Auto merge of #94255 - b-naber:use-mir-constant-in-thir, r=oli-obk

Use mir constant in thir instead of ty::Const

This is blocked on https://github.com/rust-lang/rust/pull/94059 (does include its changes, the first two commits in this PR correspond to those changes) and https://github.com/rust-lang/rust/pull/93800 being reinstated (which had to be reverted). Mainly opening since `@lcnr` offered to give some feedback and maybe also for a perf-run (if necessary).

This currently contains a lot of duplication since some of the logic of `ty::Const` had to be copied to `mir::ConstantKind`, but with the introduction of valtrees a lot of that functionality will disappear from `ty::Const`.

Only the last commit contains changes that need to be reviewed here. Did leave some `FIXME` comments regarding future implementation decisions and some things that might be incorrectly implemented.

r? `@oli-obk`

17 files changed, 227 insertions, 55 deletions

diff --git a/compiler/rustc_middle/src/mir/mod.rs b/compiler/rustc_middle/src/mir/mod.rs
index 9f7832c8a64..db7e973fb62 100644
--- a/compiler/rustc_middle/src/mir/mod.rs
+++ b/compiler/rustc_middle/src/mir/mod.rs
@@ -9,13 +9,13 @@ use crate::ty::adjustment::PointerCast;
 use crate::ty::codec::{TyDecoder, TyEncoder};
 use crate::ty::fold::{FallibleTypeFolder, TypeFoldable, TypeVisitor};
 use crate::ty::print::{FmtPrinter, Printer};
-use crate::ty::subst::{Subst, SubstsRef};
+use crate::ty::subst::{GenericArg, InternalSubsts, Subst, SubstsRef};
 use crate::ty::{self, List, Ty, TyCtxt};
 use crate::ty::{AdtDef, InstanceDef, Region, ScalarInt, UserTypeAnnotationIndex};
 
 use rustc_errors::ErrorGuaranteed;
 use rustc_hir::def::{CtorKind, Namespace};
-use rustc_hir::def_id::{DefId, CRATE_DEF_INDEX};
+use rustc_hir::def_id::{DefId, LocalDefId, CRATE_DEF_INDEX};
 use rustc_hir::{self, GeneratorKind};
 use rustc_hir::{self as hir, HirId};
 use rustc_session::Session;
@@ -2921,6 +2921,16 @@ impl<'tcx> ConstantKind<'tcx> {
         }
     }
 
+    pub fn try_val(&self) -> Option<ConstValue<'tcx>> {
+        match self {
+            ConstantKind::Ty(c) => match c.val() {
+                ty::ConstKind::Value(v) => Some(v),
+                _ => None,
+            },
+            ConstantKind::Val(v, _) => Some(*v),
+        }
+    }
+
     #[inline]
     pub fn try_to_value(self) -> Option<interpret::ConstValue<'tcx>> {
         match self {
@@ -2950,6 +2960,32 @@ impl<'tcx> ConstantKind<'tcx> {
     }
 
     #[inline]
+    pub fn eval(self, tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>) -> Self {
+        match self {
+            Self::Ty(c) => {
+                // FIXME Need to use a different evaluation function that directly returns a `ConstValue`
+                // if evaluation succeeds and does not create a ValTree first
+                if let Some(val) = c.val().try_eval(tcx, param_env) {
+                    match val {
+                        Ok(val) => Self::Val(val, c.ty()),
+                        Err(_) => Self::Ty(tcx.const_error(self.ty())),
+                    }
+                } else {
+                    self
+                }
+            }
+            Self::Val(_, _) => self,
+        }
+    }
+
+    /// Panics if the value cannot be evaluated or doesn't contain a valid integer of the given type.
+    #[inline]
+    pub fn eval_bits(self, tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>, ty: Ty<'tcx>) -> u128 {
+        self.try_eval_bits(tcx, param_env, ty)
+            .unwrap_or_else(|| bug!("expected bits of {:#?}, got {:#?}", ty, self))
+    }
+
+    #[inline]
     pub fn try_eval_bits(
         &self,
         tcx: TyCtxt<'tcx>,
@@ -2983,25 +3019,142 @@ impl<'tcx> ConstantKind<'tcx> {
         }
     }
 
