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