This PR adds support for returning the result of a `co_await` via
`co_return`. A new variable, `__coawait_resume_rval`, is introduced to
store the returned value.
This PR partially upstreams support for the `co_return` keyword. It
still needs to address the case where a `co_return` returns a value from
a `co_await`.
Additionally, this change focuses on `emitBodyAndFallthrough`, where
depending on whether the function falls through or not it will emit the
user written `co_await`. Another thing to note is the difference from
classic CodeGen, previously it checked whether it could fall through by
using `GetInsertBlock()` to verify that the block existed. In our case,
when a `co_return` is emitted, we mark `setCoreturn()` to indicate that
the coroutine contains a `co_return`.
This PR upstreams the emission of the `cir.await` resume branch.
Handling the case where the return value of `co_await` is not ignored is
deferred to a future PR, which will be added once `co_return` is
upstreamed. Additionally, the `forLValue` variable is always `false` in
the current implementation. When support for emitting `coro_yield` is
added, this variable will be set to `true`, so that work is also
deferred to a future PR.
This PR adds codegen for `cir.await` ready and suspend. One notable
difference from the classic codegen is that, in the suspend branch, it
emits an `AwaitSuspendWrapper`(`.__await_suspend_wrapper__init`)
function that is always inlined. This function wraps the suspend logic
inside an internal wrapper that gets inlined. Example here:
https://godbolt.org/z/rWYGcaaG4
This PR upstreams `cir.await` and adds initial codegen for emitting a
skeleton of the ready, suspend, and resume branches. Codegen for these
branches is left for a future PR. It also adds a test for the invalid
case where a `cir.func` is marked as a coroutine but does not contain a
`cir.await` op in its body.
This PR adds new `FuncOp` attributes (`coroutine` and `builtin`) and
begins the implementation of the `emitCoroutineBody` function. Feature
markers were also added for guidance in future PRs.
