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),
216 if let Some(..) = ty {
217 // The first argument (index 0), but add 1 for the return value.
218 let dropee_ptr = Place::Local(Local::new(1+0));
219 if tcx.sess.opts.debugging_opts.mir_emit_retag {
220 // Function arguments should be retagged, and we make this one raw.
221 mir.basic_blocks_mut()[START_BLOCK].statements.insert(0, Statement {
223 kind: StatementKind::Retag(RetagKind::Raw, dropee_ptr.clone()),
227 let param_env = tcx.param_env(def_id).with_reveal_all();
228 let mut elaborator = DropShimElaborator {
230 patch: MirPatch::new(&mir),
234 let dropee = dropee_ptr.deref();
235 let resume_block = elaborator.patch.resume_block();
236 elaborate_drops::elaborate_drop(
242 elaborate_drops::Unwind::To(resume_block),
247 patch.apply(&mut mir);
253 pub struct DropShimElaborator<'a, 'tcx: 'a> {
254 pub mir: &'a Mir<'tcx>,
255 pub patch: MirPatch<'tcx>,
256 pub tcx: TyCtxt<'a, 'tcx, 'tcx>,
257 pub param_env: ty::ParamEnv<'tcx>,
260 impl<'a, 'tcx> fmt::Debug for DropShimElaborator<'a, 'tcx> {
261 fn fmt(&self, _f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
266 impl<'a, 'tcx> DropElaborator<'a, 'tcx> for DropShimElaborator<'a, 'tcx> {
269 fn patch(&mut self) -> &mut MirPatch<'tcx> { &mut self.patch }
270 fn mir(&self) -> &'a Mir<'tcx> { self.mir }
271 fn tcx(&self) -> TyCtxt<'a, 'tcx, 'tcx> { self.tcx }
272 fn param_env(&self) -> ty::ParamEnv<'tcx> { self.param_env }
274 fn drop_style(&self, _path: Self::Path, mode: DropFlagMode) -> DropStyle {
275 if let DropFlagMode::Shallow = mode {
282 fn get_drop_flag(&mut self, _path: Self::Path) -> Option<Operand<'tcx>> {
286 fn clear_drop_flag(&mut self, _location: Location, _path: Self::Path, _mode: DropFlagMode) {
289 fn field_subpath(&self, _path: Self::Path, _field: Field) -> Option<Self::Path> {
292 fn deref_subpath(&self, _path: Self::Path) -> Option<Self::Path> {
295 fn downcast_subpath(&self, _path: Self::Path, _variant: VariantIdx) -> Option<Self::Path> {
298 fn array_subpath(&self, _path: Self::Path, _index: u32, _size: u32) -> Option<Self::Path> {
303 /// Build a `Clone::clone` shim for `self_ty`. Here, `def_id` is `Clone::clone`.
304 fn build_clone_shim<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
309 debug!("build_clone_shim(def_id={:?})", def_id);
311 let mut builder = CloneShimBuilder::new(tcx, def_id, self_ty);
312 let is_copy = !self_ty.moves_by_default(tcx, tcx.param_env(def_id), builder.span);
314 let dest = Place::Local(RETURN_PLACE);
315 let src = Place::Local(Local::new(1+0)).deref();
318 _ if is_copy => builder.copy_shim(),
319 ty::Array(ty, len) => {
320 let len = len.unwrap_usize(tcx);
321 builder.array_shim(dest, src, ty, len)
323 ty::Closure(def_id, substs) => {
324 builder.tuple_like_shim(
326 substs.upvar_tys(def_id, tcx)
329 ty::Tuple(tys) => builder.tuple_like_shim(dest, src, tys.iter().cloned()),
331 bug!("clone shim for `{:?}` which is not `Copy` and is not an aggregate", self_ty)
338 struct CloneShimBuilder<'a, 'tcx: 'a> {
339 tcx: TyCtxt<'a, 'tcx, 'tcx>,
341 local_decls: IndexVec<Local, LocalDecl<'tcx>>,
342 blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>,
344 sig: ty::FnSig<'tcx>,
347 impl<'a, 'tcx> CloneShimBuilder<'a, 'tcx> {
348 fn new(tcx: TyCtxt<'a, 'tcx, 'tcx>,
350 self_ty: Ty<'tcx>) -> Self {
351 // we must subst the self_ty because it's
352 // otherwise going to be TySelf and we can't index
353 // or access fields of a Place of type TySelf.
