Revert "Auto merge of #129827 - bvanjoi:less-decoding, r=petrochenkov"

Reverting because of a performance regression.

This reverts commit d4812c8638173ec163825d56a72a33589483ec4c, reversing
changes made to 5cc60728e7ee10eb2ae5f61f7d412d9805b22f0c.

5 files changed, 158 insertions, 81 deletions

diff --git a/compiler/rustc_metadata/src/rmeta/mod.rs b/compiler/rustc_metadata/src/rmeta/mod.rs
index 34e4f2f2602..dc453b1e747 100644
--- a/compiler/rustc_metadata/src/rmeta/mod.rs
+++ b/compiler/rustc_metadata/src/rmeta/mod.rs
@@ -36,7 +36,7 @@ use rustc_serialize::opaque::FileEncoder;
 use rustc_session::config::{SymbolManglingVersion, TargetModifier};
 use rustc_session::cstore::{CrateDepKind, ForeignModule, LinkagePreference, NativeLib};
 use rustc_span::edition::Edition;
-use rustc_span::hygiene::{ExpnIndex, MacroKind, SyntaxContextKey};
+use rustc_span::hygiene::{ExpnIndex, MacroKind, SyntaxContextData};
 use rustc_span::{self, ExpnData, ExpnHash, ExpnId, Ident, Span, Symbol};
 use rustc_target::spec::{PanicStrategy, TargetTuple};
 use table::TableBuilder;
@@ -193,7 +193,7 @@ enum LazyState {
     Previous(NonZero<usize>),
 }
 
-type SyntaxContextTable = LazyTable<u32, Option<LazyValue<SyntaxContextKey>>>;
+type SyntaxContextTable = LazyTable<u32, Option<LazyValue<SyntaxContextData>>>;
 type ExpnDataTable = LazyTable<ExpnIndex, Option<LazyValue<ExpnData>>>;
 type ExpnHashTable = LazyTable<ExpnIndex, Option<LazyValue<ExpnHash>>>;
 
diff --git a/compiler/rustc_middle/src/query/on_disk_cache.rs b/compiler/rustc_middle/src/query/on_disk_cache.rs
index ce6219c207f..14e3ce8bef6 100644
--- a/compiler/rustc_middle/src/query/on_disk_cache.rs
+++ b/compiler/rustc_middle/src/query/on_disk_cache.rs
@@ -16,7 +16,7 @@ use rustc_serialize::opaque::{FileEncodeResult, FileEncoder, IntEncodedWithFixed
 use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
 use rustc_session::Session;
 use rustc_span::hygiene::{
-    ExpnId, HygieneDecodeContext, HygieneEncodeContext, SyntaxContext, SyntaxContextKey,
+    ExpnId, HygieneDecodeContext, HygieneEncodeContext, SyntaxContext, SyntaxContextData,
 };
 use rustc_span::source_map::Spanned;
 use rustc_span::{
@@ -75,9 +75,9 @@ pub struct OnDiskCache {
     alloc_decoding_state: AllocDecodingState,
 
     // A map from syntax context ids to the position of their associated
-    // `SyntaxContextKey`. We use a `u32` instead of a `SyntaxContext`
+    // `SyntaxContextData`. We use a `u32` instead of a `SyntaxContext`
     // to represent the fact that we are storing *encoded* ids. When we decode
-    // a `SyntaxContextKey`, a new id will be allocated from the global `HygieneData`,
+    // a `SyntaxContext`, a new id will be allocated from the global `HygieneData`,
     // which will almost certainly be different than the serialized id.
     syntax_contexts: FxHashMap<u32, AbsoluteBytePos>,
     // A map from the `DefPathHash` of an `ExpnId` to the position
@@ -305,7 +305,7 @@ impl OnDiskCache {
             let mut expn_data = UnhashMap::default();
             let mut foreign_expn_data = UnhashMap::default();
 
-            // Encode all hygiene data (`SyntaxContextKey` and `ExpnData`) from the current
+            // Encode all hygiene data (`SyntaxContextData` and `ExpnData`) from the current
             // session.
 
