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     BuilderMethods, ConstMethods, BaseTypeMethods, DerivedTypeMethods, DerivedIntrinsicMethods,
  26     StaticMethods,
  27 };
  28
  29 use super::{FunctionCx, LocalRef};
  30 use super::operand::{OperandRef, OperandValue};
  31
  32 #[derive(Copy, Clone, Debug)]
  33 pub struct PlaceRef<'tcx, V> {
  34     /// Pointer to the contents of the place
  35     pub llval: V,
  36
  37     /// This place's extra data if it is unsized, or null
  38     pub llextra: Option<V>,
  39
  40     /// Monomorphized type of this place, including variant information
  41     pub layout: TyLayout<'tcx>,
  42
  43     /// What alignment we know for this place
  44     pub align: Align,
  45 }
  46
  47 impl PlaceRef<'tcx, &'ll Value> {
  48     pub fn new_sized(
  49         llval: &'ll Value,
  50         layout: TyLayout<'tcx>,
  51         align: Align,
  52     ) -> PlaceRef<'tcx, &'ll Value> {
  53         assert!(!layout.is_unsized());
  54         PlaceRef {
  55             llval,
  56             llextra: None,
  57             layout,
  58             align
  59         }
  60     }
  61
  62     pub fn from_const_alloc(
  63         bx: &Builder<'a, 'll, 'tcx>,
  64         layout: TyLayout<'tcx>,
  65         alloc: &mir::interpret::Allocation,
  66         offset: Size,
  67     ) -> PlaceRef<'tcx, &'ll Value> {
  68         let init = const_alloc_to_llvm(bx.cx(), alloc);
  69         let base_addr = bx.cx().static_addr_of(init, layout.align, None);
  70
  71         let llval = unsafe { LLVMConstInBoundsGEP(
  72             bx.cx().static_bitcast(base_addr, bx.cx().type_i8p()),
  73             &bx.cx().const_usize(offset.bytes()),
  74             1,
  75         )};
  76         let llval = bx.cx().static_bitcast(llval, bx.cx().type_ptr_to(layout.llvm_type(bx.cx())));
  77         PlaceRef::new_sized(llval, layout, alloc.align)
  78     }
  79
  80     pub fn alloca(bx: &Builder<'a, 'll, 'tcx>, layout: TyLayout<'tcx>, name: &str)
  81                   -> PlaceRef<'tcx, &'ll Value> {
  82         debug!("alloca({:?}: {:?})", name, layout);
  83         assert!(!layout.is_unsized(), "tried to statically allocate unsized place");
  84         let tmp = bx.alloca(layout.llvm_type(bx.cx()), name, layout.align);
  85         Self::new_sized(tmp, layout, layout.align)
  86     }
  87
  88     /// Returns a place for an indirect reference to an unsized place.
  89     pub fn alloca_unsized_indirect(
  90         bx: &Builder<'a, 'll, 'tcx>,
  91         layout: TyLayout<'tcx>,
  92         name: &str,
  93     ) -> PlaceRef<'tcx, &'ll Value> {
  94         debug!("alloca_unsized_indirect({:?}: {:?})", name, layout);
  95         assert!(layout.is_unsized(), "tried to allocate indirect place for sized values");
  96         let ptr_ty = bx.cx().tcx.mk_mut_ptr(layout.ty);
  97         let ptr_layout = bx.cx().layout_of(ptr_ty);
  98         Self::alloca(bx, ptr_layout, name)
  99     }
 100
 101     pub fn len(&self, cx: &CodegenCx<'ll, 'tcx>) -> &'ll Value {
 102         if let layout::FieldPlacement::Array { count, .. } = self.layout.fields {
 103             if self.layout.is_unsized() {
 104                 assert_eq!(count, 0);
 105                 self.llextra.unwrap()
 106             } else {
 107                 cx.const_usize(count)
 108             }
 109         } else {
 110             bug!("unexpected layout `{:#?}` in PlaceRef::len", self.layout)
 111         }
 112     }
 113
 114     pub fn load(&self, bx: &Builder<'a, 'll, 'tcx>) -> OperandRef<'tcx, &'ll Value> {
 115         debug!("PlaceRef::load: {:?}", self);
 116
 117         assert_eq!(self.llextra.is_some(), self.layout.is_unsized());
 118
