src/librustc_codegen_ssa/mir/place.rs

   1 use rustc::ty::{self, Ty};
   2 use rustc::ty::layout::{self, Align, TyLayout, LayoutOf, VariantIdx, HasTyCtxt};
   3 use rustc::mir;
   4 use rustc::mir::tcx::PlaceTy;
   5 use crate::MemFlags;
   6 use crate::common::IntPredicate;
   7 use crate::glue;
   8
   9 use crate::traits::*;
  10
  11 use super::{FunctionCx, LocalRef};
  12 use super::operand::OperandValue;
  13
  14 #[derive(Copy, Clone, Debug)]
  15 pub struct PlaceRef<'tcx, V> {
  16     /// Pointer to the contents of the place.
  17     pub llval: V,
  18
  19     /// This place's extra data if it is unsized, or null.
  20     pub llextra: Option<V>,
  21
  22     /// Monomorphized type of this place, including variant information.
  23     pub layout: TyLayout<'tcx>,
  24
  25     /// What alignment we know for this place.
  26     pub align: Align,
  27 }
  28
  29 impl<'a, 'tcx: 'a, V: CodegenObject> PlaceRef<'tcx, V> {
  30     pub fn new_sized(
  31         llval: V,
  32         layout: TyLayout<'tcx>,
  33         align: Align,
  34     ) -> PlaceRef<'tcx, V> {
  35         assert!(!layout.is_unsized());
  36         PlaceRef {
  37             llval,
  38             llextra: None,
  39             layout,
  40             align
  41         }
  42     }
  43
  44     fn new_thin_place<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
  45         bx: &mut Bx,
  46         llval: V,
  47         layout: TyLayout<'tcx>,
  48         align: Align,
  49     ) -> PlaceRef<'tcx, V> {
  50         assert!(!bx.cx().type_has_metadata(layout.ty));
  51         PlaceRef {
  52             llval,
  53             llextra: None,
  54             layout,
  55             align
  56         }
  57     }
  58
  59     pub fn alloca<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
  60         bx: &mut Bx,
  61         layout: TyLayout<'tcx>,
  62         name: &str
  63     ) -> Self {
  64         debug!("alloca({:?}: {:?})", name, layout);
  65         assert!(!layout.is_unsized(), "tried to statically allocate unsized place");
  66         let tmp = bx.alloca(bx.cx().backend_type(layout), name, layout.align.abi);
  67         Self::new_sized(tmp, layout, layout.align.abi)
  68     }
  69
  70     /// Returns a place for an indirect reference to an unsized place.
  71     pub fn alloca_unsized_indirect<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
  72         bx: &mut Bx,
  73         layout: TyLayout<'tcx>,
  74         name: &str,
  75     ) -> Self {
  76         debug!("alloca_unsized_indirect({:?}: {:?})", name, layout);
  77         assert!(layout.is_unsized(), "tried to allocate indirect place for sized values");
  78         let ptr_ty = bx.cx().tcx().mk_mut_ptr(layout.ty);
  79         let ptr_layout = bx.cx().layout_of(ptr_ty);
  80         Self::alloca(bx, ptr_layout, name)
  81     }
  82
  83     pub fn len<Cx: CodegenMethods<'tcx, Value = V>>(
  84         &self,
  85         cx: &Cx
  86     ) -> V {
  87         if let layout::FieldPlacement::Array { count, .. } = self.layout.fields {
  88             if self.layout.is_unsized() {
  89                 assert_eq!(count, 0);
  90                 self.llextra.unwrap()
  91             } else {
  92                 cx.const_usize(count)
  93             }
  94         } else {
  95             bug!("unexpected layout `{:#?}` in PlaceRef::len", self.layout)
  96         }
  97     }
  98
  99 }
 100
 101 impl<'a, 'tcx: 'a, V: CodegenObject> PlaceRef<'tcx, V> {
 102     /// Access a field, at a point when the value's case is known.
 103     pub fn project_field<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
 104         self, bx: &mut Bx,
 105         ix: usize,
 106     ) -> Self {
 107         let field = self.layout.field(bx.cx(), ix);
 108         let offset = self.layout.fields.offset(ix);
 109         let effective_field_align = self.align.restrict_for_offset(offset);
 110
 111         let mut simple = || {
 112             // Unions and newtypes only use an offset of 0.
 113             let llval = if offset.bytes() == 0 {
 114                 self.llval
 115             } else if let layout::Abi::ScalarPair(ref a, ref b) = self.layout.abi {
 116                 // Offsets have to match either first or second field.
