1 use super::operand::OperandValue;
2 use super::{FunctionCx, LocalRef};
4 use crate::common::IntPredicate;
9 use rustc_middle::mir::tcx::PlaceTy;
10 use rustc_middle::ty::layout::{HasTyCtxt, LayoutOf, TyAndLayout};
11 use rustc_middle::ty::{self, Ty};
12 use rustc_target::abi::{Abi, Align, FieldsShape, Int, TagEncoding};
13 use rustc_target::abi::{VariantIdx, Variants};
15 #[derive(Copy, Clone, Debug)]
16 pub struct PlaceRef<'tcx, V> {
17 /// A pointer to the contents of the place.
20 /// This place's extra data if it is unsized, or `None` if null.
21 pub llextra: Option<V>,
23 /// The monomorphized type of this place, including variant information.
24 pub layout: TyAndLayout<'tcx>,
26 /// The alignment we know for this place.
30 impl<'a, 'tcx, V: CodegenObject> PlaceRef<'tcx, V> {
31 pub fn new_sized(llval: V, layout: TyAndLayout<'tcx>) -> PlaceRef<'tcx, V> {
32 assert!(layout.is_sized());
33 PlaceRef { llval, llextra: None, layout, align: layout.align.abi }
36 pub fn new_sized_aligned(
38 layout: TyAndLayout<'tcx>,
40 ) -> PlaceRef<'tcx, V> {
41 assert!(layout.is_sized());
42 PlaceRef { llval, llextra: None, layout, align }
45 // FIXME(eddyb) pass something else for the name so no work is done
46 // unless LLVM IR names are turned on (e.g. for `--emit=llvm-ir`).
47 pub fn alloca<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
49 layout: TyAndLayout<'tcx>,
51 assert!(layout.is_sized(), "tried to statically allocate unsized place");
52 let tmp = bx.alloca(bx.cx().backend_type(layout), layout.align.abi);
53 Self::new_sized(tmp, layout)
56 /// Returns a place for an indirect reference to an unsized place.
57 // FIXME(eddyb) pass something else for the name so no work is done
58 // unless LLVM IR names are turned on (e.g. for `--emit=llvm-ir`).
59 pub fn alloca_unsized_indirect<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
61 layout: TyAndLayout<'tcx>,
63 assert!(layout.is_unsized(), "tried to allocate indirect place for sized values");
64 let ptr_ty = bx.cx().tcx().mk_mut_ptr(layout.ty);
65 let ptr_layout = bx.cx().layout_of(ptr_ty);
66 Self::alloca(bx, ptr_layout)
69 pub fn len<Cx: ConstMethods<'tcx, Value = V>>(&self, cx: &Cx) -> V {
70 if let FieldsShape::Array { count, .. } = self.layout.fields {
71 if self.layout.is_unsized() {
78 bug!("unexpected layout `{:#?}` in PlaceRef::len", self.layout)
83 impl<'a, 'tcx, V: CodegenObject> PlaceRef<'tcx, V> {
84 /// Access a field, at a point when the value's case is known.
85 pub fn project_field<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
90 let field = self.layout.field(bx.cx(), ix);
91 let offset = self.layout.fields.offset(ix);
92 let effective_field_align = self.align.restrict_for_offset(offset);
95 let llval = match self.layout.abi {
96 _ if offset.bytes() == 0 => {
97 // Unions and newtypes only use an offset of 0.
98 // Also handles the first field of Scalar, ScalarPair, and Vector layouts.
101 Abi::ScalarPair(a, b)
102 if offset == a.size(bx.cx()).align_to(b.align(bx.cx()).abi) =>
104 // Offset matches second field.
105 let ty = bx.backend_type(self.layout);
106 bx.struct_gep(ty, self.llval, 1)
108 Abi::Scalar(_) | Abi::ScalarPair(..) | Abi::Vector { .. } if field.is_zst() => {
109 // ZST fields are not included in Scalar, ScalarPair, and Vector layouts, so manually offset the pointer.
110 let byte_ptr = bx.pointercast(self.llval, bx.cx().type_i8p());
111 bx.gep(bx.cx().type_i8(), byte_ptr, &[bx.const_usize(offset.bytes())])
113 Abi::Scalar(_) | Abi::ScalarPair(..) => {
114 // All fields of Scalar and ScalarPair layouts must have been handled by this point.
115 // Vector layouts have additional fields for each element of the vector, so don't panic in that case.
