diff --git a/crates/hir-ty/src/display.rs b/crates/hir-ty/src/display.rs
index d81926f7c976..4468b96b7764 100644
--- a/crates/hir-ty/src/display.rs
+++ b/crates/hir-ty/src/display.rs
@@ -515,7 +515,7 @@ fn render_const_scalar(
             TyKind::Dyn(_) => {
                 let addr = usize::from_le_bytes(b[0..b.len() / 2].try_into().unwrap());
                 let ty_id = usize::from_le_bytes(b[b.len() / 2..].try_into().unwrap());
-                let Ok(t) = memory_map.vtable.ty(ty_id) else {
+                let Ok(t) = memory_map.vtable_ty(ty_id) else {
                     return f.write_str("<ty-missing-in-vtable-map>");
                 };
                 let Ok(layout) = f.db.layout_of_ty(t.clone(), trait_env) else {
diff --git a/crates/hir-ty/src/infer/closure.rs b/crates/hir-ty/src/infer/closure.rs
index ac00b00fcd97..8a832b6b9042 100644
--- a/crates/hir-ty/src/infer/closure.rs
+++ b/crates/hir-ty/src/infer/closure.rs
@@ -1,6 +1,6 @@
 //! Inference of closure parameter types based on the closure's expected type.
 
-use std::{cmp, collections::HashMap, convert::Infallible, mem};
+use std::{cmp, convert::Infallible, mem};
 
 use chalk_ir::{
     cast::Cast,
@@ -778,7 +778,7 @@ impl InferenceContext<'_> {
 
     fn minimize_captures(&mut self) {
         self.current_captures.sort_by_key(|it| it.place.projections.len());
-        let mut hash_map = HashMap::<HirPlace, usize>::new();
+        let mut hash_map = FxHashMap::<HirPlace, usize>::default();
         let result = mem::take(&mut self.current_captures);
         for item in result {
             let mut lookup_place = HirPlace { local: item.place.local, projections: vec![] };
diff --git a/crates/hir-ty/src/lib.rs b/crates/hir-ty/src/lib.rs
index 964ca7ce940e..793b52b49faa 100644
--- a/crates/hir-ty/src/lib.rs
+++ b/crates/hir-ty/src/lib.rs
@@ -37,8 +37,8 @@ mod tests;
 mod test_db;
 
 use std::{
-    collections::{hash_map::Entry, HashMap},
-    hash::Hash,
+    collections::hash_map::Entry,
+    hash::{BuildHasherDefault, Hash},
 };
 
 use chalk_ir::{
@@ -52,7 +52,7 @@ use hir_def::{hir::ExprId, type_ref::Rawness, GeneralConstId, TypeOrConstParamId
 use hir_expand::name;
 use la_arena::{Arena, Idx};
 use mir::{MirEvalError, VTableMap};
-use rustc_hash::FxHashSet;
+use rustc_hash::{FxHashMap, FxHashSet};
 use syntax::ast::{make, ConstArg};
 use traits::FnTrait;
 use triomphe::Arc;
@@ -171,24 +171,45 @@ pub type Variances = chalk_ir::Variances<Interner>;
 /// the necessary bits of memory of the const eval session to keep the constant
 /// meaningful.
 #[derive(Debug, Default, Clone, PartialEq, Eq)]
-pub struct MemoryMap {
-    pub memory: HashMap<usize, Vec<u8>>,
-    pub vtable: VTableMap,
+pub enum MemoryMap {
+    #[default]
+    Empty,
+    Simple(Box<[u8]>),
+    Complex(Box<ComplexMemoryMap>),
 }
 
-impl MemoryMap {
-    fn insert(&mut self, addr: usize, x: Vec<u8>) {
+#[derive(Debug, Default, Clone, PartialEq, Eq)]
+pub struct ComplexMemoryMap {
+    memory: FxHashMap<usize, Box<[u8]>>,
+    vtable: VTableMap,
+}
+
+impl ComplexMemoryMap {
+    fn insert(&mut self, addr: usize, val: Box<[u8]>) {
         match self.memory.entry(addr) {
             Entry::Occupied(mut e) => {
-                if e.get().len() < x.len() {
-                    e.insert(x);
+                if e.get().len() < val.len() {
+                    e.insert(val);
                 }
             }
             Entry::Vacant(e) => {
-                e.insert(x);
+                e.insert(val);
             }
         }
     }
+}
+
+impl MemoryMap {
+    pub fn vtable_ty(&self, id: usize) -> Result<&Ty, MirEvalError> {
+        match self {
+            MemoryMap::Empty | MemoryMap::Simple(_) => Err(MirEvalError::InvalidVTableId(id)),
+            MemoryMap::Complex(cm) => cm.vtable.ty(id),
+        }
+    }
+
+    fn simple(v: Box<[u8]>) -> Self {
+        MemoryMap::Simple(v)
+    }
 
