implement valtree -> constvalue conversion

6 files changed, 537 insertions, 150 deletions

diff --git a/compiler/rustc_const_eval/src/const_eval/eval_queries.rs b/compiler/rustc_const_eval/src/const_eval/eval_queries.rs
index 7cca6178ab2..38fecf7232e 100644
--- a/compiler/rustc_const_eval/src/const_eval/eval_queries.rs
+++ b/compiler/rustc_const_eval/src/const_eval/eval_queries.rs
@@ -106,6 +106,7 @@ pub(super) fn mk_eval_cx<'mir, 'tcx>(
 
 /// This function converts an interpreter value into a constant that is meant for use in the
 /// type system.
+#[instrument(skip(ecx), level = "debug")]
 pub(super) fn op_to_const<'tcx>(
     ecx: &CompileTimeEvalContext<'_, 'tcx>,
     op: &OpTy<'tcx>,
@@ -140,21 +141,26 @@ pub(super) fn op_to_const<'tcx>(
         op.try_as_mplace()
     };
 
+    debug!(?immediate);
+
     // We know `offset` is relative to the allocation, so we can use `into_parts`.
-    let to_const_value = |mplace: &MPlaceTy<'_>| match mplace.ptr.into_parts() {
-        (Some(alloc_id), offset) => {
-            let alloc = ecx.tcx.global_alloc(alloc_id).unwrap_memory();
-            ConstValue::ByRef { alloc, offset }
-        }
-        (None, offset) => {
-            assert!(mplace.layout.is_zst());
-            assert_eq!(
-                offset.bytes() % mplace.layout.align.abi.bytes(),
-                0,
-                "this MPlaceTy must come from a validated constant, thus we can assume the \
+    let to_const_value = |mplace: &MPlaceTy<'_>| {
+        debug!("to_const_value(mplace: {:?})", mplace);
+        match mplace.ptr.into_parts() {
+            (Some(alloc_id), offset) => {
+                let alloc = ecx.tcx.global_alloc(alloc_id).unwrap_memory();
+                ConstValue::ByRef { alloc, offset }
+            }
+            (None, offset) => {
+                assert!(mplace.layout.is_zst());
+                assert_eq!(
+                    offset.bytes() % mplace.layout.align.abi.bytes(),
+                    0,
+                    "this MPlaceTy must come from a validated constant, thus we can assume the \
                 alignment is correct",
-            );
-            ConstValue::Scalar(Scalar::ZST)
+                );
+                ConstValue::Scalar(Scalar::ZST)
+            }
         }
     };
     match immediate {
@@ -166,6 +172,7 @@ pub(super) fn op_to_const<'tcx>(
                 ScalarMaybeUninit::Uninit => to_const_value(&op.assert_mem_place()),
             },
             Immediate::ScalarPair(a, b) => {
+                debug!("ScalarPair(a: {:?}, b: {:?})", a, b);
                 // We know `offset` is relative to the allocation, so we can use `into_parts`.
                 let (data, start) =
                     match ecx.scalar_to_ptr(a.check_init().unwrap()).unwrap().into_parts() {
@@ -209,7 +216,10 @@ fn turn_into_const_value<'tcx>(
     );
 
     // Turn this into a proper constant.
-    op_to_const(&ecx, &mplace.into())
+    let const_val = op_to_const(&ecx, &mplace.into());
+    debug!(?const_val);
+
+    const_val
 }
 
 pub fn eval_to_const_value_raw_provider<'tcx>(
diff --git a/compiler/rustc_const_eval/src/const_eval/mod.rs b/compiler/rustc_const_eval/src/const_eval/mod.rs
index 68f9bee593f..96c18d488ee 100644
--- a/compiler/rustc_const_eval/src/const_eval/mod.rs
+++ b/compiler/rustc_const_eval/src/const_eval/mod.rs
@@ -3,29 +3,26 @@
 use std::convert::TryFrom;
 
 use rustc_hir::Mutability;
-use rustc_middle::ty::layout::HasTyCtxt;
+use rustc_middle::mir;
 use rustc_middle::ty::{self, TyCtxt};
-use rustc_middle::{
-    mir::{self, interpret::ConstAlloc},
-    ty::ScalarInt,
-};
 use rustc_span::{source_map::DUMMY_SP, symbol::Symbol};
-use rustc_target::abi::VariantIdx;
 
 use crate::interpret::{
-    intern_const_alloc_recursive, ConstValue, InternKind, InterpCx, InterpResult, MPlaceTy,
-    MemPlaceMeta, Scalar,
+    intern_const_alloc_recursive, ConstValue, InternKind, InterpCx, InterpResult, MemPlaceMeta,
+    Scalar,
 };
 
 mod error;
 mod eval_queries;
 mod fn_queries;
 mod machine;
+mod valtrees;
 
 pub use error::*;
 pub use eval_queries::*;
 pub use fn_queries::*;
 pub use machine::*;
+pub(crate) use valtrees::{const_to_valtree, valtree_to_const_value};
 
 pub(crate) fn const_caller_location(
     tcx: TyCtxt<'_>,
@@ -41,128 +38,6 @@ pub(crate) fn const_caller_location(
     ConstValue::Scalar(Scalar::from_maybe_pointer(loc_place.ptr, &tcx))
 }
 
