compiler/rustc_codegen_ssa/src/mir/block.rs

   1 use super::operand::OperandRef;
   2 use super::operand::OperandValue::{Immediate, Pair, Ref};
   3 use super::place::PlaceRef;
   4 use super::{FunctionCx, LocalRef};
   5
   6 use crate::base;
   7 use crate::common::{self, IntPredicate};
   8 use crate::meth;
   9 use crate::traits::*;
  10 use crate::MemFlags;
  11
  12 use rustc_ast as ast;
  13 use rustc_hir::lang_items::LangItem;
  14 use rustc_index::vec::Idx;
  15 use rustc_middle::mir::AssertKind;
  16 use rustc_middle::mir::{self, SwitchTargets};
  17 use rustc_middle::ty::layout::{FnAbiExt, HasTyCtxt};
  18 use rustc_middle::ty::print::with_no_trimmed_paths;
  19 use rustc_middle::ty::{self, Instance, Ty, TypeFoldable};
  20 use rustc_span::source_map::Span;
  21 use rustc_span::{sym, Symbol};
  22 use rustc_target::abi::call::{ArgAbi, FnAbi, PassMode};
  23 use rustc_target::abi::{self, LayoutOf};
  24 use rustc_target::spec::abi::Abi;
  25
  26 /// Used by `FunctionCx::codegen_terminator` for emitting common patterns
  27 /// e.g., creating a basic block, calling a function, etc.
  28 struct TerminatorCodegenHelper<'tcx> {
  29     bb: mir::BasicBlock,
  30     terminator: &'tcx mir::Terminator<'tcx>,
  31     funclet_bb: Option<mir::BasicBlock>,
  32 }
  33
  34 impl<'a, 'tcx> TerminatorCodegenHelper<'tcx> {
  35     /// Returns the associated funclet from `FunctionCx::funclets` for the
  36     /// `funclet_bb` member if it is not `None`.
  37     fn funclet<'b, Bx: BuilderMethods<'a, 'tcx>>(
  38         &self,
  39         fx: &'b FunctionCx<'a, 'tcx, Bx>,
  40     ) -> Option<&'b Bx::Funclet> {
  41         self.funclet_bb.and_then(|funcl| fx.funclets[funcl].as_ref())
  42     }
  43
  44     fn lltarget<Bx: BuilderMethods<'a, 'tcx>>(
  45         &self,
  46         fx: &mut FunctionCx<'a, 'tcx, Bx>,
  47         target: mir::BasicBlock,
  48     ) -> (Bx::BasicBlock, bool) {
  49         let span = self.terminator.source_info.span;
  50         let lltarget = fx.blocks[target];
  51         let target_funclet = fx.cleanup_kinds[target].funclet_bb(target);
  52         match (self.funclet_bb, target_funclet) {
  53             (None, None) => (lltarget, false),
  54             (Some(f), Some(t_f)) if f == t_f || !base::wants_msvc_seh(fx.cx.tcx().sess) => {
  55                 (lltarget, false)
  56             }
  57             // jump *into* cleanup - need a landing pad if GNU
  58             (None, Some(_)) => (fx.landing_pad_to(target), false),
  59             (Some(_), None) => span_bug!(span, "{:?} - jump out of cleanup?", self.terminator),
  60             (Some(_), Some(_)) => (fx.landing_pad_to(target), true),
  61         }
  62     }
  63
  64     /// Create a basic block.
  65     fn llblock<Bx: BuilderMethods<'a, 'tcx>>(
  66         &self,
  67         fx: &mut FunctionCx<'a, 'tcx, Bx>,
  68         target: mir::BasicBlock,
  69     ) -> Bx::BasicBlock {
  70         let (lltarget, is_cleanupret) = self.lltarget(fx, target);
  71         if is_cleanupret {
  72             // MSVC cross-funclet jump - need a trampoline
  73
  74             debug!("llblock: creating cleanup trampoline for {:?}", target);
  75             let name = &format!("{:?}_cleanup_trampoline_{:?}", self.bb, target);
  76             let mut trampoline = fx.new_block(name);
  77             trampoline.cleanup_ret(self.funclet(fx).unwrap(), Some(lltarget));
  78             trampoline.llbb()
  79         } else {
  80             lltarget
  81         }
  82     }
  83
  84     fn funclet_br<Bx: BuilderMethods<'a, 'tcx>>(
  85         &self,
  86         fx: &mut FunctionCx<'a, 'tcx, Bx>,
  87         bx: &mut Bx,
  88         target: mir::BasicBlock,
  89     ) {
  90         let (lltarget, is_cleanupret) = self.lltarget(fx, target);
  91         if is_cleanupret {
  92             // micro-optimization: generate a `ret` rather than a jump
  93             // to a trampoline.
  94             bx.cleanup_ret(self.funclet(fx).unwrap(), Some(lltarget));
  95         } else {
  96             bx.br(lltarget);
  97         }
  98     }
  99
 100     /// Call `fn_ptr` of `fn_abi` with the arguments `llargs`, the optional
 101     /// return destination `destination` and the cleanup function `cleanup`.
 102     fn do_call<Bx: BuilderMethods<'a, 'tcx>>(
 103         &self,
 104         fx: &mut FunctionCx<'a, 'tcx, Bx>,
 105         bx: &mut Bx,
 106         fn_abi: FnAbi<'tcx, Ty<'tcx>>,
 107         fn_ptr: Bx::Value,
 108         llargs: &[Bx::Value],
 109         destination: Option<(ReturnDest<'tcx, Bx::Value>, mir::BasicBlock)>,
 110         cleanup: Option<mir::BasicBlock>,
 111     ) {
 112         // If there is a cleanup block and the function we're calling can unwind, then
 113         // do an invoke, otherwise do a call.
 114         if let Some(cleanup) = cleanup.filter(|_| fn_abi.can_unwind) {
 115             let ret_bx = if let Some((_, target)) = destination {
 116                 fx.blocks[target]
 117             } else {
 118                 fx.unreachable_block()
 119             };
 120             let invokeret =
 121                 bx.invoke(fn_ptr, &llargs, ret_bx, self.llblock(fx, cleanup), self.funclet(fx));
 122             bx.apply_attrs_callsite(&fn_abi, invokeret);
 123
 124             if let Some((ret_dest, target)) = destination {
 125                 let mut ret_bx = fx.build_block(target);
 126                 fx.set_debug_loc(&mut ret_bx, self.terminator.source_info);
 127                 fx.store_return(&mut ret_bx, ret_dest, &fn_abi.ret, invokeret);
 128             }
 129         } else {
 130             let llret = bx.call(fn_ptr, &llargs, self.funclet(fx));
 131             bx.apply_attrs_callsite(&fn_abi, llret);
 132             if fx.mir[self.bb].is_cleanup {
 133                 // Cleanup is always the cold path. Don't inline
 134                 // drop glue. Also, when there is a deeply-nested
 135                 // struct, there are "symmetry" issues that cause
 136                 // exponential inlining - see issue #41696.
 137                 bx.do_not_inline(llret);
 138             }
 139
 140             if let Some((ret_dest, target)) = destination {
 141                 fx.store_return(bx, ret_dest, &fn_abi.ret, llret);
 142                 self.funclet_br(fx, bx, target);
 143             } else {
 144                 bx.unreachable();
 145             }
 146         }
 147     }
 148 }
 149
 150 /// Codegen implementations for some terminator variants.
 151 impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
 152     /// Generates code for a `Resume` terminator.
