Merge from rustc

alloc/src/lib.rs

@@ -106,6 +106,7 @@
 #![feature(const_size_of_val)]
 #![feature(const_align_of_val)]
 #![feature(const_ptr_read)]
+#![feature(const_maybe_uninit_zeroed)]
 #![feature(const_maybe_uninit_write)]
 #![feature(const_maybe_uninit_as_mut_ptr)]
 #![feature(const_refs_to_cell)]

alloc/src/str.rs

@@ -559,10 +559,9 @@ impl str {
     #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
     #[inline]
     pub fn to_ascii_uppercase(&self) -> String {
-        let mut bytes = self.as_bytes().to_vec();
-        bytes.make_ascii_uppercase();
-        // make_ascii_uppercase() preserves the UTF-8 invariant.
-        unsafe { String::from_utf8_unchecked(bytes) }
+        let mut s = self.to_owned();
+        s.make_ascii_uppercase();
+        s
     }
 
     /// Returns a copy of this string where each character is mapped to its
@@ -592,10 +591,9 @@ impl str {
     #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
     #[inline]
     pub fn to_ascii_lowercase(&self) -> String {
-        let mut bytes = self.as_bytes().to_vec();
-        bytes.make_ascii_lowercase();
-        // make_ascii_lowercase() preserves the UTF-8 invariant.
-        unsafe { String::from_utf8_unchecked(bytes) }
+        let mut s = self.to_owned();
+        s.make_ascii_lowercase();
+        s
     }
 }
 

alloc/src/vec/drain.rs

@@ -223,9 +223,9 @@ impl<T, A: Allocator> Drop for Drain<'_, T, A> {
         }
 
         // as_slice() must only be called when iter.len() is > 0 because
-        // vec::Splice modifies vec::Drain fields and may grow the vec which would invalidate
-        // the iterator's internal pointers. Creating a reference to deallocated memory
-        // is invalid even when it is zero-length
+        // it also gets touched by vec::Splice which may turn it into a dangling pointer
+        // which would make it and the vec pointer point to different allocations which would
+        // lead to invalid pointer arithmetic below.
         let drop_ptr = iter.as_slice().as_ptr();
 
         unsafe {

alloc/src/vec/is_zero.rs

@@ -4,7 +4,8 @@ use crate::boxed::Box;
 
 #[rustc_specialization_trait]
 pub(super) unsafe trait IsZero {
-    /// Whether this value's representation is all zeros
+    /// Whether this value's representation is all zeros,
+    /// or can be represented with all zeroes.
     fn is_zero(&self) -> bool;
 }
 
@@ -147,6 +148,23 @@ impl_is_zero_option_of_nonzero!(
     NonZeroIsize,
 );
 
+macro_rules! impl_is_zero_option_of_num {
+    ($($t:ty,)+) => {$(
+        unsafe impl IsZero for Option<$t> {
+            #[inline]
+            fn is_zero(&self) -> bool {
+                const {
+                    let none: Self = unsafe { core::mem::MaybeUninit::zeroed().assume_init() };
+                    assert!(none.is_none());
+                }
+                self.is_none()
+            }
+        }
+    )+};
+}
+
+impl_is_zero_option_of_num!(u8, u16, u32, u64, u128, i8, i16, i32, i64, i128, usize, isize,);
+
 unsafe impl<T: IsZero> IsZero for Wrapping<T> {
     #[inline]
     fn is_zero(&self) -> bool {

alloc/src/vec/splice.rs

@@ -54,6 +54,12 @@ impl<I: Iterator, A: Allocator> ExactSizeIterator for Splice<'_, I, A> {}
 impl<I: Iterator, A: Allocator> Drop for Splice<'_, I, A> {
     fn drop(&mut self) {
         self.drain.by_ref().for_each(drop);
+        // At this point draining is done and the only remaining tasks are splicing
+        // and moving things into the final place.
+        // Which means we can replace the slice::Iter with pointers that won't point to deallocated
+        // memory, so that Drain::drop is still allowed to call iter.len(), otherwise it would break
+        // the ptr.sub_ptr contract.
+        self.drain.iter = (&[]).iter();
 
         unsafe {
             if self.drain.tail_len == 0 {

alloc/tests/lib.rs

@@ -1,7 +1,6 @@
 #![feature(allocator_api)]
 #![feature(alloc_layout_extra)]
 #![feature(assert_matches)]
-#![feature(box_syntax)]
 #![feature(btree_drain_filter)]
 #![feature(cow_is_borrowed)]
 #![feature(const_box)]

