Re: Let's start a survey on our userbase

On Tue, Sep 23, 2025 at 1:06 PM Damien Stewart <[email protected]> wrote:
>
> On 22/9/25 4:33 am, John Paul Adrian Glaubitz wrote:
> > Modern compilers are already extremely good at optimizing code such that they
> > use specific CPU extensions such that you often don't need handwritten assembly
> > for optimal performance.
>
> [...]
>
> You've likely read an article about The Byte Order Fallacy. While I
> agree in principle I disagree in practice. No one in this day and age or
> any other I can imagine would split a scalar load/store into discrete
> parts by the byte to be cross portable. It also doesn't produce
> efficient code.

As someone who has written a lot of SIMD code and cryptographic code
-- and timed the operations -- I can say it does matter in practice.
It may be the operation is a nop for one endian, and a byte swap for
another endian. But it does matter.

> Even on x64 the latest GCC doesn't even know or doesn't
> figure out what code is doing that reads data bytes and shifts it in
> place. For either endian. It doesn't see what is going on to reduce it
> to direct access or a movebe. It lacks endian AI.

Yeah, it is hit or miss whether Clang and GCC will produce optimal
code for some endian related patterns, like reading a byte array and
turning it into a machine word.

Jeff