Auto merge of #108794 - nnethercote:avoid-unnecessary-hashing, r=cjgillot

Avoid unnecessary hashing

I noticed some stable hashing being done in a non-incremental build. It turns out that some of this is necessary to compute the crate hash, but some of it is not. Removing the unnecessary hashing is a perf win.

r? `@cjgillot`

2 files changed, 6 insertions, 6 deletions

diff --git a/compiler/rustc_middle/src/hir/map/mod.rs b/compiler/rustc_middle/src/hir/map/mod.rs
index 43eef1c770c..746cf488589 100644
--- a/compiler/rustc_middle/src/hir/map/mod.rs
+++ b/compiler/rustc_middle/src/hir/map/mod.rs
@@ -1134,7 +1134,7 @@ impl<'hir> intravisit::Map<'hir> for Map<'hir> {
 pub(super) fn crate_hash(tcx: TyCtxt<'_>, crate_num: CrateNum) -> Svh {
     debug_assert_eq!(crate_num, LOCAL_CRATE);
     let krate = tcx.hir_crate(());
-    let hir_body_hash = krate.hir_hash;
+    let hir_body_hash = krate.opt_hir_hash.expect("HIR hash missing while computing crate hash");
 
     let upstream_crates = upstream_crates(tcx);
 
diff --git a/compiler/rustc_middle/src/hir/mod.rs b/compiler/rustc_middle/src/hir/mod.rs
index 6706b9db3f5..6c0566cd9e8 100644
--- a/compiler/rustc_middle/src/hir/mod.rs
+++ b/compiler/rustc_middle/src/hir/mod.rs
@@ -8,7 +8,6 @@ pub mod place;
 
 use crate::ty::query::Providers;
 use crate::ty::{ImplSubject, TyCtxt};
-use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::sync::{par_for_each_in, Send, Sync};
 use rustc_hir::def_id::{DefId, LocalDefId};
@@ -24,14 +23,15 @@ use rustc_span::{ExpnId, DUMMY_SP};
 #[derive(Copy, Clone, Debug)]
 pub struct Owner<'tcx> {
     node: OwnerNode<'tcx>,
-    hash_without_bodies: Fingerprint,
 }
 
 impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for Owner<'tcx> {
     #[inline]
     fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
-        let Owner { node: _, hash_without_bodies } = self;
-        hash_without_bodies.hash_stable(hcx, hasher)
+        // Perform a shallow hash instead using the deep hash saved in `OwnerNodes`. This lets us
+        // differentiate queries that depend on the full HIR tree from those that only depend on
+        // the item signature.
+        hcx.without_hir_bodies(|hcx| self.node.hash_stable(hcx, hasher));
     }
 }
 
@@ -123,7 +123,7 @@ pub fn provide(providers: &mut Providers) {
     providers.hir_owner = |tcx, id| {
         let owner = tcx.hir_crate(()).owners.get(id.def_id)?.as_owner()?;
         let node = owner.node();
-        Some(Owner { node, hash_without_bodies: owner.nodes.hash_without_bodies })
+        Some(Owner { node })
     };
     providers.opt_local_def_id_to_hir_id = |tcx, id| {
         let owner = tcx.hir_crate(()).owners[id].map(|_| ());