-/// Convert an evaluated constant to a type level constant
-pub(crate) fn const_to_valtree<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    param_env: ty::ParamEnv<'tcx>,
-    raw: ConstAlloc<'tcx>,
-) -> Option<ty::ValTree<'tcx>> {
-    let ecx = mk_eval_cx(
-        tcx, DUMMY_SP, param_env,
-        // It is absolutely crucial for soundness that
-        // we do not read from static items or other mutable memory.
-        false,
-    );
-    let place = ecx.raw_const_to_mplace(raw).unwrap();
-    const_to_valtree_inner(&ecx, &place)
-}
-
-#[instrument(skip(ecx), level = "debug")]
-fn branches<'tcx>(
-    ecx: &CompileTimeEvalContext<'tcx, 'tcx>,
-    place: &MPlaceTy<'tcx>,
-    n: usize,
-    variant: Option<VariantIdx>,
-) -> Option<ty::ValTree<'tcx>> {
-    let place = match variant {
-        Some(variant) => ecx.mplace_downcast(&place, variant).unwrap(),
-        None => *place,
-    };
-    let variant = variant.map(|variant| Some(ty::ValTree::Leaf(ScalarInt::from(variant.as_u32()))));
-    debug!(?place, ?variant);
-
-    let fields = (0..n).map(|i| {
-        let field = ecx.mplace_field(&place, i).unwrap();
-        const_to_valtree_inner(ecx, &field)
-    });
-    // For enums, we prepend their variant index before the variant's fields so we can figure out
-    // the variant again when just seeing a valtree.
-    let branches = variant.into_iter().chain(fields);
-    Some(ty::ValTree::Branch(ecx.tcx.arena.alloc_from_iter(branches.collect::<Option<Vec<_>>>()?)))
-}
-
-fn slice_branches<'tcx>(
-    ecx: &CompileTimeEvalContext<'tcx, 'tcx>,
-    place: &MPlaceTy<'tcx>,
-) -> Option<ty::ValTree<'tcx>> {
-    let n = place.len(&ecx.tcx()).expect(&format!("expected to use len of place {:?}", place));
-    let branches = (0..n).map(|i| {
-        let place_elem = ecx.mplace_index(place, i).unwrap();
-        const_to_valtree_inner(ecx, &place_elem)
-    });
-
-    Some(ty::ValTree::Branch(ecx.tcx.arena.alloc_from_iter(branches.collect::<Option<Vec<_>>>()?)))
-}
-
-#[instrument(skip(ecx), level = "debug")]
-fn const_to_valtree_inner<'tcx>(
-    ecx: &CompileTimeEvalContext<'tcx, 'tcx>,
-    place: &MPlaceTy<'tcx>,
-) -> Option<ty::ValTree<'tcx>> {
-    match place.layout.ty.kind() {
-        ty::FnDef(..) => Some(ty::ValTree::zst()),
-        ty::Bool | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Char => {
-            let val = ecx.read_immediate(&place.into()).unwrap();
-            let val = val.to_scalar().unwrap();
-            Some(ty::ValTree::Leaf(val.assert_int()))
-        }
-
-        // Raw pointers are not allowed in type level constants, as we cannot properly test them for
-        // equality at compile-time (see `ptr_guaranteed_eq`/`_ne`).
-        // Technically we could allow function pointers (represented as `ty::Instance`), but this is not guaranteed to
-        // agree with runtime equality tests.
-        ty::FnPtr(_) | ty::RawPtr(_) => None,
-
-        ty::Ref(_, _, _)  => {
-            let derefd_place = ecx.deref_operand(&place.into()).unwrap_or_else(|e| bug!("couldn't deref {:?}, error: {:?}", place, e));
-            debug!(?derefd_place);
-
-            const_to_valtree_inner(ecx, &derefd_place)
-        }
-
-        ty::Str | ty::Slice(_) | ty::Array(_, _) => {
-            let valtree = slice_branches(ecx, place);
-            debug!(?valtree);
-
-            valtree
-        }
-        // Trait objects are not allowed in type level constants, as we have no concept for
-        // resolving their backing type, even if we can do that at const eval time. We may
-        // hypothetically be able to allow `dyn StructuralEq` trait objects in the future,
-        // but it is unclear if this is useful.
-        ty::Dynamic(..) => None,
-
-        ty::Tuple(substs) => branches(ecx, place, substs.len(), None),
-
-        ty::Adt(def, _) => {
-            if def.variants().is_empty() {
-                bug!("uninhabited types should have errored and never gotten converted to valtree")
-            }
-
-            let variant = ecx.read_discriminant(&place.into()).unwrap().1;
-
-            branches(ecx, place, def.variant(variant).fields.len(), def.is_enum().then_some(variant))
-        }
-
-        ty::Never
-        | ty::Error(_)
-        | ty::Foreign(..)
-        | ty::Infer(ty::FreshIntTy(_))
-        | ty::Infer(ty::FreshFloatTy(_))
-        | ty::Projection(..)
-        | ty::Param(_)
-        | ty::Bound(..)
-        | ty::Placeholder(..)
-        // FIXME(oli-obk): we could look behind opaque types
-        | ty::Opaque(..)
-        | ty::Infer(_)
-        // FIXME(oli-obk): we can probably encode closures just like structs
-        | ty::Closure(..)
-        | ty::Generator(..)
-        | ty::GeneratorWitness(..) => None,
-    }
-}
-
 /// This function should never fail for validated constants. However, it is also invoked from the
 /// pretty printer which might attempt to format invalid constants and in that case it might fail.
 pub(crate) fn try_destructure_const<'tcx>(
@@ -202,6 +77,7 @@ pub(crate) fn try_destructure_const<'tcx>(
     Ok(mir::DestructuredConst { variant, fields })
 }
 
