1 use super::operand::OperandRef;
2 use super::operand::OperandValue::{Immediate, Pair, Ref};
3 use super::place::PlaceRef;
4 use super::{FunctionCx, LocalRef};
7 use crate::common::{self, IntPredicate};
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, HasDataLayout, LayoutOf};
24 use rustc_target::spec::abi::Abi;
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> {
30 terminator: &'tcx mir::Terminator<'tcx>,
31 funclet_bb: Option<mir::BasicBlock>,
34 impl<'a, 'tcx> TerminatorCodegenHelper<'tcx> {
35 /// Returns the appropriate `Funclet` for the current funclet, if on MSVC,
36 /// either already previously cached, or newly created, by `landing_pad_for`.
37 fn funclet<'b, Bx: BuilderMethods<'a, 'tcx>>(
39 fx: &'b mut FunctionCx<'a, 'tcx, Bx>,
40 ) -> Option<&'b Bx::Funclet> {
41 let funclet_bb = self.funclet_bb?;
42 if base::wants_msvc_seh(fx.cx.tcx().sess) {
43 // If `landing_pad_for` hasn't been called yet to create the `Funclet`,
44 // it has to be now. This may not seem necessary, as RPO should lead
45 // to all the unwind edges being visited (and so to `landing_pad_for`
46 // getting called for them), before building any of the blocks inside
47 // the funclet itself - however, if MIR contains edges that end up not
48 // being needed in the LLVM IR after monomorphization, the funclet may
49 // be unreachable, and we don't have yet a way to skip building it in
50 // such an eventuality (which may be a better solution than this).
51 if fx.funclets[funclet_bb].is_none() {
52 fx.landing_pad_for(funclet_bb);
56 fx.funclets[funclet_bb]
58 .expect("landing_pad_for didn't also create funclets entry"),
65 fn lltarget<Bx: BuilderMethods<'a, 'tcx>>(
67 fx: &mut FunctionCx<'a, 'tcx, Bx>,
68 target: mir::BasicBlock,
69 ) -> (Bx::BasicBlock, bool) {
70 let span = self.terminator.source_info.span;
71 let lltarget = fx.llbb(target);
72 let target_funclet = fx.cleanup_kinds[target].funclet_bb(target);
73 match (self.funclet_bb, target_funclet) {
74 (None, None) => (lltarget, false),
75 (Some(f), Some(t_f)) if f == t_f || !base::wants_msvc_seh(fx.cx.tcx().sess) => {
78 // jump *into* cleanup - need a landing pad if GNU, cleanup pad if MSVC
79 (None, Some(_)) => (fx.landing_pad_for(target), false),
80 (Some(_), None) => span_bug!(span, "{:?} - jump out of cleanup?", self.terminator),
81 (Some(_), Some(_)) => (fx.landing_pad_for(target), true),
85 /// Create a basic block.
86 fn llblock<Bx: BuilderMethods<'a, 'tcx>>(
88 fx: &mut FunctionCx<'a, 'tcx, Bx>,
89 target: mir::BasicBlock,
91 let (lltarget, is_cleanupret) = self.lltarget(fx, target);
93 // MSVC cross-funclet jump - need a trampoline
95 debug!("llblock: creating cleanup trampoline for {:?}", target);
96 let name = &format!("{:?}_cleanup_trampoline_{:?}", self.bb, target);
97 let mut trampoline = fx.new_block(name);
98 trampoline.cleanup_ret(self.funclet(fx).unwrap(), Some(lltarget));
105 fn funclet_br<Bx: BuilderMethods<'a, 'tcx>>(
107 fx: &mut FunctionCx<'a, 'tcx, Bx>,
109 target: mir::BasicBlock,
111 let (lltarget, is_cleanupret) = self.lltarget(fx, target);
113 // micro-optimization: generate a `ret` rather than a jump
115 bx.cleanup_ret(self.funclet(fx).unwrap(), Some(lltarget));
121 /// Call `fn_ptr` of `fn_abi` with the arguments `llargs`, the optional
122 /// return destination `destination` and the cleanup function `cleanup`.
123 fn do_call<Bx: BuilderMethods<'a, 'tcx>>(
125 fx: &mut FunctionCx<'a, 'tcx, Bx>,
127 fn_abi: FnAbi<'tcx, Ty<'tcx>>,
129 llargs: &[Bx::Value],
130 destination: Option<(ReturnDest<'tcx, Bx::Value>, mir::BasicBlock)>,
131 cleanup: Option<mir::BasicBlock>,
133 // If there is a cleanup block and the function we're calling can unwind, then
134 // do an invoke, otherwise do a call.
135 if let Some(cleanup) = cleanup.filter(|_| fn_abi.can_unwind) {
136 let ret_llbb = if let Some((_, target)) = destination {
139 fx.unreachable_block()
142 bx.invoke(fn_ptr, &llargs, ret_llbb, self.llblock(fx, cleanup), self.funclet(fx));
143 bx.apply_attrs_callsite(&fn_abi, invokeret);
145 if let Some((ret_dest, target)) = destination {
146 let mut ret_bx = fx.build_block(target);
147 fx.set_debug_loc(&mut ret_bx, self.terminator.source_info);
148 fx.store_return(&mut ret_bx, ret_dest, &fn_abi.ret, invokeret);
151 let llret = bx.call(fn_ptr, &llargs, self.funclet(fx));
152 bx.apply_attrs_callsite(&fn_abi, llret);
153 if fx.mir[self.bb].is_cleanup {
154 // Cleanup is always the cold path. Don't inline
155 // drop glue. Also, when there is a deeply-nested
156 // struct, there are "symmetry" issues that cause
157 // exponential inlining - see issue #41696.
158 bx.do_not_inline(llret);
161 if let Some((ret_dest, target)) = destination {
162 fx.store_return(bx, ret_dest, &fn_abi.ret, llret);
163 self.funclet_br(fx, bx, target);
171 /// Codegen implementations for some terminator variants.
172 impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
173 /// Generates code for a `Resume` terminator.
