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[Flang] Add a Fortran Standards Support doc #132195

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[Flang] Add a Fortran Standards Support doc
kiranchandramohan Mar 20, 2025
8499992
Address review comments
kiranchandramohan Mar 21, 2025
6c4b380
Add support tables for Fortran 2023 and Fortran 2018 standards
kiranchandramohan Mar 23, 2025
84165a7
Move MIN MAX extension to Fortran 2003 table
kiranchandramohan Mar 23, 2025
8f9db84
Remove line about extending support for Fortran 2018 and Fortran 2023
kiranchandramohan Mar 24, 2025
8eb16e4
Address review comments
kiranchandramohan Mar 24, 2025
6781534
Address review comment about multi-image execution
kiranchandramohan Mar 24, 2025
66199ad
Partially address comments from Mark
kiranchandramohan Apr 19, 2025
04fb498
Address Steve's comments
kiranchandramohan Apr 20, 2025
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Remove duplicate sentence
kiranchandramohan Apr 21, 2025
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Address comment from h.vetinari
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63 changes: 63 additions & 0 deletions flang/docs/FortranStandardsSupport.md
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<!--===- docs/FortranStandardsSupport.md

Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
See https://llvm.org/LICENSE.txt for license information.
SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

-->

# Flang's Fortran standards support
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@mjklemm mjklemm Mar 20, 2025

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Suggested change
# Flang's Fortran standards support
# Flang Fortran Standards Support

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@kiranchandramohan kiranchandramohan Mar 21, 2025

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Done


```{contents}
---
local:
---
```

This document summarizes Flang's Fortran standards support. The information is only provided as a guideline. The compiler emits
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@kkwli kkwli Mar 20, 2025

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If we take the suggested change above, should we also remove 's here? Or just rephrase it to:

This document summarizes Fortran standards support in Flang.

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@kiranchandramohan kiranchandramohan Mar 21, 2025

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Done

TODOs/Not Yet Implemented messages for unimplemented features and that should be treated as the authoratative information.
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@tarunprabhu tarunprabhu Mar 20, 2025

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Suggested change
This document summarizes Flang's Fortran standards support. The information is only provided as a guideline. The compiler emits
TODOs/Not Yet Implemented messages for unimplemented features and that should be treated as the authoratative information.
This document summarizes Flang's Fortran standards support. 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.

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@kiranchandramohan kiranchandramohan Mar 21, 2025

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Done

Standards support is provided upto Fortran 2008 for now. It will be later extended for Fortran 2018 and Fortran 2023.
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@tarunprabhu tarunprabhu Mar 20, 2025

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Standards support is provided upto Fortran 2008 for now. It will be later extended for Fortran 2018 and Fortran 2023.
Standards support is provided upto Fortran 2008 for now. It will be extended later for Fortran 2018 and Fortran 2023.

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@kiranchandramohan kiranchandramohan Mar 21, 2025

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Done

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@rouson rouson Mar 24, 2025

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"upto" should be "up to"

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@kiranchandramohan kiranchandramohan Mar 24, 2025

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I have removed this sentence.


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 various implementation status.
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@mjklemm mjklemm Mar 20, 2025

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the letters **P**, **Y**, **N** for the various implementation status.
the letters **P**, **Y**, **N** for the implementation status:

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@kiranchandramohan kiranchandramohan Mar 21, 2025

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Done

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

Note 1 : No distinction is made between the support in the Parser/Semantics and MLIR or Lowering support.
Note 2 : Besides the features listed below a few intrinsics like MIN/MAX are not supported for a few cases with CHARACTER type.
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@tarunprabhu tarunprabhu Mar 20, 2025

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Do we have a list of the intrinsics where support for CHARACTER types is incomplete? If it is not too difficult to identify these, a complete list may be better than alluding to "a few intrinsics".

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@kiranchandramohan kiranchandramohan Mar 21, 2025

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I do not have a list of intrinsics here. The only ones I am actually aware or the MIN/MAX intrinsic. Since I was not 100% I am making a conservative statement here. Do we want to just say MIN/MAX only? Do you have additional info in the gfortran testsuite?

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@tarunprabhu tarunprabhu Mar 21, 2025

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I can check to see if there are any failures as a result of this. I don't know off the top of my head.


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@kkwli kkwli Mar 20, 2025

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Since all the contents in the first three sections are the same, I suggest to consolidate to the FORTRAN77, Fortran 90 and Fortran 95 section. In addition, if we take Michael's suggestion to populate the Fortran 2018 and Fortran 2023 sections, I suggest to re-order the sections to start with Fortran 2023 first. I think people are more interested in which newer features that flang support nowadays.

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@kiranchandramohan kiranchandramohan Mar 21, 2025

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I have reorganized in descending order of standards. I do not have entries for 2018 and 2023 now. If it is OK, we can add that in subsequent PRs.
I have not consolidated FORTRAN77, Fortran 90 and Fortran 95. I can do so before submitting if there are no reports of unsupported features in this review.

## Fortran 77
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@kkwli kkwli Mar 20, 2025

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FORTRAN 77 - consistent with what we use in FortranFeatureHistory.md

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@kiranchandramohan kiranchandramohan Mar 21, 2025

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Done

All features are supported.

## Fortran 90
All features are supported.

## Fortran 95
All features are supported.

## Fortran 2003
All features except those listed in the following table are supported.

| Feature | Status | Comments |
|------------------------------------------------------------|--------|---------------------------------------------------------|
| Parameterized Derived Types | P | PDT with length type is not supported. See [Proposal](ParameterizedDerivedTypes.md) |
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@DanielCChen DanielCChen Mar 20, 2025

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length type => length type parameters

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@kiranchandramohan kiranchandramohan Mar 21, 2025

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Done

| Assignment to allocatable | P | Assignment to whole allocatable in FORALL is not implemented |
| Pointer Assignment | P | Polymorphic assignment in FORALL is not implemented |
| The VOLATILE attribute | P | Volatile in procedure interfaces is not implemented |
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@DanielCChen DanielCChen Mar 20, 2025

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Volatile => VOLATILE
as it refers to the attribute.

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@kiranchandramohan kiranchandramohan Mar 21, 2025

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Done

| Asynchronous input/output | P | IO will happen synchronously |

## Fortran 2008
All features except those listed in the following table are supported.

| Feature | Status | Comments |
|------------------------------------------------------------|--------|---------------------------------------------------------|
| Coarrays | N | Lowering and runtime support is not implemented |
| do concurrent | P | Sequential execution works. Parallel support in progress|
| Internal procedure as an actual argument or pointer target | Y | Current implementation requires stack to be executable. See [Proposal](InternalProcedureTrampolines.md) |

## Fortran 2018
TBD

## Fortran 2023
TBD
1 change: 1 addition & 0 deletions flang/docs/index.md
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Expand Up @@ -26,6 +26,7 @@ on how to get in touch with us and to learn more about the current status.
C++style
DesignGuideline
FortranForCProgrammers
FortranStandardsSupport
GettingInvolved
GettingStarted
ImplementingASemanticCheck
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