+#[instrument(skip(tcx), level = "debug")]
 pub(crate) fn deref_const<'tcx>(
     tcx: TyCtxt<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
diff --git a/compiler/rustc_const_eval/src/const_eval/valtrees.rs b/compiler/rustc_const_eval/src/const_eval/valtrees.rs
new file mode 100644
index 00000000000..ded539fd340
--- /dev/null
+++ b/compiler/rustc_const_eval/src/const_eval/valtrees.rs
@@ -0,0 +1,479 @@
+use super::eval_queries::{mk_eval_cx, op_to_const};
+use super::machine::CompileTimeEvalContext;
+use crate::interpret::{
+    intern_const_alloc_recursive, ConstValue, ImmTy, Immediate, InternKind, MemoryKind, PlaceTy,
+    Pointer, Scalar, ScalarMaybeUninit,
+};
+use rustc_middle::mir::interpret::{ConstAlloc, GlobalAlloc};
+use rustc_middle::mir::{Field, ProjectionElem};
+use rustc_middle::ty::{self, ScalarInt, Ty, TyCtxt};
+use rustc_span::source_map::DUMMY_SP;
+use rustc_target::abi::VariantIdx;
+
+use crate::interpret::visitor::Value;
+use crate::interpret::MPlaceTy;
+
+/// Convert an evaluated constant to a type level constant
+#[instrument(skip(tcx), level = "debug")]
+pub(crate) fn const_to_valtree<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    param_env: ty::ParamEnv<'tcx>,
+    raw: ConstAlloc<'tcx>,
+) -> Option<ty::ValTree<'tcx>> {
+    let ecx = mk_eval_cx(
+        tcx, DUMMY_SP, param_env,
+        // It is absolutely crucial for soundness that
+        // we do not read from static items or other mutable memory.
+        false,
+    );
+    let place = ecx.raw_const_to_mplace(raw).unwrap();
+    const_to_valtree_inner(&ecx, &place)
+}
+
+#[instrument(skip(ecx), level = "debug")]
+fn branches<'tcx>(
+    ecx: &CompileTimeEvalContext<'tcx, 'tcx>,
+    place: &MPlaceTy<'tcx>,
+    n: usize,
+    variant: Option<VariantIdx>,
+) -> Option<ty::ValTree<'tcx>> {
+    let place = match variant {
+        Some(variant) => ecx.mplace_downcast(&place, variant).unwrap(),
+        None => *place,
+    };
+    let variant = variant.map(|variant| Some(ty::ValTree::Leaf(ScalarInt::from(variant.as_u32()))));
+    debug!(?place, ?variant);
+
+    let fields = (0..n).map(|i| {
+        let field = ecx.mplace_field(&place, i).unwrap();
+        const_to_valtree_inner(ecx, &field)
+    });
+    // For enums, we preped their variant index before the variant's fields so we can figure out
+    // the variant again when just seeing a valtree.
+    let branches = variant.into_iter().chain(fields);
+    Some(ty::ValTree::Branch(ecx.tcx.arena.alloc_from_iter(branches.collect::<Option<Vec<_>>>()?)))
+}
+
+fn slice_branches<'tcx>(
+    ecx: &CompileTimeEvalContext<'tcx, 'tcx>,
+    place: &MPlaceTy<'tcx>,
+) -> Option<ty::ValTree<'tcx>> {
+    let n = place.len(&ecx.tcx.tcx).expect(&format!("expected to use len of place {:?}", place));
+    let branches = (0..n).map(|i| {
+        let place_elem = ecx.mplace_index(place, i).unwrap();
+        const_to_valtree_inner(ecx, &place_elem)
+    });
+
+    Some(ty::ValTree::Branch(ecx.tcx.arena.alloc_from_iter(branches.collect::<Option<Vec<_>>>()?)))
+}
+
+#[instrument(skip(ecx), level = "debug")]
+fn const_to_valtree_inner<'tcx>(
+    ecx: &CompileTimeEvalContext<'tcx, 'tcx>,
+    place: &MPlaceTy<'tcx>,
+) -> Option<ty::ValTree<'tcx>> {
+    match place.layout.ty.kind() {
+        ty::FnDef(..) => Some(ty::ValTree::zst()),
+        ty::Bool | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Char => {
+            let val = ecx.read_immediate(&place.into()).unwrap();
+            let val = val.to_scalar().unwrap();
+            Some(ty::ValTree::Leaf(val.assert_int()))
+        }
+
+        // Raw pointers are not allowed in type level constants, as we cannot properly test them for
+        // equality at compile-time (see `ptr_guaranteed_eq`/`_ne`).
+        // Technically we could allow function pointers (represented as `ty::Instance`), but this is not guaranteed to
+        // agree with runtime equality tests.
+        ty::FnPtr(_) | ty::RawPtr(_) => None,
+
+        ty::Ref(_, _, _)  => {
+            let derefd_place = ecx.deref_operand(&place.into()).unwrap_or_else(|e| bug!("couldn't deref {:?}, error: {:?}", place, e));
+            debug!(?derefd_place);
+
+            const_to_valtree_inner(ecx, &derefd_place)
+        }
+
+        ty::Str | ty::Slice(_) | ty::Array(_, _) => {
+            let valtree = slice_branches(ecx, place);
+            debug!(?valtree);
+
+            valtree
+        }
+        // Trait objects are not allowed in type level constants, as we have no concept for
+        // resolving their backing type, even if we can do that at const eval time. We may
+        // hypothetically be able to allow `dyn StructuralEq` trait objects in the future,
+        // but it is unclear if this is useful.
+        ty::Dynamic(..) => None,
+
+        ty::Tuple(substs) => branches(ecx, place, substs.len(), None),
+
+        ty::Adt(def, _) => {
+            if def.variants().is_empty() {
+                bug!("uninhabited types should have errored and never gotten converted to valtree")
+            }
+
+            let variant = ecx.read_discriminant(&place.into()).unwrap().1;
+
+            branches(ecx, place, def.variant(variant).fields.len(), def.is_enum().then_some(variant))
+        }
+
+        ty::Never
+        | ty::Error(_)
+        | ty::Foreign(..)
+        | ty::Infer(ty::FreshIntTy(_))
+        | ty::Infer(ty::FreshFloatTy(_))
+        | ty::Projection(..)
+        | ty::Param(_)
+        | ty::Bound(..)
+        | ty::Placeholder(..)
+        // FIXME(oli-obk): we could look behind opaque types
+        | ty::Opaque(..)
+        | ty::Infer(_)
+        // FIXME(oli-obk): we can probably encode closures just like structs
+        | ty::Closure(..)
+        | ty::Generator(..)
+        | ty::GeneratorWitness(..) => None,
+    }
+}
+
+#[instrument(skip(ecx), level = "debug")]
+fn create_mplace_from_layout<'tcx>(
+    ecx: &mut CompileTimeEvalContext<'tcx, 'tcx>,
+    param_env_ty: ty::ParamEnvAnd<'tcx, Ty<'tcx>>,
+) -> MPlaceTy<'tcx> {
+    let tcx = ecx.tcx;
+    let layout = tcx.layout_of(param_env_ty).unwrap();
+    debug!(?layout);
+
+    ecx.allocate(layout, MemoryKind::Stack).unwrap()
+}
+
+/// Converts a `ValTree` to a `ConstValue`, which is needed after mir
+/// construction has finished.
+#[instrument(skip(tcx), level = "debug")]
+pub fn valtree_to_const_value<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    param_env_ty: ty::ParamEnvAnd<'tcx, Ty<'tcx>>,
+    valtree: ty::ValTree<'tcx>,
+) -> ConstValue<'tcx> {
+    // Basic idea: We directly construct `Scalar` values from trivial `ValTree`s
+    // (those for constants with type bool, int, uint, float or char).
+    // For all other types we create an `MPlace` and fill that by walking
+    // the `ValTree` and using `place_projection` and `place_field` to
+    // create inner `MPlace`s which are filled recursively.
+    // FIXME Does this need an example?
+
