Move drop elaboration infrastructure.

`rustc_mir_dataflow/src/elaborate_drops.rs` contains some infrastructure
used by a few MIR passes: the `elaborate_drop` function, the
`DropElaborator` trait, etc.

`rustc_mir_transform/src/elaborate_drops.rs` (same file name, different
crate) contains the `ElaborateDrops` pass. It relies on a lot of the
infrastructure from `rustc_mir_dataflow/src/elaborate_drops.rs`.

It turns out that the drop infrastructure is only used in
`rustc_mir_transform`, so this commit moves it there. (The only
exception is the small `DropFlagState` type, which is moved to the
existing `rustc_mir_dataflow/src/drop_flag_effects.rs`.) The file is
renamed from `rustc_mir_dataflow/src/elaborate_drops.rs` to
`rustc_mir_transform/src/elaborate_drop.rs` (with no trailing `s`)
because (a) the `elaborate_drop` function is the most important export,
and (b) `rustc_mir_transform/src/elaborate_drops.rs` already exists.

All the infrastructure pieces that used to be `pub` are now
`pub(crate)`, because they are now only used within
`rustc_mir_transform`.

4 files changed, 22 insertions, 1046 deletions

diff --git a/compiler/rustc_mir_dataflow/src/drop_flag_effects.rs b/compiler/rustc_mir_dataflow/src/drop_flag_effects.rs
index e5cddd0e5e4..496a342cf4c 100644
--- a/compiler/rustc_mir_dataflow/src/drop_flag_effects.rs
+++ b/compiler/rustc_mir_dataflow/src/drop_flag_effects.rs
@@ -3,7 +3,26 @@ use rustc_middle::mir::{self, Body, Location, Terminator, TerminatorKind};
 use tracing::debug;
 
 use super::move_paths::{InitKind, LookupResult, MoveData, MovePathIndex};
-use crate::elaborate_drops::DropFlagState;
+
+/// The value of an inserted drop flag.
+#[derive(Debug, PartialEq, Eq, Copy, Clone)]
+pub enum DropFlagState {
+    /// The tracked value is initialized and needs to be dropped when leaving its scope.
+    Present,
+
+    /// The tracked value is uninitialized or was moved out of and does not need to be dropped when
+    /// leaving its scope.
+    Absent,
+}
+
+impl DropFlagState {
+    pub fn value(self) -> bool {
+        match self {
+            DropFlagState::Present => true,
+            DropFlagState::Absent => false,
+        }
+    }
+}
 
 pub fn move_path_children_matching<'tcx, F>(
     move_data: &MoveData<'tcx>,
diff --git a/compiler/rustc_mir_dataflow/src/elaborate_drops.rs b/compiler/rustc_mir_dataflow/src/elaborate_drops.rs
deleted file mode 100644
index c1c47ecccf3..00000000000
--- a/compiler/rustc_mir_dataflow/src/elaborate_drops.rs
+++ /dev/null
@@ -1,1042 +0,0 @@
-use std::{fmt, iter, mem};
-
-use rustc_abi::{FIRST_VARIANT, FieldIdx, VariantIdx};
-use rustc_hir::lang_items::LangItem;
-use rustc_index::Idx;
-use rustc_middle::mir::patch::MirPatch;
-use rustc_middle::mir::*;
-use rustc_middle::span_bug;
-use rustc_middle::ty::adjustment::PointerCoercion;
-use rustc_middle::ty::util::IntTypeExt;
-use rustc_middle::ty::{self, GenericArgsRef, Ty, TyCtxt};
-use rustc_span::DUMMY_SP;
-use rustc_span::source_map::Spanned;
-use tracing::{debug, instrument};
-
-/// The value of an inserted drop flag.
-#[derive(Debug, PartialEq, Eq, Copy, Clone)]
-pub enum DropFlagState {
-    /// The tracked value is initialized and needs to be dropped when leaving its scope.
-    Present,
-
-    /// The tracked value is uninitialized or was moved out of and does not need to be dropped when
-    /// leaving its scope.
-    Absent,
-}
-
-impl DropFlagState {
-    pub fn value(self) -> bool {
-        match self {
-            DropFlagState::Present => true,
-            DropFlagState::Absent => false,
-        }
-    }
-}
-
-/// Describes how/if a value should be dropped.
-#[derive(Debug)]
-pub enum DropStyle {
-    /// The value is already dead at the drop location, no drop will be executed.
-    Dead,
-
-    /// The value is known to always be initialized at the drop location, drop will always be
-    /// executed.
-    Static,
-
-    /// Whether the value needs to be dropped depends on its drop flag.
-    Conditional,
-
-    /// An "open" drop is one where only the fields of a value are dropped.
-    ///
-    /// For example, this happens when moving out of a struct field: The rest of the struct will be
-    /// dropped in such an "open" drop. It is also used to generate drop glue for the individual
-    /// components of a value, for example for dropping array elements.
-    Open,
-}
-
-/// Which drop flags to affect/check with an operation.
-#[derive(Debug)]
-pub enum DropFlagMode {
-    /// Only affect the top-level drop flag, not that of any contained fields.
-    Shallow,
-    /// Affect all nested drop flags in addition to the top-level one.
-    Deep,
-}
-
-/// Describes if unwinding is necessary and where to unwind to if a panic occurs.
-#[derive(Copy, Clone, Debug)]
-pub enum Unwind {
-    /// Unwind to this block.
-    To(BasicBlock),
-    /// Already in an unwind path, any panic will cause an abort.
