Required to avoid crash due to missing encoding on convert layout ops.
This can happen when warp specialization is enabled, which calls into OptimizePartitionWarps,
which resets all layouts during its execution.
--- a/lib/Dialect/TritonGPU/IR/Ops.cpp
+++ b/lib/Dialect/TritonGPU/IR/Ops.cpp
@@ -66,6 +66,8 @@ bool isConvertTrivial(ConvertLayoutOp op) {
   auto dstType = op.getType();
   auto srcEncoding = srcType.getEncoding();
   auto dstEncoding = dstType.getEncoding();
+  if (!srcEncoding || !dstEncoding)
+    return false;
   return cast<DialectInferLayoutInterface>(&srcEncoding.getDialect())
       ->verifyLayoutsAreEqual(srcType.getShape(), srcEncoding, dstEncoding, {})
       .succeeded();