Rollup merge of #119668 - cjgillot:transform-promote, r=oli-obk

Simplify implementation of MIR promotion

Non-functional changes.
Best read ignoring whitespace.

2 files changed, 0 insertions, 1026 deletions

diff --git a/compiler/rustc_const_eval/src/transform/mod.rs b/compiler/rustc_const_eval/src/transform/mod.rs
index a2928bdf51b..e3582c7d317 100644
--- a/compiler/rustc_const_eval/src/transform/mod.rs
+++ b/compiler/rustc_const_eval/src/transform/mod.rs
@@ -1,3 +1,2 @@
 pub mod check_consts;
-pub mod promote_consts;
 pub mod validate;
diff --git a/compiler/rustc_const_eval/src/transform/promote_consts.rs b/compiler/rustc_const_eval/src/transform/promote_consts.rs
deleted file mode 100644
index 155cf4ff9e2..00000000000
--- a/compiler/rustc_const_eval/src/transform/promote_consts.rs
+++ /dev/null
@@ -1,1025 +0,0 @@
-//! A pass that promotes borrows of constant rvalues.
-//!
-//! The rvalues considered constant are trees of temps,
-//! each with exactly one initialization, and holding
-//! a constant value with no interior mutability.
-//! They are placed into a new MIR constant body in
-//! `promoted` and the borrow rvalue is replaced with
-//! a `Literal::Promoted` using the index into `promoted`
-//! of that constant MIR.
-//!
-//! This pass assumes that every use is dominated by an
-//! initialization and can otherwise silence errors, if
-//! move analysis runs after promotion on broken MIR.
-
-use rustc_hir as hir;
-use rustc_middle::mir;
-use rustc_middle::mir::visit::{MutVisitor, MutatingUseContext, PlaceContext, Visitor};
-use rustc_middle::mir::*;
-use rustc_middle::ty::GenericArgs;
-use rustc_middle::ty::{self, List, Ty, TyCtxt, TypeVisitableExt};
-use rustc_span::Span;
-
-use rustc_index::{Idx, IndexSlice, IndexVec};
-
-use std::cell::Cell;
-use std::{cmp, iter, mem};
-
-use crate::transform::check_consts::{qualifs, ConstCx};
-
-/// A `MirPass` for promotion.
-///
-/// Promotion is the extraction of promotable temps into separate MIR bodies so they can have
-/// `'static` lifetime.
-///
-/// After this pass is run, `promoted_fragments` will hold the MIR body corresponding to each
-/// newly created `Constant`.
-#[derive(Default)]
-pub struct PromoteTemps<'tcx> {
-    pub promoted_fragments: Cell<IndexVec<Promoted, Body<'tcx>>>,
-}
-
-impl<'tcx> MirPass<'tcx> for PromoteTemps<'tcx> {
-    fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
-        // There's not really any point in promoting errorful MIR.
-        //
-        // This does not include MIR that failed const-checking, which we still try to promote.
-        if let Err(_) = body.return_ty().error_reported() {
-            debug!("PromoteTemps: MIR had errors");
-            return;
-        }
-        if body.source.promoted.is_some() {
-            return;
-        }
-
-        let ccx = ConstCx::new(tcx, body);
-        let (mut temps, all_candidates) = collect_temps_and_candidates(&ccx);
-
-        let promotable_candidates = validate_candidates(&ccx, &mut temps, &all_candidates);
-
-        let promoted = promote_candidates(body, tcx, temps, promotable_candidates);
-        self.promoted_fragments.set(promoted);
-    }
-}
-
-/// State of a temporary during collection and promotion.
-#[derive(Copy, Clone, PartialEq, Eq, Debug)]
-pub enum TempState {
-    /// No references to this temp.
-    Undefined,
-    /// One direct assignment and any number of direct uses.
-    /// A borrow of this temp is promotable if the assigned
-    /// value is qualified as constant.
-    Defined { location: Location, uses: usize, valid: Result<(), ()> },
-    /// Any other combination of assignments/uses.
-    Unpromotable,
-    /// This temp was part of an rvalue which got extracted
-    /// during promotion and needs cleanup.
-    PromotedOut,
-}
-
-impl TempState {
-    pub fn is_promotable(&self) -> bool {
-        debug!("is_promotable: self={:?}", self);
-        matches!(self, TempState::Defined { .. })
-    }
-}
-
-/// A "root candidate" for promotion, which will become the
-/// returned value in a promoted MIR, unless it's a subset
-/// of a larger candidate.
