Techniques are disclosed relating to specification of instruction operands. In some embodiments, this may involve assigning operands to source inputs. In one embodiment, an instruction includes one or more mapping values, each of which corresponds to a source of the instruction and each of which specifies a location value. In this embodiment, the instruction includes one or more location values that are each usable to identify an operand for the instruction. In this embodiment, a method may include accessing operands using the location values and assigning accessed operands to sources using the mapping values. In one embodiment, the sources may correspond to inputs of an execution block. In one embodiment, a destination mapping value in the instruction may specify a location value that indicates a destination for storing an instruction result.