src/librustc_codegen_llvm/mir/rvalue.rs

   1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use rustc::ty::{self, Ty};
  12 use rustc::ty::cast::{CastTy, IntTy};
  13 use rustc::ty::layout::{self, LayoutOf, HasTyCtxt};
  14 use rustc::mir;
  15 use rustc::middle::lang_items::ExchangeMallocFnLangItem;
  16 use rustc_apfloat::{ieee, Float, Status, Round};
  17 use std::{u128, i128};
  18
  19 use base;
  20 use builder::{Builder, MemFlags};
  21 use callee;
  22 use common::{self, IntPredicate, RealPredicate};
  23 use monomorphize;
  24 use type_::Type;
  25 use type_of::LayoutLlvmExt;
  26 use value::Value;
  27
  28 use interfaces::*;
  29
  30 use super::{FunctionCx, LocalRef};
  31 use super::operand::{OperandRef, OperandValue};
  32 use super::place::PlaceRef;
  33
  34 impl FunctionCx<'a, 'll, 'tcx, &'ll Value> {
  35     pub fn codegen_rvalue(&mut self,
  36                         bx: Builder<'a, 'll, 'tcx>,
  37                         dest: PlaceRef<'tcx, &'ll Value>,
  38                         rvalue: &mir::Rvalue<'tcx>)
  39                         -> Builder<'a, 'll, 'tcx>
  40     {
  41         debug!("codegen_rvalue(dest.llval={:?}, rvalue={:?})",
  42                dest.llval, rvalue);
  43
  44         match *rvalue {
  45            mir::Rvalue::Use(ref operand) => {
  46                let cg_operand = self.codegen_operand(&bx, operand);
  47                // FIXME: consider not copying constants through stack. (fixable by codegenning
  48                // constants into OperandValue::Ref, why don’t we do that yet if we don’t?)
  49                cg_operand.val.store(&bx, dest);
  50                bx
  51            }
  52
  53             mir::Rvalue::Cast(mir::CastKind::Unsize, ref source, _) => {
  54                 // The destination necessarily contains a fat pointer, so if
  55                 // it's a scalar pair, it's a fat pointer or newtype thereof.
  56                 if dest.layout.is_llvm_scalar_pair() {
  57                     // into-coerce of a thin pointer to a fat pointer - just
  58                     // use the operand path.
  59                     let (bx, temp) = self.codegen_rvalue_operand(bx, rvalue);
  60                     temp.val.store(&bx, dest);
  61                     return bx;
  62                 }
  63
  64                 // Unsize of a nontrivial struct. I would prefer for
  65                 // this to be eliminated by MIR building, but
  66                 // `CoerceUnsized` can be passed by a where-clause,
  67                 // so the (generic) MIR may not be able to expand it.
  68                 let operand = self.codegen_operand(&bx, source);
  69                 match operand.val {
  70                     OperandValue::Pair(..) |
  71                     OperandValue::Immediate(_) => {
  72                         // unsize from an immediate structure. We don't
  73                         // really need a temporary alloca here, but
  74                         // avoiding it would require us to have
  75                         // `coerce_unsized_into` use extractvalue to
  76                         // index into the struct, and this case isn't
  77                         // important enough for it.
  78                         debug!("codegen_rvalue: creating ugly alloca");
  79                         let scratch = PlaceRef::alloca(&bx, operand.layout, "__unsize_temp");
  80                         scratch.storage_live(&bx);
  81                         operand.val.store(&bx, scratch);
  82                         base::coerce_unsized_into(&bx, scratch, dest);
  83                         scratch.storage_dead(&bx);
  84                     }
  85                     OperandValue::Ref(llref, None, align) => {
  86                         let source = PlaceRef::new_sized(llref, operand.layout, align);
  87                         base::coerce_unsized_into(&bx, source, dest);
  88                     }
  89                     OperandValue::Ref(_, Some(_), _) => {
  90                         bug!("unsized coercion on an unsized rvalue")
  91                     }
  92                 }
  93                 bx
  94             }
  95
  96             mir::Rvalue::Repeat(ref elem, count) => {
  97                 let cg_elem = self.codegen_operand(&bx, elem);
  98
  99                 // Do not generate the loop for zero-sized elements or empty arrays.
 100                 if dest.layout.is_zst() {
 101                     return bx;
 102                 }
 103
 104                 let start = dest.project_index(&bx, bx.cx().const_usize(0)).llval;
 105
 106                 if let OperandValue::Immediate(v) = cg_elem.val {
 107                     let size = bx.cx().const_usize(dest.layout.size.bytes());
 108
 109                     // Use llvm.memset.p0i8.* to initialize all zero arrays
 110                     if bx.cx().is_const_integral(v) && bx.cx().const_to_uint(v) == 0 {
 111                         let fill = bx.cx().const_u8(0);
 112                         bx.memset(start, fill, size, dest.align, MemFlags::empty());
 113                         return bx;
 114                     }
 115
 116                     // Use llvm.memset.p0i8.* to initialize byte arrays
 117                     let v = base::from_immediate(&bx, v);
 118                     if bx.cx().val_ty(v) == bx.cx().type_i8() {
 119                         bx.memset(start, v, size, dest.align, MemFlags::empty());
 120                         return bx;
 121                     }
 122                 }
 123
 124                 let count = bx.cx().const_usize(count);
 125                 let end = dest.project_index(&bx, count).llval;
 126
 127                 let header_bx = bx.build_sibling_block("repeat_loop_header");
 128                 let body_bx = bx.build_sibling_block("repeat_loop_body");
 129                 let next_bx = bx.build_sibling_block("repeat_loop_next");
 130
 131                 bx.br(header_bx.llbb());
 132                 let current = header_bx.phi(bx.cx().val_ty(start), &[start], &[bx.llbb()]);
 133
 134                 let keep_going = header_bx.icmp(IntPredicate::IntNE, current, end);
 135                 header_bx.cond_br(keep_going, body_bx.llbb(), next_bx.llbb());
 136
 137                 cg_elem.val.store(&body_bx,
 138                     PlaceRef::new_sized(current, cg_elem.layout, dest.align));
 139
 140                 let next = body_bx.inbounds_gep(current, &[bx.cx().const_usize(1)]);
 141                 body_bx.br(header_bx.llbb());
 142                 header_bx.add_incoming_to_phi(current, next, body_bx.llbb());
 143
 144                 next_bx
 145             }
 146
 147             mir::Rvalue::Aggregate(ref kind, ref operands) => {
 148                 let (dest, active_field_index) = match **kind {
 149                     mir::AggregateKind::Adt(adt_def, variant_index, _, _, active_field_index) => {
 150                         dest.codegen_set_discr(&bx, variant_index);
 151                         if adt_def.is_enum() {
 152                             (dest.project_downcast(&bx, variant_index), active_field_index)
 153                         } else {
 154                             (dest, active_field_index)
 155                         }
 156                     }
 157                     _ => (dest, None)
 158                 };
 159                 for (i, operand) in operands.iter().enumerate() {
 160                     let op = self.codegen_operand(&bx, operand);
 161                     // Do not generate stores and GEPis for zero-sized fields.
