Auto merge of #94876 - b-naber:thir-abstract-const-changes, r=lcnr

Change Thir to lazily create constants

To allow `AbstractConst`s to work with the previous thir changes we made and those we want to make, i.e. to avoid problems due to `ValTree` and `ConstValue` conversions, we instead switch to a thir representation for constants that allows us to lazily create constants.

r? `@oli-obk`

compiler/rustc_middle/src/query/mod.rs

@@ -955,6 +955,7 @@ rustc_queries! {
         desc { "get a &core::panic::Location referring to a span" }
     }
 
+    // FIXME get rid of this with valtrees
     query lit_to_const(
         key: LitToConstInput<'tcx>
     ) -> Result<ty::Const<'tcx>, LitToConstError> {

compiler/rustc_middle/src/thir.rs

@@ -369,7 +369,8 @@ pub enum ExprKind<'tcx> {
     },
     /// An inline `const` block, e.g. `const {}`.
     ConstBlock {
-        value: Const<'tcx>,
+        did: DefId,
+        substs: SubstsRef<'tcx>,
     },
     /// An array literal constructed from one repeated element, e.g. `[1; 5]`.
     Repeat {
@@ -408,13 +409,25 @@ pub enum ExprKind<'tcx> {
     },
     /// A literal.
     Literal {
-        literal: Const<'tcx>,
-        user_ty: Option<Canonical<'tcx, UserType<'tcx>>>,
-        /// The `DefId` of the `const` item this literal
-        /// was produced from, if this is not a user-written
-        /// literal value.
-        const_id: Option<DefId>,
+        lit: &'tcx hir::Lit,
+        neg: bool,
     },
+    /// For literals that don't correspond to anything in the HIR
+    NonHirLiteral {
+        lit: ty::ScalarInt,
+        user_ty: Option<Canonical<'tcx, UserType<'tcx>>>,
+    },
+    /// Associated constants and named constants
+    NamedConst {
+        def_id: DefId,
+        substs: SubstsRef<'tcx>,
+        user_ty: Option<Canonical<'tcx, UserType<'tcx>>>,
+    },
+    ConstParam {
+        param: ty::ParamConst,
+        def_id: DefId,
+    },
+    // FIXME improve docs for `StaticRef` by distinguishing it from `NamedConst`
     /// A literal containing the address of a `static`.
     ///
     /// This is only distinguished from `Literal` so that we can register some
@@ -439,6 +452,12 @@ pub enum ExprKind<'tcx> {
     },
 }
 
+impl<'tcx> ExprKind<'tcx> {
+    pub fn zero_sized_literal(user_ty: Option<Canonical<'tcx, UserType<'tcx>>>) -> Self {
+        ExprKind::NonHirLiteral { lit: ty::ScalarInt::ZST, user_ty }
+    }
+}
+
 /// Represents the association of a field identifier and an expression.
 ///
 /// This is used in struct constructors.

compiler/rustc_middle/src/thir/visit.rs

@@ -1,7 +1,6 @@
 use super::{
     Arm, Block, Expr, ExprKind, Guard, InlineAsmOperand, Pat, PatKind, Stmt, StmtKind, Thir,
 };
-use rustc_middle::ty::Const;
 
 pub trait Visitor<'a, 'tcx: 'a>: Sized {
     fn thir(&self) -> &'a Thir<'tcx>;
@@ -25,8 +24,6 @@ pub trait Visitor<'a, 'tcx: 'a>: Sized {
     fn visit_pat(&mut self, pat: &Pat<'tcx>) {
         walk_pat(self, pat);
     }
-
-    fn visit_const(&mut self, _cnst: Const<'tcx>) {}
 }
 
 pub fn walk_expr<'a, 'tcx: 'a, V: Visitor<'a, 'tcx>>(visitor: &mut V, expr: &Expr<'tcx>) {
@@ -93,10 +90,9 @@ pub fn walk_expr<'a, 'tcx: 'a, V: Visitor<'a, 'tcx>>(visitor: &mut V, expr: &Exp
                 visitor.visit_expr(&visitor.thir()[value])
             }
         }
-        ConstBlock { value } => visitor.visit_const(value),
-        Repeat { value, count } => {
+        ConstBlock { did: _, substs: _ } => {}
+        Repeat { value, count: _ } => {
             visitor.visit_expr(&visitor.thir()[value]);
-            visitor.visit_const(count);
         }
         Array { ref fields } | Tuple { ref fields } => {
             for &field in &**fields {
@@ -122,7 +118,10 @@ pub fn walk_expr<'a, 'tcx: 'a, V: Visitor<'a, 'tcx>>(visitor: &mut V, expr: &Exp
             visitor.visit_expr(&visitor.thir()[source])
         }
         Closure { closure_id: _, substs: _, upvars: _, movability: _, fake_reads: _ } => {}
-        Literal { literal, user_ty: _, const_id: _ } => visitor.visit_const(literal),
+        Literal { lit: _, neg: _ } => {}
+        NonHirLiteral { lit: _, user_ty: _ } => {}
+        NamedConst { def_id: _, substs: _, user_ty: _ } => {}
+        ConstParam { param: _, def_id: _ } => {}
         StaticRef { alloc_id: _, ty: _, def_id: _ } => {}
         InlineAsm { ref operands, template: _, options: _, line_spans: _ } => {
             for op in &**operands {
@@ -209,11 +208,8 @@ pub fn walk_pat<'a, 'tcx: 'a, V: Visitor<'a, 'tcx>>(visitor: &mut V, pat: &Pat<'
                 visitor.visit_pat(&subpattern.pattern);
             }
         }
-        Constant { value } => visitor.visit_const(*value),
-        Range(range) => {
-            visitor.visit_const(range.lo);
-            visitor.visit_const(range.hi);
-        }
+        Constant { value: _ } => {}
+        Range(_) => {}
         Slice { prefix, slice, suffix } | Array { prefix, slice, suffix } => {
             for subpattern in prefix {
                 visitor.visit_pat(&subpattern);