about Instruction flags set .noRemovable

[brookate]

Hi, at this comit 872e46814409399dbfacd885495c49f673e54780

...We also add a Flags struct to the Instruction class which allows us to
    mark Instructions as not-removable by the minimizer. ...

and I can find, program default set .empty flag

return internalAppend(Instruction(op, inouts: inouts, flags: .empty))

it seems there are no way set flag by users in ProgramBuilder, such as

b.loadString("hh", flags: .noRemovable) 

or is there a way to set flags to users if have?