core/src/any.rs

@@ -662,7 +662,8 @@ impl dyn Any + Send + Sync {
 /// While `TypeId` implements `Hash`, `PartialOrd`, and `Ord`, it is worth
 /// noting that the hashes and ordering will vary between Rust releases. Beware
 /// of relying on them inside of your code!
-#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug, Hash)]
+#[derive(Clone, Copy, Debug, Hash, Eq)]
+#[derive_const(PartialEq, PartialOrd, Ord)]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct TypeId {
     t: u64,

core/src/fmt/mod.rs

@@ -1355,11 +1355,11 @@ impl<'a> Formatter<'a> {
     ///     }
     /// }
     ///
-    /// assert_eq!(&format!("{}", Foo::new(2)), "2");
-    /// assert_eq!(&format!("{}", Foo::new(-1)), "-1");
-    /// assert_eq!(&format!("{}", Foo::new(0)), "0");
-    /// assert_eq!(&format!("{:#}", Foo::new(-1)), "-Foo 1");
-    /// assert_eq!(&format!("{:0>#8}", Foo::new(-1)), "00-Foo 1");
+    /// assert_eq!(format!("{}", Foo::new(2)), "2");
+    /// assert_eq!(format!("{}", Foo::new(-1)), "-1");
+    /// assert_eq!(format!("{}", Foo::new(0)), "0");
+    /// assert_eq!(format!("{:#}", Foo::new(-1)), "-Foo 1");
+    /// assert_eq!(format!("{:0>#8}", Foo::new(-1)), "00-Foo 1");
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn pad_integral(&mut self, is_nonnegative: bool, prefix: &str, buf: &str) -> Result {
@@ -1452,8 +1452,8 @@ impl<'a> Formatter<'a> {
     ///     }
     /// }
     ///
-    /// assert_eq!(&format!("{Foo:<4}"), "Foo ");
-    /// assert_eq!(&format!("{Foo:0>4}"), "0Foo");
+    /// assert_eq!(format!("{Foo:<4}"), "Foo ");
+    /// assert_eq!(format!("{Foo:0>4}"), "0Foo");
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn pad(&mut self, s: &str) -> Result {
@@ -1636,8 +1636,8 @@ impl<'a> Formatter<'a> {
     ///     }
     /// }
     ///
-    /// assert_eq!(&format!("{Foo}"), "Foo");
-    /// assert_eq!(&format!("{Foo:0>8}"), "Foo");
+    /// assert_eq!(format!("{Foo}"), "Foo");
+    /// assert_eq!(format!("{Foo:0>8}"), "Foo");
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn write_str(&mut self, data: &str) -> Result {
@@ -1659,8 +1659,8 @@ impl<'a> Formatter<'a> {
     ///     }
     /// }
     ///
-    /// assert_eq!(&format!("{}", Foo(-1)), "Foo -1");
-    /// assert_eq!(&format!("{:0>8}", Foo(2)), "Foo 2");
+    /// assert_eq!(format!("{}", Foo(-1)), "Foo -1");
+    /// assert_eq!(format!("{:0>8}", Foo(2)), "Foo 2");
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result {
@@ -1703,8 +1703,8 @@ impl<'a> Formatter<'a> {
     /// }
     ///
     /// // We set alignment to the right with ">".
-    /// assert_eq!(&format!("{Foo:G>3}"), "GGG");
-    /// assert_eq!(&format!("{Foo:t>6}"), "tttttt");
+    /// assert_eq!(format!("{Foo:G>3}"), "GGG");
+    /// assert_eq!(format!("{Foo:t>6}"), "tttttt");
     /// ```
     #[must_use]
     #[stable(feature = "fmt_flags", since = "1.5.0")]
@@ -1738,10 +1738,10 @@ impl<'a> Formatter<'a> {
     ///     }
     /// }
     ///
-    /// assert_eq!(&format!("{Foo:<}"), "left");
-    /// assert_eq!(&format!("{Foo:>}"), "right");
-    /// assert_eq!(&format!("{Foo:^}"), "center");
-    /// assert_eq!(&format!("{Foo}"), "into the void");
+    /// assert_eq!(format!("{Foo:<}"), "left");
+    /// assert_eq!(format!("{Foo:>}"), "right");