     /// This functions convert each address by a function `f` which gets the byte intervals and assign an address
     /// to them. It is useful when you want to load a constant with a memory map in a new memory. You can pass an
@@ -196,22 +217,33 @@ impl MemoryMap {
     fn transform_addresses(
         &self,
         mut f: impl FnMut(&[u8], usize) -> Result<usize, MirEvalError>,
-    ) -> Result<HashMap<usize, usize>, MirEvalError> {
-        self.memory
-            .iter()
-            .map(|x| {
-                let addr = *x.0;
-                let align = if addr == 0 { 64 } else { (addr - (addr & (addr - 1))).min(64) };
-                Ok((addr, f(x.1, align)?))
-            })
-            .collect()
+    ) -> Result<FxHashMap<usize, usize>, MirEvalError> {
+        let mut transform = |(addr, val): (&usize, &Box<[u8]>)| {
+            let addr = *addr;
+            let align = if addr == 0 { 64 } else { (addr - (addr & (addr - 1))).min(64) };
+            f(val, align).and_then(|it| Ok((addr, it)))
+        };
+        match self {
+            MemoryMap::Empty => Ok(Default::default()),
+            MemoryMap::Simple(m) => transform((&0, m)).map(|(addr, val)| {
+                let mut map = FxHashMap::with_capacity_and_hasher(1, BuildHasherDefault::default());
+                map.insert(addr, val);
+                map
+            }),
+            MemoryMap::Complex(cm) => cm.memory.iter().map(transform).collect(),
+        }
     }
 
-    fn get<'a>(&'a self, addr: usize, size: usize) -> Option<&'a [u8]> {
+    fn get(&self, addr: usize, size: usize) -> Option<&[u8]> {
         if size == 0 {
             Some(&[])
         } else {
-            self.memory.get(&addr)?.get(0..size)
+            match self {
+                MemoryMap::Empty => Some(&[]),
+                MemoryMap::Simple(m) if addr == 0 => m.get(0..size),
+                MemoryMap::Simple(_) => None,
+                MemoryMap::Complex(cm) => cm.memory.get(&addr)?.get(0..size),
+            }
         }
     }
 }
diff --git a/crates/hir-ty/src/mir/eval.rs b/crates/hir-ty/src/mir/eval.rs
index 4c06566e7ce0..5650956d2f4c 100644
--- a/crates/hir-ty/src/mir/eval.rs
+++ b/crates/hir-ty/src/mir/eval.rs
@@ -1,13 +1,6 @@
 //! This module provides a MIR interpreter, which is used in const eval.
 
-use std::{
-    borrow::Cow,
-    cell::RefCell,
-    collections::{HashMap, HashSet},
-    fmt::Write,
-    iter, mem,
-    ops::Range,
-};
+use std::{borrow::Cow, cell::RefCell, fmt::Write, iter, mem, ops::Range};
 
 use base_db::{CrateId, FileId};
 use chalk_ir::{cast::Cast, Mutability};
@@ -40,8 +33,8 @@ use crate::{
     name, static_lifetime,
     traits::FnTrait,
     utils::{detect_variant_from_bytes, ClosureSubst},
-    CallableDefId, ClosureId, Const, ConstScalar, FnDefId, Interner, MemoryMap, Substitution,
-    TraitEnvironment, Ty, TyBuilder, TyExt, TyKind,
+    CallableDefId, ClosureId, ComplexMemoryMap, Const, ConstScalar, FnDefId, Interner, MemoryMap,
+    Substitution, TraitEnvironment, Ty, TyBuilder, TyExt, TyKind,
 };
 
 use super::{
@@ -98,6 +91,15 @@ impl VTableMap {
         let id = from_bytes!(usize, bytes);
         self.ty(id)
     }
+
+    pub fn shrink_to_fit(&mut self) {
+        self.id_to_ty.shrink_to_fit();
+        self.ty_to_id.shrink_to_fit();
+    }
+
+    fn is_empty(&self) -> bool {
+        self.id_to_ty.is_empty() && self.ty_to_id.is_empty()
+    }
 }
 
