Merge branch 'master' into copied

52 files changed, 600 insertions, 333 deletions

diff --git a/src/libcore/Cargo.toml b/src/libcore/Cargo.toml
index 7fd61f07d5e..fa2ab11243b 100644
--- a/src/libcore/Cargo.toml
+++ b/src/libcore/Cargo.toml
@@ -20,7 +20,7 @@ name = "corebenches"
 path = "../libcore/benches/lib.rs"
 
 [dev-dependencies]
-rand = "0.5"
+rand = "0.6"
 
 [features]
 # Make panics and failed asserts immediately abort without formatting any message
diff --git a/src/libcore/alloc.rs b/src/libcore/alloc.rs
index 58639808fae..8db7d33bdec 100644
--- a/src/libcore/alloc.rs
+++ b/src/libcore/alloc.rs
@@ -69,7 +69,7 @@ impl Layout {
     /// * `align` must be a power of two,
     ///
     /// * `size`, when rounded up to the nearest multiple of `align`,
-    ///    must not overflow (i.e. the rounded value must be less than
+    ///    must not overflow (i.e., the rounded value must be less than
     ///    `usize::MAX`).
     #[stable(feature = "alloc_layout", since = "1.28.0")]
     #[inline]
@@ -177,7 +177,7 @@ impl Layout {
     /// to ensure that the following address will satisfy `align`
     /// (measured in bytes).
     ///
-    /// E.g. if `self.size()` is 9, then `self.padding_needed_for(4)`
+    /// e.g., if `self.size()` is 9, then `self.padding_needed_for(4)`
     /// returns 3, because that is the minimum number of bytes of
     /// padding required to get a 4-aligned address (assuming that the
     /// corresponding memory block starts at a 4-aligned address).
@@ -455,7 +455,7 @@ pub unsafe trait GlobalAlloc {
     /// if the caller does not ensure that `layout` has non-zero size.
     ///
     /// (Extension subtraits might provide more specific bounds on
-    /// behavior, e.g. guarantee a sentinel address or a null pointer
+    /// behavior, e.g., guarantee a sentinel address or a null pointer
     /// in response to a zero-size allocation request.)
     ///
     /// The allocated block of memory may or may not be initialized.
@@ -550,10 +550,10 @@ pub unsafe trait GlobalAlloc {
     /// * `new_size` must be greater than zero.
     ///
     /// * `new_size`, when rounded up to the nearest multiple of `layout.align()`,
-    ///   must not overflow (i.e. the rounded value must be less than `usize::MAX`).
+    ///   must not overflow (i.e., the rounded value must be less than `usize::MAX`).
     ///
     /// (Extension subtraits might provide more specific bounds on
-    /// behavior, e.g. guarantee a sentinel address or a null pointer
+    /// behavior, e.g., guarantee a sentinel address or a null pointer
     /// in response to a zero-size allocation request.)
     ///
     /// # Errors
@@ -616,7 +616,7 @@ pub unsafe trait GlobalAlloc {
 ///   whether to return `Err`, or to return `Ok` with some pointer.
 ///
 /// * If an `Alloc` implementation chooses to return `Ok` in this
-///   case (i.e. the pointer denotes a zero-sized inaccessible block)
+///   case (i.e., the pointer denotes a zero-sized inaccessible block)
 ///   then that returned pointer must be considered "currently
 ///   allocated". On such an allocator, *all* methods that take
 ///   currently-allocated pointers as inputs must accept these
@@ -651,7 +651,7 @@ pub unsafe trait GlobalAlloc {
 ///
 ///  * if a layout `k` fits a memory block (denoted by `ptr`)
 ///    currently allocated via an allocator `a`, then it is legal to
-///    use that layout to deallocate it, i.e. `a.dealloc(ptr, k);`.
+///    use that layout to deallocate it, i.e., `a.dealloc(ptr, k);`.
 ///
 /// # Unsafety
 ///
@@ -673,7 +673,7 @@ pub unsafe trait Alloc {
 
     // (Note: some existing allocators have unspecified but well-defined
     // behavior in response to a zero size allocation request ;
-    // e.g. in C, `malloc` of 0 will either return a null pointer or a
+    // e.g., in C, `malloc` of 0 will either return a null pointer or a
     // unique pointer, but will not have arbitrary undefined
     // behavior.
     // However in jemalloc for example,
@@ -688,7 +688,7 @@ pub unsafe trait Alloc {
     ///
     /// The returned block of storage may or may not have its contents
     /// initialized. (Extension subtraits might restrict this
-    /// behavior, e.g. to ensure initialization to particular sets of
+    /// behavior, e.g., to ensure initialization to particular sets of
     /// bit patterns.)
     ///
     /// # Safety
@@ -697,7 +697,7 @@ pub unsafe trait Alloc {
     /// if the caller does not ensure that `layout` has non-zero size.
     ///
     /// (Extension subtraits might provide more specific bounds on
-    /// behavior, e.g. guarantee a sentinel address or a null pointer
+    /// behavior, e.g., guarantee a sentinel address or a null pointer
     /// in response to a zero-size allocation request.)
     ///
     /// # Errors
@@ -803,10 +803,10 @@ pub unsafe trait Alloc {
     /// * `new_size` must be greater than zero.
     ///
     /// * `new_size`, when rounded up to the nearest multiple of `layout.align()`,
-    ///   must not overflow (i.e. the rounded value must be less than `usize::MAX`).
+    ///   must not overflow (i.e., the rounded value must be less than `usize::MAX`).
     ///
     /// (Extension subtraits might provide more specific bounds on
-    /// behavior, e.g. guarantee a sentinel address or a null pointer
+    /// behavior, e.g., guarantee a sentinel address or a null pointer
     /// in response to a zero-size allocation request.)
     ///
     /// # Errors
diff --git a/src/libcore/any.rs b/src/libcore/any.rs
index c2113dfd2a0..f521ab994cd 100644
--- a/src/libcore/any.rs
+++ b/src/libcore/any.rs
@@ -126,7 +126,7 @@ impl fmt::Debug for dyn Any {
     }
 }
 
-// Ensure that the result of e.g. joining a thread can be printed and
+// Ensure that the result of e.g., joining a thread can be printed and
 // hence used with `unwrap`. May eventually no longer be needed if
 // dispatch works with upcasting.
 #[stable(feature = "rust1", since = "1.0.0")]
diff --git a/src/libcore/benches/iter.rs b/src/libcore/benches/iter.rs
index 6c597301ac2..b0aca658343 100644
--- a/src/libcore/benches/iter.rs
+++ b/src/libcore/benches/iter.rs
@@ -282,6 +282,12 @@ bench_sums! {
     (0i64..1000000).chain(1000000..).take_while(|&x| x < 1111111)
 }
 
+bench_sums! {
+    bench_cycle_take_sum,
+    bench_cycle_take_ref_sum,
+    (0i64..10000).cycle().take(1000000)
+}
+
 // Checks whether Skip<Zip<A,B>> is as fast as Zip<Skip<A>, Skip<B>>, from
 // https://users.rust-lang.org/t/performance-difference-between-iterator-zip-and-skip-order/15743
 #[bench]
diff --git a/src/libcore/cell.rs b/src/libcore/cell.rs
index d8d51f53377..0a16c92928d 100644
--- a/src/libcore/cell.rs
+++ b/src/libcore/cell.rs
@@ -97,7 +97,7 @@
 //! ## Implementation details of logically-immutable methods
 //!
 //! Occasionally it may be desirable not to expose in an API that there is mutation happening
-//! "under the hood". This may be because logically the operation is immutable, but e.g. caching
+//! "under the hood". This may be because logically the operation is immutable, but e.g., caching
 //! forces the implementation to perform mutation; or because you must employ mutation to implement
 //! a trait method that was originally defined to take `&self`.
 //!
@@ -1227,7 +1227,7 @@ impl<T: ?Sized + fmt::Display> fmt::Display for Ref<'_, T> {
 }
 
 impl<'b, T: ?Sized> RefMut<'b, T> {
-    /// Make a new `RefMut` for a component of the borrowed data, e.g. an enum
+    /// Make a new `RefMut` for a component of the borrowed data, e.g., an enum
     /// variant.
     ///
     /// The `RefCell` is already mutably borrowed, so this cannot fail.
diff --git a/src/libcore/char/mod.rs b/src/libcore/char/mod.rs
index 7e1313747ee..e07a0f5d712 100644
--- a/src/libcore/char/mod.rs
+++ b/src/libcore/char/mod.rs
@@ -131,7 +131,7 @@ pub struct EscapeUnicode {
     state: EscapeUnicodeState,
 
     // The index of the next hex digit to be printed (0 if none),
-    // i.e. the number of remaining hex digits to be printed;
+    // i.e., the number of remaining hex digits to be printed;
     // increasing from the least significant digit: 0x543210
     hex_digit_idx: usize,
 }
diff --git a/src/libcore/clone.rs b/src/libcore/clone.rs
index 46bb580dcdd..225ea3de9cd 100644
--- a/src/libcore/clone.rs
+++ b/src/libcore/clone.rs
@@ -13,7 +13,7 @@
 //! In Rust, some simple types are "implicitly copyable" and when you
 //! assign them or pass them as arguments, the receiver will get a copy,
 //! leaving the original value in place. These types do not require
-//! allocation to copy and do not have finalizers (i.e. they do not
+//! allocation to copy and do not have finalizers (i.e., they do not
 //! contain owned boxes or implement [`Drop`]), so the compiler considers
 //! them cheap and safe to copy. For other types copies must be made
 //! explicitly, by convention implementing the [`Clone`] trait and calling
@@ -93,10 +93,10 @@
 /// In addition to the [implementors listed below][impls],
 /// the following types also implement `Clone`:
 ///
-/// * Function item types (i.e. the distinct types defined for each function)
-/// * Function pointer types (e.g. `fn() -> i32`)
-/// * Array types, for all sizes, if the item type also implements `Clone` (e.g. `[i32; 123456]`)
-/// * Tuple types, if each component also implements `Clone` (e.g. `()`, `(i32, bool)`)
+/// * Function item types (i.e., the distinct types defined for each function)
+/// * Function pointer types (e.g., `fn() -> i32`)
+/// * Array types, for all sizes, if the item type also implements `Clone` (e.g., `[i32; 123456]`)
+/// * Tuple types, if each component also implements `Clone` (e.g., `()`, `(i32, bool)`)
 /// * Closure types, if they capture no value from the environment
 ///   or if all such captured values implement `Clone` themselves.
 ///   Note that variables captured by shared reference always implement `Clone`
diff --git a/src/libcore/convert.rs b/src/libcore/convert.rs
index dbc28ef7cf6..2d4813718f4 100644
--- a/src/libcore/convert.rs
+++ b/src/libcore/convert.rs
@@ -327,7 +327,8 @@ pub trait Into<T>: Sized {
 /// An example usage for error handling:
 ///
 /// ```
-/// use std::io::{self, Read};
+/// use std::fs;
+/// use std::io;
 /// use std::num;
 ///
 /// enum CliError {
@@ -348,9 +349,7 @@ pub trait Into<T>: Sized {
 /// }
 ///
 /// fn open_and_parse_file(file_name: &str) -> Result<i32, CliError> {
-///     let mut file = std::fs::File::open("test")?;
-///     let mut contents = String::new();
-///     file.read_to_string(&mut contents)?;
+///     let mut contents = fs::read_to_string(&file_name)?;
 ///     let num: i32 = contents.trim().parse()?;
 ///     Ok(num)
 /// }
diff --git a/src/libcore/ffi.rs b/src/libcore/ffi.rs
index edeb3b0d368..899fae90946 100644
--- a/src/libcore/ffi.rs
+++ b/src/libcore/ffi.rs
@@ -1,7 +1,6 @@
 #![stable(feature = "", since = "1.30.0")]
 
 #![allow(non_camel_case_types)]
-#![cfg_attr(stage0, allow(dead_code))]
 
 //! Utilities related to FFI bindings.
 
@@ -18,7 +17,7 @@ use ::fmt;
 ///
 /// [`!`]: ../../std/primitive.never.html
 /// [pointer]: ../../std/primitive.pointer.html
-// NB: For LLVM to recognize the void pointer type and by extension
+// N.B., for LLVM to recognize the void pointer type and by extension
 //     functions like malloc(), we need to have it represented as i8* in
 //     LLVM bitcode. The enum used here ensures this and prevents misuse
 //     of the "raw" type by only having private variants.. We need two
@@ -45,6 +44,7 @@ impl fmt::Debug for c_void {
 /// Basic implementation of a `va_list`.
 #[cfg(any(all(not(target_arch = "aarch64"), not(target_arch = "powerpc"),
               not(target_arch = "x86_64")),
+          all(target_arch = "aarch4", target_os = "ios"),
           windows))]
 #[unstable(feature = "c_variadic",
            reason = "the `c_variadic` feature has not been properly tested on \
@@ -122,7 +122,6 @@ struct VaListImpl {
                      all supported platforms",
            issue = "27745")]
 #[repr(transparent)]
-#[cfg(not(stage0))]
 pub struct VaList<'a>(&'a mut VaListImpl);
 
 // The VaArgSafe trait needs to be used in public interfaces, however, the trait
@@ -172,7 +171,6 @@ impl<T> sealed_trait::VaArgSafe for *mut T {}
            issue = "27745")]
 impl<T> sealed_trait::VaArgSafe for *const T {}
 
-#[cfg(not(stage0))]
 impl<'a> VaList<'a> {
     /// Advance to the next arg.
     #[unstable(feature = "c_variadic",
@@ -192,6 +190,7 @@ impl<'a> VaList<'a> {
             where F: for<'copy> FnOnce(VaList<'copy>) -> R {
         #[cfg(any(all(not(target_arch = "aarch64"), not(target_arch = "powerpc"),
                       not(target_arch = "x86_64")),
+                  all(target_arch = "aarch4", target_os = "ios"),
                   windows))]
         let mut ap = va_copy(self);
         #[cfg(all(any(target_arch = "aarch64", target_arch = "powerpc", target_arch = "x86_64"),
@@ -206,7 +205,6 @@ impl<'a> VaList<'a> {
     }
 }
 
-#[cfg(not(stage0))]
 extern "rust-intrinsic" {
     /// Destroy the arglist `ap` after initialization with `va_start` or
     /// `va_copy`.
diff --git a/src/libcore/fmt/mod.rs b/src/libcore/fmt/mod.rs
index 75ec0d7d50b..8e0caa5ae33 100644
--- a/src/libcore/fmt/mod.rs
+++ b/src/libcore/fmt/mod.rs
@@ -609,10 +609,15 @@ pub trait Debug {
 /// println!("The origin is: {}", origin);
 /// ```
 #[rustc_on_unimplemented(
+    on(
+        _Self="std::path::Path",
+        label="`{Self}` cannot be formatted with the default formatter; call `.display()` on it",
+        note="call `.display()` or `.to_string_lossy()` to safely print paths, \
+              as they may contain non-Unicode data"
+    ),
     message="`{Self}` doesn't implement `{Display}`",
     label="`{Self}` cannot be formatted with the default formatter",
-    note="in format strings you may be able to use `{{:?}}` \
-          (or {{:#?}} for pretty-print) instead",
+    note="in format strings you may be able to use `{{:?}}` (or {{:#?}} for pretty-print) instead",
 )]
 #[doc(alias = "{}")]
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -1381,7 +1386,7 @@ impl<'a> Formatter<'a> {
         for part in formatted.parts {
             match *part {
                 flt2dec::Part::Zero(mut nzeroes) => {
-                    const ZEROES: &'static str = // 64 zeroes
+                    const ZEROES: &str = // 64 zeroes
                         "0000000000000000000000000000000000000000000000000000000000000000";
                     while nzeroes > ZEROES.len() {
                         self.buf.write_str(ZEROES)?;
diff --git a/src/libcore/future/future.rs b/src/libcore/future/future.rs
index 0c870f9e404..5dee1d6dd3a 100644
--- a/src/libcore/future/future.rs
+++ b/src/libcore/future/future.rs
@@ -33,6 +33,7 @@ use task::{Poll, LocalWaker};
 ///
 /// When using a future, you generally won't call `poll` directly, but instead
 /// `await!` the value.
+#[must_use]
 pub trait Future {
     /// The result of the `Future`.
     type Output;
diff --git a/src/libcore/hash/mod.rs b/src/libcore/hash/mod.rs
index bbebadd452a..3e59ee1f8e5 100644
--- a/src/libcore/hash/mod.rs
+++ b/src/libcore/hash/mod.rs
@@ -408,7 +408,7 @@ impl<H: Hasher + ?Sized> Hasher for &mut H {
 
 /// A trait for creating instances of [`Hasher`].
 ///
-/// A `BuildHasher` is typically used (e.g. by [`HashMap`]) to create
+/// A `BuildHasher` is typically used (e.g., by [`HashMap`]) to create
 /// [`Hasher`]s for each key such that they are hashed independently of one
 /// another, since [`Hasher`]s contain state.
 ///
diff --git a/src/libcore/hint.rs b/src/libcore/hint.rs
index f4e96e67b2c..0bfdd937abd 100644
--- a/src/libcore/hint.rs
+++ b/src/libcore/hint.rs
@@ -24,7 +24,7 @@ use intrinsics;
 /// therefore will eliminate all branches that reach to a call to
 /// `unreachable_unchecked()`.
 ///
-/// Like all instances of UB, if this assumption turns out to be wrong, i.e. the
+/// Like all instances of UB, if this assumption turns out to be wrong, i.e., the
 /// `unreachable_unchecked()` call is actually reachable among all possible
 /// control flow, the compiler will apply the wrong optimization strategy, and
 /// may sometimes even corrupt seemingly unrelated code, causing
diff --git a/src/libcore/intrinsics.rs b/src/libcore/intrinsics.rs
index 16f0299c18b..b94d5b4adcf 100644
--- a/src/libcore/intrinsics.rs
+++ b/src/libcore/intrinsics.rs
@@ -52,7 +52,7 @@
 pub use ptr::drop_in_place;
 
 extern "rust-intrinsic" {
-    // NB: These intrinsics take raw pointers because they mutate aliased
+    // N.B., these intrinsics take raw pointers because they mutate aliased
     // memory, which is not valid for either `&` or `&mut`.
 