-    InCleanup,
-}
-
-impl Unwind {
-    fn is_cleanup(self) -> bool {
-        match self {
-            Unwind::To(..) => false,
-            Unwind::InCleanup => true,
-        }
-    }
-
-    fn into_action(self) -> UnwindAction {
-        match self {
-            Unwind::To(bb) => UnwindAction::Cleanup(bb),
-            Unwind::InCleanup => UnwindAction::Terminate(UnwindTerminateReason::InCleanup),
-        }
-    }
-
-    fn map<F>(self, f: F) -> Self
-    where
-        F: FnOnce(BasicBlock) -> BasicBlock,
-    {
-        match self {
-            Unwind::To(bb) => Unwind::To(f(bb)),
-            Unwind::InCleanup => Unwind::InCleanup,
-        }
-    }
-}
-
-pub trait DropElaborator<'a, 'tcx>: fmt::Debug {
-    /// The type representing paths that can be moved out of.
-    ///
-    /// Users can move out of individual fields of a struct, such as `a.b.c`. This type is used to
-    /// represent such move paths. Sometimes tracking individual move paths is not necessary, in
-    /// which case this may be set to (for example) `()`.
-    type Path: Copy + fmt::Debug;
-
-    // Accessors
-
-    fn patch(&mut self) -> &mut MirPatch<'tcx>;
-    fn body(&self) -> &'a Body<'tcx>;
-    fn tcx(&self) -> TyCtxt<'tcx>;
-    fn typing_env(&self) -> ty::TypingEnv<'tcx>;
-
-    // Drop logic
-
-    /// Returns how `path` should be dropped, given `mode`.
-    fn drop_style(&self, path: Self::Path, mode: DropFlagMode) -> DropStyle;
-
-    /// Returns the drop flag of `path` as a MIR `Operand` (or `None` if `path` has no drop flag).
-    fn get_drop_flag(&mut self, path: Self::Path) -> Option<Operand<'tcx>>;
-
-    /// Modifies the MIR patch so that the drop flag of `path` (if any) is cleared at `location`.
-    ///
-    /// If `mode` is deep, drop flags of all child paths should also be cleared by inserting
-    /// additional statements.
-    fn clear_drop_flag(&mut self, location: Location, path: Self::Path, mode: DropFlagMode);
-
-    // Subpaths
-
-    /// Returns the subpath of a field of `path` (or `None` if there is no dedicated subpath).
-    ///
-    /// If this returns `None`, `field` will not get a dedicated drop flag.
-    fn field_subpath(&self, path: Self::Path, field: FieldIdx) -> Option<Self::Path>;
-
-    /// Returns the subpath of a dereference of `path` (or `None` if there is no dedicated subpath).
-    ///
-    /// If this returns `None`, `*path` will not get a dedicated drop flag.
-    ///
-    /// This is only relevant for `Box<T>`, where the contained `T` can be moved out of the box.
-    fn deref_subpath(&self, path: Self::Path) -> Option<Self::Path>;
-
-    /// Returns the subpath of downcasting `path` to one of its variants.
-    ///
-    /// If this returns `None`, the downcast of `path` will not get a dedicated drop flag.
-    fn downcast_subpath(&self, path: Self::Path, variant: VariantIdx) -> Option<Self::Path>;
-
-    /// Returns the subpath of indexing a fixed-size array `path`.
-    ///
-    /// If this returns `None`, elements of `path` will not get a dedicated drop flag.
-    ///
-    /// This is only relevant for array patterns, which can move out of individual array elements.
-    fn array_subpath(&self, path: Self::Path, index: u64, size: u64) -> Option<Self::Path>;
-}
-
-#[derive(Debug)]
-struct DropCtxt<'a, 'b, 'tcx, D>
-where
-    D: DropElaborator<'b, 'tcx>,
-{
-    elaborator: &'a mut D,
-
-    source_info: SourceInfo,
-
-    place: Place<'tcx>,
-    path: D::Path,
-    succ: BasicBlock,
-    unwind: Unwind,
-}
-
-/// "Elaborates" a drop of `place`/`path` and patches `bb`'s terminator to execute it.
-///
-/// The passed `elaborator` is used to determine what should happen at the drop terminator. It
-/// decides whether the drop can be statically determined or whether it needs a dynamic drop flag,
-/// and whether the drop is "open", ie. should be expanded to drop all subfields of the dropped
-/// value.
-///
-/// When this returns, the MIR patch in the `elaborator` contains the necessary changes.
-pub fn elaborate_drop<'b, 'tcx, D>(
-    elaborator: &mut D,
-    source_info: SourceInfo,
-    place: Place<'tcx>,
-    path: D::Path,
-    succ: BasicBlock,
-    unwind: Unwind,
-    bb: BasicBlock,
-) where
-    D: DropElaborator<'b, 'tcx>,
-    'tcx: 'b,
-{
-    DropCtxt { elaborator, source_info, place, path, succ, unwind }.elaborate_drop(bb)
-}
-
-impl<'a, 'b, 'tcx, D> DropCtxt<'a, 'b, 'tcx, D>
-where
-    D: DropElaborator<'b, 'tcx>,
-    'tcx: 'b,
-{
-    #[instrument(level = "trace", skip(self), ret)]
-    fn place_ty(&self, place: Place<'tcx>) -> Ty<'tcx> {
-        place.ty(self.elaborator.body(), self.tcx()).ty
-    }
-
-    fn tcx(&self) -> TyCtxt<'tcx> {
-        self.elaborator.tcx()
-    }
-
-    /// This elaborates a single drop instruction, located at `bb`, and
-    /// patches over it.
-    ///
-    /// The elaborated drop checks the drop flags to only drop what
-    /// is initialized.
-    ///
-    /// In addition, the relevant drop flags also need to be cleared
-    /// to avoid double-drops. However, in the middle of a complex
-    /// drop, one must avoid clearing some of the flags before they
-    /// are read, as that would cause a memory leak.
