forked from OSchip/llvm-project
81 lines
2.4 KiB
ReStructuredText
81 lines
2.4 KiB
ReStructuredText
.. _omp121:
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Value has potential side effects preventing SPMD-mode execution. Add `__attribute__((assume(\"ompx_spmd_amenable\")))` to the called function to override. [OMP121]
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===================================================================================================================================================================
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This analysis remarks indicates that a potential side-effect that cannot be
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guarded prevents the target region from executing in SPMD-mode. SPMD-mode
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requires that each thread is active inside the region. Any instruction that
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cannot be either recomputed by each thread independently or guarded and executed
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by a single thread prevents the region from executing in SPMD-mode.
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This remark will attempt to print out the instructions preventing the region
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from being executed in SPMD-mode. Calls to functions outside the current
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translation unit will prevent this transformation from occurring as well, but
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can be overridden using an assumption stating that it contains no calls that
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prevent SPMD execution.
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Examples
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--------
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Calls to functions outside the current translation unit may contain instructions
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or operations that cannot be executed in SPMD-mode.
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.. code-block:: c++
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extern int work();
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void use(int x);
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void foo() {
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#pragma omp target teams
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{
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int x = work();
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#pragma omp parallel
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use(x);
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}
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}
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.. code-block:: console
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$ clang++ -fopenmp -fopenmp-targets=nvptx64 -O2 -Rpass-analysis=openmp-opt omp121.cpp
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omp121.cpp:8:13: remark: Value has potential side effects preventing SPMD-mode
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execution. Add `__attribute__((assume("ompx_spmd_amenable")))` to the called function
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to override. [OMP121]
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int x = work();
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^
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As the remark suggests, the problem is caused by the unknown call to the
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external function ``work``. This can be overridden by asserting that it does not
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contain any code that prevents SPMD-mode execution.
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.. code-block:: c++
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__attribute__((assume("ompx_spmd_amenable"))) extern int work();
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void use(int x);
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void foo() {
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#pragma omp target teams
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{
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int x = work();
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#pragma omp parallel
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use(x);
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}
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}
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.. code-block:: console
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$ clang++ -fopenmp -fopenmp-targets=nvptx64 -O2 -Rpass=openmp-opt omp121.cpp
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omp121.cpp:6:1: remark: Transformed generic-mode kernel to SPMD-mode. [OMP120]
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#pragma omp target teams
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^
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Diagnostic Scope
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----------------
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OpenMP target offloading analysis remark.
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