     /// Stores a value if the current value is the same as the `old` value.
@@ -635,7 +635,7 @@ extern "rust-intrinsic" {
     /// Tells LLVM that this point in the code is not reachable, enabling
     /// further optimizations.
     ///
-    /// NB: This is very different from the `unreachable!()` macro: Unlike the
+    /// N.B., this is very different from the `unreachable!()` macro: Unlike the
     /// macro, which panics when it is executed, it is *undefined behavior* to
     /// reach code marked with this function.
     ///
@@ -718,7 +718,6 @@ extern "rust-intrinsic" {
     pub fn uninit<T>() -> T;
 
     /// Moves a value out of scope without running drop glue.
-    #[cfg(not(stage0))]
     pub fn forget<T: ?Sized>(_: T);
 
     /// Reinterprets the bits of a value of one type as another type.
@@ -1476,14 +1475,12 @@ extern "rust-intrinsic" {
     /// The stabilized versions of this intrinsic are available on the integer
     /// primitives via the `rotate_left` method. For example,
     /// [`std::u32::rotate_left`](../../std/primitive.u32.html#method.rotate_left)
-    #[cfg(not(stage0))]
     pub fn rotate_left<T>(x: T, y: T) -> T;
 
     /// Performs rotate right.
     /// The stabilized versions of this intrinsic are available on the integer
     /// primitives via the `rotate_right` method. For example,
     /// [`std::u32::rotate_right`](../../std/primitive.u32.html#method.rotate_right)
-    #[cfg(not(stage0))]
     pub fn rotate_right<T>(x: T, y: T) -> T;
 
     /// Returns (a + b) mod 2<sup>N</sup>, where N is the width of T in bits.
diff --git a/src/libcore/iter/iterator.rs b/src/libcore/iter/iterator.rs
index 80bd5698c47..d0b0fd1ab31 100644
--- a/src/libcore/iter/iterator.rs
+++ b/src/libcore/iter/iterator.rs
@@ -87,7 +87,7 @@ fn _assert_is_object_safe(_: &dyn Iterator<Item=()>) {}
     on(
         _Self="[]",
         label="borrow the array with `&` or call `.iter()` on it to iterate over it",
-        note="arrays are not an iterators, but slices like the following are: `&[1, 2, 3]`"
+        note="arrays are not iterators, but slices like the following are: `&[1, 2, 3]`"
     ),
     on(
         _Self="{integral}",
@@ -98,6 +98,7 @@ fn _assert_is_object_safe(_: &dyn Iterator<Item=()>) {}
     message="`{Self}` is not an iterator"
 )]
 #[doc(spotlight)]
+#[must_use]
 pub trait Iterator {
     /// The type of the elements being iterated over.
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -154,7 +155,7 @@ pub trait Iterator {
     ///
     /// `size_hint()` is primarily intended to be used for optimizations such as
     /// reserving space for the elements of the iterator, but must not be
-    /// trusted to e.g. omit bounds checks in unsafe code. An incorrect
+    /// trusted to e.g., omit bounds checks in unsafe code. An incorrect
     /// implementation of `size_hint()` should not lead to memory safety
     /// violations.
     ///
diff --git a/src/libcore/iter/mod.rs b/src/libcore/iter/mod.rs
index de1a318cfb2..aa130754f83 100644
--- a/src/libcore/iter/mod.rs
+++ b/src/libcore/iter/mod.rs
@@ -429,6 +429,9 @@ impl<I> Iterator for Rev<I> where I: DoubleEndedIterator {
     #[inline]
     fn size_hint(&self) -> (usize, Option<usize>) { self.iter.size_hint() }
 
+    #[inline]
+    fn nth(&mut self, n: usize) -> Option<<I as Iterator>::Item> { self.iter.nth_back(n) }
+
     fn try_fold<B, F, R>(&mut self, init: B, f: F) -> R where
         Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try<Ok=B>
     {
@@ -461,6 +464,9 @@ impl<I> DoubleEndedIterator for Rev<I> where I: DoubleEndedIterator {
     #[inline]
     fn next_back(&mut self) -> Option<<I as Iterator>::Item> { self.iter.next() }
 
+    #[inline]
+    fn nth_back(&mut self, n: usize) -> Option<<I as Iterator>::Item> { self.iter.nth(n) }
+
     fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R where
         Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try<Ok=B>
     {
@@ -702,7 +708,9 @@ unsafe impl<'a, I, T: 'a> TrustedRandomAccess for Cloned<I>
     }
 
     #[inline]
-    fn may_have_side_effect() -> bool { false }
+    fn may_have_side_effect() -> bool {
+        I::may_have_side_effect()
+    }
 }
 
 #[unstable(feature = "trusted_len", issue = "37572")]
@@ -1953,18 +1961,11 @@ impl<I: Iterator> Iterator for Peekable<I> {
 
     #[inline]
     fn nth(&mut self, n: usize) -> Option<I::Item> {
-        // FIXME(#43234): merge these when borrow-checking gets better.
-        if n == 0 {
-            match self.peeked.take() {
-                Some(v) => v,
-                None => self.iter.nth(n),
-            }
-        } else {
-            match self.peeked.take() {
-                Some(None) => None,
-                Some(Some(_)) => self.iter.nth(n - 1),
-                None => self.iter.nth(n),
-            }
+        match self.peeked.take() {
+            Some(None) => None,
+            Some(v @ Some(_)) if n == 0 => v,
+            Some(Some(_)) => self.iter.nth(n - 1),
+            None => self.iter.nth(n),
         }
     }
 
@@ -2063,14 +2064,8 @@ impl<I: Iterator> Peekable<I> {
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn peek(&mut self) -> Option<&I::Item> {
-        if self.peeked.is_none() {
-            self.peeked = Some(self.iter.next());
-        }
-        match self.peeked {
-            Some(Some(ref value)) => Some(value),
-            Some(None) => None,
-            _ => unreachable!(),
-        }
+        let iter = &mut self.iter;
+        self.peeked.get_or_insert_with(|| iter.next()).as_ref()
     }
 }
 
@@ -2207,8 +2202,12 @@ impl<I: Iterator, P> Iterator for TakeWhile<I, P>
 
     #[inline]
     fn size_hint(&self) -> (usize, Option<usize>) {
-        let (_, upper) = self.iter.size_hint();
-        (0, upper) // can't know a lower bound, due to the predicate
+        if self.flag {
+            (0, Some(0))
+        } else {
+            let (_, upper) = self.iter.size_hint();
+            (0, upper) // can't know a lower bound, due to the predicate
+        }
     }
 
     #[inline]
@@ -2419,6 +2418,10 @@ impl<I> Iterator for Take<I> where I: Iterator{
 
     #[inline]
     fn size_hint(&self) -> (usize, Option<usize>) {
+        if self.n == 0 {
+            return (0, Some(0));
+        }
+
         let (lower, upper) = self.iter.size_hint();
 
         let lower = cmp::min(lower, self.n);
diff --git a/src/libcore/iter/traits.rs b/src/libcore/iter/traits.rs
index d2c5a3bed28..727a60e3596 100644
--- a/src/libcore/iter/traits.rs
+++ b/src/libcore/iter/traits.rs
@@ -427,6 +427,62 @@ pub trait DoubleEndedIterator: Iterator {
     #[stable(feature = "rust1", since = "1.0.0")]
     fn next_back(&mut self) -> Option<Self::Item>;
 
+    /// Returns the `n`th element from the end of the iterator.
+    ///
+    /// This is essentially the reversed version of [`nth`]. Although like most indexing
+    /// operations, the count starts from zero, so `nth_back(0)` returns the first value fro
+    /// the end, `nth_back(1)` the second, and so on.
+    ///
+    /// Note that all elements between the end and the returned element will be
+    /// consumed, including the returned element. This also means that calling
+    /// `nth_back(0)` multiple times on the same iterator will return different
+    /// elements.
+    ///
+    /// `nth_back()` will return [`None`] if `n` is greater than or equal to the length of the
+    /// iterator.
+    ///
+    /// [`None`]: ../../std/option/enum.Option.html#variant.None
+    /// [`nth`]: ../../std/iter/trait.Iterator.html#method.nth
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// #![feature(iter_nth_back)]
+    /// let a = [1, 2, 3];
+    /// assert_eq!(a.iter().nth_back(2), Some(&1));
+    /// ```
+    ///
+    /// Calling `nth_back()` multiple times doesn't rewind the iterator:
+    ///
+    /// ```
+    /// #![feature(iter_nth_back)]
+    /// let a = [1, 2, 3];
+    ///
+    /// let mut iter = a.iter();
+    ///
+    /// assert_eq!(iter.nth_back(1), Some(&2));
+    /// assert_eq!(iter.nth_back(1), None);
+    /// ```
+    ///
+    /// Returning `None` if there are less than `n + 1` elements:
+    ///
+    /// ```
+    /// #![feature(iter_nth_back)]
+    /// let a = [1, 2, 3];
+    /// assert_eq!(a.iter().nth_back(10), None);
+    /// ```
+    #[inline]
+    #[unstable(feature = "iter_nth_back", issue = "56995")]
+    fn nth_back(&mut self, mut n: usize) -> Option<Self::Item> {
+        for x in self.rev() {
+            if n == 0 { return Some(x) }
+            n -= 1;
+        }
+        None
+    }
+
     /// This is the reverse version of [`try_fold()`]: it takes elements
     /// starting from the back of the iterator.
     ///
@@ -461,8 +517,11 @@ pub trait DoubleEndedIterator: Iterator {
     /// ```
     #[inline]
     #[stable(feature = "iterator_try_fold", since = "1.27.0")]
-    fn try_rfold<B, F, R>(&mut self, init: B, mut f: F) -> R where
-        Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try<Ok=B>
+    fn try_rfold<B, F, R>(&mut self, init: B, mut f: F) -> R
+    where
+        Self: Sized,
+        F: FnMut(B, Self::Item) -> R,
+        R: Try<Ok=B>
     {
         let mut accum = init;
         while let Some(x) = self.next_back() {
@@ -524,8 +583,10 @@ pub trait DoubleEndedIterator: Iterator {
     /// ```
     #[inline]
     #[stable(feature = "iter_rfold", since = "1.27.0")]
-    fn rfold<B, F>(mut self, accum: B, mut f: F) -> B where
-        Self: Sized, F: FnMut(B, Self::Item) -> B,
+    fn rfold<B, F>(mut self, accum: B, mut f: F) -> B
+    where
+        Self: Sized,
+        F: FnMut(B, Self::Item) -> B,
     {
         self.try_rfold(accum, move |acc, x| Ok::<B, !>(f(acc, x))).unwrap()
     }
@@ -574,7 +635,8 @@ pub trait DoubleEndedIterator: Iterator {
     /// ```
     #[inline]
     #[stable(feature = "iter_rfind", since = "1.27.0")]
-    fn rfind<P>(&mut self, mut predicate: P) -> Option<Self::Item> where
+    fn rfind<P>(&mut self, mut predicate: P) -> Option<Self::Item>
+    where
         Self: Sized,
         P: FnMut(&Self::Item) -> bool
     {
@@ -587,7 +649,12 @@ pub trait DoubleEndedIterator: Iterator {
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, I: DoubleEndedIterator + ?Sized> DoubleEndedIterator for &'a mut I {
-    fn next_back(&mut self) -> Option<I::Item> { (**self).next_back() }
+    fn next_back(&mut self) -> Option<I::Item> {
+        (**self).next_back()
+    }
+    fn nth_back(&mut self, n: usize) -> Option<I::Item> {
+        (**self).nth_back(n)
+    }
 }
 
 /// An iterator that knows its exact length.
@@ -770,7 +837,7 @@ pub trait Product<A = Self>: Sized {
     fn product<I: Iterator<Item=A>>(iter: I) -> Self;
 }
 
-// NB: explicitly use Add and Mul here to inherit overflow checks
+// N.B., explicitly use Add and Mul here to inherit overflow checks
 macro_rules! integer_sum_product {
     (@impls $zero:expr, $one:expr, #[$attr:meta], $($a:ty)*) => ($(
         #[$attr]
diff --git a/src/libcore/lib.rs b/src/libcore/lib.rs
index 726e891df0c..2124458dc55 100644
--- a/src/libcore/lib.rs
+++ b/src/libcore/lib.rs
@@ -71,6 +71,7 @@
 
 #![no_core]
 #![deny(missing_docs)]
+#![deny(intra_doc_link_resolution_failure)]
 #![deny(missing_debug_implementations)]
 
 #![feature(allow_internal_unstable)]
@@ -92,6 +93,7 @@
 #![feature(link_llvm_intrinsics)]
 #![feature(never_type)]
 #![feature(nll)]
+#![feature(bind_by_move_pattern_guards)]
 #![feature(exhaustive_patterns)]
 #![feature(no_core)]
 #![feature(on_unimplemented)]
@@ -120,7 +122,6 @@
 #![feature(const_slice_len)]
 #![feature(const_str_as_bytes)]
 #![feature(const_str_len)]
-#![feature(const_let)]
 #![feature(const_int_rotate)]
 #![feature(const_int_wrapping)]
 #![feature(const_int_sign)]
@@ -250,9 +251,7 @@ macro_rules! vector_impl { ($([$f:ident, $($args:tt)*]),*) => { $($f!($($args)*)
 #[path = "../stdsimd/coresimd/mod.rs"]
 #[allow(missing_docs, missing_debug_implementations, dead_code, unused_imports)]
 #[unstable(feature = "stdsimd", issue = "48556")]
-#[cfg(not(stage0))] // allow changes to how stdsimd works in stage0
 mod coresimd;
 
 #[stable(feature = "simd_arch", since = "1.27.0")]
-#[cfg(not(stage0))]
 pub use coresimd::arch;
diff --git a/src/libcore/macros.rs b/src/libcore/macros.rs
index 8b1855800c2..5ba0e949483 100644
--- a/src/libcore/macros.rs
+++ b/src/libcore/macros.rs
@@ -238,6 +238,10 @@ macro_rules! debug_assert_ne {
 /// with converting downstream errors.
 ///
 /// The `?` operator was added to replace `try!` and should be used instead.
+/// Furthermore, `try` is a reserved word in Rust 2018, so if you must use
+/// it, you will need to use the [raw-identifier syntax][ris]: `r#try`.
+///
+/// [ris]: https://doc.rust-lang.org/nightly/rust-by-example/compatibility/raw_identifiers.html
 ///
 /// `try!` matches the given [`Result`]. In case of the `Ok` variant, the
 /// expression has the value of the wrapped value.
diff --git a/src/libcore/marker.rs b/src/libcore/marker.rs
index 3bcdfabbb24..d3d16127ed5 100644
--- a/src/libcore/marker.rs
+++ b/src/libcore/marker.rs
@@ -274,10 +274,10 @@ pub trait Unsize<T: ?Sized> {
 /// In addition to the [implementors listed below][impls],
 /// the following types also implement `Copy`:
 ///
-/// * Function item types (i.e. the distinct types defined for each function)
-/// * Function pointer types (e.g. `fn() -> i32`)
-/// * Array types, for all sizes, if the item type also implements `Copy` (e.g. `[i32; 123456]`)
-/// * Tuple types, if each component also implements `Copy` (e.g. `()`, `(i32, bool)`)
+/// * Function item types (i.e., the distinct types defined for each function)
+/// * Function pointer types (e.g., `fn() -> i32`)
+/// * Array types, for all sizes, if the item type also implements `Copy` (e.g., `[i32; 123456]`)
+/// * Tuple types, if each component also implements `Copy` (e.g., `()`, `(i32, bool)`)
 /// * Closure types, if they capture no value from the environment
 ///   or if all such captured values implement `Copy` themselves.
 ///   Note that variables captured by shared reference always implement `Copy`
@@ -596,7 +596,7 @@ mod impls {
 /// This affects, for example, whether a `static` of that type is
 /// placed in read-only static memory or writable static memory.
 #[lang = "freeze"]
-unsafe auto trait Freeze {}
+pub(crate) unsafe auto trait Freeze {}
 
 impl<T: ?Sized> !Freeze for UnsafeCell<T> {}
 unsafe impl<T: ?Sized> Freeze for PhantomData<T> {}
@@ -640,15 +640,15 @@ unsafe impl<T: ?Sized> Freeze for &mut T {}
 #[unstable(feature = "pin", issue = "49150")]
 pub auto trait Unpin {}
 
