src/librustc_trans/trans/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::ValueRef;
  12 use rustc::middle::ty::{self, Ty};
  13 use middle::ty::cast::{CastTy, IntTy};
  14 use rustc::mir::repr as mir;
  15
  16 use trans::asm;
  17 use trans::base;
  18 use trans::common::{self, BlockAndBuilder, Result};
  19 use trans::debuginfo::DebugLoc;
  20 use trans::declare;
  21 use trans::expr;
  22 use trans::adt;
  23 use trans::machine;
  24 use trans::type_::Type;
  25 use trans::type_of;
  26 use trans::tvec;
  27 use trans::Disr;
  28
  29 use super::MirContext;
  30 use super::operand::{OperandRef, OperandValue};
  31 use super::lvalue::LvalueRef;
  32
  33 impl<'bcx, 'tcx> MirContext<'bcx, 'tcx> {
  34     pub fn trans_rvalue(&mut self,
  35                         bcx: BlockAndBuilder<'bcx, 'tcx>,
  36                         dest: LvalueRef<'tcx>,
  37                         rvalue: &mir::Rvalue<'tcx>)
  38                         -> BlockAndBuilder<'bcx, 'tcx>
  39     {
  40         debug!("trans_rvalue(dest.llval={}, rvalue={:?})",
  41                bcx.val_to_string(dest.llval),
  42                rvalue);
  43
  44         match *rvalue {
  45            mir::Rvalue::Use(ref operand) => {
  46                let tr_operand = self.trans_operand(&bcx, operand);
  47                // FIXME: consider not copying constants through stack. (fixable by translating
  48                // constants into OperandValue::Ref, why don’t we do that yet if we don’t?)
  49                self.store_operand(&bcx, dest.llval, tr_operand);
  50                self.set_operand_dropped(&bcx, operand);
  51                bcx
  52            }
  53
  54             mir::Rvalue::Cast(mir::CastKind::Unsize, ref operand, cast_ty) => {
  55                 if common::type_is_fat_ptr(bcx.tcx(), cast_ty) {
  56                     // into-coerce of a thin pointer to a fat pointer - just
  57                     // use the operand path.
  58                     let (bcx, temp) = self.trans_rvalue_operand(bcx, rvalue);
  59                     self.store_operand(&bcx, dest.llval, temp);
  60                     return bcx;
  61                 }
  62
  63                 // Unsize of a nontrivial struct. I would prefer for
  64                 // this to be eliminated by MIR translation, but
  65                 // `CoerceUnsized` can be passed by a where-clause,
  66                 // so the (generic) MIR may not be able to expand it.
  67                 let operand = self.trans_operand(&bcx, operand);
  68                 bcx.with_block(|bcx| {
  69                     match operand.val {
  70                         OperandValue::FatPtr(..) => unreachable!(),
  71                         OperandValue::Immediate(llval) => {
  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!("trans_rvalue: creating ugly alloca");
  79                             let lltemp = base::alloc_ty(bcx, operand.ty, "__unsize_temp");
  80                             base::store_ty(bcx, llval, lltemp, operand.ty);
  81                             base::coerce_unsized_into(bcx,
  82                                                       lltemp, operand.ty,
  83                                                       dest.llval, cast_ty);
  84                         }
  85                         OperandValue::Ref(llref) => {
  86                             base::coerce_unsized_into(bcx,
  87                                                       llref, operand.ty,
  88                                                       dest.llval, cast_ty);
  89                         }
  90                     }
  91                 });
  92                 bcx
  93             }
  94
  95             mir::Rvalue::Repeat(ref elem, ref count) => {
  96                 let tr_elem = self.trans_operand(&bcx, elem);
  97                 let size = self.trans_constval(&bcx, &count.value, count.ty).immediate();
  98                 let bcx = bcx.map_block(|block| {
  99                     let base = expr::get_dataptr(block, dest.llval);
 100                     tvec::iter_vec_raw(block, base, tr_elem.ty, size, |block, llslot, _| {
 101                         self.store_operand_direct(block, llslot, tr_elem);
 102                         block
 103                     })
 104                 });
 105                 self.set_operand_dropped(&bcx, elem);
 106                 bcx
 107             }
 108
 109             mir::Rvalue::Aggregate(ref kind, ref operands) => {
 110                 match *kind {
 111                     mir::AggregateKind::Adt(adt_def, index, _) => {
 112                         let repr = adt::represent_type(bcx.ccx(), dest.ty.to_ty(bcx.tcx()));
 113                         let disr = Disr::from(adt_def.variants[index].disr_val);
 114                         bcx.with_block(|bcx| {
 115                             adt::trans_set_discr(bcx, &repr, dest.llval, Disr::from(disr));
 116                         });
 117                         for (i, operand) in operands.iter().enumerate() {
 118                             let op = self.trans_operand(&bcx, operand);
 119                             // Do not generate stores and GEPis for zero-sized fields.
