[CI][Hardware][AMD] Fix test_rotary_embedding_mla_cache_fused (#32408)

Signed-off-by: Matthew Wong <Matthew.Wong2@amd.com>

tests/kernels/core/test_rotary_embedding_mla_cache_fused.py

@@ -13,6 +13,7 @@ from tests.kernels.allclose_default import get_default_atol, get_default_rtol
 from tests.kernels.utils import DEFAULT_OPCHECK_TEST_UTILS, opcheck
 from vllm import _custom_ops as ops
 from vllm.model_executor.layers.rotary_embedding import RotaryEmbedding
+from vllm.platforms import current_platform
 from vllm.utils.torch_utils import set_random_seed
 
 
@@ -68,6 +69,14 @@ def test_concat_and_cache_mla_rope_fused(
     k_pe = torch.flatten(key[..., :qk_rope_head_dim], start_dim=1).to(device=device)
     kv_c = torch.flatten(key[..., qk_rope_head_dim:], start_dim=1).to(device=device)
 
+    if current_platform.is_rocm():
+        # We use forward_hip for the same numerics as the fused custom kernel on ROCm
+        # when dtype is FP16. The torch-native implementation implicitly upcasts
+        # FP16 x FP16 multiplications to FP32 before downcasting them, which leads
+        # to notable output divergences.
+        # Clone the tensors because the implementation modifies them in-place
+        ref_q_pe, ref_k_pe = rope.forward_hip(positions, query.clone(), k_pe.clone())
+    else:
         # NOTE(woosuk): The reference implementation should be executed first
         # because the custom kernel is in-place.
         ref_q_pe, ref_k_pe = rope.forward_native(positions, query, k_pe)