src/librustc_codegen_llvm/mir/place.rs

   1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use rustc::ty::{self, Ty};
  12 use rustc::ty::layout::{self, Align, TyLayout, LayoutOf, VariantIdx, HasTyCtxt};
  13 use rustc::mir;
  14 use rustc::mir::tcx::PlaceTy;
  15 use builder::MemFlags;
  16 use rustc_codegen_ssa::common::IntPredicate;
  17 use type_of::LayoutLlvmExt;
  18 use glue;
  19
  20 use interfaces::*;
  21
  22 use super::{FunctionCx, LocalRef};
  23 use super::operand::OperandValue;
  24
  25 #[derive(Copy, Clone, Debug)]
  26 pub struct PlaceRef<'tcx, V> {
  27     /// Pointer to the contents of the place
  28     pub llval: V,
  29
  30     /// This place's extra data if it is unsized, or null
  31     pub llextra: Option<V>,
  32
  33     /// Monomorphized type of this place, including variant information
  34     pub layout: TyLayout<'tcx>,
  35
  36     /// What alignment we know for this place
  37     pub align: Align,
  38 }
  39
  40 impl<'a, 'tcx: 'a, V: CodegenObject> PlaceRef<'tcx, V> {
  41     pub fn new_sized(
  42         llval: V,
  43         layout: TyLayout<'tcx>,
  44         align: Align,
  45     ) -> PlaceRef<'tcx, V> {
  46         assert!(!layout.is_unsized());
  47         PlaceRef {
  48             llval,
  49             llextra: None,
  50             layout,
  51             align
  52         }
  53     }
  54
  55     pub fn alloca<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
  56         bx: &Bx,
  57         layout: TyLayout<'tcx>,
  58         name: &str
  59     ) -> Self {
  60         debug!("alloca({:?}: {:?})", name, layout);
  61         assert!(!layout.is_unsized(), "tried to statically allocate unsized place");
  62         let tmp = bx.alloca(bx.cx().backend_type(layout), name, layout.align);
  63         Self::new_sized(tmp, layout, layout.align)
  64     }
  65
  66     /// Returns a place for an indirect reference to an unsized place.
  67     pub fn alloca_unsized_indirect<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
  68         bx: &Bx,
  69         layout: TyLayout<'tcx>,
  70         name: &str,
  71     ) -> Self {
  72         debug!("alloca_unsized_indirect({:?}: {:?})", name, layout);
  73         assert!(layout.is_unsized(), "tried to allocate indirect place for sized values");
  74         let ptr_ty = bx.cx().tcx().mk_mut_ptr(layout.ty);
  75         let ptr_layout = bx.cx().layout_of(ptr_ty);
  76         Self::alloca(bx, ptr_layout, name)
  77     }
  78
  79     pub fn len<Cx: CodegenMethods<'tcx, Value = V>>(
  80         &self,
  81         cx: &Cx
  82     ) -> V {
  83         if let layout::FieldPlacement::Array { count, .. } = self.layout.fields {
  84             if self.layout.is_unsized() {
  85                 assert_eq!(count, 0);
  86                 self.llextra.unwrap()
  87             } else {
  88                 cx.const_usize(count)
  89             }
  90         } else {
  91             bug!("unexpected layout `{:#?}` in PlaceRef::len", self.layout)
  92         }
  93     }
  94
  95 }
  96
  97 impl<'a, 'tcx: 'a, V: CodegenObject> PlaceRef<'tcx, V> {
  98     /// Access a field, at a point when the value's case is known.
  99     pub fn project_field<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
 100         self, bx: &Bx,
 101         ix: usize,
 102     ) -> Self {
 103         let cx = bx.cx();
 104         let field = self.layout.field(cx, ix);
 105         let offset = self.layout.fields.offset(ix);
 106         let effective_field_align = self.align.restrict_for_offset(offset);
 107
 108         let simple = || {
 109             // Unions and newtypes only use an offset of 0.
 110             let llval = if offset.bytes() == 0 {
 111                 self.llval
 112             } else if let layout::Abi::ScalarPair(ref a, ref b) = self.layout.abi {
 113                 // Offsets have to match either first or second field.
