src/librustc_codegen_ssa/mir/place.rs

   1 use rustc::ty::{self, Instance, Ty};
   2 use rustc::ty::subst::Subst;
   3 use rustc::ty::layout::{self, Align, TyLayout, LayoutOf, VariantIdx, HasTyCtxt};
   4 use rustc::mir;
   5 use rustc::mir::tcx::PlaceTy;
   6 use crate::MemFlags;
   7 use crate::common::IntPredicate;
   8 use crate::glue;
   9
  10 use crate::traits::*;
  11
  12 use super::{FunctionCx, LocalRef};
  13 use super::operand::OperandValue;
  14
  15 #[derive(Copy, Clone, Debug)]
  16 pub struct PlaceRef<'tcx, V> {
  17     /// Pointer to the contents of the place.
  18     pub llval: V,
  19
  20     /// This place's extra data if it is unsized, or null.
  21     pub llextra: Option<V>,
  22
  23     /// Monomorphized type of this place, including variant information.
  24     pub layout: TyLayout<'tcx>,
  25
  26     /// What alignment we know for this place.
  27     pub align: Align,
  28 }
  29
  30 impl<'a, 'tcx, V: CodegenObject> PlaceRef<'tcx, V> {
  31     pub fn new_sized(
  32         llval: V,
  33         layout: TyLayout<'tcx>,
  34         align: Align,
  35     ) -> PlaceRef<'tcx, V> {
  36         assert!(!layout.is_unsized());
  37         PlaceRef {
  38             llval,
  39             llextra: None,
  40             layout,
  41             align
  42         }
  43     }
  44
  45     fn new_thin_place<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
  46         bx: &mut Bx,
  47         llval: V,
  48         layout: TyLayout<'tcx>,
  49         align: Align,
  50     ) -> PlaceRef<'tcx, V> {
  51         assert!(!bx.cx().type_has_metadata(layout.ty));
  52         PlaceRef {
  53             llval,
  54             llextra: None,
  55             layout,
  56             align
  57         }
  58     }
  59
  60     pub fn alloca<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
  61         bx: &mut Bx,
  62         layout: TyLayout<'tcx>,
  63         name: &str
  64     ) -> Self {
  65         debug!("alloca({:?}: {:?})", name, layout);
  66         assert!(!layout.is_unsized(), "tried to statically allocate unsized place");
  67         let tmp = bx.alloca(bx.cx().backend_type(layout), name, layout.align.abi);
  68         Self::new_sized(tmp, layout, layout.align.abi)
  69     }
  70
  71     /// Returns a place for an indirect reference to an unsized place.
  72     pub fn alloca_unsized_indirect<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
  73         bx: &mut Bx,
  74         layout: TyLayout<'tcx>,
  75         name: &str,
  76     ) -> Self {
  77         debug!("alloca_unsized_indirect({:?}: {:?})", name, layout);
  78         assert!(layout.is_unsized(), "tried to allocate indirect place for sized values");
  79         let ptr_ty = bx.cx().tcx().mk_mut_ptr(layout.ty);
  80         let ptr_layout = bx.cx().layout_of(ptr_ty);
  81         Self::alloca(bx, ptr_layout, name)
  82     }
  83
  84     pub fn len<Cx: ConstMethods<'tcx, Value = V>>(
  85         &self,
  86         cx: &Cx
  87     ) -> V {
  88         if let layout::FieldPlacement::Array { count, .. } = self.layout.fields {
  89             if self.layout.is_unsized() {
  90                 assert_eq!(count, 0);
  91                 self.llextra.unwrap()
  92             } else {
  93                 cx.const_usize(count)
  94             }
  95         } else {
  96             bug!("unexpected layout `{:#?}` in PlaceRef::len", self.layout)
  97         }
  98     }
  99
 100 }
 101
 102 impl<'a, 'tcx, V: CodegenObject> PlaceRef<'tcx, V> {
 103     /// Access a field, at a point when the value's case is known.
 104     pub fn project_field<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
 105         self, bx: &mut Bx,
 106         ix: usize,
 107     ) -> Self {
 108         let field = self.layout.field(bx.cx(), ix);
 109         let offset = self.layout.fields.offset(ix);
 110         let effective_field_align = self.align.restrict_for_offset(offset);
 111
 112         let mut simple = || {
 113             // Unions and newtypes only use an offset of 0.
