Auto merge of #40873 - cramertj:on-demandify-queries, r=nikomatsakis

On demandify reachability

cc https://github.com/rust-lang/rust/issues/40746

I tried following this guidance from #40746:
> The following tasks currently execute before a tcx is built, but they could be easily converted into queries that are requested after tcx is built. The main reason they are the way they are was to avoid a gratuitious refcell (but using the refcell map seems fine)...

but the result of moving `region_maps` out of `TyCtxt` and into a query caused a lot of churn, and seems like it could potentially result in a rather large performance hit, since it means a dep-graph lookup on every use of `region_maps` (rather than just a field access). Possibly `TyCtxt` could store a `RefCell<Option<RegionMap>>` internally and use that to prevent repeat lookups, but that feels like it's duplicating the work of the dep-graph. @nikomatsakis What did you have in mind for this?

src/librustc/middle/reachable.rs

@@ -15,11 +15,11 @@
 // makes all other generics or inline functions that it references
 // reachable as well.
 
-use dep_graph::DepNode;
 use hir::map as hir_map;
 use hir::def::Def;
-use hir::def_id::DefId;
+use hir::def_id::{DefId, CrateNum};
 use ty::{self, TyCtxt};
+use ty::maps::Providers;
 use middle::privacy;
 use session::config;
 use util::nodemap::{NodeSet, FxHashSet};
@@ -362,7 +362,11 @@ impl<'a, 'tcx: 'a> ItemLikeVisitor<'tcx> for CollectPrivateImplItemsVisitor<'a,
 }
 
 pub fn find_reachable<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) -> NodeSet {
-    let _task = tcx.dep_graph.in_task(DepNode::Reachability);
+    ty::queries::reachable_set::get(tcx, DUMMY_SP, LOCAL_CRATE)
+}
+
+fn reachable_set<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, crate_num: CrateNum) -> NodeSet {
+    debug_assert!(crate_num == LOCAL_CRATE);
 
     let access_levels = &ty::queries::privacy_access_levels::get(tcx, DUMMY_SP, LOCAL_CRATE);
 
@@ -408,3 +412,10 @@ pub fn find_reachable<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) -> NodeSet {
     // Return the set of reachable symbols.
     reachable_context.reachable_symbols
 }
+
+pub fn provide(providers: &mut Providers) {
+    *providers = Providers {
+        reachable_set,
+        ..*providers
+    };
+}

src/librustc/ty/maps.rs

@@ -15,6 +15,7 @@ use middle::privacy::AccessLevels;
 use mir;
 use session::CompileResult;
 use ty::{self, CrateInherentImpls, Ty, TyCtxt};
+use util::nodemap::NodeSet;
 
 use rustc_data_structures::indexed_vec::IndexVec;
 use std::cell::{RefCell, RefMut};
@@ -209,6 +210,11 @@ impl<'tcx> QueryDescription for queries::typeck_item_bodies<'tcx> {
     }
 }
 
+impl<'tcx> QueryDescription for queries::reachable_set<'tcx> {
+    fn describe(_: TyCtxt, _: CrateNum) -> String {
+        format!("reachability")
+    }
+}
 
 macro_rules! define_maps {
     (<$tcx:tt>
@@ -440,6 +446,8 @@ define_maps! { <'tcx>
     /// Performs the privacy check and computes "access levels".
     pub privacy_access_levels: PrivacyAccessLevels(CrateNum) -> Rc<AccessLevels>,
 
+    pub reachable_set: reachability_dep_node(CrateNum) -> NodeSet,
+
     pub mir_shims: mir_shim(ty::InstanceDef<'tcx>) -> &'tcx RefCell<mir::Mir<'tcx>>
 }
 
@@ -451,6 +459,10 @@ fn crate_inherent_impls_dep_node(_: CrateNum) -> DepNode<DefId> {
     DepNode::Coherence
 }
 
+fn reachability_dep_node(_: CrateNum) -> DepNode<DefId> {
+    DepNode::Reachability
+}
+
 fn mir_shim(instance: ty::InstanceDef) -> DepNode<DefId> {
     instance.dep_node()
 }

src/librustc_driver/driver.rs

@@ -889,6 +889,7 @@ pub fn phase_3_run_analysis_passes<'tcx, F, R>(sess: &'tcx Session,
     rustc_privacy::provide(&mut local_providers);
     typeck::provide(&mut local_providers);
     ty::provide(&mut local_providers);
+    reachable::provide(&mut local_providers);
 
     let mut extern_providers = ty::maps::Providers::default();
     cstore::provide(&mut extern_providers);