compiler/rustc_codegen_ssa/src/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::LangItem;
  12 use rustc_middle::mir;
  13 use rustc_middle::ty::cast::{CastTy, IntTy};
  14 use rustc_middle::ty::layout::{HasTyCtxt, LayoutOf};
  15 use rustc_middle::ty::{self, adjustment::PointerCast, Instance, Ty, TyCtxt};
  16 use rustc_span::source_map::{Span, DUMMY_SP};
  17 use rustc_target::abi::{Abi, Int, Variants};
  18
  19 impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
  20     pub fn codegen_rvalue(
  21         &mut self,
  22         mut bx: Bx,
  23         dest: PlaceRef<'tcx, Bx::Value>,
  24         rvalue: &mir::Rvalue<'tcx>,
  25     ) -> Bx {
  26         debug!("codegen_rvalue(dest.llval={:?}, rvalue={:?})", dest.llval, rvalue);
  27
  28         match *rvalue {
  29             mir::Rvalue::Use(ref operand) => {
  30                 let cg_operand = self.codegen_operand(&mut bx, operand);
  31                 // FIXME: consider not copying constants through stack. (Fixable by codegen'ing
  32                 // constants into `OperandValue::Ref`; why don’t we do that yet if we don’t?)
  33                 cg_operand.val.store(&mut bx, dest);
  34                 bx
  35             }
  36
  37             mir::Rvalue::Cast(mir::CastKind::Pointer(PointerCast::Unsize), ref source, _) => {
  38                 // The destination necessarily contains a fat pointer, so if
  39                 // it's a scalar pair, it's a fat pointer or newtype thereof.
  40                 if bx.cx().is_backend_scalar_pair(dest.layout) {
  41                     // Into-coerce of a thin pointer to a fat pointer -- just
  42                     // use the operand path.
  43                     let (mut bx, temp) = self.codegen_rvalue_operand(bx, rvalue);
  44                     temp.val.store(&mut bx, dest);
  45                     return bx;
  46                 }
  47
  48                 // Unsize of a nontrivial struct. I would prefer for
  49                 // this to be eliminated by MIR building, but
  50                 // `CoerceUnsized` can be passed by a where-clause,
  51                 // so the (generic) MIR may not be able to expand it.
  52                 let operand = self.codegen_operand(&mut bx, source);
  53                 match operand.val {
  54                     OperandValue::Pair(..) | OperandValue::Immediate(_) => {
  55                         // Unsize from an immediate structure. We don't
  56                         // really need a temporary alloca here, but
  57                         // avoiding it would require us to have
  58                         // `coerce_unsized_into` use `extractvalue` to
  59                         // index into the struct, and this case isn't
  60                         // important enough for it.
  61                         debug!("codegen_rvalue: creating ugly alloca");
  62                         let scratch = PlaceRef::alloca(&mut bx, operand.layout);
  63                         scratch.storage_live(&mut bx);
  64                         operand.val.store(&mut bx, scratch);
  65                         base::coerce_unsized_into(&mut bx, scratch, dest);
  66                         scratch.storage_dead(&mut bx);
  67                     }
  68                     OperandValue::Ref(llref, None, align) => {
  69                         let source = PlaceRef::new_sized_aligned(llref, operand.layout, align);
  70                         base::coerce_unsized_into(&mut bx, source, dest);
  71                     }
  72                     OperandValue::Ref(_, Some(_), _) => {
  73                         bug!("unsized coercion on an unsized rvalue");
  74                     }
  75                 }
  76                 bx
  77             }
  78
  79             mir::Rvalue::Repeat(ref elem, count) => {
  80                 let cg_elem = self.codegen_operand(&mut bx, elem);
  81
  82                 // Do not generate the loop for zero-sized elements or empty arrays.
  83                 if dest.layout.is_zst() {
  84                     return bx;
  85                 }
  86
  87                 if let OperandValue::Immediate(v) = cg_elem.val {
  88                     let zero = bx.const_usize(0);
  89                     let start = dest.project_index(&mut bx, zero).llval;
  90                     let size = bx.const_usize(dest.layout.size.bytes());
  91
  92                     // Use llvm.memset.p0i8.* to initialize all zero arrays
  93                     if bx.cx().const_to_opt_uint(v) == Some(0) {
  94                         let fill = bx.cx().const_u8(0);
  95                         bx.memset(start, fill, size, dest.align, MemFlags::empty());
  96                         return bx;
  97                     }
  98
  99                     // Use llvm.memset.p0i8.* to initialize byte arrays
 100                     let v = bx.from_immediate(v);
 101                     if bx.cx().val_ty(v) == bx.cx().type_i8() {
 102                         bx.memset(start, v, size, dest.align, MemFlags::empty());
 103                         return bx;
 104                     }
 105                 }
 106
 107                 let count =
 108                     self.monomorphize(count).eval_usize(bx.cx().tcx(), ty::ParamEnv::reveal_all());
 109
 110                 bx.write_operand_repeatedly(cg_elem, count, dest)
 111             }
 112
 113             mir::Rvalue::Aggregate(ref kind, ref operands) => {
 114                 let (dest, active_field_index) = match **kind {
 115                     mir::AggregateKind::Adt(adt_def, variant_index, _, _, active_field_index) => {
 116                         dest.codegen_set_discr(&mut bx, variant_index);
 117                         if adt_def.is_enum() {
 118                             (dest.project_downcast(&mut bx, variant_index), active_field_index)
 119                         } else {
 120                             (dest, active_field_index)
 121                         }
 122                     }
 123                     _ => (dest, None),
 124                 };
 125                 for (i, operand) in operands.iter().enumerate() {
 126                     let op = self.codegen_operand(&mut bx, operand);
 127                     // Do not generate stores and GEPis for zero-sized fields.