 120                             if !common::type_is_zero_size(bcx.ccx(), op.ty) {
 121                                 let val = adt::MaybeSizedValue::sized(dest.llval);
 122                                 let lldest_i = bcx.with_block(|bcx| {
 123                                     adt::trans_field_ptr(bcx, &repr, val, disr, i)
 124                                 });
 125                                 self.store_operand(&bcx, lldest_i, op);
 126                                 self.set_operand_dropped(&bcx, operand);
 127                             }
 128                         }
 129                     },
 130                     _ => {
 131                         for (i, operand) in operands.iter().enumerate() {
 132                             let op = self.trans_operand(&bcx, operand);
 133                             // Do not generate stores and GEPis for zero-sized fields.
 134                             if !common::type_is_zero_size(bcx.ccx(), op.ty) {
 135                                 // Note: perhaps this should be StructGep, but
 136                                 // note that in some cases the values here will
 137                                 // not be structs but arrays.
 138                                 let dest = bcx.gepi(dest.llval, &[0, i]);
 139                                 self.store_operand(&bcx, dest, op);
 140                                 self.set_operand_dropped(&bcx, operand);
 141                             }
 142                         }
 143                     }
 144                 }
 145                 bcx
 146             }
 147
 148             mir::Rvalue::Slice { ref input, from_start, from_end } => {
 149                 let ccx = bcx.ccx();
 150                 let input = self.trans_lvalue(&bcx, input);
 151                 let (llbase, lllen) = bcx.with_block(|bcx| {
 152                     tvec::get_base_and_len(bcx,
 153                                            input.llval,
 154                                            input.ty.to_ty(bcx.tcx()))
 155                 });
 156                 let llbase1 = bcx.gepi(llbase, &[from_start]);
 157                 let adj = common::C_uint(ccx, from_start + from_end);
 158                 let lllen1 = bcx.sub(lllen, adj);
 159                 let (lladdrdest, llmetadest) = bcx.with_block(|bcx| {
 160                     (expr::get_dataptr(bcx, dest.llval), expr::get_meta(bcx, dest.llval))
 161                 });
 162                 bcx.store(llbase1, lladdrdest);
 163                 bcx.store(lllen1, llmetadest);
 164                 bcx
 165             }
 166
 167             mir::Rvalue::InlineAsm(ref inline_asm) => {
 168                 bcx.map_block(|bcx| {
 169                     asm::trans_inline_asm(bcx, inline_asm)
 170                 })
 171             }
 172
 173             _ => {
 174                 assert!(rvalue_creates_operand(rvalue));
 175                 let (bcx, temp) = self.trans_rvalue_operand(bcx, rvalue);
 176                 self.store_operand(&bcx, dest.llval, temp);
 177                 bcx
 178             }
 179         }
 180     }
 181
 182     pub fn trans_rvalue_operand(&mut self,
 183                                 bcx: BlockAndBuilder<'bcx, 'tcx>,
 184                                 rvalue: &mir::Rvalue<'tcx>)
 185                                 -> (BlockAndBuilder<'bcx, 'tcx>, OperandRef<'tcx>)
 186     {
 187         assert!(rvalue_creates_operand(rvalue), "cannot trans {:?} to operand", rvalue);
 188
 189         match *rvalue {
 190             mir::Rvalue::Cast(ref kind, ref operand, cast_ty) => {
 191                 let operand = self.trans_operand(&bcx, operand);
 192                 debug!("cast operand is {}", operand.repr(&bcx));
 193                 let cast_ty = bcx.monomorphize(&cast_ty);
 194
 195                 let val = match *kind {
 196                     mir::CastKind::ReifyFnPointer |
 197                     mir::CastKind::UnsafeFnPointer => {
 198                         // these are no-ops at the LLVM level
 199                         operand.val
 200                     }
 201                     mir::CastKind::Unsize => {
 202                         // unsize targets other than to a fat pointer currently
 203                         // can't be operands.
