src/librustc_codegen_ssa/mir/block.rs

   1 use rustc_index::vec::Idx;
   2 use rustc::middle::lang_items;
   3 use rustc::ty::{self, Ty, TypeFoldable, Instance};
   4 use rustc::ty::layout::{self, LayoutOf, HasTyCtxt, FnTypeExt};
   5 use rustc::mir::{self, PlaceBase, Static, StaticKind};
   6 use rustc::mir::interpret::PanicInfo;
   7 use rustc_target::abi::call::{ArgType, FnType, PassMode};
   8 use rustc_target::spec::abi::Abi;
   9 use crate::base;
  10 use crate::MemFlags;
  11 use crate::common::{self, IntPredicate};
  12 use crate::meth;
  13
  14 use crate::traits::*;
  15
  16 use std::borrow::Cow;
  17
  18 use syntax::{source_map::Span, symbol::Symbol};
  19
  20 use super::{FunctionCx, LocalRef};
  21 use super::place::PlaceRef;
  22 use super::operand::OperandRef;
  23 use super::operand::OperandValue::{Pair, Ref, Immediate};
  24
  25 /// Used by `FunctionCx::codegen_terminator` for emitting common patterns
  26 /// e.g., creating a basic block, calling a function, etc.
  27 struct TerminatorCodegenHelper<'a, 'tcx> {
  28     bb: &'a mir::BasicBlock,
  29     terminator: &'a mir::Terminator<'tcx>,
  30     funclet_bb: Option<mir::BasicBlock>,
  31 }
  32
  33 impl<'a, 'tcx> TerminatorCodegenHelper<'a, 'tcx> {
  34     /// Returns the associated funclet from `FunctionCx::funclets` for the
  35     /// `funclet_bb` member if it is not `None`.
  36     fn funclet<'c, 'b, Bx: BuilderMethods<'b, 'tcx>>(
  37         &self,
  38         fx: &'c mut FunctionCx<'b, 'tcx, Bx>,
  39     ) -> Option<&'c Bx::Funclet> {
  40         match self.funclet_bb {
  41             Some(funcl) => fx.funclets[funcl].as_ref(),
  42             None => None,
  43         }
  44     }
  45
  46     fn lltarget<'b, 'c, Bx: BuilderMethods<'b, 'tcx>>(
  47         &self,
  48         fx: &'c mut FunctionCx<'b, 'tcx, Bx>,
  49         target: mir::BasicBlock,
  50     ) -> (Bx::BasicBlock, bool) {
  51         let span = self.terminator.source_info.span;
  52         let lltarget = fx.blocks[target];
  53         let target_funclet = fx.cleanup_kinds[target].funclet_bb(target);
  54         match (self.funclet_bb, target_funclet) {
  55             (None, None) => (lltarget, false),
  56             (Some(f), Some(t_f)) if f == t_f || !base::wants_msvc_seh(fx.cx.tcx().sess) =>
  57                 (lltarget, false),
  58             // jump *into* cleanup - need a landing pad if GNU
  59             (None, Some(_)) => (fx.landing_pad_to(target), false),
  60             (Some(_), None) => span_bug!(span, "{:?} - jump out of cleanup?", self.terminator),
  61             (Some(_), Some(_)) => (fx.landing_pad_to(target), true),
  62         }
  63     }
  64
  65     /// Create a basic block.
  66     fn llblock<'c, 'b, Bx: BuilderMethods<'b, 'tcx>>(
  67         &self,
  68         fx: &'c mut FunctionCx<'b, 'tcx, Bx>,
  69         target: mir::BasicBlock,
  70     ) -> Bx::BasicBlock {
  71         let (lltarget, is_cleanupret) = self.lltarget(fx, target);
  72         if is_cleanupret {
  73             // MSVC cross-funclet jump - need a trampoline
  74
  75             debug!("llblock: creating cleanup trampoline for {:?}", target);
  76             let name = &format!("{:?}_cleanup_trampoline_{:?}", self.bb, target);
  77             let mut trampoline = fx.new_block(name);
  78             trampoline.cleanup_ret(self.funclet(fx).unwrap(),
  79                                    Some(lltarget));
  80             trampoline.llbb()
  81         } else {
  82             lltarget
  83         }
  84     }
  85
  86     fn funclet_br<'c, 'b, Bx: BuilderMethods<'b, 'tcx>>(
  87         &self,
  88         fx: &'c mut FunctionCx<'b, 'tcx, Bx>,
  89         bx: &mut Bx,
  90         target: mir::BasicBlock,
  91     ) {
  92         let (lltarget, is_cleanupret) = self.lltarget(fx, target);
  93         if is_cleanupret {
  94             // micro-optimization: generate a `ret` rather than a jump
  95             // to a trampoline.
  96             bx.cleanup_ret(self.funclet(fx).unwrap(), Some(lltarget));
  97         } else {
  98             bx.br(lltarget);
  99         }
 100     }
 101
 102     /// Call `fn_ptr` of `fn_ty` with the arguments `llargs`, the optional
 103     /// return destination `destination` and the cleanup function `cleanup`.
 104     fn do_call<'c, 'b, Bx: BuilderMethods<'b, 'tcx>>(
 105         &self,
 106         fx: &'c mut FunctionCx<'b, 'tcx, Bx>,
 107         bx: &mut Bx,
 108         fn_ty: FnType<'tcx, Ty<'tcx>>,
 109         fn_ptr: Bx::Value,
 110         llargs: &[Bx::Value],
 111         destination: Option<(ReturnDest<'tcx, Bx::Value>, mir::BasicBlock)>,
 112         cleanup: Option<mir::BasicBlock>,
 113     ) {
 114         if let Some(cleanup) = cleanup {
 115             let ret_bx = if let Some((_, target)) = destination {
 116                 fx.blocks[target]
 117             } else {
 118                 fx.unreachable_block()
 119             };
 120             let invokeret = bx.invoke(fn_ptr,
 121                                       &llargs,
 122                                       ret_bx,
 123                                       self.llblock(fx, cleanup),
 124                                       self.funclet(fx));
 125             bx.apply_attrs_callsite(&fn_ty, invokeret);
 126
 127             if let Some((ret_dest, target)) = destination {
 128                 let mut ret_bx = fx.build_block(target);
 129                 fx.set_debug_loc(&mut ret_bx, self.terminator.source_info);
 130                 fx.store_return(&mut ret_bx, ret_dest, &fn_ty.ret, invokeret);
 131             }
 132         } else {
 133             let llret = bx.call(fn_ptr, &llargs, self.funclet(fx));
 134             bx.apply_attrs_callsite(&fn_ty, llret);
 135             if fx.mir[*self.bb].is_cleanup {
 136                 // Cleanup is always the cold path. Don't inline
 137                 // drop glue. Also, when there is a deeply-nested
 138                 // struct, there are "symmetry" issues that cause
 139                 // exponential inlining - see issue #41696.
