flang/docs/FortranStandardsSupport.md - third_party/llvm-project - Git at Google

 <!--===- 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 Fortran Standards Support

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

 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.

 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

 There is no distinction made between support in the Parser/Semantics and the MLIR or Lowering stages.

 Note: The two major missing features in Flang at present are coarrays and parameterized derived types (PDTs) with length type parameters.


 ## 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).

 | 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      | |

 ## 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).

 | 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 |

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

 | 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                         |

 ## Fortran 95
 All features are supported.

 ## Fortran 90
 All features are supported.

 ## FORTRAN 77
 All features are supported.
	<!--===- 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 Fortran Standards Support

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

	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.

	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

	There is no distinction made between support in the Parser/Semantics and the MLIR or Lowering stages.

	Note: The two major missing features in Flang at present are coarrays and parameterized derived types (PDTs) with length type parameters.


	## 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).

	\| 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 \| \|

	## 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).

	\| 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 \|

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

	\| 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 \|

	## Fortran 95
	All features are supported.

	## Fortran 90
	All features are supported.

	## FORTRAN 77
	All features are supported.