[llvm-dev] [RFC] IR-level Region Annotations

[Hal Finkel via llvm-dev]

On 01/17/2017 06:59 PM, Mehdi Amini wrote:
>
>> On Jan 17, 2017, at 4:36 PM, Hal Finkel via llvm-dev 
>> <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>>
>>
>> On 01/17/2017 05:36 PM, Wael Yehia via llvm-dev wrote:
>>> Hi. Regarding the token approach, I've read some documentation 
>>> (review D11861, EH in llvm, and Reid and David's presentation) but 
>>> couldn't answer the following question.
>>> Does the intrinsic or the instruction returning a /token/ type 
>>> object act as a code motion barrier? In other words, does it prevent 
>>> other operations from being reordered with it?
>>> If the answer is no, then does it mean the intrinsic has to be 
>>> marked with the /convergent/ property to achieve the code motion 
>>> barrier effect?
>>
>> To clarify, convergent does not form a code-motion barrier. It 
>> prevents transformations from adding additional control dependencies. 
>> I suspect that the token type does the same (because tokens can't 
>> appear in PHIs).
>
> What if the only user of the token is in a branch? It seems to me that 
> you’d be allowed to sink the token producer there, but not if it is 
> marked convergent.

Can that happen if you start out with a "well formed" region?

  -Hal

>
> —
> Mehdi
>
>
>
>>
>> Actual code motion barriers are generally achieved by adding unknown 
>> memory dependencies.
>>
>>  -Hal
>>
>>> If yes, can someone explain how is that achieved in llvm?
>>> Greatly appreciated. Thanks.
>>>
>>> Wael
>>>
>>>
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>> -- 
>> Hal Finkel
>> Lead, Compiler Technology and Programming Languages
>> Leadership Computing Facility
>> Argonne National Laboratory
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>

-- 
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory

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