diff --git a/library/core/benches/fmt.rs b/library/core/benches/fmt.rs
index ff726ff7559..d1cdb12e50f 100644
--- a/library/core/benches/fmt.rs
+++ b/library/core/benches/fmt.rs
@@ -1,13 +1,13 @@
 use std::fmt::{self, Write as FmtWrite};
 use std::io::{self, Write as IoWrite};
-use test::Bencher;
+use test::{black_box, Bencher};
 
 #[bench]
 fn write_vec_value(bh: &mut Bencher) {
     bh.iter(|| {
         let mut mem = Vec::new();
         for _ in 0..1000 {
-            mem.write_all("abc".as_bytes()).unwrap();
+            mem.write_all(black_box("abc").as_bytes()).unwrap();
         }
     });
 }
@@ -18,7 +18,7 @@ fn write_vec_ref(bh: &mut Bencher) {
         let mut mem = Vec::new();
         let wr = &mut mem as &mut dyn io::Write;
         for _ in 0..1000 {
-            wr.write_all("abc".as_bytes()).unwrap();
+            wr.write_all(black_box("abc").as_bytes()).unwrap();
         }
     });
 }
@@ -29,7 +29,7 @@ fn write_vec_macro1(bh: &mut Bencher) {
         let mut mem = Vec::new();
         let wr = &mut mem as &mut dyn io::Write;
         for _ in 0..1000 {
-            write!(wr, "abc").unwrap();
+            write!(wr, "{}", black_box("abc")).unwrap();
         }
     });
 }
@@ -40,7 +40,7 @@ fn write_vec_macro2(bh: &mut Bencher) {
         let mut mem = Vec::new();
         let wr = &mut mem as &mut dyn io::Write;
         for _ in 0..1000 {
-            write!(wr, "{}", "abc").unwrap();
+            write!(wr, "{}", black_box("abc")).unwrap();
         }
     });
 }
@@ -51,7 +51,7 @@ fn write_vec_macro_debug(bh: &mut Bencher) {
         let mut mem = Vec::new();
         let wr = &mut mem as &mut dyn io::Write;
         for _ in 0..1000 {
-            write!(wr, "{:?}", "☃").unwrap();
+            write!(wr, "{:?}", black_box("☃")).unwrap();
         }
     });
 }
@@ -61,7 +61,7 @@ fn write_str_value(bh: &mut Bencher) {
     bh.iter(|| {
         let mut mem = String::new();
         for _ in 0..1000 {
-            mem.write_str("abc").unwrap();
+            mem.write_str(black_box("abc")).unwrap();
         }
     });
 }
@@ -72,7 +72,7 @@ fn write_str_ref(bh: &mut Bencher) {
         let mut mem = String::new();
         let wr = &mut mem as &mut dyn fmt::Write;
         for _ in 0..1000 {
-            wr.write_str("abc").unwrap();
+            wr.write_str(black_box("abc")).unwrap();
         }
     });
 }
@@ -82,7 +82,7 @@ fn write_str_macro1(bh: &mut Bencher) {
     bh.iter(|| {
         let mut mem = String::new();
         for _ in 0..1000 {
-            write!(mem, "abc").unwrap();
+            write!(mem, "{}", black_box("abc")).unwrap();
         }
     });
 }
@@ -93,7 +93,7 @@ fn write_str_macro2(bh: &mut Bencher) {
         let mut mem = String::new();
         let wr = &mut mem as &mut dyn fmt::Write;
         for _ in 0..1000 {
-            write!(wr, "{}", "abc").unwrap();
+            write!(wr, "{}", black_box("abc")).unwrap();
         }
     });
 }
@@ -104,7 +104,7 @@ fn write_str_macro_debug(bh: &mut Bencher) {
         let mut mem = String::new();
         let wr = &mut mem as &mut dyn fmt::Write;
         for _ in 0..1000 {
-            write!(wr, "{:?}", "☃").unwrap();
+            write!(wr, "{:?}", black_box("☃")).unwrap();
         }
     });
 }
@@ -115,7 +115,7 @@ fn write_str_macro_debug_ascii(bh: &mut Bencher) {
         let mut mem = String::new();
         let wr = &mut mem as &mut dyn fmt::Write;
         for _ in 0..1000 {
-            write!(wr, "{:?}", "Hello, World!").unwrap();
+            write!(wr, "{:?}", black_box("Hello, World!")).unwrap();
         }
     });
 }
diff --git a/library/core/benches/num/dec2flt/mod.rs b/library/core/benches/num/dec2flt/mod.rs
index 305baa68729..fb4a786b27e 100644
--- a/library/core/benches/num/dec2flt/mod.rs
+++ b/library/core/benches/num/dec2flt/mod.rs
@@ -1,57 +1,57 @@
-use test::Bencher;
+use test::{black_box, Bencher};
 
 #[bench]
 fn bench_0(b: &mut Bencher) {
-    b.iter(|| "0.0".parse::<f64>());
+    b.iter(|| black_box("0.0").parse::<f64>());
 }
 
