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Auto merge of #36351 - pnkfelix:fix-36278-size-miscalc, r=eddyb 

When sizing DST, don't double-count nested struct prefixes.

When computing size of `struct P<T>(Q<T>)`, don't double-count prefix added by `Q`

Fix #36278. Fix #36294.
This commit is contained in:
bors 2016-09-10 13:10:29 -07:00 committed by GitHub
parent f8ba7cb863 dd570d64be
commit 1fca1ab0e7
2 changed files with 40 additions and 1 deletions
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13
src/librustc_trans/glue.rs
View File

@ -348,9 +348,20 @@ pub fn size_and_align_of_dst<'blk, 'tcx>(bcx: &BlockAndBuilder<'blk, 'tcx>,
let layout = ccx.layout_of(t);
debug!("DST {} layout: {:?}", t, layout);
// Returns size in bytes of all fields except the last one
// (we will be recursing on the last one).
fn local_prefix_bytes(variant: &ty::layout::Struct) -> u64 {
let fields = variant.offset_after_field.len();
if fields > 1 {
variant.offset_after_field[fields - 2].bytes()
} else {
0
}
}
let (sized_size, sized_align) = match *layout {
ty::layout::Layout::Univariant { ref variant, .. } => {
(variant.min_size().bytes(), variant.align.abi())
(local_prefix_bytes(variant), variant.align.abi())
}
_ => {
bug!("size_and_align_of_dst: expcted Univariant for `{}`, found {:#?}",

28
src/test/run-pass/issue-36278-prefix-nesting.rs Normal file
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@ -0,0 +1,28 @@
// 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.
// Issue 36278: On an unsized struct with >1 level of nontrivial
// nesting, ensure we are computing dynamic size of prefix correctly.
use std::mem;
const SZ: usize = 100;
struct P<T: ?Sized>([u8; SZ], T);
type Ack<T> = P<P<T>>;
fn main() {
let size_of_sized; let size_of_unsized;
let x: Box<Ack<[u8; 0]>> = Box::new(P([0; SZ], P([0; SZ], [0; 0])));
size_of_sized = mem::size_of_val::<Ack<_>>(&x);
let y: Box<Ack<[u8 ]>> = x;
size_of_unsized = mem::size_of_val::<Ack<_>>(&y);
assert_eq!(size_of_sized, size_of_unsized);
}