Switch QueryJobId to a single global counter

This replaces the per-shard counters with a single global counter, simplifying
the JobId struct down to just a u64 and removing the need to pipe a DepKind
generic through a bunch of code. The performance implications on non-parallel
compilers are likely minimal (this switches to `Cell<u64>` as the backing
storage over a `u64`, but the latter was already inside a `RefCell` so it's not
really a significance divergence). On parallel compilers, the cost of a single
global u64 counter may be more significant: it adds a serialization point in
theory. On the other hand, we can imagine changing the counter to have a
thread-local component if it becomes worrisome or some similar structure.

The new design is sufficiently simpler that it warrants the potential for slight
changes down the line if/when we get parallel compilation to be more of a
default.

A u64 counter, instead of u32 (the old per-shard width), is chosen to avoid
possibly overflowing it and causing problems; it is effectively impossible that
we would overflow a u64 counter in this context.

2 files changed, 22 insertions, 12 deletions

diff --git a/compiler/rustc_query_impl/src/lib.rs b/compiler/rustc_query_impl/src/lib.rs
index bf859decc70..f6bce748679 100644
--- a/compiler/rustc_query_impl/src/lib.rs
+++ b/compiler/rustc_query_impl/src/lib.rs
@@ -15,6 +15,7 @@ extern crate rustc_macros;
 extern crate rustc_middle;
 
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
+use rustc_data_structures::sync::AtomicU64;
 use rustc_middle::arena::Arena;
 use rustc_middle::dep_graph::{self, DepKindStruct, SerializedDepNodeIndex};
 use rustc_middle::ty::query::{query_keys, query_storage, query_stored, query_values};
diff --git a/compiler/rustc_query_impl/src/plumbing.rs b/compiler/rustc_query_impl/src/plumbing.rs
index 6d76d09f619..326ba999bc3 100644
--- a/compiler/rustc_query_impl/src/plumbing.rs
+++ b/compiler/rustc_query_impl/src/plumbing.rs
@@ -3,7 +3,7 @@
 //! manage the caches, and so forth.
 
 use crate::{on_disk_cache, Queries};
-use rustc_middle::dep_graph::{DepKind, DepNodeIndex, SerializedDepNodeIndex};
+use rustc_middle::dep_graph::{DepNodeIndex, SerializedDepNodeIndex};
 use rustc_middle::ty::tls::{self, ImplicitCtxt};
 use rustc_middle::ty::TyCtxt;
 use rustc_query_system::dep_graph::HasDepContext;
@@ -15,6 +15,7 @@ use rustc_errors::{Diagnostic, Handler};
 use rustc_serialize::opaque;
 
 use std::any::Any;
+use std::num::NonZeroU64;
 
 #[derive(Copy, Clone)]
 pub struct QueryCtxt<'tcx> {
@@ -42,11 +43,20 @@ impl<'tcx> HasDepContext for QueryCtxt<'tcx> {
 }
 
 impl QueryContext for QueryCtxt<'_> {
-    fn current_query_job(&self) -> Option<QueryJobId<Self::DepKind>> {
+    fn next_job_id(&self) -> QueryJobId {
+        QueryJobId(
+            NonZeroU64::new(
+                self.queries.jobs.fetch_add(1, rustc_data_structures::sync::Ordering::Relaxed),
+            )
+            .unwrap(),
+        )
+    }
+
+    fn current_query_job(&self) -> Option<QueryJobId> {
         tls::with_related_context(**self, |icx| icx.query)
     }
 
-    fn try_collect_active_jobs(&self) -> Option<QueryMap<Self::DepKind>> {
+    fn try_collect_active_jobs(&self) -> Option<QueryMap> {
         self.queries.try_collect_active_jobs(**self)
     }
 
@@ -81,7 +91,7 @@ impl QueryContext for QueryCtxt<'_> {
     #[inline(always)]
     fn start_query<R>(
         &self,
-        token: QueryJobId<Self::DepKind>,
+        token: QueryJobId,
         diagnostics: Option<&Lock<ThinVec<Diagnostic>>>,
         compute: impl FnOnce() -> R,
     ) -> R {
@@ -152,7 +162,7 @@ impl<'tcx> QueryCtxt<'tcx> {
 
     pub fn try_print_query_stack(
         self,
-        query: Option<QueryJobId<DepKind>>,
+        query: Option<QueryJobId>,
         handler: &Handler,
         num_frames: Option<usize>,
     ) -> usize {
@@ -320,7 +330,7 @@ macro_rules! define_queries {
             type Cache = query_storage::$name<$tcx>;
 
             #[inline(always)]
-            fn query_state<'a>(tcx: QueryCtxt<$tcx>) -> &'a QueryState<crate::dep_graph::DepKind, Self::Key>
+            fn query_state<'a>(tcx: QueryCtxt<$tcx>) -> &'a QueryState<Self::Key>
                 where QueryCtxt<$tcx>: 'a
             {
                 &tcx.queries.$name
@@ -471,10 +481,9 @@ macro_rules! define_queries_struct {
 
             pub on_disk_cache: Option<OnDiskCache<$tcx>>,
 
-            $($(#[$attr])*  $name: QueryState<
-                crate::dep_graph::DepKind,
-                query_keys::$name<$tcx>,
-            >,)*
+            jobs: AtomicU64,
+
+            $($(#[$attr])*  $name: QueryState<query_keys::$name<$tcx>>,)*
         }
 
         impl<$tcx> Queries<$tcx> {
@@ -487,6 +496,7 @@ macro_rules! define_queries_struct {
                     local_providers: Box::new(local_providers),
                     extern_providers: Box::new(extern_providers),
                     on_disk_cache,
+                    jobs: AtomicU64::new(1),
                     $($name: Default::default()),*
                 }
             }
@@ -494,14 +504,13 @@ macro_rules! define_queries_struct {
             pub(crate) fn try_collect_active_jobs(
                 &$tcx self,
                 tcx: TyCtxt<$tcx>,
-            ) -> Option<QueryMap<crate::dep_graph::DepKind>> {
+            ) -> Option<QueryMap> {
                 let tcx = QueryCtxt { tcx, queries: self };
                 let mut jobs = QueryMap::default();
 
                 $(
                     self.$name.try_collect_active_jobs(
                         tcx,
-                        dep_graph::DepKind::$name,
                         make_query::$name,
                         &mut jobs,
                     )?;