[PATCH] D62766: [Attributor] Deduce "nosync" function attribute.

Wed Jun 12 16:58:04 PDT 2019

arsenm added inline comments.

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Comment at: llvm/docs/LangRef.rst:1476-1478
+    This function attribute indicates that the function does not communicate
+    (synchronize) with another thread. If the function does ever synchronize 
+    with another thread, the behavior is undefined.
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arsenm wrote:
> I think this is a bit vague. In particular I don't think the LangRef defines what a "thread" means anywhere. I also think this needs to be more clear on what kinds of synchronization is allowed. Is this only communication through some addressable memory? What about GPU cross lane communication operations?
> 
> I'm wondering if this is sufficient to solve this problem: http://lists.llvm.org/pipermail/llvm-dev/2013-November/067359.html
> TLDR, memory instructions can currently be hoisted over an arbitrary call if they are accessing a noalias argument
This is also mentioned as a proper attribute here (which I would greatly prefer to adding another string attribute), but only handled as a string attribute

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  https://reviews.llvm.org/D62766/new/

https://reviews.llvm.org/D62766