src/librustc_codegen_ssa/mir/rvalue.rs

   1 use super::operand::{OperandRef, OperandValue};
   2 use super::place::PlaceRef;
   3 use super::{FunctionCx, LocalRef};
   4
   5 use crate::base;
   6 use crate::common::{self, IntPredicate, RealPredicate};
   7 use crate::traits::*;
   8 use crate::MemFlags;
   9
  10 use rustc_apfloat::{ieee, Float, Round, Status};
  11 use rustc_hir::lang_items::ExchangeMallocFnLangItem;
  12 use rustc_middle::mir;
  13 use rustc_middle::ty::cast::{CastTy, IntTy};
  14 use rustc_middle::ty::layout::HasTyCtxt;
  15 use rustc_middle::ty::{self, adjustment::PointerCast, Instance, Ty, TyCtxt};
  16 use rustc_span::source_map::{Span, DUMMY_SP};
  17 use rustc_span::symbol::sym;
  18 use rustc_target::abi::{Abi, Int, LayoutOf, Variants};
  19
  20 impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
  21     pub fn codegen_rvalue(
  22         &mut self,
  23         mut bx: Bx,
  24         dest: PlaceRef<'tcx, Bx::Value>,
  25         rvalue: &mir::Rvalue<'tcx>,
  26     ) -> Bx {
  27         debug!("codegen_rvalue(dest.llval={:?}, rvalue={:?})", dest.llval, rvalue);
  28
  29         match *rvalue {
  30             mir::Rvalue::Use(ref operand) => {
  31                 let cg_operand = self.codegen_operand(&mut bx, operand);
  32                 // FIXME: consider not copying constants through stack. (Fixable by codegen'ing
  33                 // constants into `OperandValue::Ref`; why don’t we do that yet if we don’t?)
  34                 cg_operand.val.store(&mut bx, dest);
  35                 bx
  36             }
  37
  38             mir::Rvalue::Cast(mir::CastKind::Pointer(PointerCast::Unsize), ref source, _) => {
  39                 // The destination necessarily contains a fat pointer, so if
  40                 // it's a scalar pair, it's a fat pointer or newtype thereof.
  41                 if bx.cx().is_backend_scalar_pair(dest.layout) {
  42                     // Into-coerce of a thin pointer to a fat pointer -- just
  43                     // use the operand path.
  44                     let (mut bx, temp) = self.codegen_rvalue_operand(bx, rvalue);
  45                     temp.val.store(&mut bx, dest);
  46                     return bx;
  47                 }
  48
  49                 // Unsize of a nontrivial struct. I would prefer for
  50                 // this to be eliminated by MIR building, but
  51                 // `CoerceUnsized` can be passed by a where-clause,
  52                 // so the (generic) MIR may not be able to expand it.
  53                 let operand = self.codegen_operand(&mut bx, source);
  54                 match operand.val {
  55                     OperandValue::Pair(..) | OperandValue::Immediate(_) => {
  56                         // Unsize from an immediate structure. We don't
  57                         // really need a temporary alloca here, but
  58                         // avoiding it would require us to have
  59                         // `coerce_unsized_into` use `extractvalue` to
  60                         // index into the struct, and this case isn't
  61                         // important enough for it.
  62                         debug!("codegen_rvalue: creating ugly alloca");
  63                         let scratch = PlaceRef::alloca(&mut bx, operand.layout);
  64                         scratch.storage_live(&mut bx);
  65                         operand.val.store(&mut bx, scratch);
  66                         base::coerce_unsized_into(&mut bx, scratch, dest);
  67                         scratch.storage_dead(&mut bx);
  68                     }
  69                     OperandValue::Ref(llref, None, align) => {
  70                         let source = PlaceRef::new_sized_aligned(llref, operand.layout, align);
  71                         base::coerce_unsized_into(&mut bx, source, dest);
  72                     }
  73                     OperandValue::Ref(_, Some(_), _) => {
  74                         bug!("unsized coercion on an unsized rvalue");
  75                     }
  76                 }
  77                 bx
  78             }
  79
  80             mir::Rvalue::Repeat(ref elem, count) => {
  81                 let cg_elem = self.codegen_operand(&mut bx, elem);
  82
  83                 // Do not generate the loop for zero-sized elements or empty arrays.
  84                 if dest.layout.is_zst() {
  85                     return bx;
  86                 }
  87
  88                 if let OperandValue::Immediate(v) = cg_elem.val {
  89                     let zero = bx.const_usize(0);
  90                     let start = dest.project_index(&mut bx, zero).llval;
  91                     let size = bx.const_usize(dest.layout.size.bytes());
  92
  93                     // Use llvm.memset.p0i8.* to initialize all zero arrays
  94                     if bx.cx().const_to_opt_uint(v) == Some(0) {
  95                         let fill = bx.cx().const_u8(0);
  96                         bx.memset(start, fill, size, dest.align, MemFlags::empty());
  97                         return bx;
  98                     }
  99
 100                     // Use llvm.memset.p0i8.* to initialize byte arrays
 101                     let v = base::from_immediate(&mut bx, v);
 102                     if bx.cx().val_ty(v) == bx.cx().type_i8() {
 103                         bx.memset(start, v, size, dest.align, MemFlags::empty());
 104                         return bx;
 105                     }
 106                 }
 107
 108                 let count =
 109                     self.monomorphize(&count).eval_usize(bx.cx().tcx(), ty::ParamEnv::reveal_all());
 110
 111                 bx.write_operand_repeatedly(cg_elem, count, dest)
 112             }
 113
 114             mir::Rvalue::Aggregate(ref kind, ref operands) => {
 115                 let (dest, active_field_index) = match **kind {
 116                     mir::AggregateKind::Adt(adt_def, variant_index, _, _, active_field_index) => {
 117                         dest.codegen_set_discr(&mut bx, variant_index);
 118                         if adt_def.is_enum() {
 119                             (dest.project_downcast(&mut bx, variant_index), active_field_index)
 120                         } else {
 121                             (dest, active_field_index)
 122                         }
 123                     }
 124                     _ => (dest, None),
 125                 };
 126                 for (i, operand) in operands.iter().enumerate() {
 127                     let op = self.codegen_operand(&mut bx, operand);
 128                     // Do not generate stores and GEPis for zero-sized fields.
