PatRangeBoundary::compare_with: als add a fast-path for signed integers

Author: RalfJung

Diff for: compiler/rustc_middle/src/thir.rs

@@ -1006,15 +1006,18 @@ 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
-            // unsigned int comparisons are appropriate. E.g. `unicode-normalization` has
+            // we can do scalar comparisons. 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) => {
+            (Finite(a), Finite(b)) if matches!(ty.kind(), ty::Int(_) | ty::Uint(_) | ty::Char) => {
                 if let (Some(a), Some(b)) = (a.try_to_scalar_int(), b.try_to_scalar_int()) {
                     let sz = ty.primitive_size(tcx);
-                    let a = a.assert_uint(sz);
-                    let b = b.assert_uint(sz);
-                    return Some(a.cmp(&b));
+                    let cmp = match ty.kind() {
+                        ty::Uint(_) | ty::Char => a.assert_uint(sz).cmp(&b.assert_uint(sz)),
+                        ty::Int(_) => a.assert_int(sz).cmp(&b.assert_int(sz)),
+                        _ => unreachable!(),
+                    };
+                    return Some(cmp);
                 }
             }
             _ => {}