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