1use std::assert_matches::assert_matches;
14use std::cell::Cell;
15use std::{cmp, iter, mem};
16
17use either::{Left, Right};
18use rustc_const_eval::check_consts::{ConstCx, qualifs};
19use rustc_data_structures::fx::FxHashSet;
20use rustc_hir as hir;
21use rustc_index::{IndexSlice, IndexVec};
22use rustc_middle::mir::visit::{MutVisitor, MutatingUseContext, PlaceContext, Visitor};
23use rustc_middle::mir::*;
24use rustc_middle::ty::{self, GenericArgs, List, Ty, TyCtxt, TypeVisitableExt};
25use rustc_middle::{bug, mir, span_bug};
26use rustc_span::Span;
27use rustc_span::source_map::Spanned;
28use tracing::{debug, instrument};
29
30#[derive(Default)]
38pub(super) struct PromoteTemps<'tcx> {
39 pub promoted_fragments: Cell<IndexVec<Promoted, Body<'tcx>>>,
41}
42
43impl<'tcx> crate::MirPass<'tcx> for PromoteTemps<'tcx> {
44 fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
45 if let Err(_) = body.return_ty().error_reported() {
49 debug!("PromoteTemps: MIR had errors");
50 return;
51 }
52 if body.source.promoted.is_some() {
53 return;
54 }
55
56 let ccx = ConstCx::new(tcx, body);
57 let (mut temps, all_candidates) = collect_temps_and_candidates(&ccx);
58
59 let promotable_candidates = validate_candidates(&ccx, &mut temps, all_candidates);
60
61 let promoted = promote_candidates(body, tcx, temps, promotable_candidates);
62 self.promoted_fragments.set(promoted);
63 }
64
65 fn is_required(&self) -> bool {
66 true
67 }
68}
69
70#[derive(Copy, Clone, PartialEq, Eq, Debug)]
72enum TempState {
73 Undefined,
75 Defined { location: Location, uses: usize, valid: Result<(), ()> },
79 Unpromotable,
81 PromotedOut,
84}
85
86#[derive(Copy, Clone, PartialEq, Eq, Debug)]
90struct Candidate {
91 location: Location,
92}
93
94struct Collector<'a, 'tcx> {
95 ccx: &'a ConstCx<'a, 'tcx>,
96 temps: IndexVec<Local, TempState>,
97 candidates: Vec<Candidate>,
98}
99
100impl<'tcx> Visitor<'tcx> for Collector<'_, 'tcx> {
101 #[instrument(level = "debug", skip(self))]
102 fn visit_local(&mut self, index: Local, context: PlaceContext, location: Location) {
103 match self.ccx.body.local_kind(index) {
105 LocalKind::Arg => return,
106 LocalKind::Temp if self.ccx.body.local_decls[index].is_user_variable() => return,
107 LocalKind::ReturnPointer | LocalKind::Temp => {}
108 }
109
110 if context.is_drop() || !context.is_use() {
114 debug!(is_drop = context.is_drop(), is_use = context.is_use());
115 return;
116 }
117
118 let temp = &mut self.temps[index];
119 debug!(?temp);
120 *temp = match *temp {
121 TempState::Undefined => match context {
122 PlaceContext::MutatingUse(MutatingUseContext::Store | MutatingUseContext::Call) => {
123 TempState::Defined { location, uses: 0, valid: Err(()) }
124 }
125 _ => TempState::Unpromotable,
126 },
127 TempState::Defined { ref mut uses, .. } => {
128 let allowed_use = match context {
131 PlaceContext::MutatingUse(MutatingUseContext::Borrow)
132 | PlaceContext::NonMutatingUse(_) => true,
133 PlaceContext::MutatingUse(_) | PlaceContext::NonUse(_) => false,
134 };
135 debug!(?allowed_use);
136 if allowed_use {
137 *uses += 1;
138 return;
139 }
140 TempState::Unpromotable
141 }
142 TempState::Unpromotable | TempState::PromotedOut => TempState::Unpromotable,
143 };
144 debug!(?temp);
145 }
146
147 fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
148 self.super_rvalue(rvalue, location);
149
150 if let Rvalue::Ref(..) = *rvalue {
