[AMD] Add fused GemmaRMSNorm forward_hip to use aiter/vllm kernels for qwen3.5 (#21188)

python/sglang/srt/layers/layernorm.py

@@ -451,9 +451,6 @@ class GemmaRMSNorm(MultiPlatformOp):
         super().__init__()
         self.weight = nn.Parameter(torch.zeros(hidden_size))
         self.variance_epsilon = eps
-        # Re-dispatch
-        if _is_hip:
-            self._forward_method = self.forward_native
 
     def _forward_impl(
         self,
@@ -499,6 +496,47 @@ class GemmaRMSNorm(MultiPlatformOp):
     ) -> Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]]:
         return self._forward_impl(x, residual, post_residual_addition)
 
+    def forward_hip(
+        self,
+        x: torch.Tensor,
+        residual: Optional[torch.Tensor] = None,
+        post_residual_addition: Optional[torch.Tensor] = None,
+    ) -> Union[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]]:
+        if not _has_vllm_rms_norm:
+            return self.forward_native(x, residual, post_residual_addition)
+
+        w = self.weight.data + 1.0
+        if _use_aiter:
+            # aiter API: rms_norm(input, weight, eps) -> output
+            #            fused_add_rms_norm(output, input, residual, residual_out, weight, eps)
+            if residual is not None:
+                output = torch.empty_like(x)
+                residual_out = torch.empty_like(x)
+                if post_residual_addition is not None:
+                    residual = residual + post_residual_addition
+                fused_add_rms_norm(
+                    output, x, residual, residual_out, w, self.variance_epsilon
+                )
+                return output, residual_out
+            return rms_norm(x, w, self.variance_epsilon)
+        else:
+            # vllm API: rms_norm(out, input, weight, eps) -> None (in-place)
+            #           fused_add_rms_norm(out, input, residual_out, residual, weight, eps)
+            if not x.is_contiguous():
+                x = x.contiguous()
+            if residual is not None:
+                out = torch.empty_like(x)
+                residual_out = torch.empty_like(x)
+                if post_residual_addition is not None:
+                    residual = residual + post_residual_addition
+                fused_add_rms_norm(
+                    out, x, residual_out, residual, w, self.variance_epsilon
+                )
+                return out, residual_out
+            out = torch.empty_like(x)
+            rms_norm(out, x, w, self.variance_epsilon)
+            return out
+
     def forward_cpu(
         self,
         x: torch.Tensor,