diff --git a/compiler/rustc_ast/src/ast.rs b/compiler/rustc_ast/src/ast.rs
index 4e2495ab14c9a..e5b61d7000a32 100644
--- a/compiler/rustc_ast/src/ast.rs
+++ b/compiler/rustc_ast/src/ast.rs
@@ -31,7 +31,7 @@ use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_data_structures::sync::Lrc;
 use rustc_data_structures::thin_vec::ThinVec;
 use rustc_macros::HashStable_Generic;
-use rustc_serialize::{self, Decoder, Encoder};
+use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
 use rustc_span::source_map::{respan, Spanned};
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::{Span, DUMMY_SP};
@@ -2488,11 +2488,11 @@ rustc_index::newtype_index! {
     }
 }
 
-impl<S: Encoder> rustc_serialize::Encodable<S> for AttrId {
+impl<S: Encoder> Encodable<S> for AttrId {
     fn encode(&self, _s: &mut S) {}
 }
 
-impl<D: Decoder> rustc_serialize::Decodable<D> for AttrId {
+impl<D: Decoder> Decodable<D> for AttrId {
     fn decode(_: &mut D) -> AttrId {
         crate::attr::mk_attr_id()
     }
diff --git a/compiler/rustc_codegen_ssa/src/lib.rs b/compiler/rustc_codegen_ssa/src/lib.rs
index 771157dcad954..750432b0b2653 100644
--- a/compiler/rustc_codegen_ssa/src/lib.rs
+++ b/compiler/rustc_codegen_ssa/src/lib.rs
@@ -29,7 +29,8 @@ use rustc_middle::dep_graph::WorkProduct;
 use rustc_middle::middle::dependency_format::Dependencies;
 use rustc_middle::middle::exported_symbols::SymbolExportKind;
 use rustc_middle::ty::query::{ExternProviders, Providers};
-use rustc_serialize::{opaque, Decodable, Decoder, Encodable, Encoder};
+use rustc_serialize::opaque::{MemDecoder, MemEncoder};
+use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
 use rustc_session::config::{CrateType, OutputFilenames, OutputType, RUST_CGU_EXT};
 use rustc_session::cstore::{self, CrateSource};
 use rustc_session::utils::NativeLibKind;
@@ -203,7 +204,7 @@ const RUSTC_VERSION: Option<&str> = option_env!("CFG_VERSION");
 
 impl CodegenResults {
     pub fn serialize_rlink(codegen_results: &CodegenResults) -> Vec<u8> {
-        let mut encoder = opaque::Encoder::new();
+        let mut encoder = MemEncoder::new();
         encoder.emit_raw_bytes(RLINK_MAGIC);
         // `emit_raw_bytes` is used to make sure that the version representation does not depend on
         // Encoder's inner representation of `u32`.
@@ -230,7 +231,7 @@ impl CodegenResults {
             return Err(".rlink file was produced with encoding version {version_array}, but the current version is {RLINK_VERSION}".to_string());
         }
 
-        let mut decoder = opaque::Decoder::new(&data[4..], 0);
+        let mut decoder = MemDecoder::new(&data[4..], 0);
         let rustc_version = decoder.read_str();
         let current_version = RUSTC_VERSION.unwrap();
         if rustc_version != current_version {
diff --git a/compiler/rustc_data_structures/src/fingerprint.rs b/compiler/rustc_data_structures/src/fingerprint.rs
index a032b039f34ef..5ff2d18dd2be3 100644
--- a/compiler/rustc_data_structures/src/fingerprint.rs
+++ b/compiler/rustc_data_structures/src/fingerprint.rs
@@ -1,5 +1,5 @@
 use crate::stable_hasher;
-use rustc_serialize::{Decodable, Encodable};
+use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
 use std::convert::TryInto;
 use std::hash::{Hash, Hasher};
 
@@ -142,14 +142,14 @@ impl stable_hasher::StableHasherResult for Fingerprint {
 
 impl_stable_hash_via_hash!(Fingerprint);
 
-impl<E: rustc_serialize::Encoder> Encodable<E> for Fingerprint {
+impl<E: Encoder> Encodable<E> for Fingerprint {
     #[inline]
     fn encode(&self, s: &mut E) {
         s.emit_raw_bytes(&self.to_le_bytes());
     }
 }
 
-impl<D: rustc_serialize::Decoder> Decodable<D> for Fingerprint {
+impl<D: Decoder> Decodable<D> for Fingerprint {
     #[inline]
     fn decode(d: &mut D) -> Self {
         Fingerprint::from_le_bytes(d.read_raw_bytes(16).try_into().unwrap())
@@ -184,7 +184,7 @@ impl std::fmt::Display for PackedFingerprint {
     }
 }
 
-impl<E: rustc_serialize::Encoder> Encodable<E> for PackedFingerprint {
+impl<E: Encoder> Encodable<E> for PackedFingerprint {
     #[inline]
     fn encode(&self, s: &mut E) {
         // Copy to avoid taking reference to packed field.
@@ -193,7 +193,7 @@ impl<E: rustc_serialize::Encoder> Encodable<E> for PackedFingerprint {
     }
 }
 
