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 rust-lang/rust#94059 (does include its changes, the first two commits in this PR correspond to those changes) and rust-lang/rust#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`

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),

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 {

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),