1.. _omp121: 2 3Value has potential side effects preventing SPMD-mode execution. Add `[[omp::assume(\"ompx_spmd_amenable\")]]` to the called function to override. [OMP121] 4=================================================================================================================================================================== 5 6This analysis remarks indicates that a potential side-effect that cannot be 7guarded prevents the target region from executing in SPMD-mode. SPMD-mode 8requires that each thread is active inside the region. Any instruction that 9cannot be either recomputed by each thread independently or guarded and executed 10by a single thread prevents the region from executing in SPMD-mode. 11 12This remark will attempt to print out the instructions preventing the region 13from being executed in SPMD-mode. Calls to functions outside the current 14translation unit will prevent this transformation from occurring as well, but 15can be overridden using an assumption stating that it contains no calls that 16prevent SPMD execution. 17 18Examples 19-------- 20 21Calls to functions outside the current translation unit may contain instructions 22or operations that cannot be executed in SPMD-mode. 23 24.. code-block:: c++ 25 26 extern int work(); 27 28 void use(int x); 29 30 void foo() { 31 #pragma omp target teams 32 { 33 int x = work(); 34 #pragma omp parallel 35 use(x); 36 37 } 38 } 39 40 41.. code-block:: console 42 43 $ clang++ -fopenmp -fopenmp-targets=nvptx64 -O2 -Rpass-analysis=openmp-opt omp121.cpp 44 omp121.cpp:8:13: remark: Value has potential side effects preventing SPMD-mode 45 execution. Add `[[omp::assume("ompx_spmd_amenable")]]` to the called function 46 to override. [OMP121] 47 int x = work(); 48 ^ 49 50As the remark suggests, the problem is caused by the unknown call to the 51external function ``work``. This can be overridden by asserting that it does not 52contain any code that prevents SPMD-mode execution. 53 54.. code-block:: c++ 55 56 [[omp::assume("ompx_spmd_amenable")]] extern int work(); 57 58 void use(int x); 59 60 void foo() { 61 #pragma omp target teams 62 { 63 int x = work(); 64 #pragma omp parallel 65 use(x); 66 67 } 68 } 69 70.. code-block:: console 71 72 $ clang++ -fopenmp -fopenmp-targets=nvptx64 -O2 -Rpass=openmp-opt omp121.cpp 73 omp121.cpp:6:1: remark: Transformed generic-mode kernel to SPMD-mode. [OMP120] 74 #pragma omp target teams 75 ^ 76 77Diagnostic Scope 78---------------- 79 80OpenMP target offloading analysis remark. 81