-    ///
-    /// In particular, when dropping an ADT, multiple fields may be
-    /// joined together under the `rest` subpath. They are all controlled
-    /// by the primary drop flag, but only the last rest-field dropped
-    /// should clear it (and it must also not clear anything else).
-    //
-    // FIXME: I think we should just control the flags externally,
-    // and then we do not need this machinery.
-    #[instrument(level = "debug")]
-    fn elaborate_drop(&mut self, bb: BasicBlock) {
-        match self.elaborator.drop_style(self.path, DropFlagMode::Deep) {
-            DropStyle::Dead => {
-                self.elaborator
-                    .patch()
-                    .patch_terminator(bb, TerminatorKind::Goto { target: self.succ });
-            }
-            DropStyle::Static => {
-                self.elaborator.patch().patch_terminator(
-                    bb,
-                    TerminatorKind::Drop {
-                        place: self.place,
-                        target: self.succ,
-                        unwind: self.unwind.into_action(),
-                        replace: false,
-                    },
-                );
-            }
-            DropStyle::Conditional => {
-                let drop_bb = self.complete_drop(self.succ, self.unwind);
-                self.elaborator
-                    .patch()
-                    .patch_terminator(bb, TerminatorKind::Goto { target: drop_bb });
-            }
-            DropStyle::Open => {
-                let drop_bb = self.open_drop();
-                self.elaborator
-                    .patch()
-                    .patch_terminator(bb, TerminatorKind::Goto { target: drop_bb });
-            }
-        }
-    }
-
-    /// Returns the place and move path for each field of `variant`,
-    /// (the move path is `None` if the field is a rest field).
-    fn move_paths_for_fields(
-        &self,
-        base_place: Place<'tcx>,
-        variant_path: D::Path,
-        variant: &'tcx ty::VariantDef,
-        args: GenericArgsRef<'tcx>,
-    ) -> Vec<(Place<'tcx>, Option<D::Path>)> {
-        variant
-            .fields
-            .iter()
-            .enumerate()
-            .map(|(i, f)| {
-                let field = FieldIdx::new(i);
-                let subpath = self.elaborator.field_subpath(variant_path, field);
-                let tcx = self.tcx();
-
-                assert_eq!(self.elaborator.typing_env().typing_mode, ty::TypingMode::PostAnalysis);
-                let field_ty =
-                    tcx.normalize_erasing_regions(self.elaborator.typing_env(), f.ty(tcx, args));
-
-                (tcx.mk_place_field(base_place, field, field_ty), subpath)
-            })
-            .collect()
-    }
-
-    fn drop_subpath(
-        &mut self,
-        place: Place<'tcx>,
-        path: Option<D::Path>,
-        succ: BasicBlock,
-        unwind: Unwind,
-    ) -> BasicBlock {
-        if let Some(path) = path {
-            debug!("drop_subpath: for std field {:?}", place);
-
-            DropCtxt {
-                elaborator: self.elaborator,
-                source_info: self.source_info,
-                path,
-                place,
-                succ,
-                unwind,
-            }
-            .elaborated_drop_block()
-        } else {
-            debug!("drop_subpath: for rest field {:?}", place);
-
-            DropCtxt {
-                elaborator: self.elaborator,
-                source_info: self.source_info,
-                place,
-                succ,
-                unwind,
-                // Using `self.path` here to condition the drop on
-                // our own drop flag.
-                path: self.path,
-            }
-            .complete_drop(succ, unwind)
-        }
-    }
-
-    /// Creates one-half of the drop ladder for a list of fields, and return
-    /// the list of steps in it in reverse order, with the first step
-    /// dropping 0 fields and so on.
-    ///
-    /// `unwind_ladder` is such a list of steps in reverse order,
-    /// which is called if the matching step of the drop glue panics.
-    fn drop_halfladder(
-        &mut self,
-        unwind_ladder: &[Unwind],
-        mut succ: BasicBlock,
-        fields: &[(Place<'tcx>, Option<D::Path>)],
-    ) -> Vec<BasicBlock> {
-        iter::once(succ)
-            .chain(fields.iter().rev().zip(unwind_ladder).map(|(&(place, path), &unwind_succ)| {
-                succ = self.drop_subpath(place, path, succ, unwind_succ);
-                succ
-            }))
-            .collect()
-    }
-
-    fn drop_ladder_bottom(&mut self) -> (BasicBlock, Unwind) {
-        // Clear the "master" drop flag at the end. This is needed
-        // because the "master" drop protects the ADT's discriminant,
-        // which is invalidated after the ADT is dropped.
-        (self.drop_flag_reset_block(DropFlagMode::Shallow, self.succ, self.unwind), self.unwind)
-    }
-
-    /// Creates a full drop ladder, consisting of 2 connected half-drop-ladders
-    ///
-    /// For example, with 3 fields, the drop ladder is
-    ///
-    /// .d0:
-    ///     ELAB(drop location.0 [target=.d1, unwind=.c1])
-    /// .d1:
-    ///     ELAB(drop location.1 [target=.d2, unwind=.c2])
-    /// .d2:
-    ///     ELAB(drop location.2 [target=`self.succ`, unwind=`self.unwind`])
-    /// .c1:
-    ///     ELAB(drop location.1 [target=.c2])
-    /// .c2:
-    ///     ELAB(drop location.2 [target=`self.unwind`])
-    ///
-    /// NOTE: this does not clear the master drop flag, so you need
-    /// to point succ/unwind on a `drop_ladder_bottom`.