354 let substs = tcx.mk_substs_trait(self_ty, &[]);
355 let sig = tcx.fn_sig(def_id).subst(tcx, substs);
356 let sig = tcx.erase_late_bound_regions(&sig);
357 let span = tcx.def_span(def_id);
362 local_decls: local_decls_for_sig(&sig, span),
363 blocks: IndexVec::new(),
369 fn into_mir(self) -> Mir<'tcx> {
372 IndexVec::from_elem_n(
373 SourceScopeData { span: self.span, parent_scope: None }, 1
375 ClearCrossCrate::Clear,
379 self.sig.inputs().len(),
386 fn source_info(&self) -> SourceInfo {
387 SourceInfo { span: self.span, scope: OUTERMOST_SOURCE_SCOPE }
392 statements: Vec<Statement<'tcx>>,
393 kind: TerminatorKind<'tcx>,
396 let source_info = self.source_info();
397 self.blocks.push(BasicBlockData {
399 terminator: Some(Terminator { source_info, kind }),
404 /// Gives the index of an upcoming BasicBlock, with an offset.
405 /// offset=0 will give you the index of the next BasicBlock,
406 /// offset=1 will give the index of the next-to-next block,
407 /// offset=-1 will give you the index of the last-created block
408 fn block_index_offset(&mut self, offset: usize) -> BasicBlock {
409 BasicBlock::new(self.blocks.len() + offset)
412 fn make_statement(&self, kind: StatementKind<'tcx>) -> Statement<'tcx> {
414 source_info: self.source_info(),
419 fn copy_shim(&mut self) {
420 let rcvr = Place::Local(Local::new(1+0)).deref();
421 let ret_statement = self.make_statement(
422 StatementKind::Assign(
423 Place::Local(RETURN_PLACE),
424 box Rvalue::Use(Operand::Copy(rcvr))
427 self.block(vec![ret_statement], TerminatorKind::Return, false);
430 fn make_place(&mut self, mutability: Mutability, ty: Ty<'tcx>) -> Place<'tcx> {
431 let span = self.span;
433 self.local_decls.push(temp_decl(mutability, ty, span))
447 let substs = Substs::for_item(tcx, self.def_id, |param, _| {
449 GenericParamDefKind::Lifetime => tcx.types.re_erased.into(),
450 GenericParamDefKind::Type {..} => ty.into(),
454 // `func == Clone::clone(&ty) -> ty`
455 let func_ty = tcx.mk_fn_def(self.def_id, substs);
456 let func = Operand::Constant(box Constant {
460 literal: ty::Const::zero_sized(self.tcx, func_ty),
463 let ref_loc = self.make_place(
465 tcx.mk_ref(tcx.types.re_erased, ty::TypeAndMut {
467 mutbl: hir::Mutability::MutImmutable,
471 // `let ref_loc: &ty = &src;`
472 let statement = self.make_statement(
473 StatementKind::Assign(
475 box Rvalue::Ref(tcx.types.re_erased, BorrowKind::Shared, src)
479 // `let loc = Clone::clone(ref_loc);`
480 self.block(vec![statement], TerminatorKind::Call {
482 args: vec![Operand::Move(ref_loc)],
483 destination: Some((dest, next)),
484 cleanup: Some(cleanup),
493 loop_body: BasicBlock,
494 loop_end: BasicBlock,
499 let cond = self.make_place(Mutability::Mut, tcx.types.bool);
500 let compute_cond = self.make_statement(
501 StatementKind::Assign(
503 box Rvalue::BinaryOp(BinOp::Ne, Operand::Copy(end), Operand::Copy(beg))
507 // `if end != beg { goto loop_body; } else { goto loop_end; }`
510 TerminatorKind::if_(tcx, Operand::Move(cond), loop_body, loop_end),
515 fn make_usize(&self, value: u64) -> Box<Constant<'tcx>> {
518 ty: self.tcx.types.usize,
520 literal: ty::Const::from_usize(self.tcx, value),
524 fn array_shim(&mut self, dest: Place<'tcx>, src: Place<'tcx>, ty: Ty<'tcx>, len: u64) {
526 let span = self.span;
528 let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
529 let end = self.make_place(Mutability::Not, tcx.types.usize);
532 // `let mut beg = 0;`
537 StatementKind::Assign(
539 box Rvalue::Use(Operand::Constant(self.make_usize(0)))
543 StatementKind::Assign(
545 box Rvalue::Use(Operand::Constant(self.make_usize(len)))
549 self.block(inits, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
556 self.loop_header(Place::Local(beg), end, BasicBlock::new(2), BasicBlock::new(4), false);
559 // `dest[i] = Clone::clone(src[beg])`;
560 // Goto #3 if ok, #5 if unwinding happens.