 128                     if !op.layout.is_zst() {
 129                         let field_index = active_field_index.unwrap_or(i);
 130                         let field = dest.project_field(&mut bx, field_index);
 131                         op.val.store(&mut bx, field);
 132                     }
 133                 }
 134                 bx
 135             }
 136
 137             _ => {
 138                 assert!(self.rvalue_creates_operand(rvalue, DUMMY_SP));
 139                 let (mut bx, temp) = self.codegen_rvalue_operand(bx, rvalue);
 140                 temp.val.store(&mut bx, dest);
 141                 bx
 142             }
 143         }
 144     }
 145
 146     pub fn codegen_rvalue_unsized(
 147         &mut self,
 148         mut bx: Bx,
 149         indirect_dest: PlaceRef<'tcx, Bx::Value>,
 150         rvalue: &mir::Rvalue<'tcx>,
 151     ) -> Bx {
 152         debug!(
 153             "codegen_rvalue_unsized(indirect_dest.llval={:?}, rvalue={:?})",
 154             indirect_dest.llval, rvalue
 155         );
 156
 157         match *rvalue {
 158             mir::Rvalue::Use(ref operand) => {
 159                 let cg_operand = self.codegen_operand(&mut bx, operand);
 160                 cg_operand.val.store_unsized(&mut bx, indirect_dest);
 161                 bx
 162             }
 163
 164             _ => bug!("unsized assignment other than `Rvalue::Use`"),
 165         }
 166     }
 167
 168     pub fn codegen_rvalue_operand(
 169         &mut self,
 170         mut bx: Bx,
 171         rvalue: &mir::Rvalue<'tcx>,
 172     ) -> (Bx, OperandRef<'tcx, Bx::Value>) {
 173         assert!(
 174             self.rvalue_creates_operand(rvalue, DUMMY_SP),
 175             "cannot codegen {:?} to operand",
 176             rvalue,
 177         );
 178
 179         match *rvalue {
 180             mir::Rvalue::Cast(ref kind, ref source, mir_cast_ty) => {
 181                 let operand = self.codegen_operand(&mut bx, source);
 182                 debug!("cast operand is {:?}", operand);
 183                 let cast = bx.cx().layout_of(self.monomorphize(mir_cast_ty));
 184
 185                 let val = match *kind {
 186                     mir::CastKind::Pointer(PointerCast::ReifyFnPointer) => {
 187                         match *operand.layout.ty.kind() {
 188                             ty::FnDef(def_id, substs) => {
 189                                 let instance = ty::Instance::resolve_for_fn_ptr(
 190                                     bx.tcx(),
 191                                     ty::ParamEnv::reveal_all(),
 192                                     def_id,
 193                                     substs,
 194                                 )
 195                                 .unwrap()
 196                                 .polymorphize(bx.cx().tcx());
 197                                 OperandValue::Immediate(bx.get_fn_addr(instance))
 198                             }
 199                             _ => bug!("{} cannot be reified to a fn ptr", operand.layout.ty),
 200                         }
 201                     }
 202                     mir::CastKind::Pointer(PointerCast::ClosureFnPointer(_)) => {
 203                         match *operand.layout.ty.kind() {
 204                             ty::Closure(def_id, substs) => {
 205                                 let instance = Instance::resolve_closure(
 206                                     bx.cx().tcx(),
 207                                     def_id,
 208                                     substs,
 209                                     ty::ClosureKind::FnOnce,
 210                                 )
 211                                 .polymorphize(bx.cx().tcx());
 212                                 OperandValue::Immediate(bx.cx().get_fn_addr(instance))
 213                             }
 214                             _ => bug!("{} cannot be cast to a fn ptr", operand.layout.ty),
 215                         }
 216                     }
 217                     mir::CastKind::Pointer(PointerCast::UnsafeFnPointer) => {
 218                         // This is a no-op at the LLVM level.
