Convert GA_FLOAT16 to ncclHalf in cuda collectives

Author: tsirif

src/gpuarray_collectives_cuda_nccl.c

@@ -175,11 +175,14 @@ static inline ncclDataType_t convert_data_type(int typecode) {
   switch (typecode) {
   case GA_BYTE: return ncclChar;
   case GA_INT: return ncclInt;
-  case GA_HALF: return ncclHalf;
   case GA_FLOAT: return ncclFloat;
   case GA_DOUBLE: return ncclDouble;
   case GA_LONG: return ncclInt64;
   case GA_ULONG: return ncclUint64;
+  #ifdef CUDA_HAS_HALF
+  case GA_HALF: return ncclHalf;
+  case GA_FLOAT16: return ncclHalf;
+  #endif
   }
   return nccl_NUM_TYPES;
 }