Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 734 insertions, 0 deletions

diff --git a/compiler/rustc_mir_transform/src/const_prop_lint.rs b/compiler/rustc_mir_transform/src/const_prop_lint.rs
new file mode 100644
index 000000000..c2ea55af4
--- /dev/null
+++ b/compiler/rustc_mir_transform/src/const_prop_lint.rs
@@ -0,0 +1,734 @@
+//! Propagates constants for early reporting of statically known
+//! assertion failures
+
+use crate::const_prop::CanConstProp;
+use crate::const_prop::ConstPropMachine;
+use crate::const_prop::ConstPropMode;
+use crate::MirLint;
+use rustc_const_eval::const_eval::ConstEvalErr;
+use rustc_const_eval::interpret::{
+    self, InterpCx, InterpResult, LocalState, LocalValue, MemoryKind, OpTy, Scalar,
+    ScalarMaybeUninit, StackPopCleanup,
+};
+use rustc_hir::def::DefKind;
+use rustc_hir::HirId;
+use rustc_index::bit_set::BitSet;
+use rustc_index::vec::IndexVec;
+use rustc_middle::mir::visit::Visitor;
+use rustc_middle::mir::{
+    AssertKind, BinOp, Body, Constant, ConstantKind, Local, LocalDecl, Location, Operand, Place,
+    Rvalue, SourceInfo, SourceScope, SourceScopeData, Statement, StatementKind, Terminator,
+    TerminatorKind, UnOp, RETURN_PLACE,
+};
+use rustc_middle::ty::layout::{LayoutError, LayoutOf, LayoutOfHelpers, TyAndLayout};
+use rustc_middle::ty::subst::{InternalSubsts, Subst};
+use rustc_middle::ty::{
+    self, ConstInt, ConstKind, Instance, ParamEnv, ScalarInt, Ty, TyCtxt, TypeVisitable,
+};
+use rustc_session::lint;
+use rustc_span::Span;
+use rustc_target::abi::{HasDataLayout, Size, TargetDataLayout};
+use rustc_trait_selection::traits;
+use std::cell::Cell;
+
+/// The maximum number of bytes that we'll allocate space for a local or the return value.
+/// Needed for #66397, because otherwise we eval into large places and that can cause OOM or just
+/// Severely regress performance.
+const MAX_ALLOC_LIMIT: u64 = 1024;
+pub struct ConstProp;
+
+impl<'tcx> MirLint<'tcx> for ConstProp {
+    fn run_lint(&self, tcx: TyCtxt<'tcx>, body: &Body<'tcx>) {
+        // will be evaluated by miri and produce its errors there
+        if body.source.promoted.is_some() {
+            return;
+        }
+
+        let def_id = body.source.def_id().expect_local();
+        let is_fn_like = tcx.def_kind(def_id).is_fn_like();
+        let is_assoc_const = tcx.def_kind(def_id) == DefKind::AssocConst;
+
+        // Only run const prop on functions, methods, closures and associated constants
+        if !is_fn_like && !is_assoc_const {
+            // skip anon_const/statics/consts because they'll be evaluated by miri anyway
+            trace!("ConstProp skipped for {:?}", def_id);
+            return;
+        }
+
+        let is_generator = tcx.type_of(def_id.to_def_id()).is_generator();
+        // FIXME(welseywiser) const prop doesn't work on generators because of query cycles
+        // computing their layout.
+        if is_generator {
+            trace!("ConstProp skipped for generator {:?}", def_id);
+            return;
+        }
+
+        // Check if it's even possible to satisfy the 'where' clauses
+        // for this item.
+        // This branch will never be taken for any normal function.
+        // However, it's possible to `#!feature(trivial_bounds)]` to write
+        // a function with impossible to satisfy clauses, e.g.:
+        // `fn foo() where String: Copy {}`
+        //
+        // We don't usually need to worry about this kind of case,
+        // since we would get a compilation error if the user tried
+        // to call it. However, since we can do const propagation
+        // even without any calls to the function, we need to make
+        // sure that it even makes sense to try to evaluate the body.
+        // If there are unsatisfiable where clauses, then all bets are
+        // off, and we just give up.