 119         if self.layout.is_zst() {
 120             return OperandRef::new_zst(bx.cx(), self.layout);
 121         }
 122
 123         let scalar_load_metadata = |load, scalar: &layout::Scalar| {
 124             let vr = scalar.valid_range.clone();
 125             match scalar.value {
 126                 layout::Int(..) => {
 127                     let range = scalar.valid_range_exclusive(bx.cx());
 128                     if range.start != range.end {
 129                         bx.range_metadata(load, range);
 130                     }
 131                 }
 132                 layout::Pointer if vr.start() < vr.end() && !vr.contains(&0) => {
 133                     bx.nonnull_metadata(load);
 134                 }
 135                 _ => {}
 136             }
 137         };
 138
 139         let val = if let Some(llextra) = self.llextra {
 140             OperandValue::Ref(self.llval, Some(llextra), self.align)
 141         } else if self.layout.is_llvm_immediate() {
 142             let mut const_llval = None;
 143             unsafe {
 144                 if let Some(global) = llvm::LLVMIsAGlobalVariable(self.llval) {
 145                     if llvm::LLVMIsGlobalConstant(global) == llvm::True {
 146                         const_llval = llvm::LLVMGetInitializer(global);
 147                     }
 148                 }
 149             }
 150             let llval = const_llval.unwrap_or_else(|| {
 151                 let load = bx.load(self.llval, self.align);
 152                 if let layout::Abi::Scalar(ref scalar) = self.layout.abi {
 153                     scalar_load_metadata(load, scalar);
 154                 }
 155                 load
 156             });
 157             OperandValue::Immediate(base::to_immediate(bx, llval, self.layout))
 158         } else if let layout::Abi::ScalarPair(ref a, ref b) = self.layout.abi {
 159             let load = |i, scalar: &layout::Scalar| {
 160                 let llptr = bx.struct_gep(self.llval, i as u64);
 161                 let load = bx.load(llptr, self.align);
 162                 scalar_load_metadata(load, scalar);
 163                 if scalar.is_bool() {
 164                     bx.trunc(load, bx.cx().type_i1())
 165                 } else {
 166                     load
 167                 }
 168             };
 169             OperandValue::Pair(load(0, a), load(1, b))
 170         } else {
 171             OperandValue::Ref(self.llval, None, self.align)
 172         };
 173
 174         OperandRef { val, layout: self.layout }
 175     }
 176
 177     /// Access a field, at a point when the value's case is known.
 178     pub fn project_field(
 179         self,
 180         bx: &Builder<'a, 'll, 'tcx>,
 181         ix: usize,
 182     ) -> PlaceRef<'tcx, &'ll Value> {
 183         let cx = bx.cx();
 184         let field = self.layout.field(cx, ix);
 185         let offset = self.layout.fields.offset(ix);
 186         let effective_field_align = self.align.restrict_for_offset(offset);
 187
 188         let simple = || {
 189             // Unions and newtypes only use an offset of 0.
 190             let llval = if offset.bytes() == 0 {
 191                 self.llval
 192             } else if let layout::Abi::ScalarPair(ref a, ref b) = self.layout.abi {
 193                 // Offsets have to match either first or second field.
 194                 assert_eq!(offset, a.value.size(cx).abi_align(b.value.align(cx)));
 195                 bx.struct_gep(self.llval, 1)
 196             } else {
 197                 bx.struct_gep(self.llval, self.layout.llvm_field_index(ix))
 198             };
 199             PlaceRef {
 200                 // HACK(eddyb) have to bitcast pointers until LLVM removes pointee types.