+    pub fn from_bits(
+        tcx: TyCtxt<'tcx>,
+        bits: u128,
+        param_env_ty: ty::ParamEnvAnd<'tcx, Ty<'tcx>>,
+    ) -> Self {
+        let size = tcx
+            .layout_of(param_env_ty)
+            .unwrap_or_else(|e| {
+                bug!("could not compute layout for {:?}: {:?}", param_env_ty.value, e)
+            })
+            .size;
+        let cv = ConstValue::Scalar(Scalar::from_uint(bits, size));
+
+        Self::Val(cv, param_env_ty.value)
+    }
+
     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 {
+    pub fn 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::from_bits(tcx, n as u128, ty::ParamEnv::empty().and(ty))
+    }
 
-        Self::Val(cv, ty)
+    /// Literals are converted to `ConstantKindVal`, const generic parameters are eagerly
+    /// converted to a constant, everything else becomes `Unevaluated`.
+    pub fn from_anon_const(
+        tcx: TyCtxt<'tcx>,
+        def_id: LocalDefId,
+        param_env: ty::ParamEnv<'tcx>,
+    ) -> Self {
+        Self::from_opt_const_arg_anon_const(tcx, ty::WithOptConstParam::unknown(def_id), param_env)
+    }
+
+    #[instrument(skip(tcx), level = "debug")]
+    fn from_opt_const_arg_anon_const(
+        tcx: TyCtxt<'tcx>,
+        def: ty::WithOptConstParam<LocalDefId>,
+        param_env: ty::ParamEnv<'tcx>,
+    ) -> Self {
+        let body_id = match tcx.hir().get_by_def_id(def.did) {
+            hir::Node::AnonConst(ac) => ac.body,
+            _ => span_bug!(
+                tcx.def_span(def.did.to_def_id()),
+                "from_anon_const can only process anonymous constants"
+            ),
+        };
+
+        let expr = &tcx.hir().body(body_id).value;
+        debug!(?expr);
+
+        // Unwrap a block, so that e.g. `{ P }` is recognised as a parameter. Const arguments
+        // currently have to be wrapped in curly brackets, so it's necessary to special-case.
+        let expr = match &expr.kind {
+            hir::ExprKind::Block(block, _) if block.stmts.is_empty() && block.expr.is_some() => {
+                block.expr.as_ref().unwrap()
+            }
+            _ => expr,
+        };
+
+        let ty = tcx.type_of(def.def_id_for_type_of());
+
+        // FIXME(const_generics): We currently have to special case parameters because `min_const_generics`
+        // does not provide the parents generics to anonymous constants. We still allow generic const
+        // parameters by themselves however, e.g. `N`.  These constants would cause an ICE if we were to
+        // ever try to substitute the generic parameters in their bodies.
+        //
+        // While this doesn't happen as these constants are always used as `ty::ConstKind::Param`, it does
+        // cause issues if we were to remove that special-case and try to evaluate the constant instead.
+        use hir::{def::DefKind::ConstParam, def::Res, ExprKind, Path, QPath};
+        match expr.kind {
+            ExprKind::Path(QPath::Resolved(_, &Path { res: Res::Def(ConstParam, def_id), .. })) => {
+                // Find the name and index of the const parameter by indexing the generics of
+                // the parent item and construct a `ParamConst`.
+                let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
+                let item_id = tcx.hir().get_parent_node(hir_id);
+                let item_def_id = tcx.hir().local_def_id(item_id);
+                let generics = tcx.generics_of(item_def_id.to_def_id());
+                let index = generics.param_def_id_to_index[&def_id];
+                let name = tcx.hir().name(hir_id);
+                let ty_const = tcx.mk_const(ty::ConstS {
+                    val: ty::ConstKind::Param(ty::ParamConst::new(index, name)),
+                    ty,
+                });
+
+                return Self::Ty(ty_const);
+            }
+            _ => {}
+        }
+
+        let hir_id = tcx.hir().local_def_id_to_hir_id(def.did);
+        let parent_substs = if let Some(parent_hir_id) = tcx.hir().find_parent_node(hir_id) {
+            if let Some(parent_did) = tcx.hir().opt_local_def_id(parent_hir_id) {
+                InternalSubsts::identity_for_item(tcx, parent_did.to_def_id())
+            } else {
+                tcx.mk_substs(Vec::<GenericArg<'tcx>>::new().into_iter())
+            }
+        } else {
+            tcx.mk_substs(Vec::<GenericArg<'tcx>>::new().into_iter())
+        };
+        debug!(?parent_substs);
+
+        let did = def.did.to_def_id();
+        let child_substs = InternalSubsts::identity_for_item(tcx, did);
+        let substs = tcx.mk_substs(parent_substs.into_iter().chain(child_substs.into_iter()));
+        debug!(?substs);
+
+        let hir_id = tcx.hir().local_def_id_to_hir_id(def.did);
+        let span = tcx.hir().span(hir_id);
+        let uneval = ty::Unevaluated::new(def.to_global(), substs);
+        debug!(?span, ?param_env);
+
+        match tcx.const_eval_resolve(param_env, uneval, Some(span)) {
+            Ok(val) => Self::Val(val, ty),
+            Err(_) => {
+                // Error was handled in `const_eval_resolve`. Here we just create a
+                // new unevaluated const and error hard later in codegen
+                let ty_const = tcx.mk_const(ty::ConstS {
+                    val: ty::ConstKind::Unevaluated(ty::Unevaluated {
+                        def: def.to_global(),
+                        substs: InternalSubsts::identity_for_item(tcx, def.did.to_def_id()),
+                        promoted: None,
+                    }),
+                    ty,
+                });
+
+                Self::Ty(ty_const)
+            }
+        }
     }
 }
 
