1 files changed, 527 insertions, 0 deletions
diff --git a/compiler/rustc_middle/src/ty/codec.rs b/compiler/rustc_middle/src/ty/codec.rs
new file mode 100644
index 000000000..51137c526
--- /dev/null
+++ b/compiler/rustc_middle/src/ty/codec.rs
@@ -0,0 +1,527 @@
+//! 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 crate::arena::ArenaAllocatable;
+use crate::infer::canonical::{CanonicalVarInfo, CanonicalVarInfos};
+use crate::mir::{
+    self,
+    interpret::{AllocId, ConstAllocation},
+};
+use crate::traits;
+use crate::ty::subst::SubstsRef;
+use crate::ty::{self, AdtDef, Ty};
+use rustc_data_structures::fx::FxHashMap;
+use rustc_middle::ty::TyCtxt;
+use rustc_serialize::{Decodable, Encodable};
+use rustc_span::Span;
+pub use rustc_type_ir::{TyDecoder, TyEncoder};
+use std::hash::Hash;
+use std::intrinsics;
+use std::marker::DiscriminantKind;
+
+/// 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 EncodableWithShorthand<E: TyEncoder>: Copy + Eq + Hash {
+    type Variant: Encodable<E>;
+    fn variant(&self) -> &Self::Variant;
+}
+
+#[allow(rustc::usage_of_ty_tykind)]
+impl<'tcx, E: TyEncoder<I = TyCtxt<'tcx>>> EncodableWithShorthand<E> for Ty<'tcx> {
+    type Variant = ty::TyKind<'tcx>;
+
+    #[inline]
+    fn variant(&self) -> &Self::Variant {
+        self.kind()
+    }
+}
+
+impl<'tcx, E: TyEncoder<I = TyCtxt<'tcx>>> EncodableWithShorthand<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.
+pub trait RefDecodable<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> {
+    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<I = TyCtxt<'tcx>>,
+    M: for<'b> Fn(&'b mut E) -> &'b mut FxHashMap<T, usize>,
+    T: EncodableWithShorthand<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<I = TyCtxt<'tcx>>> Encodable<E> for Ty<'tcx> {
+    fn encode(&self, e: &mut E) {
+        encode_with_shorthand(e, self, TyEncoder::type_shorthands);
+    }
+}
+
+impl<'tcx, E: TyEncoder<I = TyCtxt<'tcx>>> Encodable<E>
+    for ty::Binder<'tcx, ty::PredicateKind<'tcx>>
+{
+    fn encode(&self, e: &mut E) {
+        self.bound_vars().encode(e);
+        encode_with_shorthand(e, &self.skip_binder(), TyEncoder::predicate_shorthands);
+    }
+}
+
+impl<'tcx, E: TyEncoder<I = TyCtxt<'tcx>>> Encodable<E> for ty::Predicate<'tcx> {
+    fn encode(&self, e: &mut E) {
+        self.kind().encode(e);
+    }
+}
+
+impl<'tcx, E: TyEncoder<I = TyCtxt<'tcx>>> Encodable<E> for ty::Region<'tcx> {
+    fn encode(&self, e: &mut E) {
+        self.kind().encode(e);
+    }
+}
+
+impl<'tcx, E: TyEncoder<I = TyCtxt<'tcx>>> Encodable<E> for ty::Const<'tcx> {
+    fn encode(&self, e: &mut E) {
+        self.0.0.encode(e);
+    }
+}
+
+impl<'tcx, E: TyEncoder<I = TyCtxt<'tcx>>> Encodable<E> for ConstAllocation<'tcx> {
+    fn encode(&self, e: &mut E) {
+        self.inner().encode(e)
+    }
+}
+
+impl<'tcx, E: TyEncoder<I = TyCtxt<'tcx>>> Encodable<E> for AdtDef<'tcx> {
+    fn encode(&self, e: &mut E) {
+        self.0.0.encode(e)
+    }
+}
+
+impl<'tcx, E: TyEncoder<I = TyCtxt<'tcx>>> Encodable<E> for AllocId {
+    fn encode(&self, e: &mut E) {
+        e.encode_alloc_id(self)
+    }
+}
+
+#[inline]
+fn decode_arena_allocable<
+    'tcx,
+    D: TyDecoder<I = TyCtxt<'tcx>>,
+    T: ArenaAllocatable<'tcx> + Decodable<D>,
+>(
+    decoder: &mut D,
+) -> &'tcx T
+where
+    D: TyDecoder,
+{
+    decoder.interner().arena.alloc(Decodable::decode(decoder))
+}
+
+#[inline]
+fn decode_arena_allocable_slice<
+    'tcx,
+    D: TyDecoder<I = TyCtxt<'tcx>>,
+    T: ArenaAllocatable<'tcx> + Decodable<D>,
+>(
+    decoder: &mut D,
+) -> &'tcx [T]
+where