 219                         operand.val
 220                     }
 221                     mir::CastKind::Pointer(PointerCast::Unsize) => {
 222                         assert!(bx.cx().is_backend_scalar_pair(cast));
 223                         let (lldata, llextra) = match operand.val {
 224                             OperandValue::Pair(lldata, llextra) => {
 225                                 // unsize from a fat pointer -- this is a
 226                                 // "trait-object-to-supertrait" coercion.
 227                                 (lldata, Some(llextra))
 228                             }
 229                             OperandValue::Immediate(lldata) => {
 230                                 // "standard" unsize
 231                                 (lldata, None)
 232                             }
 233                             OperandValue::Ref(..) => {
 234                                 bug!("by-ref operand {:?} in `codegen_rvalue_operand`", operand);
 235                             }
 236                         };
 237                         let (lldata, llextra) =
 238                             base::unsize_ptr(&mut bx, lldata, operand.layout.ty, cast.ty, llextra);
 239                         OperandValue::Pair(lldata, llextra)
 240                     }
 241                     mir::CastKind::Pointer(PointerCast::MutToConstPointer)
 242                     | mir::CastKind::Misc
 243                         if bx.cx().is_backend_scalar_pair(operand.layout) =>
 244                     {
 245                         if let OperandValue::Pair(data_ptr, meta) = operand.val {
 246                             if bx.cx().is_backend_scalar_pair(cast) {
 247                                 let data_cast = bx.pointercast(
 248                                     data_ptr,
 249                                     bx.cx().scalar_pair_element_backend_type(cast, 0, true),
 250                                 );
 251                                 OperandValue::Pair(data_cast, meta)
 252                             } else {
 253                                 // cast to thin-ptr
 254                                 // Cast of fat-ptr to thin-ptr is an extraction of data-ptr and
 255                                 // pointer-cast of that pointer to desired pointer type.
 256                                 let llcast_ty = bx.cx().immediate_backend_type(cast);
 257                                 let llval = bx.pointercast(data_ptr, llcast_ty);
 258                                 OperandValue::Immediate(llval)
 259                             }
 260                         } else {
 261                             bug!("unexpected non-pair operand");
 262                         }
 263                     }
 264                     mir::CastKind::Pointer(
 265                         PointerCast::MutToConstPointer | PointerCast::ArrayToPointer,
 266                     )
 267                     | mir::CastKind::Misc => {
 268                         assert!(bx.cx().is_backend_immediate(cast));
 269                         let ll_t_out = bx.cx().immediate_backend_type(cast);
 270                         if operand.layout.abi.is_uninhabited() {
 271                             let val = OperandValue::Immediate(bx.cx().const_undef(ll_t_out));
 272                             return (bx, OperandRef { val, layout: cast });
 273                         }
 274                         let r_t_in =
 275                             CastTy::from_ty(operand.layout.ty).expect("bad input type for cast");
 276                         let r_t_out = CastTy::from_ty(cast.ty).expect("bad output type for cast");
 277                         let ll_t_in = bx.cx().immediate_backend_type(operand.layout);
 278                         match operand.layout.variants {
 279                             Variants::Single { index } => {
 280                                 if let Some(discr) =
 281                                     operand.layout.ty.discriminant_for_variant(bx.tcx(), index)
 282                                 {
 283                                     let discr_layout = bx.cx().layout_of(discr.ty);
 284                                     let discr_t = bx.cx().immediate_backend_type(discr_layout);
 285                                     let discr_val = bx.cx().const_uint_big(discr_t, discr.val);
 286                                     let discr_val =
 287                                         bx.intcast(discr_val, ll_t_out, discr.ty.is_signed());
 288
 289                                     return (
 290                                         bx,
 291                                         OperandRef {
 292                                             val: OperandValue::Immediate(discr_val),
 293                                             layout: cast,
 294                                         },
 295                                     );
 296                                 }
 297                             }
 298                             Variants::Multiple { .. } => {}
 299                         }
 300                         let llval = operand.immediate();
 301
 302                         let mut signed = false;
 303                         if let Abi::Scalar(ref scalar) = operand.layout.abi {
 304                             if let Int(_, s) = scalar.value {
 305                                 // We use `i1` for bytes that are always `0` or `1`,
 306                                 // e.g., `#[repr(i8)] enum E { A, B }`, but we can't
 307                                 // let LLVM interpret the `i1` as signed, because
 308                                 // then `i1 1` (i.e., E::B) is effectively `i8 -1`.
 309                                 signed = !scalar.is_bool() && s;
 310
 311                                 let er = scalar.valid_range_exclusive(bx.cx());
 312                                 if er.end != er.start
 313                                     && scalar.valid_range.end >= scalar.valid_range.start
 314                                 {
 315                                     // We want `table[e as usize ± k]` to not
 316                                     // have bound checks, and this is the most
 317                                     // convenient place to put the `assume`s.
