[llvm-dev] Enable STATISTIC all the time again?

[Reid Kleckner via llvm-dev]

I think adding an option to cmake is fine, but it should definitely be off
by default in release builds. If we make STATISTIC useful, then people will
eventually put it on some hot path, and that will kill multi-threaded
performance for users like ThinLTO, because multiple threads doing
read-modify-write on the same memory is just slow.

On Wed, May 31, 2017 at 7:39 AM, Daniel Berlin via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Right now, the LLVM Statistic class does not increment values if we are in
> non-debug mode, unless you define LLVM_ENABLE_STATS (which, sadly, is also
> not available from cmake).
>
> Before i go and add it to cmake, i ran numbers.
>
> I can't find a single testcase, large or small, where enabling statistics
> all the time isn't completely noise.
>
> It looks like it was disabled in march  2013.
> https://reviews.llvm.org/D486
>
> The only discussion i can find in the same time period is around fastisel
> using a lot of per-instruction stats, and it causing some slow-down.
>
> However, I can't find any actual data/testcases in this discussion at all,
> and disabling stats globally is actually fairly annoying for performance
> work.
> :(
>
> Does anyone have any testcases where it is actually slow that i can look
> at?
>
>
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