// We increase the size of the discriminant to avoid LLVM copying
// padding when it doesn't need to. This normally causes unaligned
// load/stores and excessive memcpy/memset operations. By using a
- // bigger integer size, LLVM can be sure about it's contents and
+ // bigger integer size, LLVM can be sure about its contents and
// won't be so conservative.
// Use the initial field alignment
- let mut ity = Integer::for_abi_align(dl, start_align).unwrap_or(min_ity);
+ let mut ity = if def.repr.c() || def.repr.int.is_some() {
+ min_ity
+ } else {
+ Integer::for_abi_align(dl, start_align).unwrap_or(min_ity)
+ };
// If the alignment is not larger than the chosen discriminant size,
// don't use the alignment as the final size.
--- /dev/null
+// 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-flags: -O
+
+#![allow(dead_code)]
+
+#[repr(C, u8)]
+enum ReprCu8 {
+ A(u16),
+ B,
+}
+
+#[repr(C)]
+struct ReprC {
+ tag: u8,
+ padding: u8,
+ payload: u16,
+}
+
+fn main() {
+ let r1 = ReprC { tag: 0, padding: 0, payload: 0 };
+ let r2 = ReprC { tag: 0, padding: 1, payload: 1 };
+
+ let t1: &ReprCu8 = unsafe { std::mem::transmute(&r1) };
+ let t2: &ReprCu8 = unsafe { std::mem::transmute(&r2) };
+
+ match (t1, t2) {
+ (ReprCu8::A(_), ReprCu8::A(_)) => (),
+ _ => assert!(false)
+ };
+}