Auto merge of rust-lang#83649 - bjorn3:dedup_providers, r=petrochenkov

Don't duplicate the extern providers once for each crate

This should give a small perf improvement for small crates by avoiding a memcpy of a pretty big struct for each loaded crate. In addition would be useful for replacing the sequential `CrateNum` everywhere with the hash based `StableCrateId` introduced in rust-lang#81635, which would allow avoiding remapping of `CrateNum`'s when loading crate metadata. While this PR is not strictly needed for that, it is necessary to prevent a performance loss due to it.

I think this duplication was done in rust-lang#40008 (which introduced the query system) to make it possible to compile multiple crates in a single session in the future. I think this is unlikely to be implemented any time soon. In addition this PR can easily be reverted if necessary to implement this.

Author: bors

compiler/rustc_interface/src/passes.rs

@@ -15,7 +15,6 @@ use rustc_expand::base::ExtCtxt;
 use rustc_hir::def_id::{CrateNum, LOCAL_CRATE};
 use rustc_hir::definitions::Definitions;
 use rustc_hir::Crate;
-use rustc_index::vec::IndexVec;
 use rustc_lint::LintStore;
 use rustc_middle::arena::Arena;
 use rustc_middle::dep_graph::DepGraph;
@@ -788,13 +787,7 @@ pub fn create_global_ctxt<'tcx>(
         callback(sess, &mut local_providers, &mut extern_providers);
     }
 
-    let queries = {
-        let crates = resolver_outputs.cstore.crates_untracked();
-        let max_cnum = crates.iter().map(|c| c.as_usize()).max().unwrap_or(0);
-        let mut providers = IndexVec::from_elem_n(extern_providers, max_cnum + 1);
-        providers[LOCAL_CRATE] = local_providers;
-        queries.get_or_init(|| TcxQueries::new(providers, extern_providers))
-    };
+    let queries = queries.get_or_init(|| TcxQueries::new(local_providers, extern_providers));
 
     let gcx = sess.time("setup_global_ctxt", || {
         global_ctxt.get_or_init(|| {

compiler/rustc_query_impl/src/lib.rs

@@ -19,8 +19,7 @@ extern crate tracing;
 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_errors::{DiagnosticBuilder, Handler};
-use rustc_hir::def_id::CrateNum;
-use rustc_index::vec::IndexVec;
+use rustc_hir::def_id::LOCAL_CRATE;
 use rustc_middle::dep_graph;
 use rustc_middle::ich::StableHashingContext;
 use rustc_middle::ty::query::{query_keys, query_storage, query_stored, query_values};

compiler/rustc_query_impl/src/plumbing.rs

@@ -390,13 +390,12 @@ macro_rules! define_queries {
 
             #[inline]
             fn compute(tcx: QueryCtxt<'tcx>, key: Self::Key) -> Self::Value {
-                let provider = tcx.queries.providers.get(key.query_crate())
-                    // HACK(eddyb) it's possible crates may be loaded after
-                    // the query engine is created, and because crate loading
-                    // is not yet integrated with the query engine, such crates
-                    // would be missing appropriate entries in `providers`.
-                    .unwrap_or(&tcx.queries.fallback_extern_providers)
-                    .$name;
+                let is_local = key.query_crate() == LOCAL_CRATE;
+                let provider = if is_local {
+                    tcx.queries.local_providers.$name
+                } else {
+                    tcx.queries.extern_providers.$name
+                };
                 provider(*tcx, key)
             }
 
@@ -507,8 +506,8 @@ macro_rules! define_queries_struct {
     (tcx: $tcx:tt,
      input: ($(([$($modifiers:tt)*] [$($attr:tt)*] [$name:ident]))*)) => {
         pub struct Queries<$tcx> {
-            providers: IndexVec<CrateNum, Providers>,
-            fallback_extern_providers: Box<Providers>,
+            local_providers: Box<Providers>,
+            extern_providers: Box<Providers>,
 
             $($(#[$attr])*  $name: QueryState<
                 crate::dep_graph::DepKind,
@@ -518,12 +517,12 @@ macro_rules! define_queries_struct {
 
         impl<$tcx> Queries<$tcx> {
             pub fn new(
-                providers: IndexVec<CrateNum, Providers>,
-                fallback_extern_providers: Providers,
+                local_providers: Providers,
+                extern_providers: Providers,
             ) -> Self {
                 Queries {
-                    providers,
-                    fallback_extern_providers: Box::new(fallback_extern_providers),
+                    local_providers: Box::new(local_providers),
+                    extern_providers: Box::new(extern_providers),
                     $($name: Default::default()),*
                 }
             }