 114             let llval = if offset.bytes() == 0 {
 115                 self.llval
 116             } else if let layout::Abi::ScalarPair(ref a, ref b) = self.layout.abi {
 117                 // Offsets have to match either first or second field.
 118                 assert_eq!(offset, a.value.size(bx.cx()).align_to(b.value.align(bx.cx()).abi));
 119                 bx.struct_gep(self.llval, 1)
 120             } else {
 121                 bx.struct_gep(self.llval, bx.cx().backend_field_index(self.layout, ix))
 122             };
 123             PlaceRef {
 124                 // HACK(eddyb): have to bitcast pointers until LLVM removes pointee types.
 125                 llval: bx.pointercast(llval, bx.cx().type_ptr_to(bx.cx().backend_type(field))),
 126                 llextra: if bx.cx().type_has_metadata(field.ty) {
 127                     self.llextra
 128                 } else {
 129                     None
 130                 },
 131                 layout: field,
 132                 align: effective_field_align,
 133             }
 134         };
 135
 136         // Simple cases, which don't need DST adjustment:
 137         //   * no metadata available - just log the case
 138         //   * known alignment - sized types, `[T]`, `str` or a foreign type
 139         //   * packed struct - there is no alignment padding
 140         match field.ty.sty {
 141             _ if self.llextra.is_none() => {
 142                 debug!("unsized field `{}`, of `{:?}` has no metadata for adjustment",
 143                     ix, self.llval);
 144                 return simple();
 145             }
 146             _ if !field.is_unsized() => return simple(),
 147             ty::Slice(..) | ty::Str | ty::Foreign(..) => return simple(),
 148             ty::Adt(def, _) => {
 149                 if def.repr.packed() {
 150                     // FIXME(eddyb) generalize the adjustment when we
 151                     // start supporting packing to larger alignments.
 152                     assert_eq!(self.layout.align.abi.bytes(), 1);
 153                     return simple();
 154                 }
 155             }
 156             _ => {}
 157         }
 158
 159         // We need to get the pointer manually now.
 160         // We do this by casting to a `*i8`, then offsetting it by the appropriate amount.
 161         // We do this instead of, say, simply adjusting the pointer from the result of a GEP
 162         // because the field may have an arbitrary alignment in the LLVM representation
 163         // anyway.
 164         //
 165         // To demonstrate:
 166         //
 167         //     struct Foo<T: ?Sized> {
 168         //         x: u16,
 169         //         y: T
 170         //     }
 171         //
 172         // The type `Foo<Foo<Trait>>` is represented in LLVM as `{ u16, { u16, u8 }}`, meaning that
 173         // the `y` field has 16-bit alignment.
 174
 175         let meta = self.llextra;
 176
 177         let unaligned_offset = bx.cx().const_usize(offset.bytes());
 178
 179         // Get the alignment of the field
 180         let (_, unsized_align) = glue::size_and_align_of_dst(bx, field.ty, meta);
 181
 182         // Bump the unaligned offset up to the appropriate alignment using the
 183         // following expression:
 184         //
 185         //     (unaligned offset + (align - 1)) & -align
 186
 187         // Calculate offset.
 188         let align_sub_1 = bx.sub(unsized_align, bx.cx().const_usize(1u64));
 189         let and_lhs = bx.add(unaligned_offset, align_sub_1);
 190         let and_rhs = bx.neg(unsized_align);
 191         let offset = bx.and(and_lhs, and_rhs);
 192
 193         debug!("struct_field_ptr: DST field offset: {:?}", offset);
 194
 195         // Cast and adjust pointer.
 196         let byte_ptr = bx.pointercast(self.llval, bx.cx().type_i8p());
 197         let byte_ptr = bx.gep(byte_ptr, &[offset]);
 198
 199         // Finally, cast back to the type expected.
 200         let ll_fty = bx.cx().backend_type(field);
 201         debug!("struct_field_ptr: Field type is {:?}", ll_fty);
 202
 203         PlaceRef {
 204             llval: bx.pointercast(byte_ptr, bx.cx().type_ptr_to(ll_fty)),
 205             llextra: self.llextra,
 206             layout: field,
 207             align: effective_field_align,
 208         }
 209     }
 210
 211     /// Obtain the actual discriminant of a value.
