Use only ty::Unevaluated<'tcx, ()> in type system

compiler/rustc_borrowck/src/renumber.rs

@@ -2,6 +2,7 @@ use rustc_index::vec::IndexVec;
 use rustc_infer::infer::{InferCtxt, NllRegionVariableOrigin};
 use rustc_middle::mir::visit::{MutVisitor, TyContext};
 use rustc_middle::mir::{Body, Location, Promoted};
+use rustc_middle::mir::{Constant, ConstantKind};
 use rustc_middle::ty::subst::SubstsRef;
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeFoldable};
 
@@ -37,6 +38,21 @@ where
     })
 }
 
+// FIXME(valtrees): This function is necessary because `fold_regions`
+// panics for mir constants in the visitor.
+//
+// Once `visit_mir_constant` is removed we can also remove this function
+// and just use `renumber_regions`.
+fn renumber_regions_in_mir_constant<'tcx>(
+    infcx: &InferCtxt<'_, 'tcx>,
+    value: ConstantKind<'tcx>,
+) -> ConstantKind<'tcx> {
+    infcx.tcx.super_fold_regions(value, |_region, _depth| {
+        let origin = NllRegionVariableOrigin::Existential { from_forall: false };
+        infcx.next_nll_region_var(origin)
+    })
+}
+
 struct NllVisitor<'a, 'tcx> {
     infcx: &'a InferCtxt<'a, 'tcx>,
 }
@@ -48,6 +64,13 @@ impl<'a, 'tcx> NllVisitor<'a, 'tcx> {
     {
         renumber_regions(self.infcx, value)
     }
+
+    fn renumber_regions_in_mir_constant(
+        &mut self,
+        value: ConstantKind<'tcx>,
+    ) -> ConstantKind<'tcx> {
+        renumber_regions_in_mir_constant(self.infcx, value)
+    }
 }
 
 impl<'a, 'tcx> MutVisitor<'tcx> for NllVisitor<'a, 'tcx> {
@@ -77,7 +100,10 @@ impl<'a, 'tcx> MutVisitor<'tcx> for NllVisitor<'a, 'tcx> {
         debug!(?region);
     }
 
-    fn visit_const(&mut self, constant: &mut ty::Const<'tcx>, _location: Location) {
-        *constant = self.renumber_regions(*constant);
+    #[instrument(skip(self), level = "debug")]
+    fn visit_constant(&mut self, constant: &mut Constant<'tcx>, _location: Location) {
+        let literal = constant.literal;
+        constant.literal = self.renumber_regions_in_mir_constant(literal);
+        debug!("constant: {:#?}", constant);
     }
 }

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -354,11 +354,15 @@ impl<'a, 'b, 'tcx> Visitor<'tcx> for TypeVerifier<'a, 'b, 'tcx> {
             let tcx = self.tcx();
             let maybe_uneval = match constant.literal {
                 ConstantKind::Ty(ct) => match ct.kind() {
-                    ty::ConstKind::Unevaluated(uv) => Some(uv),
+                    ty::ConstKind::Unevaluated(_) => {
+                        bug!("should not encounter unevaluated ConstantKind::Ty here, got {:?}", ct)
+                    }
                     _ => None,
                 },
+                ConstantKind::Unevaluated(uv, _) => Some(uv),
                 _ => None,
             };
+
             if let Some(uv) = maybe_uneval {
                 if let Some(promoted) = uv.promoted {
                     let check_err = |verifier: &mut TypeVerifier<'a, 'b, 'tcx>,
@@ -1812,12 +1816,10 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
     fn check_operand(&mut self, op: &Operand<'tcx>, location: Location) {
         if let Operand::Constant(constant) = op {
             let maybe_uneval = match constant.literal {
-                ConstantKind::Ty(ct) => match ct.kind() {
-                    ty::ConstKind::Unevaluated(uv) => Some(uv),
-                    _ => None,
-                },
-                _ => None,
+                ConstantKind::Val(..) | ConstantKind::Ty(_) => None,
+                ConstantKind::Unevaluated(uv, _) => Some(uv),
             };
+
             if let Some(uv) = maybe_uneval {
                 if uv.promoted.is_none() {
                     let tcx = self.tcx();