 153     fn codegen_resume_terminator(&mut self, helper: TerminatorCodegenHelper<'tcx>, mut bx: Bx) {
 154         if let Some(funclet) = helper.funclet(self) {
 155             bx.cleanup_ret(funclet, None);
 156         } else {
 157             let slot = self.get_personality_slot(&mut bx);
 158             let lp0 = slot.project_field(&mut bx, 0);
 159             let lp0 = bx.load_operand(lp0).immediate();
 160             let lp1 = slot.project_field(&mut bx, 1);
 161             let lp1 = bx.load_operand(lp1).immediate();
 162             slot.storage_dead(&mut bx);
 163
 164             let mut lp = bx.const_undef(self.landing_pad_type());
 165             lp = bx.insert_value(lp, lp0, 0);
 166             lp = bx.insert_value(lp, lp1, 1);
 167             bx.resume(lp);
 168         }
 169     }
 170
 171     fn codegen_switchint_terminator(
 172         &mut self,
 173         helper: TerminatorCodegenHelper<'tcx>,
 174         mut bx: Bx,
 175         discr: &mir::Operand<'tcx>,
 176         switch_ty: Ty<'tcx>,
 177         targets: &SwitchTargets,
 178     ) {
 179         let discr = self.codegen_operand(&mut bx, &discr);
 180         // `switch_ty` is redundant, sanity-check that.
 181         assert_eq!(discr.layout.ty, switch_ty);
 182         let mut target_iter = targets.iter();
 183         if target_iter.len() == 1 {
 184             // If there are two targets (one conditional, one fallback), emit br instead of switch
 185             let (test_value, target) = target_iter.next().unwrap();
 186             let lltrue = helper.llblock(self, target);
 187             let llfalse = helper.llblock(self, targets.otherwise());
 188             if switch_ty == bx.tcx().types.bool {
 189                 // Don't generate trivial icmps when switching on bool
 190                 match test_value {
 191                     0 => bx.cond_br(discr.immediate(), llfalse, lltrue),
 192                     1 => bx.cond_br(discr.immediate(), lltrue, llfalse),
 193                     _ => bug!(),
 194                 }
 195             } else {
 196                 let switch_llty = bx.immediate_backend_type(bx.layout_of(switch_ty));
 197                 let llval = bx.const_uint_big(switch_llty, test_value);
 198                 let cmp = bx.icmp(IntPredicate::IntEQ, discr.immediate(), llval);
 199                 bx.cond_br(cmp, lltrue, llfalse);
 200             }
 201         } else {
 202             bx.switch(
 203                 discr.immediate(),
 204                 helper.llblock(self, targets.otherwise()),
 205                 target_iter.map(|(value, target)| (value, helper.llblock(self, target))),
 206             );
 207         }
 208     }
 209
 210     fn codegen_return_terminator(&mut self, mut bx: Bx) {
 211         // Call `va_end` if this is the definition of a C-variadic function.
 212         if self.fn_abi.c_variadic {
 213             // The `VaList` "spoofed" argument is just after all the real arguments.
 214             let va_list_arg_idx = self.fn_abi.args.len();
 215             match self.locals[mir::Local::new(1 + va_list_arg_idx)] {
 216                 LocalRef::Place(va_list) => {
 217                     bx.va_end(va_list.llval);
 218                 }
 219                 _ => bug!("C-variadic function must have a `VaList` place"),
 220             }
 221         }
 222         if self.fn_abi.ret.layout.abi.is_uninhabited() {
 223             // Functions with uninhabited return values are marked `noreturn`,
 224             // so we should make sure that we never actually do.
 225             // We play it safe by using a well-defined `abort`, but we could go for immediate UB
 226             // if that turns out to be helpful.
 227             bx.abort();
 228             // `abort` does not terminate the block, so we still need to generate
 229             // an `unreachable` terminator after it.
 230             bx.unreachable();
 231             return;
 232         }
 233         let llval = match self.fn_abi.ret.mode {
 234             PassMode::Ignore | PassMode::Indirect { .. } => {
 235                 bx.ret_void();
 236                 return;
 237             }
 238
 239             PassMode::Direct(_) | PassMode::Pair(..) => {
 240                 let op = self.codegen_consume(&mut bx, mir::Place::return_place().as_ref());
 241                 if let Ref(llval, _, align) = op.val {
 242                     bx.load(llval, align)
 243                 } else {
 244                     op.immediate_or_packed_pair(&mut bx)
 245                 }
 246             }
 247
 248             PassMode::Cast(cast_ty) => {
 249                 let op = match self.locals[mir::RETURN_PLACE] {
 250                     LocalRef::Operand(Some(op)) => op,
 251                     LocalRef::Operand(None) => bug!("use of return before def"),
 252                     LocalRef::Place(cg_place) => OperandRef {
 253                         val: Ref(cg_place.llval, None, cg_place.align),
 254                         layout: cg_place.layout,
 255                     },
 256                     LocalRef::UnsizedPlace(_) => bug!("return type must be sized"),
 257                 };
 258                 let llslot = match op.val {
 259                     Immediate(_) | Pair(..) => {
 260                         let scratch = PlaceRef::alloca(&mut bx, self.fn_abi.ret.layout);
 261                         op.val.store(&mut bx, scratch);
 262                         scratch.llval
 263                     }
 264                     Ref(llval, _, align) => {
 265                         assert_eq!(align, op.layout.align.abi, "return place is unaligned!");
 266                         llval
 267                     }
 268                 };
 269                 let addr = bx.pointercast(llslot, bx.type_ptr_to(bx.cast_backend_type(&cast_ty)));
 270                 bx.load(addr, self.fn_abi.ret.layout.align.abi)
 271             }
 272         };
 273         bx.ret(llval);
 274     }
 275
 276     fn codegen_drop_terminator(
 277         &mut self,
 278         helper: TerminatorCodegenHelper<'tcx>,
 279         mut bx: Bx,
 280         location: mir::Place<'tcx>,
 281         target: mir::BasicBlock,
 282         unwind: Option<mir::BasicBlock>,
 283     ) {
 284         let ty = location.ty(self.mir, bx.tcx()).ty;
 285         let ty = self.monomorphize(ty);
 286         let drop_fn = Instance::resolve_drop_in_place(bx.tcx(), ty);
 287
 288         if let ty::InstanceDef::DropGlue(_, None) = drop_fn.def {
 289             // we don't actually need to drop anything.
 290             helper.funclet_br(self, &mut bx, target);
 291             return;
 292         }
 293
 294         let place = self.codegen_place(&mut bx, location.as_ref());
 295         let (args1, args2);
 296         let mut args = if let Some(llextra) = place.llextra {
 297             args2 = [place.llval, llextra];
 298             &args2[..]
 299         } else {
 300             args1 = [place.llval];
 301             &args1[..]
 302         };
 303         let (drop_fn, fn_abi) = match ty.kind() {
 304             // FIXME(eddyb) perhaps move some of this logic into
 305             // `Instance::resolve_drop_in_place`?
