Introduce new `TaskDepsRef` enum to track allow/ignore/forbid status

compiler/rustc_middle/src/dep_graph/mod.rs

 use crate::ty::{self, TyCtxt};
 use rustc_data_structures::profiling::SelfProfilerRef;
-use rustc_data_structures::sync::Lock;
 use rustc_query_system::ich::StableHashingContext;
 use rustc_session::Session;
 
@@ -17,6 +16,7 @@
 
 pub type DepGraph = rustc_query_system::dep_graph::DepGraph<DepKind>;
 pub type TaskDeps = rustc_query_system::dep_graph::TaskDeps<DepKind>;
+pub type TaskDepsRef<'a> = rustc_query_system::dep_graph::TaskDepsRef<'a, DepKind>;
 pub type DepGraphQuery = rustc_query_system::dep_graph::DepGraphQuery<DepKind>;
 pub type SerializedDepGraph = rustc_query_system::dep_graph::SerializedDepGraph<DepKind>;
 pub type EdgeFilter = rustc_query_system::dep_graph::debug::EdgeFilter<DepKind>;
@@ -45,7 +45,7 @@ fn debug_node(node: &DepNode, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Resu
         write!(f, ")")
     }
 
-    fn with_deps<OP, R>(task_deps: Option<&Lock<TaskDeps>>, op: OP) -> R
+    fn with_deps<OP, R>(task_deps: TaskDepsRef<'_>, op: OP) -> R
     where
         OP: FnOnce() -> R,
     {
@@ -58,7 +58,7 @@ fn with_deps<OP, R>(task_deps: Option<&Lock<TaskDeps>>, op: OP) -> R
 
     fn read_deps<OP>(op: OP)
     where
-        OP: for<'a> FnOnce(Option<&'a Lock<TaskDeps>>),
+        OP: for<'a> FnOnce(TaskDepsRef<'a>),
     {
         ty::tls::with_context_opt(|icx| {
             let icx = if let Some(icx) = icx { icx } else { return };

compiler/rustc_middle/src/ty/context.rs

@@ -1661,7 +1661,7 @@ fn lift_to_tcx(self, tcx: TyCtxt<'tcx>) -> Option<Self::Lifted> {
 pub mod tls {
     use super::{ptr_eq, GlobalCtxt, TyCtxt};
 
-    use crate::dep_graph::{DepKind, TaskDeps};
+    use crate::dep_graph::{DepKind, TaskDepsRef};
     use crate::ty::query;
     use rustc_data_structures::sync::{self, Lock};
     use rustc_data_structures::thin_vec::ThinVec;
@@ -1697,13 +1697,19 @@ pub struct ImplicitCtxt<'a, 'tcx> {
 
         /// The current dep graph task. This is used to add dependencies to queries
         /// when executing them.
-        pub task_deps: Option<&'a Lock<TaskDeps>>,
+        pub task_deps: TaskDepsRef<'a>,
     }
 
     impl<'a, 'tcx> ImplicitCtxt<'a, 'tcx> {
         pub fn new(gcx: &'tcx GlobalCtxt<'tcx>) -> Self {
             let tcx = TyCtxt { gcx };
-            ImplicitCtxt { tcx, query: None, diagnostics: None, layout_depth: 0, task_deps: None }
+            ImplicitCtxt {
+                tcx,
+                query: None,
+                diagnostics: None,
+                layout_depth: 0,
+                task_deps: TaskDepsRef::Ignore,
+            }
         }
     }
 

compiler/rustc_query_system/src/dep_graph/graph.rs

@@ -9,6 +9,7 @@
 use rustc_index::vec::IndexVec;
 use rustc_serialize::opaque::{FileEncodeResult, FileEncoder};
 use smallvec::{smallvec, SmallVec};
+use std::assert_matches::assert_matches;
 use std::collections::hash_map::Entry;
 use std::fmt::Debug;
 use std::hash::Hash;
@@ -165,7 +166,11 @@ pub fn with_query(&self, f: impl Fn(&DepGraphQuery<K>)) {
     pub fn assert_ignored(&self) {
         if let Some(..) = self.data {
             K::read_deps(|task_deps| {
-                assert!(task_deps.is_none(), "expected no task dependency tracking");
+                assert_matches!(
+                    task_deps,
+                    TaskDepsRef::Ignore,
+                    "expected no task dependency tracking"
+                );
             })
         }
     }
@@ -174,7 +179,7 @@ pub fn with_ignore<OP, R>(&self, op: OP) -> R
     where
         OP: FnOnce() -> R,
     {
-        K::with_deps(None, op)
+        K::with_deps(TaskDepsRef::Ignore, op)
     }
 
