add comment

Author: RalfJung

src/librustc_lint/builtin.rs

@@ -1633,6 +1633,7 @@ fn check_const(cx: &LateContext, body_id: hir::BodyId, what: &str) {
     let def_id = cx.tcx.hir.body_owner_def_id(body_id);
     let is_static = cx.tcx.is_static(def_id).is_some();
     let param_env = if is_static {
+        // Use the same param_env as `codegen_static_initializer`, to reuse the cache.
         ty::ParamEnv::reveal_all()
     } else {
         cx.tcx.param_env(def_id)