+        //
+        // We manually filter the predicates, skipping anything that's not
+        // "global". We are in a potentially generic context
+        // (e.g. we are evaluating a function without substituting generic
+        // parameters, so this filtering serves two purposes:
+        //
+        // 1. We skip evaluating any predicates that we would
+        // never be able prove are unsatisfiable (e.g. `<T as Foo>`
+        // 2. We avoid trying to normalize predicates involving generic
+        // parameters (e.g. `<T as Foo>::MyItem`). This can confuse
+        // the normalization code (leading to cycle errors), since
+        // it's usually never invoked in this way.
+        let predicates = tcx
+            .predicates_of(def_id.to_def_id())
+            .predicates
+            .iter()
+            .filter_map(|(p, _)| if p.is_global() { Some(*p) } else { None });
+        if traits::impossible_predicates(
+            tcx,
+            traits::elaborate_predicates(tcx, predicates).map(|o| o.predicate).collect(),
+        ) {
+            trace!("ConstProp skipped for {:?}: found unsatisfiable predicates", def_id);
+            return;
+        }
+
+        trace!("ConstProp starting for {:?}", def_id);
+
+        let dummy_body = &Body::new(
+            body.source,
+            body.basic_blocks().clone(),
+            body.source_scopes.clone(),
+            body.local_decls.clone(),
+            Default::default(),
+            body.arg_count,
+            Default::default(),
+            body.span,
+            body.generator_kind(),
+            body.tainted_by_errors,
+        );
+
+        // FIXME(oli-obk, eddyb) Optimize locals (or even local paths) to hold
+        // constants, instead of just checking for const-folding succeeding.
+        // That would require a uniform one-def no-mutation analysis
+        // and RPO (or recursing when needing the value of a local).
+        let mut optimization_finder = ConstPropagator::new(body, dummy_body, tcx);
+        optimization_finder.visit_body(body);
+
+        trace!("ConstProp done for {:?}", def_id);
+    }
+}
+
+/// Finds optimization opportunities on the MIR.
+struct ConstPropagator<'mir, 'tcx> {
+    ecx: InterpCx<'mir, 'tcx, ConstPropMachine<'mir, 'tcx>>,
+    tcx: TyCtxt<'tcx>,
+    param_env: ParamEnv<'tcx>,
+    source_scopes: &'mir IndexVec<SourceScope, SourceScopeData<'tcx>>,
+    local_decls: &'mir IndexVec<Local, LocalDecl<'tcx>>,
+    // Because we have `MutVisitor` we can't obtain the `SourceInfo` from a `Location`. So we store
+    // the last known `SourceInfo` here and just keep revisiting it.
+    source_info: Option<SourceInfo>,
+}
+
+impl<'tcx> LayoutOfHelpers<'tcx> for ConstPropagator<'_, 'tcx> {
+    type LayoutOfResult = Result<TyAndLayout<'tcx>, LayoutError<'tcx>>;
+
+    #[inline]
+    fn handle_layout_err(&self, err: LayoutError<'tcx>, _: Span, _: Ty<'tcx>) -> LayoutError<'tcx> {
+        err
+    }
+}
+
+impl HasDataLayout for ConstPropagator<'_, '_> {
+    #[inline]
+    fn data_layout(&self) -> &TargetDataLayout {
+        &self.tcx.data_layout
+    }
+}
+
+impl<'tcx> ty::layout::HasTyCtxt<'tcx> for ConstPropagator<'_, 'tcx> {
+    #[inline]
+    fn tcx(&self) -> TyCtxt<'tcx> {
+        self.tcx
+    }
+}
+
+impl<'tcx> ty::layout::HasParamEnv<'tcx> for ConstPropagator<'_, 'tcx> {
+    #[inline]
+    fn param_env(&self) -> ty::ParamEnv<'tcx> {
+        self.param_env
+    }
+}
+
+impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
+    fn new(
+        body: &Body<'tcx>,
+        dummy_body: &'mir Body<'tcx>,
+        tcx: TyCtxt<'tcx>,
+    ) -> ConstPropagator<'mir, 'tcx> {
+        let def_id = body.source.def_id();
+        let substs = &InternalSubsts::identity_for_item(tcx, def_id);
+        let param_env = tcx.param_env_reveal_all_normalized(def_id);
+
+        let can_const_prop = CanConstProp::check(tcx, param_env, body);
+        let mut only_propagate_inside_block_locals = BitSet::new_empty(can_const_prop.len());
+        for (l, mode) in can_const_prop.iter_enumerated() {
+            if *mode == ConstPropMode::OnlyInsideOwnBlock {
+                only_propagate_inside_block_locals.insert(l);
+            }
+        }
+        let mut ecx = InterpCx::new(
+            tcx,
+            tcx.def_span(def_id),
+            param_env,
+            ConstPropMachine::new(only_propagate_inside_block_locals, can_const_prop),
+        );
+
+        let ret_layout = ecx
+            .layout_of(body.bound_return_ty().subst(tcx, substs))
+            .ok()
+            // Don't bother allocating memory for large values.
