B.4  Version 4.5 to 5.0 Differences

• The memory model was extended to distinguish different types of flush operations according to specified flush properties (see Section 1.4.4) and to define a happens before order based on synchronizing flush operations (see Section 1.4.5).
• Various changes throughout the specification were made to provide initial support of C11, C++11, C++14, C++17 and Fortran 2008 (see Section 1.7).
• Full support of Fortran 2003 was completed (see Section 1.7).
• The target-offload-var internal control variable (see Chapter 2) and the OMP_TARGET_OFFLOAD environment variable (see Section 21.2.8) were added to support runtime control of the execution of device constructs.
• Control over whether nested parallelism is enabled or disabled was integrated into the max-active-levels-var internal control variable (see Section 2.2), the default value of which is now implementation defined, unless determined according to the values of the OMP_NUM_THREADS (see Section 21.1.2) or OMP_PROC_BIND (see Section 21.1.7) environment variables.
• Support for array shaping (see Section 3.2.4) and for array sections with non-unit strides in C and C++ (see Section 3.2.5) was added to facilitate specification of discontiguous storage, and the target update construct (see Section 13.9) and the depend clause (see Section 15.9.5) were extended to allow the use of shape-operators (see Section 3.2.4).
• Iterators (see Section 3.2.6) were added to support expressions in a list that expand to multiple expressions.
• The canonical loop form was defined for Fortran and, for all base languages, extended to permit non-rectangular loop nests (see Section 4.4.1).
• The relational-op in the canonical loop form for C/C++ was extended to include != (see Section 4.4.1).
• To support conditional assignment to lastprivate variables, the conditional modifier was added to the lastprivate clause (see Section 5.4.5).
• The inscan modifier for the reduction clause (see Section 5.5.8) and the scan directive (see Section 5.6) were added to support inclusive and exclusive scan computations.
• To support task reductions, the task modifier was added to the reduction clause (see Section 5.5.8), the task_reduction clause (see Section 5.5.9) was added to the taskgroup construct (see Section 15.4), and the in_reduction clause (see Section 5.5.10) was added to the task (see Section 12.5) and target (see Section 13.8) constructs.
• To support taskloop reductions, the reduction (see Section 5.5.8) and in_reduction (see Section 5.5.10) clauses were added to the taskloop construct (see Section 12.6).
• The description of the map clause was modified to clarify the mapping order when multiple map-types are specified for a variable or structure members of a variable on the same construct. The close map-type-modifier was added as a hint for the runtime to allocate memory close to the target device (see Section 5.8.3).
• The capability to map C/C++ pointer variables and to assign the address of device memory that is mapped by an array section to them was added. Support for mapping of Fortran pointer and allocatable variables, including pointer and allocatable components of variables, was added (see Section 5.8.3).
• The defaultmap clause (see Section 5.8.7) was extended to allow selecting the data-mapping or data-sharing attributes for any of the scalar, aggregate, pointer, or allocatable classes on a per-region basis. Additionally it accepts the none parameter to support the requirement that all variables referenced in the construct must be explicitly mapped or privatized.
• The declare mapper directive was added to support mapping of data types with direct and indirect members (see Section 5.8.8).
• Predefined memory spaces (see Section 6.1), predefined memory allocators and allocator traits (see Section 6.2) and directives, clauses and API routines (see Chapter 6 and Section 18.13) to use them were added to support different kinds of memories.
• Metadirectives (see Section 7.4) and declare variant directives (see Section 7.5) were added to support selection of directive variants and declared function variants at a call site, respectively, based on compile-time traits of the enclosing context.
• Support for nested declare target directives was added (see Section 7.8).
• The requires directive (see Section 8.2) was added to support applications that require implementation-specific features.
• The teams construct (see Section 10.2) was extended to support execution on the host device without an enclosing target construct (see Section 13.8).
• The loop construct and the order(concurrent) clause were added to support compiler optimization and parallelization of loops for which iterations may execute in any order, including concurrently (see Section 10.3 and Section 11.7).
