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::{CachedLlbb, 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_ast::{InlineAsmOptions, InlineAsmTemplatePiece};
  14 use rustc_hir::lang_items::LangItem;
  15 use rustc_index::vec::Idx;
  16 use rustc_middle::mir::{self, AssertKind, SwitchTargets};
  17 use rustc_middle::ty::layout::{HasTyCtxt, LayoutOf};
  18 use rustc_middle::ty::print::{with_no_trimmed_paths, with_no_visible_paths};
  19 use rustc_middle::ty::{self, Instance, Ty, TypeVisitable};
  20 use rustc_session::config::OptLevel;
  21 use rustc_span::source_map::Span;
  22 use rustc_span::{sym, Symbol};
  23 use rustc_symbol_mangling::typeid::typeid_for_fnabi;
  24 use rustc_target::abi::call::{ArgAbi, FnAbi, PassMode, Reg};
  25 use rustc_target::abi::{self, HasDataLayout, WrappingRange};
  26 use rustc_target::spec::abi::Abi;
  27
  28 // Indicates if we are in the middle of merging a BB's successor into it. This
  29 // can happen when BB jumps directly to its successor and the successor has no
  30 // other predecessors.
  31 #[derive(Debug, PartialEq)]
  32 enum MergingSucc {
  33     False,
  34     True,
  35 }
  36
  37 /// Used by `FunctionCx::codegen_terminator` for emitting common patterns
  38 /// e.g., creating a basic block, calling a function, etc.
  39 struct TerminatorCodegenHelper<'tcx> {
  40     bb: mir::BasicBlock,
  41     terminator: &'tcx mir::Terminator<'tcx>,
  42     funclet_bb: Option<mir::BasicBlock>,
  43 }
  44
  45 impl<'a, 'tcx> TerminatorCodegenHelper<'tcx> {
  46     /// Returns the appropriate `Funclet` for the current funclet, if on MSVC,
  47     /// either already previously cached, or newly created, by `landing_pad_for`.
  48     fn funclet<'b, Bx: BuilderMethods<'a, 'tcx>>(
  49         &self,
  50         fx: &'b mut FunctionCx<'a, 'tcx, Bx>,
  51     ) -> Option<&'b Bx::Funclet> {
  52         let funclet_bb = self.funclet_bb?;
  53         if base::wants_msvc_seh(fx.cx.tcx().sess) {
  54             // If `landing_pad_for` hasn't been called yet to create the `Funclet`,
  55             // it has to be now. This may not seem necessary, as RPO should lead
  56             // to all the unwind edges being visited (and so to `landing_pad_for`
  57             // getting called for them), before building any of the blocks inside
  58             // the funclet itself - however, if MIR contains edges that end up not
  59             // being needed in the LLVM IR after monomorphization, the funclet may
  60             // be unreachable, and we don't have yet a way to skip building it in
  61             // such an eventuality (which may be a better solution than this).
  62             if fx.funclets[funclet_bb].is_none() {
  63                 fx.landing_pad_for(funclet_bb);
  64             }
  65
  66             Some(
  67                 fx.funclets[funclet_bb]
  68                     .as_ref()
  69                     .expect("landing_pad_for didn't also create funclets entry"),
  70             )
  71         } else {
  72             None
  73         }
  74     }
  75
  76     /// Get a basic block (creating it if necessary), possibly with cleanup
  77     /// stuff in it or next to it.
  78     fn llbb_with_cleanup<Bx: BuilderMethods<'a, 'tcx>>(
  79         &self,
  80         fx: &mut FunctionCx<'a, 'tcx, Bx>,
  81         target: mir::BasicBlock,
  82     ) -> Bx::BasicBlock {
  83         let (needs_landing_pad, is_cleanupret) = self.llbb_characteristics(fx, target);
  84         let mut lltarget = fx.llbb(target);
  85         if needs_landing_pad {
  86             lltarget = fx.landing_pad_for(target);
  87         }
  88         if is_cleanupret {
  89             // MSVC cross-funclet jump - need a trampoline
  90             debug_assert!(base::wants_msvc_seh(fx.cx.tcx().sess));
  91             debug!("llbb_with_cleanup: creating cleanup trampoline for {:?}", target);
  92             let name = &format!("{:?}_cleanup_trampoline_{:?}", self.bb, target);
  93             let trampoline_llbb = Bx::append_block(fx.cx, fx.llfn, name);
  94             let mut trampoline_bx = Bx::build(fx.cx, trampoline_llbb);
  95             trampoline_bx.cleanup_ret(self.funclet(fx).unwrap(), Some(lltarget));
  96             trampoline_llbb
  97         } else {
  98             lltarget
  99         }
 100     }
 101
 102     fn llbb_characteristics<Bx: BuilderMethods<'a, 'tcx>>(
 103         &self,
 104         fx: &mut FunctionCx<'a, 'tcx, Bx>,
 105         target: mir::BasicBlock,
 106     ) -> (bool, bool) {
 107         let target_funclet = fx.cleanup_kinds[target].funclet_bb(target);
 108         let (needs_landing_pad, is_cleanupret) = match (self.funclet_bb, target_funclet) {
 109             (None, None) => (false, false),
 110             (None, Some(_)) => (true, false),
 111             (Some(_), None) => {
 112                 let span = self.terminator.source_info.span;
 113                 span_bug!(span, "{:?} - jump out of cleanup?", self.terminator);
 114             }
 115             (Some(f), Some(t_f)) => {
 116                 if f == t_f || !base::wants_msvc_seh(fx.cx.tcx().sess) {
 117                     (false, false)
 118                 } else {
 119                     (true, true)
 120                 }
 121             }
 122         };
 123         (needs_landing_pad, is_cleanupret)
 124     }
 125
 126     fn funclet_br<Bx: BuilderMethods<'a, 'tcx>>(
 127         &self,
 128         fx: &mut FunctionCx<'a, 'tcx, Bx>,
 129         bx: &mut Bx,
 130         target: mir::BasicBlock,
 131         mergeable_succ: bool,
 132     ) -> MergingSucc {
 133         let (needs_landing_pad, is_cleanupret) = self.llbb_characteristics(fx, target);
 134         if mergeable_succ && !needs_landing_pad && !is_cleanupret {
 135             // We can merge the successor into this bb, so no need for a `br`.
 136             MergingSucc::True
 137         } else {
 138             let mut lltarget = fx.llbb(target);
 139             if needs_landing_pad {
 140                 lltarget = fx.landing_pad_for(target);
 141             }
 142             if is_cleanupret {
 143                 // micro-optimization: generate a `ret` rather than a jump
 144                 // to a trampoline.
 145                 bx.cleanup_ret(self.funclet(fx).unwrap(), Some(lltarget));
 146             } else {
 147                 bx.br(lltarget);
 148             }
 149             MergingSucc::False
 150         }
 151     }
 152
 153     /// Call `fn_ptr` of `fn_abi` with the arguments `llargs`, the optional
 154     /// return destination `destination` and the cleanup function `cleanup`.
 155     fn do_call<Bx: BuilderMethods<'a, 'tcx>>(
 156         &self,
 157         fx: &mut FunctionCx<'a, 'tcx, Bx>,
 158         bx: &mut Bx,
 159         fn_abi: &'tcx FnAbi<'tcx, Ty<'tcx>>,
 160         fn_ptr: Bx::Value,
 161         llargs: &[Bx::Value],
 162         destination: Option<(ReturnDest<'tcx, Bx::Value>, mir::BasicBlock)>,
 163         cleanup: Option<mir::BasicBlock>,
 164         copied_constant_arguments: &[PlaceRef<'tcx, <Bx as BackendTypes>::Value>],
 165         mergeable_succ: bool,
 166     ) -> MergingSucc {
 167         // If there is a cleanup block and the function we're calling can unwind, then
 168         // do an invoke, otherwise do a call.
 169         let fn_ty = bx.fn_decl_backend_type(&fn_abi);
 170
 171         let unwind_block = if let Some(cleanup) = cleanup.filter(|_| fn_abi.can_unwind) {
 172             Some(self.llbb_with_cleanup(fx, cleanup))
 173         } else if fx.mir[self.bb].is_cleanup
 174             && fn_abi.can_unwind
 175             && !base::wants_msvc_seh(fx.cx.tcx().sess)
 176         {
 177             // Exception must not propagate out of the execution of a cleanup (doing so
 178             // can cause undefined behaviour). We insert a double unwind guard for
 179             // functions that can potentially unwind to protect against this.
 180             //
 181             // This is not necessary for SEH which does not use successive unwinding
 182             // like Itanium EH. EH frames in SEH are different from normal function
 183             // frames and SEH will abort automatically if an exception tries to
 184             // propagate out from cleanup.
 185             Some(fx.double_unwind_guard())
 186         } else {
 187             None
 188         };
 189
 190         if let Some(unwind_block) = unwind_block {
 191             let ret_llbb = if let Some((_, target)) = destination {
 192                 fx.llbb(target)
 193             } else {
 194                 fx.unreachable_block()
 195             };
 196             let invokeret = bx.invoke(
 197                 fn_ty,
 198                 Some(&fn_abi),
 199                 fn_ptr,
 200                 &llargs,
 201                 ret_llbb,
 202                 unwind_block,
 203                 self.funclet(fx),
 204             );
 205             if fx.mir[self.bb].is_cleanup {
 206                 bx.do_not_inline(invokeret);
 207             }
 208
 209             if let Some((ret_dest, target)) = destination {
 210                 bx.switch_to_block(fx.llbb(target));
 211                 fx.set_debug_loc(bx, self.terminator.source_info);
 212                 for tmp in copied_constant_arguments {
 213                     bx.lifetime_end(tmp.llval, tmp.layout.size);
 214                 }
 215                 fx.store_return(bx, ret_dest, &fn_abi.ret, invokeret);
 216             }
 217             MergingSucc::False
 218         } else {
 219             let llret = bx.call(fn_ty, Some(&fn_abi), fn_ptr, &llargs, self.funclet(fx));
 220             if fx.mir[self.bb].is_cleanup {
 221                 // Cleanup is always the cold path. Don't inline
 222                 // drop glue. Also, when there is a deeply-nested
 223                 // struct, there are "symmetry" issues that cause
 224                 // exponential inlining - see issue #41696.
