[Flang][OpenMP] Add OpenMP standards support doc #132707

kiranchandramohan · 2025-03-24T10:39:14Z

No description provided.

kiranchandramohan · 2025-03-24T10:40:37Z

flang/docs/OpenMPStandardsSupport.md

+| target teams distribute parallel loop construct            | P      | |
+| teams distribute parallel loop simd construct              | P      | |
+| target teams distribute parallel loop simd construct       | P      | |
+


I am conservatively marking all target-related constructs (including combined ones) as Partial support. I can correct the entries if they are fully supported.

tblah

Thanks for putting this together Kiran.

flang/docs/OpenMPStandardsSupport.md

kiranchandramohan

Thanks @tblah for the quick review.

flang/docs/OpenMPStandardsSupport.md

tarunprabhu

Just some minor suggestions

tarunprabhu · 2025-03-24T14:03:03Z

flang/docs/OpenMPStandardsSupport.md

+
+This document summarizes OpenMP standards support in Flang. The information is only provided as a guideline. The
+TODOs/Not Yet Implemented messages emitted by the compiler for unimplemented features should be treated as authoritative.
+Standards support is provided upto OpenMP 4.0 for now. It will be extended later for OpenMP 4.5, OpenMP 5.* and OpenMP 6.0.


Would it be worth putting in a date here, so there is some indication of how valid this sentence is?

Suggested change

Standards support is provided upto OpenMP 4.0 for now. It will be extended later for OpenMP 4.5, OpenMP 5.* and OpenMP 6.0.

As of March 2025, standards support is provided upto OpenMP 4.0. It will be extended later for OpenMP 4.5, OpenMP 5.* and OpenMP 6.0.

Are we working on support for OpenMP > 4.0? If so, perhaps the second sentence could be rephrased to better reflect this. Perhaps

We are actively working towards supporting OpenMP 4.5, OpenMP 5.* and OpenMP 6.0.

Are we working on support for OpenMP > 4.0?

Yes. Some might be working already. Just that I have not spent time characterising the support.

Your suggestions look good. Have made the change.

tarunprabhu · 2025-03-24T18:51:25Z

flang/docs/OpenMPStandardsSupport.md

+- **Y** : When the implementation is complete
+- **N** : When the implementation is absent
+
+Note : No distinction is made between the support in the Parser/Semantics, MLIR or Lowering support, and OpenMPIRBuilder support.


Another optional rephrase (if I understand your intent correctly)

Suggested change

Note : No distinction is made between the support in the Parser/Semantics, MLIR or Lowering support, and OpenMPIRBuilder support.

Note : No distinction is made between the support in Parser/Semantics, MLIR, Lowering or the OpenMPIRBuilder.

NimishMishra

Thanks for compiling this. I am okay with the list and their current status.

Are we not adding task construct though?

kiranktp · 2025-03-25T06:38:21Z

I think we are missing taskgroup as well.

kiranchandramohan · 2025-03-25T08:17:44Z

Are we not adding task construct though?

I think we are missing taskgroup as well.

These came in OpenMP 3.0/3.1. Or do you mean there is something unsupported that you want to report?

NimishMishra · 2025-03-25T12:03:47Z

These came in OpenMP 3.0/3.1. Or do you mean there is something unsupported that you want to report?

Okay understood. I think we want to say we support OpenMP 4.0 + additional features which we list in the table. I got confused with the line "The standards support information is provided as a table with three columns that are self explanatory. The Status column uses the letters P, Y, N for the implementation status"

mjklemm · 2025-03-28T11:26:07Z

flang/docs/OpenMPStandardsSupport.md

+---
+```
+
+This document summarizes OpenMP standards support in Flang. The information is only provided as a guideline. The


Suggested change

This document summarizes OpenMP standards support in Flang. The information is only provided as a guideline. The

This document summarizes the supported features of the OpenMP API in Flang. The information is only provided as a guideline. The

(OpenMP is not a standard in the true sense, like with the ISO standards.)

