Rollup merge of #130715 - compiler-errors:mir-build-const-eval, r=BoxyUwU

Replace calls to `ty::Const::{try_}eval` in mir build/pattern analysis

We normalize consts in writeback: #130645. This means that consts are gonna be as normalized as they're ever gonna get in MIR building and pattern analysis. Therefore we can just use `try_to_target_usize` rather than calling `eval_target_usize`.

Regarding the `.expect` calls, I'm not totally certain whether they're correct given rigid unevaluated consts. But this PR shouldn't make *more* ICEs occur; we may have to squash these ICEs when mGCE comes around, tho 😺

compiler/rustc_mir_build/src/build/expr/as_rvalue.rs

@@ -57,7 +57,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 this.in_scope(region_scope, lint_level, |this| this.as_rvalue(block, scope, value))
             }
             ExprKind::Repeat { value, count } => {
-                if Some(0) == count.try_eval_target_usize(this.tcx, this.param_env) {
+                if Some(0) == count.try_to_target_usize(this.tcx) {
                     this.build_zero_repeat(block, value, scope, source_info)
                 } else {
                     let value_operand = unpack!(

compiler/rustc_mir_build/src/build/matches/match_pair.rs

@@ -42,7 +42,12 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         let tcx = self.tcx;
         let (min_length, exact_size) = if let Some(place_resolved) = place.try_to_place(self) {
             match place_resolved.ty(&self.local_decls, tcx).ty.kind() {
-                ty::Array(_, length) => (length.eval_target_usize(tcx, self.param_env), true),
+                ty::Array(_, length) => (
+                    length
+                        .try_to_target_usize(tcx)
+                        .expect("expected len of array pat to be definite"),
+                    true,
+                ),
                 _ => ((prefix.len() + suffix.len()).try_into().unwrap(), false),
             }
         } else {

compiler/rustc_mir_build/src/thir/pattern/mod.rs

@@ -441,7 +441,9 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
             ty::Slice(..) => PatKind::Slice { prefix, slice, suffix },
             // Fixed-length array, `[T; len]`.
             ty::Array(_, len) => {
-                let len = len.eval_target_usize(self.tcx, self.param_env);
+                let len = len
+                    .try_to_target_usize(self.tcx)
+                    .expect("expected len of array pat to be definite");
                 assert!(len >= prefix.len() as u64 + suffix.len() as u64);
                 PatKind::Array { prefix, slice, suffix }
             }

compiler/rustc_pattern_analysis/src/rustc.rs

@@ -352,7 +352,7 @@ impl<'p, 'tcx: 'p> RustcPatCtxt<'p, 'tcx> {
             ty::Array(sub_ty, len) => {
                 // We treat arrays of a constant but unknown length like slices.
                 ConstructorSet::Slice {
-                    array_len: len.try_eval_target_usize(cx.tcx, cx.param_env).map(|l| l as usize),
+                    array_len: len.try_to_target_usize(cx.tcx).map(|l| l as usize),
                     subtype_is_empty: cx.is_uninhabited(*sub_ty),
                 }
             }
@@ -685,9 +685,12 @@ impl<'p, 'tcx: 'p> RustcPatCtxt<'p, 'tcx> {
             }
             PatKind::Array { prefix, slice, suffix } | PatKind::Slice { prefix, slice, suffix } => {
                 let array_len = match ty.kind() {
-                    ty::Array(_, length) => {
+                    ty::Array(_, length) => Some(
-                        Some(length.eval_target_usize(cx.tcx, cx.param_env) as usize)
+                        length
-                    }
+                            .try_to_target_usize(cx.tcx)
+                            .expect("expected len of array pat to be definite")
+                            as usize,
+                    ),
                     ty::Slice(_) => None,
                     _ => span_bug!(pat.span, "bad ty {} for slice pattern", ty.inner()),
                 };