Flang OpenMP Support¶

This document outlines the OpenMP API features supported by Flang. It is intended as a general reference. For the most accurate information on unimplemented features, rely on the compiler’s TODO or “Not Yet Implemented” messages, which are considered authoritative. Flang provides complete implementation of the OpenMP 3.1 specification and partial implementation of OpenMP 4.0. The sections below summarize support status for OpenMP 4.0, 5.0, 5.1, 5.2, 6.0, and future 6.1. The table entries are derived from the information provided in the Version Differences subsection of the Features History section in the OpenMP standard.

The Status column uses the following values:

unclaimed : No implementation is known to be underway.
partial : Some support exists, but important cases are still missing.
in progress : Work is actively underway, or the implementation is available only experimentally.
done : The feature is considered implemented.

The OpenMP 4.0 section uses the historical Feature/Status/Comments format with an added Claimed By column. OpenMP 5.0 and newer sections use Feature/Status/Claimed By/Notes/Reviews to capture implementation state, ownership, and upstream references. Use GitHub usernames in Claimed By (for example @alice). Leave the cell blank when nobody has claimed the work.

This page is for OpenMP features that require changes in Flang compiler components (parser, semantics, lowering, diagnostics) and that may additionally entail corresponding runtime support. OpenMP features whose status does not involve updates to the Flang compiler are tracked under the Clang OpenMP Support page (clang/docs/OpenMPSupport.rst).

Updating This Page ¶

When claiming a feature, set Status to in progress and add the GitHub username in Claimed By.
When a GitHub PR is opened, add the PR link in Reviews. Keep the claimant listed until the work is finished or unclaimed.
When support lands but remains incomplete, set Status to partial and summarize the missing parser, semantics, lowering, diagnostics, or test work in Notes.
When support is complete, set Status to done. Clear Claimed By if no further follow-up is expected.
When work is abandoned or not yet started, set Status to unclaimed, remove the claimant, and keep Notes focused on the missing implementation work.

Note: In the OpenMP 4.0 section, no distinction is made between support in Parser/Semantics, MLIR, Lowering, or the OpenMPIRBuilder.

OpenMP 4.0 ¶

Feature	Status	Comments
proc_bind clause	done
simd construct	partial	Implicit linearization is skipped if iv is a pointer or allocatable
declare simd construct	partial	Semantics coverage exists (for example `flang/test/Semantics/OpenMP/declarative-directive01.f90`) and lowering exists for key forms (for example `flang/test/Lower/OpenMP/declare-simd-interface-body.f90`), but coverage is not yet complete for all variants.
do simd construct	partial	Implicit linearization is skipped if iv is a pointer or allocatable
target data construct	done
target construct	done
target update construct	done
declare target directive	done
teams construct	done
distribute construct	done
distribute simd construct	partial	Implicit linearization is skipped if iv is a pointer or allocatable
distribute parallel loop construct	done
distribute parallel loop simd construct	partial	Implicit linearization is skipped if iv is a pointer or allocatable
depend clause	done
declare reduction construct	partial	Partial support, including user-defined reductions with derived types.
atomic construct extensions	done
cancel construct	done
cancellation point construct	done
parallel do simd construct	partial	Implicit linearization is skipped if iv is a pointer or allocatable
target teams construct	done
teams distribute construct	done
teams distribute simd construct	partial	Implicit linearization is skipped if iv is a pointer or allocatable
target teams distribute construct	done
teams distribute parallel loop construct	done
target teams distribute parallel loop construct	done
teams distribute parallel loop simd construct	partial	Implicit linearization is skipped if iv is a pointer or allocatable
target teams distribute parallel loop simd construct	partial	Implicit linearization is completely skipped