151 self.candidates.push(Candidate { location });
152 }
153 }
154}
155
156fn collect_temps_and_candidates<'tcx>(
157 ccx: &ConstCx<'_, 'tcx>,
158) -> (IndexVec<Local, TempState>, Vec<Candidate>) {
159 let mut collector = Collector {
160 temps: IndexVec::from_elem(TempState::Undefined, &ccx.body.local_decls),
161 candidates: vec![],
162 ccx,
163 };
164 for (bb, data) in traversal::reverse_postorder(ccx.body) {
165 collector.visit_basic_block_data(bb, data);
166 }
167 (collector.temps, collector.candidates)
168}
169
170struct Validator<'a, 'tcx> {
174 ccx: &'a ConstCx<'a, 'tcx>,
175 temps: &'a mut IndexSlice<Local, TempState>,
176 promotion_safe_blocks: Option<FxHashSet<BasicBlock>>,
182}
183
184impl<'a, 'tcx> std::ops::Deref for Validator<'a, 'tcx> {
185 type Target = ConstCx<'a, 'tcx>;
186
187 fn deref(&self) -> &Self::Target {
188 self.ccx
189 }
190}
191
192struct Unpromotable;
193
194impl<'tcx> Validator<'_, 'tcx> {
195 fn validate_candidate(&mut self, candidate: Candidate) -> Result<(), Unpromotable> {
196 let Left(statement) = self.body.stmt_at(candidate.location) else { bug!() };
197 let Some((_, Rvalue::Ref(_, kind, place))) = statement.kind.as_assign() else { bug!() };
198
199 self.validate_local(place.local)?;
202
203 self.validate_ref(*kind, place)?;
206
207 if place.projection.contains(&ProjectionElem::Deref) {
210 return Err(Unpromotable);
211 }
212
213 Ok(())
214 }
215
216 fn qualif_local<Q: qualifs::Qualif>(&mut self, local: Local) -> bool {
218 let TempState::Defined { location: loc, .. } = self.temps[local] else {
219 return false;
220 };
221
222 let stmt_or_term = self.body.stmt_at(loc);
223 match stmt_or_term {
224 Left(statement) => {
225 let Some((_, rhs)) = statement.kind.as_assign() else {
226 span_bug!(statement.source_info.span, "{:?} is not an assignment", statement)
227 };
228 qualifs::in_rvalue::<Q, _>(self.ccx, &mut |l| self.qualif_local::<Q>(l), rhs)
229 }
230 Right(terminator) => {
231 assert_matches!(terminator.kind, TerminatorKind::Call { .. });
232 let return_ty = self.body.local_decls[local].ty;
233 Q::in_any_value_of_ty(self.ccx, return_ty)
234 }
235 }
236 }
237
238 fn validate_local(&mut self, local: Local) -> Result<(), Unpromotable> {
239 let TempState::Defined { location: loc, uses, valid } = self.temps[local] else {
240 return Err(Unpromotable);
241 };
242
243 if self.qualif_local::<qualifs::NeedsDrop>(local) {
246 return Err(Unpromotable);
247 }
248
249 if valid.is_ok() {
250 return Ok(());
251 }
252
253 let ok = {
254 let stmt_or_term = self.body.stmt_at(loc);
255 match stmt_or_term {
256 Left(statement) => {
257 let Some((_, rhs)) = statement.kind.as_assign() else {
258 span_bug!(
259 statement.source_info.span,
260 "{:?} is not an assignment",
261 statement
262 )
263 };
264 self.validate_rvalue(rhs)
265 }
266 Right(terminator) => match &terminator.kind {
267 TerminatorKind::Call { func, args, .. } => {
268 self.validate_call(func, args, loc.block)
269 }
270 TerminatorKind::Yield { .. } => Err(Unpromotable),
271 kind => {
272 span_bug!(terminator.source_info.span, "{:?} not promotable", kind);
273 }
274 },
275 }
276 };
277
278 self.temps[local] = match ok {
279 Ok(()) => TempState::Defined { location: loc, uses, valid: Ok(()) },
280 Err(_) => TempState::Unpromotable,
281 };
282
283 ok
284 }
285
286 fn validate_place(&mut self, place: PlaceRef<'tcx>) -> Result<(), Unpromotable> {
287 let Some((place_base, elem)) = place.last_projection() else {