-    fn drop_ladder(
-        &mut self,
-        fields: Vec<(Place<'tcx>, Option<D::Path>)>,
-        succ: BasicBlock,
-        unwind: Unwind,
-    ) -> (BasicBlock, Unwind) {
-        debug!("drop_ladder({:?}, {:?})", self, fields);
-
-        let mut fields = fields;
-        fields.retain(|&(place, _)| {
-            self.place_ty(place).needs_drop(self.tcx(), self.elaborator.typing_env())
-        });
-
-        debug!("drop_ladder - fields needing drop: {:?}", fields);
-
-        let unwind_ladder = vec![Unwind::InCleanup; fields.len() + 1];
-        let unwind_ladder: Vec<_> = if let Unwind::To(target) = unwind {
-            let halfladder = self.drop_halfladder(&unwind_ladder, target, &fields);
-            halfladder.into_iter().map(Unwind::To).collect()
-        } else {
-            unwind_ladder
-        };
-
-        let normal_ladder = self.drop_halfladder(&unwind_ladder, succ, &fields);
-
-        (*normal_ladder.last().unwrap(), *unwind_ladder.last().unwrap())
-    }
-
-    fn open_drop_for_tuple(&mut self, tys: &[Ty<'tcx>]) -> BasicBlock {
-        debug!("open_drop_for_tuple({:?}, {:?})", self, tys);
-
-        let fields = tys
-            .iter()
-            .enumerate()
-            .map(|(i, &ty)| {
-                (
-                    self.tcx().mk_place_field(self.place, FieldIdx::new(i), ty),
-                    self.elaborator.field_subpath(self.path, FieldIdx::new(i)),
-                )
-            })
-            .collect();
-
-        let (succ, unwind) = self.drop_ladder_bottom();
-        self.drop_ladder(fields, succ, unwind).0
-    }
-
-    /// Drops the T contained in a `Box<T>` if it has not been moved out of
-    #[instrument(level = "debug", ret)]
-    fn open_drop_for_box_contents(
-        &mut self,
-        adt: ty::AdtDef<'tcx>,
-        args: GenericArgsRef<'tcx>,
-        succ: BasicBlock,
-        unwind: Unwind,
-    ) -> BasicBlock {
-        // drop glue is sent straight to codegen
-        // box cannot be directly dereferenced
-        let unique_ty = adt.non_enum_variant().fields[FieldIdx::ZERO].ty(self.tcx(), args);
-        let unique_variant = unique_ty.ty_adt_def().unwrap().non_enum_variant();
-        let nonnull_ty = unique_variant.fields[FieldIdx::ZERO].ty(self.tcx(), args);
-        let ptr_ty = Ty::new_imm_ptr(self.tcx(), args[0].expect_ty());
-
-        let unique_place = self.tcx().mk_place_field(self.place, FieldIdx::ZERO, unique_ty);
-        let nonnull_place = self.tcx().mk_place_field(unique_place, FieldIdx::ZERO, nonnull_ty);
-        let ptr_place = self.tcx().mk_place_field(nonnull_place, FieldIdx::ZERO, ptr_ty);
-        let interior = self.tcx().mk_place_deref(ptr_place);
-
-        let interior_path = self.elaborator.deref_subpath(self.path);
-
-        self.drop_subpath(interior, interior_path, succ, unwind)
-    }
-
-    #[instrument(level = "debug", ret)]
-    fn open_drop_for_adt(
-        &mut self,
-        adt: ty::AdtDef<'tcx>,
-        args: GenericArgsRef<'tcx>,
-    ) -> BasicBlock {
-        if adt.variants().is_empty() {
-            return self.elaborator.patch().new_block(BasicBlockData {
-                statements: vec![],
-                terminator: Some(Terminator {
-                    source_info: self.source_info,
-                    kind: TerminatorKind::Unreachable,
-                }),
-                is_cleanup: self.unwind.is_cleanup(),
-            });
-        }
-
-        let skip_contents = adt.is_union() || adt.is_manually_drop();
-        let contents_drop = if skip_contents {
-            (self.succ, self.unwind)
-        } else {
-            self.open_drop_for_adt_contents(adt, args)
-        };
-
-        if adt.is_box() {
-            // we need to drop the inside of the box before running the destructor
-            let succ = self.destructor_call_block(contents_drop);
-            let unwind = contents_drop
-                .1
-                .map(|unwind| self.destructor_call_block((unwind, Unwind::InCleanup)));
-
-            self.open_drop_for_box_contents(adt, args, succ, unwind)
-        } else if adt.has_dtor(self.tcx()) {
-            self.destructor_call_block(contents_drop)
-        } else {
-            contents_drop.0
-        }
-    }
-
-    fn open_drop_for_adt_contents(
-        &mut self,
-        adt: ty::AdtDef<'tcx>,
-        args: GenericArgsRef<'tcx>,
-    ) -> (BasicBlock, Unwind) {
-        let (succ, unwind) = self.drop_ladder_bottom();
-        if !adt.is_enum() {
-            let fields =
-                self.move_paths_for_fields(self.place, self.path, adt.variant(FIRST_VARIANT), args);
-            self.drop_ladder(fields, succ, unwind)
-        } else {
-            self.open_drop_for_multivariant(adt, args, succ, unwind)
-        }
-    }
-
-    fn open_drop_for_multivariant(
-        &mut self,
-        adt: ty::AdtDef<'tcx>,
-        args: GenericArgsRef<'tcx>,
-        succ: BasicBlock,
-        unwind: Unwind,
-    ) -> (BasicBlock, Unwind) {
-        let mut values = Vec::with_capacity(adt.variants().len());
-        let mut normal_blocks = Vec::with_capacity(adt.variants().len());
-        let mut unwind_blocks =
-            if unwind.is_cleanup() { None } else { Some(Vec::with_capacity(adt.variants().len())) };
-
-        let mut have_otherwise_with_drop_glue = false;
-        let mut have_otherwise = false;
-        let tcx = self.tcx();
-
-        for (variant_index, discr) in adt.discriminants(tcx) {
-            let variant = &adt.variant(variant_index);
-            let subpath = self.elaborator.downcast_subpath(self.path, variant_index);
-
-            if let Some(variant_path) = subpath {
-                let base_place = tcx.mk_place_elem(
-                    self.place,
-                    ProjectionElem::Downcast(Some(variant.name), variant_index),
-                );
-                let fields = self.move_paths_for_fields(base_place, variant_path, variant, args);
-                values.push(discr.val);
-                if let Unwind::To(unwind) = unwind {
-                    // We can't use the half-ladder from the original
-                    // drop ladder, because this breaks the
-                    // "funclet can't have 2 successor funclets"
-                    // requirement from MSVC:
-                    //
-                    //           switch       unwind-switch
-                    //          /      \         /        \
-                    //         v1.0    v2.0  v2.0-unwind  v1.0-unwind
-                    //         |        |      /             |
-                    //    v1.1-unwind  v2.1-unwind           |
-                    //      ^                                |
-                    //       \-------------------------------/
-                    //
-                    // Create a duplicate half-ladder to avoid that. We
-                    // could technically only do this on MSVC, but I
-                    // I want to minimize the divergence between MSVC
-                    // and non-MSVC.
