Auto merge of #116583 - saethlin:inline-small-core-fns, r=<try>

Add #[inline] to small functions in core

Where "small" is strictly defined as optimized_mir with 5 or less statements and no calls. I've also applied that heuristic recursively; applying it once causes some functions to become eligible for MIR inlining bring other functions under the threshold.

r? `@ghost`

library/core/src/alloc/layout.rs

@@ -16,6 +16,7 @@ use crate::ptr::{Alignment, NonNull};
 //
 // * https://github.com/rust-lang/rust/pull/72189
 // * https://github.com/rust-lang/rust/pull/79827
+#[inline]
 const fn size_align<T>() -> (usize, usize) {
     (mem::size_of::<T>(), mem::align_of::<T>())
 }

library/core/src/array/iter.rs

@@ -54,6 +54,7 @@ impl<T, const N: usize> IntoIterator for [T; N] {
     /// 2021 edition -- see the [array] Editions section for more information.
     ///
     /// [array]: prim@array
+    #[inline]
     fn into_iter(self) -> Self::IntoIter {
         // SAFETY: The transmute here is actually safe. The docs of `MaybeUninit`
         // promise:
@@ -77,6 +78,7 @@ impl<T, const N: usize> IntoIter<T, N> {
     /// Creates a new iterator over the given `array`.
     #[stable(feature = "array_value_iter", since = "1.51.0")]
     #[deprecated(since = "1.59.0", note = "use `IntoIterator::into_iter` instead")]
+    #[inline]
     pub fn new(array: [T; N]) -> Self {
         IntoIterator::into_iter(array)
     }
@@ -139,6 +141,7 @@ impl<T, const N: usize> IntoIter<T, N> {
     /// ```
     #[unstable(feature = "array_into_iter_constructors", issue = "91583")]
     #[rustc_const_unstable(feature = "const_array_into_iter_constructors", issue = "91583")]
+    #[inline]
     pub const unsafe fn new_unchecked(
         buffer: [MaybeUninit<T>; N],
         initialized: Range<usize>,
@@ -357,9 +360,11 @@ impl<T, const N: usize> Drop for IntoIter<T, N> {
 
 #[stable(feature = "array_value_iter_impls", since = "1.40.0")]
 impl<T, const N: usize> ExactSizeIterator for IntoIter<T, N> {
+    #[inline]
     fn len(&self) -> usize {
         self.alive.len()
     }
+    #[inline]
     fn is_empty(&self) -> bool {
         self.alive.is_empty()
     }

library/core/src/array/mod.rs

@@ -113,6 +113,7 @@ where
 /// Converts a reference to `T` into a reference to an array of length 1 (without copying).
 #[stable(feature = "array_from_ref", since = "1.53.0")]
 #[rustc_const_stable(feature = "const_array_from_ref_shared", since = "1.63.0")]
+#[inline]
 pub const fn from_ref<T>(s: &T) -> &[T; 1] {
     // SAFETY: Converting `&T` to `&[T; 1]` is sound.
     unsafe { &*(s as *const T).cast::<[T; 1]>() }
@@ -121,6 +122,7 @@ pub const fn from_ref<T>(s: &T) -> &[T; 1] {
 /// Converts a mutable reference to `T` into a mutable reference to an array of length 1 (without copying).
 #[stable(feature = "array_from_ref", since = "1.53.0")]
 #[rustc_const_unstable(feature = "const_array_from_ref", issue = "90206")]
+#[inline]
 pub const fn from_mut<T>(s: &mut T) -> &mut [T; 1] {
     // SAFETY: Converting `&mut T` to `&mut [T; 1]` is sound.
     unsafe { &mut *(s as *mut T).cast::<[T; 1]>() }
@@ -143,13 +145,15 @@ impl fmt::Display for TryFromSliceError {
 #[stable(feature = "try_from", since = "1.34.0")]
 impl Error for TryFromSliceError {
     #[allow(deprecated)]
+    #[inline]
     fn description(&self) -> &str {
         "could not convert slice to array"
     }
 }
 
 #[stable(feature = "try_from_slice_error", since = "1.36.0")]
 impl From<Infallible> for TryFromSliceError {
+    #[inline]
     fn from(x: Infallible) -> TryFromSliceError {
         match x {}
     }
@@ -173,13 +177,15 @@ impl<T, const N: usize> AsMut<[T]> for [T; N] {
 
 #[stable(feature = "array_borrow", since = "1.4.0")]
 impl<T, const N: usize> Borrow<[T]> for [T; N] {
+    #[inline]
     fn borrow(&self) -> &[T] {
         self
     }
 }
 
 #[stable(feature = "array_borrow", since = "1.4.0")]
 impl<T, const N: usize> BorrowMut<[T]> for [T; N] {
+    #[inline]
     fn borrow_mut(&mut self) -> &mut [T] {
         self
     }
@@ -321,6 +327,7 @@ impl<'a, T, const N: usize> IntoIterator for &'a [T; N] {
     type Item = &'a T;
     type IntoIter = Iter<'a, T>;
 
