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;
  18 use common::{CodegenCx, C_undef, C_usize, C_u8, C_u32, C_uint, C_null, C_uint_big};
  19 use consts;
  20 use type_of::LayoutLlvmExt;
  21 use type_::Type;
  22 use value::Value;
  23 use glue;
  24 use mir::constant::const_alloc_to_llvm;
  25
  26 use traits::{IntPredicate,BuilderMethods};
  27
  28 use super::{FunctionCx, LocalRef};
  29 use super::operand::{OperandRef, OperandValue};
  30
  31 #[derive(Copy, Clone, Debug)]
  32 pub struct PlaceRef<'tcx, V> {
  33     /// Pointer to the contents of the place
  34     pub llval: V,
  35
  36     /// This place's extra data if it is unsized, or null
  37     pub llextra: Option<V>,
  38
  39     /// Monomorphized type of this place, including variant information
  40     pub layout: TyLayout<'tcx>,
  41
  42     /// What alignment we know for this place
  43     pub align: Align,
  44 }
  45
  46 impl PlaceRef<'tcx, &'ll Value> {
  47     pub fn new_sized(
  48         llval: &'ll Value,
  49         layout: TyLayout<'tcx>,
  50         align: Align,
  51     ) -> PlaceRef<'tcx, &'ll Value> {
  52         assert!(!layout.is_unsized());
  53         PlaceRef {
  54             llval,
  55             llextra: None,
  56             layout,
  57             align
  58         }
  59     }
  60
  61     pub fn from_const_alloc(
  62         bx: &Builder<'a, 'll, 'tcx>,
  63         layout: TyLayout<'tcx>,
  64         alloc: &mir::interpret::Allocation,
  65         offset: Size,
  66     ) -> PlaceRef<'tcx, &'ll Value> {
  67         let init = const_alloc_to_llvm(bx.cx, alloc);
  68         let base_addr = consts::addr_of(bx.cx, init, layout.align, None);
  69
  70         let llval = unsafe { LLVMConstInBoundsGEP(
  71             consts::bitcast(base_addr, Type::i8p(bx.cx)),
  72             &C_usize(bx.cx, offset.bytes()),
  73             1,
  74         )};
  75         let llval = consts::bitcast(llval, layout.llvm_type(bx.cx).ptr_to());
  76         PlaceRef::new_sized(llval, layout, alloc.align)
  77     }
  78
  79     pub fn alloca(bx: &Builder<'a, 'll, 'tcx>, layout: TyLayout<'tcx>, name: &str)
  80                   -> PlaceRef<'tcx, &'ll Value> {
  81         debug!("alloca({:?}: {:?})", name, layout);
  82         assert!(!layout.is_unsized(), "tried to statically allocate unsized place");
  83         let tmp = bx.alloca(layout.llvm_type(bx.cx), name, layout.align);
  84         Self::new_sized(tmp, layout, layout.align)
  85     }
  86
  87     /// Returns a place for an indirect reference to an unsized place.
