================
@@ -1965,9 +1965,15 @@ bool Sema::buildCoroutineParameterMoves(SourceLocation
Loc) {
if (PD->getType()->isDependentType())
continue;
+ // Preserve the referenced state for unused parameter diagnostics.
+ bool DeclReferenced = PD->isReferenced();
----------------
yuxuanchen1997 wrote:
`PD->isReferenced()` may be true. The order `Sema` processes things is based on
how Parser is sending information to it. I can try to explain based on my
limited understanding and corroborate with a test case. So please feel free to
correct me if I am wrong.
Let's take a look at this very simple coroutine. Suppose `task` is defined
somewhere as a return object.
```
task foo(int a, int b) {
a = a + 1;
co_return;
}
```
Sema is first asked to compile `foo` like a normal function. Decl `a` and `b`
are processed normally. When we use `a` in the `a = a + 1` statement,
references are setup.
When the parser encounters `co_return`, it calls `Sema::ActOnCoreturn`.
What `Sema::ActOnCoreturn` (and its siblings handling other `co_` family of
statements) does is to call `Sema::ActOnCoroutineBodyStart`. It checks if clang
is already treating `foo` as a coroutine. It will find out that, no. We are not
compiling `foo` like a coroutine yet, let's perform necessary checks and
establish this context. `buildCoroutineParameterMoves` is called as a result.
At that time `a` already has references we need to carry along.
Suppose that our function has subsequent `co_*` statements, `Sema` knows that
we already established the context and doesn't build them again.
The aforementioned `foo` coroutine will cause clang ICE if we
`assert(!PD->isReferenced())` here.
https://github.com/llvm/llvm-project/pull/70973
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