+    D: TyDecoder,
+{
+    decoder.interner().arena.alloc_from_iter(<Vec<T> as Decodable<D>>::decode(decoder))
+}
+
+impl<'tcx, D: TyDecoder<I = TyCtxt<'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(rustc_type_ir::TyKind::decode(decoder))
+        }
+    }
+}
+
+impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> Decodable<D>
+    for ty::Binder<'tcx, ty::PredicateKind<'tcx>>
+{
+    fn decode(decoder: &mut D) -> ty::Binder<'tcx, ty::PredicateKind<'tcx>> {
+        let bound_vars = Decodable::decode(decoder);
+        // Handle shorthands first, if we have a usize > 0x80.
+        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::decode)
+            } else {
+                ty::PredicateKind::decode(decoder)
+            },
+            bound_vars,
+        )
+    }
+}
+
+impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> Decodable<D> for ty::Predicate<'tcx> {
+    fn decode(decoder: &mut D) -> ty::Predicate<'tcx> {
+        let predicate_kind = Decodable::decode(decoder);
+        decoder.interner().mk_predicate(predicate_kind)
+    }
+}
+
+impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> Decodable<D> for SubstsRef<'tcx> {
+    fn decode(decoder: &mut D) -> Self {
+        let len = decoder.read_usize();
+        let tcx = decoder.interner();
+        tcx.mk_substs(
+            (0..len).map::<ty::subst::GenericArg<'tcx>, _>(|_| Decodable::decode(decoder)),
+        )
+    }
+}
+
+impl<'tcx, D: TyDecoder<I = TyCtxt<'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(
+            (0..len).map::<mir::PlaceElem<'tcx>, _>(|_| Decodable::decode(decoder)),
+        );
+        mir::Place { local, projection }
+    }
+}
+
+impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> Decodable<D> for ty::Region<'tcx> {
+    fn decode(decoder: &mut D) -> Self {
+        decoder.interner().mk_region(Decodable::decode(decoder))
+    }
+}
+
+impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> Decodable<D> for CanonicalVarInfos<'tcx> {
+    fn decode(decoder: &mut D) -> Self {
+        let len = decoder.read_usize();
+        let interned: Vec<CanonicalVarInfo<'tcx>> =
+            (0..len).map(|_| Decodable::decode(decoder)).collect();
+        decoder.interner().intern_canonical_var_infos(interned.as_slice())
+    }
+}
+
+impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> Decodable<D> for AllocId {
+    fn decode(decoder: &mut D) -> Self {
+        decoder.decode_alloc_id()
+    }
+}
+
+impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> Decodable<D> for ty::SymbolName<'tcx> {
+    fn decode(decoder: &mut D) -> Self {
+        ty::SymbolName::new(decoder.interner(), &decoder.read_str())
+    }
+}
+
+macro_rules! impl_decodable_via_ref {
+    ($($t:ty),+) => {
+        $(impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> Decodable<D> for $t {
+            fn decode(decoder: &mut D) -> Self {
+                RefDecodable::decode(decoder)
+            }
+        })*
+    }
+}
+
+impl<'tcx, D: TyDecoder<I = TyCtxt<'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((0..len).map::<Ty<'tcx>, _>(|_| Decodable::decode(decoder)))
+    }
+}
+
+impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> RefDecodable<'tcx, D>
+    for ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>
+{
+    fn decode(decoder: &mut D) -> &'tcx Self {
+        let len = decoder.read_usize();
+        decoder.interner().mk_poly_existential_predicates(
+            (0..len).map::<ty::Binder<'tcx, _>, _>(|_| Decodable::decode(decoder)),
+        )
+    }
+}
+
+impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> Decodable<D> for ty::Const<'tcx> {
+    fn decode(decoder: &mut D) -> Self {
+        decoder.interner().mk_const(Decodable::decode(decoder))
+    }
+}
+
+impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> RefDecodable<'tcx, D> for [ty::ValTree<'tcx>] {
+    fn decode(decoder: &mut D) -> &'tcx Self {
+        decoder.interner().arena.alloc_from_iter(
+            (0..decoder.read_usize()).map(|_| Decodable::decode(decoder)).collect::<Vec<_>>(),
+        )
+    }
+}
+
+impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> Decodable<D> for ConstAllocation<'tcx> {
+    fn decode(decoder: &mut D) -> Self {
+        decoder.interner().intern_const_alloc(Decodable::decode(decoder))
+    }
+}
+
+impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> Decodable<D> for AdtDef<'tcx> {
+    fn decode(decoder: &mut D) -> Self {
+        decoder.interner().intern_adt_def(Decodable::decode(decoder))
+    }
+}
+
+impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> RefDecodable<'tcx, D>
+    for [(ty::Predicate<'tcx>, Span)]
+{
+    fn decode(decoder: &mut D) -> &'tcx Self {
+        decoder.interner().arena.alloc_from_iter(
+            (0..decoder.read_usize()).map(|_| Decodable::decode(decoder)).collect::<Vec<_>>(),
+        )
+    }
+}
+
+impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> RefDecodable<'tcx, D>
+    for [ty::abstract_const::Node<'tcx>]
+{
+    fn decode(decoder: &mut D) -> &'tcx Self {
+        decoder.interner().arena.alloc_from_iter(
+            (0..decoder.read_usize()).map(|_| Decodable::decode(decoder)).collect::<Vec<_>>(),
+        )
+    }
+}
+
+impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> RefDecodable<'tcx, D>
+    for [ty::abstract_const::NodeId]
+{
+    fn decode(decoder: &mut D) -> &'tcx Self {
+        decoder.interner().arena.alloc_from_iter(
+            (0..decoder.read_usize()).map(|_| Decodable::decode(decoder)).collect::<Vec<_>>(),
+        )
+    }
+}
+
+impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> RefDecodable<'tcx, D>
+    for ty::List<ty::BoundVariableKind>
+{
+    fn decode(decoder: &mut D) -> &'tcx Self {
+        let len = decoder.read_usize();
+        decoder.interner().mk_bound_variable_kinds(
+            (0..len).map::<ty::BoundVariableKind, _>(|_| Decodable::decode(decoder)),
+        )
+    }
+}
+
+impl_decodable_via_ref! {
+    &'tcx ty::TypeckResults<'tcx>,
+    &'tcx ty::List<Ty<'tcx>>,
+    &'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>,
+    &'tcx traits::ImplSource<'tcx, ()>,
+    &'tcx mir::Body<'tcx>,
+    &'tcx mir::UnsafetyCheckResult,
+    &'tcx mir::BorrowCheckResult<'tcx>,
+    &'tcx mir::coverage::CodeRegion,
+    &'tcx ty::List<ty::BoundVariableKind>
+}
+
+#[macro_export]
+macro_rules! __impl_decoder_methods {
+    ($($name:ident -> $ty:ty;)*) => {
+        $(
+            #[inline]
+            fn $name(&mut self) -> $ty {
+                self.opaque.$name()
+            }
+        )*
+    }
+}
+
+macro_rules! impl_arena_allocatable_decoder {
+    ([]$args:tt) => {};
+    ([decode $(, $attrs:ident)*]
+     [$name:ident: $ty:ty]) => {
+        impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> RefDecodable<'tcx, D> for $ty {
+            #[inline]
+            fn decode(decoder: &mut D) -> &'tcx Self {
+                decode_arena_allocable(decoder)
+            }
+        }
+
+        impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> RefDecodable<'tcx, D> for [$ty] {
+            #[inline]
+            fn decode(decoder: &mut D) -> &'tcx Self {
+                decode_arena_allocable_slice(decoder)
