Auto merge of #94059 - b-naber:constantkind-val-transformation, r=lcnr

Treat constant values as mir::ConstantKind::Val

Another step that is necessary for the introduction of Valtrees: we don't want to treat `ty::Const` instances of kind `ty::ConstKind::Value` as `mir::ConstantKind::Ty` anymore.

r? `@oli-obk`

Author: bors

compiler/rustc_const_eval/src/interpret/eval_context.rs

@@ -164,7 +164,7 @@ pub enum StackPopCleanup {
 }
 
 /// State of a local variable including a memoized layout
-#[derive(Clone, PartialEq, Eq, HashStable)]
+#[derive(Clone, Debug, PartialEq, Eq, HashStable)]
 pub struct LocalState<'tcx, Tag: Provenance = AllocId> {
     pub value: LocalValue<Tag>,
     /// Don't modify if `Some`, this is only used to prevent computing the layout twice
@@ -714,13 +714,15 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         self.size_and_align_of(&mplace.meta, &mplace.layout)
     }
 
+    #[instrument(skip(self, body, return_place, return_to_block), level = "debug")]
     pub fn push_stack_frame(
         &mut self,
         instance: ty::Instance<'tcx>,
         body: &'mir mir::Body<'tcx>,
         return_place: Option<&PlaceTy<'tcx, M::PointerTag>>,
         return_to_block: StackPopCleanup,
     ) -> InterpResult<'tcx> {
+        debug!("body: {:#?}", body);
         // first push a stack frame so we have access to the local substs
         let pre_frame = Frame {
             body,
@@ -824,6 +826,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
     /// `Drop` impls for any locals that have been initialized at this point.
     /// The cleanup block ends with a special `Resume` terminator, which will
     /// cause us to continue unwinding.
+    #[instrument(skip(self), level = "debug")]
     pub(super) fn pop_stack_frame(&mut self, unwinding: bool) -> InterpResult<'tcx> {
         info!(
             "popping stack frame ({})",
@@ -876,6 +879,8 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             return Ok(());
         }
 
+        debug!("locals: {:#?}", frame.locals);
+
         // Cleanup: deallocate all locals that are backed by an allocation.
         for local in &frame.locals {
             self.deallocate_local(local.value)?;
@@ -935,6 +940,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         Ok(())
     }
 
+    #[instrument(skip(self), level = "debug")]
     fn deallocate_local(&mut self, local: LocalValue<M::PointerTag>) -> InterpResult<'tcx> {
         if let LocalValue::Live(Operand::Indirect(MemPlace { ptr, .. })) = local {
             // All locals have a backing allocation, even if the allocation is empty

compiler/rustc_const_eval/src/interpret/intern.rs

@@ -359,6 +359,8 @@ pub fn intern_const_alloc_recursive<
     // pointers, ... So we can't intern them according to their type rules
 
     let mut todo: Vec<_> = leftover_allocations.iter().cloned().collect();
+    debug!(?todo);
+    debug!("dead_alloc_map: {:#?}", ecx.memory.dead_alloc_map);
     while let Some(alloc_id) = todo.pop() {
         if let Some((_, mut alloc)) = ecx.memory.alloc_map.remove(&alloc_id) {
             // We can't call the `intern_shallow` method here, as its logic is tailored to safe

compiler/rustc_const_eval/src/interpret/memory.rs

@@ -275,6 +275,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
         Ok(new_ptr)
     }
 
+    #[instrument(skip(self), level = "debug")]
     pub fn deallocate(
         &mut self,
         ptr: Pointer<Option<M::PointerTag>>,
@@ -305,6 +306,8 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
             .into());
         };
 
+        debug!(?alloc);
+
         if alloc.mutability == Mutability::Not {
             throw_ub_format!("deallocating immutable allocation {}", alloc_id);
         }

compiler/rustc_middle/src/mir/mod.rs

@@ -2557,7 +2557,14 @@ impl<'tcx> Constant<'tcx> {
 impl<'tcx> From<ty::Const<'tcx>> for ConstantKind<'tcx> {
     #[inline]
     fn from(ct: ty::Const<'tcx>) -> Self {
-        Self::Ty(ct)
+        match ct.val() {
+            ty::ConstKind::Value(cv) => {
+                // FIXME Once valtrees are introduced we need to convert those
+                // into `ConstValue` instances here
+                Self::Val(cv, ct.ty())
+            }
+            _ => Self::Ty(ct),
+        }
     }
 }
 