117 "offset of non-ZST field `{:?}` does not match layout `{:#?}`",
123 let ty = bx.backend_type(self.layout);
124 bx.struct_gep(ty, self.llval, bx.cx().backend_field_index(self.layout, ix))
128 // HACK(eddyb): have to bitcast pointers until LLVM removes pointee types.
129 llval: bx.pointercast(llval, bx.cx().type_ptr_to(bx.cx().backend_type(field))),
130 llextra: if bx.cx().type_has_metadata(field.ty) { self.llextra } else { None },
132 align: effective_field_align,
136 // Simple cases, which don't need DST adjustment:
137 // * no metadata available - just log the case
138 // * known alignment - sized types, `[T]`, `str` or a foreign type
139 // * packed struct - there is no alignment padding
140 match field.ty.kind() {
141 _ if self.llextra.is_none() => {
143 "unsized field `{}`, of `{:?}` has no metadata for adjustment",
148 _ if field.is_sized() => return simple(),
149 ty::Slice(..) | ty::Str | ty::Foreign(..) => return simple(),
151 if def.repr().packed() {
152 // FIXME(eddyb) generalize the adjustment when we
153 // start supporting packing to larger alignments.
154 assert_eq!(self.layout.align.abi.bytes(), 1);
161 // We need to get the pointer manually now.
162 // We do this by casting to a `*i8`, then offsetting it by the appropriate amount.
163 // We do this instead of, say, simply adjusting the pointer from the result of a GEP
164 // because the field may have an arbitrary alignment in the LLVM representation
169 // struct Foo<T: ?Sized> {
174 // The type `Foo<Foo<Trait>>` is represented in LLVM as `{ u16, { u16, u8 }}`, meaning that
175 // the `y` field has 16-bit alignment.
177 let meta = self.llextra;
179 let unaligned_offset = bx.cx().const_usize(offset.bytes());
181 // Get the alignment of the field
182 let (_, unsized_align) = glue::size_and_align_of_dst(bx, field.ty, meta);
184 // Bump the unaligned offset up to the appropriate alignment
185 let offset = round_up_const_value_to_alignment(bx, unaligned_offset, unsized_align);
187 debug!("struct_field_ptr: DST field offset: {:?}", offset);
189 // Cast and adjust pointer.
190 let byte_ptr = bx.pointercast(self.llval, bx.cx().type_i8p());
191 let byte_ptr = bx.gep(bx.cx().type_i8(), byte_ptr, &[offset]);
193 // Finally, cast back to the type expected.
194 let ll_fty = bx.cx().backend_type(field);
195 debug!("struct_field_ptr: Field type is {:?}", ll_fty);
198 llval: bx.pointercast(byte_ptr, bx.cx().type_ptr_to(ll_fty)),
199 llextra: self.llextra,
201 align: effective_field_align,
205 /// Obtain the actual discriminant of a value.
206 #[instrument(level = "trace", skip(bx))]
207 pub fn codegen_get_discr<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
212 let cast_to_layout = bx.cx().layout_of(cast_to);
213 let cast_to_size = cast_to_layout.layout.size();
214 let cast_to = bx.cx().immediate_backend_type(cast_to_layout);
215 if self.layout.abi.is_uninhabited() {
216 return bx.cx().const_undef(cast_to);
218 let (tag_scalar, tag_encoding, tag_field) = match self.layout.variants {
219 Variants::Single { index } => {
223 .discriminant_for_variant(bx.cx().tcx(), index)
224 .map_or(index.as_u32() as u128, |discr| discr.val);
225 return bx.cx().const_uint_big(cast_to, discr_val);
227 Variants::Multiple { tag, ref tag_encoding, tag_field, .. } => {
228 (tag, tag_encoding, tag_field)
232 // Read the tag/niche-encoded discriminant from memory.
233 let tag = self.project_field(bx, tag_field);
234 let tag_op = bx.load_operand(tag);
235 let tag_imm = tag_op.immediate();
237 // Decode the discriminant (specifically if it's niche-encoded).
238 match *tag_encoding {
239 TagEncoding::Direct => {
240 let signed = match tag_scalar.primitive() {
241 // We use `i1` for bytes that are always `0` or `1`,
242 // e.g., `#[repr(i8)] enum E { A, B }`, but we can't
243 // let LLVM interpret the `i1` as signed, because
244 // then `i1 1` (i.e., `E::B`) is effectively `i8 -1`.