 140                 bx.do_not_inline(llret);
 141             }
 142
 143             if let Some((ret_dest, target)) = destination {
 144                 fx.store_return(bx, ret_dest, &fn_ty.ret, llret);
 145                 self.funclet_br(fx, bx, target);
 146             } else {
 147                 bx.unreachable();
 148             }
 149         }
 150     }
 151
 152     // Generate sideeffect intrinsic if jumping to any of the targets can form
 153     // a loop.
 154     fn maybe_sideeffect<'b, 'tcx2: 'b, Bx: BuilderMethods<'b, 'tcx2>>(
 155         &self,
 156         mir: &'b mir::Body<'tcx>,
 157         bx: &mut Bx,
 158         targets: &[mir::BasicBlock],
 159     ) {
 160         if bx.tcx().sess.opts.debugging_opts.insert_sideeffect {
 161             if targets.iter().any(|target| {
 162                 *target <= *self.bb
 163                     && target
 164                         .start_location()
 165                         .is_predecessor_of(self.bb.start_location(), mir)
 166             }) {
 167                 bx.sideeffect();
 168             }
 169         }
 170     }
 171 }
 172
 173 /// Codegen implementations for some terminator variants.
 174 impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
 175     /// Generates code for a `Resume` terminator.
 176     fn codegen_resume_terminator<'b>(
 177         &mut self,
 178         helper: TerminatorCodegenHelper<'b, 'tcx>,
 179         mut bx: Bx,
 180     ) {
 181         if let Some(funclet) = helper.funclet(self) {
 182             bx.cleanup_ret(funclet, None);
 183         } else {
 184             let slot = self.get_personality_slot(&mut bx);
 185             let lp0 = slot.project_field(&mut bx, 0);
 186             let lp0 = bx.load_operand(lp0).immediate();
 187             let lp1 = slot.project_field(&mut bx, 1);
 188             let lp1 = bx.load_operand(lp1).immediate();
 189             slot.storage_dead(&mut bx);
 190
 191             if !bx.sess().target.target.options.custom_unwind_resume {
 192                 let mut lp = bx.const_undef(self.landing_pad_type());
 193                 lp = bx.insert_value(lp, lp0, 0);
 194                 lp = bx.insert_value(lp, lp1, 1);
 195                 bx.resume(lp);
 196             } else {
 197                 bx.call(bx.eh_unwind_resume(), &[lp0],
 198                         helper.funclet(self));
 199                 bx.unreachable();
 200             }
 201         }
 202     }
 203
 204     fn codegen_switchint_terminator<'b>(
 205         &mut self,
 206         helper: TerminatorCodegenHelper<'b, 'tcx>,
 207         mut bx: Bx,
 208         discr: &mir::Operand<'tcx>,
 209         switch_ty: Ty<'tcx>,
 210         values: &Cow<'tcx, [u128]>,
 211         targets: &Vec<mir::BasicBlock>,
 212     ) {
 213         let discr = self.codegen_operand(&mut bx, &discr);
 214         if targets.len() == 2 {
 215             // If there are two targets, emit br instead of switch
 216             let lltrue = helper.llblock(self, targets[0]);
 217             let llfalse = helper.llblock(self, targets[1]);
 218             if switch_ty == bx.tcx().types.bool {
 219                 helper.maybe_sideeffect(self.mir, &mut bx, targets.as_slice());
 220                 // Don't generate trivial icmps when switching on bool
 221                 if let [0] = values[..] {
 222                     bx.cond_br(discr.immediate(), llfalse, lltrue);
 223                 } else {
 224                     assert_eq!(&values[..], &[1]);
 225                     bx.cond_br(discr.immediate(), lltrue, llfalse);
 226                 }
 227             } else {
 228                 let switch_llty = bx.immediate_backend_type(
 229                     bx.layout_of(switch_ty)
 230                 );
 231                 let llval = bx.const_uint_big(switch_llty, values[0]);
 232                 let cmp = bx.icmp(IntPredicate::IntEQ, discr.immediate(), llval);
 233                 helper.maybe_sideeffect(self.mir, &mut bx, targets.as_slice());
 234                 bx.cond_br(cmp, lltrue, llfalse);
 235             }
 236         } else {
 237             helper.maybe_sideeffect(self.mir, &mut bx, targets.as_slice());
 238             let (otherwise, targets) = targets.split_last().unwrap();
 239             bx.switch(
 240                 discr.immediate(),
 241                 helper.llblock(self, *otherwise),
 242                 values.iter().zip(targets).map(|(&value, target)| {
 243                     (value, helper.llblock(self, *target))
 244                 })
 245             );
 246         }
 247     }
 248
 249     fn codegen_return_terminator(&mut self, mut bx: Bx) {
 250         // Call `va_end` if this is the definition of a C-variadic function.
 251         if self.fn_ty.c_variadic {
 252             // The `VaList` "spoofed" argument is just after all the real arguments.
 253             let va_list_arg_idx = self.fn_ty.args.len();
 254             match self.locals[mir::Local::new(1 + va_list_arg_idx)] {
 255                 LocalRef::Place(va_list) => {
 256                     bx.va_end(va_list.llval);
 257                 }
 258                 _ => bug!("C-variadic function must have a `VaList` place"),
 259             }
 260         }
 261         if self.fn_ty.ret.layout.abi.is_uninhabited() {
 262             // Functions with uninhabited return values are marked `noreturn`,
 263             // so we should make sure that we never actually do.
