Auto merge of rust-lang#27582 - pnkfelix:disable-nonzeroing-move-hint…

…-by-default, r=nikomatsakis

Turn nonzeroing move hints back off by default.

Works around bugs injected by PR rust-lang#26173.

 * (@pnkfelix is unavailable in the short-term (i.e. for the next week) to fix them.)

 * When the bugs are fixed, we will turn nonzeroing move hints back on by default.

Fix rust-lang#27401

src/librustc/session/config.rs

@@ -596,8 +596,8 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
  "Force drop flag checks on or off"),
  trace_macros: bool = (false, parse_bool,
  "For every macro invocation, print its name and arguments"),
- disable_nonzeroing_move_hints: bool = (false, parse_bool,
- "Force nonzeroing move optimization off"),
+ enable_nonzeroing_move_hints: bool = (false, parse_bool,
+ "Force nonzeroing move optimization on"),
 }
 
 pub fn default_lib_output() -> CrateType {

src/librustc/session/mod.rs

@@ -273,7 +273,7 @@ impl Session {
  self.opts.debugging_opts.print_enum_sizes
  }
  pub fn nonzeroing_move_hints(&self) -> bool {
- !self.opts.debugging_opts.disable_nonzeroing_move_hints
+ self.opts.debugging_opts.enable_nonzeroing_move_hints
  }
  pub fn sysroot<'a>(&'a self) -> &'a Path {
  match self.opts.maybe_sysroot {

src/test/run-pass/issue-27401-dropflag-reinit.rs

@@ -0,0 +1,36 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http:https://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http:https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http:https://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// ignore-pretty #27582
+
+// Check that when a `let`-binding occurs in a loop, its associated
+// drop-flag is reinitialized (to indicate "needs-drop" at the end of
+// the owning variable's scope).
+
+struct A<'a>(&'a mut i32);
+
+impl<'a> Drop for A<'a> {
+ fn drop(&mut self) {
+ *self.0 += 1;
+ }
+}
+
+fn main() {
+ let mut cnt = 0;
+ for i in 0..2 {
+ let a = A(&mut cnt);
+ if i == 1 { // Note that
+ break; // both this break
+ } // and also
+ drop(a); // this move of `a`
+ // are necessary to expose the bug
+ }
+ assert_eq!(cnt, 2);
+}