 129                     if !op.layout.is_zst() {
 130                         let field_index = active_field_index.unwrap_or(i);
 131                         let field = dest.project_field(&mut bx, field_index);
 132                         op.val.store(&mut bx, field);
 133                     }
 134                 }
 135                 bx
 136             }
 137
 138             _ => {
 139                 assert!(self.rvalue_creates_operand(rvalue, DUMMY_SP));
 140                 let (mut bx, temp) = self.codegen_rvalue_operand(bx, rvalue);
 141                 temp.val.store(&mut bx, dest);
 142                 bx
 143             }
 144         }
 145     }
 146
 147     pub fn codegen_rvalue_unsized(
 148         &mut self,
 149         mut bx: Bx,
 150         indirect_dest: PlaceRef<'tcx, Bx::Value>,
 151         rvalue: &mir::Rvalue<'tcx>,
 152     ) -> Bx {
 153         debug!(
 154             "codegen_rvalue_unsized(indirect_dest.llval={:?}, rvalue={:?})",
 155             indirect_dest.llval, rvalue
 156         );
 157
 158         match *rvalue {
 159             mir::Rvalue::Use(ref operand) => {
 160                 let cg_operand = self.codegen_operand(&mut bx, operand);
 161                 cg_operand.val.store_unsized(&mut bx, indirect_dest);
 162                 bx
 163             }
 164
 165             _ => bug!("unsized assignment other than `Rvalue::Use`"),
 166         }
 167     }
 168
 169     pub fn codegen_rvalue_operand(
 170         &mut self,
 171         mut bx: Bx,
 172         rvalue: &mir::Rvalue<'tcx>,
 173     ) -> (Bx, OperandRef<'tcx, Bx::Value>) {
 174         assert!(
 175             self.rvalue_creates_operand(rvalue, DUMMY_SP),
 176             "cannot codegen {:?} to operand",
 177             rvalue,
 178         );
 179
 180         match *rvalue {
 181             mir::Rvalue::Cast(ref kind, ref source, mir_cast_ty) => {
 182                 let operand = self.codegen_operand(&mut bx, source);
 183                 debug!("cast operand is {:?}", operand);
 184                 let cast = bx.cx().layout_of(self.monomorphize(&mir_cast_ty));
 185
 186                 let val = match *kind {
 187                     mir::CastKind::Pointer(PointerCast::ReifyFnPointer) => {
 188                         match operand.layout.ty.kind {
 189                             ty::FnDef(def_id, substs) => {
 190                                 if bx.cx().tcx().has_attr(def_id, sym::rustc_args_required_const) {
 191                                     bug!("reifying a fn ptr that requires const arguments");
 192                                 }
 193                                 OperandValue::Immediate(
 194                                     bx.get_fn_addr(
 195                                         ty::Instance::resolve_for_fn_ptr(
 196                                             bx.tcx(),
 197                                             ty::ParamEnv::reveal_all(),
 198                                             def_id,
 199                                             substs,
 200                                         )
 201                                         .unwrap(),
 202                                     ),
 203                                 )
 204                             }
 205                             _ => bug!("{} cannot be reified to a fn ptr", operand.layout.ty),
 206                         }
 207                     }
 208                     mir::CastKind::Pointer(PointerCast::ClosureFnPointer(_)) => {
 209                         match operand.layout.ty.kind {
 210                             ty::Closure(def_id, substs) => {
 211                                 let instance = Instance::resolve_closure(
 212                                     bx.cx().tcx(),
 213                                     def_id,
 214                                     substs,
 215                                     ty::ClosureKind::FnOnce,
 216                                 );
 217                                 OperandValue::Immediate(bx.cx().get_fn_addr(instance))
 218                             }
 219                             _ => bug!("{} cannot be cast to a fn ptr", operand.layout.ty),
 220                         }
 221                     }
 222                     mir::CastKind::Pointer(PointerCast::UnsafeFnPointer) => {
 223                         // This is a no-op at the LLVM level.
 224                         operand.val
 225                     }
 226                     mir::CastKind::Pointer(PointerCast::Unsize) => {
 227                         assert!(bx.cx().is_backend_scalar_pair(cast));
 228                         match operand.val {
 229                             OperandValue::Pair(lldata, llextra) => {
 230                                 // unsize from a fat pointer -- this is a
 231                                 // "trait-object-to-supertrait" coercion, for
 232                                 // example, `&'a fmt::Debug + Send => &'a fmt::Debug`.
 233
 234                                 // HACK(eddyb) have to bitcast pointers
 235                                 // until LLVM removes pointee types.
