On Mon, 9 Aug 2010 16:43:00 -0500, Peurifoy, Richard L wrote: >----- "David Bond" <[email protected]> wrote: >> There is a millicode-only instruction with a mnemonic of MVCX. It is >> used by millicode for variable-length moves without the need for EX+MVC. >> (The "Execute" instructions are really slow on modern machines.) MVCX >> is used by the millicode for MVCL and other instructions. We know of >> the MVCX mnemonic but not the op-code or the operand format.
>This seems like a good instruction for general use, any idea why it was >not made available outside of millicode? David, thanks for your explanation. Richard, one can only guess. They keep their mouths pretty well shut :-( There's a chance that MVCX uses address fields (Displacement-Base, probably) to indirectly address one or more registers partaking in the execution of the instruction. The physical processor has an array of 256 registers. There's a set 16 assigned to be GPRs, a set assigned to be ARs, FPRs, CRs, Millicode-only registers, etc. Addressing them by number is not something that makes sense outside the millicode scope... Just a guess... Cheers, Abe Kornelis. =============
