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::{self, LLVMConstInBoundsGEP};
  12 use rustc::ty::{self, Ty};
  13 use rustc::ty::layout::{self, Align, TyLayout, LayoutOf, Size, VariantIdx};
  14 use rustc::mir;
  15 use rustc::mir::tcx::PlaceTy;
  16 use base;
  17 use builder::{Builder, MemFlags};
  18 use common::{CodegenCx, IntPredicate};
  19 use type_of::LayoutLlvmExt;
  20 use value::Value;
  21 use glue;
  22 use mir::constant::const_alloc_to_llvm;
  23
  24 use interfaces::*;
  25
  26 use super::{FunctionCx, LocalRef};
  27 use super::operand::{OperandRef, OperandValue};
  28
  29 #[derive(Copy, Clone, Debug)]
  30 pub struct PlaceRef<'tcx, V> {
  31     /// Pointer to the contents of the place
  32     pub llval: V,
  33
  34     /// This place's extra data if it is unsized, or null
  35     pub llextra: Option<V>,
  36
  37     /// Monomorphized type of this place, including variant information
  38     pub layout: TyLayout<'tcx>,
  39
  40     /// What alignment we know for this place
  41     pub align: Align,
  42 }
  43
  44 impl PlaceRef<'tcx, &'ll Value> {
  45     pub fn new_sized(
  46         llval: &'ll Value,
  47         layout: TyLayout<'tcx>,
  48         align: Align,
  49     ) -> PlaceRef<'tcx, &'ll Value> {
  50         assert!(!layout.is_unsized());
  51         PlaceRef {
  52             llval,
  53             llextra: None,
  54             layout,
  55             align
  56         }
  57     }
  58
  59     pub fn from_const_alloc(
  60         bx: &Builder<'a, 'll, 'tcx>,
  61         layout: TyLayout<'tcx>,
  62         alloc: &mir::interpret::Allocation,
  63         offset: Size,
  64     ) -> PlaceRef<'tcx, &'ll Value> {
  65         let init = const_alloc_to_llvm(bx.cx(), alloc);
  66         let base_addr = bx.cx().static_addr_of(init, layout.align, None);
  67
  68         let llval = unsafe { LLVMConstInBoundsGEP(
  69             bx.cx().static_bitcast(base_addr, bx.cx().type_i8p()),
  70             &bx.cx().const_usize(offset.bytes()),
  71             1,
  72         )};
  73         let llval = bx.cx().static_bitcast(llval, bx.cx().type_ptr_to(layout.llvm_type(bx.cx())));
  74         PlaceRef::new_sized(llval, layout, alloc.align)
  75     }
  76
  77     pub fn alloca(bx: &Builder<'a, 'll, 'tcx>, layout: TyLayout<'tcx>, name: &str)
  78                   -> PlaceRef<'tcx, &'ll Value> {
  79         debug!("alloca({:?}: {:?})", name, layout);
  80         assert!(!layout.is_unsized(), "tried to statically allocate unsized place");
  81         let tmp = bx.alloca(layout.llvm_type(bx.cx()), name, layout.align);
  82         Self::new_sized(tmp, layout, layout.align)
  83     }
  84
  85     /// Returns a place for an indirect reference to an unsized place.