compiler/rustc_codegen_cranelift/src/constant.rs

@@ -41,36 +41,30 @@ impl ConstantCx {
 pub(crate) fn check_constants(fx: &mut FunctionCx<'_, '_, '_>) -> bool {
     let mut all_constants_ok = true;
     for constant in &fx.mir.required_consts {
-        let const_ = match fx.monomorphize(constant.literal) {
-            ConstantKind::Ty(ct) => ct,
+        let unevaluated = match fx.monomorphize(constant.literal) {
+            ConstantKind::Ty(ct) => match ct.kind() {
+                ConstKind::Unevaluated(uv) => uv.expand(),
+                ConstKind::Value(_) => continue,
+                ConstKind::Param(_)
+                | ConstKind::Infer(_)
+                | ConstKind::Bound(_, _)
+                | ConstKind::Placeholder(_)
+                | ConstKind::Error(_) => unreachable!("{:?}", ct),
+            },
+            ConstantKind::Unevaluated(uv, _) => uv,
             ConstantKind::Val(..) => continue,
         };
-        match const_.kind() {
-            ConstKind::Value(_) => {}
-            ConstKind::Unevaluated(unevaluated) => {
-                if let Err(err) =
-                    fx.tcx.const_eval_resolve(ParamEnv::reveal_all(), unevaluated, None)
-                {
-                    all_constants_ok = false;
-                    match err {
-                        ErrorHandled::Reported(_) | ErrorHandled::Linted => {
-                            fx.tcx.sess.span_err(constant.span, "erroneous constant encountered");
-                        }
-                        ErrorHandled::TooGeneric => {
-                            span_bug!(
-                                constant.span,
-                                "codegen encountered polymorphic constant: {:?}",
-                                err
-                            );
-                        }
-                    }
+
+        if let Err(err) = fx.tcx.const_eval_resolve(ParamEnv::reveal_all(), unevaluated, None) {
+            all_constants_ok = false;
+            match err {
+                ErrorHandled::Reported(_) | ErrorHandled::Linted => {
+                    fx.tcx.sess.span_err(constant.span, "erroneous constant encountered");
+                }
+                ErrorHandled::TooGeneric => {
+                    span_bug!(constant.span, "codegen encountered polymorphic constant: {:?}", err);
                 }
             }
-            ConstKind::Param(_)
-            | ConstKind::Infer(_)
-            | ConstKind::Bound(_, _)
-            | ConstKind::Placeholder(_)
-            | ConstKind::Error(_) => unreachable!("{:?}", const_),
         }
     }
     all_constants_ok
@@ -122,36 +116,28 @@ pub(crate) fn codegen_constant<'tcx>(
     fx: &mut FunctionCx<'_, '_, 'tcx>,
     constant: &Constant<'tcx>,
 ) -> CValue<'tcx> {
-    let const_ = match fx.monomorphize(constant.literal) {
-        ConstantKind::Ty(ct) => ct,
-        ConstantKind::Val(val, ty) => return codegen_const_value(fx, val, ty),
-    };
-    let const_val = match const_.kind() {
-        ConstKind::Value(valtree) => fx.tcx.valtree_to_const_val((const_.ty(), valtree)),
-        ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted })
+    let (const_val, ty) = match fx.monomorphize(constant.literal) {
+        ConstantKind::Ty(const_) => unreachable!("{:?}", const_),
+        ConstantKind::Unevaluated(ty::Unevaluated { def, substs, promoted }, ty)
             if fx.tcx.is_static(def.did) =>
         {
             assert!(substs.is_empty());
             assert!(promoted.is_none());
 
-            return codegen_static_ref(fx, def.did, fx.layout_of(const_.ty())).to_cvalue(fx);
+            return codegen_static_ref(fx, def.did, fx.layout_of(ty)).to_cvalue(fx);
         }
-        ConstKind::Unevaluated(unevaluated) => {
+        ConstantKind::Unevaluated(unevaluated, ty) => {
             match fx.tcx.const_eval_resolve(ParamEnv::reveal_all(), unevaluated, None) {
-                Ok(const_val) => const_val,
+                Ok(const_val) => (const_val, ty),
                 Err(_) => {
                     span_bug!(constant.span, "erroneous constant not captured by required_consts");
                 }
             }
         }
-        ConstKind::Param(_)
-        | ConstKind::Infer(_)
-        | ConstKind::Bound(_, _)
-        | ConstKind::Placeholder(_)
-        | ConstKind::Error(_) => unreachable!("{:?}", const_),
+        ConstantKind::Val(val, ty) => (val, ty),
     };
 