561 let dest_field = dest.clone().index(beg);
562 let src_field = src.index(beg);
563 self.make_clone_call(dest_field, src_field, ty, BasicBlock::new(3),
569 let statements = vec![
571 StatementKind::Assign(
573 box Rvalue::BinaryOp(
575 Operand::Copy(Place::Local(beg)),
576 Operand::Constant(self.make_usize(1))
581 self.block(statements, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);
585 self.block(vec![], TerminatorKind::Return, false);
589 // `let mut beg = 0;`
592 let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
593 let init = self.make_statement(
594 StatementKind::Assign(
596 box Rvalue::Use(Operand::Constant(self.make_usize(0)))
599 self.block(vec![init], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
601 // BB #6 (cleanup): loop {
606 self.loop_header(Place::Local(beg), Place::Local(end),
607 BasicBlock::new(7), BasicBlock::new(9), true);
610 // `drop(dest[beg])`;
611 self.block(vec![], TerminatorKind::Drop {
612 location: dest.index(beg),
613 target: BasicBlock::new(8),
620 let statement = self.make_statement(
621 StatementKind::Assign(
623 box Rvalue::BinaryOp(
625 Operand::Copy(Place::Local(beg)),
626 Operand::Constant(self.make_usize(1))
630 self.block(vec![statement], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);
633 self.block(vec![], TerminatorKind::Resume, true);
636 fn tuple_like_shim<I>(&mut self, dest: Place<'tcx>,
637 src: Place<'tcx>, tys: I)
638 where I: Iterator<Item = ty::Ty<'tcx>> {
639 let mut previous_field = None;
640 for (i, ity) in tys.enumerate() {
641 let field = Field::new(i);
642 let src_field = src.clone().field(field, ity);
644 let dest_field = dest.clone().field(field, ity);
646 // #(2i + 1) is the cleanup block for the previous clone operation
647 let cleanup_block = self.block_index_offset(1);
648 // #(2i + 2) is the next cloning block
649 // (or the Return terminator if this is the last block)
650 let next_block = self.block_index_offset(2);
653 // `dest.i = Clone::clone(&src.i);`
654 // Goto #(2i + 2) if ok, #(2i + 1) if unwinding happens.
655 self.make_clone_call(
663 // BB #(2i + 1) (cleanup)
664 if let Some((previous_field, previous_cleanup)) = previous_field.take() {
665 // Drop previous field and goto previous cleanup block.
666 self.block(vec![], TerminatorKind::Drop {
667 location: previous_field,
668 target: previous_cleanup,
672 // Nothing to drop, just resume.
673 self.block(vec![], TerminatorKind::Resume, true);
676 previous_field = Some((dest_field, cleanup_block));
679 self.block(vec![], TerminatorKind::Return, false);
683 /// Build a "call" shim for `def_id`. The shim calls the
684 /// function specified by `call_kind`, first adjusting its first
685 /// argument according to `rcvr_adjustment`.
687 /// If `untuple_args` is a vec of types, the second argument of the
688 /// function will be untupled as these types.
689 fn build_call_shim<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
691 rcvr_adjustment: Adjustment,
693 untuple_args: Option<&[Ty<'tcx>]>)
696 debug!("build_call_shim(def_id={:?}, rcvr_adjustment={:?}, \
697 call_kind={:?}, untuple_args={:?})",
698 def_id, rcvr_adjustment, call_kind, untuple_args);
700 let sig = tcx.fn_sig(def_id);
701 let sig = tcx.erase_late_bound_regions(&sig);
702 let span = tcx.def_span(def_id);
704 debug!("build_call_shim: sig={:?}", sig);
706 let mut local_decls = local_decls_for_sig(&sig, span);
707 let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };
709 let rcvr_arg = Local::new(1+0);
710 let rcvr_l = Place::Local(rcvr_arg);
711 let mut statements = vec![];
713 let rcvr = match rcvr_adjustment {
714 Adjustment::Identity => Operand::Move(rcvr_l),
715 Adjustment::Deref => Operand::Copy(rcvr_l.deref()),
716 Adjustment::DerefMove => {
717 // fn(Self, ...) -> fn(*mut Self, ...)
