rustc_middle/ty/

codec.rs

//! This module contains some shared code for encoding and decoding various
//! things from the `ty` module, and in particular implements support for
//! "shorthands" which allow to have pointers back into the already encoded
//! stream instead of re-encoding the same thing twice.
//!
//! The functionality in here is shared between persisting to crate metadata and
//! persisting to incr. comp. caches.

use std::hash::Hash;
use std::intrinsics;
use std::marker::{DiscriminantKind, PointeeSized};

use rustc_abi::FieldIdx;
use rustc_data_structures::fx::FxHashMap;
use rustc_hir::def_id::LocalDefId;
use rustc_middle::ty::Const;
use rustc_serialize::{Decodable, Encodable};
use rustc_span::{Span, SpanDecoder, SpanEncoder, Spanned};

use crate::infer::canonical::{CanonicalVarKind, CanonicalVarKinds};
use crate::mir::interpret::{AllocId, ConstAllocation, CtfeProvenance};
use crate::mono::MonoItem;
use crate::ty::{self, AdtDef, GenericArgsRef, Ty, TyCtxt};
use crate::{mir, traits};

/// The shorthand encoding uses an enum's variant index `usize`
/// and is offset by this value so it never matches a real variant.
/// This offset is also chosen so that the first byte is never < 0x80.
pub const SHORTHAND_OFFSET: usize = 0x80;

pub trait TyEncoder<'tcx>: SpanEncoder {
    const CLEAR_CROSS_CRATE: bool;

    fn position(&self) -> usize;

    fn type_shorthands(&mut self) -> &mut FxHashMap<Ty<'tcx>, usize>;

    fn predicate_shorthands(&mut self) -> &mut FxHashMap<ty::PredicateKind<'tcx>, usize>;

    fn encode_alloc_id(&mut self, alloc_id: &AllocId);
}

pub trait TyDecoder<'tcx>:
    SpanDecoder + rustc_type_ir::InternerDecoder<Interner = TyCtxt<'tcx>>
{
    const CLEAR_CROSS_CRATE: bool;

    fn cached_ty_for_shorthand<F>(&mut self, shorthand: usize, or_insert_with: F) -> Ty<'tcx>
    where
        F: FnOnce(&mut Self) -> Ty<'tcx>;

    fn with_position<F, R>(&mut self, pos: usize, f: F) -> R
    where
        F: FnOnce(&mut Self) -> R;

    fn positioned_at_shorthand(&self) -> bool {
        (self.peek_byte() & (SHORTHAND_OFFSET as u8)) != 0
    }

    fn decode_alloc_id(&mut self) -> AllocId;
}

pub trait EncodableWithShorthand<'tcx, E: TyEncoder<'tcx>>: Copy + Eq + Hash {
    type Variant: Encodable<E>;
    fn variant(&self) -> &Self::Variant;
}

#[allow(rustc::usage_of_ty_tykind)]
impl<'tcx, E: TyEncoder<'tcx>> EncodableWithShorthand<'tcx, E> for Ty<'tcx> {
    type Variant = ty::TyKind<'tcx>;

    #[inline]
    fn variant(&self) -> &Self::Variant {
        self.kind()
    }
}

impl<'tcx, E: TyEncoder<'tcx>> EncodableWithShorthand<'tcx, E> for ty::PredicateKind<'tcx> {
    type Variant = ty::PredicateKind<'tcx>;

    #[inline]
    fn variant(&self) -> &Self::Variant {
        self
    }
}

/// Trait for decoding to a reference.
///
/// This is a separate trait from `Decodable` so that we can implement it for
/// upstream types, such as `FxHashSet`.
///
/// The `TyDecodable` derive macro will use this trait for fields that are
/// references (and don't use a type alias to hide that).
///
/// `Decodable` can still be implemented in cases where `Decodable` is required
/// by a trait bound.
///
/// Implementations of this trait will typically allocate into an arena or interner,
/// e.g. see `impl_ref_decodable_into_arena!`.
pub trait RefDecodable<'tcx, D: TyDecoder<'tcx>>: PointeeSized {
    fn decode(d: &mut D) -> &'tcx Self;
}

/// Encode the given value or a previously cached shorthand.
pub fn encode_with_shorthand<'tcx, E, T, M>(encoder: &mut E, value: &T, cache: M)
where
    E: TyEncoder<'tcx>,
    M: for<'b> Fn(&'b mut E) -> &'b mut FxHashMap<T, usize>,
    T: EncodableWithShorthand<'tcx, E>,
    // The discriminant and shorthand must have the same size.
    T::Variant: DiscriminantKind<Discriminant = isize>,
{
    let existing_shorthand = cache(encoder).get(value).copied();
    if let Some(shorthand) = existing_shorthand {
        encoder.emit_usize(shorthand);
        return;
    }

    let variant = value.variant();

    let start = encoder.position();
    variant.encode(encoder);
    let len = encoder.position() - start;