  88     pub fn alloca_unsized_indirect(
  89         bx: &Builder<'a, 'll, 'tcx>,
  90         layout: TyLayout<'tcx>,
  91         name: &str,
  92     ) -> PlaceRef<'tcx, &'ll Value> {
  93         debug!("alloca_unsized_indirect({:?}: {:?})", name, layout);
  94         assert!(layout.is_unsized(), "tried to allocate indirect place for sized values");
  95         let ptr_ty = bx.cx.tcx.mk_mut_ptr(layout.ty);
  96         let ptr_layout = bx.cx.layout_of(ptr_ty);
  97         Self::alloca(bx, ptr_layout, name)
  98     }
  99
 100     pub fn len(&self, cx: &CodegenCx<'ll, 'tcx>) -> &'ll Value {
 101         if let layout::FieldPlacement::Array { count, .. } = self.layout.fields {
 102             if self.layout.is_unsized() {
 103                 assert_eq!(count, 0);
 104                 self.llextra.unwrap()
 105             } else {
 106                 C_usize(cx, count)
 107             }
 108         } else {
 109             bug!("unexpected layout `{:#?}` in PlaceRef::len", self.layout)
 110         }
 111     }
 112
 113     pub fn load(&self, bx: &Builder<'a, 'll, 'tcx>) -> OperandRef<'tcx, &'ll Value> {
 114         debug!("PlaceRef::load: {:?}", self);
 115
 116         assert_eq!(self.llextra.is_some(), self.layout.is_unsized());
 117
 118         if self.layout.is_zst() {
 119             return OperandRef::new_zst(bx.cx, self.layout);
 120         }
 121
 122         let scalar_load_metadata = |load, scalar: &layout::Scalar| {
 123             let vr = scalar.valid_range.clone();
 124             match scalar.value {
 125                 layout::Int(..) => {
 126                     let range = scalar.valid_range_exclusive(bx.cx);
 127                     if range.start != range.end {
 128                         bx.range_metadata(load, range);
 129                     }
 130                 }
 131                 layout::Pointer if vr.start() < vr.end() && !vr.contains(&0) => {
 132                     bx.nonnull_metadata(load);
 133                 }
 134                 _ => {}
 135             }
 136         };
 137
 138         let val = if let Some(llextra) = self.llextra {
 139             OperandValue::Ref(self.llval, Some(llextra), self.align)
 140         } else if self.layout.is_llvm_immediate() {
 141             let mut const_llval = None;
 142             unsafe {
 143                 if let Some(global) = llvm::LLVMIsAGlobalVariable(self.llval) {
 144                     if llvm::LLVMIsGlobalConstant(global) == llvm::True {
 145                         const_llval = llvm::LLVMGetInitializer(global);
 146                     }
 147                 }
 148             }
 149             let llval = const_llval.unwrap_or_else(|| {
 150                 let load = bx.load(self.llval, self.align);
 151                 if let layout::Abi::Scalar(ref scalar) = self.layout.abi {
 152                     scalar_load_metadata(load, scalar);
 153                 }
 154                 load
 155             });
 156             OperandValue::Immediate(base::to_immediate(bx, llval, self.layout))
 157         } else if let layout::Abi::ScalarPair(ref a, ref b) = self.layout.abi {
 158             let load = |i, scalar: &layout::Scalar| {
 159                 let llptr = bx.struct_gep(self.llval, i as u64);
 160                 let load = bx.load(llptr, self.align);
 161                 scalar_load_metadata(load, scalar);
 162                 if scalar.is_bool() {
 163                     bx.trunc(load, Type::i1(bx.cx))
 164                 } else {
 165                     load
 166                 }
 167             };
 168             OperandValue::Pair(load(0, a), load(1, b))
 169         } else {
 170             OperandValue::Ref(self.llval, None, self.align)
 171         };
 172
 173         OperandRef { val, layout: self.layout }
 174     }
 175
 176     /// Access a field, at a point when the value's case is known.
 177     pub fn project_field(
 178         self,
 179         bx: &Builder<'a, 'll, 'tcx>,
 180         ix: usize,
 181     ) -> PlaceRef<'tcx, &'ll Value> {
 182         let cx = bx.cx;
 183         let field = self.layout.field(cx, ix);
 184         let offset = self.layout.fields.offset(ix);
 185         let effective_field_align = self.align.restrict_for_offset(offset);
 186
 187         let simple = || {
 188             // Unions and newtypes only use an offset of 0.
 189             let llval = if offset.bytes() == 0 {
 190                 self.llval
 191             } else if let layout::Abi::ScalarPair(ref a, ref b) = self.layout.abi {
 192                 // Offsets have to match either first or second field.
 193                 assert_eq!(offset, a.value.size(cx).abi_align(b.value.align(cx)));
 194                 bx.struct_gep(self.llval, 1)
 195             } else {
 196                 bx.struct_gep(self.llval, self.layout.llvm_field_index(ix))
 197             };
 198             PlaceRef {
 199                 // HACK(eddyb) have to bitcast pointers until LLVM removes pointee types.