OpenMP 5.0 ¶

Feature	Status	Notes	Reviews
taskloop and combined taskloop forms	partial	Covered in semantics/lowering tests including `flang/test/Semantics/OpenMP/taskloop01.f90`, `flang/test/Semantics/OpenMP/taskloop-simd01.f90`, `flang/test/Lower/OpenMP/taskloop.f90`, and `flang/test/Lower/OpenMP/master_taskloop_simd.f90`. Lowering for taskloop simd and combined forms is still TODO.	llvm/llvm-project#138646, llvm/llvm-project#165851, llvm/llvm-project#187222
memory allocators	partial	Semantics coverage exists in `flang/test/Semantics/OpenMP/allocators01.f90`-`flang/test/Semantics/OpenMP/allocators07.f90`; lowering gaps remain (for example `flang/lib/Lower/OpenMP/OpenMP.cpp` TODO paths).
allocate directive and allocate clause	partial	Semantics coverage exists in `flang/test/Semantics/OpenMP/allocate-directive.f90` and `flang/test/Semantics/OpenMP/allocate-clause01.f90`; lowering support expanded, with remaining TODO coverage (`flang/test/Lower/OpenMP/Todo/allocate-clause-align.f90`, `flang/test/Lower/OpenMP/Todo/allocate-clause-allocator.f90`).	llvm/llvm-project#121356, llvm/llvm-project#165719, llvm/llvm-project#165865, llvm/llvm-project#187167
metadirective	partial	Semantics coverage exists in `flang/test/Semantics/OpenMP/metadirective-construct.f90`; lowering support exists for several construct-selector paths (`flang/test/Lower/OpenMP/metadirective-construct.f90`, `flang/test/Lower/OpenMP/metadirective-nothing.f90`), but some selector/variant paths remain TODO-tracked in lowering.	llvm/llvm-project#159945, llvm/llvm-project#193664, llvm/llvm-project#194402, llvm/llvm-project#194424
support full defaultmap functionality	partial	Core coverage exists (`flang/test/Lower/OpenMP/defaultmap.f90`, `flang/test/Semantics/OpenMP/defaultmap-clause-v50.f90`), but lowering has known partial paths (for example defaultmap-firstprivate TODO tests).	llvm/llvm-project#135226, llvm/llvm-project#166715, llvm/llvm-project#167806, llvm/llvm-project#177389, llvm/llvm-project#190764
clause: uses_allocators	partial	Parsed/checked in semantics allocator tests, but lowering has explicit TODO handling (`cp.processTODO<...UsesAllocators>` in `flang/lib/Lower/OpenMP/OpenMP.cpp`).
clause: in_reduction	partial	Semantics and lowering coverage exists for several task/taskgroup/taskloop forms (`flang/test/Semantics/OpenMP/in-reduction.f90`, `flang/test/Lower/OpenMP/task-inreduction.f90`, `flang/test/Lower/OpenMP/taskloop-inreduction.f90`, `flang/test/Lower/OpenMP/taskgroup-task_reduction02.f90`); some target-related forms remain TODO (for example `flang/test/Lower/OpenMP/Todo/target-inreduction.f90`).	llvm/llvm-project#139704, llvm/llvm-project#205124
user-defined mappers	done	Supported with semantics/lowering/transform coverage.	llvm/llvm-project#140560, llvm/llvm-project#163860, llvm/llvm-project#167903, llvm/llvm-project#179936, llvm/llvm-project#189136
map array-section with implicit mapper	partial	Mapper and map coverage exists (`flang/test/Lower/OpenMP/map-mapper.f90`, `flang/test/Lower/OpenMP/target-data-skip-mapper-calls.f90`), with remaining iterator/modifier gaps in lowering (`flang/lib/Lower/OpenMP/ClauseProcessor.cpp` TODOs).	llvm/llvm-project#175133, llvm/llvm-project#177389
clause: use_device_addr for target data	done	Supported for core forms.	llvm/llvm-project#82834, llvm/llvm-project#176815
support non-contiguous array sections for target update	partial	Target update coverage exists (`flang/test/Semantics/OpenMP/target-update01.f90`, `flang/test/Semantics/OpenMP/target-update-mapper.f90`), with additional corner-case validation still ongoing.
pointer attachment	partial	Pointer mapping coverage exists (`flang/test/Semantics/OpenMP/use_device_ptr.f90`, `flang/test/Lower/OpenMP/pointer-to-array.f90`), with descriptor and attach-related TODOs remaining in lowering.
hints for the atomic construct	partial	Semantics coverage exists (`flang/test/Semantics/OpenMP/atomic-hint-clause.f90`) and lowering coverage exists for common atomic forms; compare/fail forms remain partial.
conditional modifier for lastprivate clause	unclaimed	Lastprivate lowering/semantics coverage exists for base forms, but no dedicated support coverage for the conditional modifier was identified in current Flang tests.
task affinity	partial	Semantics and lowering coverage exists, including iterator-based affinity in task constructs (`flang/test/Semantics/OpenMP/affinity-clause.f90`, `flang/test/Lower/OpenMP/task-affinity.f90`).	llvm/llvm-project#179003, llvm/llvm-project#182222

