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