 162                     if !op.layout.is_zst() {
 163                         let field_index = active_field_index.unwrap_or(i);
 164                         op.val.store(&bx, dest.project_field(&bx, field_index));
 165                     }
 166                 }
 167                 bx
 168             }
 169
 170             _ => {
 171                 assert!(self.rvalue_creates_operand(rvalue));
 172                 let (bx, temp) = self.codegen_rvalue_operand(bx, rvalue);
 173                 temp.val.store(&bx, dest);
 174                 bx
 175             }
 176         }
 177     }
 178
 179     pub fn codegen_rvalue_unsized(&mut self,
 180                         bx: Builder<'a, 'll, 'tcx>,
 181                         indirect_dest: PlaceRef<'tcx, &'ll Value>,
 182                         rvalue: &mir::Rvalue<'tcx>)
 183                         -> Builder<'a, 'll, 'tcx>
 184     {
 185         debug!("codegen_rvalue_unsized(indirect_dest.llval={:?}, rvalue={:?})",
 186                indirect_dest.llval, rvalue);
 187
 188         match *rvalue {
 189             mir::Rvalue::Use(ref operand) => {
 190                 let cg_operand = self.codegen_operand(&bx, operand);
 191                 cg_operand.val.store_unsized(&bx, indirect_dest);
 192                 bx
 193             }
 194
 195             _ => bug!("unsized assignment other than Rvalue::Use"),
 196         }
 197     }
 198
 199     pub fn codegen_rvalue_operand(
 200         &mut self,
 201         bx: Builder<'a, 'll, 'tcx>,
 202         rvalue: &mir::Rvalue<'tcx>
 203     ) -> (Builder<'a, 'll, 'tcx>, OperandRef<'tcx, &'ll Value>) {
 204         assert!(self.rvalue_creates_operand(rvalue), "cannot codegen {:?} to operand", rvalue);
 205
 206         match *rvalue {
 207             mir::Rvalue::Cast(ref kind, ref source, mir_cast_ty) => {
 208                 let operand = self.codegen_operand(&bx, source);
 209                 debug!("cast operand is {:?}", operand);
 210                 let cast = bx.cx().layout_of(self.monomorphize(&mir_cast_ty));
 211
 212                 let val = match *kind {
 213                     mir::CastKind::ReifyFnPointer => {
 214                         match operand.layout.ty.sty {
 215                             ty::FnDef(def_id, substs) => {
 216                                 if bx.cx().tcx.has_attr(def_id, "rustc_args_required_const") {
 217                                     bug!("reifying a fn ptr that requires \
 218                                           const arguments");
 219                                 }
 220                                 OperandValue::Immediate(
 221                                     callee::resolve_and_get_fn(bx.cx(), def_id, substs))
 222                             }
 223                             _ => {
 224                                 bug!("{} cannot be reified to a fn ptr", operand.layout.ty)
 225                             }
 226                         }
 227                     }
 228                     mir::CastKind::ClosureFnPointer => {
 229                         match operand.layout.ty.sty {
 230                             ty::Closure(def_id, substs) => {
 231                                 let instance = monomorphize::resolve_closure(
 232                                     bx.cx().tcx, def_id, substs, ty::ClosureKind::FnOnce);
 233                                 OperandValue::Immediate(callee::get_fn(bx.cx(), instance))
 234                             }
 235                             _ => {
 236                                 bug!("{} cannot be cast to a fn ptr", operand.layout.ty)
 237                             }
 238                         }
 239                     }
 240                     mir::CastKind::UnsafeFnPointer => {
 241                         // this is a no-op at the LLVM level
 242                         operand.val
 243                     }
 244                     mir::CastKind::Unsize => {
 245                         assert!(cast.is_llvm_scalar_pair());
 246                         match operand.val {
 247                             OperandValue::Pair(lldata, llextra) => {
 248                                 // unsize from a fat pointer - this is a
 249                                 // "trait-object-to-supertrait" coercion, for
 250                                 // example,
 251                                 //   &'a fmt::Debug+Send => &'a fmt::Debug,
 252
 253                                 // HACK(eddyb) have to bitcast pointers
 254                                 // until LLVM removes pointee types.
 255                                 let lldata = bx.pointercast(lldata,
 256                                     cast.scalar_pair_element_llvm_type(bx.cx(), 0, true));
 257                                 OperandValue::Pair(lldata, llextra)
 258                             }
 259                             OperandValue::Immediate(lldata) => {
 260                                 // "standard" unsize
 261                                 let (lldata, llextra) = base::unsize_thin_ptr(&bx, lldata,
 262                                     operand.layout.ty, cast.ty);
 263                                 OperandValue::Pair(lldata, llextra)
 264                             }
 265                             OperandValue::Ref(..) => {
 266                                 bug!("by-ref operand {:?} in codegen_rvalue_operand",
 267                                      operand);
 268                             }
 269                         }
 270                     }
 271                     mir::CastKind::Misc if operand.layout.is_llvm_scalar_pair() => {
 272                         if let OperandValue::Pair(data_ptr, meta) = operand.val {
 273                             if cast.is_llvm_scalar_pair() {
 274                                 let data_cast = bx.pointercast(data_ptr,
 275                                     cast.scalar_pair_element_llvm_type(bx.cx(), 0, true));
 276                                 OperandValue::Pair(data_cast, meta)
 277                             } else { // cast to thin-ptr
 278                                 // Cast of fat-ptr to thin-ptr is an extraction of data-ptr and
 279                                 // pointer-cast of that pointer to desired pointer type.