 236                                 let lldata = bx.pointercast(
 237                                     lldata,
 238                                     bx.cx().scalar_pair_element_backend_type(cast, 0, true),
 239                                 );
 240                                 OperandValue::Pair(lldata, llextra)
 241                             }
 242                             OperandValue::Immediate(lldata) => {
 243                                 // "standard" unsize
 244                                 let (lldata, llextra) = base::unsize_thin_ptr(
 245                                     &mut bx,
 246                                     lldata,
 247                                     operand.layout.ty,
 248                                     cast.ty,
 249                                 );
 250                                 OperandValue::Pair(lldata, llextra)
 251                             }
 252                             OperandValue::Ref(..) => {
 253                                 bug!("by-ref operand {:?} in `codegen_rvalue_operand`", operand);
 254                             }
 255                         }
 256                     }
 257                     mir::CastKind::Pointer(PointerCast::MutToConstPointer)
 258                     | mir::CastKind::Misc
 259                         if bx.cx().is_backend_scalar_pair(operand.layout) =>
 260                     {
 261                         if let OperandValue::Pair(data_ptr, meta) = operand.val {
 262                             if bx.cx().is_backend_scalar_pair(cast) {
 263                                 let data_cast = bx.pointercast(
 264                                     data_ptr,
 265                                     bx.cx().scalar_pair_element_backend_type(cast, 0, true),
 266                                 );
 267                                 OperandValue::Pair(data_cast, meta)
 268                             } else {
 269                                 // cast to thin-ptr
 270                                 // Cast of fat-ptr to thin-ptr is an extraction of data-ptr and
 271                                 // pointer-cast of that pointer to desired pointer type.
 272                                 let llcast_ty = bx.cx().immediate_backend_type(cast);
 273                                 let llval = bx.pointercast(data_ptr, llcast_ty);
 274                                 OperandValue::Immediate(llval)
 275                             }
 276                         } else {
 277                             bug!("unexpected non-pair operand");
 278                         }
 279                     }
 280                     mir::CastKind::Pointer(
 281                         PointerCast::MutToConstPointer | PointerCast::ArrayToPointer,
 282                     )
 283                     | mir::CastKind::Misc => {
 284                         assert!(bx.cx().is_backend_immediate(cast));
 285                         let ll_t_out = bx.cx().immediate_backend_type(cast);
 286                         if operand.layout.abi.is_uninhabited() {
 287                             let val = OperandValue::Immediate(bx.cx().const_undef(ll_t_out));
 288                             return (bx, OperandRef { val, layout: cast });
 289                         }
 290                         let r_t_in =
 291                             CastTy::from_ty(operand.layout.ty).expect("bad input type for cast");
 292                         let r_t_out = CastTy::from_ty(cast.ty).expect("bad output type for cast");
 293                         let ll_t_in = bx.cx().immediate_backend_type(operand.layout);
 294                         match operand.layout.variants {
 295                             Variants::Single { index } => {
 296                                 if let Some(discr) =
 297                                     operand.layout.ty.discriminant_for_variant(bx.tcx(), index)
 298                                 {
 299                                     let discr_layout = bx.cx().layout_of(discr.ty);
 300                                     let discr_t = bx.cx().immediate_backend_type(discr_layout);
 301                                     let discr_val = bx.cx().const_uint_big(discr_t, discr.val);
 302                                     let discr_val =
 303                                         bx.intcast(discr_val, ll_t_out, discr.ty.is_signed());
 304
 305                                     return (
 306                                         bx,
 307                                         OperandRef {
 308                                             val: OperandValue::Immediate(discr_val),
 309                                             layout: cast,
 310                                         },
 311                                     );
 312                                 }
 313                             }
 314                             Variants::Multiple { .. } => {}
 315                         }
 316                         let llval = operand.immediate();
 317
 318                         let mut signed = false;
 319                         if let Abi::Scalar(ref scalar) = operand.layout.abi {
 320                             if let Int(_, s) = scalar.value {
 321                                 // We use `i1` for bytes that are always `0` or `1`,
 322                                 // e.g., `#[repr(i8)] enum E { A, B }`, but we can't
 323                                 // let LLVM interpret the `i1` as signed, because
 324                                 // then `i1 1` (i.e., E::B) is effectively `i8 -1`.
 325                                 signed = !scalar.is_bool() && s;
 326
 327                                 let er = scalar.valid_range_exclusive(bx.cx());
 328                                 if er.end != er.start
 329                                     && scalar.valid_range.end() > scalar.valid_range.start()
 330                                 {
 331                                     // We want `table[e as usize]` to not
 332                                     // have bound checks, and this is the most
 333                                     // convenient place to put the `assume`.