718 let arg_ty = local_decls[rcvr_arg].ty;
719 assert!(arg_ty.is_self());
720 local_decls[rcvr_arg].ty = tcx.mk_mut_ptr(arg_ty);
722 Operand::Move(rcvr_l.deref())
724 Adjustment::RefMut => {
725 // let rcvr = &mut rcvr;
726 let ref_rcvr = local_decls.push(temp_decl(
728 tcx.mk_ref(tcx.types.re_erased, ty::TypeAndMut {
730 mutbl: hir::Mutability::MutMutable
734 let borrow_kind = BorrowKind::Mut {
735 allow_two_phase_borrow: false,
737 statements.push(Statement {
739 kind: StatementKind::Assign(
740 Place::Local(ref_rcvr),
741 box Rvalue::Ref(tcx.types.re_erased, borrow_kind, rcvr_l)
744 Operand::Move(Place::Local(ref_rcvr))
748 let (callee, mut args) = match call_kind {
749 CallKind::Indirect => (rcvr, vec![]),
750 CallKind::Direct(def_id) => {
751 let ty = tcx.type_of(def_id);
752 (Operand::Constant(box Constant {
756 literal: ty::Const::zero_sized(tcx, ty),
762 if let Some(untuple_args) = untuple_args {
763 args.extend(untuple_args.iter().enumerate().map(|(i, ity)| {
764 let arg_place = Place::Local(Local::new(1+1));
765 Operand::Move(arg_place.field(Field::new(i), *ity))
768 args.extend((1..sig.inputs().len()).map(|i| {
769 Operand::Move(Place::Local(Local::new(1+i)))
773 let n_blocks = if let Adjustment::RefMut = rcvr_adjustment { 5 } else { 2 };
774 let mut blocks = IndexVec::with_capacity(n_blocks);
775 let block = |blocks: &mut IndexVec<_, _>, statements, kind, is_cleanup| {
776 blocks.push(BasicBlockData {
778 terminator: Some(Terminator { source_info, kind }),
784 block(&mut blocks, statements, TerminatorKind::Call {
787 destination: Some((Place::Local(RETURN_PLACE),
788 BasicBlock::new(1))),
789 cleanup: if let Adjustment::RefMut = rcvr_adjustment {
790 Some(BasicBlock::new(3))
797 if let Adjustment::RefMut = rcvr_adjustment {
798 // BB #1 - drop for Self
799 block(&mut blocks, vec![], TerminatorKind::Drop {
800 location: Place::Local(rcvr_arg),
801 target: BasicBlock::new(2),
806 block(&mut blocks, vec![], TerminatorKind::Return, false);
807 if let Adjustment::RefMut = rcvr_adjustment {
808 // BB #3 - drop if closure panics
809 block(&mut blocks, vec![], TerminatorKind::Drop {
810 location: Place::Local(rcvr_arg),
811 target: BasicBlock::new(4),
816 block(&mut blocks, vec![], TerminatorKind::Resume, true);
819 let mut mir = Mir::new(
821 IndexVec::from_elem_n(
822 SourceScopeData { span: span, parent_scope: None }, 1
824 ClearCrossCrate::Clear,
833 if let Abi::RustCall = sig.abi {
834 mir.spread_arg = Some(Local::new(sig.inputs().len()));
839 pub fn build_adt_ctor<'a, 'gcx, 'tcx>(infcx: &infer::InferCtxt<'a, 'gcx, 'tcx>,
840 ctor_id: ast::NodeId,
841 fields: &[hir::StructField],
846 let gcx = tcx.global_tcx();
847 let def_id = tcx.hir().local_def_id(ctor_id);
848 let param_env = gcx.param_env(def_id);
850 // Normalize the sig.
851 let sig = gcx.fn_sig(def_id)
853 .expect("LBR in ADT constructor signature");
854 let sig = gcx.normalize_erasing_regions(param_env, sig);
856 let (adt_def, substs) = match sig.output().sty {
857 ty::Adt(adt_def, substs) => (adt_def, substs),
858 _ => bug!("unexpected type for ADT ctor {:?}", sig.output())
861 debug!("build_ctor: def_id={:?} sig={:?} fields={:?}", def_id, sig, fields);
863 let local_decls = local_decls_for_sig(&sig, span);
865 let source_info = SourceInfo {
867 scope: OUTERMOST_SOURCE_SCOPE
870 let variant_no = if adt_def.is_enum() {
871 adt_def.variant_index_with_id(def_id)
876 // return = ADT(arg0, arg1, ...); return
877 let start_block = BasicBlockData {
878 statements: vec![Statement {
880 kind: StatementKind::Assign(
881 Place::Local(RETURN_PLACE),
882 box Rvalue::Aggregate(
883 box AggregateKind::Adt(adt_def, variant_no, substs, None, None),
884 (1..sig.inputs().len()+1).map(|i| {
885 Operand::Move(Place::Local(Local::new(i)))
890 terminator: Some(Terminator {
892 kind: TerminatorKind::Return,
898 IndexVec::from_elem_n(start_block, 1),
899 IndexVec::from_elem_n(
900 SourceScopeData { span: span, parent_scope: None }, 1
902 ClearCrossCrate::Clear,