 117                 assert_eq!(offset, a.value.size(bx.cx()).align_to(b.value.align(bx.cx()).abi));
 118                 bx.struct_gep(self.llval, 1)
 119             } else {
 120                 bx.struct_gep(self.llval, bx.cx().backend_field_index(self.layout, ix))
 121             };
 122             PlaceRef {
 123                 // HACK(eddyb) have to bitcast pointers until LLVM removes pointee types.
 124                 llval: bx.pointercast(llval, bx.cx().type_ptr_to(bx.cx().backend_type(field))),
 125                 llextra: if bx.cx().type_has_metadata(field.ty) {
 126                     self.llextra
 127                 } else {
 128                     None
 129                 },
 130                 layout: field,
 131                 align: effective_field_align,
 132             }
 133         };
 134
 135         // Simple cases, which don't need DST adjustment:
 136         //   * no metadata available - just log the case
 137         //   * known alignment - sized types, [T], str or a foreign type
 138         //   * packed struct - there is no alignment padding
 139         match field.ty.sty {
 140             _ if self.llextra.is_none() => {
 141                 debug!("Unsized field `{}`, of `{:?}` has no metadata for adjustment",
 142                     ix, self.llval);
 143                 return simple();
 144             }
 145             _ if !field.is_unsized() => return simple(),
 146             ty::Slice(..) | ty::Str | ty::Foreign(..) => return simple(),
 147             ty::Adt(def, _) => {
 148                 if def.repr.packed() {
 149                     // FIXME(eddyb) generalize the adjustment when we
 150                     // start supporting packing to larger alignments.
 151                     assert_eq!(self.layout.align.abi.bytes(), 1);
 152                     return simple();
 153                 }
 154             }
 155             _ => {}
 156         }
 157
 158         // We need to get the pointer manually now.
 159         // We do this by casting to a *i8, then offsetting it by the appropriate amount.
 160         // We do this instead of, say, simply adjusting the pointer from the result of a GEP
 161         // because the field may have an arbitrary alignment in the LLVM representation
 162         // anyway.
 163         //
 164         // To demonstrate:
 165         //   struct Foo<T: ?Sized> {
 166         //      x: u16,
 167         //      y: T
 168         //   }
 169         //
 170         // The type Foo<Foo<Trait>> is represented in LLVM as { u16, { u16, u8 }}, meaning that
 171         // the `y` field has 16-bit alignment.
 172
 173         let meta = self.llextra;
 174
 175         let unaligned_offset = bx.cx().const_usize(offset.bytes());
 176
 177         // Get the alignment of the field
 178         let (_, unsized_align) = glue::size_and_align_of_dst(bx, field.ty, meta);
 179
 180         // Bump the unaligned offset up to the appropriate alignment using the
 181         // following expression:
 182         //
 183         //   (unaligned offset + (align - 1)) & -align
 184
 185         // Calculate offset
 186         let align_sub_1 = bx.sub(unsized_align, bx.cx().const_usize(1u64));
 187         let and_lhs = bx.add(unaligned_offset, align_sub_1);
 188         let and_rhs = bx.neg(unsized_align);
 189         let offset = bx.and(and_lhs, and_rhs);
 190
 191         debug!("struct_field_ptr: DST field offset: {:?}", offset);
 192
 193         // Cast and adjust pointer
 194         let byte_ptr = bx.pointercast(self.llval, bx.cx().type_i8p());
 195         let byte_ptr = bx.gep(byte_ptr, &[offset]);
 196
 197         // Finally, cast back to the type expected
 198         let ll_fty = bx.cx().backend_type(field);
 199         debug!("struct_field_ptr: Field type is {:?}", ll_fty);
 200
 201         PlaceRef {
 202             llval: bx.pointercast(byte_ptr, bx.cx().type_ptr_to(ll_fty)),
 203             llextra: self.llextra,
 204             layout: field,
 205             align: effective_field_align,
 206         }
 207     }
 208
 209     /// Obtain the actual discriminant of a value.