174 fn codegen_resume_terminator(&mut self, helper: TerminatorCodegenHelper<'tcx>, mut bx: Bx) {
175 if let Some(funclet) = helper.funclet(self) {
176 bx.cleanup_ret(funclet, None);
178 let slot = self.get_personality_slot(&mut bx);
179 let lp0 = slot.project_field(&mut bx, 0);
180 let lp0 = bx.load_operand(lp0).immediate();
181 let lp1 = slot.project_field(&mut bx, 1);
182 let lp1 = bx.load_operand(lp1).immediate();
183 slot.storage_dead(&mut bx);
185 let mut lp = bx.const_undef(self.landing_pad_type());
186 lp = bx.insert_value(lp, lp0, 0);
187 lp = bx.insert_value(lp, lp1, 1);
192 fn codegen_switchint_terminator(
194 helper: TerminatorCodegenHelper<'tcx>,
196 discr: &mir::Operand<'tcx>,
198 targets: &SwitchTargets,
200 let discr = self.codegen_operand(&mut bx, &discr);
201 // `switch_ty` is redundant, sanity-check that.
202 assert_eq!(discr.layout.ty, switch_ty);
203 let mut target_iter = targets.iter();
204 if target_iter.len() == 1 {
205 // If there are two targets (one conditional, one fallback), emit br instead of switch
206 let (test_value, target) = target_iter.next().unwrap();
207 let lltrue = helper.llblock(self, target);
208 let llfalse = helper.llblock(self, targets.otherwise());
209 if switch_ty == bx.tcx().types.bool {
210 // Don't generate trivial icmps when switching on bool
212 0 => bx.cond_br(discr.immediate(), llfalse, lltrue),
213 1 => bx.cond_br(discr.immediate(), lltrue, llfalse),
217 let switch_llty = bx.immediate_backend_type(bx.layout_of(switch_ty));
218 let llval = bx.const_uint_big(switch_llty, test_value);
219 let cmp = bx.icmp(IntPredicate::IntEQ, discr.immediate(), llval);
220 bx.cond_br(cmp, lltrue, llfalse);
225 helper.llblock(self, targets.otherwise()),
226 target_iter.map(|(value, target)| (value, helper.llblock(self, target))),
231 fn codegen_return_terminator(&mut self, mut bx: Bx) {
232 // Call `va_end` if this is the definition of a C-variadic function.
233 if self.fn_abi.c_variadic {
234 // The `VaList` "spoofed" argument is just after all the real arguments.
235 let va_list_arg_idx = self.fn_abi.args.len();
236 match self.locals[mir::Local::new(1 + va_list_arg_idx)] {
237 LocalRef::Place(va_list) => {
238 bx.va_end(va_list.llval);
240 _ => bug!("C-variadic function must have a `VaList` place"),
243 if self.fn_abi.ret.layout.abi.is_uninhabited() {
244 // Functions with uninhabited return values are marked `noreturn`,
245 // so we should make sure that we never actually do.
246 // We play it safe by using a well-defined `abort`, but we could go for immediate UB
247 // if that turns out to be helpful.
249 // `abort` does not terminate the block, so we still need to generate
250 // an `unreachable` terminator after it.
254 let llval = match self.fn_abi.ret.mode {
255 PassMode::Ignore | PassMode::Indirect { .. } => {
260 PassMode::Direct(_) | PassMode::Pair(..) => {
261 let op = self.codegen_consume(&mut bx, mir::Place::return_place().as_ref());
262 if let Ref(llval, _, align) = op.val {
263 bx.load(bx.backend_type(op.layout), llval, align)
265 op.immediate_or_packed_pair(&mut bx)
269 PassMode::Cast(cast_ty) => {
270 let op = match self.locals[mir::RETURN_PLACE] {
271 LocalRef::Operand(Some(op)) => op,
272 LocalRef::Operand(None) => bug!("use of return before def"),
273 LocalRef::Place(cg_place) => OperandRef {
274 val: Ref(cg_place.llval, None, cg_place.align),
275 layout: cg_place.layout,
277 LocalRef::UnsizedPlace(_) => bug!("return type must be sized"),
279 let llslot = match op.val {
280 Immediate(_) | Pair(..) => {
281 let scratch = PlaceRef::alloca(&mut bx, self.fn_abi.ret.layout);
282 op.val.store(&mut bx, scratch);
285 Ref(llval, _, align) => {
286 assert_eq!(align, op.layout.align.abi, "return place is unaligned!");
290 let ty = bx.cast_backend_type(&cast_ty);
291 let addr = bx.pointercast(llslot, bx.type_ptr_to(ty));
292 bx.load(ty, addr, self.fn_abi.ret.layout.align.abi)
298 fn codegen_drop_terminator(
300 helper: TerminatorCodegenHelper<'tcx>,
302 location: mir::Place<'tcx>,
303 target: mir::BasicBlock,
304 unwind: Option<mir::BasicBlock>,
306 let ty = location.ty(self.mir, bx.tcx()).ty;
307 let ty = self.monomorphize(ty);
308 let drop_fn = Instance::resolve_drop_in_place(bx.tcx(), ty);
310 if let ty::InstanceDef::DropGlue(_, None) = drop_fn.def {
311 // we don't actually need to drop anything.
312 helper.funclet_br(self, &mut bx, target);
316 let place = self.codegen_place(&mut bx, location.as_ref());
318 let mut args = if let Some(llextra) = place.llextra {
319 args2 = [place.llval, llextra];
322 args1 = [place.llval];
325 let (drop_fn, fn_abi) = match ty.kind() {
326 // FIXME(eddyb) perhaps move some of this logic into
327 // `Instance::resolve_drop_in_place`?
329 let virtual_drop = Instance {
330 def: ty::InstanceDef::Virtual(drop_fn.def_id(), 0),
331 substs: drop_fn.substs,
333 let fn_abi = FnAbi::of_instance(&bx, virtual_drop, &[]);
334 let vtable = args[1];
337 meth::VirtualIndex::from_index(ty::COMMON_VTABLE_ENTRIES_DROPINPLACE)
338 .get_fn(&mut bx, vtable, &fn_abi),
342 _ => (bx.get_fn_addr(drop_fn), FnAbi::of_instance(&bx, drop_fn, &[])),
350 Some((ReturnDest::Nothing, target)),
355 fn codegen_assert_terminator(
357 helper: TerminatorCodegenHelper<'tcx>,
359 terminator: &mir::Terminator<'tcx>,
360 cond: &mir::Operand<'tcx>,
362 msg: &mir::AssertMessage<'tcx>,
363 target: mir::BasicBlock,
364 cleanup: Option<mir::BasicBlock>,
366 let span = terminator.source_info.span;
367 let cond = self.codegen_operand(&mut bx, cond).immediate();
368 let mut const_cond = bx.const_to_opt_u128(cond, false).map(|c| c == 1);
370 // This case can currently arise only from functions marked
371 // with #[rustc_inherit_overflow_checks] and inlined from
372 // another crate (mostly core::num generic/#[inline] fns),
373 // while the current crate doesn't use overflow checks.