+    /// assert_eq!(format!("{Foo:^}"), "center");
+    /// assert_eq!(format!("{Foo}"), "into the void");
     /// ```
     #[must_use]
     #[stable(feature = "fmt_flags_align", since = "1.28.0")]
@@ -1767,16 +1767,16 @@ impl<'a> Formatter<'a> {
     ///     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
     ///         if let Some(width) = formatter.width() {
     ///             // If we received a width, we use it
-    ///             write!(formatter, "{:width$}", &format!("Foo({})", self.0), width = width)
+    ///             write!(formatter, "{:width$}", format!("Foo({})", self.0), width = width)
     ///         } else {
     ///             // Otherwise we do nothing special
     ///             write!(formatter, "Foo({})", self.0)
     ///         }
     ///     }
     /// }
     ///
-    /// assert_eq!(&format!("{:10}", Foo(23)), "Foo(23)   ");
-    /// assert_eq!(&format!("{}", Foo(23)), "Foo(23)");
+    /// assert_eq!(format!("{:10}", Foo(23)), "Foo(23)   ");
+    /// assert_eq!(format!("{}", Foo(23)), "Foo(23)");
     /// ```
     #[must_use]
     #[stable(feature = "fmt_flags", since = "1.5.0")]
@@ -1806,8 +1806,8 @@ impl<'a> Formatter<'a> {
     ///     }
     /// }
     ///
-    /// assert_eq!(&format!("{:.4}", Foo(23.2)), "Foo(23.2000)");
-    /// assert_eq!(&format!("{}", Foo(23.2)), "Foo(23.20)");
+    /// assert_eq!(format!("{:.4}", Foo(23.2)), "Foo(23.2000)");
+    /// assert_eq!(format!("{}", Foo(23.2)), "Foo(23.20)");
     /// ```
     #[must_use]
     #[stable(feature = "fmt_flags", since = "1.5.0")]
@@ -1837,9 +1837,9 @@ impl<'a> Formatter<'a> {
     ///     }
     /// }
     ///
-    /// assert_eq!(&format!("{:+}", Foo(23)), "Foo(+23)");
-    /// assert_eq!(&format!("{:+}", Foo(-23)), "Foo(-23)");
-    /// assert_eq!(&format!("{}", Foo(23)), "Foo(23)");
+    /// assert_eq!(format!("{:+}", Foo(23)), "Foo(+23)");
+    /// assert_eq!(format!("{:+}", Foo(-23)), "Foo(-23)");
+    /// assert_eq!(format!("{}", Foo(23)), "Foo(23)");
     /// ```
     #[must_use]
     #[stable(feature = "fmt_flags", since = "1.5.0")]
@@ -1867,8 +1867,8 @@ impl<'a> Formatter<'a> {
     ///     }
     /// }
     ///
-    /// assert_eq!(&format!("{:-}", Foo(23)), "-Foo(23)");
-    /// assert_eq!(&format!("{}", Foo(23)), "Foo(23)");
+    /// assert_eq!(format!("{:-}", Foo(23)), "-Foo(23)");
+    /// assert_eq!(format!("{}", Foo(23)), "Foo(23)");
     /// ```
     #[must_use]
     #[stable(feature = "fmt_flags", since = "1.5.0")]
@@ -1895,8 +1895,8 @@ impl<'a> Formatter<'a> {
     ///     }
     /// }
     ///
-    /// assert_eq!(&format!("{:#}", Foo(23)), "Foo(23)");
-    /// assert_eq!(&format!("{}", Foo(23)), "23");
+    /// assert_eq!(format!("{:#}", Foo(23)), "Foo(23)");
+    /// assert_eq!(format!("{}", Foo(23)), "23");
     /// ```
     #[must_use]
     #[stable(feature = "fmt_flags", since = "1.5.0")]
@@ -1922,7 +1922,7 @@ impl<'a> Formatter<'a> {
     ///     }
     /// }
     ///
-    /// assert_eq!(&format!("{:04}", Foo(23)), "23");
+    /// assert_eq!(format!("{:04}", Foo(23)), "23");
     /// ```
     #[must_use]
     #[stable(feature = "fmt_flags", since = "1.5.0")]

core/src/future/mod.rs

@@ -112,6 +112,10 @@ pub unsafe fn get_context<'a, 'b>(cx: ResumeTy) -> &'a mut Context<'b> {
     unsafe { &mut *cx.0.as_ptr().cast() }
 }
 