@@ -2638,6 +2645,27 @@ impl<'tcx> ConstantKind<'tcx> {
             Self::Val(val, _) => val.try_to_machine_usize(tcx),
         }
     }
+
+    pub fn from_bool(tcx: TyCtxt<'tcx>, v: bool) -> Self {
+        let cv = ConstValue::from_bool(v);
+        Self::Val(cv, tcx.types.bool)
+    }
+
+    pub fn from_zero_sized(ty: Ty<'tcx>) -> Self {
+        let cv = ConstValue::Scalar(Scalar::ZST);
+        Self::Val(cv, ty)
+    }
+
+    pub fn from_usize(tcx: TyCtxt<'tcx>, n: u64) -> Self {
+        let ty = tcx.types.usize;
+        let size = tcx
+            .layout_of(ty::ParamEnv::empty().and(ty))
+            .unwrap_or_else(|e| bug!("could not compute layout for {:?}: {:?}", ty, e))
+            .size;
+        let cv = ConstValue::Scalar(Scalar::from_uint(n as u128, size));
+
+        Self::Val(cv, ty)
+    }
 }
 
 /// A collection of projections into user types.

compiler/rustc_mir_build/src/build/cfg.rs

@@ -2,7 +2,7 @@
 
 use crate::build::CFG;
 use rustc_middle::mir::*;
-use rustc_middle::ty::{self, TyCtxt};
+use rustc_middle::ty::TyCtxt;
 
 impl<'tcx> CFG<'tcx> {
     crate fn block_data(&self, blk: BasicBlock) -> &BasicBlockData<'tcx> {
@@ -73,7 +73,7 @@ impl<'tcx> CFG<'tcx> {
             Rvalue::Use(Operand::Constant(Box::new(Constant {
                 span: source_info.span,
                 user_ty: None,
-                literal: ty::Const::zero_sized(tcx, tcx.types.unit).into(),
+                literal: ConstantKind::from_zero_sized(tcx.types.unit),
             }))),
         );
     }

compiler/rustc_mir_build/src/build/expr/into.rs

@@ -9,7 +9,7 @@ use rustc_hir as hir;
 use rustc_index::vec::Idx;
 use rustc_middle::mir::*;
 use rustc_middle::thir::*;
-use rustc_middle::ty::{self, CanonicalUserTypeAnnotation};
+use rustc_middle::ty::CanonicalUserTypeAnnotation;
 use std::iter;
 
 impl<'a, 'tcx> Builder<'a, 'tcx> {
@@ -107,7 +107,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     Constant {
                         span: expr_span,
                         user_ty: None,
-                        literal: ty::Const::from_bool(this.tcx, true).into(),
+                        literal: ConstantKind::from_bool(this.tcx, true),
                     },
                 );
 
@@ -118,7 +118,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     Constant {
                         span: expr_span,
                         user_ty: None,
-                        literal: ty::Const::from_bool(this.tcx, false).into(),
+                        literal: ConstantKind::from_bool(this.tcx, false),
                     },
                 );
 
@@ -183,8 +183,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                         span: expr_span,
                         user_ty: None,
                         literal: match op {
-                            LogicalOp::And => ty::Const::from_bool(this.tcx, false).into(),
-                            LogicalOp::Or => ty::Const::from_bool(this.tcx, true).into(),
+                            LogicalOp::And => ConstantKind::from_bool(this.tcx, false),
+                            LogicalOp::Or => ConstantKind::from_bool(this.tcx, true),
                         },
                     },
                 );

compiler/rustc_mir_build/src/build/misc.rs

@@ -54,7 +54,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             Constant {
                 span: source_info.span,
                 user_ty: None,
-                literal: ty::Const::from_usize(self.tcx, value).into(),
+                literal: ConstantKind::from_usize(self.tcx, value),
             },
         );
         temp

compiler/rustc_mir_build/src/thir/cx/expr.rs

@@ -569,6 +569,9 @@ impl<'tcx> Cx<'tcx> {
 
             hir::ExprKind::ConstBlock(ref anon_const) => {
                 let anon_const_def_id = self.tcx.hir().local_def_id(anon_const.hir_id);
+
+                // FIXME Do we want to use `from_inline_const` once valtrees
+                // are introduced? This would create `ValTree`s that will never be used...
                 let value = ty::Const::from_inline_const(self.tcx, anon_const_def_id);
 