-impl<D: rustc_serialize::Decoder> Decodable<D> for PackedFingerprint {
+impl<D: Decoder> Decodable<D> for PackedFingerprint {
     #[inline]
     fn decode(d: &mut D) -> Self {
         Self(Fingerprint::decode(d))
diff --git a/compiler/rustc_incremental/src/persist/load.rs b/compiler/rustc_incremental/src/persist/load.rs
index 9de14950aa8d3..9c325faae8058 100644
--- a/compiler/rustc_incremental/src/persist/load.rs
+++ b/compiler/rustc_incremental/src/persist/load.rs
@@ -4,7 +4,7 @@ use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::memmap::Mmap;
 use rustc_middle::dep_graph::{SerializedDepGraph, WorkProduct, WorkProductId};
 use rustc_middle::ty::OnDiskCache;
-use rustc_serialize::opaque::Decoder;
+use rustc_serialize::opaque::MemDecoder;
 use rustc_serialize::Decodable;
 use rustc_session::config::IncrementalStateAssertion;
 use rustc_session::Session;
@@ -156,7 +156,7 @@ pub fn load_dep_graph(sess: &Session) -> DepGraphFuture {
 
         if let LoadResult::Ok { data: (work_products_data, start_pos) } = load_result {
             // Decode the list of work_products
-            let mut work_product_decoder = Decoder::new(&work_products_data[..], start_pos);
+            let mut work_product_decoder = MemDecoder::new(&work_products_data[..], start_pos);
             let work_products: Vec<SerializedWorkProduct> =
                 Decodable::decode(&mut work_product_decoder);
 
@@ -193,7 +193,7 @@ pub fn load_dep_graph(sess: &Session) -> DepGraphFuture {
             LoadResult::DataOutOfDate => LoadResult::DataOutOfDate,
             LoadResult::Error { message } => LoadResult::Error { message },
             LoadResult::Ok { data: (bytes, start_pos) } => {
-                let mut decoder = Decoder::new(&bytes, start_pos);
+                let mut decoder = MemDecoder::new(&bytes, start_pos);
                 let prev_commandline_args_hash = u64::decode(&mut decoder);
 
                 if prev_commandline_args_hash != expected_hash {
diff --git a/compiler/rustc_metadata/src/rmeta/decoder.rs b/compiler/rustc_metadata/src/rmeta/decoder.rs
index 186031d4586aa..c1ded99a25af5 100644
--- a/compiler/rustc_metadata/src/rmeta/decoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/decoder.rs
@@ -26,7 +26,8 @@ use rustc_middle::ty::codec::TyDecoder;
 use rustc_middle::ty::fast_reject::SimplifiedType;
 use rustc_middle::ty::GeneratorDiagnosticData;
 use rustc_middle::ty::{self, ParameterizedOverTcx, Ty, TyCtxt, Visibility};
-use rustc_serialize::{opaque, Decodable, Decoder};
+use rustc_serialize::opaque::MemDecoder;
+use rustc_serialize::{Decodable, Decoder};
 use rustc_session::cstore::{
     CrateSource, ExternCrate, ForeignModule, LinkagePreference, NativeLib,
 };
@@ -154,7 +155,7 @@ struct ImportedSourceFile {
 }
 
 pub(super) struct DecodeContext<'a, 'tcx> {
-    opaque: opaque::Decoder<'a>,
+    opaque: MemDecoder<'a>,
     cdata: Option<CrateMetadataRef<'a>>,
     blob: &'a MetadataBlob,
     sess: Option<&'tcx Session>,
@@ -186,7 +187,7 @@ pub(super) trait Metadata<'a, 'tcx>: Copy {
     fn decoder(self, pos: usize) -> DecodeContext<'a, 'tcx> {
         let tcx = self.tcx();
         DecodeContext {
-            opaque: opaque::Decoder::new(self.blob(), pos),
+            opaque: MemDecoder::new(self.blob(), pos),
             cdata: self.cdata(),
             blob: self.blob(),
             sess: self.sess().or(tcx.map(|tcx| tcx.sess)),
@@ -418,7 +419,7 @@ impl<'a, 'tcx> TyDecoder for DecodeContext<'a, 'tcx> {
     where
         F: FnOnce(&mut Self) -> R,
     {
-        let new_opaque = opaque::Decoder::new(self.opaque.data, pos);
+        let new_opaque = MemDecoder::new(self.opaque.data, pos);
         let old_opaque = mem::replace(&mut self.opaque, new_opaque);
         let old_state = mem::replace(&mut self.lazy_state, LazyState::NoNode);
         let r = f(self);
diff --git a/compiler/rustc_metadata/src/rmeta/encoder.rs b/compiler/rustc_metadata/src/rmeta/encoder.rs
index 50c09aaf8d445..26fb21020008a 100644
--- a/compiler/rustc_metadata/src/rmeta/encoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/encoder.rs
@@ -27,7 +27,8 @@ use rustc_middle::ty::codec::TyEncoder;
 use rustc_middle::ty::fast_reject::{self, SimplifiedType, TreatParams};
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::{self, SymbolName, Ty, TyCtxt};
-use rustc_serialize::{opaque, Encodable, Encoder};
+use rustc_serialize::opaque::MemEncoder;
+use rustc_serialize::{Encodable, Encoder};
 use rustc_session::config::CrateType;
 use rustc_session::cstore::{ForeignModule, LinkagePreference, NativeLib};
 use rustc_span::hygiene::{ExpnIndex, HygieneEncodeContext, MacroKind};
@@ -43,7 +44,7 @@ use std::num::NonZeroUsize;
 use tracing::{debug, trace};
 
 pub(super) struct EncodeContext<'a, 'tcx> {
-    opaque: opaque::Encoder,
+    opaque: MemEncoder,
     tcx: TyCtxt<'tcx>,
     feat: &'tcx rustc_feature::Features,
 
