Compute hir hash lazily

Author: oli-obk

compiler/rustc_ast_lowering/src/lib.rs

@@ -47,17 +47,15 @@ use std::sync::Arc;
 use rustc_ast::node_id::NodeMap;
 use rustc_ast::{self as ast, *};
 use rustc_attr_parsing::{AttributeParser, OmitDoc};
-use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::sorted_map::SortedMap;
-use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::tagged_ptr::TaggedRef;
 use rustc_errors::{DiagArgFromDisplay, DiagCtxtHandle, StashKey};
 use rustc_hir::def::{DefKind, LifetimeRes, Namespace, PartialRes, PerNS, Res};
 use rustc_hir::def_id::{CRATE_DEF_ID, LOCAL_CRATE, LocalDefId};
 use rustc_hir::{
     self as hir, ConstArg, GenericArg, HirId, ItemLocalMap, LangItem, ParamName, TraitCandidate,
 };
-use rustc_index::{Idx, IndexSlice, IndexVec};
+use rustc_index::{Idx, IndexVec};
 use rustc_macros::extension;
 use rustc_middle::span_bug;
 use rustc_middle::ty::{ResolverAstLowering, TyCtxt};
@@ -408,29 +406,6 @@ fn index_crate<'a>(
     }
 }
 
-/// Compute the hash for the HIR of the full crate.
-/// This hash will then be part of the crate_hash which is stored in the metadata.
-fn compute_hir_hash(
-    tcx: TyCtxt<'_>,
-    owners: &IndexSlice<LocalDefId, hir::MaybeOwner<'_>>,
-) -> Fingerprint {
-    let mut hir_body_nodes: Vec<_> = owners
-        .iter_enumerated()
-        .filter_map(|(def_id, info)| {
-            let info = info.as_owner()?;
-            let def_path_hash = tcx.hir_def_path_hash(def_id);
-            Some((def_path_hash, info))
-        })
-        .collect();
-    hir_body_nodes.sort_unstable_by_key(|bn| bn.0);
-
-    tcx.with_stable_hashing_context(|mut hcx| {
-        let mut stable_hasher = StableHasher::new();
-        hir_body_nodes.hash_stable(&mut hcx, &mut stable_hasher);
-        stable_hasher.finish()
-    })
-}
-
 pub fn lower_to_hir(tcx: TyCtxt<'_>, (): ()) -> hir::Crate<'_> {
     let sess = tcx.sess;
     // Queries that borrow `resolver_for_lowering`.
@@ -460,10 +435,7 @@ pub fn lower_to_hir(tcx: TyCtxt<'_>, (): ()) -> hir::Crate<'_> {
     drop(ast_index);
     sess.time("drop_ast", || drop(krate));
 
-    // Don't hash unless necessary, because it's expensive.
-    let opt_hir_hash =
-        if tcx.needs_crate_hash() { Some(compute_hir_hash(tcx, &owners)) } else { None };
-    hir::Crate { owners, opt_hir_hash }
+    hir::Crate { owners }
 }
 
 #[derive(Copy, Clone, PartialEq, Debug)]

compiler/rustc_hir/src/hir.rs

@@ -1425,8 +1425,6 @@ impl<'tcx> MaybeOwner<'tcx> {
 #[derive(Debug)]
 pub struct Crate<'hir> {
     pub owners: IndexVec<LocalDefId, MaybeOwner<'hir>>,
-    // Only present when incr. comp. is enabled.
-    pub opt_hir_hash: Option<Fingerprint>,
 }
 
 #[derive(Debug, Clone, Copy, HashStable_Generic)]

compiler/rustc_hir/src/stable_hash_impls.rs

@@ -3,7 +3,7 @@ use rustc_span::def_id::DefPathHash;
 
 use crate::HashIgnoredAttrId;
 use crate::hir::{
-    AttributeMap, BodyId, Crate, ForeignItemId, ImplItemId, ItemId, OwnerNodes, TraitItemId,
+    AttributeMap, BodyId, ForeignItemId, ImplItemId, ItemId, OwnerNodes, TraitItemId,
 };
 use crate::hir_id::{HirId, ItemLocalId};
 
@@ -111,13 +111,6 @@ impl<'tcx, HirCtx: crate::HashStableContext> HashStable<HirCtx> for AttributeMap
     }
 }
 
-impl<HirCtx: crate::HashStableContext> HashStable<HirCtx> for Crate<'_> {
-    fn hash_stable(&self, hcx: &mut HirCtx, hasher: &mut StableHasher) {
-        let Crate { owners: _, opt_hir_hash } = self;
-        opt_hir_hash.unwrap().hash_stable(hcx, hasher)
-    }
-}
-
 impl<HirCtx: crate::HashStableContext> HashStable<HirCtx> for HashIgnoredAttrId {
     fn hash_stable(&self, hcx: &mut HirCtx, hasher: &mut StableHasher) {
         hcx.hash_attr_id(self, hasher)

compiler/rustc_middle/src/hir/map.rs

@@ -10,6 +10,7 @@ use rustc_hir::definitions::{DefKey, DefPath, DefPathHash};
 use rustc_hir::intravisit::Visitor;
 use rustc_hir::*;
 use rustc_hir_pretty as pprust_hir;
+use rustc_index::IndexSlice;
 use rustc_span::def_id::StableCrateId;
 use rustc_span::{ErrorGuaranteed, Ident, Span, Symbol, kw, sym, with_metavar_spans};
 
@@ -1127,9 +1128,32 @@ impl<'tcx> pprust_hir::PpAnn for TyCtxt<'tcx> {
     }
 }
 
+/// Compute the hash for the HIR of the full crate.
+/// This hash will then be part of the crate_hash which is stored in the metadata.
+fn compute_hir_hash(
+    tcx: TyCtxt<'_>,
+    owners: &IndexSlice<LocalDefId, MaybeOwner<'_>>,
+) -> Fingerprint {
+    let mut hir_body_nodes: Vec<_> = owners
+        .iter_enumerated()
+        .filter_map(|(def_id, info)| {
+            let info = info.as_owner()?;
+            let def_path_hash = tcx.hir_def_path_hash(def_id);
+            Some((def_path_hash, info))
+        })
+        .collect();
+    hir_body_nodes.sort_unstable_by_key(|bn| bn.0);
+
+    tcx.with_stable_hashing_context(|mut hcx| {
+        let mut stable_hasher = StableHasher::new();
+        hir_body_nodes.hash_stable(&mut hcx, &mut stable_hasher);
+        stable_hasher.finish()
+    })
+}
+
 pub(super) fn crate_hash(tcx: TyCtxt<'_>, _: LocalCrate) -> Svh {
     let krate = tcx.hir_crate(());
-    let hir_body_hash = krate.opt_hir_hash.expect("HIR hash missing while computing crate hash");
+    let hir_body_hash = compute_hir_hash(tcx, &krate.owners);
 
     let upstream_crates = upstream_crates(tcx);
 

compiler/rustc_middle/src/query/mod.rs

@@ -151,6 +151,7 @@ rustc_queries! {
     query hir_crate(key: ()) -> &'tcx Crate<'tcx> {
         arena_cache
         eval_always
+        no_hash
         desc { "getting the crate HIR" }
     }