-#[derive(Copy, Clone, PartialEq, Eq, Debug)]
-pub struct Candidate {
-    location: Location,
-}
-
-struct Collector<'a, 'tcx> {
-    ccx: &'a ConstCx<'a, 'tcx>,
-    temps: IndexVec<Local, TempState>,
-    candidates: Vec<Candidate>,
-}
-
-impl<'tcx> Visitor<'tcx> for Collector<'_, 'tcx> {
-    fn visit_local(&mut self, index: Local, context: PlaceContext, location: Location) {
-        debug!("visit_local: index={:?} context={:?} location={:?}", index, context, location);
-        // We're only interested in temporaries and the return place
-        match self.ccx.body.local_kind(index) {
-            LocalKind::Arg => return,
-            LocalKind::Temp if self.ccx.body.local_decls[index].is_user_variable() => return,
-            LocalKind::ReturnPointer | LocalKind::Temp => {}
-        }
-
-        // Ignore drops, if the temp gets promoted,
-        // then it's constant and thus drop is noop.
-        // Non-uses are also irrelevant.
-        if context.is_drop() || !context.is_use() {
-            debug!(
-                "visit_local: context.is_drop={:?} context.is_use={:?}",
-                context.is_drop(),
-                context.is_use(),
-            );
-            return;
-        }
-
-        let temp = &mut self.temps[index];
-        debug!("visit_local: temp={:?}", temp);
-        if *temp == TempState::Undefined {
-            match context {
-                PlaceContext::MutatingUse(MutatingUseContext::Store)
-                | PlaceContext::MutatingUse(MutatingUseContext::Call) => {
-                    *temp = TempState::Defined { location, uses: 0, valid: Err(()) };
-                    return;
-                }
-                _ => { /* mark as unpromotable below */ }
-            }
-        } else if let TempState::Defined { uses, .. } = temp {
-            // We always allow borrows, even mutable ones, as we need
-            // to promote mutable borrows of some ZSTs e.g., `&mut []`.
-            let allowed_use = match context {
-                PlaceContext::MutatingUse(MutatingUseContext::Borrow)
-                | PlaceContext::NonMutatingUse(_) => true,
-                PlaceContext::MutatingUse(_) | PlaceContext::NonUse(_) => false,
-            };
-            debug!("visit_local: allowed_use={:?}", allowed_use);
-            if allowed_use {
-                *uses += 1;
-                return;
-            }
-            /* mark as unpromotable below */
-        }
-        *temp = TempState::Unpromotable;
-    }
-
-    fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
-        self.super_rvalue(rvalue, location);
-
-        match *rvalue {
-            Rvalue::Ref(..) => {
-                self.candidates.push(Candidate { location });
-            }
-            _ => {}
-        }
-    }
-}
-
-pub fn collect_temps_and_candidates<'tcx>(
-    ccx: &ConstCx<'_, 'tcx>,
-) -> (IndexVec<Local, TempState>, Vec<Candidate>) {
-    let mut collector = Collector {
-        temps: IndexVec::from_elem(TempState::Undefined, &ccx.body.local_decls),
-        candidates: vec![],
-        ccx,
-    };
-    for (bb, data) in traversal::reverse_postorder(ccx.body) {
-        collector.visit_basic_block_data(bb, data);
-    }
-    (collector.temps, collector.candidates)
-}
-
-/// Checks whether locals that appear in a promotion context (`Candidate`) are actually promotable.
-///
-/// This wraps an `Item`, and has access to all fields of that `Item` via `Deref` coercion.
-struct Validator<'a, 'tcx> {
-    ccx: &'a ConstCx<'a, 'tcx>,
-    temps: &'a mut IndexSlice<Local, TempState>,
-}
-
-impl<'a, 'tcx> std::ops::Deref for Validator<'a, 'tcx> {
-    type Target = ConstCx<'a, 'tcx>;
-
-    fn deref(&self) -> &Self::Target {
-        self.ccx
-    }
-}
-
-struct Unpromotable;
-
-impl<'tcx> Validator<'_, 'tcx> {
-    fn validate_candidate(&mut self, candidate: Candidate) -> Result<(), Unpromotable> {
-        let loc = candidate.location;
-        let statement = &self.body[loc.block].statements[loc.statement_index];
-        match &statement.kind {
-            StatementKind::Assign(box (_, Rvalue::Ref(_, kind, place))) => {
-                // We can only promote interior borrows of promotable temps (non-temps
-                // don't get promoted anyway).
-                self.validate_local(place.local)?;
-
-                // The reference operation itself must be promotable.
-                // (Needs to come after `validate_local` to avoid ICEs.)
-                self.validate_ref(*kind, place)?;
-
-                // We do not check all the projections (they do not get promoted anyway),
-                // but we do stay away from promoting anything involving a dereference.
-                if place.projection.contains(&ProjectionElem::Deref) {
-                    return Err(Unpromotable);
-                }
-
-                Ok(())
-            }
-            _ => bug!(),
-        }
-    }
-
-    // FIXME(eddyb) maybe cache this?