-
-                    let unwind_blocks = unwind_blocks.as_mut().unwrap();
-                    let unwind_ladder = vec![Unwind::InCleanup; fields.len() + 1];
-                    let halfladder = self.drop_halfladder(&unwind_ladder, unwind, &fields);
-                    unwind_blocks.push(halfladder.last().cloned().unwrap());
-                }
-                let (normal, _) = self.drop_ladder(fields, succ, unwind);
-                normal_blocks.push(normal);
-            } else {
-                have_otherwise = true;
-
-                let typing_env = self.elaborator.typing_env();
-                let have_field_with_drop_glue = variant
-                    .fields
-                    .iter()
-                    .any(|field| field.ty(tcx, args).needs_drop(tcx, typing_env));
-                if have_field_with_drop_glue {
-                    have_otherwise_with_drop_glue = true;
-                }
-            }
-        }
-
-        if !have_otherwise {
-            values.pop();
-        } else if !have_otherwise_with_drop_glue {
-            normal_blocks.push(self.goto_block(succ, unwind));
-            if let Unwind::To(unwind) = unwind {
-                unwind_blocks.as_mut().unwrap().push(self.goto_block(unwind, Unwind::InCleanup));
-            }
-        } else {
-            normal_blocks.push(self.drop_block(succ, unwind));
-            if let Unwind::To(unwind) = unwind {
-                unwind_blocks.as_mut().unwrap().push(self.drop_block(unwind, Unwind::InCleanup));
-            }
-        }
-
-        (
-            self.adt_switch_block(adt, normal_blocks, &values, succ, unwind),
-            unwind.map(|unwind| {
-                self.adt_switch_block(
-                    adt,
-                    unwind_blocks.unwrap(),
-                    &values,
-                    unwind,
-                    Unwind::InCleanup,
-                )
-            }),
-        )
-    }
-
-    fn adt_switch_block(
-        &mut self,
-        adt: ty::AdtDef<'tcx>,
-        blocks: Vec<BasicBlock>,
-        values: &[u128],
-        succ: BasicBlock,
-        unwind: Unwind,
-    ) -> BasicBlock {
-        // If there are multiple variants, then if something
-        // is present within the enum the discriminant, tracked
-        // by the rest path, must be initialized.
-        //
-        // Additionally, we do not want to switch on the
-        // discriminant after it is free-ed, because that
-        // way lies only trouble.
-        let discr_ty = adt.repr().discr_type().to_ty(self.tcx());
-        let discr = Place::from(self.new_temp(discr_ty));
-        let discr_rv = Rvalue::Discriminant(self.place);
-        let switch_block = BasicBlockData {
-            statements: vec![self.assign(discr, discr_rv)],
-            terminator: Some(Terminator {
-                source_info: self.source_info,
-                kind: TerminatorKind::SwitchInt {
-                    discr: Operand::Move(discr),
-                    targets: SwitchTargets::new(
-                        values.iter().copied().zip(blocks.iter().copied()),
-                        *blocks.last().unwrap(),
-                    ),
-                },
-            }),
-            is_cleanup: unwind.is_cleanup(),
-        };
-        let switch_block = self.elaborator.patch().new_block(switch_block);
-        self.drop_flag_test_block(switch_block, succ, unwind)
-    }
-
-    fn destructor_call_block(&mut self, (succ, unwind): (BasicBlock, Unwind)) -> BasicBlock {
-        debug!("destructor_call_block({:?}, {:?})", self, succ);
-        let tcx = self.tcx();
-        let drop_trait = tcx.require_lang_item(LangItem::Drop, None);
-        let drop_fn = tcx.associated_item_def_ids(drop_trait)[0];
-        let ty = self.place_ty(self.place);
-
-        let ref_ty = Ty::new_mut_ref(tcx, tcx.lifetimes.re_erased, ty);
-        let ref_place = self.new_temp(ref_ty);
-        let unit_temp = Place::from(self.new_temp(tcx.types.unit));
-
-        let result = BasicBlockData {
-            statements: vec![self.assign(
-                Place::from(ref_place),
-                Rvalue::Ref(
-                    tcx.lifetimes.re_erased,
-                    BorrowKind::Mut { kind: MutBorrowKind::Default },
-                    self.place,
-                ),
-            )],
