[PATCH] D74918: Add method to TargetInfo to get CPU cache line size

[Eric Christopher via cfe-commits]

I'm agreed with James on all points fwiw.

On Thu, Feb 27, 2020, 2:00 PM James Y Knight via Phabricator <
reviews at reviews.llvm.org> wrote:

> jyknight requested changes to this revision.
> jyknight added a comment.
> This revision now requires changes to proceed.
>
> In D74918#1885869 <https://reviews.llvm.org/D74918#1885869>, @zoecarver
> wrote:
>
> > @jyknight It would probably be best if we could account for CPUs who
> like to use aligned pairs when getting a cache line. It's probably also
> important that we don't change the value `getCPUCacheLineSize` returns, so,
> if we are going to account for that, we should probably update
> `getCPUCacheLineSize ` before this patch lands.
>
>
> It would be extremely unfortunate to go to all the trouble of attempting
> to return accurate results from the P0154 interfaces, and then to return an
> answer insufficient to actually achieve the performance benefit it's
> intended for, and then be unable to fix it due to ABI concerns. So, yes, I
> do believe that this issue must be decided.
>
> Additionally, my opinion here has really not changed from a couple of
> years ago. I continue to believe it was a mistake to standardize these
> constexpr values, and that absolutely the best course of action would be to
> continue to decline to implement this part of the standard, forever. (And
> that GCC should similarly also continue to decline to implement it).
>
> That said, the list of cacheline sizes collected in this review is still
> useful in any case, since it needs to be copied into LLVM's X86Subtarget to
> implement the backend getCacheLineSize function.
>
>
> Repository:
>   rG LLVM Github Monorepo
>
> CHANGES SINCE LAST ACTION
>   https://reviews.llvm.org/D74918/new/
>
> https://reviews.llvm.org/D74918
>
>
>
>
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