Compiler Directives

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Date 10/31/2024

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Compiler Directives

The following tables list available compiler directives.

Each OpenMP* Fortran directive name is preceded by the prefix !$OMP in free format source; in fixed format source the prefix is c$OMP, where c is one of the following: !, C (or c), or *; for example, !$OMP ATOMIC.

Directives that are extensions to OpenMP are preceded by the prefix !$OMPX in free format source; in fixed format source the prefix is c$OMP, where c is one of the following: !, C (or c), or *.

Compiler directives are specially formatted comments in the source file that provide information to the compiler. Some directives, such as line length or conditional compilation directives, provide the compiler information that is used in interpreting the source file. Other directives, such as optimization directives, provide hints or suggestions to the compiler, which, in some cases, may be ignored or overridden by the compiler, based on the heuristics of the optimizer and/or code generator. If the directive is ignored by the compiler, no diagnostic message is issued.

You do not need to specify a compiler option to enable general directives.

Some directives may perform differently on Intel® microprocessors than on non-Intel microprocessors.

General Directives

Name	Description
ALIAS	Specifies an alternate external name to be used when referring to an external subprogram.
ASSUME	Provides heuristic information to the compiler optimizer.
ASSUME_ALIGNED	Specifies that an entity in memory is aligned.
ATTRIBUTES	Applies attributes to variables and procedures.
BLOCK_LOOP	Enables loop blocking for the immediately following nested DO loops.
DECLARE	Generates warning messages for undeclared variables.
DEFINE	Creates a variable whose existence can be tested during conditional compilation.
DISTRIBUTE POINT	Suggests a location at which a DO loop may be split.
ELSE	Marks the beginning of an alternative conditional-compilation block to an IF directive construct.
ELSEIF	Marks the beginning of an alternative conditional-compilation block to an IF directive construct.
ENDIF	Marks the end of a conditional-compilation block.
FIXEDFORMLINESIZE	Sets fixed-form line length. This directive has no effect on freeform code.
FMA	Tells the compiler to allow generation of fused multiply-add (FMA) instructions, also known as floating-point contractions.
FORCEINLINE	Specifies that a routine should be inlined whenever the compiler can do so.
FREEFORM	Uses freeform format for source code.
IDENT	Specifies an identifier for an object module.
IF	Marks the beginning of a conditional-compilation block.
IF DEFINED	Marks the beginning of a conditional-compilation block.
INLINE	Specifies that the routines can be inlined.
INTEGER	Selects default integer size.
IVDEP	Assists the compiler's dependence analysis of iterative DO loops.
LOOP COUNT	Specifies the typical trip loop count for a DO loop; which assists the optimizer.
MESSAGE	Sends a character string to the standard output device.
NOBLOCK_LOOP	Disables loop blocking for the immediately following nested DO loops.
NODECLARE	(Default) Turns off warning messages for undeclared variables.
NOFMA	Disables the generation of FMA instructions.
NOFREEFORM	(Default) Uses standard FORTRAN 77 code formatting column rules.
NOFUSION	Prevents a loop from fusing with adjacent loops.
NOINLINE	Specifies that a routine should not be inlined.
NOOPTIMIZE	Disables optimizations for the program unit.
NOPREFETCH	Disables a data prefetch from memory.
NOSTRICT	(Default) Disables a previous STRICT directive.
NOUNROLL	Disables the unrolling of a DO loop.
NOUNROLL_AND_JAM	Disables loop unrolling and jamming.
NOVECTOR	Disables vectorization of a DO loop.
OBJCOMMENT	Specifies a library search path in an object file.
OPTIMIZE	Enables optimizations for the program unit.
OPTIONS	Controls whether fields in records and data items in common blocks are naturally aligned or packed on arbitrary byte boundaries.
PACK	Specifies the memory alignment of derived-type items.
PREFETCH	Hints to the compiler to prefetch data from memory.
PSECT	Modifies certain characteristics of a common block.
REAL	Selects default real size.
STRICT	Disables Intel® Fortran features not in the language standard specified on the command line.
UNDEFINE	Removes a symbolic variable name created with the DEFINE directive.
UNROLL	Tells the compiler's optimizer how many times to unroll a DO loop.
UNROLL_AND_JAM	Enables loop unrolling and jamming.
VECTOR	Overrides default heuristics for vectorization of DO loops.