+            // I don't know how return types can seem to be unsized but this happens in the
+            // `type/type-unsatisfiable.rs` test.
+            .filter(|ret_layout| {
+                !ret_layout.is_unsized() && ret_layout.size < Size::from_bytes(MAX_ALLOC_LIMIT)
+            })
+            .unwrap_or_else(|| ecx.layout_of(tcx.types.unit).unwrap());
+
+        let ret = ecx
+            .allocate(ret_layout, MemoryKind::Stack)
+            .expect("couldn't perform small allocation")
+            .into();
+
+        ecx.push_stack_frame(
+            Instance::new(def_id, substs),
+            dummy_body,
+            &ret,
+            StackPopCleanup::Root { cleanup: false },
+        )
+        .expect("failed to push initial stack frame");
+
+        ConstPropagator {
+            ecx,
+            tcx,
+            param_env,
+            source_scopes: &dummy_body.source_scopes,
+            local_decls: &dummy_body.local_decls,
+            source_info: None,
+        }
+    }
+
+    fn get_const(&self, place: Place<'tcx>) -> Option<OpTy<'tcx>> {
+        let op = match self.ecx.eval_place_to_op(place, None) {
+            Ok(op) => op,
+            Err(e) => {
+                trace!("get_const failed: {}", e);
+                return None;
+            }
+        };
+
+        // Try to read the local as an immediate so that if it is representable as a scalar, we can
+        // handle it as such, but otherwise, just return the value as is.
+        Some(match self.ecx.read_immediate_raw(&op, /*force*/ false) {
+            Ok(Ok(imm)) => imm.into(),
+            _ => op,
+        })
+    }
+
+    /// Remove `local` from the pool of `Locals`. Allows writing to them,
+    /// but not reading from them anymore.
+    fn remove_const(ecx: &mut InterpCx<'mir, 'tcx, ConstPropMachine<'mir, 'tcx>>, local: Local) {
+        ecx.frame_mut().locals[local] = LocalState {
+            value: LocalValue::Live(interpret::Operand::Immediate(interpret::Immediate::Uninit)),
+            layout: Cell::new(None),
+        };
+    }
+
+    fn lint_root(&self, source_info: SourceInfo) -> Option<HirId> {
+        source_info.scope.lint_root(self.source_scopes)
+    }
+
+    fn use_ecx<F, T>(&mut self, source_info: SourceInfo, f: F) -> Option<T>
+    where
+        F: FnOnce(&mut Self) -> InterpResult<'tcx, T>,
+    {
+        // Overwrite the PC -- whatever the interpreter does to it does not make any sense anyway.
+        self.ecx.frame_mut().loc = Err(source_info.span);
+        match f(self) {
+            Ok(val) => Some(val),
+            Err(error) => {
+                trace!("InterpCx operation failed: {:?}", error);
+                // Some errors shouldn't come up because creating them causes
+                // an allocation, which we should avoid. When that happens,
+                // dedicated error variants should be introduced instead.
+                assert!(
+                    !error.kind().formatted_string(),
+                    "const-prop encountered formatting error: {}",
+                    error
+                );
+                None
+            }
+        }
+    }
+
+    /// Returns the value, if any, of evaluating `c`.
+    fn eval_constant(&mut self, c: &Constant<'tcx>, source_info: SourceInfo) -> Option<OpTy<'tcx>> {
+        // FIXME we need to revisit this for #67176
+        if c.needs_subst() {
+            return None;
+        }
+
+        match self.ecx.mir_const_to_op(&c.literal, None) {
+            Ok(op) => Some(op),
+            Err(error) => {
+                let tcx = self.ecx.tcx.at(c.span);
+                let err = ConstEvalErr::new(&self.ecx, error, Some(c.span));
+                if let Some(lint_root) = self.lint_root(source_info) {
+                    let lint_only = match c.literal {
+                        ConstantKind::Ty(ct) => match ct.kind() {
+                            // Promoteds must lint and not error as the user didn't ask for them
+                            ConstKind::Unevaluated(ty::Unevaluated {
+                                def: _,
+                                substs: _,
+                                promoted: Some(_),
+                            }) => true,
+                            // Out of backwards compatibility we cannot report hard errors in unused
+                            // generic functions using associated constants of the generic parameters.