 204                         assert!(common::type_is_fat_ptr(bcx.tcx(), cast_ty));
 205
 206                         match operand.val {
 207                             OperandValue::FatPtr(..) => {
 208                                 // unsize from a fat pointer - this is a
 209                                 // "trait-object-to-supertrait" coercion, for
 210                                 // example,
 211                                 //   &'a fmt::Debug+Send => &'a fmt::Debug,
 212                                 // and is a no-op at the LLVM level
 213                                 operand.val
 214                             }
 215                             OperandValue::Immediate(lldata) => {
 216                                 // "standard" unsize
 217                                 let (lldata, llextra) = bcx.with_block(|bcx| {
 218                                     base::unsize_thin_ptr(bcx, lldata,
 219                                                           operand.ty, cast_ty)
 220                                 });
 221                                 OperandValue::FatPtr(lldata, llextra)
 222                             }
 223                             OperandValue::Ref(_) => {
 224                                 bcx.sess().bug(
 225                                     &format!("by-ref operand {} in trans_rvalue_operand",
 226                                              operand.repr(&bcx)));
 227                             }
 228                         }
 229                     }
 230                     mir::CastKind::Misc if common::type_is_immediate(bcx.ccx(), operand.ty) => {
 231                         debug_assert!(common::type_is_immediate(bcx.ccx(), cast_ty));
 232                         let r_t_in = CastTy::from_ty(operand.ty).expect("bad input type for cast");
 233                         let r_t_out = CastTy::from_ty(cast_ty).expect("bad output type for cast");
 234                         let ll_t_in = type_of::arg_type_of(bcx.ccx(), operand.ty);
 235                         let ll_t_out = type_of::arg_type_of(bcx.ccx(), cast_ty);
 236                         let (llval, ll_t_in, signed) = if let CastTy::Int(IntTy::CEnum) = r_t_in {
 237                             let repr = adt::represent_type(bcx.ccx(), operand.ty);
 238                             let llval = operand.immediate();
 239                             let discr = bcx.with_block(|bcx| {
 240                                 adt::trans_get_discr(bcx, &repr, llval, None, true)
 241                             });
 242                             (discr, common::val_ty(discr), adt::is_discr_signed(&repr))
 243                         } else {
 244                             (operand.immediate(), ll_t_in, operand.ty.is_signed())
 245                         };
 246
 247                         let newval = match (r_t_in, r_t_out) {
 248                             (CastTy::Int(_), CastTy::Int(_)) => {
 249                                 let srcsz = ll_t_in.int_width();
 250                                 let dstsz = ll_t_out.int_width();
 251                                 if srcsz == dstsz {
 252                                     bcx.bitcast(llval, ll_t_out)
 253                                 } else if srcsz > dstsz {
 254                                     bcx.trunc(llval, ll_t_out)
 255                                 } else if signed {
 256                                     bcx.sext(llval, ll_t_out)
 257                                 } else {
 258                                     bcx.zext(llval, ll_t_out)
 259                                 }
 260                             }
 261                             (CastTy::Float, CastTy::Float) => {
 262                                 let srcsz = ll_t_in.float_width();
 263                                 let dstsz = ll_t_out.float_width();
 264                                 if dstsz > srcsz {
 265                                     bcx.fpext(llval, ll_t_out)
 266                                 } else if srcsz > dstsz {
 267                                     bcx.fptrunc(llval, ll_t_out)
 268                                 } else {
 269                                     llval
 270                                 }
 271                             }
 272                             (CastTy::Ptr(_), CastTy::Ptr(_)) |
 273                             (CastTy::FnPtr, CastTy::Ptr(_)) |
 274                             (CastTy::RPtr(_), CastTy::Ptr(_)) =>
 275                                 bcx.pointercast(llval, ll_t_out),
 276                             (CastTy::Ptr(_), CastTy::Int(_)) |
 277                             (CastTy::FnPtr, CastTy::Int(_)) =>
 278                                 bcx.ptrtoint(llval, ll_t_out),
 279                             (CastTy::Int(_), CastTy::Ptr(_)) =>
 280                                 bcx.inttoptr(llval, ll_t_out),
 281                             (CastTy::Int(_), CastTy::Float) if signed =>
 282                                 bcx.sitofp(llval, ll_t_out),
 283                             (CastTy::Int(_), CastTy::Float) =>
 284                                 bcx.uitofp(llval, ll_t_out),
 285                             (CastTy::Float, CastTy::Int(IntTy::I)) =>
 286                                 bcx.fptosi(llval, ll_t_out),
 287                             (CastTy::Float, CastTy::Int(_)) =>
 288                                 bcx.fptoui(llval, ll_t_out),
 289                             _ => bcx.ccx().sess().bug(
 290                                 &format!("unsupported cast: {:?} to {:?}", operand.ty, cast_ty)
 291                             )
 292                         };
 293                         OperandValue::Immediate(newval)
 294                     }
 295                     mir::CastKind::Misc => { // Casts from a fat-ptr.