    // The shorthand encoding uses the same usize as the
    // discriminant, with an offset so they can't conflict.
    let discriminant = intrinsics::discriminant_value(variant);
    assert!(SHORTHAND_OFFSET > discriminant as usize);

    let shorthand = start + SHORTHAND_OFFSET;

    // Get the number of bits that leb128 could fit
    // in the same space as the fully encoded type.
    let leb128_bits = len * 7;

    // Check that the shorthand is a not longer than the
    // full encoding itself, i.e., it's an obvious win.
    if leb128_bits >= 64 || (shorthand as u64) < (1 << leb128_bits) {
        cache(encoder).insert(*value, shorthand);
    }
}

impl<'tcx, E: TyEncoder<'tcx>> Encodable<E> for Ty<'tcx> {
    fn encode(&self, e: &mut E) {
        encode_with_shorthand(e, self, TyEncoder::type_shorthands);
    }
}

impl<'tcx, E: TyEncoder<'tcx>> Encodable<E> for ty::Predicate<'tcx> {
    fn encode(&self, e: &mut E) {
        let kind = self.kind();
        kind.bound_vars().encode(e);
        encode_with_shorthand(e, &kind.skip_binder(), TyEncoder::predicate_shorthands);
    }
}

impl<'tcx, E: TyEncoder<'tcx>> Encodable<E> for ty::Clause<'tcx> {
    fn encode(&self, e: &mut E) {
        self.as_predicate().encode(e);
    }
}

impl<'tcx, E: TyEncoder<'tcx>> Encodable<E> for ty::Const<'tcx> {
    fn encode(&self, e: &mut E) {
        self.0.0.encode(e);
    }
}

impl<'tcx, E: TyEncoder<'tcx>> Encodable<E> for ty::Pattern<'tcx> {
    fn encode(&self, e: &mut E) {
        self.0.0.encode(e);
    }
}

impl<'tcx, E: TyEncoder<'tcx>> Encodable<E> for ty::ValTree<'tcx> {
    fn encode(&self, e: &mut E) {
        self.0.0.encode(e);
    }
}

impl<'tcx, E: TyEncoder<'tcx>> Encodable<E> for ConstAllocation<'tcx> {
    fn encode(&self, e: &mut E) {
        self.inner().encode(e)
    }
}

impl<'tcx, E: TyEncoder<'tcx>> Encodable<E> for AdtDef<'tcx> {
    fn encode(&self, e: &mut E) {
        self.0.0.encode(e)
    }
}

impl<'tcx, E: TyEncoder<'tcx>> Encodable<E> for AllocId {
    fn encode(&self, e: &mut E) {
        e.encode_alloc_id(self)
    }
}

impl<'tcx, E: TyEncoder<'tcx>> Encodable<E> for CtfeProvenance {
    fn encode(&self, e: &mut E) {
        self.into_parts().encode(e);
    }
}

impl<'tcx, E: TyEncoder<'tcx>> Encodable<E> for ty::ParamEnv<'tcx> {
    fn encode(&self, e: &mut E) {
        self.caller_bounds().encode(e);
    }
}

impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for Ty<'tcx> {
    #[allow(rustc::usage_of_ty_tykind)]
    fn decode(decoder: &mut D) -> Ty<'tcx> {
        // Handle shorthands first, if we have a usize > 0x80.
        if decoder.positioned_at_shorthand() {
            let pos = decoder.read_usize();
            assert!(pos >= SHORTHAND_OFFSET);
            let shorthand = pos - SHORTHAND_OFFSET;

            decoder.cached_ty_for_shorthand(shorthand, |decoder| {
                decoder.with_position(shorthand, Ty::decode)
            })
        } else {
            let tcx = decoder.interner();
            tcx.mk_ty_from_kind(ty::TyKind::decode(decoder))
        }
    }
}

impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for ty::Predicate<'tcx> {
    fn decode(decoder: &mut D) -> ty::Predicate<'tcx> {
        let bound_vars = Decodable::decode(decoder);
        // Handle shorthands first, if we have a usize > 0x80.
        let predicate_kind = ty::Binder::bind_with_vars(
            if decoder.positioned_at_shorthand() {
                let pos = decoder.read_usize();
                assert!(pos >= SHORTHAND_OFFSET);
                let shorthand = pos - SHORTHAND_OFFSET;