 264             bx.abort();
 265             bx.unreachable();
 266             return;
 267         }
 268         let llval = match self.fn_ty.ret.mode {
 269             PassMode::Ignore | PassMode::Indirect(..) => {
 270                 bx.ret_void();
 271                 return;
 272             }
 273
 274             PassMode::Direct(_) | PassMode::Pair(..) => {
 275                 let op =
 276                     self.codegen_consume(&mut bx, &mir::Place::return_place().as_ref());
 277                 if let Ref(llval, _, align) = op.val {
 278                     bx.load(llval, align)
 279                 } else {
 280                     op.immediate_or_packed_pair(&mut bx)
 281                 }
 282             }
 283
 284             PassMode::Cast(cast_ty) => {
 285                 let op = match self.locals[mir::RETURN_PLACE] {
 286                     LocalRef::Operand(Some(op)) => op,
 287                     LocalRef::Operand(None) => bug!("use of return before def"),
 288                     LocalRef::Place(cg_place) => {
 289                         OperandRef {
 290                             val: Ref(cg_place.llval, None, cg_place.align),
 291                             layout: cg_place.layout
 292                         }
 293                     }
 294                     LocalRef::UnsizedPlace(_) => bug!("return type must be sized"),
 295                 };
 296                 let llslot = match op.val {
 297                     Immediate(_) | Pair(..) => {
 298                         let scratch =
 299                             PlaceRef::alloca(&mut bx, self.fn_ty.ret.layout);
 300                         op.val.store(&mut bx, scratch);
 301                         scratch.llval
 302                     }
 303                     Ref(llval, _, align) => {
 304                         assert_eq!(align, op.layout.align.abi,
 305                                    "return place is unaligned!");
 306                         llval
 307                     }
 308                 };
 309                 let addr = bx.pointercast(llslot, bx.type_ptr_to(
 310                     bx.cast_backend_type(&cast_ty)
 311                 ));
 312                 bx.load(addr, self.fn_ty.ret.layout.align.abi)
 313             }
 314         };
 315         bx.ret(llval);
 316     }
 317
 318
 319     fn codegen_drop_terminator<'b>(
 320         &mut self,
 321         helper: TerminatorCodegenHelper<'b, 'tcx>,
 322         mut bx: Bx,
 323         location: &mir::Place<'tcx>,
 324         target: mir::BasicBlock,
 325         unwind: Option<mir::BasicBlock>,
 326     ) {
 327         let ty = location.ty(self.mir, bx.tcx()).ty;
 328         let ty = self.monomorphize(&ty);
 329         let drop_fn = Instance::resolve_drop_in_place(bx.tcx(), ty);
 330
 331         if let ty::InstanceDef::DropGlue(_, None) = drop_fn.def {
 332             // we don't actually need to drop anything.
 333             helper.maybe_sideeffect(self.mir, &mut bx, &[target]);
 334             helper.funclet_br(self, &mut bx, target);
 335             return
 336         }
 337
 338         let place = self.codegen_place(&mut bx, &location.as_ref());
 339         let (args1, args2);
 340         let mut args = if let Some(llextra) = place.llextra {
 341             args2 = [place.llval, llextra];
 342             &args2[..]
 343         } else {
 344             args1 = [place.llval];
 345             &args1[..]
 346         };
 347         let (drop_fn, fn_ty) = match ty.kind {
 348             ty::Dynamic(..) => {
 349                 let sig = drop_fn.fn_sig(self.cx.tcx());
 350                 let sig = self.cx.tcx().normalize_erasing_late_bound_regions(
 351                     ty::ParamEnv::reveal_all(),
 352                     &sig,
 353                 );
 354                 let fn_ty = FnType::new_vtable(&bx, sig, &[]);
 355                 let vtable = args[1];
 356                 args = &args[..1];
 357                 (meth::DESTRUCTOR.get_fn(&mut bx, vtable, &fn_ty), fn_ty)
 358             }
 359             _ => {
 360                 (bx.get_fn_addr(drop_fn),
 361                  FnType::of_instance(&bx, drop_fn))
 362             }
 363         };
 364         helper.maybe_sideeffect(self.mir, &mut bx, &[target]);
 365         helper.do_call(self, &mut bx, fn_ty, drop_fn, args,
 366                        Some((ReturnDest::Nothing, target)),
 367                        unwind);
 368     }
 369
 370     fn codegen_assert_terminator<'b>(
 371         &mut self,
 372         helper: TerminatorCodegenHelper<'b, 'tcx>,
 373         mut bx: Bx,
 374         terminator: &mir::Terminator<'tcx>,
 375         cond: &mir::Operand<'tcx>,
 376         expected: bool,
 377         msg: &mir::AssertMessage<'tcx>,
 378         target: mir::BasicBlock,
 379         cleanup: Option<mir::BasicBlock>,
 380     ) {
 381         let span = terminator.source_info.span;
 382         let cond = self.codegen_operand(&mut bx, cond).immediate();
 383         let mut const_cond = bx.const_to_opt_u128(cond, false).map(|c| c == 1);
 384
 385         // This case can currently arise only from functions marked
 386         // with #[rustc_inherit_overflow_checks] and inlined from
 387         // another crate (mostly core::num generic/#[inline] fns),
 388         // while the current crate doesn't use overflow checks.
 389         // NOTE: Unlike binops, negation doesn't have its own
 390         // checked operation, just a comparison with the minimum
 391         // value, so we have to check for the assert message.
 392         if !bx.check_overflow() {
 393             if let PanicInfo::OverflowNeg = *msg {
 394                 const_cond = Some(expected);
 395             }
 396         }
 397
 398         // Don't codegen the panic block if success if known.
 399         if const_cond == Some(expected) {
 400             helper.maybe_sideeffect(self.mir, &mut bx, &[target]);
 401             helper.funclet_br(self, &mut bx, target);
 402             return;
 403         }
 404
 405         // Pass the condition through llvm.expect for branch hinting.
 406         let cond = bx.expect(cond, expected);
 407
 408         // Create the failure block and the conditional branch to it.
 409         let lltarget = helper.llblock(self, target);
 410         let panic_block = self.new_block("panic");
 411         helper.maybe_sideeffect(self.mir, &mut bx, &[target]);
 412         if expected {
 413             bx.cond_br(cond, lltarget, panic_block.llbb());
 414         } else {
 415             bx.cond_br(cond, panic_block.llbb(), lltarget);
 416         }
 417
 418         // After this point, bx is the block for the call to panic.
 419         bx = panic_block;
 420         self.set_debug_loc(&mut bx, terminator.source_info);
 421
 422         // Get the location information.
 423         let location = self.get_caller_location(&mut bx, span).immediate();
 424
 425         // Put together the arguments to the panic entry point.
 426         let (lang_item, args) = match msg {
 427             PanicInfo::BoundsCheck { ref len, ref index } => {
 428                 let len = self.codegen_operand(&mut bx, len).immediate();
 429                 let index = self.codegen_operand(&mut bx, index).immediate();
 430                 (lang_items::PanicBoundsCheckFnLangItem, vec![location, index, len])
 431             }
 432             _ => {
 433                 let msg_str = Symbol::intern(msg.description());
 434                 let msg = bx.const_str(msg_str);
 435                 (lang_items::PanicFnLangItem, vec![msg.0, msg.1, location])
 436             }
 437         };
 438
 439         // Obtain the panic entry point.
 440         let def_id = common::langcall(bx.tcx(), Some(span), "", lang_item);
 441         let instance = ty::Instance::mono(bx.tcx(), def_id);
 442         let fn_ty = FnType::of_instance(&bx, instance);
 443         let llfn = bx.get_fn_addr(instance);
 444
 445         // Codegen the actual panic invoke/call.
