IndexVec<Local, LocalDecl<'tcx>>
159 iter::once(temp_decl(Mutability::Mut, sig.output(), span))
160 .chain(sig.inputs().iter().map(
161 |ity| temp_decl(Mutability::Not, ity, span)))
165 fn build_drop_shim<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
167 ty: Option<Ty<'tcx>>)
170 debug!("build_drop_shim(def_id={:?}, ty={:?})", def_id, ty);
172 // Check if this is a generator, if so, return the drop glue for it
173 if let Some(&ty::TyS { sty: ty::Generator(gen_def_id, substs, _), .. }) = ty {
174 let mir = &**tcx.optimized_mir(gen_def_id).generator_drop.as_ref().unwrap();
175 return mir.subst(tcx, substs.substs);
178 let substs = if let Some(ty) = ty {
179 tcx.intern_substs(&[ty.into()])
181 Substs::identity_for_item(tcx, def_id)
183 let sig = tcx.fn_sig(def_id).subst(tcx, substs);
184 let sig = tcx.erase_late_bound_regions(&sig);
185 let span = tcx.def_span(def_id);
187 let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
189 let return_block = BasicBlock::new(1);
190 let mut blocks = IndexVec::with_capacity(2);
191 let block = |blocks: &mut IndexVec<_, _>, kind| {
192 blocks.push(BasicBlockData {
194 terminator: Some(Terminator { source_info, kind }),
198 block(&mut blocks, TerminatorKind::Goto { target: return_block });
199 block(&mut blocks, TerminatorKind::Return);
201 let mut mir = Mir::new(
203 IndexVec::from_elem_n(
204 SourceScopeData { span: span, parent_scope: None }, 1
206 ClearCrossCrate::Clear,
209 local_decls_for_sig(&sig, span),
217 if let Some(..) = ty {
218 // The first argument (index 0), but add 1 for the return value.
219 let dropee_ptr = Place::Local(Local::new(1+0));
220 if tcx.sess.opts.debugging_opts.mir_emit_retag {
221 // Function arguments should be retagged, and we make this one raw.
222 mir.basic_blocks_mut()[START_BLOCK].statements.insert(0, Statement {
224 kind: StatementKind::Retag(RetagKind::Raw, dropee_ptr.clone()),
228 let param_env = tcx.param_env(def_id).with_reveal_all();
229 let mut elaborator = DropShimElaborator {
231 patch: MirPatch::new(&mir),
235 let dropee = dropee_ptr.deref();
236 let resume_block = elaborator.patch.resume_block();
237 elaborate_drops::elaborate_drop(
243 elaborate_drops::Unwind::To(resume_block),
248 patch.apply(&mut mir);
254 pub struct DropShimElaborator<'a, 'tcx: 'a> {
255 pub mir: &'a Mir<'tcx>,
256 pub patch: MirPatch<'tcx>,
257 pub tcx: TyCtxt<'a, 'tcx, 'tcx>,
258 pub param_env: ty::ParamEnv<'tcx>,
261 impl<'a, 'tcx> fmt::Debug for DropShimElaborator<'a, 'tcx> {
262 fn fmt(&self, _f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
267 impl<'a, 'tcx> DropElaborator<'a, 'tcx> for DropShimElaborator<'a, 'tcx> {
270 fn patch(&mut self) -> &mut MirPatch<'tcx> { &mut self.patch }
271 fn mir(&self) -> &'a Mir<'tcx> { self.mir }
272 fn tcx(&self) -> TyCtxt<'a, 'tcx, 'tcx> { self.tcx }
273 fn param_env(&self) -> ty::ParamEnv<'tcx> { self.param_env }
275 fn drop_style(&self, _path: Self::Path, mode: DropFlagMode) -> DropStyle {
276 if let DropFlagMode::Shallow = mode {
283 fn get_drop_flag(&mut self, _path: Self::Path) -> Option<Operand<'tcx>> {
287 fn clear_drop_flag(&mut self, _location: Location, _path: Self::Path, _mode: DropFlagMode) {
290 fn field_subpath(&self, _path: Self::Path, _field: Field) -> Option<Self::Path> {
293 fn deref_subpath(&self, _path: Self::Path) -> Option<Self::Path> {
296 fn downcast_subpath(&self, _path: Self::Path, _variant: VariantIdx) -> Option<Self::Path> {
299 fn array_subpath(&self, _path: Self::Path, _index: u32, _size: u32) -> Option<Self::Path> {
304 /// Build a `Clone::clone` shim for `self_ty`. Here, `def_id` is `Clone::clone`.
