From 4b6a4821b71221a46576100a5ab3fc92011fad16 Mon Sep 17 00:00:00 2001
From: Jonas Schievink <jonasschievink@gmail.com>
Date: Tue, 22 Sep 2020 20:19:00 +0200
Subject: [PATCH] Fix dest prop miscompilation around references

---
 compiler/rustc_mir/src/transform/dest_prop.rs |  2 +-
 src/test/ui/issues/issue-77002.rs             | 16 ++++++++++++++++
 2 files changed, 17 insertions(+), 1 deletion(-)
 create mode 100644 src/test/ui/issues/issue-77002.rs

diff --git a/compiler/rustc_mir/src/transform/dest_prop.rs b/compiler/rustc_mir/src/transform/dest_prop.rs
index 46cbced2d54..97d26176077 100644
--- a/compiler/rustc_mir/src/transform/dest_prop.rs
+++ b/compiler/rustc_mir/src/transform/dest_prop.rs
@@ -905,7 +905,7 @@ impl<'a, 'tcx> Visitor<'tcx> for FindAssignments<'a, 'tcx> {
             // FIXME: This can be smarter and take `StorageDead` into account (which
             // invalidates borrows).
             if self.ever_borrowed_locals.contains(dest.local)
-                && self.ever_borrowed_locals.contains(src.local)
+                || self.ever_borrowed_locals.contains(src.local)
             {
                 return;
             }
diff --git a/src/test/ui/issues/issue-77002.rs b/src/test/ui/issues/issue-77002.rs
new file mode 100644
index 00000000000..c7dd3cf8109
--- /dev/null
+++ b/src/test/ui/issues/issue-77002.rs
@@ -0,0 +1,16 @@
+// compile-flags: -Zmir-opt-level=2 -Copt-level=0
+// run-pass
+
+type M = [i64; 2];
+
+fn f(a: &M) -> M {
+    let mut b: M = M::default();
+    b[0] = a[0] * a[0];
+    b
+}
+
+fn main() {
+    let mut a: M = [1, 1];
+    a = f(&a);
+    assert_eq!(a[0], 1);
+}