 446         helper.do_call(self, &mut bx, fn_ty, llfn, &args, None, cleanup);
 447     }
 448
 449     fn codegen_call_terminator<'b>(
 450         &mut self,
 451         helper: TerminatorCodegenHelper<'b, 'tcx>,
 452         mut bx: Bx,
 453         terminator: &mir::Terminator<'tcx>,
 454         func: &mir::Operand<'tcx>,
 455         args: &Vec<mir::Operand<'tcx>>,
 456         destination: &Option<(mir::Place<'tcx>, mir::BasicBlock)>,
 457         cleanup: Option<mir::BasicBlock>,
 458     ) {
 459         let span = terminator.source_info.span;
 460         // Create the callee. This is a fn ptr or zero-sized and hence a kind of scalar.
 461         let callee = self.codegen_operand(&mut bx, func);
 462
 463         let (instance, mut llfn) = match callee.layout.ty.kind {
 464             ty::FnDef(def_id, substs) => {
 465                 (Some(ty::Instance::resolve(bx.tcx(),
 466                                             ty::ParamEnv::reveal_all(),
 467                                             def_id,
 468                                             substs).unwrap()),
 469                  None)
 470             }
 471             ty::FnPtr(_) => {
 472                 (None, Some(callee.immediate()))
 473             }
 474             _ => bug!("{} is not callable", callee.layout.ty),
 475         };
 476         let def = instance.map(|i| i.def);
 477         let sig = callee.layout.ty.fn_sig(bx.tcx());
 478         let sig = bx.tcx().normalize_erasing_late_bound_regions(
 479             ty::ParamEnv::reveal_all(),
 480             &sig,
 481         );
 482         let abi = sig.abi;
 483
 484         // Handle intrinsics old codegen wants Expr's for, ourselves.
 485         let intrinsic = match def {
 486             Some(ty::InstanceDef::Intrinsic(def_id)) =>
 487                 Some(bx.tcx().item_name(def_id).as_str()),
 488             _ => None
 489         };
 490         let intrinsic = intrinsic.as_ref().map(|s| &s[..]);
 491
 492         if intrinsic == Some("transmute") {
 493             if let Some(destination_ref) = destination.as_ref() {
 494                 let &(ref dest, target) = destination_ref;
 495                 self.codegen_transmute(&mut bx, &args[0], dest);
 496                 helper.maybe_sideeffect(self.mir, &mut bx, &[target]);
 497                 helper.funclet_br(self, &mut bx, target);
 498             } else {
 499                 // If we are trying to transmute to an uninhabited type,
 500                 // it is likely there is no allotted destination. In fact,
 501                 // transmuting to an uninhabited type is UB, which means
 502                 // we can do what we like. Here, we declare that transmuting
 503                 // into an uninhabited type is impossible, so anything following
 504                 // it must be unreachable.
 505                 assert_eq!(bx.layout_of(sig.output()).abi, layout::Abi::Uninhabited);
 506                 bx.unreachable();
 507             }
 508             return;
 509         }
 510
 511         let extra_args = &args[sig.inputs().len()..];
 512         let extra_args = extra_args.iter().map(|op_arg| {
 513             let op_ty = op_arg.ty(self.mir, bx.tcx());
 514             self.monomorphize(&op_ty)
 515         }).collect::<Vec<_>>();
 516
 517         let fn_ty = match def {
 518             Some(ty::InstanceDef::Virtual(..)) => {
 519                 FnType::new_vtable(&bx, sig, &extra_args)
 520             }
 521             Some(ty::InstanceDef::DropGlue(_, None)) => {
 522                 // Empty drop glue; a no-op.
 523                 let &(_, target) = destination.as_ref().unwrap();
 524                 helper.maybe_sideeffect(self.mir, &mut bx, &[target]);
 525                 helper.funclet_br(self, &mut bx, target);
 526                 return;
 527             }
 528             _ => FnType::new(&bx, sig, &extra_args)
 529         };
 530
 531         // Emit a panic or a no-op for `panic_if_uninhabited`.
 532         if intrinsic == Some("panic_if_uninhabited") {
 533             let ty = instance.unwrap().substs.type_at(0);
 534             let layout = bx.layout_of(ty);
 535             if layout.abi.is_uninhabited() {
 536                 let msg_str = format!("Attempted to instantiate uninhabited type {}", ty);
 537                 let msg = bx.const_str(Symbol::intern(&msg_str));
 538                 let location = self.get_caller_location(&mut bx, span).immediate();
 539
 540                 // Obtain the panic entry point.
 541                 let def_id =
 542                     common::langcall(bx.tcx(), Some(span), "", lang_items::PanicFnLangItem);
 543                 let instance = ty::Instance::mono(bx.tcx(), def_id);
 544                 let fn_ty = FnType::of_instance(&bx, instance);
 545                 let llfn = bx.get_fn_addr(instance);
 546
 547                 if let Some((_, target)) = destination.as_ref() {
 548                     helper.maybe_sideeffect(self.mir, &mut bx, &[*target]);
 549                 }
 550                 // Codegen the actual panic invoke/call.
 551                 helper.do_call(
 552                     self,
 553                     &mut bx,
 554                     fn_ty,
 555                     llfn,
 556                     &[msg.0, msg.1, location],
 557                     destination.as_ref().map(|(_, bb)| (ReturnDest::Nothing, *bb)),
 558                     cleanup,
 559                 );
 560             } else {
 561                 // a NOP
 562                 let target = destination.as_ref().unwrap().1;
 563                 helper.maybe_sideeffect(self.mir, &mut bx, &[target]);
 564                 helper.funclet_br(self, &mut bx, target);
 565             }
 566             return;
 567         }
 568
 569         // The arguments we'll be passing. Plus one to account for outptr, if used.
