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use super::operand::OperandValue;
use super::{FunctionCx, LocalRef};
use crate::common::IntPredicate;
use crate::glue;
use crate::traits::*;
use rustc_middle::mir;
use rustc_middle::mir::tcx::PlaceTy;
use rustc_middle::ty::layout::{HasTyCtxt, LayoutOf, TyAndLayout};
use rustc_middle::ty::{self, Ty};
use rustc_target::abi::{Abi, Align, FieldsShape, Int, Pointer, TagEncoding};
use rustc_target::abi::{VariantIdx, Variants};
#[derive(Copy, Clone, Debug)]
pub struct PlaceRef<'tcx, V> {
/// A pointer to the contents of the place.
pub llval: V,
/// This place's extra data if it is unsized, or `None` if null.
pub llextra: Option<V>,
/// The monomorphized type of this place, including variant information.
pub layout: TyAndLayout<'tcx>,
/// The alignment we know for this place.
pub align: Align,
}
impl<'a, 'tcx, V: CodegenObject> PlaceRef<'tcx, V> {
pub fn new_sized(llval: V, layout: TyAndLayout<'tcx>) -> PlaceRef<'tcx, V> {
assert!(layout.is_sized());
PlaceRef { llval, llextra: None, layout, align: layout.align.abi }
}
pub fn new_sized_aligned(
llval: V,
layout: TyAndLayout<'tcx>,
align: Align,
) -> PlaceRef<'tcx, V> {
assert!(layout.is_sized());
PlaceRef { llval, llextra: None, layout, align }
}
// FIXME(eddyb) pass something else for the name so no work is done
// unless LLVM IR names are turned on (e.g. for `--emit=llvm-ir`).
pub fn alloca<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
bx: &mut Bx,
layout: TyAndLayout<'tcx>,
) -> Self {
Self::alloca_aligned(bx, layout, layout.align.abi)
}
pub fn alloca_aligned<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
bx: &mut Bx,
layout: TyAndLayout<'tcx>,
align: Align,
) -> Self {
assert!(layout.is_sized(), "tried to statically allocate unsized place");
let tmp = bx.alloca(bx.cx().backend_type(layout), align);
Self::new_sized_aligned(tmp, layout, align)
}
/// Returns a place for an indirect reference to an unsized place.
// FIXME(eddyb) pass something else for the name so no work is done
// unless LLVM IR names are turned on (e.g. for `--emit=llvm-ir`).
pub fn alloca_unsized_indirect<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
bx: &mut Bx,
layout: TyAndLayout<'tcx>,
) -> Self {
assert!(layout.is_unsized(), "tried to allocate indirect place for sized values");
let ptr_ty = Ty::new_mut_ptr(bx.cx().tcx(), layout.ty);
let ptr_layout = bx.cx().layout_of(ptr_ty);
Self::alloca(bx, ptr_layout)
}
pub fn len<Cx: ConstMethods<'tcx, Value = V>>(&self, cx: &Cx) -> V {
if let FieldsShape::Array { count, .. } = self.layout.fields {
if self.layout.is_unsized() {
assert_eq!(count, 0);
self.llextra.unwrap()
} else {
cx.const_usize(count)
}
} else {
bug!("unexpected layout `{:#?}` in PlaceRef::len", self.layout)
}
}
}
impl<'a, 'tcx, V: CodegenObject> PlaceRef<'tcx, V> {
/// Access a field, at a point when the value's case is known.
pub fn project_field<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
self,
bx: &mut Bx,
ix: usize,
) -> Self {
let field = self.layout.field(bx.cx(), ix);
let offset = self.layout.fields.offset(ix);
let effective_field_align = self.align.restrict_for_offset(offset);
let mut simple = || {
let llval = match self.layout.abi {
_ if offset.bytes() == 0 => {
// Unions and newtypes only use an offset of 0.