+    let (param_env, ty) = param_env_ty.into_parts();
+    let mut ecx = mk_eval_cx(tcx, DUMMY_SP, param_env, false);
+
+    match ty.kind() {
+        ty::Bool | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Char => match valtree {
+            ty::ValTree::Leaf(scalar_int) => ConstValue::Scalar(Scalar::Int(scalar_int)),
+            ty::ValTree::Branch(_) => bug!(
+                "ValTrees for Bool, Int, Uint, Float or Char should have the form ValTree::Leaf"
+            ),
+        },
+        ty::Ref(_, inner_ty, _) => {
+            match inner_ty.kind() {
+                ty::Slice(_) | ty::Str => {
+                    let slice_ty = match inner_ty.kind() {
+                        ty::Slice(slice_ty) => *slice_ty,
+                        ty::Str => tcx.mk_ty(ty::Uint(ty::UintTy::U8)),
+                        _ => bug!("expected ty::Slice | ty::Str"),
+                    };
+                    debug!(?slice_ty);
+
+                    let valtrees = valtree.unwrap_branch();
+
+                    // Create a place for the underlying array
+                    let len = valtrees.len();
+                    let arr_ty = tcx.mk_array(slice_ty, len as u64);
+                    let mut place =
+                        create_mplace_from_layout(&mut ecx, ty::ParamEnv::empty().and(arr_ty));
+                    debug!(?place);
+
+                    // Insert elements of `arr_valtree` into `place`
+                    fill_place_recursively(&mut ecx, &mut place, valtree, arr_ty);
+                    dump_place(&ecx, place.into());
+
+                    // The allocation behind `place` is local, we need to intern it
+                    intern_const_alloc_recursive(&mut ecx, InternKind::Constant, &place).unwrap();
+
+                    // Now we need to get the Allocation
+                    let alloc_id = place.mplace.ptr.provenance.unwrap();
+                    debug!(?alloc_id);
+
+                    let data = match tcx.get_global_alloc(alloc_id) {
+                        Some(GlobalAlloc::Memory(const_alloc)) => const_alloc,
+                        _ => bug!("expected memory allocation"),
+                    };
+                    debug!(?data);
+
+                    return ConstValue::Slice { data, start: 0, end: len as usize };
+                }
+                _ => {
+                    match valtree {
+                        ty::ValTree::Branch(_) => {
+                            // create a place for the pointee
+                            let mut place = create_mplace_from_layout(
+                                &mut ecx,
+                                ty::ParamEnv::empty().and(*inner_ty),
+                            );
+                            debug!(?place);
+
+                            // insert elements of valtree into `place`
+                            fill_place_recursively(&mut ecx, &mut place, valtree, *inner_ty);
+                            dump_place(&ecx, place.into());
+                            intern_const_alloc_recursive(&mut ecx, InternKind::Constant, &place)
+                                .unwrap();
+
+                            let ref_place = place.mplace.to_ref(&tcx);
+                            let imm = ImmTy::from_immediate(
+                                ref_place,
+                                tcx.layout_of(param_env_ty).unwrap(),
+                            );
+
+                            let const_val = op_to_const(&ecx, &imm.into());
+                            debug!(?const_val);
+
+                            const_val
+                        }
+                        ty::ValTree::Leaf(_) => {
+                            let mut place = create_mplace_from_layout(
+                                &mut ecx,
+                                ty::ParamEnv::empty().and(*inner_ty),
+                            );
+
+                            fill_place_recursively(&mut ecx, &mut place, valtree, *inner_ty);
+                            dump_place(&ecx, place.into());
+
+                            let ref_place = place.mplace.to_ref(&tcx);
+                            let imm = ImmTy::from_immediate(
+                                ref_place,
+                                tcx.layout_of(param_env_ty).unwrap(),
+                            );
+
+                            op_to_const(&ecx, &imm.into())
+                        }
+                    }
+                }
+            }
+        }
+        ty::Tuple(_) | ty::Array(_, _) | ty::Adt(..) => {
+            let mut place = create_mplace_from_layout(&mut ecx, param_env_ty);
+            debug!(?place);
+
+            fill_place_recursively(&mut ecx, &mut place, valtree, ty);
+            dump_place(&ecx, place.into());
+            intern_const_alloc_recursive(&mut ecx, InternKind::Constant, &place).unwrap();
+
+            let const_val = op_to_const(&ecx, &place.into());
+            debug!(?const_val);
+
+            const_val
+        }
+        ty::Never
+        | ty::FnDef(..)
+        | ty::Error(_)
+        | ty::Foreign(..)
+        | ty::Infer(ty::FreshIntTy(_))
+        | ty::Infer(ty::FreshFloatTy(_))
+        | ty::Projection(..)
+        | ty::Param(_)
+        | ty::Bound(..)
+        | ty::Placeholder(..)
+        | ty::Opaque(..)
+        | ty::Infer(_)
+        | ty::Closure(..)
+        | ty::Generator(..)
+        | ty::GeneratorWitness(..)
+        | ty::FnPtr(_)
+        | ty::RawPtr(_)
+        | ty::Str
+        | ty::Slice(_)
+        | ty::Dynamic(..) => bug!("no ValTree should have been created for type {:?}", ty.kind()),
+    }
+}
+
+// FIXME Needs a better/correct name
+#[instrument(skip(ecx), level = "debug")]
+fn fill_place_recursively<'tcx>(
+    ecx: &mut CompileTimeEvalContext<'tcx, 'tcx>,
+    place: &mut MPlaceTy<'tcx>,
+    valtree: ty::ValTree<'tcx>,
+    ty: Ty<'tcx>,
+) {
+    // This will match on valtree and write the value(s) corresponding to the ValTree
+    // inside the place recursively.
+
+    let tcx = ecx.tcx.tcx;
+
+    match ty.kind() {
+        ty::Bool | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Char => {
+            let scalar_int = valtree.unwrap_leaf();
+            debug!("writing trivial valtree {:?} to place {:?}", scalar_int, place);
+            ecx.write_immediate(
+                Immediate::Scalar(ScalarMaybeUninit::Scalar(scalar_int.into())),
+                &(*place).into(),
+            )
+            .unwrap();
+        }
+        ty::Ref(_, inner_ty, _) => {
+            match inner_ty.kind() {
+                ty::Slice(_) | ty::Str => {
+                    let slice_ty = match inner_ty.kind() {
+                        ty::Slice(slice_ty) => *slice_ty,
+                        ty::Str => tcx.mk_ty(ty::Uint(ty::UintTy::U8)),
+                        _ => bug!("expected ty::Slice | ty::Str"),
+                    };
+                    debug!(?slice_ty);
+