 570         let arg_count = fn_ty.args.len() + fn_ty.ret.is_indirect() as usize;
 571         let mut llargs = Vec::with_capacity(arg_count);
 572
 573         // Prepare the return value destination
 574         let ret_dest = if let Some((ref dest, _)) = *destination {
 575             let is_intrinsic = intrinsic.is_some();
 576             self.make_return_dest(&mut bx, dest, &fn_ty.ret, &mut llargs,
 577                                   is_intrinsic)
 578         } else {
 579             ReturnDest::Nothing
 580         };
 581
 582         if intrinsic == Some("caller_location") {
 583             if let Some((_, target)) = destination.as_ref() {
 584                 let location = self.get_caller_location(&mut bx, span);
 585
 586                 if let ReturnDest::IndirectOperand(tmp, _) = ret_dest {
 587                     location.val.store(&mut bx, tmp);
 588                 }
 589                 self.store_return(&mut bx, ret_dest, &fn_ty.ret, location.immediate());
 590
 591                 helper.maybe_sideeffect(self.mir, &mut bx, &[*target]);
 592                 helper.funclet_br(self, &mut bx, *target);
 593             }
 594             return;
 595         }
 596
 597         if intrinsic.is_some() && intrinsic != Some("drop_in_place") {
 598             let dest = match ret_dest {
 599                 _ if fn_ty.ret.is_indirect() => llargs[0],
 600                 ReturnDest::Nothing =>
 601                     bx.const_undef(bx.type_ptr_to(bx.memory_ty(&fn_ty.ret))),
 602                 ReturnDest::IndirectOperand(dst, _) | ReturnDest::Store(dst) =>
 603                     dst.llval,
 604                 ReturnDest::DirectOperand(_) =>
 605                     bug!("Cannot use direct operand with an intrinsic call"),
 606             };
 607
 608             let args: Vec<_> = args.iter().enumerate().map(|(i, arg)| {
 609                 // The indices passed to simd_shuffle* in the
 610                 // third argument must be constant. This is
 611                 // checked by const-qualification, which also
 612                 // promotes any complex rvalues to constants.
 613                 if i == 2 && intrinsic.unwrap().starts_with("simd_shuffle") {
 614                     match arg {
 615                         // The shuffle array argument is usually not an explicit constant,
 616                         // but specified directly in the code. This means it gets promoted
 617                         // and we can then extract the value by evaluating the promoted.
 618                         mir::Operand::Copy(place) | mir::Operand::Move(place) => {
 619                             if let mir::PlaceRef {
 620                                 base:
 621                                     &PlaceBase::Static(box Static {
 622                                         kind: StaticKind::Promoted(promoted, _),
 623                                         ty,
 624                                         def_id: _,
 625                                     }),
 626                                 projection: &[],
 627                             } = place.as_ref()
 628                             {
 629                                 let param_env = ty::ParamEnv::reveal_all();
 630                                 let cid = mir::interpret::GlobalId {
 631                                     instance: self.instance,
 632                                     promoted: Some(promoted),
 633                                 };
 634                                 let c = bx.tcx().const_eval(param_env.and(cid));
 635                                 let (llval, ty) = self.simd_shuffle_indices(
 636                                     &bx,
 637                                     terminator.source_info.span,
 638                                     ty,
 639                                     c,
 640                                 );
 641                                 return OperandRef {
 642                                     val: Immediate(llval),
 643                                     layout: bx.layout_of(ty),
 644                                 };
 645                             } else {
 646                                 span_bug!(span, "shuffle indices must be constant");
 647                             }
 648                         }
 649
 650                         mir::Operand::Constant(constant) => {
 651                             let c = self.eval_mir_constant(constant);
 652                             let (llval, ty) = self.simd_shuffle_indices(
 653                                 &bx,
 654                                 constant.span,
 655                                 constant.literal.ty,
 656                                 c,
 657                             );
 658                             return OperandRef {
 659                                 val: Immediate(llval),
 660                                 layout: bx.layout_of(ty)
 661                             };
 662                         }
 663                     }
 664                 }
 665
 666                 self.codegen_operand(&mut bx, arg)
 667             }).collect();
 668
 669
 670             bx.codegen_intrinsic_call(*instance.as_ref().unwrap(), &fn_ty, &args, dest,
 671                                       terminator.source_info.span);
 672
 673             if let ReturnDest::IndirectOperand(dst, _) = ret_dest {
 674                 self.store_return(&mut bx, ret_dest, &fn_ty.ret, dst.llval);
 675             }
 676
 677             if let Some((_, target)) = *destination {
 678                 helper.maybe_sideeffect(self.mir, &mut bx, &[target]);
 679                 helper.funclet_br(self, &mut bx, target);
 680             } else {
 681                 bx.unreachable();
 682             }
 683
 684             return;
 685         }
 686
 687         // Split the rust-call tupled arguments off.
 688         let (first_args, untuple) = if abi == Abi::RustCall && !args.is_empty() {
 689             let (tup, args) = args.split_last().unwrap();
 690             (args, Some(tup))
 691         } else {
 692             (&args[..], None)
 693         };
 694
 695         'make_args: for (i, arg) in first_args.iter().enumerate() {
 696             let mut op = self.codegen_operand(&mut bx, arg);
 697
 698             if let (0, Some(ty::InstanceDef::Virtual(_, idx))) = (i, def) {
 699                 if let Pair(..) = op.val {
 700                     // In the case of Rc<Self>, we need to explicitly pass a
 701                     // *mut RcBox<Self> with a Scalar (not ScalarPair) ABI. This is a hack
 702                     // that is understood elsewhere in the compiler as a method on
 703                     // `dyn Trait`.
 704                     // To get a `*mut RcBox<Self>`, we just keep unwrapping newtypes until
 705                     // we get a value of a built-in pointer type
 706                     'descend_newtypes: while !op.layout.ty.is_unsafe_ptr()
 707                                     && !op.layout.ty.is_region_ptr()
 708                     {
 709                         'iter_fields: for i in 0..op.layout.fields.count() {
 710                             let field = op.extract_field(&mut bx, i);
 711                             if !field.layout.is_zst() {
 712                                 // we found the one non-zero-sized field that is allowed
 713                                 // now find *its* non-zero-sized field, or stop if it's a
 714                                 // pointer
 715                                 op = field;
 716                                 continue 'descend_newtypes
 717                             }
 718                         }
 719
 720                         span_bug!(span, "receiver has no non-zero-sized fields {:?}", op);
 721                     }
 722
 723                     // now that we have `*dyn Trait` or `&dyn Trait`, split it up into its
 724                     // data pointer and vtable. Look up the method in the vtable, and pass
 725                     // the data pointer as the first argument
 726                     match op.val {
 727                         Pair(data_ptr, meta) => {
 728                             llfn = Some(meth::VirtualIndex::from_index(idx)
 729                                 .get_fn(&mut bx, meta, &fn_ty));
 730                             llargs.push(data_ptr);
 731                             continue 'make_args
 732                         }
 733                         other => bug!("expected a Pair, got {:?}", other),
 734                     }
 735                 } else if let Ref(data_ptr, Some(meta), _) = op.val {
 736                     // by-value dynamic dispatch
 737                     llfn = Some(meth::VirtualIndex::from_index(idx)
 738                         .get_fn(&mut bx, meta, &fn_ty));
 739                     llargs.push(data_ptr);
 740                     continue;
 741                 } else {
 742                     span_bug!(span, "can't codegen a virtual call on {:?}", op);
 743                 }
 744             }
 745
 746             // The callee needs to own the argument memory if we pass it
 747             // by-ref, so make a local copy of non-immediate constants.
