From db15596c5747eed0344f2622a9d85ad9534b23f9 Mon Sep 17 00:00:00 2001
From: Sergio Benitez <sb@sergio.bz>
Date: Thu, 22 Oct 2020 03:22:13 -0700
Subject: [PATCH] Only load LOCAL_STREAMS if they are being used

---
 library/std/src/io/stdio.rs | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/library/std/src/io/stdio.rs b/library/std/src/io/stdio.rs
index 5b50ce4c2ee..2eb5fb45286 100644
--- a/library/std/src/io/stdio.rs
+++ b/library/std/src/io/stdio.rs
@@ -963,6 +963,11 @@ pub fn set_print(sink: Option<Box<dyn LocalOutput>>) -> Option<Box<dyn LocalOutp
 }
 
 pub(crate) fn clone_io() -> (Option<Box<dyn LocalOutput>>, Option<Box<dyn LocalOutput>>) {
+    // Don't waste time when LOCAL_{STDOUT,STDERR} are definitely None.
+    if !LOCAL_STREAMS.load(Ordering::Relaxed) {
+        return (None, None);
+    }
+
     LOCAL_STDOUT.with(|stdout| {
         LOCAL_STDERR.with(|stderr| {
             (