1 // Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
13 // Code relating to drop glue.
21 use rustc::ty::layout::LayoutOf;
22 use rustc::ty::{self, Ty};
25 pub fn size_and_align_of_dst(bx: &Builder<'_, 'll, 'tcx>, t: Ty<'tcx>, info: Option<&'ll Value>)
26 -> (&'ll Value, &'ll Value) {
27 debug!("calculate size of DST: {}; with lost info: {:?}",
29 if bx.cx.type_is_sized(t) {
30 let (size, align) = bx.cx.size_and_align_of(t);
31 debug!("size_and_align_of_dst t={} info={:?} size: {:?} align: {:?}",
32 t, info, size, align);
33 let size = C_usize(bx.cx, size.bytes());
34 let align = C_usize(bx.cx, align.abi());
39 // load size/align from vtable
40 let vtable = info.unwrap();
41 (meth::SIZE.get_usize(bx, vtable), meth::ALIGN.get_usize(bx, vtable))
43 ty::Slice(_) | ty::Str => {
44 let unit = t.sequence_element_type(bx.tcx());
45 // The info in this case is the length of the str, so the size is that
46 // times the unit size.
47 let (size, align) = bx.cx.size_and_align_of(unit);
48 (bx.mul(info.unwrap(), C_usize(bx.cx, size.bytes())),
49 C_usize(bx.cx, align.abi()))
53 // First get the size of all statically known fields.
54 // Don't use size_of because it also rounds up to alignment, which we
55 // want to avoid, as the unsized field's alignment could be smaller.
56 assert!(!t.is_simd());
57 let layout = cx.layout_of(t);
58 debug!("DST {} layout: {:?}", t, layout);
60 let i = layout.fields.count() - 1;
61 let sized_size = layout.fields.offset(i).bytes();
62 let sized_align = layout.align.abi();
63 debug!("DST {} statically sized prefix size: {} align: {}",
64 t, sized_size, sized_align);
65 let sized_size = C_usize(cx, sized_size);
66 let sized_align = C_usize(cx, sized_align);
68 // Recurse to get the size of the dynamically sized field (must be
70 let field_ty = layout.field(cx, i).ty;
71 let (unsized_size, mut unsized_align) = size_and_align_of_dst(bx, field_ty, info);
73 // FIXME (#26403, #27023): We should be adding padding
74 // to `sized_size` (to accommodate the `unsized_align`
75 // required of the unsized field that follows) before
76 // summing it with `sized_size`. (Note that since #26403
77 // is unfixed, we do not yet add the necessary padding
78 // here. But this is where the add would go.)
80 // Return the sum of sizes and max of aligns.
81 let size = bx.add(sized_size, unsized_size);
83 // Packed types ignore the alignment of their fields.
84 if let ty::Adt(def, _) = t.sty {
85 if def.repr.packed() {
86 unsized_align = sized_align;
90 // Choose max of two known alignments (combined value must
91 // be aligned according to more restrictive of the two).
92 let align = match (const_to_opt_u128(sized_align, false),
93 const_to_opt_u128(unsized_align, false)) {
94 (Some(sized_align), Some(unsized_align)) => {
95 // If both alignments are constant, (the sized_align should always be), then
96 // pick the correct alignment statically.
97 C_usize(cx, std::cmp::max(sized_align, unsized_align) as u64)
99 _ => bx.select(bx.icmp(llvm::IntUGT, sized_align, unsized_align),
104 // Issue #27023: must add any necessary padding to `size`
105 // (to make it a multiple of `align`) before returning it.
107 // Namely, the returned size should be, in C notation:
109 // `size + ((size & (align-1)) ? align : 0)`
111 // emulated via the semi-standard fast bit trick:
113 // `(size + (align-1)) & -align`
115 let addend = bx.sub(align, C_usize(bx.cx, 1));
116 let size = bx.and(bx.add(size, addend), bx.neg(align));