Update other codegens to use tcx managed vtable allocations.

Author: crlf0710

compiler/rustc_codegen_cranelift/src/common.rs

@@ -233,7 +233,7 @@ pub(crate) struct FunctionCx<'m, 'clif, 'tcx: 'm> {
     pub(crate) module: &'m mut dyn Module,
     pub(crate) tcx: TyCtxt<'tcx>,
     pub(crate) pointer_type: Type, // Cached from module
-    pub(crate) vtables: FxHashMap<(Ty<'tcx>, Option<ty::PolyExistentialTraitRef<'tcx>>), DataId>,
+    pub(crate) vtables: FxHashMap<(Ty<'tcx>, Option<ty::PolyExistentialTraitRef<'tcx>>), Pointer>,
     pub(crate) constants_cx: ConstantCx,
 
     pub(crate) instance: Instance<'tcx>,

compiler/rustc_codegen_cranelift/src/constant.rs

@@ -249,7 +249,7 @@ pub(crate) fn codegen_const_value<'tcx>(
     }
 }
 
-fn pointer_for_allocation<'tcx>(
+pub(crate) fn pointer_for_allocation<'tcx>(
     fx: &mut FunctionCx<'_, '_, 'tcx>,
     alloc: &'tcx Allocation,
 ) -> crate::pointer::Pointer {

compiler/rustc_codegen_cranelift/src/lib.rs

@@ -98,7 +98,7 @@ mod prelude {
     pub(crate) use cranelift_codegen::isa::{self, CallConv};
     pub(crate) use cranelift_codegen::Context;
     pub(crate) use cranelift_frontend::{FunctionBuilder, FunctionBuilderContext, Variable};
-    pub(crate) use cranelift_module::{self, DataContext, DataId, FuncId, Linkage, Module};
+    pub(crate) use cranelift_module::{self, DataContext, FuncId, Linkage, Module};
 
     pub(crate) use crate::abi::*;
     pub(crate) use crate::base::{codegen_operand, codegen_place};

compiler/rustc_codegen_cranelift/src/unsize.rs

@@ -31,9 +31,7 @@ pub(crate) fn unsized_info<'tcx>(
             // change to the vtable.
             old_info.expect("unsized_info: missing old info for trait upcast")
         }
-        (_, &ty::Dynamic(ref data, ..)) => {
-            crate::vtable::get_vtable(fx, fx.layout_of(source), data.principal())
-        }
+        (_, &ty::Dynamic(ref data, ..)) => crate::vtable::get_vtable(fx, source, data.principal()),
         _ => bug!("unsized_info: invalid unsizing {:?} -> {:?}", source, target),
     }
 }

compiler/rustc_codegen_cranelift/src/vtable.rs

@@ -4,7 +4,7 @@
 // FIXME dedup this logic between miri, cg_llvm and cg_clif
 
 use crate::prelude::*;
-use ty::VtblEntry;
+use super::constant::pointer_for_allocation;
 
 fn vtable_memflags() -> MemFlags {
     let mut flags = MemFlags::trusted(); // A vtable access is always aligned and will never trap.
@@ -66,105 +66,19 @@ pub(crate) fn get_ptr_and_method_ref<'tcx>(
 
 pub(crate) fn get_vtable<'tcx>(
     fx: &mut FunctionCx<'_, '_, 'tcx>,
-    layout: TyAndLayout<'tcx>,
+    ty: Ty<'tcx>,
     trait_ref: Option<ty::PolyExistentialTraitRef<'tcx>>,
 ) -> Value {
-    let data_id = if let Some(data_id) = fx.vtables.get(&(layout.ty, trait_ref)) {
-        *data_id
+    let vtable_ptr = if let Some(vtable_ptr) = fx.vtables.get(&(ty, trait_ref)) {
+        *vtable_ptr
     } else {
-        let data_id = build_vtable(fx, layout, trait_ref);
-        fx.vtables.insert((layout.ty, trait_ref), data_id);
-        data_id
-    };
-
-    let local_data_id = fx.module.declare_data_in_func(data_id, &mut fx.bcx.func);
-    fx.bcx.ins().global_value(fx.pointer_type, local_data_id)
-}
-
-fn build_vtable<'tcx>(
-    fx: &mut FunctionCx<'_, '_, 'tcx>,
-    layout: TyAndLayout<'tcx>,
-    trait_ref: Option<ty::PolyExistentialTraitRef<'tcx>>,
-) -> DataId {
-    let tcx = fx.tcx;
-    let usize_size = fx.layout_of(fx.tcx.types.usize).size.bytes() as usize;
+        let vtable_alloc_id = fx.tcx.vtable_allocation(ty, trait_ref);
+        let vtable_allocation = fx.tcx.global_alloc(vtable_alloc_id).unwrap_memory();
+        let vtable_ptr = pointer_for_allocation(fx, vtable_allocation);
 
