Re: Downwardly Scalable Systems

On Mon, 15 Apr 2024, Richard Kettlewell wrote:

not@telling.you.invalid (Computer Nerd Kev) writes:

D <nospam@example.net> wrote:

On Sun, 14 Apr 2024, Computer Nerd Kev wrote:

In fact in terms of memory and disk storage GCC keeps going
backwards that even for C/C++. Compiling large C/C++ programs with
-Os in ever newer GCC versions keeps producing ever bigger binaries
for unchanged code. Of course other compilers are available and I'm
not sure how other popular ones compare.

>
Why do they go backwards?

>
I'd be quite interested to find out as well. When it comes to the
more fine-tuned optimisation options (a set of which -Os enables),
the GCC documentation is often very lacking in detail, especially
when it comes to changes between versions.

>
Interesting question, and I don’t know the answer, but it’s not hard to
come up with a small concrete example. https://godbolt.org/z/sG5d99v5z
has the same code compiled at -Os with three different versions, plus
-O2 for comparison, and it does get a bit longer somewhere between 9.1
and 11.1.
>
The longer code uses one extra register (ebp) and because it’s run out
of callee-owned registers it must generate a push/pop pair for it
(adding 2 bytes to a 90-byte function, in this case).
>
It’s not easily explainable why it would do so: the gcc 9.1 object code
happily uses eax for the same purpose, without having to shuffle else
anything around, since eax isn’t being used for anything else at the
time.
>
Perhaps worth a bug report.

Or maybe, just maybe... another legendary supply chain attack? ;)