             hygiene_encode_context.encode(
@@ -566,7 +566,7 @@ impl<'a, 'tcx> SpanDecoder for CacheDecoder<'a, 'tcx> {
             // We look up the position of the associated `SyntaxData` and decode it.
             let pos = syntax_contexts.get(&id).unwrap();
             this.with_position(pos.to_usize(), |decoder| {
-                let data: SyntaxContextKey = decode_tagged(decoder, TAG_SYNTAX_CONTEXT);
+                let data: SyntaxContextData = decode_tagged(decoder, TAG_SYNTAX_CONTEXT);
                 data
             })
         })
diff --git a/compiler/rustc_middle/src/ty/parameterized.rs b/compiler/rustc_middle/src/ty/parameterized.rs
index 134f76d7248..19e2b574563 100644
--- a/compiler/rustc_middle/src/ty/parameterized.rs
+++ b/compiler/rustc_middle/src/ty/parameterized.rs
@@ -111,7 +111,7 @@ trivially_parameterized_over_tcx! {
     rustc_span::Span,
     rustc_span::Symbol,
     rustc_span::def_id::DefPathHash,
-    rustc_span::hygiene::SyntaxContextKey,
+    rustc_span::hygiene::SyntaxContextData,
     rustc_span::Ident,
     rustc_type_ir::Variance,
     rustc_hir::Attribute,
diff --git a/compiler/rustc_span/src/hygiene.rs b/compiler/rustc_span/src/hygiene.rs
index f9485885672..4390085cd04 100644
--- a/compiler/rustc_span/src/hygiene.rs
+++ b/compiler/rustc_span/src/hygiene.rs
@@ -24,6 +24,9 @@
 // because getting it wrong can lead to nested `HygieneData::with` calls that
 // trigger runtime aborts. (Fortunately these are obvious and easy to fix.)
 
+use std::cell::RefCell;
+use std::collections::hash_map::Entry;
+use std::collections::hash_set::Entry as SetEntry;
 use std::hash::Hash;
 use std::sync::Arc;
 use std::{fmt, iter, mem};
@@ -31,7 +34,7 @@ use std::{fmt, iter, mem};
 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::stable_hasher::{HashStable, HashingControls, StableHasher};
-use rustc_data_structures::sync::Lock;
+use rustc_data_structures::sync::{Lock, WorkerLocal};
 use rustc_data_structures::unhash::UnhashMap;
 use rustc_hashes::Hash64;
 use rustc_index::IndexVec;
@@ -56,10 +59,10 @@ impl !PartialOrd for SyntaxContext {}
 
 /// If this part of two syntax contexts is equal, then the whole syntax contexts should be equal.
 /// The other fields are only for caching.
-pub type SyntaxContextKey = (SyntaxContext, ExpnId, Transparency);
+type SyntaxContextKey = (SyntaxContext, ExpnId, Transparency);
 
 #[derive(Clone, Copy, PartialEq, Debug, Encodable, Decodable)]
-struct SyntaxContextData {
+pub struct SyntaxContextData {
     outer_expn: ExpnId,
     outer_transparency: Transparency,
     parent: SyntaxContext,
@@ -91,21 +94,6 @@ impl SyntaxContextData {
         self.dollar_crate_name == kw::Empty
     }
 
-    fn new(
-        (parent, outer_expn, outer_transparency): SyntaxContextKey,
-        opaque: SyntaxContext,
-        opaque_and_semitransparent: SyntaxContext,
-    ) -> Self {
-        SyntaxContextData {
-            parent,
-            outer_expn,
-            outer_transparency,
-            opaque,
-            opaque_and_semitransparent,
-            dollar_crate_name: kw::DollarCrate,
-        }
-    }
-
     fn key(&self) -> SyntaxContextKey {
         (self.parent, self.outer_expn, self.outer_transparency)
     }
@@ -586,49 +574,67 @@ impl HygieneData {
 