 210     pub fn codegen_get_discr<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
 211         self,
 212         bx: &mut Bx,
 213         cast_to: Ty<'tcx>
 214     ) -> V {
 215         let cast_to = bx.cx().immediate_backend_type(bx.cx().layout_of(cast_to));
 216         if self.layout.abi.is_uninhabited() {
 217             return bx.cx().const_undef(cast_to);
 218         }
 219         match self.layout.variants {
 220             layout::Variants::Single { index } => {
 221                 let discr_val = self.layout.ty.ty_adt_def().map_or(
 222                     index.as_u32() as u128,
 223                     |def| def.discriminant_for_variant(bx.cx().tcx(), index).val);
 224                 return bx.cx().const_uint_big(cast_to, discr_val);
 225             }
 226             layout::Variants::Tagged { .. } |
 227             layout::Variants::NicheFilling { .. } => {},
 228         }
 229
 230         let discr = self.project_field(bx, 0);
 231         let lldiscr = bx.load_operand(discr).immediate();
 232         match self.layout.variants {
 233             layout::Variants::Single { .. } => bug!(),
 234             layout::Variants::Tagged { ref tag, .. } => {
 235                 let signed = match tag.value {
 236                     // We use `i1` for bytes that are always `0` or `1`,
 237                     // e.g., `#[repr(i8)] enum E { A, B }`, but we can't
 238                     // let LLVM interpret the `i1` as signed, because
 239                     // then `i1 1` (i.e., E::B) is effectively `i8 -1`.
 240                     layout::Int(_, signed) => !tag.is_bool() && signed,
 241                     _ => false
 242                 };
 243                 bx.intcast(lldiscr, cast_to, signed)
 244             }
 245             layout::Variants::NicheFilling {
 246                 dataful_variant,
 247                 ref niche_variants,
 248                 niche_start,
 249                 ..
 250             } => {
 251                 let niche_llty = bx.cx().immediate_backend_type(discr.layout);
 252                 if niche_variants.start() == niche_variants.end() {
 253                     // FIXME(eddyb) Check the actual primitive type here.
 254                     let niche_llval = if niche_start == 0 {
 255                         // HACK(eddyb) Using `c_null` as it works on all types.
 256                         bx.cx().const_null(niche_llty)
 257                     } else {
 258                         bx.cx().const_uint_big(niche_llty, niche_start)
 259                     };
 260                     let select_arg = bx.icmp(IntPredicate::IntEQ, lldiscr, niche_llval);
 261                     bx.select(select_arg,
 262                         bx.cx().const_uint(cast_to, niche_variants.start().as_u32() as u64),
 263                         bx.cx().const_uint(cast_to, dataful_variant.as_u32() as u64))
 264                 } else {
 265                     // Rebase from niche values to discriminant values.
 266                     let delta = niche_start.wrapping_sub(niche_variants.start().as_u32() as u128);
 267                     let lldiscr = bx.sub(lldiscr, bx.cx().const_uint_big(niche_llty, delta));
 268                     let lldiscr_max =
 269                         bx.cx().const_uint(niche_llty, niche_variants.end().as_u32() as u64);
 270                     let select_arg = bx.icmp(IntPredicate::IntULE, lldiscr, lldiscr_max);
 271                     let cast = bx.intcast(lldiscr, cast_to, false);
 272                     bx.select(select_arg,
 273                         cast,
 274                         bx.cx().const_uint(cast_to, dataful_variant.as_u32() as u64))
 275                 }
 276             }
 277         }
 278     }
 279
 280     /// Sets the discriminant for a new value of the given case of the given
 281     /// representation.
 282     pub fn codegen_set_discr<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
 283         &self,
 284         bx: &mut Bx,
 285         variant_index: VariantIdx
 286     ) {
 287         if self.layout.for_variant(bx.cx(), variant_index).abi.is_uninhabited() {
 288             return;
 289         }
 290         match self.layout.variants {
 291             layout::Variants::Single { index } => {
 292                 assert_eq!(index, variant_index);
 293             }
 294             layout::Variants::Tagged { .. } => {
 295                 let ptr = self.project_field(bx, 0);
 296                 let to = self.layout.ty.ty_adt_def().unwrap()
 297                     .discriminant_for_variant(bx.tcx(), variant_index)
 298                     .val;
 299                 bx.store(
 300                     bx.cx().const_uint_big(bx.cx().backend_type(ptr.layout), to),
 301                     ptr.llval,
 302                     ptr.align);
 303             }
 304             layout::Variants::NicheFilling {
 305                 dataful_variant,
 306                 ref niche_variants,
 307                 niche_start,
 308                 ..
 309             } => {
 310                 if variant_index != dataful_variant {
 311                     if bx.cx().sess().target.target.arch == "arm" ||
 312                        bx.cx().sess().target.target.arch == "aarch64" {
 313                         // Issue #34427: As workaround for LLVM bug on ARM,
 314                         // use memset of 0 before assigning niche value.