diff --git a/compiler/rustc_middle/src/thir.rs b/compiler/rustc_middle/src/thir.rs
index b31cc17a959..b17343d7692 100644
--- a/compiler/rustc_middle/src/thir.rs
+++ b/compiler/rustc_middle/src/thir.rs
@@ -19,11 +19,11 @@ use rustc_middle::infer::canonical::Canonical;
 use rustc_middle::middle::region;
 use rustc_middle::mir::interpret::AllocId;
 use rustc_middle::mir::{
-    BinOp, BorrowKind, FakeReadCause, Field, Mutability, UnOp, UserTypeProjection,
+    self, BinOp, BorrowKind, FakeReadCause, Field, Mutability, UnOp, UserTypeProjection,
 };
 use rustc_middle::ty::adjustment::PointerCast;
 use rustc_middle::ty::subst::SubstsRef;
-use rustc_middle::ty::{self, AdtDef, Const, Ty, UpvarSubsts, UserType};
+use rustc_middle::ty::{self, AdtDef, Ty, UpvarSubsts, UserType};
 use rustc_middle::ty::{
     CanonicalUserType, CanonicalUserTypeAnnotation, CanonicalUserTypeAnnotations,
 };
@@ -375,7 +375,7 @@ pub enum ExprKind<'tcx> {
     /// An array literal constructed from one repeated element, e.g. `[1; 5]`.
     Repeat {
         value: ExprId,
-        count: Const<'tcx>,
+        count: ty::Const<'tcx>,
     },
     /// An array, e.g. `[a, b, c, d]`.
     Array {
@@ -522,7 +522,7 @@ pub enum InlineAsmOperand<'tcx> {
         out_expr: Option<ExprId>,
     },
     Const {
-        value: Const<'tcx>,
+        value: mir::ConstantKind<'tcx>,
         span: Span,
     },
     SymFn {
diff --git a/compiler/rustc_middle/src/thir/visit.rs b/compiler/rustc_middle/src/thir/visit.rs
index 451fa466387..ef7becde69a 100644
--- a/compiler/rustc_middle/src/thir/visit.rs
+++ b/compiler/rustc_middle/src/thir/visit.rs
@@ -24,6 +24,15 @@ pub trait Visitor<'a, 'tcx: 'a>: Sized {
     fn visit_pat(&mut self, pat: &Pat<'tcx>) {
         walk_pat(self, pat);
     }
+
+    // Note: We don't have visitors for `ty::Const` and `mir::ConstantKind`
+    // (even though these types occur in THIR) for consistency and to reduce confusion,
+    // since the lazy creation of constants during thir construction causes most
+    // 'constants' to not be of type `ty::Const` or `mir::ConstantKind` at that
+    // stage (they are mostly still identified by `DefId` or `hir::Lit`, see
+    // the variants `Literal`, `NonHirLiteral` and `NamedConst` in `thir::ExprKind`).
+    // You have to manually visit `ty::Const` and `mir::ConstantKind` through the
+    // other `visit*` functions.
 }
 