 318                                     if scalar.valid_range.start > 0 {
 319                                         let enum_value_lower_bound = bx
 320                                             .cx()
 321                                             .const_uint_big(ll_t_in, scalar.valid_range.start);
 322                                         let cmp_start = bx.icmp(
 323                                             IntPredicate::IntUGE,
 324                                             llval,
 325                                             enum_value_lower_bound,
 326                                         );
 327                                         bx.assume(cmp_start);
 328                                     }
 329
 330                                     let enum_value_upper_bound =
 331                                         bx.cx().const_uint_big(ll_t_in, scalar.valid_range.end);
 332                                     let cmp_end = bx.icmp(
 333                                         IntPredicate::IntULE,
 334                                         llval,
 335                                         enum_value_upper_bound,
 336                                     );
 337                                     bx.assume(cmp_end);
 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, box (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, box (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_ty = self.monomorphize(discr_ty);
 478                 let discr = self
 479                     .codegen_place(&mut bx, place.as_ref())
 480                     .codegen_get_discr(&mut bx, discr_ty);
 481                 (
 482                     bx,
 483                     OperandRef {
 484                         val: OperandValue::Immediate(discr),
 485                         layout: self.cx.layout_of(discr_ty),
 486                     },
 487                 )
 488             }
 489
 490             mir::Rvalue::NullaryOp(mir::NullOp::Box, content_ty) => {
 491                 let content_ty = self.monomorphize(content_ty);
 492                 let content_layout = bx.cx().layout_of(content_ty);
 493                 let llsize = bx.cx().const_usize(content_layout.size.bytes());
 494                 let llalign = bx.cx().const_usize(content_layout.align.abi.bytes());
 495                 let box_layout = bx.cx().layout_of(bx.tcx().mk_box(content_ty));
 496                 let llty_ptr = bx.cx().backend_type(box_layout);
 497
 498                 // Allocate space:
 499                 let def_id = match bx.tcx().lang_items().require(LangItem::ExchangeMalloc) {
 500                     Ok(id) => id,
 501                     Err(s) => {
 502                         bx.cx().sess().fatal(&format!("allocation of `{}` {}", box_layout.ty, s));
 503                     }
 504                 };
 505                 let instance = ty::Instance::mono(bx.tcx(), def_id);
 506                 let r = bx.cx().get_fn_addr(instance);
 507                 let ty = bx.type_func(&[bx.type_isize(), bx.type_isize()], bx.type_i8p());
 508                 let call = bx.call(ty, r, &[llsize, llalign], None);
 509                 let val = bx.pointercast(call, llty_ptr);
 510
 511                 let operand = OperandRef { val: OperandValue::Immediate(val), layout: box_layout };
 512                 (bx, operand)
 513             }
 514
 515             mir::Rvalue::NullaryOp(null_op, ty) => {
 516                 let ty = self.monomorphize(ty);
 517                 assert!(bx.cx().type_is_sized(ty));
 518                 let layout = bx.cx().layout_of(ty);
 519                 let val = match null_op {
 520                     mir::NullOp::SizeOf => layout.size.bytes(),
 521                     mir::NullOp::AlignOf => layout.align.abi.bytes(),
 522                     mir::NullOp::Box => unreachable!(),
 523                 };
 524                 let val = bx.cx().const_usize(val);
 525                 let tcx = self.cx.tcx();
 526                 (
 527                     bx,
 528                     OperandRef {
 529                         val: OperandValue::Immediate(val),
 530                         layout: self.cx.layout_of(tcx.types.usize),
 531                     },
 532                 )
 533             }
 534
 535             mir::Rvalue::ThreadLocalRef(def_id) => {
 536                 assert!(bx.cx().tcx().is_static(def_id));
 537                 let static_ = bx.get_static(def_id);
 538                 let layout = bx.layout_of(bx.cx().tcx().static_ptr_ty(def_id));
 539                 let operand = OperandRef::from_immediate_or_packed_pair(&mut bx, static_, layout);
 540                 (bx, operand)
 541             }
 542             mir::Rvalue::Use(ref operand) => {
 543                 let operand = self.codegen_operand(&mut bx, operand);
 544                 (bx, operand)
 545             }
 546             mir::Rvalue::Repeat(..) | mir::Rvalue::Aggregate(..) => {
 547                 // According to `rvalue_creates_operand`, only ZST
 548                 // aggregate rvalues are allowed to be operands.
 549                 let ty = rvalue.ty(self.mir, self.cx.tcx());
 550                 let operand =
 551                     OperandRef::new_zst(&mut bx, self.cx.layout_of(self.monomorphize(ty)));
 552                 (bx, operand)
 553             }
 554         }
 555     }
 556
 557     fn evaluate_array_len(&mut self, bx: &mut Bx, place: mir::Place<'tcx>) -> Bx::Value {
 558         // ZST are passed as operands and require special handling
 559         // because codegen_place() panics if Local is operand.