 114                 assert_eq!(offset, a.value.size(cx).abi_align(b.value.align(cx)));
 115                 bx.struct_gep(self.llval, 1)
 116             } else {
 117                 bx.struct_gep(self.llval, self.layout.llvm_field_index(ix))
 118             };
 119             PlaceRef {
 120                 // HACK(eddyb) have to bitcast pointers until LLVM removes pointee types.
 121                 llval: bx.pointercast(llval, cx.type_ptr_to(cx.backend_type(field))),
 122                 llextra: if cx.type_has_metadata(field.ty) {
 123                     self.llextra
 124                 } else {
 125                     None
 126                 },
 127                 layout: field,
 128                 align: effective_field_align,
 129             }
 130         };
 131
 132         // Simple cases, which don't need DST adjustment:
 133         //   * no metadata available - just log the case
 134         //   * known alignment - sized types, [T], str or a foreign type
 135         //   * packed struct - there is no alignment padding
 136         match field.ty.sty {
 137             _ if self.llextra.is_none() => {
 138                 debug!("Unsized field `{}`, of `{:?}` has no metadata for adjustment",
 139                     ix, self.llval);
 140                 return simple();
 141             }
 142             _ if !field.is_unsized() => return simple(),
 143             ty::Slice(..) | ty::Str | ty::Foreign(..) => return simple(),
 144             ty::Adt(def, _) => {
 145                 if def.repr.packed() {
 146                     // FIXME(eddyb) generalize the adjustment when we
 147                     // start supporting packing to larger alignments.
 148                     assert_eq!(self.layout.align.abi(), 1);
 149                     return simple();
 150                 }
 151             }
 152             _ => {}
 153         }
 154
 155         // We need to get the pointer manually now.
 156         // We do this by casting to a *i8, then offsetting it by the appropriate amount.
 157         // We do this instead of, say, simply adjusting the pointer from the result of a GEP
 158         // because the field may have an arbitrary alignment in the LLVM representation
 159         // anyway.
 160         //
 161         // To demonstrate:
 162         //   struct Foo<T: ?Sized> {
 163         //      x: u16,
 164         //      y: T
 165         //   }
 166         //
 167         // The type Foo<Foo<Trait>> is represented in LLVM as { u16, { u16, u8 }}, meaning that
 168         // the `y` field has 16-bit alignment.
 169
 170         let meta = self.llextra;
 171
 172         let unaligned_offset = cx.const_usize(offset.bytes());
 173
 174         // Get the alignment of the field
 175         let (_, unsized_align) = glue::size_and_align_of_dst(bx, field.ty, meta);
 176
 177         // Bump the unaligned offset up to the appropriate alignment using the
 178         // following expression:
 179         //
 180         //   (unaligned offset + (align - 1)) & -align
 181
 182         // Calculate offset
 183         let align_sub_1 = bx.sub(unsized_align, cx.const_usize(1u64));
 184         let offset = bx.and(bx.add(unaligned_offset, align_sub_1),
 185         bx.neg(unsized_align));
 186
 187         debug!("struct_field_ptr: DST field offset: {:?}", offset);
 188
 189         // Cast and adjust pointer
 190         let byte_ptr = bx.pointercast(self.llval, cx.type_i8p());
 191         let byte_ptr = bx.gep(byte_ptr, &[offset]);
 192
 193         // Finally, cast back to the type expected
 194         let ll_fty = cx.backend_type(field);
 195         debug!("struct_field_ptr: Field type is {:?}", ll_fty);
 196
 197         PlaceRef {
 198             llval: bx.pointercast(byte_ptr, bx.cx().type_ptr_to(ll_fty)),
 199             llextra: self.llextra,
 200             layout: field,
 201             align: effective_field_align,
 202         }
 203     }
 204
 205     /// Obtain the actual discriminant of a value.
