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 llvm::{self, ValueRef};
  12 use rustc::ty::{self, Ty};
  13 use rustc::ty::cast::{CastTy, IntTy};
  14 use rustc::ty::layout::{self, LayoutOf};
  15 use rustc::mir;
  16 use rustc::middle::lang_items::ExchangeMallocFnLangItem;
  17 use rustc_apfloat::{ieee, Float, Status, Round};
  18 use std::{u128, i128};
  19
  20 use base;
  21 use builder::Builder;
  22 use callee;
  23 use common::{self, val_ty};
  24 use common::{C_bool, C_u8, C_i32, C_u32, C_u64, C_undef, C_null, C_usize, C_uint, C_uint_big};
  25 use consts;
  26 use monomorphize;
  27 use type_::Type;
  28 use type_of::LayoutLlvmExt;
  29 use value::Value;
  30
  31 use super::{FunctionCx, LocalRef};
  32 use super::operand::{OperandRef, OperandValue};
  33 use super::place::PlaceRef;
  34
  35 impl FunctionCx<'a, 'll, 'tcx> {
  36     pub fn codegen_rvalue(&mut self,
  37                         bx: Builder<'a, 'll, 'tcx>,
  38                         dest: PlaceRef<'tcx>,
  39                         rvalue: &mir::Rvalue<'tcx>)
  40                         -> Builder<'a, 'll, 'tcx>
  41     {
  42         debug!("codegen_rvalue(dest.llval={:?}, rvalue={:?})",
  43                Value(dest.llval), rvalue);
  44
  45         match *rvalue {
  46            mir::Rvalue::Use(ref operand) => {
  47                let cg_operand = self.codegen_operand(&bx, operand);
  48                // FIXME: consider not copying constants through stack. (fixable by codegenning
  49                // constants into OperandValue::Ref, why don’t we do that yet if we don’t?)
  50                cg_operand.val.store(&bx, dest);
  51                bx
  52            }
  53
  54             mir::Rvalue::Cast(mir::CastKind::Unsize, ref source, _) => {
  55                 // The destination necessarily contains a fat pointer, so if
  56                 // it's a scalar pair, it's a fat pointer or newtype thereof.
  57                 if dest.layout.is_llvm_scalar_pair() {
  58                     // into-coerce of a thin pointer to a fat pointer - just
  59                     // use the operand path.
  60                     let (bx, temp) = self.codegen_rvalue_operand(bx, rvalue);
  61                     temp.val.store(&bx, dest);
  62                     return bx;
  63                 }
  64
  65                 // Unsize of a nontrivial struct. I would prefer for
  66                 // this to be eliminated by MIR building, but
  67                 // `CoerceUnsized` can be passed by a where-clause,
  68                 // so the (generic) MIR may not be able to expand it.
  69                 let operand = self.codegen_operand(&bx, source);
  70                 match operand.val {
  71                     OperandValue::Pair(..) |
  72                     OperandValue::Immediate(_) => {
  73                         // unsize from an immediate structure. We don't
  74                         // really need a temporary alloca here, but
  75                         // avoiding it would require us to have
  76                         // `coerce_unsized_into` use extractvalue to
  77                         // index into the struct, and this case isn't
  78                         // important enough for it.
  79                         debug!("codegen_rvalue: creating ugly alloca");
  80                         let scratch = PlaceRef::alloca(&bx, operand.layout, "__unsize_temp");
  81                         scratch.storage_live(&bx);
  82                         operand.val.store(&bx, scratch);
  83                         base::coerce_unsized_into(&bx, scratch, dest);
  84                         scratch.storage_dead(&bx);
  85                     }
  86                     OperandValue::Ref(llref, align) => {
  87                         let source = PlaceRef::new_sized(llref, operand.layout, align);
  88                         base::coerce_unsized_into(&bx, source, dest);
  89                     }
  90                 }
  91                 bx
  92             }
  93
  94             mir::Rvalue::Repeat(ref elem, count) => {
  95                 let cg_elem = self.codegen_operand(&bx, elem);
  96
  97                 // Do not generate the loop for zero-sized elements or empty arrays.
  98                 if dest.layout.is_zst() {
  99                     return bx;
 100                 }
 101
 102                 let start = dest.project_index(&bx, C_usize(bx.cx, 0)).llval;
 103
 104                 if let OperandValue::Immediate(v) = cg_elem.val {
 105                     let align = C_i32(bx.cx, dest.align.abi() as i32);
 106                     let size = C_usize(bx.cx, dest.layout.size.bytes());
 107
 108                     // Use llvm.memset.p0i8.* to initialize all zero arrays
 109                     if common::is_const_integral(v) && common::const_to_uint(v) == 0 {
 110                         let fill = C_u8(bx.cx, 0);
 111                         base::call_memset(&bx, start, fill, size, align, false);
 112                         return bx;
 113                     }
 114
 115                     // Use llvm.memset.p0i8.* to initialize byte arrays
 116                     let v = base::from_immediate(&bx, v);
 117                     if common::val_ty(v) == Type::i8(bx.cx) {
 118                         base::call_memset(&bx, start, v, size, align, false);
 119                         return bx;
 120                     }
 121                 }
 122
 123                 let count = C_usize(bx.cx, count);
 124                 let end = dest.project_index(&bx, count).llval;
 125
 126                 let header_bx = bx.build_sibling_block("repeat_loop_header");
 127                 let body_bx = bx.build_sibling_block("repeat_loop_body");
 128                 let next_bx = bx.build_sibling_block("repeat_loop_next");
 129
 130                 bx.br(header_bx.llbb());
 131                 let current = header_bx.phi(common::val_ty(start), &[start], &[bx.llbb()]);
 132
 133                 let keep_going = header_bx.icmp(llvm::IntNE, current, end);
 134                 header_bx.cond_br(keep_going, body_bx.llbb(), next_bx.llbb());
 135
 136                 cg_elem.val.store(&body_bx,
 137                     PlaceRef::new_sized(current, cg_elem.layout, dest.align));
 138
 139                 let next = body_bx.inbounds_gep(current, &[C_usize(bx.cx, 1)]);
 140                 body_bx.br(header_bx.llbb());
 141                 header_bx.add_incoming_to_phi(current, next, body_bx.llbb());
 142
 143                 next_bx
 144             }
 145
 146             mir::Rvalue::Aggregate(ref kind, ref operands) => {
 147                 let (dest, active_field_index) = match **kind {
 148                     mir::AggregateKind::Adt(adt_def, variant_index, _, active_field_index) => {
 149                         dest.codegen_set_discr(&bx, variant_index);
 150                         if adt_def.is_enum() {
 151                             (dest.project_downcast(&bx, variant_index), active_field_index)
 152                         } else {
 153                             (dest, active_field_index)
 154                         }
 155                     }
 156                     _ => (dest, None)
 157                 };
 158                 for (i, operand) in operands.iter().enumerate() {
 159                     let op = self.codegen_operand(&bx, operand);
 160                     // Do not generate stores and GEPis for zero-sized fields.