 560         if let Some(index) = place.as_local() {
 561             if let LocalRef::Operand(Some(op)) = self.locals[index] {
 562                 if let ty::Array(_, n) = op.layout.ty.kind() {
 563                     let n = n.eval_usize(bx.cx().tcx(), ty::ParamEnv::reveal_all());
 564                     return bx.cx().const_usize(n);
 565                 }
 566             }
 567         }
 568         // use common size calculation for non zero-sized types
 569         let cg_value = self.codegen_place(bx, place.as_ref());
 570         cg_value.len(bx.cx())
 571     }
 572
 573     /// Codegen an `Rvalue::AddressOf` or `Rvalue::Ref`
 574     fn codegen_place_to_pointer(
 575         &mut self,
 576         mut bx: Bx,
 577         place: mir::Place<'tcx>,
 578         mk_ptr_ty: impl FnOnce(TyCtxt<'tcx>, Ty<'tcx>) -> Ty<'tcx>,
 579     ) -> (Bx, OperandRef<'tcx, Bx::Value>) {
 580         let cg_place = self.codegen_place(&mut bx, place.as_ref());
 581
 582         let ty = cg_place.layout.ty;
 583
 584         // Note: places are indirect, so storing the `llval` into the
 585         // destination effectively creates a reference.
 586         let val = if !bx.cx().type_has_metadata(ty) {
 587             OperandValue::Immediate(cg_place.llval)
 588         } else {
 589             OperandValue::Pair(cg_place.llval, cg_place.llextra.unwrap())
 590         };
 591         (bx, OperandRef { val, layout: self.cx.layout_of(mk_ptr_ty(self.cx.tcx(), ty)) })
 592     }
 593
 594     pub fn codegen_scalar_binop(
 595         &mut self,
 596         bx: &mut Bx,
 597         op: mir::BinOp,
 598         lhs: Bx::Value,
 599         rhs: Bx::Value,
 600         input_ty: Ty<'tcx>,
 601     ) -> Bx::Value {
 602         let is_float = input_ty.is_floating_point();
 603         let is_signed = input_ty.is_signed();
 604         match op {
 605             mir::BinOp::Add => {
 606                 if is_float {
 607                     bx.fadd(lhs, rhs)
 608                 } else {
 609                     bx.add(lhs, rhs)
 610                 }
 611             }
 612             mir::BinOp::Sub => {
 613                 if is_float {
 614                     bx.fsub(lhs, rhs)
 615                 } else {
 616                     bx.sub(lhs, rhs)
 617                 }
 618             }
 619             mir::BinOp::Mul => {
 620                 if is_float {
 621                     bx.fmul(lhs, rhs)
 622                 } else {
 623                     bx.mul(lhs, rhs)
 624                 }
 625             }
 626             mir::BinOp::Div => {
 627                 if is_float {
 628                     bx.fdiv(lhs, rhs)
 629                 } else if is_signed {
 630                     bx.sdiv(lhs, rhs)
 631                 } else {
 632                     bx.udiv(lhs, rhs)
 633                 }
 634             }
 635             mir::BinOp::Rem => {
 636                 if is_float {
 637                     bx.frem(lhs, rhs)
 638                 } else if is_signed {
 639                     bx.srem(lhs, rhs)
 640                 } else {
 641                     bx.urem(lhs, rhs)
 642                 }
 643             }
 644             mir::BinOp::BitOr => bx.or(lhs, rhs),
 645             mir::BinOp::BitAnd => bx.and(lhs, rhs),
 646             mir::BinOp::BitXor => bx.xor(lhs, rhs),
 647             mir::BinOp::Offset => {
 648                 let pointee_type = input_ty
 649                     .builtin_deref(true)
 650                     .unwrap_or_else(|| bug!("deref of non-pointer {:?}", input_ty))
 651                     .ty;
 652                 let llty = bx.cx().backend_type(bx.cx().layout_of(pointee_type));
 653                 bx.inbounds_gep(llty, lhs, &[rhs])
 654             }
 655             mir::BinOp::Shl => common::build_unchecked_lshift(bx, lhs, rhs),
 656             mir::BinOp::Shr => common::build_unchecked_rshift(bx, input_ty, lhs, rhs),
 657             mir::BinOp::Ne
 658             | mir::BinOp::Lt
 659             | mir::BinOp::Gt
 660             | mir::BinOp::Eq
 661             | mir::BinOp::Le
 662             | mir::BinOp::Ge => {
 663                 if is_float {
 664                     bx.fcmp(base::bin_op_to_fcmp_predicate(op.to_hir_binop()), lhs, rhs)
 665                 } else {
 666                     bx.icmp(base::bin_op_to_icmp_predicate(op.to_hir_binop(), is_signed), lhs, rhs)
 667                 }
 668             }
 669         }
 670     }
 671
 672     pub fn codegen_fat_ptr_binop(
 673         &mut self,
 674         bx: &mut Bx,
 675         op: mir::BinOp,
 676         lhs_addr: Bx::Value,
 677         lhs_extra: Bx::Value,
 678         rhs_addr: Bx::Value,
 679         rhs_extra: Bx::Value,