 306             ty::Dynamic(..) => {
 307                 let virtual_drop = Instance {
 308                     def: ty::InstanceDef::Virtual(drop_fn.def_id(), 0),
 309                     substs: drop_fn.substs,
 310                 };
 311                 let fn_abi = FnAbi::of_instance(&bx, virtual_drop, &[]);
 312                 let vtable = args[1];
 313                 args = &args[..1];
 314                 (meth::DESTRUCTOR.get_fn(&mut bx, vtable, &fn_abi), fn_abi)
 315             }
 316             _ => (bx.get_fn_addr(drop_fn), FnAbi::of_instance(&bx, drop_fn, &[])),
 317         };
 318         helper.do_call(
 319             self,
 320             &mut bx,
 321             fn_abi,
 322             drop_fn,
 323             args,
 324             Some((ReturnDest::Nothing, target)),
 325             unwind,
 326         );
 327     }
 328
 329     fn codegen_assert_terminator(
 330         &mut self,
 331         helper: TerminatorCodegenHelper<'tcx>,
 332         mut bx: Bx,
 333         terminator: &mir::Terminator<'tcx>,
 334         cond: &mir::Operand<'tcx>,
 335         expected: bool,
 336         msg: &mir::AssertMessage<'tcx>,
 337         target: mir::BasicBlock,
 338         cleanup: Option<mir::BasicBlock>,
 339     ) {
 340         let span = terminator.source_info.span;
 341         let cond = self.codegen_operand(&mut bx, cond).immediate();
 342         let mut const_cond = bx.const_to_opt_u128(cond, false).map(|c| c == 1);
 343
 344         // This case can currently arise only from functions marked
 345         // with #[rustc_inherit_overflow_checks] and inlined from
 346         // another crate (mostly core::num generic/#[inline] fns),
 347         // while the current crate doesn't use overflow checks.
 348         // NOTE: Unlike binops, negation doesn't have its own
 349         // checked operation, just a comparison with the minimum
 350         // value, so we have to check for the assert message.
 351         if !bx.check_overflow() {
 352             if let AssertKind::OverflowNeg(_) = *msg {
 353                 const_cond = Some(expected);
 354             }
 355         }
 356
 357         // Don't codegen the panic block if success if known.
 358         if const_cond == Some(expected) {
 359             helper.funclet_br(self, &mut bx, target);
 360             return;
 361         }
 362
 363         // Pass the condition through llvm.expect for branch hinting.
 364         let cond = bx.expect(cond, expected);
 365
 366         // Create the failure block and the conditional branch to it.
 367         let lltarget = helper.llblock(self, target);
 368         let panic_block = self.new_block("panic");
 369         if expected {
 370             bx.cond_br(cond, lltarget, panic_block.llbb());
 371         } else {
 372             bx.cond_br(cond, panic_block.llbb(), lltarget);
 373         }
 374
 375         // After this point, bx is the block for the call to panic.
 376         bx = panic_block;
 377         self.set_debug_loc(&mut bx, terminator.source_info);
 378
 379         // Get the location information.
 380         let location = self.get_caller_location(&mut bx, terminator.source_info).immediate();
 381
 382         // Put together the arguments to the panic entry point.
 383         let (lang_item, args) = match msg {
 384             AssertKind::BoundsCheck { ref len, ref index } => {
 385                 let len = self.codegen_operand(&mut bx, len).immediate();
 386                 let index = self.codegen_operand(&mut bx, index).immediate();
 387                 // It's `fn panic_bounds_check(index: usize, len: usize)`,
 388                 // and `#[track_caller]` adds an implicit third argument.
 389                 (LangItem::PanicBoundsCheck, vec![index, len, location])
 390             }
 391             _ => {
 392                 let msg_str = Symbol::intern(msg.description());
 393                 let msg = bx.const_str(msg_str);
 394                 // It's `pub fn panic(expr: &str)`, with the wide reference being passed
 395                 // as two arguments, and `#[track_caller]` adds an implicit third argument.
 396                 (LangItem::Panic, vec![msg.0, msg.1, location])
 397             }
 398         };
 399
 400         // Obtain the panic entry point.
 401         let def_id = common::langcall(bx.tcx(), Some(span), "", lang_item);
 402         let instance = ty::Instance::mono(bx.tcx(), def_id);
 403         let fn_abi = FnAbi::of_instance(&bx, instance, &[]);
 404         let llfn = bx.get_fn_addr(instance);
 405
 406         // Codegen the actual panic invoke/call.
 407         helper.do_call(self, &mut bx, fn_abi, llfn, &args, None, cleanup);
 408     }
 409
 410     /// Returns `true` if this is indeed a panic intrinsic and codegen is done.
 411     fn codegen_panic_intrinsic(
 412         &mut self,
 413         helper: &TerminatorCodegenHelper<'tcx>,
 414         bx: &mut Bx,
 415         intrinsic: Option<Symbol>,
 416         instance: Option<Instance<'tcx>>,
 417         source_info: mir::SourceInfo,
 418         destination: &Option<(mir::Place<'tcx>, mir::BasicBlock)>,
 419         cleanup: Option<mir::BasicBlock>,
 420     ) -> bool {
 421         // Emit a panic or a no-op for `assert_*` intrinsics.
 422         // These are intrinsics that compile to panics so that we can get a message
 423         // which mentions the offending type, even from a const context.
 424         #[derive(Debug, PartialEq)]
 425         enum AssertIntrinsic {
 426             Inhabited,
 427             ZeroValid,
 428             UninitValid,
 429         }
 430         let panic_intrinsic = intrinsic.and_then(|i| match i {
 431             sym::assert_inhabited => Some(AssertIntrinsic::Inhabited),
 432             sym::assert_zero_valid => Some(AssertIntrinsic::ZeroValid),
 433             sym::assert_uninit_valid => Some(AssertIntrinsic::UninitValid),
 434             _ => None,
 435         });
 436         if let Some(intrinsic) = panic_intrinsic {
 437             use AssertIntrinsic::*;
 438             let ty = instance.unwrap().substs.type_at(0);
 439             let layout = bx.layout_of(ty);
 440             let do_panic = match intrinsic {
 441                 Inhabited => layout.abi.is_uninhabited(),
 442                 // We unwrap as the error type is `!`.
 443                 ZeroValid => !layout.might_permit_raw_init(bx, /*zero:*/ true).unwrap(),
 444                 // We unwrap as the error type is `!`.
 445                 UninitValid => !layout.might_permit_raw_init(bx, /*zero:*/ false).unwrap(),
 446             };
 447             if do_panic {
 448                 let msg_str = with_no_trimmed_paths(|| {
 449                     if layout.abi.is_uninhabited() {
 450                         // Use this error even for the other intrinsics as it is more precise.
 451                         format!("attempted to instantiate uninhabited type `{}`", ty)
 452                     } else if intrinsic == ZeroValid {
 453                         format!("attempted to zero-initialize type `{}`, which is invalid", ty)
 454                     } else {
 455                         format!("attempted to leave type `{}` uninitialized, which is invalid", ty)
 456                     }
 457                 });
 458                 let msg = bx.const_str(Symbol::intern(&msg_str));
 459                 let location = self.get_caller_location(bx, source_info).immediate();
 460
 461                 // Obtain the panic entry point.
 462                 // FIXME: dedup this with `codegen_assert_terminator` above.
 463                 let def_id =
 464                     common::langcall(bx.tcx(), Some(source_info.span), "", LangItem::Panic);
 465                 let instance = ty::Instance::mono(bx.tcx(), def_id);
 466                 let fn_abi = FnAbi::of_instance(bx, instance, &[]);
 467                 let llfn = bx.get_fn_addr(instance);
 468
 469                 // Codegen the actual panic invoke/call.