@@ -93,8 +94,8 @@ macro_rules! encoder_methods {
 }
 
 impl<'a, 'tcx> Encoder for EncodeContext<'a, 'tcx> {
-    type Ok = <opaque::Encoder as Encoder>::Ok;
-    type Err = <opaque::Encoder as Encoder>::Err;
+    type Ok = <MemEncoder as Encoder>::Ok;
+    type Err = <MemEncoder as Encoder>::Err;
 
     encoder_methods! {
         emit_usize(usize);
@@ -2180,7 +2181,7 @@ pub fn encode_metadata(tcx: TyCtxt<'_>) -> EncodedMetadata {
 }
 
 fn encode_metadata_impl(tcx: TyCtxt<'_>) -> EncodedMetadata {
-    let mut encoder = opaque::Encoder::new();
+    let mut encoder = MemEncoder::new();
     encoder.emit_raw_bytes(METADATA_HEADER);
 
     // Will be filled with the root position after encoding everything.
diff --git a/compiler/rustc_metadata/src/rmeta/mod.rs b/compiler/rustc_metadata/src/rmeta/mod.rs
index fb2ffe1d73d96..04f0847f5cccc 100644
--- a/compiler/rustc_metadata/src/rmeta/mod.rs
+++ b/compiler/rustc_metadata/src/rmeta/mod.rs
@@ -22,7 +22,7 @@ use rustc_middle::ty::fast_reject::SimplifiedType;
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::{self, ReprOptions, Ty};
 use rustc_middle::ty::{GeneratorDiagnosticData, ParameterizedOverTcx, TyCtxt};
-use rustc_serialize::opaque::Encoder;
+use rustc_serialize::opaque::MemEncoder;
 use rustc_session::config::SymbolManglingVersion;
 use rustc_session::cstore::{CrateDepKind, ForeignModule, LinkagePreference, NativeLib};
 use rustc_span::edition::Edition;
@@ -323,7 +323,7 @@ macro_rules! define_tables {
         }
 
         impl TableBuilders {
-            fn encode(&self, buf: &mut Encoder) -> LazyTables {
+            fn encode(&self, buf: &mut MemEncoder) -> LazyTables {
                 LazyTables {
                     $($name: self.$name.encode(buf)),+
                 }
diff --git a/compiler/rustc_metadata/src/rmeta/table.rs b/compiler/rustc_metadata/src/rmeta/table.rs
index 8baa67a8f9fcf..5ab4269ae99ad 100644
--- a/compiler/rustc_metadata/src/rmeta/table.rs
+++ b/compiler/rustc_metadata/src/rmeta/table.rs
@@ -4,8 +4,8 @@ use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_hir::def::{CtorKind, CtorOf};
 use rustc_index::vec::Idx;
 use rustc_middle::ty::ParameterizedOverTcx;
-use rustc_serialize::opaque::Encoder;
-use rustc_serialize::Encoder as _;
+use rustc_serialize::opaque::MemEncoder;
+use rustc_serialize::Encoder;
 use rustc_span::hygiene::MacroKind;
 use std::convert::TryInto;
 use std::marker::PhantomData;
@@ -281,7 +281,7 @@ where
         Some(value).write_to_bytes(&mut self.blocks[i]);
     }
 
-    pub(crate) fn encode<const N: usize>(&self, buf: &mut Encoder) -> LazyTable<I, T>
+    pub(crate) fn encode<const N: usize>(&self, buf: &mut MemEncoder) -> LazyTable<I, T>
     where
         Option<T>: FixedSizeEncoding<ByteArray = [u8; N]>,
     {
diff --git a/compiler/rustc_middle/src/mir/graph_cyclic_cache.rs b/compiler/rustc_middle/src/mir/graph_cyclic_cache.rs
index 096bf8cbc158a..1279f5aee3691 100644
--- a/compiler/rustc_middle/src/mir/graph_cyclic_cache.rs
+++ b/compiler/rustc_middle/src/mir/graph_cyclic_cache.rs
@@ -3,7 +3,7 @@ use rustc_data_structures::graph::{
 };
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::sync::OnceCell;
-use rustc_serialize as serialize;
+use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
 
 /// Helper type to cache the result of `graph::is_cyclic`.
 #[derive(Clone, Debug)]
@@ -36,17 +36,17 @@ impl GraphIsCyclicCache {
     }
 }
 
-impl<S: serialize::Encoder> serialize::Encodable<S> for GraphIsCyclicCache {
+impl<S: Encoder> Encodable<S> for GraphIsCyclicCache {
     #[inline]
     fn encode(&self, s: &mut S) {
-        serialize::Encodable::encode(&(), s);
+        Encodable::encode(&(), s);
     }
 }
 
-impl<D: serialize::Decoder> serialize::Decodable<D> for GraphIsCyclicCache {
+impl<D: Decoder> Decodable<D> for GraphIsCyclicCache {
     #[inline]
     fn decode(d: &mut D) -> Self {
-        let () = serialize::Decodable::decode(d);
+        let () = Decodable::decode(d);
         Self::new()
     }
 }
diff --git a/compiler/rustc_middle/src/mir/predecessors.rs b/compiler/rustc_middle/src/mir/predecessors.rs
index 9bc0cb1138ff1..620cf7e336ba4 100644
--- a/compiler/rustc_middle/src/mir/predecessors.rs
+++ b/compiler/rustc_middle/src/mir/predecessors.rs
@@ -3,7 +3,7 @@
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::sync::OnceCell;
 use rustc_index::vec::IndexVec;
-use rustc_serialize as serialize;
+use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
 use smallvec::SmallVec;
 
 use crate::mir::{BasicBlock, BasicBlockData};
@@ -54,12 +54,12 @@ impl PredecessorCache {
     }
 }
 
