use npu_moe_gating_top_k_softmax (#1355)

### What this PR does / why we need it?
The optimization solution for non-deepseek select_experts is to replace
gating_topk_softmax with softmax+topk+to, which is optimized from 37us
to 14us on bf16/fp16 of qwen3-235b

- vLLM version: v0.9.2
- vLLM main:
1a4f35e2ea

---------

Signed-off-by: ttanzhiqiang <389825161@qq.com>

vllm_ascend/ops/fused_moe.py

@@ -49,6 +49,7 @@ from vllm_ascend.utils import (FusedMoEState, dispose_tensor,
                                npu_stream_switch, npu_wait_tensor)
 
 MOE_ALL2ALL_BUFFER: bool = envs_ascend.MOE_ALL2ALL_BUFFER
+SELECT_GATING_TOPK_SOTFMAX_EXPERTS: bool = envs_ascend.SELECT_GATING_TOPK_SOTFMAX_EXPERTS
 
 
 def process_topk_ids(topk_ids: torch.Tensor, expert_num: int, ep_size: int,
@@ -821,6 +822,39 @@ def fused_experts(
     return final_hidden_states
 
 
+def select_gating_top_k_softmax_experts(
+        hidden_states: torch.Tensor, router_logits: torch.Tensor, top_k: int,
+        renormalize: bool) -> tuple[torch.Tensor, torch.Tensor]:
+    """
+    Select top-k experts based on router logits.
+    only supports float16、bfloat16、float32
+
+    Args:
+        hidden_states: Hidden states of shape (num_tokens, hidden_size).
+        router_logits: Router logits of shape (num_tokens, num_experts).
+        top_k: Number of experts to select.
+        renormalize: Whether to renormalize the routing weights.
+
+    Returns:
+        topk_weights: Routing weights of shape (num_tokens, top_k).
+        topk_ids: Selected expert IDs of shape (num_tokens, top_k).
+
+    Raises:
+        ValueError: If an unsupported scoring function is provided.
+    """
+    topk_weights, topk_ids, row_idx = torch_npu.npu_moe_gating_top_k_softmax(
+        router_logits, None, k=top_k)
+
+    # # Required by npu_moe_init_routing
+    # topk_weights = topk_weights.to(hidden_states.dtype)
+    # topk_ids = topk_ids.to(torch.int32)
+
+    if renormalize:
+        topk_weights = topk_weights / topk_weights.sum(dim=-1, keepdim=True)
+
+    return topk_weights, topk_ids
+
+
 def native_grouped_topk(
     topk_weights: torch.Tensor,
     num_expert_group: Optional[int],
@@ -1013,6 +1047,12 @@ class AscendUnquantizedFusedMoEMethod(UnquantizedFusedMoEMethod):
                 # y2_flag=False, # old api; 第三个输出是否输出
                 routed_scaling_factor=1,
                 eps=float(1e-20))
+        elif SELECT_GATING_TOPK_SOTFMAX_EXPERTS:
+            topk_weights, topk_ids = select_gating_top_k_softmax_experts(
+                hidden_states=x,
+                router_logits=router_logits,
+                top_k=top_k,
+                renormalize=renormalize)
         else:
             topk_weights, topk_ids = select_experts(
                 hidden_states=x,