 225                 bx.do_not_inline(llret);
 226             }
 227
 228             if let Some((ret_dest, target)) = destination {
 229                 for tmp in copied_constant_arguments {
 230                     bx.lifetime_end(tmp.llval, tmp.layout.size);
 231                 }
 232                 fx.store_return(bx, ret_dest, &fn_abi.ret, llret);
 233                 self.funclet_br(fx, bx, target, mergeable_succ)
 234             } else {
 235                 bx.unreachable();
 236                 MergingSucc::False
 237             }
 238         }
 239     }
 240
 241     /// Generates inline assembly with optional `destination` and `cleanup`.
 242     fn do_inlineasm<Bx: BuilderMethods<'a, 'tcx>>(
 243         &self,
 244         fx: &mut FunctionCx<'a, 'tcx, Bx>,
 245         bx: &mut Bx,
 246         template: &[InlineAsmTemplatePiece],
 247         operands: &[InlineAsmOperandRef<'tcx, Bx>],
 248         options: InlineAsmOptions,
 249         line_spans: &[Span],
 250         destination: Option<mir::BasicBlock>,
 251         cleanup: Option<mir::BasicBlock>,
 252         instance: Instance<'_>,
 253         mergeable_succ: bool,
 254     ) -> MergingSucc {
 255         if let Some(cleanup) = cleanup {
 256             let ret_llbb = if let Some(target) = destination {
 257                 fx.llbb(target)
 258             } else {
 259                 fx.unreachable_block()
 260             };
 261
 262             bx.codegen_inline_asm(
 263                 template,
 264                 &operands,
 265                 options,
 266                 line_spans,
 267                 instance,
 268                 Some((ret_llbb, self.llbb_with_cleanup(fx, cleanup), self.funclet(fx))),
 269             );
 270             MergingSucc::False
 271         } else {
 272             bx.codegen_inline_asm(template, &operands, options, line_spans, instance, None);
 273
 274             if let Some(target) = destination {
 275                 self.funclet_br(fx, bx, target, mergeable_succ)
 276             } else {
 277                 bx.unreachable();
 278                 MergingSucc::False
 279             }
 280         }
 281     }
 282 }
 283
 284 /// Codegen implementations for some terminator variants.
 285 impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
 286     /// Generates code for a `Resume` terminator.
 287     fn codegen_resume_terminator(&mut self, helper: TerminatorCodegenHelper<'tcx>, bx: &mut Bx) {
 288         if let Some(funclet) = helper.funclet(self) {
 289             bx.cleanup_ret(funclet, None);
 290         } else {
 291             let slot = self.get_personality_slot(bx);
 292             let lp0 = slot.project_field(bx, 0);
 293             let lp0 = bx.load_operand(lp0).immediate();
 294             let lp1 = slot.project_field(bx, 1);
 295             let lp1 = bx.load_operand(lp1).immediate();
 296             slot.storage_dead(bx);
 297
 298             let mut lp = bx.const_undef(self.landing_pad_type());
 299             lp = bx.insert_value(lp, lp0, 0);
 300             lp = bx.insert_value(lp, lp1, 1);
 301             bx.resume(lp);
 302         }
 303     }
 304
 305     fn codegen_switchint_terminator(
 306         &mut self,
 307         helper: TerminatorCodegenHelper<'tcx>,
 308         bx: &mut Bx,
 309         discr: &mir::Operand<'tcx>,
 310         switch_ty: Ty<'tcx>,
 311         targets: &SwitchTargets,
 312     ) {
 313         let discr = self.codegen_operand(bx, &discr);
 314         // `switch_ty` is redundant, sanity-check that.
 315         assert_eq!(discr.layout.ty, switch_ty);
 316         let mut target_iter = targets.iter();
 317         if target_iter.len() == 1 {
 318             // If there are two targets (one conditional, one fallback), emit `br` instead of
 319             // `switch`.
 320             let (test_value, target) = target_iter.next().unwrap();
 321             let lltrue = helper.llbb_with_cleanup(self, target);
 322             let llfalse = helper.llbb_with_cleanup(self, targets.otherwise());
 323             if switch_ty == bx.tcx().types.bool {
 324                 // Don't generate trivial icmps when switching on bool.
 325                 match test_value {
 326                     0 => bx.cond_br(discr.immediate(), llfalse, lltrue),
 327                     1 => bx.cond_br(discr.immediate(), lltrue, llfalse),
 328                     _ => bug!(),
 329                 }
 330             } else {
 331                 let switch_llty = bx.immediate_backend_type(bx.layout_of(switch_ty));
 332                 let llval = bx.const_uint_big(switch_llty, test_value);
 333                 let cmp = bx.icmp(IntPredicate::IntEQ, discr.immediate(), llval);
 334                 bx.cond_br(cmp, lltrue, llfalse);
 335             }
 336         } else if self.cx.sess().opts.optimize == OptLevel::No
 337             && target_iter.len() == 2
 338             && self.mir[targets.otherwise()].is_empty_unreachable()
 339         {
 340             // In unoptimized builds, if there are two normal targets and the `otherwise` target is
 341             // an unreachable BB, emit `br` instead of `switch`. This leaves behind the unreachable
 342             // BB, which will usually (but not always) be dead code.
 343             //
 344             // Why only in unoptimized builds?
 345             // - In unoptimized builds LLVM uses FastISel which does not support switches, so it
 346             //   must fall back to the to the slower SelectionDAG isel. Therefore, using `br` gives
 347             //   significant compile time speedups for unoptimized builds.
 348             // - In optimized builds the above doesn't hold, and using `br` sometimes results in
 349             //   worse generated code because LLVM can no longer tell that the value being switched
 350             //   on can only have two values, e.g. 0 and 1.
 351             //
 352             let (test_value1, target1) = target_iter.next().unwrap();
 353             let (_test_value2, target2) = target_iter.next().unwrap();
 354             let ll1 = helper.llbb_with_cleanup(self, target1);
 355             let ll2 = helper.llbb_with_cleanup(self, target2);
 356             let switch_llty = bx.immediate_backend_type(bx.layout_of(switch_ty));
 357             let llval = bx.const_uint_big(switch_llty, test_value1);
 358             let cmp = bx.icmp(IntPredicate::IntEQ, discr.immediate(), llval);
 359             bx.cond_br(cmp, ll1, ll2);
 360         } else {
 361             bx.switch(
 362                 discr.immediate(),
 363                 helper.llbb_with_cleanup(self, targets.otherwise()),
 364                 target_iter.map(|(value, target)| (value, helper.llbb_with_cleanup(self, target))),
 365             );
 366         }
 367     }
 368
 369     fn codegen_return_terminator(&mut self, bx: &mut Bx) {
 370         // Call `va_end` if this is the definition of a C-variadic function.
 371         if self.fn_abi.c_variadic {
 372             // The `VaList` "spoofed" argument is just after all the real arguments.
 373             let va_list_arg_idx = self.fn_abi.args.len();
 374             match self.locals[mir::Local::new(1 + va_list_arg_idx)] {
 375                 LocalRef::Place(va_list) => {
 376                     bx.va_end(va_list.llval);
 377                 }
 378                 _ => bug!("C-variadic function must have a `VaList` place"),
 379             }
 380         }
 381         if self.fn_abi.ret.layout.abi.is_uninhabited() {
 382             // Functions with uninhabited return values are marked `noreturn`,
 383             // so we should make sure that we never actually do.
 384             // We play it safe by using a well-defined `abort`, but we could go for immediate UB
 385             // if that turns out to be helpful.
 386             bx.abort();
 387             // `abort` does not terminate the block, so we still need to generate
 388             // an `unreachable` terminator after it.
 389             bx.unreachable();
 390             return;
 391         }
 392         let llval = match &self.fn_abi.ret.mode {
 393             PassMode::Ignore | PassMode::Indirect { .. } => {
 394                 bx.ret_void();
 395                 return;
 396             }
 397
 398             PassMode::Direct(_) | PassMode::Pair(..) => {
 399                 let op = self.codegen_consume(bx, mir::Place::return_place().as_ref());
 400                 if let Ref(llval, _, align) = op.val {
 401                     bx.load(bx.backend_type(op.layout), llval, align)
 402                 } else {
 403                     op.immediate_or_packed_pair(bx)
 404                 }
 405             }
 406
 407             PassMode::Cast(cast_ty, _) => {
 408                 let op = match self.locals[mir::RETURN_PLACE] {
 409                     LocalRef::Operand(Some(op)) => op,
 410                     LocalRef::Operand(None) => bug!("use of return before def"),
 411                     LocalRef::Place(cg_place) => OperandRef {
 412                         val: Ref(cg_place.llval, None, cg_place.align),
 413                         layout: cg_place.layout,
 414                     },
 415                     LocalRef::UnsizedPlace(_) => bug!("return type must be sized"),
 416                 };
 417                 let llslot = match op.val {
 418                     Immediate(_) | Pair(..) => {
 419                         let scratch = PlaceRef::alloca(bx, self.fn_abi.ret.layout);
 420                         op.val.store(bx, scratch);
 421                         scratch.llval
 422                     }
 423                     Ref(llval, _, align) => {
 424                         assert_eq!(align, op.layout.align.abi, "return place is unaligned!");
 425                         llval
 426                     }
 427                 };
 428                 let ty = bx.cast_backend_type(cast_ty);
 429                 let addr = bx.pointercast(llslot, bx.type_ptr_to(ty));
 430                 bx.load(ty, addr, self.fn_abi.ret.layout.align.abi)
 431             }
 432         };
 433         bx.ret(llval);
 434     }
 435
 436     #[tracing::instrument(level = "trace", skip(self, helper, bx))]
 437     fn codegen_drop_terminator(
 438         &mut self,
 439         helper: TerminatorCodegenHelper<'tcx>,
 440         bx: &mut Bx,
 441         location: mir::Place<'tcx>,
 442         target: mir::BasicBlock,
 443         unwind: Option<mir::BasicBlock>,
 444         mergeable_succ: bool,
 445     ) -> MergingSucc {
 446         let ty = location.ty(self.mir, bx.tcx()).ty;
 447         let ty = self.monomorphize(ty);
 448         let drop_fn = Instance::resolve_drop_in_place(bx.tcx(), ty);
 449
 450         if let ty::InstanceDef::DropGlue(_, None) = drop_fn.def {
 451             // we don't actually need to drop anything.
