Auto merge of #149109 - scottmcm:align-always-alignment, r=<try>

See if this is the time we can remove `layout::size_align`

Author: rust-bors[bot]

library/core/src/alloc/layout.rs

@@ -10,16 +10,6 @@ use crate::mem::SizedTypeProperties;
 use crate::ptr::{Alignment, NonNull};
 use crate::{assert_unsafe_precondition, fmt, mem};
 
-// While this function is used in one place and its implementation
-// could be inlined, the previous attempts to do so made rustc
-// slower:
-//
-// * https://github.com/rust-lang/rust/pull/72189
-// * https://github.com/rust-lang/rust/pull/79827
-const fn size_align<T>() -> (usize, usize) {
-    (size_of::<T>(), align_of::<T>())
-}
-
 /// Layout of a block of memory.
 ///
 /// An instance of `Layout` describes a particular layout of memory.
@@ -168,11 +158,7 @@ impl Layout {
     #[must_use]
     #[inline]
     pub const fn new<T>() -> Self {
-        let (size, align) = size_align::<T>();
-        // SAFETY: if the type is instantiated, rustc already ensures that its
-        // layout is valid. Use the unchecked constructor to avoid inserting a
-        // panicking codepath that needs to be optimized out.
-        unsafe { Layout::from_size_align_unchecked(size, align) }
+        <T as SizedTypeProperties>::LAYOUT
     }
 
     /// Produces layout describing a record that could be used to

library/core/src/mem/mod.rs

@@ -1283,7 +1283,12 @@ pub trait SizedTypeProperties: Sized {
 
     #[doc(hidden)]
     #[unstable(feature = "sized_type_properties", issue = "none")]
-    const LAYOUT: Layout = Layout::new::<Self>();
+    const LAYOUT: Layout = {
+        // SAFETY: if the type is instantiated, rustc already ensures that its
+        // layout is valid. Use the unchecked constructor to avoid inserting a
+        // panicking codepath that needs to be optimized out.
+        unsafe { Layout::from_size_align_unchecked(Self::SIZE, Self::ALIGN) }
+    };
 
     /// The largest safe length for a `[Self]`.
     ///