110 lines
4.3 KiB
Rust
110 lines
4.3 KiB
Rust
//!
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//
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// Code relating to drop glue.
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use crate::common::IntPredicate;
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use crate::meth;
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use crate::traits::*;
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use rustc_middle::ty::{self, Ty};
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pub fn size_and_align_of_dst<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
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bx: &mut Bx,
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t: Ty<'tcx>,
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info: Option<Bx::Value>,
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) -> (Bx::Value, Bx::Value) {
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let layout = bx.layout_of(t);
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debug!("size_and_align_of_dst(ty={}, info={:?}): layout: {:?}", t, info, layout);
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if !layout.is_unsized() {
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let size = bx.const_usize(layout.size.bytes());
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let align = bx.const_usize(layout.align.abi.bytes());
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return (size, align);
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}
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match t.kind() {
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ty::Dynamic(..) => {
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// load size/align from vtable
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let vtable = info.unwrap();
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(meth::SIZE.get_usize(bx, vtable), meth::ALIGN.get_usize(bx, vtable))
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}
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ty::Slice(_) | ty::Str => {
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let unit = layout.field(bx, 0);
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// The info in this case is the length of the str, so the size is that
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// times the unit size.
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(
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bx.mul(info.unwrap(), bx.const_usize(unit.size.bytes())),
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bx.const_usize(unit.align.abi.bytes()),
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)
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}
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_ => {
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// First get the size of all statically known fields.
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// Don't use size_of because it also rounds up to alignment, which we
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// want to avoid, as the unsized field's alignment could be smaller.
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assert!(!t.is_simd());
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debug!("DST {} layout: {:?}", t, layout);
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let i = layout.fields.count() - 1;
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let sized_size = layout.fields.offset(i).bytes();
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let sized_align = layout.align.abi.bytes();
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debug!("DST {} statically sized prefix size: {} align: {}", t, sized_size, sized_align);
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let sized_size = bx.const_usize(sized_size);
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let sized_align = bx.const_usize(sized_align);
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// Recurse to get the size of the dynamically sized field (must be
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// the last field).
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let field_ty = layout.field(bx, i).ty;
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let (unsized_size, mut unsized_align) = size_and_align_of_dst(bx, field_ty, info);
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// FIXME (#26403, #27023): We should be adding padding
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// to `sized_size` (to accommodate the `unsized_align`
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// required of the unsized field that follows) before
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// summing it with `sized_size`. (Note that since #26403
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// is unfixed, we do not yet add the necessary padding
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// here. But this is where the add would go.)
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// Return the sum of sizes and max of aligns.
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let size = bx.add(sized_size, unsized_size);
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// Packed types ignore the alignment of their fields.
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if let ty::Adt(def, _) = t.kind() {
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if def.repr.packed() {
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unsized_align = sized_align;
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}
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}
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// Choose max of two known alignments (combined value must
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// be aligned according to more restrictive of the two).
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let align = match (
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bx.const_to_opt_u128(sized_align, false),
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bx.const_to_opt_u128(unsized_align, false),
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) {
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(Some(sized_align), Some(unsized_align)) => {
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// If both alignments are constant, (the sized_align should always be), then
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// pick the correct alignment statically.
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bx.const_usize(std::cmp::max(sized_align, unsized_align) as u64)
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}
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_ => {
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let cmp = bx.icmp(IntPredicate::IntUGT, sized_align, unsized_align);
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bx.select(cmp, sized_align, unsized_align)
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}
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};
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// Issue #27023: must add any necessary padding to `size`
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// (to make it a multiple of `align`) before returning it.
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//
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// Namely, the returned size should be, in C notation:
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//
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// `size + ((size & (align-1)) ? align : 0)`
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//
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// emulated via the semi-standard fast bit trick:
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//
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// `(size + (align-1)) & -align`
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let one = bx.const_usize(1);
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let addend = bx.sub(align, one);
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let add = bx.add(size, addend);
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let neg = bx.neg(align);
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let size = bx.and(add, neg);
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(size, align)
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}
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}
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}
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