  86     pub fn alloca_unsized_indirect(
  87         bx: &Builder<'a, 'll, 'tcx>,
  88         layout: TyLayout<'tcx>,
  89         name: &str,
  90     ) -> PlaceRef<'tcx, &'ll Value> {
  91         debug!("alloca_unsized_indirect({:?}: {:?})", name, layout);
  92         assert!(layout.is_unsized(), "tried to allocate indirect place for sized values");
  93         let ptr_ty = bx.cx().tcx.mk_mut_ptr(layout.ty);
  94         let ptr_layout = bx.cx().layout_of(ptr_ty);
  95         Self::alloca(bx, ptr_layout, name)
  96     }
  97
  98     pub fn len(&self, cx: &CodegenCx<'ll, 'tcx>) -> &'ll Value {
  99         if let layout::FieldPlacement::Array { count, .. } = self.layout.fields {
 100             if self.layout.is_unsized() {
 101                 assert_eq!(count, 0);
 102                 self.llextra.unwrap()
 103             } else {
 104                 cx.const_usize(count)
 105             }
 106         } else {
 107             bug!("unexpected layout `{:#?}` in PlaceRef::len", self.layout)
 108         }
 109     }
 110
 111     pub fn load(&self, bx: &Builder<'a, 'll, 'tcx>) -> OperandRef<'tcx, &'ll Value> {
 112         debug!("PlaceRef::load: {:?}", self);
 113
 114         assert_eq!(self.llextra.is_some(), self.layout.is_unsized());
 115
 116         if self.layout.is_zst() {
 117             return OperandRef::new_zst(bx.cx(), self.layout);
 118         }
 119
 120         let scalar_load_metadata = |load, scalar: &layout::Scalar| {
 121             let vr = scalar.valid_range.clone();
 122             match scalar.value {
 123                 layout::Int(..) => {
 124                     let range = scalar.valid_range_exclusive(bx.cx());
 125                     if range.start != range.end {
 126                         bx.range_metadata(load, range);
 127                     }
 128                 }
 129                 layout::Pointer if vr.start() < vr.end() && !vr.contains(&0) => {
 130                     bx.nonnull_metadata(load);
 131                 }
 132                 _ => {}
 133             }
 134         };
 135
 136         let val = if let Some(llextra) = self.llextra {
 137             OperandValue::Ref(self.llval, Some(llextra), self.align)
 138         } else if self.layout.is_llvm_immediate() {
 139             let mut const_llval = None;
 140             unsafe {
 141                 if let Some(global) = llvm::LLVMIsAGlobalVariable(self.llval) {
 142                     if llvm::LLVMIsGlobalConstant(global) == llvm::True {
 143                         const_llval = llvm::LLVMGetInitializer(global);
 144                     }
 145                 }
 146             }
 147             let llval = const_llval.unwrap_or_else(|| {
 148                 let load = bx.load(self.llval, self.align);
 149                 if let layout::Abi::Scalar(ref scalar) = self.layout.abi {
 150                     scalar_load_metadata(load, scalar);
 151                 }
 152                 load
 153             });
 154             OperandValue::Immediate(base::to_immediate(bx, llval, self.layout))
 155         } else if let layout::Abi::ScalarPair(ref a, ref b) = self.layout.abi {
 156             let load = |i, scalar: &layout::Scalar| {
 157                 let llptr = bx.struct_gep(self.llval, i as u64);
 158                 let load = bx.load(llptr, self.align);
 159                 scalar_load_metadata(load, scalar);
 160                 if scalar.is_bool() {
 161                     bx.trunc(load, bx.cx().type_i1())
 162                 } else {
 163                     load
 164                 }
 165             };
 166             OperandValue::Pair(load(0, a), load(1, b))
 167         } else {
 168             OperandValue::Ref(self.llval, None, self.align)
 169         };
 170
 171         OperandRef { val, layout: self.layout }
 172     }
 173
 174     /// Access a field, at a point when the value's case is known.
 175     pub fn project_field(
 176         self,
 177         bx: &Builder<'a, 'll, 'tcx>,
 178         ix: usize,
 179     ) -> PlaceRef<'tcx, &'ll Value> {
 180         let cx = bx.cx();
 181         let field = self.layout.field(cx, ix);
 182         let offset = self.layout.fields.offset(ix);
 183         let effective_field_align = self.align.restrict_for_offset(offset);
 184
 185         let simple = || {
 186             // Unions and newtypes only use an offset of 0.
 187             let llval = if offset.bytes() == 0 {
 188                 self.llval
 189             } else if let layout::Abi::ScalarPair(ref a, ref b) = self.layout.abi {
 190                 // Offsets have to match either first or second field.
 191                 assert_eq!(offset, a.value.size(cx).abi_align(b.value.align(cx)));
 192                 bx.struct_gep(self.llval, 1)
 193             } else {
 194                 bx.struct_gep(self.llval, self.layout.llvm_field_index(ix))
 195             };
 196             PlaceRef {
 197                 // HACK(eddyb) have to bitcast pointers until LLVM removes pointee types.