 280                                 let llcast_ty = cast.immediate_llvm_type(bx.cx());
 281                                 let llval = bx.pointercast(data_ptr, llcast_ty);
 282                                 OperandValue::Immediate(llval)
 283                             }
 284                         } else {
 285                             bug!("Unexpected non-Pair operand")
 286                         }
 287                     }
 288                     mir::CastKind::Misc => {
 289                         assert!(cast.is_llvm_immediate());
 290                         let ll_t_out = cast.immediate_llvm_type(bx.cx());
 291                         if operand.layout.abi.is_uninhabited() {
 292                             let val = OperandValue::Immediate(bx.cx().const_undef(ll_t_out));
 293                             return (bx, OperandRef {
 294                                 val,
 295                                 layout: cast,
 296                             });
 297                         }
 298                         let r_t_in = CastTy::from_ty(operand.layout.ty)
 299                             .expect("bad input type for cast");
 300                         let r_t_out = CastTy::from_ty(cast.ty).expect("bad output type for cast");
 301                         let ll_t_in = operand.layout.immediate_llvm_type(bx.cx());
 302                         match operand.layout.variants {
 303                             layout::Variants::Single { index } => {
 304                                 if let Some(def) = operand.layout.ty.ty_adt_def() {
 305                                     let discr_val = def
 306                                         .discriminant_for_variant(bx.cx().tcx, index)
 307                                         .val;
 308                                     let discr = bx.cx().const_uint_big(ll_t_out, discr_val);
 309                                     return (bx, OperandRef {
 310                                         val: OperandValue::Immediate(discr),
 311                                         layout: cast,
 312                                     });
 313                                 }
 314                             }
 315                             layout::Variants::Tagged { .. } |
 316                             layout::Variants::NicheFilling { .. } => {},
 317                         }
 318                         let llval = operand.immediate();
 319
 320                         let mut signed = false;
 321                         if let layout::Abi::Scalar(ref scalar) = operand.layout.abi {
 322                             if let layout::Int(_, s) = scalar.value {
 323                                 // We use `i1` for bytes that are always `0` or `1`,
 324                                 // e.g. `#[repr(i8)] enum E { A, B }`, but we can't
 325                                 // let LLVM interpret the `i1` as signed, because
 326                                 // then `i1 1` (i.e. E::B) is effectively `i8 -1`.
 327                                 signed = !scalar.is_bool() && s;
 328
 329                                 let er = scalar.valid_range_exclusive(bx.cx());
 330                                 if er.end != er.start &&
 331                                    scalar.valid_range.end() > scalar.valid_range.start() {
 332                                     // We want `table[e as usize]` to not
 333                                     // have bound checks, and this is the most
 334                                     // convenient place to put the `assume`.
 335
 336                                     base::call_assume(&bx, bx.icmp(
 337                                         IntPredicate::IntULE,
 338                                         llval,
 339                                         bx.cx().const_uint_big(ll_t_in, *scalar.valid_range.end())
 340                                     ));
 341                                 }
 342                             }
 343                         }
 344
 345                         let newval = match (r_t_in, r_t_out) {
 346                             (CastTy::Int(_), CastTy::Int(_)) => {
 347                                 bx.intcast(llval, ll_t_out, signed)
 348                             }
 349                             (CastTy::Float, CastTy::Float) => {
 350                                 let srcsz = bx.cx().float_width(ll_t_in);
 351                                 let dstsz = bx.cx().float_width(ll_t_out);
 352                                 if dstsz > srcsz {
 353                                     bx.fpext(llval, ll_t_out)
 354                                 } else if srcsz > dstsz {
 355                                     bx.fptrunc(llval, ll_t_out)
 356                                 } else {
 357                                     llval
 358                                 }
 359                             }
 360                             (CastTy::Ptr(_), CastTy::Ptr(_)) |
 361                             (CastTy::FnPtr, CastTy::Ptr(_)) |
 362                             (CastTy::RPtr(_), CastTy::Ptr(_)) =>
 363                                 bx.pointercast(llval, ll_t_out),
 364                             (CastTy::Ptr(_), CastTy::Int(_)) |
 365                             (CastTy::FnPtr, CastTy::Int(_)) =>
 366                                 bx.ptrtoint(llval, ll_t_out),
 367                             (CastTy::Int(_), CastTy::Ptr(_)) => {
 368                                 let usize_llval = bx.intcast(llval, bx.cx().isize_ty, signed);
 369                                 bx.inttoptr(usize_llval, ll_t_out)
 370                             }
 371                             (CastTy::Int(_), CastTy::Float) =>
 372                                 cast_int_to_float(&bx, signed, llval, ll_t_in, ll_t_out),
 373                             (CastTy::Float, CastTy::Int(IntTy::I)) =>
 374                                 cast_float_to_int(&bx, true, llval, ll_t_in, ll_t_out),
 375                             (CastTy::Float, CastTy::Int(_)) =>
 376                                 cast_float_to_int(&bx, false, llval, ll_t_in, ll_t_out),
 377                             _ => bug!("unsupported cast: {:?} to {:?}", operand.layout.ty, cast.ty)
 378                         };
 379                         OperandValue::Immediate(newval)
 380                     }
 381                 };
 382                 (bx, OperandRef {
 383                     val,
 384                     layout: cast
 385                 })
 386             }
 387
 388             mir::Rvalue::Ref(_, bk, ref place) => {
 389                 let cg_place = self.codegen_place(&bx, place);
 390
 391                 let ty = cg_place.layout.ty;
 392
 393                 // Note: places are indirect, so storing the `llval` into the
 394                 // destination effectively creates a reference.