 315                         let fill_byte = bx.cx().const_u8(0);
 316                         let size = bx.cx().const_usize(self.layout.size.bytes());
 317                         bx.memset(self.llval, fill_byte, size, self.align, MemFlags::empty());
 318                     }
 319
 320                     let niche = self.project_field(bx, 0);
 321                     let niche_llty = bx.cx().immediate_backend_type(niche.layout);
 322                     let niche_value = variant_index.as_u32() - niche_variants.start().as_u32();
 323                     let niche_value = (niche_value as u128)
 324                         .wrapping_add(niche_start);
 325                     // FIXME(eddyb) Check the actual primitive type here.
 326                     let niche_llval = if niche_value == 0 {
 327                         // HACK(eddyb) Using `c_null` as it works on all types.
 328                         bx.cx().const_null(niche_llty)
 329                     } else {
 330                         bx.cx().const_uint_big(niche_llty, niche_value)
 331                     };
 332                     OperandValue::Immediate(niche_llval).store(bx, niche);
 333                 }
 334             }
 335         }
 336     }
 337
 338     pub fn project_index<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
 339         &self,
 340         bx: &mut Bx,
 341         llindex: V
 342     ) -> Self {
 343         // Statically compute the offset if we can, otherwise just use the element size,
 344         // as this will yield the lowest alignment.
 345         let layout = self.layout.field(bx, 0);
 346         let offset = if bx.is_const_integral(llindex) {
 347             layout.size.checked_mul(bx.const_to_uint(llindex), bx).unwrap_or(layout.size)
 348         } else {
 349             layout.size
 350         };
 351
 352         PlaceRef {
 353             llval: bx.inbounds_gep(self.llval, &[bx.cx().const_usize(0), llindex]),
 354             llextra: None,
 355             layout,
 356             align: self.align.restrict_for_offset(offset),
 357         }
 358     }
 359
 360     pub fn project_downcast<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
 361         &self,
 362         bx: &mut Bx,
 363         variant_index: VariantIdx
 364     ) -> Self {
 365         let mut downcast = *self;
 366         downcast.layout = self.layout.for_variant(bx.cx(), variant_index);
 367
 368         // Cast to the appropriate variant struct type.
 369         let variant_ty = bx.cx().backend_type(downcast.layout);
 370         downcast.llval = bx.pointercast(downcast.llval, bx.cx().type_ptr_to(variant_ty));
 371
 372         downcast
 373     }
 374
 375     pub fn storage_live<Bx: BuilderMethods<'a, 'tcx, Value = V>>(&self, bx: &mut Bx) {
 376         bx.lifetime_start(self.llval, self.layout.size);
 377     }
 378
 379     pub fn storage_dead<Bx: BuilderMethods<'a, 'tcx, Value = V>>(&self, bx: &mut Bx) {
 380         bx.lifetime_end(self.llval, self.layout.size);
 381     }
 382 }
 383
 384 impl<'a, 'tcx: 'a, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
 385     pub fn codegen_place(
 386         &mut self,
 387         bx: &mut Bx,
 388         place: &mir::Place<'tcx>
 389     ) -> PlaceRef<'tcx, Bx::Value> {
 390         debug!("codegen_place(place={:?})", place);
 391
 392         let cx = self.cx;
 393         let tcx = self.cx.tcx();
 394
 395         if let mir::Place::Base(mir::PlaceBase::Local(index)) = *place {
 396             match self.locals[index] {
 397                 LocalRef::Place(place) => {
 398                     return place;
 399                 }
 400                 LocalRef::UnsizedPlace(place) => {
 401                     return bx.load_operand(place).deref(cx);
 402                 }
 403                 LocalRef::Operand(..) => {
 404                     bug!("using operand local {:?} as place", place);
 405                 }
 406             }
 407         }
 408
 409         let result = match *place {
 410             mir::Place::Base(mir::PlaceBase::Local(_)) => bug!(), // handled above
 411             mir::Place::Base(mir::PlaceBase::Promoted(box (index, ty))) => {
 412                 let param_env = ty::ParamEnv::reveal_all();
 413                 let cid = mir::interpret::GlobalId {
 414                     instance: self.instance,
 415                     promoted: Some(index),
 416                 };
 417                 let layout = cx.layout_of(self.monomorphize(&ty));
 418                 match bx.tcx().const_eval(param_env.and(cid)) {
 419                     Ok(val) => match val.val {
 420                         mir::interpret::ConstValue::ByRef(ptr, alloc) => {
 421                             bx.cx().from_const_alloc(layout, alloc, ptr.offset)
 422                         }
 423                         _ => bug!("promoteds should have an allocation: {:?}", val),
 424                     },
 425                     Err(_) => {
 426                         // this is unreachable as long as runtime
 427                         // and compile-time agree on values
 428                         // With floats that won't always be true
 429                         // so we generate an abort
 430                         bx.abort();
 431                         let llval = bx.cx().const_undef(
 432                             bx.cx().type_ptr_to(bx.cx().backend_type(layout))
 433                         );
 434                         PlaceRef::new_sized(llval, layout, layout.align.abi)
 435                     }
 436                 }
 437             }
 438             mir::Place::Base(mir::PlaceBase::Static(box mir::Static { def_id, ty })) => {
 439                 // NB: The layout of a static may be unsized as is the case when working
 440                 // with a static that is an extern_type.