OpenMP 5.1 ¶

Feature	Status	Notes	Reviews
compare clause on atomic construct	partial	Semantics and lowering coverage exist (`flang/test/Semantics/OpenMP/atomic-compare.f90`, `flang/test/Lower/OpenMP/atomic-compare.f90`); remaining gaps are primarily fail/capture combinations and broader type coverage.	llvm/llvm-project#184761
fail clause on atomic construct	partial	Semantics coverage exists (`flang/test/Semantics/OpenMP/atomic-compare.f90`), but lowering for `fail(...)` paths is still TODO (`flang/test/Lower/OpenMP/Todo/atomic-compare-fail.f90`). Complete lowering for compare+fail(+capture), then add non-TODO lowering tests.	llvm/llvm-project#184761
interop construct	partial	Semantics coverage exists (`flang/test/Semantics/OpenMP/interop-construct.f90`), but lowering remains TODO-tracked (`flang/lib/Lower/OpenMP/OpenMP.cpp` TODO: `OpenMPInteropConstruct`; `flang/test/Lower/OpenMP/Todo/interop-construct.f90`).
dispatch construct	partial	Semantics coverage exists (`flang/test/Semantics/OpenMP/dispatch.f90`), but lowering remains TODO-tracked (`flang/lib/Lower/OpenMP/OpenMP.cpp` TODO: `OpenMPDispatchConstruct`; `flang/test/Lower/OpenMP/Todo/dispatch.f90`).
masked construct	partial	Covered in semantics/lowering (`flang/test/Semantics/OpenMP/masked.f90`, `flang/test/Lower/OpenMP/masked.f90`).	llvm/llvm-project#91432
masked combined constructs	partial	Covered in lowering tests (`flang/test/Lower/OpenMP/masked_taskloop.f90`, `flang/test/Lower/OpenMP/parallel-masked-taskloop.f90`) with ongoing breadth expansion.
present map type modifier	partial	Semantics coverage exists (`flang/test/Semantics/OpenMP/present.f90`) and map lowering exists, with ongoing completeness checks.
present modifier in motion clauses	partial	Motion/update coverage exists (`flang/test/Semantics/OpenMP/target-update01.f90`, `flang/test/Semantics/OpenMP/target-update-mapper.f90`), with ongoing completeness checks.
present in defaultmap clause	partial	Defaultmap semantics coverage exists (`flang/test/Semantics/OpenMP/defaultmap-clause-v50.f90`), with ongoing completeness checks.
thread_limit clause on target construct	partial	Lowering/semantics coverage exists for thread-limit dimensions (`flang/test/Lower/OpenMP/thread-limit-dims.f90`), with additional target interactions still under validation.	llvm/llvm-project#171454, llvm/llvm-project#171825
has_device_addr clause on target construct	partial	Semantics/lowering coverage exists (`flang/test/Lower/OpenMP/has_device_addr-mapinfo.f90`) with ongoing validation for all mapping combinations.
iterators in map or motion clauses	partial	Some iterator coverage exists (`flang/test/Lower/OpenMP/depend-iterator.f90`), but lowering still has explicit iterator TODOs in `flang/lib/Lower/OpenMP/ClauseProcessor.cpp`.
scope construct	partial	Scope construct support is available, with follow-on completeness work still in progress for some combinations (see also OpenMP 5.2 scope-related rows).	llvm/llvm-project#113700, llvm/llvm-project#193098
assumes directives	unclaimed	Lowering still has explicit TODO (`flang/lib/Lower/OpenMP/OpenMP.cpp` TODO: `OpenMP ASSUMES declaration`; `flang/test/Lower/OpenMP/Todo/assumes.f90`).	llvm/llvm-project#102008
assume directive	unclaimed	Lowering still has explicit TODO (`flang/lib/Lower/OpenMP/OpenMP.cpp` TODO: `OpenMP ASSUME construct`; `flang/test/Lower/OpenMP/Todo/assume.f90`).	llvm/llvm-project#102008
default(firstprivate)	partial	Semantics coverage exists (`flang/test/Semantics/OpenMP/default02.f90`), but defaultmap-firstprivate lowering remains partial (`flang/test/Lower/OpenMP/Todo/defaultmap-clause-firstprivate.f90`).
default(private)	partial	Semantics/default-clause coverage exists (`flang/test/Semantics/OpenMP/default.f90`, `flang/test/Semantics/OpenMP/default02.f90`) with ongoing lowering completeness checks.
inoutset in depend clause	partial	Semantics coverage exists (`flang/test/Semantics/OpenMP/depend06.f90`) with broader lowering/runtime verification ongoing.
nowait clause on taskwait	partial	Taskwait coverage exists (`flang/test/Semantics/OpenMP/taskwait.f90`, `flang/test/Lower/OpenMP/taskwait.f90`), with nowait+depend combinations still partial (`flang/test/Lower/OpenMP/Todo/taskwait-nowait.f90`).
strict modifier for taskloop construct	unclaimed	No dedicated parser/semantics/lowering coverage for the taskloop strict modifier was identified in current Flang OpenMP tests.

