[llvm-dev] PSA: Parallel STL algorithms available in LLVM

Bryce Lelbach via llvm-dev llvm-dev at lists.llvm.org
Wed May 17 07:19:41 PDT 2017


Apologies for my delayed reply - I've been on travel the past few days.

On Fri, May 12, 2017 at 9:00 AM, Scott Smith
<scott.smith at purestorage.com> wrote:
> Can't they fall back on serial execution?  I thought the executor is a hint,
> not a requirement (certainly the standard doesn't say it has to execute on
> multiple threads, just that it may).

Yes. However, it is a quality-of-implementation issue.

> I fear what you're describing is another 1.5 year long standards
> committee-like process, involving multiple stakeholders, discussions, etc.

Yep. I don't think it will take quite that long, but it's not a trivial task.

> As it is, we have a real use case today for this behavior, but not the
> resources/time to invest in coming up with defining how a shared library
> interface should look, separate from the C++17 parallelism interface, just
> so that libc++ may (or may not) pick it up somewhere down the line.

Ah, alright. I think I understand your requirements a bit better now.

> IMO it makes more sense to continue with the separate implementation of
> "kinda mostly C++17 parallelism" with minimal changes/improvements as
> necessary inside LLVM, and then switch to libc++/libstdc++/etc standard
> implementation later once those interfaces are implemented and pervasive
> across all the architectures that LLVM needs to work on.  Otherwise, we hold
> up progress in LLVM/LLDB today.

I agree, this sounds quite sensible to me.

-- 
Bryce Adelstein Lelbach aka wash
Lawrence Berkeley National Laboratory
ISO C++ Committee Member
CppCon and C++Now Program Chair

Compiler ICE Hunter
--


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