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9af6fee87d
Support tail calls in mir via `TerminatorKind::TailCall`
This is one of the interesting bits in tail call implementation — MIR support.
This adds a new `TerminatorKind` which represents a tail call:
```rust
TailCall {
func: Operand<'tcx>,
args: Vec<Operand<'tcx>>,
fn_span: Span,
},
```
*Structurally* this is very similar to a normal `Call` but is missing a few fields:
- `destination` — tail calls don't write to destination, instead they pass caller's destination to the callee (such that eventual `return` will write to the caller of the function that used tail call)
- `target` — similarly to `destination` tail calls pass the caller's return address to the callee, so there is nothing to do
- `unwind` — I _think_ this is applicable too, although it's a bit confusing
- `call_source` — `become` forbids operators and is not created as a lowering of something else; tail calls always come from HIR (at least for now)
It might be helpful to read the interpreter implementation to understand what `TailCall` means exactly, although I've tried documenting it too.
-----
There are a few `FIXME`-questions still left, ideally we'd be able to answer them during review ':)
-----
r? `@oli-obk`
cc `@scottmcm` `@DrMeepster` `@JakobDegen`
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| .. | ||
| constraints | ||
| diagnostics | ||
| polonius | ||
| region_infer | ||
| type_check | ||
| util | ||
| borrow_set.rs | ||
| borrowck_errors.rs | ||
| consumers.rs | ||
| dataflow.rs | ||
| def_use.rs | ||
| facts.rs | ||
| lib.rs | ||
| location.rs | ||
| member_constraints.rs | ||
| nll.rs | ||
| path_utils.rs | ||
| place_ext.rs | ||
| places_conflict.rs | ||
| prefixes.rs | ||
| renumber.rs | ||
| session_diagnostics.rs | ||
| universal_regions.rs | ||
| used_muts.rs | ||