-    fn qualif_local<Q: qualifs::Qualif>(&mut self, local: Local) -> bool {
-        if let TempState::Defined { location: loc, .. } = self.temps[local] {
-            let num_stmts = self.body[loc.block].statements.len();
-
-            if loc.statement_index < num_stmts {
-                let statement = &self.body[loc.block].statements[loc.statement_index];
-                match &statement.kind {
-                    StatementKind::Assign(box (_, rhs)) => qualifs::in_rvalue::<Q, _>(
-                        self.ccx,
-                        &mut |l| self.qualif_local::<Q>(l),
-                        rhs,
-                    ),
-                    _ => {
-                        span_bug!(
-                            statement.source_info.span,
-                            "{:?} is not an assignment",
-                            statement
-                        );
-                    }
-                }
-            } else {
-                let terminator = self.body[loc.block].terminator();
-                match &terminator.kind {
-                    TerminatorKind::Call { .. } => {
-                        let return_ty = self.body.local_decls[local].ty;
-                        Q::in_any_value_of_ty(self.ccx, return_ty)
-                    }
-                    kind => {
-                        span_bug!(terminator.source_info.span, "{:?} not promotable", kind);
-                    }
-                }
-            }
-        } else {
-            false
-        }
-    }
-
-    fn validate_local(&mut self, local: Local) -> Result<(), Unpromotable> {
-        if let TempState::Defined { location: loc, uses, valid } = self.temps[local] {
-            // We cannot promote things that need dropping, since the promoted value
-            // would not get dropped.
-            if self.qualif_local::<qualifs::NeedsDrop>(local) {
-                return Err(Unpromotable);
-            }
-            valid.or_else(|_| {
-                let ok = {
-                    let block = &self.body[loc.block];
-                    let num_stmts = block.statements.len();
-
-                    if loc.statement_index < num_stmts {
-                        let statement = &block.statements[loc.statement_index];
-                        match &statement.kind {
-                            StatementKind::Assign(box (_, rhs)) => self.validate_rvalue(rhs),
-                            _ => {
-                                span_bug!(
-                                    statement.source_info.span,
-                                    "{:?} is not an assignment",
-                                    statement
-                                );
-                            }
-                        }
-                    } else {
-                        let terminator = block.terminator();
-                        match &terminator.kind {
-                            TerminatorKind::Call { func, args, .. } => {
-                                self.validate_call(func, args)
-                            }
-                            TerminatorKind::Yield { .. } => Err(Unpromotable),
-                            kind => {
-                                span_bug!(terminator.source_info.span, "{:?} not promotable", kind);
-                            }
-                        }
-                    }
-                };
-                self.temps[local] = match ok {
-                    Ok(()) => TempState::Defined { location: loc, uses, valid: Ok(()) },
-                    Err(_) => TempState::Unpromotable,
-                };
-                ok
-            })
-        } else {
-            Err(Unpromotable)
-        }
-    }
-
-    fn validate_place(&mut self, place: PlaceRef<'tcx>) -> Result<(), Unpromotable> {
-        match place.last_projection() {
-            None => self.validate_local(place.local),
-            Some((place_base, elem)) => {
-                // Validate topmost projection, then recurse.
-                match elem {
-                    ProjectionElem::Deref => {
-                        let mut promotable = false;
-                        // When a static is used by-value, that gets desugared to `*STATIC_ADDR`,
-                        // and we need to be able to promote this. So check if this deref matches
-                        // that specific pattern.
-
-                        // We need to make sure this is a `Deref` of a local with no further projections.
-                        // Discussion can be found at
-                        // https://github.com/rust-lang/rust/pull/74945#discussion_r463063247
-                        if let Some(local) = place_base.as_local() {
-                            if let TempState::Defined { location, .. } = self.temps[local] {
-                                let def_stmt = self.body[location.block]
-                                    .statements
-                                    .get(location.statement_index);
-                                if let Some(Statement {
-                                    kind:
-                                        StatementKind::Assign(box (
-                                            _,
-                                            Rvalue::Use(Operand::Constant(c)),
-                                        )),
-                                    ..
-                                }) = def_stmt
-                                {
-                                    if let Some(did) = c.check_static_ptr(self.tcx) {
-                                        // Evaluating a promoted may not read statics except if it got
-                                        // promoted from a static (this is a CTFE check). So we
-                                        // can only promote static accesses inside statics.
-                                        if let Some(hir::ConstContext::Static(..)) = self.const_kind
-                                        {
-                                            if !self.tcx.is_thread_local_static(did) {
-                                                promotable = true;
-                                            }
-                                        }
-                                    }
-                                }
-                            }
-                        }
-                        if !promotable {
-                            return Err(Unpromotable);
-                        }
-                    }
-                    ProjectionElem::OpaqueCast(..) | ProjectionElem::Downcast(..) => {
-                        return Err(Unpromotable);
-                    }
-
-                    ProjectionElem::ConstantIndex { .. }
-                    | ProjectionElem::Subtype(_)
-                    | ProjectionElem::Subslice { .. } => {}
-
-                    ProjectionElem::Index(local) => {
-                        let mut promotable = false;
-                        // Only accept if we can predict the index and are indexing an array.