 198                 llval: bx.pointercast(llval, cx.type_ptr_to(field.llvm_type(cx))),
 199                 llextra: if cx.type_has_metadata(field.ty) {
 200                     self.llextra
 201                 } else {
 202                     None
 203                 },
 204                 layout: field,
 205                 align: effective_field_align,
 206             }
 207         };
 208
 209         // Simple cases, which don't need DST adjustment:
 210         //   * no metadata available - just log the case
 211         //   * known alignment - sized types, [T], str or a foreign type
 212         //   * packed struct - there is no alignment padding
 213         match field.ty.sty {
 214             _ if self.llextra.is_none() => {
 215                 debug!("Unsized field `{}`, of `{:?}` has no metadata for adjustment",
 216                     ix, self.llval);
 217                 return simple();
 218             }
 219             _ if !field.is_unsized() => return simple(),
 220             ty::Slice(..) | ty::Str | ty::Foreign(..) => return simple(),
 221             ty::Adt(def, _) => {
 222                 if def.repr.packed() {
 223                     // FIXME(eddyb) generalize the adjustment when we
 224                     // start supporting packing to larger alignments.
 225                     assert_eq!(self.layout.align.abi(), 1);
 226                     return simple();
 227                 }
 228             }
 229             _ => {}
 230         }
 231
 232         // We need to get the pointer manually now.
 233         // We do this by casting to a *i8, then offsetting it by the appropriate amount.
 234         // We do this instead of, say, simply adjusting the pointer from the result of a GEP
 235         // because the field may have an arbitrary alignment in the LLVM representation
 236         // anyway.
 237         //
 238         // To demonstrate:
 239         //   struct Foo<T: ?Sized> {
 240         //      x: u16,
 241         //      y: T
 242         //   }
 243         //
 244         // The type Foo<Foo<Trait>> is represented in LLVM as { u16, { u16, u8 }}, meaning that
 245         // the `y` field has 16-bit alignment.
 246
 247         let meta = self.llextra;
 248
 249         let unaligned_offset = cx.const_usize(offset.bytes());
 250
 251         // Get the alignment of the field
 252         let (_, unsized_align) = glue::size_and_align_of_dst(bx, field.ty, meta);
 253
 254         // Bump the unaligned offset up to the appropriate alignment using the
 255         // following expression:
 256         //
 257         //   (unaligned offset + (align - 1)) & -align
 258
 259         // Calculate offset
 260         let align_sub_1 = bx.sub(unsized_align, cx.const_usize(1u64));
 261         let offset = bx.and(bx.add(unaligned_offset, align_sub_1),
 262         bx.neg(unsized_align));
 263
 264         debug!("struct_field_ptr: DST field offset: {:?}", offset);
 265
 266         // Cast and adjust pointer
 267         let byte_ptr = bx.pointercast(self.llval, cx.type_i8p());
 268         let byte_ptr = bx.gep(byte_ptr, &[offset]);
 269
 270         // Finally, cast back to the type expected
 271         let ll_fty = field.llvm_type(cx);
 272         debug!("struct_field_ptr: Field type is {:?}", ll_fty);
 273
 274         PlaceRef {
 275             llval: bx.pointercast(byte_ptr, bx.cx().type_ptr_to(ll_fty)),
 276             llextra: self.llextra,
 277             layout: field,
 278             align: effective_field_align,
 279         }
 280     }
 281
 282     /// Obtain the actual discriminant of a value.
 283     pub fn codegen_get_discr(
 284         self,
 285         bx: &Builder<'a, 'll, 'tcx>,
 286         cast_to: Ty<'tcx>
 287     ) -> &'ll Value {
 288         let cast_to = bx.cx().layout_of(cast_to).immediate_llvm_type(bx.cx());
 289         if self.layout.abi.is_uninhabited() {
 290             return bx.cx().const_undef(cast_to);
 291         }
 292         match self.layout.variants {
 293             layout::Variants::Single { index } => {
 294                 let discr_val = self.layout.ty.ty_adt_def().map_or(
 295                     index.as_u32() as u128,
 296                     |def| def.discriminant_for_variant(bx.cx().tcx, index).val);
 297                 return bx.cx().const_uint_big(cast_to, discr_val);
 298             }
 299             layout::Variants::Tagged { .. } |
 300             layout::Variants::NicheFilling { .. } => {},
 301         }
 302
 303         let discr = self.project_field(bx, 0);
 304         let lldiscr = discr.load(bx).immediate();
 305         match self.layout.variants {
 306             layout::Variants::Single { .. } => bug!(),
 307             layout::Variants::Tagged { ref tag, .. } => {
 308                 let signed = match tag.value {
 309                     // We use `i1` for bytes that are always `0` or `1`,
 310                     // e.g. `#[repr(i8)] enum E { A, B }`, but we can't
 311                     // let LLVM interpret the `i1` as signed, because
 312                     // then `i1 1` (i.e. E::B) is effectively `i8 -1`.
