4 files changed, 11 insertions, 15 deletions
diff --git a/src/libcore/tests/cell.rs b/src/libcore/tests/cell.rs
index 73bdaab5861..b16416022c0 100644
--- a/src/libcore/tests/cell.rs
+++ b/src/libcore/tests/cell.rs
@@ -1,5 +1,3 @@
-#![cfg(not(miri))]
-
 use core::cell::*;
 use core::default::Default;
 use std::mem::drop;
@@ -111,6 +109,7 @@ fn double_borrow_single_release_no_borrow_mut() {
 
 #[test]
 #[should_panic]
+#[cfg(not(miri))] // Miri does not support panics
 fn discard_doesnt_unborrow() {
     let x = RefCell::new(0);
     let _b = x.borrow();
@@ -351,6 +350,7 @@ fn refcell_ref_coercion() {
 
 #[test]
 #[should_panic]
+#[cfg(not(miri))] // Miri does not support panics
 fn refcell_swap_borrows() {
     let x = RefCell::new(0);
     let _b = x.borrow();
@@ -360,6 +360,7 @@ fn refcell_swap_borrows() {
 
 #[test]
 #[should_panic]
+#[cfg(not(miri))] // Miri does not support panics
 fn refcell_replace_borrows() {
     let x = RefCell::new(0);
     let _b = x.borrow();
diff --git a/src/libcore/tests/iter.rs b/src/libcore/tests/iter.rs
index 04c5bf7e95b..bc951829bd7 100644
--- a/src/libcore/tests/iter.rs
+++ b/src/libcore/tests/iter.rs
@@ -190,7 +190,6 @@ fn test_iterator_step_by() {
 }
 
 #[test]
-#[cfg(not(miri))]
 fn test_iterator_step_by_nth() {
     let mut it = (0..16).step_by(5);
     assert_eq!(it.nth(0), Some(0));
@@ -209,7 +208,6 @@ fn test_iterator_step_by_nth() {
 }
 
 #[test]
-#[cfg(not(miri))]
 fn test_iterator_step_by_nth_overflow() {
     #[cfg(target_pointer_width = "8")]
     type Bigger = u16;
@@ -262,7 +260,6 @@ fn test_iterator_step_by_zero() {
 }
 
 #[test]
-#[cfg(not(miri))]
 fn test_iterator_step_by_size_hint() {
     struct StubSizeHint(usize, Option<usize>);
     impl Iterator for StubSizeHint {
@@ -1657,7 +1654,6 @@ fn test_range_inclusive_nth() {
 }
 
 #[test]
-#[cfg(not(miri))]
 fn test_range_step() {
     #![allow(deprecated)]
 
@@ -1665,7 +1661,9 @@ fn test_range_step() {
     assert_eq!((1..21).rev().step_by(5).collect::<Vec<isize>>(), [20, 15, 10, 5]);
     assert_eq!((1..21).rev().step_by(6).collect::<Vec<isize>>(), [20, 14, 8, 2]);
     assert_eq!((200..255).step_by(50).collect::<Vec<u8>>(), [200, 250]);
+    #[cfg(not(miri))] // Miri cannot compare empty slices
     assert_eq!((200..-5).step_by(1).collect::<Vec<isize>>(), []);
+    #[cfg(not(miri))] // Miri cannot compare empty slices
     assert_eq!((200..200).step_by(1).collect::<Vec<isize>>(), []);
 
     assert_eq!((0..20).step_by(1).size_hint(), (20, Some(20)));
@@ -1681,7 +1679,6 @@ fn test_range_step() {
 }
 
 #[test]
-#[cfg(not(miri))]
 fn test_step_by_skip() {
     assert_eq!((0..640).step_by(128).skip(1).collect::<Vec<_>>(), [128, 256, 384, 512]);
     assert_eq!((0..=50).step_by(10).nth(3), Some(30));
@@ -1689,7 +1686,6 @@ fn test_step_by_skip() {
 }
 
 #[test]
-#[cfg(not(miri))]
 fn test_range_inclusive_step() {
     assert_eq!((0..=50).step_by(10).collect::<Vec<_>>(), [0, 10, 20, 30, 40, 50]);
     assert_eq!((0..=5).step_by(1).collect::<Vec<_>>(), [0, 1, 2, 3, 4, 5]);
diff --git a/src/libcore/tests/slice.rs b/src/libcore/tests/slice.rs
index 454c1235c81..31d16e0e320 100644
--- a/src/libcore/tests/slice.rs
+++ b/src/libcore/tests/slice.rs
@@ -1015,7 +1015,7 @@ fn test_rotate_right() {
 
 #[test]
 #[cfg(not(target_arch = "wasm32"))]
-#[cfg(not(miri))]
+#[cfg(not(miri))] // Miri does not support entropy
 fn sort_unstable() {
     use core::cmp::Ordering::{Equal, Greater, Less};
     use core::slice::heapsort;
@@ -1171,7 +1171,7 @@ pub mod memchr {
 }
 
 #[test]
-#[cfg(not(miri))]
+#[cfg(not(miri))] // Miri cannot compute actual alignment of an allocation
 fn test_align_to_simple() {
     let bytes = [1u8, 2, 3, 4, 5, 6, 7];
     let (prefix, aligned, suffix) = unsafe { bytes.align_to::<u16>() };
@@ -1187,7 +1187,6 @@ fn test_align_to_simple() {
 }
 
 #[test]
-#[cfg(not(miri))]
 fn test_align_to_zst() {
     let bytes = [1, 2, 3, 4, 5, 6, 7];
     let (prefix, aligned, suffix) = unsafe { bytes.align_to::<()>() };
@@ -1196,7 +1195,7 @@ fn test_align_to_zst() {
 }
 
 #[test]
-#[cfg(not(miri))]
+#[cfg(not(miri))] // Miri cannot compute actual alignment of an allocation
 fn test_align_to_non_trivial() {
     #[repr(align(8))] struct U64(u64, u64);
     #[repr(align(8))] struct U64U64U32(u64, u64, u32);
@@ -1208,7 +1207,6 @@ fn test_align_to_non_trivial() {
 }
 
 #[test]
-#[cfg(not(miri))]
 fn test_align_to_empty_mid() {
     use core::mem;
 
diff --git a/src/libcore/tests/time.rs b/src/libcore/tests/time.rs
index d39bd06930a..f7d00304df5 100644
--- a/src/libcore/tests/time.rs
+++ b/src/libcore/tests/time.rs
@@ -1,5 +1,3 @@
-#![cfg(not(miri))]
-
 use core::time::Duration;
 
 #[test]
@@ -109,12 +107,14 @@ fn checked_sub() {
 
 #[test]
 #[should_panic]
+#[cfg(not(miri))] // Miri does not support panics
 fn sub_bad1() {
     let _ = Duration::new(0, 0) - Duration::new(0, 1);
 }
 
 #[test]
 #[should_panic]
+#[cfg(not(miri))] // Miri does not support panics
 fn sub_bad2() {
     let _ = Duration::new(0, 0) - Duration::new(1, 0);
 }
@@ -287,6 +287,7 @@ fn debug_formatting_precision_two() {
 }
 
 #[test]
+#[cfg(not(miri))] // FIXME: A bug in Miri breaks padding in string formatting
 fn debug_formatting_precision_high() {
     assert_eq!(format!("{:.5?}",  Duration::new(0, 23_678)), "23.67800µs");