 452             return helper.funclet_br(self, bx, target, mergeable_succ);
 453         }
 454
 455         let place = self.codegen_place(bx, location.as_ref());
 456         let (args1, args2);
 457         let mut args = if let Some(llextra) = place.llextra {
 458             args2 = [place.llval, llextra];
 459             &args2[..]
 460         } else {
 461             args1 = [place.llval];
 462             &args1[..]
 463         };
 464         let (drop_fn, fn_abi) = match ty.kind() {
 465             // FIXME(eddyb) perhaps move some of this logic into
 466             // `Instance::resolve_drop_in_place`?
 467             ty::Dynamic(_, _, ty::Dyn) => {
 468                 // IN THIS ARM, WE HAVE:
 469                 // ty = *mut (dyn Trait)
 470                 // which is: exists<T> ( *mut T,    Vtable<T: Trait> )
 471                 //                       args[0]    args[1]
 472                 //
 473                 // args = ( Data, Vtable )
 474                 //                  |
 475                 //                  v
 476                 //                /-------\
 477                 //                | ...   |
 478                 //                \-------/
 479                 //
 480                 let virtual_drop = Instance {
 481                     def: ty::InstanceDef::Virtual(drop_fn.def_id(), 0),
 482                     substs: drop_fn.substs,
 483                 };
 484                 debug!("ty = {:?}", ty);
 485                 debug!("drop_fn = {:?}", drop_fn);
 486                 debug!("args = {:?}", args);
 487                 let fn_abi = bx.fn_abi_of_instance(virtual_drop, ty::List::empty());
 488                 let vtable = args[1];
 489                 // Truncate vtable off of args list
 490                 args = &args[..1];
 491                 (
 492                     meth::VirtualIndex::from_index(ty::COMMON_VTABLE_ENTRIES_DROPINPLACE)
 493                         .get_fn(bx, vtable, ty, &fn_abi),
 494                     fn_abi,
 495                 )
 496             }
 497             ty::Dynamic(_, _, ty::DynStar) => {
 498                 // IN THIS ARM, WE HAVE:
 499                 // ty = *mut (dyn* Trait)
 500                 // which is: *mut exists<T: sizeof(T) == sizeof(usize)> (T, Vtable<T: Trait>)
 501                 //
 502                 // args = [ * ]
 503                 //          |
 504                 //          v
 505                 //      ( Data, Vtable )
 506                 //                |
 507                 //                v
 508                 //              /-------\
 509                 //              | ...   |
 510                 //              \-------/
 511                 //
 512                 //
 513                 // WE CAN CONVERT THIS INTO THE ABOVE LOGIC BY DOING
 514                 //
 515                 // data = &(*args[0]).0    // gives a pointer to Data above (really the same pointer)
 516                 // vtable = (*args[0]).1   // loads the vtable out
 517                 // (data, vtable)          // an equivalent Rust `*mut dyn Trait`
 518                 //
 519                 // SO THEN WE CAN USE THE ABOVE CODE.
 520                 let virtual_drop = Instance {
 521                     def: ty::InstanceDef::Virtual(drop_fn.def_id(), 0),
 522                     substs: drop_fn.substs,
 523                 };
 524                 debug!("ty = {:?}", ty);
 525                 debug!("drop_fn = {:?}", drop_fn);
 526                 debug!("args = {:?}", args);
 527                 let fn_abi = bx.fn_abi_of_instance(virtual_drop, ty::List::empty());
 528                 let data = args[0];
 529                 let data_ty = bx.cx().backend_type(place.layout);
 530                 let vtable_ptr =
 531                     bx.gep(data_ty, data, &[bx.cx().const_i32(0), bx.cx().const_i32(1)]);
 532                 let vtable = bx.load(bx.type_i8p(), vtable_ptr, abi::Align::ONE);
 533                 // Truncate vtable off of args list
 534                 args = &args[..1];
 535                 debug!("args' = {:?}", args);
 536                 (
 537                     meth::VirtualIndex::from_index(ty::COMMON_VTABLE_ENTRIES_DROPINPLACE)
 538                         .get_fn(bx, vtable, ty, &fn_abi),
 539                     fn_abi,
 540                 )
 541             }
 542             _ => (bx.get_fn_addr(drop_fn), bx.fn_abi_of_instance(drop_fn, ty::List::empty())),
 543         };
 544         helper.do_call(
 545             self,
 546             bx,
 547             fn_abi,
 548             drop_fn,
 549             args,
 550             Some((ReturnDest::Nothing, target)),
 551             unwind,
 552             &[],
 553             mergeable_succ,
 554         )
 555     }
 556
 557     fn codegen_assert_terminator(
 558         &mut self,
 559         helper: TerminatorCodegenHelper<'tcx>,
 560         bx: &mut Bx,
 561         terminator: &mir::Terminator<'tcx>,
 562         cond: &mir::Operand<'tcx>,
 563         expected: bool,
 564         msg: &mir::AssertMessage<'tcx>,
 565         target: mir::BasicBlock,
 566         cleanup: Option<mir::BasicBlock>,
 567         mergeable_succ: bool,
 568     ) -> MergingSucc {
 569         let span = terminator.source_info.span;
 570         let cond = self.codegen_operand(bx, cond).immediate();
 571         let mut const_cond = bx.const_to_opt_u128(cond, false).map(|c| c == 1);
 572
 573         // This case can currently arise only from functions marked
 574         // with #[rustc_inherit_overflow_checks] and inlined from
 575         // another crate (mostly core::num generic/#[inline] fns),
 576         // while the current crate doesn't use overflow checks.
 577         // NOTE: Unlike binops, negation doesn't have its own
 578         // checked operation, just a comparison with the minimum
 579         // value, so we have to check for the assert message.
 580         if !bx.check_overflow() {
 581             if let AssertKind::OverflowNeg(_) = *msg {
 582                 const_cond = Some(expected);
 583             }
 584         }
 585
 586         // Don't codegen the panic block if success if known.
 587         if const_cond == Some(expected) {
 588             return helper.funclet_br(self, bx, target, mergeable_succ);
 589         }
 590
 591         // Pass the condition through llvm.expect for branch hinting.
 592         let cond = bx.expect(cond, expected);
 593
 594         // Create the failure block and the conditional branch to it.
 595         let lltarget = helper.llbb_with_cleanup(self, target);
 596         let panic_block = bx.append_sibling_block("panic");
 597         if expected {
 598             bx.cond_br(cond, lltarget, panic_block);
 599         } else {
 600             bx.cond_br(cond, panic_block, lltarget);
 601         }
 602
 603         // After this point, bx is the block for the call to panic.
 604         bx.switch_to_block(panic_block);
 605         self.set_debug_loc(bx, terminator.source_info);
 606
 607         // Get the location information.
 608         let location = self.get_caller_location(bx, terminator.source_info).immediate();
 609
 610         // Put together the arguments to the panic entry point.
 611         let (lang_item, args) = match msg {
 612             AssertKind::BoundsCheck { ref len, ref index } => {
 613                 let len = self.codegen_operand(bx, len).immediate();
 614                 let index = self.codegen_operand(bx, index).immediate();
 615                 // It's `fn panic_bounds_check(index: usize, len: usize)`,
 616                 // and `#[track_caller]` adds an implicit third argument.
 617                 (LangItem::PanicBoundsCheck, vec![index, len, location])
 618             }
 619             _ => {
 620                 let msg = bx.const_str(msg.description());
 621                 // It's `pub fn panic(expr: &str)`, with the wide reference being passed
 622                 // as two arguments, and `#[track_caller]` adds an implicit third argument.
 623                 (LangItem::Panic, vec![msg.0, msg.1, location])
 624             }
 625         };
 626
 627         let (fn_abi, llfn) = common::build_langcall(bx, Some(span), lang_item);
 628
 629         // Codegen the actual panic invoke/call.
 630         let merging_succ = helper.do_call(self, bx, fn_abi, llfn, &args, None, cleanup, &[], false);
 631         assert_eq!(merging_succ, MergingSucc::False);
 632         MergingSucc::False
 633     }
 634
 635     fn codegen_abort_terminator(
 636         &mut self,
 637         helper: TerminatorCodegenHelper<'tcx>,
 638         bx: &mut Bx,
 639         terminator: &mir::Terminator<'tcx>,
 640     ) {
 641         let span = terminator.source_info.span;
 642         self.set_debug_loc(bx, terminator.source_info);
 643
 644         // Obtain the panic entry point.
 645         let (fn_abi, llfn) = common::build_langcall(bx, Some(span), LangItem::PanicNoUnwind);
 646
 647         // Codegen the actual panic invoke/call.
 648         let merging_succ = helper.do_call(self, bx, fn_abi, llfn, &[], None, None, &[], false);
 649         assert_eq!(merging_succ, MergingSucc::False);
 650     }
 651
 652     /// Returns `Some` if this is indeed a panic intrinsic and codegen is done.
 653     fn codegen_panic_intrinsic(
 654         &mut self,
 655         helper: &TerminatorCodegenHelper<'tcx>,
 656         bx: &mut Bx,
 657         intrinsic: Option<Symbol>,
 658         instance: Option<Instance<'tcx>>,
 659         source_info: mir::SourceInfo,
 660         target: Option<mir::BasicBlock>,
 661         cleanup: Option<mir::BasicBlock>,
 662         mergeable_succ: bool,
 663     ) -> Option<MergingSucc> {
 664         // Emit a panic or a no-op for `assert_*` intrinsics.
 665         // These are intrinsics that compile to panics so that we can get a message
 666         // which mentions the offending type, even from a const context.