 313                     layout::Int(_, signed) => !tag.is_bool() && signed,
 314                     _ => false
 315                 };
 316                 bx.intcast(lldiscr, cast_to, signed)
 317             }
 318             layout::Variants::NicheFilling {
 319                 dataful_variant,
 320                 ref niche_variants,
 321                 niche_start,
 322                 ..
 323             } => {
 324                 let niche_llty = discr.layout.immediate_llvm_type(bx.cx());
 325                 if niche_variants.start() == niche_variants.end() {
 326                     // FIXME(eddyb) Check the actual primitive type here.
 327                     let niche_llval = if niche_start == 0 {
 328                         // HACK(eddyb) Using `c_null` as it works on all types.
 329                         bx.cx().const_null(niche_llty)
 330                     } else {
 331                         bx.cx().const_uint_big(niche_llty, niche_start)
 332                     };
 333                     bx.select(bx.icmp(IntPredicate::IntEQ, lldiscr, niche_llval),
 334                         bx.cx().const_uint(cast_to, niche_variants.start().as_u32() as u64),
 335                         bx.cx().const_uint(cast_to, dataful_variant.as_u32() as u64))
 336                 } else {
 337                     // Rebase from niche values to discriminant values.
 338                     let delta = niche_start.wrapping_sub(niche_variants.start().as_u32() as u128);
 339                     let lldiscr = bx.sub(lldiscr, bx.cx().const_uint_big(niche_llty, delta));
 340                     let lldiscr_max =
 341                         bx.cx().const_uint(niche_llty, niche_variants.end().as_u32() as u64);
 342                     bx.select(bx.icmp(IntPredicate::IntULE, lldiscr, lldiscr_max),
 343                         bx.intcast(lldiscr, cast_to, false),
 344                         bx.cx().const_uint(cast_to, dataful_variant.as_u32() as u64))
 345                 }
 346             }
 347         }
 348     }
 349
 350     /// Set the discriminant for a new value of the given case of the given
 351     /// representation.
 352     pub fn codegen_set_discr(&self, bx: &Builder<'a, 'll, 'tcx>, variant_index: VariantIdx) {
 353         if self.layout.for_variant(bx.cx(), variant_index).abi.is_uninhabited() {
 354             return;
 355         }
 356         match self.layout.variants {
 357             layout::Variants::Single { index } => {
 358                 assert_eq!(index, variant_index);
 359             }
 360             layout::Variants::Tagged { .. } => {
 361                 let ptr = self.project_field(bx, 0);
 362                 let to = self.layout.ty.ty_adt_def().unwrap()
 363                     .discriminant_for_variant(bx.tcx(), variant_index)
 364                     .val;
 365                 bx.store(
 366                     bx.cx().const_uint_big(ptr.layout.llvm_type(bx.cx()), to),
 367                     ptr.llval,
 368                     ptr.align);
 369             }
 370             layout::Variants::NicheFilling {
 371                 dataful_variant,
 372                 ref niche_variants,
 373                 niche_start,
 374                 ..
 375             } => {
 376                 if variant_index != dataful_variant {
 377                     if bx.sess().target.target.arch == "arm" ||
 378                        bx.sess().target.target.arch == "aarch64" {
 379                         // Issue #34427: As workaround for LLVM bug on ARM,
 380                         // use memset of 0 before assigning niche value.
