From 86062ef930a756cb993832fbfce2467500050268 Mon Sep 17 00:00:00 2001
From: Paul Lietar <paul@lietar.net>
Date: Sat, 5 Nov 2016 02:53:02 +0000
Subject: [PATCH] Read discriminant as a signed integer if specified by layout.

This ensures it gets sign extended correctly.

Fixes #78
---
 src/interpreter/terminator/mod.rs       |  7 ++++++-
 tests/run-pass/negative_discriminant.rs | 13 +++++++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)
 create mode 100644 tests/run-pass/negative_discriminant.rs

diff --git a/src/interpreter/terminator/mod.rs b/src/interpreter/terminator/mod.rs
index fdd703e940b..414fdeb936d 100644
--- a/src/interpreter/terminator/mod.rs
+++ b/src/interpreter/terminator/mod.rs
@@ -252,11 +252,16 @@ fn read_discriminant_value(&self, adt_ptr: Pointer, adt_ty: Ty<'tcx>) -> EvalRes
         let adt_layout = self.type_layout(adt_ty);
 
         let discr_val = match *adt_layout {
-            General { discr, .. } | CEnum { discr, .. } => {
+            General { discr, .. } | CEnum { discr, signed: false, .. } => {
                 let discr_size = discr.size().bytes();
                 self.memory.read_uint(adt_ptr, discr_size as usize)?
             }
 
+            CEnum { discr, signed: true, .. } => {
+                let discr_size = discr.size().bytes();
+                self.memory.read_int(adt_ptr, discr_size as usize)? as u64
+            }
+
             RawNullablePointer { nndiscr, .. } => {
                 self.read_nonnull_discriminant_value(adt_ptr, nndiscr)?
             }
diff --git a/tests/run-pass/negative_discriminant.rs b/tests/run-pass/negative_discriminant.rs
new file mode 100644
index 00000000000..16f175e7dfc
--- /dev/null
+++ b/tests/run-pass/negative_discriminant.rs
@@ -0,0 +1,13 @@
+enum AB { A = -1, B = 1 }
+
+fn main() {
+    match AB::A {
+        AB::A => (),
+        AB::B => panic!(),
+    }
+
+    match AB::B {
+        AB::A => panic!(),
+        AB::B => (),
+    }
+}