288 return self.validate_local(place.local);
289 };
290
291 match elem {
293 ProjectionElem::ConstantIndex { .. }
295 | ProjectionElem::Subslice { .. }
296 | ProjectionElem::UnwrapUnsafeBinder(_) => {}
297
298 ProjectionElem::OpaqueCast(..) | ProjectionElem::Downcast(..) => {
300 return Err(Unpromotable);
301 }
302
303 ProjectionElem::Deref => {
304 if let Some(local) = place_base.as_local()
312 && let TempState::Defined { location, .. } = self.temps[local]
313 && let Left(def_stmt) = self.body.stmt_at(location)
314 && let Some((_, Rvalue::Use(Operand::Constant(c)))) = def_stmt.kind.as_assign()
315 && let Some(did) = c.check_static_ptr(self.tcx)
316 && let Some(hir::ConstContext::Static(..)) = self.const_kind
320 && !self.tcx.is_thread_local_static(did)
321 {
322 } else {
324 return Err(Unpromotable);
325 }
326 }
327 ProjectionElem::Index(local) => {
328 if let TempState::Defined { location: loc, .. } = self.temps[local]
330 && let Left(statement) = self.body.stmt_at(loc)
331 && let Some((_, Rvalue::Use(Operand::Constant(c)))) = statement.kind.as_assign()
332 && let Some(idx) = c.const_.try_eval_target_usize(self.tcx, self.typing_env)
333 && let ty::Array(_, len) = place_base.ty(self.body, self.tcx).ty.kind()
335 && let Some(len) = len.try_to_target_usize(self.tcx)
337 && idx < len
339 {
340 self.validate_local(local)?;
341 } else {
343 return Err(Unpromotable);
344 }
345 }
346
347 ProjectionElem::Field(..) => {
348 let base_ty = place_base.ty(self.body, self.tcx).ty;
349 if base_ty.is_union() {
350 return Err(Unpromotable);
352 }
353 }
354 }
355
356 self.validate_place(place_base)
357 }
358
359 fn validate_operand(&mut self, operand: &Operand<'tcx>) -> Result<(), Unpromotable> {
360 match operand {
361 Operand::Copy(place) | Operand::Move(place) => self.validate_place(place.as_ref()),
362
363 Operand::Constant(c) => {
366 if let Some(def_id) = c.check_static_ptr(self.tcx) {
367 let is_static = matches!(self.const_kind, Some(hir::ConstContext::Static(_)));
374 if !is_static {
375 return Err(Unpromotable);
376 }
377
378 let is_thread_local = self.tcx.is_thread_local_static(def_id);
379 if is_thread_local {
380 return Err(Unpromotable);
381 }
382 }
383
384 Ok(())
385 }
386 }
387 }
388
389 fn validate_ref(&mut self, kind: BorrowKind, place: &Place<'tcx>) -> Result<(), Unpromotable> {
390 match kind {
391 BorrowKind::Fake(_) | BorrowKind::Mut { kind: MutBorrowKind::ClosureCapture } => {
395 return Err(Unpromotable);
396 }
397
398 BorrowKind::Shared => {
399 let has_mut_interior = self.qualif_local::<qualifs::HasMutInterior>(place.local);
400 if has_mut_interior {
401 return Err(Unpromotable);
402 }
403 }
404
405 BorrowKind::Mut { kind: MutBorrowKind::Default | MutBorrowKind::TwoPhaseBorrow } => {
408 let ty = place.ty(self.body, self.tcx).ty;
409
410 if let ty::Array(_, len) = ty.kind() {
414 match len.try_to_target_usize(self.tcx) {
415 Some(0) => {}
416 _ => return Err(Unpromotable),
417 }
418 } else {
419 return Err(Unpromotable);
420 }
421 }
422 }
423
424 Ok(())
425 }
426
427 fn validate_rvalue(&mut self, rvalue: &Rvalue<'tcx>) -> Result<(), Unpromotable> {
428 match rvalue {
429 Rvalue::Use(operand)
430 | Rvalue::Repeat(operand, _)
431 | Rvalue::WrapUnsafeBinder(operand, _) => {
432 self.validate_operand(operand)?;
433 }
434 Rvalue::CopyForDeref(place) => {
435 let op = &Operand::Copy(*place);
436 self.validate_operand(op)?