OpenMP 5.2 ¶

Feature	Status	Notes	Reviews
if clause on teams construct	partial	Semantics coverage exists for teams-specific `if` forms (for example `flang/test/Semantics/OpenMP/if-clause.f90` with `if(teams: ...)` cases).
step modifier	unclaimed	Add parser+semantics acceptance/diagnostics for OpenMP 5.2 step-modifier forms, then add lowering coverage showing emitted loop metadata/ops for accepted cases.
declare mapper iterator modifier	unclaimed	Parser and semantics should accept iterator-modified DECLARE MAPPER forms, then lowering must thread iterator bounds through map info generation (see related TODO test `flang/test/Lower/OpenMP/Todo/declare-mapper-iterator.f90`).
otherwise clause on metadirectives	unclaimed	BEGIN/END METADIRECTIVE frontend support exists, but metadirective lowering remains TODO (`flang/lib/Lower/OpenMP/OpenMP.cpp`). Implement lowering selection for OTHERWISE and add dedicated lowering tests for construct selection.	llvm/llvm-project#194402
doacross with omp_cur_iteration	unclaimed	Implement parser/semantics validation for `omp_cur_iteration` placement and lowering of doacross dependence tokens, then add semantics+lowering tests for source/sink combinations.
implicit map type for target enter and exit data	unclaimed	Define implicit-map behavior for enter/exit data in lowering map finalization and add dedicated tests covering pointer/allocatable/component cases and mapper interactions.
allocate and firstprivate on scope directive	partial	Scope lowering coverage includes `allocate` and `firstprivate` on scope directives (`flang/test/Lower/OpenMP/scope.f90`, `flang/test/Lower/OpenMP/target-scope.f90`).	llvm/llvm-project#193098
loop consistency changes for order clause	unclaimed	Extend semantic loop-consistency checks for updated ORDER rules and add diagnostics tests for invalid nest/ordering combinations.
keep original base pointer on map without matched candidate	unclaimed	Update map finalization so unmatched candidates preserve original base-pointer mapping semantics; add lowering tests for pointer-member mapping regressions.
pure procedure support for certain directives	unclaimed	Codify semantics restrictions for PURE procedures with these directives and add lowering tests ensuring no illegal side-effecting ops are introduced.
ALLOCATE statement support for allocators	unclaimed	Wire OpenMP allocator semantics into Fortran ALLOCATE statement handling and add semantics+lowering tests for allocator traits and error paths.
dispatch extension supporting end directive	unclaimed	Base dispatch support is partial, and no dedicated support coverage for the OpenMP 5.2 dispatch end-directive extension was identified.
minus operator deprecation handling	partial	Partially handled in semantic diagnostics.
linear clause syntax deprecation	unclaimed	Add semantic deprecation diagnostics with fix-it guidance and tests for accepted/deprecated spellings.
map clause modifiers without commas (deprecation)	unclaimed	Add parser/semantics deprecation diagnostics for comma-less map modifiers and tests that verify warning text and accepted replacements.
uses_allocators list syntax (deprecation)	unclaimed	Add diagnostics for deprecated uses_allocators list syntax and ensure lowering still handles canonical replacements.
default clause on metadirectives (deprecation)	unclaimed	Add dedicated metadirective deprecation diagnostics and tests for legacy/default-clause usage.
destroy clause syntax on depobj (deprecation)	partial	Deprecation diagnostics are implemented (for example warning coverage in `flang/test/Semantics/OpenMP/depobj-construct-v52.f90`).
source and sink task-dependence modifiers (deprecation)	partial	Deprecation diagnostics are implemented (for example warning coverage in `flang/test/Semantics/OpenMP/depobj-construct-v52.f90`).
interop type position on init clause (deprecation)	unclaimed	Add parser+semantics deprecation diagnostics for legacy interop init type-position forms and tests showing canonical replacement.

