auto merge of #19548 : luqmana/rust/mfb, r=nikomatsakis

Fixes #19367.

src/test/run-pass/issue-19367.rs

@@ -0,0 +1,42 @@
+// Copyright 2014 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.
+
+#![feature(tuple_indexing)]
+struct S {
+    o: Option<String>
+}
+
+// Make sure we don't reuse the same alloca when matching
+// on field of struct or tuple which we reassign in the match body.
+
+fn main() {
+    let mut a = (0i, Some("right".into_string()));
+    let b = match a.1 {
+        Some(v) => {
+            a.1 = Some("wrong".into_string());
+            v
+        }
+        None => String::new()
+    };
+    println!("{}", b);
+    assert_eq!(b, "right");
+
+
+    let mut s = S{ o: Some("right".into_string()) };
+    let b = match s.o {
+        Some(v) => {
+            s.o = Some("wrong".into_string());
+            v
+        }
+        None => String::new(),
+    };
+    println!("{}", b);
+    assert_eq!(b, "right");
+}