Re: [xmlvm-dev] C backend and library

[Sascha H. <sa...@gm...>]

Are we even sure that linking against such a huge library would really be
that much faster? From my experience linking huge binaries can take a long
time as well.

In the end it looks like this:   timeSaved = (timePipelineNow -
timePipelineThen)  - timeLinking

If the times saved is small, the question is whether it makes sense
investing time into it at all. Therefore it would be good to have some
estimates first.

// Sascha

2011/6/10 Arno Puder <ar...@pu...>

> Yes, we've had this discussion before. Basically creating a Unix-like
> library (.a) that speeds things compilation time. However, the problem
> is that (at least) for now it wouldn't work with the C backend. We do
> optimizations that go beyond the simple decision "should this file be
> included or not" (what the linker typically does, and which, btw, is
> also performed by XMLVM at compile-time). We also optimize things like
> vtables, e.g., if a method never gets overridden, it will not end up
> in the vtable. This knowledge, however, only exists if we take the
> application into account. If the application overrides a library
> method, then the cross-compilation of the library also needs to
> change.
>
> I agree that for a regular development cycle it would make sense to
> have something like a library and only do full optimizations for the
> final release. We would need a way to cross-compile without
> optimizations. One big problem I see here are interface methods
> (because of the selector coloring scheme that is used), but I better
> let Markus respond to this since he implemented those optimizations.
>
> Arno
>
>
> On Jun 10, 2011, at 6:26 AM, Panayotis Katsaloulis
> <pan...@pa...> wrote:
>
> >
> > On 10 Ιουν 2011, at 3:11 μ.μ., Sascha Haeberling wrote:
> >
> >> Panayotis,
> >>
> >> sorry, I didn't understand what you mean. What do you mean by "the
> library"? The C backend does compute all dependencies so that the number of
> classes that are compiled and outputted in the end is at a minimum. Only
> required classes will be pulled in. Why would you want to replace this and
> with what?
> >>
> >> // Sascha
> >
> >
> > This is from an old discussion.
> >
> > The idea is to compile the whole JDK and iPhone compatibility library
> (and probably other dependencies) into a C library (i.e. in a form of .a
> file) and compile the project against this library.
> > Thus the Xcode project will compile much much faster and even the
> production of the Xcode project will be faster (and smaller) since no files
> from the JDK and the compatibility library will be required any more.
> >
> > This idea was also in the earlier days of ObjC backend, but due to the
> way ObjC handled dependencies and late binding, the gain was far less.
> > Now with the strong typed C language, things should be much better.
> >
> > For example, if a function is not used at all, the C compiler understands
> that and never embeds it into the output binary - we have optimizations in
> the method-level, instead of the class-level.
> >
> >
> > I don't know how virtual functions are handled and probably Arno could
> help with this.
> >
> >
> > PS: I remember that ProGuard is also able to perform this type of
> optimizations and it is already used for this reason in Android projects.
> Probably we should also do something similar?
> >
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