[Flang] Add a Fortran Standards Support doc #132195
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| <!--===- docs/FortranStandardsSupport.md | ||
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| 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 | ||
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| # Flang Fortran Standards Support | ||
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| ```{contents} | ||
| --- | ||
| local: | ||
| --- | ||
| ``` | ||
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| This document summarizes Fortran 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. | ||
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| The standards support information is provided as a table with three columns that are self explanatory. | ||
| The Status column uses the letters **Y**, **P**, **N** for the implementation status: | ||
| - **Y** : Yes. When the implementation is complete | ||
| - **P** : Partial. When the implementation is incomplete for a few cases | ||
| - **N** : No. When the implementation is absent | ||
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| There is no distinction made between support in the Parser/Semantics and the MLIR or Lowering stages. | ||
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There was a problem hiding this comment. Since all the contents in the first three sections are the same, I suggest to consolidate to the There was a problem hiding this comment. 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. |
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| Note: The two major missing features in Flang at present are coarrays and parameterized derived types (PDTs) with length type parameters. | ||
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| ## Fortran 2023 | ||
| See [document](F202X.md) for a brief discussion about the new features in Fortran 2023. The following table summarizes the | ||
| status of all important Fortran 2023 features. The table entries are based on the document [The new features in Fortran 2023](https://wg5-fortran.org/N2201-N2250/N2212.pdf). | ||
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| | Feature | Status | Comments | | ||
| |------------------------------------------------------------|--------|---------------------------------------------------------| | ||
| | Allow longer statement lines and overall statement length | Y | | | ||
| | Automatic allocation of lengths of character variables | N | | | ||
| | The specifiers typeof and classof | N | | | ||
| | Conditional expressions and arguments | N | | | ||
| | More use of boz constants | P | All usages other than enum are supported | | ||
| | Intrinsics for extracting tokens from a string | N | | | ||
| | Intrinsics for Trig functions that work in degrees | N | | | ||
| | Intrinsics for Trig functions that work in half revolutions| N | | | ||
| | Changes to system_clock | N | | | ||
| | Changes for conformance with the new IEEE standard | Y | | | ||
| | Additional named constants to specify kinds | Y | | | ||
| | Extensions for c_f_pointer intrinsic | N | | | ||
| | Procedures for converting between fortran and c strings | N | | | ||
| | The at edit descriptor | N | | | ||
| | Control over leading zeros in output of real values | N | | | ||
| | Extensions for Namelist | N | | | ||
| | Allow an object of a type with a coarray ultimate component to be an array or allocatable | N | | | ||
| | Put with Notify | N | | | ||
| | Error conditions in collectives | N | | | ||
| | Simple procedures | N | | | ||
| | Using integer arrays to specify subscripts | N | | | ||
| | Using integer arrays to specify rank and bound of an array | N | | | ||
| | Using an integer constant to specify rank | N | | | ||
| | Reduction specifier for do concurrent | P | Syntax is accepted | | ||
| | Enumerations | N | | | ||
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| ## Fortran 2018 | ||
| All features except those listed in the following table are supported. Almost all of the unsupported features are related to | ||
| the multi-image execution. The table entries are based on the document [The new features in Fortran 2018](https://wg5-fortran.org/N2151-N2200/ISO-IECJTC1-SC22-WG5_N2161_The_New_Features_of_Fortran_2018.pdf). | ||
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| | Feature | Status | Comments | | ||
| |------------------------------------------------------------|--------|---------------------------------------------------------| | ||
| | Asynchronous communication | P | Syntax is accepted | | ||
| | Teams | N | Multi-image/Coarray feature | | ||
| | Image failure | P | Multi-image/Coarray feature. stat_failed_image is added | | ||
| | Form team statement | N | Multi-image/Coarray feature | | ||
| | Change team construct | N | Multi-image/Coarray feature | | ||
| | Coarrays allocated in teams | N | Multi-image/Coarray feature | | ||
| | Critical construct | N | Multi-image/Coarray feature | | ||
| | Lock and unlock statements | N | Multi-image/Coarray feature | | ||
| | Events | N | Multi-image/Coarray feature | | ||
| | Sync team construct | N | Multi-image/Coarray feature | | ||
| | Image selectors | N | Multi-image/Coarray feature | | ||
| | Intrinsic functions get_team and team_number | N | Multi-image/Coarray feature | | ||
| | Intrinsic function image_index | N | Multi-image/Coarray feature | | ||
| | Intrinsic function num_images | N | Multi-image/Coarray feature | | ||
| | Intrinsic function this_image | N | Multi-image/Coarray feature | | ||
| | Intrinsic move_alloc extensions | P | Multi-image/Coarray feature | | ||
| | Detecting failed and stopped images | N | Multi-image/Coarray feature | | ||
| | Collective subroutines | N | Multi-image/Coarray feature | | ||
| | New and enhanced atomic subroutines | N | Multi-image/Coarray feature | | ||
| | Failed images and stat= specifiers | N | Multi-image/Coarray feature | | ||
| | Intrinsic function coshape | N | Multi-image/Coarray feature | | ||
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| ## Fortran 2008 | ||
| All features except those listed in the following table are supported. | ||
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| | 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) | | ||
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| ## Fortran 2003 | ||
| All features except those listed in the following table are supported. | ||
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| | Feature | Status | Comments | | ||
| |------------------------------------------------------------|--------|---------------------------------------------------------| | ||
| | Parameterized Derived Types | P | PDT with length type parameters is not supported. See [Proposal](ParameterizedDerivedTypes.md) | | ||
| | Assignment to allocatable | P | Assignment to whole allocatable in FORALL is not implemented | | ||
| | The VOLATILE attribute | P | VOLATILE in procedure interfaces is not implemented | | ||
| | Asynchronous input/output | P | IO will happen synchronously | | ||
| | MIN/MAX extensions for CHARACTER | P | Some variants are not supported | | ||
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| ## Fortran 95 | ||
| All features are supported. | ||
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| ## Fortran 90 | ||
| All features are supported. | ||
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| ## FORTRAN 77 | ||
| All features are supported. | ||
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This sentence is now repeated (just above the P/Y/N there's an equivalent one).
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Thanks. Removed the former occurence.