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  • Jim Cownie's avatar
    I apologise in advance for the size of this check-in. At Intel we do · 4cc4bb4c
    Jim Cownie authored
    understand that this is not friendly, and are working to change our
    internal code-development to make it easier to make development
    features available more frequently and in finer (more functional)
    chunks. Unfortunately we haven't got that in place yet, and unpicking
    this into multiple separate check-ins would be non-trivial, so please
    bear with me on this one. We should be better in the future.
    
    Apologies over, what do we have here?
    
    GGC 4.9 compatibility
    --------------------
    * We have implemented the new entrypoints used by code compiled by GCC
    4.9 to implement the same functionality in gcc 4.8. Therefore code
    compiled with gcc 4.9 that used to work will continue to do so.
    However, there are some other new entrypoints (associated with task
    cancellation) which are not implemented. Therefore user code compiled
    by gcc 4.9 that uses these new features will not link against the LLVM
    runtime. (It remains unclear how to handle those entrypoints, since
    the GCC interface has potentially unpleasant performance implications
    for join barriers even when cancellation is not used)
    
    --- new parallel entry points ---
    new entry points that aren't OpenMP 4.0 related
    These are implemented fully :-
          GOMP_parallel_loop_dynamic()
          GOMP_parallel_loop_guided()
          GOMP_parallel_loop_runtime()
          GOMP_parallel_loop_static()
          GOMP_parallel_sections()
          GOMP_parallel()
    
    --- cancellation entry points ---
    Currently, these only give a runtime error if OMP_CANCELLATION is true
    because our plain barriers don't check for cancellation while waiting
            GOMP_barrier_cancel()
            GOMP_cancel()
            GOMP_cancellation_point()
            GOMP_loop_end_cancel()
            GOMP_sections_end_cancel()
    
    --- taskgroup entry points ---
    These are implemented fully.
          GOMP_taskgroup_start()
          GOMP_taskgroup_end()
    
    --- target entry points ---
    These are empty (as they are in libgomp)
         GOMP_target()
         GOMP_target_data()
         GOMP_target_end_data()
         GOMP_target_update()
         GOMP_teams()
    
    Improvements in Barriers and Fork/Join
    --------------------------------------
    * Barrier and fork/join code is now in its own file (which makes it
    easier to understand and modify).
    * Wait/release code is now templated and in its own file; suspend/resume code is also templated
    * There's a new, hierarchical, barrier, which exploits the
    cache-hierarchy of the Intel(r) Xeon Phi(tm) coprocessor to improve
    fork/join and barrier performance.
    
    ***BEWARE*** the new source files have *not* been added to the legacy
    Cmake build system. If you want to use that fixes wil be required.
    
    Statistics Collection Code
    --------------------------
    * New code has been added to collect application statistics (if this
    is enabled at library compile time; by default it is not). The
    statistics code itself is generally useful, the lightweight timing
    code uses the X86 rdtsc instruction, so will require changes for other
    architectures.
    The intent of this code is not for users to tune their codes but
    rather 
    1) For timing code-paths inside the runtime
    2) For gathering general properties of OpenMP codes to focus attention
    on which OpenMP features are most used. 
    
    Nested Hot Teams
    ----------------
    * The runtime now maintains more state to reduce the overhead of
    creating and destroying inner parallel teams. This improves the
    performance of code that repeatedly uses nested parallelism with the
    same resource allocation. Set the new KMP_HOT_TEAMS_MAX_LEVEL
    envirable to a depth to enable this (and, of course, OMP_NESTED=true
    to enable nested parallelism at all).
    
    Improved Intel(r) VTune(Tm) Amplifier support
    ---------------------------------------------
    * The runtime provides additional information to Vtune via the
    itt_notify interface to allow it to display better OpenMP specific
    analyses of load-imbalance.
    
    Support for OpenMP Composite Statements
    ---------------------------------------
    * Implement new entrypoints required by some of the OpenMP 4.1
    composite statements.
    
    Improved ifdefs
    ---------------
    * More separation of concepts ("Does this platform do X?") from
    platforms ("Are we compiling for platform Y?"), which should simplify
    future porting.
    
    
    ScaleMP* contribution
    ---------------------
    Stack padding to improve the performance in their environment where
    cross-node coherency is managed at the page level.
    
    Redesign of wait and release code
    ---------------------------------
    The code is simplified and performance improved.
    
    Bug Fixes
    ---------
        *Fixes for Windows multiple processor groups.
        *Fix Fortran module build on Linux: offload attribute added.
        *Fix entry names for distribute-parallel-loop construct to be consistent with the compiler codegen.
        *Fix an inconsistent error message for KMP_PLACE_THREADS environment variable.
    
    llvm-svn: 219214
    4cc4bb4c
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