Would it be OK to go with OpenMP specification?
This document summarizes the supported features of the OpenMP specification in Flang

mjklemm · 2025-03-28T11:28:12Z

flang/docs/OpenMPStandardsSupport.md

+
+This document summarizes OpenMP standards support in Flang. The information is only provided as a guideline. The
+TODOs/Not Yet Implemented messages emitted by the compiler for unimplemented features should be treated as authoritative.
+As of March 2025, standards support is provided upto OpenMP 4.0. We are actively working towards supporting OpenMP 4.5, OpenMP 5.* and OpenMP 6.0.


I know that it has been requested to have a date in the document, but I would treat the modification date of the file in the commit log as being more accurate than the date in the document that could easily be missed when updating the file (plus, it does not protect us from the document becoming outdated over time).

Note that https://clang.llvm.org/docs/OpenMPSupport.html has split OpenMP support into C/C++ & Fortran already. Presumably it makes sense to either fully join those documents, or remove the Fortran side from the clang docs, and just add a reference to this document.

Also typo

Suggested change

As of March 2025, standards support is provided upto OpenMP 4.0. We are actively working towards supporting OpenMP 4.5, OpenMP 5.* and OpenMP 6.0.

As of March 2025, standards support is provided up to OpenMP 4.0. We are actively working towards supporting OpenMP 4.5, OpenMP 5.* and OpenMP 6.0.

From the table below, OpenMP 4.0 support is not 100% complete yet, so maybe "up to" gives a wrong impression here; I'd read it as "4.0 support is fully implemented".

Note that https://clang.llvm.org/docs/OpenMPSupport.html has split OpenMP support into C/C++ & Fortran already. Presumably it makes sense to either fully join those documents, or remove the Fortran side from the clang docs, and just add a reference to this document.

Would it be all right to address this separately? Ideally, each Frontend should list its OpenMP support separately. Removing the entry from Clang would require a separate set of reviewers.

Rewrote the statement regarding standards support.

Changing the support statement in Clang docs is out of scope for this PR.

mjklemm · 2025-03-28T11:29:02Z

flang/docs/OpenMPStandardsSupport.md

+| target teams distribute parallel loop simd construct       | P      | |
+
+## OpenMP 3.1, OpenMP 2.5, OpenMP 1.1
+All features except a few corner cases in atomic, copyin constructs/clauses are supported 


Should these corner cases be made explicit?

Precise OpenMP standards support information is being documented in llvm#132707 Flang now has good support for OpenMP Version 3.1 and earlier.

Precise OpenMP standards support information is being documented in #132707 Flang now has good support for OpenMP Version 3.1 and earlier.

h-vetinari

I'm excited to see this, thanks for adding it! This will close an old issue of mine :)

[Flang] Fortran / OpenMP conformance page #62310

h-vetinari · 2025-04-03T05:00:18Z

flang/docs/OpenMPStandardsSupport.md

+- **P** : When the implementation is incomplete for a few cases
+- **Y** : When the implementation is complete
+- **N** : When the implementation is absent


Might want to explain that this is Yes/No/Partial (presumably)

h-vetinari · 2025-04-03T05:02:20Z

flang/docs/OpenMPStandardsSupport.md

+
+This document summarizes OpenMP standards support in Flang. The information is only provided as a guideline. The
+TODOs/Not Yet Implemented messages emitted by the compiler for unimplemented features should be treated as authoritative.
+As of March 2025, standards support is provided upto OpenMP 4.0. We are actively working towards supporting OpenMP 4.5, OpenMP 5.* and OpenMP 6.0.


Note that https://clang.llvm.org/docs/OpenMPSupport.html has split OpenMP support into C/C++ & Fortran already. Presumably it makes sense to either fully join those documents, or remove the Fortran side from the clang docs, and just add a reference to this document.

Also typo

Suggested change

As of March 2025, standards support is provided upto OpenMP 4.0. We are actively working towards supporting OpenMP 4.5, OpenMP 5.* and OpenMP 6.0.

As of March 2025, standards support is provided up to OpenMP 4.0. We are actively working towards supporting OpenMP 4.5, OpenMP 5.* and OpenMP 6.0.

From the table below, OpenMP 4.0 support is not 100% complete yet, so maybe "up to" gives a wrong impression here; I'd read it as "4.0 support is fully implemented".

