OpenMP* Fortran Compiler Directives

Intel® Fortran supports OpenMP* Fortran compiler directives that comply with OpenMP Fortran Application Program Interface (API) specification Version TR4: Version 5.0.

To use these directives, you must specify compiler option -qopenmp (Linux* and macOS*) or /Qopenmp (Windows*).

OpenMP directives are specially formatted Fortran comment lines embedded in the source file which provide the compiler with hints and suggestions for parallelization, optimization, vectorization, and offloading code to accelerator hardware. The compiler uses the information specified in the directives with compiler heuristic algorithms to generate more efficient code. At times, these heuristics may choose to ignore or override the information provided by a directive. If the directive is ignored by the compiler, no diagnostic message is issued.

Options that use OpenMP* are available for both Intel® microprocessors and non-Intel microprocessors, but these options may perform additional optimizations on Intel® microprocessors than they perform on non-Intel microprocessors. The list of major, user-visible OpenMP constructs and features that may perform differently on Intel® microprocessors vs. non-Intel microprocessors includes: locks (internal and user visible), the SINGLE construct, barriers (explicit and implicit), parallel loop scheduling, reductions, memory allocation, thread affinity, and binding.

This section discusses clauses used in multiple OpenMP* Fortran directives, conditional compilation rules, nesting and binding rules, and the following directives:

• ATOMIC directive

  Specifies that a specific memory location is to be updated atomically.

• BARRIER directive

  Synchronizes all the threads in a team.

• CANCEL directive

  Requests cancellation of the innermost enclosing region of the type specified, and causes the encountering implicit or explicit task to proceed to the end of the canceled construct.

• CANCELLATION POINT directive

  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.

• CRITICAL directive

  Restricts access for a block of code to only one thread at a time.

• DECLARE REDUCTION directive

  Declares a user-defined reduction for one or more types.

• DECLARE SIMD directive

  Generates a SIMD procedure.

• DECLARE TARGET directive

  Causes the creation of a device-specific version of a named routine that can be called from a target region. This directive only applies to Intel® MIC Architecture.

• DISTRIBUTE directive

  Specifies that loop iterations will be executed by thread teams in the context of their implicit tasks.

• DISTRIBUTE PARALLEL DO directive

  Specifies a loop that can be executed in parallel by multiple threads that are members of multiple teams.

• DISTRIBUTE PARALLEL DO SIMD directive

  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.

• DISTRIBUTE SIMD

  Specifies a loop that will be distributed across the master threads of the teams region. It will be executed concurrently using SIMD instructions.

• DO directive

  Specifies that the iterations of the immediately following DO loop must be executed in parallel.

• DO SIMD directive

  Specifies a loop that can be executed concurrently using SIMD instructions.

• FLUSH directive

  Specifies synchronization points where the threads in a team must have a consistent view of memory.

• MASTER directive

  Specifies a block of code to be executed by the master thread of the team.

• ORDERED directive

  Specifies a block of code that the threads in a team must execute in the natural order of the loop iterations.

• PARALLEL directive

  Defines a parallel region.

• PARALLEL DO directive

  Defines a parallel region that contains a single DO directive.

• PARALLEL DO SIMD directive

  Specifies a loop that can be executed concurrently using SIMD instructions. It provides a shortcut for specifying a PARALLEL construct containing one SIMD loop construct and no other statement.

• PARALLEL SECTIONS directive

  Defines a parallel region that contains a single SECTIONS directive.

• PARALLEL WORKSHARE directive

  Defines a parallel region that contains a single WORKSHARE directive.

• SECTIONS directive

  Specifies that the enclosed SECTION directives define blocks of code to be divided among threads in a team.

• SIMD directive

  Requires and controls SIMD vectorization of loops.

• SINGLE directive

  Specifies a block of code to be executed by only one thread in a team at a time.

• TARGET directive

  Creates a device data environment and executes the construct on the same device. This directive only applies to Intel® MIC Architecture.