 667         #[derive(Debug, PartialEq)]
 668         enum AssertIntrinsic {
 669             Inhabited,
 670             ZeroValid,
 671             UninitValid,
 672         }
 673         let panic_intrinsic = intrinsic.and_then(|i| match i {
 674             sym::assert_inhabited => Some(AssertIntrinsic::Inhabited),
 675             sym::assert_zero_valid => Some(AssertIntrinsic::ZeroValid),
 676             sym::assert_uninit_valid => Some(AssertIntrinsic::UninitValid),
 677             _ => None,
 678         });
 679         if let Some(intrinsic) = panic_intrinsic {
 680             use AssertIntrinsic::*;
 681
 682             let ty = instance.unwrap().substs.type_at(0);
 683             let layout = bx.layout_of(ty);
 684             let do_panic = match intrinsic {
 685                 Inhabited => layout.abi.is_uninhabited(),
 686                 ZeroValid => !bx.tcx().permits_zero_init(layout),
 687                 UninitValid => !bx.tcx().permits_uninit_init(layout),
 688             };
 689             Some(if do_panic {
 690                 let msg_str = with_no_visible_paths!({
 691                     with_no_trimmed_paths!({
 692                         if layout.abi.is_uninhabited() {
 693                             // Use this error even for the other intrinsics as it is more precise.
 694                             format!("attempted to instantiate uninhabited type `{}`", ty)
 695                         } else if intrinsic == ZeroValid {
 696                             format!("attempted to zero-initialize type `{}`, which is invalid", ty)
 697                         } else {
 698                             format!(
 699                                 "attempted to leave type `{}` uninitialized, which is invalid",
 700                                 ty
 701                             )
 702                         }
 703                     })
 704                 });
 705                 let msg = bx.const_str(&msg_str);
 706                 let location = self.get_caller_location(bx, source_info).immediate();
 707
 708                 // Obtain the panic entry point.
 709                 let (fn_abi, llfn) =
 710                     common::build_langcall(bx, Some(source_info.span), LangItem::Panic);
 711
 712                 // Codegen the actual panic invoke/call.
 713                 helper.do_call(
 714                     self,
 715                     bx,
 716                     fn_abi,
 717                     llfn,
 718                     &[msg.0, msg.1, location],
 719                     target.as_ref().map(|bb| (ReturnDest::Nothing, *bb)),
 720                     cleanup,
 721                     &[],
 722                     mergeable_succ,
 723                 )
 724             } else {
 725                 // a NOP
 726                 let target = target.unwrap();
 727                 helper.funclet_br(self, bx, target, mergeable_succ)
 728             })
 729         } else {
 730             None
 731         }
 732     }
 733
 734     fn codegen_call_terminator(
 735         &mut self,
 736         helper: TerminatorCodegenHelper<'tcx>,
 737         bx: &mut Bx,
 738         terminator: &mir::Terminator<'tcx>,
 739         func: &mir::Operand<'tcx>,
 740         args: &[mir::Operand<'tcx>],
 741         destination: mir::Place<'tcx>,
 742         target: Option<mir::BasicBlock>,
 743         cleanup: Option<mir::BasicBlock>,
 744         fn_span: Span,
 745         mergeable_succ: bool,
 746     ) -> MergingSucc {
 747         let source_info = terminator.source_info;
 748         let span = source_info.span;
 749
 750         // Create the callee. This is a fn ptr or zero-sized and hence a kind of scalar.
 751         let callee = self.codegen_operand(bx, func);
 752
 753         let (instance, mut llfn) = match *callee.layout.ty.kind() {
 754             ty::FnDef(def_id, substs) => (
 755                 Some(
 756                     ty::Instance::resolve(bx.tcx(), ty::ParamEnv::reveal_all(), def_id, substs)
 757                         .unwrap()
 758                         .unwrap()
 759                         .polymorphize(bx.tcx()),
 760                 ),
 761                 None,
 762             ),
 763             ty::FnPtr(_) => (None, Some(callee.immediate())),
 764             _ => bug!("{} is not callable", callee.layout.ty),
 765         };
 766         let def = instance.map(|i| i.def);
 767
 768         if let Some(ty::InstanceDef::DropGlue(_, None)) = def {
 769             // Empty drop glue; a no-op.
 770             let target = target.unwrap();
 771             return helper.funclet_br(self, bx, target, mergeable_succ);
 772         }
 773
 774         // FIXME(eddyb) avoid computing this if possible, when `instance` is
 775         // available - right now `sig` is only needed for getting the `abi`
 776         // and figuring out how many extra args were passed to a C-variadic `fn`.
 777         let sig = callee.layout.ty.fn_sig(bx.tcx());
 778         let abi = sig.abi();
 779
 780         // Handle intrinsics old codegen wants Expr's for, ourselves.
 781         let intrinsic = match def {
 782             Some(ty::InstanceDef::Intrinsic(def_id)) => Some(bx.tcx().item_name(def_id)),
 783             _ => None,
 784         };
 785
 786         let extra_args = &args[sig.inputs().skip_binder().len()..];
 787         let extra_args = bx.tcx().mk_type_list(extra_args.iter().map(|op_arg| {
 788             let op_ty = op_arg.ty(self.mir, bx.tcx());
 789             self.monomorphize(op_ty)
 790         }));
 791
 792         let fn_abi = match instance {
 793             Some(instance) => bx.fn_abi_of_instance(instance, extra_args),
 794             None => bx.fn_abi_of_fn_ptr(sig, extra_args),
 795         };
 796
 797         if intrinsic == Some(sym::transmute) {
 798             return if let Some(target) = target {
 799                 self.codegen_transmute(bx, &args[0], destination);
 800                 helper.funclet_br(self, bx, target, mergeable_succ)
 801             } else {
 802                 // If we are trying to transmute to an uninhabited type,
 803                 // it is likely there is no allotted destination. In fact,
 804                 // transmuting to an uninhabited type is UB, which means
 805                 // we can do what we like. Here, we declare that transmuting
 806                 // into an uninhabited type is impossible, so anything following
 807                 // it must be unreachable.
 808                 assert_eq!(fn_abi.ret.layout.abi, abi::Abi::Uninhabited);
 809                 bx.unreachable();
 810                 MergingSucc::False
 811             };
 812         }
 813
 814         if let Some(merging_succ) = self.codegen_panic_intrinsic(
 815             &helper,
 816             bx,
 817             intrinsic,
 818             instance,
 819             source_info,
 820             target,
 821             cleanup,
 822             mergeable_succ,
 823         ) {
 824             return merging_succ;
 825         }
 826
 827         // The arguments we'll be passing. Plus one to account for outptr, if used.
 828         let arg_count = fn_abi.args.len() + fn_abi.ret.is_indirect() as usize;
 829         let mut llargs = Vec::with_capacity(arg_count);
 830
 831         // Prepare the return value destination
 832         let ret_dest = if target.is_some() {
 833             let is_intrinsic = intrinsic.is_some();
 834             self.make_return_dest(bx, destination, &fn_abi.ret, &mut llargs, is_intrinsic)
 835         } else {
 836             ReturnDest::Nothing
 837         };
 838
 839         if intrinsic == Some(sym::caller_location) {
 840             return if let Some(target) = target {
 841                 let location =
 842                     self.get_caller_location(bx, mir::SourceInfo { span: fn_span, ..source_info });
 843
 844                 if let ReturnDest::IndirectOperand(tmp, _) = ret_dest {
 845                     location.val.store(bx, tmp);
 846                 }
 847                 self.store_return(bx, ret_dest, &fn_abi.ret, location.immediate());
 848                 helper.funclet_br(self, bx, target, mergeable_succ)
 849             } else {
 850                 MergingSucc::False
 851             };
 852         }
 853
 854         match intrinsic {
 855             None | Some(sym::drop_in_place) => {}
 856             Some(sym::copy_nonoverlapping) => unreachable!(),
 857             Some(intrinsic) => {
 858                 let dest = match ret_dest {
 859                     _ if fn_abi.ret.is_indirect() => llargs[0],
 860                     ReturnDest::Nothing => {
 861                         bx.const_undef(bx.type_ptr_to(bx.arg_memory_ty(&fn_abi.ret)))
 862                     }
 863                     ReturnDest::IndirectOperand(dst, _) | ReturnDest::Store(dst) => dst.llval,
 864                     ReturnDest::DirectOperand(_) => {
 865                         bug!("Cannot use direct operand with an intrinsic call")
 866                     }
 867                 };
 868
 869                 let args: Vec<_> = args
 870                     .iter()
 871                     .enumerate()
 872                     .map(|(i, arg)| {
 873                         // The indices passed to simd_shuffle* in the
 874                         // third argument must be constant. This is
 875                         // checked by const-qualification, which also
 876                         // promotes any complex rvalues to constants.
 877                         if i == 2 && intrinsic.as_str().starts_with("simd_shuffle") {
 878                             if let mir::Operand::Constant(constant) = arg {
 879                                 let c = self.eval_mir_constant(constant);
 880                                 let (llval, ty) = self.simd_shuffle_indices(
 881                                     &bx,
 882                                     constant.span,
 883                                     self.monomorphize(constant.ty()),
 884                                     c,
 885                                 );
 886                                 return OperandRef {
 887                                     val: Immediate(llval),
 888                                     layout: bx.layout_of(ty),
 889                                 };
 890                             } else {
 891                                 span_bug!(span, "shuffle indices must be constant");
 892                             }
 893                         }
 894
 895                         self.codegen_operand(bx, arg)
 896                     })
 897                     .collect();
 898
 899                 Self::codegen_intrinsic_call(
 900                     bx,
 901                     *instance.as_ref().unwrap(),
 902                     &fn_abi,
 903                     &args,
 904                     dest,
 905                     span,
 906                 );
 907
 908                 if let ReturnDest::IndirectOperand(dst, _) = ret_dest {
 909                     self.store_return(bx, ret_dest, &fn_abi.ret, dst.llval);
 910                 }
 911
 912                 return if let Some(target) = target {
 913                     helper.funclet_br(self, bx, target, mergeable_succ)
 914                 } else {
 915                     bx.unreachable();
 916                     MergingSucc::False
 917                 };
 918             }
 919         }
 920
 921         // Split the rust-call tupled arguments off.
