Rollup merge of #75485 - RalfJung:pin, r=nagisa

[rust.git] / src / librustc_middle / ty / list.rs

diff --git a/src/librustc_middle/ty/list.rs b/src/librustc_middle/ty/list.rs
index 76c72e4c2603d53f7d8673b4fe9e73c548351ed9..fe390adf89f9fe70c32c94338f69807f3f7821e3 100644 (file)
--- a/src/librustc_middle/ty/list.rs
+++ b/src/librustc_middle/ty/list.rs
@@ -2,7 +2,8 @@
 
 use rustc_serialize::{Encodable, Encoder};
 
-use std::cmp::{self, Ordering};
+use std::alloc::Layout;
+use std::cmp::Ordering;
 use std::fmt;
 use std::hash::{Hash, Hasher};
 use std::iter;
@@ -43,17 +44,9 @@ pub(super) fn from_arena<'tcx>(arena: &'tcx Arena<'tcx>, slice: &[T]) -> &'tcx L
         assert!(mem::size_of::<T>() != 0);
         assert!(!slice.is_empty());
 
-        // Align up the size of the len (usize) field
-        let align = mem::align_of::<T>();
-        let align_mask = align - 1;
-        let offset = mem::size_of::<usize>();
-        let offset = (offset + align_mask) & !align_mask;
-
-        let size = offset + slice.len() * mem::size_of::<T>();
-
-        let mem = arena
-            .dropless
-            .alloc_raw(size, cmp::max(mem::align_of::<T>(), mem::align_of::<usize>()));
+        let (layout, _offset) =
+            Layout::new::<usize>().extend(Layout::for_value::<[T]>(slice)).unwrap();
+        let mem = arena.dropless.alloc_raw(layout);
         unsafe {
             let result = &mut *(mem as *mut List<T>);
             // Write the length
@@ -83,9 +76,16 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
     }
 }
 
-impl<T: Encodable> Encodable for List<T> {
+impl<S: Encoder, T: Encodable<S>> Encodable<S> for List<T> {
+    #[inline]
+    fn encode(&self, s: &mut S) -> Result<(), S::Error> {
+        (**self).encode(s)
+    }
+}
+
+impl<S: Encoder, T: Encodable<S>> Encodable<S> for &List<T> {
     #[inline]
-    fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
+    fn encode(&self, s: &mut S) -> Result<(), S::Error> {
         (**self).encode(s)
     }
 }