Auto merge of #59178 - oli-obk:lazy_const, r=eddyb

Revert the `LazyConst` PR

The introduction of `LazyConst` did not actually achieve the code simplicity improvements that were the main reason it was introduced. Especially in the presence of const generics, the differences between the "levels of evaluatedness" of a constant become less clear. As it can be seen by the changes in this PR, further simplifications were possible by folding `LazyConst` back into `ConstValue`. We have been able to keep all the advantages gained during the `LazyConst` refactoring (like `const_eval` not returning an interned value, thus making all the `match` code simpler and more performant).

fixes #59209

r? @eddyb @varkor

src/librustc/mir/interpret/value.rs

@@ -1,7 +1,8 @@
 use std::fmt;
 use rustc_macros::HashStable;
 
-use crate::ty::{Ty, InferConst, ParamConst, layout::{HasDataLayout, Size}};
+use crate::ty::{Ty, InferConst, ParamConst, layout::{HasDataLayout, Size}, subst::SubstsRef};
+use crate::hir::def_id::DefId;
 
 use super::{EvalResult, Pointer, PointerArithmetic, Allocation, AllocId, sign_extend, truncate};
 
@@ -42,6 +43,10 @@ pub enum ConstValue<'tcx> {
     /// An allocation together with a pointer into the allocation.
     /// Invariant: the pointer's `AllocId` resolves to the allocation.
     ByRef(Pointer, &'tcx Allocation),
+
+    /// Used in the HIR by using `Unevaluated` everywhere and later normalizing to one of the other
+    /// variants when the code is monomorphic enough for that.
+    Unevaluated(DefId, SubstsRef<'tcx>),
 }
 
 #[cfg(target_arch = "x86_64")]
@@ -54,6 +59,7 @@ impl<'tcx> ConstValue<'tcx> {
             ConstValue::Param(_) |
             ConstValue::Infer(_) |
             ConstValue::ByRef(..) |
+            ConstValue::Unevaluated(..) |
             ConstValue::Slice(..) => None,
             ConstValue::Scalar(val) => Some(val),
         }

src/librustc/mir/mod.rs

@@ -2179,8 +2179,8 @@ impl<'tcx> Operand<'tcx> {
             span,
             ty,
             user_ty: None,
-            literal: tcx.mk_lazy_const(
-                ty::LazyConst::Evaluated(ty::Const::zero_sized(ty)),
+            literal: tcx.mk_const(
+                ty::Const::zero_sized(ty),
             ),
         })
     }
@@ -2497,7 +2497,7 @@ pub struct Constant<'tcx> {
     /// Needed for NLL to impose user-given type constraints.
     pub user_ty: Option<UserTypeAnnotationIndex>,
 
-    pub literal: &'tcx ty::LazyConst<'tcx>,
+    pub literal: &'tcx ty::Const<'tcx>,
 }
 
 /// A collection of projections into user types.
@@ -2696,18 +2696,9 @@ newtype_index! {
 impl<'tcx> Debug for Constant<'tcx> {
     fn fmt(&self, fmt: &mut Formatter<'_>) -> fmt::Result {
         write!(fmt, "const ")?;
-        fmt_lazy_const_val(fmt, self.literal)
+        fmt_const_val(fmt, *self.literal)
     }
 }
-
-/// Write a `ConstValue` in a way closer to the original source code than the `Debug` output.
-pub fn fmt_lazy_const_val(f: &mut impl Write, const_val: &ty::LazyConst<'_>) -> fmt::Result {
-    match *const_val {
-        ty::LazyConst::Unevaluated(..) => write!(f, "{:?}", const_val),
-        ty::LazyConst::Evaluated(c) => fmt_const_val(f, c),
-    }
-}
-
 /// Write a `ConstValue` in a way closer to the original source code than the `Debug` output.
 pub fn fmt_const_val(f: &mut impl Write, const_val: ty::Const<'_>) -> fmt::Result {
     use crate::ty::TyKind::*;
@@ -2760,7 +2751,7 @@ pub fn fmt_const_val(f: &mut impl Write, const_val: ty::Const<'_>) -> fmt::Resul
         }
     }
     // just raw dump everything else
-    write!(f, "{:?}:{}", value, ty)
+    write!(f, "{:?} : {}", value, ty)
 }
 
 fn def_path_str(def_id: DefId) -> String {

src/librustc/mir/visit.rs

@@ -232,7 +232,7 @@ macro_rules! make_mir_visitor {
             }
 
             fn visit_const(&mut self,
-                           constant: & $($mutability)? &'tcx ty::LazyConst<'tcx>,
+                           constant: & $($mutability)? &'tcx ty::Const<'tcx>,
                            _: Location) {
                 self.super_const(constant);
             }
@@ -886,7 +886,7 @@ macro_rules! make_mir_visitor {
             fn super_region(&mut self, _region: & $($mutability)? ty::Region<'tcx>) {
             }
 