 922         let (first_args, untuple) = if abi == Abi::RustCall && !args.is_empty() {
 923             let (tup, args) = args.split_last().unwrap();
 924             (args, Some(tup))
 925         } else {
 926             (args, None)
 927         };
 928
 929         let mut copied_constant_arguments = vec![];
 930         'make_args: for (i, arg) in first_args.iter().enumerate() {
 931             let mut op = self.codegen_operand(bx, arg);
 932
 933             if let (0, Some(ty::InstanceDef::Virtual(_, idx))) = (i, def) {
 934                 match op.val {
 935                     Pair(data_ptr, meta) => {
 936                         // In the case of Rc<Self>, we need to explicitly pass a
 937                         // *mut RcBox<Self> with a Scalar (not ScalarPair) ABI. This is a hack
 938                         // that is understood elsewhere in the compiler as a method on
 939                         // `dyn Trait`.
 940                         // To get a `*mut RcBox<Self>`, we just keep unwrapping newtypes until
 941                         // we get a value of a built-in pointer type
 942                         'descend_newtypes: while !op.layout.ty.is_unsafe_ptr()
 943                             && !op.layout.ty.is_region_ptr()
 944                         {
 945                             for i in 0..op.layout.fields.count() {
 946                                 let field = op.extract_field(bx, i);
 947                                 if !field.layout.is_zst() {
 948                                     // we found the one non-zero-sized field that is allowed
 949                                     // now find *its* non-zero-sized field, or stop if it's a
 950                                     // pointer
 951                                     op = field;
 952                                     continue 'descend_newtypes;
 953                                 }
 954                             }
 955
 956                             span_bug!(span, "receiver has no non-zero-sized fields {:?}", op);
 957                         }
 958
 959                         // now that we have `*dyn Trait` or `&dyn Trait`, split it up into its
 960                         // data pointer and vtable. Look up the method in the vtable, and pass
 961                         // the data pointer as the first argument
 962                         llfn = Some(meth::VirtualIndex::from_index(idx).get_fn(
 963                             bx,
 964                             meta,
 965                             op.layout.ty,
 966                             &fn_abi,
 967                         ));
 968                         llargs.push(data_ptr);
 969                         continue 'make_args;
 970                     }
 971                     Ref(data_ptr, Some(meta), _) => {
 972                         // by-value dynamic dispatch
 973                         llfn = Some(meth::VirtualIndex::from_index(idx).get_fn(
 974                             bx,
 975                             meta,
 976                             op.layout.ty,
 977                             &fn_abi,
 978                         ));
 979                         llargs.push(data_ptr);
 980                         continue;
 981                     }
 982                     Immediate(_) => {
 983                         let ty::Ref(_, ty, _) = op.layout.ty.kind() else {
 984                             span_bug!(span, "can't codegen a virtual call on {:#?}", op);
 985                         };
 986                         if !ty.is_dyn_star() {
 987                             span_bug!(span, "can't codegen a virtual call on {:#?}", op);
 988                         }
 989                         // FIXME(dyn-star): Make sure this is done on a &dyn* receiver
 990                         let place = op.deref(bx.cx());
 991                         let data_ptr = place.project_field(bx, 0);
 992                         let meta_ptr = place.project_field(bx, 1);
 993                         let meta = bx.load_operand(meta_ptr);
 994                         llfn = Some(meth::VirtualIndex::from_index(idx).get_fn(
 995                             bx,
 996                             meta.immediate(),
 997                             op.layout.ty,
 998                             &fn_abi,
 999                         ));
1000                         llargs.push(data_ptr.llval);
1001                         continue;
1002                     }
1003                     _ => {
1004                         span_bug!(span, "can't codegen a virtual call on {:#?}", op);
1005                     }
1006                 }
1007             }
1008
1009             // The callee needs to own the argument memory if we pass it
1010             // by-ref, so make a local copy of non-immediate constants.
1011             match (arg, op.val) {
1012                 (&mir::Operand::Copy(_), Ref(_, None, _))
1013                 | (&mir::Operand::Constant(_), Ref(_, None, _)) => {
1014                     let tmp = PlaceRef::alloca(bx, op.layout);
1015                     bx.lifetime_start(tmp.llval, tmp.layout.size);
1016                     op.val.store(bx, tmp);
1017                     op.val = Ref(tmp.llval, None, tmp.align);
1018                     copied_constant_arguments.push(tmp);
1019                 }
1020                 _ => {}
1021             }
1022
1023             self.codegen_argument(bx, op, &mut llargs, &fn_abi.args[i]);
1024         }
1025         let num_untupled = untuple.map(|tup| {
1026             self.codegen_arguments_untupled(bx, tup, &mut llargs, &fn_abi.args[first_args.len()..])
1027         });
1028
1029         let needs_location =
1030             instance.map_or(false, |i| i.def.requires_caller_location(self.cx.tcx()));
1031         if needs_location {
1032             let mir_args = if let Some(num_untupled) = num_untupled {
1033                 first_args.len() + num_untupled
1034             } else {
1035                 args.len()
1036             };
1037             assert_eq!(
1038                 fn_abi.args.len(),
1039                 mir_args + 1,
1040                 "#[track_caller] fn's must have 1 more argument in their ABI than in their MIR: {:?} {:?} {:?}",
1041                 instance,
1042                 fn_span,
1043                 fn_abi,
1044             );
1045             let location =
1046                 self.get_caller_location(bx, mir::SourceInfo { span: fn_span, ..source_info });
1047             debug!(
1048                 "codegen_call_terminator({:?}): location={:?} (fn_span {:?})",
1049                 terminator, location, fn_span
1050             );
1051
1052             let last_arg = fn_abi.args.last().unwrap();
1053             self.codegen_argument(bx, location, &mut llargs, last_arg);
1054         }
1055
1056         let (is_indirect_call, fn_ptr) = match (llfn, instance) {
1057             (Some(llfn), _) => (true, llfn),
1058             (None, Some(instance)) => (false, bx.get_fn_addr(instance)),
1059             _ => span_bug!(span, "no llfn for call"),
1060         };
1061
1062         // For backends that support CFI using type membership (i.e., testing whether a given
1063         // pointer is associated with a type identifier).
1064         if bx.tcx().sess.is_sanitizer_cfi_enabled() && is_indirect_call {
1065             // Emit type metadata and checks.
1066             // FIXME(rcvalle): Add support for generalized identifiers.
1067             // FIXME(rcvalle): Create distinct unnamed MDNodes for internal identifiers.
1068             let typeid = typeid_for_fnabi(bx.tcx(), fn_abi);
1069             let typeid_metadata = self.cx.typeid_metadata(typeid);
1070
1071             // Test whether the function pointer is associated with the type identifier.
1072             let cond = bx.type_test(fn_ptr, typeid_metadata);
1073             let bb_pass = bx.append_sibling_block("type_test.pass");
1074             let bb_fail = bx.append_sibling_block("type_test.fail");
1075             bx.cond_br(cond, bb_pass, bb_fail);
1076
1077             bx.switch_to_block(bb_pass);
1078             let merging_succ = helper.do_call(
1079                 self,
1080                 bx,
1081                 fn_abi,
1082                 fn_ptr,
1083                 &llargs,
1084                 target.as_ref().map(|&target| (ret_dest, target)),
1085                 cleanup,
1086                 &copied_constant_arguments,
1087                 false,
1088             );
1089             assert_eq!(merging_succ, MergingSucc::False);
1090
1091             bx.switch_to_block(bb_fail);
1092             bx.abort();
1093             bx.unreachable();
1094
1095             return MergingSucc::False;
1096         }
1097
1098         helper.do_call(
1099             self,
1100             bx,
1101             fn_abi,
1102             fn_ptr,
1103             &llargs,
1104             target.as_ref().map(|&target| (ret_dest, target)),
1105             cleanup,
1106             &copied_constant_arguments,
1107             mergeable_succ,
1108         )
1109     }
1110
1111     fn codegen_asm_terminator(
1112         &mut self,
1113         helper: TerminatorCodegenHelper<'tcx>,
1114         bx: &mut Bx,
1115         terminator: &mir::Terminator<'tcx>,
1116         template: &[ast::InlineAsmTemplatePiece],
1117         operands: &[mir::InlineAsmOperand<'tcx>],
1118         options: ast::InlineAsmOptions,
1119         line_spans: &[Span],
1120         destination: Option<mir::BasicBlock>,
1121         cleanup: Option<mir::BasicBlock>,
1122         instance: Instance<'_>,
1123         mergeable_succ: bool,
1124     ) -> MergingSucc {
1125         let span = terminator.source_info.span;
1126
1127         let operands: Vec<_> = operands
1128             .iter()
1129             .map(|op| match *op {
1130                 mir::InlineAsmOperand::In { reg, ref value } => {
1131                     let value = self.codegen_operand(bx, value);
1132                     InlineAsmOperandRef::In { reg, value }
1133                 }
1134                 mir::InlineAsmOperand::Out { reg, late, ref place } => {
1135                     let place = place.map(|place| self.codegen_place(bx, place.as_ref()));
1136                     InlineAsmOperandRef::Out { reg, late, place }
1137                 }
1138                 mir::InlineAsmOperand::InOut { reg, late, ref in_value, ref out_place } => {
1139                     let in_value = self.codegen_operand(bx, in_value);
1140                     let out_place =
1141                         out_place.map(|out_place| self.codegen_place(bx, out_place.as_ref()));
1142                     InlineAsmOperandRef::InOut { reg, late, in_value, out_place }
1143                 }
1144                 mir::InlineAsmOperand::Const { ref value } => {
1145                     let const_value = self
1146                         .eval_mir_constant(value)
1147                         .unwrap_or_else(|_| span_bug!(span, "asm const cannot be resolved"));
1148                     let string = common::asm_const_to_str(
1149                         bx.tcx(),
1150                         span,
1151                         const_value,
1152                         bx.layout_of(value.ty()),
1153                     );
1154                     InlineAsmOperandRef::Const { string }
1155                 }
1156                 mir::InlineAsmOperand::SymFn { ref value } => {
1157                     let literal = self.monomorphize(value.literal);
1158                     if let ty::FnDef(def_id, substs) = *literal.ty().kind() {
1159                         let instance = ty::Instance::resolve_for_fn_ptr(
1160                             bx.tcx(),
1161                             ty::ParamEnv::reveal_all(),
1162                             def_id,
1163                             substs,
1164                         )
1165                         .unwrap();
1166                         InlineAsmOperandRef::SymFn { instance }
1167                     } else {
1168                         span_bug!(span, "invalid type for asm sym (fn)");
1169                     }
1170                 }
1171                 mir::InlineAsmOperand::SymStatic { def_id } => {
1172                     InlineAsmOperandRef::SymStatic { def_id }
1173                 }
1174             })
1175             .collect();
1176
1177         helper.do_inlineasm(
1178             self,
1179             bx,
1180             template,
1181             &operands,
1182             options,
1183             line_spans,
1184             destination,
1185             cleanup,
1186             instance,
1187             mergeable_succ,
1188         )
1189     }
1190 }
1191
1192 impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
1193     pub fn codegen_block(&mut self, mut bb: mir::BasicBlock) {
1194         let llbb = match self.try_llbb(bb) {
1195             Some(llbb) => llbb,
1196             None => return,
1197         };
1198         let bx = &mut Bx::build(self.cx, llbb);
1199         let mir = self.mir;
1200
1201         // MIR basic blocks stop at any function call. This may not be the case
1202         // for the backend's basic blocks, in which case we might be able to
1203         // combine multiple MIR basic blocks into a single backend basic block.