 748             match (arg, op.val) {
 749                 (&mir::Operand::Copy(_), Ref(_, None, _)) |
 750                 (&mir::Operand::Constant(_), Ref(_, None, _)) => {
 751                     let tmp = PlaceRef::alloca(&mut bx, op.layout);
 752                     op.val.store(&mut bx, tmp);
 753                     op.val = Ref(tmp.llval, None, tmp.align);
 754                 }
 755                 _ => {}
 756             }
 757
 758             self.codegen_argument(&mut bx, op, &mut llargs, &fn_ty.args[i]);
 759         }
 760         if let Some(tup) = untuple {
 761             self.codegen_arguments_untupled(&mut bx, tup, &mut llargs,
 762                 &fn_ty.args[first_args.len()..])
 763         }
 764
 765         let fn_ptr = match (llfn, instance) {
 766             (Some(llfn), _) => llfn,
 767             (None, Some(instance)) => bx.get_fn_addr(instance),
 768             _ => span_bug!(span, "no llfn for call"),
 769         };
 770
 771         if let Some((_, target)) = destination.as_ref() {
 772             helper.maybe_sideeffect(self.mir, &mut bx, &[*target]);
 773         }
 774         helper.do_call(self, &mut bx, fn_ty, fn_ptr, &llargs,
 775                        destination.as_ref().map(|&(_, target)| (ret_dest, target)),
 776                        cleanup);
 777     }
 778 }
 779
 780 impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
 781     pub fn codegen_block(
 782         &mut self,
 783         bb: mir::BasicBlock,
 784     ) {
 785         let mut bx = self.build_block(bb);
 786         let data = &self.mir[bb];
 787
 788         debug!("codegen_block({:?}={:?})", bb, data);
 789
 790         for statement in &data.statements {
 791             bx = self.codegen_statement(bx, statement);
 792         }
 793
 794         self.codegen_terminator(bx, bb, data.terminator());
 795     }
 796
 797     fn codegen_terminator(
 798         &mut self,
 799         mut bx: Bx,
 800         bb: mir::BasicBlock,
 801         terminator: &mir::Terminator<'tcx>
 802     ) {
 803         debug!("codegen_terminator: {:?}", terminator);
 804
 805         // Create the cleanup bundle, if needed.
 806         let funclet_bb = self.cleanup_kinds[bb].funclet_bb(bb);
 807         let helper = TerminatorCodegenHelper {
 808             bb: &bb, terminator, funclet_bb
 809         };
 810
 811         self.set_debug_loc(&mut bx, terminator.source_info);
 812         match terminator.kind {
 813             mir::TerminatorKind::Resume => {
 814                 self.codegen_resume_terminator(helper, bx)
 815             }
 816
 817             mir::TerminatorKind::Abort => {
 818                 bx.abort();
 819                 bx.unreachable();
 820             }
 821
 822             mir::TerminatorKind::Goto { target } => {
 823                 helper.maybe_sideeffect(self.mir, &mut bx, &[target]);
 824                 helper.funclet_br(self, &mut bx, target);
 825             }
 826
 827             mir::TerminatorKind::SwitchInt {
 828                 ref discr, switch_ty, ref values, ref targets
 829             } => {
 830                 self.codegen_switchint_terminator(helper, bx, discr, switch_ty,
 831                                                   values, targets);
 832             }
 833
 834             mir::TerminatorKind::Return => {
 835                 self.codegen_return_terminator(bx);
 836             }
 837
 838             mir::TerminatorKind::Unreachable => {
 839                 bx.unreachable();
 840             }
 841
 842             mir::TerminatorKind::Drop { ref location, target, unwind } => {
 843                 self.codegen_drop_terminator(helper, bx, location, target, unwind);
 844             }
 845
 846             mir::TerminatorKind::Assert { ref cond, expected, ref msg, target, cleanup } => {
 847                 self.codegen_assert_terminator(helper, bx, terminator, cond,
 848                                                expected, msg, target, cleanup);
 849             }
 850
 851             mir::TerminatorKind::DropAndReplace { .. } => {
 852                 bug!("undesugared DropAndReplace in codegen: {:?}", terminator);
 853             }
 854
 855             mir::TerminatorKind::Call {
 856                 ref func,
 857                 ref args,
 858                 ref destination,
 859                 cleanup,
 860                 from_hir_call: _
 861             } => {
 862                 self.codegen_call_terminator(helper, bx, terminator, func,
 863                                              args, destination, cleanup);
 864             }
 865             mir::TerminatorKind::GeneratorDrop |
 866             mir::TerminatorKind::Yield { .. } => bug!("generator ops in codegen"),
 867             mir::TerminatorKind::FalseEdges { .. } |
 868             mir::TerminatorKind::FalseUnwind { .. } => bug!("borrowck false edges in codegen"),
 869         }
 870     }
 871
 872     fn codegen_argument(
 873         &mut self,
 874         bx: &mut Bx,
 875         op: OperandRef<'tcx, Bx::Value>,
 876         llargs: &mut Vec<Bx::Value>,
 877         arg: &ArgType<'tcx, Ty<'tcx>>
 878     ) {
 879         // Fill padding with undef value, where applicable.
 880         if let Some(ty) = arg.pad {
 881             llargs.push(bx.const_undef(bx.reg_backend_type(&ty)))
 882         }
 883
 884         if arg.is_ignore() {
 885             return;
 886         }
 887
 888         if let PassMode::Pair(..) = arg.mode {
 889             match op.val {
 890                 Pair(a, b) => {
 891                     llargs.push(a);
 892                     llargs.push(b);
 893                     return;
 894                 }
 895                 _ => bug!("codegen_argument: {:?} invalid for pair argument", op)
 896             }
 897         } else if arg.is_unsized_indirect() {
 898             match op.val {
 899                 Ref(a, Some(b), _) => {
 900                     llargs.push(a);
 901                     llargs.push(b);
 902                     return;
 903                 }
 904                 _ => bug!("codegen_argument: {:?} invalid for unsized indirect argument", op)
 905             }
 906         }
 907
 908         // Force by-ref if we have to load through a cast pointer.
 909         let (mut llval, align, by_ref) = match op.val {
 910             Immediate(_) | Pair(..) => {
 911                 match arg.mode {
 912                     PassMode::Indirect(..) | PassMode::Cast(_) => {
 913                         let scratch = PlaceRef::alloca(bx, arg.layout);
 914                         op.val.store(bx, scratch);
 915                         (scratch.llval, scratch.align, true)
 916                     }
 917                     _ => {
 918                         (op.immediate_or_packed_pair(bx), arg.layout.align.abi, false)
 919                     }
 920                 }
 921             }
 922             Ref(llval, _, align) => {
 923                 if arg.is_indirect() && align < arg.layout.align.abi {
 924                     // `foo(packed.large_field)`. We can't pass the (unaligned) field directly. I
 925                     // think that ATM (Rust 1.16) we only pass temporaries, but we shouldn't
 926                     // have scary latent bugs around.