OpenMP 6.0 ¶

Feature	Status	Notes	Reviews
threadset clause	partial	Semantics coverage exists (`flang/test/Semantics/OpenMP/threadset-clause.f90`) with ongoing lowering/runtime validation.	llvm/llvm-project#169856
groupprivate directive	partial	Semantics and lowering coverage exists (`flang/test/Semantics/OpenMP/groupprivate.f90`, `flang/test/Lower/OpenMP/groupprivate.f90`, `flang/test/Lower/OpenMP/groupprivate-modfile.f90`), with remaining limitations in lowering scope/placement (for example currently materialized for `teams`-based paths).	llvm/llvm-project#166199, llvm/llvm-project#166214, llvm/llvm-project#180934
recording of task graphs	in progress	Semantics coverage exists (`flang/test/Semantics/OpenMP/taskgraph.f90`).
workdistribute construct	partial	Semantics/lowering/transform coverage exists (`flang/test/Semantics/OpenMP/workdistribute01.f90`, `flang/test/Lower/OpenMP/workdistribute.f90`, `flang/test/Transforms/OpenMP/lower-workdistribute-fission.mlir`) including `target teams` placement updates; some team-nesting combinations still intentionally diagnose as unsupported.	llvm/llvm-project#154377, llvm/llvm-project#154378, llvm/llvm-project#140523, llvm/llvm-project#199006
map clause updates (v6.0 forms)	partial	Semantics coverage exists (`flang/test/Semantics/OpenMP/map-clause-v60.f90`) with ongoing lowering completeness work.
map modifier updates (v6.0 and v6.1 forms)	partial	Semantics coverage exists (`flang/test/Semantics/OpenMP/map-modifiers-v60.f90`, `flang/test/Semantics/OpenMP/map-modifiers-v61.f90`) with ongoing lowering completeness work.	llvm/llvm-project#172080, llvm/llvm-project#176810
loop fusion transformation	done	Supported.	llvm/llvm-project#161213
loop construct with DO CONCURRENT	in progress	Experimental support is available and under active development.	llvm/llvm-project#178138, llvm/llvm-project#190990
optional argument for all clauses	partial	Semantics coverage exists across clause tests (for example `flang/test/Semantics/OpenMP/if-clause-50.f90`).
canonical loop sequences	partial	Related loop/transform coverage exists (`flang/test/Semantics/OpenMP/loop-transformation-construct01.f90`, `flang/test/Lower/OpenMP/loop-directive.f90`).	llvm/llvm-project#161213, llvm/llvm-project#168884, llvm/llvm-project#170734, llvm/llvm-project#170735
pure directives in DO CONCURRENT	unclaimed	Define exact PURE+DO CONCURRENT directive legality in semantics and add lowering tests proving accepted forms remain side-effect safe.
extensions to depobj construct	unclaimed	Semantics and deprecation diagnostics exist for several depobj forms, but extension support remains incomplete in lowering (for example `flang/test/Lower/OpenMP/Todo/depobj-construct.f90`). Implement lowering for extension operands/modifiers and add non-TODO lowering tests.
extensions to atomic construct	partial	Atomic compare lowering is now available (`flang/test/Lower/OpenMP/atomic-compare.f90`), but fail/capture-related extension paths remain incomplete (`flang/test/Lower/OpenMP/Todo/atomic-compare-fail.f90`).	llvm/llvm-project#184761
clarifications to Fortran map semantics	unclaimed	Document each 6.0 clarification point against existing map finalization behavior, then add focused semantics/lowering regression tests for unresolved points.