                 ExprKind::ConstBlock { value }

compiler/rustc_trait_selection/src/traits/query/normalize.rs

@@ -334,6 +334,21 @@ impl<'cx, 'tcx> FallibleTypeFolder<'tcx> for QueryNormalizer<'cx, 'tcx> {
         &mut self,
         constant: mir::ConstantKind<'tcx>,
     ) -> Result<mir::ConstantKind<'tcx>, Self::Error> {
-        constant.try_super_fold_with(self)
+        let constant_kind = match constant {
+            mir::ConstantKind::Ty(c) => {
+                let const_folded = c.try_fold_with(self)?;
+                match const_folded.val() {
+                    ty::ConstKind::Value(cv) => {
+                        // FIXME With Valtrees we need to convert `cv: ValTree`
+                        // to a `ConstValue` here.
+                        mir::ConstantKind::Val(cv, const_folded.ty())
+                    }
+                    _ => mir::ConstantKind::Ty(const_folded),
+                }
+            }
+            mir::ConstantKind::Val(_, _) => constant.try_super_fold_with(self)?,
+        };
+
+        Ok(constant_kind)
     }
 }

src/test/mir-opt/inline/inline_generator.main.Inline.diff

@@ -46,11 +46,11 @@
 -     bb1: {
 +         discriminant(_4) = 0;            // scope 2 at $DIR/inline-generator.rs:15:5: 15:41
           _3 = &mut _4;                    // scope 0 at $DIR/inline-generator.rs:9:23: 9:31
--         _2 = Pin::<&mut impl Generator<bool>>::new(move _3) -> [return: bb2, unwind: bb4]; // scope 0 at $DIR/inline-generator.rs:9:14: 9:32
+-         _2 = Pin::<&mut [generator@$DIR/inline-generator.rs:15:5: 15:41]>::new(move _3) -> [return: bb2, unwind: bb4]; // scope 0 at $DIR/inline-generator.rs:9:14: 9:32
 -                                          // mir::Constant
 -                                          // + span: $DIR/inline-generator.rs:9:14: 9:22
 -                                          // + user_ty: UserType(0)
--                                          // + literal: Const { ty: fn(&mut impl Generator<bool>) -> Pin<&mut impl Generator<bool>> {Pin::<&mut impl Generator<bool>>::new}, val: Value(Scalar(<ZST>)) }
+-                                          // + literal: Const { ty: fn(&mut [generator@$DIR/inline-generator.rs:15:5: 15:41]) -> Pin<&mut [generator@$DIR/inline-generator.rs:15:5: 15:41]> {Pin::<&mut [generator@$DIR/inline-generator.rs:15:5: 15:41]>::new}, val: Value(Scalar(<ZST>)) }
 -     }
 - 
 -     bb2: {
@@ -62,10 +62,10 @@
 +         StorageDead(_6);                 // scope 5 at $SRC_DIR/core/src/pin.rs:LL:COL
 +         StorageDead(_5);                 // scope 4 at $SRC_DIR/core/src/pin.rs:LL:COL
           StorageDead(_3);                 // scope 0 at $DIR/inline-generator.rs:9:31: 9:32
--         _1 = <impl Generator<bool> as Generator<bool>>::resume(move _2, const false) -> [return: bb3, unwind: bb4]; // scope 0 at $DIR/inline-generator.rs:9:14: 9:46
+-         _1 = <[generator@$DIR/inline-generator.rs:15:5: 15:41] as Generator<bool>>::resume(move _2, const false) -> [return: bb3, unwind: bb4]; // scope 0 at $DIR/inline-generator.rs:9:14: 9:46
 -                                          // mir::Constant
 -                                          // + span: $DIR/inline-generator.rs:9:33: 9:39
--                                          // + literal: Const { ty: for<'r> fn(Pin<&'r mut impl Generator<bool>>, bool) -> GeneratorState<<impl Generator<bool> as Generator<bool>>::Yield, <impl Generator<bool> as Generator<bool>>::Return> {<impl Generator<bool> as Generator<bool>>::resume}, val: Value(Scalar(<ZST>)) }
+-                                          // + literal: Const { ty: for<'r> fn(Pin<&'r mut [generator@$DIR/inline-generator.rs:15:5: 15:41]>, bool) -> GeneratorState<<[generator@$DIR/inline-generator.rs:15:5: 15:41] as Generator<bool>>::Yield, <[generator@$DIR/inline-generator.rs:15:5: 15:41] as Generator<bool>>::Return> {<[generator@$DIR/inline-generator.rs:15:5: 15:41] as Generator<bool>>::resume}, val: Value(Scalar(<ZST>)) }
 +         StorageLive(_7);                 // scope 0 at $DIR/inline-generator.rs:9:14: 9:46
 +         _7 = const false;                // scope 0 at $DIR/inline-generator.rs:9:14: 9:46
 +         StorageLive(_10);                // scope 0 at $DIR/inline-generator.rs:9:14: 9:46