 200                 llval: bx.pointercast(llval, field.llvm_type(cx).ptr_to()),
 201                 llextra: if cx.type_has_metadata(field.ty) {
 202                     self.llextra
 203                 } else {
 204                     None
 205                 },
 206                 layout: field,
 207                 align: effective_field_align,
 208             }
 209         };
 210
 211         // Simple cases, which don't need DST adjustment:
 212         //   * no metadata available - just log the case
 213         //   * known alignment - sized types, [T], str or a foreign type
 214         //   * packed struct - there is no alignment padding
 215         match field.ty.sty {
 216             _ if self.llextra.is_none() => {
 217                 debug!("Unsized field `{}`, of `{:?}` has no metadata for adjustment",
 218                     ix, self.llval);
 219                 return simple();
 220             }
 221             _ if !field.is_unsized() => return simple(),
 222             ty::Slice(..) | ty::Str | ty::Foreign(..) => return simple(),
 223             ty::Adt(def, _) => {
 224                 if def.repr.packed() {
 225                     // FIXME(eddyb) generalize the adjustment when we
 226                     // start supporting packing to larger alignments.
 227                     assert_eq!(self.layout.align.abi(), 1);
 228                     return simple();
 229                 }
 230             }
 231             _ => {}
 232         }
 233
 234         // We need to get the pointer manually now.
 235         // We do this by casting to a *i8, then offsetting it by the appropriate amount.
 236         // We do this instead of, say, simply adjusting the pointer from the result of a GEP
 237         // because the field may have an arbitrary alignment in the LLVM representation
 238         // anyway.
 239         //
 240         // To demonstrate:
 241         //   struct Foo<T: ?Sized> {
 242         //      x: u16,
 243         //      y: T
 244         //   }
 245         //
 246         // The type Foo<Foo<Trait>> is represented in LLVM as { u16, { u16, u8 }}, meaning that
 247         // the `y` field has 16-bit alignment.
 248
 249         let meta = self.llextra;
 250
 251         let unaligned_offset = C_usize(cx, offset.bytes());
 252
 253         // Get the alignment of the field
 254         let (_, unsized_align) = glue::size_and_align_of_dst(bx, field.ty, meta);
 255
 256         // Bump the unaligned offset up to the appropriate alignment using the
 257         // following expression:
 258         //
 259         //   (unaligned offset + (align - 1)) & -align
 260
 261         // Calculate offset
 262         let align_sub_1 = bx.sub(unsized_align, C_usize(cx, 1u64));
 263         let offset = bx.and(bx.add(unaligned_offset, align_sub_1),
 264         bx.neg(unsized_align));
 265
 266         debug!("struct_field_ptr: DST field offset: {:?}", offset);
 267
 268         // Cast and adjust pointer
 269         let byte_ptr = bx.pointercast(self.llval, Type::i8p(cx));
 270         let byte_ptr = bx.gep(byte_ptr, &[offset]);
 271
 272         // Finally, cast back to the type expected
 273         let ll_fty = field.llvm_type(cx);
 274         debug!("struct_field_ptr: Field type is {:?}", ll_fty);
 275
 276         PlaceRef {
 277             llval: bx.pointercast(byte_ptr, ll_fty.ptr_to()),
 278             llextra: self.llextra,
 279             layout: field,
 280             align: effective_field_align,
 281         }
 282     }
 283
 284     /// Obtain the actual discriminant of a value.
 285     pub fn codegen_get_discr(
 286         self,
 287         bx: &Builder<'a, 'll, 'tcx, &'ll Value>,
 288         cast_to: Ty<'tcx>
 289     ) -> &'ll Value {
 290         let cast_to = bx.cx.layout_of(cast_to).immediate_llvm_type(bx.cx);
 291         if self.layout.abi.is_uninhabited() {
 292             return C_undef(cast_to);
 293         }
 294         match self.layout.variants {
 295             layout::Variants::Single { index } => {
 296                 let discr_val = self.layout.ty.ty_adt_def().map_or(
 297                     index.as_u32() as u128,
 298                     |def| def.discriminant_for_variant(bx.cx.tcx, index).val);
 299                 return C_uint_big(cast_to, discr_val);
 300             }
 301             layout::Variants::Tagged { .. } |
 302             layout::Variants::NicheFilling { .. } => {},
 303         }
 304
 305         let discr = self.project_field(bx, 0);
 306         let lldiscr = discr.load(bx).immediate();
 307         match self.layout.variants {
 308             layout::Variants::Single { .. } => bug!(),
 309             layout::Variants::Tagged { ref tag, .. } => {
 310                 let signed = match tag.value {
 311                     // We use `i1` for bytes that are always `0` or `1`,
 312                     // e.g. `#[repr(i8)] enum E { A, B }`, but we can't
 313                     // let LLVM interpret the `i1` as signed, because
 314                     // then `i1 1` (i.e. E::B) is effectively `i8 -1`.
