slo, slow, sloi, sloiw, sro, srow, sroi, sroiw are erroneously missing from the table of instructions in the extensions defined in the Bitmanip 0.93 spec, though they are present in the document and the Change History at the end shows they were moved to Zbp.
These are implemented by Ibex, and we currently use .insn instead of mnemonics to write the instructions in assembly: Ibex ISA Test