[flang-dev] [EXTERNAL] Status of Flang runtime

[Arnamoy Bhattacharyya via flang-dev]

Thanks Kiran for sharing and Thanks Jean for creating the tutorial,
this is very helpful.

On Sat, Mar 27, 2021 at 6:59 PM Kiran Chandramohan
<Kiran.Chandramohan at arm.com> wrote:
>
> Hello Arnamoy,
>
> Jean Perier from Nvidia recently created a tutorial for adding intrinsics to llvm/flang.
>
> https://github.com/flang-compiler/f18-llvm-project/blob/fir-dev/flang/docs/tutorials/addingIntrinsics.md
>
> Thanks,
> Kiran
>
> ________________________________
> From: flang-dev <flang-dev-bounces at lists.llvm.org> on behalf of Kiran Chandramohan via flang-dev <flang-dev at lists.llvm.org>
> Sent: 01 February 2021 19:02
> To: Arnamoy Bhattacharyya <arnamoy at ualberta.ca>; flang-dev at lists.llvm.org <flang-dev at lists.llvm.org>; Perry-Holby, Alexis <aperry at lanl.gov>
> Subject: Re: [flang-dev] [EXTERNAL] Status of Flang runtime
>
> Hello Arnamoy,
>
> Thanks for your question. I think this is a question that you can ask during the Flang calls. I will share what I know, but this info might not be accurate.
>
> I am assuming that your question is about the non-I/O part of the flang runtime. The focus till a couple of months back was to get Flang/F18 working for F77. Since F77 does not have much of a runtime component there might not have been much thought gone into sharing a design or keeping a public todo list for the runtime.
>
> There was a lot of work that happened initially for the implementation of folding of intrinsics with constant inputs. You can see the implementation of these in the flang/lib/Evaluate directory. You can see some TODOs in the files in the Evaluate directory. I think this is an area that you might be able to contribute to. Also see the following links.
> https://github.com/llvm/llvm-project/blob/main/flang/docs/Intrinsics.md
> https://github.com/llvm/llvm-project/blob/main/flang/docs/Intrinsics.md#intrinsic-functions-with-missing-folding-support
>
> As of now, I am only aware of the date_and_time intrinsic which is implemented with a runtime function. You can see the implementation in the PR #412 (https://github.com/flang-compiler/f18-llvm-project/pull/412) in fir-dev branch. If you are interested in the runtime implementation, I believe you can take inspiration from the classic flang runtime (as hinted in https://github.com/flang-compiler/f18-llvm-project/pull/415#pullrequestreview-481755947). Since the array descriptors of classic flang and f18 are different there will be changes needed.
>
> In general, I have often heard the following in relation to intrinsics/runtime.
> For math intrinsics, the plan is to use libpgmath.
> If llvm intrinsics are available, we will try to use that.
> The runtime should be kept free of other libraries.
>
> Jean Perier did much of the folding and the lowering/runtime work in fir-dev branch. He might know more. CCing @Jean Perier.
>
> Thanks,
> Kiran
> ________________________________
> From: flang-dev <flang-dev-bounces at lists.llvm.org> on behalf of Perry-Holby, Alexis via flang-dev <flang-dev at lists.llvm.org>
> Sent: 27 January 2021 23:13
> To: Arnamoy Bhattacharyya <arnamoy at ualberta.ca>; flang-dev at lists.llvm.org <flang-dev at lists.llvm.org>
> Subject: Re: [flang-dev] [EXTERNAL] Status of Flang runtime
>
> Hi Arnamoy,
>
> I'm not 100% certain what the status of the runtime is, but if you are looking for ways to contribute you can check out the issues list here: https://github.com/flang-compiler/f18-llvm-project/issues .  There are a couple that I see that have the "Runtime" label attached, which may be a good place to start.
>
> Thanks!
> Alexis Perry-Holby
> Los Alamos National Laboratory
> Applied Computer Science (CCS-7)
>
> On 1/9/21, 2:03 PM, "flang-dev on behalf of Arnamoy Bhattacharyya via flang-dev" <flang-dev-bounces at lists.llvm.org on behalf of flang-dev at lists.llvm.org> wrote:
>
>     Hello all;
>
>     I just wanted to ask what is the status of the flang runtime?  I see a
>     few commits from 5 days ago in fir-dev, but could not find any status
>     tracking info or any milestones?  Can anyone shed some light on what
>     contribution areas are open in the runtime?
>
>     Thank you very much.
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-- 
Dr. Arnamoy Bhattacharyya
R&D Compiler Engineer
Huawei