                decoder.with_position(shorthand, <ty::PredicateKind<'tcx> as Decodable<D>>::decode)
            } else {
                <ty::PredicateKind<'tcx> as Decodable<D>>::decode(decoder)
            },
            bound_vars,
        );
        decoder.interner().mk_predicate(predicate_kind)
    }
}

impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for ty::Clause<'tcx> {
    fn decode(decoder: &mut D) -> ty::Clause<'tcx> {
        let pred: ty::Predicate<'tcx> = Decodable::decode(decoder);
        pred.expect_clause()
    }
}

impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for GenericArgsRef<'tcx> {
    fn decode(decoder: &mut D) -> Self {
        let len = decoder.read_usize();
        let tcx = decoder.interner();
        tcx.mk_args_from_iter(
            (0..len).map::<ty::GenericArg<'tcx>, _>(|_| Decodable::decode(decoder)),
        )
    }
}

impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for mir::Place<'tcx> {
    fn decode(decoder: &mut D) -> Self {
        let local: mir::Local = Decodable::decode(decoder);
        let len = decoder.read_usize();
        let projection = decoder.interner().mk_place_elems_from_iter(
            (0..len).map::<mir::PlaceElem<'tcx>, _>(|_| Decodable::decode(decoder)),
        );
        mir::Place { local, projection }
    }
}

impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for CanonicalVarKinds<'tcx> {
    fn decode(decoder: &mut D) -> Self {
        let len = decoder.read_usize();
        decoder.interner().mk_canonical_var_infos_from_iter(
            (0..len).map::<CanonicalVarKind<'tcx>, _>(|_| Decodable::decode(decoder)),
        )
    }
}

impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for AllocId {
    fn decode(decoder: &mut D) -> Self {
        decoder.decode_alloc_id()
    }
}

impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for CtfeProvenance {
    fn decode(decoder: &mut D) -> Self {
        let parts = Decodable::decode(decoder);
        CtfeProvenance::from_parts(parts)
    }
}

impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for ty::SymbolName<'tcx> {
    fn decode(decoder: &mut D) -> Self {
        ty::SymbolName::new(decoder.interner(), decoder.read_str())
    }
}

impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for ty::ParamEnv<'tcx> {
    fn decode(d: &mut D) -> Self {
        let caller_bounds = Decodable::decode(d);
        ty::ParamEnv::new(caller_bounds)
    }
}

macro_rules! impl_decodable_via_ref {
    ($($t:ty,)+) => {
        $(impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for $t {
            fn decode(decoder: &mut D) -> Self {
                RefDecodable::decode(decoder)
            }
        })*
    }
}

impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D> for ty::List<Ty<'tcx>> {
    fn decode(decoder: &mut D) -> &'tcx Self {
        let len = decoder.read_usize();
        decoder
            .interner()
            .mk_type_list_from_iter((0..len).map::<Ty<'tcx>, _>(|_| Decodable::decode(decoder)))
    }
}

impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D>
    for ty::List<ty::PolyExistentialPredicate<'tcx>>
{
    fn decode(decoder: &mut D) -> &'tcx Self {
        let len = decoder.read_usize();
        decoder.interner().mk_poly_existential_predicates_from_iter(
            (0..len).map::<ty::Binder<'tcx, _>, _>(|_| Decodable::decode(decoder)),
        )
    }
}

impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for ty::Const<'tcx> {
    fn decode(decoder: &mut D) -> Self {
        let kind: ty::ConstKind<'tcx> = Decodable::decode(decoder);
        decoder.interner().mk_ct_from_kind(kind)
    }
}

impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for ty::Pattern<'tcx> {
    fn decode(decoder: &mut D) -> Self {
        decoder.interner().mk_pat(Decodable::decode(decoder))
    }
}

impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for ty::ValTree<'tcx> {
    fn decode(decoder: &mut D) -> Self {
        decoder.interner().intern_valtree(Decodable::decode(decoder))
    }
}

impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for ConstAllocation<'tcx> {
    fn decode(decoder: &mut D) -> Self {
        decoder.interner().mk_const_alloc(Decodable::decode(decoder))
    }
}

impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for AdtDef<'tcx> {
    fn decode(decoder: &mut D) -> Self {
        decoder.interner().mk_adt_def_from_data(Decodable::decode(decoder))
    }
}

impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D> for [(ty::Clause<'tcx>, Span)] {
    fn decode(decoder: &mut D) -> &'tcx Self {
        decoder
            .interner()
            .arena
            .alloc_from_iter((0..decoder.read_usize()).map(|_| Decodable::decode(decoder)))
    }
}

impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D> for [(ty::PolyTraitRef<'tcx>, Span)] {
    fn decode(decoder: &mut D) -> &'tcx Self {
        decoder
            .interner()
            .arena
            .alloc_from_iter((0..decoder.read_usize()).map(|_| Decodable::decode(decoder)))
    }
}

impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D> for [Spanned<MonoItem<'tcx>>] {
    fn decode(decoder: &mut D) -> &'tcx Self {
        decoder
            .interner()
            .arena
            .alloc_from_iter((0..decoder.read_usize()).map(|_| Decodable::decode(decoder)))
    }
}

impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D> for ty::List<ty::BoundVariableKind<'tcx>> {
    fn decode(decoder: &mut D) -> &'tcx Self {
        let len = decoder.read_usize();
        decoder.interner().mk_bound_variable_kinds_from_iter(
            (0..len).map::<ty::BoundVariableKind<'tcx>, _>(|_| Decodable::decode(decoder)),
        )
    }
}

impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D> for ty::List<ty::Pattern<'tcx>> {
    fn decode(decoder: &mut D) -> &'tcx Self {
        let len = decoder.read_usize();
        decoder.interner().mk_patterns_from_iter(
            (0..len).map::<ty::Pattern<'tcx>, _>(|_| Decodable::decode(decoder)),
        )
    }
}

impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D> for ty::List<ty::Const<'tcx>> {
    fn decode(decoder: &mut D) -> &'tcx Self {
        let len = decoder.read_usize();
        decoder.interner().mk_const_list_from_iter(
            (0..len).map::<ty::Const<'tcx>, _>(|_| Decodable::decode(decoder)),
        )
    }
}

impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D>
    for ty::ListWithCachedTypeInfo<ty::Clause<'tcx>>
{
    fn decode(decoder: &mut D) -> &'tcx Self {
        let len = decoder.read_usize();
        decoder.interner().mk_clauses_from_iter(
            (0..len).map::<ty::Clause<'tcx>, _>(|_| Decodable::decode(decoder)),
        )
    }
}

impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D> for ty::List<FieldIdx> {
    fn decode(decoder: &mut D) -> &'tcx Self {
        let len = decoder.read_usize();
        decoder
            .interner()
            .mk_fields_from_iter((0..len).map::<FieldIdx, _>(|_| Decodable::decode(decoder)))
    }
}

impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D> for ty::List<LocalDefId> {
    fn decode(decoder: &mut D) -> &'tcx Self {
        let len = decoder.read_usize();
        decoder.interner().mk_local_def_ids_from_iter(
            (0..len).map::<LocalDefId, _>(|_| Decodable::decode(decoder)),
        )
    }
}

impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for &'tcx ty::List<LocalDefId> {
    fn decode(d: &mut D) -> Self {
        RefDecodable::decode(d)
    }
}

impl_decodable_via_ref! {
    &'tcx ty::TypeckResults<'tcx>,
    &'tcx ty::List<Ty<'tcx>>,
    &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
    &'tcx traits::ImplSource<'tcx, ()>,
    &'tcx mir::Body<'tcx>,
    &'tcx ty::List<ty::BoundVariableKind<'tcx>>,
    &'tcx ty::List<ty::Pattern<'tcx>>,
    &'tcx ty::ListWithCachedTypeInfo<ty::Clause<'tcx>>,
    &'tcx ty::List<Const<'tcx>>,
}

#[macro_export]
macro_rules! __impl_decoder_methods {
    ($($name:ident -> $ty:ty;)*) => {
        $(
            #[inline]
            fn $name(&mut self) -> $ty {
                self.opaque.$name()
            }
        )*
    }
}

#[macro_export]
macro_rules! implement_ty_decoder {
    ($DecoderName:ident <$($typaram:tt),*>) => {
        mod __ty_decoder_impl {
            use rustc_serialize::Decoder;

            use super::$DecoderName;

            impl<$($typaram ),*> Decoder for $DecoderName<$($typaram),*> {
                $crate::__impl_decoder_methods! {
                    read_usize -> usize;
                    read_u128 -> u128;
                    read_u64 -> u64;
                    read_u32 -> u32;
                    read_u16 -> u16;
                    read_u8 -> u8;

                    read_isize -> isize;
                    read_i128 -> i128;
                    read_i64 -> i64;
                    read_i32 -> i32;
                    read_i16 -> i16;
                }

                #[inline]
                fn read_raw_bytes(&mut self, len: usize) -> &[u8] {
                    self.opaque.read_raw_bytes(len)
                }

                #[inline]
                fn peek_byte(&self) -> u8 {
                    self.opaque.peek_byte()
                }

                #[inline]
                fn position(&self) -> usize {
                    self.opaque.position()
                }
            }
        }
    }
}