+// FIXME(swatinem): This fn is currently needed to work around shortcomings
+// in type and lifetime inference.
+// See the comment at the bottom of `LoweringContext::make_async_expr` and
+// <https://github.com/rust-lang/rust/issues/104826>.
 #[doc(hidden)]
 #[unstable(feature = "gen_future", issue = "50547")]
 #[inline]

core/src/hint.rs

@@ -219,6 +219,75 @@ pub fn spin_loop() {
 /// backend used. Programs cannot rely on `black_box` for *correctness* in any way.
 ///
 /// [`std::convert::identity`]: crate::convert::identity
+///
+/// # When is this useful?
+///
+/// First and foremost: `black_box` does _not_ guarantee any exact behavior and, in some cases, may
+/// do nothing at all. As such, it **must not be relied upon to control critical program behavior.**
+/// This _immediately_ precludes any direct use of this function for cryptographic or security
+/// purposes.
+///
+/// While not suitable in those mission-critical cases, `back_box`'s functionality can generally be
+/// relied upon for benchmarking, and should be used there. It will try to ensure that the
+/// compiler doesn't optimize away part of the intended test code based on context. For
+/// example:
+///
+/// ```
+/// fn contains(haystack: &[&str], needle: &str) -> bool {
+///     haystack.iter().any(|x| x == &needle)
+/// }
+///
+/// pub fn benchmark() {
+///     let haystack = vec!["abc", "def", "ghi", "jkl", "mno"];
+///     let needle = "ghi";
+///     for _ in 0..10 {
+///         contains(&haystack, needle);
+///     }
+/// }
+/// ```
+///
+/// The compiler could theoretically make optimizations like the following:
+///
+/// - `needle` and `haystack` are always the same, move the call to `contains` outside the loop and
+///   delete the loop
+/// - Inline `contains`
+/// - `needle` and `haystack` have values known at compile time, `contains` is always true. Remove
+///   the call and replace with `true`
+/// - Nothing is done with the result of `contains`: delete this function call entirely
+/// - `benchmark` now has no purpose: delete this function
+///
+/// It is not likely that all of the above happens, but the compiler is definitely able to make some
+/// optimizations that could result in a very inaccurate benchmark. This is where `black_box` comes
+/// in:
+///
+/// ```
+/// use std::hint::black_box;
+///
+/// // Same `contains` function
+/// fn contains(haystack: &[&str], needle: &str) -> bool {
+///     haystack.iter().any(|x| x == &needle)
+/// }
+///
+/// pub fn benchmark() {
+///     let haystack = vec!["abc", "def", "ghi", "jkl", "mno"];
+///     let needle = "ghi";
+///     for _ in 0..10 {
+///         // Adjust our benchmark loop contents
+///         black_box(contains(black_box(&haystack), black_box(needle)));
+///     }
+/// }
+/// ```
+///
+/// This essentially tells the compiler to block optimizations across any calls to `black_box`. So,
+/// it now:
+///
+/// - Treats both arguments to `contains` as unpredictable: the body of `contains` can no longer be
+///   optimized based on argument values
+/// - Treats the call to `contains` and its result as volatile: the body of `benchmark` cannot
+///   optimize this away
+///
+/// This makes our benchmark much more realistic to how the function would be used in situ, where
+/// arguments are usually not known at compile time and the result is used in some way.
 #[inline]
 #[stable(feature = "bench_black_box", since = "1.66.0")]
 #[rustc_const_unstable(feature = "const_black_box", issue = "none")]

core/src/intrinsics/mir.rs

@@ -259,6 +259,8 @@ define!("mir_unreachable", fn Unreachable() -> BasicBlock);
 define!("mir_drop", fn Drop<T>(place: T, goto: BasicBlock));
 define!("mir_drop_and_replace", fn DropAndReplace<T>(place: T, value: T, goto: BasicBlock));
 define!("mir_call", fn Call<T>(place: T, goto: BasicBlock, call: T));
+define!("mir_storage_live", fn StorageLive<T>(local: T));
+define!("mir_storage_dead", fn StorageDead<T>(local: T));
 define!("mir_retag", fn Retag<T>(place: T));
 define!("mir_move", fn Move<T>(place: T) -> T);
 define!("mir_static", fn Static<T>(s: T) -> &'static T);