+                    let valtrees = valtree.unwrap_branch();
+                    debug!(?valtrees);
+                    let len = valtrees.len();
+                    debug!(?len);
+
+                    // create a place for the underlying array
+                    let arr_ty = tcx.mk_array(slice_ty, len as u64);
+                    let mut arr_place =
+                        create_mplace_from_layout(ecx, ty::ParamEnv::empty().and(arr_ty));
+                    debug!(?arr_place);
+
+                    // Insert elements of `arr_valtree` into `place`
+                    fill_place_recursively(ecx, &mut arr_place, valtree, arr_ty);
+                    dump_place(&ecx, arr_place.into());
+
+                    // Now we need to create a `ScalarPair` from the filled `place`
+                    // and write that into `place`
+                    let (alloc_id, offset) = arr_place.mplace.ptr.into_parts();
+                    debug!(?alloc_id, ?offset);
+                    let unwrapped_ptr = Pointer { offset, provenance: alloc_id.unwrap() };
+                    let len_scalar = ScalarMaybeUninit::Scalar(Scalar::from_u64(len as u64));
+
+                    let imm = Immediate::ScalarPair(
+                        ScalarMaybeUninit::from_pointer(unwrapped_ptr, &tcx),
+                        len_scalar,
+                    );
+                    debug!(?imm);
+
+                    // Now write the ScalarPair into the original place we wanted to fill
+                    // in this call
+                    let _ = ecx.write_immediate(imm, &(*place).into()).unwrap();
+
+                    dump_place(&ecx, (*place).into());
+                }
+                _ => {
+                    let mut pointee_place =
+                        create_mplace_from_layout(ecx, ty::ParamEnv::empty().and(*inner_ty));
+                    debug!(?pointee_place);
+                    fill_place_recursively(ecx, &mut pointee_place, valtree, *inner_ty);
+
+                    dump_place(ecx, pointee_place.into());
+                    intern_const_alloc_recursive(ecx, InternKind::Constant, &pointee_place)
+                        .unwrap();
+
+                    let imm = pointee_place.mplace.to_ref(&tcx);
+                    debug!(?imm);
+
+                    ecx.write_immediate(imm, &(*place).into()).unwrap();
+                }
+            }
+        }
+        ty::Tuple(tuple_types) => {
+            let branches = valtree.unwrap_branch();
+            assert_eq!(tuple_types.len(), branches.len());
+
+            for (i, inner_valtree) in branches.iter().enumerate() {
+                debug!(?i, ?inner_valtree);
+                let inner_ty = tuple_types.get(i).expect(&format!(
+                    "expected to be able to index at position {} into {:?}",
+                    i, tuple_types
+                ));
+                debug!(?inner_ty);
+
+                // Create the mplace for the tuple element
+                let mut place_inner = ecx.mplace_field(place, i).unwrap();
+                debug!(?place_inner);
+
+                // insert valtree corresponding to tuple element into place
+                fill_place_recursively(ecx, &mut place_inner, *inner_valtree, *inner_ty);
+            }
+        }
+        ty::Array(inner_ty, _) => {
+            let inner_valtrees = valtree.unwrap_branch();
+            for (i, inner_valtree) in inner_valtrees.iter().enumerate() {
+                debug!(?i, ?inner_valtree);
+
+                let mut place_inner = ecx.mplace_field(place, i).unwrap();
+                debug!(?place_inner);
+
+                fill_place_recursively(ecx, &mut place_inner, *inner_valtree, *inner_ty)
+            }
+        }
+        ty::Adt(def, substs) if def.is_enum() => {
+            debug!("enum, substs: {:?}", substs);
+            let inner_valtrees = valtree.unwrap_branch();
+
+            // First element of valtree corresponds to variant
+            let scalar_int = inner_valtrees[0].unwrap_leaf();
+            let variant_idx = VariantIdx::from_u32(scalar_int.try_to_u32().unwrap());
+            let variant = def.variant(variant_idx);
+            debug!(?variant);
+
+            // Need to downcast place
+            let place_downcast = place.project_downcast(ecx, variant_idx).unwrap();
+            debug!(?place_downcast);
+
+            // fill `place_downcast` with the valtree elements corresponding to
+            // the fields of the enum
+            let fields = &variant.fields;
+            let inner_valtrees = &inner_valtrees[1..];
+            for (i, field) in fields.iter().enumerate() {
+                debug!(?i, ?field);
+
+                let field_ty = field.ty(tcx, substs);
+                debug!(?field_ty);
+
+                let mut field_mplace = ecx.mplace_field(&place_downcast, i).unwrap();
+                debug!(?field_mplace);
+                let inner_valtree = inner_valtrees[i];
+
+                fill_place_recursively(ecx, &mut field_mplace, inner_valtree, field_ty);
+                dump_place(&ecx, field_mplace.into());
+            }
+
+            debug!("dump of place_downcast");
+            dump_place(ecx, place_downcast.into());
+
+            // don't forget filling the place with the discriminant of the enum
+            ecx.write_discriminant(variant_idx, &(*place).into()).unwrap();
+            dump_place(ecx, (*place).into());
+        }
+        ty::Adt(def, substs) => {
+            debug!("Adt def: {:?} with substs: {:?}", def, substs);
+            let inner_valtrees = valtree.unwrap_branch();
+            debug!(?inner_valtrees);
+            let (fields, inner_valtrees) =
+                (&def.variant(VariantIdx::from_usize(0)).fields[..], inner_valtrees);
+
+            debug!("fields: {:?}", fields);
+
+            for (i, field) in fields.iter().enumerate() {
+                let field_ty = field.ty(tcx, substs);
+                debug!(?field_ty);
+                let old_field_ty = tcx.type_of(field.did);
+                debug!(?old_field_ty);
+                let projection_elem = ProjectionElem::Field(Field::from_usize(i), field_ty);
+                let mut field_place = ecx.mplace_projection(place, projection_elem).unwrap();
+                let inner_valtree = inner_valtrees[i];
+
+                fill_place_recursively(ecx, &mut field_place, inner_valtree, field_ty);
+            }
+        }
+        _ => {}
+    }
+}
+
+fn dump_place<'tcx>(ecx: &CompileTimeEvalContext<'tcx, 'tcx>, place: PlaceTy<'tcx>) {
+    trace!("{:?}", ecx.dump_place(place.place));
+}
diff --git a/compiler/rustc_const_eval/src/interpret/mod.rs b/compiler/rustc_const_eval/src/interpret/mod.rs
index 2b9fe565997..dba746e72e2 100644
--- a/compiler/rustc_const_eval/src/interpret/mod.rs
+++ b/compiler/rustc_const_eval/src/interpret/mod.rs
@@ -14,7 +14,7 @@ mod terminator;
 mod traits;
 mod util;
 mod validity;
-mod visitor;
+pub(crate) mod visitor;
 
