Reexport std::hint::black_box

Cargo.toml

@@ -18,6 +18,7 @@ keywords    = ["criterion", "benchmark"]
 categories  = ["development-tools::profiling"]
 license     = "Apache-2.0 OR MIT"
 exclude     = ["book/*"]
+rust-version = "1.66"
 
 [dependencies]
 anes           = "0.1.4"
@@ -71,7 +72,7 @@ stable = [
   "async_tokio",
   "async_std",
 ]
-default = ["rayon", "plotters", "cargo_bench_support"]
+default = ["rayon", "plotters", "cargo_bench_support", "real_blackbox"]
 
 # Enable use of the nightly-only test::black_box function to discourage compiler optimizations.
 real_blackbox = []

src/lib.rs

@@ -17,7 +17,6 @@
 
 #![warn(missing_docs)]
 #![warn(bare_trait_objects)]
-#![cfg_attr(feature = "real_blackbox", feature(test))]
 #![allow(
         clippy::just_underscores_and_digits, // Used in the stats code
         clippy::transmute_ptr_to_ptr, // Used in the stats code
@@ -35,9 +34,6 @@ extern crate quickcheck;
 
 use regex::Regex;
 
-#[cfg(feature = "real_blackbox")]
-extern crate test;
-
 #[macro_use]
 extern crate serde_derive;
 
@@ -72,6 +68,7 @@ mod stats;
 use std::cell::RefCell;
 use std::collections::HashSet;
 use std::env;
+use std::hint;
 use std::io::{stdout, IsTerminal};
 use std::net::TcpStream;
 use std::path::{Path, PathBuf};
@@ -147,24 +144,10 @@ fn debug_enabled() -> bool {
 /// A function that is opaque to the optimizer, used to prevent the compiler from
 /// optimizing away computations in a benchmark.
 ///
-/// This variant is backed by the (unstable) test::black_box function.
-#[cfg(feature = "real_blackbox")]
-pub fn black_box<T>(dummy: T) -> T {
-    test::black_box(dummy)
-}
-
-/// A function that is opaque to the optimizer, used to prevent the compiler from
-/// optimizing away computations in a benchmark.
-///
-/// This variant is stable-compatible, but it may cause some performance overhead
-/// or fail to prevent code from being eliminated.
-#[cfg(not(feature = "real_blackbox"))]
+/// This function is deprecated in favour of `std::hint::black_box`.
+#[deprecated(note = "use `std::hint::black_box` instead")]
 pub fn black_box<T>(dummy: T) -> T {
-    unsafe {
-        let ret = std::ptr::read_volatile(&dummy);
-        std::mem::forget(dummy);
-        ret
-    }
+    hint::black_box(dummy)
 }
 
 /// Argument to [`Bencher::iter_batched`] and [`Bencher::iter_batched_ref`] which controls the