[Info-vax] CPU architectures, was: Re: problem with 64-bit pointers in C

[Simon Clubley]

On 2018-02-13, Jan-Erik Soderholm <jan-erik.soderholm at telia.com> wrote:
> Den 2018-02-13 kl. 07:36, skrev Simon Clubley:
>> 
>> Those code size changes from VAX to Alpha were not helped by the lousy
>> code density on Alpha when compared to VAX.
>
> But that was not a mistake in the Alpha part, that is a known and
> predictable difference between CISC and RISC. You get higher speed
> instead due to a "cleaner" architecture.
>
> And as the hardware and memory development has been, code density
> has hardly been an issue as such.
>

I am currently operating under somewhat different memory constraints
for my Macro-32 and Macro-64 code. :-)

>> 
>> Macro-32 is a much nicer assembly language than Macro-64 is.
>> 
>
> For the same reason, a CISC environment does more with fewer
> instructions. Also a know effect from RISC, to get higher speed.
>

This is somewhat architecture specific, even on RISC. ARM is a much
nicer architecture to write assembly language for than Alpha.

> And at the same time, you where expected to switch from assembler
> to higher lever languages. And if I'm not wrong, it is easier to
> design a good compiler on a cleaner architecture (like Alpha).
>

Alpha is cleaner than x86 (and hence writing compilers for Alpha is
easier) but VAX was also a clean architecture when it came to
writing compilers.

Don't confuse a simple architecture with a clean architecture.

Simon.

-- 
Simon Clubley, clubley at remove_me.eisner.decus.org-Earth.UFP
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