 927
 928                     let scratch = PlaceRef::alloca(bx, arg.layout);
 929                     base::memcpy_ty(bx, scratch.llval, scratch.align, llval, align,
 930                                     op.layout, MemFlags::empty());
 931                     (scratch.llval, scratch.align, true)
 932                 } else {
 933                     (llval, align, true)
 934                 }
 935             }
 936         };
 937
 938         if by_ref && !arg.is_indirect() {
 939             // Have to load the argument, maybe while casting it.
 940             if let PassMode::Cast(ty) = arg.mode {
 941                 let addr = bx.pointercast(llval, bx.type_ptr_to(
 942                     bx.cast_backend_type(&ty))
 943                 );
 944                 llval = bx.load(addr, align.min(arg.layout.align.abi));
 945             } else {
 946                 // We can't use `PlaceRef::load` here because the argument
 947                 // may have a type we don't treat as immediate, but the ABI
 948                 // used for this call is passing it by-value. In that case,
 949                 // the load would just produce `OperandValue::Ref` instead
 950                 // of the `OperandValue::Immediate` we need for the call.
 951                 llval = bx.load(llval, align);
 952                 if let layout::Abi::Scalar(ref scalar) = arg.layout.abi {
 953                     if scalar.is_bool() {
 954                         bx.range_metadata(llval, 0..2);
 955                     }
 956                 }
 957                 // We store bools as `i8` so we need to truncate to `i1`.
 958                 llval = base::to_immediate(bx, llval, arg.layout);
 959             }
 960         }
 961
 962         llargs.push(llval);
 963     }
 964
 965     fn codegen_arguments_untupled(
 966         &mut self,
 967         bx: &mut Bx,
 968         operand: &mir::Operand<'tcx>,
 969         llargs: &mut Vec<Bx::Value>,
 970         args: &[ArgType<'tcx, Ty<'tcx>>]
 971     ) {
 972         let tuple = self.codegen_operand(bx, operand);
 973
 974         // Handle both by-ref and immediate tuples.
 975         if let Ref(llval, None, align) = tuple.val {
 976             let tuple_ptr = PlaceRef::new_sized_aligned(llval, tuple.layout, align);
 977             for i in 0..tuple.layout.fields.count() {
 978                 let field_ptr = tuple_ptr.project_field(bx, i);
 979                 let field = bx.load_operand(field_ptr);
 980                 self.codegen_argument(bx, field, llargs, &args[i]);
 981             }
 982         } else if let Ref(_, Some(_), _) = tuple.val {
 983             bug!("closure arguments must be sized")
 984         } else {
 985             // If the tuple is immediate, the elements are as well.
 986             for i in 0..tuple.layout.fields.count() {
 987                 let op = tuple.extract_field(bx, i);
 988                 self.codegen_argument(bx, op, llargs, &args[i]);
 989             }
 990         }
 991     }
 992
 993     fn get_caller_location(
 994         &mut self,
 995         bx: &mut Bx,
 996         span: Span,
 997     ) -> OperandRef<'tcx, Bx::Value> {
 998         let caller = bx.tcx().sess.source_map().lookup_char_pos(span.lo());
 999         let const_loc = bx.tcx().const_caller_location((
1000             Symbol::intern(&caller.file.name.to_string()),
1001             caller.line as u32,
1002             caller.col_display as u32 + 1,
1003         ));
1004         OperandRef::from_const(bx, const_loc)
1005     }
1006
1007     fn get_personality_slot(
1008         &mut self,
1009         bx: &mut Bx
1010     ) -> PlaceRef<'tcx, Bx::Value> {
1011         let cx = bx.cx();
1012         if let Some(slot) = self.personality_slot {
1013             slot
1014         } else {
1015             let layout = cx.layout_of(cx.tcx().intern_tup(&[
1016                 cx.tcx().mk_mut_ptr(cx.tcx().types.u8),
1017                 cx.tcx().types.i32
1018             ]));
1019             let slot = PlaceRef::alloca(bx, layout);
1020             self.personality_slot = Some(slot);
1021             slot
1022         }
1023     }
1024
1025     /// Returns the landing-pad wrapper around the given basic block.
1026     ///
1027     /// No-op in MSVC SEH scheme.
1028     fn landing_pad_to(
1029         &mut self,
1030         target_bb: mir::BasicBlock
1031     ) -> Bx::BasicBlock {
1032         if let Some(block) = self.landing_pads[target_bb] {
1033             return block;
1034         }
1035
1036         let block = self.blocks[target_bb];
1037         let landing_pad = self.landing_pad_uncached(block);
1038         self.landing_pads[target_bb] = Some(landing_pad);
1039         landing_pad
1040     }
1041
1042     fn landing_pad_uncached(
1043         &mut self,
1044         target_bb: Bx::BasicBlock
1045     ) -> Bx::BasicBlock {
1046         if base::wants_msvc_seh(self.cx.sess()) {
1047             span_bug!(self.mir.span, "landing pad was not inserted?")
1048         }
1049
1050         let mut bx = self.new_block("cleanup");
1051
1052         let llpersonality = self.cx.eh_personality();
1053         let llretty = self.landing_pad_type();
1054         let lp = bx.landing_pad(llretty, llpersonality, 1);
1055         bx.set_cleanup(lp);
1056
1057         let slot = self.get_personality_slot(&mut bx);
1058         slot.storage_live(&mut bx);
1059         Pair(bx.extract_value(lp, 0), bx.extract_value(lp, 1)).store(&mut bx, slot);
1060
1061         bx.br(target_bb);
1062         bx.llbb()
1063     }
1064
1065     fn landing_pad_type(&self) -> Bx::Type {
1066         let cx = self.cx;
1067         cx.type_struct(&[cx.type_i8p(), cx.type_i32()], false)
1068     }
1069
1070     fn unreachable_block(
1071         &mut self
1072     ) -> Bx::BasicBlock {
1073         self.unreachable_block.unwrap_or_else(|| {
1074             let mut bx = self.new_block("unreachable");
1075             bx.unreachable();
1076             self.unreachable_block = Some(bx.llbb());
1077             bx.llbb()
1078         })
1079     }
1080
1081     pub fn new_block(&self, name: &str) -> Bx {
1082         Bx::new_block(self.cx, self.llfn, name)
1083     }
1084
1085     pub fn build_block(
1086         &self,
1087         bb: mir::BasicBlock
1088     ) -> Bx {
1089         let mut bx = Bx::with_cx(self.cx);
1090         bx.position_at_end(self.blocks[bb]);
1091         bx
1092     }
1093
1094     fn make_return_dest(
1095         &mut self,
1096         bx: &mut Bx,
1097         dest: &mir::Place<'tcx>,
1098         fn_ret: &ArgType<'tcx, Ty<'tcx>>,
1099         llargs: &mut Vec<Bx::Value>, is_intrinsic: bool
1100     ) -> ReturnDest<'tcx, Bx::Value> {
1101         // If the return is ignored, we can just return a do-nothing `ReturnDest`.