 #[derive(Debug, Default, Clone, PartialEq, Eq)]
@@ -251,13 +253,6 @@ impl From<Interval> for IntervalOrOwned {
 }
 
 impl IntervalOrOwned {
-    pub(crate) fn to_vec(self, memory: &Evaluator<'_>) -> Result<Vec<u8>> {
-        Ok(match self {
-            IntervalOrOwned::Owned(o) => o,
-            IntervalOrOwned::Borrowed(b) => b.get(memory)?.to_vec(),
-        })
-    }
-
     fn get<'a>(&'a self, memory: &'a Evaluator<'a>) -> Result<&'a [u8]> {
         Ok(match self {
             IntervalOrOwned::Owned(o) => o,
@@ -291,8 +286,8 @@ impl Address {
         }
     }
 
-    fn to_bytes(&self) -> Vec<u8> {
-        usize::to_le_bytes(self.to_usize()).to_vec()
+    fn to_bytes(&self) -> [u8; mem::size_of::<usize>()] {
+        usize::to_le_bytes(self.to_usize())
     }
 
     fn to_usize(&self) -> usize {
@@ -510,6 +505,20 @@ struct Locals {
     drop_flags: DropFlags,
 }
 
+pub struct MirOutput {
+    stdout: Vec<u8>,
+    stderr: Vec<u8>,
+}
+
+impl MirOutput {
+    pub fn stdout(&self) -> Cow<'_, str> {
+        String::from_utf8_lossy(&self.stdout)
+    }
+    pub fn stderr(&self) -> Cow<'_, str> {
+        String::from_utf8_lossy(&self.stderr)
+    }
+}
+
 pub fn interpret_mir(
     db: &dyn HirDatabase,
     body: Arc<MirBody>,
@@ -520,7 +529,7 @@ pub fn interpret_mir(
     // (and probably should) do better here, for example by excluding bindings outside of the target expression.
     assert_placeholder_ty_is_unused: bool,
     trait_env: Option<Arc<TraitEnvironment>>,
-) -> (Result<Const>, String, String) {
+) -> (Result<Const>, MirOutput) {
     let ty = body.locals[return_slot()].ty.clone();
     let mut evaluator = Evaluator::new(db, body.owner, assert_placeholder_ty_is_unused, trait_env);
     let it: Result<Const> = (|| {
@@ -534,14 +543,17 @@ pub fn interpret_mir(
             &ty,
             &Locals { ptr: ArenaMap::new(), body, drop_flags: DropFlags::default() },
         )?;
-        memory_map.vtable = evaluator.vtable_map.clone();
-        return Ok(intern_const_scalar(ConstScalar::Bytes(bytes.into(), memory_map), ty));
+        let bytes = bytes.into();
+        let memory_map = if memory_map.memory.is_empty() && evaluator.vtable_map.is_empty() {
+            MemoryMap::Empty
+        } else {
+            memory_map.vtable = mem::take(&mut evaluator.vtable_map);
+            memory_map.vtable.shrink_to_fit();
+            MemoryMap::Complex(Box::new(memory_map))
+        };
+        return Ok(intern_const_scalar(ConstScalar::Bytes(bytes, memory_map), ty));
     })();
-    (
-        it,
-        String::from_utf8_lossy(&evaluator.stdout).into_owned(),
-        String::from_utf8_lossy(&evaluator.stderr).into_owned(),
-    )
+    (it, MirOutput { stdout: evaluator.stdout, stderr: evaluator.stderr })
 }
 