 201                 llval: bx.pointercast(llval, cx.type_ptr_to(field.llvm_type(cx))),
 202                 llextra: if cx.type_has_metadata(field.ty) {
 203                     self.llextra
 204                 } else {
 205                     None
 206                 },
 207                 layout: field,
 208                 align: effective_field_align,
 209             }
 210         };
 211
 212         // Simple cases, which don't need DST adjustment:
 213         //   * no metadata available - just log the case
 214         //   * known alignment - sized types, [T], str or a foreign type
 215         //   * packed struct - there is no alignment padding
 216         match field.ty.sty {
 217             _ if self.llextra.is_none() => {
 218                 debug!("Unsized field `{}`, of `{:?}` has no metadata for adjustment",
 219                     ix, self.llval);
 220                 return simple();
 221             }
 222             _ if !field.is_unsized() => return simple(),
 223             ty::Slice(..) | ty::Str | ty::Foreign(..) => return simple(),
 224             ty::Adt(def, _) => {
 225                 if def.repr.packed() {
 226                     // FIXME(eddyb) generalize the adjustment when we
 227                     // start supporting packing to larger alignments.
 228                     assert_eq!(self.layout.align.abi(), 1);
 229                     return simple();
 230                 }
 231             }
 232             _ => {}
 233         }
 234
 235         // We need to get the pointer manually now.
 236         // We do this by casting to a *i8, then offsetting it by the appropriate amount.
 237         // We do this instead of, say, simply adjusting the pointer from the result of a GEP
 238         // because the field may have an arbitrary alignment in the LLVM representation
 239         // anyway.
 240         //
 241         // To demonstrate:
 242         //   struct Foo<T: ?Sized> {
 243         //      x: u16,
 244         //      y: T
 245         //   }
 246         //
 247         // The type Foo<Foo<Trait>> is represented in LLVM as { u16, { u16, u8 }}, meaning that
 248         // the `y` field has 16-bit alignment.
 249
 250         let meta = self.llextra;
 251
 252         let unaligned_offset = cx.const_usize(offset.bytes());
 253
 254         // Get the alignment of the field
 255         let (_, unsized_align) = glue::size_and_align_of_dst(bx, field.ty, meta);
 256
 257         // Bump the unaligned offset up to the appropriate alignment using the
 258         // following expression:
 259         //
 260         //   (unaligned offset + (align - 1)) & -align
 261
 262         // Calculate offset
 263         let align_sub_1 = bx.sub(unsized_align, cx.const_usize(1u64));
 264         let offset = bx.and(bx.add(unaligned_offset, align_sub_1),
 265         bx.neg(unsized_align));
 266
 267         debug!("struct_field_ptr: DST field offset: {:?}", offset);
 268
 269         // Cast and adjust pointer
 270         let byte_ptr = bx.pointercast(self.llval, cx.type_i8p());
 271         let byte_ptr = bx.gep(byte_ptr, &[offset]);
 272
 273         // Finally, cast back to the type expected
 274         let ll_fty = field.llvm_type(cx);
 275         debug!("struct_field_ptr: Field type is {:?}", ll_fty);
 276
 277         PlaceRef {
 278             llval: bx.pointercast(byte_ptr, bx.cx().type_ptr_to(ll_fty)),
 279             llextra: self.llextra,
 280             layout: field,
 281             align: effective_field_align,
 282         }
 283     }
 284
 285     /// Obtain the actual discriminant of a value.
 286     pub fn codegen_get_discr(
 287         self,
 288         bx: &Builder<'a, 'll, 'tcx>,
 289         cast_to: Ty<'tcx>
 290     ) -> &'ll Value {
 291         let cast_to = bx.cx().layout_of(cast_to).immediate_llvm_type(bx.cx());
 292         if self.layout.abi.is_uninhabited() {
 293             return bx.cx().const_undef(cast_to);
 294         }
 295         match self.layout.variants {
 296             layout::Variants::Single { index } => {
 297                 let discr_val = self.layout.ty.ty_adt_def().map_or(
 298                     index.as_u32() as u128,
 299                     |def| def.discriminant_for_variant(bx.cx().tcx, index).val);
 300                 return bx.cx().const_uint_big(cast_to, discr_val);
 301             }
 302             layout::Variants::Tagged { .. } |
 303             layout::Variants::NicheFilling { .. } => {},
 304         }
 305
 306         let discr = self.project_field(bx, 0);
 307         let lldiscr = discr.load(bx).immediate();
 308         match self.layout.variants {
 309             layout::Variants::Single { .. } => bug!(),
 310             layout::Variants::Tagged { ref tag, .. } => {
 311                 let signed = match tag.value {
 312                     // We use `i1` for bytes that are always `0` or `1`,
 313                     // e.g. `#[repr(i8)] enum E { A, B }`, but we can't
 314                     // let LLVM interpret the `i1` as signed, because
 315                     // then `i1 1` (i.e. E::B) is effectively `i8 -1`.
