From 94aa02855defad20fe63d46a5df9506e82b78ff3 Mon Sep 17 00:00:00 2001
From: Ralf Jung <post@ralfj.de>
Date: Thu, 21 May 2020 16:30:27 +0200
Subject: [PATCH] fix discriminant sign extension

---
 src/librustc_mir/interpret/intrinsics.rs | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/librustc_mir/interpret/intrinsics.rs b/src/librustc_mir/interpret/intrinsics.rs
index 42b969c99917f..fc4be82ad90ad 100644
--- a/src/librustc_mir/interpret/intrinsics.rs
+++ b/src/librustc_mir/interpret/intrinsics.rs
@@ -219,7 +219,10 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 let place = self.deref_operand(args[0])?;
                 let discr_val = self.read_discriminant(place.into())?.0;
                 let scalar = match dest.layout.ty.kind {
-                    ty::Int(_) => Scalar::from_int(discr_val as i128, dest.layout.size),
+                    ty::Int(_) => Scalar::from_int(
+                        self.sign_extend(discr_val, dest.layout) as i128,
+                        dest.layout.size,
+                    ),
                     ty::Uint(_) => Scalar::from_uint(discr_val, dest.layout.size),
                     _ => bug!("invalid `discriminant_value` return layout: {:?}", dest.layout),
                 };