-/// A type which does not implement `Unpin`.
+/// A marker type which does not implement `Unpin`.
 ///
-/// If a type contains a `Pinned`, it will not implement `Unpin` by default.
+/// If a type contains a `PhantomPinned`, it will not implement `Unpin` by default.
 #[unstable(feature = "pin", issue = "49150")]
 #[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
-pub struct Pinned;
+pub struct PhantomPinned;
 
 #[unstable(feature = "pin", issue = "49150")]
-impl !Unpin for Pinned {}
+impl !Unpin for PhantomPinned {}
 
 #[unstable(feature = "pin", issue = "49150")]
 impl<'a, T: ?Sized + 'a> Unpin for &'a T {}
diff --git a/src/libcore/mem.rs b/src/libcore/mem.rs
index e4b2800ae21..87dde906601 100644
--- a/src/libcore/mem.rs
+++ b/src/libcore/mem.rs
@@ -149,7 +149,6 @@ pub fn forget<T>(t: T) {
 ///
 /// [`forget`]: fn.forget.html
 #[inline]
-#[cfg(not(stage0))]
 #[unstable(feature = "forget_unsized", issue = "0")]
 pub fn forget_unsized<T: ?Sized>(t: T) {
     unsafe { intrinsics::forget(t) }
@@ -305,7 +304,7 @@ pub const fn size_of<T>() -> usize {
 /// Returns the size of the pointed-to value in bytes.
 ///
 /// This is usually the same as `size_of::<T>()`. However, when `T` *has* no
-/// statically known size, e.g. a slice [`[T]`][slice] or a [trait object],
+/// statically known size, e.g., a slice [`[T]`][slice] or a [trait object],
 /// then `size_of_val` can be used to get the dynamically-known size.
 ///
 /// [slice]: ../../std/primitive.slice.html
@@ -531,6 +530,12 @@ pub unsafe fn zeroed<T>() -> T {
 /// it goes out of scope (and therefore would be dropped). Note that this
 /// includes a `panic` occurring and unwinding the stack suddenly.
 ///
+/// If you partially initialize an array, you may need to use
+/// [`ptr::drop_in_place`][drop_in_place] to remove the elements you have fully
+/// initialized followed by [`mem::forget`][mem_forget] to prevent drop running
+/// on the array. If a partially allocated array is dropped this will lead to
+/// undefined behaviour.
+///
 /// # Examples
 ///
 /// Here's how to safely initialize an array of [`Vec`]s.
@@ -584,11 +589,44 @@ pub unsafe fn zeroed<T>() -> T {
 /// println!("{:?}", &data[0]);
 /// ```
 ///
+/// This example shows how to handle partially initialized arrays, which could
+/// be found in low-level datastructures.
+///
+/// ```
+/// use std::mem;
+/// use std::ptr;
+///
+/// // Count the number of elements we have assigned.
+/// let mut data_len: usize = 0;
+/// let mut data: [String; 1000];
+///
+/// unsafe {
+///     data = mem::uninitialized();
+///
+///     for elem in &mut data[0..500] {
+///         ptr::write(elem, String::from("hello"));
+///         data_len += 1;
+///     }
+///
+///     // For each item in the array, drop if we allocated it.
+///     for i in &mut data[0..data_len] {
+///         ptr::drop_in_place(i);
+///     }
+/// }
+/// // Forget the data. If this is allowed to drop, you may see a crash such as:
+/// // 'mem_uninit_test(2457,0x7fffb55dd380) malloc: *** error for object
+/// // 0x7ff3b8402920: pointer being freed was not allocated'
+/// mem::forget(data);
+/// ```
+///
 /// [`Vec`]: ../../std/vec/struct.Vec.html
 /// [`vec!`]: ../../std/macro.vec.html
 /// [`Clone`]: ../../std/clone/trait.Clone.html
 /// [ub]: ../../reference/behavior-considered-undefined.html
 /// [write]: ../ptr/fn.write.html
+/// [drop_in_place]: ../ptr/fn.drop_in_place.html
+/// [mem_zeroed]: fn.zeroed.html
+/// [mem_forget]: fn.forget.html
 /// [copy]: ../intrinsics/fn.copy.html
 /// [copy_no]: ../intrinsics/fn.copy_nonoverlapping.html
 /// [`Drop`]: ../ops/trait.Drop.html
@@ -985,6 +1023,9 @@ impl<T> ManuallyDrop<T> {
     ///
     /// This function semantically moves out the contained value without preventing further usage.
     /// It is up to the user of this method to ensure that this container is not used again.
+    ///
+    /// [`ManuallyDrop::drop`]: #method.drop
+    /// [`ManuallyDrop::into_inner`]: #method.into_inner
     #[must_use = "if you don't need the value, you can use `ManuallyDrop::drop` instead"]
     #[unstable(feature = "manually_drop_take", issue = "55422")]
     #[inline]
@@ -1119,7 +1160,7 @@ impl<T> MaybeUninit<T> {
     /// It is up to the caller to guarantee that the `MaybeUninit` really is in an initialized
     /// state, otherwise this will immediately cause undefined behavior.
     // FIXME(#53491): We currently rely on the above being incorrect, i.e., we have references
-    // to uninitialized data (e.g. in `libcore/fmt/float.rs`).  We should make
+    // to uninitialized data (e.g., in `libcore/fmt/float.rs`).  We should make
     // a final decision about the rules before stabilization.
     #[unstable(feature = "maybe_uninit", issue = "53491")]
     #[inline(always)]
diff --git a/src/libcore/nonzero.rs b/src/libcore/nonzero.rs
index 436cd1fc057..a89c6ca60cb 100644
--- a/src/libcore/nonzero.rs
+++ b/src/libcore/nonzero.rs
@@ -11,14 +11,23 @@
 //! Exposes the NonZero lang item which provides optimization hints.
 
 use ops::{CoerceUnsized, DispatchFromDyn};
+use marker::Freeze;
 
 /// A wrapper type for raw pointers and integers that will never be
 /// NULL or 0 that might allow certain optimizations.
 #[rustc_layout_scalar_valid_range_start(1)]
-#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
+#[derive(Copy, Eq, PartialEq, Ord, PartialOrd, Hash)]
 #[repr(transparent)]
-pub(crate) struct NonZero<T>(pub(crate) T);
+pub(crate) struct NonZero<T: Freeze>(pub(crate) T);
 
-impl<T: CoerceUnsized<U>, U> CoerceUnsized<NonZero<U>> for NonZero<T> {}
+// Do not call `T::clone` as theoretically it could turn the field into `0`
+// invalidating `NonZero`'s invariant.
+impl<T: Copy + Freeze> Clone for NonZero<T> {
+    fn clone(&self) -> Self {
+        unsafe { NonZero(self.0) }
+    }
+}
 
-impl<T: DispatchFromDyn<U>, U> DispatchFromDyn<NonZero<U>> for NonZero<T> {}
+impl<T: CoerceUnsized<U> + Freeze, U: Freeze> CoerceUnsized<NonZero<U>> for NonZero<T> {}
+
+impl<T: DispatchFromDyn<U> + Freeze, U: Freeze> DispatchFromDyn<NonZero<U>> for NonZero<T> {}
diff --git a/src/libcore/num/bignum.rs b/src/libcore/num/bignum.rs
index 732a02e8c42..2bfb49c0682 100644
--- a/src/libcore/num/bignum.rs
+++ b/src/libcore/num/bignum.rs
@@ -183,7 +183,7 @@ macro_rules! define_bignum {
                 let nonzero = &digits[..end];
 
                 if nonzero.is_empty() {
-                    // There are no non-zero digits, i.e. the number is zero.
+                    // There are no non-zero digits, i.e., the number is zero.
                     return 0;
                 }
                 // This could be optimized with leading_zeros() and bit shifts, but that's
diff --git a/src/libcore/num/dec2flt/algorithm.rs b/src/libcore/num/dec2flt/algorithm.rs
index ccf3950c2ba..c3a983d0f0e 100644
--- a/src/libcore/num/dec2flt/algorithm.rs
+++ b/src/libcore/num/dec2flt/algorithm.rs
@@ -61,9 +61,9 @@ mod fpu_precision {
     ///
     /// The only field which is relevant for the following code is PC, Precision Control. This
     /// field determines the precision of the operations performed by the  FPU. It can be set to:
-    ///  - 0b00, single precision i.e. 32-bits
-    ///  - 0b10, double precision i.e. 64-bits
-    ///  - 0b11, double extended precision i.e. 80-bits (default state)
+    ///  - 0b00, single precision i.e., 32-bits
+    ///  - 0b10, double precision i.e., 64-bits
+    ///  - 0b11, double extended precision i.e., 80-bits (default state)
     /// The 0b01 value is reserved and should not be used.
     pub struct FPUControlWord(u16);
 
diff --git a/src/libcore/num/dec2flt/rawfp.rs b/src/libcore/num/dec2flt/rawfp.rs
index 38f4e4687a9..18c30e29c79 100644
--- a/src/libcore/num/dec2flt/rawfp.rs
+++ b/src/libcore/num/dec2flt/rawfp.rs
@@ -349,7 +349,7 @@ pub fn prev_float<T: RawFloat>(x: T) -> T {
 }
 
 // Find the smallest floating point number strictly larger than the argument.
-// This operation is saturating, i.e. next_float(inf) == inf.
+// This operation is saturating, i.e., next_float(inf) == inf.
 // Unlike most code in this module, this function does handle zero, subnormals, and infinities.
 // However, like all other code here, it does not deal with NaN and negative numbers.
 pub fn next_float<T: RawFloat>(x: T) -> T {
diff --git a/src/libcore/num/flt2dec/mod.rs b/src/libcore/num/flt2dec/mod.rs
index d58015beecb..097240e58ae 100644
--- a/src/libcore/num/flt2dec/mod.rs
+++ b/src/libcore/num/flt2dec/mod.rs
@@ -23,7 +23,7 @@ representation `V = 0.d[0..n-1] * 10^k` such that:
 - `d[0]` is non-zero.
 
 - It's correctly rounded when parsed back: `v - minus < V < v + plus`.
-  Furthermore it is shortest such one, i.e. there is no representation
+  Furthermore it is shortest such one, i.e., there is no representation
   with less than `n` digits that is correctly rounded.
 
 - It's closest to the original value: `abs(V - v) <= 10^(k-n) / 2`. Note that
@@ -398,7 +398,7 @@ fn determine_sign(sign: Sign, decoded: &FullDecoded, negative: bool) -> &'static
 /// given number of fractional digits. The result is stored to the supplied parts
 /// array while utilizing given byte buffer as a scratch. `upper` is currently
 /// unused but left for the future decision to change the case of non-finite values,
-/// i.e. `inf` and `nan`. The first part to be rendered is always a `Part::Sign`
+/// i.e., `inf` and `nan`. The first part to be rendered is always a `Part::Sign`
 /// (which can be an empty string if no sign is rendered).
 ///
 /// `format_shortest` should be the underlying digit-generation function.
@@ -591,7 +591,7 @@ pub fn to_exact_exp_str<'a, T, F>(mut format_exact: F, v: T,
 /// given number of fractional digits. The result is stored to the supplied parts
 /// array while utilizing given byte buffer as a scratch. `upper` is currently
 /// unused but left for the future decision to change the case of non-finite values,
-/// i.e. `inf` and `nan`. The first part to be rendered is always a `Part::Sign`
+/// i.e., `inf` and `nan`. The first part to be rendered is always a `Part::Sign`
 /// (which can be an empty string if no sign is rendered).
 ///
 /// `format_exact` should be the underlying digit-generation function.
diff --git a/src/libcore/num/flt2dec/strategy/dragon.rs b/src/libcore/num/flt2dec/strategy/dragon.rs
index aa6a08cb205..cda0773afbd 100644
--- a/src/libcore/num/flt2dec/strategy/dragon.rs
+++ b/src/libcore/num/flt2dec/strategy/dragon.rs
@@ -81,11 +81,11 @@ pub fn format_shortest(d: &Decoded, buf: &mut [u8]) -> (/*#digits*/ usize, /*exp
     // - followed by `(mant + 2 * plus) * 2^exp` in the original type.
     //
     // obviously, `minus` and `plus` cannot be zero. (for infinities, we use out-of-range values.)
-    // also we assume that at least one digit is generated, i.e. `mant` cannot be zero too.
+    // also we assume that at least one digit is generated, i.e., `mant` cannot be zero too.
     //
     // this also means that any number between `low = (mant - minus) * 2^exp` and
     // `high = (mant + plus) * 2^exp` will map to this exact floating point number,
-    // with bounds included when the original mantissa was even (i.e. `!mant_was_odd`).
+    // with bounds included when the original mantissa was even (i.e., `!mant_was_odd`).
 
     assert!(d.mant > 0);
     assert!(d.minus > 0);
@@ -172,7 +172,7 @@ pub fn format_shortest(d: &Decoded, buf: &mut [u8]) -> (/*#digits*/ usize, /*exp
         // - `high - v = plus / scale * 10^(k-n)`
         //
         // assume that `d[0..n-1]` is the shortest representation between `low` and `high`,
-        // i.e. `d[0..n-1]` satisfies both of the following but `d[0..n-2]` doesn't:
+        // i.e., `d[0..n-1]` satisfies both of the following but `d[0..n-2]` doesn't:
         // - `low < d[0..n-1] * 10^(k-n) < high` (bijectivity: digits round to `v`); and
         // - `abs(v / 10^(k-n) - d[0..n-1]) <= 1/2` (the last digit is correct).
         //
@@ -304,7 +304,7 @@ pub fn format_exact(d: &Decoded, buf: &mut [u8], limit: i16) -> (/*#digits*/ usi
 
