[Hardware][CPU][PowerPC]Disable torch.compile() in toptopk sampling (#26987)

Signed-off-by: Akash Kaothalkar <akash.kaothalkar@ibm.com>
Co-authored-by: Akash Kaothalkar <akash.kaothalkar@ibm.com>

vllm/v1/sample/ops/topk_topp_sampler.py

@@ -65,7 +65,11 @@ class TopKTopPSampler(nn.Module):
                 )
                 self.forward = self.forward_native
         elif current_platform.is_cpu():
-            if current_platform.get_cpu_architecture() == CpuArchEnum.RISCV:
+            arch = current_platform.get_cpu_architecture()
+            # Fall back to native implementation for POWERPC and RISCV.
+            # On PowerPC argmax produces incorrect output with torch.compile.
+            # PR: https://github.com/vllm-project/vllm/pull/26987
+            if arch in (CpuArchEnum.RISCV, CpuArchEnum.POWERPC):
                 self.forward = self.forward_native
             else:
                 self.forward = self.forward_cpu