• The collapse of associated loops that are imperfectly nested loops was defined for the simd (see Section 10.4), worksharing-loop (see Section 11.5), distribute (see Section 11.6) and taskloop (see Section 12.6) constructs.
• The simd construct (see Section 10.4) was extended to accept the if, nontemporal, and order(concurrent) clauses and to allow the use of atomic constructs within it.
• The default loop schedule modifier for worksharing-loop constructs without the static schedule and the ordered clause was changed to nonmonotonic (see Section 11.5).
• The affinity clause was added to the task construct (see Section 12.5) to support hints that indicate data affinity of explicit tasks.
• The detach clause for the task construct (see Section 12.5) and the omp_fulfill_event runtime routine (see Section 18.11.1) were added to support execution of detachable tasks.
• The taskloop construct (see Section 12.6) was added to the list of constructs that can be canceled by the cancel construct (see Section 16.1)).
• To support mutually exclusive inout sets, a mutexinoutset dependence-type was added to the depend clause (see Section 12.9 and Section 15.9.5).
• The semantics of the use_device_ptr clause for pointer variables was clarified and the use_device_addr clause for using the device address of non-pointer variables inside the target data construct was added (see Section 13.5).
• To support reverse offload, the ancestor modifier was added to the device clause for the target construct (see Section 13.8).
• To reduce programmer effort, implicit declare target directives for some functions (C, C++, Fortran) and subroutines (Fortran) were added (see Section 13.8 and Section 7.8).
• The target update construct (see Section 13.9) was modified to allow array sections that specify discontiguous storage.
• The to and from clauses on the target update construct (see Section 13.9), the depend clause on task generating constructs (see Section 15.9.5), and the map clause (see Section 5.8.3) were extended to allow any lvalue expression as a list item for C/C++.
• Lock hints were renamed to synchronization hints, and the old names were deprecated (see Section 15.1).
• The depend clause was added to the taskwait construct (see Section 15.5).
• To support acquire and release semantics with weak memory ordering, the acq_rel, acquire, and release clauses were added to the atomic construct (see Section 15.8.4) and flush construct (see Section 15.8.5), and the memory ordering semantics of implicit flushes on various constructs and runtime routines were clarified (see Section 15.8.6).
• The atomic construct was extended with the hint clause (see Section 15.8.4).
• The depend clause (see Section 15.9.5) was extended to support iterators and to support depend objects that can be created with the new depobj construct.
• New combined constructs master taskloop, parallel master, parallel master taskloop, master taskloop simd parallel master taskloop simd (see Section 17.3) were added.
• The omp_set_nested (see Section 18.2.9) and omp_get_nested (see Section 18.2.10) routines and the OMP_NESTED environment variable (see Section 21.1.5) were deprecated.
• The omp_get_supported_active_levels routine was added to query the number of active levels of parallelism supported by the implementation (see Section 18.2.14).
• Runtime routines omp_set_affinity_format (see Section 18.3.8), omp_get_affinity_format (see Section 18.3.9), omp_set_affinity (see Section 18.3.10), and omp_capture_affinity (see Section 18.3.11) and environment variables OMP_DISPLAY_AFFINITY (see Section 21.2.4) and OMP_AFFINITY_FORMAT (see Section 21.2.5) were added to provide OpenMP runtime thread affinity information.
• The omp_pause_resource and omp_pause_resource_all runtime routines were added to allow the runtime to relinquish resources used by OpenMP (see Section 18.6.1 and Section 18.6.2).
• The omp_get_device_num runtime routine (see Section 18.7.5) was added to support determination of the device on which a thread is executing.
• Support for a first-party tool interface (see Chapter 19) was added.
• Support for a third-party tool interface (see Chapter 20) was added.
• Support for controlling offloading behavior with the OMP_TARGET_OFFLOAD environment variable was added (see Section 21.2.8).
• Stubs for Runtime Library Routines (previously Appendix A) were moved to a separate document.
• Interface Declarations (previously Appendix B) were moved to a separate document.