• TARGET DATA directive

  Creates a device data environment for the extent of the region. This directive only applies to Intel® MIC Architecture.

• TARGET ENTER DATA

  Specifies that variables are mapped to a device data environment. This directive only applies to Intel® MIC Architecture.

• TARGET EXIT DATA

  Specifies that variables are unmapped from a device data environment. This directive only applies to Intel® MIC Architecture.

• TARGET PARALLEL

  Creates a device data environment in a parallel region and executes the construct on that device. This directive only applies to Intel® MIC Architecture.

• TARGET PARALLEL DO

  Provides an abbreviated way to specify a TARGET directive containing a PARALLEL DO directive and no other statements.

• TARGET PARALLEL DO SIMD

  Specifies a TARGET construct that contains a PARALLEL DO SIMD construct and no other statement.

• TARGET SIMD

  Specifies a TARGET construct that contains a SIMD construct and no other statement.

• 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 master thread in each team executing the structured block. This directive only applies to Intel® MIC Architecture.

• TARGET TEAMS DISTRIBUTE

  Creates a device data environment and executes the construct on the same device. It also specifies that loop iterations will be shared among the master threads of all thread teams in a league created by a TEAMS construct. This directive only applies to Intel® MIC Architecture.

• TARGET TEAMS DISTRIBUTE PARALLEL DO

  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. This directive only applies to Intel® MIC Architecture.

• TARGET TEAMS DISTRIBUTE PARALLEL DO 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. This directive only applies to Intel® MIC Architecture.

• TARGET TEAMS DISTRIBUTE SIMD

  Creates a device data environment and executes the construct on the same device. It also specifies that loop iterations will be shared among the master threads of all thread teams in a league created by a teams construct. It will be executed concurrently using SIMD instructions. This directive only applies to Intel® MIC Architecture.

• TARGET UPDATE directive

  Makes the list items in the device data environment consistent with their corresponding original list items. This directive only applies to Intel® MIC Architecture.

• TASK directive

  Defines a task region.

• TASKGROUP directive

  Specifies a wait for the completion of all child tasks of the current task and all of their descendant tasks.

• TASKLOOP directive

  Specifies that the iterations of one or more associated DO loops should be executed in parallel using OpenMP* tasks. The iterations are distributed across tasks that are created by the construct and scheduled to be executed.

• TASKLOOP SIMD directive

  Specifies a loop that can be executed concurrently using SIMD instructions and that those iterations will also be executed in parallel using OpenMP* tasks.

• TASKWAIT directive

  Specifies a wait on the completion of child tasks generated since the beginning of the current task.

• TASKYIELD directive

  Specifies that the current task can be suspended at this point in favor of execution of a different task.

• TEAMS

  Creates a group of thread teams to be used in a parallel region.

• TEAMS DISTRIBUTE

  Creates a league of thread teams to execute a structured block in the master thread of each team. It also specifies that loop iterations will be shared among the master threads of all thread teams in a league created by a TEAMS construct.

• TEAMS DISTRIBUTE PARALLEL DO

  Creates a league of thread teams to execute a structured block in the master thread of each team. It also specifies a loop that can be executed in parallel by multiple threads that are members of multiple teams.

• TEAMS DISTRIBUTE PARALLEL DO SIMD

  Creates a league of thread teams to execute a structured block in the master thread of each team. It also specifies a loop that can be executed in parallel by multiple threads that are members of multiple teams. The loop will be distributed across the master threads of the teams region, which will be executed concurrently using SIMD instructions.

• TEAMS DISTRIBUTE SIMD

  Creates a league of thread teams to execute the structured block in the master thread of each team. It also specifies a loop that will be distributed across the master threads of the teams region. The loop will be executed concurrently using SIMD instructions.

• THREADPRIVATE directive

  Makes named common blocks private to each thread, but global within the thread.

• WORKSHARE directive

  Divides the work of executing a block of statements or constructs into separate units.

The OpenMP parallel directives can be grouped into the categories. For more information about the categories for these directives, see OpenMP* Directives Summary.