     fn apply_mark_internal(
         &mut self,
-        parent: SyntaxContext,
+        ctxt: SyntaxContext,
         expn_id: ExpnId,
         transparency: Transparency,
     ) -> SyntaxContext {
-        debug_assert!(!self.syntax_context_data[parent.0 as usize].is_decode_placeholder());
-        // Look into the cache first.
-        let key = (parent, expn_id, transparency);
-        if let Some(ctxt) = self.syntax_context_map.get(&key) {
-            return *ctxt;
+        let syntax_context_data = &mut self.syntax_context_data;
+        debug_assert!(!syntax_context_data[ctxt.0 as usize].is_decode_placeholder());
+        let mut opaque = syntax_context_data[ctxt.0 as usize].opaque;
+        let mut opaque_and_semitransparent =
+            syntax_context_data[ctxt.0 as usize].opaque_and_semitransparent;
+
+        if transparency >= Transparency::Opaque {
+            let parent = opaque;
+            opaque = *self
+                .syntax_context_map
+                .entry((parent, expn_id, transparency))
+                .or_insert_with(|| {
+                    let new_opaque = SyntaxContext::from_usize(syntax_context_data.len());
+                    syntax_context_data.push(SyntaxContextData {
+                        outer_expn: expn_id,
+                        outer_transparency: transparency,
+                        parent,
+                        opaque: new_opaque,
+                        opaque_and_semitransparent: new_opaque,
+                        dollar_crate_name: kw::DollarCrate,
+                    });
+                    new_opaque
+                });
+        }
+
+        if transparency >= Transparency::SemiTransparent {
+            let parent = opaque_and_semitransparent;
+            opaque_and_semitransparent = *self
+                .syntax_context_map
+                .entry((parent, expn_id, transparency))
+                .or_insert_with(|| {
+                    let new_opaque_and_semitransparent =
+                        SyntaxContext::from_usize(syntax_context_data.len());
+                    syntax_context_data.push(SyntaxContextData {
+                        outer_expn: expn_id,
+                        outer_transparency: transparency,
+                        parent,
+                        opaque,
+                        opaque_and_semitransparent: new_opaque_and_semitransparent,
+                        dollar_crate_name: kw::DollarCrate,
+                    });
+                    new_opaque_and_semitransparent
+                });
         }
-        // Reserve a new syntax context.
-        let ctxt = SyntaxContext::from_usize(self.syntax_context_data.len());
-        self.syntax_context_data.push(SyntaxContextData::decode_placeholder());
-        self.syntax_context_map.insert(key, ctxt);
-
-        // Opaque and semi-transparent versions of the parent. Note that they may be equal to the
-        // parent itself. E.g. `parent_opaque` == `parent` if the expn chain contains only opaques,
-        // and `parent_opaque_and_semitransparent` == `parent` if the expn contains only opaques
-        // and semi-transparents.
-        let parent_opaque = self.syntax_context_data[parent.0 as usize].opaque;
-        let parent_opaque_and_semitransparent =
-            self.syntax_context_data[parent.0 as usize].opaque_and_semitransparent;
-
-        // Evaluate opaque and semi-transparent versions of the new syntax context.
-        let (opaque, opaque_and_semitransparent) = match transparency {
-            Transparency::Transparent => (parent_opaque, parent_opaque_and_semitransparent),
-            Transparency::SemiTransparent => (
-                parent_opaque,
-                // Will be the same as `ctxt` if the expn chain contains only opaques and semi-transparents.
-                self.apply_mark_internal(parent_opaque_and_semitransparent, expn_id, transparency),
-            ),
-            Transparency::Opaque => (
-                // Will be the same as `ctxt` if the expn chain contains only opaques.
-                self.apply_mark_internal(parent_opaque, expn_id, transparency),
-                // Will be the same as `ctxt` if the expn chain contains only opaques and semi-transparents.
-                self.apply_mark_internal(parent_opaque_and_semitransparent, expn_id, transparency),
-            ),
-        };
 
-        // Fill the full data, now that we have it.
-        self.syntax_context_data[ctxt.as_u32() as usize] =
-            SyntaxContextData::new(key, opaque, opaque_and_semitransparent);
-        ctxt
+        let parent = ctxt;
+        *self.syntax_context_map.entry((parent, expn_id, transparency)).or_insert_with(|| {
+            syntax_context_data.push(SyntaxContextData {
+                outer_expn: expn_id,
+                outer_transparency: transparency,
+                parent,
+                opaque,
+                opaque_and_semitransparent,
+                dollar_crate_name: kw::DollarCrate,
+            });
+            SyntaxContext::from_usize(syntax_context_data.len() - 1)
+        })
     }
 }
 