+    #[inline]
     fn into_iter(self) -> Iter<'a, T> {
         self.iter()
     }
@@ -331,6 +338,7 @@ impl<'a, T, const N: usize> IntoIterator for &'a mut [T; N] {
     type Item = &'a mut T;
     type IntoIter = IterMut<'a, T>;
 
+    #[inline]
     fn into_iter(self) -> IterMut<'a, T> {
         self.iter_mut()
     }
@@ -435,6 +443,7 @@ macro_rules! array_impl_default {
     {$n:expr, $t:ident $($ts:ident)*} => {
         #[stable(since = "1.4.0", feature = "array_default")]
         impl<T> Default for [T; $n] where T: Default {
+            #[inline]
             fn default() -> [T; $n] {
                 [$t::default(), $($ts::default()),*]
             }
@@ -444,6 +453,7 @@ macro_rules! array_impl_default {
     {$n:expr,} => {
         #[stable(since = "1.4.0", feature = "array_default")]
         impl<T> Default for [T; $n] {
+            #[inline]
             fn default() -> [T; $n] { [] }
         }
     };
@@ -541,13 +551,15 @@ impl<T, const N: usize> [T; N] {
     /// Returns a slice containing the entire array. Equivalent to `&s[..]`.
     #[stable(feature = "array_as_slice", since = "1.57.0")]
     #[rustc_const_stable(feature = "array_as_slice", since = "1.57.0")]
+    #[inline]
     pub const fn as_slice(&self) -> &[T] {
         self
     }
 
     /// Returns a mutable slice containing the entire array. Equivalent to
     /// `&mut s[..]`.
     #[stable(feature = "array_as_slice", since = "1.57.0")]
+    #[inline]
     pub fn as_mut_slice(&mut self) -> &mut [T] {
         self
     }
@@ -783,7 +795,7 @@ where
     R: Try<Output = T>,
     R::Residual: Residual<[T; N]>,
 {
-    assert!(iter.size_hint().0 >= N);
+    #[inline]
     fn next<T>(mut iter: impl UncheckedIterator<Item = T>) -> impl FnMut(usize) -> T {
         move |_| {
             // SAFETY: We know that `from_fn` will call this at most N times,
@@ -792,6 +804,7 @@ where
         }
     }
 
+    assert!(iter.size_hint().0 >= N);
     try_from_fn(next(iter))
 }
 

library/core/src/borrow.rs

@@ -207,34 +207,39 @@ pub trait BorrowMut<Borrowed: ?Sized>: Borrow<Borrowed> {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: ?Sized> Borrow<T> for T {
     #[rustc_diagnostic_item = "noop_method_borrow"]
+    #[inline]
     fn borrow(&self) -> &T {
         self
     }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: ?Sized> BorrowMut<T> for T {
+    #[inline]
     fn borrow_mut(&mut self) -> &mut T {
         self
     }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: ?Sized> Borrow<T> for &T {
+    #[inline]
     fn borrow(&self) -> &T {
         &**self
     }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: ?Sized> Borrow<T> for &mut T {
+    #[inline]
     fn borrow(&self) -> &T {
         &**self
     }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: ?Sized> BorrowMut<T> for &mut T {
+    #[inline]
     fn borrow_mut(&mut self) -> &mut T {
         &mut **self
     }