 334                                     let ll_t_in_const =
 335                                         bx.cx().const_uint_big(ll_t_in, *scalar.valid_range.end());
 336                                     let cmp = bx.icmp(IntPredicate::IntULE, llval, ll_t_in_const);
 337                                     bx.assume(cmp);
 338                                 }
 339                             }
 340                         }
 341
 342                         let newval = match (r_t_in, r_t_out) {
 343                             (CastTy::Int(_), CastTy::Int(_)) => bx.intcast(llval, ll_t_out, signed),
 344                             (CastTy::Float, CastTy::Float) => {
 345                                 let srcsz = bx.cx().float_width(ll_t_in);
 346                                 let dstsz = bx.cx().float_width(ll_t_out);
 347                                 if dstsz > srcsz {
 348                                     bx.fpext(llval, ll_t_out)
 349                                 } else if srcsz > dstsz {
 350                                     bx.fptrunc(llval, ll_t_out)
 351                                 } else {
 352                                     llval
 353                                 }
 354                             }
 355                             (CastTy::Int(_), CastTy::Float) => {
 356                                 if signed {
 357                                     bx.sitofp(llval, ll_t_out)
 358                                 } else {
 359                                     bx.uitofp(llval, ll_t_out)
 360                                 }
 361                             }
 362                             (CastTy::Ptr(_) | CastTy::FnPtr, CastTy::Ptr(_)) => {
 363                                 bx.pointercast(llval, ll_t_out)
 364                             }
 365                             (CastTy::Ptr(_) | CastTy::FnPtr, CastTy::Int(_)) => {
 366                                 bx.ptrtoint(llval, ll_t_out)
 367                             }
 368                             (CastTy::Int(_), CastTy::Ptr(_)) => {
 369                                 let usize_llval = bx.intcast(llval, bx.cx().type_isize(), signed);
 370                                 bx.inttoptr(usize_llval, ll_t_out)
 371                             }
 372                             (CastTy::Float, CastTy::Int(IntTy::I)) => {
 373                                 cast_float_to_int(&mut bx, true, llval, ll_t_in, ll_t_out)
 374                             }
 375                             (CastTy::Float, CastTy::Int(_)) => {
 376                                 cast_float_to_int(&mut bx, false, llval, ll_t_in, ll_t_out)
 377                             }
 378                             _ => bug!("unsupported cast: {:?} to {:?}", operand.layout.ty, cast.ty),
 379                         };
 380                         OperandValue::Immediate(newval)
 381                     }
 382                 };
 383                 (bx, OperandRef { val, layout: cast })
 384             }
 385
 386             mir::Rvalue::Ref(_, bk, place) => {
 387                 let mk_ref = move |tcx: TyCtxt<'tcx>, ty: Ty<'tcx>| {
 388                     tcx.mk_ref(
 389                         tcx.lifetimes.re_erased,
 390                         ty::TypeAndMut { ty, mutbl: bk.to_mutbl_lossy() },
 391                     )
 392                 };
 393                 self.codegen_place_to_pointer(bx, place, mk_ref)
 394             }
 395
 396             mir::Rvalue::AddressOf(mutability, place) => {
 397                 let mk_ptr = move |tcx: TyCtxt<'tcx>, ty: Ty<'tcx>| {
 398                     tcx.mk_ptr(ty::TypeAndMut { ty, mutbl: mutability })
 399                 };
 400                 self.codegen_place_to_pointer(bx, place, mk_ptr)
 401             }
 402
 403             mir::Rvalue::Len(place) => {
 404                 let size = self.evaluate_array_len(&mut bx, place);
 405                 let operand = OperandRef {
 406                     val: OperandValue::Immediate(size),
 407                     layout: bx.cx().layout_of(bx.tcx().types.usize),
 408                 };
 409                 (bx, operand)
 410             }
 411
 412             mir::Rvalue::BinaryOp(op, ref lhs, ref rhs) => {
 413                 let lhs = self.codegen_operand(&mut bx, lhs);
 414                 let rhs = self.codegen_operand(&mut bx, rhs);
 415                 let llresult = match (lhs.val, rhs.val) {
 416                     (
 417                         OperandValue::Pair(lhs_addr, lhs_extra),
 418                         OperandValue::Pair(rhs_addr, rhs_extra),
 419                     ) => self.codegen_fat_ptr_binop(
 420                         &mut bx,
 421                         op,
 422                         lhs_addr,
 423                         lhs_extra,
 424                         rhs_addr,
 425                         rhs_extra,
 426                         lhs.layout.ty,
 427                     ),
 428
 429                     (OperandValue::Immediate(lhs_val), OperandValue::Immediate(rhs_val)) => {
 430                         self.codegen_scalar_binop(&mut bx, op, lhs_val, rhs_val, lhs.layout.ty)
 431                     }
 432
 433                     _ => bug!(),
 434                 };
 435                 let operand = OperandRef {
 436                     val: OperandValue::Immediate(llresult),
 437                     layout: bx.cx().layout_of(op.ty(bx.tcx(), lhs.layout.ty, rhs.layout.ty)),
 438                 };
 439                 (bx, operand)
 440             }
 441             mir::Rvalue::CheckedBinaryOp(op, ref lhs, ref rhs) => {
 442                 let lhs = self.codegen_operand(&mut bx, lhs);
 443                 let rhs = self.codegen_operand(&mut bx, rhs);
 444                 let result = self.codegen_scalar_checked_binop(
 445                     &mut bx,
