shrink `ty::PredicateKind` again

compiler/rustc_infer/src/infer/mod.rs

@@ -675,8 +675,8 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     /// canonicalizing the consts.
     pub fn try_unify_abstract_consts(
         &self,
-        a: ty::Unevaluated<'tcx>,
-        b: ty::Unevaluated<'tcx>,
+        a: ty::Unevaluated<'tcx, ()>,
+        b: ty::Unevaluated<'tcx, ()>,
     ) -> bool {
         let canonical = self.canonicalize_query((a, b), &mut OriginalQueryValues::default());
         debug!("canonical consts: {:?}", &canonical.value);

compiler/rustc_middle/src/query/mod.rs

@@ -303,7 +303,7 @@ rustc_queries! {
     }
 
     query try_unify_abstract_consts(key: (
-        ty::Unevaluated<'tcx>, ty::Unevaluated<'tcx>
+        ty::Unevaluated<'tcx, ()>, ty::Unevaluated<'tcx, ()>
     )) -> bool {
         desc {
             |tcx| "trying to unify the generic constants {} and {}",

compiler/rustc_middle/src/ty/consts/kind.rs

@@ -1,4 +1,5 @@
 use std::convert::TryInto;
+use std::fmt;
 
 use crate::mir::interpret::{AllocId, ConstValue, Scalar};
 use crate::mir::Promoted;
@@ -20,20 +21,38 @@ use super::ScalarInt;
 /// so refer to that check for more info.
 #[derive(Copy, Clone, Debug, Eq, PartialEq, PartialOrd, Ord, TyEncodable, TyDecodable, Lift)]
 #[derive(Hash, HashStable)]
-pub struct Unevaluated<'tcx> {
+pub struct Unevaluated<'tcx, P = Option<Promoted>> {
     pub def: ty::WithOptConstParam<DefId>,
     pub substs_: Option<SubstsRef<'tcx>>,
-    pub promoted: Option<Promoted>,
+    pub promoted: P,
 }
 
 impl<'tcx> Unevaluated<'tcx> {
-    pub fn new(def: ty::WithOptConstParam<DefId>, substs: SubstsRef<'tcx>) -> Unevaluated<'tcx> {
-        Unevaluated { def, substs_: Some(substs), promoted: None }
+    pub fn shrink(self) -> Unevaluated<'tcx, ()> {
+        debug_assert_eq!(self.promoted, None);
+        Unevaluated { def: self.def, substs_: self.substs_, promoted: () }
     }
+}
 
+impl<'tcx> Unevaluated<'tcx, ()> {
+    pub fn expand(self) -> Unevaluated<'tcx> {
+        Unevaluated { def: self.def, substs_: self.substs_, promoted: None }
+    }
+}
+
+impl<'tcx, P: Default> Unevaluated<'tcx, P> {
+    pub fn new(def: ty::WithOptConstParam<DefId>, substs: SubstsRef<'tcx>) -> Unevaluated<'tcx, P> {
+        Unevaluated { def, substs_: Some(substs), promoted: Default::default() }
+    }
+}
+
+impl<'tcx, P: Default + PartialEq + fmt::Debug> Unevaluated<'tcx, P> {
     pub fn substs(self, tcx: TyCtxt<'tcx>) -> SubstsRef<'tcx> {
         self.substs_.unwrap_or_else(|| {
-            debug_assert_eq!(self.promoted, None);
+            // We must not use the parents default substs for promoted constants
+            // as that can result in incorrect substs and calls the `default_anon_const_substs`
+            // for something that might not actually be a constant.
+            debug_assert_eq!(self.promoted, Default::default());
             tcx.default_anon_const_substs(self.def.did)
         })
     }

compiler/rustc_middle/src/ty/flags.rs

@@ -310,7 +310,7 @@ impl FlagComputation {
         }
     }
 
-    fn add_unevaluated_const(&mut self, ct: ty::Unevaluated<'tcx>) {
+    fn add_unevaluated_const<P>(&mut self, ct: ty::Unevaluated<'tcx, P>) {
         if let Some(substs) = ct.substs_ {
             self.add_substs(substs);
         } else {

compiler/rustc_middle/src/ty/mod.rs

@@ -406,7 +406,7 @@ crate struct PredicateInner<'tcx> {
 }
 
 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
-static_assert_size!(PredicateInner<'_>, 56);
+static_assert_size!(PredicateInner<'_>, 48);
 