 470                 helper.do_call(
 471                     self,
 472                     bx,
 473                     fn_abi,
 474                     llfn,
 475                     &[msg.0, msg.1, location],
 476                     destination.as_ref().map(|(_, bb)| (ReturnDest::Nothing, *bb)),
 477                     cleanup,
 478                 );
 479             } else {
 480                 // a NOP
 481                 let target = destination.as_ref().unwrap().1;
 482                 helper.funclet_br(self, bx, target)
 483             }
 484             true
 485         } else {
 486             false
 487         }
 488     }
 489
 490     fn codegen_call_terminator(
 491         &mut self,
 492         helper: TerminatorCodegenHelper<'tcx>,
 493         mut bx: Bx,
 494         terminator: &mir::Terminator<'tcx>,
 495         func: &mir::Operand<'tcx>,
 496         args: &[mir::Operand<'tcx>],
 497         destination: &Option<(mir::Place<'tcx>, mir::BasicBlock)>,
 498         cleanup: Option<mir::BasicBlock>,
 499         fn_span: Span,
 500     ) {
 501         let source_info = terminator.source_info;
 502         let span = source_info.span;
 503
 504         // Create the callee. This is a fn ptr or zero-sized and hence a kind of scalar.
 505         let callee = self.codegen_operand(&mut bx, func);
 506
 507         let (instance, mut llfn) = match *callee.layout.ty.kind() {
 508             ty::FnDef(def_id, substs) => (
 509                 Some(
 510                     ty::Instance::resolve(bx.tcx(), ty::ParamEnv::reveal_all(), def_id, substs)
 511                         .unwrap()
 512                         .unwrap()
 513                         .polymorphize(bx.tcx()),
 514                 ),
 515                 None,
 516             ),
 517             ty::FnPtr(_) => (None, Some(callee.immediate())),
 518             _ => bug!("{} is not callable", callee.layout.ty),
 519         };
 520         let def = instance.map(|i| i.def);
 521
 522         if let Some(ty::InstanceDef::DropGlue(_, None)) = def {
 523             // Empty drop glue; a no-op.
 524             let &(_, target) = destination.as_ref().unwrap();
 525             helper.funclet_br(self, &mut bx, target);
 526             return;
 527         }
 528
 529         // FIXME(eddyb) avoid computing this if possible, when `instance` is
 530         // available - right now `sig` is only needed for getting the `abi`
 531         // and figuring out how many extra args were passed to a C-variadic `fn`.
 532         let sig = callee.layout.ty.fn_sig(bx.tcx());
 533         let abi = sig.abi();
 534
 535         // Handle intrinsics old codegen wants Expr's for, ourselves.
 536         let intrinsic = match def {
 537             Some(ty::InstanceDef::Intrinsic(def_id)) => Some(bx.tcx().item_name(def_id)),
 538             _ => None,
 539         };
 540
 541         let extra_args = &args[sig.inputs().skip_binder().len()..];
 542         let extra_args = extra_args
 543             .iter()
 544             .map(|op_arg| {
 545                 let op_ty = op_arg.ty(self.mir, bx.tcx());
 546                 self.monomorphize(op_ty)
 547             })
 548             .collect::<Vec<_>>();
 549
 550         let fn_abi = match instance {
 551             Some(instance) => FnAbi::of_instance(&bx, instance, &extra_args),
 552             None => FnAbi::of_fn_ptr(&bx, sig, &extra_args),
 553         };
 554
 555         if intrinsic == Some(sym::transmute) {
 556             if let Some(destination_ref) = destination.as_ref() {
 557                 let &(dest, target) = destination_ref;
 558                 self.codegen_transmute(&mut bx, &args[0], dest);
 559                 helper.funclet_br(self, &mut bx, target);
 560             } else {
 561                 // If we are trying to transmute to an uninhabited type,
 562                 // it is likely there is no allotted destination. In fact,
 563                 // transmuting to an uninhabited type is UB, which means
 564                 // we can do what we like. Here, we declare that transmuting
 565                 // into an uninhabited type is impossible, so anything following
 566                 // it must be unreachable.
 567                 assert_eq!(fn_abi.ret.layout.abi, abi::Abi::Uninhabited);
 568                 bx.unreachable();
 569             }
 570             return;
 571         }
 572
 573         if self.codegen_panic_intrinsic(
 574             &helper,
 575             &mut bx,
 576             intrinsic,
 577             instance,
 578             source_info,
 579             destination,
 580             cleanup,
 581         ) {
 582             return;
 583         }
 584
 585         // The arguments we'll be passing. Plus one to account for outptr, if used.
 586         let arg_count = fn_abi.args.len() + fn_abi.ret.is_indirect() as usize;
 587         let mut llargs = Vec::with_capacity(arg_count);
 588
 589         // Prepare the return value destination
 590         let ret_dest = if let Some((dest, _)) = *destination {
 591             let is_intrinsic = intrinsic.is_some();
 592             self.make_return_dest(&mut bx, dest, &fn_abi.ret, &mut llargs, is_intrinsic)
 593         } else {
 594             ReturnDest::Nothing
 595         };
 596
 597         if intrinsic == Some(sym::caller_location) {
 598             if let Some((_, target)) = destination.as_ref() {
 599                 let location = self
 600                     .get_caller_location(&mut bx, mir::SourceInfo { span: fn_span, ..source_info });
 601
 602                 if let ReturnDest::IndirectOperand(tmp, _) = ret_dest {
 603                     location.val.store(&mut bx, tmp);
 604                 }
 605                 self.store_return(&mut bx, ret_dest, &fn_abi.ret, location.immediate());
 606                 helper.funclet_br(self, &mut bx, *target);
 607             }
 608             return;
 609         }
 610
 611         match intrinsic {
 612             None | Some(sym::drop_in_place) => {}
 613             Some(sym::copy_nonoverlapping) => unreachable!(),
 614             Some(intrinsic) => {
 615                 let dest = match ret_dest {
 616                     _ if fn_abi.ret.is_indirect() => llargs[0],
 617                     ReturnDest::Nothing => {
 618                         bx.const_undef(bx.type_ptr_to(bx.arg_memory_ty(&fn_abi.ret)))
 619                     }
 620                     ReturnDest::IndirectOperand(dst, _) | ReturnDest::Store(dst) => dst.llval,
 621                     ReturnDest::DirectOperand(_) => {
 622                         bug!("Cannot use direct operand with an intrinsic call")
 623                     }
 624                 };
 625
 626                 let args: Vec<_> = args
 627                     .iter()
 628                     .enumerate()
 629                     .map(|(i, arg)| {
 630                         // The indices passed to simd_shuffle* in the
 631                         // third argument must be constant. This is
 632                         // checked by const-qualification, which also
 633                         // promotes any complex rvalues to constants.
 634                         if i == 2 && intrinsic.as_str().starts_with("simd_shuffle") {
 635                             if let mir::Operand::Constant(constant) = arg {
 636                                 let c = self.eval_mir_constant(constant);
 637                                 let (llval, ty) =
 638                                     self.simd_shuffle_indices(&bx, constant.span, constant.ty(), c);
 639                                 return OperandRef {
 640                                     val: Immediate(llval),
 641                                     layout: bx.layout_of(ty),
 642                                 };
 643                             } else {
 644                                 span_bug!(span, "shuffle indices must be constant");
 645                             }
 646                         }
 647
 648                         self.codegen_operand(&mut bx, arg)
 649                     })
 650                     .collect();
 651
 652                 Self::codegen_intrinsic_call(
 653                     &mut bx,
 654                     *instance.as_ref().unwrap(),
 655                     &fn_abi,
 656                     &args,
 657                     dest,
 658                     span,
 659                 );
 660
 661                 if let ReturnDest::IndirectOperand(dst, _) = ret_dest {
 662                     self.store_return(&mut bx, ret_dest, &fn_abi.ret, dst.llval);
 663                 }
 664
 665                 if let Some((_, target)) = *destination {
 666                     helper.funclet_br(self, &mut bx, target);
 667                 } else {
 668                     bx.unreachable();
 669                 }
 670
 671                 return;
 672             }
 673         }
 674
 675         // Split the rust-call tupled arguments off.
