Skip to content

Commit

Permalink
Browse files Browse the repository at this point in the history
clear discriminant drop flag at the bottom of a ladder
Fixes #38437.
  • Loading branch information
Ariel Ben-Yehuda committed Dec 25, 2016
1 parent e60aa62 commit 521b2ea
Show file tree
Hide file tree
Showing 2 changed files with 93 additions and 38 deletions.
77 changes: 39 additions & 38 deletions src/librustc_borrowck/borrowck/mir/elaborate_drops.rs
Expand Up @@ -481,54 +481,55 @@ impl<'b, 'tcx> ElaborateDropsCtxt<'b, 'tcx> {
is_cleanup: bool)
-> Vec<BasicBlock>
{
let mut succ = succ;
let mut unwind_succ = if is_cleanup {
None
} else {
c.unwind
};
let mut update_drop_flag = true;

let mut succ = self.new_block(
c, c.is_cleanup, TerminatorKind::Goto { target: succ }
);

// Always clear the "master" drop flag at the bottom of the
// ladder. This is needed because the "master" drop flag
// protects the ADT's discriminant, which is invalidated
// after the ADT is dropped.
self.set_drop_flag(
Location { block: succ, statement_index: 0 },
c.path,
DropFlagState::Absent
);

fields.iter().rev().enumerate().map(|(i, &(ref lv, path))| {
let drop_block = match path {
Some(path) => {
debug!("drop_ladder: for std field {} ({:?})", i, lv);

self.elaborated_drop_block(&DropCtxt {
source_info: c.source_info,
is_cleanup: is_cleanup,
init_data: c.init_data,
lvalue: lv,
path: path,
succ: succ,
unwind: unwind_succ,
})
}
None => {
debug!("drop_ladder: for rest field {} ({:?})", i, lv);

let blk = self.complete_drop(&DropCtxt {
source_info: c.source_info,
is_cleanup: is_cleanup,
init_data: c.init_data,
lvalue: lv,
path: c.path,
succ: succ,
unwind: unwind_succ,
}, update_drop_flag);

// the drop flag has been updated - updating
// it again would clobber it.
update_drop_flag = false;

blk
}
succ = if let Some(path) = path {
debug!("drop_ladder: for std field {} ({:?})", i, lv);

self.elaborated_drop_block(&DropCtxt {
source_info: c.source_info,
is_cleanup: is_cleanup,
init_data: c.init_data,
lvalue: lv,
path: path,
succ: succ,
unwind: unwind_succ,
})
} else {
debug!("drop_ladder: for rest field {} ({:?})", i, lv);

self.complete_drop(&DropCtxt {
source_info: c.source_info,
is_cleanup: is_cleanup,
init_data: c.init_data,
lvalue: lv,
path: c.path,
succ: succ,
unwind: unwind_succ,
}, false)
};

succ = drop_block;
unwind_succ = unwind_ladder.as_ref().map(|p| p[i]);

drop_block
succ
}).collect()
}

Expand Down
54 changes: 54 additions & 0 deletions src/test/run-pass/issue-38437.rs
@@ -0,0 +1,54 @@
// Copyright 2016 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 drop elaboration clears the "master" discriminant
// drop flag even if it protects no fields.

struct Good(usize);
impl Drop for Good {
#[inline(never)]
fn drop(&mut self) {
println!("dropping Good({})", self.0);
}
}

struct Void;
impl Drop for Void {
#[inline(never)]
fn drop(&mut self) {
panic!("Suddenly, a Void appears.");
}
}

enum E {
Never(Void),
Fine(Good)
}

fn main() {
let mut go = true;

loop {
let next;
match go {
true => next = E::Fine(Good(123)),
false => return,
}

match next {
E::Never(_) => return,
E::Fine(_good) => go = false,
}

// `next` is dropped and StorageDead'd here. We must reset the
// discriminant's drop flag to avoid random variants being
// dropped.
}
}

0 comments on commit 521b2ea

Please sign in to comment.