 315                     layout::Int(_, signed) => !tag.is_bool() && signed,
 316                     _ => false
 317                 };
 318                 bx.intcast(lldiscr, cast_to, signed)
 319             }
 320             layout::Variants::NicheFilling {
 321                 dataful_variant,
 322                 ref niche_variants,
 323                 niche_start,
 324                 ..
 325             } => {
 326                 let niche_llty = discr.layout.immediate_llvm_type(bx.cx);
 327                 if niche_variants.start() == niche_variants.end() {
 328                     // FIXME(eddyb) Check the actual primitive type here.
 329                     let niche_llval = if niche_start == 0 {
 330                         // HACK(eddyb) Using `C_null` as it works on all types.
 331                         C_null(niche_llty)
 332                     } else {
 333                         C_uint_big(niche_llty, niche_start)
 334                     };
 335                     bx.select(bx.icmp(IntPredicate::IntEQ, lldiscr, niche_llval),
 336                         C_uint(cast_to, niche_variants.start().as_u32() as u64),
 337                         C_uint(cast_to, dataful_variant.as_u32() as u64))
 338                 } else {
 339                     // Rebase from niche values to discriminant values.
 340                     let delta = niche_start.wrapping_sub(niche_variants.start().as_u32() as u128);
 341                     let lldiscr = bx.sub(lldiscr, C_uint_big(niche_llty, delta));
 342                     let lldiscr_max = C_uint(niche_llty, niche_variants.end().as_u32() as u64);
 343                     bx.select(bx.icmp(IntPredicate::IntULE, lldiscr, lldiscr_max),
 344                         bx.intcast(lldiscr, cast_to, false),
 345                         C_uint(cast_to, dataful_variant.as_u32() as u64))
 346                 }
 347             }
 348         }
 349     }
 350
 351     /// Set the discriminant for a new value of the given case of the given
 352     /// representation.
 353     pub fn codegen_set_discr(&self, bx: &Builder<'a, 'll, 'tcx>, variant_index: VariantIdx) {
 354         if self.layout.for_variant(bx.cx, variant_index).abi.is_uninhabited() {
 355             return;
 356         }
 357         match self.layout.variants {
 358             layout::Variants::Single { index } => {
 359                 assert_eq!(index, variant_index);
 360             }
 361             layout::Variants::Tagged { .. } => {
 362                 let ptr = self.project_field(bx, 0);
 363                 let to = self.layout.ty.ty_adt_def().unwrap()
 364                     .discriminant_for_variant(bx.tcx(), variant_index)
 365                     .val;
 366                 bx.store(
 367                     C_uint_big(ptr.layout.llvm_type(bx.cx), to),
 368                     ptr.llval,
 369                     ptr.align);
 370             }
 371             layout::Variants::NicheFilling {
 372                 dataful_variant,
 373                 ref niche_variants,
 374                 niche_start,
 375                 ..
 376             } => {
 377                 if variant_index != dataful_variant {
 378                     if bx.sess().target.target.arch == "arm" ||
 379                        bx.sess().target.target.arch == "aarch64" {
 380                         // Issue #34427: As workaround for LLVM bug on ARM,
 381                         // use memset of 0 before assigning niche value.