 676         let (first_args, untuple) = if abi == Abi::RustCall && !args.is_empty() {
 677             let (tup, args) = args.split_last().unwrap();
 678             (args, Some(tup))
 679         } else {
 680             (args, None)
 681         };
 682
 683         'make_args: for (i, arg) in first_args.iter().enumerate() {
 684             let mut op = self.codegen_operand(&mut bx, arg);
 685
 686             if let (0, Some(ty::InstanceDef::Virtual(_, idx))) = (i, def) {
 687                 if let Pair(..) = op.val {
 688                     // In the case of Rc<Self>, we need to explicitly pass a
 689                     // *mut RcBox<Self> with a Scalar (not ScalarPair) ABI. This is a hack
 690                     // that is understood elsewhere in the compiler as a method on
 691                     // `dyn Trait`.
 692                     // To get a `*mut RcBox<Self>`, we just keep unwrapping newtypes until
 693                     // we get a value of a built-in pointer type
 694                     'descend_newtypes: while !op.layout.ty.is_unsafe_ptr()
 695                         && !op.layout.ty.is_region_ptr()
 696                     {
 697                         for i in 0..op.layout.fields.count() {
 698                             let field = op.extract_field(&mut bx, i);
 699                             if !field.layout.is_zst() {
 700                                 // we found the one non-zero-sized field that is allowed
 701                                 // now find *its* non-zero-sized field, or stop if it's a
 702                                 // pointer
 703                                 op = field;
 704                                 continue 'descend_newtypes;
 705                             }
 706                         }
 707
 708                         span_bug!(span, "receiver has no non-zero-sized fields {:?}", op);
 709                     }
 710
 711                     // now that we have `*dyn Trait` or `&dyn Trait`, split it up into its
 712                     // data pointer and vtable. Look up the method in the vtable, and pass
 713                     // the data pointer as the first argument
 714                     match op.val {
 715                         Pair(data_ptr, meta) => {
 716                             llfn = Some(
 717                                 meth::VirtualIndex::from_index(idx).get_fn(&mut bx, meta, &fn_abi),
 718                             );
 719                             llargs.push(data_ptr);
 720                             continue 'make_args;
 721                         }
 722                         other => bug!("expected a Pair, got {:?}", other),
 723                     }
 724                 } else if let Ref(data_ptr, Some(meta), _) = op.val {
 725                     // by-value dynamic dispatch
 726                     llfn = Some(meth::VirtualIndex::from_index(idx).get_fn(&mut bx, meta, &fn_abi));
 727                     llargs.push(data_ptr);
 728                     continue;
 729                 } else {
 730                     span_bug!(span, "can't codegen a virtual call on {:?}", op);
 731                 }
 732             }
 733
 734             // The callee needs to own the argument memory if we pass it
 735             // by-ref, so make a local copy of non-immediate constants.
 736             match (arg, op.val) {
 737                 (&mir::Operand::Copy(_), Ref(_, None, _))
 738                 | (&mir::Operand::Constant(_), Ref(_, None, _)) => {
 739                     let tmp = PlaceRef::alloca(&mut bx, op.layout);
 740                     op.val.store(&mut bx, tmp);
 741                     op.val = Ref(tmp.llval, None, tmp.align);
 742                 }
 743                 _ => {}
 744             }
 745
 746             self.codegen_argument(&mut bx, op, &mut llargs, &fn_abi.args[i]);
 747         }
 748         if let Some(tup) = untuple {
 749             self.codegen_arguments_untupled(
 750                 &mut bx,
 751                 tup,
 752                 &mut llargs,
 753                 &fn_abi.args[first_args.len()..],
 754             )
 755         }
 756
 757         let needs_location =
 758             instance.map_or(false, |i| i.def.requires_caller_location(self.cx.tcx()));
 759         if needs_location {
 760             assert_eq!(
 761                 fn_abi.args.len(),
 762                 args.len() + 1,
 763                 "#[track_caller] fn's must have 1 more argument in their ABI than in their MIR",
 764             );
 765             let location =
 766                 self.get_caller_location(&mut bx, mir::SourceInfo { span: fn_span, ..source_info });
 767             debug!(
 768                 "codegen_call_terminator({:?}): location={:?} (fn_span {:?})",
 769                 terminator, location, fn_span
 770             );
 771
 772             let last_arg = fn_abi.args.last().unwrap();
 773             self.codegen_argument(&mut bx, location, &mut llargs, last_arg);
 774         }
 775
 776         let fn_ptr = match (llfn, instance) {
 777             (Some(llfn), _) => llfn,
 778             (None, Some(instance)) => bx.get_fn_addr(instance),
 779             _ => span_bug!(span, "no llfn for call"),
 780         };
 781
 782         helper.do_call(
 783             self,
 784             &mut bx,
 785             fn_abi,
 786             fn_ptr,
 787             &llargs,
 788             destination.as_ref().map(|&(_, target)| (ret_dest, target)),
 789             cleanup,
 790         );
 791     }
 792
 793     fn codegen_asm_terminator(
 794         &mut self,
 795         helper: TerminatorCodegenHelper<'tcx>,
 796         mut bx: Bx,
 797         terminator: &mir::Terminator<'tcx>,
 798         template: &[ast::InlineAsmTemplatePiece],
 799         operands: &[mir::InlineAsmOperand<'tcx>],
 800         options: ast::InlineAsmOptions,
 801         line_spans: &[Span],
 802         destination: Option<mir::BasicBlock>,
 803     ) {
 804         let span = terminator.source_info.span;
 805
 806         let operands: Vec<_> = operands
 807             .iter()
 808             .map(|op| match *op {
 809                 mir::InlineAsmOperand::In { reg, ref value } => {
 810                     let value = self.codegen_operand(&mut bx, value);
 811                     InlineAsmOperandRef::In { reg, value }
 812                 }
 813                 mir::InlineAsmOperand::Out { reg, late, ref place } => {
 814                     let place = place.map(|place| self.codegen_place(&mut bx, place.as_ref()));
 815                     InlineAsmOperandRef::Out { reg, late, place }
 816                 }
 817                 mir::InlineAsmOperand::InOut { reg, late, ref in_value, ref out_place } => {
 818                     let in_value = self.codegen_operand(&mut bx, in_value);
 819                     let out_place =
 820                         out_place.map(|out_place| self.codegen_place(&mut bx, out_place.as_ref()));
 821                     InlineAsmOperandRef::InOut { reg, late, in_value, out_place }
 822                 }
 823                 mir::InlineAsmOperand::Const { ref value } => {
 824                     let const_value = self
 825                         .eval_mir_constant(value)
 826                         .unwrap_or_else(|_| span_bug!(span, "asm const cannot be resolved"));
 827                     let string = common::asm_const_to_str(
 828                         bx.tcx(),
 829                         span,
 830                         const_value,
 831                         bx.layout_of(value.ty()),
 832                     );
 833                     InlineAsmOperandRef::Const { string }
 834                 }
 835                 mir::InlineAsmOperand::SymFn { ref value } => {
 836                     let literal = self.monomorphize(value.literal);
 837                     if let ty::FnDef(def_id, substs) = *literal.ty().kind() {
 838                         let instance = ty::Instance::resolve_for_fn_ptr(
 839                             bx.tcx(),
 840                             ty::ParamEnv::reveal_all(),
 841                             def_id,
 842                             substs,
 843                         )
 844                         .unwrap();
 845                         InlineAsmOperandRef::SymFn { instance }
 846                     } else {
 847                         span_bug!(span, "invalid type for asm sym (fn)");
 848                     }
 849                 }
 850                 mir::InlineAsmOperand::SymStatic { def_id } => {
 851                     InlineAsmOperandRef::SymStatic { def_id }
 852                 }
 853             })
 854             .collect();
 855
 856         bx.codegen_inline_asm(template, &operands, options, line_spans);
 857
 858         if let Some(target) = destination {
 859             helper.funclet_br(self, &mut bx, target);
 860         } else {
 861             bx.unreachable();
 862         }
 863     }
 864 }
 865
 866 impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
 867     pub fn codegen_block(&mut self, bb: mir::BasicBlock) {
 868         let mut bx = self.build_block(bb);
 869         let mir = self.mir;
 870         let data = &mir[bb];
 871
 872         debug!("codegen_block({:?}={:?})", bb, data);
 873
 874         for statement in &data.statements {
 875             bx = self.codegen_statement(bx, statement);
 876         }
 877
 878         self.codegen_terminator(bx, bb, data.terminator());
 879     }
 880
 881     fn codegen_terminator(
 882         &mut self,
 883         mut bx: Bx,
 884         bb: mir::BasicBlock,
 885         terminator: &'tcx mir::Terminator<'tcx>,
 886     ) {
 887         debug!("codegen_terminator: {:?}", terminator);
 888
 889         // Create the cleanup bundle, if needed.