+                            _ => c.literal.needs_subst(),
+                        },
+                        ConstantKind::Val(_, ty) => ty.needs_subst(),
+                    };
+                    if lint_only {
+                        // Out of backwards compatibility we cannot report hard errors in unused
+                        // generic functions using associated constants of the generic parameters.
+                        err.report_as_lint(tcx, "erroneous constant used", lint_root, Some(c.span));
+                    } else {
+                        err.report_as_error(tcx, "erroneous constant used");
+                    }
+                } else {
+                    err.report_as_error(tcx, "erroneous constant used");
+                }
+                None
+            }
+        }
+    }
+
+    /// Returns the value, if any, of evaluating `place`.
+    fn eval_place(&mut self, place: Place<'tcx>, source_info: SourceInfo) -> Option<OpTy<'tcx>> {
+        trace!("eval_place(place={:?})", place);
+        self.use_ecx(source_info, |this| this.ecx.eval_place_to_op(place, None))
+    }
+
+    /// Returns the value, if any, of evaluating `op`. Calls upon `eval_constant`
+    /// or `eval_place`, depending on the variant of `Operand` used.
+    fn eval_operand(&mut self, op: &Operand<'tcx>, source_info: SourceInfo) -> Option<OpTy<'tcx>> {
+        match *op {
+            Operand::Constant(ref c) => self.eval_constant(c, source_info),
+            Operand::Move(place) | Operand::Copy(place) => self.eval_place(place, source_info),
+        }
+    }
+
+    fn report_assert_as_lint(
+        &self,
+        lint: &'static lint::Lint,
+        source_info: SourceInfo,
+        message: &'static str,
+        panic: AssertKind<impl std::fmt::Debug>,
+    ) {
+        if let Some(lint_root) = self.lint_root(source_info) {
+            self.tcx.struct_span_lint_hir(lint, lint_root, source_info.span, |lint| {
+                let mut err = lint.build(message);
+                err.span_label(source_info.span, format!("{:?}", panic));
+                err.emit();
+            });
+        }
+    }
+
+    fn check_unary_op(
+        &mut self,
+        op: UnOp,
+        arg: &Operand<'tcx>,
+        source_info: SourceInfo,
+    ) -> Option<()> {
+        if let (val, true) = self.use_ecx(source_info, |this| {
+            let val = this.ecx.read_immediate(&this.ecx.eval_operand(arg, None)?)?;
+            let (_res, overflow, _ty) = this.ecx.overflowing_unary_op(op, &val)?;
+            Ok((val, overflow))
+        })? {
+            // `AssertKind` only has an `OverflowNeg` variant, so make sure that is
+            // appropriate to use.
+            assert_eq!(op, UnOp::Neg, "Neg is the only UnOp that can overflow");
+            self.report_assert_as_lint(
+                lint::builtin::ARITHMETIC_OVERFLOW,
+                source_info,
+                "this arithmetic operation will overflow",
+                AssertKind::OverflowNeg(val.to_const_int()),
+            );
+            return None;
+        }
+
+        Some(())
+    }
+
+    fn check_binary_op(
+        &mut self,
+        op: BinOp,
+        left: &Operand<'tcx>,
+        right: &Operand<'tcx>,
+        source_info: SourceInfo,
+    ) -> Option<()> {
+        let r = self.use_ecx(source_info, |this| {
+            this.ecx.read_immediate(&this.ecx.eval_operand(right, None)?)
+        });
+        let l = self.use_ecx(source_info, |this| {
+            this.ecx.read_immediate(&this.ecx.eval_operand(left, None)?)
+        });
+        // Check for exceeding shifts *even if* we cannot evaluate the LHS.
+        if op == BinOp::Shr || op == BinOp::Shl {
+            let r = r.clone()?;
+            // We need the type of the LHS. We cannot use `place_layout` as that is the type
+            // of the result, which for checked binops is not the same!
