# OpenMP* Pragmas

This is a summary of the OpenMP* pragmas supported in the Intel® C++ Compiler Classic. For detailed information about the OpenMP API, see the OpenMP Application Program Interface Version 5.1 specification, which is available from the OpenMP web site.

## PARALLEL Pragma

Use this pragma to form a team of threads and execute those threads in parallel.

Pragma | Description
--- | ---
omp parallel | Specifies that a structured block should be run in parallel by a team of threads.

## TASKING Pragma

Use these pragmas for deferring execution.

Pragma | Description
--- | ---
omp task | Specifies a code block whose execution may be deferred.
omp taskloop | Specifies that the iterations of one or more associated for loops should be executed using OpenMP tasks. The iterations are distributed across tasks that are created by the construct and scheduled to be executed in parallel by the current team.

## WORKSHARING Pragmas

Use these pragmas to share work among a team of threads.

Pragma | Description
--- | ---
omp for | Specifies a work-sharing loop. Iterations of the loop are executed in parallel by the threads in the team.
omp sections | Defines a set of structured blocks that will be distributed among the threads in the team.
omp single | Specifies that a block of code is to be executed by only one thread in the team.

## SYNCHRONIZATION Pragmas

Use these pragmas to synchronize between threads.

Pragma | Description
--- | ---
omp atomic | Specifies a computation that must be executed atomically.
omp barrier | Specifies a point in the code where each thread must wait until all threads in the team arrive.
omp critical | Specifies a code block that is restricted to access by only one thread at a time.
omp flush | Identifies a point at which a thread's temporary view of memory becomes consistent with the memory.
omp master | Specifies a code block that must be executed only once by the primary thread of the team.
omp ordered | Specifies a block of code that the threads in a team must execute in the natural order of the loop iterations, or as a stand-alone directive, specifies cross-iteration dependences in a doacross loop-nest. The following clauses are available as Intel-specific extensions of the OpenMP* specification: monotonic Specifies a block of code in which the value of the new list item on each iteration of the associated SIMD loop(s) corresponds to the value of the original list item before entering the associated loop, plus the number of the iterations for which the conditional update happens prior to the current iteration, times linear-step. The value corresponding to the sequentially last iteration of the associated loop(s) is assigned to the original list item. Use with the simd clause. overlap Specifies a block of code that has to be executed scalar for overlapping inx values and parallel for different inx values within SIMD loop. Use with the simd clause.
omp taskgroup | Causes the program to wait until the completion of all enclosed and descendant tasks.
omp taskwait | Specifies a wait on the completion of child tasks generated since the beginning of the current task.
omp taskyield | Specifies that the current task can be suspended at this point in favor of execution of a different task.

## Data Environment Pragmas

Use these pragmas to affect the data environment.

Pragma | Description
--- | ---
omp scan | Specifies a scan computation that updates each list item in each iteration of the loop.
omp threadprivate | Specifies a list of globally-visible variables that will be allocated private to each thread.

## Offload Target Control Pragmas

Use these pragmas to control execution on one or more offload targets.

Pragma | Description
--- | ---
omp distribute | Specifies that the iterations of one or more loops should be distributed among the initial threads of all thread teams in a league.
omp target enter data |
omp target exit data |
omp teams | Creates a league of thread teams inside a target region to execute a structured block in the initial thread of each team.

## Vectorization Pragmas

Use these pragmas to control execution on vector hardware.

Pragma | Description
--- | ---
omp simd | Transforms the loop into a loop that will be executed concurrently using SIMD instructions. The early_exit clause is an Intel-specific extension of the OpenMP* specification. early_exit Allows vectorization of multiple exit loops. When this clause is specified: Each operation before last lexical early exit of the loop may be executed as if early exit were not triggered within the SIMD chunk. After the last lexical early exit of the loop, all operations are executed as if the last iteration of the loop was found. Each list item specified in the linear clause is computed based on the last iteration number upon exiting the loop. The last value for linear clauses and conditional lastprivates clauses are preserved with respect to scalar execution. The last value for reductions clauses are computed as if the last iteration in the last SIMD chunk was executed up on exiting the loop. The shared memory state may not be preserved with regard to scalar execution. Exceptions are not allowed.
omp declare simd | Creates a version of a function that can process multiple arguments using Single Instruction Multiple Data (SIMD) instructions from a single invocation from a SIMD loop.