 #[cfg(test)]
@@ -563,7 +575,7 @@ impl Evaluator<'_> {
             code_stack: vec![],
             vtable_map: VTableMap::default(),
             thread_local_storage: TlsData::default(),
-            static_locations: HashMap::default(),
+            static_locations: Default::default(),
             db,
             random_state: oorandom::Rand64::new(0),
             trait_env: trait_env.unwrap_or_else(|| db.trait_environment_for_body(owner)),
@@ -574,11 +586,11 @@ impl Evaluator<'_> {
             stack_depth_limit: 100,
             execution_limit: EXECUTION_LIMIT,
             memory_limit: 1000_000_000, // 2GB, 1GB for stack and 1GB for heap
-            layout_cache: RefCell::new(HashMap::default()),
-            projected_ty_cache: RefCell::new(HashMap::default()),
-            not_special_fn_cache: RefCell::new(HashSet::default()),
-            mir_or_dyn_index_cache: RefCell::new(HashMap::default()),
-            unused_locals_store: RefCell::new(HashMap::default()),
+            layout_cache: RefCell::new(Default::default()),
+            projected_ty_cache: RefCell::new(Default::default()),
+            not_special_fn_cache: RefCell::new(Default::default()),
+            mir_or_dyn_index_cache: RefCell::new(Default::default()),
+            unused_locals_store: RefCell::new(Default::default()),
             cached_ptr_size: match db.target_data_layout(crate_id) {
                 Some(it) => it.pointer_size.bytes_usize(),
                 None => 8,
@@ -838,8 +850,8 @@ impl Evaluator<'_> {
                         match &statement.kind {
                             StatementKind::Assign(l, r) => {
                                 let addr = self.place_addr(l, &locals)?;
-                                let result = self.eval_rvalue(r, &mut locals)?.to_vec(&self)?;
-                                self.write_memory(addr, &result)?;
+                                let result = self.eval_rvalue(r, &mut locals)?;
+                                self.copy_from_interval_or_owned(addr, result)?;
                                 locals
                                     .drop_flags
                                     .add_place(l.clone(), &locals.body.projection_store);
@@ -1051,7 +1063,7 @@ impl Evaluator<'_> {
             Rvalue::Use(it) => Borrowed(self.eval_operand(it, locals)?),
             Rvalue::Ref(_, p) => {
                 let (addr, _, metadata) = self.place_addr_and_ty_and_metadata(p, locals)?;
-                let mut r = addr.to_bytes();
+                let mut r = addr.to_bytes().to_vec();
                 if let Some(metadata) = metadata {
                     r.extend(metadata.get(self)?);
                 }
@@ -1284,7 +1296,7 @@ impl Evaluator<'_> {
                     not_supported!("unsized box initialization");
                 };
                 let addr = self.heap_allocate(size, align)?;
-                Owned(addr.to_bytes())
+                Owned(addr.to_bytes().to_vec())
             }
             Rvalue::CopyForDeref(_) => not_supported!("copy for deref"),
             Rvalue::Aggregate(kind, values) => {
@@ -1716,7 +1728,18 @@ impl Evaluator<'_> {
         }
         let addr = self.heap_allocate(size, align)?;
         self.write_memory(addr, &v)?;
-        self.patch_addresses(&patch_map, &memory_map.vtable, addr, ty, locals)?;
+        self.patch_addresses(
+            &patch_map,
+            |bytes| match &memory_map {
+                MemoryMap::Empty | MemoryMap::Simple(_) => {
+                    Err(MirEvalError::InvalidVTableId(from_bytes!(usize, bytes)))
+                }
+                MemoryMap::Complex(cm) => cm.vtable.ty_of_bytes(bytes),
+            },
+            addr,
+            ty,
+            locals,
+        )?;
         Ok(Interval::new(addr, size))
     }
 
@@ -1768,6 +1791,13 @@ impl Evaluator<'_> {
         Ok(())
     }
 
+    fn copy_from_interval_or_owned(&mut self, addr: Address, r: IntervalOrOwned) -> Result<()> {
+        match r {
+            IntervalOrOwned::Borrowed(r) => self.copy_from_interval(addr, r),
+            IntervalOrOwned::Owned(r) => self.write_memory(addr, &r),
+        }
+    }
+
     fn copy_from_interval(&mut self, addr: Address, r: Interval) -> Result<()> {
         if r.size == 0 {
             return Ok(());
@@ -1888,13 +1918,18 @@ impl Evaluator<'_> {
         }
     }
 
-    fn create_memory_map(&self, bytes: &[u8], ty: &Ty, locals: &Locals) -> Result<MemoryMap> {
+    fn create_memory_map(
+        &self,
+        bytes: &[u8],
+        ty: &Ty,
+        locals: &Locals,
+    ) -> Result<ComplexMemoryMap> {
         fn rec(
             this: &Evaluator<'_>,
             bytes: &[u8],
             ty: &Ty,
             locals: &Locals,
-            mm: &mut MemoryMap,
+            mm: &mut ComplexMemoryMap,
         ) -> Result<()> {
             match ty.kind(Interner) {
                 TyKind::Ref(_, _, t) => {
@@ -1904,7 +1939,7 @@ impl Evaluator<'_> {
                             let addr_usize = from_bytes!(usize, bytes);
                             mm.insert(
                                 addr_usize,
-                                this.read_memory(Address::from_usize(addr_usize), size)?.to_vec(),
+                                this.read_memory(Address::from_usize(addr_usize), size)?.into(),
                             )
                         }
                         None => {
@@ -1930,7 +1965,7 @@ impl Evaluator<'_> {
                             let size = element_size * count;
                             let addr = Address::from_bytes(addr)?;
                             let b = this.read_memory(addr, size)?;
-                            mm.insert(addr.to_usize(), b.to_vec());
+                            mm.insert(addr.to_usize(), b.into());
                             if let Some(ty) = check_inner {
                                 for i in 0..count {
                                     let offset = element_size * i;
@@ -2003,15 +2038,15 @@ impl Evaluator<'_> {
             }
             Ok(())
         }
-        let mut mm = MemoryMap::default();
-        rec(self, bytes, ty, locals, &mut mm)?;
+        let mut mm = ComplexMemoryMap::default();
+        rec(&self, bytes, ty, locals, &mut mm)?;
         Ok(mm)
     }
 