// Also handles the first field of Scalar, ScalarPair, and Vector layouts.
self.llval
}
Abi::ScalarPair(a, b)
if offset == a.size(bx.cx()).align_to(b.align(bx.cx()).abi) =>
{
// Offset matches second field.
let ty = bx.backend_type(self.layout);
bx.struct_gep(ty, self.llval, 1)
}
Abi::Scalar(_) | Abi::ScalarPair(..) | Abi::Vector { .. } if field.is_zst() => {
// ZST fields (even some that require alignment) are not included in Scalar,
// ScalarPair, and Vector layouts, so manually offset the pointer.
bx.gep(bx.cx().type_i8(), self.llval, &[bx.const_usize(offset.bytes())])
}
Abi::Scalar(_) | Abi::ScalarPair(..) => {
// All fields of Scalar and ScalarPair layouts must have been handled by this point.
// Vector layouts have additional fields for each element of the vector, so don't panic in that case.
bug!(
"offset of non-ZST field `{:?}` does not match layout `{:#?}`",
field,
self.layout
);
}
_ => {
let ty = bx.backend_type(self.layout);
bx.struct_gep(ty, self.llval, bx.cx().backend_field_index(self.layout, ix))
}
};
PlaceRef {
llval,
llextra: if bx.cx().type_has_metadata(field.ty) { self.llextra } else { None },
layout: field,
align: effective_field_align,
}
};
// Simple cases, which don't need DST adjustment:
// * no metadata available - just log the case
// * known alignment - sized types, `[T]`, `str` or a foreign type
// * packed struct - there is no alignment padding
match field.ty.kind() {
_ if self.llextra.is_none() => {
debug!(
"unsized field `{}`, of `{:?}` has no metadata for adjustment",
ix, self.llval
);
return simple();
}
_ if field.is_sized() => return simple(),
ty::Slice(..) | ty::Str | ty::Foreign(..) => return simple(),
ty::Adt(def, _) => {
if def.repr().packed() {
// FIXME(eddyb) generalize the adjustment when we
// start supporting packing to larger alignments.
assert_eq!(self.layout.align.abi.bytes(), 1);
return simple();
}
}
_ => {}
}
// We need to get the pointer manually now.
// We do this by casting to a `*i8`, then offsetting it by the appropriate amount.
// We do this instead of, say, simply adjusting the pointer from the result of a GEP
// because the field may have an arbitrary alignment in the LLVM representation
// anyway.
//
// To demonstrate:
//
// struct Foo<T: ?Sized> {
// x: u16,
// y: T
// }
//
// The type `Foo<Foo<Trait>>` is represented in LLVM as `{ u16, { u16, u8 }}`, meaning that
// the `y` field has 16-bit alignment.
let meta = self.llextra;
let unaligned_offset = bx.cx().const_usize(offset.bytes());
// Get the alignment of the field
let (_, unsized_align) = glue::size_and_align_of_dst(bx, field.ty, meta);
// Bump the unaligned offset up to the appropriate alignment
let offset = round_up_const_value_to_alignment(bx, unaligned_offset, unsized_align);
debug!("struct_field_ptr: DST field offset: {:?}", offset);
// Adjust pointer.
let ptr = bx.gep(bx.cx().type_i8(), self.llval, &[offset]);
PlaceRef { llval: ptr, llextra: self.llextra, layout: field, align: effective_field_align }
}
/// Obtain the actual discriminant of a value.
#[instrument(level = "trace", skip(bx))]
pub fn codegen_get_discr<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
self,
bx: &mut Bx,
cast_to: Ty<'tcx>,
) -> V {
let dl = &bx.tcx().data_layout;
let cast_to_layout = bx.cx().layout_of(cast_to);
let cast_to = bx.cx().immediate_backend_type(cast_to_layout);
if self.layout.abi.is_uninhabited() {
return bx.cx().const_poison(cast_to);
}
let (tag_scalar, tag_encoding, tag_field) = match self.layout.variants {
Variants::Single { index } => {
let discr_val = self
.layout
.ty
.discriminant_for_variant(bx.cx().tcx(), index)
.map_or(index.as_u32() as u128, |discr| discr.val);
return bx.cx().const_uint_big(cast_to, discr_val);
}
Variants::Multiple { tag, ref tag_encoding, tag_field, .. } => {
(tag, tag_encoding, tag_field)
}
};
// Read the tag/niche-encoded discriminant from memory.