## Cancellation Constructs

Pragma | Description
--- | ---
omp cancel | Requests cancellation of the innermost enclosing region of the type specified, and causes the encountering task to proceed to the end of the cancelled construct.
omp cancellation point | Defines a point at which implicit or explicit tasks check to see if cancellation has been requested for the innermost enclosing region of the type specified. This construct does not implement a synchronization between threads or tasks.

## User-Defined Reduction Pragma

Use this pragma to define reduction identifiers that can be used as reduction operators in a reduction clause.

Pragma | Description
--- | ---
omp declare reduction | Declares User-Defined Reduction (UDR) functions (reduction identifiers) that can be used as reduction operators in a reduction clause.

## Combined and Composite Pragmas

Use these pragmas as shortcuts for multiple pragmas in sequence. A combined construct is a shortcut for specifying one construct immediately nested inside another construct. A combined construct is semantically identical to that of explicitly specifying the first construct containing one instance of the second construct and no other statements.

A composite construct is composed of two constructs but does not have identical semantics to specifying one of the constructs immediately nested inside the other. A composite construct either adds semantics not included in the constructs from which it is composed or the nesting of the one construct inside the other is not conforming.

Pragma | Description
--- | ---
omp distribute parallel for 1 | Specifies a loop that can be executed in parallel by multiple threads that are members of multiple teams.
omp distribute parallel for simd1 | Specifies a loop that will be executed in parallel by multiple threads that are members of multiple teams. It will be executed concurrently using SIMD instructions.
omp distribute simd 1 | Specifies a loop that will be distributed across the primary threads of the teams region. It will be executed concurrently using SIMD instructions.
omp for simd1 | Specifies that the iterations of the loop will be distributed across threads in the team. Iterations executed by each thread can also be executed concurrently using SIMD instructions.
omp parallel for | Provides an abbreviated way to specify a parallel region containing only a FOR construct.
omp parallel for simd | Specifies a parallel construct that contains one for simd construct and no other statement.
omp parallel sections | Specifies a parallel construct that contains only a sections construct.
| Creates a device data environment and executes the parallel region on that device.
| Provides an abbreviated way to specify a target construct that contains an omp target parallel for construct and no other statement between them.
| Specifies a target construct that contains an omp target parallel for simd construct and no other statement between them.
| Specifies a target construct that contains an omp simd construct and no other statement between them.
omp target teams | Creates a device data environment and executes the construct on the same device. It also creates a league of thread teams with the primary thread in each team executing the structured block.
omp target teams distribute | Creates a device data environment and then executes the construct on that device. It also specifies that loop iterations will be distributed among the primary threads of all thread teams in a league created by a teams construct.
omp target teams distribute parallel for | Creates a device data environment and then executes the construct on that device. It also specifies a loop that can be executed in parallel by multiple threads that are members of multiple teams created by a teams construct.
omp target teams distribute parallel for simd | Creates a device data environment and then executes the construct on that device. It also specifies a loop that can be executed in parallel by multiple threads that are members of multiple teams created by a teams construct. The loop will be distributed across the teams, which will be executed concurrently using SIMD instructions.
omp target teams distribute simd | Creates a device data environment and then executes the construct on that device. It also specifies that loop iterations will be distributed among the primary threads of all thread teams in a league created by a teams construct. It will be executed concurrently using SIMD instructions.
omp taskloop simd 1 | Specifies a loop that can be executed concurrently using SIMD instructions and that those iterations will also be executed in parallel using OpenMP* tasks.
omp teams distribute | Creates a league of thread teams and specifies that loop iterations will be distributed among the primary threads of all thread teams in the league.
omp teams distribute parallel for | Creates a league of thread teams and specifies that the associated loop can be executed in parallel by multiple threads that are members of multiple teams.
omp teams distribute parallel for simd | Creates a league of thread teams and specifies that the associated loop can be executed concurrently using SIMD instructions in parallel by multiple threads that are members of multiple teams.
omp teams distribute simd | Creates a league of thread teams and specifies that the associated loop will be distributed across the primary threads of the teams and executed concurrently using SIMD instructions.

Footnotes:

1 This directive specifies a composite construct.

Parent topic: OpenMP* Support