-            fn super_const(&mut self, _const: & $($mutability)? &'tcx ty::LazyConst<'tcx>) {
+            fn super_const(&mut self, _const: & $($mutability)? &'tcx ty::Const<'tcx>) {
             }
 
             fn super_substs(&mut self, _substs: & $($mutability)? SubstsRef<'tcx>) {

src/librustc/traits/project.rs

@@ -15,7 +15,7 @@ use super::util;
 use crate::hir::def_id::DefId;
 use crate::infer::{InferCtxt, InferOk, LateBoundRegionConversionTime};
 use crate::infer::type_variable::TypeVariableOrigin;
-use crate::mir::interpret::{GlobalId};
+use crate::mir::interpret::{GlobalId, ConstValue};
 use rustc_data_structures::snapshot_map::{Snapshot, SnapshotMap};
 use rustc_macros::HashStable;
 use syntax::ast::Ident;
@@ -397,8 +397,8 @@ impl<'a, 'b, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for AssociatedTypeNormalizer<'a,
         }
     }
 
-    fn fold_const(&mut self, constant: &'tcx ty::LazyConst<'tcx>) -> &'tcx ty::LazyConst<'tcx> {
-        if let ty::LazyConst::Unevaluated(def_id, substs) = *constant {
+    fn fold_const(&mut self, constant: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
+        if let ConstValue::Unevaluated(def_id, substs) = constant.val {
             let tcx = self.selcx.tcx().global_tcx();
             if let Some(param_env) = self.tcx().lift_to_global(&self.param_env) {
                 if substs.needs_infer() || substs.has_placeholders() {
@@ -411,8 +411,9 @@ impl<'a, 'b, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for AssociatedTypeNormalizer<'a,
                         };
                         if let Ok(evaluated) = tcx.const_eval(param_env.and(cid)) {
                             let substs = tcx.lift_to_global(&substs).unwrap();
+                            let evaluated = tcx.mk_const(evaluated);
                             let evaluated = evaluated.subst(tcx, substs);
-                            return tcx.mk_lazy_const(ty::LazyConst::Evaluated(evaluated));
+                            return evaluated;
                         }
                     }
                 } else {
@@ -424,7 +425,7 @@ impl<'a, 'b, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for AssociatedTypeNormalizer<'a,
                                 promoted: None
                             };
                             if let Ok(evaluated) = tcx.const_eval(param_env.and(cid)) {
-                                return tcx.mk_lazy_const(ty::LazyConst::Evaluated(evaluated));
+                                return tcx.mk_const(evaluated);
                             }
                         }
                     }

src/librustc/traits/query/normalize.rs

@@ -5,7 +5,7 @@
 use crate::infer::at::At;
 use crate::infer::canonical::OriginalQueryValues;
 use crate::infer::{InferCtxt, InferOk};
-use crate::mir::interpret::GlobalId;
+use crate::mir::interpret::{GlobalId, ConstValue};
 use crate::traits::project::Normalized;
 use crate::traits::{Obligation, ObligationCause, PredicateObligation, Reveal};
 use crate::ty::fold::{TypeFoldable, TypeFolder};
@@ -188,8 +188,8 @@ impl<'cx, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for QueryNormalizer<'cx, 'gcx, 'tcx
         }
     }
 
-    fn fold_const(&mut self, constant: &'tcx ty::LazyConst<'tcx>) -> &'tcx ty::LazyConst<'tcx> {
-        if let ty::LazyConst::Unevaluated(def_id, substs) = *constant {
+    fn fold_const(&mut self, constant: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
+        if let ConstValue::Unevaluated(def_id, substs) = constant.val {
             let tcx = self.infcx.tcx.global_tcx();
             if let Some(param_env) = self.tcx().lift_to_global(&self.param_env) {
                 if substs.needs_infer() || substs.has_placeholders() {
@@ -202,8 +202,9 @@ impl<'cx, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for QueryNormalizer<'cx, 'gcx, 'tcx
                         };
                         if let Ok(evaluated) = tcx.const_eval(param_env.and(cid)) {
                             let substs = tcx.lift_to_global(&substs).unwrap();
+                            let evaluated = tcx.mk_const(evaluated);
                             let evaluated = evaluated.subst(tcx, substs);
-                            return tcx.mk_lazy_const(ty::LazyConst::Evaluated(evaluated));
+                            return evaluated;
                         }
                     }
                 } else {
@@ -215,7 +216,7 @@ impl<'cx, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for QueryNormalizer<'cx, 'gcx, 'tcx
                                 promoted: None,
                             };
                             if let Ok(evaluated) = tcx.const_eval(param_env.and(cid)) {
-                                return tcx.mk_lazy_const(ty::LazyConst::Evaluated(evaluated));
+                                return tcx.mk_const(evaluated);
                             }
                         }
                     }

src/librustc/ty/codec.rs

@@ -247,12 +247,12 @@ pub fn decode_canonical_var_infos<'a, 'tcx, D>(decoder: &mut D)
 }
 
