Auto merge of #97905 - nnethercote:revert-infallible-encoder, r=bjorn3

Revert part of #94372 to improve performance

#94732 was supposed to give small but widespread performance improvements, as judged from three per-merge performance runs. But the performance run that occurred after merging included a roughly equal number of improvements and regressions, for unclear reasons.

This PR is for a test run reverting those changes, to see what happens.

r? `@ghost`

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::{Decodable, Decoder, Encodable, Encoder};
+use rustc_serialize::{self, Decoder, 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> Encodable<S> for AttrId {
+impl<S: Encoder> rustc_serialize::Encodable<S> for AttrId {
     fn encode(&self, _s: &mut S) {}
 }
 
-impl<D: Decoder> Decodable<D> for AttrId {
+impl<D: Decoder> rustc_serialize::Decodable<D> for AttrId {
     fn decode(_: &mut D) -> AttrId {
         crate::attr::mk_attr_id()
     }

compiler/rustc_codegen_ssa/src/lib.rs

@@ -29,8 +29,7 @@ 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::{MemDecoder, MemEncoder};
-use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
+use rustc_serialize::{opaque, 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;
@@ -204,14 +203,14 @@ const RUSTC_VERSION: Option<&str> = option_env!("CFG_VERSION");
 
 impl CodegenResults {
     pub fn serialize_rlink(codegen_results: &CodegenResults) -> Vec<u8> {
-        let mut encoder = MemEncoder::new();
+        let mut encoder = opaque::Encoder::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`.
         encoder.emit_raw_bytes(&RLINK_VERSION.to_be_bytes());
         encoder.emit_str(RUSTC_VERSION.unwrap());
         Encodable::encode(codegen_results, &mut encoder);
-        encoder.finish()
+        encoder.finish().unwrap()
     }
 
     pub fn deserialize_rlink(data: Vec<u8>) -> Result<Self, String> {
@@ -231,7 +230,7 @@ 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 = MemDecoder::new(&data[4..], 0);
+        let mut decoder = opaque::Decoder::new(&data[4..], 0);
         let rustc_version = decoder.read_str();
         let current_version = RUSTC_VERSION.unwrap();
         if rustc_version != current_version {

compiler/rustc_data_structures/src/fingerprint.rs

@@ -1,5 +1,5 @@
 use crate::stable_hasher;
-use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
+use rustc_serialize::{Decodable, Encodable};
 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: Encoder> Encodable<E> for Fingerprint {
+impl<E: rustc_serialize::Encoder> Encodable<E> for Fingerprint {
     #[inline]
     fn encode(&self, s: &mut E) {
         s.emit_raw_bytes(&self.to_le_bytes());
     }
 }
 
-impl<D: Decoder> Decodable<D> for Fingerprint {
+impl<D: rustc_serialize::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: Encoder> Encodable<E> for PackedFingerprint {
+impl<E: rustc_serialize::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: Encoder> Encodable<E> for PackedFingerprint {
     }
 }
 
-impl<D: Decoder> Decodable<D> for PackedFingerprint {
+impl<D: rustc_serialize::Decoder> Decodable<D> for PackedFingerprint {
     #[inline]
     fn decode(d: &mut D) -> Self {
         Self(Fingerprint::decode(d))

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::MemDecoder;
+use rustc_serialize::opaque::Decoder;
 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 = MemDecoder::new(&work_products_data[..], start_pos);
+            let mut work_product_decoder = Decoder::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 = MemDecoder::new(&bytes, start_pos);
+                let mut decoder = Decoder::new(&bytes, start_pos);
                 let prev_commandline_args_hash = u64::decode(&mut decoder);
 
                 if prev_commandline_args_hash != expected_hash {

compiler/rustc_incremental/src/persist/save.rs

@@ -3,7 +3,7 @@ use rustc_data_structures::sync::join;
 use rustc_middle::dep_graph::{DepGraph, SerializedDepGraph, WorkProduct, WorkProductId};
 use rustc_middle::ty::TyCtxt;
 use rustc_serialize::opaque::{FileEncodeResult, FileEncoder};
-use rustc_serialize::Encodable;
+use rustc_serialize::{Encodable as RustcEncodable, Encoder};
 use rustc_session::Session;
 use std::fs;
 