src/test/mir-opt/inline/issue_78442.bar.Inline.diff

@@ -25,10 +25,10 @@
       bb1: {
           _3 = &_4;                        // scope 0 at $DIR/issue-78442.rs:11:5: 11:15
           StorageLive(_5);                 // scope 0 at $DIR/issue-78442.rs:11:5: 11:17
--         _2 = <impl Fn() as Fn<()>>::call(move _3, move _5) -> [return: bb2, unwind: bb4]; // scope 0 at $DIR/issue-78442.rs:11:5: 11:17
+-         _2 = <fn() {foo} as Fn<()>>::call(move _3, move _5) -> [return: bb2, unwind: bb4]; // scope 0 at $DIR/issue-78442.rs:11:5: 11:17
 -                                          // mir::Constant
 -                                          // + span: $DIR/issue-78442.rs:11:5: 11:15
--                                          // + literal: Const { ty: for<'r> extern "rust-call" fn(&'r impl Fn(), ()) -> <impl Fn() as FnOnce<()>>::Output {<impl Fn() as Fn<()>>::call}, val: Value(Scalar(<ZST>)) }
+-                                          // + literal: Const { ty: for<'r> extern "rust-call" fn(&'r fn() {foo}, ()) -> <fn() {foo} as FnOnce<()>>::Output {<fn() {foo} as Fn<()>>::call}, val: Value(Scalar(<ZST>)) }
 +         _2 = move (*_3)() -> [return: bb5, unwind: bb3]; // scope 1 at $SRC_DIR/core/src/ops/function.rs:LL:COL
       }
 

src/test/mir-opt/inline/issue_78442.bar.RevealAll.diff

@@ -25,10 +25,12 @@
           _3 = &_4;                        // scope 0 at $DIR/issue-78442.rs:11:5: 11:15
           StorageLive(_5);                 // scope 0 at $DIR/issue-78442.rs:11:5: 11:17
           nop;                             // scope 0 at $DIR/issue-78442.rs:11:5: 11:17
-          _2 = <impl Fn() as Fn<()>>::call(move _3, move _5) -> [return: bb2, unwind: bb4]; // scope 0 at $DIR/issue-78442.rs:11:5: 11:17
+-         _2 = <impl Fn() as Fn<()>>::call(move _3, move _5) -> [return: bb2, unwind: bb4]; // scope 0 at $DIR/issue-78442.rs:11:5: 11:17
++         _2 = <fn() {foo} as Fn<()>>::call(move _3, move _5) -> [return: bb2, unwind: bb4]; // scope 0 at $DIR/issue-78442.rs:11:5: 11:17
                                            // mir::Constant
                                            // + span: $DIR/issue-78442.rs:11:5: 11:15
-                                           // + literal: Const { ty: for<'r> extern "rust-call" fn(&'r impl Fn(), ()) -> <impl Fn() as FnOnce<()>>::Output {<impl Fn() as Fn<()>>::call}, val: Value(Scalar(<ZST>)) }
+-                                          // + literal: Const { ty: for<'r> extern "rust-call" fn(&'r impl Fn(), ()) -> <impl Fn() as FnOnce<()>>::Output {<impl Fn() as Fn<()>>::call}, val: Value(Scalar(<ZST>)) }
++                                          // + literal: Const { ty: for<'r> extern "rust-call" fn(&'r fn() {foo}, ()) -> <fn() {foo} as FnOnce<()>>::Output {<fn() {foo} as Fn<()>>::call}, val: Value(Scalar(<ZST>)) }
       }
 