-    fn patch_addresses(
+    fn patch_addresses<'vtable>(
         &mut self,
-        patch_map: &HashMap<usize, usize>,
-        old_vtable: &VTableMap,
+        patch_map: &FxHashMap<usize, usize>,
+        ty_of_bytes: impl Fn(&[u8]) -> Result<&'vtable Ty> + Copy,
         addr: Address,
         ty: &Ty,
         locals: &Locals,
@@ -2038,7 +2073,7 @@ impl Evaluator<'_> {
                 }
             }
             TyKind::Function(_) => {
-                let ty = old_vtable.ty_of_bytes(self.read_memory(addr, my_size)?)?.clone();
+                let ty = ty_of_bytes(self.read_memory(addr, my_size)?)?.clone();
                 let new_id = self.vtable_map.id(ty);
                 self.write_memory(addr, &new_id.to_le_bytes())?;
             }
@@ -2049,7 +2084,7 @@ impl Evaluator<'_> {
                         let ty = ty.clone().substitute(Interner, subst);
                         self.patch_addresses(
                             patch_map,
-                            old_vtable,
+                            ty_of_bytes,
                             addr.offset(offset),
                             &ty,
                             locals,
@@ -2071,7 +2106,7 @@ impl Evaluator<'_> {
                             let ty = ty.clone().substitute(Interner, subst);
                             self.patch_addresses(
                                 patch_map,
-                                old_vtable,
+                                ty_of_bytes,
                                 addr.offset(offset),
                                 &ty,
                                 locals,
@@ -2084,7 +2119,7 @@ impl Evaluator<'_> {
                 for (id, ty) in subst.iter(Interner).enumerate() {
                     let ty = ty.assert_ty_ref(Interner); // Tuple only has type argument
                     let offset = layout.fields.offset(id).bytes_usize();
-                    self.patch_addresses(patch_map, old_vtable, addr.offset(offset), ty, locals)?;
+                    self.patch_addresses(patch_map, ty_of_bytes, addr.offset(offset), ty, locals)?;
                 }
             }
             TyKind::Array(inner, len) => {
@@ -2096,7 +2131,7 @@ impl Evaluator<'_> {
                 for i in 0..len {
                     self.patch_addresses(
                         patch_map,
-                        old_vtable,
+                        ty_of_bytes,
                         addr.offset(i * size),
                         inner,
                         locals,
@@ -2167,7 +2202,7 @@ impl Evaluator<'_> {
             .map_err(|it| MirEvalError::MirLowerErrorForClosure(closure, it))?;
         let closure_data = if mir_body.locals[mir_body.param_locals[0]].ty.as_reference().is_some()
         {
-            closure_data.addr.to_bytes()
+            closure_data.addr.to_bytes().to_vec()
         } else {
             closure_data.get(self)?.to_owned()
         };
@@ -2553,7 +2588,7 @@ impl Evaluator<'_> {
                 body,
                 locals,
                 drop_fn,
-                [IntervalOrOwned::Owned(addr.to_bytes())].into_iter(),
+                iter::once(IntervalOrOwned::Owned(addr.to_bytes().to_vec())),
                 span,
                 Interval { addr: Address::Invalid(0), size: 0 },
                 None,
diff --git a/crates/hir-ty/src/mir/eval/tests.rs b/crates/hir-ty/src/mir/eval/tests.rs
index b0f929279a5c..6552bf493377 100644
--- a/crates/hir-ty/src/mir/eval/tests.rs
+++ b/crates/hir-ty/src/mir/eval/tests.rs
@@ -31,9 +31,9 @@ fn eval_main(db: &TestDB, file_id: FileId) -> Result<(String, String), MirEvalEr
             db.trait_environment(func_id.into()),
         )
         .map_err(|e| MirEvalError::MirLowerError(func_id.into(), e))?;
-    let (result, stdout, stderr) = interpret_mir(db, body, false, None);
+    let (result, output) = interpret_mir(db, body, false, None);
     result?;
-    Ok((stdout, stderr))
+    Ok((output.stdout().into_owned(), output.stderr().into_owned()))
 }
 
