refine the compiler error for half2 operation (#29816)

paddle/fluid/operators/elementwise/elementwise_add_op.h

@@ -183,6 +183,7 @@ template <int SIZE>
 __global__ void VecFP16MatrixColReduce(const __half2 *__restrict__ in,
                                        __half2 *__restrict__ out, size_t width,
                                        size_t height) {
+#if CUDA_ARCH_FP16_SUPPORTED(__CUDA_ARCH__)
   int idx = threadIdx.x + blockIdx.x * blockDim.x;
   int by = blockIdx.y;
   __half2 zero = __half2half2(static_cast<__half>(0));
@@ -196,6 +197,7 @@ __global__ void VecFP16MatrixColReduce(const __half2 *__restrict__ in,
 
     atomicAdd(&(out[idx]), sum);
   }
+#endif
 }
 
 template <typename T>
@@ -363,7 +365,6 @@ class ElementwiseAddGradKernel : public ElemwiseGradKernel<T> {
       int max_blocks = std::max(max_physical_threads / (block_x * block_y), 1);
       int theory_block = (width + blocks.x - 1) / blocks.x;
       dim3 grids(std::min(theory_block, max_blocks));
-#if CUDA_ARCH_FP16_SUPPORTED(__CUDA_ARCH__)
       if (std::is_same<T, paddle::platform::float16>::value && width < 2048 &&
           width % 2 == 0 && height % 64 == 0) {
         auto &dev_ctx =
@@ -381,7 +382,6 @@ class ElementwiseAddGradKernel : public ElemwiseGradKernel<T> {
                                                                  width, height);
         return;
       }
-#endif
 
       if (width / height < 32) {
         MatrixColReduce<T, block_x, block_y><<<grids, blocks, 0, stream>>>(