 161                     if !op.layout.is_zst() {
 162                         let field_index = active_field_index.unwrap_or(i);
 163                         op.val.store(&bx, dest.project_field(&bx, field_index));
 164                     }
 165                 }
 166                 bx
 167             }
 168
 169             _ => {
 170                 assert!(self.rvalue_creates_operand(rvalue));
 171                 let (bx, temp) = self.codegen_rvalue_operand(bx, rvalue);
 172                 temp.val.store(&bx, dest);
 173                 bx
 174             }
 175         }
 176     }
 177
 178     pub fn codegen_rvalue_operand(&mut self,
 179                                 bx: Builder<'a, 'll, 'tcx>,
 180                                 rvalue: &mir::Rvalue<'tcx>)
 181                                 -> (Builder<'a, 'll, 'tcx>, OperandRef<'tcx>)
 182     {
 183         assert!(self.rvalue_creates_operand(rvalue), "cannot codegen {:?} to operand", rvalue);
 184
 185         match *rvalue {
 186             mir::Rvalue::Cast(ref kind, ref source, mir_cast_ty) => {
 187                 let operand = self.codegen_operand(&bx, source);
 188                 debug!("cast operand is {:?}", operand);
 189                 let cast = bx.cx.layout_of(self.monomorphize(&mir_cast_ty));
 190
 191                 let val = match *kind {
 192                     mir::CastKind::ReifyFnPointer => {
 193                         match operand.layout.ty.sty {
 194                             ty::TyFnDef(def_id, substs) => {
 195                                 if bx.cx.tcx.has_attr(def_id, "rustc_args_required_const") {
 196                                     bug!("reifying a fn ptr that requires \
 197                                           const arguments");
 198                                 }
 199                                 OperandValue::Immediate(
 200                                     callee::resolve_and_get_fn(bx.cx, def_id, substs))
 201                             }
 202                             _ => {
 203                                 bug!("{} cannot be reified to a fn ptr", operand.layout.ty)
 204                             }
 205                         }
 206                     }
 207                     mir::CastKind::ClosureFnPointer => {
 208                         match operand.layout.ty.sty {
 209                             ty::TyClosure(def_id, substs) => {
 210                                 let instance = monomorphize::resolve_closure(
 211                                     bx.cx.tcx, def_id, substs, ty::ClosureKind::FnOnce);
 212                                 OperandValue::Immediate(callee::get_fn(bx.cx, instance))
 213                             }
 214                             _ => {
 215                                 bug!("{} cannot be cast to a fn ptr", operand.layout.ty)
 216                             }
 217                         }
 218                     }
 219                     mir::CastKind::UnsafeFnPointer => {
 220                         // this is a no-op at the LLVM level
 221                         operand.val
 222                     }
 223                     mir::CastKind::Unsize => {
 224                         assert!(cast.is_llvm_scalar_pair());
 225                         match operand.val {
 226                             OperandValue::Pair(lldata, llextra) => {
 227                                 // unsize from a fat pointer - this is a
 228                                 // "trait-object-to-supertrait" coercion, for
 229                                 // example,
 230                                 //   &'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(lldata,
 235                                     cast.scalar_pair_element_llvm_type(bx.cx, 0, true));
 236                                 OperandValue::Pair(lldata, llextra)
 237                             }
 238                             OperandValue::Immediate(lldata) => {
 239                                 // "standard" unsize
 240                                 let (lldata, llextra) = base::unsize_thin_ptr(&bx, lldata,
 241                                     operand.layout.ty, cast.ty);
 242                                 OperandValue::Pair(lldata, llextra)
 243                             }
 244                             OperandValue::Ref(..) => {
 245                                 bug!("by-ref operand {:?} in codegen_rvalue_operand",
 246                                      operand);
 247                             }
 248                         }
 249                     }
 250                     mir::CastKind::Misc if operand.layout.is_llvm_scalar_pair() => {
 251                         if let OperandValue::Pair(data_ptr, meta) = operand.val {
 252                             if cast.is_llvm_scalar_pair() {
 253                                 let data_cast = bx.pointercast(data_ptr,
 254                                     cast.scalar_pair_element_llvm_type(bx.cx, 0, true));
 255                                 OperandValue::Pair(data_cast, meta)
 256                             } else { // cast to thin-ptr
 257                                 // Cast of fat-ptr to thin-ptr is an extraction of data-ptr and
 258                                 // pointer-cast of that pointer to desired pointer type.