let tag = self.project_field(bx, tag_field);
let tag_op = bx.load_operand(tag);
let tag_imm = tag_op.immediate();
// Decode the discriminant (specifically if it's niche-encoded).
match *tag_encoding {
TagEncoding::Direct => {
let signed = match tag_scalar.primitive() {
// We use `i1` for bytes that are always `0` or `1`,
// e.g., `#[repr(i8)] enum E { A, B }`, but we can't
// let LLVM interpret the `i1` as signed, because
// then `i1 1` (i.e., `E::B`) is effectively `i8 -1`.
Int(_, signed) => !tag_scalar.is_bool() && signed,
_ => false,
};
bx.intcast(tag_imm, cast_to, signed)
}
TagEncoding::Niche { untagged_variant, ref niche_variants, niche_start } => {
// Cast to an integer so we don't have to treat a pointer as a
// special case.
let (tag, tag_llty) = match tag_scalar.primitive() {
// FIXME(erikdesjardins): handle non-default addrspace ptr sizes
Pointer(_) => {
let t = bx.type_from_integer(dl.ptr_sized_integer());
let tag = bx.ptrtoint(tag_imm, t);
(tag, t)
}
_ => (tag_imm, bx.cx().immediate_backend_type(tag_op.layout)),
};
let relative_max = niche_variants.end().as_u32() - niche_variants.start().as_u32();
// We have a subrange `niche_start..=niche_end` inside `range`.
// If the value of the tag is inside this subrange, it's a
// "niche value", an increment of the discriminant. Otherwise it
// indicates the untagged variant.
// A general algorithm to extract the discriminant from the tag
// is:
// relative_tag = tag - niche_start
// is_niche = relative_tag <= (ule) relative_max
// discr = if is_niche {
// cast(relative_tag) + niche_variants.start()
// } else {
// untagged_variant
// }
// However, we will likely be able to emit simpler code.
let (is_niche, tagged_discr, delta) = if relative_max == 0 {
// Best case scenario: only one tagged variant. This will
// likely become just a comparison and a jump.
// The algorithm is:
// is_niche = tag == niche_start
// discr = if is_niche {
// niche_start
// } else {
// untagged_variant
// }
let niche_start = bx.cx().const_uint_big(tag_llty, niche_start);
let is_niche = bx.icmp(IntPredicate::IntEQ, tag, niche_start);
let tagged_discr =
bx.cx().const_uint(cast_to, niche_variants.start().as_u32() as u64);
(is_niche, tagged_discr, 0)
} else {
// The special cases don't apply, so we'll have to go with
// the general algorithm.
let relative_discr = bx.sub(tag, bx.cx().const_uint_big(tag_llty, niche_start));
let cast_tag = bx.intcast(relative_discr, cast_to, false);
let is_niche = bx.icmp(
IntPredicate::IntULE,
relative_discr,
bx.cx().const_uint(tag_llty, relative_max as u64),
);
(is_niche, cast_tag, niche_variants.start().as_u32() as u128)
};
let tagged_discr = if delta == 0 {
tagged_discr
} else {
bx.add(tagged_discr, bx.cx().const_uint_big(cast_to, delta))
};
let discr = bx.select(
is_niche,
tagged_discr,
bx.cx().const_uint(cast_to, untagged_variant.as_u32() as u64),
);
// In principle we could insert assumes on the possible range of `discr`, but
// currently in LLVM this seems to be a pessimization.
discr
}
}
}
/// Sets the discriminant for a new value of the given case of the given
/// representation.