-    let drop_in_place_fn = import_function(
-        tcx,
-        fx.module,
-        Instance::resolve_drop_in_place(tcx, layout.ty).polymorphize(fx.tcx),
-    );
-
-    let vtable_entries = if let Some(trait_ref) = trait_ref {
-        tcx.vtable_entries(trait_ref.with_self_ty(tcx, layout.ty))
-    } else {
-        ty::COMMON_VTABLE_ENTRIES
+        fx.vtables.insert((ty, trait_ref), vtable_ptr);
+        vtable_ptr
     };
 
-    let mut data_ctx = DataContext::new();
-    let mut data = ::std::iter::repeat(0u8)
-        .take(vtable_entries.len() * usize_size)
-        .collect::<Vec<u8>>()
-        .into_boxed_slice();
-
-    for (idx, entry) in vtable_entries.iter().enumerate() {
-        match entry {
-            VtblEntry::MetadataSize => {
-                write_usize(fx.tcx, &mut data, idx, layout.size.bytes());
-            }
-            VtblEntry::MetadataAlign => {
-                write_usize(fx.tcx, &mut data, idx, layout.align.abi.bytes());
-            }
-            VtblEntry::MetadataDropInPlace | VtblEntry::Vacant | VtblEntry::Method(_, _) => {}
-        }
-    }
-    data_ctx.define(data);
-
-    for (idx, entry) in vtable_entries.iter().enumerate() {
-        match entry {
-            VtblEntry::MetadataDropInPlace => {
-                let func_ref = fx.module.declare_func_in_data(drop_in_place_fn, &mut data_ctx);
-                data_ctx.write_function_addr((idx * usize_size) as u32, func_ref);
-            }
-            VtblEntry::Method(def_id, substs) => {
-                let func_id = import_function(
-                    tcx,
-                    fx.module,
-                    Instance::resolve_for_vtable(tcx, ParamEnv::reveal_all(), *def_id, substs)
-                        .unwrap()
-                        .polymorphize(fx.tcx),
-                );
-                let func_ref = fx.module.declare_func_in_data(func_id, &mut data_ctx);
-                data_ctx.write_function_addr((idx * usize_size) as u32, func_ref);
-            }
-            VtblEntry::MetadataSize | VtblEntry::MetadataAlign | VtblEntry::Vacant => {}
-        }
-    }
-
-    data_ctx.set_align(fx.tcx.data_layout.pointer_align.pref.bytes());
-
-    let data_id = fx.module.declare_anonymous_data(false, false).unwrap();
-
-    fx.module.define_data(data_id, &data_ctx).unwrap();
-
-    data_id
-}
-
-fn write_usize(tcx: TyCtxt<'_>, buf: &mut [u8], idx: usize, num: u64) {
-    let pointer_size =
-        tcx.layout_of(ParamEnv::reveal_all().and(tcx.types.usize)).unwrap().size.bytes() as usize;
-    let target = &mut buf[idx * pointer_size..(idx + 1) * pointer_size];
-
-    match tcx.data_layout.endian {
-        rustc_target::abi::Endian::Little => match pointer_size {
-            4 => target.copy_from_slice(&(num as u32).to_le_bytes()),
-            8 => target.copy_from_slice(&(num as u64).to_le_bytes()),
-            _ => todo!("pointer size {} is not yet supported", pointer_size),
-        },
-        rustc_target::abi::Endian::Big => match pointer_size {
-            4 => target.copy_from_slice(&(num as u32).to_be_bytes()),
-            8 => target.copy_from_slice(&(num as u64).to_be_bytes()),
-            _ => todo!("pointer size {} is not yet supported", pointer_size),
-        },
-    }
+    vtable_ptr.get_addr(fx)
 }

compiler/rustc_codegen_llvm/src/common.rs

@@ -282,6 +282,10 @@ impl ConstMethods<'tcx> for CodegenCx<'ll, 'tcx> {
         }
     }
 