374 // NOTE: Unlike binops, negation doesn't have its own
375 // checked operation, just a comparison with the minimum
376 // value, so we have to check for the assert message.
377 if !bx.check_overflow() {
378 if let AssertKind::OverflowNeg(_) = *msg {
379 const_cond = Some(expected);
383 // Don't codegen the panic block if success if known.
384 if const_cond == Some(expected) {
385 helper.funclet_br(self, &mut bx, target);
389 // Pass the condition through llvm.expect for branch hinting.
390 let cond = bx.expect(cond, expected);
392 // Create the failure block and the conditional branch to it.
393 let lltarget = helper.llblock(self, target);
394 let panic_block = bx.build_sibling_block("panic");
396 bx.cond_br(cond, lltarget, panic_block.llbb());
398 bx.cond_br(cond, panic_block.llbb(), lltarget);
401 // After this point, bx is the block for the call to panic.
403 self.set_debug_loc(&mut bx, terminator.source_info);
405 // Get the location information.
406 let location = self.get_caller_location(&mut bx, terminator.source_info).immediate();
408 // Put together the arguments to the panic entry point.
409 let (lang_item, args) = match msg {
410 AssertKind::BoundsCheck { ref len, ref index } => {
411 let len = self.codegen_operand(&mut bx, len).immediate();
412 let index = self.codegen_operand(&mut bx, index).immediate();
413 // It's `fn panic_bounds_check(index: usize, len: usize)`,
414 // and `#[track_caller]` adds an implicit third argument.
415 (LangItem::PanicBoundsCheck, vec![index, len, location])
418 let msg_str = Symbol::intern(msg.description());
419 let msg = bx.const_str(msg_str);
420 // It's `pub fn panic(expr: &str)`, with the wide reference being passed
421 // as two arguments, and `#[track_caller]` adds an implicit third argument.
422 (LangItem::Panic, vec![msg.0, msg.1, location])
426 // Obtain the panic entry point.
427 let def_id = common::langcall(bx.tcx(), Some(span), "", lang_item);
428 let instance = ty::Instance::mono(bx.tcx(), def_id);
429 let fn_abi = FnAbi::of_instance(&bx, instance, &[]);
430 let llfn = bx.get_fn_addr(instance);
432 // Codegen the actual panic invoke/call.
433 helper.do_call(self, &mut bx, fn_abi, llfn, &args, None, cleanup);
436 /// Returns `true` if this is indeed a panic intrinsic and codegen is done.
437 fn codegen_panic_intrinsic(
439 helper: &TerminatorCodegenHelper<'tcx>,
441 intrinsic: Option<Symbol>,
442 instance: Option<Instance<'tcx>>,
443 source_info: mir::SourceInfo,
444 destination: &Option<(mir::Place<'tcx>, mir::BasicBlock)>,
445 cleanup: Option<mir::BasicBlock>,
447 // Emit a panic or a no-op for `assert_*` intrinsics.
448 // These are intrinsics that compile to panics so that we can get a message
449 // which mentions the offending type, even from a const context.
450 #[derive(Debug, PartialEq)]
451 enum AssertIntrinsic {
456 let panic_intrinsic = intrinsic.and_then(|i| match i {
457 sym::assert_inhabited => Some(AssertIntrinsic::Inhabited),
458 sym::assert_zero_valid => Some(AssertIntrinsic::ZeroValid),
459 sym::assert_uninit_valid => Some(AssertIntrinsic::UninitValid),
462 if let Some(intrinsic) = panic_intrinsic {
463 use AssertIntrinsic::*;
464 let ty = instance.unwrap().substs.type_at(0);
465 let layout = bx.layout_of(ty);
466 let do_panic = match intrinsic {
467 Inhabited => layout.abi.is_uninhabited(),
468 // We unwrap as the error type is `!`.
469 ZeroValid => !layout.might_permit_raw_init(bx, /*zero:*/ true).unwrap(),
470 // We unwrap as the error type is `!`.
471 UninitValid => !layout.might_permit_raw_init(bx, /*zero:*/ false).unwrap(),
474 let msg_str = with_no_trimmed_paths(|| {
475 if layout.abi.is_uninhabited() {
476 // Use this error even for the other intrinsics as it is more precise.
477 format!("attempted to instantiate uninhabited type `{}`", ty)
478 } else if intrinsic == ZeroValid {
479 format!("attempted to zero-initialize type `{}`, which is invalid", ty)
481 format!("attempted to leave type `{}` uninitialized, which is invalid", ty)
484 let msg = bx.const_str(Symbol::intern(&msg_str));
485 let location = self.get_caller_location(bx, source_info).immediate();
487 // Obtain the panic entry point.
488 // FIXME: dedup this with `codegen_assert_terminator` above.
490 common::langcall(bx.tcx(), Some(source_info.span), "", LangItem::Panic);
491 let instance = ty::Instance::mono(bx.tcx(), def_id);
492 let fn_abi = FnAbi::of_instance(bx, instance, &[]);
493 let llfn = bx.get_fn_addr(instance);
495 // Codegen the actual panic invoke/call.
501 &[msg.0, msg.1, location],
502 destination.as_ref().map(|(_, bb)| (ReturnDest::Nothing, *bb)),
507 let target = destination.as_ref().unwrap().1;
508 helper.funclet_br(self, bx, target)
516 fn codegen_call_terminator(
518 helper: TerminatorCodegenHelper<'tcx>,
520 terminator: &mir::Terminator<'tcx>,
521 func: &mir::Operand<'tcx>,
522 args: &[mir::Operand<'tcx>],
523 destination: &Option<(mir::Place<'tcx>, mir::BasicBlock)>,
524 cleanup: Option<mir::BasicBlock>,
527 let source_info = terminator.source_info;
528 let span = source_info.span;
530 // Create the callee. This is a fn ptr or zero-sized and hence a kind of scalar.
