From 22f6163db47dfb1c5c02bcd0543eb0f4f92dd164 Mon Sep 17 00:00:00 2001
From: Michael Woerister <michaelwoerister@posteo>
Date: Tue, 29 May 2018 10:26:26 +0200
Subject: [PATCH] Make metadata decoding use AllocDecodingState/Session.

---
 src/librustc_metadata/creader.rs |  5 ++++
 src/librustc_metadata/cstore.rs  |  5 +++-
 src/librustc_metadata/decoder.rs | 44 ++++++++------------------------
 3 files changed, 19 insertions(+), 35 deletions(-)

diff --git a/src/librustc_metadata/creader.rs b/src/librustc_metadata/creader.rs
index 2467d5cf97c17..e41b3f5f53b25 100644
--- a/src/librustc_metadata/creader.rs
+++ b/src/librustc_metadata/creader.rs
@@ -19,6 +19,7 @@ use rustc::hir::def_id::{CrateNum, CRATE_DEF_INDEX};
 use rustc::hir::svh::Svh;
 use rustc::middle::allocator::AllocatorKind;
 use rustc::middle::cstore::DepKind;
+use rustc::mir::interpret::AllocDecodingState;
 use rustc::session::{Session, CrateDisambiguator};
 use rustc::session::config::{Sanitizer, self};
 use rustc_target::spec::{PanicStrategy, TargetTriple};
@@ -222,6 +223,9 @@ impl<'a> CrateLoader<'a> {
             crate_root.def_path_table.decode((&metadata, self.sess))
         });
 
+        let interpret_alloc_index: Vec<u32> = crate_root.interpret_alloc_index
+                                                        .decode(&metadata)
+                                                        .collect();
         let trait_impls = crate_root
             .impls
             .decode((&metadata, self.sess))
@@ -242,6 +246,7 @@ impl<'a> CrateLoader<'a> {
             cnum,
             dependencies: Lock::new(dependencies),
             codemap_import_info: RwLock::new(vec![]),
+            alloc_decoding_state: AllocDecodingState::new(interpret_alloc_index),
             dep_kind: Lock::new(dep_kind),
             source: cstore::CrateSource {
                 dylib,
diff --git a/src/librustc_metadata/cstore.rs b/src/librustc_metadata/cstore.rs
index 763563eabe0e9..2bc5f60748664 100644
--- a/src/librustc_metadata/cstore.rs
+++ b/src/librustc_metadata/cstore.rs
@@ -12,10 +12,10 @@
 // crates and libraries
 
 use schema;
-
 use rustc::hir::def_id::{CrateNum, DefIndex};
 use rustc::hir::map::definitions::DefPathTable;
 use rustc::middle::cstore::{DepKind, ExternCrate, MetadataLoader};
+use rustc::mir::interpret::AllocDecodingState;
 use rustc_data_structures::indexed_vec::IndexVec;
 use rustc::util::nodemap::{FxHashMap, NodeMap};
 
@@ -66,6 +66,9 @@ pub struct CrateMetadata {
     pub dependencies: Lock<Vec<CrateNum>>,
     pub codemap_import_info: RwLock<Vec<ImportedFileMap>>,
 
+    /// Used for decoding interpret::AllocIds in a cached & thread-safe manner.
+    pub alloc_decoding_state: AllocDecodingState,
+
     pub root: schema::CrateRoot,
 
     /// For each public item in this crate, we encode a key.  When the
diff --git a/src/librustc_metadata/decoder.rs b/src/librustc_metadata/decoder.rs
index 11c653895fce0..69e873bb95d25 100644
--- a/src/librustc_metadata/decoder.rs
+++ b/src/librustc_metadata/decoder.rs
@@ -25,12 +25,12 @@ use rustc::hir::def_id::{CrateNum, DefId, DefIndex,
 use rustc::ich::Fingerprint;
 use rustc::middle::lang_items;
 use rustc::mir::{self, interpret};
+use rustc::mir::interpret::AllocDecodingSession;
 use rustc::session::Session;
 use rustc::ty::{self, Ty, TyCtxt};
 use rustc::ty::codec::TyDecoder;
 use rustc::mir::Mir;
 use rustc::util::captures::Captures;
-use rustc::util::nodemap::FxHashMap;
 
 use std::io;
 use std::mem;
@@ -55,11 +55,8 @@ pub struct DecodeContext<'a, 'tcx: 'a> {
 
     lazy_state: LazyState,
 
-    // interpreter allocation cache
-    interpret_alloc_cache: FxHashMap<usize, interpret::AllocId>,
-
-    // Read from the LazySeq CrateRoot::inpterpret_alloc_index on demand
-    interpret_alloc_index: Option<Vec<u32>>,
+    // Used for decoding interpret::AllocIds in a cached & thread-safe manner.
+    alloc_decoding_session: Option<AllocDecodingSession<'a>>,
 }
 
 /// Abstract over the various ways one can create metadata decoders.
@@ -78,8 +75,9 @@ pub trait Metadata<'a, 'tcx>: Copy {
             tcx,
             last_filemap_index: 0,
             lazy_state: LazyState::NoNode,
-            interpret_alloc_cache: FxHashMap::default(),
-            interpret_alloc_index: None,
+            alloc_decoding_session: self.cdata().map(|cdata| {
+                cdata.alloc_decoding_state.new_decoding_session()
+            }),
         }
     }
 }
@@ -178,17 +176,6 @@ impl<'a, 'tcx> DecodeContext<'a, 'tcx> {
         self.lazy_state = LazyState::Previous(position + min_size);
         Ok(position)
     }
-
-    fn interpret_alloc(&mut self, idx: usize) -> usize {
-        if let Some(index) = self.interpret_alloc_index.as_mut() {
-            return index[idx] as usize;
-        }
-        let cdata = self.cdata();
-        let index: Vec<u32> = cdata.root.interpret_alloc_index.decode(cdata).collect();
-        let pos = index[idx];
-        self.interpret_alloc_index = Some(index);
-        pos as usize
-    }
 }
 
 impl<'a, 'tcx: 'a> TyDecoder<'a, 'tcx> for DecodeContext<'a, 'tcx> {
@@ -299,22 +286,11 @@ impl<'a, 'tcx> SpecializedDecoder<LocalDefId> for DecodeContext<'a, 'tcx> {
 
 impl<'a, 'tcx> SpecializedDecoder<interpret::AllocId> for DecodeContext<'a, 'tcx> {
     fn specialized_decode(&mut self) -> Result<interpret::AllocId, Self::Error> {
-        let tcx = self.tcx.unwrap();
-        let idx = usize::decode(self)?;
-
-        if let Some(cached) = self.interpret_alloc_cache.get(&idx).cloned() {
-            return Ok(cached);
+        if let Some(alloc_decoding_session) = self.alloc_decoding_session {
+            alloc_decoding_session.decode_alloc_id(self)
+        } else {
+            bug!("Attempting to decode interpret::AllocId without CrateMetadata")
         }
-        let pos = self.interpret_alloc(idx);
-        self.with_position(pos, |this| {
-            interpret::specialized_decode_alloc_id(
-                this,
-                tcx,
-                |this, alloc_id| {
-                    assert!(this.interpret_alloc_cache.insert(idx, alloc_id).is_none());
-                },
-            )
-        })
     }
 }