 pub fn walk_expr<'a, 'tcx: 'a, V: Visitor<'a, 'tcx>>(visitor: &mut V, expr: &Expr<'tcx>) {
diff --git a/compiler/rustc_middle/src/ty/consts/kind.rs b/compiler/rustc_middle/src/ty/consts/kind.rs
index b8da35abd47..35d286d2c57 100644
--- a/compiler/rustc_middle/src/ty/consts/kind.rs
+++ b/compiler/rustc_middle/src/ty/consts/kind.rs
@@ -126,7 +126,8 @@ impl<'tcx> ConstKind<'tcx> {
     #[inline]
     /// Tries to evaluate the constant if it is `Unevaluated`. If that isn't possible or necessary
     /// return `None`.
-    pub(super) fn try_eval(
+    // FIXME(@lcnr): Completely rework the evaluation/normalization system for `ty::Const` once valtrees are merged.
+    pub fn try_eval(
         self,
         tcx: TyCtxt<'tcx>,
         param_env: ParamEnv<'tcx>,
diff --git a/compiler/rustc_mir_build/src/build/cfg.rs b/compiler/rustc_mir_build/src/build/cfg.rs
index dca9a63120c..ac92b03e5f3 100644
--- a/compiler/rustc_mir_build/src/build/cfg.rs
+++ b/compiler/rustc_mir_build/src/build/cfg.rs
@@ -73,7 +73,7 @@ impl<'tcx> CFG<'tcx> {
             Rvalue::Use(Operand::Constant(Box::new(Constant {
                 span: source_info.span,
                 user_ty: None,
-                literal: ConstantKind::from_zero_sized(tcx.types.unit),
+                literal: ConstantKind::zero_sized(tcx.types.unit),
             }))),
         );
     }
diff --git a/compiler/rustc_mir_build/src/build/expr/as_constant.rs b/compiler/rustc_mir_build/src/build/expr/as_constant.rs
index 6856ded3498..8b9b1847e7f 100644
--- a/compiler/rustc_mir_build/src/build/expr/as_constant.rs
+++ b/compiler/rustc_mir_build/src/build/expr/as_constant.rs
@@ -2,11 +2,10 @@
 
 use crate::build::Builder;
 use crate::thir::constant::parse_float;
-use rustc_ast::ast;
+use rustc_ast as ast;
 use rustc_hir::def_id::DefId;
-use rustc_middle::mir::interpret::{
-    Allocation, ConstValue, LitToConstError, LitToConstInput, Scalar,
-};
+use rustc_middle::mir::interpret::Allocation;
+use rustc_middle::mir::interpret::{ConstValue, LitToConstError, LitToConstInput, Scalar};
 use rustc_middle::mir::*;
 use rustc_middle::thir::*;
 use rustc_middle::ty::subst::SubstsRef;
@@ -32,11 +31,11 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             }
             ExprKind::Literal { lit, neg } => {
                 let literal =
-                    match lit_to_constant(tcx, LitToConstInput { lit: &lit.node, ty, neg }) {
+                    match lit_to_mir_constant(tcx, LitToConstInput { lit: &lit.node, ty, neg }) {
                         Ok(c) => c,
                         Err(LitToConstError::Reported) => ConstantKind::Ty(tcx.const_error(ty)),
                         Err(LitToConstError::TypeError) => {
-                            bug!("encountered type error in `lit_to_constant")
+                            bug!("encountered type error in `lit_to_mir_constant")
                         }
                     };
 
@@ -90,7 +89,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     }
 }
 
-crate fn lit_to_constant<'tcx>(
+#[instrument(skip(tcx, lit_input))]
+fn lit_to_mir_constant<'tcx>(
     tcx: TyCtxt<'tcx>,
     lit_input: LitToConstInput<'tcx>,
 ) -> Result<ConstantKind<'tcx>, LitToConstError> {
diff --git a/compiler/rustc_mir_build/src/build/expr/as_rvalue.rs b/compiler/rustc_mir_build/src/build/expr/as_rvalue.rs
index 3f8a1a3f795..be777418433 100644
--- a/compiler/rustc_mir_build/src/build/expr/as_rvalue.rs
+++ b/compiler/rustc_mir_build/src/build/expr/as_rvalue.rs
@@ -322,7 +322,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 block.and(Rvalue::Use(Operand::Constant(Box::new(Constant {
                     span: expr_span,
                     user_ty: None,
-                    literal: ty::Const::zero_sized(this.tcx, this.tcx.types.unit).into(),
+                    literal: ConstantKind::zero_sized(this.tcx.types.unit),
                 }))))
             }
             ExprKind::Yield { .. }
@@ -552,7 +552,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     fn neg_1_literal(&mut self, span: Span, ty: Ty<'tcx>) -> Operand<'tcx> {
         let param_ty = ty::ParamEnv::empty().and(ty);
         let size = self.tcx.layout_of(param_ty).unwrap().size;
-        let literal = ty::Const::from_bits(self.tcx, size.unsigned_int_max(), param_ty);
+        let literal = ConstantKind::from_bits(self.tcx, size.unsigned_int_max(), param_ty);
 