531 let callee = self.codegen_operand(&mut bx, func);
533 let (instance, mut llfn) = match *callee.layout.ty.kind() {
534 ty::FnDef(def_id, substs) => (
536 ty::Instance::resolve(bx.tcx(), ty::ParamEnv::reveal_all(), def_id, substs)
539 .polymorphize(bx.tcx()),
543 ty::FnPtr(_) => (None, Some(callee.immediate())),
544 _ => bug!("{} is not callable", callee.layout.ty),
546 let def = instance.map(|i| i.def);
548 if let Some(ty::InstanceDef::DropGlue(_, None)) = def {
549 // Empty drop glue; a no-op.
550 let &(_, target) = destination.as_ref().unwrap();
551 helper.funclet_br(self, &mut bx, target);
555 // FIXME(eddyb) avoid computing this if possible, when `instance` is
556 // available - right now `sig` is only needed for getting the `abi`
557 // and figuring out how many extra args were passed to a C-variadic `fn`.
558 let sig = callee.layout.ty.fn_sig(bx.tcx());
561 // Handle intrinsics old codegen wants Expr's for, ourselves.
562 let intrinsic = match def {
563 Some(ty::InstanceDef::Intrinsic(def_id)) => Some(bx.tcx().item_name(def_id)),
567 let extra_args = &args[sig.inputs().skip_binder().len()..];
568 let extra_args = extra_args
571 let op_ty = op_arg.ty(self.mir, bx.tcx());
572 self.monomorphize(op_ty)
574 .collect::<Vec<_>>();
576 let fn_abi = match instance {
577 Some(instance) => FnAbi::of_instance(&bx, instance, &extra_args),
578 None => FnAbi::of_fn_ptr(&bx, sig, &extra_args),
581 if intrinsic == Some(sym::transmute) {
582 if let Some(destination_ref) = destination.as_ref() {
583 let &(dest, target) = destination_ref;
584 self.codegen_transmute(&mut bx, &args[0], dest);
585 helper.funclet_br(self, &mut bx, target);
587 // If we are trying to transmute to an uninhabited type,
588 // it is likely there is no allotted destination. In fact,
589 // transmuting to an uninhabited type is UB, which means
590 // we can do what we like. Here, we declare that transmuting
591 // into an uninhabited type is impossible, so anything following
592 // it must be unreachable.
593 assert_eq!(fn_abi.ret.layout.abi, abi::Abi::Uninhabited);
599 if self.codegen_panic_intrinsic(
611 // The arguments we'll be passing. Plus one to account for outptr, if used.
612 let arg_count = fn_abi.args.len() + fn_abi.ret.is_indirect() as usize;
613 let mut llargs = Vec::with_capacity(arg_count);
615 // Prepare the return value destination
616 let ret_dest = if let Some((dest, _)) = *destination {
617 let is_intrinsic = intrinsic.is_some();
618 self.make_return_dest(&mut bx, dest, &fn_abi.ret, &mut llargs, is_intrinsic)
623 if intrinsic == Some(sym::caller_location) {
624 if let Some((_, target)) = destination.as_ref() {
626 .get_caller_location(&mut bx, mir::SourceInfo { span: fn_span, ..source_info });
628 if let ReturnDest::IndirectOperand(tmp, _) = ret_dest {
629 location.val.store(&mut bx, tmp);
631 self.store_return(&mut bx, ret_dest, &fn_abi.ret, location.immediate());
632 helper.funclet_br(self, &mut bx, *target);
638 None | Some(sym::drop_in_place) => {}
639 Some(sym::copy_nonoverlapping) => unreachable!(),
641 let dest = match ret_dest {
642 _ if fn_abi.ret.is_indirect() => llargs[0],
643 ReturnDest::Nothing => {
644 bx.const_undef(bx.type_ptr_to(bx.arg_memory_ty(&fn_abi.ret)))
646 ReturnDest::IndirectOperand(dst, _) | ReturnDest::Store(dst) => dst.llval,
647 ReturnDest::DirectOperand(_) => {
648 bug!("Cannot use direct operand with an intrinsic call")
652 let args: Vec<_> = args
656 // The indices passed to simd_shuffle* in the
657 // third argument must be constant. This is
658 // checked by const-qualification, which also
659 // promotes any complex rvalues to constants.
660 if i == 2 && intrinsic.as_str().starts_with("simd_shuffle") {
661 if let mir::Operand::Constant(constant) = arg {
662 let c = self.eval_mir_constant(constant);
664 self.simd_shuffle_indices(&bx, constant.span, constant.ty(), c);
666 val: Immediate(llval),
667 layout: bx.layout_of(ty),
670 span_bug!(span, "shuffle indices must be constant");
674 self.codegen_operand(&mut bx, arg)
678 Self::codegen_intrinsic_call(
680 *instance.as_ref().unwrap(),
687 if let ReturnDest::IndirectOperand(dst, _) = ret_dest {
688 self.store_return(&mut bx, ret_dest, &fn_abi.ret, dst.llval);
691 if let Some((_, target)) = *destination {
692 helper.funclet_br(self, &mut bx, target);
701 // Split the rust-call tupled arguments off.
702 let (first_args, untuple) = if abi == Abi::RustCall && !args.is_empty() {
703 let (tup, args) = args.split_last().unwrap();
709 'make_args: for (i, arg) in first_args.iter().enumerate() {
710 let mut op = self.codegen_operand(&mut bx, arg);
712 if let (0, Some(ty::InstanceDef::Virtual(_, idx))) = (i, def) {
713 if let Pair(..) = op.val {
714 // In the case of Rc<Self>, we need to explicitly pass a
715 // *mut RcBox<Self> with a Scalar (not ScalarPair) ABI. This is a hack
716 // that is understood elsewhere in the compiler as a method on
718 // To get a `*mut RcBox<Self>`, we just keep unwrapping newtypes until
719 // we get a value of a built-in pointer type
720 'descend_newtypes: while !op.layout.ty.is_unsafe_ptr()
721 && !op.layout.ty.is_region_ptr()
723 for i in 0..op.layout.fields.count() {
724 let field = op.extract_field(&mut bx, i);
725 if !field.layout.is_zst() {
726 // we found the one non-zero-sized field that is allowed
727 // now find *its* non-zero-sized field, or stop if it's a
730 continue 'descend_newtypes;
734 span_bug!(span, "receiver has no non-zero-sized fields {:?}", op);
737 // now that we have `*dyn Trait` or `&dyn Trait`, split it up into its
738 // data pointer and vtable. Look up the method in the vtable, and pass
739 // the data pointer as the first argument
741 Pair(data_ptr, meta) => {
743 meth::VirtualIndex::from_index(idx).get_fn(&mut bx, meta, &fn_abi),
745 llargs.push(data_ptr);
748 other => bug!("expected a Pair, got {:?}", other),
750 } else if let Ref(data_ptr, Some(meta), _) = op.val {
751 // by-value dynamic dispatch
752 llfn = Some(meth::VirtualIndex::from_index(idx).get_fn(&mut bx, meta, &fn_abi));
753 llargs.push(data_ptr);
756 span_bug!(span, "can't codegen a virtual call on {:?}", op);
760 // The callee needs to own the argument memory if we pass it
761 // by-ref, so make a local copy of non-immediate constants.
