Handle CEnum layouts with signed representations.

src/interpreter.rs

@@ -688,14 +688,15 @@ fn eval_assignment(&mut self, lvalue: &mir::Lvalue<'tcx>, rvalue: &mir::Rvalue<'
                         }
                     }
 
-                    CEnum { discr, signed, min, max } => {
+                    CEnum { discr, signed, .. } => {
                         assert_eq!(operands.len(), 0);
                         if let mir::AggregateKind::Adt(adt_def, variant, _) = *kind {
+                            let val = adt_def.variants[variant].disr_val.to_u64_unchecked();
+                            let size = discr.size().bytes() as usize;
+
                             if signed {
-                                unimplemented!()
+                                try!(self.memory.write_int(dest, val as i64, size));
                             } else {
-                                let val = adt_def.variants[variant].disr_val.to_u64().unwrap();
-                                let size = discr.size().bytes() as usize;
                                 try!(self.memory.write_uint(dest, val, size));
                             }
                         } else {

tests/run-pass/c_enums.rs

@@ -7,11 +7,22 @@ enum Foo {
     Quux = 100,
 }
 
+enum Signed {
+    Bar = -42,
+    Baz,
+    Quux = 100,
+}
+
 #[miri_run]
 fn foo() -> [u8; 3] {
     [Foo::Bar as u8, Foo::Baz as u8, Foo::Quux as u8]
 }
 
+#[miri_run]
+fn signed() -> [i8; 3] {
+    [Signed::Bar as i8, Signed::Baz as i8, Signed::Quux as i8]
+}
+
 #[miri_run]
 fn unsafe_match() -> bool {
     match unsafe { std::mem::transmute::<u8, Foo>(43) } {
@@ -22,5 +33,7 @@ fn unsafe_match() -> bool {
 
 #[miri_run]
 fn main() {
+    // assert_eq!(foo(), [42, 43, 100]);
+    // assert_eq!(signed(), [-42, -41, 100]);
     assert!(unsafe_match());
 }