 pub use rustc_middle::mir::interpret::*; // have all the `interpret` symbols in one place: here
 
diff --git a/compiler/rustc_const_eval/src/interpret/operand.rs b/compiler/rustc_const_eval/src/interpret/operand.rs
index dfc0028e87f..170fbab2cce 100644
--- a/compiler/rustc_const_eval/src/interpret/operand.rs
+++ b/compiler/rustc_const_eval/src/interpret/operand.rs
@@ -98,7 +98,7 @@ impl<'tcx, Tag: Provenance> Immediate<Tag> {
 // as input for binary and cast operations.
 #[derive(Copy, Clone, Debug)]
 pub struct ImmTy<'tcx, Tag: Provenance = AllocId> {
-    imm: Immediate<Tag>,
+    pub imm: Immediate<Tag>,
     pub layout: TyAndLayout<'tcx>,
 }
 
@@ -248,7 +248,7 @@ impl<'tcx, Tag: Provenance> ImmTy<'tcx, Tag> {
 impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
     /// Try reading an immediate in memory; this is interesting particularly for `ScalarPair`.
     /// Returns `None` if the layout does not permit loading this as a value.
-    fn try_read_immediate_from_mplace(
+    pub(crate) fn try_read_immediate_from_mplace(
         &self,
         mplace: &MPlaceTy<'tcx, M::PointerTag>,
     ) -> InterpResult<'tcx, Option<ImmTy<'tcx, M::PointerTag>>> {
@@ -424,6 +424,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         })
     }
 