 381                         let fill_byte = bx.cx().const_u8(0);
 382                         let (size, align) = self.layout.size_and_align();
 383                         let size = bx.cx().const_usize(size.bytes());
 384                         bx.memset(self.llval, fill_byte, size, align, MemFlags::empty());
 385                     }
 386
 387                     let niche = self.project_field(bx, 0);
 388                     let niche_llty = niche.layout.immediate_llvm_type(bx.cx());
 389                     let niche_value = variant_index.as_u32() - niche_variants.start().as_u32();
 390                     let niche_value = (niche_value as u128)
 391                         .wrapping_add(niche_start);
 392                     // FIXME(eddyb) Check the actual primitive type here.
 393                     let niche_llval = if niche_value == 0 {
 394                         // HACK(eddyb) Using `c_null` as it works on all types.
 395                         bx.cx().const_null(niche_llty)
 396                     } else {
 397                         bx.cx().const_uint_big(niche_llty, niche_value)
 398                     };
 399                     OperandValue::Immediate(niche_llval).store(bx, niche);
 400                 }
 401             }
 402         }
 403     }
 404
 405     pub fn project_index(&self, bx: &Builder<'a, 'll, 'tcx>, llindex: &'ll Value)
 406                          -> PlaceRef<'tcx, &'ll Value> {
 407         PlaceRef {
 408             llval: bx.inbounds_gep(self.llval, &[bx.cx().const_usize(0), llindex]),
 409             llextra: None,
 410             layout: self.layout.field(bx.cx(), 0),
 411             align: self.align
 412         }
 413     }
 414
 415     pub fn project_downcast(&self, bx: &Builder<'a, 'll, 'tcx>, variant_index: VariantIdx)
 416                             -> PlaceRef<'tcx, &'ll Value> {
 417         let mut downcast = *self;
 418         downcast.layout = self.layout.for_variant(bx.cx(), variant_index);
 419
 420         // Cast to the appropriate variant struct type.
 421         let variant_ty = downcast.layout.llvm_type(bx.cx());
 422         downcast.llval = bx.pointercast(downcast.llval, bx.cx().type_ptr_to(variant_ty));
 423
 424         downcast
 425     }
 426
 427     pub fn storage_live(&self, bx: &Builder<'a, 'll, 'tcx>) {
 428         bx.lifetime_start(self.llval, self.layout.size);
 429     }
 430
 431     pub fn storage_dead(&self, bx: &Builder<'a, 'll, 'tcx>) {
 432         bx.lifetime_end(self.llval, self.layout.size);
 433     }
 434 }
 435
 436 impl FunctionCx<'a, 'll, 'tcx, &'ll Value> {
 437     pub fn codegen_place(&mut self,
 438                         bx: &Builder<'a, 'll, 'tcx>,
 439                         place: &mir::Place<'tcx>)
 440                         -> PlaceRef<'tcx, &'ll Value> {
 441         debug!("codegen_place(place={:?})", place);
 442
 443         let cx = bx.cx();
 444         let tcx = cx.tcx;
 445
 446         if let mir::Place::Local(index) = *place {
 447             match self.locals[index] {
 448                 LocalRef::Place(place) => {
 449                     return place;
 450                 }
 451                 LocalRef::UnsizedPlace(place) => {
 452                     return place.load(bx).deref(&cx);
 453                 }
 454                 LocalRef::Operand(..) => {
 455                     bug!("using operand local {:?} as place", place);
 456                 }
 457             }
 458         }
 459
 460         let result = match *place {
 461             mir::Place::Local(_) => bug!(), // handled above
 462             mir::Place::Promoted(box (index, ty)) => {
 463                 let param_env = ty::ParamEnv::reveal_all();
 464                 let cid = mir::interpret::GlobalId {
 465                     instance: self.instance,
 466                     promoted: Some(index),
 467                 };
 468                 let layout = cx.layout_of(self.monomorphize(&ty));
 469                 match bx.tcx().const_eval(param_env.and(cid)) {
 470                     Ok(val) => match val.val {
 471                         mir::interpret::ConstValue::ByRef(_, alloc, offset) => {
 472                             PlaceRef::from_const_alloc(bx, layout, alloc, offset)
 473                         }
 474                         _ => bug!("promoteds should have an allocation: {:?}", val),
 475                     },
 476                     Err(_) => {
 477                         // this is unreachable as long as runtime
 478                         // and compile-time agree on values
 479                         // With floats that won't always be true
 480                         // so we generate an abort
 481                         let fnname = bx.cx().get_intrinsic(&("llvm.trap"));
 482                         bx.call(fnname, &[], None);
 483                         let llval = bx.cx().const_undef(
 484                             bx.cx().type_ptr_to(layout.llvm_type(bx.cx()))
 485                         );
 486                         PlaceRef::new_sized(llval, layout, layout.align)
 487                     }
 488                 }
 489             }
 490             mir::Place::Static(box mir::Static { def_id, ty }) => {
 491                 let layout = cx.layout_of(self.monomorphize(&ty));
 492                 PlaceRef::new_sized(cx.get_static(def_id), layout, layout.align)
 493             },
 494             mir::Place::Projection(box mir::Projection {
 495                 ref base,
 496                 elem: mir::ProjectionElem::Deref
 497             }) => {
 498                 // Load the pointer from its location.
