try to improve perf

Author: RalfJung

compiler/rustc_middle/src/thir.rs

@@ -16,7 +16,7 @@ use rustc_hir::{BindingAnnotation, ByRef, HirId, MatchSource, RangeEnd};
 use rustc_index::newtype_index;
 use rustc_index::IndexVec;
 use rustc_middle::middle::region;
-use rustc_middle::mir::interpret::AllocId;
+use rustc_middle::mir::interpret::{AllocId, Scalar};
 use rustc_middle::mir::{self, BinOp, BorrowKind, FakeReadCause, UnOp};
 use rustc_middle::ty::adjustment::PointerCoercion;
 use rustc_middle::ty::layout::IntegerExt;
@@ -1009,11 +1009,16 @@ impl<'tcx> PatRangeBoundary<'tcx> {
 
             // This code is hot when compiling matches with many ranges. So we
             // special-case extraction of evaluated scalars for speed, for types where
-            // raw data comparisons are appropriate. E.g. `unicode-normalization` has
+            // unsigned int comparisons are appropriate. E.g. `unicode-normalization` has
             // many ranges such as '\u{037A}'..='\u{037F}', and chars can be compared
             // in this way.
             (Finite(a), Finite(b)) if matches!(ty.kind(), ty::Uint(_) | ty::Char) => {
-                if let (Some(a), Some(b)) = (a.try_to_scalar_int(), b.try_to_scalar_int()) {
+                let to_scalar_int = |x| match x {
+                    mir::Const::Val(mir::ConstValue::Scalar(Scalar::Int(x)), _) => Some(x),
+                    mir::Const::Ty(x) => Some(x.to_valtree().unwrap_leaf()),
+                    _ => None,
+                };
+                if let (Some(a), Some(b)) = (to_scalar_int(a), to_scalar_int(b)) {
                     let sz = ty.primitive_size(tcx);
                     let a = a.assert_uint(sz);
                     let b = b.assert_uint(sz);