[llvm-dev] Using std::chrono

[Hal Finkel via llvm-dev]

----- Original Message -----
> From: "Pavel Labath via llvm-dev" <llvm-dev at lists.llvm.org>
> To: "Zachary Turner" <zturner at google.com>
> Cc: llvm-dev at lists.llvm.org
> Sent: Sunday, October 9, 2016 9:29:17 PM
> Subject: Re: [llvm-dev] Using std::chrono
> 
> Hello all,
> 
> I'd like to add a std::chrono support header to libSupport
> <https://reviews.llvm.org/D25416>. My main motivation is remove
> LLDB's
> TimeValue class in favor of std::chrono, but I think we could do the
> same for llvm::sys::TimeValue as well - the class was added a very
> long time ago, when std::chrono did not exist yet, but now it should
> be supported by all compilers. I've tried rewriting some of the uses
> in llvm, and despite the apparent verboseness of std::chrono, it
> makes
> the code shorter most of the time, and (due to the separation between
> time points and durations) also safer - I think I also found some
> bugs
> where we were adding two time points, but I'll need to verify that.
> 
> What do you think?

I think this makes sense. As you say, our TimeValue pre-dates std::chrono. If the implementations are now generally usable, we should transition to the standard functionality.

 -Hal

> pl
> 
> 
> On 6 October 2016 at 23:52, Zachary Turner via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
> > VS2013 support is dropped in about 1 week from now :)
> >
> > On Thu, Oct 6, 2016 at 11:37 PM Mueller-Roemer, Johannes Sebastian
> > <Johannes.Sebastian.Mueller-Roemer at igd.fraunhofer.de> wrote:
> >>
> >> Visual Studio up to and including VS2013 implements
> >> std::chrono::high_resolution_clock in an absolutely unusable
> >> manner (it is a
> >> very low resolution clock…) [1]. Also, division is implemented
> >> incorrectly
> >> [2]. I have run into both issues in my private developments, so I
> >> would
> >> avoid them as long as VS2013 is supported by LLVM (I believe it
> >> still is?).
> >>
> >>
> >>
> >>     [1]: https://stackoverflow.com/questions/31643279
> >>
> >>     [2]: https://stackoverflow.com/questions/26372596
> >>
> >>
> >>
> >>
> >>
> >> From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf
> >> Of
> >> Zachary Turner via llvm-dev
> >> Sent: Friday, October 7, 2016 03:11
> >> To: llvm-dev <llvm-dev at lists.llvm.org>
> >> Subject: [llvm-dev] Using std::chrono
> >>
> >>
> >>
> >> Hi all,
> >>
> >> We're considering using std::chrono more heavily in lldb. However,
> >> A quick
> >> search of the llvm, clang, and lld codebases shos almost zero
> >> usage of
> >> chrono. I wanted to see if this was for technical reasons (eg some
> >> compiler
> >> doesn't support it well) or simply because nobody has needed it
> >> yet. If it's
> >> the former then I'd like to be aware of the issues so we don't
> >> fall into any
> >> traps.
> >>
> >> If it's the latter, then we're good to go. Would it be worth
> >> adding any
> >> chrono helper functions to llvm/Support? On the one hand, it seems
> >> generally
> >> useful. But on the other hand, if nobody's using it yet, maybe
> >> it's not
> >> generally useful enough.
> >>
> >> Also, are there any chrono experts around who would be willing to
> >> review
> >> some patches?
> >
> >
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> >
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-- 
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory