From 5258871825965b8231b69c080a8c3a0e8c0b8376 Mon Sep 17 00:00:00 2001
From: Oliver Schneider <git-no-reply-9879165716479413131@oli-obk.de>
Date: Mon, 7 May 2018 15:53:44 +0200
Subject: [PATCH] Fix thinning pointers to extern types in miri

---
 src/librustc_mir/interpret/eval_context.rs   |  5 ++++-
 src/test/ui/const-eval/extern_fat_pointer.rs | 23 ++++++++++++++++++++
 src/tools/miri                               |  2 +-
 3 files changed, 28 insertions(+), 2 deletions(-)
 create mode 100644 src/test/ui/const-eval/extern_fat_pointer.rs

diff --git a/src/librustc_mir/interpret/eval_context.rs b/src/librustc_mir/interpret/eval_context.rs
index f5fd14036c4d0..d8f1324206500 100644
--- a/src/librustc_mir/interpret/eval_context.rs
+++ b/src/librustc_mir/interpret/eval_context.rs
@@ -654,6 +654,9 @@ impl<'a, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M
                         if self.type_is_fat_ptr(src.ty) {
                             match (src.value, self.type_is_fat_ptr(dest_ty)) {
                                 (Value::ByRef { .. }, _) |
+                                // pointers to extern types
+                                (Value::ByVal(_),_) |
+                                // slices and trait objects to other slices/trait objects
                                 (Value::ByValPair(..), true) => {
                                     let valty = ValTy {
                                         value: src.value,
@@ -661,6 +664,7 @@ impl<'a, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M
                                     };
                                     self.write_value(valty, dest)?;
                                 }
+                                // slices and trait objects to thin pointers (dropping the metadata)
                                 (Value::ByValPair(data, _), false) => {
                                     let valty = ValTy {
                                         value: Value::ByVal(data),
@@ -668,7 +672,6 @@ impl<'a, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M
                                     };
                                     self.write_value(valty, dest)?;
                                 }
-                                (Value::ByVal(_), _) => bug!("expected fat ptr"),
                             }
                         } else {
                             let src_layout = self.layout_of(src.ty)?;
diff --git a/src/test/ui/const-eval/extern_fat_pointer.rs b/src/test/ui/const-eval/extern_fat_pointer.rs
new file mode 100644
index 0000000000000..071311430a878
--- /dev/null
+++ b/src/test/ui/const-eval/extern_fat_pointer.rs
@@ -0,0 +1,23 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-pass
+
+#![feature(extern_types)]
+
+extern {
+    type Opaque;
+}
+
+const FOO: *const u8 = &42 as *const _ as *const Opaque as *const u8;
+
+fn main() {
+    let _foo = FOO;
+}
diff --git a/src/tools/miri b/src/tools/miri
index f48fed70d4447..e0e1bd7ff778e 160000
--- a/src/tools/miri
+++ b/src/tools/miri
@@ -1 +1 @@
-Subproject commit f48fed70d4447445b586a35c4ae88683542ffc72
+Subproject commit e0e1bd7ff778e5913b566c9e03224faecc0eb486