make operands live to the end of their containing expression

In MIR construction, operands need to live exactly until they are used,
which is during the (sub)expression that made the call to `as_operand`.

Before this PR, operands lived until the end of the temporary scope,
which was sometimes unnecessarily longer and sometimes too short.

Fixes #38669.

1 files changed, 85 insertions, 0 deletions

diff --git a/src/test/mir-opt/basic_assignment.rs b/src/test/mir-opt/basic_assignment.rs
new file mode 100644
index 00000000000..9c924a23903
--- /dev/null
+++ b/src/test/mir-opt/basic_assignment.rs
@@ -0,0 +1,85 @@
+// Copyright 2017 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.
+
+// this tests move up progration, which is not yet implemented
+// Copyright 2017 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.
+
+// check that codegen of assignment expressions is sane. Assignments
+// tend to be absent in simple code, so subtle breakage in them can
+// leave a quite hard-to-find trail of destruction.
+
+fn main() {
+    let nodrop_x = false;
+    let nodrop_y;
+
+    nodrop_y = nodrop_x;
+
+    let drop_x : Option<Box<u32>> = None;
+    let drop_y;
+
+    drop_y = drop_x;
+}
+
+// END RUST SOURCE
+// START rustc.node4.SimplifyCfg.initial-after.mir
+//     bb0: {
+//         StorageLive(_1);
+//         _1 = const false;
+//         StorageLive(_2);
+//         StorageLive(_3);
+//         _3 = _1;
+//         _2 = _3;
+//         StorageDead(_3);
+//         StorageLive(_4);
+//         _4 = std::option::Option<std::boxed::Box<u32>>::None;
+//         StorageLive(_6);
+//         StorageLive(_7);
+//         _7 = _4;
+//         replace(_6 <- _7) -> [return: bb5, unwind: bb4];
+//     }
+//     bb1: {
+//         resume;
+//     }
+//     bb2: {
+//         drop(_4) -> bb1;
+//     }
+//     bb3: {
+//         drop(_6) -> bb2;
+//     }
+//     bb4: {
+//         drop(_7) -> bb3;
+//     }
+//     bb5: {
+//         drop(_7) -> [return: bb6, unwind: bb3];
+//     }
+//     bb6: {
+//         StorageDead(_7);
+//         _0 = ();
+//         drop(_6) -> [return: bb7, unwind: bb2];
+//     }
+//     bb7: {
+//         StorageDead(_6);
+//         drop(_4) -> bb8;
+//     }
+//     bb8: {
+//         StorageDead(_4);
+//         StorageDead(_2);
+//         StorageDead(_1);
+//         return;
+//     }
+// END rustc.node4.SimplifyCfg.initial-after.mir