 680         _input_ty: Ty<'tcx>,
 681     ) -> Bx::Value {
 682         match op {
 683             mir::BinOp::Eq => {
 684                 let lhs = bx.icmp(IntPredicate::IntEQ, lhs_addr, rhs_addr);
 685                 let rhs = bx.icmp(IntPredicate::IntEQ, lhs_extra, rhs_extra);
 686                 bx.and(lhs, rhs)
 687             }
 688             mir::BinOp::Ne => {
 689                 let lhs = bx.icmp(IntPredicate::IntNE, lhs_addr, rhs_addr);
 690                 let rhs = bx.icmp(IntPredicate::IntNE, lhs_extra, rhs_extra);
 691                 bx.or(lhs, rhs)
 692             }
 693             mir::BinOp::Le | mir::BinOp::Lt | mir::BinOp::Ge | mir::BinOp::Gt => {
 694                 // a OP b ~ a.0 STRICT(OP) b.0 | (a.0 == b.0 && a.1 OP a.1)
 695                 let (op, strict_op) = match op {
 696                     mir::BinOp::Lt => (IntPredicate::IntULT, IntPredicate::IntULT),
 697                     mir::BinOp::Le => (IntPredicate::IntULE, IntPredicate::IntULT),
 698                     mir::BinOp::Gt => (IntPredicate::IntUGT, IntPredicate::IntUGT),
 699                     mir::BinOp::Ge => (IntPredicate::IntUGE, IntPredicate::IntUGT),
 700                     _ => bug!(),
 701                 };
 702                 let lhs = bx.icmp(strict_op, lhs_addr, rhs_addr);
 703                 let and_lhs = bx.icmp(IntPredicate::IntEQ, lhs_addr, rhs_addr);
 704                 let and_rhs = bx.icmp(op, lhs_extra, rhs_extra);
 705                 let rhs = bx.and(and_lhs, and_rhs);
 706                 bx.or(lhs, rhs)
 707             }
 708             _ => {
 709                 bug!("unexpected fat ptr binop");
 710             }
 711         }
 712     }
 713
 714     pub fn codegen_scalar_checked_binop(
 715         &mut self,
 716         bx: &mut Bx,
 717         op: mir::BinOp,
 718         lhs: Bx::Value,
 719         rhs: Bx::Value,
 720         input_ty: Ty<'tcx>,
 721     ) -> OperandValue<Bx::Value> {
 722         // This case can currently arise only from functions marked
 723         // with #[rustc_inherit_overflow_checks] and inlined from
 724         // another crate (mostly core::num generic/#[inline] fns),
 725         // while the current crate doesn't use overflow checks.
 726         if !bx.cx().check_overflow() {
 727             let val = self.codegen_scalar_binop(bx, op, lhs, rhs, input_ty);
 728             return OperandValue::Pair(val, bx.cx().const_bool(false));
 729         }
 730
 731         let (val, of) = match op {
 732             // These are checked using intrinsics
 733             mir::BinOp::Add | mir::BinOp::Sub | mir::BinOp::Mul => {
 734                 let oop = match op {
 735                     mir::BinOp::Add => OverflowOp::Add,
 736                     mir::BinOp::Sub => OverflowOp::Sub,
 737                     mir::BinOp::Mul => OverflowOp::Mul,
 738                     _ => unreachable!(),
 739                 };
 740                 bx.checked_binop(oop, input_ty, lhs, rhs)
 741             }
 742             mir::BinOp::Shl | mir::BinOp::Shr => {
 743                 let lhs_llty = bx.cx().val_ty(lhs);
 744                 let rhs_llty = bx.cx().val_ty(rhs);
 745                 let invert_mask = common::shift_mask_val(bx, lhs_llty, rhs_llty, true);
 746                 let outer_bits = bx.and(rhs, invert_mask);
 747
 748                 let of = bx.icmp(IntPredicate::IntNE, outer_bits, bx.cx().const_null(rhs_llty));
 749                 let val = self.codegen_scalar_binop(bx, op, lhs, rhs, input_ty);
 750
 751                 (val, of)
 752             }
 753             _ => bug!("Operator `{:?}` is not a checkable operator", op),
 754         };
 755
 756         OperandValue::Pair(val, of)
 757     }
 758 }
 759
 760 impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
 761     pub fn rvalue_creates_operand(&self, rvalue: &mir::Rvalue<'tcx>, span: Span) -> bool {
 762         match *rvalue {
 763             mir::Rvalue::Ref(..) |
 764             mir::Rvalue::AddressOf(..) |
 765             mir::Rvalue::Len(..) |
 766             mir::Rvalue::Cast(..) | // (*)
 767             mir::Rvalue::BinaryOp(..) |
 768             mir::Rvalue::CheckedBinaryOp(..) |
 769             mir::Rvalue::UnaryOp(..) |
 770             mir::Rvalue::Discriminant(..) |
 771             mir::Rvalue::NullaryOp(..) |
 772             mir::Rvalue::ThreadLocalRef(_) |
 773             mir::Rvalue::Use(..) => // (*)
 774                 true,
 775             mir::Rvalue::Repeat(..) |
 776             mir::Rvalue::Aggregate(..) => {
 777                 let ty = rvalue.ty(self.mir, self.cx.tcx());
 778                 let ty = self.monomorphize(ty);
 779                 self.cx.spanned_layout_of(ty, span).is_zst()
 780             }