+            let left_ty = left.ty(self.local_decls, self.tcx);
+            let left_size = self.ecx.layout_of(left_ty).ok()?.size;
+            let right_size = r.layout.size;
+            let r_bits = r.to_scalar().ok();
+            let r_bits = r_bits.and_then(|r| r.to_bits(right_size).ok());
+            if r_bits.map_or(false, |b| b >= left_size.bits() as u128) {
+                debug!("check_binary_op: reporting assert for {:?}", source_info);
+                self.report_assert_as_lint(
+                    lint::builtin::ARITHMETIC_OVERFLOW,
+                    source_info,
+                    "this arithmetic operation will overflow",
+                    AssertKind::Overflow(
+                        op,
+                        match l {
+                            Some(l) => l.to_const_int(),
+                            // Invent a dummy value, the diagnostic ignores it anyway
+                            None => ConstInt::new(
+                                ScalarInt::try_from_uint(1_u8, left_size).unwrap(),
+                                left_ty.is_signed(),
+                                left_ty.is_ptr_sized_integral(),
+                            ),
+                        },
+                        r.to_const_int(),
+                    ),
+                );
+                return None;
+            }
+        }
+
+        if let (Some(l), Some(r)) = (l, r) {
+            // The remaining operators are handled through `overflowing_binary_op`.
+            if self.use_ecx(source_info, |this| {
+                let (_res, overflow, _ty) = this.ecx.overflowing_binary_op(op, &l, &r)?;
+                Ok(overflow)
+            })? {
+                self.report_assert_as_lint(
+                    lint::builtin::ARITHMETIC_OVERFLOW,
+                    source_info,
+                    "this arithmetic operation will overflow",
+                    AssertKind::Overflow(op, l.to_const_int(), r.to_const_int()),
+                );
+                return None;
+            }
+        }
+        Some(())
+    }
+
+    fn const_prop(
+        &mut self,
+        rvalue: &Rvalue<'tcx>,
+        source_info: SourceInfo,
+        place: Place<'tcx>,
+    ) -> Option<()> {
+        // Perform any special handling for specific Rvalue types.
+        // Generally, checks here fall into one of two categories:
+        //   1. Additional checking to provide useful lints to the user
+        //        - In this case, we will do some validation and then fall through to the
+        //          end of the function which evals the assignment.
+        //   2. Working around bugs in other parts of the compiler
+        //        - In this case, we'll return `None` from this function to stop evaluation.
+        match rvalue {
+            // Additional checking: give lints to the user if an overflow would occur.
+            // We do this here and not in the `Assert` terminator as that terminator is
+            // only sometimes emitted (overflow checks can be disabled), but we want to always
+            // lint.
+            Rvalue::UnaryOp(op, arg) => {
+                trace!("checking UnaryOp(op = {:?}, arg = {:?})", op, arg);
+                self.check_unary_op(*op, arg, source_info)?;
+            }
+            Rvalue::BinaryOp(op, box (left, right)) => {
+                trace!("checking BinaryOp(op = {:?}, left = {:?}, right = {:?})", op, left, right);
+                self.check_binary_op(*op, left, right, source_info)?;
+            }
+            Rvalue::CheckedBinaryOp(op, box (left, right)) => {
+                trace!(
+                    "checking CheckedBinaryOp(op = {:?}, left = {:?}, right = {:?})",
+                    op,
+                    left,
+                    right
+                );
+                self.check_binary_op(*op, left, right, source_info)?;
+            }
+
+            // Do not try creating references (#67862)
+            Rvalue::AddressOf(_, place) | Rvalue::Ref(_, _, place) => {
+                trace!("skipping AddressOf | Ref for {:?}", place);
+
+                // This may be creating mutable references or immutable references to cells.
+                // If that happens, the pointed to value could be mutated via that reference.
+                // Since we aren't tracking references, the const propagator loses track of what
+                // value the local has right now.
+                // Thus, all locals that have their reference taken
+                // must not take part in propagation.
+                Self::remove_const(&mut self.ecx, place.local);
+
+                return None;
+            }
+            Rvalue::ThreadLocalRef(def_id) => {
+                trace!("skipping ThreadLocalRef({:?})", def_id);
+
+                return None;
+            }
+
+            // There's no other checking to do at this time.
+            Rvalue::Aggregate(..)
+            | Rvalue::Use(..)
+            | Rvalue::CopyForDeref(..)
+            | Rvalue::Repeat(..)
+            | Rvalue::Len(..)
+            | Rvalue::Cast(..)
+            | Rvalue::ShallowInitBox(..)
+            | Rvalue::Discriminant(..)
