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use std::fmt;
use crate::mir::interpret::{alloc_range, AllocId, Allocation, Pointer, Scalar};
use crate::ty::{self, Instance, PolyTraitRef, Ty, TyCtxt};
use rustc_ast::Mutability;
#[derive(Clone, Copy, PartialEq, HashStable)]
pub enum VtblEntry<'tcx> {
/// destructor of this type (used in vtable header)
MetadataDropInPlace,
/// layout size of this type (used in vtable header)
MetadataSize,
/// layout align of this type (used in vtable header)
MetadataAlign,
/// non-dispatchable associated function that is excluded from trait object
Vacant,
/// dispatchable associated function
Method(Instance<'tcx>),
/// pointer to a separate supertrait vtable, can be used by trait upcasting coercion
TraitVPtr(PolyTraitRef<'tcx>),
}
impl<'tcx> fmt::Debug for VtblEntry<'tcx> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
// We want to call `Display` on `Instance` and `PolyTraitRef`,
// so we implement this manually.
match self {
VtblEntry::MetadataDropInPlace => write!(f, "MetadataDropInPlace"),
VtblEntry::MetadataSize => write!(f, "MetadataSize"),
VtblEntry::MetadataAlign => write!(f, "MetadataAlign"),
VtblEntry::Vacant => write!(f, "Vacant"),
VtblEntry::Method(instance) => write!(f, "Method({})", instance),
VtblEntry::TraitVPtr(trait_ref) => write!(f, "TraitVPtr({})", trait_ref),
}
}
}
// Needs to be associated with the `'tcx` lifetime
impl<'tcx> TyCtxt<'tcx> {
pub const COMMON_VTABLE_ENTRIES: &'tcx [VtblEntry<'tcx>] =
&[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;
/// Retrieves an allocation that represents the contents of a vtable.
/// Since this is a query, allocations are cached and not duplicated.
pub(super) fn vtable_allocation_provider<'tcx>(
tcx: TyCtxt<'tcx>,
key: (Ty<'tcx>, Option<ty::PolyExistentialTraitRef<'tcx>>),
) -> AllocId {
let (ty, poly_trait_ref) = key;
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 {
TyCtxt::COMMON_VTABLE_ENTRIES
};
let layout = tcx
.layout_of(ty::ParamEnv::reveal_all().and(ty))
.expect("failed to build vtable representation");
assert!(layout.is_sized(), "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, /* panic_on_fail */ true).unwrap();
// 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);
Scalar::from_pointer(fn_ptr, &tcx)
}
VtblEntry::MetadataSize => Scalar::from_uint(size, ptr_size),
VtblEntry::MetadataAlign => Scalar::from_uint(align, ptr_size),
VtblEntry::Vacant => continue,
VtblEntry::Method(instance) => {
// Prepare the fn ptr we write into the vtable.
let instance = instance.polymorphize(tcx);
let fn_alloc_id = tcx.create_fn_alloc(instance);
let fn_ptr = Pointer::from(fn_alloc_id);
Scalar::from_pointer(fn_ptr, &tcx)
}
VtblEntry::TraitVPtr(trait_ref) => {
let super_trait_ref = trait_ref
.map_bound(|trait_ref| ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref));
let supertrait_alloc_id = tcx.vtable_allocation((ty, Some(super_trait_ref)));
let vptr = Pointer::from(supertrait_alloc_id);
Scalar::from_pointer(vptr, &tcx)
}
};
vtable
.write_scalar(&tcx, alloc_range(ptr_size * idx, ptr_size), scalar)
.expect("failed to build vtable representation");
}
vtable.mutability = Mutability::Not;
tcx.create_memory_alloc(tcx.mk_const_alloc(vtable))
}
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