update comment

diff --git a/compiler/rustc_borrowck/src/type_check/free_region_relations.rs b/compiler/rustc_borrowck/src/type_check/free_region_relations.rs
index 0b9d0a0e9220b29c9f6779a146e89fc6f164d825..f8439d2e163559f5c51faa2364f18c15b2dc1aed 100644 (file)
--- a/compiler/rustc_borrowck/src/type_check/free_region_relations.rs
+++ b/compiler/rustc_borrowck/src/type_check/free_region_relations.rs
@@ -253,8 +253,10 @@ impl<'tcx> UniversalRegionRelationsBuilder<'_, 'tcx> {
         let constraint_sets: Vec<_> = unnormalized_input_output_tys
             .flat_map(|ty| {
                 debug!("build: input_or_output={:?}", ty);
-                // We add implied bounds from both the unnormalized and normalized ty
-                // See issue #87748
+                // We only add implied bounds for the normalized type as the unnormalized
+                // type may not actually get checked by the caller.
+                //
+                // Can otherwise be unsound, see #91068.
                 let TypeOpOutput { output: norm_ty, constraints: constraints1, .. } = self
                     .param_env
                     .and(type_op::normalize::Normalize::new(ty))