 259                                 let llcast_ty = cast.immediate_llvm_type(bx.cx);
 260                                 let llval = bx.pointercast(data_ptr, llcast_ty);
 261                                 OperandValue::Immediate(llval)
 262                             }
 263                         } else {
 264                             bug!("Unexpected non-Pair operand")
 265                         }
 266                     }
 267                     mir::CastKind::Misc => {
 268                         assert!(cast.is_llvm_immediate());
 269                         let ll_t_out = cast.immediate_llvm_type(bx.cx);
 270                         if operand.layout.abi == layout::Abi::Uninhabited {
 271                             return (bx, OperandRef {
 272                                 val: OperandValue::Immediate(C_undef(ll_t_out)),
 273                                 layout: cast,
 274                             });
 275                         }
 276                         let r_t_in = CastTy::from_ty(operand.layout.ty)
 277                             .expect("bad input type for cast");
 278                         let r_t_out = CastTy::from_ty(cast.ty).expect("bad output type for cast");
 279                         let ll_t_in = operand.layout.immediate_llvm_type(bx.cx);
 280                         match operand.layout.variants {
 281                             layout::Variants::Single { index } => {
 282                                 if let Some(def) = operand.layout.ty.ty_adt_def() {
 283                                     let discr_val = def
 284                                         .discriminant_for_variant(bx.cx.tcx, index)
 285                                         .val;
 286                                     let discr = C_uint_big(ll_t_out, discr_val);
 287                                     return (bx, OperandRef {
 288                                         val: OperandValue::Immediate(discr),
 289                                         layout: cast,
 290                                     });
 291                                 }
 292                             }
 293                             layout::Variants::Tagged { .. } |
 294                             layout::Variants::NicheFilling { .. } => {},
 295                         }
 296                         let llval = operand.immediate();
 297
 298                         let mut signed = false;
 299                         if let layout::Abi::Scalar(ref scalar) = operand.layout.abi {
 300                             if let layout::Int(_, s) = scalar.value {
 301                                 // We use `i1` for bytes that are always `0` or `1`,
 302                                 // e.g. `#[repr(i8)] enum E { A, B }`, but we can't
 303                                 // let LLVM interpret the `i1` as signed, because
 304                                 // then `i1 1` (i.e. E::B) is effectively `i8 -1`.
 305                                 signed = !scalar.is_bool() && s;
 306
 307                                 if scalar.valid_range.end() > scalar.valid_range.start() {
 308                                     // We want `table[e as usize]` to not
 309                                     // have bound checks, and this is the most
 310                                     // convenient place to put the `assume`.
 311
 312                                     base::call_assume(&bx, bx.icmp(
 313                                         llvm::IntULE,
 314                                         llval,
 315                                         C_uint_big(ll_t_in, *scalar.valid_range.end())
 316                                     ));
 317                                 }
 318                             }
 319                         }
 320
 321                         let newval = match (r_t_in, r_t_out) {
 322                             (CastTy::Int(_), CastTy::Int(_)) => {
 323                                 bx.intcast(llval, ll_t_out, signed)
 324                             }
 325                             (CastTy::Float, CastTy::Float) => {
 326                                 let srcsz = ll_t_in.float_width();
 327                                 let dstsz = ll_t_out.float_width();
 328                                 if dstsz > srcsz {
 329                                     bx.fpext(llval, ll_t_out)
 330                                 } else if srcsz > dstsz {
 331                                     bx.fptrunc(llval, ll_t_out)
 332                                 } else {
 333                                     llval
 334                                 }
 335                             }
 336                             (CastTy::Ptr(_), CastTy::Ptr(_)) |
 337                             (CastTy::FnPtr, CastTy::Ptr(_)) |
 338                             (CastTy::RPtr(_), CastTy::Ptr(_)) =>
 339                                 bx.pointercast(llval, ll_t_out),
 340                             (CastTy::Ptr(_), CastTy::Int(_)) |
 341                             (CastTy::FnPtr, CastTy::Int(_)) =>
 342                                 bx.ptrtoint(llval, ll_t_out),
 343                             (CastTy::Int(_), CastTy::Ptr(_)) => {
 344                                 let usize_llval = bx.intcast(llval, bx.cx.isize_ty, signed);
 345                                 bx.inttoptr(usize_llval, ll_t_out)
 346                             }
 347                             (CastTy::Int(_), CastTy::Float) =>
 348                                 cast_int_to_float(&bx, signed, llval, ll_t_in, ll_t_out),
 349                             (CastTy::Float, CastTy::Int(IntTy::I)) =>
 350                                 cast_float_to_int(&bx, true, llval, ll_t_in, ll_t_out),
 351                             (CastTy::Float, CastTy::Int(_)) =>
 352                                 cast_float_to_int(&bx, false, llval, ll_t_in, ll_t_out),
 353                             _ => bug!("unsupported cast: {:?} to {:?}", operand.layout.ty, cast.ty)
 354                         };
 355                         OperandValue::Immediate(newval)
 356                     }
 357                 };
 358                 (bx, OperandRef {
 359                     val,
 360                     layout: cast
 361                 })
 362             }
 363
 364             mir::Rvalue::Ref(_, bk, ref place) => {
 365                 let cg_place = self.codegen_place(&bx, place);
 366
 367                 let ty = cg_place.layout.ty;
 368
 369                 // Note: places are indirect, so storing the `llval` into the
 370                 // destination effectively creates a reference.