+            | Rvalue::NullaryOp(..) => {}
+        }
+
+        // FIXME we need to revisit this for #67176
+        if rvalue.needs_subst() {
+            return None;
+        }
+
+        self.use_ecx(source_info, |this| this.ecx.eval_rvalue_into_place(rvalue, place))
+    }
+}
+
+impl<'tcx> Visitor<'tcx> for ConstPropagator<'_, 'tcx> {
+    fn visit_body(&mut self, body: &Body<'tcx>) {
+        for (bb, data) in body.basic_blocks().iter_enumerated() {
+            self.visit_basic_block_data(bb, data);
+        }
+    }
+
+    fn visit_operand(&mut self, operand: &Operand<'tcx>, location: Location) {
+        self.super_operand(operand, location);
+    }
+
+    fn visit_constant(&mut self, constant: &Constant<'tcx>, location: Location) {
+        trace!("visit_constant: {:?}", constant);
+        self.super_constant(constant, location);
+        self.eval_constant(constant, self.source_info.unwrap());
+    }
+
+    fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
+        trace!("visit_statement: {:?}", statement);
+        let source_info = statement.source_info;
+        self.source_info = Some(source_info);
+        if let StatementKind::Assign(box (place, ref rval)) = statement.kind {
+            let can_const_prop = self.ecx.machine.can_const_prop[place.local];
+            if let Some(()) = self.const_prop(rval, source_info, place) {
+                match can_const_prop {
+                    ConstPropMode::OnlyInsideOwnBlock => {
+                        trace!(
+                            "found local restricted to its block. \
+                                Will remove it from const-prop after block is finished. Local: {:?}",
+                            place.local
+                        );
+                    }
+                    ConstPropMode::OnlyPropagateInto | ConstPropMode::NoPropagation => {
+                        trace!("can't propagate into {:?}", place);
+                        if place.local != RETURN_PLACE {
+                            Self::remove_const(&mut self.ecx, place.local);
+                        }
+                    }
+                    ConstPropMode::FullConstProp => {}
+                }
+            } else {
+                // Const prop failed, so erase the destination, ensuring that whatever happens
+                // from here on, does not know about the previous value.
+                // This is important in case we have
+                // ```rust
+                // let mut x = 42;
+                // x = SOME_MUTABLE_STATIC;
+                // // x must now be uninit
+                // ```
+                // FIXME: we overzealously erase the entire local, because that's easier to
+                // implement.
+                trace!(
+                    "propagation into {:?} failed.
+                        Nuking the entire site from orbit, it's the only way to be sure",
+                    place,
+                );
+                Self::remove_const(&mut self.ecx, place.local);
+            }
+        } else {
+            match statement.kind {
+                StatementKind::SetDiscriminant { ref place, .. } => {
+                    match self.ecx.machine.can_const_prop[place.local] {
+                        ConstPropMode::FullConstProp | ConstPropMode::OnlyInsideOwnBlock => {
+                            if self
+                                .use_ecx(source_info, |this| this.ecx.statement(statement))
+                                .is_some()
+                            {
+                                trace!("propped discriminant into {:?}", place);
+                            } else {
+                                Self::remove_const(&mut self.ecx, place.local);
+                            }
+                        }
+                        ConstPropMode::OnlyPropagateInto | ConstPropMode::NoPropagation => {
+                            Self::remove_const(&mut self.ecx, place.local);
+                        }
+                    }
+                }
+                StatementKind::StorageLive(local) | StatementKind::StorageDead(local) => {
+                    let frame = self.ecx.frame_mut();
+                    frame.locals[local].value =
+                        if let StatementKind::StorageLive(_) = statement.kind {
+                            LocalValue::Live(interpret::Operand::Immediate(
+                                interpret::Immediate::Uninit,
+                            ))
+                        } else {
+                            LocalValue::Dead
+                        };
+                }
+                _ => {}
+            }
+        }
+
+        self.super_statement(statement, location);
+    }
+
+    fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
+        let source_info = terminator.source_info;
+        self.source_info = Some(source_info);
+        self.super_terminator(terminator, location);
+        match &terminator.kind {
+            TerminatorKind::Assert { expected, ref msg, ref cond, .. } => {
+                if let Some(ref value) = self.eval_operand(&cond, source_info) {
+                    trace!("assertion on {:?} should be {:?}", value, expected);
+                    let expected = ScalarMaybeUninit::from(Scalar::from_bool(*expected));
+                    let value_const = self.ecx.read_scalar(&value).unwrap();
+                    if expected != value_const {
+                        enum DbgVal<T> {
+                            Val(T),
+                            Underscore,
+                        }
+                        impl<T: std::fmt::Debug> std::fmt::Debug for DbgVal<T> {
+                            fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+                                match self {
+                                    Self::Val(val) => val.fmt(fmt),
+                                    Self::Underscore => fmt.write_str("_"),
+                                }
+                            }
+                        }
+                        let mut eval_to_int = |op| {
+                            // This can be `None` if the lhs wasn't const propagated and we just
+                            // triggered the assert on the value of the rhs.
