A conditional fetch-and-phi operation tests a memory location to determine if the memory locations stores a specified value and, if so, modifies the value at the memory location. The conditional fetch-and-phi operation can be implemented so that it can be concurrently executed by a plurality of concurrently executing threads, such as the threads of wavefront at a GPU. To execute the conditional fetch-and-phi operation, one of the concurrently executing threads is selected to execute a compare-and-swap (CAS) operation at the memory location, while the other threads await the results. The CAS operation tests the value at the memory location and, if the CAS operation is successful, the value is passed to each of the concurrently executing threads.