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

[Jan-Erik Soderholm]

Den 2018-02-13 kl. 09:27, skrev 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. :-)
> 

But you refered to the "lousy code density on Alpha".

Your specific needs are probably not a valid benchmark to
evalute processor architectures against. :-)

>>>
>>> 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.

ARM was to a higher degree designed for assembled programming.
Then in later days ARM has grown higher up into areas where other
processorn (such as Alpha) had made its living. And in the same
way, Alpha was designed no as much for assembler programming,
but for efficient compiler designs and high speed.

> 
>> 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.
> 

Of course it helps to write assembler on a very-CISC architecture,
since each instruction does more. But with the expense of speed
(at that time).

Today, even x86 has got some steorids to get up in speed in a way
that was not predicable 15-20 years ago.

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

I was saying that the Alpha code density is "lousy" by-design
and not by some mistake.


> Simon.
>