+    fn const_data_from_alloc(&self, alloc: &Allocation) -> Self::Value {
+        const_alloc_to_llvm(self, alloc)
+    }
+
     fn from_const_alloc(
         &self,
         layout: TyAndLayout<'tcx>,

compiler/rustc_codegen_ssa/src/meth.rs

@@ -1,6 +1,6 @@
 use crate::traits::*;
 
-use rustc_middle::ty::{self, Instance, Ty, VtblEntry, COMMON_VTABLE_ENTRIES};
+use rustc_middle::ty::{self, Ty};
 use rustc_target::abi::call::FnAbi;
 
 #[derive(Copy, Clone, Debug)]
@@ -70,48 +70,13 @@ pub fn get_vtable<'tcx, Cx: CodegenMethods<'tcx>>(
         return val;
     }
 
-    // Not in the cache; build it.
-    let nullptr = cx.const_null(cx.type_i8p_ext(cx.data_layout().instruction_address_space));
-
-    let vtable_entries = if let Some(trait_ref) = trait_ref {
-        tcx.vtable_entries(trait_ref.with_self_ty(tcx, ty))
-    } else {
-        COMMON_VTABLE_ENTRIES
-    };
-
-    let layout = cx.layout_of(ty);
-    // /////////////////////////////////////////////////////////////////////////////////////////////
-    // If you touch this code, be sure to also make the corresponding changes to
-    // `get_vtable` in `rust_mir/interpret/traits.rs`.
-    // /////////////////////////////////////////////////////////////////////////////////////////////
-    let components: Vec<_> = vtable_entries
-        .iter()
-        .map(|entry| match entry {
-            VtblEntry::MetadataDropInPlace => {
-                cx.get_fn_addr(Instance::resolve_drop_in_place(cx.tcx(), ty))
-            }
-            VtblEntry::MetadataSize => cx.const_usize(layout.size.bytes()),
-            VtblEntry::MetadataAlign => cx.const_usize(layout.align.abi.bytes()),
-            VtblEntry::Vacant => nullptr,
-            VtblEntry::Method(def_id, substs) => cx.get_fn_addr(
-                ty::Instance::resolve_for_vtable(
-                    cx.tcx(),
-                    ty::ParamEnv::reveal_all(),
-                    *def_id,
-                    substs,
-                )
-                .unwrap()
-                .polymorphize(cx.tcx()),
-            ),
-        })
-        .collect();
-
-    let vtable_const = cx.const_struct(&components, false);
+    let vtable_alloc_id = tcx.vtable_allocation(ty, trait_ref);
+    let vtable_allocation = tcx.global_alloc(vtable_alloc_id).unwrap_memory();
+    let vtable_const = cx.const_data_from_alloc(vtable_allocation);
     let align = cx.data_layout().pointer_align.abi;
     let vtable = cx.static_addr_of(vtable_const, align, Some("vtable"));
 
     cx.create_vtable_metadata(ty, vtable);
-
     cx.vtables().borrow_mut().insert((ty, trait_ref), vtable);
     vtable
 }

compiler/rustc_codegen_ssa/src/traits/consts.rs

@@ -26,6 +26,8 @@ pub trait ConstMethods<'tcx>: BackendTypes {
     fn const_to_opt_uint(&self, v: Self::Value) -> Option<u64>;
     fn const_to_opt_u128(&self, v: Self::Value, sign_ext: bool) -> Option<u128>;
 
+    fn const_data_from_alloc(&self, alloc: &Allocation) -> Self::Value;
+
     fn scalar_to_backend(&self, cv: Scalar, layout: &abi::Scalar, llty: Self::Type) -> Self::Value;
     fn from_const_alloc(
         &self,

compiler/rustc_middle/src/ty/context.rs

@@ -11,7 +11,7 @@ use crate::middle;
 use crate::middle::cstore::{CrateStoreDyn, EncodedMetadata};
 use crate::middle::resolve_lifetime::{self, LifetimeScopeForPath, ObjectLifetimeDefault};
 use crate::middle::stability;
-use crate::mir::interpret::{self, Allocation, ConstValue, Scalar};
+use crate::mir::interpret::{self, AllocId, Allocation, ConstValue, Scalar};
 use crate::mir::{Body, Field, Local, Place, PlaceElem, ProjectionKind, Promoted};
 use crate::thir::Thir;
 use crate::traits;
@@ -1045,6 +1045,9 @@ pub struct GlobalCtxt<'tcx> {
     output_filenames: Arc<OutputFilenames>,
 
     pub main_def: Option<MainDefinition>,
+
+    pub(super) vtables_cache:
+        Lock<FxHashMap<(Ty<'tcx>, Option<ty::PolyExistentialTraitRef<'tcx>>), AllocId>>,
 }
 