     // rounding up if we stop in the middle of digits
     // if the following digits are exactly 5000..., check the prior digit and try to
-    // round to even (i.e. avoid rounding up when the prior digit is even).
+    // round to even (i.e., avoid rounding up when the prior digit is even).
     let order = mant.cmp(scale.mul_small(5));
     if order == Ordering::Greater || (order == Ordering::Equal &&
                                       (len == 0 || buf[len-1] & 1 == 1)) {
diff --git a/src/libcore/num/flt2dec/strategy/grisu.rs b/src/libcore/num/flt2dec/strategy/grisu.rs
index effe073c381..3e76feca885 100644
--- a/src/libcore/num/flt2dec/strategy/grisu.rs
+++ b/src/libcore/num/flt2dec/strategy/grisu.rs
@@ -242,7 +242,7 @@ pub fn format_shortest_opt(d: &Decoded,
     //
     // find the digit length `kappa` between `(minus1, plus1)` as per Theorem 6.2.
     // Theorem 6.2 can be adopted to exclude `x` by requiring `y mod 10^k < y - x` instead.
-    // (e.g. `x` = 32000, `y` = 32777; `kappa` = 2 since `y mod 10^3 = 777 < y - x = 777`.)
+    // (e.g., `x` = 32000, `y` = 32777; `kappa` = 2 since `y mod 10^3 = 777 < y - x = 777`.)
     // the algorithm relies on the later verification phase to exclude `y`.
     let delta1 = plus1 - minus1;
 //  let delta1int = (delta1 >> e) as usize; // only for explanation
@@ -362,19 +362,19 @@ pub fn format_shortest_opt(d: &Decoded,
             // proceed, but we then have at least one valid representation known to be closest to
             // `v + 1 ulp` anyway. we will denote them as TC1 through TC3 for brevity.
             //
-            // TC1: `w(n) <= v + 1 ulp`, i.e. this is the last repr that can be the closest one.
+            // TC1: `w(n) <= v + 1 ulp`, i.e., this is the last repr that can be the closest one.
             // this is equivalent to `plus1 - w(n) = plus1w(n) >= plus1 - (v + 1 ulp) = plus1v_up`.
             // combined with TC2 (which checks if `w(n+1)` is valid), this prevents the possible
             // overflow on the calculation of `plus1w(n)`.
             //
-            // TC2: `w(n+1) < minus1`, i.e. the next repr definitely does not round to `v`.
+            // TC2: `w(n+1) < minus1`, i.e., the next repr definitely does not round to `v`.
             // this is equivalent to `plus1 - w(n) + 10^kappa = plus1w(n) + 10^kappa >
             // plus1 - minus1 = threshold`. the left hand side can overflow, but we know
             // `threshold > plus1v`, so if TC1 is false, `threshold - plus1w(n) >
             // threshold - (plus1v - 1 ulp) > 1 ulp` and we can safely test if
             // `threshold - plus1w(n) < 10^kappa` instead.
             //
-            // TC3: `abs(w(n) - (v + 1 ulp)) <= abs(w(n+1) - (v + 1 ulp))`, i.e. the next repr is
+            // TC3: `abs(w(n) - (v + 1 ulp)) <= abs(w(n+1) - (v + 1 ulp))`, i.e., the next repr is
             // no closer to `v + 1 ulp` than the current repr. given `z(n) = plus1v_up - plus1w(n)`,
             // this becomes `abs(z(n)) <= abs(z(n+1))`. again assuming that TC1 is false, we have
             // `z(n) > 0`. we have two cases to consider:
@@ -384,7 +384,7 @@ pub fn format_shortest_opt(d: &Decoded,
             // - when `z(n+1) < 0`:
             //   - TC3a: the precondition is `plus1v_up < plus1w(n) + 10^kappa`. assuming TC2 is
             //     false, `threshold >= plus1w(n) + 10^kappa` so it cannot overflow.
-            //   - TC3b: TC3 becomes `z(n) <= -z(n+1)`, i.e. `plus1v_up - plus1w(n) >=
+            //   - TC3b: TC3 becomes `z(n) <= -z(n+1)`, i.e., `plus1v_up - plus1w(n) >=
             //     plus1w(n+1) - plus1v_up = plus1w(n) + 10^kappa - plus1v_up`. the negated TC1
             //     gives `plus1v_up > plus1w(n)`, so it cannot overflow or underflow when
             //     combined with TC3a.
@@ -414,7 +414,7 @@ pub fn format_shortest_opt(d: &Decoded,
 
         // now we have the closest representation to `v` between `plus1` and `minus1`.
         // this is too liberal, though, so we reject any `w(n)` not between `plus0` and `minus0`,
-        // i.e. `plus1 - plus1w(n) <= minus0` or `plus1 - plus1w(n) >= plus0`. we utilize the facts
+        // i.e., `plus1 - plus1w(n) <= minus0` or `plus1 - plus1w(n) >= plus0`. we utilize the facts
         // that `threshold = plus1 - minus1` and `plus1 - plus0 = minus0 - minus1 = 2 ulp`.
         if 2 * ulp <= plus1w && plus1w <= threshold - 4 * ulp {
             Some((buf.len(), exp))
@@ -675,7 +675,7 @@ pub fn format_exact_opt(d: &Decoded, buf: &mut [u8], limit: i16)
             return Some((len, exp));
         }
 
-        // otherwise we are doomed (i.e. some values between `v - 1 ulp` and `v + 1 ulp` are
+        // otherwise we are doomed (i.e., some values between `v - 1 ulp` and `v + 1 ulp` are
         // rounding down and others are rounding up) and give up.
         None
     }
diff --git a/src/libcore/num/mod.rs b/src/libcore/num/mod.rs
index 805be431328..7ffb81901c6 100644
--- a/src/libcore/num/mod.rs
+++ b/src/libcore/num/mod.rs
@@ -78,7 +78,7 @@ assert_eq!(size_of::<Option<std::num::", stringify!($Ty), ">>(), size_of::<", st
                 #[inline]
                 pub fn new(n: $Int) -> Option<Self> {
                     if n != 0 {
-                        Some($Ty(NonZero(n)))
+                        Some($Ty(unsafe { NonZero(n) }))
                     } else {
                         None
                     }
@@ -673,7 +673,7 @@ $EndFeature, "
         }
 
         doc_comment! {
-            concat!("Checked Euclidean division. Computes `self.div_euc(rhs)`,
+            concat!("Checked Euclidean division. Computes `self.div_euclid(rhs)`,
 returning `None` if `rhs == 0` or the division results in overflow.
 
 # Examples
@@ -683,17 +683,17 @@ Basic usage:
 ```
 #![feature(euclidean_division)]
 assert_eq!((", stringify!($SelfT),
-"::min_value() + 1).checked_div_euc(-1), Some(", stringify!($Max), "));
-assert_eq!(", stringify!($SelfT), "::min_value().checked_div_euc(-1), None);
-assert_eq!((1", stringify!($SelfT), ").checked_div_euc(0), None);
+"::min_value() + 1).checked_div_euclid(-1), Some(", stringify!($Max), "));
+assert_eq!(", stringify!($SelfT), "::min_value().checked_div_euclid(-1), None);
+assert_eq!((1", stringify!($SelfT), ").checked_div_euclid(0), None);
 ```"),
             #[unstable(feature = "euclidean_division", issue = "49048")]
             #[inline]
-            pub fn checked_div_euc(self, rhs: Self) -> Option<Self> {
+            pub fn checked_div_euclid(self, rhs: Self) -> Option<Self> {
                 if rhs == 0 || (self == Self::min_value() && rhs == -1) {
                     None
                 } else {
-                    Some(self.div_euc(rhs))
+                    Some(self.div_euclid(rhs))
                 }
             }
         }
@@ -726,8 +726,8 @@ $EndFeature, "
         }
 
         doc_comment! {
-            concat!("Checked Euclidean modulo. Computes `self.mod_euc(rhs)`, returning `None` if
-`rhs == 0` or the division results in overflow.
+            concat!("Checked Euclidean remainder. Computes `self.rem_euclid(rhs)`, returning `None`
+if `rhs == 0` or the division results in overflow.
 
 # Examples
 
@@ -737,17 +737,17 @@ Basic usage:
 #![feature(euclidean_division)]
 use std::", stringify!($SelfT), ";
 
-assert_eq!(5", stringify!($SelfT), ".checked_mod_euc(2), Some(1));
-assert_eq!(5", stringify!($SelfT), ".checked_mod_euc(0), None);
-assert_eq!(", stringify!($SelfT), "::MIN.checked_mod_euc(-1), None);
+assert_eq!(5", stringify!($SelfT), ".checked_rem_euclid(2), Some(1));
+assert_eq!(5", stringify!($SelfT), ".checked_rem_euclid(0), None);
+assert_eq!(", stringify!($SelfT), "::MIN.checked_rem_euclid(-1), None);
 ```"),
             #[unstable(feature = "euclidean_division", issue = "49048")]
             #[inline]
-            pub fn checked_mod_euc(self, rhs: Self) -> Option<Self> {
+            pub fn checked_rem_euclid(self, rhs: Self) -> Option<Self> {
                 if rhs == 0 || (self == Self::min_value() && rhs == -1) {
                     None
                 } else {
-                    Some(self.mod_euc(rhs))
+                    Some(self.rem_euclid(rhs))
                 }
             }
         }
@@ -1089,7 +1089,7 @@ $EndFeature, "
         }
 
         doc_comment! {
-            concat!("Wrapping Euclidean division. Computes `self.div_euc(rhs)`,
+            concat!("Wrapping Euclidean division. Computes `self.div_euclid(rhs)`,
 wrapping around at the boundary of the type.
 
 Wrapping will only occur in `MIN / -1` on a signed type (where `MIN` is the negative minimal value
@@ -1106,13 +1106,13 @@ Basic usage:
 
 ```
 #![feature(euclidean_division)]
-assert_eq!(100", stringify!($SelfT), ".wrapping_div_euc(10), 10);
-assert_eq!((-128i8).wrapping_div_euc(-1), -128);
+assert_eq!(100", stringify!($SelfT), ".wrapping_div_euclid(10), 10);
+assert_eq!((-128i8).wrapping_div_euclid(-1), -128);
 ```"),
             #[unstable(feature = "euclidean_division", issue = "49048")]
             #[inline]
-            pub fn wrapping_div_euc(self, rhs: Self) -> Self {
-                self.overflowing_div_euc(rhs).0
+            pub fn wrapping_div_euclid(self, rhs: Self) -> Self {
+                self.overflowing_div_euclid(rhs).0
             }
         }
 
@@ -1145,8 +1145,8 @@ $EndFeature, "
         }
 
         doc_comment! {
-            concat!("Wrapping Euclidean modulo. Computes `self.mod_euc(rhs)`, wrapping around at the
-boundary of the type.
+            concat!("Wrapping Euclidean remainder. Computes `self.rem_euclid(rhs)`, wrapping around
+at the boundary of the type.
 
 Wrapping will only occur in `MIN % -1` on a signed type (where `MIN` is the negative minimal value
 for the type). In this case, this method returns 0.
@@ -1161,13 +1161,13 @@ Basic usage:
 
 ```
 #![feature(euclidean_division)]
-assert_eq!(100", stringify!($SelfT), ".wrapping_mod_euc(10), 0);
-assert_eq!((-128i8).wrapping_mod_euc(-1), 0);
+assert_eq!(100", stringify!($SelfT), ".wrapping_rem_euclid(10), 0);
+assert_eq!((-128i8).wrapping_rem_euclid(-1), 0);
 ```"),
             #[unstable(feature = "euclidean_division", issue = "49048")]
             #[inline]
-            pub fn wrapping_mod_euc(self, rhs: Self) -> Self {
-                self.overflowing_mod_euc(rhs).0
+            pub fn wrapping_rem_euclid(self, rhs: Self) -> Self {
+                self.overflowing_rem_euclid(rhs).0
             }
         }
 
@@ -1442,7 +1442,7 @@ $EndFeature, "
         }
 
         doc_comment! {
-            concat!("Calculates the quotient of Euclidean division `self.div_euc(rhs)`.
+            concat!("Calculates the quotient of Euclidean division `self.div_euclid(rhs)`.
 
 Returns a tuple of the divisor along with a boolean indicating whether an arithmetic overflow would
 occur. If an overflow would occur then `self` is returned.
@@ -1459,17 +1459,17 @@ Basic usage:
 #![feature(euclidean_division)]
 use std::", stringify!($SelfT), ";
 
-assert_eq!(5", stringify!($SelfT), ".overflowing_div_euc(2), (2, false));
-assert_eq!(", stringify!($SelfT), "::MIN.overflowing_div_euc(-1), (", stringify!($SelfT),
+assert_eq!(5", stringify!($SelfT), ".overflowing_div_euclid(2), (2, false));
+assert_eq!(", stringify!($SelfT), "::MIN.overflowing_div_euclid(-1), (", stringify!($SelfT),
 "::MIN, true));
 ```"),
             #[inline]
             #[unstable(feature = "euclidean_division", issue = "49048")]
-            pub fn overflowing_div_euc(self, rhs: Self) -> (Self, bool) {
+            pub fn overflowing_div_euclid(self, rhs: Self) -> (Self, bool) {
                 if self == Self::min_value() && rhs == -1 {
                     (self, true)
                 } else {
-                    (self.div_euc(rhs), false)
+                    (self.div_euclid(rhs), false)
                 }
             }
         }
@@ -1508,7 +1508,7 @@ $EndFeature, "
 
 
         doc_comment! {
-            concat!("Calculates the remainder `self.mod_euc(rhs)` by Euclidean division.
+            concat!("Overflowing Euclidean remainder. Calculates `self.rem_euclid(rhs)`.
 
 Returns a tuple of the remainder after dividing along with a boolean indicating whether an
 arithmetic overflow would occur. If an overflow would occur then 0 is returned.
@@ -1525,16 +1525,16 @@ Basic usage:
 #![feature(euclidean_division)]
 use std::", stringify!($SelfT), ";
 
-assert_eq!(5", stringify!($SelfT), ".overflowing_mod_euc(2), (1, false));
-assert_eq!(", stringify!($SelfT), "::MIN.overflowing_mod_euc(-1), (0, true));
+assert_eq!(5", stringify!($SelfT), ".overflowing_rem_euclid(2), (1, false));
+assert_eq!(", stringify!($SelfT), "::MIN.overflowing_rem_euclid(-1), (0, true));
 ```"),
             #[unstable(feature = "euclidean_division", issue = "49048")]
             #[inline]
-            pub fn overflowing_mod_euc(self, rhs: Self) -> (Self, bool) {
+            pub fn overflowing_rem_euclid(self, rhs: Self) -> (Self, bool) {
                 if self == Self::min_value() && rhs == -1 {
                     (0, true)
                 } else {
-                    (self.mod_euc(rhs), false)
+                    (self.rem_euclid(rhs), false)
                 }
             }
         }
@@ -1544,7 +1544,7 @@ assert_eq!(", stringify!($SelfT), "::MIN.overflowing_mod_euc(-1), (0, true));
             concat!("Negates self, overflowing if this is equal to the minimum value.
 
 Returns a tuple of the negated version of self along with a boolean indicating whether an overflow
-happened. If `self` is the minimum value (e.g. `i32::MIN` for values of type `i32`), then the
+happened. If `self` is the minimum value (e.g., `i32::MIN` for values of type `i32`), then the
 minimum value will be returned again and `true` will be returned for an overflow happening.
 
 # Examples
@@ -1621,7 +1621,7 @@ $EndFeature, "
             concat!("Computes the absolute value of `self`.
 
 Returns a tuple of the absolute version of self along with a boolean indicating whether an overflow
-happened. If self is the minimum value (e.g. ", stringify!($SelfT), "::MIN for values of type
+happened. If self is the minimum value (e.g., ", stringify!($SelfT), "::MIN for values of type
  ", stringify!($SelfT), "), then the minimum value will be returned again and true will be returned
 for an overflow happening.
 
@@ -1739,9 +1739,13 @@ $EndFeature, "
         doc_comment! {
             concat!("Calculates the quotient of Euclidean division of `self` by `rhs`.
 
-This computes the integer `n` such that `self = n * rhs + self.mod_euc(rhs)`.
+This computes the integer `n` such that `self = n * rhs + self.rem_euclid(rhs)`,
+with `0 <= self.rem_euclid(rhs) < rhs`.
+
 In other words, the result is `self / rhs` rounded to the integer `n`
 such that `self >= n * rhs`.
+If `self > 0`, this is equal to round towards zero (the default in Rust);
+if `self < 0`, this is equal to round towards +/- infinity.
 
 # Panics
 
@@ -1756,15 +1760,15 @@ Basic usage:
 let a: ", stringify!($SelfT), " = 7; // or any other integer type
 let b = 4;
 
-assert_eq!(a.div_euc(b), 1); // 7 >= 4 * 1
-assert_eq!(a.div_euc(-b), -1); // 7 >= -4 * -1
-assert_eq!((-a).div_euc(b), -2); // -7 >= 4 * -2
-assert_eq!((-a).div_euc(-b), 2); // -7 >= -4 * 2
+assert_eq!(a.div_euclid(b), 1); // 7 >= 4 * 1
+assert_eq!(a.div_euclid(-b), -1); // 7 >= -4 * -1
+assert_eq!((-a).div_euclid(b), -2); // -7 >= 4 * -2
+assert_eq!((-a).div_euclid(-b), 2); // -7 >= -4 * 2
 ```"),
             #[unstable(feature = "euclidean_division", issue = "49048")]
             #[inline]
             #[rustc_inherit_overflow_checks]
-            pub fn div_euc(self, rhs: Self) -> Self {
+            pub fn div_euclid(self, rhs: Self) -> Self {
                 let q = self / rhs;
                 if self % rhs < 0 {
                     return if rhs > 0 { q - 1 } else { q + 1 }
@@ -1775,9 +1779,11 @@ assert_eq!((-a).div_euc(-b), 2); // -7 >= -4 * 2
 
 
         doc_comment! {
-            concat!("Calculates the remainder `self mod rhs` by Euclidean division.
+            concat!("Calculates the least nonnegative remainder of `self (mod rhs)`.
 
-In particular, the result `n` satisfies `0 <= n < rhs.abs()`.
+This is done as if by the Euclidean division algorithm -- given
+`r = self.rem_euclid(rhs)`, `self = rhs * self.div_euclid(rhs) + r`, and
+`0 <= r < abs(rhs)`.
 