OpenMP standard -> OpenMP API specify corner cases for atomic, threadprivate Nit spellings

bhandarkar-pranav

Thank you, Kiran. Just one minor nit.

bhandarkar-pranav · 2025-04-09T14:41:13Z

flang/docs/OpenMPSupport.md

+
+This document outlines the OpenMP API features supported by Flang. It is intended as a general reference.
+For the most accurate information on unimplemented features, rely on the compiler’s TODO or “Not Yet Implemented”
+messages, which are considered authoritative. Flang provides full support for OpenMP 3.1 and partial support for


Nit: Like you mention in the section on previous standards (<=3.1) there are some, albeit very few, corner cases that are not supported. I think this line here is then misleading; it'll make a reader believe 3.1 is fully supported and chances are he won't bother to scroll down to the section below to find info about the corner cases. Perhaps consider something like, but not necessary exactly, the following

Aside from very few corner cases, Flang provides full support for OpenMP 3.1 [See detail here](#OpenMP 3.1,-OpenMP 2.5,-OpenMP-1.1). There is also partial (in development) support for OpenMP 4.0

(Note: I may have got the link syntax wrong especially around the use of commas).

Done. Thanks.

kparzysz

LGTM.

For any target construct we don't support the device clause. For distribute we don't support dist_schedule. For teams, we don't fully support reduction (e.g. no declare reduction).

kiranchandramohan · 2025-04-18T22:25:59Z

I plan to submit this PR early next week if there are no objections.

NimishMishra

LGTM. Thanks for this.

[Flang][OpenMP] Add OpenMP standards support doc

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llvmbot added the flang Flang issues not falling into any other category label Mar 24, 2025

kiranchandramohan commented Mar 24, 2025

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tblah added a commit to tblah/llvm-project that referenced this pull request Mar 31, 2025

[flang][OpenMP] Bump default OpenMP version to 3.1

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Precise OpenMP standards support information is being documented in llvm#132707 Flang now has good support for OpenMP Version 3.1 and earlier.

tblah mentioned this pull request Mar 31, 2025

[flang][OpenMP] Bump default OpenMP version to 3.1 #133745

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[flang][OpenMP] Bump default OpenMP version to 3.1 (#133745)

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Precise OpenMP standards support information is being documented in #132707 Flang now has good support for OpenMP Version 3.1 and earlier.

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tblah mentioned this pull request Apr 3, 2025

[ATfL] Add package documentation arm/arm-toolchain#248

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[Flang] Fortran / OpenMP conformance page #62310

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kiranchandramohan added 2 commits April 9, 2025 13:47

Address review comments

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OpenMP standard -> OpenMP API specify corner cases for atomic, threadprivate Nit spellings

Rename file in index.md

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kiranchandramohan added 2 commits April 9, 2025 17:45

Address comments from Pranav

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Fix link - attempt 1

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kiranchandramohan force-pushed the openmp_standards_support branch from 292a350 to 3230516 Compare April 9, 2025 16:55

Remove redundant sentence

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kparzysz approved these changes Apr 11, 2025

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Update target directives using info provided by Kryztof

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kiranchandramohan merged commit 2c2ba7e into llvm:main Apr 22, 2025
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[Flang][OpenMP] Add OpenMP standards support doc #132707

[Flang][OpenMP] Add OpenMP standards support doc #132707

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	Standards support is provided upto OpenMP 4.0 for now. It will be extended later for OpenMP 4.5, OpenMP 5.* and OpenMP 6.0.
	As of March 2025, standards support is provided upto OpenMP 4.0. It will be extended later for OpenMP 4.5, OpenMP 5.* and OpenMP 6.0.

	Note : No distinction is made between the support in the Parser/Semantics, MLIR or Lowering support, and OpenMPIRBuilder support.
	Note : No distinction is made between the support in Parser/Semantics, MLIR, Lowering or the OpenMPIRBuilder.

	This document summarizes OpenMP standards support in Flang. The information is only provided as a guideline. The
	This document summarizes the supported features of the OpenMP API in Flang. The information is only provided as a guideline. The

[Flang][OpenMP] Add OpenMP standards support doc #132707

[Flang][OpenMP] Add OpenMP standards support doc #132707

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