 296                         let ll_cast_ty = type_of::arg_type_of(bcx.ccx(), cast_ty);
 297                         let ll_from_ty = type_of::arg_type_of(bcx.ccx(), operand.ty);
 298                         if let OperandValue::FatPtr(data_ptr, meta_ptr) = operand.val {
 299                             if common::type_is_fat_ptr(bcx.tcx(), cast_ty) {
 300                                 let ll_cft = ll_cast_ty.field_types();
 301                                 let ll_fft = ll_from_ty.field_types();
 302                                 let data_cast = bcx.pointercast(data_ptr, ll_cft[0]);
 303                                 assert_eq!(ll_cft[1].kind(), ll_fft[1].kind());
 304                                 OperandValue::FatPtr(data_cast, meta_ptr)
 305                             } else { // cast to thin-ptr
 306                                 // Cast of fat-ptr to thin-ptr is an extraction of data-ptr and
 307                                 // pointer-cast of that pointer to desired pointer type.
 308                                 let llval = bcx.pointercast(data_ptr, ll_cast_ty);
 309                                 OperandValue::Immediate(llval)
 310                             }
 311                         } else {
 312                             panic!("Unexpected non-FatPtr operand")
 313                         }
 314                     }
 315                 };
 316                 let operand = OperandRef {
 317                     val: val,
 318                     ty: cast_ty
 319                 };
 320                 (bcx, operand)
 321             }
 322
 323             mir::Rvalue::Ref(_, bk, ref lvalue) => {
 324                 let tr_lvalue = self.trans_lvalue(&bcx, lvalue);
 325
 326                 let ty = tr_lvalue.ty.to_ty(bcx.tcx());
 327                 let ref_ty = bcx.tcx().mk_ref(
 328                     bcx.tcx().mk_region(ty::ReStatic),
 329                     ty::TypeAndMut { ty: ty, mutbl: bk.to_mutbl_lossy() }
 330                 );
 331
 332                 // Note: lvalues are indirect, so storing the `llval` into the
 333                 // destination effectively creates a reference.
 334                 let operand = if common::type_is_sized(bcx.tcx(), ty) {
 335                     OperandRef {
 336                         val: OperandValue::Immediate(tr_lvalue.llval),
 337                         ty: ref_ty,
 338                     }
 339                 } else {
 340                     OperandRef {
 341                         val: OperandValue::FatPtr(tr_lvalue.llval,
 342                                                   tr_lvalue.llextra),
 343                         ty: ref_ty,
 344                     }
 345                 };
 346                 (bcx, operand)
 347             }
 348
 349             mir::Rvalue::Len(ref lvalue) => {
 350                 let tr_lvalue = self.trans_lvalue(&bcx, lvalue);
 351                 let operand = OperandRef {
 352                     val: OperandValue::Immediate(self.lvalue_len(&bcx, tr_lvalue)),
 353                     ty: bcx.tcx().types.usize,
 354                 };
 355                 (bcx, operand)
 356             }
 357
 358             mir::Rvalue::BinaryOp(op, ref lhs, ref rhs) => {
 359                 let lhs = self.trans_operand(&bcx, lhs);
 360                 let rhs = self.trans_operand(&bcx, rhs);
 361                 let llresult = if common::type_is_fat_ptr(bcx.tcx(), lhs.ty) {
 362                     match (lhs.val, rhs.val) {
 363                         (OperandValue::FatPtr(lhs_addr, lhs_extra),
 364                          OperandValue::FatPtr(rhs_addr, rhs_extra)) => {
 365                             bcx.with_block(|bcx| {
 366                                 base::compare_fat_ptrs(bcx,
 367                                                        lhs_addr, lhs_extra,
 368                                                        rhs_addr, rhs_extra,
 369                                                        lhs.ty, op.to_hir_binop(),
 370                                                        DebugLoc::None)
 371                             })
 372                         }
 373                         _ => unreachable!()
 374                     }
 375
 376                 } else {
 377                     self.trans_scalar_binop(&bcx, op,
 378                                             lhs.immediate(), rhs.immediate(),
 379                                             lhs.ty)
 380                 };
 381                 let operand = OperandRef {
 382                     val: OperandValue::Immediate(llresult),
