"Invalidated the current SCC" assertion failure after #79712

[smeenai]

For the source file in https://gist.github.com/smeenai/fcd14380467e813a28f1ef8c5484b775 (reduced from a large example that uses libunifex; it's probably possible to reduce this further but I'm not at all familiar with coroutines), the following command succeeds with Clang 18 but fails with Clang 19 and trunk:

$ clang -c -o /dev/null coroutine_crash.cpp -std=c++20 -w
clang: llvm/lib/Analysis/CGSCCPassManager.cpp:1167: LazyCallGraph::SCC &updateCGAndAnalysisManagerForPass(llvm::LazyCallGraph &, LazyCallGraph::SCC &, LazyCallGraph::Node &, llvm::CGSCCAnalysisManager &, llvm::CGSCCUpdateResult &, llvm::FunctionAnalysisManager &, bool): Assertion `!UR.InvalidatedSCCs.count(C) && "Invalidated the current SCC!"' failed.

I bisected this to #79712. CC @fpasserby, @ChuanqiXu9, and @yuxuanchen1997

[yuxuanchen1997]

I took a look at this and I think it was due to incorrect call graph updates. updateCGAndAnalysisManagerFor(CGSCC|Function)Pass seems to return an updated SCC but we discarded the updated SCC.

See example usage: https://github.com/llvm/llvm-project/blob/main/llvm/lib/Analysis/CGSCCPassManager.cpp#L561-L562
See implementation: https://github.com/llvm/llvm-project/blob/main/llvm/lib/Analysis/CGSCCPassManager.cpp#L1170-L1175

I have a patch #107935 but still need some time for a test case.

[yuxuanchen1997]

This happens when foo has is not a single node SCC:

define void @foo() presplitcoroutine personality ptr null {
entry:
  %0 = call token @llvm.coro.id(i32 0, ptr null, ptr null, ptr null)
  %1 = call ptr @llvm.coro.begin(token %0, ptr null)
  %2 = call token @llvm.coro.save(ptr null)
  %3 = call i8 @llvm.coro.suspend(token none, i1 false)
  %4 = call token @llvm.coro.save(ptr null)
  call void @llvm.coro.await.suspend.void(ptr null, ptr null, ptr @bar)
  ret void
}

define void @bar(ptr %0, ptr %1) {
entry:
  call void @foo()
  ret void
}

declare token @llvm.coro.id(i32, ptr readnone, ptr nocapture readonly, ptr) #0
declare ptr @llvm.coro.begin(token, ptr writeonly) nounwind
declare token @llvm.coro.save(ptr) nomerge nounwind
declare void @llvm.coro.await.suspend.void(ptr, ptr, ptr)
declare i8 @llvm.coro.suspend(token, i1) nounwind

attributes #0 = { nocallback nofree nosync nounwind willreturn memory(argmem: read) }

Repro the crash with clang -O0 bad.ll.

[yuxuanchen1997]

The 3rd argument to @llvm.coro.await.suspend is the await_suspend function in C++. This happens when await_suspend() calls the same coroutine from its body.