Merge from rustc

Author: RalfJung

alloc/src/boxed/thin.rs

@@ -67,6 +67,26 @@ impl<T> ThinBox<T> {
         let ptr = WithOpaqueHeader::new(meta, value);
         ThinBox { ptr, _marker: PhantomData }
     }
+
+    /// Moves a type to the heap with its [`Metadata`] stored in the heap allocation instead of on
+    /// the stack. Returns an error if allocation fails, instead of aborting.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(allocator_api)]
+    /// #![feature(thin_box)]
+    /// use std::boxed::ThinBox;
+    ///
+    /// let five = ThinBox::try_new(5)?;
+    /// # Ok::<(), std::alloc::AllocError>(())
+    /// ```
+    ///
+    /// [`Metadata`]: core::ptr::Pointee::Metadata
+    pub fn try_new(value: T) -> Result<Self, core::alloc::AllocError> {
+        let meta = ptr::metadata(&value);
+        WithOpaqueHeader::try_new(meta, value).map(|ptr| ThinBox { ptr, _marker: PhantomData })
+    }
 }
 
 #[unstable(feature = "thin_box", issue = "92791")]
@@ -179,6 +199,10 @@ impl WithOpaqueHeader {
         let ptr = WithHeader::new(header, value);
         Self(ptr.0)
     }
+
+    fn try_new<H, T>(header: H, value: T) -> Result<Self, core::alloc::AllocError> {
+        WithHeader::try_new(header, value).map(|ptr| Self(ptr.0))
+    }
 }
 
 impl<H> WithHeader<H> {
@@ -224,6 +248,46 @@ impl<H> WithHeader<H> {
         }
     }
 
+    /// Non-panicking version of `new`.
+    /// Any error is returned as `Err(core::alloc::AllocError)`.
+    fn try_new<T>(header: H, value: T) -> Result<WithHeader<H>, core::alloc::AllocError> {
+        let value_layout = Layout::new::<T>();
+        let Ok((layout, value_offset)) = Self::alloc_layout(value_layout) else {
+            return Err(core::alloc::AllocError);
+        };
+
+        unsafe {
+            // Note: It's UB to pass a layout with a zero size to `alloc::alloc`, so
+            // we use `layout.dangling()` for this case, which should have a valid
+            // alignment for both `T` and `H`.
+            let ptr = if layout.size() == 0 {
+                // Some paranoia checking, mostly so that the ThinBox tests are
+                // more able to catch issues.
+                debug_assert!(
+                    value_offset == 0 && mem::size_of::<T>() == 0 && mem::size_of::<H>() == 0
+                );
+                layout.dangling()
+            } else {
+                let ptr = alloc::alloc(layout);
+                if ptr.is_null() {
+                    return Err(core::alloc::AllocError);
+                }
+
+                // Safety:
+                // - The size is at least `aligned_header_size`.
+                let ptr = ptr.add(value_offset) as *mut _;
+
+                NonNull::new_unchecked(ptr)
+            };
+
+            let result = WithHeader(ptr, PhantomData);
+            ptr::write(result.header(), header);
+            ptr::write(result.value().cast(), value);
+
+            Ok(result)
+        }
+    }
+
     // Safety:
     // - Assumes that either `value` can be dereferenced, or is the
     //   `NonNull::dangling()` we use when both `T` and `H` are ZSTs.

alloc/src/fmt.rs

@@ -188,6 +188,10 @@
 //!     * `#X` - precedes the argument with a `0x`
 //!     * `#b` - precedes the argument with a `0b`
 //!     * `#o` - precedes the argument with a `0o`
+//!
+//!   See [Formatting traits](#formatting-traits) for a description of what the `?`, `x`, `X`,
+//!   `b`, and `o` flags do.
+//!
 //! * `0` - This is used to indicate for integer formats that the padding to `width` should
 //!         both be done with a `0` character as well as be sign-aware. A format
 //!         like `{:08}` would yield `00000001` for the integer `1`, while the
@@ -197,6 +201,7 @@
 //!         and before the digits. When used together with the `#` flag, a similar
 //!         rule applies: padding zeros are inserted after the prefix but before
 //!         the digits. The prefix is included in the total width.
+//!         This flag overrides the [fill character and alignment flag](#fillalignment).
 //!
 //! ## Precision
 //!

core/src/cell.rs

@@ -237,9 +237,9 @@
 
 use crate::cmp::Ordering;
 use crate::fmt::{self, Debug, Display};
-use crate::intrinsics::is_nonoverlapping;
+use crate::intrinsics;
 use crate::marker::{PhantomData, Unsize};
-use crate::mem;
+use crate::mem::{self, size_of};
 use crate::ops::{CoerceUnsized, Deref, DerefMut, DispatchFromDyn};
 use crate::ptr::{self, NonNull};
 