437 }
438
439 Rvalue::Discriminant(place) => self.validate_place(place.as_ref())?,
440
441 Rvalue::ThreadLocalRef(_) => return Err(Unpromotable),
442
443 Rvalue::Cast(CastKind::PointerExposeProvenance, _, _) => return Err(Unpromotable),
445
446 Rvalue::Cast(_, operand, _) => {
449 self.validate_operand(operand)?;
450 }
451
452 Rvalue::NullaryOp(op, _) => match op {
453 NullOp::SizeOf => {}
454 NullOp::AlignOf => {}
455 NullOp::OffsetOf(_) => {}
456 NullOp::UbChecks => {}
457 NullOp::ContractChecks => {}
458 },
459
460 Rvalue::ShallowInitBox(_, _) => return Err(Unpromotable),
461
462 Rvalue::UnaryOp(op, operand) => {
463 match op {
464 UnOp::Neg | UnOp::Not | UnOp::PtrMetadata => {}
466 }
467
468 self.validate_operand(operand)?;
469 }
470
471 Rvalue::BinaryOp(op, box (lhs, rhs)) => {
472 let op = *op;
473 let lhs_ty = lhs.ty(self.body, self.tcx);
474
475 if let ty::RawPtr(_, _) | ty::FnPtr(..) = lhs_ty.kind() {
476 assert_matches!(
479 op,
480 BinOp::Eq
481 | BinOp::Ne
482 | BinOp::Le
483 | BinOp::Lt
484 | BinOp::Ge
485 | BinOp::Gt
486 | BinOp::Offset
487 );
488 return Err(Unpromotable);
489 }
490
491 match op {
492 BinOp::Div | BinOp::Rem => {
493 if lhs_ty.is_integral() {
494 let sz = lhs_ty.primitive_size(self.tcx);
495 let rhs_val = match rhs {
497 Operand::Constant(c) => {
498 c.const_.try_eval_scalar_int(self.tcx, self.typing_env)
499 }
500 _ => None,
501 };
502 match rhs_val.map(|x| x.to_uint(sz)) {
503 Some(x) if x != 0 => {} _ => return Err(Unpromotable), }
507 if lhs_ty.is_signed() {
510 match rhs_val.map(|x| x.to_int(sz)) {
511 Some(-1) | None => {
512 let lhs_val = match lhs {
515 Operand::Constant(c) => c
516 .const_
517 .try_eval_scalar_int(self.tcx, self.typing_env),
518 _ => None,
519 };
520 let lhs_min = sz.signed_int_min();
521 match lhs_val.map(|x| x.to_int(sz)) {
522 Some(x) if x != lhs_min => {}
524
525 _ => return Err(Unpromotable),
527 }
528 }
529 _ => {}
530 }
531 }
532 }
533 }
534 BinOp::Eq
536 | BinOp::Ne
537 | BinOp::Le
538 | BinOp::Lt
539 | BinOp::Ge
540 | BinOp::Gt
541 | BinOp::Cmp
542 | BinOp::Offset
543 | BinOp::Add
544 | BinOp::AddUnchecked
545 | BinOp::AddWithOverflow
546 | BinOp::Sub
547 | BinOp::SubUnchecked
548 | BinOp::SubWithOverflow
549 | BinOp::Mul
550 | BinOp::MulUnchecked
551 | BinOp::MulWithOverflow
552 | BinOp::BitXor
553 | BinOp::BitAnd
554 | BinOp::BitOr
555 | BinOp::Shl
556 | BinOp::ShlUnchecked
557 | BinOp::Shr
558 | BinOp::ShrUnchecked => {}
559 }
560
561 self.validate_operand(lhs)?;
562 self.validate_operand(rhs)?;
563 }
564
565 Rvalue::RawPtr(_, place) => {
566 if let Some((place_base, ProjectionElem::Deref)) = place.as_ref().last_projection()
569 {
570 let base_ty = place_base.ty(self.body, self.tcx).ty;
571 if let ty::Ref(..) = base_ty.kind() {
572 return self.validate_place(place_base);
573 }
574 }
575 return Err(Unpromotable);
576 }
577
578 Rvalue::Ref(_, kind, place) => {
579 let mut place_simplified = place.as_ref();