1204         loop {
1205             let data = &mir[bb];
1206
1207             debug!("codegen_block({:?}={:?})", bb, data);
1208
1209             for statement in &data.statements {
1210                 self.codegen_statement(bx, statement);
1211             }
1212
1213             let merging_succ = self.codegen_terminator(bx, bb, data.terminator());
1214             if let MergingSucc::False = merging_succ {
1215                 break;
1216             }
1217
1218             // We are merging the successor into the produced backend basic
1219             // block. Record that the successor should be skipped when it is
1220             // reached.
1221             //
1222             // Note: we must not have already generated code for the successor.
1223             // This is implicitly ensured by the reverse postorder traversal,
1224             // and the assertion explicitly guarantees that.
1225             let mut successors = data.terminator().successors();
1226             let succ = successors.next().unwrap();
1227             assert!(matches!(self.cached_llbbs[succ], CachedLlbb::None));
1228             self.cached_llbbs[succ] = CachedLlbb::Skip;
1229             bb = succ;
1230         }
1231     }
1232
1233     fn codegen_terminator(
1234         &mut self,
1235         bx: &mut Bx,
1236         bb: mir::BasicBlock,
1237         terminator: &'tcx mir::Terminator<'tcx>,
1238     ) -> MergingSucc {
1239         debug!("codegen_terminator: {:?}", terminator);
1240
1241         // Create the cleanup bundle, if needed.
1242         let funclet_bb = self.cleanup_kinds[bb].funclet_bb(bb);
1243         let helper = TerminatorCodegenHelper { bb, terminator, funclet_bb };
1244
1245         let mergeable_succ = || {
1246             // Note: any call to `switch_to_block` will invalidate a `true` value
1247             // of `mergeable_succ`.
1248             let mut successors = terminator.successors();
1249             if let Some(succ) = successors.next()
1250                 && successors.next().is_none()
1251                 && let &[succ_pred] = self.mir.basic_blocks.predecessors()[succ].as_slice()
1252             {
1253                 // bb has a single successor, and bb is its only predecessor. This
1254                 // makes it a candidate for merging.
1255                 assert_eq!(succ_pred, bb);
1256                 true
1257             } else {
1258                 false
1259             }
1260         };
1261
1262         self.set_debug_loc(bx, terminator.source_info);
1263         match terminator.kind {
1264             mir::TerminatorKind::Resume => {
1265                 self.codegen_resume_terminator(helper, bx);
1266                 MergingSucc::False
1267             }
1268
1269             mir::TerminatorKind::Abort => {
1270                 self.codegen_abort_terminator(helper, bx, terminator);
1271                 MergingSucc::False
1272             }
1273
1274             mir::TerminatorKind::Goto { target } => {
1275                 helper.funclet_br(self, bx, target, mergeable_succ())
1276             }
1277
1278             mir::TerminatorKind::SwitchInt { ref discr, switch_ty, ref targets } => {
1279                 self.codegen_switchint_terminator(helper, bx, discr, switch_ty, targets);
1280                 MergingSucc::False
1281             }
1282
1283             mir::TerminatorKind::Return => {
1284                 self.codegen_return_terminator(bx);
1285                 MergingSucc::False
1286             }
1287
1288             mir::TerminatorKind::Unreachable => {
1289                 bx.unreachable();
1290                 MergingSucc::False
1291             }
1292
1293             mir::TerminatorKind::Drop { place, target, unwind } => {
1294                 self.codegen_drop_terminator(helper, bx, place, target, unwind, mergeable_succ())
1295             }
1296
1297             mir::TerminatorKind::Assert { ref cond, expected, ref msg, target, cleanup } => self
1298                 .codegen_assert_terminator(
1299                     helper,
1300                     bx,
1301                     terminator,
1302                     cond,
1303                     expected,
1304                     msg,
1305                     target,
1306                     cleanup,
1307                     mergeable_succ(),
1308                 ),
1309
1310             mir::TerminatorKind::DropAndReplace { .. } => {
1311                 bug!("undesugared DropAndReplace in codegen: {:?}", terminator);
1312             }
1313
1314             mir::TerminatorKind::Call {
1315                 ref func,
1316                 ref args,
1317                 destination,
1318                 target,
1319                 cleanup,
1320                 from_hir_call: _,
1321                 fn_span,
1322             } => self.codegen_call_terminator(
1323                 helper,
1324                 bx,
1325                 terminator,
1326                 func,
1327                 args,
1328                 destination,
1329                 target,
1330                 cleanup,
1331                 fn_span,
1332                 mergeable_succ(),
1333             ),
1334             mir::TerminatorKind::GeneratorDrop | mir::TerminatorKind::Yield { .. } => {
1335                 bug!("generator ops in codegen")
1336             }
1337             mir::TerminatorKind::FalseEdge { .. } | mir::TerminatorKind::FalseUnwind { .. } => {
1338                 bug!("borrowck false edges in codegen")
1339             }
1340
1341             mir::TerminatorKind::InlineAsm {
1342                 template,
1343                 ref operands,
1344                 options,
1345                 line_spans,
1346                 destination,
1347                 cleanup,
1348             } => self.codegen_asm_terminator(
1349                 helper,
1350                 bx,
1351                 terminator,
1352                 template,
1353                 operands,
1354                 options,
1355                 line_spans,
1356                 destination,
1357                 cleanup,
1358                 self.instance,
1359                 mergeable_succ(),
1360             ),
1361         }
1362     }
1363
1364     fn codegen_argument(
1365         &mut self,
1366         bx: &mut Bx,
1367         op: OperandRef<'tcx, Bx::Value>,
1368         llargs: &mut Vec<Bx::Value>,
1369         arg: &ArgAbi<'tcx, Ty<'tcx>>,
1370     ) {
1371         match arg.mode {
1372             PassMode::Ignore => return,
1373             PassMode::Cast(_, true) => {
1374                 // Fill padding with undef value, where applicable.
1375                 llargs.push(bx.const_undef(bx.reg_backend_type(&Reg::i32())));
1376             }
1377             PassMode::Pair(..) => match op.val {
1378                 Pair(a, b) => {
1379                     llargs.push(a);
1380                     llargs.push(b);
1381                     return;
1382                 }
1383                 _ => bug!("codegen_argument: {:?} invalid for pair argument", op),
1384             },
1385             PassMode::Indirect { attrs: _, extra_attrs: Some(_), on_stack: _ } => match op.val {
1386                 Ref(a, Some(b), _) => {
1387                     llargs.push(a);
1388                     llargs.push(b);
1389                     return;
1390                 }
1391                 _ => bug!("codegen_argument: {:?} invalid for unsized indirect argument", op),
1392             },
1393             _ => {}
1394         }
1395
1396         // Force by-ref if we have to load through a cast pointer.
1397         let (mut llval, align, by_ref) = match op.val {
1398             Immediate(_) | Pair(..) => match arg.mode {
1399                 PassMode::Indirect { .. } | PassMode::Cast(..) => {
1400                     let scratch = PlaceRef::alloca(bx, arg.layout);
1401                     op.val.store(bx, scratch);
1402                     (scratch.llval, scratch.align, true)
1403                 }
1404                 _ => (op.immediate_or_packed_pair(bx), arg.layout.align.abi, false),
1405             },
1406             Ref(llval, _, align) => {
1407                 if arg.is_indirect() && align < arg.layout.align.abi {
1408                     // `foo(packed.large_field)`. We can't pass the (unaligned) field directly. I
1409                     // think that ATM (Rust 1.16) we only pass temporaries, but we shouldn't
1410                     // have scary latent bugs around.
1411
1412                     let scratch = PlaceRef::alloca(bx, arg.layout);
1413                     base::memcpy_ty(
1414                         bx,
1415                         scratch.llval,
1416                         scratch.align,
1417                         llval,
1418                         align,
1419                         op.layout,
1420                         MemFlags::empty(),
1421                     );
1422                     (scratch.llval, scratch.align, true)
1423                 } else {
1424                     (llval, align, true)
1425                 }
1426             }
1427         };
1428
1429         if by_ref && !arg.is_indirect() {
1430             // Have to load the argument, maybe while casting it.