 781         }
 782
 783         // (*) this is only true if the type is suitable
 784     }
 785 }
 786
 787 fn cast_float_to_int<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
 788     bx: &mut Bx,
 789     signed: bool,
 790     x: Bx::Value,
 791     float_ty: Bx::Type,
 792     int_ty: Bx::Type,
 793 ) -> Bx::Value {
 794     if let Some(false) = bx.cx().sess().opts.debugging_opts.saturating_float_casts {
 795         return if signed { bx.fptosi(x, int_ty) } else { bx.fptoui(x, int_ty) };
 796     }
 797
 798     let try_sat_result = if signed { bx.fptosi_sat(x, int_ty) } else { bx.fptoui_sat(x, int_ty) };
 799     if let Some(try_sat_result) = try_sat_result {
 800         return try_sat_result;
 801     }
 802
 803     let int_width = bx.cx().int_width(int_ty);
 804     let float_width = bx.cx().float_width(float_ty);
 805     // LLVM's fpto[su]i returns undef when the input x is infinite, NaN, or does not fit into the
 806     // destination integer type after rounding towards zero. This `undef` value can cause UB in
 807     // safe code (see issue #10184), so we implement a saturating conversion on top of it:
 808     // Semantically, the mathematical value of the input is rounded towards zero to the next
 809     // mathematical integer, and then the result is clamped into the range of the destination
 810     // integer type. Positive and negative infinity are mapped to the maximum and minimum value of
 811     // the destination integer type. NaN is mapped to 0.
 812     //
 813     // Define f_min and f_max as the largest and smallest (finite) floats that are exactly equal to
 814     // a value representable in int_ty.
 815     // They are exactly equal to int_ty::{MIN,MAX} if float_ty has enough significand bits.
 816     // Otherwise, int_ty::MAX must be rounded towards zero, as it is one less than a power of two.
 817     // int_ty::MIN, however, is either zero or a negative power of two and is thus exactly
 818     // representable. Note that this only works if float_ty's exponent range is sufficiently large.
 819     // f16 or 256 bit integers would break this property. Right now the smallest float type is f32
 820     // with exponents ranging up to 127, which is barely enough for i128::MIN = -2^127.
 821     // On the other hand, f_max works even if int_ty::MAX is greater than float_ty::MAX. Because
 822     // we're rounding towards zero, we just get float_ty::MAX (which is always an integer).
 823     // This already happens today with u128::MAX = 2^128 - 1 > f32::MAX.
 824     let int_max = |signed: bool, int_width: u64| -> u128 {
 825         let shift_amount = 128 - int_width;
 826         if signed { i128::MAX as u128 >> shift_amount } else { u128::MAX >> shift_amount }
 827     };
 828     let int_min = |signed: bool, int_width: u64| -> i128 {
 829         if signed { i128::MIN >> (128 - int_width) } else { 0 }
 830     };
 831
 832     let compute_clamp_bounds_single = |signed: bool, int_width: u64| -> (u128, u128) {
 833         let rounded_min = ieee::Single::from_i128_r(int_min(signed, int_width), Round::TowardZero);
 834         assert_eq!(rounded_min.status, Status::OK);
 835         let rounded_max = ieee::Single::from_u128_r(int_max(signed, int_width), Round::TowardZero);
 836         assert!(rounded_max.value.is_finite());
 837         (rounded_min.value.to_bits(), rounded_max.value.to_bits())
 838     };
 839     let compute_clamp_bounds_double = |signed: bool, int_width: u64| -> (u128, u128) {
 840         let rounded_min = ieee::Double::from_i128_r(int_min(signed, int_width), Round::TowardZero);
 841         assert_eq!(rounded_min.status, Status::OK);
 842         let rounded_max = ieee::Double::from_u128_r(int_max(signed, int_width), Round::TowardZero);
 843         assert!(rounded_max.value.is_finite());
 844         (rounded_min.value.to_bits(), rounded_max.value.to_bits())
 845     };
 846
 847     let mut float_bits_to_llval = |bits| {
 848         let bits_llval = match float_width {
 849             32 => bx.cx().const_u32(bits as u32),
 850             64 => bx.cx().const_u64(bits as u64),
 851             n => bug!("unsupported float width {}", n),
 852         };
 853         bx.bitcast(bits_llval, float_ty)
 854     };
 855     let (f_min, f_max) = match float_width {
 856         32 => compute_clamp_bounds_single(signed, int_width),
 857         64 => compute_clamp_bounds_double(signed, int_width),
 858         n => bug!("unsupported float width {}", n),
 859     };
 860     let f_min = float_bits_to_llval(f_min);
 861     let f_max = float_bits_to_llval(f_max);
 862     // To implement saturation, we perform the following steps:
 863     //
 864     // 1. Cast x to an integer with fpto[su]i. This may result in undef.
