openmp/docs/remarks/OptimizationRemarks.md

# OpenMP Optimization Remarks

The {doc}`OpenMP-Aware optimization pass </optimizations/OpenMPOpt>` is able to
generate compiler remarks for performed and missed optimisations. To emit them,
pass these options to the Clang invocation: `-Rpass=openmp-opt
-Rpass-analysis=openmp-opt -Rpass-missed=openmp-opt`. For more information and
features of the remark system, consult the clang documentation:

- [Clang options to emit optimization reports](https://clang.llvm.org/docs/UsersManual.html#options-to-emit-optimization-reports)
- [Clang diagnostic and remark flags](https://clang.llvm.org/docs/ClangCommandLineReference.html#diagnostic-flags)
- The [-foptimization-record-file flag](https://clang.llvm.org/docs/ClangCommandLineReference.html#cmdoption-clang-foptimization-record-file)
  and the [-fsave-optimization-record flag](https://clang.llvm.org/docs/ClangCommandLineReference.html#cmdoption-clang1-fsave-optimization-record)

## OpenMP Remarks

:::{toctree}
:hidden: true
:maxdepth: 1

OMP100
OMP101
OMP102
OMP110
OMP111
OMP112
OMP113
OMP120
OMP121
OMP130
OMP131
OMP132
OMP133
OMP140
OMP150
OMP160
OMP170
OMP180
OMP190
:::

:::{list-table}
:widths: 15 15 70
:header-rows: 1

   * - Diagnostics Number
     - Diagnostics Kind
     - Diagnostics Description
   * - {ref}`OMP100 <omp100>`
     - Analysis
     - Potentially unknown OpenMP target region caller.
   * - {ref}`OMP101 <omp101>`
     - Analysis
     - Parallel region is used in unknown / unexpected ways. Will not attempt to
       rewrite the state machine.
   * - {ref}`OMP102 <omp102>`
     - Analysis
     - Parallel region is not called from a unique kernel. Will not attempt to
       rewrite the state machine.
   * - {ref}`OMP110 <omp110>`
     - Optimization
     - Moving globalized variable to the stack.
   * - {ref}`OMP111 <omp111>`
     - Optimization
     - Replaced globalized variable with X bytes of shared memory.
   * - {ref}`OMP112 <omp112>`
     - Missed
     - Found thread data sharing on the GPU. Expect degraded performance due to
       data globalization.
   * - {ref}`OMP113 <omp113>`
     - Missed
     - Could not move globalized variable to the stack. Variable is potentially
       captured in call. Mark parameter as {title-reference}`__attribute__((noescape))` to
       override.
   * - {ref}`OMP120 <omp120>`
     - Optimization
     - Transformed generic-mode kernel to SPMD-mode.
   * - {ref}`OMP121 <omp121>`
     - Analysis
     - Value has potential side effects preventing SPMD-mode execution. Add
       {title-reference}`[[omp::assume(\"ompx_spmd_amenable\")]]` to the called function
       to override.
   * - {ref}`OMP130 <omp130>`
     - Optimization
     - Removing unused state machine from generic-mode kernel.
   * - {ref}`OMP131 <omp131>`
     - Optimization
     - Rewriting generic-mode kernel with a customized state machine.
   * - {ref}`OMP132 <omp132>`
     - Analysis
     - Generic-mode kernel is executed with a customized state machine that
       requires a fallback.
   * - {ref}`OMP133 <omp133>`
     - Analysis
     - Call may contain unknown parallel regions. Use
       {title-reference}`[[omp::assume("omp_no_parallelism")]]` to override.
   * - {ref}`OMP140 <omp140>`
     - Analysis
     - Could not internalize function. Some optimizations may not be possible.
   * - {ref}`OMP150 <omp150>`
     - Optimization
     - Parallel region merged with parallel region at \<location>.
   * - {ref}`OMP160 <omp160>`
     - Optimization
     - Removing parallel region with no side-effects.
   * - {ref}`OMP170 <omp170>`
     - Optimization
     - OpenMP runtime call \<call> deduplicated.
   * - {ref}`OMP180 <omp180>`
     - Optimization
     - Replacing OpenMP runtime call \<call> with \<value>.
   * - {ref}`OMP190 <omp190>`
     - Optimization
     - Redundant barrier eliminated. (device only)
:::