 # Panics
 
@@ -1792,15 +1798,15 @@ Basic usage:
 let a: ", stringify!($SelfT), " = 7; // or any other integer type
 let b = 4;
 
-assert_eq!(a.mod_euc(b), 3);
-assert_eq!((-a).mod_euc(b), 1);
-assert_eq!(a.mod_euc(-b), 3);
-assert_eq!((-a).mod_euc(-b), 1);
+assert_eq!(a.rem_euclid(b), 3);
+assert_eq!((-a).rem_euclid(b), 1);
+assert_eq!(a.rem_euclid(-b), 3);
+assert_eq!((-a).rem_euclid(-b), 1);
 ```"),
             #[unstable(feature = "euclidean_division", issue = "49048")]
             #[inline]
             #[rustc_inherit_overflow_checks]
-            pub fn mod_euc(self, rhs: Self) -> Self {
+            pub fn rem_euclid(self, rhs: Self) -> Self {
                 let r = self % rhs;
                 if r < 0 {
                     if rhs < 0 {
@@ -2150,19 +2156,6 @@ impl isize {
          "[0x12, 0x34, 0x56, 0x78, 0x90, 0x12, 0x34, 0x56]" }
 }
 
-// Emits the correct `cttz` call, depending on the size of the type.
-macro_rules! uint_cttz_call {
-    // As of LLVM 3.6 the codegen for the zero-safe cttz8 intrinsic
-    // emits two conditional moves on x86_64. By promoting the value to
-    // u16 and setting bit 8, we get better code without any conditional
-    // operations.
-    // FIXME: There's a LLVM patch (http://reviews.llvm.org/D9284)
-    // pending, remove this workaround once LLVM generates better code
-    // for cttz8.
-    ($value:expr, 8) => { intrinsics::cttz($value as u16 | 0x100) };
-    ($value:expr, $_BITS:expr) => { intrinsics::cttz($value) }
-}
-
 // `Int` + `UnsignedInt` implemented for unsigned integers
 macro_rules! uint_impl {
     ($SelfT:ty, $ActualT:ty, $BITS:expr, $MaxV:expr, $Feature:expr, $EndFeature:expr,
@@ -2306,7 +2299,7 @@ assert_eq!(n.trailing_zeros(), 3);", $EndFeature, "
             #[rustc_const_unstable(feature = "const_int_ops")]
             #[inline]
             pub const fn trailing_zeros(self) -> u32 {
-                unsafe { uint_cttz_call!(self, $BITS) as u32 }
+                unsafe { intrinsics::cttz(self) as u32 }
             }
         }
 
@@ -2330,12 +2323,7 @@ assert_eq!(n.rotate_left(", $rot, "), m);
             #[rustc_const_unstable(feature = "const_int_rotate")]
             #[inline]
             pub const fn rotate_left(self, n: u32) -> Self {
-                #[cfg(not(stage0))] {
-                    unsafe { intrinsics::rotate_left(self, n as $SelfT) }
-                }
-                #[cfg(stage0)] {
-                    (self << (n % $BITS)) | (self >> (($BITS - (n % $BITS)) % $BITS))
-                }
+                unsafe { intrinsics::rotate_left(self, n as $SelfT) }
             }
         }
 
@@ -2360,12 +2348,7 @@ assert_eq!(n.rotate_right(", $rot, "), m);
             #[rustc_const_unstable(feature = "const_int_rotate")]
             #[inline]
             pub const fn rotate_right(self, n: u32) -> Self {
-                #[cfg(not(stage0))] {
-                    unsafe { intrinsics::rotate_right(self, n as $SelfT) }
-                }
-                #[cfg(stage0)] {
-                    (self >> (n % $BITS)) | (self << (($BITS - (n % $BITS)) % $BITS))
-                }
+                unsafe { intrinsics::rotate_right(self, n as $SelfT) }
             }
         }
 
@@ -2634,7 +2617,7 @@ assert_eq!(1", stringify!($SelfT), ".checked_div(0), None);", $EndFeature, "
         }
 
         doc_comment! {
-            concat!("Checked Euclidean division. Computes `self.div_euc(rhs)`, returning `None`
+            concat!("Checked Euclidean division. Computes `self.div_euclid(rhs)`, returning `None`
 if `rhs == 0`.
 
 # Examples
@@ -2643,16 +2626,16 @@ Basic usage:
 
 ```
 #![feature(euclidean_division)]
-assert_eq!(128", stringify!($SelfT), ".checked_div(2), Some(64));
-assert_eq!(1", stringify!($SelfT), ".checked_div_euc(0), None);
+assert_eq!(128", stringify!($SelfT), ".checked_div_euclid(2), Some(64));
+assert_eq!(1", stringify!($SelfT), ".checked_div_euclid(0), None);
 ```"),
             #[unstable(feature = "euclidean_division", issue = "49048")]
             #[inline]
-            pub fn checked_div_euc(self, rhs: Self) -> Option<Self> {
+            pub fn checked_div_euclid(self, rhs: Self) -> Option<Self> {
                 if rhs == 0 {
                     None
                 } else {
-                    Some(self.div_euc(rhs))
+                    Some(self.div_euclid(rhs))
                 }
             }
         }
@@ -2682,7 +2665,7 @@ assert_eq!(5", stringify!($SelfT), ".checked_rem(0), None);", $EndFeature, "
         }
 
         doc_comment! {
-            concat!("Checked Euclidean modulo. Computes `self.mod_euc(rhs)`, returning `None`
+            concat!("Checked Euclidean modulo. Computes `self.rem_euclid(rhs)`, returning `None`
 if `rhs == 0`.
 
 # Examples
@@ -2691,16 +2674,16 @@ Basic usage:
 
 ```
 #![feature(euclidean_division)]
-assert_eq!(5", stringify!($SelfT), ".checked_mod_euc(2), Some(1));
-assert_eq!(5", stringify!($SelfT), ".checked_mod_euc(0), None);
+assert_eq!(5", stringify!($SelfT), ".checked_rem_euclid(2), Some(1));
+assert_eq!(5", stringify!($SelfT), ".checked_rem_euclid(0), None);
 ```"),
             #[unstable(feature = "euclidean_division", issue = "49048")]
             #[inline]
-            pub fn checked_mod_euc(self, rhs: Self) -> Option<Self> {
+            pub fn checked_rem_euclid(self, rhs: Self) -> Option<Self> {
                 if rhs == 0 {
                     None
                 } else {
-                    Some(self.mod_euc(rhs))
+                    Some(self.rem_euclid(rhs))
                 }
             }
         }
@@ -2988,11 +2971,14 @@ Basic usage:
         }
 
         doc_comment! {
-            concat!("Wrapping Euclidean division. Computes `self.div_euc(rhs)`.
+            concat!("Wrapping Euclidean division. Computes `self.div_euclid(rhs)`.
 Wrapped division on unsigned types is just normal division.
 There's no way wrapping could ever happen.
 This function exists, so that all operations
 are accounted for in the wrapping operations.
+Since, for the positive integers, all common
+definitions of division are equal, this
+is exactly equal to `self.wrapping_div(rhs)`.
 
 # Examples
 
@@ -3000,11 +2986,11 @@ Basic usage:
 
 ```
 #![feature(euclidean_division)]
-assert_eq!(100", stringify!($SelfT), ".wrapping_div_euc(10), 10);
+assert_eq!(100", stringify!($SelfT), ".wrapping_div_euclid(10), 10);
 ```"),
             #[unstable(feature = "euclidean_division", issue = "49048")]
             #[inline]
-            pub fn wrapping_div_euc(self, rhs: Self) -> Self {
+            pub fn wrapping_div_euclid(self, rhs: Self) -> Self {
                 self / rhs
             }
         }
@@ -3032,12 +3018,15 @@ Basic usage:
         }
 
         doc_comment! {
-            concat!("Wrapping Euclidean modulo. Computes `self.mod_euc(rhs)`.
+            concat!("Wrapping Euclidean modulo. Computes `self.rem_euclid(rhs)`.
 Wrapped modulo calculation on unsigned types is
 just the regular remainder calculation.
 There's no way wrapping could ever happen.
 This function exists, so that all operations
 are accounted for in the wrapping operations.
+Since, for the positive integers, all common
+definitions of division are equal, this
+is exactly equal to `self.wrapping_rem(rhs)`.
 
 # Examples
 
@@ -3045,11 +3034,11 @@ Basic usage:
 
 ```
 #![feature(euclidean_division)]
-assert_eq!(100", stringify!($SelfT), ".wrapping_mod_euc(10), 0);
+assert_eq!(100", stringify!($SelfT), ".wrapping_rem_euclid(10), 0);
 ```"),
             #[unstable(feature = "euclidean_division", issue = "49048")]
             #[inline]
-            pub fn wrapping_mod_euc(self, rhs: Self) -> Self {
+            pub fn wrapping_rem_euclid(self, rhs: Self) -> Self {
                 self % rhs
             }
         }
@@ -3293,12 +3282,15 @@ Basic usage
         }
 
         doc_comment! {
-            concat!("Calculates the quotient of Euclidean division `self.div_euc(rhs)`.
+            concat!("Calculates the quotient of Euclidean division `self.div_euclid(rhs)`.
 
 Returns a tuple of the divisor along with a boolean indicating
 whether an arithmetic overflow would occur. Note that for unsigned
 integers overflow never occurs, so the second value is always
 `false`.
+Since, for the positive integers, all common
+definitions of division are equal, this
+is exactly equal to `self.overflowing_div(rhs)`.
 
 # Panics
 
@@ -3310,11 +3302,11 @@ Basic usage
 
 ```
 #![feature(euclidean_division)]
-assert_eq!(5", stringify!($SelfT), ".overflowing_div_euc(2), (2, false));
+assert_eq!(5", stringify!($SelfT), ".overflowing_div_euclid(2), (2, false));
 ```"),
             #[inline]
             #[unstable(feature = "euclidean_division", issue = "49048")]
-            pub fn overflowing_div_euc(self, rhs: Self) -> (Self, bool) {
+            pub fn overflowing_div_euclid(self, rhs: Self) -> (Self, bool) {
                 (self / rhs, false)
             }
         }
@@ -3346,12 +3338,15 @@ Basic usage
         }
 
         doc_comment! {
-            concat!("Calculates the remainder `self.mod_euc(rhs)` by Euclidean division.
+            concat!("Calculates the remainder `self.rem_euclid(rhs)` as if by Euclidean division.
 
 Returns a tuple of the modulo after dividing along with a boolean
 indicating whether an arithmetic overflow would occur. Note that for
 unsigned integers overflow never occurs, so the second value is
 always `false`.
+Since, for the positive integers, all common
+definitions of division are equal, this operation
+is exactly equal to `self.overflowing_rem(rhs)`.
 
 # Panics
 
@@ -3363,11 +3358,11 @@ Basic usage
 
 ```
 #![feature(euclidean_division)]
-assert_eq!(5", stringify!($SelfT), ".overflowing_mod_euc(2), (1, false));
+assert_eq!(5", stringify!($SelfT), ".overflowing_rem_euclid(2), (1, false));
 ```"),
             #[inline]
             #[unstable(feature = "euclidean_division", issue = "49048")]
-            pub fn overflowing_mod_euc(self, rhs: Self) -> (Self, bool) {
+            pub fn overflowing_rem_euclid(self, rhs: Self) -> (Self, bool) {
                 (self % rhs, false)
             }
         }
@@ -3534,7 +3529,9 @@ Basic usage:
             doc_comment! {
             concat!("Performs Euclidean division.
 
-For unsigned types, this is just the same as `self / rhs`.
+Since, for the positive integers, all common
+definitions of division are equal, this
+is exactly equal to `self / rhs`.
 
 # Examples
 
@@ -3542,21 +3539,23 @@ Basic usage:
 
 ```
 #![feature(euclidean_division)]
-assert_eq!(7", stringify!($SelfT), ".div_euc(4), 1); // or any other integer type
+assert_eq!(7", stringify!($SelfT), ".div_euclid(4), 1); // or any other integer type
 ```"),
             #[unstable(feature = "euclidean_division", issue = "49048")]
             #[inline]
             #[rustc_inherit_overflow_checks]
-            pub fn div_euc(self, rhs: Self) -> Self {
+            pub fn div_euclid(self, rhs: Self) -> Self {
                 self / rhs
             }
         }
 
 
         doc_comment! {
-            concat!("Calculates the remainder `self mod rhs` by Euclidean division.
+            concat!("Calculates the least remainder of `self (mod rhs)`.
 
-For unsigned types, this is just the same as `self % rhs`.
+Since, for the positive integers, all common
+definitions of division are equal, this
+is exactly equal to `self % rhs`.
 
 # Examples
 
@@ -3564,12 +3563,12 @@ Basic usage:
 