 371                 let val = if !bx.cx.type_has_metadata(ty) {
 372                     OperandValue::Immediate(cg_place.llval)
 373                 } else {
 374                     OperandValue::Pair(cg_place.llval, cg_place.llextra)
 375                 };
 376                 (bx, OperandRef {
 377                     val,
 378                     layout: self.cx.layout_of(self.cx.tcx.mk_ref(
 379                         self.cx.tcx.types.re_erased,
 380                         ty::TypeAndMut { ty, mutbl: bk.to_mutbl_lossy() }
 381                     )),
 382                 })
 383             }
 384
 385             mir::Rvalue::Len(ref place) => {
 386                 let size = self.evaluate_array_len(&bx, place);
 387                 let operand = OperandRef {
 388                     val: OperandValue::Immediate(size),
 389                     layout: bx.cx.layout_of(bx.tcx().types.usize),
 390                 };
 391                 (bx, operand)
 392             }
 393
 394             mir::Rvalue::BinaryOp(op, ref lhs, ref rhs) => {
 395                 let lhs = self.codegen_operand(&bx, lhs);
 396                 let rhs = self.codegen_operand(&bx, rhs);
 397                 let llresult = match (lhs.val, rhs.val) {
 398                     (OperandValue::Pair(lhs_addr, lhs_extra),
 399                      OperandValue::Pair(rhs_addr, rhs_extra)) => {
 400                         self.codegen_fat_ptr_binop(&bx, op,
 401                                                  lhs_addr, lhs_extra,
 402                                                  rhs_addr, rhs_extra,
 403                                                  lhs.layout.ty)
 404                     }
 405
 406                     (OperandValue::Immediate(lhs_val),
 407                      OperandValue::Immediate(rhs_val)) => {
 408                         self.codegen_scalar_binop(&bx, op, lhs_val, rhs_val, lhs.layout.ty)
 409                     }
 410
 411                     _ => bug!()
 412                 };
 413                 let operand = OperandRef {
 414                     val: OperandValue::Immediate(llresult),
 415                     layout: bx.cx.layout_of(
 416                         op.ty(bx.tcx(), lhs.layout.ty, rhs.layout.ty)),
 417                 };
 418                 (bx, operand)
 419             }
 420             mir::Rvalue::CheckedBinaryOp(op, ref lhs, ref rhs) => {
 421                 let lhs = self.codegen_operand(&bx, lhs);
 422                 let rhs = self.codegen_operand(&bx, rhs);
 423                 let result = self.codegen_scalar_checked_binop(&bx, op,
 424                                                              lhs.immediate(), rhs.immediate(),
 425                                                              lhs.layout.ty);
 426                 let val_ty = op.ty(bx.tcx(), lhs.layout.ty, rhs.layout.ty);
 427                 let operand_ty = bx.tcx().intern_tup(&[val_ty, bx.tcx().types.bool]);
 428                 let operand = OperandRef {
 429                     val: result,
 430                     layout: bx.cx.layout_of(operand_ty)
 431                 };
 432
 433                 (bx, operand)
 434             }
 435
 436             mir::Rvalue::UnaryOp(op, ref operand) => {
 437                 let operand = self.codegen_operand(&bx, operand);
 438                 let lloperand = operand.immediate();
 439                 let is_float = operand.layout.ty.is_fp();
 440                 let llval = match op {
 441                     mir::UnOp::Not => bx.not(lloperand),
 442                     mir::UnOp::Neg => if is_float {
 443                         bx.fneg(lloperand)
 444                     } else {
 445                         bx.neg(lloperand)
 446                     }
 447                 };
 448                 (bx, OperandRef {
 449                     val: OperandValue::Immediate(llval),
 450                     layout: operand.layout,
 451                 })
 452             }
 453
 454             mir::Rvalue::Discriminant(ref place) => {
 455                 let discr_ty = rvalue.ty(&*self.mir, bx.tcx());
 456                 let discr =  self.codegen_place(&bx, place)
 457                     .codegen_get_discr(&bx, discr_ty);
 458                 (bx, OperandRef {
 459                     val: OperandValue::Immediate(discr),
 460                     layout: self.cx.layout_of(discr_ty)
 461                 })
 462             }
 463
 464             mir::Rvalue::NullaryOp(mir::NullOp::SizeOf, ty) => {
 465                 assert!(bx.cx.type_is_sized(ty));
 466                 let val = C_usize(bx.cx, bx.cx.size_of(ty).bytes());
 467                 let tcx = bx.tcx();
 468                 (bx, OperandRef {
 469                     val: OperandValue::Immediate(val),
 470                     layout: self.cx.layout_of(tcx.types.usize),
 471                 })
 472             }
 473
 474             mir::Rvalue::NullaryOp(mir::NullOp::Box, content_ty) => {
 475                 let content_ty: Ty<'tcx> = self.monomorphize(&content_ty);
 476                 let (size, align) = bx.cx.size_and_align_of(content_ty);
 477                 let llsize = C_usize(bx.cx, size.bytes());
 478                 let llalign = C_usize(bx.cx, align.abi());
 479                 let box_layout = bx.cx.layout_of(bx.tcx().mk_box(content_ty));
 480                 let llty_ptr = box_layout.llvm_type(bx.cx);
 481
 482                 // Allocate space:
 483                 let def_id = match bx.tcx().lang_items().require(ExchangeMallocFnLangItem) {
 484                     Ok(id) => id,
 485                     Err(s) => {
 486                         bx.sess().fatal(&format!("allocation of `{}` {}", box_layout.ty, s));
 487                     }
 488                 };
 489                 let instance = ty::Instance::mono(bx.tcx(), def_id);
 490                 let r = callee::get_fn(bx.cx, instance);
 491                 let val = bx.pointercast(bx.call(r, &[llsize, llalign], None), llty_ptr);
 492
 493                 let operand = OperandRef {
 494                     val: OperandValue::Immediate(val),
 495                     layout: box_layout,
 496                 };
 497                 (bx, operand)
 498             }
 499             mir::Rvalue::Use(ref operand) => {
 500                 let operand = self.codegen_operand(&bx, operand);
 501                 (bx, operand)
 502             }
 503             mir::Rvalue::Repeat(..) |
 504             mir::Rvalue::Aggregate(..) => {
 505                 // According to `rvalue_creates_operand`, only ZST
 506                 // aggregate rvalues are allowed to be operands.
