avoid hash in client code

compiler/rustc_query_system/src/dep_graph/graph.rs

@@ -378,24 +378,16 @@ impl<K: DepKind> DepGraph<K> {
     /// Executes something within an "anonymous" task, that is, a task the
     /// `DepNode` of which is determined by the list of inputs it read from.
     #[inline]
-    pub fn with_anon_task<Tcx: DepContext<DepKind = K>, OP, R>(        &self,
+    pub fn with_anon_task<Tcx: DepContext<DepKind = K>, OP, R>(
+        &self,
         cx: Tcx,
         dep_kind: K,
         op: OP,
     ) -> (R, DepNodeIndex)
     where
         OP: FnOnce() -> R,
     {
-        self.with_hash_task(cx, dep_kind, op, |task_deps| {
-            // The dep node indices are hashed here instead of hashing the dep nodes of the
-            // dependencies. These indices may refer to different nodes per session, but this isn't
-            // a problem here because we that ensure the final dep node hash is per session only by
-            // combining it with the per session random number `anon_id_seed`. This hash only need
-            // to map the dependencies to a single value on a per session basis.
-            let mut hasher = StableHasher::new();
-            task_deps.reads.hash(&mut hasher);
-            hasher.finish()
-        })
+        self.with_hash_task(cx, dep_kind, op, None::<()>)
     }
 
     /// Executes something within an "anonymous" task. The `hash` is used for
@@ -405,20 +397,21 @@ impl<K: DepKind> DepGraph<K> {
         cx: Ctxt,
         dep_kind: K,
         op: OP,
-        hash: H,
+        hash: Option<H>,
     ) -> (R, DepNodeIndex)
     where
         OP: FnOnce() -> R,
-        H: FnOnce(&TaskDeps<K>) -> Fingerprint,
+        H: Hash,
     {
         debug_assert!(!cx.is_eval_always(dep_kind));
 
         if let Some(ref data) = self.data {
             let task_deps = Lock::new(TaskDeps::default());
             let result = K::with_deps(TaskDepsRef::Allow(&task_deps), op);
             let task_deps = task_deps.into_inner();
+            let task_deps = task_deps.reads;
 
-            let dep_node_index = match task_deps.reads.len() {
+            let dep_node_index = match task_deps.len() {
                 0 => {
                     // Because the dep-node id of anon nodes is computed from the sets of its
                     // dependencies we already know what the ID of this dependency-less node is
@@ -429,23 +422,33 @@ impl<K: DepKind> DepGraph<K> {
                 }
                 1 => {
                     // When there is only one dependency, don't bother creating a node.
-                    task_deps.reads[0]
+                    task_deps[0]
                 }
                 _ => {
-                    let hash_result = hash(&task_deps);
+                    let mut hasher = StableHasher::new();
+                    if let Some(hash) = hash {
+                        hash.hash(&mut hasher);
+                    } else {
+                        // The dep node indices are hashed here instead of hashing the dep nodes of the
+                        // dependencies. These indices may refer to different nodes per session, but this isn't
+                        // a problem here because we that ensure the final dep node hash is per session only by
+                        // combining it with the per session random number `anon_id_seed`. This hash only need
+                        // to map the dependencies to a single value on a per session basis.
+                        task_deps.hash(&mut hasher);
+                    }
 
                     let target_dep_node = DepNode {
                         kind: dep_kind,
                         // Fingerprint::combine() is faster than sending Fingerprint
                         // through the StableHasher (at least as long as StableHasher
                         // is so slow).
-                        hash: data.current.anon_id_seed.combine(hash_result).into(),
+                        hash: data.current.anon_id_seed.combine(hasher.finish()).into(),
                     };
 
                     data.current.intern_new_node(
                         cx.profiler(),
                         target_dep_node,
-                        task_deps.reads,
+                        task_deps,
                         Fingerprint::ZERO,
                     )
                 }

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -49,8 +49,6 @@ use rustc_middle::ty::{self, EarlyBinder, PolyProjectionPredicate, ToPolyTraitRe
 use rustc_middle::ty::{Ty, TyCtxt, TypeFoldable, TypeVisitable};
 use rustc_span::symbol::sym;
 
-use rustc_data_structures::fingerprint::Fingerprint;
-use rustc_data_structures::stable_hasher::StableHasher;
 use std::cell::{Cell, RefCell};
 use std::cmp;
 use std::fmt::{self, Display};
@@ -59,8 +57,6 @@ use std::iter;
 
 pub use rustc_middle::traits::select::*;
 use rustc_middle::ty::print::with_no_trimmed_paths;
-use rustc_query_system::dep_graph::TaskDeps;
-
 mod candidate_assembly;
 mod confirmation;
 
@@ -1021,18 +1017,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             return Ok(cycle_result);
         }
 
-        let (result, dep_node) = if cfg!(parallel_compiler) {
-            self.in_task_with_hash(
-                |this| this.evaluate_stack(&stack),
-                |_| {
-                    let mut hasher = StableHasher::new();
-                    (param_env, fresh_trait_pred).hash(&mut hasher);
-                    hasher.finish()
-                },
-            )
-        } else {
-            self.in_task(|this| this.evaluate_stack(&stack))
-        };
+        let (result, dep_node) = self
+            .in_task_with_hash(|this| this.evaluate_stack(&stack), &(param_env, fresh_trait_pred));
 
         let result = result?;
 
@@ -1359,13 +1345,13 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
     fn in_task_with_hash<OP, R, H>(&mut self, op: OP, hash: H) -> (R, DepNodeIndex)
     where
         OP: FnOnce(&mut Self) -> R,
-        H: FnOnce(&TaskDeps<DepKind>) -> Fingerprint,
+        H: Hash,
     {
         let (result, dep_node) = self.tcx().dep_graph.with_hash_task(
             self.tcx(),
             DepKind::TraitSelect,
             || op(self),
-            hash,
+            Some(hash),
         );
         self.tcx().dep_graph.read_index(dep_node);
         (result, dep_node)