-                        let val = if let TempState::Defined { location: loc, .. } =
-                            self.temps[local]
-                        {
-                            let block = &self.body[loc.block];
-                            if loc.statement_index < block.statements.len() {
-                                let statement = &block.statements[loc.statement_index];
-                                match &statement.kind {
-                                    StatementKind::Assign(box (
-                                        _,
-                                        Rvalue::Use(Operand::Constant(c)),
-                                    )) => c.const_.try_eval_target_usize(self.tcx, self.param_env),
-                                    _ => None,
-                                }
-                            } else {
-                                None
-                            }
-                        } else {
-                            None
-                        };
-                        if let Some(idx) = val {
-                            // Determine the type of the thing we are indexing.
-                            let ty = place_base.ty(self.body, self.tcx).ty;
-                            match ty.kind() {
-                                ty::Array(_, len) => {
-                                    // It's an array; determine its length.
-                                    if let Some(len) =
-                                        len.try_eval_target_usize(self.tcx, self.param_env)
-                                    {
-                                        // If the index is in-bounds, go ahead.
-                                        if idx < len {
-                                            promotable = true;
-                                        }
-                                    }
-                                }
-                                _ => {}
-                            }
-                        }
-                        if !promotable {
-                            return Err(Unpromotable);
-                        }
-
-                        self.validate_local(local)?;
-                    }
-
-                    ProjectionElem::Field(..) => {
-                        let base_ty = place_base.ty(self.body, self.tcx).ty;
-                        if base_ty.is_union() {
-                            // No promotion of union field accesses.
-                            return Err(Unpromotable);
-                        }
-                    }
-                }
-
-                self.validate_place(place_base)
-            }
-        }
-    }
-
-    fn validate_operand(&mut self, operand: &Operand<'tcx>) -> Result<(), Unpromotable> {
-        match operand {
-            Operand::Copy(place) | Operand::Move(place) => self.validate_place(place.as_ref()),
-
-            // The qualifs for a constant (e.g. `HasMutInterior`) are checked in
-            // `validate_rvalue` upon access.
-            Operand::Constant(c) => {
-                if let Some(def_id) = c.check_static_ptr(self.tcx) {
-                    // Only allow statics (not consts) to refer to other statics.
-                    // FIXME(eddyb) does this matter at all for promotion?
-                    // FIXME(RalfJung) it makes little sense to not promote this in `fn`/`const fn`,
-                    // and in `const` this cannot occur anyway. The only concern is that we might
-                    // promote even `let x = &STATIC` which would be useless, but this applies to
-                    // promotion inside statics as well.
-                    let is_static = matches!(self.const_kind, Some(hir::ConstContext::Static(_)));
-                    if !is_static {
-                        return Err(Unpromotable);
-                    }
-
-                    let is_thread_local = self.tcx.is_thread_local_static(def_id);
-                    if is_thread_local {
-                        return Err(Unpromotable);
-                    }
-                }
-
-                Ok(())
-            }
-        }
-    }
-
-    fn validate_ref(&mut self, kind: BorrowKind, place: &Place<'tcx>) -> Result<(), Unpromotable> {
-        match kind {
-            // Reject these borrow types just to be safe.
-            // FIXME(RalfJung): could we allow them? Should we? No point in it until we have a usecase.
-            BorrowKind::Fake | BorrowKind::Mut { kind: MutBorrowKind::ClosureCapture } => {
-                return Err(Unpromotable);
-            }
-
-            BorrowKind::Shared => {
-                let has_mut_interior = self.qualif_local::<qualifs::HasMutInterior>(place.local);
-                if has_mut_interior {
-                    return Err(Unpromotable);
-                }
-            }
-
-            // FIXME: consider changing this to only promote &mut [] for default borrows,
-            // also forbidding two phase borrows
-            BorrowKind::Mut { kind: MutBorrowKind::Default | MutBorrowKind::TwoPhaseBorrow } => {
-                let ty = place.ty(self.body, self.tcx).ty;
-
-                // In theory, any zero-sized value could be borrowed
-                // mutably without consequences. However, only &mut []
-                // is allowed right now.
-                if let ty::Array(_, len) = ty.kind() {
-                    match len.try_eval_target_usize(self.tcx, self.param_env) {
-                        Some(0) => {}
-                        _ => return Err(Unpromotable),
-                    }
-                } else {
-                    return Err(Unpromotable);
-                }
-            }
-        }
-
-        Ok(())
-    }
-
-    fn validate_rvalue(&mut self, rvalue: &Rvalue<'tcx>) -> Result<(), Unpromotable> {
-        match rvalue {
-            Rvalue::Use(operand) | Rvalue::Repeat(operand, _) => {
-                self.validate_operand(operand)?;
-            }
-            Rvalue::CopyForDeref(place) => {
-                let op = &Operand::Copy(*place);
-                self.validate_operand(op)?
