diff --git a/library/core/benches/char/methods.rs b/library/core/benches/char/methods.rs
index 9408f83c32f..5d4df1ac8bd 100644
--- a/library/core/benches/char/methods.rs
+++ b/library/core/benches/char/methods.rs
@@ -1,26 +1,26 @@
-use test::Bencher;
+use test::{black_box, Bencher};
 
 const CHARS: [char; 9] = ['0', 'x', '2', '5', 'A', 'f', '7', '8', '9'];
 const RADIX: [u32; 5] = [2, 8, 10, 16, 32];
 
 #[bench]
 fn bench_to_digit_radix_2(b: &mut Bencher) {
-    b.iter(|| CHARS.iter().cycle().take(10_000).map(|c| c.to_digit(2)).min())
+    b.iter(|| CHARS.iter().cycle().take(10_000).map(|c| black_box(c).to_digit(2)).min())
 }
 
 #[bench]
 fn bench_to_digit_radix_10(b: &mut Bencher) {
-    b.iter(|| CHARS.iter().cycle().take(10_000).map(|c| c.to_digit(10)).min())
+    b.iter(|| CHARS.iter().cycle().take(10_000).map(|c| black_box(c).to_digit(10)).min())
 }
 
 #[bench]
 fn bench_to_digit_radix_16(b: &mut Bencher) {
-    b.iter(|| CHARS.iter().cycle().take(10_000).map(|c| c.to_digit(16)).min())
+    b.iter(|| CHARS.iter().cycle().take(10_000).map(|c| black_box(c).to_digit(16)).min())
 }
 
 #[bench]
 fn bench_to_digit_radix_36(b: &mut Bencher) {
-    b.iter(|| CHARS.iter().cycle().take(10_000).map(|c| c.to_digit(36)).min())
+    b.iter(|| CHARS.iter().cycle().take(10_000).map(|c| black_box(c).to_digit(36)).min())
 }
 
 #[bench]
@@ -31,47 +31,59 @@ fn bench_to_digit_radix_var(b: &mut Bencher) {
             .cycle()
             .zip(RADIX.iter().cycle())
             .take(10_000)
-            .map(|(c, radix)| c.to_digit(*radix))
+            .map(|(c, radix)| black_box(c).to_digit(*radix))
             .min()
     })
 }
 
 #[bench]
 fn bench_to_ascii_uppercase(b: &mut Bencher) {
-    b.iter(|| CHARS.iter().cycle().take(10_000).map(|c| c.to_ascii_uppercase()).min())
+    b.iter(|| CHARS.iter().cycle().take(10_000).map(|c| black_box(c).to_ascii_uppercase()).min())
 }
 
 #[bench]
 fn bench_to_ascii_lowercase(b: &mut Bencher) {
-    b.iter(|| CHARS.iter().cycle().take(10_000).map(|c| c.to_ascii_lowercase()).min())
+    b.iter(|| CHARS.iter().cycle().take(10_000).map(|c| black_box(c).to_ascii_lowercase()).min())
 }
 
 #[bench]
 fn bench_ascii_mix_to_uppercase(b: &mut Bencher) {
-    b.iter(|| (0..=255).cycle().take(10_000).map(|b| char::from(b).to_uppercase()).count())
+    b.iter(|| {
+        (0..=255).cycle().take(10_000).map(|b| black_box(char::from(b)).to_uppercase()).count()
+    })
 }
 
 #[bench]
 fn bench_ascii_mix_to_lowercase(b: &mut Bencher) {
-    b.iter(|| (0..=255).cycle().take(10_000).map(|b| char::from(b).to_lowercase()).count())
+    b.iter(|| {
+        (0..=255).cycle().take(10_000).map(|b| black_box(char::from(b)).to_lowercase()).count()
+    })
 }
 
 #[bench]
 fn bench_ascii_char_to_uppercase(b: &mut Bencher) {
-    b.iter(|| (0..=127).cycle().take(10_000).map(|b| char::from(b).to_uppercase()).count())
+    b.iter(|| {
+        (0..=127).cycle().take(10_000).map(|b| black_box(char::from(b)).to_uppercase()).count()
+    })
 }
 