library/core/src/cell.rs

@@ -373,6 +373,7 @@ impl<T: Ord + Copy> Ord for Cell<T> {
 #[stable(feature = "cell_from", since = "1.12.0")]
 impl<T> From<T> for Cell<T> {
     /// Creates a new `Cell<T>` containing the given value.
+    #[inline]
     fn from(t: T) -> Cell<T> {
         Cell::new(t)
     }
@@ -488,6 +489,7 @@ impl<T> Cell<T> {
     /// ```
     #[stable(feature = "move_cell", since = "1.17.0")]
     #[rustc_const_unstable(feature = "const_cell_into_inner", issue = "78729")]
+    #[inline]
     pub const fn into_inner(self) -> T {
         self.value.into_inner()
     }
@@ -658,6 +660,7 @@ impl<T> Cell<[T]> {
     /// assert_eq!(slice_cell.len(), 3);
     /// ```
     #[stable(feature = "as_cell", since = "1.37.0")]
+    #[inline]
     pub fn as_slice_of_cells(&self) -> &[Cell<T>] {
         // SAFETY: `Cell<T>` has the same memory layout as `T`.
         unsafe { &*(self as *const Cell<[T]> as *const [Cell<T>]) }
@@ -678,6 +681,7 @@ impl<T, const N: usize> Cell<[T; N]> {
     /// let array_cell: &[Cell<i32>; 3] = cell_array.as_array_of_cells();
     /// ```
     #[unstable(feature = "as_array_of_cells", issue = "88248")]
+    #[inline]
     pub fn as_array_of_cells(&self) -> &[Cell<T>; N] {
         // SAFETY: `Cell<T>` has the same memory layout as `T`.
         unsafe { &*(self as *const Cell<[T; N]> as *const [Cell<T>; N]) }
@@ -1172,6 +1176,7 @@ impl<T: ?Sized> RefCell<T> {
     /// assert!(c.try_borrow().is_ok());
     /// ```
     #[unstable(feature = "cell_leak", issue = "69099")]
+    #[inline]
     pub fn undo_leak(&mut self) -> &mut T {
         *self.borrow.get_mut() = UNUSED;
         self.get_mut()
@@ -1356,6 +1361,7 @@ impl<T: ?Sized + Ord> Ord for RefCell<T> {
 #[stable(feature = "cell_from", since = "1.12.0")]
 impl<T> From<T> for RefCell<T> {
     /// Creates a new `RefCell<T>` containing the given value.
+    #[inline]
     fn from(t: T) -> RefCell<T> {
         RefCell::new(t)
     }
@@ -1577,6 +1583,7 @@ impl<'b, T: ?Sized> Ref<'b, T> {
     /// assert!(cell.try_borrow_mut().is_err());
     /// ```
     #[unstable(feature = "cell_leak", issue = "69099")]
+    #[inline]
     pub fn leak(orig: Ref<'b, T>) -> &'b T {
         // By forgetting this Ref we ensure that the borrow counter in the RefCell can't go back to
         // UNUSED within the lifetime `'b`. Resetting the reference tracking state would require a
@@ -1743,6 +1750,7 @@ impl<'b, T: ?Sized> RefMut<'b, T> {
     /// assert!(cell.try_borrow_mut().is_err());
     /// ```
     #[unstable(feature = "cell_leak", issue = "69099")]
+    #[inline]
     pub fn leak(mut orig: RefMut<'b, T>) -> &'b mut T {
         // By forgetting this BorrowRefMut we ensure that the borrow counter in the RefCell can't
         // go back to UNUSED within the lifetime `'b`. Resetting the reference tracking state would
@@ -2190,6 +2198,7 @@ impl<T: Default> Default for UnsafeCell<T> {
 #[stable(feature = "cell_from", since = "1.12.0")]
 impl<T> From<T> for UnsafeCell<T> {
     /// Creates a new `UnsafeCell<T>` containing the given value.
+    #[inline]
     fn from(t: T) -> UnsafeCell<T> {
         UnsafeCell::new(t)
     }
@@ -2290,6 +2299,7 @@ impl<T: Default> Default for SyncUnsafeCell<T> {
 #[unstable(feature = "sync_unsafe_cell", issue = "95439")]
 impl<T> From<T> for SyncUnsafeCell<T> {
     /// Creates a new `SyncUnsafeCell<T>` containing the given value.
+    #[inline]
     fn from(t: T) -> SyncUnsafeCell<T> {
         SyncUnsafeCell::new(t)
     }

library/core/src/char/decode.rs

@@ -109,6 +109,7 @@ impl DecodeUtf16Error {
     /// Returns the unpaired surrogate which caused this error.
     #[must_use]
     #[stable(feature = "decode_utf16", since = "1.9.0")]
+    #[inline]
     pub fn unpaired_surrogate(&self) -> u16 {
         self.code
     }
@@ -124,6 +125,7 @@ impl fmt::Display for DecodeUtf16Error {
 #[stable(feature = "decode_utf16", since = "1.9.0")]
 impl Error for DecodeUtf16Error {
     #[allow(deprecated)]
+    #[inline]
     fn description(&self) -> &str {
         "unpaired surrogate found"
     }

library/core/src/char/mod.rs

@@ -219,16 +219,19 @@ impl fmt::Display for EscapeUnicode {
 pub struct EscapeDefault(escape::EscapeIterInner<10>);
 
 impl EscapeDefault {
+    #[inline]
     fn printable(chr: ascii::Char) -> Self {
         let data = [chr];
         Self(escape::EscapeIterInner::from_array(data))
     }
 
+    #[inline]
     fn backslash(chr: ascii::Char) -> Self {
         let data = [ascii::Char::ReverseSolidus, chr];
         Self(escape::EscapeIterInner::from_array(data))
     }
 
+    #[inline]
     fn from_unicode(esc: EscapeUnicode) -> Self {
         Self(esc.0)
     }
@@ -304,20 +307,24 @@ enum EscapeDebugInner {
 }
 
 impl EscapeDebug {
+    #[inline]
     fn printable(chr: char) -> Self {
         Self(EscapeDebugInner::Char(chr))
     }
 
+    #[inline]
     fn backslash(chr: ascii::Char) -> Self {
         let data = [ascii::Char::ReverseSolidus, chr];
         let iter = escape::EscapeIterInner::from_array(data);
         Self(EscapeDebugInner::Bytes(iter))
     }
 
+    #[inline]
     fn from_unicode(esc: EscapeUnicode) -> Self {
         Self(EscapeDebugInner::Bytes(esc.0))
     }
 
+    #[inline]
     fn clear(&mut self) {
         let bytes = escape::EscapeIterInner::from_array([]);
         self.0 = EscapeDebugInner::Bytes(bytes);