Freeze Definitions earlier

compiler/rustc_hir_analysis/src/lib.rs

@@ -237,6 +237,10 @@ pub fn check_crate(tcx: TyCtxt<'_>) -> Result<(), ErrorGuaranteed> {
         tcx.hir().for_each_module(|module| tcx.ensure().check_mod_item_types(module))
     });
 
+    // Freeze definitions as we don't add new ones at this point. This improves performance by
+    // allowing lock-free access to them.
+    tcx.untracked().definitions.freeze();
+
     // FIXME: Remove this when we implement creating `DefId`s
     // for anon constants during their parents' typeck.
     // Typeck all body owners in parallel will produce queries