         self.literal_operand(span, literal)
     }
@@ -563,7 +563,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         let param_ty = ty::ParamEnv::empty().and(ty);
         let bits = self.tcx.layout_of(param_ty).unwrap().size.bits();
         let n = 1 << (bits - 1);
-        let literal = ty::Const::from_bits(self.tcx, n, param_ty);
+        let literal = ConstantKind::from_bits(self.tcx, n, param_ty);
 
         self.literal_operand(span, literal)
     }
diff --git a/compiler/rustc_mir_build/src/build/matches/test.rs b/compiler/rustc_mir_build/src/build/matches/test.rs
index 96069f05b40..806c260d110 100644
--- a/compiler/rustc_mir_build/src/build/matches/test.rs
+++ b/compiler/rustc_mir_build/src/build/matches/test.rs
@@ -264,7 +264,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     );
                 } else if let [success, fail] = *make_target_blocks(self) {
                     assert_eq!(value.ty(), ty);
-                    let expect = self.literal_operand(test.span, value);
+                    let expect = self.literal_operand(test.span, value.into());
                     let val = Operand::Copy(place);
                     self.compare(block, success, fail, source_info, BinOp::Eq, expect, val);
                 } else {
@@ -277,8 +277,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 let target_blocks = make_target_blocks(self);
 
                 // Test `val` by computing `lo <= val && val <= hi`, using primitive comparisons.
-                let lo = self.literal_operand(test.span, lo);
-                let hi = self.literal_operand(test.span, hi);
+                let lo = self.literal_operand(test.span, lo.into());
+                let hi = self.literal_operand(test.span, hi.into());
                 let val = Operand::Copy(place);
 
                 let [success, fail] = *target_blocks else {
@@ -370,7 +370,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         place: Place<'tcx>,
         mut ty: Ty<'tcx>,
     ) {
-        let mut expect = self.literal_operand(source_info.span, value);
+        let mut expect = self.literal_operand(source_info.span, value.into());
         let mut val = Operand::Copy(place);
 
         // If we're using `b"..."` as a pattern, we need to insert an
@@ -823,7 +823,7 @@ fn trait_method<'tcx>(
     method_name: Symbol,
     self_ty: Ty<'tcx>,
     params: &[GenericArg<'tcx>],
-) -> ty::Const<'tcx> {
+) -> ConstantKind<'tcx> {
     let substs = tcx.mk_substs_trait(self_ty, params);
 
     // The unhygienic comparison here is acceptable because this is only
@@ -836,5 +836,6 @@ fn trait_method<'tcx>(
 
     let method_ty = tcx.type_of(item.def_id);
     let method_ty = method_ty.subst(tcx, substs);
-    ty::Const::zero_sized(tcx, method_ty)
+
+    ConstantKind::zero_sized(method_ty)
 }
diff --git a/compiler/rustc_mir_build/src/build/misc.rs b/compiler/rustc_mir_build/src/build/misc.rs
index 3516eca1c14..84762d602f8 100644
--- a/compiler/rustc_mir_build/src/build/misc.rs
+++ b/compiler/rustc_mir_build/src/build/misc.rs
@@ -3,6 +3,7 @@
 
 use crate::build::Builder;
 
+use rustc_middle::mir;
 use rustc_middle::mir::*;
 use rustc_middle::ty::{self, Ty};
 use rustc_span::{Span, DUMMY_SP};
@@ -25,8 +26,11 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 
     /// Convenience function for creating a literal operand, one
     /// without any user type annotation.
-    crate fn literal_operand(&mut self, span: Span, literal: ty::Const<'tcx>) -> Operand<'tcx> {
-        let literal = literal.into();
+    crate fn literal_operand(
+        &mut self,
+        span: Span,
+        literal: mir::ConstantKind<'tcx>,
+    ) -> Operand<'tcx> {
         let constant = Box::new(Constant { span, user_ty: None, literal });
         Operand::Constant(constant)
     }
@@ -34,7 +38,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     // Returns a zero literal operand for the appropriate type, works for
     // bool, char and integers.
     crate fn zero_literal(&mut self, span: Span, ty: Ty<'tcx>) -> Operand<'tcx> {
-        let literal = ty::Const::from_bits(self.tcx, 0, ty::ParamEnv::empty().and(ty));
+        let literal = ConstantKind::from_bits(self.tcx, 0, ty::ParamEnv::empty().and(ty));
 
