Auto merge of #29963 - dotdash:fat_copy, r=eddyb

Since fat pointers do not qualify as structural types, they got copied
using load_ty and store_ty, which means that we load an FCA and use
extractvalue to get the components of the fat pointer. This breaks
certain optimizations in LLVM.

Found via apasel422/ref_count#13

1 files changed, 22 insertions, 0 deletions

diff --git a/src/test/codegen/fatptr.rs b/src/test/codegen/fatptr.rs
new file mode 100644
index 00000000000..b9e6508dfff
--- /dev/null
+++ b/src/test/codegen/fatptr.rs
@@ -0,0 +1,22 @@
+// Copyright 2015 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: -C no-prepopulate-passes
+
+#![crate_type = "lib"]
+
+pub trait T {}
+
+// CHECK-LABEL: @copy_fat_ptr
+#[no_mangle]
+pub fn copy_fat_ptr(x: &T) {
+// CHECK-NOT: extractvalue
+    let x2 = x;
+}