OpenMP* Fortran Directives

OpenMP* directives are specially formatted Fortran comment lines embedded in the source file that 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.

To use the following directives, you must specify compiler option [q or Q]openmp. For more information, refer to the option description in the Compiler Options reference.

Name	Description
ALLOCATE	Specifies memory allocators to use for object allocation and deallocation.
ALLOCATORS	Specifies memory allocators to be used to allocate variables in the associated Fortran ALLOCATE statement and to use in their deallocation.
ASSUMES	Provides hints to the optimizer about the current compilation unit and all the code it can reach through procedure calls.
ATOMIC	Specifies that a specific memory location is to be updated atomically.
BARRIER	Synchronizes all the threads in a team.
CANCEL	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	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	Restricts access for a block of code to only one thread at a time.
DECLARE MAPPER	Declares a user defined data mapper for derived types and local variables that can subsequently be used in MAP clauses.
DECLARE REDUCTION	Declares a user defined reduction for one or more types.
DECLARE SIMD	Generates a SIMD procedure.
DECLARE TARGET	Specifies that named variables, common blocks, functions, and subroutines are mapped to a device.
DECLARE VARIANT	Identifies a variant of a base procedure and specifies the context in which this variant is used.
DEPOBJ	Initializes, updates, or uninitializes an OpenMP depend object.
DISPATCH	Determines if a variant of a procedure is called for a given function or subroutine call.
DISTRIBUTE	Specifies that loop iterations will be executed by thread teams in the context of their implicit tasks.
DISTRIBUTE PARALLEL DO	Specifies a loop that can be executed in parallel by multiple threads that are members of multiple teams.
DISTRIBUTE PARALLEL DO SIMD	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 primary threads of the teams region. It will be executed concurrently using SIMD instructions.
DO	Specifies that the iterations of the immediately following DO loop must be executed in parallel.
DO SIMD	Specifies a loop that can be executed concurrently using SIMD instructions.
ERROR	Causes the compiler or runtime system to process an error condition.
FLUSH	Specifies synchronization points where the implementation must have a consistent view of memory.
GROUPPRIVATE	Specifies that a variable is replicated once per group of threads participating in a parallel region.
INTEROP	Identifies a foreign runtime context and identifies runtime characteristics of that context, enabling interoperability with it.
LOOP	Specifies that all iterations of the associated DO loop(s) can execute in any order or concurrently.
MASKED	Specifies a block of code to be executed by a subset of threads of the current team.
MASKED TASKLOOP	Provides an abbreviated way to specify a TASKLOOP construct inside a MASKED construct.
MASKED TASKLOOP SIMD	Provides an abbreviated way to specify a TASKLOOP SIMD construct inside a MASKED construct.
MASTER	(Deprecated, see MASKED) Specifies a block of code to be executed by the master thread of the team.
MASTER TASKLOOP	Deprecated; provides an abbreviated way to specify a TASKLOOP construct inside a MASTER construct.
MASTER TASKLOOP SIMD	Deprecated; provides an abbreviated way to specify a TASKLOOP SIMD construct inside a MASTER construct.
METADIRECTIVE	Specifies variant OpenMP directives, one of which may conditionally replace the metadirective based on the OpenMP context enclosing the metadirective.
NOTHING	Provides documentary clarity in conditionally compiled code or conditional OpenMP* code. It has no effect on the semantics or execution of the program.
ORDERED	Specifies a block of code to be executed sequentially.
PARALLEL	Defines a parallel region.
PARALLEL DO	Defines a parallel region that contains a single DO directive.
PARALLEL DO SIMD	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 LOOP	Provides an abbreviated way to specify a PARALLEL region containing a single LOOP construct and no other statements.
PARALLEL MASKED	Provides an abbreviated way to specify a MASKED construct inside a PARALLEL construct, with no other statements inside the PARALLEL construct.
PARALLEL MASKED TASKLOOP	Provides an abbreviated way to specify a MASKED TASKLOOP construct inside a PARALLEL construct, with no other statements inside the PARALLEL construct.
PARALLEL MASKED TASKLOOP SIMD	Provides an abbreviated way to specify a MASKED TASKLOOP SIMD construct inside a PARALLEL construct, with no other statements inside the PARALLEL construct.
PARALLEL MASTER	Deprecated; provides an abbreviated way to specify a MASTER construct inside a PARALLEL construct, with no other statements inside the PARALLEL construct.