 382                         let llptr = bx.pointercast(self.llval, Type::i8(bx.cx).ptr_to());
 383                         let fill_byte = C_u8(bx.cx, 0);
 384                         let (size, align) = self.layout.size_and_align();
 385                         let size = C_usize(bx.cx, size.bytes());
 386                         let align = C_u32(bx.cx, align.abi() as u32);
 387                         base::call_memset(bx, llptr, fill_byte, size, align, false);
 388                     }
 389
 390                     let niche = self.project_field(bx, 0);
 391                     let niche_llty = niche.layout.immediate_llvm_type(bx.cx);
 392                     let niche_value = variant_index.as_u32() - niche_variants.start().as_u32();
 393                     let niche_value = (niche_value as u128)
 394                         .wrapping_add(niche_start);
 395                     // FIXME(eddyb) Check the actual primitive type here.
 396                     let niche_llval = if niche_value == 0 {
 397                         // HACK(eddyb) Using `C_null` as it works on all types.
 398                         C_null(niche_llty)
 399                     } else {
 400                         C_uint_big(niche_llty, niche_value)
 401                     };
 402                     OperandValue::Immediate(niche_llval).store(bx, niche);
 403                 }
 404             }
 405         }
 406     }
 407
 408     pub fn project_index(&self, bx: &Builder<'a, 'll, 'tcx>, llindex: &'ll Value)
 409                          -> PlaceRef<'tcx, &'ll Value> {
 410         PlaceRef {
 411             llval: bx.inbounds_gep(self.llval, &[C_usize(bx.cx, 0), llindex]),
 412             llextra: None,
 413             layout: self.layout.field(bx.cx, 0),
 414             align: self.align
 415         }
 416     }
 417
 418     pub fn project_downcast(&self, bx: &Builder<'a, 'll, 'tcx>, variant_index: VariantIdx)
 419                             -> PlaceRef<'tcx, &'ll Value> {
 420         let mut downcast = *self;
 421         downcast.layout = self.layout.for_variant(bx.cx, variant_index);
 422
 423         // Cast to the appropriate variant struct type.
 424         let variant_ty = downcast.layout.llvm_type(bx.cx);
 425         downcast.llval = bx.pointercast(downcast.llval, variant_ty.ptr_to());
 426
 427         downcast
 428     }
 429
 430     pub fn storage_live(&self, bx: &Builder<'a, 'll, 'tcx>) {
 431         bx.lifetime_start(self.llval, self.layout.size);
 432     }
 433
 434     pub fn storage_dead(&self, bx: &Builder<'a, 'll, 'tcx>) {
 435         bx.lifetime_end(self.llval, self.layout.size);
 436     }
 437 }
 438
 439 impl FunctionCx<'a, 'll, 'tcx, &'ll Value> {
 440     pub fn codegen_place(&mut self,
 441                         bx: &Builder<'a, 'll, 'tcx>,
 442                         place: &mir::Place<'tcx>)
 443                         -> PlaceRef<'tcx, &'ll Value> {
 444         debug!("codegen_place(place={:?})", place);
 445
 446         let cx = bx.cx;
 447         let tcx = cx.tcx;
 448
 449         if let mir::Place::Local(index) = *place {
 450             match self.locals[index] {
 451                 LocalRef::Place(place) => {
 452                     return place;
 453                 }
 454                 LocalRef::UnsizedPlace(place) => {
 455                     return place.load(bx).deref(&cx);
 456                 }
 457                 LocalRef::Operand(..) => {
 458                     bug!("using operand local {:?} as place", place);
 459                 }
 460             }
 461         }
 462
 463         let result = match *place {
 464             mir::Place::Local(_) => bug!(), // handled above
 465             mir::Place::Promoted(box (index, ty)) => {
 466                 let param_env = ty::ParamEnv::reveal_all();
 467                 let cid = mir::interpret::GlobalId {
 468                     instance: self.instance,
 469                     promoted: Some(index),
 470                 };
 471                 let layout = cx.layout_of(self.monomorphize(&ty));
 472                 match bx.tcx().const_eval(param_env.and(cid)) {
 473                     Ok(val) => match val.val {
 474                         mir::interpret::ConstValue::ByRef(_, alloc, offset) => {
 475                             PlaceRef::from_const_alloc(bx, layout, alloc, offset)
 476                         }
 477                         _ => bug!("promoteds should have an allocation: {:?}", val),
 478                     },
 479                     Err(_) => {
 480                         // this is unreachable as long as runtime
 481                         // and compile-time agree on values
 482                         // With floats that won't always be true
 483                         // so we generate an abort
 484                         let fnname = bx.cx.get_intrinsic(&("llvm.trap"));
 485                         bx.call(fnname, &[], None);
 486                         let llval = C_undef(layout.llvm_type(bx.cx).ptr_to());
 487                         PlaceRef::new_sized(llval, layout, layout.align)
 488                     }
 489                 }
 490             }
 491             mir::Place::Static(box mir::Static { def_id, ty }) => {
 492                 let layout = cx.layout_of(self.monomorphize(&ty));
 493                 PlaceRef::new_sized(consts::get_static(cx, def_id), layout, layout.align)
 494             },
 495             mir::Place::Projection(box mir::Projection {
 496                 ref base,
 497                 elem: mir::ProjectionElem::Deref
 498             }) => {
 499                 // Load the pointer from its location.