-impl<S: serialize::Encoder> serialize::Encodable<S> for PredecessorCache {
+impl<S: Encoder> Encodable<S> for PredecessorCache {
     #[inline]
     fn encode(&self, _s: &mut S) {}
 }
 
-impl<D: serialize::Decoder> serialize::Decodable<D> for PredecessorCache {
+impl<D: Decoder> Decodable<D> for PredecessorCache {
     #[inline]
     fn decode(_: &mut D) -> Self {
         Self::new()
diff --git a/compiler/rustc_middle/src/mir/switch_sources.rs b/compiler/rustc_middle/src/mir/switch_sources.rs
index 4872a7835e3fa..99d13fcfef43e 100644
--- a/compiler/rustc_middle/src/mir/switch_sources.rs
+++ b/compiler/rustc_middle/src/mir/switch_sources.rs
@@ -5,7 +5,7 @@ use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::stable_map::FxHashMap;
 use rustc_data_structures::sync::OnceCell;
 use rustc_index::vec::IndexVec;
-use rustc_serialize as serialize;
+use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
 use smallvec::SmallVec;
 
 use crate::mir::{BasicBlock, BasicBlockData, Terminator, TerminatorKind};
@@ -54,12 +54,12 @@ impl SwitchSourceCache {
     }
 }
 
-impl<S: serialize::Encoder> serialize::Encodable<S> for SwitchSourceCache {
+impl<S: Encoder> Encodable<S> for SwitchSourceCache {
     #[inline]
     fn encode(&self, _s: &mut S) {}
 }
 
-impl<D: serialize::Decoder> serialize::Decodable<D> for SwitchSourceCache {
+impl<D: Decoder> Decodable<D> for SwitchSourceCache {
     #[inline]
     fn decode(_: &mut D) -> Self {
         Self::new()
diff --git a/compiler/rustc_middle/src/mir/traversal.rs b/compiler/rustc_middle/src/mir/traversal.rs
index f745e55307ae2..7228e3f33b126 100644
--- a/compiler/rustc_middle/src/mir/traversal.rs
+++ b/compiler/rustc_middle/src/mir/traversal.rs
@@ -1,7 +1,7 @@
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::sync::OnceCell;
 use rustc_index::bit_set::BitSet;
-use rustc_serialize as serialize;
+use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
 
 use super::*;
 
@@ -365,12 +365,12 @@ impl PostorderCache {
     }
 }
 
-impl<S: serialize::Encoder> serialize::Encodable<S> for PostorderCache {
+impl<S: Encoder> Encodable<S> for PostorderCache {
     #[inline]
     fn encode(&self, _s: &mut S) {}
 }
 
-impl<D: serialize::Decoder> serialize::Decodable<D> for PostorderCache {
+impl<D: Decoder> Decodable<D> for PostorderCache {
     #[inline]
     fn decode(_: &mut D) -> Self {
         Self::new()
diff --git a/compiler/rustc_query_impl/src/on_disk_cache.rs b/compiler/rustc_query_impl/src/on_disk_cache.rs
index c2c876f7f1a12..d7327ca4bc602 100644
--- a/compiler/rustc_query_impl/src/on_disk_cache.rs
+++ b/compiler/rustc_query_impl/src/on_disk_cache.rs
@@ -15,7 +15,7 @@ use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_query_system::dep_graph::DepContext;
 use rustc_query_system::query::{QueryCache, QueryContext, QuerySideEffects};
 use rustc_serialize::{
-    opaque::{self, FileEncodeResult, FileEncoder, IntEncodedWithFixedSize},
+    opaque::{FileEncodeResult, FileEncoder, IntEncodedWithFixedSize, MemDecoder},
     Decodable, Decoder, Encodable, Encoder,
 };
 use rustc_session::Session;
@@ -158,7 +158,7 @@ impl<'sess> rustc_middle::ty::OnDiskCache<'sess> for OnDiskCache<'sess> {
 
         // Wrap in a scope so we can borrow `data`.
         let footer: Footer = {
-            let mut decoder = opaque::Decoder::new(&data, start_pos);
+            let mut decoder = MemDecoder::new(&data, start_pos);
 
             // Decode the *position* of the footer, which can be found in the
             // last 8 bytes of the file.
@@ -437,7 +437,7 @@ impl<'sess> OnDiskCache<'sess> {
         let serialized_data = self.serialized_data.read();
         let mut decoder = CacheDecoder {
             tcx,
-            opaque: opaque::Decoder::new(serialized_data.as_deref().unwrap_or(&[]), pos.to_usize()),
+            opaque: MemDecoder::new(serialized_data.as_deref().unwrap_or(&[]), pos.to_usize()),
             source_map: self.source_map,
             file_index_to_file: &self.file_index_to_file,
             file_index_to_stable_id: &self.file_index_to_stable_id,
@@ -458,7 +458,7 @@ impl<'sess> OnDiskCache<'sess> {
 /// will also handle things that contain `Ty` instances.
 pub struct CacheDecoder<'a, 'tcx> {
     tcx: TyCtxt<'tcx>,
-    opaque: opaque::Decoder<'a>,
+    opaque: MemDecoder<'a>,
     source_map: &'a SourceMap,
     file_index_to_file: &'a Lock<FxHashMap<SourceFileIndex, Lrc<SourceFile>>>,
     file_index_to_stable_id: &'a FxHashMap<SourceFileIndex, EncodedSourceFileId>,
@@ -510,7 +510,7 @@ trait DecoderWithPosition: Decoder {
     fn position(&self) -> usize;
 }
 
