Use aiter triton fused_add_rmsnorm_pad for gpt-oss (#30976)

Signed-off-by: Rohan138 <rohanpotdar138@gmail.com>

vllm/config/compilation.py

@@ -126,6 +126,10 @@ class PassConfig:
     fuse_allreduce_rms: bool = Field(default=None)
     """Enable flashinfer allreduce fusion."""
 
+    # ROCm/AITER specific fusions
+    fuse_act_padding: bool = Field(default=None)
+    """Fuse the custom RMSNorm + padding ops."""
+
     fi_allreduce_fusion_max_size_mb: float | None = None
     """The threshold of the communicated tensor sizes under which
     vllm should use flashinfer fused allreduce. Specified as a
@@ -194,6 +198,7 @@ class PassConfig:
         "enable_sp",
         "fuse_gemm_comms",
         "fuse_allreduce_rms",
+        "fuse_act_padding",
         mode="wrap",
     )
     @classmethod
@@ -222,12 +227,23 @@ class PassConfig:
                     "Fusion enabled but reshape elimination disabled. "
                     "Allreduce + rms norm + quant (fp8) fusion might not work"
                 )
+            if self.fuse_act_padding:
+                logger.warning_once(
+                    "Fusion enabled but reshape elimination disabled. "
+                    "RMSNorm + padding fusion might not work"
+                )
         if self.enable_qk_norm_rope_fusion and not current_platform.is_cuda_alike():
             logger.warning_once(
                 "QK Norm + RoPE fusion enabled but the current platform is not "
                 "CUDA or ROCm. The fusion will be disabled."
             )
             self.enable_qk_norm_rope_fusion = False
+        if self.fuse_act_padding and not current_platform.is_rocm():
+            logger.warning_once(
+                "Padding fusion enabled but the current platform is not ROCm. "
+                "The fusion will be disabled."
+            )
+            self.fuse_act_padding = False
 
 
 class DynamicShapesType(str, enum.Enum):