 499                 self.codegen_consume(bx, base).deref(bx.cx())
 500             }
 501             mir::Place::Projection(ref projection) => {
 502                 let cg_base = self.codegen_place(bx, &projection.base);
 503
 504                 match projection.elem {
 505                     mir::ProjectionElem::Deref => bug!(),
 506                     mir::ProjectionElem::Field(ref field, _) => {
 507                         cg_base.project_field(bx, field.index())
 508                     }
 509                     mir::ProjectionElem::Index(index) => {
 510                         let index = &mir::Operand::Copy(mir::Place::Local(index));
 511                         let index = self.codegen_operand(bx, index);
 512                         let llindex = index.immediate();
 513                         cg_base.project_index(bx, llindex)
 514                     }
 515                     mir::ProjectionElem::ConstantIndex { offset,
 516                                                          from_end: false,
 517                                                          min_length: _ } => {
 518                         let lloffset = bx.cx().const_usize(offset as u64);
 519                         cg_base.project_index(bx, lloffset)
 520                     }
 521                     mir::ProjectionElem::ConstantIndex { offset,
 522                                                          from_end: true,
 523                                                          min_length: _ } => {
 524                         let lloffset = bx.cx().const_usize(offset as u64);
 525                         let lllen = cg_base.len(bx.cx());
 526                         let llindex = bx.sub(lllen, lloffset);
 527                         cg_base.project_index(bx, llindex)
 528                     }
 529                     mir::ProjectionElem::Subslice { from, to } => {
 530                         let mut subslice = cg_base.project_index(bx,
 531                             bx.cx().const_usize(from as u64));
 532                         let projected_ty = PlaceTy::Ty { ty: cg_base.layout.ty }
 533                             .projection_ty(tcx, &projection.elem)
 534                             .to_ty(bx.tcx());
 535                         subslice.layout = bx.cx().layout_of(self.monomorphize(&projected_ty));
 536
 537                         if subslice.layout.is_unsized() {
 538                             subslice.llextra = Some(bx.sub(cg_base.llextra.unwrap(),
 539                                 bx.cx().const_usize((from as u64) + (to as u64))));
 540                         }
 541
 542                         // Cast the place pointer type to the new
 543                         // array or slice type (*[%_; new_len]).
 544                         subslice.llval = bx.pointercast(subslice.llval,
 545                             bx.cx().type_ptr_to(subslice.layout.llvm_type(bx.cx())));
 546
 547                         subslice
 548                     }
 549                     mir::ProjectionElem::Downcast(_, v) => {
 550                         cg_base.project_downcast(bx, v)
 551                     }
 552                 }
 553             }
 554         };
 555         debug!("codegen_place(place={:?}) => {:?}", place, result);
 556         result
 557     }
 558
 559     pub fn monomorphized_place_ty(&self, place: &mir::Place<'tcx>) -> Ty<'tcx> {
 560         let tcx = self.cx.tcx;
 561         let place_ty = place.ty(self.mir, tcx);
 562         self.monomorphize(&place_ty.to_ty(tcx))
 563     }
 564 }