Get rid of o_rows_are_valid since we don't have headdim=16 anymore

csrc/flash_attn/src/fmha_fprop_kernel_1xN.h

@@ -554,20 +554,13 @@ inline __device__ void device_1xN_(const Params &params, const int bidb, const i
         for (int jj = 0; jj < Gmem_tile_o::STGS_PER_LOOP; jj++) {
             rows[jj] = tidx / Gmem_tile_o::THREADS_PER_ROW + jj * Gmem_tile_o::ROWS_PER_STG;
         }
-        // When d = 16, O only has 16 x 16 = 256 elements, and each of the 128 threads wants
-        // to write 4 elements, so only half of the thread should deal with O.
-        bool o_rows_are_valid =
-            (Kernel_traits::THREADS <= Gmem_tile_o::THREADS_PER_ROW * Gmem_tile_o::ROWS)
-            || (tidx / Gmem_tile_o::THREADS_PER_ROW < Gmem_tile_o::ROWS);
-        if (o_rows_are_valid) {
-            softmax.reduce_max_after_sync_(p_max_o, rows);
-        }
+        softmax.reduce_max_after_sync_(p_max_o, rows);
         static_assert(Mma_tile_o::MMAS_M == 1);
         for (int jj = 0; jj < Gmem_tile_o::STGS_PER_LOOP; jj++) {
             p_max_o[jj][0] *= params.scale_bmm1f;
         }
         float p_prev_scale_o[Gmem_tile_o::STGS_PER_LOOP];
-        if ((!Is_first) && o_rows_are_valid) {
+        if (!Is_first) {
             smem_softmax_lse.load(p_prev_scale_o, rows);
         }
         // if (!Is_first) {
@@ -586,9 +579,7 @@ inline __device__ void device_1xN_(const Params &params, const int bidb, const i
 
         static_assert(Mma_tile_o::MMAS_M == 1);
         float p_sum_o[Gmem_tile_o::STGS_PER_LOOP][Mma_tile_o::MMAS_M];
-        if (o_rows_are_valid) {
-            softmax.reduce_sum_after_sync_(p_sum_o, rows);
-        }
+        softmax.reduce_sum_after_sync_(p_sum_o, rows);
         if (!Is_first) {
             for (int jj = 0; jj < Gmem_tile_o::STGS_PER_LOOP; jj++) {
                 p_prev_scale_o[jj] = expf(p_prev_scale_o[jj] - p_max_o[jj][0]);
@@ -609,7 +600,7 @@ inline __device__ void device_1xN_(const Params &params, const int bidb, const i
             //         printf("p_sum_log=%.6f\n", p_sum_log[jj][0]);
             //     }
             // }
-            if ((tidx % Gmem_tile_o::THREADS_PER_ROW == 0) && o_rows_are_valid) {
+            if (tidx % Gmem_tile_o::THREADS_PER_ROW == 0) {
                 gmem_softmax_lse.store_row(
                     reinterpret_cast<uint32_t(&)[Mma_tile_p::MMAS_M]>(p_sum_log[jj]), rows[jj]);
             }