[PATCH] D89066: [Coroutine][Sema] Only tighten the suspend call temp lifetime for final awaiter

Mon Oct 12 09:44:26 PDT 2020

lxfind added a comment.

In D89066#2324291 <https://reviews.llvm.org/D89066#2324291>, @junparser wrote:

> In D89066#2324151 <https://reviews.llvm.org/D89066#2324151>, @lxfind wrote:
>
>> In D89066#2324115 <https://reviews.llvm.org/D89066#2324115>, @junparser wrote:
>>
>>> why we should not do this with normal await call?
>>
>> To be honest, I don't know yet. My understanding of how expression cleanup and temp lifetime management is insufficient at the moment.
>> But first of all, without adding any cleanup expression here, I saw ASAN failures due to heap-use-after-free, because sometimes the frame have already been destroyed after the await_suspend call, and yet we are still writing into the frame due to unnecessarily cross-suspend lifetime. However, if I apply the cleanup to all await_suepend calls, it also causes ASAN failures as it's cleaning up data that's still alive.
>> So this patch is more of a temporary walkaround to stop bleeding without causing any trouble.
>> I plan to get back to this latter after I am done with the spilling/alloca issues.
>
> I'm not familiar with ASAN instrumentation. Do you have any testcases to explain this?

Unfortunately I don't.  But this is not related to ASAN. Basically, this is causing destructing of objects that should still be alive. I suspect that it's because ExprWithCleanups always clean up temps that belongs to the full expression, not just the sub-expression in it.

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https://reviews.llvm.org/D89066