 507                 let ty = rvalue.ty(self.mir, self.cx.tcx);
 508                 (bx, OperandRef::new_zst(self.cx,
 509                     self.cx.layout_of(self.monomorphize(&ty))))
 510             }
 511         }
 512     }
 513
 514     fn evaluate_array_len(&mut self,
 515                           bx: &Builder<'a, 'll, 'tcx>,
 516                           place: &mir::Place<'tcx>) -> ValueRef
 517     {
 518         // ZST are passed as operands and require special handling
 519         // because codegen_place() panics if Local is operand.
 520         if let mir::Place::Local(index) = *place {
 521             if let LocalRef::Operand(Some(op)) = self.locals[index] {
 522                 if let ty::TyArray(_, n) = op.layout.ty.sty {
 523                     let n = n.unwrap_usize(bx.cx.tcx);
 524                     return common::C_usize(bx.cx, n);
 525                 }
 526             }
 527         }
 528         // use common size calculation for non zero-sized types
 529         let cg_value = self.codegen_place(&bx, place);
 530         return cg_value.len(bx.cx);
 531     }
 532
 533     pub fn codegen_scalar_binop(&mut self,
 534                               bx: &Builder<'a, 'll, 'tcx>,
 535                               op: mir::BinOp,
 536                               lhs: ValueRef,
 537                               rhs: ValueRef,
 538                               input_ty: Ty<'tcx>) -> ValueRef {
 539         let is_float = input_ty.is_fp();
 540         let is_signed = input_ty.is_signed();
 541         let is_nil = input_ty.is_nil();
 542         match op {
 543             mir::BinOp::Add => if is_float {
 544                 bx.fadd(lhs, rhs)
 545             } else {
 546                 bx.add(lhs, rhs)
 547             },
 548             mir::BinOp::Sub => if is_float {
 549                 bx.fsub(lhs, rhs)
 550             } else {
 551                 bx.sub(lhs, rhs)
 552             },
 553             mir::BinOp::Mul => if is_float {
 554                 bx.fmul(lhs, rhs)
 555             } else {
 556                 bx.mul(lhs, rhs)
 557             },
 558             mir::BinOp::Div => if is_float {
 559                 bx.fdiv(lhs, rhs)
 560             } else if is_signed {
 561                 bx.sdiv(lhs, rhs)
 562             } else {
 563                 bx.udiv(lhs, rhs)
 564             },
 565             mir::BinOp::Rem => if is_float {
 566                 bx.frem(lhs, rhs)
 567             } else if is_signed {
 568                 bx.srem(lhs, rhs)
 569             } else {
 570                 bx.urem(lhs, rhs)
 571             },
 572             mir::BinOp::BitOr => bx.or(lhs, rhs),
 573             mir::BinOp::BitAnd => bx.and(lhs, rhs),
 574             mir::BinOp::BitXor => bx.xor(lhs, rhs),
 575             mir::BinOp::Offset => bx.inbounds_gep(lhs, &[rhs]),
 576             mir::BinOp::Shl => common::build_unchecked_lshift(bx, lhs, rhs),
 577             mir::BinOp::Shr => common::build_unchecked_rshift(bx, input_ty, lhs, rhs),
 578             mir::BinOp::Ne | mir::BinOp::Lt | mir::BinOp::Gt |
 579             mir::BinOp::Eq | mir::BinOp::Le | mir::BinOp::Ge => if is_nil {
 580                 C_bool(bx.cx, match op {
 581                     mir::BinOp::Ne | mir::BinOp::Lt | mir::BinOp::Gt => false,
 582                     mir::BinOp::Eq | mir::BinOp::Le | mir::BinOp::Ge => true,
 583                     _ => unreachable!()
 584                 })
 585             } else if is_float {
 586                 bx.fcmp(
 587                     base::bin_op_to_fcmp_predicate(op.to_hir_binop()),
 588                     lhs, rhs
 589                 )
 590             } else {
 591                 bx.icmp(
 592                     base::bin_op_to_icmp_predicate(op.to_hir_binop(), is_signed),
 593                     lhs, rhs
 594                 )
 595             }
 596         }
 597     }
 598
 599     pub fn codegen_fat_ptr_binop(&mut self,
 600                                bx: &Builder<'a, 'll, 'tcx>,
 601                                op: mir::BinOp,
 602                                lhs_addr: ValueRef,
 603                                lhs_extra: ValueRef,
 604                                rhs_addr: ValueRef,
 605                                rhs_extra: ValueRef,
 606                                _input_ty: Ty<'tcx>)
 607                                -> ValueRef {
 608         match op {
 609             mir::BinOp::Eq => {
 610                 bx.and(
 611                     bx.icmp(llvm::IntEQ, lhs_addr, rhs_addr),
 612                     bx.icmp(llvm::IntEQ, lhs_extra, rhs_extra)
 613                 )
 614             }
 615             mir::BinOp::Ne => {
 616                 bx.or(
 617                     bx.icmp(llvm::IntNE, lhs_addr, rhs_addr),
 618                     bx.icmp(llvm::IntNE, lhs_extra, rhs_extra)
 619                 )
 620             }
 621             mir::BinOp::Le | mir::BinOp::Lt |
 622             mir::BinOp::Ge | mir::BinOp::Gt => {
 623                 // a OP b ~ a.0 STRICT(OP) b.0 | (a.0 == b.0 && a.1 OP a.1)
 624                 let (op, strict_op) = match op {
 625                     mir::BinOp::Lt => (llvm::IntULT, llvm::IntULT),
 626                     mir::BinOp::Le => (llvm::IntULE, llvm::IntULT),
 627                     mir::BinOp::Gt => (llvm::IntUGT, llvm::IntUGT),
 628                     mir::BinOp::Ge => (llvm::IntUGE, llvm::IntUGT),
 629                     _ => bug!(),
 630                 };
 631
 632                 bx.or(
 633                     bx.icmp(strict_op, lhs_addr, rhs_addr),
 634                     bx.and(
 635                         bx.icmp(llvm::IntEQ, lhs_addr, rhs_addr),
 636                         bx.icmp(op, lhs_extra, rhs_extra)
 637                     )
 638                 )
 639             }
 640             _ => {
 641                 bug!("unexpected fat ptr binop");
 642             }
 643         }
 644     }
 645
 646     pub fn codegen_scalar_checked_binop(&mut self,
 647                                       bx: &Builder<'a, 'll, 'tcx>,
 648                                       op: mir::BinOp,
 649                                       lhs: ValueRef,
 650                                       rhs: ValueRef,
 651                                       input_ty: Ty<'tcx>) -> OperandValue {
 652         // This case can currently arise only from functions marked
 653         // with #[rustc_inherit_overflow_checks] and inlined from
 654         // another crate (mostly core::num generic/#[inline] fns),
 655         // while the current crate doesn't use overflow checks.