 #[derive(Clone, Copy, Lift)]
 pub struct Predicate<'tcx> {
@@ -502,7 +502,7 @@ pub enum PredicateKind<'tcx> {
     Coerce(CoercePredicate<'tcx>),
 
     /// Constant initializer must evaluate successfully.
-    ConstEvaluatable(ty::Unevaluated<'tcx>),
+    ConstEvaluatable(ty::Unevaluated<'tcx, ()>),
 
     /// Constants must be equal. The first component is the const that is expected.
     ConstEquate(&'tcx Const<'tcx>, &'tcx Const<'tcx>),

compiler/rustc_middle/src/ty/relate.rs

@@ -579,7 +579,7 @@ pub fn super_relate_consts<R: TypeRelation<'tcx>>(
         (ty::ConstKind::Unevaluated(au), ty::ConstKind::Unevaluated(bu))
             if tcx.features().const_evaluatable_checked =>
         {
-            tcx.try_unify_abstract_consts((au, bu))
+            tcx.try_unify_abstract_consts((au.shrink(), bu.shrink()))
         }
 
         // While this is slightly incorrect, it shouldn't matter for `min_const_generics`

compiler/rustc_middle/src/ty/structural_impls.rs

@@ -1105,3 +1105,28 @@ impl<'tcx> TypeFoldable<'tcx> for ty::Unevaluated<'tcx> {
         }
     }
 }
+
+impl<'tcx> TypeFoldable<'tcx> for ty::Unevaluated<'tcx, ()> {
+    fn super_fold_with<F: TypeFolder<'tcx>>(self, folder: &mut F) -> Self {
+        ty::Unevaluated {
+            def: self.def,
+            substs_: Some(self.substs(folder.tcx()).fold_with(folder)),
+            promoted: self.promoted,
+        }
+    }
+
+    fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
+        visitor.visit_unevaluated_const(self.expand())
+    }
+
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
+        if let Some(tcx) = visitor.tcx_for_anon_const_substs() {
+            self.substs(tcx).visit_with(visitor)
+        } else if let Some(substs) = self.substs_ {
+            substs.visit_with(visitor)
+        } else {
+            debug!("ignoring default substs of `{:?}`", self.def);
+            ControlFlow::CONTINUE
+        }
+    }
+}

compiler/rustc_query_impl/src/keys.rs

@@ -217,7 +217,7 @@ impl<'tcx> Key for (DefId, SubstsRef<'tcx>) {
     }
 }
 
-impl<'tcx> Key for (ty::Unevaluated<'tcx>, ty::Unevaluated<'tcx>) {
+impl<'tcx> Key for (ty::Unevaluated<'tcx, ()>, ty::Unevaluated<'tcx, ()>) {
     #[inline(always)]
     fn query_crate_is_local(&self) -> bool {
         (self.0).def.did.krate == LOCAL_CRATE

compiler/rustc_trait_selection/src/traits/const_evaluatable.rs

@@ -29,7 +29,7 @@ use std::ops::ControlFlow;
 /// Check if a given constant can be evaluated.
 pub fn is_const_evaluatable<'cx, 'tcx>(
     infcx: &InferCtxt<'cx, 'tcx>,
-    uv: ty::Unevaluated<'tcx>,
+    uv: ty::Unevaluated<'tcx, ()>,
     param_env: ty::ParamEnv<'tcx>,
     span: Span,
 ) -> Result<(), NotConstEvaluatable> {
@@ -149,7 +149,7 @@ pub fn is_const_evaluatable<'cx, 'tcx>(
     // and hopefully soon change this to an error.
     //
     // See #74595 for more details about this.
-    let concrete = infcx.const_eval_resolve(param_env, uv, Some(span));
+    let concrete = infcx.const_eval_resolve(param_env, uv.expand(), Some(span));
 