 395                 let val = if !bx.cx().type_has_metadata(ty) {
 396                     OperandValue::Immediate(cg_place.llval)
 397                 } else {
 398                     OperandValue::Pair(cg_place.llval, cg_place.llextra.unwrap())
 399                 };
 400                 (bx, OperandRef {
 401                     val,
 402                     layout: self.cx.layout_of(self.cx.tcx.mk_ref(
 403                         self.cx.tcx.types.re_erased,
 404                         ty::TypeAndMut { ty, mutbl: bk.to_mutbl_lossy() }
 405                     )),
 406                 })
 407             }
 408
 409             mir::Rvalue::Len(ref place) => {
 410                 let size = self.evaluate_array_len(&bx, place);
 411                 let operand = OperandRef {
 412                     val: OperandValue::Immediate(size),
 413                     layout: bx.cx().layout_of(bx.tcx().types.usize),
 414                 };
 415                 (bx, operand)
 416             }
 417
 418             mir::Rvalue::BinaryOp(op, ref lhs, ref rhs) => {
 419                 let lhs = self.codegen_operand(&bx, lhs);
 420                 let rhs = self.codegen_operand(&bx, rhs);
 421                 let llresult = match (lhs.val, rhs.val) {
 422                     (OperandValue::Pair(lhs_addr, lhs_extra),
 423                      OperandValue::Pair(rhs_addr, rhs_extra)) => {
 424                         self.codegen_fat_ptr_binop(&bx, op,
 425                                                  lhs_addr, lhs_extra,
 426                                                  rhs_addr, rhs_extra,
 427                                                  lhs.layout.ty)
 428                     }
 429
 430                     (OperandValue::Immediate(lhs_val),
 431                      OperandValue::Immediate(rhs_val)) => {
 432                         self.codegen_scalar_binop(&bx, op, lhs_val, rhs_val, lhs.layout.ty)
 433                     }
 434
 435                     _ => bug!()
 436                 };
 437                 let operand = OperandRef {
 438                     val: OperandValue::Immediate(llresult),
 439                     layout: bx.cx().layout_of(
 440                         op.ty(bx.tcx(), lhs.layout.ty, rhs.layout.ty)),
 441                 };
 442                 (bx, operand)
 443             }
 444             mir::Rvalue::CheckedBinaryOp(op, ref lhs, ref rhs) => {
 445                 let lhs = self.codegen_operand(&bx, lhs);
 446                 let rhs = self.codegen_operand(&bx, rhs);
 447                 let result = self.codegen_scalar_checked_binop(&bx, op,
 448                                                              lhs.immediate(), rhs.immediate(),
 449                                                              lhs.layout.ty);
 450                 let val_ty = op.ty(bx.tcx(), lhs.layout.ty, rhs.layout.ty);
 451                 let operand_ty = bx.tcx().intern_tup(&[val_ty, bx.tcx().types.bool]);
 452                 let operand = OperandRef {
 453                     val: result,
 454                     layout: bx.cx().layout_of(operand_ty)
 455                 };
 456
 457                 (bx, operand)
 458             }
 459
 460             mir::Rvalue::UnaryOp(op, ref operand) => {
 461                 let operand = self.codegen_operand(&bx, operand);
 462                 let lloperand = operand.immediate();
 463                 let is_float = operand.layout.ty.is_fp();
 464                 let llval = match op {
 465                     mir::UnOp::Not => bx.not(lloperand),
 466                     mir::UnOp::Neg => if is_float {
 467                         bx.fneg(lloperand)
 468                     } else {
 469                         bx.neg(lloperand)
 470                     }
 471                 };
 472                 (bx, OperandRef {
 473                     val: OperandValue::Immediate(llval),
 474                     layout: operand.layout,
 475                 })
 476             }
 477
 478             mir::Rvalue::Discriminant(ref place) => {
 479                 let discr_ty = rvalue.ty(&*self.mir, bx.tcx());
 480                 let discr =  self.codegen_place(&bx, place)
 481                     .codegen_get_discr(&bx, discr_ty);
 482                 (bx, OperandRef {
 483                     val: OperandValue::Immediate(discr),
 484                     layout: self.cx.layout_of(discr_ty)
 485                 })
 486             }
 487
 488             mir::Rvalue::NullaryOp(mir::NullOp::SizeOf, ty) => {
 489                 assert!(bx.cx().type_is_sized(ty));
 490                 let val = bx.cx().const_usize(bx.cx().size_of(ty).bytes());
 491                 let tcx = self.cx.tcx;
 492                 (bx, OperandRef {
 493                     val: OperandValue::Immediate(val),
 494                     layout: self.cx.layout_of(tcx.types.usize),
 495                 })
 496             }
 497
 498             mir::Rvalue::NullaryOp(mir::NullOp::Box, content_ty) => {
 499                 let content_ty: Ty<'tcx> = self.monomorphize(&content_ty);
 500                 let (size, align) = bx.cx().size_and_align_of(content_ty);
 501                 let llsize = bx.cx().const_usize(size.bytes());
 502                 let llalign = bx.cx().const_usize(align.abi());
 503                 let box_layout = bx.cx().layout_of(bx.tcx().mk_box(content_ty));
 504                 let llty_ptr = box_layout.llvm_type(bx.cx());
 505
 506                 // Allocate space:
 507                 let def_id = match bx.tcx().lang_items().require(ExchangeMallocFnLangItem) {
 508                     Ok(id) => id,
 509                     Err(s) => {
 510                         bx.sess().fatal(&format!("allocation of `{}` {}", box_layout.ty, s));
 511                     }
 512                 };
 513                 let instance = ty::Instance::mono(bx.tcx(), def_id);
 514                 let r = callee::get_fn(bx.cx(), instance);
 515                 let val = bx.pointercast(bx.call(r, &[llsize, llalign], None), llty_ptr);
 516
 517                 let operand = OperandRef {
 518                     val: OperandValue::Immediate(val),
 519                     layout: box_layout,
 520                 };
 521                 (bx, operand)
 522             }
 523             mir::Rvalue::Use(ref operand) => {
 524                 let operand = self.codegen_operand(&bx, operand);
 525                 (bx, operand)
 526             }
 527             mir::Rvalue::Repeat(..) |
 528             mir::Rvalue::Aggregate(..) => {
 529                 // According to `rvalue_creates_operand`, only ZST
 530                 // aggregate rvalues are allowed to be operands.