 212     pub fn codegen_get_discr<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
 213         self,
 214         bx: &mut Bx,
 215         cast_to: Ty<'tcx>
 216     ) -> V {
 217         let cast_to = bx.cx().immediate_backend_type(bx.cx().layout_of(cast_to));
 218         if self.layout.abi.is_uninhabited() {
 219             return bx.cx().const_undef(cast_to);
 220         }
 221         let (discr_scalar, discr_kind, discr_index) = match self.layout.variants {
 222             layout::Variants::Single { index } => {
 223                 let discr_val = self.layout.ty.discriminant_for_variant(bx.cx().tcx(), index)
 224                     .map_or(index.as_u32() as u128, |discr| discr.val);
 225                 return bx.cx().const_uint_big(cast_to, discr_val);
 226             }
 227             layout::Variants::Multiple { ref discr, ref discr_kind, discr_index, .. } => {
 228                 (discr, discr_kind, discr_index)
 229             }
 230         };
 231
 232         // Read the tag/niche-encoded discriminant from memory.
 233         let encoded_discr = self.project_field(bx, discr_index);
 234         let encoded_discr = bx.load_operand(encoded_discr);
 235
 236         // Decode the discriminant (specifically if it's niche-encoded).
 237         match *discr_kind {
 238             layout::DiscriminantKind::Tag => {
 239                 let signed = match discr_scalar.value {
 240                     // We use `i1` for bytes that are always `0` or `1`,
 241                     // e.g., `#[repr(i8)] enum E { A, B }`, but we can't
 242                     // let LLVM interpret the `i1` as signed, because
 243                     // then `i1 1` (i.e., `E::B`) is effectively `i8 -1`.
 244                     layout::Int(_, signed) => !discr_scalar.is_bool() && signed,
 245                     _ => false
 246                 };
 247                 bx.intcast(encoded_discr.immediate(), cast_to, signed)
 248             }
 249             layout::DiscriminantKind::Niche {
 250                 dataful_variant,
 251                 ref niche_variants,
 252                 niche_start,
 253             } => {
 254                 // Rebase from niche values to discriminants, and check
 255                 // whether the result is in range for the niche variants.
 256                 let niche_llty = bx.cx().immediate_backend_type(encoded_discr.layout);
 257                 let encoded_discr = encoded_discr.immediate();
 258
 259                 // We first compute the "relative discriminant" (wrt `niche_variants`),
 260                 // that is, if `n = niche_variants.end() - niche_variants.start()`,
 261                 // we remap `niche_start..=niche_start + n` (which may wrap around)
 262                 // to (non-wrap-around) `0..=n`, to be able to check whether the
 263                 // discriminant corresponds to a niche variant with one comparison.
 264                 // We also can't go directly to the (variant index) discriminant
 265                 // and check that it is in the range `niche_variants`, because
 266                 // that might not fit in the same type, on top of needing an extra
 267                 // comparison (see also the comment on `let niche_discr`).
 268                 let relative_discr = if niche_start == 0 {
 269                     // Avoid subtracting `0`, which wouldn't work for pointers.
 270                     // FIXME(eddyb) check the actual primitive type here.
 271                     encoded_discr
 272                 } else {
 273                     bx.sub(encoded_discr, bx.cx().const_uint_big(niche_llty, niche_start))
 274                 };
 275                 let relative_max = niche_variants.end().as_u32() - niche_variants.start().as_u32();
 276                 let is_niche = {
 277                     let relative_max = if relative_max == 0 {
 278                         // Avoid calling `const_uint`, which wouldn't work for pointers.
 279                         // FIXME(eddyb) check the actual primitive type here.
 280                         bx.cx().const_null(niche_llty)
 281                     } else {
 282                         bx.cx().const_uint(niche_llty, relative_max as u64)
 283                     };
 284                     bx.icmp(IntPredicate::IntULE, relative_discr, relative_max)
 285                 };
 286
 287                 // NOTE(eddyb) this addition needs to be performed on the final
 288                 // type, in case the niche itself can't represent all variant
 289                 // indices (e.g. `u8` niche with more than `256` variants,
 290                 // but enough uninhabited variants so that the remaining variants
 291                 // fit in the niche).