762 match (arg, op.val) {
763 (&mir::Operand::Copy(_), Ref(_, None, _))
764 | (&mir::Operand::Constant(_), Ref(_, None, _)) => {
765 let tmp = PlaceRef::alloca(&mut bx, op.layout);
766 op.val.store(&mut bx, tmp);
767 op.val = Ref(tmp.llval, None, tmp.align);
772 self.codegen_argument(&mut bx, op, &mut llargs, &fn_abi.args[i]);
774 if let Some(tup) = untuple {
775 self.codegen_arguments_untupled(
779 &fn_abi.args[first_args.len()..],
784 instance.map_or(false, |i| i.def.requires_caller_location(self.cx.tcx()));
789 "#[track_caller] fn's must have 1 more argument in their ABI than in their MIR",
792 self.get_caller_location(&mut bx, mir::SourceInfo { span: fn_span, ..source_info });
794 "codegen_call_terminator({:?}): location={:?} (fn_span {:?})",
795 terminator, location, fn_span
798 let last_arg = fn_abi.args.last().unwrap();
799 self.codegen_argument(&mut bx, location, &mut llargs, last_arg);
802 let fn_ptr = match (llfn, instance) {
803 (Some(llfn), _) => llfn,
804 (None, Some(instance)) => bx.get_fn_addr(instance),
805 _ => span_bug!(span, "no llfn for call"),
814 destination.as_ref().map(|&(_, target)| (ret_dest, target)),
819 fn codegen_asm_terminator(
821 helper: TerminatorCodegenHelper<'tcx>,
823 terminator: &mir::Terminator<'tcx>,
824 template: &[ast::InlineAsmTemplatePiece],
825 operands: &[mir::InlineAsmOperand<'tcx>],
826 options: ast::InlineAsmOptions,
828 destination: Option<mir::BasicBlock>,
830 let span = terminator.source_info.span;
832 let operands: Vec<_> = operands
834 .map(|op| match *op {
835 mir::InlineAsmOperand::In { reg, ref value } => {
836 let value = self.codegen_operand(&mut bx, value);
837 InlineAsmOperandRef::In { reg, value }
839 mir::InlineAsmOperand::Out { reg, late, ref place } => {
840 let place = place.map(|place| self.codegen_place(&mut bx, place.as_ref()));
841 InlineAsmOperandRef::Out { reg, late, place }
843 mir::InlineAsmOperand::InOut { reg, late, ref in_value, ref out_place } => {
844 let in_value = self.codegen_operand(&mut bx, in_value);
846 out_place.map(|out_place| self.codegen_place(&mut bx, out_place.as_ref()));
847 InlineAsmOperandRef::InOut { reg, late, in_value, out_place }
849 mir::InlineAsmOperand::Const { ref value } => {
850 let const_value = self
851 .eval_mir_constant(value)
852 .unwrap_or_else(|_| span_bug!(span, "asm const cannot be resolved"));
853 let string = common::asm_const_to_str(
857 bx.layout_of(value.ty()),
859 InlineAsmOperandRef::Const { string }
861 mir::InlineAsmOperand::SymFn { ref value } => {
862 let literal = self.monomorphize(value.literal);
863 if let ty::FnDef(def_id, substs) = *literal.ty().kind() {
864 let instance = ty::Instance::resolve_for_fn_ptr(
866 ty::ParamEnv::reveal_all(),
871 InlineAsmOperandRef::SymFn { instance }
873 span_bug!(span, "invalid type for asm sym (fn)");
876 mir::InlineAsmOperand::SymStatic { def_id } => {
877 InlineAsmOperandRef::SymStatic { def_id }
882 bx.codegen_inline_asm(template, &operands, options, line_spans);
884 if let Some(target) = destination {
885 helper.funclet_br(self, &mut bx, target);
892 impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
893 pub fn codegen_block(&mut self, bb: mir::BasicBlock) {
894 let mut bx = self.build_block(bb);
898 debug!("codegen_block({:?}={:?})", bb, data);
900 for statement in &data.statements {
901 bx = self.codegen_statement(bx, statement);
904 self.codegen_terminator(bx, bb, data.terminator());
907 fn codegen_terminator(
911 terminator: &'tcx mir::Terminator<'tcx>,
913 debug!("codegen_terminator: {:?}", terminator);
915 // Create the cleanup bundle, if needed.
916 let funclet_bb = self.cleanup_kinds[bb].funclet_bb(bb);
917 let helper = TerminatorCodegenHelper { bb, terminator, funclet_bb };
919 self.set_debug_loc(&mut bx, terminator.source_info);
920 match terminator.kind {
921 mir::TerminatorKind::Resume => self.codegen_resume_terminator(helper, bx),
923 mir::TerminatorKind::Abort => {
925 // `abort` does not terminate the block, so we still need to generate
926 // an `unreachable` terminator after it.
930 mir::TerminatorKind::Goto { target } => {
932 // This is an unconditional branch back to this same basic block. That means we
933 // have something like a `loop {}` statement. LLVM versions before 12.0
934 // miscompile this because they assume forward progress. For older versions
935 // try to handle just this specific case which comes up commonly in practice
936 // (e.g., in embedded code).
938 // NB: the `sideeffect` currently checks for the LLVM version used internally.