 fn check_pass(ra_fixture: &str) {
diff --git a/crates/hir-ty/src/mir/lower.rs b/crates/hir-ty/src/mir/lower.rs
index a94da818b622..947fa3c21d6b 100644
--- a/crates/hir-ty/src/mir/lower.rs
+++ b/crates/hir-ty/src/mir/lower.rs
@@ -1403,31 +1403,27 @@ impl<'ctx> MirLowerCtx<'ctx> {
         const USIZE_SIZE: usize = mem::size_of::<usize>();
         let bytes: Box<[_]> = match l {
             hir_def::hir::Literal::String(b) => {
-                let b = b.as_bytes();
-                let mut data = Box::new([0; { 2 * USIZE_SIZE }]);
+                let mut data = [0; { 2 * USIZE_SIZE }];
                 data[..USIZE_SIZE].copy_from_slice(&0usize.to_le_bytes());
                 data[USIZE_SIZE..].copy_from_slice(&b.len().to_le_bytes());
-                let mut mm = MemoryMap::default();
-                mm.insert(0, b.to_vec());
-                return Ok(Operand::from_concrete_const(data, mm, ty));
+                let mm = MemoryMap::simple(b.as_bytes().into());
+                return Ok(Operand::from_concrete_const(Box::new(data), mm, ty));
             }
             hir_def::hir::Literal::CString(b) => {
-                let bytes = b.iter().copied().chain(iter::once(0)).collect::<Vec<_>>();
+                let bytes = b.iter().copied().chain(iter::once(0)).collect::<Box<_>>();
 
-                let mut data = Box::new([0; { 2 * USIZE_SIZE }]);
+                let mut data = [0; { 2 * USIZE_SIZE }];
                 data[..USIZE_SIZE].copy_from_slice(&0usize.to_le_bytes());
                 data[USIZE_SIZE..].copy_from_slice(&bytes.len().to_le_bytes());
-                let mut mm = MemoryMap::default();
-                mm.insert(0, bytes);
-                return Ok(Operand::from_concrete_const(data, mm, ty));
+                let mm = MemoryMap::simple(bytes);
+                return Ok(Operand::from_concrete_const(Box::new(data), mm, ty));
             }
             hir_def::hir::Literal::ByteString(b) => {
-                let mut data = Box::new([0; { 2 * USIZE_SIZE }]);
+                let mut data = [0; { 2 * USIZE_SIZE }];
                 data[..USIZE_SIZE].copy_from_slice(&0usize.to_le_bytes());
                 data[USIZE_SIZE..].copy_from_slice(&b.len().to_le_bytes());
-                let mut mm = MemoryMap::default();
-                mm.insert(0, b.to_vec());
-                return Ok(Operand::from_concrete_const(data, mm, ty));
+                let mm = MemoryMap::simple(b.clone());
+                return Ok(Operand::from_concrete_const(Box::new(data), mm, ty));
             }
             hir_def::hir::Literal::Char(c) => Box::new(u32::from(*c).to_le_bytes()),
             hir_def::hir::Literal::Bool(b) => Box::new([*b as u8]),
diff --git a/crates/hir/src/lib.rs b/crates/hir/src/lib.rs
index 4e4b758264f4..49f599a67a1a 100644
--- a/crates/hir/src/lib.rs
+++ b/crates/hir/src/lib.rs
@@ -2183,7 +2183,7 @@ impl Function {
                 return r;
             }
         };
-        let (result, stdout, stderr) = interpret_mir(db, body, false, None);
+        let (result, output) = interpret_mir(db, body, false, None);
         let mut text = match result {
             Ok(_) => "pass".to_string(),
             Err(e) => {
@@ -2192,10 +2192,12 @@ impl Function {
                 r
             }
         };
+        let stdout = output.stdout().into_owned();
         if !stdout.is_empty() {
             text += "\n--------- stdout ---------\n";
             text += &stdout;
         }
+        let stderr = output.stdout().into_owned();
         if !stderr.is_empty() {
             text += "\n--------- stderr ---------\n";
             text += &stderr;