581 if let Some((place_base, ProjectionElem::Deref)) =
582 place_simplified.last_projection()
583 {
584 let base_ty = place_base.ty(self.body, self.tcx).ty;
585 if let ty::Ref(..) = base_ty.kind() {
586 place_simplified = place_base;
587 }
588 }
589
590 self.validate_place(place_simplified)?;
591
592 self.validate_ref(*kind, place)?;
595 }
596
597 Rvalue::Aggregate(_, operands) => {
598 for o in operands {
599 self.validate_operand(o)?;
600 }
601 }
602 }
603
604 Ok(())
605 }
606
607 fn promotion_safe_blocks(body: &mir::Body<'tcx>) -> FxHashSet<BasicBlock> {
611 let mut safe_blocks = FxHashSet::default();
612 let mut safe_block = START_BLOCK;
613 loop {
614 safe_blocks.insert(safe_block);
615 safe_block = match body.basic_blocks[safe_block].terminator().kind {
617 TerminatorKind::Goto { target } => target,
618 TerminatorKind::Call { target: Some(target), .. }
619 | TerminatorKind::Drop { target, .. } => {
620 target
624 }
625 TerminatorKind::Assert { target, .. } => {
626 target
628 }
629 _ => {
630 break;
632 }
633 };
634 }
635 safe_blocks
636 }
637
638 fn is_promotion_safe_block(&mut self, block: BasicBlock) -> bool {
641 let body = self.body;
642 let safe_blocks =
643 self.promotion_safe_blocks.get_or_insert_with(|| Self::promotion_safe_blocks(body));
644 safe_blocks.contains(&block)
645 }
646
647 fn validate_call(
648 &mut self,
649 callee: &Operand<'tcx>,
650 args: &[Spanned<Operand<'tcx>>],
651 block: BasicBlock,
652 ) -> Result<(), Unpromotable> {
653 self.validate_operand(callee)?;
655 for arg in args {
656 self.validate_operand(&arg.node)?;
657 }
658
659 let fn_ty = callee.ty(self.body, self.tcx);
662 if let ty::FnDef(def_id, _) = *fn_ty.kind() {
663 if self.tcx.is_promotable_const_fn(def_id) {
664 return Ok(());
665 }
666 }
667
668 let promote_all_fn = matches!(
673 self.const_kind,
674 Some(hir::ConstContext::Static(_) | hir::ConstContext::Const { inline: false })
675 );
676 if !promote_all_fn {
677 return Err(Unpromotable);
678 }
679 let is_const_fn = match *fn_ty.kind() {
681 ty::FnDef(def_id, _) => self.tcx.is_const_fn(def_id),
682 _ => false,
683 };
684 if !is_const_fn {
685 return Err(Unpromotable);
686 }
687 if !self.is_promotion_safe_block(block) {
691 return Err(Unpromotable);
692 }
693 Ok(())
695 }
696}
697
698fn validate_candidates(
699 ccx: &ConstCx<'_, '_>,
700 temps: &mut IndexSlice<Local, TempState>,
701 mut candidates: Vec<Candidate>,
702) -> Vec<Candidate> {
703 let mut validator = Validator { ccx, temps, promotion_safe_blocks: None };
704
705 candidates.retain(|&candidate| validator.validate_candidate(candidate).is_ok());
706 candidates
707}
708
709struct Promoter<'a, 'tcx> {
710 tcx: TyCtxt<'tcx>,
711 source: &'a mut Body<'tcx>,
712 promoted: Body<'tcx>,
713 temps: &'a mut IndexVec<Local, TempState>,
714 extra_statements: &'a mut Vec<(Location, Statement<'tcx>)>,
715
716 required_consts: Vec<ConstOperand<'tcx>>,
718
719 keep_original: bool,
722
723 add_to_required: bool,
726}
727