 441                 let layout = cx.layout_of(self.monomorphize(&ty));
 442                 PlaceRef::new_thin_place(bx, bx.get_static(def_id), layout, layout.align.abi)
 443             },
 444             mir::Place::Projection(box mir::Projection {
 445                 ref base,
 446                 elem: mir::ProjectionElem::Deref
 447             }) => {
 448                 // Load the pointer from its location.
 449                 self.codegen_consume(bx, base).deref(bx.cx())
 450             }
 451             mir::Place::Projection(ref projection) => {
 452                 let cg_base = self.codegen_place(bx, &projection.base);
 453
 454                 match projection.elem {
 455                     mir::ProjectionElem::Deref => bug!(),
 456                     mir::ProjectionElem::Field(ref field, _) => {
 457                         cg_base.project_field(bx, field.index())
 458                     }
 459                     mir::ProjectionElem::Index(index) => {
 460                         let index = &mir::Operand::Copy(
 461                             mir::Place::Base(mir::PlaceBase::Local(index))
 462                         );
 463                         let index = self.codegen_operand(bx, index);
 464                         let llindex = index.immediate();
 465                         cg_base.project_index(bx, llindex)
 466                     }
 467                     mir::ProjectionElem::ConstantIndex { offset,
 468                                                          from_end: false,
 469                                                          min_length: _ } => {
 470                         let lloffset = bx.cx().const_usize(offset as u64);
 471                         cg_base.project_index(bx, lloffset)
 472                     }
 473                     mir::ProjectionElem::ConstantIndex { offset,
 474                                                          from_end: true,
 475                                                          min_length: _ } => {
 476                         let lloffset = bx.cx().const_usize(offset as u64);
 477                         let lllen = cg_base.len(bx.cx());
 478                         let llindex = bx.sub(lllen, lloffset);
 479                         cg_base.project_index(bx, llindex)
 480                     }
 481                     mir::ProjectionElem::Subslice { from, to } => {
 482                         let mut subslice = cg_base.project_index(bx,
 483                             bx.cx().const_usize(from as u64));
 484                         let projected_ty = PlaceTy::Ty { ty: cg_base.layout.ty }
 485                             .projection_ty(tcx, &projection.elem).to_ty(tcx);
 486                         subslice.layout = bx.cx().layout_of(self.monomorphize(&projected_ty));
 487
 488                         if subslice.layout.is_unsized() {
 489                             subslice.llextra = Some(bx.sub(cg_base.llextra.unwrap(),
 490                                 bx.cx().const_usize((from as u64) + (to as u64))));
 491                         }
 492
 493                         // Cast the place pointer type to the new
 494                         // array or slice type (*[%_; new_len]).
 495                         subslice.llval = bx.pointercast(subslice.llval,
 496                             bx.cx().type_ptr_to(bx.cx().backend_type(subslice.layout)));
 497
 498                         subslice
 499                     }
 500                     mir::ProjectionElem::Downcast(_, v) => {
 501                         cg_base.project_downcast(bx, v)
 502                     }
 503                 }
 504             }
 505         };
 506         debug!("codegen_place(place={:?}) => {:?}", place, result);
 507         result
 508     }
 509
 510     pub fn monomorphized_place_ty(&self, place: &mir::Place<'tcx>) -> Ty<'tcx> {
 511         let tcx = self.cx.tcx();
 512         let place_ty = place.ty(self.mir, tcx);
 513         self.monomorphize(&place_ty.to_ty(tcx))
 514     }
 515 }