       bb2: {

src/test/mir-opt/nll/named_lifetimes_basic.use_x.nll.0.mir

@@ -42,7 +42,7 @@ fn use_x(_1: &'_#6r mut i32, _2: &'_#7r u32, _3: &'_#8r u32, _4: &'_#9r u32) ->
     let mut _0: bool;                    // return place in scope 0 at $DIR/named-lifetimes-basic.rs:12:81: 12:85
 
     bb0: {
-        _0 = const Const(Value(Scalar(0x01)): bool); // bb0[0]: scope 0 at $DIR/named-lifetimes-basic.rs:12:88: 12:92
+        _0 = const ConstValue(Scalar(0x01): bool); // bb0[0]: scope 0 at $DIR/named-lifetimes-basic.rs:12:88: 12:92
         return;                          // bb0[1]: scope 0 at $DIR/named-lifetimes-basic.rs:12:94: 12:94
     }
 }

src/test/mir-opt/nll/region_subtyping_basic.main.nll.0.32bit.mir

@@ -45,11 +45,11 @@ fn main() -> () {
 
     bb0: {
         StorageLive(_1);                 // bb0[0]: scope 0 at $DIR/region-subtyping-basic.rs:17:9: 17:14
-        _1 = [const Const(Value(Scalar(0x00000001)): usize), const Const(Value(Scalar(0x00000002)): usize), const Const(Value(Scalar(0x00000003)): usize)]; // bb0[1]: scope 0 at $DIR/region-subtyping-basic.rs:17:17: 17:26
+        _1 = [const ConstValue(Scalar(0x00000001): usize), const ConstValue(Scalar(0x00000002): usize), const ConstValue(Scalar(0x00000003): usize)]; // bb0[1]: scope 0 at $DIR/region-subtyping-basic.rs:17:17: 17:26
         FakeRead(ForLet(None), _1);      // bb0[2]: scope 0 at $DIR/region-subtyping-basic.rs:17:9: 17:14
         StorageLive(_2);                 // bb0[3]: scope 1 at $DIR/region-subtyping-basic.rs:18:9: 18:10
         StorageLive(_3);                 // bb0[4]: scope 1 at $DIR/region-subtyping-basic.rs:18:16: 18:17
-        _3 = const Const(Value(Scalar(0x00000000)): usize); // bb0[5]: scope 1 at $DIR/region-subtyping-basic.rs:18:16: 18:17
+        _3 = const ConstValue(Scalar(0x00000000): usize); // bb0[5]: scope 1 at $DIR/region-subtyping-basic.rs:18:16: 18:17
         _4 = Len(_1);                    // bb0[6]: scope 1 at $DIR/region-subtyping-basic.rs:18:14: 18:18
         _5 = Lt(_3, _4);                 // bb0[7]: scope 1 at $DIR/region-subtyping-basic.rs:18:14: 18:18
         assert(move _5, "index out of bounds: the length is {} but the index is {}", move _4, _3) -> [success: bb1, unwind: bb7]; // bb0[8]: scope 1 at $DIR/region-subtyping-basic.rs:18:14: 18:18
@@ -62,15 +62,15 @@ fn main() -> () {
         _6 = _2;                         // bb1[3]: scope 2 at $DIR/region-subtyping-basic.rs:19:13: 19:14
         FakeRead(ForLet(None), _6);      // bb1[4]: scope 2 at $DIR/region-subtyping-basic.rs:19:9: 19:10
         StorageLive(_7);                 // bb1[5]: scope 3 at $DIR/region-subtyping-basic.rs:20:8: 20:12
-        _7 = const Const(Value(Scalar(0x01)): bool); // bb1[6]: scope 3 at $DIR/region-subtyping-basic.rs:20:8: 20:12
+        _7 = const ConstValue(Scalar(0x01): bool); // bb1[6]: scope 3 at $DIR/region-subtyping-basic.rs:20:8: 20:12
         switchInt(move _7) -> [Const(Value(Scalar(0x00)): bool): bb4, otherwise: bb2]; // bb1[7]: scope 3 at $DIR/region-subtyping-basic.rs:20:8: 20:12
     }
 