-            }
-
-            Rvalue::Discriminant(place) | Rvalue::Len(place) => {
-                self.validate_place(place.as_ref())?
-            }
-
-            Rvalue::ThreadLocalRef(_) => return Err(Unpromotable),
-
-            // ptr-to-int casts are not possible in consts and thus not promotable
-            Rvalue::Cast(CastKind::PointerExposeAddress, _, _) => return Err(Unpromotable),
-
-            // all other casts including int-to-ptr casts are fine, they just use the integer value
-            // at pointer type.
-            Rvalue::Cast(_, operand, _) => {
-                self.validate_operand(operand)?;
-            }
-
-            Rvalue::NullaryOp(op, _) => match op {
-                NullOp::SizeOf => {}
-                NullOp::AlignOf => {}
-                NullOp::OffsetOf(_) => {}
-            },
-
-            Rvalue::ShallowInitBox(_, _) => return Err(Unpromotable),
-
-            Rvalue::UnaryOp(op, operand) => {
-                match op {
-                    // These operations can never fail.
-                    UnOp::Neg | UnOp::Not => {}
-                }
-
-                self.validate_operand(operand)?;
-            }
-
-            Rvalue::BinaryOp(op, box (lhs, rhs)) | Rvalue::CheckedBinaryOp(op, box (lhs, rhs)) => {
-                let op = *op;
-                let lhs_ty = lhs.ty(self.body, self.tcx);
-
-                if let ty::RawPtr(_) | ty::FnPtr(..) = lhs_ty.kind() {
-                    // Raw and fn pointer operations are not allowed inside consts and thus not promotable.
-                    assert!(matches!(
-                        op,
-                        BinOp::Eq
-                            | BinOp::Ne
-                            | BinOp::Le
-                            | BinOp::Lt
-                            | BinOp::Ge
-                            | BinOp::Gt
-                            | BinOp::Offset
-                    ));
-                    return Err(Unpromotable);
-                }
-
-                match op {
-                    BinOp::Div | BinOp::Rem => {
-                        if lhs_ty.is_integral() {
-                            // Integer division: the RHS must be a non-zero const.
-                            let const_val = match rhs {
-                                Operand::Constant(c) => {
-                                    c.const_.try_eval_bits(self.tcx, self.param_env)
-                                }
-                                _ => None,
-                            };
-                            match const_val {
-                                Some(x) if x != 0 => {}        // okay
-                                _ => return Err(Unpromotable), // value not known or 0 -- not okay
-                            }
-                        }
-                    }
-                    // The remaining operations can never fail.
-                    BinOp::Eq
-                    | BinOp::Ne
-                    | BinOp::Le
-                    | BinOp::Lt
-                    | BinOp::Ge
-                    | BinOp::Gt
-                    | BinOp::Offset
-                    | BinOp::Add
-                    | BinOp::AddUnchecked
-                    | BinOp::Sub
-                    | BinOp::SubUnchecked
-                    | BinOp::Mul
-                    | BinOp::MulUnchecked
-                    | BinOp::BitXor
-                    | BinOp::BitAnd
-                    | BinOp::BitOr
-                    | BinOp::Shl
-                    | BinOp::ShlUnchecked
-                    | BinOp::Shr
-                    | BinOp::ShrUnchecked => {}
-                }
-
-                self.validate_operand(lhs)?;
-                self.validate_operand(rhs)?;
-            }
-
-            Rvalue::AddressOf(_, place) => {
-                // We accept `&raw *`, i.e., raw reborrows -- creating a raw pointer is
-                // no problem, only using it is.
-                if let Some((place_base, ProjectionElem::Deref)) = place.as_ref().last_projection()
-                {
-                    let base_ty = place_base.ty(self.body, self.tcx).ty;
-                    if let ty::Ref(..) = base_ty.kind() {
-                        return self.validate_place(place_base);
-                    }
-                }
-                return Err(Unpromotable);
-            }
-
-            Rvalue::Ref(_, kind, place) => {
-                // Special-case reborrows to be more like a copy of the reference.
-                let mut place_simplified = place.as_ref();
-                if let Some((place_base, ProjectionElem::Deref)) =
-                    place_simplified.last_projection()
-                {
-                    let base_ty = place_base.ty(self.body, self.tcx).ty;
-                    if let ty::Ref(..) = base_ty.kind() {
-                        place_simplified = place_base;
-                    }
-                }
-
-                self.validate_place(place_simplified)?;
-
-                // Check that the reference is fine (using the original place!).