-impl<'a> DecoderWithPosition for opaque::Decoder<'a> {
+impl<'a> DecoderWithPosition for MemDecoder<'a> {
     fn position(&self) -> usize {
         self.position()
     }
@@ -586,7 +586,7 @@ impl<'a, 'tcx> TyDecoder for CacheDecoder<'a, 'tcx> {
     {
         debug_assert!(pos < self.opaque.data.len());
 
-        let new_opaque = opaque::Decoder::new(self.opaque.data, pos);
+        let new_opaque = MemDecoder::new(self.opaque.data, pos);
         let old_opaque = mem::replace(&mut self.opaque, new_opaque);
         let r = f(self);
         self.opaque = old_opaque;
diff --git a/compiler/rustc_query_system/src/dep_graph/serialized.rs b/compiler/rustc_query_system/src/dep_graph/serialized.rs
index 7fde9c0119b85..d583b45698ac4 100644
--- a/compiler/rustc_query_system/src/dep_graph/serialized.rs
+++ b/compiler/rustc_query_system/src/dep_graph/serialized.rs
@@ -19,7 +19,7 @@ use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::profiling::SelfProfilerRef;
 use rustc_data_structures::sync::Lock;
 use rustc_index::vec::{Idx, IndexVec};
-use rustc_serialize::opaque::{self, FileEncodeResult, FileEncoder, IntEncodedWithFixedSize};
+use rustc_serialize::opaque::{FileEncodeResult, FileEncoder, IntEncodedWithFixedSize, MemDecoder};
 use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
 use smallvec::SmallVec;
 use std::convert::TryInto;
@@ -96,11 +96,11 @@ impl<K: DepKind> SerializedDepGraph<K> {
     }
 }
 
-impl<'a, K: DepKind + Decodable<opaque::Decoder<'a>>> Decodable<opaque::Decoder<'a>>
+impl<'a, K: DepKind + Decodable<MemDecoder<'a>>> Decodable<MemDecoder<'a>>
     for SerializedDepGraph<K>
 {
     #[instrument(level = "debug", skip(d))]
-    fn decode(d: &mut opaque::Decoder<'a>) -> SerializedDepGraph<K> {
+    fn decode(d: &mut MemDecoder<'a>) -> SerializedDepGraph<K> {
         let start_position = d.position();
 
         // The last 16 bytes are the node count and edge count.
diff --git a/compiler/rustc_serialize/src/opaque.rs b/compiler/rustc_serialize/src/opaque.rs
index b2dbf937eb75a..f828c0b71063d 100644
--- a/compiler/rustc_serialize/src/opaque.rs
+++ b/compiler/rustc_serialize/src/opaque.rs
@@ -1,5 +1,5 @@
 use crate::leb128::{self, max_leb128_len};
-use crate::serialize::{self, Decoder as _, Encoder as _};
+use crate::serialize::{Decodable, Decoder, Encodable, Encoder};
 use std::convert::TryInto;
 use std::fs::File;
 use std::io::{self, Write};
@@ -11,13 +11,13 @@ use std::ptr;
 // Encoder
 // -----------------------------------------------------------------------------
 
-pub struct Encoder {
+pub struct MemEncoder {
     pub data: Vec<u8>,
 }
 
-impl Encoder {
-    pub fn new() -> Encoder {
-        Encoder { data: vec![] }
+impl MemEncoder {
+    pub fn new() -> MemEncoder {
+        MemEncoder { data: vec![] }
     }
 
     #[inline]
@@ -53,7 +53,7 @@ macro_rules! write_leb128 {
 /// [utf8]: https://en.wikipedia.org/w/index.php?title=UTF-8&oldid=1058865525#Codepage_layout
 const STR_SENTINEL: u8 = 0xC1;
 
-impl serialize::Encoder for Encoder {
+impl Encoder for MemEncoder {
     type Ok = Vec<u8>;
     type Err = !;
 
@@ -161,7 +161,7 @@ pub type FileEncodeResult = Result<usize, io::Error>;
 // `FileEncoder` encodes data to file via fixed-size buffer.
 //
 // When encoding large amounts of data to a file, using `FileEncoder` may be
-// preferred over using `Encoder` to encode to a `Vec`, and then writing the
+// preferred over using `MemEncoder` to encode to a `Vec`, and then writing the
 // `Vec` to file, as the latter uses as much memory as there is encoded data,
 // while the former uses the fixed amount of memory allocated to the buffer.
 // `FileEncoder` also has the advantage of not needing to reallocate as data
@@ -425,7 +425,7 @@ macro_rules! file_encoder_write_leb128 {
     }};
 }
 
-impl serialize::Encoder for FileEncoder {
+impl Encoder for FileEncoder {
     type Ok = usize;
     type Err = io::Error;
 
@@ -535,15 +535,15 @@ impl serialize::Encoder for FileEncoder {
 // Decoder
 // -----------------------------------------------------------------------------
 
-pub struct Decoder<'a> {
+pub struct MemDecoder<'a> {
     pub data: &'a [u8],
     position: usize,
 }
 
-impl<'a> Decoder<'a> {
+impl<'a> MemDecoder<'a> {
     #[inline]
-    pub fn new(data: &'a [u8], position: usize) -> Decoder<'a> {
-        Decoder { data, position }
+    pub fn new(data: &'a [u8], position: usize) -> MemDecoder<'a> {
+        MemDecoder { data, position }
     }
 