305 fn build_clone_shim<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
310 debug!("build_clone_shim(def_id={:?})", def_id);
312 let mut builder = CloneShimBuilder::new(tcx, def_id, self_ty);
313 let is_copy = !self_ty.moves_by_default(tcx, tcx.param_env(def_id), builder.span);
315 let dest = Place::Local(RETURN_PLACE);
316 let src = Place::Local(Local::new(1+0)).deref();
319 _ if is_copy => builder.copy_shim(),
320 ty::Array(ty, len) => {
321 let len = len.unwrap_usize(tcx);
322 builder.array_shim(dest, src, ty, len)
324 ty::Closure(def_id, substs) => {
325 builder.tuple_like_shim(
327 substs.upvar_tys(def_id, tcx)
330 ty::Tuple(tys) => builder.tuple_like_shim(dest, src, tys.iter().cloned()),
332 bug!("clone shim for `{:?}` which is not `Copy` and is not an aggregate", self_ty)
339 struct CloneShimBuilder<'a, 'tcx: 'a> {
340 tcx: TyCtxt<'a, 'tcx, 'tcx>,
342 local_decls: IndexVec<Local, LocalDecl<'tcx>>,
343 blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>,
345 sig: ty::FnSig<'tcx>,
348 impl<'a, 'tcx> CloneShimBuilder<'a, 'tcx> {
349 fn new(tcx: TyCtxt<'a, 'tcx, 'tcx>,
351 self_ty: Ty<'tcx>) -> Self {
352 // we must subst the self_ty because it's
353 // otherwise going to be TySelf and we can't index
354 // or access fields of a Place of type TySelf.
355 let substs = tcx.mk_substs_trait(self_ty, &[]);
356 let sig = tcx.fn_sig(def_id).subst(tcx, substs);
357 let sig = tcx.erase_late_bound_regions(&sig);
358 let span = tcx.def_span(def_id);
363 local_decls: local_decls_for_sig(&sig, span),
364 blocks: IndexVec::new(),
370 fn into_mir(self) -> Mir<'tcx> {
373 IndexVec::from_elem_n(
374 SourceScopeData { span: self.span, parent_scope: None }, 1
376 ClearCrossCrate::Clear,
381 self.sig.inputs().len(),
388 fn source_info(&self) -> SourceInfo {
389 SourceInfo { span: self.span, scope: OUTERMOST_SOURCE_SCOPE }
394 statements: Vec<Statement<'tcx>>,
395 kind: TerminatorKind<'tcx>,
398 let source_info = self.source_info();
399 self.blocks.push(BasicBlockData {
401 terminator: Some(Terminator { source_info, kind }),
406 /// Gives the index of an upcoming BasicBlock, with an offset.
