[cfe-dev] [RFC] C++17 hardware constructive / destructive interference size

[Friedman, Eli via cfe-dev]

On 5/25/2018 11:46 AM, JF Bastien wrote:
>
>
>> On May 25, 2018, at 11:38 AM, Friedman, Eli <efriedma at codeaurora.org 
>> <mailto:efriedma at codeaurora.org>> wrote:
>>
>> On 5/25/2018 11:29 AM, JF Bastien via cfe-dev wrote:
>>>
>>>  1. Teach the target infrastructure that hardware interference size
>>>     is something they can specify (in tablegen files somewhere).
>>>  2. Allow overriding the value in sub-targets using -march or -mcpu
>>>     (the sub-target defines the numeric value, and the user gets the
>>>     overriden one by using -march or -mcpu).
>>>
>>
>> We can't change the value based on -mcpu.  We generally allow mixing 
>> code built with different values of -mcpu. And any code which is 
>> linked together must use the same value for 
>> hardware_destructive_interference_size, or else we violate ODR.
>
> Interesting point. The case I’d like to cover is one where the 
> developer wants to get the exact right value for their particular CPU, 
> instead of a conservative answer with extra padding. How do you think 
> we should meet this use case?
>

Go back to the standards committee and ask for a function that isn't 
constexpr?  I can't think of any other reasonable solution.

-Eli

-- 
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project

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