     #[inline]
@@ -566,7 +566,7 @@ macro_rules! read_leb128 {
     ($dec:expr, $fun:ident) => {{ leb128::$fun($dec.data, &mut $dec.position) }};
 }
 
-impl<'a> serialize::Decoder for Decoder<'a> {
+impl<'a> Decoder for MemDecoder<'a> {
     #[inline]
     fn read_u128(&mut self) -> u128 {
         read_leb128!(self, read_u128_leb128)
@@ -688,25 +688,25 @@ impl<'a> serialize::Decoder for Decoder<'a> {
 
 // Specialize encoding byte slices. This specialization also applies to encoding `Vec<u8>`s, etc.,
 // since the default implementations call `encode` on their slices internally.
-impl serialize::Encodable<Encoder> for [u8] {
-    fn encode(&self, e: &mut Encoder) {
-        serialize::Encoder::emit_usize(e, self.len());
+impl Encodable<MemEncoder> for [u8] {
+    fn encode(&self, e: &mut MemEncoder) {
+        Encoder::emit_usize(e, self.len());
         e.emit_raw_bytes(self);
     }
 }
 
-impl serialize::Encodable<FileEncoder> for [u8] {
+impl Encodable<FileEncoder> for [u8] {
     fn encode(&self, e: &mut FileEncoder) {
-        serialize::Encoder::emit_usize(e, self.len());
+        Encoder::emit_usize(e, self.len());
         e.emit_raw_bytes(self);
     }
 }
 
 // Specialize decoding `Vec<u8>`. This specialization also applies to decoding `Box<[u8]>`s, etc.,
 // since the default implementations call `decode` to produce a `Vec<u8>` internally.
-impl<'a> serialize::Decodable<Decoder<'a>> for Vec<u8> {
-    fn decode(d: &mut Decoder<'a>) -> Self {
-        let len = serialize::Decoder::read_usize(d);
+impl<'a> Decodable<MemDecoder<'a>> for Vec<u8> {
+    fn decode(d: &mut MemDecoder<'a>) -> Self {
+        let len = Decoder::read_usize(d);
         d.read_raw_bytes(len).to_owned()
     }
 }
@@ -718,9 +718,9 @@ impl IntEncodedWithFixedSize {
     pub const ENCODED_SIZE: usize = 8;
 }
 
-impl serialize::Encodable<Encoder> for IntEncodedWithFixedSize {
+impl Encodable<MemEncoder> for IntEncodedWithFixedSize {
     #[inline]
-    fn encode(&self, e: &mut Encoder) {
+    fn encode(&self, e: &mut MemEncoder) {
         let _start_pos = e.position();
         e.emit_raw_bytes(&self.0.to_le_bytes());
         let _end_pos = e.position();
@@ -728,7 +728,7 @@ impl serialize::Encodable<Encoder> for IntEncodedWithFixedSize {
     }
 }
 
-impl serialize::Encodable<FileEncoder> for IntEncodedWithFixedSize {
+impl Encodable<FileEncoder> for IntEncodedWithFixedSize {
     #[inline]
     fn encode(&self, e: &mut FileEncoder) {
         let _start_pos = e.position();
@@ -738,9 +738,9 @@ impl serialize::Encodable<FileEncoder> for IntEncodedWithFixedSize {
     }
 }
 
-impl<'a> serialize::Decodable<Decoder<'a>> for IntEncodedWithFixedSize {
+impl<'a> Decodable<MemDecoder<'a>> for IntEncodedWithFixedSize {
     #[inline]
-    fn decode(decoder: &mut Decoder<'a>) -> IntEncodedWithFixedSize {
+    fn decode(decoder: &mut MemDecoder<'a>) -> IntEncodedWithFixedSize {
         let _start_pos = decoder.position();
         let bytes = decoder.read_raw_bytes(IntEncodedWithFixedSize::ENCODED_SIZE);
         let value = u64::from_le_bytes(bytes.try_into().unwrap());
diff --git a/compiler/rustc_serialize/tests/opaque.rs b/compiler/rustc_serialize/tests/opaque.rs
index 703b7f5e7a5f4..4eafb6fabde8e 100644
--- a/compiler/rustc_serialize/tests/opaque.rs
+++ b/compiler/rustc_serialize/tests/opaque.rs
@@ -1,7 +1,7 @@
 #![allow(rustc::internal)]
 
 use rustc_macros::{Decodable, Encodable};
-use rustc_serialize::opaque::{Decoder, Encoder};
+use rustc_serialize::opaque::{MemDecoder, MemEncoder};
 use rustc_serialize::{Decodable, Encodable, Encoder as EncoderTrait};
 use std::fmt::Debug;
 
@@ -28,16 +28,18 @@ struct Struct {
     q: Option<u32>,
 }
 
-fn check_round_trip<T: Encodable<Encoder> + for<'a> Decodable<Decoder<'a>> + PartialEq + Debug>(
+fn check_round_trip<
+    T: Encodable<MemEncoder> + for<'a> Decodable<MemDecoder<'a>> + PartialEq + Debug,
+>(
     values: Vec<T>,
 ) {
-    let mut encoder = Encoder::new();
+    let mut encoder = MemEncoder::new();
     for value in &values {
         Encodable::encode(value, &mut encoder);
     }
 
     let data = encoder.finish().unwrap();
-    let mut decoder = Decoder::new(&data[..], 0);
+    let mut decoder = MemDecoder::new(&data[..], 0);
 
     for value in values {
         let decoded = Decodable::decode(&mut decoder);
diff --git a/compiler/rustc_span/src/lib.rs b/compiler/rustc_span/src/lib.rs
index d7e2f621065f0..5d3d56b1e6699 100644
--- a/compiler/rustc_span/src/lib.rs
+++ b/compiler/rustc_span/src/lib.rs
@@ -1911,13 +1911,13 @@ impl_pos! {
     pub struct CharPos(pub usize);
 }
 