 292                 // In other words, `niche_variants.end - niche_variants.start`
 293                 // is representable in the niche, but `niche_variants.end`
 294                 // might not be, in extreme cases.
 295                 let niche_discr = {
 296                     let relative_discr = if relative_max == 0 {
 297                         // HACK(eddyb) since we have only one niche, we know which
 298                         // one it is, and we can avoid having a dynamic value here.
 299                         bx.cx().const_uint(cast_to, 0)
 300                     } else {
 301                         bx.intcast(relative_discr, cast_to, false)
 302                     };
 303                     bx.add(
 304                         relative_discr,
 305                         bx.cx().const_uint(cast_to, niche_variants.start().as_u32() as u64),
 306                     )
 307                 };
 308
 309                 bx.select(
 310                     is_niche,
 311                     niche_discr,
 312                     bx.cx().const_uint(cast_to, dataful_variant.as_u32() as u64),
 313                 )
 314             }
 315         }
 316     }
 317
 318     /// Sets the discriminant for a new value of the given case of the given
 319     /// representation.
 320     pub fn codegen_set_discr<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
 321         &self,
 322         bx: &mut Bx,
 323         variant_index: VariantIdx
 324     ) {
 325         if self.layout.for_variant(bx.cx(), variant_index).abi.is_uninhabited() {
 326             return;
 327         }
 328         match self.layout.variants {
 329             layout::Variants::Single { index } => {
 330                 assert_eq!(index, variant_index);
 331             }
 332             layout::Variants::Multiple {
 333                 discr_kind: layout::DiscriminantKind::Tag,
 334                 discr_index,
 335                 ..
 336             } => {
 337                 let ptr = self.project_field(bx, discr_index);
 338                 let to =
 339                     self.layout.ty.discriminant_for_variant(bx.tcx(), variant_index).unwrap().val;
 340                 bx.store(
 341                     bx.cx().const_uint_big(bx.cx().backend_type(ptr.layout), to),
 342                     ptr.llval,
 343                     ptr.align);
 344             }
 345             layout::Variants::Multiple {
 346                 discr_kind: layout::DiscriminantKind::Niche {
 347                     dataful_variant,
 348                     ref niche_variants,
 349                     niche_start,
 350                 },
 351                 discr_index,
 352                 ..
 353             } => {
 354                 if variant_index != dataful_variant {
 355                     if bx.cx().sess().target.target.arch == "arm" ||
 356                        bx.cx().sess().target.target.arch == "aarch64" {
 357                         // FIXME(#34427): as workaround for LLVM bug on ARM,
 358                         // use memset of 0 before assigning niche value.
 359                         let fill_byte = bx.cx().const_u8(0);
 360                         let size = bx.cx().const_usize(self.layout.size.bytes());
 361                         bx.memset(self.llval, fill_byte, size, self.align, MemFlags::empty());
 362                     }
 363
 364                     let niche = self.project_field(bx, discr_index);
 365                     let niche_llty = bx.cx().immediate_backend_type(niche.layout);
 366                     let niche_value = variant_index.as_u32() - niche_variants.start().as_u32();
 367                     let niche_value = (niche_value as u128)
 368                         .wrapping_add(niche_start);
 369                     // FIXME(eddyb): check the actual primitive type here.
 370                     let niche_llval = if niche_value == 0 {
 371                         // HACK(eddyb): using `c_null` as it works on all types.
 372                         bx.cx().const_null(niche_llty)
 373                     } else {
 374                         bx.cx().const_uint_big(niche_llty, niche_value)
 375                     };
 376                     OperandValue::Immediate(niche_llval).store(bx, niche);
 377                 }
 378             }
 379         }
 380     }
 381
 382     pub fn project_index<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
 383         &self,
 384         bx: &mut Bx,
 385         llindex: V
 386     ) -> Self {
 387         // Statically compute the offset if we can, otherwise just use the element size,
 388         // as this will yield the lowest alignment.