-    codegen_const_value(fx, const_val, const_.ty())
+    codegen_const_value(fx, const_val, ty)
 }
 
 pub(crate) fn codegen_const_value<'tcx>(
@@ -496,6 +482,9 @@ pub(crate) fn mir_operand_get_const_val<'tcx>(
                 .eval_for_mir(fx.tcx, ParamEnv::reveal_all())
                 .try_to_value(fx.tcx),
             ConstantKind::Val(val, _) => Some(val),
+            ConstantKind::Unevaluated(uv, _) => {
+                fx.tcx.const_eval_resolve(ParamEnv::reveal_all(), uv, None).ok()
+            }
         },
         // FIXME(rust-lang/rust#85105): Casts like `IMM8 as u32` result in the const being stored
         // inside a temporary before being passed to the intrinsic requiring the const argument.

compiler/rustc_codegen_ssa/src/mir/constant.rs

@@ -25,26 +25,26 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         constant: &mir::Constant<'tcx>,
     ) -> Result<ConstValue<'tcx>, ErrorHandled> {
         let ct = self.monomorphize(constant.literal);
-        let ct = match ct {
-            mir::ConstantKind::Ty(ct) => ct,
+        let uv = match ct {
+            mir::ConstantKind::Ty(ct) => match ct.kind() {
+                ty::ConstKind::Unevaluated(uv) => uv.expand(),
+                ty::ConstKind::Value(val) => {
+                    return Ok(self.cx.tcx().valtree_to_const_val((ct.ty(), val)));
+                }
+                err => span_bug!(
+                    constant.span,
+                    "encountered bad ConstKind after monomorphizing: {:?}",
+                    err
+                ),
+            },
+            mir::ConstantKind::Unevaluated(uv, _) => uv,
             mir::ConstantKind::Val(val, _) => return Ok(val),
         };
-        match ct.kind() {
-            ty::ConstKind::Unevaluated(ct) => self
-                .cx
-                .tcx()
-                .const_eval_resolve(ty::ParamEnv::reveal_all(), ct, None)
-                .map_err(|err| {
-                    self.cx.tcx().sess.span_err(constant.span, "erroneous constant encountered");
-                    err
-                }),
-            ty::ConstKind::Value(val) => Ok(self.cx.tcx().valtree_to_const_val((ct.ty(), val))),
-            err => span_bug!(
-                constant.span,
-                "encountered bad ConstKind after monomorphizing: {:?}",
-                err
-            ),
-        }
+
+        self.cx.tcx().const_eval_resolve(ty::ParamEnv::reveal_all(), uv, None).map_err(|err| {
+            self.cx.tcx().sess.span_err(constant.span, "erroneous constant encountered");
+            err
+        })
     }
 
     /// process constant containing SIMD shuffle indices

compiler/rustc_const_eval/src/interpret/operand.rs

@@ -564,8 +564,16 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 throw_inval!(AlreadyReported(reported))
             }
             ty::ConstKind::Unevaluated(uv) => {
+                // NOTE: We evaluate to a `ValTree` here as a check to ensure
+                // we're working with valid constants, even though we never need it.
                 let instance = self.resolve(uv.def, uv.substs)?;
-                Ok(self.eval_to_allocation(GlobalId { instance, promoted: uv.promoted })?.into())
+                let cid = GlobalId { instance, promoted: None };
+                let _valtree = self
+                    .tcx
+                    .eval_to_valtree(self.param_env.and(cid))?
+                    .unwrap_or_else(|| bug!("unable to create ValTree for {:?}", uv));
+
+                Ok(self.eval_to_allocation(cid)?.into())
             }
             ty::ConstKind::Bound(..) | ty::ConstKind::Infer(..) => {
                 span_bug!(self.cur_span(), "const_to_op: Unexpected ConstKind {:?}", c)
@@ -586,6 +594,10 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         match val {
             mir::ConstantKind::Ty(ct) => self.const_to_op(*ct, layout),
             mir::ConstantKind::Val(val, ty) => self.const_val_to_op(*val, *ty, layout),
+            mir::ConstantKind::Unevaluated(uv, _) => {
+                let instance = self.resolve(uv.def, uv.substs)?;
+                Ok(self.eval_to_allocation(GlobalId { instance, promoted: uv.promoted })?.into())
+            }
         }
     }
 

compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs

@@ -346,31 +346,43 @@ where
     };
 