-                // (Needs to come after `validate_place` to avoid ICEs.)
-                self.validate_ref(*kind, place)?;
-            }
-
-            Rvalue::Aggregate(_, operands) => {
-                for o in operands {
-                    self.validate_operand(o)?;
-                }
-            }
-        }
-
-        Ok(())
-    }
-
-    fn validate_call(
-        &mut self,
-        callee: &Operand<'tcx>,
-        args: &[Operand<'tcx>],
-    ) -> Result<(), Unpromotable> {
-        let fn_ty = callee.ty(self.body, self.tcx);
-
-        // Inside const/static items, we promote all (eligible) function calls.
-        // Everywhere else, we require `#[rustc_promotable]` on the callee.
-        let promote_all_const_fn = matches!(
-            self.const_kind,
-            Some(hir::ConstContext::Static(_) | hir::ConstContext::Const { inline: false })
-        );
-        if !promote_all_const_fn {
-            if let ty::FnDef(def_id, _) = *fn_ty.kind() {
-                // Never promote runtime `const fn` calls of
-                // functions without `#[rustc_promotable]`.
-                if !self.tcx.is_promotable_const_fn(def_id) {
-                    return Err(Unpromotable);
-                }
-            }
-        }
-
-        let is_const_fn = match *fn_ty.kind() {
-            ty::FnDef(def_id, _) => self.tcx.is_const_fn_raw(def_id),
-            _ => false,
-        };
-        if !is_const_fn {
-            return Err(Unpromotable);
-        }
-
-        self.validate_operand(callee)?;
-        for arg in args {
-            self.validate_operand(arg)?;
-        }
-
-        Ok(())
-    }
-}
-
-// FIXME(eddyb) remove the differences for promotability in `static`, `const`, `const fn`.
-pub fn validate_candidates(
-    ccx: &ConstCx<'_, '_>,
-    temps: &mut IndexSlice<Local, TempState>,
-    candidates: &[Candidate],
-) -> Vec<Candidate> {
-    let mut validator = Validator { ccx, temps };
-
-    candidates
-        .iter()
-        .copied()
-        .filter(|&candidate| validator.validate_candidate(candidate).is_ok())
-        .collect()
-}
-
-struct Promoter<'a, 'tcx> {
-    tcx: TyCtxt<'tcx>,
-    source: &'a mut Body<'tcx>,
-    promoted: Body<'tcx>,
-    temps: &'a mut IndexVec<Local, TempState>,
-    extra_statements: &'a mut Vec<(Location, Statement<'tcx>)>,
-
-    /// If true, all nested temps are also kept in the
-    /// source MIR, not moved to the promoted MIR.
-    keep_original: bool,
-}
-
-impl<'a, 'tcx> Promoter<'a, 'tcx> {
-    fn new_block(&mut self) -> BasicBlock {
-        let span = self.promoted.span;
-        self.promoted.basic_blocks_mut().push(BasicBlockData {
-            statements: vec![],
-            terminator: Some(Terminator {
-                source_info: SourceInfo::outermost(span),
-                kind: TerminatorKind::Return,
-            }),
-            is_cleanup: false,
-        })
-    }
-
-    fn assign(&mut self, dest: Local, rvalue: Rvalue<'tcx>, span: Span) {
-        let last = self.promoted.basic_blocks.last_index().unwrap();
-        let data = &mut self.promoted[last];
-        data.statements.push(Statement {
-            source_info: SourceInfo::outermost(span),
-            kind: StatementKind::Assign(Box::new((Place::from(dest), rvalue))),
-        });
-    }
-
-    fn is_temp_kind(&self, local: Local) -> bool {
-        self.source.local_kind(local) == LocalKind::Temp
-    }
-
-    /// Copies the initialization of this temp to the
-    /// promoted MIR, recursing through temps.
-    fn promote_temp(&mut self, temp: Local) -> Local {
-        let old_keep_original = self.keep_original;
-        let loc = match self.temps[temp] {
-            TempState::Defined { location, uses, .. } if uses > 0 => {
-                if uses > 1 {
-                    self.keep_original = true;
-                }
-                location
-            }
-            state => {
-                span_bug!(self.promoted.span, "{:?} not promotable: {:?}", temp, state);
-            }
-        };
-        if !self.keep_original {
-            self.temps[temp] = TempState::PromotedOut;
-        }
-
-        let num_stmts = self.source[loc.block].statements.len();
-        let new_temp = self.promoted.local_decls.push(LocalDecl::new(
-            self.source.local_decls[temp].ty,
-            self.source.local_decls[temp].source_info.span,
-        ));
-
-        debug!("promote({:?} @ {:?}/{:?}, {:?})", temp, loc, num_stmts, self.keep_original);
-
-        // First, take the Rvalue or Call out of the source MIR,
-        // or duplicate it, depending on keep_original.