 656         if !bx.cx.check_overflow {
 657             let val = self.codegen_scalar_binop(bx, op, lhs, rhs, input_ty);
 658             return OperandValue::Pair(val, C_bool(bx.cx, false));
 659         }
 660
 661         let (val, of) = match op {
 662             // These are checked using intrinsics
 663             mir::BinOp::Add | mir::BinOp::Sub | mir::BinOp::Mul => {
 664                 let oop = match op {
 665                     mir::BinOp::Add => OverflowOp::Add,
 666                     mir::BinOp::Sub => OverflowOp::Sub,
 667                     mir::BinOp::Mul => OverflowOp::Mul,
 668                     _ => unreachable!()
 669                 };
 670                 let intrinsic = get_overflow_intrinsic(oop, bx, input_ty);
 671                 let res = bx.call(intrinsic, &[lhs, rhs], None);
 672
 673                 (bx.extract_value(res, 0),
 674                  bx.extract_value(res, 1))
 675             }
 676             mir::BinOp::Shl | mir::BinOp::Shr => {
 677                 let lhs_llty = val_ty(lhs);
 678                 let rhs_llty = val_ty(rhs);
 679                 let invert_mask = common::shift_mask_val(&bx, lhs_llty, rhs_llty, true);
 680                 let outer_bits = bx.and(rhs, invert_mask);
 681
 682                 let of = bx.icmp(llvm::IntNE, outer_bits, C_null(rhs_llty));
 683                 let val = self.codegen_scalar_binop(bx, op, lhs, rhs, input_ty);
 684
 685                 (val, of)
 686             }
 687             _ => {
 688                 bug!("Operator `{:?}` is not a checkable operator", op)
 689             }
 690         };
 691
 692         OperandValue::Pair(val, of)
 693     }
 694
 695     pub fn rvalue_creates_operand(&self, rvalue: &mir::Rvalue<'tcx>) -> bool {
 696         match *rvalue {
 697             mir::Rvalue::Ref(..) |
 698             mir::Rvalue::Len(..) |
 699             mir::Rvalue::Cast(..) | // (*)
 700             mir::Rvalue::BinaryOp(..) |
 701             mir::Rvalue::CheckedBinaryOp(..) |
 702             mir::Rvalue::UnaryOp(..) |
 703             mir::Rvalue::Discriminant(..) |
 704             mir::Rvalue::NullaryOp(..) |
 705             mir::Rvalue::Use(..) => // (*)
 706                 true,
 707             mir::Rvalue::Repeat(..) |
 708             mir::Rvalue::Aggregate(..) => {
 709                 let ty = rvalue.ty(self.mir, self.cx.tcx);
 710                 let ty = self.monomorphize(&ty);
 711                 self.cx.layout_of(ty).is_zst()
 712             }
 713         }
 714
 715         // (*) this is only true if the type is suitable
 716     }
 717 }
 718
 719 #[derive(Copy, Clone)]
 720 enum OverflowOp {
 721     Add, Sub, Mul
 722 }
 723
 724 fn get_overflow_intrinsic(oop: OverflowOp, bx: &Builder, ty: Ty) -> ValueRef {
 725     use syntax::ast::IntTy::*;
 726     use syntax::ast::UintTy::*;
 727     use rustc::ty::{TyInt, TyUint};
 728
 729     let tcx = bx.tcx();
 730
 731     let new_sty = match ty.sty {
 732         TyInt(Isize) => match &tcx.sess.target.target.target_pointer_width[..] {
 733             "16" => TyInt(I16),
 734             "32" => TyInt(I32),
 735             "64" => TyInt(I64),
 736             _ => panic!("unsupported target word size")
 737         },
 738         TyUint(Usize) => match &tcx.sess.target.target.target_pointer_width[..] {
 739             "16" => TyUint(U16),
 740             "32" => TyUint(U32),
 741             "64" => TyUint(U64),
 742             _ => panic!("unsupported target word size")
 743         },
 744         ref t @ TyUint(_) | ref t @ TyInt(_) => t.clone(),
 745         _ => panic!("tried to get overflow intrinsic for op applied to non-int type")
 746     };
 747
 748     let name = match oop {
 749         OverflowOp::Add => match new_sty {
 750             TyInt(I8) => "llvm.sadd.with.overflow.i8",
 751             TyInt(I16) => "llvm.sadd.with.overflow.i16",
 752             TyInt(I32) => "llvm.sadd.with.overflow.i32",
 753             TyInt(I64) => "llvm.sadd.with.overflow.i64",
 754             TyInt(I128) => "llvm.sadd.with.overflow.i128",
 755
 756             TyUint(U8) => "llvm.uadd.with.overflow.i8",
 757             TyUint(U16) => "llvm.uadd.with.overflow.i16",
 758             TyUint(U32) => "llvm.uadd.with.overflow.i32",
 759             TyUint(U64) => "llvm.uadd.with.overflow.i64",
 760             TyUint(U128) => "llvm.uadd.with.overflow.i128",
 761
 762             _ => unreachable!(),
 763         },
 764         OverflowOp::Sub => match new_sty {
 765             TyInt(I8) => "llvm.ssub.with.overflow.i8",
 766             TyInt(I16) => "llvm.ssub.with.overflow.i16",
 767             TyInt(I32) => "llvm.ssub.with.overflow.i32",
 768             TyInt(I64) => "llvm.ssub.with.overflow.i64",