 206     pub fn codegen_get_discr<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
 207         self,
 208         bx: &Bx,
 209         cast_to: Ty<'tcx>
 210     ) -> V {
 211         let cast_to = bx.cx().immediate_backend_type(bx.cx().layout_of(cast_to));
 212         if self.layout.abi.is_uninhabited() {
 213             return bx.cx().const_undef(cast_to);
 214         }
 215         match self.layout.variants {
 216             layout::Variants::Single { index } => {
 217                 let discr_val = self.layout.ty.ty_adt_def().map_or(
 218                     index.as_u32() as u128,
 219                     |def| def.discriminant_for_variant(bx.cx().tcx(), index).val);
 220                 return bx.cx().const_uint_big(cast_to, discr_val);
 221             }
 222             layout::Variants::Tagged { .. } |
 223             layout::Variants::NicheFilling { .. } => {},
 224         }
 225
 226         let discr = self.project_field(bx, 0);
 227         let lldiscr = bx.load_operand(discr).immediate();
 228         match self.layout.variants {
 229             layout::Variants::Single { .. } => bug!(),
 230             layout::Variants::Tagged { ref tag, .. } => {
 231                 let signed = match tag.value {
 232                     // We use `i1` for bytes that are always `0` or `1`,
 233                     // e.g. `#[repr(i8)] enum E { A, B }`, but we can't
 234                     // let LLVM interpret the `i1` as signed, because
 235                     // then `i1 1` (i.e. E::B) is effectively `i8 -1`.
 236                     layout::Int(_, signed) => !tag.is_bool() && signed,
 237                     _ => false
 238                 };
 239                 bx.intcast(lldiscr, cast_to, signed)
 240             }
 241             layout::Variants::NicheFilling {
 242                 dataful_variant,
 243                 ref niche_variants,
 244                 niche_start,
 245                 ..
 246             } => {
 247                 let niche_llty = bx.cx().immediate_backend_type(discr.layout);
 248                 if niche_variants.start() == niche_variants.end() {
 249                     // FIXME(eddyb) Check the actual primitive type here.
 250                     let niche_llval = if niche_start == 0 {
 251                         // HACK(eddyb) Using `c_null` as it works on all types.
 252                         bx.cx().const_null(niche_llty)
 253                     } else {
 254                         bx.cx().const_uint_big(niche_llty, niche_start)
 255                     };
 256                     bx.select(bx.icmp(IntPredicate::IntEQ, lldiscr, niche_llval),
 257                         bx.cx().const_uint(cast_to, niche_variants.start().as_u32() as u64),
 258                         bx.cx().const_uint(cast_to, dataful_variant.as_u32() as u64))
 259                 } else {
 260                     // Rebase from niche values to discriminant values.
 261                     let delta = niche_start.wrapping_sub(niche_variants.start().as_u32() as u128);
 262                     let lldiscr = bx.sub(lldiscr, bx.cx().const_uint_big(niche_llty, delta));
 263                     let lldiscr_max =
 264                         bx.cx().const_uint(niche_llty, niche_variants.end().as_u32() as u64);
 265                     bx.select(bx.icmp(IntPredicate::IntULE, lldiscr, lldiscr_max),
 266                         bx.intcast(lldiscr, cast_to, false),
 267                         bx.cx().const_uint(cast_to, dataful_variant.as_u32() as u64))
 268                 }
 269             }
 270         }
 271     }
 272
 273     /// Set the discriminant for a new value of the given case of the given
 274     /// representation.
 275     pub fn codegen_set_discr<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
 276         &self,
 277         bx: &Bx,
 278         variant_index: VariantIdx
 279     ) {
 280         if self.layout.for_variant(bx.cx(), variant_index).abi.is_uninhabited() {
 281             return;
 282         }
 283         match self.layout.variants {
 284             layout::Variants::Single { index } => {
 285                 assert_eq!(index, variant_index);
 286             }
 287             layout::Variants::Tagged { .. } => {
 288                 let ptr = self.project_field(bx, 0);
 289                 let to = self.layout.ty.ty_adt_def().unwrap()
 290                     .discriminant_for_variant(bx.tcx(), variant_index)
 291                     .val;
 292                 bx.store(
 293                     bx.cx().const_uint_big(bx.cx().backend_type(ptr.layout), to),
 294                     ptr.llval,
 295                     ptr.align);
 296             }
 297             layout::Variants::NicheFilling {
 298                 dataful_variant,
 299                 ref niche_variants,
 300                 niche_start,
 301                 ..
