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