Rollup merge of rust-lang#144123 - oli-obk:ctfe-unsize, r=RalfJung

Generalize `unsize` and `unsize_into` destinations

Just something that I noticed during other work. We do this for most such functions, so let's do it here, too.

r? ``@RalfJung``

Author: matthiaskrgr

compiler/rustc_const_eval/src/interpret/cast.rs

@@ -17,6 +17,7 @@ use super::{
     throw_ub_custom,
 };
 use crate::fluent_generated as fluent;
+use crate::interpret::Writeable;
 
 impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
     pub fn cast(
@@ -358,7 +359,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
     fn unsize_into_ptr(
         &mut self,
         src: &OpTy<'tcx, M::Provenance>,
-        dest: &PlaceTy<'tcx, M::Provenance>,
+        dest: &impl Writeable<'tcx, M::Provenance>,
         // The pointee types
         source_ty: Ty<'tcx>,
         cast_ty: Ty<'tcx>,
@@ -455,7 +456,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         &mut self,
         src: &OpTy<'tcx, M::Provenance>,
         cast_ty: TyAndLayout<'tcx>,
-        dest: &PlaceTy<'tcx, M::Provenance>,
+        dest: &impl Writeable<'tcx, M::Provenance>,
     ) -> InterpResult<'tcx> {
         trace!("Unsizing {:?} of type {} into {}", *src, src.layout.ty, cast_ty.ty);
         match (src.layout.ty.kind(), cast_ty.ty.kind()) {
@@ -496,7 +497,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                     self.cur_span(),
                     "unsize_into: invalid conversion: {:?} -> {:?}",
                     src.layout,
-                    dest.layout
+                    dest.layout()
                 )
             }
         }

compiler/rustc_mir_transform/src/gvn.rs

@@ -579,7 +579,7 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
                 CastKind::PointerCoercion(ty::adjustment::PointerCoercion::Unsize, _) => {
                     let src = self.evaluated[value].as_ref()?;
                     let dest = self.ecx.allocate(ty, MemoryKind::Stack).discard_err()?;
-                    self.ecx.unsize_into(src, ty, &dest.clone().into()).discard_err()?;
+                    self.ecx.unsize_into(src, ty, &dest).discard_err()?;
                     self.ecx
                         .alloc_mark_immutable(dest.ptr().provenance.unwrap().alloc_id())
                         .discard_err()?;