 impl<'tcx> TyCtxt<'tcx> {
@@ -1202,6 +1205,7 @@ impl<'tcx> TyCtxt<'tcx> {
             alloc_map: Lock::new(interpret::AllocMap::new()),
             output_filenames: Arc::new(output_filenames),
             main_def: resolutions.main_def,
+            vtables_cache: Default::default(),
         }
     }
 

compiler/rustc_middle/src/ty/mod.rs

@@ -18,6 +18,7 @@ pub use adt::*;
 pub use assoc::*;
 pub use closure::*;
 pub use generics::*;
+pub use vtable::*;
 
 use crate::hir::exports::ExportMap;
 use crate::ich::StableHashingContext;
@@ -94,6 +95,7 @@ pub mod relate;
 pub mod subst;
 pub mod trait_def;
 pub mod util;
+pub mod vtable;
 pub mod walk;
 
 mod adt;
@@ -2009,19 +2011,3 @@ impl<'tcx> fmt::Debug for SymbolName<'tcx> {
         fmt::Display::fmt(&self.name, fmt)
     }
 }
-
-#[derive(Clone, Copy, Debug, PartialEq, HashStable)]
-pub enum VtblEntry<'tcx> {
-    MetadataDropInPlace,
-    MetadataSize,
-    MetadataAlign,
-    Vacant,
-    Method(DefId, SubstsRef<'tcx>),
-}
-
-pub const COMMON_VTABLE_ENTRIES: &[VtblEntry<'_>] =
-    &[VtblEntry::MetadataDropInPlace, VtblEntry::MetadataSize, VtblEntry::MetadataAlign];
-
-pub const COMMON_VTABLE_ENTRIES_DROPINPLACE: usize = 0;
-pub const COMMON_VTABLE_ENTRIES_SIZE: usize = 1;
-pub const COMMON_VTABLE_ENTRIES_ALIGN: usize = 2;