 ```
 #![feature(euclidean_division)]
-assert_eq!(7", stringify!($SelfT), ".mod_euc(4), 3); // or any other integer type
+assert_eq!(7", stringify!($SelfT), ".rem_euclid(4), 3); // or any other integer type
 ```"),
             #[unstable(feature = "euclidean_division", issue = "49048")]
             #[inline]
             #[rustc_inherit_overflow_checks]
-            pub fn mod_euc(self, rhs: Self) -> Self {
+            pub fn rem_euclid(self, rhs: Self) -> Self {
                 self % rhs
             }
         }
@@ -3617,7 +3616,7 @@ assert!(!10", stringify!($SelfT), ".is_power_of_two());", $EndFeature, "
         doc_comment! {
             concat!("Returns the smallest power of two greater than or equal to `self`.
 
-When return value overflows (i.e. `self > (1 << (N-1))` for type
+When return value overflows (i.e., `self > (1 << (N-1))` for type
 `uN`), it panics in debug mode and return value is wrapped to 0 in
 release mode (the only situation in which method can return 0).
 
@@ -4827,7 +4826,7 @@ fn from_str_radix<T: FromStrRadixHelper>(src: &str, radix: u32) -> Result<T, Par
 /// # Potential causes
 ///
 /// Among other causes, `ParseIntError` can be thrown because of leading or trailing whitespace
-/// in the string e.g. when it is obtained from the standard input.
+/// in the string e.g., when it is obtained from the standard input.
 /// Using the [`str.trim()`] method ensures that no whitespace remains before parsing.
 ///
 /// [`str.trim()`]: ../../std/primitive.str.html#method.trim
diff --git a/src/libcore/num/wrapping.rs b/src/libcore/num/wrapping.rs
index 00134a58d30..94dd657ec97 100644
--- a/src/libcore/num/wrapping.rs
+++ b/src/libcore/num/wrapping.rs
@@ -865,7 +865,7 @@ assert!(!Wrapping(10", stringify!($t), ").is_power_of_two());
             doc_comment! {
                 concat!("Returns the smallest power of two greater than or equal to `self`.
 
-When return value overflows (i.e. `self > (1 << (N-1))` for type
+When return value overflows (i.e., `self > (1 << (N-1))` for type
 `uN`), overflows to `2^N = 0`.
 
 # Examples
diff --git a/src/libcore/ops/deref.rs b/src/libcore/ops/deref.rs
index 91a3d77e8b2..ff836f4aa69 100644
--- a/src/libcore/ops/deref.rs
+++ b/src/libcore/ops/deref.rs
@@ -177,3 +177,19 @@ pub trait DerefMut: Deref {
 impl<T: ?Sized> DerefMut for &mut T {
     fn deref_mut(&mut self) -> &mut T { *self }
 }
+
+/// Indicates that a struct can be used as a method receiver, without the
+/// `arbitrary_self_types` feature. This is implemented by stdlib pointer types like `Box<T>`,
+/// `Rc<T>`, `&T`, and `Pin<P>`.
+#[cfg_attr(not(stage0), lang = "receiver")]
+#[unstable(feature = "receiver_trait", issue = "0")]
+#[doc(hidden)]
+pub trait Receiver {
+    // Empty.
+}
+
+#[unstable(feature = "receiver_trait", issue = "0")]
+impl<T: ?Sized> Receiver for &T {}
+
+#[unstable(feature = "receiver_trait", issue = "0")]
+impl<T: ?Sized> Receiver for &mut T {}
diff --git a/src/libcore/ops/function.rs b/src/libcore/ops/function.rs
index c9591c3f57b..3b356b9a1e7 100644
--- a/src/libcore/ops/function.rs
+++ b/src/libcore/ops/function.rs
@@ -26,7 +26,7 @@
 /// is expected.
 ///
 /// Use `Fn` as a bound when you want to accept a parameter of function-like
-/// type and need to call it repeatedly and without mutating state (e.g. when
+/// type and need to call it repeatedly and without mutating state (e.g., when
 /// calling it concurrently). If you do not need such strict requirements, use
 /// [`FnMut`] or [`FnOnce`] as bounds.
 ///
@@ -72,6 +72,7 @@
     label="expected an `Fn<{Args}>` closure, found `{Self}`",
 )]
 #[fundamental] // so that regex can rely that `&str: !FnMut`
+#[must_use]
 pub trait Fn<Args> : FnMut<Args> {
     /// Performs the call operation.
     #[unstable(feature = "fn_traits", issue = "29625")]
@@ -84,7 +85,7 @@ pub trait Fn<Args> : FnMut<Args> {
 ///
 /// `FnMut` is implemented automatically by closures which take mutable
 /// references to captured variables, as well as all types that implement
-/// [`Fn`], e.g. (safe) [function pointers][] (since `FnMut` is a supertrait of
+/// [`Fn`], e.g., (safe) [function pointers][] (since `FnMut` is a supertrait of
 /// [`Fn`]). Additionally, for any type `F` that implements `FnMut`, `&mut F`
 /// implements `FnMut`, too.
 ///
@@ -150,6 +151,7 @@ pub trait Fn<Args> : FnMut<Args> {
     label="expected an `FnMut<{Args}>` closure, found `{Self}`",
 )]
 #[fundamental] // so that regex can rely that `&str: !FnMut`
+#[must_use]
 pub trait FnMut<Args> : FnOnce<Args> {
     /// Performs the call operation.
     #[unstable(feature = "fn_traits", issue = "29625")]
@@ -163,7 +165,7 @@ pub trait FnMut<Args> : FnOnce<Args> {
 /// implements `FnOnce`, it can only be called once.
 ///
 /// `FnOnce` is implemented automatically by closure that might consume captured
-/// variables, as well as all types that implement [`FnMut`], e.g. (safe)
+/// variables, as well as all types that implement [`FnMut`], e.g., (safe)
 /// [function pointers][] (since `FnOnce` is a supertrait of [`FnMut`]).
 ///
 /// Since both [`Fn`] and [`FnMut`] are subtraits of `FnOnce`, any instance of
@@ -228,6 +230,7 @@ pub trait FnMut<Args> : FnOnce<Args> {
     label="expected an `FnOnce<{Args}>` closure, found `{Self}`",
 )]
 #[fundamental] // so that regex can rely that `&str: !FnMut`
+#[must_use]
 pub trait FnOnce<Args> {
     /// The returned type after the call operator is used.
     #[stable(feature = "fn_once_output", since = "1.12.0")]
diff --git a/src/libcore/ops/mod.rs b/src/libcore/ops/mod.rs
index edfa6df11ac..06740d2e4cd 100644
--- a/src/libcore/ops/mod.rs
+++ b/src/libcore/ops/mod.rs
@@ -27,7 +27,7 @@
 //! should have some resemblance to multiplication (and share expected
 //! properties like associativity).
 //!
-//! Note that the `&&` and `||` operators short-circuit, i.e. they only
+//! Note that the `&&` and `||` operators short-circuit, i.e., they only
 //! evaluate their second operand if it contributes to the result. Since this
 //! behavior is not enforceable by traits, `&&` and `||` are not supported as
 //! overloadable operators.
@@ -178,6 +178,9 @@ pub use self::bit::{BitAndAssign, BitOrAssign, BitXorAssign, ShlAssign, ShrAssig
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use self::deref::{Deref, DerefMut};
 
+#[unstable(feature = "receiver_trait", issue = "0")]
+pub use self::deref::Receiver;
+
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use self::drop::Drop;
 
diff --git a/src/libcore/ops/unsize.rs b/src/libcore/ops/unsize.rs
index 4d9a40a1b90..e86a392a2c8 100644
--- a/src/libcore/ops/unsize.rs
+++ b/src/libcore/ops/unsize.rs
@@ -93,7 +93,7 @@ impl<T: ?Sized+Unsize<U>, U: ?Sized> CoerceUnsized<*const U> for *const T {}
 /// {}
 /// ```
 #[unstable(feature = "dispatch_from_dyn", issue = "0")]
-#[cfg_attr(not(stage0), lang = "dispatch_from_dyn")]
+#[lang = "dispatch_from_dyn"]
 pub trait DispatchFromDyn<T> {
     // Empty.
 }
diff --git a/src/libcore/option.rs b/src/libcore/option.rs
index 67bed63e6ff..3147b21f86b 100644
--- a/src/libcore/option.rs
+++ b/src/libcore/option.rs
@@ -62,7 +62,7 @@
 //! The following example uses [`Option`] to create an optional box of
 //! [`i32`]. Notice that in order to use the inner [`i32`] value first, the
 //! `check_optional` function needs to use pattern matching to
-//! determine whether the box has a value (i.e. it is [`Some(...)`][`Some`]) or
+//! determine whether the box has a value (i.e., it is [`Some(...)`][`Some`]) or
 //! not ([`None`]).
 //!
 //! ```
diff --git a/src/libcore/pin.rs b/src/libcore/pin.rs
index 308dd9c79fa..521ce9b5f6b 100644
--- a/src/libcore/pin.rs
+++ b/src/libcore/pin.rs
@@ -7,23 +7,33 @@
 //! since moving an object with pointers to itself will invalidate them,
 //! which could cause undefined behavior.
 //!
-//! In order to prevent objects from moving, they must be pinned
-//! by wrapping a pointer to the data in the [`Pin`] type. A pointer wrapped
-//! in a `Pin` is otherwise equivalent to its normal version, e.g. `Pin<Box<T>>`
-//! and `Box<T>` work the same way except that the first is pinning the value
-//! of `T` in place.
+//! By default, all types in Rust are movable. Rust allows passing all types by-value,
+//! and common smart-pointer types such as `Box`, `Rc`, and `&mut` allow replacing and
+//! moving the values they contain. In order to prevent objects from moving, they must
+//! be pinned by wrapping a pointer to the data in the [`Pin`] type.
+//! Doing this prohibits moving the value behind the pointer.
+//! For example, `Pin<Box<T>>` functions much like a regular `Box<T>`,
+//! but doesn't allow moving `T`. The pointer value itself (the `Box`) can still be moved,
+//! but the value behind it cannot.
 //!
-//! First of all, these are pointer types because pinned data mustn't be passed around by value
-//! (that would change its location in memory).
-//! Secondly, since data can be moved out of `&mut` and `Box` with functions such as [`swap`],
-//! which causes their contents to swap places in memory,
-//! we need dedicated types that prohibit such operations.
+//! Since data can be moved out of `&mut` and `Box` with functions such as [`swap`],
+//! changing the location of the underlying data, [`Pin`] prohibits accessing the
+//! underlying pointer type (the `&mut` or `Box`) directly, and provides its own set of
+//! APIs for accessing and using the value. [`Pin`] also guarantees that no other
+//! functions will move the pointed-to value. This allows for the creation of
+//! self-references and other special behaviors that are only possible for unmovable
+//! values.
 //!
-//! However, these restrictions are usually not necessary,
-//! so most types implement the [`Unpin`] auto-trait,
-//! which indicates that the type can be moved out safely.
-//! Doing so removes the limitations of pinning types,
-//! making them the same as their non-pinning counterparts.
+//! However, these restrictions are usually not necessary. Many types are always freely
+//! movable. These types implement the [`Unpin`] auto-trait, which nullifies the affect
+//! of [`Pin`]. For `T: Unpin`, `Pin<Box<T>>` and `Box<T>` function identically, as do
+//! `Pin<&mut T>` and `&mut T`.
+//!
+//! Note that pinning and `Unpin` only affect the pointed-to type. For example, whether
+//! or not `Box<T>` is `Unpin` has no affect on the behavior of `Pin<Box<T>>`. Similarly,
+//! `Pin<Box<T>>` and `Pin<&mut T>` are always `Unpin` themselves, even though the
+//! `T` underneath them isn't, because the pointers in `Pin<Box<_>>` and `Pin<&mut _>`
+//! are always freely movable, even if the data they point to isn't.
 //!
 //! [`Pin`]: struct.Pin.html
 //! [`Unpin`]: trait.Unpin.html
@@ -36,7 +46,7 @@
 //! #![feature(pin)]
 //!
 //! use std::pin::Pin;
-//! use std::marker::Pinned;
+//! use std::marker::PhantomPinned;
 //! use std::ptr::NonNull;
 //!
 //! // This is a self-referential struct since the slice field points to the data field.
@@ -47,7 +57,7 @@
 //! struct Unmovable {
 //!     data: String,
 //!     slice: NonNull<String>,
-//!     _pin: Pinned,
+//!     _pin: PhantomPinned,
 //! }
 //!
 //! impl Unmovable {
@@ -60,7 +70,7 @@
 //!             // we only create the pointer once the data is in place
 //!             // otherwise it will have already moved before we even started
 //!             slice: NonNull::dangling(),
-//!             _pin: Pinned,
+//!             _pin: PhantomPinned,
 //!         };
 //!         let mut boxed = Box::pinned(res);
 //!
@@ -91,7 +101,7 @@
 
 use fmt;
 use marker::Sized;
-use ops::{Deref, DerefMut, CoerceUnsized, DispatchFromDyn};
+use ops::{Deref, DerefMut, Receiver, CoerceUnsized, DispatchFromDyn};
 
 #[doc(inline)]
 pub use marker::Unpin;
@@ -292,6 +302,9 @@ where
     }
 }
 
+#[unstable(feature = "receiver_trait", issue = "0")]
+impl<P: Receiver> Receiver for Pin<P> {}
+
 #[unstable(feature = "pin", issue = "49150")]
 impl<P: fmt::Debug> fmt::Debug for Pin<P> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
diff --git a/src/libcore/ptr.rs b/src/libcore/ptr.rs
index d3a74ed2a68..b3c93ae1fa7 100644
--- a/src/libcore/ptr.rs
+++ b/src/libcore/ptr.rs
@@ -103,7 +103,7 @@ pub use intrinsics::write_bytes;
 ///   dropped normally.
 ///
 /// * It is friendlier to the optimizer to do this over [`ptr::read`] when
-///   dropping manually allocated memory (e.g. when writing Box/Rc/Vec),
+///   dropping manually allocated memory (e.g., when writing Box/Rc/Vec),
 ///   as the compiler doesn't need to prove that it's sound to elide the
 ///   copy.
 ///
@@ -836,7 +836,7 @@ pub unsafe fn write_unaligned<T>(dst: *mut T, src: T) {
 ///
 /// The compiler shouldn't change the relative order or number of volatile
 /// memory operations. However, volatile memory operations on zero-sized types
-/// (e.g. if a zero-sized type is passed to `read_volatile`) are no-ops
+/// (e.g., if a zero-sized type is passed to `read_volatile`) are no-ops
 /// and may be ignored.
 ///
 /// [c11]: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf
@@ -913,7 +913,7 @@ pub unsafe fn read_volatile<T>(src: *const T) -> T {
 ///
 /// The compiler shouldn't change the relative order or number of volatile
 /// memory operations. However, volatile memory operations on zero-sized types
-/// (e.g. if a zero-sized type is passed to `write_volatile`) are no-ops
+/// (e.g., if a zero-sized type is passed to `write_volatile`) are no-ops
 /// and may be ignored.
 ///
 /// [c11]: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf
@@ -1035,7 +1035,7 @@ impl<T: ?Sized> *const T {
 
     /// Calculates the offset from a pointer.
     ///
-    /// `count` is in units of T; e.g. a `count` of 3 represents a pointer
+    /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
     /// offset of `3 * size_of::<T>()` bytes.
     ///
     /// # Safety
@@ -1089,7 +1089,7 @@ impl<T: ?Sized> *const T {
 
     /// Calculates the offset from a pointer using wrapping arithmetic.
     ///
-    /// `count` is in units of T; e.g. a `count` of 3 represents a pointer
+    /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
     /// offset of `3 * size_of::<T>()` bytes.
     ///
     /// # Safety
@@ -1253,7 +1253,7 @@ impl<T: ?Sized> *const T {
 
     /// Calculates the offset from a pointer (convenience for `.offset(count as isize)`).
     ///
-    /// `count` is in units of T; e.g. a `count` of 3 represents a pointer
+    /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
     /// offset of `3 * size_of::<T>()` bytes.
     ///
     /// # Safety
@@ -1310,7 +1310,7 @@ impl<T: ?Sized> *const T {
     /// Calculates the offset from a pointer (convenience for
     /// `.offset((count as isize).wrapping_neg())`).
     ///
-    /// `count` is in units of T; e.g. a `count` of 3 represents a pointer
+    /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
     /// offset of `3 * size_of::<T>()` bytes.
     ///
     /// # Safety
@@ -1367,7 +1367,7 @@ impl<T: ?Sized> *const T {
     /// Calculates the offset from a pointer using wrapping arithmetic.
     /// (convenience for `.wrapping_offset(count as isize)`)
     ///
-    /// `count` is in units of T; e.g. a `count` of 3 represents a pointer
+    /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
     /// offset of `3 * size_of::<T>()` bytes.
     ///
     /// # Safety
@@ -1408,7 +1408,7 @@ impl<T: ?Sized> *const T {
     /// Calculates the offset from a pointer using wrapping arithmetic.
     /// (convenience for `.wrapping_offset((count as isize).wrapping_sub())`)
     ///
-    /// `count` is in units of T; e.g. a `count` of 3 represents a pointer