 #[inline]
-pub fn decode_lazy_const<'a, 'tcx, D>(decoder: &mut D)
-                                 -> Result<&'tcx ty::LazyConst<'tcx>, D::Error>
+pub fn decode_const<'a, 'tcx, D>(decoder: &mut D)
+                                 -> Result<&'tcx ty::Const<'tcx>, D::Error>
     where D: TyDecoder<'a, 'tcx>,
           'tcx: 'a,
 {
-    Ok(decoder.tcx().mk_lazy_const(Decodable::decode(decoder)?))
+    Ok(decoder.tcx().mk_const(Decodable::decode(decoder)?))
 }
 
 #[inline]
@@ -389,10 +389,10 @@ macro_rules! implement_ty_decoder {
                 }
             }
 
-            impl<$($typaram),*> SpecializedDecoder<&'tcx $crate::ty::LazyConst<'tcx>>
+            impl<$($typaram),*> SpecializedDecoder<&'tcx $crate::ty::Const<'tcx>>
             for $DecoderName<$($typaram),*> {
-                fn specialized_decode(&mut self) -> Result<&'tcx ty::LazyConst<'tcx>, Self::Error> {
-                    decode_lazy_const(self)
+                fn specialized_decode(&mut self) -> Result<&'tcx ty::Const<'tcx>, Self::Error> {
+                    decode_const(self)
                 }
             }
 

src/librustc/ty/context.rs

@@ -28,7 +28,7 @@ use crate::traits;
 use crate::traits::{Clause, Clauses, GoalKind, Goal, Goals};
 use crate::ty::{self, DefIdTree, Ty, TypeAndMut};
 use crate::ty::{TyS, TyKind, List};
-use crate::ty::{AdtKind, AdtDef, ClosureSubsts, GeneratorSubsts, Region, Const, LazyConst};
+use crate::ty::{AdtKind, AdtDef, ClosureSubsts, GeneratorSubsts, Region, Const};
 use crate::ty::{PolyFnSig, InferTy, ParamTy, ProjectionTy, ExistentialPredicate, Predicate};
 use crate::ty::RegionKind;
 use crate::ty::{TyVar, TyVid, IntVar, IntVid, FloatVar, FloatVid, ConstVid};
@@ -126,7 +126,7 @@ pub struct CtxtInterners<'tcx> {
     goal: InternedSet<'tcx, GoalKind<'tcx>>,
     goal_list: InternedSet<'tcx, List<Goal<'tcx>>>,
     projs: InternedSet<'tcx, List<ProjectionKind<'tcx>>>,
-    lazy_const: InternedSet<'tcx, LazyConst<'tcx>>,
+    const_: InternedSet<'tcx, Const<'tcx>>,
 }
 
 impl<'gcx: 'tcx, 'tcx> CtxtInterners<'tcx> {
@@ -144,7 +144,7 @@ impl<'gcx: 'tcx, 'tcx> CtxtInterners<'tcx> {
             goal: Default::default(),
             goal_list: Default::default(),
             projs: Default::default(),
-            lazy_const: Default::default(),
+            const_: Default::default(),
         }
     }
 
@@ -874,14 +874,11 @@ impl CanonicalUserType<'gcx> {
                             _ => false,
                         },
 
-                        UnpackedKind::Const(ct) => match ct {
-                            ty::LazyConst::Evaluated(ty::Const {
-                                val: ConstValue::Infer(InferConst::Canonical(debruijn, b)),
-                                ..
-                            }) => {
+                        UnpackedKind::Const(ct) => match ct.val {
+                            ConstValue::Infer(InferConst::Canonical(debruijn, b)) => {
                                 // We only allow a `ty::INNERMOST` index in substitutions.
-                                assert_eq!(*debruijn, ty::INNERMOST);
-                                cvar == *b
+                                assert_eq!(debruijn, ty::INNERMOST);
+                                cvar == b
                             }
                             _ => false,
                         },
@@ -1788,7 +1785,7 @@ macro_rules! nop_list_lift {
 nop_lift!{Ty<'a> => Ty<'tcx>}
 nop_lift!{Region<'a> => Region<'tcx>}
 nop_lift!{Goal<'a> => Goal<'tcx>}
-nop_lift!{&'a LazyConst<'a> => &'tcx LazyConst<'tcx>}
+nop_lift!{&'a Const<'a> => &'tcx Const<'tcx>}
 