+                            self.eval_operand(op, source_info).map_or(DbgVal::Underscore, |op| {
+                                DbgVal::Val(self.ecx.read_immediate(&op).unwrap().to_const_int())
+                            })
+                        };
+                        let msg = match msg {
+                            AssertKind::DivisionByZero(op) => {
+                                Some(AssertKind::DivisionByZero(eval_to_int(op)))
+                            }
+                            AssertKind::RemainderByZero(op) => {
+                                Some(AssertKind::RemainderByZero(eval_to_int(op)))
+                            }
+                            AssertKind::Overflow(bin_op @ (BinOp::Div | BinOp::Rem), op1, op2) => {
+                                // Division overflow is *UB* in the MIR, and different than the
+                                // other overflow checks.
+                                Some(AssertKind::Overflow(
+                                    *bin_op,
+                                    eval_to_int(op1),
+                                    eval_to_int(op2),
+                                ))
+                            }
+                            AssertKind::BoundsCheck { ref len, ref index } => {
+                                let len = eval_to_int(len);
+                                let index = eval_to_int(index);
+                                Some(AssertKind::BoundsCheck { len, index })
+                            }
+                            // Remaining overflow errors are already covered by checks on the binary operators.
+                            AssertKind::Overflow(..) | AssertKind::OverflowNeg(_) => None,
+                            // Need proper const propagator for these.
+                            _ => None,
+                        };
+                        // Poison all places this operand references so that further code
+                        // doesn't use the invalid value
+                        match cond {
+                            Operand::Move(ref place) | Operand::Copy(ref place) => {
+                                Self::remove_const(&mut self.ecx, place.local);
+                            }
+                            Operand::Constant(_) => {}
+                        }
+                        if let Some(msg) = msg {
+                            self.report_assert_as_lint(
+                                lint::builtin::UNCONDITIONAL_PANIC,
+                                source_info,
+                                "this operation will panic at runtime",
+                                msg,
+                            );
+                        }
+                    }
+                }
+            }
+            // None of these have Operands to const-propagate.
+            TerminatorKind::Goto { .. }
+            | TerminatorKind::Resume
+            | TerminatorKind::Abort
+            | TerminatorKind::Return
+            | TerminatorKind::Unreachable
+            | TerminatorKind::Drop { .. }
+            | TerminatorKind::DropAndReplace { .. }
+            | TerminatorKind::Yield { .. }
+            | TerminatorKind::GeneratorDrop
+            | TerminatorKind::FalseEdge { .. }
+            | TerminatorKind::FalseUnwind { .. }
+            | TerminatorKind::SwitchInt { .. }
+            | TerminatorKind::Call { .. }
+            | TerminatorKind::InlineAsm { .. } => {}
+        }
+
+        // We remove all Locals which are restricted in propagation to their containing blocks and
+        // which were modified in the current block.
+        // Take it out of the ecx so we can get a mutable reference to the ecx for `remove_const`.
+        let mut locals = std::mem::take(&mut self.ecx.machine.written_only_inside_own_block_locals);
+        for &local in locals.iter() {
+            Self::remove_const(&mut self.ecx, local);
+        }
+        locals.clear();
+        // Put it back so we reuse the heap of the storage
+        self.ecx.machine.written_only_inside_own_block_locals = locals;
+        if cfg!(debug_assertions) {
+            // Ensure we are correctly erasing locals with the non-debug-assert logic.
+            for local in self.ecx.machine.only_propagate_inside_block_locals.iter() {
+                assert!(
+                    self.get_const(local.into()).is_none()
+                        || self
+                            .layout_of(self.local_decls[local].ty)
+                            .map_or(true, |layout| layout.is_zst())
+                )
+            }
+        }
+    }
+}