     // Check the qualifs of the value of `const` items.
-    if let Some(ct) = constant.literal.const_for_ty() {
-        if let ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs: _, promoted }) = ct.kind()
-        {
-            // Use qualifs of the type for the promoted. Promoteds in MIR body should be possible
-            // only for `NeedsNonConstDrop` with precise drop checking. This is the only const
-            // check performed after the promotion. Verify that with an assertion.
-            assert!(promoted.is_none() || Q::ALLOW_PROMOTED);
-            // Don't peek inside trait associated constants.
-            if promoted.is_none() && cx.tcx.trait_of_item(def.did).is_none() {
-                let qualifs = if let Some((did, param_did)) = def.as_const_arg() {
-                    cx.tcx.at(constant.span).mir_const_qualif_const_arg((did, param_did))
-                } else {
-                    cx.tcx.at(constant.span).mir_const_qualif(def.did)
-                };
-
-                if !Q::in_qualifs(&qualifs) {
-                    return false;
-                }
+    // FIXME(valtrees): check whether const qualifs should behave the same
+    // way for type and mir constants.
+    let uneval = match constant.literal {
+        ConstantKind::Ty(ct) if matches!(ct.kind(), ty::ConstKind::Unevaluated(_)) => {
+            let ty::ConstKind::Unevaluated(uv) = ct.kind() else { unreachable!() };
 
-                // Just in case the type is more specific than
-                // the definition, e.g., impl associated const
-                // with type parameters, take it into account.
+            Some(uv.expand())
+        }
+        ConstantKind::Ty(_) => None,
+        ConstantKind::Unevaluated(uv, _) => Some(uv),
+        ConstantKind::Val(..) => None,
+    };
+
+    if let Some(ty::Unevaluated { def, substs: _, promoted }) = uneval {
+        // Use qualifs of the type for the promoted. Promoteds in MIR body should be possible
+        // only for `NeedsNonConstDrop` with precise drop checking. This is the only const
+        // check performed after the promotion. Verify that with an assertion.
+        assert!(promoted.is_none() || Q::ALLOW_PROMOTED);
+
+        // Don't peek inside trait associated constants.
+        if promoted.is_none() && cx.tcx.trait_of_item(def.did).is_none() {
+            let qualifs = if let Some((did, param_did)) = def.as_const_arg() {
+                cx.tcx.at(constant.span).mir_const_qualif_const_arg((did, param_did))
+            } else {
+                cx.tcx.at(constant.span).mir_const_qualif(def.did)
+            };
+
+            if !Q::in_qualifs(&qualifs) {
+                return false;
             }
+
+            // Just in case the type is more specific than
+            // the definition, e.g., impl associated const
+            // with type parameters, take it into account.
         }
     }
+
     // Otherwise use the qualifs of the type.
     Q::in_any_value_of_ty(cx, constant.literal.ty())
 }

compiler/rustc_const_eval/src/transform/promote_consts.rs

@@ -840,21 +840,15 @@ impl<'a, 'tcx> Promoter<'a, 'tcx> {
                 promoted.span = span;
                 promoted.local_decls[RETURN_PLACE] = LocalDecl::new(ty, span);
                 let substs = tcx.erase_regions(InternalSubsts::identity_for_item(tcx, def.did));
-                let _const = tcx.mk_const(ty::ConstS {
-                    ty,
-                    kind: ty::ConstKind::Unevaluated(ty::Unevaluated {
-                        def,
-                        substs,
-                        promoted: Some(promoted_id),
-                    }),
-                });
+                let uneval = ty::Unevaluated { def, substs, promoted: Some(promoted_id) };
 
                 Operand::Constant(Box::new(Constant {
                     span,
                     user_ty: None,
-                    literal: ConstantKind::from_const(_const, tcx),
+                    literal: ConstantKind::Unevaluated(uneval, ty),
                 }))
             };
+
             let blocks = self.source.basic_blocks.as_mut();
             let local_decls = &mut self.source.local_decls;
             let loc = candidate.location;

compiler/rustc_infer/src/infer/combine.rs

@@ -743,7 +743,8 @@ impl<'tcx> TypeRelation<'tcx> for Generalizer<'_, 'tcx> {
                 }
             }
             ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted }) => {
-                assert_eq!(promoted, None);
+                assert_eq!(promoted, ());
+
                 let substs = self.relate_with_variance(
                     ty::Variance::Invariant,
                     ty::VarianceDiagInfo::default(),
@@ -964,13 +965,15 @@ impl<'tcx> TypeRelation<'tcx> for ConstInferUnifier<'_, 'tcx> {
                 }
             }
             ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted }) => {
-                assert_eq!(promoted, None);
+                assert_eq!(promoted, ());
+
                 let substs = self.relate_with_variance(
                     ty::Variance::Invariant,
                     ty::VarianceDiagInfo::default(),
                     substs,
                     substs,
                 )?;
+
                 Ok(self.tcx().mk_const(ty::ConstS {
                     ty: c.ty(),
                     kind: ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted }),