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|
//!
//
// Code relating to drop glue.
use crate::common::IntPredicate;
use crate::meth;
use crate::traits::*;
use rustc_middle::ty::{self, Ty};
use rustc_target::abi::WrappingRange;
pub fn size_and_align_of_dst<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
bx: &mut Bx,
t: Ty<'tcx>,
info: Option<Bx::Value>,
) -> (Bx::Value, Bx::Value) {
let layout = bx.layout_of(t);
debug!("size_and_align_of_dst(ty={}, info={:?}): layout: {:?}", t, info, layout);
if layout.is_sized() {
let size = bx.const_usize(layout.size.bytes());
let align = bx.const_usize(layout.align.abi.bytes());
return (size, align);
}
match t.kind() {
ty::Dynamic(..) => {
// Load size/align from vtable.
let vtable = info.unwrap();
let size = meth::VirtualIndex::from_index(ty::COMMON_VTABLE_ENTRIES_SIZE)
.get_usize(bx, vtable);
let align = meth::VirtualIndex::from_index(ty::COMMON_VTABLE_ENTRIES_ALIGN)
.get_usize(bx, vtable);
// Size is always <= isize::MAX.
let size_bound = bx.data_layout().ptr_sized_integer().signed_max() as u128;
bx.range_metadata(size, WrappingRange { start: 0, end: size_bound });
// Alignment is always nonzero.
bx.range_metadata(align, WrappingRange { start: 1, end: !0 });
(size, align)
}
ty::Slice(_) | ty::Str => {
let unit = layout.field(bx, 0);
// The info in this case is the length of the str, so the size is that
// times the unit size.
(
// All slice sizes must fit into `isize`, so this multiplication cannot (signed) wrap.
// NOTE: ideally, we want the effects of both `unchecked_smul` and `unchecked_umul`
// (resulting in `mul nsw nuw` in LLVM IR), since we know that the multiplication
// cannot signed wrap, and that both operands are non-negative. But at the time of writing,
// the `LLVM-C` binding can't do this, and it doesn't seem to enable any further optimizations.
bx.unchecked_smul(info.unwrap(), bx.const_usize(unit.size.bytes())),
bx.const_usize(unit.align.abi.bytes()),
)
}
_ => {
// First get the size of all statically known fields.
// Don't use size_of because it also rounds up to alignment, which we
// want to avoid, as the unsized field's alignment could be smaller.
assert!(!t.is_simd());
debug!("DST {} layout: {:?}", t, layout);
let i = layout.fields.count() - 1;
let sized_size = layout.fields.offset(i).bytes();
let sized_align = layout.align.abi.bytes();
debug!("DST {} statically sized prefix size: {} align: {}", t, sized_size, sized_align);
let sized_size = bx.const_usize(sized_size);
let sized_align = bx.const_usize(sized_align);
// Recurse to get the size of the dynamically sized field (must be
// the last field).
let field_ty = layout.field(bx, i).ty;
let (unsized_size, mut unsized_align) = size_and_align_of_dst(bx, field_ty, info);
// FIXME (#26403, #27023): We should be adding padding
// to `sized_size` (to accommodate the `unsized_align`
// required of the unsized field that follows) before
// summing it with `sized_size`. (Note that since #26403
// is unfixed, we do not yet add the necessary padding
// here. But this is where the add would go.)
// Return the sum of sizes and max of aligns.
let size = bx.add(sized_size, unsized_size);
// Packed types ignore the alignment of their fields.
if let ty::Adt(def, _) = t.kind() {
if def.repr().packed() {
unsized_align = sized_align;
}
}
// Choose max of two known alignments (combined value must
// be aligned according to more restrictive of the two).
let align = match (
bx.const_to_opt_u128(sized_align, false),
bx.const_to_opt_u128(unsized_align, false),
) {
(Some(sized_align), Some(unsized_align)) => {
// If both alignments are constant, (the sized_align should always be), then
// pick the correct alignment statically.
bx.const_usize(std::cmp::max(sized_align, unsized_align) as u64)
}
_ => {
let cmp = bx.icmp(IntPredicate::IntUGT, sized_align, unsized_align);
bx.select(cmp, sized_align, unsized_align)
}
};
// Issue #27023: must add any necessary padding to `size`
// (to make it a multiple of `align`) before returning it.
//
// Namely, the returned size should be, in C notation:
//
// `size + ((size & (align-1)) ? align : 0)`
//
// emulated via the semi-standard fast bit trick:
//
// `(size + (align-1)) & -align`
let one = bx.const_usize(1);
let addend = bx.sub(align, one);
let add = bx.add(size, addend);
let neg = bx.neg(align);
let size = bx.and(add, neg);
(size, align)
}
}
}
|
