Hi.
I stay at my position, and keep saying it has nothing to deal with a
compiler !
It deals with assumptions concerning the main aim of data structures.
It seems that you know how to code it, so if tcc can compile this it's
fine and enough.
But, FOR SURE, it does not have to translate an index-by-index array
elements sum !!!
Regards, ian.
Le 09/01/2020 à 12:34, Rasmus Riiner via Tinycc-devel a écrit :
> I would say that it is okay to generate low quality code, that it's
> better than nothing, as long the implementation doesn't impact the
> rest of the compiler too much... but of course that is from my biased
> point of view.
>
> Which is that the only thing presently keeping TCC compile times out
> of my reach is that a bunch of code akin to this in C++:
>
> vec2 v4 = vel + a3 * dt;
> vec2 p4 = pos + v4 * dt;
> vec2 a4 = entity_acceleration(p4, v4, entity);
>
> *dpos = (v1 + (v2 + v3) * 2.0 + v4) * (dt * (1.0 / 6.0));
> *dvel = (a1 + (a2 + a3) * 2.0 + a4) * (dt * (1.0 / 6.0));
>
> Would have to be rewritten to something like this for plain C:
>
> vec2 v4 = v2Add(vel + v2Scale(a3 * dt));
> vec2 p4 = v2Add(pos + v2Scale(v4 * dt));
> vec2 a4 = entity_acceleration(p4, v4, entity);
>
> *dpos = v2Scale(v2Add(v2Add(v1, v2Scale(v2Add(v2, v3), 2.0)), v4),
> dt * (1.0 / 6.0));
> *dvel = v2Scale(v2Add(v2Add(a1, v2Scale(v2Add(a2, a3), 2.0)), a4),
> dt * (1.0 / 6.0));
>
> Operator overloading doesn't fit C, and I'm glad it's not in there,
> but then the only way to fix this particular inefficiency is with some
> kind of built-in array math, perhaps as an extension... which is
> exactly what the GCC extension would provide. The extension goes a bit
> too far perhaps, what with supporting every basic type as a vector
> element, I can see why they did that though. For TCC, it might be
> sensible to limit the possible element types to 32bit floats or
> integers, and cap the possible vector length to 4...
>
> I'm not sure what I would do in your position, implementing the
> extension (or a subset of it) might not be what's ultimately best for
> the project, but hopefully you can see where I'm coming from. Compile
> times for basic C++ programs take entire seconds with the available
> compilers, whereas I could literally tcc -run and be in-game, with
> immediate feedback, nearly instantly.
> I could bite the bullet and start using function syntax for basic
> vector operations, I just wanted to confirm whether the GCC extension
> is outside the scope of TCC, or not, first. I don't actually use any
> C++ features over C, other than operator overloading and a little bit
> of function overloading (which I could do just fine without). It feels
> like so close, yet so far, you know?
>
> Rasmus.
>
> ----- Reply to message -----
>
> Sure, Rasmus asked to have this extension in TCC to be able to use
> it for
> writing libraries or apps; i.e. he asked if TCC could be extended to
> compile code like this:
>
> ---------------------
> typedef int v4si __attribute__ ((vector_size (16)));
> void foo (void) {
> v4si a = {1,2,3,4}, b = {5,6,7,8}, c;
> c = a + b;
> bar(c[0], c[1], c[2], c[3]);
> }
> ---------------------
>
> For that TCC would need to be extended somewhat, and I was
> alluding to the
> fact that this extension isn't totally trivial if it shouldn't
> generate
> very low quality code. If it's okay to generate low quality code and
> not adhere to the psABI for parameter passing of these types then
> it's not
> too much work.
>
> If you were asking if such extension is really a must have in a
> compiler: no, otherwise it wouldn't be an extension. It's a nice
> to have,
> and I can see why Rasmus wants it, but it comes at a non-trivial
> cost to
> support it in a small compiler.
>
>
> Ciao,
> Michael.
>
>
>
>
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