728impl<'a, 'tcx> Promoter<'a, 'tcx> {
729 fn new_block(&mut self) -> BasicBlock {
730 let span = self.promoted.span;
731 self.promoted.basic_blocks_mut().push(BasicBlockData::new(
732 Some(Terminator {
733 source_info: SourceInfo::outermost(span),
734 kind: TerminatorKind::Return,
735 }),
736 false,
737 ))
738 }
739
740 fn assign(&mut self, dest: Local, rvalue: Rvalue<'tcx>, span: Span) {
741 let last = self.promoted.basic_blocks.last_index().unwrap();
742 let data = &mut self.promoted[last];
743 data.statements.push(Statement::new(
744 SourceInfo::outermost(span),
745 StatementKind::Assign(Box::new((Place::from(dest), rvalue))),
746 ));
747 }
748
749 fn is_temp_kind(&self, local: Local) -> bool {
750 self.source.local_kind(local) == LocalKind::Temp
751 }
752
753 fn promote_temp(&mut self, temp: Local) -> Local {
756 let old_keep_original = self.keep_original;
757 let loc = match self.temps[temp] {
758 TempState::Defined { location, uses, .. } if uses > 0 => {
759 if uses > 1 {
760 self.keep_original = true;
761 }
762 location
763 }
764 state => {
765 span_bug!(self.promoted.span, "{:?} not promotable: {:?}", temp, state);
766 }
767 };
768 if !self.keep_original {
769 self.temps[temp] = TempState::PromotedOut;
770 }
771
772 let num_stmts = self.source[loc.block].statements.len();
773 let new_temp = self.promoted.local_decls.push(LocalDecl::new(
774 self.source.local_decls[temp].ty,
775 self.source.local_decls[temp].source_info.span,
776 ));
777
778 debug!("promote({:?} @ {:?}/{:?}, {:?})", temp, loc, num_stmts, self.keep_original);
779
780 if loc.statement_index < num_stmts {
783 let (mut rvalue, source_info) = {
784 let statement = &mut self.source[loc.block].statements[loc.statement_index];
785 let StatementKind::Assign(box (_, rhs)) = &mut statement.kind else {
786 span_bug!(statement.source_info.span, "{:?} is not an assignment", statement);
787 };
788
789 (
790 if self.keep_original {
791 rhs.clone()
792 } else {
793 let unit = Rvalue::Use(Operand::Constant(Box::new(ConstOperand {
794 span: statement.source_info.span,
795 user_ty: None,
796 const_: Const::zero_sized(self.tcx.types.unit),
797 })));
798 mem::replace(rhs, unit)
799 },
800 statement.source_info,
801 )
802 };
803
804 self.visit_rvalue(&mut rvalue, loc);
805 self.assign(new_temp, rvalue, source_info.span);
806 } else {
807 let terminator = if self.keep_original {
808 self.source[loc.block].terminator().clone()
809 } else {
810 let terminator = self.source[loc.block].terminator_mut();
811 let target = match &terminator.kind {
812 TerminatorKind::Call { target: Some(target), .. } => *target,
813 kind => {
814 span_bug!(terminator.source_info.span, "{:?} not promotable", kind);
815 }
816 };
817 Terminator {
818 source_info: terminator.source_info,
819 kind: mem::replace(&mut terminator.kind, TerminatorKind::Goto { target }),
820 }
821 };
822
823 match terminator.kind {
824 TerminatorKind::Call {
825 mut func, mut args, call_source: desugar, fn_span, ..