         self.literal_operand(span, literal)
     }
diff --git a/compiler/rustc_mir_build/src/thir/cx/expr.rs b/compiler/rustc_mir_build/src/thir/cx/expr.rs
index e6afc89baa0..7ef33011234 100644
--- a/compiler/rustc_mir_build/src/thir/cx/expr.rs
+++ b/compiler/rustc_mir_build/src/thir/cx/expr.rs
@@ -8,7 +8,7 @@ use rustc_middle::hir::place::Place as HirPlace;
 use rustc_middle::hir::place::PlaceBase as HirPlaceBase;
 use rustc_middle::hir::place::ProjectionKind as HirProjectionKind;
 use rustc_middle::middle::region;
-use rustc_middle::mir::{BinOp, BorrowKind, Field, UnOp};
+use rustc_middle::mir::{self, BinOp, BorrowKind, Field, UnOp};
 use rustc_middle::thir::*;
 use rustc_middle::ty::adjustment::{
     Adjust, Adjustment, AutoBorrow, AutoBorrowMutability, PointerCast,
@@ -491,7 +491,11 @@ impl<'tcx> Cx<'tcx> {
                             hir::InlineAsmOperand::Const { ref anon_const } => {
                                 let anon_const_def_id =
                                     self.tcx.hir().local_def_id(anon_const.hir_id);
-                                let value = ty::Const::from_anon_const(self.tcx, anon_const_def_id);
+                                let value = mir::ConstantKind::from_anon_const(
+                                    self.tcx,
+                                    anon_const_def_id,
+                                    self.param_env,
+                                );
                                 let span = self.tcx.hir().span(anon_const.hir_id);
 
                                 InlineAsmOperand::Const { value, span }
diff --git a/compiler/rustc_mir_build/src/thir/pattern/deconstruct_pat.rs b/compiler/rustc_mir_build/src/thir/pattern/deconstruct_pat.rs
index bb3ba3e596d..72f0d07c260 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/deconstruct_pat.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/deconstruct_pat.rs
@@ -55,7 +55,7 @@ use rustc_hir::{HirId, RangeEnd};
 use rustc_middle::mir::Field;
 use rustc_middle::thir::{FieldPat, Pat, PatKind, PatRange};
 use rustc_middle::ty::layout::IntegerExt;
-use rustc_middle::ty::{self, Const, Ty, TyCtxt, VariantDef};
+use rustc_middle::ty::{self, Ty, TyCtxt, VariantDef};
 use rustc_middle::{middle::stability::EvalResult, mir::interpret::ConstValue};
 use rustc_session::lint;
 use rustc_span::{Span, DUMMY_SP};
@@ -136,7 +136,7 @@ impl IntRange {
     fn from_const<'tcx>(
         tcx: TyCtxt<'tcx>,
         param_env: ty::ParamEnv<'tcx>,
-        value: Const<'tcx>,
+        value: ty::Const<'tcx>,
     ) -> Option<IntRange> {
         let ty = value.ty();
         if let Some((target_size, bias)) = Self::integral_size_and_signed_bias(tcx, ty) {
@@ -829,7 +829,8 @@ impl<'tcx> Constructor<'tcx> {
                 }
             }
             (Str(self_val), Str(other_val)) => {
-                // FIXME: there's probably a more direct way of comparing for equality
+                // FIXME Once valtrees are available we can directly use the bytes
+                // in the `Str` variant of the valtree for the comparison here.
                 match compare_const_vals(
                     pcx.cx.tcx,
                     *self_val,
diff --git a/compiler/rustc_mir_build/src/thir/pattern/mod.rs b/compiler/rustc_mir_build/src/thir/pattern/mod.rs
index 72b597bb13d..dbcd701c1ad 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/mod.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/mod.rs
@@ -488,9 +488,7 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
 
         match self.tcx.const_eval_instance(param_env_reveal_all, instance, Some(span)) {
             Ok(value) => {
-                let const_ =
-                    ty::Const::from_value(self.tcx, value, self.typeck_results.node_type(id));
-
+                let const_ = ty::Const::from_value(self.tcx, value, ty);
                 let pattern = self.const_to_pat(const_, id, span, mir_structural_match_violation);
 
                 if !is_associated_const {
@@ -585,7 +583,7 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
         let lit_input =
             LitToConstInput { lit: &lit.node, ty: self.typeck_results.expr_ty(expr), neg };
         match self.tcx.at(expr.span).lit_to_const(lit_input) {
-            Ok(val) => *self.const_to_pat(val, expr.hir_id, lit.span, false).kind,
+            Ok(constant) => *self.const_to_pat(constant, expr.hir_id, lit.span, false).kind,
             Err(LitToConstError::Reported) => PatKind::Wild,
             Err(LitToConstError::TypeError) => bug!("lower_lit: had type error"),
         }
@@ -739,6 +737,7 @@ impl<'tcx> PatternFoldable<'tcx> for PatKind<'tcx> {
     }
 }
 
