Re: Avoid treating the stack as an array [Re: "Back & Forth" is back!]

Stephen Pelc <stephen@vfxforth.com> writes:

On 15 Sep 2024 at 18:16:34 CEST, "Anton Ertl" <Anton Ertl> wrote:
>

I can buy a lot of CPU cycles for the cost of one day of programmer
time.

 
Some guy called Stephen Pelc (must be a different one) recentlu posted
<vbkdu0$1v8lq$1@dont-email.me>:
 
|We (MPE) converted much of our TCP/IP stack not to use locals. This
|was mostly on ARM7 devices, but the figures for other 32 bit CPUs of
|the period (say 15 years ago) were similar. Code density improved by
|about 25% and performance by about 50%.
 
How much time did that conversion cost?  And this Stephen Pelc
suggested that Buzz McCool (and probably everyone else) should also
spend their time on avoiding and eliminating locals from their code.
 
I am with you here, not with the other Stephen Pelc: Programmers
should use locals liberally if it saves them time, even in the face of
slow locals implementations, because you can buy a lot of CPU cycles
for the additional programming cost of avoiding locals.

>
What you ignore is that the constraints of embedded systems with small
alow CPUs (by comparison with desktop CPUs) are very different from
those of desktop CPUs. Converting the TCP/IP stack was driven by the
client requirement to fit a TCP/IP app into 128k/256k Flash and 16k RAM.
>
I would not make that trade off today.

Interesting.  So why mention it in <vbkdu0$1v8lq$1@dont-email.me>
without adding that?  And why do you write "What you ignore is [...]"
if the situation has vanished.

In any case, if such a situation still exists or reappears, and/or
customers who want more performance or smaller code appear, it seems
to me that the better (more general, i.e., the ultimate evil in the
eyes of some) solution is a native-code compiler that tries to keep
all values in registers, whether from the data, return, or FP stack or
in locals, and tries to do that throughout the definition, not just in
a basic block.

I should have found the time to do that long ago, maybe some day I
will.

- anton
--
M. Anton Ertl  http://www.complang.tuwien.ac.at/anton/home.html
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