+    /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
     /// offset of `3 * size_of::<T>()` bytes.
     ///
     /// # Safety
@@ -1655,7 +1655,7 @@ impl<T: ?Sized> *mut T {
 
     /// Calculates the offset from a pointer.
     ///
-    /// `count` is in units of T; e.g. a `count` of 3 represents a pointer
+    /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
     /// offset of `3 * size_of::<T>()` bytes.
     ///
     /// # Safety
@@ -1708,7 +1708,7 @@ impl<T: ?Sized> *mut T {
     }
 
     /// Calculates the offset from a pointer using wrapping arithmetic.
-    /// `count` is in units of T; e.g. a `count` of 3 represents a pointer
+    /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
     /// offset of `3 * size_of::<T>()` bytes.
     ///
     /// # Safety
@@ -1891,7 +1891,7 @@ impl<T: ?Sized> *mut T {
 
     /// Calculates the offset from a pointer (convenience for `.offset(count as isize)`).
     ///
-    /// `count` is in units of T; e.g. a `count` of 3 represents a pointer
+    /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
     /// offset of `3 * size_of::<T>()` bytes.
     ///
     /// # Safety
@@ -1948,7 +1948,7 @@ impl<T: ?Sized> *mut T {
     /// Calculates the offset from a pointer (convenience for
     /// `.offset((count as isize).wrapping_neg())`).
     ///
-    /// `count` is in units of T; e.g. a `count` of 3 represents a pointer
+    /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
     /// offset of `3 * size_of::<T>()` bytes.
     ///
     /// # Safety
@@ -2005,7 +2005,7 @@ impl<T: ?Sized> *mut T {
     /// Calculates the offset from a pointer using wrapping arithmetic.
     /// (convenience for `.wrapping_offset(count as isize)`)
     ///
-    /// `count` is in units of T; e.g. a `count` of 3 represents a pointer
+    /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
     /// offset of `3 * size_of::<T>()` bytes.
     ///
     /// # Safety
@@ -2046,7 +2046,7 @@ impl<T: ?Sized> *mut T {
     /// Calculates the offset from a pointer using wrapping arithmetic.
     /// (convenience for `.wrapping_offset((count as isize).wrapping_sub())`)
     ///
-    /// `count` is in units of T; e.g. a `count` of 3 represents a pointer
+    /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
     /// offset of `3 * size_of::<T>()` bytes.
     ///
     /// # Safety
@@ -2375,7 +2375,7 @@ pub(crate) unsafe fn align_offset<T: Sized>(p: *const T, a: usize) -> usize {
     fn mod_inv(x: usize, m: usize) -> usize {
         /// Multiplicative modular inverse table modulo 2⁴ = 16.
         ///
-        /// Note, that this table does not contain values where inverse does not exist (i.e. for
+        /// Note, that this table does not contain values where inverse does not exist (i.e., for
         /// `0⁻¹ mod 16`, `2⁻¹ mod 16`, etc.)
         const INV_TABLE_MOD_16: [u8; 8] = [1, 11, 13, 7, 9, 3, 5, 15];
         /// Modulo for which the `INV_TABLE_MOD_16` is intended.
@@ -2398,7 +2398,7 @@ pub(crate) unsafe fn align_offset<T: Sized>(p: *const T, a: usize) -> usize {
                 // y = y * (2 - xy) mod n
                 //
                 // Note, that we use wrapping operations here intentionally – the original formula
-                // uses e.g. subtraction `mod n`. It is entirely fine to do them `mod
+                // uses e.g., subtraction `mod n`. It is entirely fine to do them `mod
                 // usize::max_value()` instead, because we take the result `mod n` at the end
                 // anyway.
                 inverse = inverse.wrapping_mul(
@@ -2516,6 +2516,39 @@ pub fn eq<T: ?Sized>(a: *const T, b: *const T) -> bool {
     a == b
 }
 
+/// Hash a raw pointer.
+///
+/// This can be used to hash a `&T` reference (which coerces to `*const T` implicitly)
+/// by its address rather than the value it points to
+/// (which is what the `Hash for &T` implementation does).
+///
+/// # Examples
+///
+/// ```
+/// #![feature(ptr_hash)]
+/// use std::collections::hash_map::DefaultHasher;
+/// use std::hash::{Hash, Hasher};
+/// use std::ptr;
+///
+/// let five = 5;
+/// let five_ref = &five;
+///
+/// let mut hasher = DefaultHasher::new();
+/// ptr::hash(five_ref, &mut hasher);
+/// let actual = hasher.finish();
+///
+/// let mut hasher = DefaultHasher::new();
+/// (five_ref as *const i32).hash(&mut hasher);
+/// let expected = hasher.finish();
+///
+/// assert_eq!(actual, expected);
+/// ```
+#[unstable(feature = "ptr_hash", reason = "newly added", issue = "56286")]
+pub fn hash<T: ?Sized, S: hash::Hasher>(hashee: *const T, into: &mut S) {
+    use hash::Hash;
+    hashee.hash(into);
+}
+
 // Impls for function pointers
 macro_rules! fnptr_impls_safety_abi {
     ($FnTy: ty, $($Arg: ident),*) => {
@@ -2759,7 +2792,7 @@ impl<T: ?Sized> Unique<T> {
     /// Creates a new `Unique` if `ptr` is non-null.
     pub fn new(ptr: *mut T) -> Option<Self> {
         if !ptr.is_null() {
-            Some(Unique { pointer: NonZero(ptr as _), _marker: PhantomData })
+            Some(Unique { pointer: unsafe { NonZero(ptr as _) }, _marker: PhantomData })
         } else {
             None
         }
@@ -2815,14 +2848,14 @@ impl<T: ?Sized> fmt::Pointer for Unique<T> {
 #[unstable(feature = "ptr_internals", issue = "0")]
 impl<'a, T: ?Sized> From<&'a mut T> for Unique<T> {
     fn from(reference: &'a mut T) -> Self {
-        Unique { pointer: NonZero(reference as _), _marker: PhantomData }
+        Unique { pointer: unsafe { NonZero(reference as *mut T) }, _marker: PhantomData }
     }
 }
 
 #[unstable(feature = "ptr_internals", issue = "0")]
 impl<'a, T: ?Sized> From<&'a T> for Unique<T> {
     fn from(reference: &'a T) -> Self {
-        Unique { pointer: NonZero(reference as _), _marker: PhantomData }
+        Unique { pointer: unsafe { NonZero(reference as *const T) }, _marker: PhantomData }
     }
 }
 
@@ -2857,12 +2890,12 @@ pub struct NonNull<T: ?Sized> {
 }
 
 /// `NonNull` pointers are not `Send` because the data they reference may be aliased.
-// NB: This impl is unnecessary, but should provide better error messages.
+// N.B., this impl is unnecessary, but should provide better error messages.
 #[stable(feature = "nonnull", since = "1.25.0")]
 impl<T: ?Sized> !Send for NonNull<T> { }
 
 /// `NonNull` pointers are not `Sync` because the data they reference may be aliased.
-// NB: This impl is unnecessary, but should provide better error messages.
+// N.B., this impl is unnecessary, but should provide better error messages.
 #[stable(feature = "nonnull", since = "1.25.0")]
 impl<T: ?Sized> !Sync for NonNull<T> { }
 
@@ -2903,7 +2936,7 @@ impl<T: ?Sized> NonNull<T> {
     #[inline]
     pub fn new(ptr: *mut T) -> Option<Self> {
         if !ptr.is_null() {
-            Some(NonNull { pointer: NonZero(ptr as _) })
+            Some(unsafe { Self::new_unchecked(ptr) })
         } else {
             None
         }
@@ -3025,7 +3058,7 @@ impl<T: ?Sized> From<Unique<T>> for NonNull<T> {
 impl<'a, T: ?Sized> From<&'a mut T> for NonNull<T> {
     #[inline]
     fn from(reference: &'a mut T) -> Self {
-        NonNull { pointer: NonZero(reference as _) }
+        NonNull { pointer: unsafe { NonZero(reference as *mut T) } }
     }
 }
 
@@ -3033,6 +3066,6 @@ impl<'a, T: ?Sized> From<&'a mut T> for NonNull<T> {
 impl<'a, T: ?Sized> From<&'a T> for NonNull<T> {
     #[inline]
     fn from(reference: &'a T) -> Self {
-        NonNull { pointer: NonZero(reference as _) }
+        NonNull { pointer: unsafe { NonZero(reference as *const T) } }
     }
 }
diff --git a/src/libcore/raw.rs b/src/libcore/raw.rs
index 3d4bccb4f9d..4f1af8bf110 100644
--- a/src/libcore/raw.rs
+++ b/src/libcore/raw.rs
@@ -24,7 +24,7 @@
 /// `Box<dyn AnotherTrait>`.
 ///
 /// `TraitObject` is guaranteed to match layouts, but it is not the
-/// type of trait objects (e.g. the fields are not directly accessible
+/// type of trait objects (e.g., the fields are not directly accessible
 /// on a `&SomeTrait`) nor does it control that layout (changing the
 /// definition will not change the layout of a `&SomeTrait`). It is
 /// only designed to be used by unsafe code that needs to manipulate
diff --git a/src/libcore/slice/mod.rs b/src/libcore/slice/mod.rs
index 8c55a16f3c8..193061457b5 100644
--- a/src/libcore/slice/mod.rs
+++ b/src/libcore/slice/mod.rs
@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-//! Slice management and manipulation
+//! Slice management and manipulation.
 //!
 //! For more details see [`std::slice`].
 //!
@@ -702,8 +702,7 @@ impl<T> [T] {
     /// resulting code better than in the case of [`chunks`].
     ///
     /// See [`chunks`] for a variant of this iterator that also returns the remainder as a smaller
-    /// chunk, and [`rchunks_exact`] for the same iterator but starting at the end of the slice of
-    /// the slice.
+    /// chunk, and [`rchunks_exact`] for the same iterator but starting at the end of the slice.
     ///
     /// # Panics
     ///
@@ -878,6 +877,7 @@ impl<T> [T] {
     /// assert_eq!(iter.remainder(), &['l']);
     /// ```
     ///
+    /// [`chunks`]: #method.chunks
     /// [`rchunks`]: #method.rchunks
     /// [`chunks_exact`]: #method.chunks_exact
     #[stable(feature = "rchunks", since = "1.31.0")]
@@ -922,6 +922,7 @@ impl<T> [T] {
     /// assert_eq!(v, &[0, 2, 2, 1, 1]);
     /// ```
     ///
+    /// [`chunks_mut`]: #method.chunks_mut
     /// [`rchunks_mut`]: #method.rchunks_mut
     /// [`chunks_exact_mut`]: #method.chunks_exact_mut
     #[stable(feature = "rchunks", since = "1.31.0")]
@@ -1152,7 +1153,7 @@ impl<T> [T] {
     ///
     /// # Examples
     ///
-    /// Print the slice split once by numbers divisible by 3 (i.e. `[10, 40]`,
+    /// Print the slice split once by numbers divisible by 3 (i.e., `[10, 40]`,
     /// `[20, 60, 50]`):
     ///
     /// ```
@@ -1216,7 +1217,7 @@ impl<T> [T] {
     /// # Examples
     ///
     /// Print the slice split once, starting from the end, by numbers divisible
-    /// by 3 (i.e. `[50]`, `[10, 40, 30, 20]`):
+    /// by 3 (i.e., `[50]`, `[10, 40, 30, 20]`):
     ///
     /// ```
     /// let v = [10, 40, 30, 20, 60, 50];
@@ -1472,8 +1473,8 @@ impl<T> [T] {
 
     /// Sorts the slice, but may not preserve the order of equal elements.
     ///
-    /// This sort is unstable (i.e. may reorder equal elements), in-place (i.e. does not allocate),
-    /// and `O(n log n)` worst-case.
+    /// This sort is unstable (i.e., may reorder equal elements), in-place
+    /// (i.e., does not allocate), and `O(n log n)` worst-case.
     ///
     /// # Current implementation
     ///
@@ -1483,7 +1484,7 @@ impl<T> [T] {
     /// randomization to avoid degenerate cases, but with a fixed seed to always provide
     /// deterministic behavior.
     ///
-    /// It is typically faster than stable sorting, except in a few special cases, e.g. when the
+    /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
     /// slice consists of several concatenated sorted sequences.
     ///
     /// # Examples
@@ -1507,8 +1508,8 @@ impl<T> [T] {
     /// Sorts the slice with a comparator function, but may not preserve the order of equal
     /// elements.
     ///
-    /// This sort is unstable (i.e. may reorder equal elements), in-place (i.e. does not allocate),
-    /// and `O(n log n)` worst-case.
+    /// This sort is unstable (i.e., may reorder equal elements), in-place
+    /// (i.e., does not allocate), and `O(n log n)` worst-case.
     ///
     /// The comparator function must define a total ordering for the elements in the slice. If
     /// the ordering is not total, the order of the elements is unspecified. An order is a
@@ -1534,7 +1535,7 @@ impl<T> [T] {
     /// randomization to avoid degenerate cases, but with a fixed seed to always provide
     /// deterministic behavior.
     ///
-    /// It is typically faster than stable sorting, except in a few special cases, e.g. when the
+    /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
     /// slice consists of several concatenated sorted sequences.
     ///
     /// # Examples
@@ -1561,8 +1562,9 @@ impl<T> [T] {
     /// Sorts the slice with a key extraction function, but may not preserve the order of equal
     /// elements.
     ///
-    /// This sort is unstable (i.e. may reorder equal elements), in-place (i.e. does not allocate),
-    /// and `O(m n log(m n))` worst-case, where the key function is `O(m)`.
+    /// This sort is unstable (i.e., may reorder equal elements), in-place
+    /// (i.e., does not allocate), and `O(m n log(m n))` worst-case, where the key function is
+    /// `O(m)`.
     ///
     /// # Current implementation
     ///
@@ -2459,13 +2461,13 @@ impl<T> SliceIndex<[T]> for usize {
 
     #[inline]
     fn index(self, slice: &[T]) -> &T {
-        // NB: use intrinsic indexing
+        // N.B., use intrinsic indexing
         &(*slice)[self]
     }
 
     #[inline]
     fn index_mut(self, slice: &mut [T]) -> &mut T {
-        // NB: use intrinsic indexing
+        // N.B., use intrinsic indexing
         &mut (*slice)[self]
     }
 }
diff --git a/src/libcore/str/mod.rs b/src/libcore/str/mod.rs
index 89efa120a6f..4a22d929fed 100644
--- a/src/libcore/str/mod.rs
+++ b/src/libcore/str/mod.rs
@@ -482,7 +482,7 @@ fn utf8_first_byte(byte: u8, width: u32) -> u32 { (byte & (0x7F >> width)) as u3
 #[inline]
 fn utf8_acc_cont_byte(ch: u32, byte: u8) -> u32 { (ch << 6) | (byte & CONT_MASK) as u32 }
 
-/// Checks whether the byte is a UTF-8 continuation byte (i.e. starts with the
+/// Checks whether the byte is a UTF-8 continuation byte (i.e., starts with the
 /// bits `10`).
 #[inline]
 fn utf8_is_cont_byte(byte: u8) -> bool { (byte & !CONT_MASK) == TAG_CONT_U8 }
@@ -536,10 +536,9 @@ fn next_code_point_reverse<'a, I>(bytes: &mut I) -> Option<u32>
     where I: DoubleEndedIterator<Item = &'a u8>,
 {
     // Decode UTF-8
-    let w = match bytes.next_back() {
-        None => return None,
-        Some(&next_byte) if next_byte < 128 => return Some(next_byte as u32),
-        Some(&back_byte) => back_byte,
+    let w = match *bytes.next_back()? {
+        next_byte if next_byte < 128 => return Some(next_byte as u32),
+        back_byte => back_byte,
     };
 
     // Multibyte case follows
diff --git a/src/libcore/str/pattern.rs b/src/libcore/str/pattern.rs
index 1c974533e10..2059160ddfe 100644
--- a/src/libcore/str/pattern.rs
+++ b/src/libcore/str/pattern.rs
@@ -397,7 +397,7 @@ unsafe impl<'a> ReverseSearcher<'a> for CharSearcher<'a> {
                     let found_char = index - shift;
                     if let Some(slice) = haystack.get(found_char..(found_char + self.utf8_size)) {
                         if slice == &self.utf8_encoded[0..self.utf8_size] {
-                            // move finger to before the character found (i.e. at its start index)
+                            // move finger to before the character found (i.e., at its start index)
                             self.finger_back = found_char;
                             return Some((self.finger_back, self.finger_back + self.utf8_size));
                         }
@@ -1016,7 +1016,7 @@ struct TwoWaySearcher {
     It can be proven that the following is an equivalent definition of a local period
     for a factorization (u, v): any positive integer r such that x[i] == x[i+r] for
     all i such that |u| - r <= i <= |u| - 1 and such that both x[i] and x[i+r] are
-    defined. (i.e. i > 0 and i + r < |x|).
+    defined. (i.e., i > 0 and i + r < |x|).
 
     Using the above reformulation, it is easy to prove that
 
diff --git a/src/libcore/sync/atomic.rs b/src/libcore/sync/atomic.rs
index 27eeb045bb1..70d940e2b55 100644
