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.
19 use rustc::ty::layout::LayoutOf;
20 use rustc::ty::{self, Ty};
23 pub fn size_and_align_of_dst<'a, 'tcx: 'a, Bx: BuilderMethods<'a, 'tcx>>(
26 info: Option<Bx::Value>
27 ) -> (Bx::Value, Bx::Value) {
28 debug!("calculate size of DST: {}; with lost info: {:?}",
30 if bx.cx().type_is_sized(t) {
31 let (size, align) = bx.cx().layout_of(t).size_and_align();
32 debug!("size_and_align_of_dst t={} info={:?} size: {:?} align: {:?}",
33 t, info, size, align);
34 let size = bx.cx().const_usize(size.bytes());
35 let align = bx.cx().const_usize(align.abi());
40 // load size/align from vtable
41 let vtable = info.unwrap();
42 (meth::SIZE.get_usize(bx, vtable), meth::ALIGN.get_usize(bx, vtable))
44 ty::Slice(_) | ty::Str => {
45 let unit = t.sequence_element_type(bx.tcx());
46 // The info in this case is the length of the str, so the size is that
47 // times the unit size.
48 let (size, align) = bx.cx().layout_of(unit).size_and_align();
49 (bx.mul(info.unwrap(), bx.cx().const_usize(size.bytes())),
50 bx.cx().const_usize(align.abi()))
54 // First get the size of all statically known fields.
55 // Don't use size_of because it also rounds up to alignment, which we
56 // want to avoid, as the unsized field's alignment could be smaller.
57 assert!(!t.is_simd());
58 let layout = cx.layout_of(t);
59 debug!("DST {} layout: {:?}", t, layout);
61 let i = layout.fields.count() - 1;
62 let sized_size = layout.fields.offset(i).bytes();
63 let sized_align = layout.align.abi();
64 debug!("DST {} statically sized prefix size: {} align: {}",
65 t, sized_size, sized_align);
66 let sized_size = cx.const_usize(sized_size);
67 let sized_align = cx.const_usize(sized_align);
69 // Recurse to get the size of the dynamically sized field (must be
71 let field_ty = layout.field(cx, i).ty;
72 let (unsized_size, mut unsized_align) = size_and_align_of_dst(bx, field_ty, info);
74 // FIXME (#26403, #27023): We should be adding padding
75 // to `sized_size` (to accommodate the `unsized_align`
76 // required of the unsized field that follows) before
77 // summing it with `sized_size`. (Note that since #26403
78 // is unfixed, we do not yet add the necessary padding
79 // here. But this is where the add would go.)
81 // Return the sum of sizes and max of aligns.
82 let size = bx.add(sized_size, unsized_size);
84 // Packed types ignore the alignment of their fields.
85 if let ty::Adt(def, _) = t.sty {
86 if def.repr.packed() {
87 unsized_align = sized_align;
91 // Choose max of two known alignments (combined value must
92 // be aligned according to more restrictive of the two).
93 let align = match (bx.cx().const_to_opt_u128(sized_align, false),
94 bx.cx().const_to_opt_u128(unsized_align, false)) {
95 (Some(sized_align), Some(unsized_align)) => {
96 // If both alignments are constant, (the sized_align should always be), then
97 // pick the correct alignment statically.
98 cx.const_usize(std::cmp::max(sized_align, unsized_align) as u64)
100 _ => bx.select(bx.icmp(IntPredicate::IntUGT, sized_align, unsized_align),
105 // Issue #27023: must add any necessary padding to `size`
106 // (to make it a multiple of `align`) before returning it.
108 // Namely, the returned size should be, in C notation:
110 // `size + ((size & (align-1)) ? align : 0)`
112 // emulated via the semi-standard fast bit trick:
114 // `(size + (align-1)) & -align`
116 let addend = bx.sub(align, bx.cx().const_usize(1));
117 let size = bx.and(bx.add(size, addend), bx.neg(align));