-            terminator: Some(Terminator {
-                kind: TerminatorKind::Call {
-                    func: Operand::function_handle(
-                        tcx,
-                        drop_fn,
-                        [ty.into()],
-                        self.source_info.span,
-                    ),
-                    args: [Spanned { node: Operand::Move(Place::from(ref_place)), span: DUMMY_SP }]
-                        .into(),
-                    destination: unit_temp,
-                    target: Some(succ),
-                    unwind: unwind.into_action(),
-                    call_source: CallSource::Misc,
-                    fn_span: self.source_info.span,
-                },
-                source_info: self.source_info,
-            }),
-            is_cleanup: unwind.is_cleanup(),
-        };
-
-        let destructor_block = self.elaborator.patch().new_block(result);
-
-        let block_start = Location { block: destructor_block, statement_index: 0 };
-        self.elaborator.clear_drop_flag(block_start, self.path, DropFlagMode::Shallow);
-
-        self.drop_flag_test_block(destructor_block, succ, unwind)
-    }
-
-    /// Create a loop that drops an array:
-    ///
-    /// ```text
-    /// loop-block:
-    ///    can_go = cur == len
-    ///    if can_go then succ else drop-block
-    /// drop-block:
-    ///    ptr = &raw mut P[cur]
-    ///    cur = cur + 1
-    ///    drop(ptr)
-    /// ```
-    fn drop_loop(
-        &mut self,
-        succ: BasicBlock,
-        cur: Local,
-        len: Local,
-        ety: Ty<'tcx>,
-        unwind: Unwind,
-    ) -> BasicBlock {
-        let copy = |place: Place<'tcx>| Operand::Copy(place);
-        let move_ = |place: Place<'tcx>| Operand::Move(place);
-        let tcx = self.tcx();
-
-        let ptr_ty = Ty::new_mut_ptr(tcx, ety);
-        let ptr = Place::from(self.new_temp(ptr_ty));
-        let can_go = Place::from(self.new_temp(tcx.types.bool));
-        let one = self.constant_usize(1);
-
-        let drop_block = BasicBlockData {
-            statements: vec![
-                self.assign(
-                    ptr,
-                    Rvalue::RawPtr(RawPtrKind::Mut, tcx.mk_place_index(self.place, cur)),
-                ),
-                self.assign(
-                    cur.into(),
-                    Rvalue::BinaryOp(BinOp::Add, Box::new((move_(cur.into()), one))),
-                ),
-            ],
-            is_cleanup: unwind.is_cleanup(),
-            terminator: Some(Terminator {
-                source_info: self.source_info,
-                // this gets overwritten by drop elaboration.
-                kind: TerminatorKind::Unreachable,
-            }),
-        };
-        let drop_block = self.elaborator.patch().new_block(drop_block);
-
-        let loop_block = BasicBlockData {
-            statements: vec![self.assign(
-                can_go,
-                Rvalue::BinaryOp(BinOp::Eq, Box::new((copy(Place::from(cur)), copy(len.into())))),
-            )],
-            is_cleanup: unwind.is_cleanup(),
-            terminator: Some(Terminator {
-                source_info: self.source_info,
-                kind: TerminatorKind::if_(move_(can_go), succ, drop_block),
-            }),
-        };
-        let loop_block = self.elaborator.patch().new_block(loop_block);
-
-        self.elaborator.patch().patch_terminator(
-            drop_block,
-            TerminatorKind::Drop {
-                place: tcx.mk_place_deref(ptr),
-                target: loop_block,
-                unwind: unwind.into_action(),
-                replace: false,
-            },
-        );
-
-        loop_block
-    }
-
-    fn open_drop_for_array(
-        &mut self,
-        array_ty: Ty<'tcx>,
-        ety: Ty<'tcx>,
-        opt_size: Option<u64>,
-    ) -> BasicBlock {
-        debug!("open_drop_for_array({:?}, {:?}, {:?})", array_ty, ety, opt_size);
-        let tcx = self.tcx();
-
-        if let Some(size) = opt_size {
-            enum ProjectionKind<Path> {
-                Drop(std::ops::Range<u64>),
-                Keep(u64, Path),
-            }
-            // Previously, we'd make a projection for every element in the array and create a drop
-            // ladder if any `array_subpath` was `Some`, i.e. moving out with an array pattern.
