Re: is Vax addressing sane today

On Sun, 8 Sep 2024 21:09:39 +0000, Lawrence D'Oliveiro wrote:

On Sun, 8 Sep 2024 17:56:55 +0000, MitchAlsup1 wrote:
>

The problem with VAX was NOT that one could not put a lot of work in a
single instruction;
>
no,
>
The problem with VAX is that it made putting too much work in a single
instruction easy.

>
Perhaps there is also the issue of the wildly-variable instruction
length.
A single VAX operand descriptor could be up to 6 bytes; I think the
instruction with the most general-format operands could have 6 of them:
so, plus opcode, such an instruction could be 37 bytes long.

I have not heard an argument that the complex things in VAX ISA are
a) desirable
b) performance helpful
I (sort of) think VAX ISA as a grown up PDP-11, ignoring all the
dastardly complicated instructions it inflicted upon itself. AND
it did inflict those things upon itself.
Restricting a new-VAX-like ISA to 1-2-3 Operand and 1-result with
at most 1 exception would result in a MUCH cleaner and easier to
build machine.

While the shortest instruction could be just 1 byte.
>
Even those who are talking about “post-RISC” are, I think, still in
favour of RISC-style fixed instruction lengths.

I, for the record, are in favor of fixed length instruction-specifier
followed by constants the entirety is the instruction, while the
former minimizes your ability of shooting yourself in the foot.