 890         let funclet_bb = self.cleanup_kinds[bb].funclet_bb(bb);
 891         let helper = TerminatorCodegenHelper { bb, terminator, funclet_bb };
 892
 893         self.set_debug_loc(&mut bx, terminator.source_info);
 894         match terminator.kind {
 895             mir::TerminatorKind::Resume => self.codegen_resume_terminator(helper, bx),
 896
 897             mir::TerminatorKind::Abort => {
 898                 bx.abort();
 899                 // `abort` does not terminate the block, so we still need to generate
 900                 // an `unreachable` terminator after it.
 901                 bx.unreachable();
 902             }
 903
 904             mir::TerminatorKind::Goto { target } => {
 905                 if bb == target {
 906                     // This is an unconditional branch back to this same basic block. That means we
 907                     // have something like a `loop {}` statement. LLVM versions before 12.0
 908                     // miscompile this because they assume forward progress. For older versions
 909                     // try to handle just this specific case which comes up commonly in practice
 910                     // (e.g., in embedded code).
 911                     //
 912                     // NB: the `sideeffect` currently checks for the LLVM version used internally.
 913                     bx.sideeffect();
 914                 }
 915
 916                 helper.funclet_br(self, &mut bx, target);
 917             }
 918
 919             mir::TerminatorKind::SwitchInt { ref discr, switch_ty, ref targets } => {
 920                 self.codegen_switchint_terminator(helper, bx, discr, switch_ty, targets);
 921             }
 922
 923             mir::TerminatorKind::Return => {
 924                 self.codegen_return_terminator(bx);
 925             }
 926
 927             mir::TerminatorKind::Unreachable => {
 928                 bx.unreachable();
 929             }
 930
 931             mir::TerminatorKind::Drop { place, target, unwind } => {
 932                 self.codegen_drop_terminator(helper, bx, place, target, unwind);
 933             }
 934
 935             mir::TerminatorKind::Assert { ref cond, expected, ref msg, target, cleanup } => {
 936                 self.codegen_assert_terminator(
 937                     helper, bx, terminator, cond, expected, msg, target, cleanup,
 938                 );
 939             }
 940
 941             mir::TerminatorKind::DropAndReplace { .. } => {
 942                 bug!("undesugared DropAndReplace in codegen: {:?}", terminator);
 943             }
 944
 945             mir::TerminatorKind::Call {
 946                 ref func,
 947                 ref args,
 948                 ref destination,
 949                 cleanup,
 950                 from_hir_call: _,
 951                 fn_span,
 952             } => {
 953                 self.codegen_call_terminator(
 954                     helper,
 955                     bx,
 956                     terminator,
 957                     func,
 958                     args,
 959                     destination,
 960                     cleanup,
 961                     fn_span,
 962                 );
 963             }
 964             mir::TerminatorKind::GeneratorDrop | mir::TerminatorKind::Yield { .. } => {
 965                 bug!("generator ops in codegen")
 966             }
 967             mir::TerminatorKind::FalseEdge { .. } | mir::TerminatorKind::FalseUnwind { .. } => {
 968                 bug!("borrowck false edges in codegen")
 969             }
 970
 971             mir::TerminatorKind::InlineAsm {
 972                 template,
 973                 ref operands,
 974                 options,
 975                 line_spans,
 976                 destination,
 977             } => {
 978                 self.codegen_asm_terminator(
 979                     helper,
 980                     bx,
 981                     terminator,
 982                     template,
 983                     operands,
 984                     options,
 985                     line_spans,
 986                     destination,
 987                 );
 988             }
 989         }
 990     }
 991
 992     fn codegen_argument(
 993         &mut self,
 994         bx: &mut Bx,
 995         op: OperandRef<'tcx, Bx::Value>,
 996         llargs: &mut Vec<Bx::Value>,
 997         arg: &ArgAbi<'tcx, Ty<'tcx>>,
 998     ) {
 999         // Fill padding with undef value, where applicable.
1000         if let Some(ty) = arg.pad {
1001             llargs.push(bx.const_undef(bx.reg_backend_type(&ty)))
1002         }
1003
1004         if arg.is_ignore() {
1005             return;
1006         }
1007
1008         if let PassMode::Pair(..) = arg.mode {
1009             match op.val {
1010                 Pair(a, b) => {
1011                     llargs.push(a);
1012                     llargs.push(b);
1013                     return;
1014                 }
1015                 _ => bug!("codegen_argument: {:?} invalid for pair argument", op),
1016             }
1017         } else if arg.is_unsized_indirect() {
1018             match op.val {
1019                 Ref(a, Some(b), _) => {
1020                     llargs.push(a);
1021                     llargs.push(b);
1022                     return;
1023                 }
1024                 _ => bug!("codegen_argument: {:?} invalid for unsized indirect argument", op),
1025             }
1026         }
1027
1028         // Force by-ref if we have to load through a cast pointer.
1029         let (mut llval, align, by_ref) = match op.val {
1030             Immediate(_) | Pair(..) => match arg.mode {
1031                 PassMode::Indirect { .. } | PassMode::Cast(_) => {
1032                     let scratch = PlaceRef::alloca(bx, arg.layout);
1033                     op.val.store(bx, scratch);
1034                     (scratch.llval, scratch.align, true)
1035                 }
1036                 _ => (op.immediate_or_packed_pair(bx), arg.layout.align.abi, false),
1037             },
1038             Ref(llval, _, align) => {
1039                 if arg.is_indirect() && align < arg.layout.align.abi {
1040                     // `foo(packed.large_field)`. We can't pass the (unaligned) field directly. I
1041                     // think that ATM (Rust 1.16) we only pass temporaries, but we shouldn't
1042                     // have scary latent bugs around.
1043
1044                     let scratch = PlaceRef::alloca(bx, arg.layout);
1045                     base::memcpy_ty(
1046                         bx,
1047                         scratch.llval,
1048                         scratch.align,
1049                         llval,
1050                         align,
1051                         op.layout,
1052                         MemFlags::empty(),
1053                     );
1054                     (scratch.llval, scratch.align, true)
1055                 } else {
1056                     (llval, align, true)
1057                 }
1058             }
1059         };
1060
1061         if by_ref && !arg.is_indirect() {
1062             // Have to load the argument, maybe while casting it.
