Well, I dispute that. In most instructions, 0 in an R field has nothing to do with register 0. It explicitly means *no* register is used, and the value of 0 is. It's just solipsistic to say the machine "considers" register 0 to be 0. The language in the PoOp is more like you cannot use register 0 for addressing in most cases.
And as far as I can tell, you can't use access register 0 for anything other than volatile temporary storage. sas On Tue, Sep 2, 2025 at 1:37 PM Tony Harminc <t...@harminc.com> wrote: > On Tue, 2 Sept 2025 at 13:05, Steve Smith < > 00001b5163999d8a-dmarc-requ...@listserv.uga.edu> wrote: > > Is there such a thing as an implicit index register? ;-) > > > > Yes, there is. All RX instructions have an index register - it's not in any > sense optional at the machine code level - if you don't explicitly provide > one in the assembler language then the assembler will generate the > instruction using 0. (And of course register 0 when used as an index is > deemed to have the value 0.) It's extremely common for RX instructions to > be used in contexts where no index register is needed. > > But I'm sure you know all this. Now if you had asked "is there such a thing > as specifying an implicit index register?", then that would have a > different answer. ;-) > > Tony H. >