407 /// offset=0 will give you the index of the next BasicBlock,
408 /// offset=1 will give the index of the next-to-next block,
409 /// offset=-1 will give you the index of the last-created block
410 fn block_index_offset(&mut self, offset: usize) -> BasicBlock {
411 BasicBlock::new(self.blocks.len() + offset)
414 fn make_statement(&self, kind: StatementKind<'tcx>) -> Statement<'tcx> {
416 source_info: self.source_info(),
421 fn copy_shim(&mut self) {
422 let rcvr = Place::Local(Local::new(1+0)).deref();
423 let ret_statement = self.make_statement(
424 StatementKind::Assign(
425 Place::Local(RETURN_PLACE),
426 box Rvalue::Use(Operand::Copy(rcvr))
429 self.block(vec![ret_statement], TerminatorKind::Return, false);
432 fn make_place(&mut self, mutability: Mutability, ty: Ty<'tcx>) -> Place<'tcx> {
433 let span = self.span;
435 self.local_decls.push(temp_decl(mutability, ty, span))
449 let substs = Substs::for_item(tcx, self.def_id, |param, _| {
451 GenericParamDefKind::Lifetime => tcx.types.re_erased.into(),
452 GenericParamDefKind::Type {..} => ty.into(),
456 // `func == Clone::clone(&ty) -> ty`
457 let func_ty = tcx.mk_fn_def(self.def_id, substs);
458 let func = Operand::Constant(box Constant {
462 literal: ty::Const::zero_sized(self.tcx, func_ty),
465 let ref_loc = self.make_place(
467 tcx.mk_ref(tcx.types.re_erased, ty::TypeAndMut {
469 mutbl: hir::Mutability::MutImmutable,
473 // `let ref_loc: &ty = &src;`
474 let statement = self.make_statement(
475 StatementKind::Assign(
477 box Rvalue::Ref(tcx.types.re_erased, BorrowKind::Shared, src)
481 // `let loc = Clone::clone(ref_loc);`
482 self.block(vec![statement], TerminatorKind::Call {
484 args: vec![Operand::Move(ref_loc)],
485 destination: Some((dest, next)),
486 cleanup: Some(cleanup),
495 loop_body: BasicBlock,
496 loop_end: BasicBlock,
501 let cond = self.make_place(Mutability::Mut, tcx.types.bool);
502 let compute_cond = self.make_statement(
503 StatementKind::Assign(
505 box Rvalue::BinaryOp(BinOp::Ne, Operand::Copy(end), Operand::Copy(beg))
509 // `if end != beg { goto loop_body; } else { goto loop_end; }`
512 TerminatorKind::if_(tcx, Operand::Move(cond), loop_body, loop_end),
517 fn make_usize(&self, value: u64) -> Box<Constant<'tcx>> {
520 ty: self.tcx.types.usize,
522 literal: ty::Const::from_usize(self.tcx, value),
526 fn array_shim(&mut self, dest: Place<'tcx>, src: Place<'tcx>, ty: Ty<'tcx>, len: u64) {
528 let span = self.span;
530 let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
531 let end = self.make_place(Mutability::Not, tcx.types.usize);
534 // `let mut beg = 0;`
539 StatementKind::Assign(
541 box Rvalue::Use(Operand::Constant(self.make_usize(0)))
545 StatementKind::Assign(
547 box Rvalue::Use(Operand::Constant(self.make_usize(len)))
551 self.block(inits, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
558 self.loop_header(Place::Local(beg), end, BasicBlock::new(2), BasicBlock::new(4), false);
561 // `dest[i] = Clone::clone(src[beg])`;
562 // Goto #3 if ok, #5 if unwinding happens.
563 let dest_field = dest.clone().index(beg);
564 let src_field = src.index(beg);
565 self.make_clone_call(dest_field, src_field, ty, BasicBlock::new(3),
571 let statements = vec![
573 StatementKind::Assign(
575 box Rvalue::BinaryOp(
577 Operand::Copy(Place::Local(beg)),
578 Operand::Constant(self.make_usize(1))
583 self.block(statements, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
587 self.block(vec![], TerminatorKind::Return, false);
591 // `let mut beg = 0;`
594 let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
595 let init = self.make_statement(
596 StatementKind::Assign(
598 box Rvalue::Use(Operand::Constant(self.make_usize(0)))
601 self.block(vec![init], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
603 // BB #6 (cleanup): loop {
608 self.loop_header(Place::Local(beg), Place::Local(end),
609 BasicBlock::new(7), BasicBlock::new(9), true);
612 // `drop(dest[beg])`;
613 self.block(vec![], TerminatorKind::Drop {
614 location: dest.index(beg),
615 target: BasicBlock::new(8),
622 let statement = self.make_statement(
623 StatementKind::Assign(
625 box Rvalue::BinaryOp(
627 Operand::Copy(Place::Local(beg)),
628 Operand::Constant(self.make_usize(1))
632 self.block(vec![statement], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
635 self.block(vec![], TerminatorKind::Resume, true);
638 fn tuple_like_shim<I>(&mut self, dest: Place<'tcx>,
639 src: Place<'tcx>, tys: I)
640 where I: Iterator<Item = ty::Ty<'tcx>> {
641 let mut previous_field = None;
642 for (i, ity) in tys.enumerate() {
643 let field = Field::new(i);
644 let src_field = src.clone().field(field, ity);
646 let dest_field = dest.clone().field(field, ity);
648 // #(2i + 1) is the cleanup block for the previous clone operation
649 let cleanup_block = self.block_index_offset(1);
650 // #(2i + 2) is the next cloning block
651 // (or the Return terminator if this is the last block)
652 let next_block = self.block_index_offset(2);
655 // `dest.i = Clone::clone(&src.i);`
656 // Goto #(2i + 2) if ok, #(2i + 1) if unwinding happens.