 #[bench]
 fn bench_ascii_char_to_lowercase(b: &mut Bencher) {
-    b.iter(|| (0..=127).cycle().take(10_000).map(|b| char::from(b).to_lowercase()).count())
+    b.iter(|| {
+        (0..=127).cycle().take(10_000).map(|b| black_box(char::from(b)).to_lowercase()).count()
+    })
 }
 
 #[bench]
 fn bench_non_ascii_char_to_uppercase(b: &mut Bencher) {
-    b.iter(|| (128..=255).cycle().take(10_000).map(|b| char::from(b).to_uppercase()).count())
+    b.iter(|| {
+        (128..=255).cycle().take(10_000).map(|b| black_box(char::from(b)).to_uppercase()).count()
+    })
 }
 
 #[bench]
 fn bench_non_ascii_char_to_lowercase(b: &mut Bencher) {
-    b.iter(|| (128..=255).cycle().take(10_000).map(|b| char::from(b).to_lowercase()).count())
+    b.iter(|| {
+        (128..=255).cycle().take(10_000).map(|b| black_box(char::from(b)).to_lowercase()).count()
+    })
 }
diff --git a/library/core/benches/num/flt2dec/strategy/dragon.rs b/library/core/benches/num/flt2dec/strategy/dragon.rs
index 319b9773e49..377c99effd0 100644
--- a/library/core/benches/num/flt2dec/strategy/dragon.rs
+++ b/library/core/benches/num/flt2dec/strategy/dragon.rs
@@ -1,14 +1,14 @@
 use super::super::*;
 use core::num::flt2dec::strategy::dragon::*;
 use std::mem::MaybeUninit;
-use test::Bencher;
+use test::{black_box, Bencher};
 
 #[bench]
 fn bench_small_shortest(b: &mut Bencher) {
     let decoded = decode_finite(3.141592f64);
     let mut buf = [MaybeUninit::new(0); MAX_SIG_DIGITS];
     b.iter(|| {
-        format_shortest(&decoded, &mut buf);
+        format_shortest(black_box(&decoded), &mut buf);
     });
 }
 
@@ -17,7 +17,7 @@ fn bench_big_shortest(b: &mut Bencher) {
     let decoded = decode_finite(f64::MAX);
     let mut buf = [MaybeUninit::new(0); MAX_SIG_DIGITS];
     b.iter(|| {
-        format_shortest(&decoded, &mut buf);
+        format_shortest(black_box(&decoded), &mut buf);
     });
 }
 
@@ -26,7 +26,7 @@ fn bench_small_exact_3(b: &mut Bencher) {
     let decoded = decode_finite(3.141592f64);
     let mut buf = [MaybeUninit::new(0); 3];
     b.iter(|| {
-        format_exact(&decoded, &mut buf, i16::MIN);
+        format_exact(black_box(&decoded), &mut buf, i16::MIN);
     });
 }
 
@@ -35,7 +35,7 @@ fn bench_big_exact_3(b: &mut Bencher) {
     let decoded = decode_finite(f64::MAX);
     let mut buf = [MaybeUninit::new(0); 3];
     b.iter(|| {
-        format_exact(&decoded, &mut buf, i16::MIN);
+        format_exact(black_box(&decoded), &mut buf, i16::MIN);
     });
 }
 
@@ -44,7 +44,7 @@ fn bench_small_exact_12(b: &mut Bencher) {
     let decoded = decode_finite(3.141592f64);
     let mut buf = [MaybeUninit::new(0); 12];
     b.iter(|| {
-        format_exact(&decoded, &mut buf, i16::MIN);
+        format_exact(black_box(&decoded), &mut buf, i16::MIN);
     });
 }
 
@@ -53,7 +53,7 @@ fn bench_big_exact_12(b: &mut Bencher) {
     let decoded = decode_finite(f64::MAX);
     let mut buf = [MaybeUninit::new(0); 12];
     b.iter(|| {
-        format_exact(&decoded, &mut buf, i16::MIN);
+        format_exact(black_box(&decoded), &mut buf, i16::MIN);
     });
 }
 
@@ -62,7 +62,7 @@ fn bench_small_exact_inf(b: &mut Bencher) {
     let decoded = decode_finite(3.141592f64);
     let mut buf = [MaybeUninit::new(0); 1024];
     b.iter(|| {
-        format_exact(&decoded, &mut buf, i16::MIN);
+        format_exact(black_box(&decoded), &mut buf, i16::MIN);
     });
 }
 