@@ -435,11 +435,15 @@ impl<T> Cell<T> {
     #[inline]
     #[stable(feature = "move_cell", since = "1.17.0")]
     pub fn swap(&self, other: &Self) {
+        fn is_nonoverlapping<T>(src: *const T, dst: *const T) -> bool {
+            intrinsics::is_nonoverlapping(src.cast(), dst.cast(), size_of::<T>(), 1)
+        }
+
         if ptr::eq(self, other) {
             // Swapping wouldn't change anything.
             return;
         }
-        if !is_nonoverlapping(self, other, 1) {
+        if !is_nonoverlapping(self, other) {
             // See <https://github.com/rust-lang/rust/issues/80778> for why we need to stop here.
             panic!("`Cell::swap` on overlapping non-identical `Cell`s");
         }

core/src/ffi/c_str.rs

@@ -88,6 +88,7 @@ use crate::str;
 // want `repr(transparent)` but we don't want it to show up in rustdoc, so we hide it under
 // `cfg(doc)`. This is an ad-hoc implementation of attribute privacy.
 #[cfg_attr(not(doc), repr(transparent))]
+#[allow(clippy::derived_hash_with_manual_eq)]
 pub struct CStr {
     // FIXME: this should not be represented with a DST slice but rather with
     //        just a raw `c_char` along with some form of marker to make

core/src/intrinsics.rs

@@ -56,7 +56,7 @@
 
 use crate::marker::DiscriminantKind;
 use crate::marker::Tuple;
-use crate::mem::{self, align_of};
+use crate::mem::align_of;
 
 pub mod mir;
 pub mod simd;
@@ -1027,7 +1027,7 @@ extern "rust-intrinsic" {
 
     /// The size of the referenced value in bytes.
     ///
-    /// The stabilized version of this intrinsic is [`mem::size_of_val`].
+    /// The stabilized version of this intrinsic is [`crate::mem::size_of_val`].
     #[rustc_const_unstable(feature = "const_size_of_val", issue = "46571")]
     #[rustc_nounwind]
     pub fn size_of_val<T: ?Sized>(_: *const T) -> usize;
@@ -1107,7 +1107,7 @@ extern "rust-intrinsic" {
 
     /// Moves a value out of scope without running drop glue.
     ///
-    /// This exists solely for [`mem::forget_unsized`]; normal `forget` uses
+    /// This exists solely for [`crate::mem::forget_unsized`]; normal `forget` uses
     /// `ManuallyDrop` instead.
     ///
     /// Note that, unlike most intrinsics, this is safe to call;
@@ -1233,7 +1233,7 @@ extern "rust-intrinsic" {
     /// Depending on what the code is doing, the following alternatives are preferable to
     /// pointer-to-integer transmutation:
     /// - If the code just wants to store data of arbitrary type in some buffer and needs to pick a
-    ///   type for that buffer, it can use [`MaybeUninit`][mem::MaybeUninit].
+    ///   type for that buffer, it can use [`MaybeUninit`][crate::mem::MaybeUninit].
     /// - If the code actually wants to work on the address the pointer points to, it can use `as`
     ///   casts or [`ptr.addr()`][pointer::addr].
     ///
@@ -2317,7 +2317,7 @@ extern "rust-intrinsic" {
     /// Therefore, implementations must not require the user to uphold
     /// any safety invariants.
     ///
-    /// The to-be-stabilized version of this intrinsic is [`mem::variant_count`].
+    /// The to-be-stabilized version of this intrinsic is [`crate::mem::variant_count`].
     #[rustc_const_unstable(feature = "variant_count", issue = "73662")]
     #[rustc_safe_intrinsic]
     #[rustc_nounwind]
@@ -2569,6 +2569,19 @@ extern "rust-intrinsic" {
     #[rustc_nounwind]
     pub fn is_val_statically_known<T: Copy>(arg: T) -> bool;
 
