Describe why size_align have not been inlined so far

Author: tmiasko

library/core/src/alloc/layout.rs

@@ -4,6 +4,12 @@ use crate::mem;
 use crate::num::NonZeroUsize;
 use crate::ptr::NonNull;
 
+// 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) {
     (mem::size_of::<T>(), mem::align_of::<T>())
 }