@@ -1259,7 +1265,7 @@ impl HygieneEncodeContext {
     pub fn encode<T>(
         &self,
         encoder: &mut T,
-        mut encode_ctxt: impl FnMut(&mut T, u32, &SyntaxContextKey),
+        mut encode_ctxt: impl FnMut(&mut T, u32, &SyntaxContextData),
         mut encode_expn: impl FnMut(&mut T, ExpnId, &ExpnData, ExpnHash),
     ) {
         // When we serialize a `SyntaxContextData`, we may end up serializing
@@ -1317,6 +1323,9 @@ struct HygieneDecodeContextInner {
 /// Additional information used to assist in decoding hygiene data
 pub struct HygieneDecodeContext {
     inner: Lock<HygieneDecodeContextInner>,
+
+    /// A set of serialized `SyntaxContext` ids that are currently being decoded on each thread.
+    local_in_progress: WorkerLocal<RefCell<FxHashSet<u32>>>,
 }
 
 /// Register an expansion which has been decoded from the on-disk-cache for the local crate.
@@ -1387,10 +1396,10 @@ pub fn decode_expn_id(
 // to track which `SyntaxContext`s we have already decoded.
 // The provided closure will be invoked to deserialize a `SyntaxContextData`
 // if we haven't already seen the id of the `SyntaxContext` we are deserializing.
-pub fn decode_syntax_context<D: Decoder, F: FnOnce(&mut D, u32) -> SyntaxContextKey>(
+pub fn decode_syntax_context<D: Decoder, F: FnOnce(&mut D, u32) -> SyntaxContextData>(
     d: &mut D,
     context: &HygieneDecodeContext,
-    decode_ctxt_key: F,
+    decode_data: F,
 ) -> SyntaxContext {
     let raw_id: u32 = Decodable::decode(d);
     if raw_id == 0 {
@@ -1399,9 +1408,58 @@ pub fn decode_syntax_context<D: Decoder, F: FnOnce(&mut D, u32) -> SyntaxContext
         return SyntaxContext::root();
     }
 
+    let pending_ctxt = {
+        let mut inner = context.inner.lock();
+
+        // Reminder: `HygieneDecodeContext` is per-crate, so there are no collisions between
+        // raw ids from different crate metadatas.
+        if let Some(ctxt) = inner.remapped_ctxts.get(raw_id as usize).copied().flatten() {
+            // This has already been decoded.
+            return ctxt;
+        }
+
+        match inner.decoding.entry(raw_id) {
+            Entry::Occupied(ctxt_entry) => {
+                let pending_ctxt = *ctxt_entry.get();
+                match context.local_in_progress.borrow_mut().entry(raw_id) {
+                    // We're decoding this already on the current thread. Return here and let the
+                    // function higher up the stack finish decoding to handle recursive cases.
+                    // Hopefully having a `SyntaxContext` that refers to an incorrect data is ok
+                    // during reminder of the decoding process, it's certainly not ok after the
+                    // top level decoding function returns.
+                    SetEntry::Occupied(..) => return pending_ctxt,
+                    // Some other thread is currently decoding this.
+                    // Race with it (alternatively we could wait here).
+                    // We cannot return this value, unlike in the recursive case above, because it
+                    // may expose a `SyntaxContext` pointing to incorrect data to arbitrary code.
+                    SetEntry::Vacant(entry) => {
+                        entry.insert();
+                        pending_ctxt
+                    }
+                }
+            }
+            Entry::Vacant(entry) => {
+                // We are the first thread to start decoding. Mark the current thread as being progress.
+                context.local_in_progress.borrow_mut().insert(raw_id);
+
+                // Allocate and store SyntaxContext id *before* calling the decoder function,
+                // as the SyntaxContextData may reference itself.
+                let new_ctxt = HygieneData::with(|hygiene_data| {
+                    // Push a dummy SyntaxContextData to ensure that nobody else can get the
+                    // same ID as us. This will be overwritten after call `decode_data`.
+                    hygiene_data.syntax_context_data.push(SyntaxContextData::decode_placeholder());
+                    SyntaxContext::from_usize(hygiene_data.syntax_context_data.len() - 1)
+                });
+                entry.insert(new_ctxt);
+                new_ctxt
+            }
+        }
+    };
+
     // Don't try to decode data while holding the lock, since we need to
     // be able to recursively decode a SyntaxContext
-    let ctxt_key = decode_ctxt_key(d, raw_id);
+    let ctxt_data = decode_data(d, raw_id);
+    let ctxt_key = ctxt_data.key();
 