+    /// Returns the value of `cfg!(debug_assertions)`, but after monomorphization instead of in
+    /// macro expansion.
+    ///
+    /// This always returns `false` in const eval and Miri. The interpreter provides better
+    /// diagnostics than the checks that this is used to implement. However, this means
+    /// you should only be using this intrinsic to guard requirements that, if violated,
+    /// immediately lead to UB. Otherwise, const-eval and Miri will miss out on those
+    /// checks entirely.
+    ///
+    /// Since this is evaluated after monomorphization, branching on this value can be used to
+    /// implement debug assertions that are included in the precompiled standard library, but can
+    /// be optimized out by builds that monomorphize the standard library code with debug
+    /// assertions disabled. This intrinsic is primarily used by [`assert_unsafe_precondition`].
     #[rustc_const_unstable(feature = "delayed_debug_assertions", issue = "none")]
     #[rustc_safe_intrinsic]
     #[cfg(not(bootstrap))]
@@ -2597,7 +2610,7 @@ pub(crate) const fn debug_assertions() -> bool {
 /// These checks are behind a condition which is evaluated at codegen time, not expansion time like
 /// [`debug_assert`]. This means that a standard library built with optimizations and debug
 /// assertions disabled will have these checks optimized out of its monomorphizations, but if a
-/// a caller of the standard library has debug assertions enabled and monomorphizes an expansion of
+/// caller of the standard library has debug assertions enabled and monomorphizes an expansion of
 /// this macro, that monomorphization will contain the check.
 ///
 /// Since these checks cannot be optimized out in MIR, some care must be taken in both call and
@@ -2606,8 +2619,8 @@ pub(crate) const fn debug_assertions() -> bool {
 /// combination of properties ensures that the code for the checks is only compiled once, and has a
 /// minimal impact on the caller's code size.
 ///
-/// Caller should also introducing any other `let` bindings or any code outside this macro in order
-/// to call it. Since the precompiled standard library is built with full debuginfo and these
+/// Callers should also avoid introducing any other `let` bindings or any code outside this macro in
+/// order to call it. Since the precompiled standard library is built with full debuginfo and these
 /// variables cannot be optimized out in MIR, an innocent-looking `let` can produce enough
 /// debuginfo to have a measurable compile-time impact on debug builds.
 ///
@@ -2659,33 +2672,12 @@ pub(crate) fn is_valid_allocation_size(size: usize, len: usize) -> bool {
     len <= max_len
 }
 
-pub(crate) fn is_nonoverlapping_mono(
-    src: *const (),
-    dst: *const (),
-    size: usize,
-    count: usize,
-) -> bool {
-    let src_usize = src.addr();
-    let dst_usize = dst.addr();
-    let Some(size) = size.checked_mul(count) else {
-        crate::panicking::panic_nounwind(
-            "is_nonoverlapping: `size_of::<T>() * count` overflows a usize",
-        )
-    };
-    let diff = src_usize.abs_diff(dst_usize);
-    // If the absolute distance between the ptrs is at least as big as the size of the buffer,
-    // they do not overlap.
-    diff >= size
-}
-
 /// Checks whether the regions of memory starting at `src` and `dst` of size
-/// `count * size_of::<T>()` do *not* overlap.
-#[inline]
-pub(crate) fn is_nonoverlapping<T>(src: *const T, dst: *const T, count: usize) -> bool {
+/// `count * size` do *not* overlap.
+pub(crate) fn is_nonoverlapping(src: *const (), dst: *const (), size: usize, count: usize) -> bool {
     let src_usize = src.addr();
     let dst_usize = dst.addr();
-    let Some(size) = mem::size_of::<T>().checked_mul(count) else {
-        // Use panic_nounwind instead of Option::expect, so that this function is nounwind.
+    let Some(size) = size.checked_mul(count) else {
         crate::panicking::panic_nounwind(
             "is_nonoverlapping: `size_of::<T>() * count` overflows a usize",
         )
@@ -2809,7 +2801,7 @@ pub const unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: us
             ) =>
             is_aligned_and_not_null(src, align)
                 && is_aligned_and_not_null(dst, align)
-                && is_nonoverlapping_mono(src, dst, size, count)
+                && is_nonoverlapping(src, dst, size, count)
         );
         copy_nonoverlapping(src, dst, count)
     }

core/src/intrinsics/simd.rs

@@ -190,14 +190,27 @@ extern "platform-intrinsic" {
     ///
     /// `T` must be a vector.
     ///
-    /// `U` must be a const array of `i32`s.
+    /// `U` must be a **const** array of `i32`s. This means it must either refer to a named
+    /// const or be given as an inline const expression (`const { ... }`).
     ///
     /// `V` must be a vector with the same element type as `T` and the same length as `U`.
     ///
-    /// Concatenates `x` and `y`, then returns a new vector such that each element is selected from
-    /// the concatenation by the matching index in `idx`.
+    /// Returns a new vector such that element `i` is selected from `xy[idx[i]]`, where `xy`
+    /// is the concatenation of `x` and `y`. It is a compile-time error if `idx[i]` is out-of-bounds
+    /// of `xy`.
     pub fn simd_shuffle<T, U, V>(x: T, y: T, idx: U) -> V;
 