826 } => {
827 self.add_to_required = true;
830
831 self.visit_operand(&mut func, loc);
832 for arg in &mut args {
833 self.visit_operand(&mut arg.node, loc);
834 }
835
836 let last = self.promoted.basic_blocks.last_index().unwrap();
837 let new_target = self.new_block();
838
839 *self.promoted[last].terminator_mut() = Terminator {
840 kind: TerminatorKind::Call {
841 func,
842 args,
843 unwind: UnwindAction::Continue,
844 destination: Place::from(new_temp),
845 target: Some(new_target),
846 call_source: desugar,
847 fn_span,
848 },
849 source_info: SourceInfo::outermost(terminator.source_info.span),
850 ..terminator
851 };
852 }
853 kind => {
854 span_bug!(terminator.source_info.span, "{:?} not promotable", kind);
855 }
856 };
857 };
858
859 self.keep_original = old_keep_original;
860 new_temp
861 }
862
863 fn promote_candidate(
864 mut self,
865 candidate: Candidate,
866 next_promoted_index: Promoted,
867 ) -> Body<'tcx> {
868 let def = self.source.source.def_id();
869 let (mut rvalue, promoted_op) = {
870 let promoted = &mut self.promoted;
871 let tcx = self.tcx;
872 let mut promoted_operand = |ty, span| {
873 promoted.span = span;
874 promoted.local_decls[RETURN_PLACE] = LocalDecl::new(ty, span);
875 let args =
876 tcx.erase_and_anonymize_regions(GenericArgs::identity_for_item(tcx, def));
877 let uneval =
878 mir::UnevaluatedConst { def, args, promoted: Some(next_promoted_index) };
879
880 ConstOperand { span, user_ty: None, const_: Const::Unevaluated(uneval, ty) }
881 };
882
883 let blocks = self.source.basic_blocks.as_mut();
884 let local_decls = &mut self.source.local_decls;
885 let loc = candidate.location;
886 let statement = &mut blocks[loc.block].statements[loc.statement_index];
887 let StatementKind::Assign(box (_, Rvalue::Ref(region, borrow_kind, place))) =
888 &mut statement.kind
889 else {
890 bug!()
891 };
892
893 debug_assert!(region.is_erased());
895 let ty = local_decls[place.local].ty;
896 let span = statement.source_info.span;
897
898 let ref_ty =
899 Ty::new_ref(tcx, tcx.lifetimes.re_erased, ty, borrow_kind.to_mutbl_lossy());
900
901 let mut projection = vec![PlaceElem::Deref];
902 projection.extend(place.projection);
903 place.projection = tcx.mk_place_elems(&projection);
904
905 let mut promoted_ref = LocalDecl::new(ref_ty, span);
909 promoted_ref.source_info = statement.source_info;
910 let promoted_ref = local_decls.push(promoted_ref);
911 assert_eq!(self.temps.push(TempState::Unpromotable), promoted_ref);
912
913 let promoted_operand = promoted_operand(ref_ty, span);
914 let promoted_ref_statement = Statement::new(
915 statement.source_info,
916 StatementKind::Assign(Box::new((
917 Place::from(promoted_ref),
918 Rvalue::Use(Operand::Constant(Box::new(promoted_operand))),
919 ))),
920 );
921 self.extra_statements.push((loc, promoted_ref_statement));
922
923 (
924 Rvalue::Ref(
925 tcx.lifetimes.re_erased,
926 *borrow_kind,
927 Place {
928 local: mem::replace(&mut place.local, promoted_ref),
929 projection: List::empty(),
930 },
931 ),
932 promoted_operand,
933 )
934 };
935
936 assert_eq!(self.new_block(), START_BLOCK);
937 self.visit_rvalue(
938 &mut rvalue,
939 Location { block: START_BLOCK, statement_index: usize::MAX },
940 );
941
942 let span = self.promoted.span;
943 self.assign(RETURN_PLACE, rvalue, span);
944
945 if self.add_to_required {
