From 73a09f35b114d9ddf10e29df4e730d15e64f58c7 Mon Sep 17 00:00:00 2001
From: Niko Matsakis <niko@alum.mit.edu>
Date: Fri, 1 Jun 2018 13:17:45 -0400
Subject: [PATCH] skip `eq_types` and `sub_types` when the two types are equal

---
 src/librustc_mir/borrow_check/nll/type_check/mod.rs | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/src/librustc_mir/borrow_check/nll/type_check/mod.rs b/src/librustc_mir/borrow_check/nll/type_check/mod.rs
index 060313399cb5..697287d80c37 100644
--- a/src/librustc_mir/borrow_check/nll/type_check/mod.rs
+++ b/src/librustc_mir/borrow_check/nll/type_check/mod.rs
@@ -759,6 +759,11 @@ impl<'a, 'gcx, 'tcx> TypeChecker<'a, 'gcx, 'tcx> {
         sup: Ty<'tcx>,
         locations: Locations,
     ) -> UnitResult<'tcx> {
+        // Micro-optimization.
+        if sub == sup {
+            return Ok(());
+        }
+
         self.fully_perform_op(
             locations,
             || format!("sub_types({:?} <: {:?})", sub, sup),
@@ -772,6 +777,11 @@ impl<'a, 'gcx, 'tcx> TypeChecker<'a, 'gcx, 'tcx> {
 
     #[inline(never)]
     fn eq_types(&mut self, a: Ty<'tcx>, b: Ty<'tcx>, locations: Locations) -> UnitResult<'tcx> {
+        // Micro-optimization.
+        if a == b {
+            return Ok(());
+        }
+
         self.fully_perform_op(
             locations,
             || format!("eq_types({:?} = {:?})", a, b),