From bf2a6c3ff9e4c37526813f255f70f73db7119564 Mon Sep 17 00:00:00 2001
From: Oliver Schneider <public.oliver.schneider@kit.edu>
Date: Wed, 2 May 2018 12:30:45 +0200
Subject: [PATCH] Allow unaligned reads in constants

---
 src/librustc_mir/hair/pattern/mod.rs       |  2 +-
 src/librustc_mir/interpret/eval_context.rs |  4 +---
 src/test/ui/const-eval/ice-packed.rs       | 28 ++++++++++++++++++++++
 3 files changed, 30 insertions(+), 4 deletions(-)
 create mode 100644 src/test/ui/const-eval/ice-packed.rs

diff --git a/src/librustc_mir/hair/pattern/mod.rs b/src/librustc_mir/hair/pattern/mod.rs
index 619b4596b4227..623e0de478bca 100644
--- a/src/librustc_mir/hair/pattern/mod.rs
+++ b/src/librustc_mir/hair/pattern/mod.rs
@@ -792,7 +792,7 @@ impl<'a, 'tcx> PatternContext<'a, 'tcx> {
                 ConstVal::Value(miri) => const_val_field(
                     self.tcx, self.param_env, instance,
                     variant_opt, field, miri, cv.ty,
-                ).unwrap(),
+                ).expect("field access failed"),
                 _ => bug!("{:#?} is not a valid adt", cv),
             };
             self.const_to_pat(instance, val, id, span)
diff --git a/src/librustc_mir/interpret/eval_context.rs b/src/librustc_mir/interpret/eval_context.rs
index e1b358a5eb779..bea29b6926aa6 100644
--- a/src/librustc_mir/interpret/eval_context.rs
+++ b/src/librustc_mir/interpret/eval_context.rs
@@ -1340,9 +1340,7 @@ impl<'a, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M
         use syntax::ast::FloatTy;
 
         let layout = self.layout_of(ty)?;
-        // do the strongest layout check of the two
-        let align = layout.align.max(ptr_align);
-        self.memory.check_align(ptr, align)?;
+        self.memory.check_align(ptr, ptr_align)?;
 
         if layout.size.bytes() == 0 {
             return Ok(Some(Value::ByVal(PrimVal::Undef)));
diff --git a/src/test/ui/const-eval/ice-packed.rs b/src/test/ui/const-eval/ice-packed.rs
new file mode 100644
index 0000000000000..1db12a06b03c4
--- /dev/null
+++ b/src/test/ui/const-eval/ice-packed.rs
@@ -0,0 +1,28 @@
+// 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
+#[derive(Copy, Clone, PartialEq, Eq)]
+#[repr(packed)]
+pub struct Num(u64);
+
+impl Num {
+    pub const ZERO: Self = Num(0);
+}
+
+pub fn decrement(a: Num) -> Num {
+    match a {
+        Num::ZERO => Num::ZERO,
+        a => Num(a.0 - 1)
+    }
+}
+
+fn main() {
+}