pub fn codegen_set_discr<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
&self,
bx: &mut Bx,
variant_index: VariantIdx,
) {
if self.layout.for_variant(bx.cx(), variant_index).abi.is_uninhabited() {
// We play it safe by using a well-defined `abort`, but we could go for immediate UB
// if that turns out to be helpful.
bx.abort();
return;
}
match self.layout.variants {
Variants::Single { index } => {
assert_eq!(index, variant_index);
}
Variants::Multiple { tag_encoding: TagEncoding::Direct, tag_field, .. } => {
let ptr = self.project_field(bx, tag_field);
let to =
self.layout.ty.discriminant_for_variant(bx.tcx(), variant_index).unwrap().val;
bx.store(
bx.cx().const_uint_big(bx.cx().backend_type(ptr.layout), to),
ptr.llval,
ptr.align,
);
}
Variants::Multiple {
tag_encoding:
TagEncoding::Niche { untagged_variant, ref niche_variants, niche_start },
tag_field,
..
} => {
if variant_index != untagged_variant {
let niche = self.project_field(bx, tag_field);
let niche_llty = bx.cx().immediate_backend_type(niche.layout);
let niche_value = variant_index.as_u32() - niche_variants.start().as_u32();
let niche_value = (niche_value as u128).wrapping_add(niche_start);
// FIXME(eddyb): check the actual primitive type here.
let niche_llval = if niche_value == 0 {
// HACK(eddyb): using `c_null` as it works on all types.
bx.cx().const_null(niche_llty)
} else {
bx.cx().const_uint_big(niche_llty, niche_value)
};
OperandValue::Immediate(niche_llval).store(bx, niche);
}
}
}
}
pub fn project_index<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
&self,
bx: &mut Bx,
llindex: V,
) -> Self {
// Statically compute the offset if we can, otherwise just use the element size,
// as this will yield the lowest alignment.
let layout = self.layout.field(bx, 0);
let offset = if let Some(llindex) = bx.const_to_opt_uint(llindex) {
layout.size.checked_mul(llindex, bx).unwrap_or(layout.size)
} else {
layout.size
};
PlaceRef {
llval: bx.inbounds_gep(
bx.cx().backend_type(self.layout),
self.llval,
&[bx.cx().const_usize(0), llindex],
),
llextra: None,
layout,
align: self.align.restrict_for_offset(offset),
}
}
pub fn project_downcast<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
&self,
bx: &mut Bx,
variant_index: VariantIdx,
) -> Self {
let mut downcast = *self;
downcast.layout = self.layout.for_variant(bx.cx(), variant_index);
downcast
}
pub fn project_type<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
&self,
bx: &mut Bx,
ty: Ty<'tcx>,
) -> Self {
let mut downcast = *self;
downcast.layout = bx.cx().layout_of(ty);
downcast
}
pub fn storage_live<Bx: BuilderMethods<'a, 'tcx, Value = V>>(&self, bx: &mut Bx) {
bx.lifetime_start(self.llval, self.layout.size);
}
pub fn storage_dead<Bx: BuilderMethods<'a, 'tcx, Value = V>>(&self, bx: &mut Bx) {
bx.lifetime_end(self.llval, self.layout.size);
}
}
impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
#[instrument(level = "trace", skip(self, bx))]
pub fn codegen_place(
&mut self,
bx: &mut Bx,
place_ref: mir::PlaceRef<'tcx>,
) -> PlaceRef<'tcx, Bx::Value> {
let cx = self.cx;
let tcx = self.cx.tcx();
let mut base = 0;
let mut cg_base = match self.locals[place_ref.local] {
LocalRef::Place(place) => place,
LocalRef::UnsizedPlace(place) => bx.load_operand(place).deref(cx),
LocalRef::Operand(..) => {
if place_ref.is_indirect_first_projection() {
base = 1;
let cg_base = self.codegen_consume(
bx,
mir::PlaceRef { projection: &place_ref.projection[..0], ..place_ref },