+#[instrument(skip(tcx), level = "debug")]
 crate fn compare_const_vals<'tcx>(
     tcx: TyCtxt<'tcx>,
     a: ty::Const<'tcx>,
@@ -746,8 +745,6 @@ crate fn compare_const_vals<'tcx>(
     param_env: ty::ParamEnv<'tcx>,
     ty: Ty<'tcx>,
 ) -> Option<Ordering> {
-    trace!("compare_const_vals: {:?}, {:?}", a, b);
-
     let from_bool = |v: bool| v.then_some(Ordering::Equal);
 
     let fallback = || from_bool(a == b);
diff --git a/compiler/rustc_mir_build/src/thir/pattern/usefulness.rs b/compiler/rustc_mir_build/src/thir/pattern/usefulness.rs
index 15bb5adf8ba..687b2e23c9f 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/usefulness.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/usefulness.rs
@@ -765,10 +765,7 @@ fn lint_non_exhaustive_omitted_patterns<'p, 'tcx>(
 /// `is_under_guard` is used to inform if the pattern has a guard. If it
 /// has one it must not be inserted into the matrix. This shouldn't be
 /// relied on for soundness.
-#[instrument(
-    level = "debug",
-    skip(cx, matrix, witness_preference, hir_id, is_under_guard, is_top_level)
-)]
+#[instrument(level = "debug", skip(cx, matrix, hir_id))]
 fn is_useful<'p, 'tcx>(
     cx: &MatchCheckCtxt<'p, 'tcx>,
     matrix: &Matrix<'p, 'tcx>,
@@ -800,6 +797,7 @@ fn is_useful<'p, 'tcx>(
 
     let ty = v.head().ty();
     let is_non_exhaustive = cx.is_foreign_non_exhaustive_enum(ty);
+    debug!("v.head: {:?}, v.span: {:?}", v.head(), v.head().span());
     let pcx = PatCtxt { cx, ty, span: v.head().span(), is_top_level, is_non_exhaustive };
 
     // If the first pattern is an or-pattern, expand it.
@@ -809,9 +807,11 @@ fn is_useful<'p, 'tcx>(
         // We try each or-pattern branch in turn.
         let mut matrix = matrix.clone();
         for v in v.expand_or_pat() {
+            debug!(?v);
             let usefulness = ensure_sufficient_stack(|| {
                 is_useful(cx, &matrix, &v, witness_preference, hir_id, is_under_guard, false)
             });
+            debug!(?usefulness);
             ret.extend(usefulness);
             // If pattern has a guard don't add it to the matrix.
             if !is_under_guard {
@@ -822,6 +822,7 @@ fn is_useful<'p, 'tcx>(
         }
     } else {
         let v_ctor = v.head().ctor();
+        debug!(?v_ctor);
         if let Constructor::IntRange(ctor_range) = &v_ctor {
             // Lint on likely incorrect range patterns (#63987)
             ctor_range.lint_overlapping_range_endpoints(
@@ -895,7 +896,7 @@ fn is_useful<'p, 'tcx>(
 }
 
 /// The arm of a match expression.
-#[derive(Clone, Copy)]
+#[derive(Clone, Copy, Debug)]
 crate struct MatchArm<'p, 'tcx> {
     /// The pattern must have been lowered through `check_match::MatchVisitor::lower_pattern`.
     crate pat: &'p DeconstructedPat<'p, 'tcx>,
@@ -928,6 +929,7 @@ crate struct UsefulnessReport<'p, 'tcx> {
 ///
 /// Note: the input patterns must have been lowered through
 /// `check_match::MatchVisitor::lower_pattern`.
+#[instrument(skip(cx, arms), level = "debug")]
 crate fn compute_match_usefulness<'p, 'tcx>(
     cx: &MatchCheckCtxt<'p, 'tcx>,
     arms: &[MatchArm<'p, 'tcx>],
@@ -939,6 +941,7 @@ crate fn compute_match_usefulness<'p, 'tcx>(
         .iter()
         .copied()
         .map(|arm| {
+            debug!(?arm);
             let v = PatStack::from_pattern(arm.pat);
             is_useful(cx, &matrix, &v, RealArm, arm.hir_id, arm.has_guard, true);
             if !arm.has_guard {
diff --git a/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs b/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs
index 302b8b79156..5daa9796d12 100644
--- a/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs
+++ b/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs
@@ -634,6 +634,7 @@ pub(super) fn thir_abstract_const<'tcx>(
     }
 }
 