+    #[instrument(skip(self), level = "debug")]
     pub fn operand_projection(
         &self,
         base: &OpTy<'tcx, M::PointerTag>,
diff --git a/compiler/rustc_const_eval/src/interpret/place.rs b/compiler/rustc_const_eval/src/interpret/place.rs
index e4660fe090c..8caf9eee2d9 100644
--- a/compiler/rustc_const_eval/src/interpret/place.rs
+++ b/compiler/rustc_const_eval/src/interpret/place.rs
@@ -82,7 +82,7 @@ rustc_data_structures::static_assert_size!(Place, 56);
 
 #[derive(Copy, Clone, Debug)]
 pub struct PlaceTy<'tcx, Tag: Provenance = AllocId> {
-    place: Place<Tag>, // Keep this private; it helps enforce invariants.
+    pub(crate) place: Place<Tag>, // Keep this private; it helps enforce invariants.
     pub layout: TyAndLayout<'tcx>,
 }
 
@@ -100,7 +100,7 @@ impl<'tcx, Tag: Provenance> std::ops::Deref for PlaceTy<'tcx, Tag> {
 /// A MemPlace with its layout. Constructing it is only possible in this module.
 #[derive(Copy, Clone, Hash, Eq, PartialEq, Debug)]
 pub struct MPlaceTy<'tcx, Tag: Provenance = AllocId> {
-    mplace: MemPlace<Tag>,
+    pub(crate) mplace: MemPlace<Tag>,
     pub layout: TyAndLayout<'tcx>,
 }
 
@@ -294,6 +294,7 @@ where
 
     /// Take an operand, representing a pointer, and dereference it to a place -- that
     /// will always be a MemPlace.  Lives in `place.rs` because it creates a place.
+    #[instrument(skip(self), level = "debug")]
     pub fn deref_operand(
         &self,
         src: &OpTy<'tcx, M::PointerTag>,
@@ -487,7 +488,8 @@ where
     }
 
     /// Project into an mplace
-    pub(super) fn mplace_projection(
+    #[instrument(skip(self), level = "debug")]
+    pub(crate) fn mplace_projection(
         &self,
         base: &MPlaceTy<'tcx, M::PointerTag>,
         proj_elem: mir::PlaceElem<'tcx>,
@@ -548,6 +550,7 @@ where
     /// Just a convenience function, but used quite a bit.
     /// This is the only projection that might have a side-effect: We cannot project
     /// into the field of a local `ScalarPair`, we have to first allocate it.
+    #[instrument(skip(self), level = "debug")]
     pub fn place_field(
         &mut self,
         base: &PlaceTy<'tcx, M::PointerTag>,
@@ -586,6 +589,7 @@ where
     }
 
