Dan Bonachea
9879da4f92
Update `flang/docs/FortranStandardsSupport.md` to reflect the current state of multi-image (coarray) feature support. The previous list of multi-image features was incomplete, and several multi-image features added in F2008 were inaccurately listed in the F2018 section. Recent PRs adding functionality now reflected in this document include: * #205847 * #192944 * #182110 Older (pre-22) PRs adding functionality that was not previously mentioned include: * #154081 * #154166
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Flang Fortran Standards Support
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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.
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 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.
| 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 | Y | |
| 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 | Y | |
| Intrinsics for Trig functions that work in degrees | Y | |
| Intrinsics for Trig functions that work in half revolutions | Y | |
| 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 | Y | |
| Procedures for converting between fortran and c strings | N | |
| The at edit descriptor | N | |
| Control over leading zeros in output of real values | Y | |
| Extensions for Namelist | N | |
| Allow an object of a type with a coarray ultimate component to be an array or allocatable | N | Multi-image/Coarray feature |
| Put with Notify | N | Multi-image/Coarray feature |
| Error conditions in collectives | P | Experimental support via PRIF |
| 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 | Y | |
| 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.
| Feature | Status | Comments |
|---|---|---|
| Asynchronous communication | P | Syntax is accepted |
| Collective subroutines | P | Experimental support via PRIF, missing co_reduce |
| Intrinsic function coshape | P | Experimental support via PRIF |
| Form team statement | P | Experimental support via PRIF |
| Change team construct | P | Experimental support via PRIF, missing coarray association |
| Sync team statement | P | Experimental support via PRIF |
| Intrinsic functions get_team and team_number | P | Experimental support via PRIF |
| Team arguments to other intrinsics | P | Experimental support via PRIF |
| Coarrays allocated in teams | N | Multi-image/Coarray feature |
| Critical construct | N | Multi-image/Coarray feature |
| Events | N | Multi-image/Coarray feature |
| Intrinsic move_alloc extensions | P | Multi-image/Coarray feature |
| Detecting failed and stopped images | N | Multi-image/Coarray feature |
| New and enhanced atomic subroutines | N | Multi-image/Coarray feature |
| Image failure and stat= specifiers | P | Multi-image/Coarray feature. stat_failed_image is added |
Fortran 2008
All features except those listed in the following table are supported.
| Feature | Status | Comments |
|---|---|---|
| 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 FAQ and Proposal |
| Intrinsic functions this_image, num_images | P | Experimental support via PRIF |
| Sync all, sync images, sync memory statements | P | Experimental support via PRIF |
| Non-allocatable save coarrays of intrinsic type | P | Experimental support via PRIF |
| Other coarray data objects | N | Multi-image/Coarray feature |
| Intrinsic functions image_index, ucobound, lcobound | P | Experimental support via PRIF |
| Image selectors (coindexed access) | N | Multi-image/Coarray feature |
| Atomic subroutines | N | Multi-image/Coarray feature |
| Lock and unlock statements | N | Multi-image/Coarray feature |
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 |
| Assignment to allocatable | P | Assignment to whole allocatable in FORALL 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.