@@ -71,6 +71,6 @@ fn bench_big_exact_inf(b: &mut Bencher) {
     let decoded = decode_finite(f64::MAX);
     let mut buf = [MaybeUninit::new(0); 1024];
     b.iter(|| {
-        format_exact(&decoded, &mut buf, i16::MIN);
+        format_exact(black_box(&decoded), &mut buf, i16::MIN);
     });
 }
diff --git a/library/core/benches/num/flt2dec/strategy/grisu.rs b/library/core/benches/num/flt2dec/strategy/grisu.rs
index 8e47a046cde..6bea5e55d37 100644
--- a/library/core/benches/num/flt2dec/strategy/grisu.rs
+++ b/library/core/benches/num/flt2dec/strategy/grisu.rs
@@ -1,7 +1,7 @@
 use super::super::*;
 use core::num::flt2dec::strategy::grisu::*;
 use std::mem::MaybeUninit;
-use test::Bencher;
+use test::{black_box, Bencher};
 
 pub fn decode_finite<T: DecodableFloat>(v: T) -> Decoded {
     match decode(v).1 {
@@ -15,7 +15,7 @@ fn bench_small_shortest(b: &mut Bencher) {
     let decoded = decode_finite(3.141592f64);
     let mut buf = [MaybeUninit::new(0); MAX_SIG_DIGITS];
     b.iter(|| {
-        format_shortest(&decoded, &mut buf);
+        format_shortest(black_box(&decoded), &mut buf);
     });
 }
 
@@ -24,7 +24,7 @@ fn bench_big_shortest(b: &mut Bencher) {
     let decoded = decode_finite(f64::MAX);
     let mut buf = [MaybeUninit::new(0); MAX_SIG_DIGITS];
     b.iter(|| {
-        format_shortest(&decoded, &mut buf);
+        format_shortest(black_box(&decoded), &mut buf);
     });
 }
 
@@ -33,7 +33,7 @@ fn bench_small_exact_3(b: &mut Bencher) {
     let decoded = decode_finite(3.141592f64);
     let mut buf = [MaybeUninit::new(0); 3];
     b.iter(|| {
-        format_exact(&decoded, &mut buf, i16::MIN);
+        format_exact(black_box(&decoded), &mut buf, i16::MIN);
     });
 }
 
@@ -42,7 +42,7 @@ fn bench_big_exact_3(b: &mut Bencher) {
     let decoded = decode_finite(f64::MAX);
     let mut buf = [MaybeUninit::new(0); 3];
     b.iter(|| {
-        format_exact(&decoded, &mut buf, i16::MIN);
+        format_exact(black_box(&decoded), &mut buf, i16::MIN);
     });
 }
 
@@ -51,7 +51,7 @@ fn bench_small_exact_12(b: &mut Bencher) {
     let decoded = decode_finite(3.141592f64);
     let mut buf = [MaybeUninit::new(0); 12];
     b.iter(|| {
-        format_exact(&decoded, &mut buf, i16::MIN);
+        format_exact(black_box(&decoded), &mut buf, i16::MIN);
     });
 }
 
@@ -60,7 +60,7 @@ fn bench_big_exact_12(b: &mut Bencher) {
     let decoded = decode_finite(f64::MAX);
     let mut buf = [MaybeUninit::new(0); 12];
     b.iter(|| {
-        format_exact(&decoded, &mut buf, i16::MIN);
+        format_exact(black_box(&decoded), &mut buf, i16::MIN);
     });
 }
 
@@ -69,7 +69,7 @@ fn bench_small_exact_inf(b: &mut Bencher) {
     let decoded = decode_finite(3.141592f64);
     let mut buf = [MaybeUninit::new(0); 1024];
     b.iter(|| {
-        format_exact(&decoded, &mut buf, i16::MIN);
+        format_exact(black_box(&decoded), &mut buf, i16::MIN);
     });
 }
 
@@ -78,6 +78,6 @@ fn bench_big_exact_inf(b: &mut Bencher) {
     let decoded = decode_finite(f64::MAX);
     let mut buf = [MaybeUninit::new(0); 1024];
     b.iter(|| {
-        format_exact(&decoded, &mut buf, i16::MIN);
+        format_exact(black_box(&decoded), &mut buf, i16::MIN);
     });
 }