 383                     ty: self.mir.binop_ty(bcx.tcx(), op, lhs.ty, rhs.ty),
 384                 };
 385                 (bcx, operand)
 386             }
 387
 388             mir::Rvalue::UnaryOp(op, ref operand) => {
 389                 let operand = self.trans_operand(&bcx, operand);
 390                 let lloperand = operand.immediate();
 391                 let is_float = operand.ty.is_fp();
 392                 let llval = match op {
 393                     mir::UnOp::Not => bcx.not(lloperand),
 394                     mir::UnOp::Neg => if is_float {
 395                         bcx.fneg(lloperand)
 396                     } else {
 397                         bcx.neg(lloperand)
 398                     }
 399                 };
 400                 (bcx, OperandRef {
 401                     val: OperandValue::Immediate(llval),
 402                     ty: operand.ty,
 403                 })
 404             }
 405
 406             mir::Rvalue::Box(content_ty) => {
 407                 let content_ty: Ty<'tcx> = bcx.monomorphize(&content_ty);
 408                 let llty = type_of::type_of(bcx.ccx(), content_ty);
 409                 let llsize = machine::llsize_of(bcx.ccx(), llty);
 410                 let align = type_of::align_of(bcx.ccx(), content_ty);
 411                 let llalign = common::C_uint(bcx.ccx(), align);
 412                 let llty_ptr = llty.ptr_to();
 413                 let box_ty = bcx.tcx().mk_box(content_ty);
 414                 let mut llval = None;
 415                 let bcx = bcx.map_block(|bcx| {
 416                     let Result { bcx, val } = base::malloc_raw_dyn(bcx,
 417                                                                    llty_ptr,
 418                                                                    box_ty,
 419                                                                    llsize,
 420                                                                    llalign,
 421                                                                    DebugLoc::None);
 422                     llval = Some(val);
 423                     bcx
 424                 });
 425                 let operand = OperandRef {
 426                     val: OperandValue::Immediate(llval.unwrap()),
 427                     ty: box_ty,
 428                 };
 429                 (bcx, operand)
 430             }
 431
 432             mir::Rvalue::Use(..) |
 433             mir::Rvalue::Repeat(..) |
 434             mir::Rvalue::Aggregate(..) |
 435             mir::Rvalue::Slice { .. } |
 436             mir::Rvalue::InlineAsm(..) => {
 437                 bcx.tcx().sess.bug(&format!("cannot generate operand from rvalue {:?}", rvalue));
 438             }
 439         }
 440     }
 441
 442     pub fn trans_scalar_binop(&mut self,
 443                               bcx: &BlockAndBuilder<'bcx, 'tcx>,
 444                               op: mir::BinOp,
 445                               lhs: ValueRef,
 446                               rhs: ValueRef,
 447                               input_ty: Ty<'tcx>) -> ValueRef {
 448         let is_float = input_ty.is_fp();
 449         let is_signed = input_ty.is_signed();
 450         match op {
 451             mir::BinOp::Add => if is_float {
 452                 bcx.fadd(lhs, rhs)
 453             } else {
 454                 bcx.add(lhs, rhs)
 455             },
 456             mir::BinOp::Sub => if is_float {
 457                 bcx.fsub(lhs, rhs)
 458             } else {
 459                 bcx.sub(lhs, rhs)
 460             },
 461             mir::BinOp::Mul => if is_float {
 462                 bcx.fmul(lhs, rhs)
 463             } else {
 464                 bcx.mul(lhs, rhs)
 465             },
 466             mir::BinOp::Div => if is_float {
 467                 bcx.fdiv(lhs, rhs)
 468             } else if is_signed {
 469                 bcx.sdiv(lhs, rhs)
 470             } else {
 471                 bcx.udiv(lhs, rhs)
 472             },
 473             mir::BinOp::Rem => if is_float {
 474                 // LLVM currently always lowers the `frem` instructions appropriate
 475                 // library calls typically found in libm. Notably f64 gets wired up
 476                 // to `fmod` and f32 gets wired up to `fmodf`. Inconveniently for
 477                 // us, 32-bit MSVC does not actually have a `fmodf` symbol, it's
 478                 // instead just an inline function in a header that goes up to a
 479                 // f64, uses `fmod`, and then comes back down to a f32.
