[triton] Remove the zero initialization of qk_acc by directly writing the result (#1288)

python/sglang/srt/layers/extend_attention.py

@@ -127,8 +127,7 @@ def _fwd_kernel(
         )
         k = tl.load(K_Buffer + offs_buf_k, mask=mask_n[None, :], other=0.0)
 
-        qk = tl.zeros([BLOCK_M, BLOCK_N], dtype=tl.float32)
-        qk += tl.dot(q.to(k.dtype), k)
+        qk = tl.dot(q.to(k.dtype), k)
         if BLOCK_DPE > 0:
             offs_kpe = (
                 offs_kv_loc[None, :] * stride_buf_kbs
@@ -179,9 +178,7 @@ def _fwd_kernel(
         )
         k = tl.load(K_Extend + offs_k, mask=mask_n[None, :], other=0.0)
 
-        qk = tl.zeros([BLOCK_M, BLOCK_N], dtype=tl.float32)
-        qk += tl.dot(q, k)
-
+        qk = tl.dot(q, k, out_dtype=tl.float32)
         if BLOCK_DPE > 0:
             offs_kpe = (
                 (cur_seq_extend_start_contiguous + start_n + offs_n[None, :])