[PATCH] D139295: [Coroutines] Don't mark the parameter attribute of resume function as noalias

Sat Dec 10 00:50:41 PST 2022

nikic added a comment.

In D139295#3983358 <https://reviews.llvm.org/D139295#3983358>, @ChuanqiXu wrote:

> In D139295#3978335 <https://reviews.llvm.org/D139295#3978335>, @nikic wrote:
>
>> @ChuanqiXu Your first function already contains:
>>
>>   store i32 42, ptr %__promise.reload.addr.i.i, align 8, !tbaa !3, !alias.scope !18
>>   store ptr null, ptr %.reload.addr, align 8, !alias.scope !18
>>   %1 = load ptr, ptr %0, align 8
>>   musttail call fastcc void %1(ptr nonnull %0) #5, !noalias !18
>>
>> which says that the store and the call don't alias. I don't think the `noalias` argument on the function would even matter in that case. The incorrect noalias metadata must be introduced at some earlier point already.
>
> Oh, so I misunderstood the semantics of `!noalias` before. So this patch may not be correct. BTW, do you have any ideas why the `store` in the first function would't be optimized out?

This is because the caller may read it. After inlining, we see that it's an alloca that nobody reads afterwards.

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https://reviews.llvm.org/D139295