245 Int(_, signed) => !tag_scalar.is_bool() && signed,
248 bx.intcast(tag_imm, cast_to, signed)
250 TagEncoding::Niche { untagged_variant, ref niche_variants, niche_start } => {
251 // Cast to an integer so we don't have to treat a pointer as a
253 let (tag, tag_llty) = if tag_scalar.primitive().is_ptr() {
254 let t = bx.type_isize();
255 let tag = bx.ptrtoint(tag_imm, t);
258 (tag_imm, bx.cx().immediate_backend_type(tag_op.layout))
261 let tag_size = tag_scalar.size(bx.cx());
262 let max_unsigned = tag_size.unsigned_int_max();
263 let max_signed = tag_size.signed_int_max() as u128;
264 let min_signed = max_signed + 1;
265 let relative_max = niche_variants.end().as_u32() - niche_variants.start().as_u32();
266 let niche_end = niche_start.wrapping_add(relative_max as u128) & max_unsigned;
267 let range = tag_scalar.valid_range(bx.cx());
269 let sle = |lhs: u128, rhs: u128| -> bool {
270 // Signed and unsigned comparisons give the same results,
271 // except that in signed comparisons an integer with the
272 // sign bit set is less than one with the sign bit clear.
273 // Toggle the sign bit to do a signed comparison.
274 (lhs ^ min_signed) <= (rhs ^ min_signed)
277 // We have a subrange `niche_start..=niche_end` inside `range`.
278 // If the value of the tag is inside this subrange, it's a
279 // "niche value", an increment of the discriminant. Otherwise it
280 // indicates the untagged variant.
281 // A general algorithm to extract the discriminant from the tag
283 // relative_tag = tag - niche_start
284 // is_niche = relative_tag <= (ule) relative_max
285 // discr = if is_niche {
286 // cast(relative_tag) + niche_variants.start()
290 // However, we will likely be able to emit simpler code.
292 // Find the least and greatest values in `range`, considered
293 // both as signed and unsigned.
294 let (low_unsigned, high_unsigned) = if range.start <= range.end {
295 (range.start, range.end)
299 let (low_signed, high_signed) = if sle(range.start, range.end) {
300 (range.start, range.end)
302 (min_signed, max_signed)
305 let niches_ule = niche_start <= niche_end;
306 let niches_sle = sle(niche_start, niche_end);
307 let cast_smaller = cast_to_size <= tag_size;
309 // In the algorithm above, we can change
310 // cast(relative_tag) + niche_variants.start()
312 // cast(tag + (niche_variants.start() - niche_start))
313 // if either the casted type is no larger than the original
314 // type, or if the niche values are contiguous (in either the
315 // signed or unsigned sense).
316 let can_incr = cast_smaller || niches_ule || niches_sle;
318 let data_for_boundary_niche = || -> Option<(IntPredicate, u128)> {
321 } else if niche_start == low_unsigned {
322 Some((IntPredicate::IntULE, niche_end))
323 } else if niche_end == high_unsigned {
324 Some((IntPredicate::IntUGE, niche_start))
325 } else if niche_start == low_signed {
326 Some((IntPredicate::IntSLE, niche_end))
327 } else if niche_end == high_signed {
328 Some((IntPredicate::IntSGE, niche_start))
334 let (is_niche, tagged_discr, delta) = if relative_max == 0 {
335 // Best case scenario: only one tagged variant. This will
336 // likely become just a comparison and a jump.
338 // is_niche = tag == niche_start
339 // discr = if is_niche {
344 let niche_start = bx.cx().const_uint_big(tag_llty, niche_start);
345 let is_niche = bx.icmp(IntPredicate::IntEQ, tag, niche_start);
347 bx.cx().const_uint(cast_to, niche_variants.start().as_u32() as u64);
348 (is_niche, tagged_discr, 0)
349 } else if let Some((predicate, constant)) = data_for_boundary_niche() {
350 // The niche values are either the lowest or the highest in
351 // `range`. We can avoid the first subtraction in the
353 // The algorithm is now this:
354 // is_niche = tag <= niche_end
355 // discr = if is_niche {
356 // cast(tag + (niche_variants.start() - niche_start))
360 // (the first line may instead be tag >= niche_start,
361 // and may be a signed or unsigned comparison)
362 // The arithmetic must be done before the cast, so we can
363 // have the correct wrapping behavior. See issue #104519 for
364 // the consequences of getting this wrong.