--- a/src/libcore/sync/atomic.rs
+++ b/src/libcore/sync/atomic.rs
@@ -188,7 +188,7 @@ unsafe impl<T> Sync for AtomicPtr<T> {}
 /// [Ordering::Relaxed]: #variant.Relaxed
 /// [Ordering::SeqCst]: #variant.SeqCst
 #[stable(feature = "rust1", since = "1.0.0")]
-#[derive(Copy, Clone, Debug)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash)]
 #[non_exhaustive]
 pub enum Ordering {
     /// No ordering constraints, only atomic operations.
@@ -1072,6 +1072,15 @@ impl<T> AtomicPtr<T> {
 #[cfg(target_has_atomic = "8")]
 #[stable(feature = "atomic_bool_from", since = "1.24.0")]
 impl From<bool> for AtomicBool {
+    /// Converts a `bool` into an `AtomicBool`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::atomic::AtomicBool;
+    /// let atomic_bool = AtomicBool::from(true);
+    /// assert_eq!(format!("{:?}", atomic_bool), "true")
+    /// ```
     #[inline]
     fn from(b: bool) -> Self { Self::new(b) }
 }
@@ -1126,8 +1135,12 @@ macro_rules! atomic_int {
 
         #[$stable_from]
         impl From<$int_type> for $atomic_type {
-            #[inline]
-            fn from(v: $int_type) -> Self { Self::new(v) }
+            doc_comment! {
+                concat!(
+"Converts an `", stringify!($int_type), "` into an `", stringify!($atomic_type), "`."),
+                #[inline]
+                fn from(v: $int_type) -> Self { Self::new(v) }
+            }
         }
 
         #[$stable_debug]
@@ -1940,7 +1953,7 @@ atomic_int! {
     8,
     u64 AtomicU64 ATOMIC_U64_INIT
 }
-#[cfg(all(not(stage0), target_has_atomic = "128"))]
+#[cfg(target_has_atomic = "128")]
 atomic_int! {
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
@@ -1954,7 +1967,7 @@ atomic_int! {
     16,
     i128 AtomicI128 ATOMIC_I128_INIT
 }
-#[cfg(all(not(stage0), target_has_atomic = "128"))]
+#[cfg(target_has_atomic = "128")]
 atomic_int! {
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
diff --git a/src/libcore/task/wake.rs b/src/libcore/task/wake.rs
index c0ce7255d62..8ea7abce67b 100644
--- a/src/libcore/task/wake.rs
+++ b/src/libcore/task/wake.rs
@@ -227,7 +227,7 @@ pub unsafe trait UnsafeWake: Send + Sync {
     /// # Unsafety
     ///
     /// This function is unsafe to call because it's asserting the `UnsafeWake`
-    /// value is in a consistent state, i.e. hasn't been dropped.
+    /// value is in a consistent state, i.e., hasn't been dropped.
     unsafe fn clone_raw(&self) -> Waker;
 
     /// Drops this instance of `UnsafeWake`, deallocating resources
@@ -249,7 +249,7 @@ pub unsafe trait UnsafeWake: Send + Sync {
     /// # Unsafety
     ///
     /// This function is unsafe to call because it's asserting the `UnsafeWake`
-    /// value is in a consistent state, i.e. hasn't been dropped.
+    /// value is in a consistent state, i.e., hasn't been dropped.
     unsafe fn drop_raw(&self);
 
     /// Indicates that the associated task is ready to make progress and should
@@ -266,7 +266,7 @@ pub unsafe trait UnsafeWake: Send + Sync {
     /// # Unsafety
     ///
     /// This function is unsafe to call because it's asserting the `UnsafeWake`
-    /// value is in a consistent state, i.e. hasn't been dropped.
+    /// value is in a consistent state, i.e., hasn't been dropped.
     unsafe fn wake(&self);
 
     /// Indicates that the associated task is ready to make progress and should
@@ -286,7 +286,7 @@ pub unsafe trait UnsafeWake: Send + Sync {
     /// # Unsafety
     ///
     /// This function is unsafe to call because it's asserting the `UnsafeWake`
-    /// value is in a consistent state, i.e. hasn't been dropped, and that the
+    /// value is in a consistent state, i.e., hasn't been dropped, and that the
     /// `UnsafeWake` hasn't moved from the thread on which it was created.
     unsafe fn wake_local(&self) {
         self.wake()
diff --git a/src/libcore/tests/iter.rs b/src/libcore/tests/iter.rs
index 0964aae1db5..44899c3f412 100644
--- a/src/libcore/tests/iter.rs
+++ b/src/libcore/tests/iter.rs
@@ -1001,6 +1001,10 @@ fn test_cycle() {
     let mut it = (0..).step_by(1).take(0).cycle();
     assert_eq!(it.size_hint(), (0, Some(0)));
     assert_eq!(it.next(), None);
+
+    assert_eq!(empty::<i32>().cycle().fold(0, |acc, x| acc + x), 0);
+
+    assert_eq!(once(1).cycle().skip(1).take(4).fold(0, |acc, x| acc + x), 4);
 }
 
 #[test]
@@ -1013,6 +1017,33 @@ fn test_iterator_nth() {
 }
 
 #[test]
+fn test_iterator_nth_back() {
+    let v: &[_] = &[0, 1, 2, 3, 4];
+    for i in 0..v.len() {
+        assert_eq!(v.iter().nth_back(i).unwrap(), &v[v.len() - 1 - i]);
+    }
+    assert_eq!(v.iter().nth_back(v.len()), None);
+}
+
+#[test]
+fn test_iterator_rev_nth_back() {
+    let v: &[_] = &[0, 1, 2, 3, 4];
+    for i in 0..v.len() {
+        assert_eq!(v.iter().rev().nth_back(i).unwrap(), &v[i]);
+    }
+    assert_eq!(v.iter().rev().nth_back(v.len()), None);
+}
+
+#[test]
+fn test_iterator_rev_nth() {
+    let v: &[_] = &[0, 1, 2, 3, 4];
+    for i in 0..v.len() {
+        assert_eq!(v.iter().rev().nth(i).unwrap(), &v[v.len() - 1 - i]);
+    }
+    assert_eq!(v.iter().rev().nth(v.len()), None);
+}
+
+#[test]
 fn test_iterator_last() {
     let v: &[_] = &[0, 1, 2, 3, 4];
     assert_eq!(v.iter().last().unwrap(), &4);
@@ -1267,6 +1298,23 @@ fn test_cloned() {
 }
 
 #[test]
+fn test_cloned_side_effects() {
+    let mut count = 0;
+    {
+        let iter = [1, 2, 3]
+            .iter()
+            .map(|x| {
+                count += 1;
+                x
+            })
+            .cloned()
+            .zip(&[1]);
+        for _ in iter {}
+    }
+    assert_eq!(count, 2);
+}
+
+#[test]
 fn test_double_ended_map() {
     let xs = [1, 2, 3, 4, 5, 6];
     let mut it = xs.iter().map(|&x| x * -1);
diff --git a/src/libcore/tests/lib.rs b/src/libcore/tests/lib.rs
index 1f7a8b774d7..400a86d2ffe 100644
--- a/src/libcore/tests/lib.rs
+++ b/src/libcore/tests/lib.rs
@@ -21,6 +21,7 @@
 #![feature(fmt_internals)]
 #![feature(hashmap_internals)]
 #![feature(iter_copied)]
+#![feature(iter_nth_back)]
 #![feature(iter_unfold)]
 #![feature(pattern)]
 #![feature(range_is_empty)]
diff --git a/src/libcore/tests/num/dec2flt/mod.rs b/src/libcore/tests/num/dec2flt/mod.rs
index 17b2f59cd4d..879a41b4b77 100644
--- a/src/libcore/tests/num/dec2flt/mod.rs
+++ b/src/libcore/tests/num/dec2flt/mod.rs
@@ -17,7 +17,7 @@ mod rawfp;
 
 // Take a float literal, turn it into a string in various ways (that are all trusted
 // to be correct) and see if those strings are parsed back to the value of the literal.
-// Requires a *polymorphic literal*, i.e. one that can serve as f64 as well as f32.
+// Requires a *polymorphic literal*, i.e., one that can serve as f64 as well as f32.
 macro_rules! test_literal {
     ($x: expr) => ({
         let x32: f32 = $x;
diff --git a/src/libcore/tests/num/flt2dec/random.rs b/src/libcore/tests/num/flt2dec/random.rs
index ab619093d9d..21a7c9fc6b3 100644
--- a/src/libcore/tests/num/flt2dec/random.rs
+++ b/src/libcore/tests/num/flt2dec/random.rs
@@ -18,7 +18,8 @@ use core::num::flt2dec::strategy::grisu::format_exact_opt;
 use core::num::flt2dec::strategy::grisu::format_shortest_opt;
 use core::num::flt2dec::{decode, DecodableFloat, FullDecoded, Decoded};
 
-use rand::{FromEntropy, XorShiftRng};
+use rand::FromEntropy;
+use rand::rngs::SmallRng;
 use rand::distributions::{Distribution, Uniform};
 
 pub fn decode_finite<T: DecodableFloat>(v: T) -> Decoded {
@@ -71,7 +72,10 @@ fn iterate<F, G, V>(func: &str, k: usize, n: usize, mut f: F, mut g: G, mut v: V
 pub fn f32_random_equivalence_test<F, G>(f: F, g: G, k: usize, n: usize)
         where F: FnMut(&Decoded, &mut [u8]) -> Option<(usize, i16)>,
               G: FnMut(&Decoded, &mut [u8]) -> (usize, i16) {
-    let mut rng = XorShiftRng::from_entropy();
+    if cfg!(target_os = "emscripten") {
+        return // using rng pulls in i128 support, which doesn't work
+    }
+    let mut rng = SmallRng::from_entropy();
     let f32_range = Uniform::new(0x0000_0001u32, 0x7f80_0000);
     iterate("f32_random_equivalence_test", k, n, f, g, |_| {
         let x = f32::from_bits(f32_range.sample(&mut rng));
@@ -82,7 +86,10 @@ pub fn f32_random_equivalence_test<F, G>(f: F, g: G, k: usize, n: usize)
 pub fn f64_random_equivalence_test<F, G>(f: F, g: G, k: usize, n: usize)
         where F: FnMut(&Decoded, &mut [u8]) -> Option<(usize, i16)>,
               G: FnMut(&Decoded, &mut [u8]) -> (usize, i16) {
-    let mut rng = XorShiftRng::from_entropy();
+    if cfg!(target_os = "emscripten") {
+        return // using rng pulls in i128 support, which doesn't work
+    }
+    let mut rng = SmallRng::from_entropy();
     let f64_range = Uniform::new(0x0000_0000_0000_0001u64, 0x7ff0_0000_0000_0000);
     iterate("f64_random_equivalence_test", k, n, f, g, |_| {
         let x = f64::from_bits(f64_range.sample(&mut rng));
@@ -99,7 +106,7 @@ pub fn f32_exhaustive_equivalence_test<F, G>(f: F, g: G, k: usize)
     // this is of course very stressful (and thus should be behind an `#[ignore]` attribute),
     // but with `-C opt-level=3 -C lto` this only takes about an hour or so.
 
-    // iterate from 0x0000_0001 to 0x7f7f_ffff, i.e. all finite ranges
+    // iterate from 0x0000_0001 to 0x7f7f_ffff, i.e., all finite ranges
     let (npassed, nignored) = iterate("f32_exhaustive_equivalence_test",
                                       k, 0x7f7f_ffff, f, g, |i: usize| {
 
diff --git a/src/libcore/tests/num/int_macros.rs b/src/libcore/tests/num/int_macros.rs
index 71d2e794538..8b04f84007f 100644
--- a/src/libcore/tests/num/int_macros.rs
+++ b/src/libcore/tests/num/int_macros.rs
@@ -31,8 +31,8 @@ mod tests {
     }
 
     #[test]
-    fn test_mod_euc() {
-        assert!((-1 as $T).mod_euc(MIN) == MAX);
+    fn test_rem_euclid() {
+        assert!((-1 as $T).rem_euclid(MIN) == MAX);
     }
 
     #[test]
diff --git a/src/libcore/tests/num/mod.rs b/src/libcore/tests/num/mod.rs
index 0928f7560e1..e1648db5e8e 100644
--- a/src/libcore/tests/num/mod.rs
+++ b/src/libcore/tests/num/mod.rs
@@ -694,23 +694,23 @@ macro_rules! test_float {
             assert!(($nan as $fty).max($nan).is_nan());
         }
         #[test]
-        fn mod_euc() {
+        fn rem_euclid() {
             let a: $fty = 42.0;
-            assert!($inf.mod_euc(a).is_nan());
-            assert_eq!(a.mod_euc($inf), a);
-            assert!(a.mod_euc($nan).is_nan());
-            assert!($inf.mod_euc($inf).is_nan());
-            assert!($inf.mod_euc($nan).is_nan());
-            assert!($nan.mod_euc($inf).is_nan());
+            assert!($inf.rem_euclid(a).is_nan());
+            assert_eq!(a.rem_euclid($inf), a);
+            assert!(a.rem_euclid($nan).is_nan());
+            assert!($inf.rem_euclid($inf).is_nan());
+            assert!($inf.rem_euclid($nan).is_nan());
+            assert!($nan.rem_euclid($inf).is_nan());
         }
         #[test]
-        fn div_euc() {
+        fn div_euclid() {
             let a: $fty = 42.0;
-            assert_eq!(a.div_euc($inf), 0.0);
-            assert!(a.div_euc($nan).is_nan());
-            assert!($inf.div_euc($inf).is_nan());
-            assert!($inf.div_euc($nan).is_nan());
-            assert!($nan.div_euc($inf).is_nan());
+            assert_eq!(a.div_euclid($inf), 0.0);
+            assert!(a.div_euclid($nan).is_nan());
+            assert!($inf.div_euclid($inf).is_nan());
+            assert!($inf.div_euclid($nan).is_nan());
+            assert!($nan.div_euclid($inf).is_nan());
         }
     } }
 }
diff --git a/src/libcore/tests/slice.rs b/src/libcore/tests/slice.rs
index dba5a43eb21..4f00ebee1d2 100644
--- a/src/libcore/tests/slice.rs
+++ b/src/libcore/tests/slice.rs
@@ -1024,11 +1024,11 @@ fn test_rotate_right() {
 fn sort_unstable() {
     use core::cmp::Ordering::{Equal, Greater, Less};
     use core::slice::heapsort;
-    use rand::{FromEntropy, Rng, XorShiftRng};
+    use rand::{FromEntropy, Rng, rngs::SmallRng, seq::SliceRandom};
 
     let mut v = [0; 600];
     let mut tmp = [0; 600];
-    let mut rng = XorShiftRng::from_entropy();
+    let mut rng = SmallRng::from_entropy();
 
     for len in (2..25).chain(500..510) {
         let v = &mut v[0..len];
@@ -1073,7 +1073,7 @@ fn sort_unstable() {
     for i in 0..v.len() {
         v[i] = i as i32;
     }
-    v.sort_unstable_by(|_, _| *rng.choose(&[Less, Equal, Greater]).unwrap());
+    v.sort_unstable_by(|_, _| *[Less, Equal, Greater].choose(&mut rng).unwrap());
     v.sort_unstable();
     for i in 0..v.len() {
         assert_eq!(v[i], i as i32);
diff --git a/src/libcore/time.rs b/src/libcore/time.rs
index 938e97503de..475bb721f23 100644
--- a/src/libcore/time.rs
+++ b/src/libcore/time.rs
@@ -216,7 +216,7 @@ impl Duration {
     ///
     /// This method does **not** return the length of the duration when
     /// represented by milliseconds. The returned number always represents a
-    /// fractional portion of a second (i.e. it is less than one thousand).
+    /// fractional portion of a second (i.e., it is less than one thousand).
     ///
     /// # Examples
     ///
@@ -235,7 +235,7 @@ impl Duration {
     ///
     /// This method does **not** return the length of the duration when
     /// represented by microseconds. The returned number always represents a
-    /// fractional portion of a second (i.e. it is less than one million).
+    /// fractional portion of a second (i.e., it is less than one million).
     ///
     /// # Examples
     ///
@@ -254,7 +254,7 @@ impl Duration {
     ///
     /// This method does **not** return the length of the duration when
     /// represented by nanoseconds. The returned number always represents a
-    /// fractional portion of a second (i.e. it is less than one billion).
+    /// fractional portion of a second (i.e., it is less than one billion).
     ///
     /// # Examples
     ///
diff --git a/src/libcore/unicode/printable.rs b/src/libcore/unicode/printable.rs
index 519dd17bb9b..32e4b6b0fa5 100644
--- a/src/libcore/unicode/printable.rs
+++ b/src/libcore/unicode/printable.rs
@@ -80,7 +80,7 @@ pub(crate) fn is_printable(x: char) -> bool {
     }
 }
 
-const SINGLETONS0U: &'static [(u8, u8)] = &[
+const SINGLETONS0U: &[(u8, u8)] = &[
     (0x00, 1),
     (0x03, 5),
     (0x05, 6),
@@ -122,7 +122,7 @@ const SINGLETONS0U: &'static [(u8, u8)] = &[
     (0xfe, 3),
     (0xff, 9),
 ];
-const SINGLETONS0L: &'static [u8] = &[
+const SINGLETONS0L: &[u8] = &[
     0xad, 0x78, 0x79, 0x8b, 0x8d, 0xa2, 0x30, 0x57,
     0x58, 0x8b, 0x8c, 0x90, 0x1c, 0x1d, 0xdd, 0x0e,
     0x0f, 0x4b, 0x4c, 0xfb, 0xfc, 0x2e, 0x2f, 0x3f,
@@ -162,7 +162,7 @@ const SINGLETONS0L: &'static [u8] = &[
     0x91, 0xfe, 0xff, 0x53, 0x67, 0x75, 0xc8, 0xc9,
     0xd0, 0xd1, 0xd8, 0xd9, 0xe7, 0xfe, 0xff,
 ];
-const SINGLETONS1U: &'static [(u8, u8)] = &[
+const SINGLETONS1U: &[(u8, u8)] = &[
     (0x00, 6),
     (0x01, 1),
     (0x03, 1),
@@ -197,7 +197,7 @@ const SINGLETONS1U: &'static [(u8, u8)] = &[
     (0xf0, 4),
     (0xf9, 4),
 ];
-const SINGLETONS1L: &'static [u8] = &[
+const SINGLETONS1L: &[u8] = &[
     0x0c, 0x27, 0x3b, 0x3e, 0x4e, 0x4f, 0x8f, 0x9e,
     0x9e, 0x9f, 0x06, 0x07, 0x09, 0x36, 0x3d, 0x3e,
     0x56, 0xf3, 0xd0, 0xd1, 0x04, 0x14, 0x18, 0x36,
@@ -219,7 +219,7 @@ const SINGLETONS1L: &'static [u8] = &[
     0x78, 0x7d, 0x7f, 0x8a, 0xa4, 0xaa, 0xaf, 0xb0,
     0xc0, 0xd0, 0x3f, 0x71, 0x72, 0x7b,
 ];
-const NORMAL0: &'static [u8] = &[
+const NORMAL0: &[u8] = &[
     0x00, 0x20,
     0x5f, 0x22,
     0x82, 0xdf, 0x04,
@@ -363,7 +363,7 @@ const NORMAL0: &'static [u8] = &[
     0x1b, 0x03,
     0x0f, 0x0d,
 ];
-const NORMAL1: &'static [u8] = &[
+const NORMAL1: &[u8] = &[
     0x5e, 0x22,
     0x7b, 0x05,
     0x03, 0x04,