Flang Fortran Standards Support

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:

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

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

Y

See Do Concurrent Conversion To OpenMP for implementation details.

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.