 302             } => {
 303                 if variant_index != dataful_variant {
 304                     if bx.cx().sess().target.target.arch == "arm" ||
 305                        bx.cx().sess().target.target.arch == "aarch64" {
 306                         // Issue #34427: As workaround for LLVM bug on ARM,
 307                         // use memset of 0 before assigning niche value.
 308                         let fill_byte = bx.cx().const_u8(0);
 309                         let (size, align) = self.layout.size_and_align();
 310                         let size = bx.cx().const_usize(size.bytes());
 311                         bx.memset(self.llval, fill_byte, size, align, MemFlags::empty());
 312                     }
 313
 314                     let niche = self.project_field(bx, 0);
 315                     let niche_llty = bx.cx().immediate_backend_type(niche.layout);
 316                     let niche_value = variant_index.as_u32() - niche_variants.start().as_u32();
 317                     let niche_value = (niche_value as u128)
 318                         .wrapping_add(niche_start);
 319                     // FIXME(eddyb) Check the actual primitive type here.
 320                     let niche_llval = if niche_value == 0 {
 321                         // HACK(eddyb) Using `c_null` as it works on all types.
 322                         bx.cx().const_null(niche_llty)
 323                     } else {
 324                         bx.cx().const_uint_big(niche_llty, niche_value)
 325                     };
 326                     OperandValue::Immediate(niche_llval).store(bx, niche);
 327                 }
 328             }
 329         }
 330     }
 331
 332     pub fn project_index<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
 333         &self,
 334         bx: &Bx,
 335         llindex: V
 336     ) -> Self {
 337         PlaceRef {
 338             llval: bx.inbounds_gep(self.llval, &[bx.cx().const_usize(0), llindex]),
 339             llextra: None,
 340             layout: self.layout.field(bx.cx(), 0),
 341             align: self.align
 342         }
 343     }
 344
 345     pub fn project_downcast<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
 346         &self,
 347         bx: &Bx,
 348         variant_index: VariantIdx
 349     ) -> Self {
 350         let mut downcast = *self;
 351         downcast.layout = self.layout.for_variant(bx.cx(), variant_index);
 352
 353         // Cast to the appropriate variant struct type.
 354         let variant_ty = bx.cx().backend_type(downcast.layout);
 355         downcast.llval = bx.pointercast(downcast.llval, bx.cx().type_ptr_to(variant_ty));
 356
 357         downcast
 358     }
 359
 360     pub fn storage_live<Bx: BuilderMethods<'a, 'tcx, Value = V>>(&self, bx: &Bx) {
 361         bx.lifetime_start(self.llval, self.layout.size);
 362     }
 363
 364     pub fn storage_dead<Bx: BuilderMethods<'a, 'tcx, Value = V>>(&self, bx: &Bx) {
 365         bx.lifetime_end(self.llval, self.layout.size);
 366     }
 367 }
 368
 369 impl<'a, 'tcx: 'a, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
 370     pub fn codegen_place(
 371         &mut self,
 372         bx: &Bx,
 373         place: &mir::Place<'tcx>
 374     ) -> PlaceRef<'tcx, Bx::Value> {
 375         debug!("codegen_place(place={:?})", place);
 376
 377         let cx = bx.cx();
 378         let tcx = cx.tcx();
 379
 380         if let mir::Place::Local(index) = *place {
 381             match self.locals[index] {
 382                 LocalRef::Place(place) => {
 383                     return place;
 384                 }
 385                 LocalRef::UnsizedPlace(place) => {
 386                     return bx.load_operand(place).deref(cx);
 387                 }
 388                 LocalRef::Operand(..) => {
 389                     bug!("using operand local {:?} as place", place);
 390                 }
 391             }
 392         }
 393
 394         let result = match *place {
 395             mir::Place::Local(_) => bug!(), // handled above
 396             mir::Place::Promoted(box (index, ty)) => {
 397                 let param_env = ty::ParamEnv::reveal_all();
 398                 let cid = mir::interpret::GlobalId {
 399                     instance: self.instance,
 400                     promoted: Some(index),
 401                 };
 402                 let layout = cx.layout_of(self.monomorphize(&ty));
 403                 match bx.tcx().const_eval(param_env.and(cid)) {
 404                     Ok(val) => match val.val {
 405                         mir::interpret::ConstValue::ByRef(_, alloc, offset) => {
 406                             bx.cx().from_const_alloc(layout, alloc, offset)
 407                         }
 408                         _ => bug!("promoteds should have an allocation: {:?}", val),
 409                     },
 410                     Err(_) => {
 411                         // this is unreachable as long as runtime
 412                         // and compile-time agree on values
 413                         // With floats that won't always be true
 414                         // so we generate an abort
 415                         let fnname = bx.cx().get_intrinsic(&("llvm.trap"));
 416                         bx.call(fnname, &[], None);
 417                         let llval = bx.cx().const_undef(
 418                             bx.cx().type_ptr_to(bx.cx().backend_type(layout))
 419                         );
 420                         PlaceRef::new_sized(llval, layout, layout.align)
 421                     }
 422                 }
 423             }
 424             mir::Place::Static(box mir::Static { def_id, ty }) => {
 425                 let layout = cx.layout_of(self.monomorphize(&ty));
 426                 PlaceRef::new_sized(cx.get_static(def_id), layout, layout.align)
 427             },
 428             mir::Place::Projection(box mir::Projection {
 429                 ref base,
 430                 elem: mir::ProjectionElem::Deref
 431             }) => {
 432                 // Load the pointer from its location.