     bb2: {
         StorageLive(_8);                 // bb2[0]: scope 3 at $DIR/region-subtyping-basic.rs:21:9: 21:18
         StorageLive(_9);                 // bb2[1]: scope 3 at $DIR/region-subtyping-basic.rs:21:15: 21:17
         _9 = (*_6);                      // bb2[2]: scope 3 at $DIR/region-subtyping-basic.rs:21:15: 21:17
-        _8 = Const(Value(Scalar(<ZST>)): fn(usize) -> bool {use_x})(move _9) -> [return: bb3, unwind: bb7]; // bb2[3]: scope 3 at $DIR/region-subtyping-basic.rs:21:9: 21:18
+        _8 = ConstValue(Scalar(<ZST>): fn(usize) -> bool {use_x})(move _9) -> [return: bb3, unwind: bb7]; // bb2[3]: scope 3 at $DIR/region-subtyping-basic.rs:21:9: 21:18
                                          // mir::Constant
                                          // + span: $DIR/region-subtyping-basic.rs:21:9: 21:14
                                          // + literal: Const { ty: fn(usize) -> bool {use_x}, val: Value(Scalar(<ZST>)) }
@@ -79,21 +79,21 @@ fn main() -> () {
     bb3: {
         StorageDead(_9);                 // bb3[0]: scope 3 at $DIR/region-subtyping-basic.rs:21:17: 21:18
         StorageDead(_8);                 // bb3[1]: scope 3 at $DIR/region-subtyping-basic.rs:21:18: 21:19
-        _0 = const Const(Value(Scalar(<ZST>)): ()); // bb3[2]: scope 3 at $DIR/region-subtyping-basic.rs:20:13: 22:6
+        _0 = const ConstValue(Scalar(<ZST>): ()); // bb3[2]: scope 3 at $DIR/region-subtyping-basic.rs:20:13: 22:6
         goto -> bb6;                     // bb3[3]: scope 3 at $DIR/region-subtyping-basic.rs:20:5: 24:6
     }
 
     bb4: {
         StorageLive(_10);                // bb4[0]: scope 3 at $DIR/region-subtyping-basic.rs:23:9: 23:18
-        _10 = Const(Value(Scalar(<ZST>)): fn(usize) -> bool {use_x})(const Const(Value(Scalar(0x00000016)): usize)) -> [return: bb5, unwind: bb7]; // bb4[1]: scope 3 at $DIR/region-subtyping-basic.rs:23:9: 23:18
+        _10 = ConstValue(Scalar(<ZST>): fn(usize) -> bool {use_x})(const ConstValue(Scalar(0x00000016): usize)) -> [return: bb5, unwind: bb7]; // bb4[1]: scope 3 at $DIR/region-subtyping-basic.rs:23:9: 23:18
                                          // mir::Constant
                                          // + span: $DIR/region-subtyping-basic.rs:23:9: 23:14
                                          // + literal: Const { ty: fn(usize) -> bool {use_x}, val: Value(Scalar(<ZST>)) }
     }
 
     bb5: {
         StorageDead(_10);                // bb5[0]: scope 3 at $DIR/region-subtyping-basic.rs:23:18: 23:19
-        _0 = const Const(Value(Scalar(<ZST>)): ()); // bb5[1]: scope 3 at $DIR/region-subtyping-basic.rs:22:12: 24:6
+        _0 = const ConstValue(Scalar(<ZST>): ()); // bb5[1]: scope 3 at $DIR/region-subtyping-basic.rs:22:12: 24:6
         goto -> bb6;                     // bb5[2]: scope 3 at $DIR/region-subtyping-basic.rs:20:5: 24:6
     }