Adds alternative memory copy implementation option

Includes commented alternative implementation for shared memory tiled copy operation using warp contiguous layout. Preserves existing functionality while providing development path for potential performance optimization.

Author: LoserCheems

csrc/src/flash_bwd_kernel.h

@@ -382,6 +382,7 @@ inline __device__ void compute_dq_dk_dv_1colblock(const Params &params, const in
     Tensor tdSsdS = smem_thr_copy_PdS.partition_D(sdS);     // ((Atom, AtomNum), PIPE_M, PIPE_N)
 
     auto smem_tiled_copy_PdSt = make_tiled_copy_A(typename Kernel_traits::SmemCopyAtomTransposed{}, tiled_mma_dkv);
+    // auto smem_tiled_copy_PdSt = make_tiled_copy_A_warpcontiguousN<MMA_N_SdP>(typename Kernel_traits::SmemCopyAtomTransposed{}, tiled_mma_dkv);
     auto smem_thr_copy_PdSt = smem_tiled_copy_PdSt.get_thread_slice(tidx);
     Tensor tdVsPt = smem_thr_copy_PdSt.partition_S(sPt);
     Tensor tdKsdSt = smem_thr_copy_PdSt.partition_S(sdSt);