From d5a7ec0929dc438a78716585ceff827d51c8a32f Mon Sep 17 00:00:00 2001
From: Nadrieril <nadrieril+git@gmail.com>
Date: Sat, 7 Nov 2020 23:45:36 +0000
Subject: [PATCH] Unreachable subpatterns are rare

We may as well leave early when we know there's nothing to report.
---
 compiler/rustc_mir_build/src/thir/pattern/check_match.rs | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs b/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
index c6fd7bcbf90d..4766e7d178d1 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
@@ -389,6 +389,8 @@ fn check_arms<'p, 'tcx>(
                     hir::MatchSource::AwaitDesugar | hir::MatchSource::TryDesugar => {}
                 }
             }
+            Useful(unreachables) if unreachables.is_empty() => {}
+            // The arm is reachable, but contains unreachable subpatterns (from or-patterns).
             Useful(unreachables) => {
                 let mut unreachables: Vec<_> = unreachables.into_iter().flatten().collect();
                 // Emit lints in the order in which they occur in the file.