 531                 let ty = rvalue.ty(self.mir, self.cx.tcx);
 532                 (bx, OperandRef::new_zst(self.cx,
 533                     self.cx.layout_of(self.monomorphize(&ty))))
 534             }
 535         }
 536     }
 537
 538     fn evaluate_array_len(
 539         &mut self,
 540         bx: &Builder<'a, 'll, 'tcx>,
 541         place: &mir::Place<'tcx>,
 542     ) -> &'ll Value {
 543         // ZST are passed as operands and require special handling
 544         // because codegen_place() panics if Local is operand.
 545         if let mir::Place::Local(index) = *place {
 546             if let LocalRef::Operand(Some(op)) = self.locals[index] {
 547                 if let ty::Array(_, n) = op.layout.ty.sty {
 548                     let n = n.unwrap_usize(bx.cx().tcx);
 549                     return bx.cx().const_usize(n);
 550                 }
 551             }
 552         }
 553         // use common size calculation for non zero-sized types
 554         let cg_value = self.codegen_place(&bx, place);
 555         return cg_value.len(bx.cx());
 556     }
 557
 558     pub fn codegen_scalar_binop(
 559         &mut self,
 560         bx: &Builder<'a, 'll, 'tcx>,
 561         op: mir::BinOp,
 562         lhs: &'ll Value,
 563         rhs: &'ll Value,
 564         input_ty: Ty<'tcx>,
 565     ) -> &'ll Value {
 566         let is_float = input_ty.is_fp();
 567         let is_signed = input_ty.is_signed();
 568         let is_unit = input_ty.is_unit();
 569         match op {
 570             mir::BinOp::Add => if is_float {
 571                 bx.fadd(lhs, rhs)
 572             } else {
 573                 bx.add(lhs, rhs)
 574             },
 575             mir::BinOp::Sub => if is_float {
 576                 bx.fsub(lhs, rhs)
 577             } else {
 578                 bx.sub(lhs, rhs)
 579             },
 580             mir::BinOp::Mul => if is_float {
 581                 bx.fmul(lhs, rhs)
 582             } else {
 583                 bx.mul(lhs, rhs)
 584             },
 585             mir::BinOp::Div => if is_float {
 586                 bx.fdiv(lhs, rhs)
 587             } else if is_signed {
 588                 bx.sdiv(lhs, rhs)
 589             } else {
 590                 bx.udiv(lhs, rhs)
 591             },
 592             mir::BinOp::Rem => if is_float {
 593                 bx.frem(lhs, rhs)
 594             } else if is_signed {
 595                 bx.srem(lhs, rhs)
 596             } else {
 597                 bx.urem(lhs, rhs)
 598             },
 599             mir::BinOp::BitOr => bx.or(lhs, rhs),
 600             mir::BinOp::BitAnd => bx.and(lhs, rhs),
 601             mir::BinOp::BitXor => bx.xor(lhs, rhs),
 602             mir::BinOp::Offset => bx.inbounds_gep(lhs, &[rhs]),
 603             mir::BinOp::Shl => common::build_unchecked_lshift(bx, lhs, rhs),
 604             mir::BinOp::Shr => common::build_unchecked_rshift(bx, input_ty, lhs, rhs),
 605             mir::BinOp::Ne | mir::BinOp::Lt | mir::BinOp::Gt |
 606             mir::BinOp::Eq | mir::BinOp::Le | mir::BinOp::Ge => if is_unit {
 607                 bx.cx().const_bool(match op {
 608                     mir::BinOp::Ne | mir::BinOp::Lt | mir::BinOp::Gt => false,
 609                     mir::BinOp::Eq | mir::BinOp::Le | mir::BinOp::Ge => true,
 610                     _ => unreachable!()
 611                 })
 612             } else if is_float {
 613                 bx.fcmp(
 614                     base::bin_op_to_fcmp_predicate(op.to_hir_binop()),
 615                     lhs, rhs
 616                 )
 617             } else {
 618                 bx.icmp(
 619                     base::bin_op_to_icmp_predicate(op.to_hir_binop(), is_signed),
 620                     lhs, rhs
 621                 )
 622             }
 623         }
 624     }
 625
 626     pub fn codegen_fat_ptr_binop(
 627         &mut self,
 628         bx: &Builder<'a, 'll, 'tcx>,
 629         op: mir::BinOp,
 630         lhs_addr: &'ll Value,
 631         lhs_extra: &'ll Value,
 632         rhs_addr: &'ll Value,
 633         rhs_extra: &'ll Value,
 634         _input_ty: Ty<'tcx>,
 635     ) -> &'ll Value {
 636         match op {
 637             mir::BinOp::Eq => {
 638                 bx.and(
 639                     bx.icmp(IntPredicate::IntEQ, lhs_addr, rhs_addr),
 640                     bx.icmp(IntPredicate::IntEQ, lhs_extra, rhs_extra)
 641                 )
 642             }
 643             mir::BinOp::Ne => {
 644                 bx.or(
 645                     bx.icmp(IntPredicate::IntNE, lhs_addr, rhs_addr),
 646                     bx.icmp(IntPredicate::IntNE, lhs_extra, rhs_extra)
 647                 )
 648             }
 649             mir::BinOp::Le | mir::BinOp::Lt |
 650             mir::BinOp::Ge | mir::BinOp::Gt => {
 651                 // a OP b ~ a.0 STRICT(OP) b.0 | (a.0 == b.0 && a.1 OP a.1)
 652                 let (op, strict_op) = match op {
 653                     mir::BinOp::Lt => (IntPredicate::IntULT, IntPredicate::IntULT),
 654                     mir::BinOp::Le => (IntPredicate::IntULE, IntPredicate::IntULT),
 655                     mir::BinOp::Gt => (IntPredicate::IntUGT, IntPredicate::IntUGT),
 656                     mir::BinOp::Ge => (IntPredicate::IntUGE, IntPredicate::IntUGT),
 657                     _ => bug!(),
 658                 };
 659
 660                 bx.or(
 661                     bx.icmp(strict_op, lhs_addr, rhs_addr),
 662                     bx.and(
 663                         bx.icmp(IntPredicate::IntEQ, lhs_addr, rhs_addr),
 664                         bx.icmp(op, lhs_extra, rhs_extra)
 665                     )
 666                 )
 667             }
 668             _ => {
 669                 bug!("unexpected fat ptr binop");
 670             }
 671         }
 672     }
 673
 674     pub fn codegen_scalar_checked_binop(&mut self,
 675                                       bx: &Builder<'a, 'll, 'tcx>,
 676                                       op: mir::BinOp,
 677                                       lhs: &'ll Value,
 678                                       rhs: &'ll Value,
 679                                       input_ty: Ty<'tcx>) -> OperandValue<&'ll Value> {
 680         // This case can currently arise only from functions marked
 681         // with #[rustc_inherit_overflow_checks] and inlined from
 682         // another crate (mostly core::num generic/#[inline] fns),
 683         // while the current crate doesn't use overflow checks.
