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_unsized());
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_unsized());
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_unsized(), "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_unsized() => 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 = bx.cx().immediate_backend_type(bx.cx().layout_of(cast_to));
213 if self.layout.abi.is_uninhabited() {
214 return bx.cx().const_undef(cast_to);
216 let (tag_scalar, tag_encoding, tag_field) = match self.layout.variants {
217 Variants::Single { index } => {
221 .discriminant_for_variant(bx.cx().tcx(), index)
222 .map_or(index.as_u32() as u128, |discr| discr.val);
223 return bx.cx().const_uint_big(cast_to, discr_val);
225 Variants::Multiple { tag, ref tag_encoding, tag_field, .. } => {
226 (tag, tag_encoding, tag_field)
230 // Read the tag/niche-encoded discriminant from memory.
231 let tag = self.project_field(bx, tag_field);
232 let tag = bx.load_operand(tag);
234 // Decode the discriminant (specifically if it's niche-encoded).
235 match *tag_encoding {
236 TagEncoding::Direct => {
237 let signed = match tag_scalar.primitive() {
238 // We use `i1` for bytes that are always `0` or `1`,
239 // e.g., `#[repr(i8)] enum E { A, B }`, but we can't
240 // let LLVM interpret the `i1` as signed, because
241 // then `i1 1` (i.e., `E::B`) is effectively `i8 -1`.
242 Int(_, signed) => !tag_scalar.is_bool() && signed,
245 bx.intcast(tag.immediate(), cast_to, signed)
247 TagEncoding::Niche { dataful_variant, ref niche_variants, niche_start } => {
248 // Rebase from niche values to discriminants, and check
249 // whether the result is in range for the niche variants.
250 let niche_llty = bx.cx().immediate_backend_type(tag.layout);
251 let tag = tag.immediate();
253 // We first compute the "relative discriminant" (wrt `niche_variants`),
254 // that is, if `n = niche_variants.end() - niche_variants.start()`,
255 // we remap `niche_start..=niche_start + n` (which may wrap around)
256 // to (non-wrap-around) `0..=n`, to be able to check whether the
257 // discriminant corresponds to a niche variant with one comparison.
258 // We also can't go directly to the (variant index) discriminant
259 // and check that it is in the range `niche_variants`, because
260 // that might not fit in the same type, on top of needing an extra
261 // comparison (see also the comment on `let niche_discr`).
262 let relative_discr = if niche_start == 0 {
263 // Avoid subtracting `0`, which wouldn't work for pointers.
264 // FIXME(eddyb) check the actual primitive type here.
267 bx.sub(tag, bx.cx().const_uint_big(niche_llty, niche_start))
269 let relative_max = niche_variants.end().as_u32() - niche_variants.start().as_u32();
270 let is_niche = if relative_max == 0 {
271 // Avoid calling `const_uint`, which wouldn't work for pointers.
272 // Also use canonical == 0 instead of non-canonical u<= 0.
273 // FIXME(eddyb) check the actual primitive type here.
274 bx.icmp(IntPredicate::IntEQ, relative_discr, bx.cx().const_null(niche_llty))
276 let relative_max = bx.cx().const_uint(niche_llty, relative_max as u64);
277 bx.icmp(IntPredicate::IntULE, relative_discr, relative_max)
280 // NOTE(eddyb) this addition needs to be performed on the final
281 // type, in case the niche itself can't represent all variant
282 // indices (e.g. `u8` niche with more than `256` variants,
283 // but enough uninhabited variants so that the remaining variants
284 // fit in the niche).
285 // In other words, `niche_variants.end - niche_variants.start`
286 // is representable in the niche, but `niche_variants.end`
287 // might not be, in extreme cases.
289 let relative_discr = if relative_max == 0 {
290 // HACK(eddyb) since we have only one niche, we know which
291 // one it is, and we can avoid having a dynamic value here.
292 bx.cx().const_uint(cast_to, 0)
294 bx.intcast(relative_discr, cast_to, false)
298 bx.cx().const_uint(cast_to, niche_variants.start().as_u32() as u64),
305 bx.cx().const_uint(cast_to, dataful_variant.as_u32() as u64),
311 /// Sets the discriminant for a new value of the given case of the given
313 pub fn codegen_set_discr<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
316 variant_index: VariantIdx,
318 if self.layout.for_variant(bx.cx(), variant_index).abi.is_uninhabited() {
319 // We play it safe by using a well-defined `abort`, but we could go for immediate UB
320 // if that turns out to be helpful.
324 match self.layout.variants {
325 Variants::Single { index } => {
326 assert_eq!(index, variant_index);
328 Variants::Multiple { tag_encoding: TagEncoding::Direct, tag_field, .. } => {
329 let ptr = self.project_field(bx, tag_field);
331 self.layout.ty.discriminant_for_variant(bx.tcx(), variant_index).unwrap().val;
333 bx.cx().const_uint_big(bx.cx().backend_type(ptr.layout), to),
340 TagEncoding::Niche { dataful_variant, ref niche_variants, niche_start },
344 if variant_index != dataful_variant {
345 let niche = self.project_field(bx, tag_field);
346 let niche_llty = bx.cx().immediate_backend_type(niche.layout);
347 let niche_value = variant_index.as_u32() - niche_variants.start().as_u32();
348 let niche_value = (niche_value as u128).wrapping_add(niche_start);
349 // FIXME(eddyb): check the actual primitive type here.
350 let niche_llval = if niche_value == 0 {
351 // HACK(eddyb): using `c_null` as it works on all types.
352 bx.cx().const_null(niche_llty)
354 bx.cx().const_uint_big(niche_llty, niche_value)
356 OperandValue::Immediate(niche_llval).store(bx, niche);
362 pub fn project_index<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
367 // Statically compute the offset if we can, otherwise just use the element size,
368 // as this will yield the lowest alignment.