657 self.make_clone_call(
665 // BB #(2i + 1) (cleanup)
666 if let Some((previous_field, previous_cleanup)) = previous_field.take() {
667 // Drop previous field and goto previous cleanup block.
668 self.block(vec![], TerminatorKind::Drop {
669 location: previous_field,
670 target: previous_cleanup,
674 // Nothing to drop, just resume.
675 self.block(vec![], TerminatorKind::Resume, true);
678 previous_field = Some((dest_field, cleanup_block));
681 self.block(vec![], TerminatorKind::Return, false);
685 /// Build a "call" shim for `def_id`. The shim calls the
686 /// function specified by `call_kind`, first adjusting its first
687 /// argument according to `rcvr_adjustment`.
689 /// If `untuple_args` is a vec of types, the second argument of the
690 /// function will be untupled as these types.
691 fn build_call_shim<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
693 rcvr_adjustment: Adjustment,
695 untuple_args: Option<&[Ty<'tcx>]>)
698 debug!("build_call_shim(def_id={:?}, rcvr_adjustment={:?}, \
699 call_kind={:?}, untuple_args={:?})",
700 def_id, rcvr_adjustment, call_kind, untuple_args);
702 let sig = tcx.fn_sig(def_id);
703 let sig = tcx.erase_late_bound_regions(&sig);
704 let span = tcx.def_span(def_id);
706 debug!("build_call_shim: sig={:?}", sig);
708 let mut local_decls = local_decls_for_sig(&sig, span);
709 let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
711 let rcvr_arg = Local::new(1+0);
712 let rcvr_l = Place::Local(rcvr_arg);
713 let mut statements = vec![];
715 let rcvr = match rcvr_adjustment {
716 Adjustment::Identity => Operand::Move(rcvr_l),
717 Adjustment::Deref => Operand::Copy(rcvr_l.deref()),
718 Adjustment::DerefMove => {
719 // fn(Self, ...) -> fn(*mut Self, ...)