1063             if let PassMode::Cast(ty) = arg.mode {
1064                 let addr = bx.pointercast(llval, bx.type_ptr_to(bx.cast_backend_type(&ty)));
1065                 llval = bx.load(addr, align.min(arg.layout.align.abi));
1066             } else {
1067                 // We can't use `PlaceRef::load` here because the argument
1068                 // may have a type we don't treat as immediate, but the ABI
1069                 // used for this call is passing it by-value. In that case,
1070                 // the load would just produce `OperandValue::Ref` instead
1071                 // of the `OperandValue::Immediate` we need for the call.
1072                 llval = bx.load(llval, align);
1073                 if let abi::Abi::Scalar(ref scalar) = arg.layout.abi {
1074                     if scalar.is_bool() {
1075                         bx.range_metadata(llval, 0..2);
1076                     }
1077                 }
1078                 // We store bools as `i8` so we need to truncate to `i1`.
1079                 llval = bx.to_immediate(llval, arg.layout);
1080             }
1081         }
1082
1083         llargs.push(llval);
1084     }
1085
1086     fn codegen_arguments_untupled(
1087         &mut self,
1088         bx: &mut Bx,
1089         operand: &mir::Operand<'tcx>,
1090         llargs: &mut Vec<Bx::Value>,
1091         args: &[ArgAbi<'tcx, Ty<'tcx>>],
1092     ) {
1093         let tuple = self.codegen_operand(bx, operand);
1094
1095         // Handle both by-ref and immediate tuples.
1096         if let Ref(llval, None, align) = tuple.val {
1097             let tuple_ptr = PlaceRef::new_sized_aligned(llval, tuple.layout, align);
1098             for i in 0..tuple.layout.fields.count() {
1099                 let field_ptr = tuple_ptr.project_field(bx, i);
1100                 let field = bx.load_operand(field_ptr);
1101                 self.codegen_argument(bx, field, llargs, &args[i]);
1102             }
1103         } else if let Ref(_, Some(_), _) = tuple.val {
1104             bug!("closure arguments must be sized")
1105         } else {
1106             // If the tuple is immediate, the elements are as well.
1107             for i in 0..tuple.layout.fields.count() {
1108                 let op = tuple.extract_field(bx, i);
1109                 self.codegen_argument(bx, op, llargs, &args[i]);
1110             }
1111         }
1112     }
1113
1114     fn get_caller_location(
1115         &mut self,
1116         bx: &mut Bx,
1117         mut source_info: mir::SourceInfo,
1118     ) -> OperandRef<'tcx, Bx::Value> {
1119         let tcx = bx.tcx();
1120
1121         let mut span_to_caller_location = |span: Span| {
1122             let topmost = span.ctxt().outer_expn().expansion_cause().unwrap_or(span);
1123             let caller = tcx.sess.source_map().lookup_char_pos(topmost.lo());
1124             let const_loc = tcx.const_caller_location((
1125                 Symbol::intern(&caller.file.name.prefer_remapped().to_string_lossy()),
1126                 caller.line as u32,
1127                 caller.col_display as u32 + 1,
1128             ));
1129             OperandRef::from_const(bx, const_loc, bx.tcx().caller_location_ty())
1130         };
1131
1132         // Walk up the `SourceScope`s, in case some of them are from MIR inlining.
1133         // If so, the starting `source_info.span` is in the innermost inlined
1134         // function, and will be replaced with outer callsite spans as long
1135         // as the inlined functions were `#[track_caller]`.
1136         loop {
1137             let scope_data = &self.mir.source_scopes[source_info.scope];
1138
1139             if let Some((callee, callsite_span)) = scope_data.inlined {
1140                 // Stop inside the most nested non-`#[track_caller]` function,
1141                 // before ever reaching its caller (which is irrelevant).
1142                 if !callee.def.requires_caller_location(tcx) {
1143                     return span_to_caller_location(source_info.span);
1144                 }
1145                 source_info.span = callsite_span;
1146             }
1147
1148             // Skip past all of the parents with `inlined: None`.
1149             match scope_data.inlined_parent_scope {
1150                 Some(parent) => source_info.scope = parent,
1151                 None => break,
1152             }
1153         }
1154
1155         // No inlined `SourceScope`s, or all of them were `#[track_caller]`.
1156         self.caller_location.unwrap_or_else(|| span_to_caller_location(source_info.span))
1157     }
1158
1159     fn get_personality_slot(&mut self, bx: &mut Bx) -> PlaceRef<'tcx, Bx::Value> {
1160         let cx = bx.cx();
1161         if let Some(slot) = self.personality_slot {
1162             slot
1163         } else {
1164             let layout = cx.layout_of(
1165                 cx.tcx().intern_tup(&[cx.tcx().mk_mut_ptr(cx.tcx().types.u8), cx.tcx().types.i32]),
1166             );
1167             let slot = PlaceRef::alloca(bx, layout);
1168             self.personality_slot = Some(slot);
1169             slot
1170         }
1171     }
1172
1173     /// Returns the landing-pad wrapper around the given basic block.
1174     ///
1175     /// No-op in MSVC SEH scheme.
1176     fn landing_pad_to(&mut self, target_bb: mir::BasicBlock) -> Bx::BasicBlock {
1177         if let Some(block) = self.landing_pads[target_bb] {
1178             return block;
1179         }
1180
1181         let block = self.blocks[target_bb];
1182         let landing_pad = self.landing_pad_uncached(block);
1183         self.landing_pads[target_bb] = Some(landing_pad);
1184         landing_pad
1185     }
1186
1187     fn landing_pad_uncached(&mut self, target_bb: Bx::BasicBlock) -> Bx::BasicBlock {
1188         if base::wants_msvc_seh(self.cx.sess()) {
1189             span_bug!(self.mir.span, "landing pad was not inserted?")
1190         }
1191
1192         let mut bx = self.new_block("cleanup");
1193
1194         let llpersonality = self.cx.eh_personality();
1195         let llretty = self.landing_pad_type();
1196         let lp = bx.landing_pad(llretty, llpersonality, 1);
1197         bx.set_cleanup(lp);
1198
1199         let slot = self.get_personality_slot(&mut bx);
1200         slot.storage_live(&mut bx);
1201         Pair(bx.extract_value(lp, 0), bx.extract_value(lp, 1)).store(&mut bx, slot);
1202
1203         bx.br(target_bb);
1204         bx.llbb()
1205     }
1206
1207     fn landing_pad_type(&self) -> Bx::Type {
1208         let cx = self.cx;
1209         cx.type_struct(&[cx.type_i8p(), cx.type_i32()], false)
1210     }
1211
1212     fn unreachable_block(&mut self) -> Bx::BasicBlock {
1213         self.unreachable_block.unwrap_or_else(|| {
1214             let mut bx = self.new_block("unreachable");
1215             bx.unreachable();
1216             self.unreachable_block = Some(bx.llbb());
1217             bx.llbb()
1218         })
1219     }
1220
1221     pub fn new_block(&self, name: &str) -> Bx {
1222         Bx::new_block(self.cx, self.llfn, name)
1223     }
1224
1225     pub fn build_block(&self, bb: mir::BasicBlock) -> Bx {
1226         let mut bx = Bx::with_cx(self.cx);
1227         bx.position_at_end(self.blocks[bb]);
1228         bx
1229     }
1230
1231     fn make_return_dest(
1232         &mut self,
1233         bx: &mut Bx,
1234         dest: mir::Place<'tcx>,
1235         fn_ret: &ArgAbi<'tcx, Ty<'tcx>>,
1236         llargs: &mut Vec<Bx::Value>,
1237         is_intrinsic: bool,
1238     ) -> ReturnDest<'tcx, Bx::Value> {
1239         // If the return is ignored, we can just return a do-nothing `ReturnDest`.