-impl<S: rustc_serialize::Encoder> Encodable<S> for BytePos {
+impl<S: Encoder> Encodable<S> for BytePos {
     fn encode(&self, s: &mut S) {
         s.emit_u32(self.0);
     }
 }
 
-impl<D: rustc_serialize::Decoder> Decodable<D> for BytePos {
+impl<D: Decoder> Decodable<D> for BytePos {
     fn decode(d: &mut D) -> BytePos {
         BytePos(d.read_u32())
     }
diff --git a/compiler/rustc_type_ir/src/sty.rs b/compiler/rustc_type_ir/src/sty.rs
index a6a0d02c8ba99..9407218439993 100644
--- a/compiler/rustc_type_ir/src/sty.rs
+++ b/compiler/rustc_type_ir/src/sty.rs
@@ -14,7 +14,7 @@ use crate::UintTy;
 use self::TyKind::*;
 
 use rustc_data_structures::stable_hasher::HashStable;
-use rustc_serialize::{Decodable, Encodable};
+use rustc_serialize::{Decodable, Decoder, Encodable};
 
 /// Defines the kinds of types used by the type system.
 ///
@@ -833,56 +833,34 @@ where
     I::AllocId: Decodable<D>,
 {
     fn decode(d: &mut D) -> Self {
-        match rustc_serialize::Decoder::read_usize(d) {
+        match Decoder::read_usize(d) {
             0 => Bool,
             1 => Char,
-            2 => Int(rustc_serialize::Decodable::decode(d)),
-            3 => Uint(rustc_serialize::Decodable::decode(d)),
-            4 => Float(rustc_serialize::Decodable::decode(d)),
-            5 => Adt(rustc_serialize::Decodable::decode(d), rustc_serialize::Decodable::decode(d)),
-            6 => Foreign(rustc_serialize::Decodable::decode(d)),
+            2 => Int(Decodable::decode(d)),
+            3 => Uint(Decodable::decode(d)),
+            4 => Float(Decodable::decode(d)),
+            5 => Adt(Decodable::decode(d), Decodable::decode(d)),
+            6 => Foreign(Decodable::decode(d)),
             7 => Str,
-            8 => {
-                Array(rustc_serialize::Decodable::decode(d), rustc_serialize::Decodable::decode(d))
-            }
-            9 => Slice(rustc_serialize::Decodable::decode(d)),
-            10 => RawPtr(rustc_serialize::Decodable::decode(d)),
-            11 => Ref(
-                rustc_serialize::Decodable::decode(d),
-                rustc_serialize::Decodable::decode(d),
-                rustc_serialize::Decodable::decode(d),
-            ),
-            12 => {
-                FnDef(rustc_serialize::Decodable::decode(d), rustc_serialize::Decodable::decode(d))
-            }
-            13 => FnPtr(rustc_serialize::Decodable::decode(d)),
-            14 => Dynamic(
-                rustc_serialize::Decodable::decode(d),
-                rustc_serialize::Decodable::decode(d),
-            ),
-            15 => Closure(
-                rustc_serialize::Decodable::decode(d),
-                rustc_serialize::Decodable::decode(d),
-            ),
-            16 => Generator(
-                rustc_serialize::Decodable::decode(d),
-                rustc_serialize::Decodable::decode(d),
-                rustc_serialize::Decodable::decode(d),
-            ),
-            17 => GeneratorWitness(rustc_serialize::Decodable::decode(d)),
+            8 => Array(Decodable::decode(d), Decodable::decode(d)),
+            9 => Slice(Decodable::decode(d)),
+            10 => RawPtr(Decodable::decode(d)),
+            11 => Ref(Decodable::decode(d), Decodable::decode(d), Decodable::decode(d)),
+            12 => FnDef(Decodable::decode(d), Decodable::decode(d)),
+            13 => FnPtr(Decodable::decode(d)),
+            14 => Dynamic(Decodable::decode(d), Decodable::decode(d)),
+            15 => Closure(Decodable::decode(d), Decodable::decode(d)),
+            16 => Generator(Decodable::decode(d), Decodable::decode(d), Decodable::decode(d)),
+            17 => GeneratorWitness(Decodable::decode(d)),
             18 => Never,
-            19 => Tuple(rustc_serialize::Decodable::decode(d)),
-            20 => Projection(rustc_serialize::Decodable::decode(d)),
-            21 => {
-                Opaque(rustc_serialize::Decodable::decode(d), rustc_serialize::Decodable::decode(d))
-            }
-            22 => Param(rustc_serialize::Decodable::decode(d)),
-            23 => {
-                Bound(rustc_serialize::Decodable::decode(d), rustc_serialize::Decodable::decode(d))
-            }
-            24 => Placeholder(rustc_serialize::Decodable::decode(d)),
-            25 => Infer(rustc_serialize::Decodable::decode(d)),
-            26 => Error(rustc_serialize::Decodable::decode(d)),
+            19 => Tuple(Decodable::decode(d)),
+            20 => Projection(Decodable::decode(d)),
+            21 => Opaque(Decodable::decode(d), Decodable::decode(d)),
+            22 => Param(Decodable::decode(d)),
+            23 => Bound(Decodable::decode(d), Decodable::decode(d)),
+            24 => Placeholder(Decodable::decode(d)),
+            25 => Infer(Decodable::decode(d)),
+            26 => Error(Decodable::decode(d)),
             _ => panic!(
                 "{}",
                 format!(
diff --git a/src/librustdoc/scrape_examples.rs b/src/librustdoc/scrape_examples.rs
index 242f926967c93..da09ae9dd0662 100644
--- a/src/librustdoc/scrape_examples.rs
+++ b/src/librustdoc/scrape_examples.rs
@@ -17,7 +17,7 @@ use rustc_middle::hir::map::Map;
 use rustc_middle::hir::nested_filter;
 use rustc_middle::ty::{self, TyCtxt};
 use rustc_serialize::{
-    opaque::{Decoder, FileEncoder},
+    opaque::{FileEncoder, MemDecoder},
     Decodable, Encodable, Encoder,
 };
 use rustc_session::getopts;
@@ -336,7 +336,7 @@ pub(crate) fn load_call_locations(
         let mut all_calls: AllCallLocations = FxHashMap::default();
         for path in with_examples {
             let bytes = fs::read(&path).map_err(|e| format!("{} (for path {})", e, path))?;
-            let mut decoder = Decoder::new(&bytes, 0);
+            let mut decoder = MemDecoder::new(&bytes, 0);
             let calls = AllCallLocations::decode(&mut decoder);
 