 316                     layout::Int(_, signed) => !tag.is_bool() && signed,
 317                     _ => false
 318                 };
 319                 bx.intcast(lldiscr, cast_to, signed)
 320             }
 321             layout::Variants::NicheFilling {
 322                 dataful_variant,
 323                 ref niche_variants,
 324                 niche_start,
 325                 ..
 326             } => {
 327                 let niche_llty = discr.layout.immediate_llvm_type(bx.cx());
 328                 if niche_variants.start() == niche_variants.end() {
 329                     // FIXME(eddyb) Check the actual primitive type here.
 330                     let niche_llval = if niche_start == 0 {
 331                         // HACK(eddyb) Using `c_null` as it works on all types.
 332                         bx.cx().const_null(niche_llty)
 333                     } else {
 334                         bx.cx().const_uint_big(niche_llty, niche_start)
 335                     };
 336                     bx.select(bx.icmp(IntPredicate::IntEQ, lldiscr, niche_llval),
 337                         bx.cx().const_uint(cast_to, niche_variants.start().as_u32() as u64),
 338                         bx.cx().const_uint(cast_to, dataful_variant.as_u32() as u64))
 339                 } else {
 340                     // Rebase from niche values to discriminant values.
 341                     let delta = niche_start.wrapping_sub(niche_variants.start().as_u32() as u128);
 342                     let lldiscr = bx.sub(lldiscr, bx.cx().const_uint_big(niche_llty, delta));
 343                     let lldiscr_max =
 344                         bx.cx().const_uint(niche_llty, niche_variants.end().as_u32() as u64);
 345                     bx.select(bx.icmp(IntPredicate::IntULE, lldiscr, lldiscr_max),
 346                         bx.intcast(lldiscr, cast_to, false),
 347                         bx.cx().const_uint(cast_to, dataful_variant.as_u32() as u64))
 348                 }
 349             }
 350         }
 351     }
 352
 353     /// Set the discriminant for a new value of the given case of the given
 354     /// representation.
 355     pub fn codegen_set_discr(&self, bx: &Builder<'a, 'll, 'tcx>, variant_index: VariantIdx) {
 356         if self.layout.for_variant(bx.cx(), variant_index).abi.is_uninhabited() {
 357             return;
 358         }
 359         match self.layout.variants {
 360             layout::Variants::Single { index } => {
 361                 assert_eq!(index, variant_index);
 362             }
 363             layout::Variants::Tagged { .. } => {
 364                 let ptr = self.project_field(bx, 0);
 365                 let to = self.layout.ty.ty_adt_def().unwrap()
 366                     .discriminant_for_variant(bx.tcx(), variant_index)
 367                     .val;
 368                 bx.store(
 369                     bx.cx().const_uint_big(ptr.layout.llvm_type(bx.cx()), to),
 370                     ptr.llval,
 371                     ptr.align);
 372             }
 373             layout::Variants::NicheFilling {
 374                 dataful_variant,
 375                 ref niche_variants,
 376                 niche_start,
 377                 ..
 378             } => {
 379                 if variant_index != dataful_variant {
 380                     if bx.sess().target.target.arch == "arm" ||
 381                        bx.sess().target.target.arch == "aarch64" {
 382                         // Issue #34427: As workaround for LLVM bug on ARM,
 383                         // use memset of 0 before assigning niche value.
