Update compiler/rustc_middle/src/query/mod.rs

Co-authored-by: Léo Lanteri Thauvin <[email protected]>

Author: nikomatsakis

compiler/rustc_middle/src/query/mod.rs

@@ -222,6 +222,7 @@ rustc_queries! {
 
     /// Fetch the THIR for a given body. If typeck for that body failed, returns an empty `Thir`.
     query thir_body(key: ty::WithOptConstParam<LocalDefId>) -> (&'tcx Steal<thir::Thir<'tcx>>, thir::ExprId) {
+        // Perf tests revealed that hashing THIR is inefficient (see #85729).
         no_hash
         desc { |tcx| "building THIR for `{}`", tcx.def_path_str(key.did.to_def_id()) }
     }