 865     // 2. Compare x to f_min and f_max, and use the comparison results to select:
 866     //  a) int_ty::MIN if x < f_min or x is NaN
 867     //  b) int_ty::MAX if x > f_max
 868     //  c) the result of fpto[su]i otherwise
 869     // 3. If x is NaN, return 0.0, otherwise return the result of step 2.
 870     //
 871     // This avoids resulting undef because values in range [f_min, f_max] by definition fit into the
 872     // destination type. It creates an undef temporary, but *producing* undef is not UB. Our use of
 873     // undef does not introduce any non-determinism either.
 874     // More importantly, the above procedure correctly implements saturating conversion.
 875     // Proof (sketch):
 876     // If x is NaN, 0 is returned by definition.
 877     // Otherwise, x is finite or infinite and thus can be compared with f_min and f_max.
 878     // This yields three cases to consider:
 879     // (1) if x in [f_min, f_max], the result of fpto[su]i is returned, which agrees with
 880     //     saturating conversion for inputs in that range.
 881     // (2) if x > f_max, then x is larger than int_ty::MAX. This holds even if f_max is rounded
 882     //     (i.e., if f_max < int_ty::MAX) because in those cases, nextUp(f_max) is already larger
 883     //     than int_ty::MAX. Because x is larger than int_ty::MAX, the return value of int_ty::MAX
 884     //     is correct.
 885     // (3) if x < f_min, then x is smaller than int_ty::MIN. As shown earlier, f_min exactly equals
 886     //     int_ty::MIN and therefore the return value of int_ty::MIN is correct.
 887     // QED.
 888
 889     let int_max = bx.cx().const_uint_big(int_ty, int_max(signed, int_width));
 890     let int_min = bx.cx().const_uint_big(int_ty, int_min(signed, int_width) as u128);
 891     let zero = bx.cx().const_uint(int_ty, 0);
 892
 893     // Step 1 ...
 894     let fptosui_result = if signed { bx.fptosi(x, int_ty) } else { bx.fptoui(x, int_ty) };
 895     let less_or_nan = bx.fcmp(RealPredicate::RealULT, x, f_min);
 896     let greater = bx.fcmp(RealPredicate::RealOGT, x, f_max);
 897
 898     // Step 2: We use two comparisons and two selects, with %s1 being the
 899     // result:
 900     //     %less_or_nan = fcmp ult %x, %f_min
 901     //     %greater = fcmp olt %x, %f_max
 902     //     %s0 = select %less_or_nan, int_ty::MIN, %fptosi_result
 903     //     %s1 = select %greater, int_ty::MAX, %s0
 904     // Note that %less_or_nan uses an *unordered* comparison. This
 905     // comparison is true if the operands are not comparable (i.e., if x is
 906     // NaN). The unordered comparison ensures that s1 becomes int_ty::MIN if
 907     // x is NaN.
 908     //
 909     // Performance note: Unordered comparison can be lowered to a "flipped"
 910     // comparison and a negation, and the negation can be merged into the
 911     // select. Therefore, it not necessarily any more expensive than an
 912     // ordered ("normal") comparison. Whether these optimizations will be
 913     // performed is ultimately up to the backend, but at least x86 does
 914     // perform them.
 915     let s0 = bx.select(less_or_nan, int_min, fptosui_result);
 916     let s1 = bx.select(greater, int_max, s0);
 917
 918     // Step 3: NaN replacement.
 919     // For unsigned types, the above step already yielded int_ty::MIN == 0 if x is NaN.
 920     // Therefore we only need to execute this step for signed integer types.
 921     if signed {
 922         // LLVM has no isNaN predicate, so we use (x == x) instead
 923         let cmp = bx.fcmp(RealPredicate::RealOEQ, x, x);
 924         bx.select(cmp, s1, zero)
 925     } else {
 926         s1
 927     }
 928 }