 446                     op,
 447                     lhs.immediate(),
 448                     rhs.immediate(),
 449                     lhs.layout.ty,
 450                 );
 451                 let val_ty = op.ty(bx.tcx(), lhs.layout.ty, rhs.layout.ty);
 452                 let operand_ty = bx.tcx().intern_tup(&[val_ty, bx.tcx().types.bool]);
 453                 let operand = OperandRef { val: result, layout: bx.cx().layout_of(operand_ty) };
 454
 455                 (bx, operand)
 456             }
 457
 458             mir::Rvalue::UnaryOp(op, ref operand) => {
 459                 let operand = self.codegen_operand(&mut bx, operand);
 460                 let lloperand = operand.immediate();
 461                 let is_float = operand.layout.ty.is_floating_point();
 462                 let llval = match op {
 463                     mir::UnOp::Not => bx.not(lloperand),
 464                     mir::UnOp::Neg => {
 465                         if is_float {
 466                             bx.fneg(lloperand)
 467                         } else {
 468                             bx.neg(lloperand)
 469                         }
 470                     }
 471                 };
 472                 (bx, OperandRef { val: OperandValue::Immediate(llval), layout: operand.layout })
 473             }
 474
 475             mir::Rvalue::Discriminant(ref place) => {
 476                 let discr_ty = rvalue.ty(*self.mir, bx.tcx());
 477                 let discr = self
 478                     .codegen_place(&mut bx, place.as_ref())
 479                     .codegen_get_discr(&mut bx, discr_ty);
 480                 (
 481                     bx,
 482                     OperandRef {
 483                         val: OperandValue::Immediate(discr),
 484                         layout: self.cx.layout_of(discr_ty),
 485                     },
 486                 )
 487             }
 488
 489             mir::Rvalue::NullaryOp(mir::NullOp::SizeOf, ty) => {
 490                 assert!(bx.cx().type_is_sized(ty));
 491                 let val = bx.cx().const_usize(bx.cx().layout_of(ty).size.bytes());
 492                 let tcx = self.cx.tcx();
 493                 (
 494                     bx,
 495                     OperandRef {
 496                         val: OperandValue::Immediate(val),
 497                         layout: self.cx.layout_of(tcx.types.usize),
 498                     },
 499                 )
 500             }
 501
 502             mir::Rvalue::NullaryOp(mir::NullOp::Box, content_ty) => {
 503                 let content_ty = self.monomorphize(&content_ty);
 504                 let content_layout = bx.cx().layout_of(content_ty);
 505                 let llsize = bx.cx().const_usize(content_layout.size.bytes());
 506                 let llalign = bx.cx().const_usize(content_layout.align.abi.bytes());
 507                 let box_layout = bx.cx().layout_of(bx.tcx().mk_box(content_ty));
 508                 let llty_ptr = bx.cx().backend_type(box_layout);
 509
 510                 // Allocate space:
 511                 let def_id = match bx.tcx().lang_items().require(ExchangeMallocFnLangItem) {
 512                     Ok(id) => id,
 513                     Err(s) => {
 514                         bx.cx().sess().fatal(&format!("allocation of `{}` {}", box_layout.ty, s));
 515                     }
 516                 };
 517                 let instance = ty::Instance::mono(bx.tcx(), def_id);
 518                 let r = bx.cx().get_fn_addr(instance);
 519                 let call = bx.call(r, &[llsize, llalign], None);
 520                 let val = bx.pointercast(call, llty_ptr);
 521
 522                 let operand = OperandRef { val: OperandValue::Immediate(val), layout: box_layout };
 523                 (bx, operand)
 524             }
 525             mir::Rvalue::Use(ref operand) => {
 526                 let operand = self.codegen_operand(&mut bx, operand);
 527                 (bx, operand)
 528             }
 529             mir::Rvalue::Repeat(..) | mir::Rvalue::Aggregate(..) => {
 530                 // According to `rvalue_creates_operand`, only ZST
 531                 // aggregate rvalues are allowed to be operands.
 532                 let ty = rvalue.ty(*self.mir, self.cx.tcx());
 533                 let operand =
 534                     OperandRef::new_zst(&mut bx, self.cx.layout_of(self.monomorphize(&ty)));
 535                 (bx, operand)
 536             }
 537         }
 538     }
 539
 540     fn evaluate_array_len(&mut self, bx: &mut Bx, place: mir::Place<'tcx>) -> Bx::Value {
 541         // ZST are passed as operands and require special handling
 542         // because codegen_place() panics if Local is operand.
 543         if let Some(index) = place.as_local() {
 544             if let LocalRef::Operand(Some(op)) = self.locals[index] {
 545                 if let ty::Array(_, n) = op.layout.ty.kind {
 546                     let n = n.eval_usize(bx.cx().tcx(), ty::ParamEnv::reveal_all());
 547                     return bx.cx().const_usize(n);
 548                 }
 549             }
 550         }
 551         // use common size calculation for non zero-sized types
 552         let cg_value = self.codegen_place(bx, place.as_ref());
 553         cg_value.len(bx.cx())
 554     }
 555
 556     /// Codegen an `Rvalue::AddressOf` or `Rvalue::Ref`
 557     fn codegen_place_to_pointer(
 558         &mut self,
 559         mut bx: Bx,
 560         place: mir::Place<'tcx>,
 561         mk_ptr_ty: impl FnOnce(TyCtxt<'tcx>, Ty<'tcx>) -> Ty<'tcx>,
 562     ) -> (Bx, OperandRef<'tcx, Bx::Value>) {
 563         let cg_place = self.codegen_place(&mut bx, place.as_ref());
 564
 565         let ty = cg_place.layout.ty;
 566
 567         // Note: places are indirect, so storing the `llval` into the
 568         // destination effectively creates a reference.