 384                         let fill_byte = bx.cx().const_u8(0);
 385                         let (size, align) = self.layout.size_and_align();
 386                         let size = bx.cx().const_usize(size.bytes());
 387                         bx.memset(self.llval, fill_byte, size, align, MemFlags::empty());
 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                         bx.cx().const_null(niche_llty)
 399                     } else {
 400                         bx.cx().const_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, &[bx.cx().const_usize(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, bx.cx().type_ptr_to(variant_ty));
 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 = bx.cx().const_undef(
 487                             bx.cx().type_ptr_to(layout.llvm_type(bx.cx()))
 488                         );
 489                         PlaceRef::new_sized(llval, layout, layout.align)
 490                     }
 491                 }
 492             }
 493             mir::Place::Static(box mir::Static { def_id, ty }) => {
 494                 let layout = cx.layout_of(self.monomorphize(&ty));
 495                 PlaceRef::new_sized(cx.get_static(def_id), layout, layout.align)
 496             },
 497             mir::Place::Projection(box mir::Projection {
 498                 ref base,
 499                 elem: mir::ProjectionElem::Deref
 500             }) => {
 501                 // Load the pointer from its location.
 502                 self.codegen_consume(bx, base).deref(bx.cx())
 503             }
 504             mir::Place::Projection(ref projection) => {
 505                 let cg_base = self.codegen_place(bx, &projection.base);
 506
 507                 match projection.elem {
 508                     mir::ProjectionElem::Deref => bug!(),
 509                     mir::ProjectionElem::Field(ref field, _) => {
 510                         cg_base.project_field(bx, field.index())
 511                     }
 512                     mir::ProjectionElem::Index(index) => {
 513                         let index = &mir::Operand::Copy(mir::Place::Local(index));
 514                         let index = self.codegen_operand(bx, index);
 515                         let llindex = index.immediate();
 516                         cg_base.project_index(bx, llindex)
 517                     }
 518                     mir::ProjectionElem::ConstantIndex { offset,
 519                                                          from_end: false,
 520                                                          min_length: _ } => {
 521                         let lloffset = bx.cx().const_usize(offset as u64);
 522                         cg_base.project_index(bx, lloffset)
 523                     }
 524                     mir::ProjectionElem::ConstantIndex { offset,
 525                                                          from_end: true,
 526                                                          min_length: _ } => {
 527                         let lloffset = bx.cx().const_usize(offset as u64);
 528                         let lllen = cg_base.len(bx.cx());
 529                         let llindex = bx.sub(lllen, lloffset);
 530                         cg_base.project_index(bx, llindex)
 531                     }
 532                     mir::ProjectionElem::Subslice { from, to } => {
 533                         let mut subslice = cg_base.project_index(bx,
 534                             bx.cx().const_usize(from as u64));
 535                         let projected_ty = PlaceTy::Ty { ty: cg_base.layout.ty }
 536                             .projection_ty(tcx, &projection.elem)
 537                             .to_ty(bx.tcx());
 538                         subslice.layout = bx.cx().layout_of(self.monomorphize(&projected_ty));
 539
 540                         if subslice.layout.is_unsized() {
 541                             subslice.llextra = Some(bx.sub(cg_base.llextra.unwrap(),
 542                                 bx.cx().const_usize((from as u64) + (to as u64))));
 543                         }
 544
 545                         // Cast the place pointer type to the new
 546                         // array or slice type (*[%_; new_len]).
 547                         subslice.llval = bx.pointercast(subslice.llval,
 548                             bx.cx().type_ptr_to(subslice.layout.llvm_type(bx.cx())));
 549
 550                         subslice
 551                     }
 552                     mir::ProjectionElem::Downcast(_, v) => {
 553                         cg_base.project_downcast(bx, v)
 554                     }
 555                 }
 556             }
 557         };
 558         debug!("codegen_place(place={:?}) => {:?}", place, result);
 559         result
 560     }
 561
 562     pub fn monomorphized_place_ty(&self, place: &mir::Place<'tcx>) -> Ty<'tcx> {
 563         let tcx = self.cx.tcx;
 564         let place_ty = place.ty(self.mir, tcx);
 565         self.monomorphize(&place_ty.to_ty(tcx))
 566     }
 567 }