compiler/rustc_middle/src/ty/vtable.rs

@@ -0,0 +1,106 @@
+use std::convert::TryFrom;
+
+use crate::mir::interpret::{alloc_range, AllocId, Allocation, Pointer, Scalar};
+use crate::ty::fold::TypeFoldable;
+use crate::ty::{self, DefId, SubstsRef, Ty, TyCtxt};
+use rustc_ast::Mutability;
+
+#[derive(Clone, Copy, Debug, PartialEq, HashStable)]
+pub enum VtblEntry<'tcx> {
+    MetadataDropInPlace,
+    MetadataSize,
+    MetadataAlign,
+    Vacant,
+    Method(DefId, SubstsRef<'tcx>),
+}
+
+pub const COMMON_VTABLE_ENTRIES: &[VtblEntry<'_>] =
+    &[VtblEntry::MetadataDropInPlace, VtblEntry::MetadataSize, VtblEntry::MetadataAlign];
+
+pub const COMMON_VTABLE_ENTRIES_DROPINPLACE: usize = 0;
+pub const COMMON_VTABLE_ENTRIES_SIZE: usize = 1;
+pub const COMMON_VTABLE_ENTRIES_ALIGN: usize = 2;
+
+impl<'tcx> TyCtxt<'tcx> {
+    /// Retrieves an allocation that represents the contents of a vtable.
+    /// There's a cache within `TyCtxt` so it will be deduplicated.
+    pub fn vtable_allocation(
+        self,
+        ty: Ty<'tcx>,
+        poly_trait_ref: Option<ty::PolyExistentialTraitRef<'tcx>>,
+    ) -> AllocId {
+        let tcx = self;
+        let vtables_cache = tcx.vtables_cache.lock();
+        if let Some(alloc_id) = vtables_cache.get(&(ty, poly_trait_ref)).cloned() {
+            return alloc_id;
+        }
+        drop(vtables_cache);
+
+        // See https://github.com/rust-lang/rust/pull/86475#discussion_r655162674
+        assert!(
+            !ty.needs_subst() && !poly_trait_ref.map_or(false, |trait_ref| trait_ref.needs_subst())
+        );
+        let param_env = ty::ParamEnv::reveal_all();
+        let vtable_entries = if let Some(poly_trait_ref) = poly_trait_ref {
+            let trait_ref = poly_trait_ref.with_self_ty(tcx, ty);
+            let trait_ref = tcx.erase_regions(trait_ref);
+
+            tcx.vtable_entries(trait_ref)
+        } else {
+            COMMON_VTABLE_ENTRIES
+        };
+
+        let layout =
+            tcx.layout_of(param_env.and(ty)).expect("failed to build vtable representation");
+        assert!(!layout.is_unsized(), "can't create a vtable for an unsized type");
+        let size = layout.size.bytes();
+        let align = layout.align.abi.bytes();
+
+        let ptr_size = tcx.data_layout.pointer_size;
+        let ptr_align = tcx.data_layout.pointer_align.abi;
+
+        let vtable_size = ptr_size * u64::try_from(vtable_entries.len()).unwrap();
+        let mut vtable = Allocation::uninit(vtable_size, ptr_align);
+
+        // No need to do any alignment checks on the memory accesses below, because we know the
+        // allocation is correctly aligned as we created it above. Also we're only offsetting by
+        // multiples of `ptr_align`, which means that it will stay aligned to `ptr_align`.
+
+        for (idx, entry) in vtable_entries.iter().enumerate() {
+            let idx: u64 = u64::try_from(idx).unwrap();
+            let scalar = match entry {
+                VtblEntry::MetadataDropInPlace => {
+                    let instance = ty::Instance::resolve_drop_in_place(tcx, ty);
+                    let fn_alloc_id = tcx.create_fn_alloc(instance);
+                    let fn_ptr = Pointer::from(fn_alloc_id);
+                    fn_ptr.into()
+                }
+                VtblEntry::MetadataSize => Scalar::from_uint(size, ptr_size).into(),
+                VtblEntry::MetadataAlign => Scalar::from_uint(align, ptr_size).into(),
+                VtblEntry::Vacant => continue,
+                VtblEntry::Method(def_id, substs) => {
+                    // See https://github.com/rust-lang/rust/pull/86475#discussion_r655162674
+                    assert!(!substs.needs_subst());
+
+                    // Prepare the fn ptr we write into the vtable.
+                    let instance =
+                        ty::Instance::resolve_for_vtable(tcx, param_env, *def_id, substs)
+                            .expect("resolution failed during building vtable representation")
+                            .polymorphize(tcx);
+                    let fn_alloc_id = tcx.create_fn_alloc(instance);
+                    let fn_ptr = Pointer::from(fn_alloc_id);
+                    fn_ptr.into()
+                }
+            };
+            vtable
+                .write_scalar(&tcx, alloc_range(ptr_size * idx, ptr_size), scalar)
+                .expect("failed to build vtable representation");
+        }
+
+        vtable.mutability = Mutability::Not;
+        let alloc_id = tcx.create_memory_alloc(tcx.intern_const_alloc(vtable));
+        let mut vtables_cache = self.vtables_cache.lock();
+        vtables_cache.insert((ty, poly_trait_ref), alloc_id);
+        alloc_id
+    }
+}

compiler/rustc_mir/src/interpret/traits.rs

@@ -1,29 +1,14 @@
 use std::convert::TryFrom;
 
-use rustc_middle::mir::interpret::{
-    AllocError, InterpError, InterpResult, Pointer, PointerArithmetic, Scalar,
-    UndefinedBehaviorInfo, UnsupportedOpInfo,
-};
+use rustc_middle::mir::interpret::{InterpResult, Pointer, PointerArithmetic, Scalar};
 use rustc_middle::ty::{
-    self, Instance, Ty, VtblEntry, COMMON_VTABLE_ENTRIES, COMMON_VTABLE_ENTRIES_ALIGN,
+    self, Ty, COMMON_VTABLE_ENTRIES, COMMON_VTABLE_ENTRIES_ALIGN,
     COMMON_VTABLE_ENTRIES_DROPINPLACE, COMMON_VTABLE_ENTRIES_SIZE,
 };
-use rustc_target::abi::{Align, LayoutOf, Size};
+use rustc_target::abi::{Align, Size};
 
-use super::alloc_range;
 use super::util::ensure_monomorphic_enough;
-use super::{Allocation, FnVal, InterpCx, Machine};
-
-fn vtable_alloc_error_to_interp_error<'tcx>(error: AllocError) -> InterpError<'tcx> {
-    match error {
-        AllocError::ReadPointerAsBytes => {
-            InterpError::Unsupported(UnsupportedOpInfo::ReadPointerAsBytes)
-        }
-        AllocError::InvalidUninitBytes(_info) => {
-            InterpError::UndefinedBehavior(UndefinedBehaviorInfo::InvalidUninitBytes(None))
-        }
-    }
-}
+use super::{FnVal, InterpCx, Machine};
 
 impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
     /// Creates a dynamic vtable for the given type and vtable origin. This is used only for
@@ -45,79 +30,9 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         ensure_monomorphic_enough(*self.tcx, ty)?;
         ensure_monomorphic_enough(*self.tcx, poly_trait_ref)?;
 