 684         if !bx.cx().check_overflow {
 685             let val = self.codegen_scalar_binop(bx, op, lhs, rhs, input_ty);
 686             return OperandValue::Pair(val, bx.cx().const_bool(false));
 687         }
 688
 689         let (val, of) = match op {
 690             // These are checked using intrinsics
 691             mir::BinOp::Add | mir::BinOp::Sub | mir::BinOp::Mul => {
 692                 let oop = match op {
 693                     mir::BinOp::Add => OverflowOp::Add,
 694                     mir::BinOp::Sub => OverflowOp::Sub,
 695                     mir::BinOp::Mul => OverflowOp::Mul,
 696                     _ => unreachable!()
 697                 };
 698                 let intrinsic = get_overflow_intrinsic(oop, bx, input_ty);
 699                 let res = bx.call(intrinsic, &[lhs, rhs], None);
 700
 701                 (bx.extract_value(res, 0),
 702                  bx.extract_value(res, 1))
 703             }
 704             mir::BinOp::Shl | mir::BinOp::Shr => {
 705                 let lhs_llty = bx.cx().val_ty(lhs);
 706                 let rhs_llty = bx.cx().val_ty(rhs);
 707                 let invert_mask = common::shift_mask_val(&bx, lhs_llty, rhs_llty, true);
 708                 let outer_bits = bx.and(rhs, invert_mask);
 709
 710                 let of = bx.icmp(IntPredicate::IntNE, outer_bits, bx.cx().const_null(rhs_llty));
 711                 let val = self.codegen_scalar_binop(bx, op, lhs, rhs, input_ty);
 712
 713                 (val, of)
 714             }
 715             _ => {
 716                 bug!("Operator `{:?}` is not a checkable operator", op)
 717             }
 718         };
 719
 720         OperandValue::Pair(val, of)
 721     }
 722
 723     pub fn rvalue_creates_operand(&self, rvalue: &mir::Rvalue<'tcx>) -> bool {
 724         match *rvalue {
 725             mir::Rvalue::Ref(..) |
 726             mir::Rvalue::Len(..) |
 727             mir::Rvalue::Cast(..) | // (*)
 728             mir::Rvalue::BinaryOp(..) |
 729             mir::Rvalue::CheckedBinaryOp(..) |
 730             mir::Rvalue::UnaryOp(..) |
 731             mir::Rvalue::Discriminant(..) |
 732             mir::Rvalue::NullaryOp(..) |
 733             mir::Rvalue::Use(..) => // (*)
 734                 true,
 735             mir::Rvalue::Repeat(..) |
 736             mir::Rvalue::Aggregate(..) => {
 737                 let ty = rvalue.ty(self.mir, self.cx.tcx);
 738                 let ty = self.monomorphize(&ty);
 739                 self.cx.layout_of(ty).is_zst()
 740             }
 741         }
 742
 743         // (*) this is only true if the type is suitable
 744     }
 745 }
 746
 747 #[derive(Copy, Clone)]
 748 enum OverflowOp {
 749     Add, Sub, Mul
 750 }
 751
 752 fn get_overflow_intrinsic(
 753     oop: OverflowOp,
 754     bx: &Builder<'_, 'll, '_>,
 755     ty: Ty
 756 ) -> &'ll Value {
 757     use syntax::ast::IntTy::*;
 758     use syntax::ast::UintTy::*;
 759     use rustc::ty::{Int, Uint};
 760
 761     let tcx = bx.tcx();
 762
 763     let new_sty = match ty.sty {
 764         Int(Isize) => Int(tcx.sess.target.isize_ty),
 765         Uint(Usize) => Uint(tcx.sess.target.usize_ty),
 766         ref t @ Uint(_) | ref t @ Int(_) => t.clone(),
 767         _ => panic!("tried to get overflow intrinsic for op applied to non-int type")
 768     };
 769
 770     let name = match oop {
 771         OverflowOp::Add => match new_sty {
 772             Int(I8) => "llvm.sadd.with.overflow.i8",
 773             Int(I16) => "llvm.sadd.with.overflow.i16",
 774             Int(I32) => "llvm.sadd.with.overflow.i32",
 775             Int(I64) => "llvm.sadd.with.overflow.i64",
 776             Int(I128) => "llvm.sadd.with.overflow.i128",
 777
 778             Uint(U8) => "llvm.uadd.with.overflow.i8",
 779             Uint(U16) => "llvm.uadd.with.overflow.i16",
 780             Uint(U32) => "llvm.uadd.with.overflow.i32",
 781             Uint(U64) => "llvm.uadd.with.overflow.i64",
 782             Uint(U128) => "llvm.uadd.with.overflow.i128",
 783
 784             _ => unreachable!(),
 785         },
 786         OverflowOp::Sub => match new_sty {
 787             Int(I8) => "llvm.ssub.with.overflow.i8",
 788             Int(I16) => "llvm.ssub.with.overflow.i16",
 789             Int(I32) => "llvm.ssub.with.overflow.i32",
 790             Int(I64) => "llvm.ssub.with.overflow.i64",
 791             Int(I128) => "llvm.ssub.with.overflow.i128",
 792
 793             Uint(U8) => "llvm.usub.with.overflow.i8",
 794             Uint(U16) => "llvm.usub.with.overflow.i16",
 795             Uint(U32) => "llvm.usub.with.overflow.i32",
 796             Uint(U64) => "llvm.usub.with.overflow.i64",
 797             Uint(U128) => "llvm.usub.with.overflow.i128",