);
cg_base.deref(bx.cx())
} else {
bug!("using operand local {:?} as place", place_ref);
}
}
LocalRef::PendingOperand => {
bug!("using still-pending operand local {:?} as place", place_ref);
}
};
for elem in place_ref.projection[base..].iter() {
cg_base = match *elem {
mir::ProjectionElem::Deref => bx.load_operand(cg_base).deref(bx.cx()),
mir::ProjectionElem::Field(ref field, _) => {
cg_base.project_field(bx, field.index())
}
mir::ProjectionElem::OpaqueCast(ty) => {
bug!("encountered OpaqueCast({ty}) in codegen")
}
mir::ProjectionElem::Subtype(ty) => cg_base.project_type(bx, self.monomorphize(ty)),
mir::ProjectionElem::Index(index) => {
let index = &mir::Operand::Copy(mir::Place::from(index));
let index = self.codegen_operand(bx, index);
let llindex = index.immediate();
cg_base.project_index(bx, llindex)
}
mir::ProjectionElem::ConstantIndex { offset, from_end: false, min_length: _ } => {
let lloffset = bx.cx().const_usize(offset as u64);
cg_base.project_index(bx, lloffset)
}
mir::ProjectionElem::ConstantIndex { offset, from_end: true, min_length: _ } => {
let lloffset = bx.cx().const_usize(offset as u64);
let lllen = cg_base.len(bx.cx());
let llindex = bx.sub(lllen, lloffset);
cg_base.project_index(bx, llindex)
}
mir::ProjectionElem::Subslice { from, to, from_end } => {
let mut subslice = cg_base.project_index(bx, bx.cx().const_usize(from as u64));
let projected_ty =
PlaceTy::from_ty(cg_base.layout.ty).projection_ty(tcx, *elem).ty;
subslice.layout = bx.cx().layout_of(self.monomorphize(projected_ty));
if subslice.layout.is_unsized() {
assert!(from_end, "slice subslices should be `from_end`");
subslice.llextra = Some(bx.sub(
cg_base.llextra.unwrap(),
bx.cx().const_usize((from as u64) + (to as u64)),
));
}
subslice
}
mir::ProjectionElem::Downcast(_, v) => cg_base.project_downcast(bx, v),
};
}
debug!("codegen_place(place={:?}) => {:?}", place_ref, cg_base);
cg_base
}
pub fn monomorphized_place_ty(&self, place_ref: mir::PlaceRef<'tcx>) -> Ty<'tcx> {
let tcx = self.cx.tcx();
let place_ty = place_ref.ty(self.mir, tcx);
self.monomorphize(place_ty.ty)
}
}
fn round_up_const_value_to_alignment<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
bx: &mut Bx,
value: Bx::Value,
align: Bx::Value,
) -> Bx::Value {
// In pseudo code:
//
// if value & (align - 1) == 0 {
// value
// } else {
// (value & !(align - 1)) + align
// }
//
// Usually this is written without branches as
//
// (value + align - 1) & !(align - 1)
//
// But this formula cannot take advantage of constant `value`. E.g. if `value` is known
// at compile time to be `1`, this expression should be optimized to `align`. However,
// optimization only holds if `align` is a power of two. Since the optimizer doesn't know
// that `align` is a power of two, it cannot perform this optimization.
//
// Instead we use
//
// value + (-value & (align - 1))
//
// Since `align` is used only once, the expression can be optimized. For `value = 0`
// its optimized to `0` even in debug mode.
//
// NB: The previous version of this code used
//
// (value + align - 1) & -align
//
// Even though `-align == !(align - 1)`, LLVM failed to optimize this even for
// `value = 0`. Bug report: https://bugs.llvm.org/show_bug.cgi?id=48559
let one = bx.const_usize(1);
let align_minus_1 = bx.sub(align, one);
let neg_value = bx.neg(value);
let offset = bx.and(neg_value, align_minus_1);
bx.add(value, offset)
}