-            // This caused huge memory usage when generating the drops for large arrays, so we instead
-            // record the *subslices* which are dropped and the *indexes* which are kept
-            let mut drop_ranges = vec![];
-            let mut dropping = true;
-            let mut start = 0;
-            for i in 0..size {
-                let path = self.elaborator.array_subpath(self.path, i, size);
-                if dropping && path.is_some() {
-                    drop_ranges.push(ProjectionKind::Drop(start..i));
-                    dropping = false;
-                } else if !dropping && path.is_none() {
-                    dropping = true;
-                    start = i;
-                }
-                if let Some(path) = path {
-                    drop_ranges.push(ProjectionKind::Keep(i, path));
-                }
-            }
-            if !drop_ranges.is_empty() {
-                if dropping {
-                    drop_ranges.push(ProjectionKind::Drop(start..size));
-                }
-                let fields = drop_ranges
-                    .iter()
-                    .rev()
-                    .map(|p| {
-                        let (project, path) = match p {
-                            ProjectionKind::Drop(r) => (
-                                ProjectionElem::Subslice {
-                                    from: r.start,
-                                    to: r.end,
-                                    from_end: false,
-                                },
-                                None,
-                            ),
-                            &ProjectionKind::Keep(offset, path) => (
-                                ProjectionElem::ConstantIndex {
-                                    offset,
-                                    min_length: size,
-                                    from_end: false,
-                                },
-                                Some(path),
-                            ),
-                        };
-                        (tcx.mk_place_elem(self.place, project), path)
-                    })
-                    .collect::<Vec<_>>();
-                let (succ, unwind) = self.drop_ladder_bottom();
-                return self.drop_ladder(fields, succ, unwind).0;
-            }
-        }
-
-        let array_ptr_ty = Ty::new_mut_ptr(tcx, array_ty);
-        let array_ptr = self.new_temp(array_ptr_ty);
-
-        let slice_ty = Ty::new_slice(tcx, ety);
-        let slice_ptr_ty = Ty::new_mut_ptr(tcx, slice_ty);
-        let slice_ptr = self.new_temp(slice_ptr_ty);
-
-        let mut delegate_block = BasicBlockData {
-            statements: vec![
-                self.assign(Place::from(array_ptr), Rvalue::RawPtr(RawPtrKind::Mut, self.place)),
-                self.assign(
-                    Place::from(slice_ptr),
-                    Rvalue::Cast(
-                        CastKind::PointerCoercion(
-                            PointerCoercion::Unsize,
-                            CoercionSource::Implicit,
-                        ),
-                        Operand::Move(Place::from(array_ptr)),
-                        slice_ptr_ty,
-                    ),
-                ),
-            ],
-            is_cleanup: self.unwind.is_cleanup(),
-            terminator: None,
-        };
-
-        let array_place = mem::replace(
-            &mut self.place,
-            Place::from(slice_ptr).project_deeper(&[PlaceElem::Deref], tcx),
-        );
-        let slice_block = self.drop_loop_pair_for_slice(ety);
-        self.place = array_place;
-
-        delegate_block.terminator = Some(Terminator {
-            source_info: self.source_info,
-            kind: TerminatorKind::Goto { target: slice_block },
-        });
-        self.elaborator.patch().new_block(delegate_block)
-    }
-
-    /// Creates a pair of drop-loops of `place`, which drops its contents, even
-    /// in the case of 1 panic.
-    fn drop_loop_pair_for_slice(&mut self, ety: Ty<'tcx>) -> BasicBlock {
-        debug!("drop_loop_pair_for_slice({:?})", ety);
-        let tcx = self.tcx();
-        let len = self.new_temp(tcx.types.usize);
-        let cur = self.new_temp(tcx.types.usize);
-
-        let unwind =
-            self.unwind.map(|unwind| self.drop_loop(unwind, cur, len, ety, Unwind::InCleanup));
-
-        let loop_block = self.drop_loop(self.succ, cur, len, ety, unwind);
-
-        let [PlaceElem::Deref] = self.place.projection.as_slice() else {
-            span_bug!(
-                self.source_info.span,
-                "Expected place for slice drop shim to be *_n, but it's {:?}",
-                self.place,
-            );
-        };
-
-        let zero = self.constant_usize(0);
-        let block = BasicBlockData {
-            statements: vec![
-                self.assign(
-                    len.into(),
-                    Rvalue::UnaryOp(
-                        UnOp::PtrMetadata,
-                        Operand::Copy(Place::from(self.place.local)),
-                    ),
-                ),
-                self.assign(cur.into(), Rvalue::Use(zero)),
-            ],
-            is_cleanup: unwind.is_cleanup(),
-            terminator: Some(Terminator {
-                source_info: self.source_info,
-                kind: TerminatorKind::Goto { target: loop_block },
-            }),
-        };
-
-        let drop_block = self.elaborator.patch().new_block(block);
-        // FIXME(#34708): handle partially-dropped array/slice elements.
-        let reset_block = self.drop_flag_reset_block(DropFlagMode::Deep, drop_block, unwind);
-        self.drop_flag_test_block(reset_block, self.succ, unwind)
-    }
-
-    /// The slow-path - create an "open", elaborated drop for a type
-    /// which is moved-out-of only partially, and patch `bb` to a jump
-    /// to it. This must not be called on ADTs with a destructor,
-    /// as these can't be moved-out-of, except for `Box<T>`, which is
-    /// special-cased.
-    ///
-    /// This creates a "drop ladder" that drops the needed fields of the
-    /// ADT, both in the success case or if one of the destructors fail.
-    fn open_drop(&mut self) -> BasicBlock {
-        let ty = self.place_ty(self.place);
-        match ty.kind() {
-            ty::Closure(_, args) => self.open_drop_for_tuple(args.as_closure().upvar_tys()),
-            ty::CoroutineClosure(_, args) => {
-                self.open_drop_for_tuple(args.as_coroutine_closure().upvar_tys())
-            }
-            // Note that `elaborate_drops` only drops the upvars of a coroutine,
-            // and this is ok because `open_drop` here can only be reached
-            // within that own coroutine's resume function.
-            // This should only happen for the self argument on the resume function.
-            // It effectively only contains upvars until the coroutine transformation runs.
-            // See librustc_body/transform/coroutine.rs for more details.
-            ty::Coroutine(_, args) => self.open_drop_for_tuple(args.as_coroutine().upvar_tys()),
-            ty::Tuple(fields) => self.open_drop_for_tuple(fields),
-            ty::Adt(def, args) => self.open_drop_for_adt(*def, args),
-            ty::Dynamic(..) => self.complete_drop(self.succ, self.unwind),
-            ty::Array(ety, size) => {
-                let size = size.try_to_target_usize(self.tcx());
-                self.open_drop_for_array(ty, *ety, size)
-            }
-            ty::Slice(ety) => self.drop_loop_pair_for_slice(*ety),
-
-            _ => span_bug!(self.source_info.span, "open drop from non-ADT `{:?}`", ty),
-        }
-    }
-
-    fn complete_drop(&mut self, succ: BasicBlock, unwind: Unwind) -> BasicBlock {
-        debug!("complete_drop(succ={:?}, unwind={:?})", succ, unwind);
-
-        let drop_block = self.drop_block(succ, unwind);
-
-        self.drop_flag_test_block(drop_block, succ, unwind)
-    }
-
-    /// Creates a block that resets the drop flag. If `mode` is deep, all children drop flags will
-    /// also be cleared.