 389         let layout = self.layout.field(bx, 0);
 390         let offset = if bx.is_const_integral(llindex) {
 391             layout.size.checked_mul(bx.const_to_uint(llindex), bx).unwrap_or(layout.size)
 392         } else {
 393             layout.size
 394         };
 395
 396         PlaceRef {
 397             llval: bx.inbounds_gep(self.llval, &[bx.cx().const_usize(0), llindex]),
 398             llextra: None,
 399             layout,
 400             align: self.align.restrict_for_offset(offset),
 401         }
 402     }
 403
 404     pub fn project_downcast<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
 405         &self,
 406         bx: &mut Bx,
 407         variant_index: VariantIdx
 408     ) -> Self {
 409         let mut downcast = *self;
 410         downcast.layout = self.layout.for_variant(bx.cx(), variant_index);
 411
 412         // Cast to the appropriate variant struct type.
 413         let variant_ty = bx.cx().backend_type(downcast.layout);
 414         downcast.llval = bx.pointercast(downcast.llval, bx.cx().type_ptr_to(variant_ty));
 415
 416         downcast
 417     }
 418
 419     pub fn storage_live<Bx: BuilderMethods<'a, 'tcx, Value = V>>(&self, bx: &mut Bx) {
 420         bx.lifetime_start(self.llval, self.layout.size);
 421     }
 422
 423     pub fn storage_dead<Bx: BuilderMethods<'a, 'tcx, Value = V>>(&self, bx: &mut Bx) {
 424         bx.lifetime_end(self.llval, self.layout.size);
 425     }
 426 }
 427
 428 impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
 429     pub fn codegen_place(
 430         &mut self,
 431         bx: &mut Bx,
 432         place_ref: &mir::PlaceRef<'_, 'tcx>
 433     ) -> PlaceRef<'tcx, Bx::Value> {
 434         debug!("codegen_place(place_ref={:?})", place_ref);
 435         let cx = self.cx;
 436         let tcx = self.cx.tcx();
 437
 438         let result = match &place_ref {
 439             mir::PlaceRef {
 440                 base: mir::PlaceBase::Local(index),
 441                 projection: None,
 442             } => {
 443                 match self.locals[*index] {
 444                     LocalRef::Place(place) => {
 445                         return place;
 446                     }
 447                     LocalRef::UnsizedPlace(place) => {
 448                         return bx.load_operand(place).deref(cx);
 449                     }
 450                     LocalRef::Operand(..) => {
 451                         bug!("using operand local {:?} as place", place_ref);
 452                     }
 453                 }
 454             }
 455             mir::PlaceRef {
 456                 base: mir::PlaceBase::Static(box mir::Static {
 457                     ty,
 458                     kind: mir::StaticKind::Promoted(promoted, substs),
 459                     def_id,
 460                 }),
 461                 projection: None,
 462             } => {
 463                 debug!("promoted={:?}, def_id={:?}, substs={:?}, self_substs={:?}", promoted, def_id, substs, self.instance.substs);
 464                 let param_env = ty::ParamEnv::reveal_all();
 465                 let instance = Instance::new(*def_id, substs.subst(bx.tcx(), self.instance.substs));
 466                 debug!("instance: {:?}", instance);
 467                 let cid = mir::interpret::GlobalId {
 468                     instance: instance,
 469                     promoted: Some(*promoted),
 470                 };
 471                 let mono_ty = tcx.subst_and_normalize_erasing_regions(
 472                     instance.substs,
 473                     param_env,
 474                     ty,
 475                 );
 476                 let layout = cx.layout_of(mono_ty);
 477                 match bx.tcx().const_eval(param_env.and(cid)) {
 478                     Ok(val) => match val.val {
 479                         mir::interpret::ConstValue::ByRef { alloc, offset } => {
 480                             bx.cx().from_const_alloc(layout, alloc, offset)
 481                         }
 482                         _ => bug!("promoteds should have an allocation: {:?}", val),
 483                     },
 484                     Err(_) => {
 485                         // This is unreachable as long as runtime
 486                         // and compile-time agree on values
 487                         // With floats that won't always be true,
 488                         // so we generate an abort.