 798
 799             _ => unreachable!(),
 800         },
 801         OverflowOp::Mul => match new_sty {
 802             Int(I8) => "llvm.smul.with.overflow.i8",
 803             Int(I16) => "llvm.smul.with.overflow.i16",
 804             Int(I32) => "llvm.smul.with.overflow.i32",
 805             Int(I64) => "llvm.smul.with.overflow.i64",
 806             Int(I128) => "llvm.smul.with.overflow.i128",
 807
 808             Uint(U8) => "llvm.umul.with.overflow.i8",
 809             Uint(U16) => "llvm.umul.with.overflow.i16",
 810             Uint(U32) => "llvm.umul.with.overflow.i32",
 811             Uint(U64) => "llvm.umul.with.overflow.i64",
 812             Uint(U128) => "llvm.umul.with.overflow.i128",
 813
 814             _ => unreachable!(),
 815         },
 816     };
 817
 818     bx.cx().get_intrinsic(&name)
 819 }
 820
 821 fn cast_int_to_float(bx: &Builder<'_, 'll, '_>,
 822                      signed: bool,
 823                      x: &'ll Value,
 824                      int_ty: &'ll Type,
 825                      float_ty: &'ll Type) -> &'ll Value {
 826     // Most integer types, even i128, fit into [-f32::MAX, f32::MAX] after rounding.
 827     // It's only u128 -> f32 that can cause overflows (i.e., should yield infinity).
 828     // LLVM's uitofp produces undef in those cases, so we manually check for that case.
 829     let is_u128_to_f32 = !signed &&
 830         bx.cx().int_width(int_ty) == 128 &&
 831         bx.cx().float_width(float_ty) == 32;
 832     if is_u128_to_f32 {
 833         // All inputs greater or equal to (f32::MAX + 0.5 ULP) are rounded to infinity,
 834         // and for everything else LLVM's uitofp works just fine.
 835         use rustc_apfloat::ieee::Single;
 836         use rustc_apfloat::Float;
 837         const MAX_F32_PLUS_HALF_ULP: u128 = ((1 << (Single::PRECISION + 1)) - 1)
 838                                             << (Single::MAX_EXP - Single::PRECISION as i16);
 839         let max = bx.cx().const_uint_big(int_ty, MAX_F32_PLUS_HALF_ULP);
 840         let overflow = bx.icmp(IntPredicate::IntUGE, x, max);
 841         let infinity_bits = bx.cx().const_u32(ieee::Single::INFINITY.to_bits() as u32);
 842         let infinity = bx.bitcast(infinity_bits, float_ty);
 843         bx.select(overflow, infinity, bx.uitofp(x, float_ty))
 844     } else {
 845         if signed {
 846             bx.sitofp(x, float_ty)
 847         } else {
 848             bx.uitofp(x, float_ty)
 849         }
 850     }
 851 }
 852
 853 fn cast_float_to_int(bx: &Builder<'_, 'll, '_>,
 854                      signed: bool,
 855                      x: &'ll Value,
 856                      float_ty: &'ll Type,
 857                      int_ty: &'ll Type) -> &'ll Value {
 858     let fptosui_result = if signed {
 859         bx.fptosi(x, int_ty)
 860     } else {
 861         bx.fptoui(x, int_ty)
 862     };
 863
 864     if !bx.sess().opts.debugging_opts.saturating_float_casts {
 865         return fptosui_result;
 866     }
 867     // LLVM's fpto[su]i returns undef when the input x is infinite, NaN, or does not fit into the
 868     // destination integer type after rounding towards zero. This `undef` value can cause UB in
 869     // safe code (see issue #10184), so we implement a saturating conversion on top of it:
 870     // Semantically, the mathematical value of the input is rounded towards zero to the next
 871     // mathematical integer, and then the result is clamped into the range of the destination
 872     // integer type. Positive and negative infinity are mapped to the maximum and minimum value of
 873     // the destination integer type. NaN is mapped to 0.
 874     //
 875     // Define f_min and f_max as the largest and smallest (finite) floats that are exactly equal to
 876     // a value representable in int_ty.
 877     // They are exactly equal to int_ty::{MIN,MAX} if float_ty has enough significand bits.
 878     // Otherwise, int_ty::MAX must be rounded towards zero, as it is one less than a power of two.
 879     // int_ty::MIN, however, is either zero or a negative power of two and is thus exactly
 880     // representable. Note that this only works if float_ty's exponent range is sufficiently large.
 881     // f16 or 256 bit integers would break this property. Right now the smallest float type is f32
 882     // with exponents ranging up to 127, which is barely enough for i128::MIN = -2^127.
 883     // On the other hand, f_max works even if int_ty::MAX is greater than float_ty::MAX. Because
 884     // we're rounding towards zero, we just get float_ty::MAX (which is always an integer).
 885     // This already happens today with u128::MAX = 2^128 - 1 > f32::MAX.