1102         if fn_ret.is_ignore() {
1103             return ReturnDest::Nothing;
1104         }
1105         let dest = if let Some(index) = dest.as_local() {
1106             match self.locals[index] {
1107                 LocalRef::Place(dest) => dest,
1108                 LocalRef::UnsizedPlace(_) => bug!("return type must be sized"),
1109                 LocalRef::Operand(None) => {
1110                     // Handle temporary places, specifically `Operand` ones, as
1111                     // they don't have `alloca`s.
1112                     return if fn_ret.is_indirect() {
1113                         // Odd, but possible, case, we have an operand temporary,
1114                         // but the calling convention has an indirect return.
1115                         let tmp = PlaceRef::alloca(bx, fn_ret.layout);
1116                         tmp.storage_live(bx);
1117                         llargs.push(tmp.llval);
1118                         ReturnDest::IndirectOperand(tmp, index)
1119                     } else if is_intrinsic {
1120                         // Currently, intrinsics always need a location to store
1121                         // the result, so we create a temporary `alloca` for the
1122                         // result.
1123                         let tmp = PlaceRef::alloca(bx, fn_ret.layout);
1124                         tmp.storage_live(bx);
1125                         ReturnDest::IndirectOperand(tmp, index)
1126                     } else {
1127                         ReturnDest::DirectOperand(index)
1128                     };
1129                 }
1130                 LocalRef::Operand(Some(_)) => {
1131                     bug!("place local already assigned to");
1132                 }
1133             }
1134         } else {
1135             self.codegen_place(bx, &mir::PlaceRef {
1136                 base: &dest.base,
1137                 projection: &dest.projection,
1138             })
1139         };
1140         if fn_ret.is_indirect() {
1141             if dest.align < dest.layout.align.abi {
1142                 // Currently, MIR code generation does not create calls
1143                 // that store directly to fields of packed structs (in
1144                 // fact, the calls it creates write only to temps).
1145                 //
1146                 // If someone changes that, please update this code path
1147                 // to create a temporary.
1148                 span_bug!(self.mir.span, "can't directly store to unaligned value");
1149             }
1150             llargs.push(dest.llval);
1151             ReturnDest::Nothing
1152         } else {
1153             ReturnDest::Store(dest)
1154         }
1155     }
1156
1157     fn codegen_transmute(
1158         &mut self,
1159         bx: &mut Bx,
1160         src: &mir::Operand<'tcx>,
1161         dst: &mir::Place<'tcx>
1162     ) {
1163         if let Some(index) = dst.as_local() {
1164             match self.locals[index] {
1165                 LocalRef::Place(place) => self.codegen_transmute_into(bx, src, place),
1166                 LocalRef::UnsizedPlace(_) => bug!("transmute must not involve unsized locals"),
1167                 LocalRef::Operand(None) => {
1168                     let dst_layout = bx.layout_of(self.monomorphized_place_ty(&dst.as_ref()));
1169                     assert!(!dst_layout.ty.has_erasable_regions());
1170                     let place = PlaceRef::alloca(bx, dst_layout);
1171                     place.storage_live(bx);
1172                     self.codegen_transmute_into(bx, src, place);
1173                     let op = bx.load_operand(place);
1174                     place.storage_dead(bx);
1175                     self.locals[index] = LocalRef::Operand(Some(op));
1176                 }
1177                 LocalRef::Operand(Some(op)) => {
1178                     assert!(op.layout.is_zst(),
1179                             "assigning to initialized SSAtemp");
1180                 }
1181             }
1182         } else {
1183             let dst = self.codegen_place(bx, &dst.as_ref());
1184             self.codegen_transmute_into(bx, src, dst);
1185         }
1186     }
1187
1188     fn codegen_transmute_into(
1189         &mut self,
1190         bx: &mut Bx,
1191         src: &mir::Operand<'tcx>,
1192         dst: PlaceRef<'tcx, Bx::Value>
1193     ) {
1194         let src = self.codegen_operand(bx, src);
1195         let llty = bx.backend_type(src.layout);
1196         let cast_ptr = bx.pointercast(dst.llval, bx.type_ptr_to(llty));
1197         let align = src.layout.align.abi.min(dst.align);
1198         src.val.store(bx, PlaceRef::new_sized_aligned(cast_ptr, src.layout, align));
1199     }
1200
1201
1202     // Stores the return value of a function call into it's final location.
1203     fn store_return(
1204         &mut self,
1205         bx: &mut Bx,
1206         dest: ReturnDest<'tcx, Bx::Value>,
1207         ret_ty: &ArgType<'tcx, Ty<'tcx>>,
1208         llval: Bx::Value
1209     ) {
1210         use self::ReturnDest::*;
1211
1212         match dest {
1213             Nothing => (),
1214             Store(dst) => bx.store_arg_ty(&ret_ty, llval, dst),
1215             IndirectOperand(tmp, index) => {
1216                 let op = bx.load_operand(tmp);
1217                 tmp.storage_dead(bx);
1218                 self.locals[index] = LocalRef::Operand(Some(op));
1219             }
1220             DirectOperand(index) => {
1221                 // If there is a cast, we have to store and reload.
1222                 let op = if let PassMode::Cast(_) = ret_ty.mode {
1223                     let tmp = PlaceRef::alloca(bx, ret_ty.layout);
1224                     tmp.storage_live(bx);
1225                     bx.store_arg_ty(&ret_ty, llval, tmp);
1226                     let op = bx.load_operand(tmp);
1227                     tmp.storage_dead(bx);
1228                     op
1229                 } else {
1230                     OperandRef::from_immediate_or_packed_pair(bx, llval, ret_ty.layout)
1231                 };
1232                 self.locals[index] = LocalRef::Operand(Some(op));
1233             }
1234         }
1235     }
1236 }
1237
1238 enum ReturnDest<'tcx, V> {
1239     // Do nothing; the return value is indirect or ignored.
1240     Nothing,
1241     // Store the return value to the pointer.
1242     Store(PlaceRef<'tcx, V>),
1243     // Store an indirect return value to an operand local place.
1244     IndirectOperand(PlaceRef<'tcx, V>, mir::Local),
1245     // Store a direct return value to an operand local place.
1246     DirectOperand(mir::Local)
1247 }