From 2cc81ac531c10a678ee25128a36fdc56ba00aaa3 Mon Sep 17 00:00:00 2001
From: Travis Watkins <amaranth@ubuntu.com>
Date: Sat, 3 Jan 2015 02:49:42 -0600
Subject: [PATCH] Return passed value from black_box

By returning the passed value black_box can be used on data being
passed to a function being benchmarked. This ensures the compiler
does not optimize the function for the input which could result in
the entire function being optimized away.
---
 src/libtest/lib.rs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/libtest/lib.rs b/src/libtest/lib.rs
index c4cb53d6cb7..c00246598c3 100644
--- a/src/libtest/lib.rs
+++ b/src/libtest/lib.rs
@@ -1332,10 +1332,11 @@ pub fn ratchet(&self, p: &Path, pct: Option<f64>) -> (MetricDiff, bool) {
 /// elimination.
 ///
 /// This function is a no-op, and does not even read from `dummy`.
-pub fn black_box<T>(dummy: T) {
+pub fn black_box<T>(dummy: T) -> T {
     // we need to "use" the argument in some way LLVM can't
     // introspect.
     unsafe {asm!("" : : "r"(&dummy))}
+    dummy
 }