compiler/rustc_metadata/src/rmeta/decoder.rs

@@ -26,8 +26,7 @@ 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::MemDecoder;
-use rustc_serialize::{Decodable, Decoder};
+use rustc_serialize::{opaque, Decodable, Decoder};
 use rustc_session::cstore::{
     CrateSource, ExternCrate, ForeignModule, LinkagePreference, NativeLib,
 };
@@ -155,7 +154,7 @@ struct ImportedSourceFile {
 }
 
 pub(super) struct DecodeContext<'a, 'tcx> {
-    opaque: MemDecoder<'a>,
+    opaque: opaque::Decoder<'a>,
     cdata: Option<CrateMetadataRef<'a>>,
     blob: &'a MetadataBlob,
     sess: Option<&'tcx Session>,
@@ -187,7 +186,7 @@ pub(super) trait Metadata<'a, 'tcx>: Copy {
     fn decoder(self, pos: usize) -> DecodeContext<'a, 'tcx> {
         let tcx = self.tcx();
         DecodeContext {
-            opaque: MemDecoder::new(self.blob(), pos),
+            opaque: opaque::Decoder::new(self.blob(), pos),
             cdata: self.cdata(),
             blob: self.blob(),
             sess: self.sess().or(tcx.map(|tcx| tcx.sess)),
@@ -419,7 +418,7 @@ impl<'a, 'tcx> TyDecoder for DecodeContext<'a, 'tcx> {
     where
         F: FnOnce(&mut Self) -> R,
     {
-        let new_opaque = MemDecoder::new(self.opaque.data, pos);
+        let new_opaque = opaque::Decoder::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);

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -27,8 +27,7 @@ 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::MemEncoder;
-use rustc_serialize::{Encodable, Encoder};
+use rustc_serialize::{opaque, Encodable, Encoder};
 use rustc_session::config::CrateType;
 use rustc_session::cstore::{ForeignModule, LinkagePreference, NativeLib};
 use rustc_span::hygiene::{ExpnIndex, HygieneEncodeContext, MacroKind};
@@ -44,7 +43,7 @@ use std::num::NonZeroUsize;
 use tracing::{debug, trace};
 
 pub(super) struct EncodeContext<'a, 'tcx> {
-    opaque: MemEncoder,
+    opaque: opaque::Encoder,
     tcx: TyCtxt<'tcx>,
     feat: &'tcx rustc_feature::Features,
 
@@ -94,6 +93,9 @@ 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;
+
     encoder_methods! {
         emit_usize(usize);
         emit_u128(u128);
@@ -116,6 +118,10 @@ impl<'a, 'tcx> Encoder for EncodeContext<'a, 'tcx> {
         emit_str(&str);
         emit_raw_bytes(&[u8]);
     }
+
+    fn finish(self) -> Result<Self::Ok, Self::Err> {
+        self.opaque.finish()
+    }
 }
 
 impl<'a, 'tcx, T> Encodable<EncodeContext<'a, 'tcx>> for LazyValue<T> {
@@ -2182,7 +2188,7 @@ pub fn encode_metadata(tcx: TyCtxt<'_>) -> EncodedMetadata {
 }
 
 fn encode_metadata_impl(tcx: TyCtxt<'_>) -> EncodedMetadata {
-    let mut encoder = MemEncoder::new();
+    let mut encoder = opaque::Encoder::new();
     encoder.emit_raw_bytes(METADATA_HEADER);
 
     // Will be filled with the root position after encoding everything.
@@ -2217,7 +2223,7 @@ fn encode_metadata_impl(tcx: TyCtxt<'_>) -> EncodedMetadata {
     // culminating in the `CrateRoot` which points to all of it.
     let root = ecx.encode_crate_root();
 
-    let mut result = ecx.opaque.finish();
+    let mut result = ecx.opaque.finish().unwrap();
 
     // Encode the root position.
     let header = METADATA_HEADER.len();