 nop_list_lift!{Goal<'a> => Goal<'tcx>}
 nop_list_lift!{Clause<'a> => Clause<'tcx>}
@@ -2274,12 +2271,6 @@ impl<'tcx: 'lcx, 'lcx> Borrow<GoalKind<'lcx>> for Interned<'tcx, GoalKind<'tcx>>
     }
 }
 
-impl<'tcx: 'lcx, 'lcx> Borrow<LazyConst<'lcx>> for Interned<'tcx, LazyConst<'tcx>> {
-    fn borrow<'a>(&'a self) -> &'a LazyConst<'lcx> {
-        &self.0
-    }
-}
-
 impl<'tcx: 'lcx, 'lcx> Borrow<[ExistentialPredicate<'lcx>]>
     for Interned<'tcx, List<ExistentialPredicate<'tcx>>> {
     fn borrow<'a>(&'a self) -> &'a [ExistentialPredicate<'lcx>] {
@@ -2387,7 +2378,7 @@ pub fn keep_local<'tcx, T: ty::TypeFoldable<'tcx>>(x: &T) -> bool {
 direct_interners!('tcx,
     region: mk_region(|r: &RegionKind| r.keep_in_local_tcx()) -> RegionKind,
     goal: mk_goal(|c: &GoalKind<'_>| keep_local(c)) -> GoalKind<'tcx>,
-    lazy_const: mk_lazy_const(|c: &LazyConst<'_>| keep_local(&c)) -> LazyConst<'tcx>
+    const_: mk_const(|c: &Const<'_>| keep_local(&c)) -> Const<'tcx>
 );
 
 macro_rules! slice_interners {
@@ -2575,8 +2566,8 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
 
     #[inline]
     pub fn mk_array(self, ty: Ty<'tcx>, n: u64) -> Ty<'tcx> {
-        self.mk_ty(Array(ty, self.mk_lazy_const(
-            ty::LazyConst::Evaluated(ty::Const::from_usize(self.global_tcx(), n))
+        self.mk_ty(Array(ty, self.mk_const(
+            ty::Const::from_usize(self.global_tcx(), n)
         )))
     }
 
@@ -2670,11 +2661,11 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
     }
 
     #[inline]
-    pub fn mk_const_var(self, v: ConstVid<'tcx>, ty: Ty<'tcx>) -> &'tcx LazyConst<'tcx> {
-        self.mk_lazy_const(LazyConst::Evaluated(ty::Const {
+    pub fn mk_const_var(self, v: ConstVid<'tcx>, ty: Ty<'tcx>) -> &'tcx Const<'tcx> {
+        self.mk_const(ty::Const {
             val: ConstValue::Infer(InferConst::Var(v)),
             ty,
-        }))
+        })
     }
 
     #[inline]
@@ -2705,11 +2696,11 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         index: u32,
         name: InternedString,
         ty: Ty<'tcx>
-    ) -> &'tcx LazyConst<'tcx> {
-        self.mk_lazy_const(LazyConst::Evaluated(ty::Const {
+    ) -> &'tcx Const<'tcx> {
+        self.mk_const(ty::Const {
             val: ConstValue::Param(ParamConst { index, name }),
             ty,
-        }))
+        })
     }
 
     #[inline]

src/librustc/ty/error.rs

@@ -176,12 +176,9 @@ impl<'a, 'gcx, 'lcx, 'tcx> ty::TyS<'tcx> {
 
             ty::Adt(def, _) => format!("{} `{}`", def.descr(), tcx.def_path_str(def.did)).into(),
             ty::Foreign(def_id) => format!("extern type `{}`", tcx.def_path_str(def_id)).into(),
-            ty::Array(_, n) => match n {
-                ty::LazyConst::Evaluated(n) => match n.assert_usize(tcx) {
-                    Some(n) => format!("array of {} elements", n).into(),
-                    None => "array".into(),
-                },
-                ty::LazyConst::Unevaluated(..) => "array".into(),
+            ty::Array(_, n) => match n.assert_usize(tcx) {
+                Some(n) => format!("array of {} elements", n).into(),
+                None => "array".into(),
             }
             ty::Slice(_) => "slice".into(),
             ty::RawPtr(_) => "*-ptr".into(),