1431             if let PassMode::Cast(ty, _) = &arg.mode {
1432                 let llty = bx.cast_backend_type(ty);
1433                 let addr = bx.pointercast(llval, bx.type_ptr_to(llty));
1434                 llval = bx.load(llty, addr, align.min(arg.layout.align.abi));
1435             } else {
1436                 // We can't use `PlaceRef::load` here because the argument
1437                 // may have a type we don't treat as immediate, but the ABI
1438                 // used for this call is passing it by-value. In that case,
1439                 // the load would just produce `OperandValue::Ref` instead
1440                 // of the `OperandValue::Immediate` we need for the call.
1441                 llval = bx.load(bx.backend_type(arg.layout), llval, align);
1442                 if let abi::Abi::Scalar(scalar) = arg.layout.abi {
1443                     if scalar.is_bool() {
1444                         bx.range_metadata(llval, WrappingRange { start: 0, end: 1 });
1445                     }
1446                 }
1447                 // We store bools as `i8` so we need to truncate to `i1`.
1448                 llval = bx.to_immediate(llval, arg.layout);
1449             }
1450         }
1451
1452         llargs.push(llval);
1453     }
1454
1455     fn codegen_arguments_untupled(
1456         &mut self,
1457         bx: &mut Bx,
1458         operand: &mir::Operand<'tcx>,
1459         llargs: &mut Vec<Bx::Value>,
1460         args: &[ArgAbi<'tcx, Ty<'tcx>>],
1461     ) -> usize {
1462         let tuple = self.codegen_operand(bx, operand);
1463
1464         // Handle both by-ref and immediate tuples.
1465         if let Ref(llval, None, align) = tuple.val {
1466             let tuple_ptr = PlaceRef::new_sized_aligned(llval, tuple.layout, align);
1467             for i in 0..tuple.layout.fields.count() {
1468                 let field_ptr = tuple_ptr.project_field(bx, i);
1469                 let field = bx.load_operand(field_ptr);
1470                 self.codegen_argument(bx, field, llargs, &args[i]);
1471             }
1472         } else if let Ref(_, Some(_), _) = tuple.val {
1473             bug!("closure arguments must be sized")
1474         } else {
1475             // If the tuple is immediate, the elements are as well.
1476             for i in 0..tuple.layout.fields.count() {
1477                 let op = tuple.extract_field(bx, i);
1478                 self.codegen_argument(bx, op, llargs, &args[i]);
1479             }
1480         }
1481         tuple.layout.fields.count()
1482     }
1483
1484     fn get_caller_location(
1485         &mut self,
1486         bx: &mut Bx,
1487         mut source_info: mir::SourceInfo,
1488     ) -> OperandRef<'tcx, Bx::Value> {
1489         let tcx = bx.tcx();
1490
1491         let mut span_to_caller_location = |span: Span| {
1492             let topmost = span.ctxt().outer_expn().expansion_cause().unwrap_or(span);
1493             let caller = tcx.sess.source_map().lookup_char_pos(topmost.lo());
1494             let const_loc = tcx.const_caller_location((
1495                 Symbol::intern(&caller.file.name.prefer_remapped().to_string_lossy()),
1496                 caller.line as u32,
1497                 caller.col_display as u32 + 1,
1498             ));
1499             OperandRef::from_const(bx, const_loc, bx.tcx().caller_location_ty())
1500         };
1501
1502         // Walk up the `SourceScope`s, in case some of them are from MIR inlining.
1503         // If so, the starting `source_info.span` is in the innermost inlined
1504         // function, and will be replaced with outer callsite spans as long
1505         // as the inlined functions were `#[track_caller]`.
1506         loop {
1507             let scope_data = &self.mir.source_scopes[source_info.scope];
1508
1509             if let Some((callee, callsite_span)) = scope_data.inlined {
1510                 // Stop inside the most nested non-`#[track_caller]` function,
1511                 // before ever reaching its caller (which is irrelevant).
1512                 if !callee.def.requires_caller_location(tcx) {
1513                     return span_to_caller_location(source_info.span);
1514                 }
1515                 source_info.span = callsite_span;
1516             }
1517
1518             // Skip past all of the parents with `inlined: None`.
1519             match scope_data.inlined_parent_scope {
1520                 Some(parent) => source_info.scope = parent,
1521                 None => break,
1522             }
1523         }
1524
1525         // No inlined `SourceScope`s, or all of them were `#[track_caller]`.
1526         self.caller_location.unwrap_or_else(|| span_to_caller_location(source_info.span))
1527     }
1528
1529     fn get_personality_slot(&mut self, bx: &mut Bx) -> PlaceRef<'tcx, Bx::Value> {
1530         let cx = bx.cx();
1531         if let Some(slot) = self.personality_slot {
1532             slot
1533         } else {
1534             let layout = cx.layout_of(
1535                 cx.tcx().intern_tup(&[cx.tcx().mk_mut_ptr(cx.tcx().types.u8), cx.tcx().types.i32]),
1536             );
1537             let slot = PlaceRef::alloca(bx, layout);
1538             self.personality_slot = Some(slot);
1539             slot
1540         }
1541     }
1542
1543     /// Returns the landing/cleanup pad wrapper around the given basic block.
1544     // FIXME(eddyb) rename this to `eh_pad_for`.
1545     fn landing_pad_for(&mut self, bb: mir::BasicBlock) -> Bx::BasicBlock {
1546         if let Some(landing_pad) = self.landing_pads[bb] {
1547             return landing_pad;
1548         }
1549
1550         let landing_pad = self.landing_pad_for_uncached(bb);
1551         self.landing_pads[bb] = Some(landing_pad);
1552         landing_pad
1553     }
1554
1555     // FIXME(eddyb) rename this to `eh_pad_for_uncached`.
1556     fn landing_pad_for_uncached(&mut self, bb: mir::BasicBlock) -> Bx::BasicBlock {
1557         let llbb = self.llbb(bb);
1558         if base::wants_msvc_seh(self.cx.sess()) {
1559             let funclet;
1560             let ret_llbb;
1561             match self.mir[bb].terminator.as_ref().map(|t| &t.kind) {
1562                 // This is a basic block that we're aborting the program for,
1563                 // notably in an `extern` function. These basic blocks are inserted
1564                 // so that we assert that `extern` functions do indeed not panic,
1565                 // and if they do we abort the process.
1566                 //
1567                 // On MSVC these are tricky though (where we're doing funclets). If
1568                 // we were to do a cleanuppad (like below) the normal functions like
1569                 // `longjmp` would trigger the abort logic, terminating the
1570                 // program. Instead we insert the equivalent of `catch(...)` for C++
1571                 // which magically doesn't trigger when `longjmp` files over this
1572                 // frame.
1573                 //
1574                 // Lots more discussion can be found on #48251 but this codegen is
1575                 // modeled after clang's for:
1576                 //
1577                 //      try {
1578                 //          foo();
1579                 //      } catch (...) {
1580                 //          bar();
1581                 //      }
1582                 Some(&mir::TerminatorKind::Abort) => {
1583                     let cs_llbb =
1584                         Bx::append_block(self.cx, self.llfn, &format!("cs_funclet{:?}", bb));
1585                     let cp_llbb =
1586                         Bx::append_block(self.cx, self.llfn, &format!("cp_funclet{:?}", bb));
1587                     ret_llbb = cs_llbb;
1588
1589                     let mut cs_bx = Bx::build(self.cx, cs_llbb);
1590                     let cs = cs_bx.catch_switch(None, None, &[cp_llbb]);
1591
1592                     // The "null" here is actually a RTTI type descriptor for the
1593                     // C++ personality function, but `catch (...)` has no type so
1594                     // it's null. The 64 here is actually a bitfield which
1595                     // represents that this is a catch-all block.
1596                     let mut cp_bx = Bx::build(self.cx, cp_llbb);
1597                     let null = cp_bx.const_null(
1598                         cp_bx.type_i8p_ext(cp_bx.cx().data_layout().instruction_address_space),
1599                     );
1600                     let sixty_four = cp_bx.const_i32(64);
1601                     funclet = cp_bx.catch_pad(cs, &[null, sixty_four, null]);
1602                     cp_bx.br(llbb);
1603                 }
1604                 _ => {
1605                     let cleanup_llbb =
1606                         Bx::append_block(self.cx, self.llfn, &format!("funclet_{:?}", bb));
1607                     ret_llbb = cleanup_llbb;
1608                     let mut cleanup_bx = Bx::build(self.cx, cleanup_llbb);
1609                     funclet = cleanup_bx.cleanup_pad(None, &[]);
1610                     cleanup_bx.br(llbb);
1611                 }
1612             }
1613             self.funclets[bb] = Some(funclet);
1614             ret_llbb
1615         } else {
1616             let cleanup_llbb = Bx::append_block(self.cx, self.llfn, "cleanup");
1617             let mut cleanup_bx = Bx::build(self.cx, cleanup_llbb);
1618
1619             let llpersonality = self.cx.eh_personality();
1620             let llretty = self.landing_pad_type();
1621             let lp = cleanup_bx.cleanup_landing_pad(llretty, llpersonality);
1622
1623             let slot = self.get_personality_slot(&mut cleanup_bx);
1624             slot.storage_live(&mut cleanup_bx);
1625             Pair(cleanup_bx.extract_value(lp, 0), cleanup_bx.extract_value(lp, 1))
1626                 .store(&mut cleanup_bx, slot);
1627
1628             cleanup_bx.br(llbb);
1629             cleanup_llbb
1630         }
1631     }
1632
1633     fn landing_pad_type(&self) -> Bx::Type {
1634         let cx = self.cx;
1635         cx.type_struct(&[cx.type_i8p(), cx.type_i32()], false)
1636     }
1637
1638     fn unreachable_block(&mut self) -> Bx::BasicBlock {
1639         self.unreachable_block.unwrap_or_else(|| {
1640             let llbb = Bx::append_block(self.cx, self.llfn, "unreachable");
1641             let mut bx = Bx::build(self.cx, llbb);
1642             bx.unreachable();
1643             self.unreachable_block = Some(llbb);
1644             llbb
1645         })
1646     }
1647
1648     fn double_unwind_guard(&mut self) -> Bx::BasicBlock {
1649         self.double_unwind_guard.unwrap_or_else(|| {
1650             assert!(!base::wants_msvc_seh(self.cx.sess()));
1651
1652             let llbb = Bx::append_block(self.cx, self.llfn, "abort");
1653             let mut bx = Bx::build(self.cx, llbb);
1654             self.set_debug_loc(&mut bx, mir::SourceInfo::outermost(self.mir.span));
1655
1656             let llpersonality = self.cx.eh_personality();
1657             let llretty = self.landing_pad_type();
1658             bx.cleanup_landing_pad(llretty, llpersonality);
1659
1660             let (fn_abi, fn_ptr) = common::build_langcall(&bx, None, LangItem::PanicNoUnwind);
1661             let fn_ty = bx.fn_decl_backend_type(&fn_abi);
1662
1663             let llret = bx.call(fn_ty, Some(&fn_abi), fn_ptr, &[], None);
1664             bx.do_not_inline(llret);
1665
1666             bx.unreachable();
1667
1668             self.double_unwind_guard = Some(llbb);
1669             llbb
1670         })
1671     }
1672
1673     /// Get the backend `BasicBlock` for a MIR `BasicBlock`, either already
1674     /// cached in `self.cached_llbbs`, or created on demand (and cached).