-        if let Some(&vtable) = self.vtables.get(&(ty, poly_trait_ref)) {
-            // This means we guarantee that there are no duplicate vtables, we will
-            // always use the same vtable for the same (Type, Trait) combination.
-            // That's not what happens in rustc, but emulating per-crate deduplication
-            // does not sound like it actually makes anything any better.
-            return Ok(vtable);
-        }
-
-        let vtable_entries = if let Some(poly_trait_ref) = poly_trait_ref {
-            let trait_ref = poly_trait_ref.with_self_ty(*self.tcx, ty);
-            let trait_ref = self.tcx.erase_regions(trait_ref);
-
-            self.tcx.vtable_entries(trait_ref)
-        } else {
-            COMMON_VTABLE_ENTRIES
-        };
-
-        let layout = self.layout_of(ty)?;
-        assert!(!layout.is_unsized(), "can't create a vtable for an unsized type");
-        let size = layout.size.bytes();
-        let align = layout.align.abi.bytes();
-
-        let tcx = *self.tcx;
-        let ptr_size = self.pointer_size();
-        let ptr_align = tcx.data_layout.pointer_align.abi;
-        // /////////////////////////////////////////////////////////////////////////////////////////
-        // If you touch this code, be sure to also make the corresponding changes to
-        // `get_vtable` in `rust_codegen_llvm/meth.rs`.
-        // /////////////////////////////////////////////////////////////////////////////////////////
-        let vtable_size = ptr_size * u64::try_from(vtable_entries.len()).unwrap();
-        let mut vtable = Allocation::uninit(vtable_size, ptr_align);
-
-        // No need to do any alignment checks on the memory accesses below, because we know the
-        // allocation is correctly aligned as we created it above. Also we're only offsetting by
-        // multiples of `ptr_align`, which means that it will stay aligned to `ptr_align`.
-        let scalars = vtable_entries
-            .iter()
-            .map(|entry| -> InterpResult<'tcx, _> {
-                match entry {
-                    VtblEntry::MetadataDropInPlace => {
-                        let instance = Instance::resolve_drop_in_place(tcx, ty);
-                        let fn_alloc_id = tcx.create_fn_alloc(instance);
-                        let fn_ptr = Pointer::from(fn_alloc_id);
-                        Ok(Some(fn_ptr.into()))
-                    }
-                    VtblEntry::MetadataSize => Ok(Some(Scalar::from_uint(size, ptr_size).into())),
-                    VtblEntry::MetadataAlign => Ok(Some(Scalar::from_uint(align, ptr_size).into())),
-                    VtblEntry::Vacant => Ok(None),
-                    VtblEntry::Method(def_id, substs) => {
-                        // Prepare the fn ptr we write into the vtable.
-                        let instance =
-                            Instance::resolve_for_vtable(tcx, self.param_env, *def_id, substs)
-                                .ok_or_else(|| err_inval!(TooGeneric))?;
-                        let fn_alloc_id = tcx.create_fn_alloc(instance);
-                        let fn_ptr = Pointer::from(fn_alloc_id);
-                        Ok(Some(fn_ptr.into()))
-                    }
-                }
-            })
-            .collect::<Result<Vec<_>, _>>()?;
-        for (idx, scalar) in scalars.into_iter().enumerate() {
-            if let Some(scalar) = scalar {
-                let idx: u64 = u64::try_from(idx).unwrap();
-                vtable
-                    .write_scalar(self, alloc_range(ptr_size * idx, ptr_size), scalar)
-                    .map_err(vtable_alloc_error_to_interp_error)?;
-            }
-        }
-
-        let vtable_id = tcx.create_memory_alloc(tcx.intern_const_alloc(vtable));
-        let vtable_ptr = self.memory.global_base_pointer(Pointer::from(vtable_id))?;
+        let vtable_allocation = self.tcx.vtable_allocation(ty, poly_trait_ref);
 
-        assert!(self.vtables.insert((ty, poly_trait_ref), vtable_ptr).is_none());
+        let vtable_ptr = self.memory.global_base_pointer(Pointer::from(vtable_allocation))?;
 
         Ok(vtable_ptr)
     }