+#[instrument(skip(tcx), level = "debug")]
 pub(super) fn try_unify_abstract_consts<'tcx>(
     tcx: TyCtxt<'tcx>,
     (a, b): (ty::Unevaluated<'tcx, ()>, ty::Unevaluated<'tcx, ()>),
diff --git a/src/tools/clippy/clippy_lints/src/matches/overlapping_arms.rs b/src/tools/clippy/clippy_lints/src/matches/overlapping_arms.rs
index 7e658126690..c0b3e95b185 100644
--- a/src/tools/clippy/clippy_lints/src/matches/overlapping_arms.rs
+++ b/src/tools/clippy/clippy_lints/src/matches/overlapping_arms.rs
@@ -40,10 +40,8 @@ fn all_ranges<'tcx>(cx: &LateContext<'tcx>, arms: &'tcx [Arm<'_>], ty: Ty<'tcx>)
                         Some(rhs) => constant(cx, cx.typeck_results(), rhs)?.0,
                         None => miri_to_const(ty.numeric_max_val(cx.tcx)?)?,
                     };
-
                     let lhs_val = lhs_const.int_value(cx, ty)?;
                     let rhs_val = rhs_const.int_value(cx, ty)?;
-
                     let rhs_bound = match range_end {
                         RangeEnd::Included => EndBound::Included(rhs_val),
                         RangeEnd::Excluded => EndBound::Excluded(rhs_val),
diff --git a/src/tools/clippy/clippy_lints/src/neg_multiply.rs b/src/tools/clippy/clippy_lints/src/neg_multiply.rs
index 0d05c83ffe4..6ba9ba0753d 100644
--- a/src/tools/clippy/clippy_lints/src/neg_multiply.rs
+++ b/src/tools/clippy/clippy_lints/src/neg_multiply.rs
@@ -53,7 +53,7 @@ impl<'tcx> LateLintPass<'tcx> for NegMultiply {
 fn check_mul(cx: &LateContext<'_>, span: Span, lit: &Expr<'_>, exp: &Expr<'_>) {
     if_chain! {
         if let ExprKind::Lit(ref l) = lit.kind;
-        if consts::lit_to_constant(&l.node, cx.typeck_results().expr_ty_opt(lit)) == Constant::Int(1);
+        if consts::lit_to_mir_constant(&l.node, cx.typeck_results().expr_ty_opt(lit)) == Constant::Int(1);
         if cx.typeck_results().expr_ty(exp).is_integral();
 
         then {
diff --git a/src/tools/clippy/clippy_utils/src/consts.rs b/src/tools/clippy/clippy_utils/src/consts.rs
index 1d6f7acab13..be46b791aa4 100644
--- a/src/tools/clippy/clippy_utils/src/consts.rs
+++ b/src/tools/clippy/clippy_utils/src/consts.rs
@@ -179,7 +179,7 @@ impl Constant {
 }
 
 /// Parses a `LitKind` to a `Constant`.
-pub fn lit_to_constant(lit: &LitKind, ty: Option<Ty<'_>>) -> Constant {
+pub fn lit_to_mir_constant(lit: &LitKind, ty: Option<Ty<'_>>) -> Constant {
     match *lit {
         LitKind::Str(ref is, _) => Constant::Str(is.to_string()),
         LitKind::Byte(b) => Constant::Int(u128::from(b)),
@@ -301,7 +301,7 @@ impl<'a, 'tcx> ConstEvalLateContext<'a, 'tcx> {
                 if is_direct_expn_of(e.span, "cfg").is_some() {
                     None
                 } else {
-                    Some(lit_to_constant(&lit.node, self.typeck_results.expr_ty_opt(e)))
+                    Some(lit_to_mir_constant(&lit.node, self.typeck_results.expr_ty_opt(e)))
                 }
             },
             ExprKind::Array(vec) => self.multi(vec).map(Constant::Vec),