1675     // FIXME(eddyb) rename `llbb` and other `ll`-prefixed things to use a
1676     // more backend-agnostic prefix such as `cg` (i.e. this would be `cgbb`).
1677     pub fn llbb(&mut self, bb: mir::BasicBlock) -> Bx::BasicBlock {
1678         self.try_llbb(bb).unwrap()
1679     }
1680
1681     /// Like `llbb`, but may fail if the basic block should be skipped.
1682     pub fn try_llbb(&mut self, bb: mir::BasicBlock) -> Option<Bx::BasicBlock> {
1683         match self.cached_llbbs[bb] {
1684             CachedLlbb::None => {
1685                 // FIXME(eddyb) only name the block if `fewer_names` is `false`.
1686                 let llbb = Bx::append_block(self.cx, self.llfn, &format!("{:?}", bb));
1687                 self.cached_llbbs[bb] = CachedLlbb::Some(llbb);
1688                 Some(llbb)
1689             }
1690             CachedLlbb::Some(llbb) => Some(llbb),
1691             CachedLlbb::Skip => None,
1692         }
1693     }
1694
1695     fn make_return_dest(
1696         &mut self,
1697         bx: &mut Bx,
1698         dest: mir::Place<'tcx>,
1699         fn_ret: &ArgAbi<'tcx, Ty<'tcx>>,
1700         llargs: &mut Vec<Bx::Value>,
1701         is_intrinsic: bool,
1702     ) -> ReturnDest<'tcx, Bx::Value> {
1703         // If the return is ignored, we can just return a do-nothing `ReturnDest`.
1704         if fn_ret.is_ignore() {
1705             return ReturnDest::Nothing;
1706         }
1707         let dest = if let Some(index) = dest.as_local() {
1708             match self.locals[index] {
1709                 LocalRef::Place(dest) => dest,
1710                 LocalRef::UnsizedPlace(_) => bug!("return type must be sized"),
1711                 LocalRef::Operand(None) => {
1712                     // Handle temporary places, specifically `Operand` ones, as
1713                     // they don't have `alloca`s.
1714                     return if fn_ret.is_indirect() {
1715                         // Odd, but possible, case, we have an operand temporary,
1716                         // but the calling convention has an indirect return.
1717                         let tmp = PlaceRef::alloca(bx, fn_ret.layout);
1718                         tmp.storage_live(bx);
1719                         llargs.push(tmp.llval);
1720                         ReturnDest::IndirectOperand(tmp, index)
1721                     } else if is_intrinsic {
1722                         // Currently, intrinsics always need a location to store
1723                         // the result, so we create a temporary `alloca` for the
1724                         // result.
1725                         let tmp = PlaceRef::alloca(bx, fn_ret.layout);
1726                         tmp.storage_live(bx);
1727                         ReturnDest::IndirectOperand(tmp, index)
1728                     } else {
1729                         ReturnDest::DirectOperand(index)
1730                     };
1731                 }
1732                 LocalRef::Operand(Some(_)) => {
1733                     bug!("place local already assigned to");
1734                 }
1735             }
1736         } else {
1737             self.codegen_place(
1738                 bx,
1739                 mir::PlaceRef { local: dest.local, projection: &dest.projection },
1740             )
1741         };
1742         if fn_ret.is_indirect() {
1743             if dest.align < dest.layout.align.abi {
1744                 // Currently, MIR code generation does not create calls
1745                 // that store directly to fields of packed structs (in
1746                 // fact, the calls it creates write only to temps).
1747                 //
1748                 // If someone changes that, please update this code path
1749                 // to create a temporary.
1750                 span_bug!(self.mir.span, "can't directly store to unaligned value");
1751             }
1752             llargs.push(dest.llval);
1753             ReturnDest::Nothing
1754         } else {
1755             ReturnDest::Store(dest)
1756         }
1757     }
1758
1759     fn codegen_transmute(&mut self, bx: &mut Bx, src: &mir::Operand<'tcx>, dst: mir::Place<'tcx>) {
1760         if let Some(index) = dst.as_local() {
1761             match self.locals[index] {
1762                 LocalRef::Place(place) => self.codegen_transmute_into(bx, src, place),
1763                 LocalRef::UnsizedPlace(_) => bug!("transmute must not involve unsized locals"),
1764                 LocalRef::Operand(None) => {
1765                     let dst_layout = bx.layout_of(self.monomorphized_place_ty(dst.as_ref()));
1766                     assert!(!dst_layout.ty.has_erasable_regions());
1767                     let place = PlaceRef::alloca(bx, dst_layout);
1768                     place.storage_live(bx);
1769                     self.codegen_transmute_into(bx, src, place);
1770                     let op = bx.load_operand(place);
1771                     place.storage_dead(bx);
1772                     self.locals[index] = LocalRef::Operand(Some(op));
1773                     self.debug_introduce_local(bx, index);
1774                 }
1775                 LocalRef::Operand(Some(op)) => {
1776                     assert!(op.layout.is_zst(), "assigning to initialized SSAtemp");
1777                 }
1778             }
1779         } else {
1780             let dst = self.codegen_place(bx, dst.as_ref());
1781             self.codegen_transmute_into(bx, src, dst);
1782         }
1783     }
1784
1785     fn codegen_transmute_into(
1786         &mut self,
1787         bx: &mut Bx,
1788         src: &mir::Operand<'tcx>,
1789         dst: PlaceRef<'tcx, Bx::Value>,
1790     ) {
1791         let src = self.codegen_operand(bx, src);
1792
1793         // Special-case transmutes between scalars as simple bitcasts.
1794         match (src.layout.abi, dst.layout.abi) {
1795             (abi::Abi::Scalar(src_scalar), abi::Abi::Scalar(dst_scalar)) => {
1796                 // HACK(eddyb) LLVM doesn't like `bitcast`s between pointers and non-pointers.
1797                 if (src_scalar.primitive() == abi::Pointer)
1798                     == (dst_scalar.primitive() == abi::Pointer)
1799                 {
1800                     assert_eq!(src.layout.size, dst.layout.size);
1801
1802                     // NOTE(eddyb) the `from_immediate` and `to_immediate_scalar`
1803                     // conversions allow handling `bool`s the same as `u8`s.
1804                     let src = bx.from_immediate(src.immediate());
1805                     let src_as_dst = bx.bitcast(src, bx.backend_type(dst.layout));
1806                     Immediate(bx.to_immediate_scalar(src_as_dst, dst_scalar)).store(bx, dst);
1807                     return;
1808                 }
1809             }
1810             _ => {}
1811         }
1812
1813         let llty = bx.backend_type(src.layout);
1814         let cast_ptr = bx.pointercast(dst.llval, bx.type_ptr_to(llty));
1815         let align = src.layout.align.abi.min(dst.align);
1816         src.val.store(bx, PlaceRef::new_sized_aligned(cast_ptr, src.layout, align));
1817     }
1818
1819     // Stores the return value of a function call into it's final location.
1820     fn store_return(
1821         &mut self,
1822         bx: &mut Bx,
1823         dest: ReturnDest<'tcx, Bx::Value>,
1824         ret_abi: &ArgAbi<'tcx, Ty<'tcx>>,
1825         llval: Bx::Value,
1826     ) {
1827         use self::ReturnDest::*;
1828
1829         match dest {
1830             Nothing => (),
1831             Store(dst) => bx.store_arg(&ret_abi, llval, dst),
1832             IndirectOperand(tmp, index) => {
1833                 let op = bx.load_operand(tmp);
1834                 tmp.storage_dead(bx);
1835                 self.locals[index] = LocalRef::Operand(Some(op));
1836                 self.debug_introduce_local(bx, index);
1837             }
1838             DirectOperand(index) => {
1839                 // If there is a cast, we have to store and reload.
1840                 let op = if let PassMode::Cast(..) = ret_abi.mode {
1841                     let tmp = PlaceRef::alloca(bx, ret_abi.layout);
1842                     tmp.storage_live(bx);
1843                     bx.store_arg(&ret_abi, llval, tmp);
1844                     let op = bx.load_operand(tmp);
1845                     tmp.storage_dead(bx);
1846                     op
1847                 } else {
1848                     OperandRef::from_immediate_or_packed_pair(bx, llval, ret_abi.layout)
1849                 };
1850                 self.locals[index] = LocalRef::Operand(Some(op));
1851                 self.debug_introduce_local(bx, index);
1852             }
1853         }
1854     }
1855 }
1856
1857 enum ReturnDest<'tcx, V> {
1858     // Do nothing; the return value is indirect or ignored.
1859     Nothing,
1860     // Store the return value to the pointer.
1861     Store(PlaceRef<'tcx, V>),
1862     // Store an indirect return value to an operand local place.
1863     IndirectOperand(PlaceRef<'tcx, V>, mir::Local),
1864     // Store a direct return value to an operand local place.
1865     DirectOperand(mir::Local),
1866 }