 886     let int_max = |signed: bool, int_ty: &'ll Type| -> u128 {
 887         let shift_amount = 128 - bx.cx().int_width(int_ty);
 888         if signed {
 889             i128::MAX as u128 >> shift_amount
 890         } else {
 891             u128::MAX >> shift_amount
 892         }
 893     };
 894     let int_min = |signed: bool, int_ty: &'ll Type| -> i128 {
 895         if signed {
 896             i128::MIN >> (128 - bx.cx().int_width(int_ty))
 897         } else {
 898             0
 899         }
 900     };
 901
 902     let compute_clamp_bounds_single = |signed: bool, int_ty: &'ll Type| -> (u128, u128) {
 903         let rounded_min = ieee::Single::from_i128_r(int_min(signed, int_ty), Round::TowardZero);
 904         assert_eq!(rounded_min.status, Status::OK);
 905         let rounded_max = ieee::Single::from_u128_r(int_max(signed, int_ty), Round::TowardZero);
 906         assert!(rounded_max.value.is_finite());
 907         (rounded_min.value.to_bits(), rounded_max.value.to_bits())
 908     };
 909     let compute_clamp_bounds_double = |signed: bool, int_ty: &'ll Type| -> (u128, u128) {
 910         let rounded_min = ieee::Double::from_i128_r(int_min(signed, int_ty), Round::TowardZero);
 911         assert_eq!(rounded_min.status, Status::OK);
 912         let rounded_max = ieee::Double::from_u128_r(int_max(signed, int_ty), Round::TowardZero);
 913         assert!(rounded_max.value.is_finite());
 914         (rounded_min.value.to_bits(), rounded_max.value.to_bits())
 915     };
 916
 917     let float_bits_to_llval = |bits| {
 918         let bits_llval = match bx.cx().float_width(float_ty) {
 919             32 => bx.cx().const_u32(bits as u32),
 920             64 => bx.cx().const_u64(bits as u64),
 921             n => bug!("unsupported float width {}", n),
 922         };
 923         bx.bitcast(bits_llval, float_ty)
 924     };
 925     let (f_min, f_max) = match bx.cx().float_width(float_ty) {
 926         32 => compute_clamp_bounds_single(signed, int_ty),
 927         64 => compute_clamp_bounds_double(signed, int_ty),
 928         n => bug!("unsupported float width {}", n),
 929     };
 930     let f_min = float_bits_to_llval(f_min);
 931     let f_max = float_bits_to_llval(f_max);
 932     // To implement saturation, we perform the following steps:
 933     //
 934     // 1. Cast x to an integer with fpto[su]i. This may result in undef.
 935     // 2. Compare x to f_min and f_max, and use the comparison results to select:
 936     //  a) int_ty::MIN if x < f_min or x is NaN
 937     //  b) int_ty::MAX if x > f_max
 938     //  c) the result of fpto[su]i otherwise
 939     // 3. If x is NaN, return 0.0, otherwise return the result of step 2.
 940     //
 941     // This avoids resulting undef because values in range [f_min, f_max] by definition fit into the
 942     // destination type. It creates an undef temporary, but *producing* undef is not UB. Our use of
 943     // undef does not introduce any non-determinism either.
 944     // More importantly, the above procedure correctly implements saturating conversion.
 945     // Proof (sketch):
 946     // If x is NaN, 0 is returned by definition.
 947     // Otherwise, x is finite or infinite and thus can be compared with f_min and f_max.
 948     // This yields three cases to consider:
 949     // (1) if x in [f_min, f_max], the result of fpto[su]i is returned, which agrees with
 950     //     saturating conversion for inputs in that range.
 951     // (2) if x > f_max, then x is larger than int_ty::MAX. This holds even if f_max is rounded
 952     //     (i.e., if f_max < int_ty::MAX) because in those cases, nextUp(f_max) is already larger
 953     //     than int_ty::MAX. Because x is larger than int_ty::MAX, the return value of int_ty::MAX
 954     //     is correct.
 955     // (3) if x < f_min, then x is smaller than int_ty::MIN. As shown earlier, f_min exactly equals
 956     //     int_ty::MIN and therefore the return value of int_ty::MIN is correct.
 957     // QED.
 958
 959     // Step 1 was already performed above.
 960
 961     // Step 2: We use two comparisons and two selects, with %s1 being the result:
 962     //     %less_or_nan = fcmp ult %x, %f_min
 963     //     %greater = fcmp olt %x, %f_max
 964     //     %s0 = select %less_or_nan, int_ty::MIN, %fptosi_result
 965     //     %s1 = select %greater, int_ty::MAX, %s0
 966     // Note that %less_or_nan uses an *unordered* comparison. This comparison is true if the
 967     // operands are not comparable (i.e., if x is NaN). The unordered comparison ensures that s1
 968     // becomes int_ty::MIN if x is NaN.
 969     // Performance note: Unordered comparison can be lowered to a "flipped" comparison and a
 970     // negation, and the negation can be merged into the select. Therefore, it not necessarily any
 971     // more expensive than a ordered ("normal") comparison. Whether these optimizations will be
 972     // performed is ultimately up to the backend, but at least x86 does perform them.
 973     let less_or_nan = bx.fcmp(RealPredicate::RealULT, x, f_min);
 974     let greater = bx.fcmp(RealPredicate::RealOGT, x, f_max);
 975     let int_max = bx.cx().const_uint_big(int_ty, int_max(signed, int_ty));
 976     let int_min = bx.cx().const_uint_big(int_ty, int_min(signed, int_ty) as u128);
 977     let s0 = bx.select(less_or_nan, int_min, fptosui_result);
 978     let s1 = bx.select(greater, int_max, s0);
 979
 980     // Step 3: NaN replacement.
 981     // For unsigned types, the above step already yielded int_ty::MIN == 0 if x is NaN.
 982     // Therefore we only need to execute this step for signed integer types.
 983     if signed {
 984         // LLVM has no isNaN predicate, so we use (x == x) instead
 985         bx.select(bx.fcmp(RealPredicate::RealOEQ, x, x), s1, bx.cx().const_uint(int_ty, 0))
 986     } else {
 987         s1
 988     }
 989 }