+            }
+        }
+    };
+}
+
+macro_rules! impl_arena_allocatable_decoders {
+    ([$($a:tt $name:ident: $ty:ty,)*]) => {
+        $(
+            impl_arena_allocatable_decoder!($a [$name: $ty]);
+        )*
+    }
+}
+
+rustc_hir::arena_types!(impl_arena_allocatable_decoders);
+arena_types!(impl_arena_allocatable_decoders);
+
+macro_rules! impl_arena_copy_decoder {
+    (<$tcx:tt> $($ty:ty,)*) => {
+        $(impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> RefDecodable<'tcx, D> for $ty {
+            #[inline]
+            fn decode(decoder: &mut D) -> &'tcx Self {
+                decoder.interner().arena.alloc(Decodable::decode(decoder))
+            }
+        }
+
+        impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> RefDecodable<'tcx, D> for [$ty] {
+            #[inline]
+            fn decode(decoder: &mut D) -> &'tcx Self {
+                decoder.interner().arena.alloc_from_iter(<Vec<_> as Decodable<D>>::decode(decoder))
+            }
+        })*
+    };
+}
+
+impl_arena_copy_decoder! {<'tcx>
+    Span,
+    rustc_span::symbol::Ident,
+    ty::Variance,
+    rustc_span::def_id::DefId,
+    rustc_span::def_id::LocalDefId,
+    (rustc_middle::middle::exported_symbols::ExportedSymbol<'tcx>, rustc_middle::middle::exported_symbols::SymbolExportInfo),
+}
+
+#[macro_export]
+macro_rules! implement_ty_decoder {
+    ($DecoderName:ident <$($typaram:tt),*>) => {
+        mod __ty_decoder_impl {
+            use std::borrow::Cow;
+            use rustc_serialize::Decoder;
+
+            use super::$DecoderName;
+
+            impl<$($typaram ),*> Decoder for $DecoderName<$($typaram),*> {
+                $crate::__impl_decoder_methods! {
+                    read_u128 -> u128;
+                    read_u64 -> u64;
+                    read_u32 -> u32;
+                    read_u16 -> u16;
+                    read_u8 -> u8;
+                    read_usize -> usize;
+
+                    read_i128 -> i128;
+                    read_i64 -> i64;
+                    read_i32 -> i32;
+                    read_i16 -> i16;
+                    read_i8 -> i8;
+                    read_isize -> isize;
+
+                    read_bool -> bool;
+                    read_f64 -> f64;
+                    read_f32 -> f32;
+                    read_char -> char;
+                    read_str -> &str;
+                }
+
+                #[inline]
+                fn read_raw_bytes(&mut self, len: usize) -> &[u8] {
+                    self.opaque.read_raw_bytes(len)
+                }
+            }
+        }
+    }
+}
+
+macro_rules! impl_binder_encode_decode {
+    ($($t:ty),+ $(,)?) => {
+        $(
+            impl<'tcx, E: TyEncoder<I = TyCtxt<'tcx>>> Encodable<E> for ty::Binder<'tcx, $t> {
+                fn encode(&self, e: &mut E) {
+                    self.bound_vars().encode(e);
+                    self.as_ref().skip_binder().encode(e);
+                }
+            }
+            impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> Decodable<D> for ty::Binder<'tcx, $t> {
+                fn decode(decoder: &mut D) -> Self {
+                    let bound_vars = Decodable::decode(decoder);
+                    ty::Binder::bind_with_vars(Decodable::decode(decoder), bound_vars)
+                }
+            }
+        )*
+    }
+}
+
+impl_binder_encode_decode! {
+    &'tcx ty::List<Ty<'tcx>>,
+    ty::FnSig<'tcx>,
+    ty::ExistentialPredicate<'tcx>,
+    ty::TraitRef<'tcx>,
+    Vec<ty::GeneratorInteriorTypeCause<'tcx>>,
+    ty::ExistentialTraitRef<'tcx>,
+}