 433                 self.codegen_consume(bx, base).deref(bx.cx())
 434             }
 435             mir::Place::Projection(ref projection) => {
 436                 let cg_base = self.codegen_place(bx, &projection.base);
 437
 438                 match projection.elem {
 439                     mir::ProjectionElem::Deref => bug!(),
 440                     mir::ProjectionElem::Field(ref field, _) => {
 441                         cg_base.project_field(bx, field.index())
 442                     }
 443                     mir::ProjectionElem::Index(index) => {
 444                         let index = &mir::Operand::Copy(mir::Place::Local(index));
 445                         let index = self.codegen_operand(bx, index);
 446                         let llindex = index.immediate();
 447                         cg_base.project_index(bx, llindex)
 448                     }
 449                     mir::ProjectionElem::ConstantIndex { offset,
 450                                                          from_end: false,
 451                                                          min_length: _ } => {
 452                         let lloffset = bx.cx().const_usize(offset as u64);
 453                         cg_base.project_index(bx, lloffset)
 454                     }
 455                     mir::ProjectionElem::ConstantIndex { offset,
 456                                                          from_end: true,
 457                                                          min_length: _ } => {
 458                         let lloffset = bx.cx().const_usize(offset as u64);
 459                         let lllen = cg_base.len(bx.cx());
 460                         let llindex = bx.sub(lllen, lloffset);
 461                         cg_base.project_index(bx, llindex)
 462                     }
 463                     mir::ProjectionElem::Subslice { from, to } => {
 464                         let mut subslice = cg_base.project_index(bx,
 465                             bx.cx().const_usize(from as u64));
 466                         let projected_ty = PlaceTy::Ty { ty: cg_base.layout.ty }
 467                             .projection_ty(tcx, &projection.elem).to_ty(tcx);
 468                         subslice.layout = bx.cx().layout_of(self.monomorphize(&projected_ty));
 469
 470                         if subslice.layout.is_unsized() {
 471                             subslice.llextra = Some(bx.sub(cg_base.llextra.unwrap(),
 472                                 bx.cx().const_usize((from as u64) + (to as u64))));
 473                         }
 474
 475                         // Cast the place pointer type to the new
 476                         // array or slice type (*[%_; new_len]).
 477                         subslice.llval = bx.pointercast(subslice.llval,
 478                             bx.cx().type_ptr_to(bx.cx().backend_type(subslice.layout)));
 479
 480                         subslice
 481                     }
 482                     mir::ProjectionElem::Downcast(_, v) => {
 483                         cg_base.project_downcast(bx, v)
 484                     }
 485                 }
 486             }
 487         };
 488         debug!("codegen_place(place={:?}) => {:?}", place, result);
 489         result
 490     }
 491
 492     pub fn monomorphized_place_ty(&self, place: &mir::Place<'tcx>) -> Ty<'tcx> {
 493         let tcx = self.cx.tcx();
 494         let place_ty = place.ty(self.mir, tcx);
 495         self.monomorphize(&place_ty.to_ty(tcx))
 496     }
 497 }