 569         let val = if !bx.cx().type_has_metadata(ty) {
 570             OperandValue::Immediate(cg_place.llval)
 571         } else {
 572             OperandValue::Pair(cg_place.llval, cg_place.llextra.unwrap())
 573         };
 574         (bx, OperandRef { val, layout: self.cx.layout_of(mk_ptr_ty(self.cx.tcx(), ty)) })
 575     }
 576
 577     pub fn codegen_scalar_binop(
 578         &mut self,
 579         bx: &mut Bx,
 580         op: mir::BinOp,
 581         lhs: Bx::Value,
 582         rhs: Bx::Value,
 583         input_ty: Ty<'tcx>,
 584     ) -> Bx::Value {
 585         let is_float = input_ty.is_floating_point();
 586         let is_signed = input_ty.is_signed();
 587         match op {
 588             mir::BinOp::Add => {
 589                 if is_float {
 590                     bx.fadd(lhs, rhs)
 591                 } else {
 592                     bx.add(lhs, rhs)
 593                 }
 594             }
 595             mir::BinOp::Sub => {
 596                 if is_float {
 597                     bx.fsub(lhs, rhs)
 598                 } else {
 599                     bx.sub(lhs, rhs)
 600                 }
 601             }
 602             mir::BinOp::Mul => {
 603                 if is_float {
 604                     bx.fmul(lhs, rhs)
 605                 } else {
 606                     bx.mul(lhs, rhs)
 607                 }
 608             }
 609             mir::BinOp::Div => {
 610                 if is_float {
 611                     bx.fdiv(lhs, rhs)
 612                 } else if is_signed {
 613                     bx.sdiv(lhs, rhs)
 614                 } else {
 615                     bx.udiv(lhs, rhs)
 616                 }
 617             }
 618             mir::BinOp::Rem => {
 619                 if is_float {
 620                     bx.frem(lhs, rhs)
 621                 } else if is_signed {
 622                     bx.srem(lhs, rhs)
 623                 } else {
 624                     bx.urem(lhs, rhs)
 625                 }
 626             }
 627             mir::BinOp::BitOr => bx.or(lhs, rhs),
 628             mir::BinOp::BitAnd => bx.and(lhs, rhs),
 629             mir::BinOp::BitXor => bx.xor(lhs, rhs),
 630             mir::BinOp::Offset => bx.inbounds_gep(lhs, &[rhs]),
 631             mir::BinOp::Shl => common::build_unchecked_lshift(bx, lhs, rhs),
 632             mir::BinOp::Shr => common::build_unchecked_rshift(bx, input_ty, lhs, rhs),
 633             mir::BinOp::Ne
 634             | mir::BinOp::Lt
 635             | mir::BinOp::Gt
 636             | mir::BinOp::Eq
 637             | mir::BinOp::Le
 638             | mir::BinOp::Ge => {
 639                 if is_float {
 640                     bx.fcmp(base::bin_op_to_fcmp_predicate(op.to_hir_binop()), lhs, rhs)
 641                 } else {
 642                     bx.icmp(base::bin_op_to_icmp_predicate(op.to_hir_binop(), is_signed), lhs, rhs)
 643                 }
 644             }
 645         }
 646     }
 647
 648     pub fn codegen_fat_ptr_binop(
 649         &mut self,
 650         bx: &mut Bx,
 651         op: mir::BinOp,
 652         lhs_addr: Bx::Value,
 653         lhs_extra: Bx::Value,
 654         rhs_addr: Bx::Value,
 655         rhs_extra: Bx::Value,
 656         _input_ty: Ty<'tcx>,
 657     ) -> Bx::Value {
 658         match op {
 659             mir::BinOp::Eq => {
 660                 let lhs = bx.icmp(IntPredicate::IntEQ, lhs_addr, rhs_addr);
 661                 let rhs = bx.icmp(IntPredicate::IntEQ, lhs_extra, rhs_extra);
 662                 bx.and(lhs, rhs)
 663             }
 664             mir::BinOp::Ne => {
 665                 let lhs = bx.icmp(IntPredicate::IntNE, lhs_addr, rhs_addr);
 666                 let rhs = bx.icmp(IntPredicate::IntNE, lhs_extra, rhs_extra);
 667                 bx.or(lhs, rhs)
 668             }
 669             mir::BinOp::Le | mir::BinOp::Lt | mir::BinOp::Ge | mir::BinOp::Gt => {
 670                 // a OP b ~ a.0 STRICT(OP) b.0 | (a.0 == b.0 && a.1 OP a.1)
 671                 let (op, strict_op) = match op {
 672                     mir::BinOp::Lt => (IntPredicate::IntULT, IntPredicate::IntULT),
 673                     mir::BinOp::Le => (IntPredicate::IntULE, IntPredicate::IntULT),
 674                     mir::BinOp::Gt => (IntPredicate::IntUGT, IntPredicate::IntUGT),
 675                     mir::BinOp::Ge => (IntPredicate::IntUGE, IntPredicate::IntUGT),
 676                     _ => bug!(),
 677                 };
 678                 let lhs = bx.icmp(strict_op, lhs_addr, rhs_addr);
 679                 let and_lhs = bx.icmp(IntPredicate::IntEQ, lhs_addr, rhs_addr);
 680                 let and_rhs = bx.icmp(op, lhs_extra, rhs_extra);
 681                 let rhs = bx.and(and_lhs, and_rhs);
 682                 bx.or(lhs, rhs)
 683             }
 684             _ => {
 685                 bug!("unexpected fat ptr binop");
 686             }
 687         }
 688     }
 689
 690     pub fn codegen_scalar_checked_binop(
 691         &mut self,
 692         bx: &mut Bx,
 693         op: mir::BinOp,
 694         lhs: Bx::Value,
 695         rhs: Bx::Value,
 696         input_ty: Ty<'tcx>,
 697     ) -> OperandValue<Bx::Value> {
 698         // This case can currently arise only from functions marked
 699         // with #[rustc_inherit_overflow_checks] and inlined from
 700         // another crate (mostly core::num generic/#[inline] fns),
 701         // while the current crate doesn't use overflow checks.
