Make {align,size}_of_val const

Author: ecstatic-morse

library/core/src/intrinsics.rs

@@ -1004,11 +1004,13 @@ extern "rust-intrinsic" {
     ///
     /// The stabilized version of this intrinsic is
     /// [`std::mem::size_of_val`](../../std/mem/fn.size_of_val.html).
+    #[rustc_const_unstable(feature = "const_size_of_val", issue = "46571")]
     pub fn size_of_val<T: ?Sized>(_: *const T) -> usize;
     /// The required alignment of the referenced value.
     ///
     /// The stabilized version of this intrinsic is
     /// [`std::mem::align_of_val`](../../std/mem/fn.align_of_val.html).
+    #[rustc_const_unstable(feature = "const_align_of_val", issue = "46571")]
     pub fn min_align_of_val<T: ?Sized>(_: *const T) -> usize;
 
     /// Gets a static string slice containing the name of a type.

library/core/src/lib.rs

@@ -88,6 +88,8 @@
 #![feature(const_result)]
 #![feature(const_slice_from_raw_parts)]
 #![feature(const_slice_ptr_len)]
+#![feature(const_size_of_val)]
+#![feature(const_align_of_val)]
 #![feature(const_type_name)]
 #![feature(const_likely)]
 #![feature(const_unreachable_unchecked)]

library/core/src/mem/mod.rs

@@ -332,7 +332,8 @@ pub const fn size_of<T>() -> usize {
 /// ```
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
-pub fn size_of_val<T: ?Sized>(val: &T) -> usize {
+#[rustc_const_unstable(feature = "const_size_of_val", issue = "46571")]
+pub const fn size_of_val<T: ?Sized>(val: &T) -> usize {
     intrinsics::size_of_val(val)
 }
 
@@ -466,9 +467,10 @@ pub const fn align_of<T>() -> usize {
 /// ```
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_const_unstable(feature = "const_align_of_val", issue = "46571")]
 #[allow(deprecated)]
-pub fn align_of_val<T: ?Sized>(val: &T) -> usize {
-    min_align_of_val(val)
+pub const fn align_of_val<T: ?Sized>(val: &T) -> usize {
+    intrinsics::min_align_of_val(val)
 }
 
 /// Returns the [ABI]-required minimum alignment of the type of the value that `val` points to.

src/librustc_mir/interpret/intrinsics.rs

@@ -120,6 +120,21 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 self.write_scalar(location.ptr, dest)?;
             }
 
+            sym::min_align_of_val | sym::size_of_val => {
+                let place = self.deref_operand(args[0])?;
+                let (size, align) = self
+                    .size_and_align_of(place.meta, place.layout)?
+                    .ok_or_else(|| err_unsup_format!("`extern type` does not have known layout"))?;
+
+                let result = match intrinsic_name {
+                    sym::min_align_of_val => align.bytes(),
+                    sym::size_of_val => size.bytes(),
+                    _ => bug!(),
+                };
+
+                self.write_scalar(Scalar::from_machine_usize(result, self), dest)?;
+            }
+
             sym::min_align_of
             | sym::pref_align_of
             | sym::needs_drop