Auto merge of #147793 - cjgillot:no-null-op, r=scottmcm,oli-obk

Replace NullOp::SizeOf and NullOp::AlignOf by lang items.

Part of rust-lang/rust#146411

Fixes rust-lang/rust#119729
Keeps rust-lang/rust#136175 as it involves `offset_of!` which this PR does not touch.

r? `@ghost`

Author: bors

rustc_public/src/mir/body.rs

@@ -641,9 +641,7 @@ impl Rvalue {
                     .discriminant_ty()
                     .ok_or_else(|| error!("Expected a `RigidTy` but found: {place_ty:?}"))
             }
-            Rvalue::NullaryOp(NullOp::SizeOf | NullOp::AlignOf | NullOp::OffsetOf(..), _) => {
-                Ok(Ty::usize_ty())
-            }
+            Rvalue::NullaryOp(NullOp::OffsetOf(..), _) => Ok(Ty::usize_ty()),
             Rvalue::NullaryOp(NullOp::ContractChecks, _)
             | Rvalue::NullaryOp(NullOp::UbChecks, _) => Ok(Ty::bool_ty()),
             Rvalue::Aggregate(ak, ops) => match *ak {
@@ -1024,10 +1022,6 @@ pub enum CastKind {
 
 #[derive(Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub enum NullOp {
-    /// Returns the size of a value of that type.
-    SizeOf,
-    /// Returns the minimum alignment of a type.
-    AlignOf,
     /// Returns the offset of a field.
     OffsetOf(Vec<(VariantIdx, FieldIdx)>),
     /// cfg!(ub_checks), but at codegen time

rustc_public/src/unstable/convert/stable/mir.rs

@@ -323,8 +323,6 @@ impl<'tcx> Stable<'tcx> for mir::NullOp<'tcx> {
     ) -> Self::T {
         use rustc_middle::mir::NullOp::*;
         match self {
-            SizeOf => crate::mir::NullOp::SizeOf,
-            AlignOf => crate::mir::NullOp::AlignOf,
             OffsetOf(indices) => crate::mir::NullOp::OffsetOf(
                 indices.iter().map(|idx| idx.stable(tables, cx)).collect(),
             ),