     if concrete.is_ok() && uv.substs(infcx.tcx).has_param_types_or_consts(infcx.tcx) {
         match infcx.tcx.def_kind(uv.def.did) {
@@ -194,7 +194,7 @@ pub struct AbstractConst<'tcx> {
 impl<'tcx> AbstractConst<'tcx> {
     pub fn new(
         tcx: TyCtxt<'tcx>,
-        uv: ty::Unevaluated<'tcx>,
+        uv: ty::Unevaluated<'tcx, ()>,
     ) -> Result<Option<AbstractConst<'tcx>>, ErrorReported> {
         let inner = tcx.mir_abstract_const_opt_const_arg(uv.def)?;
         debug!("AbstractConst::new({:?}) = {:?}", uv, inner);
@@ -206,7 +206,7 @@ impl<'tcx> AbstractConst<'tcx> {
         ct: &ty::Const<'tcx>,
     ) -> Result<Option<AbstractConst<'tcx>>, ErrorReported> {
         match ct.val {
-            ty::ConstKind::Unevaluated(uv) => AbstractConst::new(tcx, uv),
+            ty::ConstKind::Unevaluated(uv) => AbstractConst::new(tcx, uv.shrink()),
             ty::ConstKind::Error(_) => Err(ErrorReported),
             _ => Ok(None),
         }
@@ -556,7 +556,7 @@ pub(super) fn mir_abstract_const<'tcx>(
 
 pub(super) fn try_unify_abstract_consts<'tcx>(
     tcx: TyCtxt<'tcx>,
-    (a, b): (ty::Unevaluated<'tcx>, ty::Unevaluated<'tcx>),
+    (a, b): (ty::Unevaluated<'tcx, ()>, ty::Unevaluated<'tcx, ()>),
 ) -> bool {
     (|| {
         if let Some(a) = AbstractConst::new(tcx, a)? {

compiler/rustc_trait_selection/src/traits/fulfill.rs

@@ -580,7 +580,7 @@ impl<'a, 'b, 'tcx> FulfillProcessor<'a, 'b, 'tcx> {
                         if let (ty::ConstKind::Unevaluated(a), ty::ConstKind::Unevaluated(b)) =
                             (c1.val, c2.val)
                         {
-                            if infcx.try_unify_abstract_consts(a, b) {
+                            if infcx.try_unify_abstract_consts(a.shrink(), b.shrink()) {
                                 return ProcessResult::Changed(vec![]);
                             }
                         }

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -623,7 +623,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                         if let (ty::ConstKind::Unevaluated(a), ty::ConstKind::Unevaluated(b)) =
                             (c1.val, c2.val)
                         {
-                            if self.infcx.try_unify_abstract_consts(a, b) {
+                            if self.infcx.try_unify_abstract_consts(a.shrink(), b.shrink()) {
                                 return Ok(EvaluatedToOk);
                             }
                         }

compiler/rustc_typeck/src/collect.rs

@@ -2355,8 +2355,10 @@ fn const_evaluatable_predicates_of<'tcx>(
             if let ty::ConstKind::Unevaluated(uv) = ct.val {
                 assert_eq!(uv.promoted, None);
                 let span = self.tcx.hir().span(c.hir_id);
-                self.preds
-                    .insert((ty::PredicateKind::ConstEvaluatable(uv).to_predicate(self.tcx), span));
+                self.preds.insert((
+                    ty::PredicateKind::ConstEvaluatable(uv.shrink()).to_predicate(self.tcx),
+                    span,
+                ));
             }
         }