OpenMP 6.1 (Future / Experimental)¶

Feature	Status	Notes	Reviews
dyn_groupprivate clause	in progress	Experimental and in progress (`flang/test/Semantics/OpenMP/dyn-groupprivate.f90`).	llvm/llvm-project#166199, llvm/llvm-project#166214
dims strict behavior (multidimensional teams/leagues)	in progress	Experimental and in progress (`flang/test/Lower/OpenMP/thread-limit-dims.f90`).	llvm/llvm-project#171454, llvm/llvm-project#171767, llvm/llvm-project#171825
attach map-type modifier	partial	Parser/semantics/lowering coverage exists (`flang/test/Parser/OpenMP/map-modifiers-v61.f90`, `flang/test/Semantics/OpenMP/map-modifiers-v61.f90`, `flang/test/Lower/OpenMP/attach-and-ref-modifier.f90`); broader integration coverage across additional mapping contexts is still in progress.	llvm/llvm-project#177715, llvm/llvm-project#177301, llvm/llvm-project#177302
need_device_ptr modifier for adjust_args clause	unclaimed	Add parser+semantics support for modifier placement/rules, then lower adjust_args with device-pointer selection semantics and add end-to-end tests.
fallback modifier for use_device_ptr clause	unclaimed	Add parser+semantics diagnostics and lowering behavior for fallback selection; add tests for fallback and non-fallback resolution paths.
loop flatten transformation	unclaimed	Implement parser/semantics acceptance and lowering transform plumbing, then add transform/lowering tests demonstrating flattened loop mapping.
loop grid and tile modifiers for sizes clause	unclaimed	Extend clause parsing/semantics for grid/tile size modifiers and add lowering tests showing generated loop partitioning metadata/ops.

Extensions ¶

ATOMIC construct ¶

The implementation of the ATOMIC construct follows OpenMP 6.0 with the following extensions:

x = x is an allowed form of ATOMIC UPDATE. This is motivated by the fact that the equivalent forms x = x+0 or x = x*1 are allowed.
Explicit type conversions are allowed in ATOMIC READ, WRITE or UPDATE constructs, and in the capture statement in ATOMIC UPDATE CAPTURE. The OpenMP spec requires intrinsic- or pointer-assignments, which include (as per the Fortran standard) implicit type conversions. Since such conversions need to be handled, allowing explicit conversions comes at no extra cost.
A literal .true. or .false. is an allowed condition in ATOMIC UPDATE COMPARE. [1]
A logical variable is an allowed form of the condition even if its value is not computed within the ATOMIC UPDATE COMPARE construct [1].
expr equalop x is an allowed condition in ATOMIC UPDATE COMPARE. [1]

[1] Code generation for ATOMIC UPDATE COMPARE is not implemented yet.