+    /// Shuffle two vectors by const indices.
+    ///
+    /// `T` must be a vector.
+    ///
+    /// `U` must be a vector with the same element type as `T` and the same length as `IDX`.
+    ///
+    /// Returns a new vector such that element `i` is selected from `xy[IDX[i]]`, where `xy`
+    /// is the concatenation of `x` and `y`. It is a compile-time error if `IDX[i]` is out-of-bounds
+    /// of `xy`.
+    pub fn simd_shuffle_generic<T, U, const IDX: &'static [u32]>(x: T, y: T) -> U;
+
     /// Read a vector of pointers.
     ///
     /// `T` must be a vector.
@@ -232,6 +245,9 @@ extern "platform-intrinsic" {
     /// corresponding value in `val` to the pointer.
     /// Otherwise if the corresponding value in `mask` is `0`, do nothing.
     ///
+    /// The stores happen in left-to-right order.
+    /// (This is relevant in case two of the stores overlap.)
+    ///
     /// # Safety
     /// Unmasked values in `T` must be writeable as if by `<ptr>::write` (e.g. aligned to the element
     /// type).
@@ -468,4 +484,36 @@ extern "platform-intrinsic" {
     ///
     /// `T` must be a vector of integers.
     pub fn simd_cttz<T>(x: T) -> T;
+
+    /// Round up each element to the next highest integer-valued float.
+    ///
+    /// `T` must be a vector of floats.
+    pub fn simd_ceil<T>(x: T) -> T;
+
+    /// Round down each element to the next lowest integer-valued float.
+    ///
+    /// `T` must be a vector of floats.
+    pub fn simd_floor<T>(x: T) -> T;
+
+    /// Round each element to the closest integer-valued float.
+    /// Ties are resolved by rounding away from 0.
+    ///
+    /// `T` must be a vector of floats.
+    pub fn simd_round<T>(x: T) -> T;
+
+    /// Return the integer part of each element as an integer-valued float.
+    /// In other words, non-integer values are truncated towards zero.
+    ///
+    /// `T` must be a vector of floats.
+    pub fn simd_trunc<T>(x: T) -> T;
+
+    /// Takes the square root of each element.
+    ///
+    /// `T` must be a vector of floats.
+    pub fn simd_fsqrt<T>(x: T) -> T;
+
+    /// Computes `(x*y) + z` for each element, but without any intermediate rounding.
+    ///
+    /// `T` must be a vector of floats.
+    pub fn simd_fma<T>(x: T, y: T, z: T) -> T;
 }

core/src/num/f32.rs

@@ -462,6 +462,7 @@ impl f32 {
     /// and target platforms isn't guaranteed.
     #[stable(feature = "assoc_int_consts", since = "1.43.0")]
     #[rustc_diagnostic_item = "f32_nan"]
+    #[allow(clippy::eq_op)]
     pub const NAN: f32 = 0.0_f32 / 0.0_f32;
     /// Infinity (∞).
     #[stable(feature = "assoc_int_consts", since = "1.43.0")]
@@ -483,6 +484,7 @@ impl f32 {
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
     #[inline]
+    #[allow(clippy::eq_op)] // > if you intended to check if the operand is NaN, use `.is_nan()` instead :)
     pub const fn is_nan(self) -> bool {
         self != self
     }

core/src/num/f64.rs

@@ -461,6 +461,7 @@ impl f64 {
     /// and target platforms isn't guaranteed.
     #[rustc_diagnostic_item = "f64_nan"]
     #[stable(feature = "assoc_int_consts", since = "1.43.0")]
+    #[allow(clippy::eq_op)]
     pub const NAN: f64 = 0.0_f64 / 0.0_f64;
     /// Infinity (∞).
     #[stable(feature = "assoc_int_consts", since = "1.43.0")]
@@ -482,6 +483,7 @@ impl f64 {
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
     #[inline]
+    #[allow(clippy::eq_op)] // > if you intended to check if the operand is NaN, use `.is_nan()` instead :)
     pub const fn is_nan(self) -> bool {
         self != self
     }

core/src/option.rs

@@ -567,6 +567,7 @@ use crate::{
 #[rustc_diagnostic_item = "Option"]
 #[lang = "Option"]
 #[stable(feature = "rust1", since = "1.0.0")]
+#[allow(clippy::derived_hash_with_manual_eq)] // PartialEq is specialized
 pub enum Option<T> {
     /// No value.
     #[lang = "None"]