 702         if !bx.cx().check_overflow() {
 703             let val = self.codegen_scalar_binop(bx, op, lhs, rhs, input_ty);
 704             return OperandValue::Pair(val, bx.cx().const_bool(false));
 705         }
 706
 707         let (val, of) = match op {
 708             // These are checked using intrinsics
 709             mir::BinOp::Add | mir::BinOp::Sub | mir::BinOp::Mul => {
 710                 let oop = match op {
 711                     mir::BinOp::Add => OverflowOp::Add,
 712                     mir::BinOp::Sub => OverflowOp::Sub,
 713                     mir::BinOp::Mul => OverflowOp::Mul,
 714                     _ => unreachable!(),
 715                 };
 716                 bx.checked_binop(oop, input_ty, lhs, rhs)
 717             }
 718             mir::BinOp::Shl | mir::BinOp::Shr => {
 719                 let lhs_llty = bx.cx().val_ty(lhs);
 720                 let rhs_llty = bx.cx().val_ty(rhs);
 721                 let invert_mask = common::shift_mask_val(bx, lhs_llty, rhs_llty, true);
 722                 let outer_bits = bx.and(rhs, invert_mask);
 723
 724                 let of = bx.icmp(IntPredicate::IntNE, outer_bits, bx.cx().const_null(rhs_llty));
 725                 let val = self.codegen_scalar_binop(bx, op, lhs, rhs, input_ty);
 726
 727                 (val, of)
 728             }
 729             _ => bug!("Operator `{:?}` is not a checkable operator", op),
 730         };
 731
 732         OperandValue::Pair(val, of)
 733     }
 734 }
 735
 736 impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
 737     pub fn rvalue_creates_operand(&self, rvalue: &mir::Rvalue<'tcx>, span: Span) -> bool {
 738         match *rvalue {
 739             mir::Rvalue::Ref(..) |
 740             mir::Rvalue::AddressOf(..) |
 741             mir::Rvalue::Len(..) |
 742             mir::Rvalue::Cast(..) | // (*)
 743             mir::Rvalue::BinaryOp(..) |
 744             mir::Rvalue::CheckedBinaryOp(..) |
 745             mir::Rvalue::UnaryOp(..) |
 746             mir::Rvalue::Discriminant(..) |
 747             mir::Rvalue::NullaryOp(..) |
 748             mir::Rvalue::Use(..) => // (*)
 749                 true,
 750             mir::Rvalue::Repeat(..) |
 751             mir::Rvalue::Aggregate(..) => {
 752                 let ty = rvalue.ty(*self.mir, self.cx.tcx());
 753                 let ty = self.monomorphize(&ty);
 754                 self.cx.spanned_layout_of(ty, span).is_zst()
 755             }
 756         }
 757
 758         // (*) this is only true if the type is suitable
 759     }
 760 }
 761
 762 fn cast_float_to_int<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
 763     bx: &mut Bx,
 764     signed: bool,
 765     x: Bx::Value,
 766     float_ty: Bx::Type,
 767     int_ty: Bx::Type,
 768 ) -> Bx::Value {
 769     let fptosui_result = if signed { bx.fptosi(x, int_ty) } else { bx.fptoui(x, int_ty) };
 770
 771     if !bx.cx().sess().opts.debugging_opts.saturating_float_casts {
 772         return fptosui_result;
 773     }
 774
 775     let int_width = bx.cx().int_width(int_ty);
 776     let float_width = bx.cx().float_width(float_ty);
 777     // LLVM's fpto[su]i returns undef when the input x is infinite, NaN, or does not fit into the
 778     // destination integer type after rounding towards zero. This `undef` value can cause UB in
 779     // safe code (see issue #10184), so we implement a saturating conversion on top of it:
 780     // Semantically, the mathematical value of the input is rounded towards zero to the next
 781     // mathematical integer, and then the result is clamped into the range of the destination
 782     // integer type. Positive and negative infinity are mapped to the maximum and minimum value of
 783     // the destination integer type. NaN is mapped to 0.
 784     //
 785     // Define f_min and f_max as the largest and smallest (finite) floats that are exactly equal to
 786     // a value representable in int_ty.
 787     // They are exactly equal to int_ty::{MIN,MAX} if float_ty has enough significand bits.
 788     // Otherwise, int_ty::MAX must be rounded towards zero, as it is one less than a power of two.
 789     // int_ty::MIN, however, is either zero or a negative power of two and is thus exactly
 790     // representable. Note that this only works if float_ty's exponent range is sufficiently large.
 791     // f16 or 256 bit integers would break this property. Right now the smallest float type is f32
 792     // with exponents ranging up to 127, which is barely enough for i128::MIN = -2^127.
 793     // On the other hand, f_max works even if int_ty::MAX is greater than float_ty::MAX. Because
 794     // we're rounding towards zero, we just get float_ty::MAX (which is always an integer).
 795     // This already happens today with u128::MAX = 2^128 - 1 > f32::MAX.