 769             TyInt(I128) => "llvm.ssub.with.overflow.i128",
 770
 771             TyUint(U8) => "llvm.usub.with.overflow.i8",
 772             TyUint(U16) => "llvm.usub.with.overflow.i16",
 773             TyUint(U32) => "llvm.usub.with.overflow.i32",
 774             TyUint(U64) => "llvm.usub.with.overflow.i64",
 775             TyUint(U128) => "llvm.usub.with.overflow.i128",
 776
 777             _ => unreachable!(),
 778         },
 779         OverflowOp::Mul => match new_sty {
 780             TyInt(I8) => "llvm.smul.with.overflow.i8",
 781             TyInt(I16) => "llvm.smul.with.overflow.i16",
 782             TyInt(I32) => "llvm.smul.with.overflow.i32",
 783             TyInt(I64) => "llvm.smul.with.overflow.i64",
 784             TyInt(I128) => "llvm.smul.with.overflow.i128",
 785
 786             TyUint(U8) => "llvm.umul.with.overflow.i8",
 787             TyUint(U16) => "llvm.umul.with.overflow.i16",
 788             TyUint(U32) => "llvm.umul.with.overflow.i32",
 789             TyUint(U64) => "llvm.umul.with.overflow.i64",
 790             TyUint(U128) => "llvm.umul.with.overflow.i128",
 791
 792             _ => unreachable!(),
 793         },
 794     };
 795
 796     bx.cx.get_intrinsic(&name)
 797 }
 798
 799 fn cast_int_to_float(bx: &Builder<'_, 'll, '_>,
 800                      signed: bool,
 801                      x: ValueRef,
 802                      int_ty: &'ll Type,
 803                      float_ty: &'ll Type) -> ValueRef {
 804     // Most integer types, even i128, fit into [-f32::MAX, f32::MAX] after rounding.
 805     // It's only u128 -> f32 that can cause overflows (i.e., should yield infinity).
 806     // LLVM's uitofp produces undef in those cases, so we manually check for that case.
 807     let is_u128_to_f32 = !signed && int_ty.int_width() == 128 && float_ty.float_width() == 32;
 808     if is_u128_to_f32 {
 809         // All inputs greater or equal to (f32::MAX + 0.5 ULP) are rounded to infinity,
 810         // and for everything else LLVM's uitofp works just fine.
 811         use rustc_apfloat::ieee::Single;
 812         use rustc_apfloat::Float;
 813         const MAX_F32_PLUS_HALF_ULP: u128 = ((1 << (Single::PRECISION + 1)) - 1)
 814                                             << (Single::MAX_EXP - Single::PRECISION as i16);
 815         let max = C_uint_big(int_ty, MAX_F32_PLUS_HALF_ULP);
 816         let overflow = bx.icmp(llvm::IntUGE, x, max);
 817         let infinity_bits = C_u32(bx.cx, ieee::Single::INFINITY.to_bits() as u32);
 818         let infinity = consts::bitcast(infinity_bits, float_ty);
 819         bx.select(overflow, infinity, bx.uitofp(x, float_ty))
 820     } else {
 821         if signed {
 822             bx.sitofp(x, float_ty)
 823         } else {
 824             bx.uitofp(x, float_ty)
 825         }
 826     }
 827 }
 828
 829 fn cast_float_to_int(bx: &Builder<'_, 'll, '_>,
 830                      signed: bool,
 831                      x: ValueRef,
 832                      float_ty: &'ll Type,
 833                      int_ty: &'ll Type) -> ValueRef {
 834     let fptosui_result = if signed {
 835         bx.fptosi(x, int_ty)
 836     } else {
 837         bx.fptoui(x, int_ty)
 838     };
 839
 840     if !bx.sess().opts.debugging_opts.saturating_float_casts {
 841         return fptosui_result;
 842     }
 843     // LLVM's fpto[su]i returns undef when the input x is infinite, NaN, or does not fit into the
 844     // destination integer type after rounding towards zero. This `undef` value can cause UB in
 845     // safe code (see issue #10184), so we implement a saturating conversion on top of it:
 846     // Semantically, the mathematical value of the input is rounded towards zero to the next
 847     // mathematical integer, and then the result is clamped into the range of the destination
 848     // integer type. Positive and negative infinity are mapped to the maximum and minimum value of
 849     // the destination integer type. NaN is mapped to 0.
 850     //
 851     // Define f_min and f_max as the largest and smallest (finite) floats that are exactly equal to
 852     // a value representable in int_ty.
 853     // They are exactly equal to int_ty::{MIN,MAX} if float_ty has enough significand bits.
 854     // Otherwise, int_ty::MAX must be rounded towards zero, as it is one less than a power of two.
 855     // int_ty::MIN, however, is either zero or a negative power of two and is thus exactly
 856     // representable. Note that this only works if float_ty's exponent range is sufficiently large.
 857     // f16 or 256 bit integers would break this property. Right now the smallest float type is f32
 858     // with exponents ranging up to 127, which is barely enough for i128::MIN = -2^127.