 489                         bx.abort();
 490                         let llval = bx.cx().const_undef(
 491                             bx.cx().type_ptr_to(bx.cx().backend_type(layout))
 492                         );
 493                         PlaceRef::new_sized(llval, layout, layout.align.abi)
 494                     }
 495                 }
 496             }
 497             mir::PlaceRef {
 498                 base: mir::PlaceBase::Static(box mir::Static {
 499                     ty,
 500                     kind: mir::StaticKind::Static,
 501                     def_id,
 502                 }),
 503                 projection: None,
 504             } => {
 505                 // NB: The layout of a static may be unsized as is the case when working
 506                 // with a static that is an extern_type.
 507                 let layout = cx.layout_of(self.monomorphize(&ty));
 508                 let static_ = bx.get_static(*def_id);
 509                 PlaceRef::new_thin_place(bx, static_, layout, layout.align.abi)
 510             },
 511             mir::PlaceRef {
 512                 base,
 513                 projection: Some(box mir::Projection {
 514                     base: proj_base,
 515                     elem: mir::ProjectionElem::Deref,
 516                 }),
 517             } => {
 518                 // Load the pointer from its location.
 519                 self.codegen_consume(bx, &mir::PlaceRef {
 520                     base,
 521                     projection: proj_base,
 522                 }).deref(bx.cx())
 523             }
 524             mir::PlaceRef {
 525                 base,
 526                 projection: Some(projection),
 527             } => {
 528                 // FIXME turn this recursion into iteration
 529                 let cg_base = self.codegen_place(bx, &mir::PlaceRef {
 530                     base,
 531                     projection: &projection.base,
 532                 });
 533
 534                 match projection.elem {
 535                     mir::ProjectionElem::Deref => bug!(),
 536                     mir::ProjectionElem::Field(ref field, _) => {
 537                         cg_base.project_field(bx, field.index())
 538                     }
 539                     mir::ProjectionElem::Index(index) => {
 540                         let index = &mir::Operand::Copy(
 541                             mir::Place::from(index)
 542                         );
 543                         let index = self.codegen_operand(bx, index);
 544                         let llindex = index.immediate();
 545                         cg_base.project_index(bx, llindex)
 546                     }
 547                     mir::ProjectionElem::ConstantIndex { offset,
 548                                                          from_end: false,
 549                                                          min_length: _ } => {
 550                         let lloffset = bx.cx().const_usize(offset as u64);
 551                         cg_base.project_index(bx, lloffset)
 552                     }
 553                     mir::ProjectionElem::ConstantIndex { offset,
 554                                                          from_end: true,
 555                                                          min_length: _ } => {
 556                         let lloffset = bx.cx().const_usize(offset as u64);
 557                         let lllen = cg_base.len(bx.cx());
 558                         let llindex = bx.sub(lllen, lloffset);
 559                         cg_base.project_index(bx, llindex)
 560                     }
 561                     mir::ProjectionElem::Subslice { from, to } => {
 562                         let mut subslice = cg_base.project_index(bx,
 563                             bx.cx().const_usize(from as u64));
 564                         let projected_ty = PlaceTy::from_ty(cg_base.layout.ty)
 565                             .projection_ty(tcx, &projection.elem).ty;
 566                         subslice.layout = bx.cx().layout_of(self.monomorphize(&projected_ty));
 567
 568                         if subslice.layout.is_unsized() {
 569                             subslice.llextra = Some(bx.sub(cg_base.llextra.unwrap(),
 570                                 bx.cx().const_usize((from as u64) + (to as u64))));
 571                         }
 572
 573                         // Cast the place pointer type to the new
 574                         // array or slice type (`*[%_; new_len]`).
 575                         subslice.llval = bx.pointercast(subslice.llval,
 576                             bx.cx().type_ptr_to(bx.cx().backend_type(subslice.layout)));
 577
 578                         subslice
 579                     }
 580                     mir::ProjectionElem::Downcast(_, v) => {
 581                         cg_base.project_downcast(bx, v)
 582                     }
 583                 }
 584             }
 585         };
 586         debug!("codegen_place(place={:?}) => {:?}", place_ref, result);
 587         result
 588     }
 589
 590     pub fn monomorphized_place_ty(&self, place_ref: &mir::PlaceRef<'_, 'tcx>) -> Ty<'tcx> {
 591         let tcx = self.cx.tcx();
 592         let place_ty = mir::Place::ty_from(place_ref.base, place_ref.projection, self.mir, tcx);
 593         self.monomorphize(&place_ty.ty)
 594     }
 595 }