-        if loc.statement_index < num_stmts {
-            let (mut rvalue, source_info) = {
-                let statement = &mut self.source[loc.block].statements[loc.statement_index];
-                let StatementKind::Assign(box (_, rhs)) = &mut statement.kind else {
-                    span_bug!(statement.source_info.span, "{:?} is not an assignment", statement);
-                };
-
-                (
-                    if self.keep_original {
-                        rhs.clone()
-                    } else {
-                        let unit = Rvalue::Use(Operand::Constant(Box::new(ConstOperand {
-                            span: statement.source_info.span,
-                            user_ty: None,
-                            const_: Const::zero_sized(self.tcx.types.unit),
-                        })));
-                        mem::replace(rhs, unit)
-                    },
-                    statement.source_info,
-                )
-            };
-
-            self.visit_rvalue(&mut rvalue, loc);
-            self.assign(new_temp, rvalue, source_info.span);
-        } else {
-            let terminator = if self.keep_original {
-                self.source[loc.block].terminator().clone()
-            } else {
-                let terminator = self.source[loc.block].terminator_mut();
-                let target = match &terminator.kind {
-                    TerminatorKind::Call { target: Some(target), .. } => *target,
-                    kind => {
-                        span_bug!(terminator.source_info.span, "{:?} not promotable", kind);
-                    }
-                };
-                Terminator {
-                    source_info: terminator.source_info,
-                    kind: mem::replace(&mut terminator.kind, TerminatorKind::Goto { target }),
-                }
-            };
-
-            match terminator.kind {
-                TerminatorKind::Call {
-                    mut func, mut args, call_source: desugar, fn_span, ..
-                } => {
-                    self.visit_operand(&mut func, loc);
-                    for arg in &mut args {
-                        self.visit_operand(arg, loc);
-                    }
-
-                    let last = self.promoted.basic_blocks.last_index().unwrap();
-                    let new_target = self.new_block();
-
-                    *self.promoted[last].terminator_mut() = Terminator {
-                        kind: TerminatorKind::Call {
-                            func,
-                            args,
-                            unwind: UnwindAction::Continue,
-                            destination: Place::from(new_temp),
-                            target: Some(new_target),
-                            call_source: desugar,
-                            fn_span,
-                        },
-                        source_info: SourceInfo::outermost(terminator.source_info.span),
-                        ..terminator
-                    };
-                }
-                kind => {
-                    span_bug!(terminator.source_info.span, "{:?} not promotable", kind);
-                }
-            };
-        };
-
-        self.keep_original = old_keep_original;
-        new_temp
-    }
-
-    fn promote_candidate(mut self, candidate: Candidate, next_promoted_id: usize) -> Body<'tcx> {
-        let def = self.source.source.def_id();
-        let mut rvalue = {
-            let promoted = &mut self.promoted;
-            let promoted_id = Promoted::new(next_promoted_id);
-            let tcx = self.tcx;
-            let mut promoted_operand = |ty, span| {
-                promoted.span = span;
-                promoted.local_decls[RETURN_PLACE] = LocalDecl::new(ty, span);
-                let args = tcx.erase_regions(GenericArgs::identity_for_item(tcx, def));
-                let uneval = mir::UnevaluatedConst { def, args, promoted: Some(promoted_id) };
-
-                Operand::Constant(Box::new(ConstOperand {
-                    span,
-                    user_ty: None,
-                    const_: Const::Unevaluated(uneval, ty),
-                }))
-            };
-
-            let blocks = self.source.basic_blocks.as_mut();
-            let local_decls = &mut self.source.local_decls;
-            let loc = candidate.location;
-            let statement = &mut blocks[loc.block].statements[loc.statement_index];
-            let StatementKind::Assign(box (_, Rvalue::Ref(region, borrow_kind, place))) =
-                &mut statement.kind
-            else {
-                bug!()
-            };
-
-            // Use the underlying local for this (necessarily interior) borrow.
-            debug_assert!(region.is_erased());
-            let ty = local_decls[place.local].ty;
-            let span = statement.source_info.span;
-
-            let ref_ty = Ty::new_ref(
-                tcx,
-                tcx.lifetimes.re_erased,
-                ty::TypeAndMut { ty, mutbl: borrow_kind.to_mutbl_lossy() },
-            );
-
-            let mut projection = vec![PlaceElem::Deref];
-            projection.extend(place.projection);
-            place.projection = tcx.mk_place_elems(&projection);
-
-            // Create a temp to hold the promoted reference.
-            // This is because `*r` requires `r` to be a local,
-            // otherwise we would use the `promoted` directly.