 859     // On the other hand, f_max works even if int_ty::MAX is greater than float_ty::MAX. Because
 860     // we're rounding towards zero, we just get float_ty::MAX (which is always an integer).
 861     // This already happens today with u128::MAX = 2^128 - 1 > f32::MAX.
 862     fn compute_clamp_bounds<F: Float>(signed: bool, int_ty: &Type) -> (u128, u128) {
 863         let rounded_min = F::from_i128_r(int_min(signed, int_ty), Round::TowardZero);
 864         assert_eq!(rounded_min.status, Status::OK);
 865         let rounded_max = F::from_u128_r(int_max(signed, int_ty), Round::TowardZero);
 866         assert!(rounded_max.value.is_finite());
 867         (rounded_min.value.to_bits(), rounded_max.value.to_bits())
 868     }
 869     fn int_max(signed: bool, int_ty: &Type) -> u128 {
 870         let shift_amount = 128 - int_ty.int_width();
 871         if signed {
 872             i128::MAX as u128 >> shift_amount
 873         } else {
 874             u128::MAX >> shift_amount
 875         }
 876     }
 877     fn int_min(signed: bool, int_ty: &Type) -> i128 {
 878         if signed {
 879             i128::MIN >> (128 - int_ty.int_width())
 880         } else {
 881             0
 882         }
 883     }
 884     let float_bits_to_llval = |bits| {
 885         let bits_llval = match float_ty.float_width() {
 886             32 => C_u32(bx.cx, bits as u32),
 887             64 => C_u64(bx.cx, bits as u64),
 888             n => bug!("unsupported float width {}", n),
 889         };
 890         consts::bitcast(bits_llval, float_ty)
 891     };
 892     let (f_min, f_max) = match float_ty.float_width() {
 893         32 => compute_clamp_bounds::<ieee::Single>(signed, int_ty),
 894         64 => compute_clamp_bounds::<ieee::Double>(signed, int_ty),
 895         n => bug!("unsupported float width {}", n),
 896     };
 897     let f_min = float_bits_to_llval(f_min);
 898     let f_max = float_bits_to_llval(f_max);
 899     // To implement saturation, we perform the following steps:
 900     //
 901     // 1. Cast x to an integer with fpto[su]i. This may result in undef.
 902     // 2. Compare x to f_min and f_max, and use the comparison results to select:
 903     //  a) int_ty::MIN if x < f_min or x is NaN
 904     //  b) int_ty::MAX if x > f_max
 905     //  c) the result of fpto[su]i otherwise
 906     // 3. If x is NaN, return 0.0, otherwise return the result of step 2.
 907     //
 908     // This avoids resulting undef because values in range [f_min, f_max] by definition fit into the
 909     // destination type. It creates an undef temporary, but *producing* undef is not UB. Our use of
 910     // undef does not introduce any non-determinism either.
 911     // More importantly, the above procedure correctly implements saturating conversion.
 912     // Proof (sketch):
 913     // If x is NaN, 0 is returned by definition.
 914     // Otherwise, x is finite or infinite and thus can be compared with f_min and f_max.
 915     // This yields three cases to consider:
 916     // (1) if x in [f_min, f_max], the result of fpto[su]i is returned, which agrees with
 917     //     saturating conversion for inputs in that range.
 918     // (2) if x > f_max, then x is larger than int_ty::MAX. This holds even if f_max is rounded
 919     //     (i.e., if f_max < int_ty::MAX) because in those cases, nextUp(f_max) is already larger
 920     //     than int_ty::MAX. Because x is larger than int_ty::MAX, the return value of int_ty::MAX
 921     //     is correct.
 922     // (3) if x < f_min, then x is smaller than int_ty::MIN. As shown earlier, f_min exactly equals
 923     //     int_ty::MIN and therefore the return value of int_ty::MIN is correct.
 924     // QED.
 925
 926     // Step 1 was already performed above.
 927
 928     // Step 2: We use two comparisons and two selects, with %s1 being the result:
 929     //     %less_or_nan = fcmp ult %x, %f_min
 930     //     %greater = fcmp olt %x, %f_max
 931     //     %s0 = select %less_or_nan, int_ty::MIN, %fptosi_result
 932     //     %s1 = select %greater, int_ty::MAX, %s0
 933     // Note that %less_or_nan uses an *unordered* comparison. This comparison is true if the
 934     // operands are not comparable (i.e., if x is NaN). The unordered comparison ensures that s1
 935     // becomes int_ty::MIN if x is NaN.
 936     // Performance note: Unordered comparison can be lowered to a "flipped" comparison and a
 937     // negation, and the negation can be merged into the select. Therefore, it not necessarily any
 938     // more expensive than a ordered ("normal") comparison. Whether these optimizations will be
 939     // performed is ultimately up to the backend, but at least x86 does perform them.
 940     let less_or_nan = bx.fcmp(llvm::RealULT, x, f_min);
 941     let greater = bx.fcmp(llvm::RealOGT, x, f_max);
 942     let int_max = C_uint_big(int_ty, int_max(signed, int_ty));
 943     let int_min = C_uint_big(int_ty, int_min(signed, int_ty) as u128);
 944     let s0 = bx.select(less_or_nan, int_min, fptosui_result);
 945     let s1 = bx.select(greater, int_max, s0);
 946
 947     // Step 3: NaN replacement.
 948     // For unsigned types, the above step already yielded int_ty::MIN == 0 if x is NaN.
 949     // Therefore we only need to execute this step for signed integer types.
 950     if signed {
 951         // LLVM has no isNaN predicate, so we use (x == x) instead
 952         bx.select(bx.fcmp(llvm::RealOEQ, x, x), s1, C_uint(int_ty, 0))
 953     } else {
 954         s1
 955     }
 956 }