1240         if fn_ret.is_ignore() {
1241             return ReturnDest::Nothing;
1242         }
1243         let dest = if let Some(index) = dest.as_local() {
1244             match self.locals[index] {
1245                 LocalRef::Place(dest) => dest,
1246                 LocalRef::UnsizedPlace(_) => bug!("return type must be sized"),
1247                 LocalRef::Operand(None) => {
1248                     // Handle temporary places, specifically `Operand` ones, as
1249                     // they don't have `alloca`s.
1250                     return if fn_ret.is_indirect() {
1251                         // Odd, but possible, case, we have an operand temporary,
1252                         // but the calling convention has an indirect return.
1253                         let tmp = PlaceRef::alloca(bx, fn_ret.layout);
1254                         tmp.storage_live(bx);
1255                         llargs.push(tmp.llval);
1256                         ReturnDest::IndirectOperand(tmp, index)
1257                     } else if is_intrinsic {
1258                         // Currently, intrinsics always need a location to store
1259                         // the result, so we create a temporary `alloca` for the
1260                         // result.
1261                         let tmp = PlaceRef::alloca(bx, fn_ret.layout);
1262                         tmp.storage_live(bx);
1263                         ReturnDest::IndirectOperand(tmp, index)
1264                     } else {
1265                         ReturnDest::DirectOperand(index)
1266                     };
1267                 }
1268                 LocalRef::Operand(Some(_)) => {
1269                     bug!("place local already assigned to");
1270                 }
1271             }
1272         } else {
1273             self.codegen_place(
1274                 bx,
1275                 mir::PlaceRef { local: dest.local, projection: &dest.projection },
1276             )
1277         };
1278         if fn_ret.is_indirect() {
1279             if dest.align < dest.layout.align.abi {
1280                 // Currently, MIR code generation does not create calls
1281                 // that store directly to fields of packed structs (in
1282                 // fact, the calls it creates write only to temps).
1283                 //
1284                 // If someone changes that, please update this code path
1285                 // to create a temporary.
1286                 span_bug!(self.mir.span, "can't directly store to unaligned value");
1287             }
1288             llargs.push(dest.llval);
1289             ReturnDest::Nothing
1290         } else {
1291             ReturnDest::Store(dest)
1292         }
1293     }
1294
1295     fn codegen_transmute(&mut self, bx: &mut Bx, src: &mir::Operand<'tcx>, dst: mir::Place<'tcx>) {
1296         if let Some(index) = dst.as_local() {
1297             match self.locals[index] {
1298                 LocalRef::Place(place) => self.codegen_transmute_into(bx, src, place),
1299                 LocalRef::UnsizedPlace(_) => bug!("transmute must not involve unsized locals"),
1300                 LocalRef::Operand(None) => {
1301                     let dst_layout = bx.layout_of(self.monomorphized_place_ty(dst.as_ref()));
1302                     assert!(!dst_layout.ty.has_erasable_regions());
1303                     let place = PlaceRef::alloca(bx, dst_layout);
1304                     place.storage_live(bx);
1305                     self.codegen_transmute_into(bx, src, place);
1306                     let op = bx.load_operand(place);
1307                     place.storage_dead(bx);
1308                     self.locals[index] = LocalRef::Operand(Some(op));
1309                     self.debug_introduce_local(bx, index);
1310                 }
1311                 LocalRef::Operand(Some(op)) => {
1312                     assert!(op.layout.is_zst(), "assigning to initialized SSAtemp");
1313                 }
1314             }
1315         } else {
1316             let dst = self.codegen_place(bx, dst.as_ref());
1317             self.codegen_transmute_into(bx, src, dst);
1318         }
1319     }
1320
1321     fn codegen_transmute_into(
1322         &mut self,
1323         bx: &mut Bx,
1324         src: &mir::Operand<'tcx>,
1325         dst: PlaceRef<'tcx, Bx::Value>,
1326     ) {
1327         let src = self.codegen_operand(bx, src);
1328
1329         // Special-case transmutes between scalars as simple bitcasts.
1330         match (&src.layout.abi, &dst.layout.abi) {
1331             (abi::Abi::Scalar(src_scalar), abi::Abi::Scalar(dst_scalar)) => {
1332                 // HACK(eddyb) LLVM doesn't like `bitcast`s between pointers and non-pointers.
1333                 if (src_scalar.value == abi::Pointer) == (dst_scalar.value == abi::Pointer) {
1334                     assert_eq!(src.layout.size, dst.layout.size);
1335
1336                     // NOTE(eddyb) the `from_immediate` and `to_immediate_scalar`
1337                     // conversions allow handling `bool`s the same as `u8`s.
1338                     let src = bx.from_immediate(src.immediate());
1339                     let src_as_dst = bx.bitcast(src, bx.backend_type(dst.layout));
1340                     Immediate(bx.to_immediate_scalar(src_as_dst, dst_scalar)).store(bx, dst);
1341                     return;
1342                 }
1343             }
1344             _ => {}
1345         }
1346
1347         let llty = bx.backend_type(src.layout);
1348         let cast_ptr = bx.pointercast(dst.llval, bx.type_ptr_to(llty));
1349         let align = src.layout.align.abi.min(dst.align);
1350         src.val.store(bx, PlaceRef::new_sized_aligned(cast_ptr, src.layout, align));
1351     }
1352
1353     // Stores the return value of a function call into it's final location.
1354     fn store_return(
1355         &mut self,
1356         bx: &mut Bx,
1357         dest: ReturnDest<'tcx, Bx::Value>,
1358         ret_abi: &ArgAbi<'tcx, Ty<'tcx>>,
1359         llval: Bx::Value,
1360     ) {
1361         use self::ReturnDest::*;
1362
1363         match dest {
1364             Nothing => (),
1365             Store(dst) => bx.store_arg(&ret_abi, llval, dst),
1366             IndirectOperand(tmp, index) => {
1367                 let op = bx.load_operand(tmp);
1368                 tmp.storage_dead(bx);
1369                 self.locals[index] = LocalRef::Operand(Some(op));
1370                 self.debug_introduce_local(bx, index);
1371             }
1372             DirectOperand(index) => {
1373                 // If there is a cast, we have to store and reload.
1374                 let op = if let PassMode::Cast(_) = ret_abi.mode {
1375                     let tmp = PlaceRef::alloca(bx, ret_abi.layout);
1376                     tmp.storage_live(bx);
1377                     bx.store_arg(&ret_abi, llval, tmp);
1378                     let op = bx.load_operand(tmp);
1379                     tmp.storage_dead(bx);
1380                     op
1381                 } else {
1382                     OperandRef::from_immediate_or_packed_pair(bx, llval, ret_abi.layout)
1383                 };
1384                 self.locals[index] = LocalRef::Operand(Some(op));
1385                 self.debug_introduce_local(bx, index);
1386             }
1387         }
1388     }
1389 }
1390
1391 enum ReturnDest<'tcx, V> {
1392     // Do nothing; the return value is indirect or ignored.
1393     Nothing,
1394     // Store the return value to the pointer.
1395     Store(PlaceRef<'tcx, V>),
1396     // Store an indirect return value to an operand local place.
1397     IndirectOperand(PlaceRef<'tcx, V>, mir::Local),
1398     // Store a direct return value to an operand local place.
1399     DirectOperand(mir::Local),
1400 }