942 helper.funclet_br(self, &mut bx, target);
945 mir::TerminatorKind::SwitchInt { ref discr, switch_ty, ref targets } => {
946 self.codegen_switchint_terminator(helper, bx, discr, switch_ty, targets);
949 mir::TerminatorKind::Return => {
950 self.codegen_return_terminator(bx);
953 mir::TerminatorKind::Unreachable => {
957 mir::TerminatorKind::Drop { place, target, unwind } => {
958 self.codegen_drop_terminator(helper, bx, place, target, unwind);
961 mir::TerminatorKind::Assert { ref cond, expected, ref msg, target, cleanup } => {
962 self.codegen_assert_terminator(
963 helper, bx, terminator, cond, expected, msg, target, cleanup,
967 mir::TerminatorKind::DropAndReplace { .. } => {
968 bug!("undesugared DropAndReplace in codegen: {:?}", terminator);
971 mir::TerminatorKind::Call {
979 self.codegen_call_terminator(
990 mir::TerminatorKind::GeneratorDrop | mir::TerminatorKind::Yield { .. } => {
991 bug!("generator ops in codegen")
993 mir::TerminatorKind::FalseEdge { .. } | mir::TerminatorKind::FalseUnwind { .. } => {
994 bug!("borrowck false edges in codegen")
997 mir::TerminatorKind::InlineAsm {
1004 self.codegen_asm_terminator(
1018 fn codegen_argument(
1021 op: OperandRef<'tcx, Bx::Value>,
1022 llargs: &mut Vec<Bx::Value>,
1023 arg: &ArgAbi<'tcx, Ty<'tcx>>,
1025 // Fill padding with undef value, where applicable.
1026 if let Some(ty) = arg.pad {
1027 llargs.push(bx.const_undef(bx.reg_backend_type(&ty)))
1030 if arg.is_ignore() {
1034 if let PassMode::Pair(..) = arg.mode {
1041 _ => bug!("codegen_argument: {:?} invalid for pair argument", op),
1043 } else if arg.is_unsized_indirect() {
1045 Ref(a, Some(b), _) => {
1050 _ => bug!("codegen_argument: {:?} invalid for unsized indirect argument", op),
1054 // Force by-ref if we have to load through a cast pointer.
1055 let (mut llval, align, by_ref) = match op.val {
1056 Immediate(_) | Pair(..) => match arg.mode {
1057 PassMode::Indirect { .. } | PassMode::Cast(_) => {
1058 let scratch = PlaceRef::alloca(bx, arg.layout);
1059 op.val.store(bx, scratch);
1060 (scratch.llval, scratch.align, true)
1062 _ => (op.immediate_or_packed_pair(bx), arg.layout.align.abi, false),
1064 Ref(llval, _, align) => {
1065 if arg.is_indirect() && align < arg.layout.align.abi {
1066 // `foo(packed.large_field)`. We can't pass the (unaligned) field directly. I
1067 // think that ATM (Rust 1.16) we only pass temporaries, but we shouldn't
1068 // have scary latent bugs around.
1070 let scratch = PlaceRef::alloca(bx, arg.layout);
1080 (scratch.llval, scratch.align, true)
1082 (llval, align, true)
1087 if by_ref && !arg.is_indirect() {
1088 // Have to load the argument, maybe while casting it.
1089 if let PassMode::Cast(ty) = arg.mode {
1090 let llty = bx.cast_backend_type(&ty);
1091 let addr = bx.pointercast(llval, bx.type_ptr_to(llty));
1092 llval = bx.load(llty, addr, align.min(arg.layout.align.abi));
1094 // We can't use `PlaceRef::load` here because the argument
1095 // may have a type we don't treat as immediate, but the ABI
1096 // used for this call is passing it by-value. In that case,
1097 // the load would just produce `OperandValue::Ref` instead
1098 // of the `OperandValue::Immediate` we need for the call.
1099 llval = bx.load(bx.backend_type(arg.layout), llval, align);
1100 if let abi::Abi::Scalar(ref scalar) = arg.layout.abi {
1101 if scalar.is_bool() {
1102 bx.range_metadata(llval, 0..2);
1105 // We store bools as `i8` so we need to truncate to `i1`.
1106 llval = bx.to_immediate(llval, arg.layout);
1113 fn codegen_arguments_untupled(
1116 operand: &mir::Operand<'tcx>,
1117 llargs: &mut Vec<Bx::Value>,
1118 args: &[ArgAbi<'tcx, Ty<'tcx>>],
1120 let tuple = self.codegen_operand(bx, operand);
1122 // Handle both by-ref and immediate tuples.
1123 if let Ref(llval, None, align) = tuple.val {
1124 let tuple_ptr = PlaceRef::new_sized_aligned(llval, tuple.layout, align);
1125 for i in 0..tuple.layout.fields.count() {
1126 let field_ptr = tuple_ptr.project_field(bx, i);
1127 let field = bx.load_operand(field_ptr);
1128 self.codegen_argument(bx, field, llargs, &args[i]);
1130 } else if let Ref(_, Some(_), _) = tuple.val {
1131 bug!("closure arguments must be sized")
1133 // If the tuple is immediate, the elements are as well.
1134 for i in 0..tuple.layout.fields.count() {
1135 let op = tuple.extract_field(bx, i);
1136 self.codegen_argument(bx, op, llargs, &args[i]);
1141 fn get_caller_location(
1144 mut source_info: mir::SourceInfo,
1145 ) -> OperandRef<'tcx, Bx::Value> {
1148 let mut span_to_caller_location = |span: Span| {
1149 let topmost = span.ctxt().outer_expn().expansion_cause().unwrap_or(span);
1150 let caller = tcx.sess.source_map().lookup_char_pos(topmost.lo());
1151 let const_loc = tcx.const_caller_location((
1152 Symbol::intern(&caller.file.name.prefer_remapped().to_string_lossy()),
1154 caller.col_display as u32 + 1,
1156 OperandRef::from_const(bx, const_loc, bx.tcx().caller_location_ty())
1159 // Walk up the `SourceScope`s, in case some of them are from MIR inlining.
1160 // If so, the starting `source_info.span` is in the innermost inlined
1161 // function, and will be replaced with outer callsite spans as long
1162 // as the inlined functions were `#[track_caller]`.
1164 let scope_data = &self.mir.source_scopes[source_info.scope];
1166 if let Some((callee, callsite_span)) = scope_data.inlined {
1167 // Stop inside the most nested non-`#[track_caller]` function,
1168 // before ever reaching its caller (which is irrelevant).