PARALLEL MASTER TASKLOOP	Deprecated; provides an abbreviated way to specify a MASTER TASKLOOP construct inside a PARALLEL construct, with no other statements inside the PARALLEL construct.
PARALLEL MASTER TASKLOOP SIMD	Deprecated; provides an abbreviated way to specify a MASTER TASKLOOP SIMD construct inside a PARALLEL construct, with no other statements inside the PARALLEL construct.
PARALLEL SECTIONS	Defines a parallel region that contains SECTIONS directives.
PARALLEL WORKSHARE	Defines a parallel region that contains a single WORKSHARE directive.
PREFETCH DATA	Suggests to the compiler to preload data into cache. Preloading data in cache minimizes the effects of memory latency.
REQUIRES	Lists the features that an implementation must support so that the program compiles and runs correctly.
SCAN	Specifies a scan computation that updates each list item in each iteration of the loop.
SCOPE	Specifies a block of code to be executed by all threads of a team.
SECTION	Appears within a SECTIONS construct to indicate a block (section) of code. This directive is optional for the first block of code within the SECTIONS construct.
SECTIONS	Specifies a block of code to be divided among threads in a team (a worksharing area).
SIMD	Requires and controls SIMD vectorization of loops.
SINGLE	Specifies a block of code to be executed by only one thread in a team.
TARGET	Creates a device data environment and executes the construct on the same device.
TARGET DATA	Creates a device data environment for the extent of the region.
TARGET ENTER DATA	Specifies that variables are mapped to a device data environment.
TARGET EXIT DATA	Specifies that variables are unmapped from a device data environment.
TARGET PARALLEL	Creates a device data environment in a parallel region and executes the construct on that device.
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 PARALLEL LOOP	Provides an abbreviated way to specify a TARGET region containing a single PARALLEL LOOP construct and no other statements.
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 primary thread in each team executing the structured block.
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 primary threads of all thread teams in a league created by a TEAMS construct.
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.
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.
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 primary threads of all thread teams in a league created by a teams construct. It will be executed concurrently using SIMD instructions.
TARGET TEAMS LOOP	Provides an abbreviated way to specify a TARGET region containing a single TEAMS LOOP construct and no other statements.
TARGET UPDATE	Makes the list items in the device data environment consistent with their corresponding original list items.
TASK	Defines a task region.
TASKGROUP	Specifies a wait for the completion of all child tasks of the current task and all of their descendant tasks.
TASKLOOP	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	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	Specifies a wait on the completion of child tasks generated since the beginning of the current task.
TASKYIELD	Specifies that the current task can be suspended in favor of execution of a different task.
TEAMS	Creates a league of thread teams inside a target region to execute a structured block in the primary thread of each team.
TEAMS DISTRIBUTE	Creates a league of thread teams to execute a structured block in the primary thread of each team. It also specifies that loop iterations will be shared among the primary 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 primary 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 primary 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 primary 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 primary thread of each team. It also specifies a loop that will be distributed across the primary threads of the teams region. The loop will be executed concurrently using SIMD instructions.
TEAMS LOOP	Provides an abbreviated way to specify a TEAMS region containing a single LOOP construct and no other statements.
THREADPRIVATE	Makes named common blocks private to a thread but global within the thread.
TILE	Tiles (or blocks) one or more loops in a loop nest.
UNROLL	Partially or fully unrolls a DO loop.
WORKSHARE	Divides the work of executing a block of statements or constructs into separate units.

Product and Performance Information
Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex. Notice revision #20201201

Product and Performance Information

Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.

Notice revision #20201201

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