-    fn drop_flag_reset_block(
-        &mut self,
-        mode: DropFlagMode,
-        succ: BasicBlock,
-        unwind: Unwind,
-    ) -> BasicBlock {
-        debug!("drop_flag_reset_block({:?},{:?})", self, mode);
-
-        if unwind.is_cleanup() {
-            // The drop flag isn't read again on the unwind path, so don't
-            // bother setting it.
-            return succ;
-        }
-        let block = self.new_block(unwind, TerminatorKind::Goto { target: succ });
-        let block_start = Location { block, statement_index: 0 };
-        self.elaborator.clear_drop_flag(block_start, self.path, mode);
-        block
-    }
-
-    fn elaborated_drop_block(&mut self) -> BasicBlock {
-        debug!("elaborated_drop_block({:?})", self);
-        let blk = self.drop_block(self.succ, self.unwind);
-        self.elaborate_drop(blk);
-        blk
-    }
-
-    fn drop_block(&mut self, target: BasicBlock, unwind: Unwind) -> BasicBlock {
-        let block = TerminatorKind::Drop {
-            place: self.place,
-            target,
-            unwind: unwind.into_action(),
-            replace: false,
-        };
-        self.new_block(unwind, block)
-    }
-
-    fn goto_block(&mut self, target: BasicBlock, unwind: Unwind) -> BasicBlock {
-        let block = TerminatorKind::Goto { target };
-        self.new_block(unwind, block)
-    }
-
-    /// Returns the block to jump to in order to test the drop flag and execute the drop.
-    ///
-    /// Depending on the required `DropStyle`, this might be a generated block with an `if`
-    /// terminator (for dynamic/open drops), or it might be `on_set` or `on_unset` itself, in case
-    /// the drop can be statically determined.
-    fn drop_flag_test_block(
-        &mut self,
-        on_set: BasicBlock,
-        on_unset: BasicBlock,
-        unwind: Unwind,
-    ) -> BasicBlock {
-        let style = self.elaborator.drop_style(self.path, DropFlagMode::Shallow);
-        debug!(
-            "drop_flag_test_block({:?},{:?},{:?},{:?}) - {:?}",
-            self, on_set, on_unset, unwind, style
-        );
-
-        match style {
-            DropStyle::Dead => on_unset,
-            DropStyle::Static => on_set,
-            DropStyle::Conditional | DropStyle::Open => {
-                let flag = self.elaborator.get_drop_flag(self.path).unwrap();
-                let term = TerminatorKind::if_(flag, on_set, on_unset);
-                self.new_block(unwind, term)
-            }
-        }
-    }
-
-    fn new_block(&mut self, unwind: Unwind, k: TerminatorKind<'tcx>) -> BasicBlock {
-        self.elaborator.patch().new_block(BasicBlockData {
-            statements: vec![],
-            terminator: Some(Terminator { source_info: self.source_info, kind: k }),
-            is_cleanup: unwind.is_cleanup(),
-        })
-    }
-
-    fn new_temp(&mut self, ty: Ty<'tcx>) -> Local {
-        self.elaborator.patch().new_temp(ty, self.source_info.span)
-    }
-
-    fn constant_usize(&self, val: u16) -> Operand<'tcx> {
-        Operand::Constant(Box::new(ConstOperand {
-            span: self.source_info.span,
-            user_ty: None,
-            const_: Const::from_usize(self.tcx(), val.into()),
-        }))
-    }
-
-    fn assign(&self, lhs: Place<'tcx>, rhs: Rvalue<'tcx>) -> Statement<'tcx> {
-        Statement {
-            source_info: self.source_info,
-            kind: StatementKind::Assign(Box::new((lhs, rhs))),
-        }
-    }
-}
diff --git a/compiler/rustc_mir_dataflow/src/impls/initialized.rs b/compiler/rustc_mir_dataflow/src/impls/initialized.rs
index 760f94af52d..3be450a0b3f 100644
--- a/compiler/rustc_mir_dataflow/src/impls/initialized.rs
+++ b/compiler/rustc_mir_dataflow/src/impls/initialized.rs
@@ -9,7 +9,7 @@ use rustc_middle::ty::util::Discr;
 use rustc_middle::ty::{self, TyCtxt};
 use tracing::{debug, instrument};
 
-use crate::elaborate_drops::DropFlagState;
+use crate::drop_flag_effects::DropFlagState;
 use crate::framework::SwitchIntTarget;
 use crate::move_paths::{HasMoveData, InitIndex, InitKind, LookupResult, MoveData, MovePathIndex};
 use crate::{
diff --git a/compiler/rustc_mir_dataflow/src/lib.rs b/compiler/rustc_mir_dataflow/src/lib.rs
index 0cc79b0c939..a8a56baa1ff 100644
--- a/compiler/rustc_mir_dataflow/src/lib.rs
+++ b/compiler/rustc_mir_dataflow/src/lib.rs
@@ -15,7 +15,7 @@ use rustc_middle::ty;
 // Please change the public `use` directives cautiously, as they might be used by external tools.
 // See issue #120130.
 pub use self::drop_flag_effects::{
-    drop_flag_effects_for_function_entry, drop_flag_effects_for_location,
+    DropFlagState, drop_flag_effects_for_function_entry, drop_flag_effects_for_location,
     move_path_children_matching, on_all_children_bits, on_lookup_result_bits,
 };
 pub use self::framework::{
@@ -26,7 +26,6 @@ use self::move_paths::MoveData;
 
 pub mod debuginfo;
 mod drop_flag_effects;
-pub mod elaborate_drops;
 mod errors;
 mod framework;
 pub mod impls;