1169 if !callee.def.requires_caller_location(tcx) {
1170 return span_to_caller_location(source_info.span);
1172 source_info.span = callsite_span;
1175 // Skip past all of the parents with `inlined: None`.
1176 match scope_data.inlined_parent_scope {
1177 Some(parent) => source_info.scope = parent,
1182 // No inlined `SourceScope`s, or all of them were `#[track_caller]`.
1183 self.caller_location.unwrap_or_else(|| span_to_caller_location(source_info.span))
1186 fn get_personality_slot(&mut self, bx: &mut Bx) -> PlaceRef<'tcx, Bx::Value> {
1188 if let Some(slot) = self.personality_slot {
1191 let layout = cx.layout_of(
1192 cx.tcx().intern_tup(&[cx.tcx().mk_mut_ptr(cx.tcx().types.u8), cx.tcx().types.i32]),
1194 let slot = PlaceRef::alloca(bx, layout);
1195 self.personality_slot = Some(slot);
1200 /// Returns the landing/cleanup pad wrapper around the given basic block.
1201 // FIXME(eddyb) rename this to `eh_pad_for`.
1202 fn landing_pad_for(&mut self, bb: mir::BasicBlock) -> Bx::BasicBlock {
1203 if let Some(landing_pad) = self.landing_pads[bb] {
1207 let landing_pad = self.landing_pad_for_uncached(bb);
1208 self.landing_pads[bb] = Some(landing_pad);
1212 // FIXME(eddyb) rename this to `eh_pad_for_uncached`.
1213 fn landing_pad_for_uncached(&mut self, bb: mir::BasicBlock) -> Bx::BasicBlock {
1214 let llbb = self.llbb(bb);
1215 if base::wants_msvc_seh(self.cx.sess()) {
1218 match self.mir[bb].terminator.as_ref().map(|t| &t.kind) {
1219 // This is a basic block that we're aborting the program for,
1220 // notably in an `extern` function. These basic blocks are inserted
1221 // so that we assert that `extern` functions do indeed not panic,
1222 // and if they do we abort the process.
1224 // On MSVC these are tricky though (where we're doing funclets). If
1225 // we were to do a cleanuppad (like below) the normal functions like
1226 // `longjmp` would trigger the abort logic, terminating the
1227 // program. Instead we insert the equivalent of `catch(...)` for C++
1228 // which magically doesn't trigger when `longjmp` files over this
1231 // Lots more discussion can be found on #48251 but this codegen is
1232 // modeled after clang's for:
1239 Some(&mir::TerminatorKind::Abort) => {
1240 let mut cs_bx = self.new_block(&format!("cs_funclet{:?}", bb));
1241 let mut cp_bx = self.new_block(&format!("cp_funclet{:?}", bb));
1242 ret_llbb = cs_bx.llbb();
1244 let cs = cs_bx.catch_switch(None, None, 1);
1245 cs_bx.add_handler(cs, cp_bx.llbb());
1247 // The "null" here is actually a RTTI type descriptor for the
1248 // C++ personality function, but `catch (...)` has no type so
1249 // it's null. The 64 here is actually a bitfield which
1250 // represents that this is a catch-all block.
1251 let null = cp_bx.const_null(
1252 cp_bx.type_i8p_ext(cp_bx.cx().data_layout().instruction_address_space),
1254 let sixty_four = cp_bx.const_i32(64);
1255 funclet = cp_bx.catch_pad(cs, &[null, sixty_four, null]);
1259 let mut cleanup_bx = self.new_block(&format!("funclet_{:?}", bb));
1260 ret_llbb = cleanup_bx.llbb();
1261 funclet = cleanup_bx.cleanup_pad(None, &[]);
1262 cleanup_bx.br(llbb);
1265 self.funclets[bb] = Some(funclet);
1268 let mut bx = self.new_block("cleanup");
1270 let llpersonality = self.cx.eh_personality();
1271 let llretty = self.landing_pad_type();
1272 let lp = bx.landing_pad(llretty, llpersonality, 1);
1275 let slot = self.get_personality_slot(&mut bx);
1276 slot.storage_live(&mut bx);
1277 Pair(bx.extract_value(lp, 0), bx.extract_value(lp, 1)).store(&mut bx, slot);
1284 fn landing_pad_type(&self) -> Bx::Type {
1286 cx.type_struct(&[cx.type_i8p(), cx.type_i32()], false)
1289 fn unreachable_block(&mut self) -> Bx::BasicBlock {
1290 self.unreachable_block.unwrap_or_else(|| {
1291 let mut bx = self.new_block("unreachable");
1293 self.unreachable_block = Some(bx.llbb());
1298 // FIXME(eddyb) replace with `build_sibling_block`/`append_sibling_block`
1299 // (which requires having a `Bx` already, and not all callers do).
1300 fn new_block(&self, name: &str) -> Bx {
1301 let llbb = Bx::append_block(self.cx, self.llfn, name);
1302 Bx::build(self.cx, llbb)
1305 /// Get the backend `BasicBlock` for a MIR `BasicBlock`, either already
1306 /// cached in `self.cached_llbbs`, or created on demand (and cached).
1307 // FIXME(eddyb) rename `llbb` and other `ll`-prefixed things to use a
1308 // more backend-agnostic prefix such as `cg` (i.e. this would be `cgbb`).
1309 pub fn llbb(&mut self, bb: mir::BasicBlock) -> Bx::BasicBlock {
1310 self.cached_llbbs[bb].unwrap_or_else(|| {
1311 // FIXME(eddyb) only name the block if `fewer_names` is `false`.
1312 let llbb = Bx::append_block(self.cx, self.llfn, &format!("{:?}", bb));
1313 self.cached_llbbs[bb] = Some(llbb);
1318 pub fn build_block(&mut self, bb: mir::BasicBlock) -> Bx {
1319 let llbb = self.llbb(bb);
1320 Bx::build(self.cx, llbb)
1323 fn make_return_dest(
1326 dest: mir::Place<'tcx>,
1327 fn_ret: &ArgAbi<'tcx, Ty<'tcx>>,
1328 llargs: &mut Vec<Bx::Value>,
1330 ) -> ReturnDest<'tcx, Bx::Value> {
1331 // If the return is ignored, we can just return a do-nothing `ReturnDest`.
