[llvm] r182603 - ARM: implement @llvm.readcyclecounter intrinsic

[JF Bastien]

>
> Yep, I understood. But the intrinsic you suggest doesn't really solve
> the problem (I think). For example if you were compiling a kernel
> module your code would be running at a higher privilege level and the
> MRC would be actively misleading.
>
> Now, you could say that all kernel code must be compiled with an
> arm-none-eabi compiler, or with a special override which assumes
> higher privilege and always returns 1 for __has_cyclecounter (or
> whatever), but I think that's worse than the current situation of
> requiring a degree of competence of our users.
>
> I probably wouldn't oppose such a builtin, but I don't think
> implementing it is a good use of time.
>

Well reasoned, I agree with you :-)


Well, X86 Linux certainly (though I'm not sure the architecture gives
> it the option). My experience outside Linux (X86 & ARM) is rather
> limited at the moment.
>

Ah OK, I thought you had an ARM target that did, hence my initial curiosity.
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