const_eval: Consider array length constant even if array is not

TheWastl · Jun 25, 2022 · 090872e · 090872e
1 parent ca7b7a6
commit 090872e
Showing 1 changed file with 9 additions and 3 deletions.
diff --git a/compiler/rustc_const_eval/src/interpret/step.rs b/compiler/rustc_const_eval/src/interpret/step.rs
@@ -5,6 +5,7 @@
 use rustc_middle::mir;
 use rustc_middle::mir::interpret::{InterpResult, Scalar};
 use rustc_middle::ty::layout::LayoutOf;
+use rustc_middle::ty::TyKind;
 
 use super::{InterpCx, Machine};
 
@@ -244,9 +245,14 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 
             Len(place) => {
                 let src = self.eval_place(place)?;
-                let mplace = self.force_allocation(&src)?;
-                let len = mplace.len(self)?;
-                self.write_scalar(Scalar::from_machine_usize(len, self), &dest)?;
+                if let &TyKind::Array(_, len) = src.layout.ty.kind() {
+                    let len = self.const_to_op(len, None)?;
+                    self.copy_op(&len, &dest)?;
+                } else {
+                    let mplace = self.force_allocation(&src)?;
+                    let len = mplace.len(self)?;
+                    self.write_scalar(Scalar::from_machine_usize(len, self), &dest)?;
+                }
             }
 
             AddressOf(_, place) | Ref(_, _, place) => {