369 let layout = self.layout.field(bx, 0);
370 let offset = if let Some(llindex) = bx.const_to_opt_uint(llindex) {
371 layout.size.checked_mul(llindex, bx).unwrap_or(layout.size)
377 llval: bx.inbounds_gep(
378 bx.cx().backend_type(self.layout),
380 &[bx.cx().const_usize(0), llindex],
384 align: self.align.restrict_for_offset(offset),
388 pub fn project_downcast<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
391 variant_index: VariantIdx,
393 let mut downcast = *self;
394 downcast.layout = self.layout.for_variant(bx.cx(), variant_index);
396 // Cast to the appropriate variant struct type.
397 let variant_ty = bx.cx().backend_type(downcast.layout);
398 downcast.llval = bx.pointercast(downcast.llval, bx.cx().type_ptr_to(variant_ty));
403 pub fn storage_live<Bx: BuilderMethods<'a, 'tcx, Value = V>>(&self, bx: &mut Bx) {
404 bx.lifetime_start(self.llval, self.layout.size);
407 pub fn storage_dead<Bx: BuilderMethods<'a, 'tcx, Value = V>>(&self, bx: &mut Bx) {
408 bx.lifetime_end(self.llval, self.layout.size);
412 impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
413 #[instrument(level = "trace", skip(self, bx))]
414 pub fn codegen_place(
417 place_ref: mir::PlaceRef<'tcx>,
418 ) -> PlaceRef<'tcx, Bx::Value> {
420 let tcx = self.cx.tcx();
423 let mut cg_base = match self.locals[place_ref.local] {
424 LocalRef::Place(place) => place,
425 LocalRef::UnsizedPlace(place) => bx.load_operand(place).deref(cx),
426 LocalRef::Operand(..) => {
427 if place_ref.has_deref() {
429 let cg_base = self.codegen_consume(
431 mir::PlaceRef { projection: &place_ref.projection[..0], ..place_ref },
433 cg_base.deref(bx.cx())
435 bug!("using operand local {:?} as place", place_ref);
439 for elem in place_ref.projection[base..].iter() {
440 cg_base = match *elem {
441 mir::ProjectionElem::Deref => bx.load_operand(cg_base).deref(bx.cx()),
442 mir::ProjectionElem::Field(ref field, _) => {
443 cg_base.project_field(bx, field.index())
445 mir::ProjectionElem::Index(index) => {
446 let index = &mir::Operand::Copy(mir::Place::from(index));
447 let index = self.codegen_operand(bx, index);
448 let llindex = index.immediate();
449 cg_base.project_index(bx, llindex)
451 mir::ProjectionElem::ConstantIndex { offset, from_end: false, min_length: _ } => {
452 let lloffset = bx.cx().const_usize(offset as u64);
453 cg_base.project_index(bx, lloffset)
455 mir::ProjectionElem::ConstantIndex { offset, from_end: true, min_length: _ } => {
456 let lloffset = bx.cx().const_usize(offset as u64);
457 let lllen = cg_base.len(bx.cx());
458 let llindex = bx.sub(lllen, lloffset);
459 cg_base.project_index(bx, llindex)
461 mir::ProjectionElem::Subslice { from, to, from_end } => {
462 let mut subslice = cg_base.project_index(bx, bx.cx().const_usize(from as u64));
464 PlaceTy::from_ty(cg_base.layout.ty).projection_ty(tcx, *elem).ty;
465 subslice.layout = bx.cx().layout_of(self.monomorphize(projected_ty));
467 if subslice.layout.is_unsized() {
468 assert!(from_end, "slice subslices should be `from_end`");
469 subslice.llextra = Some(bx.sub(
470 cg_base.llextra.unwrap(),
471 bx.cx().const_usize((from as u64) + (to as u64)),
475 // Cast the place pointer type to the new
476 // array or slice type (`*[%_; new_len]`).
477 subslice.llval = bx.pointercast(
479 bx.cx().type_ptr_to(bx.cx().backend_type(subslice.layout)),
484 mir::ProjectionElem::Downcast(_, v) => cg_base.project_downcast(bx, v),
487 debug!("codegen_place(place={:?}) => {:?}", place_ref, cg_base);
491 pub fn monomorphized_place_ty(&self, place_ref: mir::PlaceRef<'tcx>) -> Ty<'tcx> {
492 let tcx = self.cx.tcx();
493 let place_ty = place_ref.ty(self.mir, tcx);
494 self.monomorphize(place_ty.ty)
498 fn round_up_const_value_to_alignment<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
505 // if value & (align - 1) == 0 {
508 // (value & !(align - 1)) + align
511 // Usually this is written without branches as
513 // (value + align - 1) & !(align - 1)
515 // But this formula cannot take advantage of constant `value`. E.g. if `value` is known
516 // at compile time to be `1`, this expression should be optimized to `align`. However,
517 // optimization only holds if `align` is a power of two. Since the optimizer doesn't know
518 // that `align` is a power of two, it cannot perform this optimization.
522 // value + (-value & (align - 1))
524 // Since `align` is used only once, the expression can be optimized. For `value = 0`
525 // its optimized to `0` even in debug mode.
527 // NB: The previous version of this code used
529 // (value + align - 1) & -align
531 // Even though `-align == !(align - 1)`, LLVM failed to optimize this even for
532 // `value = 0`. Bug report: https://bugs.llvm.org/show_bug.cgi?id=48559
533 let one = bx.const_usize(1);
534 let align_minus_1 = bx.sub(align, one);
535 let neg_value = bx.neg(value);
536 let offset = bx.and(neg_value, align_minus_1);
537 bx.add(value, offset)