366 bx.icmp(predicate, tag, bx.cx().const_uint_big(tag_llty, constant));
367 let delta = (niche_variants.start().as_u32() as u128).wrapping_sub(niche_start);
368 let incr_tag = if delta == 0 {
371 bx.add(tag, bx.cx().const_uint_big(tag_llty, delta))
374 let cast_tag = if cast_smaller {
375 bx.intcast(incr_tag, cast_to, false)
376 } else if niches_ule {
377 bx.zext(incr_tag, cast_to)
379 bx.sext(incr_tag, cast_to)
382 (is_niche, cast_tag, 0)
384 // The special cases don't apply, so we'll have to go with
385 // the general algorithm.
386 let relative_discr = bx.sub(tag, bx.cx().const_uint_big(tag_llty, niche_start));
387 let cast_tag = bx.intcast(relative_discr, cast_to, false);
388 let is_niche = bx.icmp(
389 IntPredicate::IntULE,
391 bx.cx().const_uint(tag_llty, relative_max as u64),
393 (is_niche, cast_tag, niche_variants.start().as_u32() as u128)
396 let tagged_discr = if delta == 0 {
399 bx.add(tagged_discr, bx.cx().const_uint_big(cast_to, delta))
402 let discr = bx.select(
405 bx.cx().const_uint(cast_to, untagged_variant.as_u32() as u64),
408 // In principle we could insert assumes on the possible range of `discr`, but
409 // currently in LLVM this seems to be a pessimization.
416 /// Sets the discriminant for a new value of the given case of the given
418 pub fn codegen_set_discr<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
421 variant_index: VariantIdx,
423 if self.layout.for_variant(bx.cx(), variant_index).abi.is_uninhabited() {
424 // We play it safe by using a well-defined `abort`, but we could go for immediate UB
425 // if that turns out to be helpful.
429 match self.layout.variants {
430 Variants::Single { index } => {
431 assert_eq!(index, variant_index);
433 Variants::Multiple { tag_encoding: TagEncoding::Direct, tag_field, .. } => {
434 let ptr = self.project_field(bx, tag_field);
436 self.layout.ty.discriminant_for_variant(bx.tcx(), variant_index).unwrap().val;
438 bx.cx().const_uint_big(bx.cx().backend_type(ptr.layout), to),
445 TagEncoding::Niche { untagged_variant, ref niche_variants, niche_start },
449 if variant_index != untagged_variant {
450 let niche = self.project_field(bx, tag_field);
451 let niche_llty = bx.cx().immediate_backend_type(niche.layout);
452 let niche_value = variant_index.as_u32() - niche_variants.start().as_u32();
453 let niche_value = (niche_value as u128).wrapping_add(niche_start);
454 // FIXME(eddyb): check the actual primitive type here.
455 let niche_llval = if niche_value == 0 {
456 // HACK(eddyb): using `c_null` as it works on all types.
457 bx.cx().const_null(niche_llty)
459 bx.cx().const_uint_big(niche_llty, niche_value)
461 OperandValue::Immediate(niche_llval).store(bx, niche);
467 pub fn project_index<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
472 // Statically compute the offset if we can, otherwise just use the element size,
473 // as this will yield the lowest alignment.
474 let layout = self.layout.field(bx, 0);
475 let offset = if let Some(llindex) = bx.const_to_opt_uint(llindex) {
476 layout.size.checked_mul(llindex, bx).unwrap_or(layout.size)
482 llval: bx.inbounds_gep(
483 bx.cx().backend_type(self.layout),
485 &[bx.cx().const_usize(0), llindex],
489 align: self.align.restrict_for_offset(offset),
493 pub fn project_downcast<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
496 variant_index: VariantIdx,
498 let mut downcast = *self;
499 downcast.layout = self.layout.for_variant(bx.cx(), variant_index);
501 // Cast to the appropriate variant struct type.
502 let variant_ty = bx.cx().backend_type(downcast.layout);
503 downcast.llval = bx.pointercast(downcast.llval, bx.cx().type_ptr_to(variant_ty));
508 pub fn project_type<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
513 let mut downcast = *self;
514 downcast.layout = bx.cx().layout_of(ty);
516 // Cast to the appropriate type.