 #[bench]
 fn bench_42(b: &mut Bencher) {
-    b.iter(|| "42".parse::<f64>());
+    b.iter(|| black_box("42").parse::<f64>());
 }
 
 #[bench]
 fn bench_huge_int(b: &mut Bencher) {
     // 2^128 - 1
-    b.iter(|| "170141183460469231731687303715884105727".parse::<f64>());
+    b.iter(|| black_box("170141183460469231731687303715884105727").parse::<f64>());
 }
 
 #[bench]
 fn bench_short_decimal(b: &mut Bencher) {
-    b.iter(|| "1234.5678".parse::<f64>());
+    b.iter(|| black_box("1234.5678").parse::<f64>());
 }
 
 #[bench]
 fn bench_pi_long(b: &mut Bencher) {
-    b.iter(|| "3.14159265358979323846264338327950288".parse::<f64>());
+    b.iter(|| black_box("3.14159265358979323846264338327950288").parse::<f64>());
 }
 
 #[bench]
 fn bench_pi_short(b: &mut Bencher) {
-    b.iter(|| "3.141592653589793".parse::<f64>())
+    b.iter(|| black_box("3.141592653589793").parse::<f64>())
 }
 
 #[bench]
 fn bench_1e150(b: &mut Bencher) {
-    b.iter(|| "1e150".parse::<f64>());
+    b.iter(|| black_box("1e150").parse::<f64>());
 }
 
 #[bench]
 fn bench_long_decimal_and_exp(b: &mut Bencher) {
-    b.iter(|| "727501488517303786137132964064381141071e-123".parse::<f64>());
+    b.iter(|| black_box("727501488517303786137132964064381141071e-123").parse::<f64>());
 }
 
 #[bench]
 fn bench_min_subnormal(b: &mut Bencher) {
-    b.iter(|| "5e-324".parse::<f64>());
+    b.iter(|| black_box("5e-324").parse::<f64>());
 }
 
 #[bench]
 fn bench_min_normal(b: &mut Bencher) {
-    b.iter(|| "2.2250738585072014e-308".parse::<f64>());
+    b.iter(|| black_box("2.2250738585072014e-308").parse::<f64>());
 }
 
 #[bench]
 fn bench_max(b: &mut Bencher) {
-    b.iter(|| "1.7976931348623157e308".parse::<f64>());
+    b.iter(|| black_box("1.7976931348623157e308").parse::<f64>());
 }
diff --git a/library/core/benches/num/flt2dec/mod.rs b/library/core/benches/num/flt2dec/mod.rs
index 32fd5e626bc..1a330ef5fe5 100644
--- a/library/core/benches/num/flt2dec/mod.rs
+++ b/library/core/benches/num/flt2dec/mod.rs
@@ -7,7 +7,7 @@ mod strategy {
 use core::num::flt2dec::{decode, DecodableFloat, Decoded, FullDecoded};
 use std::io::Write;
 use std::vec::Vec;
-use test::Bencher;
+use test::{black_box, Bencher};
 
 pub fn decode_finite<T: DecodableFloat>(v: T) -> Decoded {
     match decode(v).1 {
@@ -22,7 +22,7 @@ fn bench_small_shortest(b: &mut Bencher) {
 
     b.iter(|| {
         buf.clear();
-        write!(&mut buf, "{}", 3.1415926f64).unwrap()
+        write!(black_box(&mut buf), "{}", black_box(3.1415926f64)).unwrap()
     });
 }
 
@@ -32,6 +32,6 @@ fn bench_big_shortest(b: &mut Bencher) {
 
     b.iter(|| {
         buf.clear();
-        write!(&mut buf, "{}", f64::MAX).unwrap()
+        write!(black_box(&mut buf), "{}", black_box(f64::MAX)).unwrap()
     });
 }
diff --git a/library/core/benches/num/mod.rs b/library/core/benches/num/mod.rs
index 2f9cad2725d..b97014d9bf9 100644
--- a/library/core/benches/num/mod.rs
+++ b/library/core/benches/num/mod.rs
@@ -3,7 +3,7 @@
 mod int_log;
 
 use std::str::FromStr;
-use test::Bencher;
+use test::{black_box, Bencher};
 
 const ASCII_NUMBERS: [&str; 19] = [
     "0",
@@ -36,7 +36,7 @@ fn $mac(b: &mut Bencher) {
                     .iter()
                     .cycle()
                     .take(5_000)
-                    .filter_map(|s| <$t>::from_str(s).ok())
+                    .filter_map(|s| <$t>::from_str(black_box(s)).ok())
                     .max()
             })
         }
@@ -52,7 +52,7 @@ fn $mac(b: &mut Bencher) {
                     .iter()
                     .cycle()
                     .take(5_000)
-                    .filter_map(|s| <$t>::from_str_radix(s, $radix).ok())
+                    .filter_map(|s| <$t>::from_str_radix(black_box(s), $radix).ok())
                     .max()
             })
         }