             for (function, fn_calls) in calls.into_iter() {
diff --git a/src/test/ui-fulldeps/deriving-encodable-decodable-box.rs b/src/test/ui-fulldeps/deriving-encodable-decodable-box.rs
index a09deeec4f182..4ad4ef60a5294 100644
--- a/src/test/ui-fulldeps/deriving-encodable-decodable-box.rs
+++ b/src/test/ui-fulldeps/deriving-encodable-decodable-box.rs
@@ -7,7 +7,7 @@ extern crate rustc_macros;
 extern crate rustc_serialize;
 
 use rustc_macros::{Decodable, Encodable};
-use rustc_serialize::opaque;
+use rustc_serialize::opaque::{MemDecoder, MemEncoder};
 use rustc_serialize::{Decodable, Encodable, Encoder};
 
 #[derive(Encodable, Decodable)]
@@ -18,11 +18,11 @@ struct A {
 fn main() {
     let obj = A { foo: Box::new([true, false]) };
 
-    let mut encoder = opaque::Encoder::new();
+    let mut encoder = MemEncoder::new();
     obj.encode(&mut encoder);
     let data = encoder.finish().unwrap();
 
-    let mut decoder = opaque::Decoder::new(&data, 0);
+    let mut decoder = MemDecoder::new(&data, 0);
     let obj2 = A::decode(&mut decoder);
 
     assert_eq!(obj.foo, obj2.foo);
diff --git a/src/test/ui-fulldeps/deriving-encodable-decodable-cell-refcell.rs b/src/test/ui-fulldeps/deriving-encodable-decodable-cell-refcell.rs
index 9b6fb0e580621..3ac3abae692af 100644
--- a/src/test/ui-fulldeps/deriving-encodable-decodable-cell-refcell.rs
+++ b/src/test/ui-fulldeps/deriving-encodable-decodable-cell-refcell.rs
@@ -9,7 +9,7 @@ extern crate rustc_macros;
 extern crate rustc_serialize;
 
 use rustc_macros::{Decodable, Encodable};
-use rustc_serialize::opaque;
+use rustc_serialize::opaque::{MemDecoder, MemEncoder};
 use rustc_serialize::{Decodable, Encodable, Encoder};
 use std::cell::{Cell, RefCell};
 
@@ -27,11 +27,11 @@ struct B {
 fn main() {
     let obj = B { foo: Cell::new(true), bar: RefCell::new(A { baz: 2 }) };
 
-    let mut encoder = opaque::Encoder::new();
+    let mut encoder = MemEncoder::new();
     obj.encode(&mut encoder);
     let data = encoder.finish().unwrap();
 
-    let mut decoder = opaque::Decoder::new(&data, 0);
+    let mut decoder = MemDecoder::new(&data, 0);
     let obj2 = B::decode(&mut decoder);
 
     assert_eq!(obj.foo.get(), obj2.foo.get());
diff --git a/src/test/ui-fulldeps/issue-14021.rs b/src/test/ui-fulldeps/issue-14021.rs
index 4241456367e46..b7b6e1b860d35 100644
--- a/src/test/ui-fulldeps/issue-14021.rs
+++ b/src/test/ui-fulldeps/issue-14021.rs
@@ -8,7 +8,7 @@ extern crate rustc_macros;
 extern crate rustc_serialize;
 
 use rustc_macros::{Decodable, Encodable};
-use rustc_serialize::opaque;
+use rustc_serialize::opaque::{MemDecoder, MemEncoder};
 use rustc_serialize::{Decodable, Encodable, Encoder};
 
 #[derive(Encodable, Decodable, PartialEq, Debug)]
@@ -17,11 +17,11 @@ struct UnitLikeStruct;
 pub fn main() {
     let obj = UnitLikeStruct;
 
-    let mut encoder = opaque::Encoder::new();
+    let mut encoder = MemEncoder::new();
     obj.encode(&mut encoder);
     let data = encoder.finish().unwrap();
 
-    let mut decoder = opaque::Decoder::new(&data, 0);
+    let mut decoder = MemDecoder::new(&data, 0);
     let obj2 = UnitLikeStruct::decode(&mut decoder);
 
     assert_eq!(obj, obj2);