517 let variant_ty = bx.cx().backend_type(downcast.layout);
518 downcast.llval = bx.pointercast(downcast.llval, bx.cx().type_ptr_to(variant_ty));
523 pub fn storage_live<Bx: BuilderMethods<'a, 'tcx, Value = V>>(&self, bx: &mut Bx) {
524 bx.lifetime_start(self.llval, self.layout.size);
527 pub fn storage_dead<Bx: BuilderMethods<'a, 'tcx, Value = V>>(&self, bx: &mut Bx) {
528 bx.lifetime_end(self.llval, self.layout.size);
532 impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
533 #[instrument(level = "trace", skip(self, bx))]
534 pub fn codegen_place(
537 place_ref: mir::PlaceRef<'tcx>,
538 ) -> PlaceRef<'tcx, Bx::Value> {
540 let tcx = self.cx.tcx();
543 let mut cg_base = match self.locals[place_ref.local] {
544 LocalRef::Place(place) => place,
545 LocalRef::UnsizedPlace(place) => bx.load_operand(place).deref(cx),
546 LocalRef::Operand(..) => {
547 if place_ref.has_deref() {
549 let cg_base = self.codegen_consume(
551 mir::PlaceRef { projection: &place_ref.projection[..0], ..place_ref },
553 cg_base.deref(bx.cx())
555 bug!("using operand local {:?} as place", place_ref);
559 for elem in place_ref.projection[base..].iter() {
560 cg_base = match *elem {
561 mir::ProjectionElem::Deref => bx.load_operand(cg_base).deref(bx.cx()),
562 mir::ProjectionElem::Field(ref field, _) => {
563 cg_base.project_field(bx, field.index())
565 mir::ProjectionElem::OpaqueCast(ty) => cg_base.project_type(bx, ty),
566 mir::ProjectionElem::Index(index) => {
567 let index = &mir::Operand::Copy(mir::Place::from(index));
568 let index = self.codegen_operand(bx, index);
569 let llindex = index.immediate();
570 cg_base.project_index(bx, llindex)
572 mir::ProjectionElem::ConstantIndex { offset, from_end: false, min_length: _ } => {
573 let lloffset = bx.cx().const_usize(offset as u64);
574 cg_base.project_index(bx, lloffset)
576 mir::ProjectionElem::ConstantIndex { offset, from_end: true, min_length: _ } => {
577 let lloffset = bx.cx().const_usize(offset as u64);
578 let lllen = cg_base.len(bx.cx());
579 let llindex = bx.sub(lllen, lloffset);
580 cg_base.project_index(bx, llindex)
582 mir::ProjectionElem::Subslice { from, to, from_end } => {
583 let mut subslice = cg_base.project_index(bx, bx.cx().const_usize(from as u64));
585 PlaceTy::from_ty(cg_base.layout.ty).projection_ty(tcx, *elem).ty;
586 subslice.layout = bx.cx().layout_of(self.monomorphize(projected_ty));
588 if subslice.layout.is_unsized() {
589 assert!(from_end, "slice subslices should be `from_end`");
590 subslice.llextra = Some(bx.sub(
591 cg_base.llextra.unwrap(),
592 bx.cx().const_usize((from as u64) + (to as u64)),
596 // Cast the place pointer type to the new
597 // array or slice type (`*[%_; new_len]`).
598 subslice.llval = bx.pointercast(
600 bx.cx().type_ptr_to(bx.cx().backend_type(subslice.layout)),
605 mir::ProjectionElem::Downcast(_, v) => cg_base.project_downcast(bx, v),
608 debug!("codegen_place(place={:?}) => {:?}", place_ref, cg_base);
612 pub fn monomorphized_place_ty(&self, place_ref: mir::PlaceRef<'tcx>) -> Ty<'tcx> {
613 let tcx = self.cx.tcx();
614 let place_ty = place_ref.ty(self.mir, tcx);
615 self.monomorphize(place_ty.ty)
619 fn round_up_const_value_to_alignment<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
626 // if value & (align - 1) == 0 {
629 // (value & !(align - 1)) + align
632 // Usually this is written without branches as
634 // (value + align - 1) & !(align - 1)
636 // But this formula cannot take advantage of constant `value`. E.g. if `value` is known
637 // at compile time to be `1`, this expression should be optimized to `align`. However,
638 // optimization only holds if `align` is a power of two. Since the optimizer doesn't know
639 // that `align` is a power of two, it cannot perform this optimization.
643 // value + (-value & (align - 1))
645 // Since `align` is used only once, the expression can be optimized. For `value = 0`
646 // its optimized to `0` even in debug mode.
648 // NB: The previous version of this code used
650 // (value + align - 1) & -align
652 // Even though `-align == !(align - 1)`, LLVM failed to optimize this even for
653 // `value = 0`. Bug report: https://bugs.llvm.org/show_bug.cgi?id=48559
654 let one = bx.const_usize(1);
655 let align_minus_1 = bx.sub(align, one);
656 let neg_value = bx.neg(value);
657 let offset = bx.and(neg_value, align_minus_1);
658 bx.add(value, offset)