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::MemEncoder;
+use rustc_serialize::opaque::Encoder;
 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 MemEncoder) -> LazyTables {
+            fn encode(&self, buf: &mut Encoder) -> LazyTables {
                 LazyTables {
                     $($name: self.$name.encode(buf)),+
                 }

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::MemEncoder;
-use rustc_serialize::Encoder;
+use rustc_serialize::opaque::Encoder;
+use rustc_serialize::Encoder as _;
 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 MemEncoder) -> LazyTable<I, T>
+    pub(crate) fn encode<const N: usize>(&self, buf: &mut Encoder) -> LazyTable<I, T>
     where
         Option<T>: FixedSizeEncoding<ByteArray = [u8; N]>,
     {

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::{Decodable, Decoder, Encodable, Encoder};
+use rustc_serialize as serialize;
 
 /// Helper type to cache the result of `graph::is_cyclic`.
 #[derive(Clone, Debug)]
@@ -36,17 +36,17 @@ impl GraphIsCyclicCache {
     }
 }
 
-impl<S: Encoder> Encodable<S> for GraphIsCyclicCache {
+impl<S: serialize::Encoder> serialize::Encodable<S> for GraphIsCyclicCache {
     #[inline]
     fn encode(&self, s: &mut S) {
-        Encodable::encode(&(), s);
+        serialize::Encodable::encode(&(), s);
     }
 }
 
-impl<D: Decoder> Decodable<D> for GraphIsCyclicCache {
+impl<D: serialize::Decoder> serialize::Decodable<D> for GraphIsCyclicCache {
     #[inline]
     fn decode(d: &mut D) -> Self {
-        let () = Decodable::decode(d);
+        let () = serialize::Decodable::decode(d);
         Self::new()
     }
 }

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::{Decodable, Decoder, Encodable, Encoder};
+use rustc_serialize as serialize;
 use smallvec::SmallVec;
 
 use crate::mir::{BasicBlock, BasicBlockData};
@@ -54,12 +54,12 @@ impl PredecessorCache {
     }
 }
 
-impl<S: Encoder> Encodable<S> for PredecessorCache {
+impl<S: serialize::Encoder> serialize::Encodable<S> for PredecessorCache {
     #[inline]
     fn encode(&self, _s: &mut S) {}
 }
 
-impl<D: Decoder> Decodable<D> for PredecessorCache {
+impl<D: serialize::Decoder> serialize::Decodable<D> for PredecessorCache {
     #[inline]
     fn decode(_: &mut D) -> Self {
         Self::new()

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::{Decodable, Decoder, Encodable, Encoder};
+use rustc_serialize as serialize;
 use smallvec::SmallVec;
 
 use crate::mir::{BasicBlock, BasicBlockData, Terminator, TerminatorKind};
@@ -54,12 +54,12 @@ impl SwitchSourceCache {
     }
 }
 
-impl<S: Encoder> Encodable<S> for SwitchSourceCache {
+impl<S: serialize::Encoder> serialize::Encodable<S> for SwitchSourceCache {
     #[inline]
     fn encode(&self, _s: &mut S) {}
 }
 
-impl<D: Decoder> Decodable<D> for SwitchSourceCache {
+impl<D: serialize::Decoder> serialize::Decodable<D> for SwitchSourceCache {
     #[inline]
     fn decode(_: &mut D) -> Self {
         Self::new()

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::{Decodable, Decoder, Encodable, Encoder};
+use rustc_serialize as serialize;
 
 use super::*;
 
@@ -365,12 +365,12 @@ impl PostorderCache {
     }
 }
 
-impl<S: Encoder> Encodable<S> for PostorderCache {
+impl<S: serialize::Encoder> serialize::Encodable<S> for PostorderCache {
     #[inline]
     fn encode(&self, _s: &mut S) {}
 }
 
-impl<D: Decoder> Decodable<D> for PostorderCache {
+impl<D: serialize::Decoder> serialize::Decodable<D> for PostorderCache {
     #[inline]
     fn decode(_: &mut D) -> Self {
         Self::new()