948 self.source.required_consts.as_mut().unwrap().push(promoted_op);
949 }
950
951 self.promoted.set_required_consts(self.required_consts);
952
953 self.promoted
954 }
955}
956
957impl<'a, 'tcx> MutVisitor<'tcx> for Promoter<'a, 'tcx> {
959 fn tcx(&self) -> TyCtxt<'tcx> {
960 self.tcx
961 }
962
963 fn visit_local(&mut self, local: &mut Local, _: PlaceContext, _: Location) {
964 if self.is_temp_kind(*local) {
965 *local = self.promote_temp(*local);
966 }
967 }
968
969 fn visit_const_operand(&mut self, constant: &mut ConstOperand<'tcx>, _location: Location) {
970 if constant.const_.is_required_const() {
971 self.required_consts.push(*constant);
972 }
973
974 }
976}
977
978fn promote_candidates<'tcx>(
979 body: &mut Body<'tcx>,
980 tcx: TyCtxt<'tcx>,
981 mut temps: IndexVec<Local, TempState>,
982 candidates: Vec<Candidate>,
983) -> IndexVec<Promoted, Body<'tcx>> {
984 debug!(promote_candidates = ?candidates);
986
987 if candidates.is_empty() {
989 return IndexVec::new();
990 }
991
992 let mut promotions = IndexVec::new();
993
994 let mut extra_statements = vec![];
995 for candidate in candidates.into_iter().rev() {
996 let Location { block, statement_index } = candidate.location;
997 if let StatementKind::Assign(box (place, _)) = &body[block].statements[statement_index].kind
998 && let Some(local) = place.as_local()
999 {
1000 if temps[local] == TempState::PromotedOut {
1001 continue;
1003 }
1004 }
1005
1006 let initial_locals = iter::once(LocalDecl::new(tcx.types.never, body.span)).collect();
1008
1009 let mut scope = body.source_scopes[body.source_info(candidate.location).scope].clone();
1010 scope.parent_scope = None;
1011
1012 let mut promoted = Body::new(
1013 body.source, IndexVec::new(),
1015 IndexVec::from_elem_n(scope, 1),
1016 initial_locals,
1017 IndexVec::new(),
1018 0,
1019 vec![],
1020 body.span,
1021 None,
1022 body.tainted_by_errors,
1023 );
1024 promoted.phase = MirPhase::Analysis(AnalysisPhase::Initial);
1025
1026 let promoter = Promoter {
1027 promoted,
1028 tcx,
1029 source: body,
1030 temps: &mut temps,
1031 extra_statements: &mut extra_statements,
1032 keep_original: false,
1033 add_to_required: false,
1034 required_consts: Vec::new(),
1035 };
1036
1037 let mut promoted = promoter.promote_candidate(candidate, promotions.next_index());
1038 promoted.source.promoted = Some(promotions.next_index());
1039 promotions.push(promoted);
1040 }
1041
1042 extra_statements.sort_by_key(|&(loc, _)| cmp::Reverse(loc));
1045 for (loc, statement) in extra_statements {
1046 body[loc.block].statements.insert(loc.statement_index, statement);
1047 }
1048
1049 let promoted = |index: Local| temps[index] == TempState::PromotedOut;
1051 for block in body.basic_blocks_mut() {
1052 block.retain_statements(|statement| match &statement.kind {
1053 StatementKind::Assign(box (place, _)) => {
1054 if let Some(index) = place.as_local() {
1055 !promoted(index)
1056 } else {
1057 true
1058 }
1059 }
1060 StatementKind::StorageLive(index) | StatementKind::StorageDead(index) => {
1061 !promoted(*index)
1062 }
1063 _ => true,
1064 });
1065 let terminator = block.terminator_mut();
1066 if let TerminatorKind::Drop { place, target, .. } = &terminator.kind
1067 && let Some(index) = place.as_local()
1068 {
1069 if promoted(index) {
1070 terminator.kind = TerminatorKind::Goto { target: *target };
1071 }
1072 }
1073 }
1074
1075 promotions
1076}