     /// Used to wrap the deserialization of a query result from disk,
@@ -227,10 +232,7 @@ pub fn with_query_deserialization<OP, R>(&self, op: OP) -> R
     where
         OP: FnOnce() -> R,
     {
-        let mut deps = TaskDeps::default();
-        deps.read_allowed = false;
-        let deps = Lock::new(deps);
-        K::with_deps(Some(&deps), op)
+        K::with_deps(TaskDepsRef::Forbid, op)
     }
 
     /// Starts a new dep-graph task. Dep-graph tasks are specified
@@ -313,10 +315,15 @@ fn with_task_impl<Ctxt: HasDepContext<DepKind = K>, A: Debug, R>(
                 reads: SmallVec::new(),
                 read_set: Default::default(),
                 phantom_data: PhantomData,
-                read_allowed: true,
             }))
         };
-        let result = K::with_deps(task_deps.as_ref(), || task(cx, arg));
+
+        let task_deps_ref = match &task_deps {
+            Some(deps) => TaskDepsRef::Allow(deps),
+            None => TaskDepsRef::Ignore,
+        };
+
+        let result = K::with_deps(task_deps_ref, || task(cx, arg));
         let edges = task_deps.map_or_else(|| smallvec![], |lock| lock.into_inner().reads);
 
         let dcx = cx.dep_context();
@@ -369,7 +376,7 @@ pub fn with_anon_task<Ctxt: DepContext<DepKind = K>, OP, R>(
 
         if let Some(ref data) = self.data {
             let task_deps = Lock::new(TaskDeps::default());
-            let result = K::with_deps(Some(&task_deps), op);
+            let result = K::with_deps(TaskDepsRef::Allow(&task_deps), op);
             let task_deps = task_deps.into_inner();
             let task_deps = task_deps.reads;
 
@@ -422,47 +429,47 @@ pub fn with_anon_task<Ctxt: DepContext<DepKind = K>, OP, R>(
     pub fn read_index(&self, dep_node_index: DepNodeIndex) {
         if let Some(ref data) = self.data {
             K::read_deps(|task_deps| {
-                if let Some(task_deps) = task_deps {
-                    let mut task_deps = task_deps.lock();
-                    let task_deps = &mut *task_deps;
-
-                    if !task_deps.read_allowed {
-                        panic!("Illegal read of: {:?}", dep_node_index);
+                let mut task_deps = match task_deps {
+                    TaskDepsRef::Allow(deps) => deps.lock(),
+                    TaskDepsRef::Ignore => return,
+                    TaskDepsRef::Forbid => {
+                        panic!("Illegal read of: {:?}", dep_node_index)
                     }
+                };
+                let task_deps = &mut *task_deps;
 
-                    if cfg!(debug_assertions) {
-                        data.current.total_read_count.fetch_add(1, Relaxed);
-                    }
+                if cfg!(debug_assertions) {
+                    data.current.total_read_count.fetch_add(1, Relaxed);
+                }
 
-                    // As long as we only have a low number of reads we can avoid doing a hash
-                    // insert and potentially allocating/reallocating the hashmap
-                    let new_read = if task_deps.reads.len() < TASK_DEPS_READS_CAP {
-                        task_deps.reads.iter().all(|other| *other != dep_node_index)
-                    } else {
-                        task_deps.read_set.insert(dep_node_index)
-                    };
-                    if new_read {
-                        task_deps.reads.push(dep_node_index);
-                        if task_deps.reads.len() == TASK_DEPS_READS_CAP {
-                            // Fill `read_set` with what we have so far so we can use the hashset
-                            // next time
-                            task_deps.read_set.extend(task_deps.reads.iter().copied());
-                        }
+                // As long as we only have a low number of reads we can avoid doing a hash
+                // insert and potentially allocating/reallocating the hashmap
+                let new_read = if task_deps.reads.len() < TASK_DEPS_READS_CAP {
+                    task_deps.reads.iter().all(|other| *other != dep_node_index)
+                } else {
+                    task_deps.read_set.insert(dep_node_index)
+                };
+                if new_read {
+                    task_deps.reads.push(dep_node_index);
+                    if task_deps.reads.len() == TASK_DEPS_READS_CAP {
+                        // Fill `read_set` with what we have so far so we can use the hashset
+                        // next time
+                        task_deps.read_set.extend(task_deps.reads.iter().copied());
+                    }
 