-            let mut promoted_ref = LocalDecl::new(ref_ty, span);
-            promoted_ref.source_info = statement.source_info;
-            let promoted_ref = local_decls.push(promoted_ref);
-            assert_eq!(self.temps.push(TempState::Unpromotable), promoted_ref);
-
-            let promoted_ref_statement = Statement {
-                source_info: statement.source_info,
-                kind: StatementKind::Assign(Box::new((
-                    Place::from(promoted_ref),
-                    Rvalue::Use(promoted_operand(ref_ty, span)),
-                ))),
-            };
-            self.extra_statements.push((loc, promoted_ref_statement));
-
-            Rvalue::Ref(
-                tcx.lifetimes.re_erased,
-                *borrow_kind,
-                Place {
-                    local: mem::replace(&mut place.local, promoted_ref),
-                    projection: List::empty(),
-                },
-            )
-        };
-
-        assert_eq!(self.new_block(), START_BLOCK);
-        self.visit_rvalue(
-            &mut rvalue,
-            Location { block: START_BLOCK, statement_index: usize::MAX },
-        );
-
-        let span = self.promoted.span;
-        self.assign(RETURN_PLACE, rvalue, span);
-        self.promoted
-    }
-}
-
-/// Replaces all temporaries with their promoted counterparts.
-impl<'a, 'tcx> MutVisitor<'tcx> for Promoter<'a, 'tcx> {
-    fn tcx(&self) -> TyCtxt<'tcx> {
-        self.tcx
-    }
-
-    fn visit_local(&mut self, local: &mut Local, _: PlaceContext, _: Location) {
-        if self.is_temp_kind(*local) {
-            *local = self.promote_temp(*local);
-        }
-    }
-}
-
-pub fn promote_candidates<'tcx>(
-    body: &mut Body<'tcx>,
-    tcx: TyCtxt<'tcx>,
-    mut temps: IndexVec<Local, TempState>,
-    candidates: Vec<Candidate>,
-) -> IndexVec<Promoted, Body<'tcx>> {
-    // Visit candidates in reverse, in case they're nested.
-    debug!("promote_candidates({:?})", candidates);
-
-    let mut promotions = IndexVec::new();
-
-    let mut extra_statements = vec![];
-    for candidate in candidates.into_iter().rev() {
-        let Location { block, statement_index } = candidate.location;
-        if let StatementKind::Assign(box (place, _)) = &body[block].statements[statement_index].kind
-        {
-            if let Some(local) = place.as_local() {
-                if temps[local] == TempState::PromotedOut {
-                    // Already promoted.
-                    continue;
-                }
-            }
-        }
-
-        // Declare return place local so that `mir::Body::new` doesn't complain.
-        let initial_locals = iter::once(LocalDecl::new(tcx.types.never, body.span)).collect();
-
-        let mut scope = body.source_scopes[body.source_info(candidate.location).scope].clone();
-        scope.parent_scope = None;
-
-        let mut promoted = Body::new(
-            body.source, // `promoted` gets filled in below
-            IndexVec::new(),
-            IndexVec::from_elem_n(scope, 1),
-            initial_locals,
-            IndexVec::new(),
-            0,
-            vec![],
-            body.span,
-            None,
-            body.tainted_by_errors,
-        );
-        promoted.phase = MirPhase::Analysis(AnalysisPhase::Initial);
-
-        let promoter = Promoter {
-            promoted,
-            tcx,
-            source: body,
-            temps: &mut temps,
-            extra_statements: &mut extra_statements,
-            keep_original: false,
-        };
-
-        let mut promoted = promoter.promote_candidate(candidate, promotions.len());
-        promoted.source.promoted = Some(promotions.next_index());
-        promotions.push(promoted);
-    }
-
-    // Insert each of `extra_statements` before its indicated location, which
-    // has to be done in reverse location order, to not invalidate the rest.
-    extra_statements.sort_by_key(|&(loc, _)| cmp::Reverse(loc));
-    for (loc, statement) in extra_statements {
-        body[loc.block].statements.insert(loc.statement_index, statement);
-    }
-
-    // Eliminate assignments to, and drops of promoted temps.
-    let promoted = |index: Local| temps[index] == TempState::PromotedOut;
-    for block in body.basic_blocks_mut() {
-        block.statements.retain(|statement| match &statement.kind {
-            StatementKind::Assign(box (place, _)) => {
-                if let Some(index) = place.as_local() {
-                    !promoted(index)
-                } else {
-                    true
-                }
-            }
-            StatementKind::StorageLive(index) | StatementKind::StorageDead(index) => {
-                !promoted(*index)
-            }
-            _ => true,
-        });
-        let terminator = block.terminator_mut();
-        if let TerminatorKind::Drop { place, target, .. } = &terminator.kind {
-            if let Some(index) = place.as_local() {
-                if promoted(index) {
-                    terminator.kind = TerminatorKind::Goto { target: *target };
-                }
-            }
-        }
-    }
-
-    promotions
-}