Auto merge of #135753 - compiler-errors:from-ty-const, r=oli-obk

Get rid of `mir::Const::from_ty_const`

This function is strange, because it turns valtrees into `mir::Const::Value`, but the rest of the const variants stay as type system consts.

All of the callsites except for one in `instsimplify` (array length simplification of `ptr_metadata` call) just go through the valtree arm of the function, so it's easier to just create a `mir::Const` directly for those.

For the instsimplify case, if we have a type system const we should *keep* having a type system const, rather than turning it into a `mir::Const::Value`; it doesn't really matter in practice, though, bc `usize` has no padding, but it feels more principled.

Author: bors

clippy_lints/src/matches/overlapping_arms.rs

@@ -3,7 +3,6 @@ use clippy_utils::diagnostics::span_lint_and_note;
 use core::cmp::Ordering;
 use rustc_hir::{Arm, Expr, PatKind, RangeEnd};
 use rustc_lint::LateContext;
-use rustc_middle::mir;
 use rustc_middle::ty::Ty;
 use rustc_span::Span;
 
@@ -36,14 +35,12 @@ fn all_ranges<'tcx>(cx: &LateContext<'tcx>, arms: &'tcx [Arm<'_>], ty: Ty<'tcx>)
                     let lhs_const = if let Some(lhs) = lhs {
                         ConstEvalCtxt::new(cx).eval_pat_expr(lhs)?
                     } else {
-                        let min_val_const = ty.numeric_min_val(cx.tcx)?;
-                        mir_to_const(cx.tcx, mir::Const::from_ty_const(min_val_const, ty, cx.tcx))?
+                        mir_to_const(cx.tcx, ty.numeric_min_val(cx.tcx)?)?
                     };
                     let rhs_const = if let Some(rhs) = rhs {
                         ConstEvalCtxt::new(cx).eval_pat_expr(rhs)?
                     } else {
-                        let max_val_const = ty.numeric_max_val(cx.tcx)?;
-                        mir_to_const(cx.tcx, mir::Const::from_ty_const(max_val_const, ty, cx.tcx))?
+                        mir_to_const(cx.tcx, ty.numeric_max_val(cx.tcx)?)?
                     };
                     let lhs_val = lhs_const.int_value(cx.tcx, ty)?;
                     let rhs_val = rhs_const.int_value(cx.tcx, ty)?;

clippy_utils/src/lib.rs

@@ -112,7 +112,6 @@ use rustc_hir::{
 use rustc_lexer::{TokenKind, tokenize};
 use rustc_lint::{LateContext, Level, Lint, LintContext};
 use rustc_middle::hir::place::PlaceBase;
-use rustc_middle::mir::Const;
 use rustc_middle::ty::adjustment::{Adjust, Adjustment, AutoBorrow};
 use rustc_middle::ty::fast_reject::SimplifiedType;
 use rustc_middle::ty::layout::IntegerExt;
@@ -1584,8 +1583,8 @@ pub fn is_range_full(cx: &LateContext<'_>, expr: &Expr<'_>, container_path: Opti
         let start_is_none_or_min = start.is_none_or(|start| {
             if let rustc_ty::Adt(_, subst) = ty.kind()
                 && let bnd_ty = subst.type_at(0)
-                && let Some(min_val) = bnd_ty.numeric_min_val(cx.tcx)
-                && let Some(min_const) = mir_to_const(cx.tcx, Const::from_ty_const(min_val, bnd_ty, cx.tcx))
+                && let Some(min_const) = bnd_ty.numeric_min_val(cx.tcx)
+                && let Some(min_const) = mir_to_const(cx.tcx, min_const)
                 && let Some(start_const) = ConstEvalCtxt::new(cx).eval(start)
             {
                 start_const == min_const
@@ -1597,8 +1596,8 @@ pub fn is_range_full(cx: &LateContext<'_>, expr: &Expr<'_>, container_path: Opti
             RangeLimits::Closed => {
                 if let rustc_ty::Adt(_, subst) = ty.kind()
                     && let bnd_ty = subst.type_at(0)
-                    && let Some(max_val) = bnd_ty.numeric_max_val(cx.tcx)
-                    && let Some(max_const) = mir_to_const(cx.tcx, Const::from_ty_const(max_val, bnd_ty, cx.tcx))
+                    && let Some(max_const) = bnd_ty.numeric_max_val(cx.tcx)
+                    && let Some(max_const) = mir_to_const(cx.tcx, max_const)
                     && let Some(end_const) = ConstEvalCtxt::new(cx).eval(end)
                 {
                     end_const == max_const