-                        #[cfg(debug_assertions)]
-                        {
-                            if let Some(target) = task_deps.node {
-                                if let Some(ref forbidden_edge) = data.current.forbidden_edge {
-                                    let src = forbidden_edge.index_to_node.lock()[&dep_node_index];
-                                    if forbidden_edge.test(&src, &target) {
-                                        panic!("forbidden edge {:?} -> {:?} created", src, target)
-                                    }
+                    #[cfg(debug_assertions)]
+                    {
+                        if let Some(target) = task_deps.node {
+                            if let Some(ref forbidden_edge) = data.current.forbidden_edge {
+                                let src = forbidden_edge.index_to_node.lock()[&dep_node_index];
+                                if forbidden_edge.test(&src, &target) {
+                                    panic!("forbidden edge {:?} -> {:?} created", src, target)
                                 }
                             }
                         }
-                    } else if cfg!(debug_assertions) {
-                        data.current.total_duplicate_read_count.fetch_add(1, Relaxed);
                     }
+                } else if cfg!(debug_assertions) {
+                    data.current.total_duplicate_read_count.fetch_add(1, Relaxed);
                 }
             })
         }
@@ -1185,21 +1192,34 @@ fn debug_assert_not_in_new_nodes(
 const TASK_DEPS_READS_CAP: usize = 8;
 type EdgesVec = SmallVec<[DepNodeIndex; TASK_DEPS_READS_CAP]>;
 
-pub struct TaskDeps<K> {
+#[derive(Debug, Clone, Copy)]
+pub enum TaskDepsRef<'a, K: DepKind> {
+    /// New dependencies can be added to the
+    /// `TaskDeps`. This is used when executing a 'normal' query
+    /// (no `eval_always` modifier)
+    Allow(&'a Lock<TaskDeps<K>>),
+    /// New dependencies are ignored. This is used when
+    /// executing an `eval_always` query, since there's no
+    /// need to track dependencies for a query that's always
+    /// re-executed. This is also used for `dep_graph.with_ignore`
+    Ignore,
+    /// Any attempt to add new dependencies will cause a panic.
+    /// This is used when decoding a query result from disk,
+    /// to ensure that the decoding process doesn't itself
+    /// require the execution of any queries.
+    Forbid,
+}
+
+#[derive(Debug)]
+pub struct TaskDeps<K: DepKind> {
     #[cfg(debug_assertions)]
     node: Option<DepNode<K>>,
     reads: EdgesVec,
     read_set: FxHashSet<DepNodeIndex>,
     phantom_data: PhantomData<DepNode<K>>,
-    /// Whether or not we allow `DepGraph::read_index` to run.
-    /// This is normally true, except inside `with_query_deserialization`,
-    /// where it set to `false` to enforce that no new `DepNode` edges are
-    /// created. See the documentation of `with_query_deserialization` for
-    /// more details.
-    read_allowed: bool,
 }
 
-impl<K> Default for TaskDeps<K> {
+impl<K: DepKind> Default for TaskDeps<K> {
     fn default() -> Self {
         Self {
             #[cfg(debug_assertions)]
@@ -1207,7 +1227,6 @@ fn default() -> Self {
             reads: EdgesVec::new(),
             read_set: FxHashSet::default(),
             phantom_data: PhantomData,
-            read_allowed: true,
         }
     }
 }

compiler/rustc_query_system/src/dep_graph/mod.rs

@@ -5,13 +5,14 @@
 mod serialized;
 
 pub use dep_node::{DepNode, DepNodeParams, WorkProductId};
-pub use graph::{hash_result, DepGraph, DepNodeColor, DepNodeIndex, TaskDeps, WorkProduct};
+pub use graph::{
+    hash_result, DepGraph, DepNodeColor, DepNodeIndex, TaskDeps, TaskDepsRef, WorkProduct,
+};
 pub use query::DepGraphQuery;
 pub use serialized::{SerializedDepGraph, SerializedDepNodeIndex};
 
 use crate::ich::StableHashingContext;
 use rustc_data_structures::profiling::SelfProfilerRef;
-use rustc_data_structures::sync::Lock;
 use rustc_serialize::{opaque::FileEncoder, Encodable};
 use rustc_session::Session;
 
@@ -90,12 +91,12 @@ pub trait DepKind: Copy + fmt::Debug + Eq + Hash + Send + Encodable<FileEncoder>
     fn debug_node(node: &DepNode<Self>, f: &mut fmt::Formatter<'_>) -> fmt::Result;
 
     /// Execute the operation with provided dependencies.
-    fn with_deps<OP, R>(deps: Option<&Lock<TaskDeps<Self>>>, op: OP) -> R
+    fn with_deps<OP, R>(deps: TaskDepsRef<'_, Self>, op: OP) -> R
     where
         OP: FnOnce() -> R;
 
     /// Access dependencies from current implicit context.
     fn read_deps<OP>(op: OP)
     where
-        OP: for<'a> FnOnce(Option<&'a Lock<TaskDeps<Self>>>);
+        OP: for<'a> FnOnce(TaskDepsRef<'a, Self>);
 }