Always outputs bytecode, not textual MLIR.
iree-import-tf \
--tf-import-type=savedmodel_v1 \
--tf-savedmodel-exported-names=serving_default \
. -o retvec.stablehlo.mlir.bytecode
Convert to textual MLIR:
iree-ir-tool cp -o retvec.stablehlo.mlir retvec.stablehlo.mlir.bytecode