 796     let int_max = |signed: bool, int_width: u64| -> u128 {
 797         let shift_amount = 128 - int_width;
 798         if signed { i128::MAX as u128 >> shift_amount } else { u128::MAX >> shift_amount }
 799     };
 800     let int_min = |signed: bool, int_width: u64| -> i128 {
 801         if signed { i128::MIN >> (128 - int_width) } else { 0 }
 802     };
 803
 804     let compute_clamp_bounds_single = |signed: bool, int_width: u64| -> (u128, u128) {
 805         let rounded_min = ieee::Single::from_i128_r(int_min(signed, int_width), Round::TowardZero);
 806         assert_eq!(rounded_min.status, Status::OK);
 807         let rounded_max = ieee::Single::from_u128_r(int_max(signed, int_width), Round::TowardZero);
 808         assert!(rounded_max.value.is_finite());
 809         (rounded_min.value.to_bits(), rounded_max.value.to_bits())
 810     };
 811     let compute_clamp_bounds_double = |signed: bool, int_width: u64| -> (u128, u128) {
 812         let rounded_min = ieee::Double::from_i128_r(int_min(signed, int_width), Round::TowardZero);
 813         assert_eq!(rounded_min.status, Status::OK);
 814         let rounded_max = ieee::Double::from_u128_r(int_max(signed, int_width), Round::TowardZero);
 815         assert!(rounded_max.value.is_finite());
 816         (rounded_min.value.to_bits(), rounded_max.value.to_bits())
 817     };
 818
 819     let mut float_bits_to_llval = |bits| {
 820         let bits_llval = match float_width {
 821             32 => bx.cx().const_u32(bits as u32),
 822             64 => bx.cx().const_u64(bits as u64),
 823             n => bug!("unsupported float width {}", n),
 824         };
 825         bx.bitcast(bits_llval, float_ty)
 826     };
 827     let (f_min, f_max) = match float_width {
 828         32 => compute_clamp_bounds_single(signed, int_width),
 829         64 => compute_clamp_bounds_double(signed, int_width),
 830         n => bug!("unsupported float width {}", n),
 831     };
 832     let f_min = float_bits_to_llval(f_min);
 833     let f_max = float_bits_to_llval(f_max);
 834     // To implement saturation, we perform the following steps:
 835     //
 836     // 1. Cast x to an integer with fpto[su]i. This may result in undef.
 837     // 2. Compare x to f_min and f_max, and use the comparison results to select:
 838     //  a) int_ty::MIN if x < f_min or x is NaN
 839     //  b) int_ty::MAX if x > f_max
 840     //  c) the result of fpto[su]i otherwise
 841     // 3. If x is NaN, return 0.0, otherwise return the result of step 2.
 842     //
 843     // This avoids resulting undef because values in range [f_min, f_max] by definition fit into the
 844     // destination type. It creates an undef temporary, but *producing* undef is not UB. Our use of
 845     // undef does not introduce any non-determinism either.
 846     // More importantly, the above procedure correctly implements saturating conversion.
 847     // Proof (sketch):
 848     // If x is NaN, 0 is returned by definition.
 849     // Otherwise, x is finite or infinite and thus can be compared with f_min and f_max.
 850     // This yields three cases to consider:
 851     // (1) if x in [f_min, f_max], the result of fpto[su]i is returned, which agrees with
 852     //     saturating conversion for inputs in that range.
 853     // (2) if x > f_max, then x is larger than int_ty::MAX. This holds even if f_max is rounded
 854     //     (i.e., if f_max < int_ty::MAX) because in those cases, nextUp(f_max) is already larger
 855     //     than int_ty::MAX. Because x is larger than int_ty::MAX, the return value of int_ty::MAX
 856     //     is correct.
 857     // (3) if x < f_min, then x is smaller than int_ty::MIN. As shown earlier, f_min exactly equals
 858     //     int_ty::MIN and therefore the return value of int_ty::MIN is correct.
 859     // QED.
 860
 861     // Step 1 was already performed above.
 862
 863     // Step 2: We use two comparisons and two selects, with %s1 being the result:
 864     //     %less_or_nan = fcmp ult %x, %f_min
 865     //     %greater = fcmp olt %x, %f_max
 866     //     %s0 = select %less_or_nan, int_ty::MIN, %fptosi_result
 867     //     %s1 = select %greater, int_ty::MAX, %s0
 868     // Note that %less_or_nan uses an *unordered* comparison. This comparison is true if the
 869     // operands are not comparable (i.e., if x is NaN). The unordered comparison ensures that s1
 870     // becomes int_ty::MIN if x is NaN.
 871     // Performance note: Unordered comparison can be lowered to a "flipped" comparison and a
 872     // negation, and the negation can be merged into the select. Therefore, it not necessarily any
 873     // more expensive than a ordered ("normal") comparison. Whether these optimizations will be
 874     // performed is ultimately up to the backend, but at least x86 does perform them.
 875     let less_or_nan = bx.fcmp(RealPredicate::RealULT, x, f_min);
 876     let greater = bx.fcmp(RealPredicate::RealOGT, x, f_max);
 877     let int_max = bx.cx().const_uint_big(int_ty, int_max(signed, int_width));
 878     let int_min = bx.cx().const_uint_big(int_ty, int_min(signed, int_width) as u128);
 879     let s0 = bx.select(less_or_nan, int_min, fptosui_result);
 880     let s1 = bx.select(greater, int_max, s0);
 881
 882     // Step 3: NaN replacement.
 883     // For unsigned types, the above step already yielded int_ty::MIN == 0 if x is NaN.
 884     // Therefore we only need to execute this step for signed integer types.
 885     if signed {
 886         // LLVM has no isNaN predicate, so we use (x == x) instead
 887         let zero = bx.cx().const_uint(int_ty, 0);
 888         let cmp = bx.fcmp(RealPredicate::RealOEQ, x, x);
 889         bx.select(cmp, s1, zero)
 890     } else {
 891         s1
 892     }
 893 }