 480                 //
 481                 // Although LLVM knows that `fmodf` doesn't exist on MSVC, it will
 482                 // still unconditionally lower frem instructions over 32-bit floats
 483                 // to a call to `fmodf`. To work around this we special case MSVC
 484                 // 32-bit float rem instructions and instead do the call out to
 485                 // `fmod` ourselves.
 486                 //
 487                 // Note that this is currently duplicated with src/libcore/ops.rs
 488                 // which does the same thing, and it would be nice to perhaps unify
 489                 // these two implementations one day! Also note that we call `fmod`
 490                 // for both 32 and 64-bit floats because if we emit any FRem
 491                 // instruction at all then LLVM is capable of optimizing it into a
 492                 // 32-bit FRem (which we're trying to avoid).
 493                 let tcx = bcx.tcx();
 494                 let use_fmod = tcx.sess.target.target.options.is_like_msvc &&
 495                     tcx.sess.target.target.arch == "x86";
 496                 if use_fmod {
 497                     let f64t = Type::f64(bcx.ccx());
 498                     let fty = Type::func(&[f64t, f64t], &f64t);
 499                     let llfn = declare::declare_cfn(bcx.ccx(), "fmod", fty,
 500                                                     tcx.types.f64);
 501                     if input_ty == tcx.types.f32 {
 502                         let lllhs = bcx.fpext(lhs, f64t);
 503                         let llrhs = bcx.fpext(rhs, f64t);
 504                         let llres = bcx.call(llfn, &[lllhs, llrhs], None, None);
 505                         bcx.fptrunc(llres, Type::f32(bcx.ccx()))
 506                     } else {
 507                         bcx.call(llfn, &[lhs, rhs], None, None)
 508                     }
 509                 } else {
 510                     bcx.frem(lhs, rhs)
 511                 }
 512             } else if is_signed {
 513                 bcx.srem(lhs, rhs)
 514             } else {
 515                 bcx.urem(lhs, rhs)
 516             },
 517             mir::BinOp::BitOr => bcx.or(lhs, rhs),
 518             mir::BinOp::BitAnd => bcx.and(lhs, rhs),
 519             mir::BinOp::BitXor => bcx.xor(lhs, rhs),
 520             mir::BinOp::Shl => {
 521                 bcx.with_block(|bcx| {
 522                     common::build_unchecked_lshift(bcx,
 523                                                    lhs,
 524                                                    rhs,
 525                                                    DebugLoc::None)
 526                 })
 527             }
 528             mir::BinOp::Shr => {
 529                 bcx.with_block(|bcx| {
 530                     common::build_unchecked_rshift(bcx,
 531                                                    input_ty,
 532                                                    lhs,
 533                                                    rhs,
 534                                                    DebugLoc::None)
 535                 })
 536             }
 537             mir::BinOp::Eq | mir::BinOp::Lt | mir::BinOp::Gt |
 538             mir::BinOp::Ne | mir::BinOp::Le | mir::BinOp::Ge => {
 539                 bcx.with_block(|bcx| {
 540                     base::compare_scalar_types(bcx, lhs, rhs, input_ty,
 541                                                op.to_hir_binop(), DebugLoc::None)
 542                 })
 543             }
 544         }
 545     }
 546 }
 547
 548 pub fn rvalue_creates_operand<'tcx>(rvalue: &mir::Rvalue<'tcx>) -> bool {
 549     match *rvalue {
 550         mir::Rvalue::Ref(..) |
 551         mir::Rvalue::Len(..) |
 552         mir::Rvalue::Cast(..) | // (*)
 553         mir::Rvalue::BinaryOp(..) |
 554         mir::Rvalue::UnaryOp(..) |
 555         mir::Rvalue::Box(..) =>
 556             true,
 557         mir::Rvalue::Use(..) | // (**)
 558         mir::Rvalue::Repeat(..) |
 559         mir::Rvalue::Aggregate(..) |
 560         mir::Rvalue::Slice { .. } |
 561         mir::Rvalue::InlineAsm(..) =>
 562             false,
 563     }
 564
 565     // (*) this is only true if the type is suitable
 566     // (**) we need to zero-out the source operand after moving, so we are restricted to either
 567     // ensuring all users of `Use` zero it out themselves or not allowing to “create” operand for
 568     // it.
 569 }