720 let arg_ty = local_decls[rcvr_arg].ty;
721 assert!(arg_ty.is_self());
722 local_decls[rcvr_arg].ty = tcx.mk_mut_ptr(arg_ty);
724 Operand::Move(rcvr_l.deref())
726 Adjustment::RefMut => {
727 // let rcvr = &mut rcvr;
728 let ref_rcvr = local_decls.push(temp_decl(
730 tcx.mk_ref(tcx.types.re_erased, ty::TypeAndMut {
732 mutbl: hir::Mutability::MutMutable
736 let borrow_kind = BorrowKind::Mut {
737 allow_two_phase_borrow: false,
739 statements.push(Statement {
741 kind: StatementKind::Assign(
742 Place::Local(ref_rcvr),
743 box Rvalue::Ref(tcx.types.re_erased, borrow_kind, rcvr_l)
746 Operand::Move(Place::Local(ref_rcvr))
750 let (callee, mut args) = match call_kind {
751 CallKind::Indirect => (rcvr, vec![]),
752 CallKind::Direct(def_id) => {
753 let ty = tcx.type_of(def_id);
754 (Operand::Constant(box Constant {
758 literal: ty::Const::zero_sized(tcx, ty),
764 if let Some(untuple_args) = untuple_args {
765 args.extend(untuple_args.iter().enumerate().map(|(i, ity)| {
766 let arg_place = Place::Local(Local::new(1+1));
767 Operand::Move(arg_place.field(Field::new(i), *ity))
770 args.extend((1..sig.inputs().len()).map(|i| {
771 Operand::Move(Place::Local(Local::new(1+i)))
775 let n_blocks = if let Adjustment::RefMut = rcvr_adjustment { 5 } else { 2 };
776 let mut blocks = IndexVec::with_capacity(n_blocks);
777 let block = |blocks: &mut IndexVec<_, _>, statements, kind, is_cleanup| {
778 blocks.push(BasicBlockData {
780 terminator: Some(Terminator { source_info, kind }),
786 block(&mut blocks, statements, TerminatorKind::Call {
789 destination: Some((Place::Local(RETURN_PLACE),
790 BasicBlock::new(1))),
791 cleanup: if let Adjustment::RefMut = rcvr_adjustment {
792 Some(BasicBlock::new(3))
799 if let Adjustment::RefMut = rcvr_adjustment {
800 // BB #1 - drop for Self
801 block(&mut blocks, vec![], TerminatorKind::Drop {
802 location: Place::Local(rcvr_arg),
803 target: BasicBlock::new(2),
808 block(&mut blocks, vec![], TerminatorKind::Return, false);
809 if let Adjustment::RefMut = rcvr_adjustment {
810 // BB #3 - drop if closure panics
811 block(&mut blocks, vec![], TerminatorKind::Drop {
812 location: Place::Local(rcvr_arg),
813 target: BasicBlock::new(4),
818 block(&mut blocks, vec![], TerminatorKind::Resume, true);
821 let mut mir = Mir::new(
823 IndexVec::from_elem_n(
824 SourceScopeData { span: span, parent_scope: None }, 1
826 ClearCrossCrate::Clear,
836 if let Abi::RustCall = sig.abi {
837 mir.spread_arg = Some(Local::new(sig.inputs().len()));
842 pub fn build_adt_ctor<'a, 'gcx, 'tcx>(infcx: &infer::InferCtxt<'a, 'gcx, 'tcx>,
843 ctor_id: ast::NodeId,
844 fields: &[hir::StructField],
849 let gcx = tcx.global_tcx();
850 let def_id = tcx.hir().local_def_id(ctor_id);
851 let param_env = gcx.param_env(def_id);
853 // Normalize the sig.
854 let sig = gcx.fn_sig(def_id)
856 .expect("LBR in ADT constructor signature");
857 let sig = gcx.normalize_erasing_regions(param_env, sig);
859 let (adt_def, substs) = match sig.output().sty {
860 ty::Adt(adt_def, substs) => (adt_def, substs),
861 _ => bug!("unexpected type for ADT ctor {:?}", sig.output())
864 debug!("build_ctor: def_id={:?} sig={:?} fields={:?}", def_id, sig, fields);
866 let local_decls = local_decls_for_sig(&sig, span);
868 let source_info = SourceInfo {
870 scope: OUTERMOST_SOURCE_SCOPE
873 let variant_no = if adt_def.is_enum() {
874 adt_def.variant_index_with_id(def_id)
879 // return = ADT(arg0, arg1, ...); return
880 let start_block = BasicBlockData {
881 statements: vec![Statement {
883 kind: StatementKind::Assign(
884 Place::Local(RETURN_PLACE),
885 box Rvalue::Aggregate(
886 box AggregateKind::Adt(adt_def, variant_no, substs, None, None),
887 (1..sig.inputs().len()+1).map(|i| {
888 Operand::Move(Place::Local(Local::new(i)))
893 terminator: Some(Terminator {
895 kind: TerminatorKind::Return,
901 IndexVec::from_elem_n(start_block, 1),
902 IndexVec::from_elem_n(
903 SourceScopeData { span: span, parent_scope: None }, 1
905 ClearCrossCrate::Clear,