VMS Help MACRO, /MIGRATION, Qualifiers, /OPTIMIZE  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /OPTIMIZE[=(option[,...])]
       /NOOPTIMIZE

    Enables or disables optimization options. All options are enabled
    by default except VAXREGS.

    Option         Description

    [NO]PEEPHOLE   Peephole optimization
    [NO]SCHEDULE   Code scheduling
    [NO]ADDRESSES  Common base address loading
    [NO]REFERENCES Common data referencing
    [NO]VAXREGS    Allow the use of VAX registers (R0 through R12) as
                   temporary registers when they appear to be unused
    ALL            All optimizations
    NONE           No optimizations

    Note that /ALL turns on VAXREGS, which may generate incorrect
    code unless all register usage of all routines in the module have
    been correctly declared.