1332 if fn_ret.is_ignore() {
1333 return ReturnDest::Nothing;
1335 let dest = if let Some(index) = dest.as_local() {
1336 match self.locals[index] {
1337 LocalRef::Place(dest) => dest,
1338 LocalRef::UnsizedPlace(_) => bug!("return type must be sized"),
1339 LocalRef::Operand(None) => {
1340 // Handle temporary places, specifically `Operand` ones, as
1341 // they don't have `alloca`s.
1342 return if fn_ret.is_indirect() {
1343 // Odd, but possible, case, we have an operand temporary,
1344 // but the calling convention has an indirect return.
1345 let tmp = PlaceRef::alloca(bx, fn_ret.layout);
1346 tmp.storage_live(bx);
1347 llargs.push(tmp.llval);
1348 ReturnDest::IndirectOperand(tmp, index)
1349 } else if is_intrinsic {
1350 // Currently, intrinsics always need a location to store
1351 // the result, so we create a temporary `alloca` for the
1353 let tmp = PlaceRef::alloca(bx, fn_ret.layout);
1354 tmp.storage_live(bx);
1355 ReturnDest::IndirectOperand(tmp, index)
1357 ReturnDest::DirectOperand(index)
1360 LocalRef::Operand(Some(_)) => {
1361 bug!("place local already assigned to");
1367 mir::PlaceRef { local: dest.local, projection: &dest.projection },
1370 if fn_ret.is_indirect() {
1371 if dest.align < dest.layout.align.abi {
1372 // Currently, MIR code generation does not create calls
1373 // that store directly to fields of packed structs (in
1374 // fact, the calls it creates write only to temps).
1376 // If someone changes that, please update this code path
1377 // to create a temporary.
1378 span_bug!(self.mir.span, "can't directly store to unaligned value");
1380 llargs.push(dest.llval);
1383 ReturnDest::Store(dest)
1387 fn codegen_transmute(&mut self, bx: &mut Bx, src: &mir::Operand<'tcx>, dst: mir::Place<'tcx>) {
1388 if let Some(index) = dst.as_local() {
1389 match self.locals[index] {
1390 LocalRef::Place(place) => self.codegen_transmute_into(bx, src, place),
1391 LocalRef::UnsizedPlace(_) => bug!("transmute must not involve unsized locals"),
1392 LocalRef::Operand(None) => {
1393 let dst_layout = bx.layout_of(self.monomorphized_place_ty(dst.as_ref()));
1394 assert!(!dst_layout.ty.has_erasable_regions());
1395 let place = PlaceRef::alloca(bx, dst_layout);
1396 place.storage_live(bx);
1397 self.codegen_transmute_into(bx, src, place);
1398 let op = bx.load_operand(place);
1399 place.storage_dead(bx);
1400 self.locals[index] = LocalRef::Operand(Some(op));
1401 self.debug_introduce_local(bx, index);
1403 LocalRef::Operand(Some(op)) => {
1404 assert!(op.layout.is_zst(), "assigning to initialized SSAtemp");
1408 let dst = self.codegen_place(bx, dst.as_ref());
1409 self.codegen_transmute_into(bx, src, dst);
1413 fn codegen_transmute_into(
1416 src: &mir::Operand<'tcx>,
1417 dst: PlaceRef<'tcx, Bx::Value>,
1419 let src = self.codegen_operand(bx, src);
1421 // Special-case transmutes between scalars as simple bitcasts.
1422 match (&src.layout.abi, &dst.layout.abi) {
1423 (abi::Abi::Scalar(src_scalar), abi::Abi::Scalar(dst_scalar)) => {
1424 // HACK(eddyb) LLVM doesn't like `bitcast`s between pointers and non-pointers.
1425 if (src_scalar.value == abi::Pointer) == (dst_scalar.value == abi::Pointer) {
1426 assert_eq!(src.layout.size, dst.layout.size);
1428 // NOTE(eddyb) the `from_immediate` and `to_immediate_scalar`
1429 // conversions allow handling `bool`s the same as `u8`s.
1430 let src = bx.from_immediate(src.immediate());
1431 let src_as_dst = bx.bitcast(src, bx.backend_type(dst.layout));
1432 Immediate(bx.to_immediate_scalar(src_as_dst, dst_scalar)).store(bx, dst);
1439 let llty = bx.backend_type(src.layout);
1440 let cast_ptr = bx.pointercast(dst.llval, bx.type_ptr_to(llty));
1441 let align = src.layout.align.abi.min(dst.align);
1442 src.val.store(bx, PlaceRef::new_sized_aligned(cast_ptr, src.layout, align));
1445 // Stores the return value of a function call into it's final location.
1449 dest: ReturnDest<'tcx, Bx::Value>,
1450 ret_abi: &ArgAbi<'tcx, Ty<'tcx>>,
1453 use self::ReturnDest::*;
1457 Store(dst) => bx.store_arg(&ret_abi, llval, dst),
1458 IndirectOperand(tmp, index) => {
1459 let op = bx.load_operand(tmp);
1460 tmp.storage_dead(bx);
1461 self.locals[index] = LocalRef::Operand(Some(op));
1462 self.debug_introduce_local(bx, index);
1464 DirectOperand(index) => {
1465 // If there is a cast, we have to store and reload.
1466 let op = if let PassMode::Cast(_) = ret_abi.mode {
1467 let tmp = PlaceRef::alloca(bx, ret_abi.layout);
1468 tmp.storage_live(bx);
1469 bx.store_arg(&ret_abi, llval, tmp);
1470 let op = bx.load_operand(tmp);
1471 tmp.storage_dead(bx);
1474 OperandRef::from_immediate_or_packed_pair(bx, llval, ret_abi.layout)
1476 self.locals[index] = LocalRef::Operand(Some(op));
1477 self.debug_introduce_local(bx, index);
1483 enum ReturnDest<'tcx, V> {
1484 // Do nothing; the return value is indirect or ignored.
1486 // Store the return value to the pointer.
1487 Store(PlaceRef<'tcx, V>),
1488 // Store an indirect return value to an operand local place.
1489 IndirectOperand(PlaceRef<'tcx, V>, mir::Local),
1490 // Store a direct return value to an operand local place.
1491 DirectOperand(mir::Local),