     let ctxt = HygieneData::with(|hygiene_data| {
         match hygiene_data.syntax_context_map.get(&ctxt_key) {
@@ -1415,10 +1473,29 @@ pub fn decode_syntax_context<D: Decoder, F: FnOnce(&mut D, u32) -> SyntaxContext
             Some(&ctxt) => ctxt,
             // This is a completely new context.
             // Overwrite its placeholder data with our decoded data.
-            None => hygiene_data.apply_mark_internal(ctxt_key.0, ctxt_key.1, ctxt_key.2),
+            None => {
+                let ctxt_data_ref =
+                    &mut hygiene_data.syntax_context_data[pending_ctxt.as_u32() as usize];
+                let prev_ctxt_data = mem::replace(ctxt_data_ref, ctxt_data);
+                // Reset `dollar_crate_name` so that it will be updated by `update_dollar_crate_names`.
+                // We don't care what the encoding crate set this to - we want to resolve it
+                // from the perspective of the current compilation session.
+                ctxt_data_ref.dollar_crate_name = kw::DollarCrate;
+                // Make sure nothing weird happened while `decode_data` was running.
+                if !prev_ctxt_data.is_decode_placeholder() {
+                    // Another thread may have already inserted the decoded data,
+                    // but the decoded data should match.
+                    assert_eq!(prev_ctxt_data, *ctxt_data_ref);
+                }
+                hygiene_data.syntax_context_map.insert(ctxt_key, pending_ctxt);
+                pending_ctxt
+            }
         }
     });
 
+    // Mark the context as completed
+    context.local_in_progress.borrow_mut().remove(&raw_id);
+
     let mut inner = context.inner.lock();
     let new_len = raw_id as usize + 1;
     if inner.remapped_ctxts.len() < new_len {
@@ -1430,7 +1507,7 @@ pub fn decode_syntax_context<D: Decoder, F: FnOnce(&mut D, u32) -> SyntaxContext
     ctxt
 }
 
-fn for_all_ctxts_in<F: FnMut(u32, SyntaxContext, &SyntaxContextKey)>(
+fn for_all_ctxts_in<F: FnMut(u32, SyntaxContext, &SyntaxContextData)>(
     ctxts: impl Iterator<Item = SyntaxContext>,
     mut f: F,
 ) {
@@ -1438,7 +1515,7 @@ fn for_all_ctxts_in<F: FnMut(u32, SyntaxContext, &SyntaxContextKey)>(
         ctxts.map(|ctxt| (ctxt, data.syntax_context_data[ctxt.0 as usize].clone())).collect()
     });
     for (ctxt, data) in all_data.into_iter() {
-        f(ctxt.0, ctxt, &data.key());
+        f(ctxt.0, ctxt, &data);
     }
 }
 