     /// Projects into a place.
+    #[instrument(skip(self), level = "debug")]
     pub fn place_projection(
         &mut self,
         base: &PlaceTy<'tcx, M::PointerTag>,
@@ -617,19 +621,23 @@ where
 
     /// Computes a place. You should only use this if you intend to write into this
     /// place; for reading, a more efficient alternative is `eval_place_for_read`.
+    #[instrument(skip(self), level = "debug")]
     pub fn eval_place(
         &mut self,
         place: mir::Place<'tcx>,
     ) -> InterpResult<'tcx, PlaceTy<'tcx, M::PointerTag>> {
+        debug!("projection: {:?}", place.projection);
         let mut place_ty = PlaceTy {
             // This works even for dead/uninitialized locals; we check further when writing
             place: Place::Local { frame: self.frame_idx(), local: place.local },
             layout: self.layout_of_local(self.frame(), place.local, None)?,
         };
+        debug!(?place_ty);
 
         for elem in place.projection.iter() {
             place_ty = self.place_projection(&place_ty, &elem)?
         }
+        debug!("place after projections: {:?}", place_ty);
 
         trace!("{:?}", self.dump_place(place_ty.place));
         // Sanity-check the type we ended up with.
@@ -646,6 +654,7 @@ where
 
     /// Write an immediate to a place
     #[inline(always)]
+    #[instrument(skip(self), level = "debug")]
     pub fn write_immediate(
         &mut self,
         src: Immediate<M::PointerTag>,
@@ -684,6 +693,7 @@ where
     /// Write an immediate to a place.
     /// If you use this you are responsible for validating that things got copied at the
     /// right type.
+    #[instrument(skip(self), level = "debug")]
     fn write_immediate_no_validate(
         &mut self,
         src: Immediate<M::PointerTag>,
@@ -736,6 +746,7 @@ where
     /// Write an immediate to memory.
     /// If you use this you are responsible for validating that things got copied at the
     /// right type.
+    #[instrument(skip(self), level = "debug")]
     fn write_immediate_to_mplace_no_validate(
         &mut self,
         value: Immediate<M::PointerTag>,
@@ -758,6 +769,7 @@ where
         // cover all the bytes!
         match value {
             Immediate::Scalar(scalar) => {
+                debug!(?scalar);
                 match dest.layout.abi {
                     Abi::Scalar(_) => {} // fine
                     _ => span_bug!(
@@ -830,6 +842,7 @@ where
     /// Copies the data from an operand to a place. This does not support transmuting!
     /// Use `copy_op_transmute` if the layouts could disagree.
     #[inline(always)]
+    #[instrument(skip(self), level = "debug")]
     pub fn copy_op(
         &mut self,
         src: &OpTy<'tcx, M::PointerTag>,
@@ -849,6 +862,7 @@ where
     /// Use `copy_op_transmute` if the layouts could disagree.
     /// Also, if you use this you are responsible for validating that things get copied at the
     /// right type.
+    #[instrument(skip(self), level = "debug")]
     fn copy_op_no_validate(
         &mut self,
         src: &OpTy<'tcx, M::PointerTag>,
@@ -868,6 +882,7 @@ where
         // Let us see if the layout is simple so we take a shortcut, avoid force_allocation.
         let src = match self.try_read_immediate(src)? {
             Ok(src_val) => {
+                debug!("immediate from src is {:?}", src_val);
                 assert!(!src.layout.is_unsized(), "cannot have unsized immediates");
                 // Yay, we got a value that we can write directly.
                 // FIXME: Add a check to make sure that if `src` is indirect,
@@ -955,6 +970,7 @@ where
     /// This supports unsized types and returns the computed size to avoid some
     /// redundant computation when copying; use `force_allocation` for a simpler, sized-only
     /// version.
+    #[instrument(skip(self), level = "debug")]
     pub fn force_allocation_maybe_sized(
         &mut self,
         place: &PlaceTy<'tcx, M::PointerTag>,
@@ -962,6 +978,7 @@ where
     ) -> InterpResult<'tcx, (MPlaceTy<'tcx, M::PointerTag>, Option<Size>)> {
         let (mplace, size) = match place.place {
             Place::Local { frame, local } => {
+                debug!("LocalPlace");
                 match M::access_local_mut(self, frame, local)? {
                     Ok(&mut local_val) => {
                         // We need to make an allocation.
@@ -975,9 +992,12 @@ where
                         let (size, align) = self
                             .size_and_align_of(&meta, &local_layout)?
                             .expect("Cannot allocate for non-dyn-sized type");
+                        debug!(?size, ?align);
                         let ptr = self.allocate_ptr(size, align, MemoryKind::Stack)?;
+                        debug!("allocated ptr: {:?}", ptr);
                         let mplace = MemPlace { ptr: ptr.into(), align, meta };
                         if let LocalValue::Live(Operand::Immediate(value)) = local_val {
+                            debug!("LocalValue::Live: immediate value {:?}", value);
                             // Preserve old value.
                             // We don't have to validate as we can assume the local
                             // was already valid for its type.
@@ -1037,6 +1057,7 @@ where
     }
 
     /// Writes the discriminant of the given variant.
+    #[instrument(skip(self), level = "debug")]
     pub fn write_discriminant(
         &mut self,
         variant_index: VariantIdx,