1.. _omp113: 2 3Could not move globalized variable to the stack. Variable is potentially captured in call. Mark parameter as `__attribute__((noescape))` to override. [OMP113] 4============================================================================================================================================================== 5 6This missed remark indicates that a globalized value could not be moved to the 7stack because it is potentially captured by a call to a function we cannot 8analyze. In order for a globalized variable to be moved to the stack, copies to 9its pointer cannot be stored. Otherwise it is considered captured and could 10potentially be shared between the threads. This can be overridden using a 11parameter level attribute as suggested in the remark text. 12 13Globalization will occur when a pointer to a thread-local variable escapes the 14current scope. In most cases it can be determined that the variable cannot be 15shared if a copy of its pointer is never made. However, this remark indicates a 16copy of the pointer is present or that sharing is possible because it is used 17outside the current translation unit. 18 19Examples 20-------- 21 22If a pointer to a thread-local variable is passed to a function not visible in 23the current translation unit we need to assume a copy is made of it that can be 24shared between the threads. This prevents :ref:`OMP110 <omp110>` from 25triggering, which will result in a performance penalty when executing on the 26target device. 27 28.. code-block:: c++ 29 30 extern void use(int *x); 31 32 void foo() { 33 int x; 34 use(&x); 35 } 36 37 int main() { 38 #pragma omp target parallel 39 foo(); 40 } 41 42.. code-block:: console 43 44 $ clang++ -fopenmp -fopenmp-targets=nvptx64 -O2 -Rpass-missed=openmp-opt omp113.cpp 45 missed.cpp:4:7: remark: Could not move globalized variable to the stack. Variable is 46 potentially captured in call. Mark parameter as `__attribute__((noescape))` to 47 override. [OMP113] 48 int x; 49 ^ 50 51As the remark suggests, this behaviour can be overridden using the ``noescape`` 52attribute. This tells the compiler that no reference to the object the pointer 53points to that is derived from the parameter value will survive after the 54function returns. The user is responsible for verifying that this assertion is 55correct. 56 57.. code-block:: c++ 58 59 extern void use(__attribute__((noescape)) int *x); 60 61 void foo() { 62 int x; 63 use(&x); 64 } 65 66 int main() { 67 #pragma omp target parallel 68 foo(); 69 } 70 71.. code-block:: console 72 73 $ clang++ -fopenmp -fopenmp-targets=nvptx64 -O2 -Rpass=openmp-opt omp113.cpp 74 missed.cpp:4:7: remark: Moving globalized variable to the stack. [OMP110] 75 int x; 76 ^ 77 78Diagnostic Scope 79---------------- 80 81OpenMP target offloading missed remark. 82