 500                 self.codegen_consume(bx, base).deref(bx.cx)
 501             }
 502             mir::Place::Projection(ref projection) => {
 503                 let cg_base = self.codegen_place(bx, &projection.base);
 504
 505                 match projection.elem {
 506                     mir::ProjectionElem::Deref => bug!(),
 507                     mir::ProjectionElem::Field(ref field, _) => {
 508                         cg_base.project_field(bx, field.index())
 509                     }
 510                     mir::ProjectionElem::Index(index) => {
 511                         let index = &mir::Operand::Copy(mir::Place::Local(index));
 512                         let index = self.codegen_operand(bx, index);
 513                         let llindex = index.immediate();
 514                         cg_base.project_index(bx, llindex)
 515                     }
 516                     mir::ProjectionElem::ConstantIndex { offset,
 517                                                          from_end: false,
 518                                                          min_length: _ } => {
 519                         let lloffset = C_usize(bx.cx, offset as u64);
 520                         cg_base.project_index(bx, lloffset)
 521                     }
 522                     mir::ProjectionElem::ConstantIndex { offset,
 523                                                          from_end: true,
 524                                                          min_length: _ } => {
 525                         let lloffset = C_usize(bx.cx, offset as u64);
 526                         let lllen = cg_base.len(bx.cx);
 527                         let llindex = bx.sub(lllen, lloffset);
 528                         cg_base.project_index(bx, llindex)
 529                     }
 530                     mir::ProjectionElem::Subslice { from, to } => {
 531                         let mut subslice = cg_base.project_index(bx,
 532                             C_usize(bx.cx, from as u64));
 533                         let projected_ty = PlaceTy::Ty { ty: cg_base.layout.ty }
 534                             .projection_ty(tcx, &projection.elem)
 535                             .to_ty(bx.tcx());
 536                         subslice.layout = bx.cx.layout_of(self.monomorphize(&projected_ty));
 537
 538                         if subslice.layout.is_unsized() {
 539                             subslice.llextra = Some(bx.sub(cg_base.llextra.unwrap(),
 540                                 C_usize(bx.cx, (from as u64) + (to as u64))));
 541                         }
 542
 543                         // Cast the place pointer type to the new
 544                         // array or slice type (*[%_; new_len]).
 545                         subslice.llval = bx.pointercast(subslice.llval,
 546                             subslice.layout.llvm_type(bx.cx).ptr_to());
 547
 548                         subslice
 549                     }
 550                     mir::ProjectionElem::Downcast(_, v) => {
 551                         cg_base.project_downcast(bx, v)
 552                     }
 553                 }
 554             }
 555         };
 556         debug!("codegen_place(place={:?}) => {:?}", place, result);
 557         result
 558     }
 559
 560     pub fn monomorphized_place_ty(&self, place: &mir::Place<'tcx>) -> Ty<'tcx> {
 561         let tcx = self.cx.tcx;
 562         let place_ty = place.ty(self.mir, tcx);
 563         self.monomorphize(&place_ty.to_ty(tcx))
 564     }
 565 }