diff --git a/tests/ui/proc-macro/nonterminal-token-hygiene.stdout b/tests/ui/proc-macro/nonterminal-token-hygiene.stdout
index 6fd6cb47469..c80a33206fb 100644
--- a/tests/ui/proc-macro/nonterminal-token-hygiene.stdout
+++ b/tests/ui/proc-macro/nonterminal-token-hygiene.stdout
@@ -5,19 +5,19 @@ PRINT-BANG INPUT (DEBUG): TokenStream [
         stream: TokenStream [
             Ident {
                 ident: "struct",
-                span: $DIR/nonterminal-token-hygiene.rs:32:5: 32:11 (#5),
+                span: $DIR/nonterminal-token-hygiene.rs:32:5: 32:11 (#4),
             },
             Ident {
                 ident: "S",
-                span: $DIR/nonterminal-token-hygiene.rs:32:12: 32:13 (#5),
+                span: $DIR/nonterminal-token-hygiene.rs:32:12: 32:13 (#4),
             },
             Punct {
                 ch: ';',
                 spacing: Alone,
-                span: $DIR/nonterminal-token-hygiene.rs:32:13: 32:14 (#5),
+                span: $DIR/nonterminal-token-hygiene.rs:32:13: 32:14 (#4),
             },
         ],
-        span: $DIR/nonterminal-token-hygiene.rs:22:27: 22:32 (#4),
+        span: $DIR/nonterminal-token-hygiene.rs:22:27: 22:32 (#5),
     },
 ]
 #![feature /* 0#0 */(prelude_import)]
@@ -59,7 +59,7 @@ macro_rules! outer
 struct S /* 0#0 */;
 macro inner /* 0#3 */ { () => { print_bang! { struct S; } } }
 
-struct S /* 0#5 */;
+struct S /* 0#4 */;
 // OK, not a duplicate definition of `S`
 
 fn main /* 0#0 */() {}
@@ -70,7 +70,7 @@ crate0::{{expn0}}: parent: crate0::{{expn0}}, call_site_ctxt: #0, def_site_ctxt:
 crate0::{{expn1}}: parent: crate0::{{expn0}}, call_site_ctxt: #0, def_site_ctxt: #0, kind: AstPass(StdImports)
 crate0::{{expn2}}: parent: crate0::{{expn0}}, call_site_ctxt: #0, def_site_ctxt: #0, kind: Macro(Bang, "outer")
 crate0::{{expn3}}: parent: crate0::{{expn2}}, call_site_ctxt: #3, def_site_ctxt: #3, kind: Macro(Bang, "inner")
-crate0::{{expn4}}: parent: crate0::{{expn3}}, call_site_ctxt: #4, def_site_ctxt: #0, kind: Macro(Bang, "print_bang")
+crate0::{{expn4}}: parent: crate0::{{expn3}}, call_site_ctxt: #5, def_site_ctxt: #0, kind: Macro(Bang, "print_bang")
 crate1::{{expnNNN}}: parent: crate0::{{expn0}}, call_site_ctxt: #0, def_site_ctxt: #0, kind: Macro(Attr, "diagnostic::on_unimplemented")
 crate1::{{expnNNN}}: parent: crate0::{{expn0}}, call_site_ctxt: #0, def_site_ctxt: #0, kind: Macro(Attr, "diagnostic::on_unimplemented")
 crate1::{{expnNNN}}: parent: crate0::{{expn0}}, call_site_ctxt: #0, def_site_ctxt: #0, kind: Macro(Attr, "diagnostic::on_unimplemented")
@@ -83,9 +83,9 @@ SyntaxContexts:
 #1: parent: #0, outer_mark: (crate0::{{expn1}}, Opaque)
 #2: parent: #0, outer_mark: (crate0::{{expn1}}, Transparent)
 #3: parent: #0, outer_mark: (crate0::{{expn2}}, SemiTransparent)
-#4: parent: #3, outer_mark: (crate0::{{expn3}}, Opaque)
-#5: parent: #0, outer_mark: (crate0::{{expn3}}, Opaque)
+#4: parent: #0, outer_mark: (crate0::{{expn3}}, Opaque)
+#5: parent: #3, outer_mark: (crate0::{{expn3}}, Opaque)
 #6: parent: #0, outer_mark: (crate0::{{expn4}}, Opaque)
-#7: parent: #4, outer_mark: (crate0::{{expn4}}, Transparent)
-#8: parent: #5, outer_mark: (crate0::{{expn4}}, SemiTransparent)
+#7: parent: #5, outer_mark: (crate0::{{expn4}}, Transparent)
+#8: parent: #4, outer_mark: (crate0::{{expn4}}, SemiTransparent)
 */