dmd for ARM

[Andrew Wiley]

On Tue, Sep 27, 2011 at 6:30 PM, Ruben <chromium at hybridsource.org> wrote:
> Hello, is there a chance an ARM backend can be written for dmd this year?  I
> realize this question has been asked periodically going back 4-5 years, but
> ARM is turning into a major platform and I feel D2 could do very well in
> this market, particularly with the renewed emphasis on mobile performance
> favoring a native compiled language.  Looking at previous newsgroup posts,
> it appears that those wanting to use ARM are pointed at gdc/ldc, but it
> seems like those two projects are usually behind in D2 support.  I think it
> would help D2 if dmd directly supported ARM, even Windows 8 runs on ARM.
>
> I don't know how much time it would require to port dmd's backend to ARM,
> but it may not require much more than that.  Android comes with an ARM
> emulator powered by QEMU, one could probably try the port simply using the
> free Android NDK.  Iain mentioned getting a SheevaPlug almost a year ago;
> I'd chip in a donation towards getting Walter or whoever a Pandaboard
> (http://pandaboard.org/content/platform) or Trim Slice
> (http://trimslice.com/web/models) to work on.  Some estimate of when dmd
> might come to ARM or why such a port is not a priority would be appreciated.
>

Frankly, I don't think this will happen. GDC is generally only a few
weeks behind DMD when a new version is released, and GCC already has a
mature backend for ARM. 64 bit DMD took at least a few months, and ARM
requires a different set of optimizations to deal with the different
challenges a RISC architecture has.
GDC has a few ARM-related bugs (I had to RMA my Trim Slice or I'd be
working on them now), but getting it running will be simpler than
trying to do a full blown DMD port, and given that GCC already does
well there performance-wise and supports the many many variants of the
ARM instruction set, porting DMD doesn't seem to have a good
cost/benefit ratio.

I do agree with you that native languages are going to get a very firm
foothold in ARM (the best VM I've seen so far on ARM is Mono, and it
has half the performance of C - Java is a few orders of magnitude
slower), and I too hope to see D moving onto ARM, but I think GDC is
probably the best bet at this point.

As for LDC, I've really used LLVM on ARM (although apparently Mono
uses it for codegen there). When I tried to build LDC there a while
back, it segfaulted while building the standard libraries, and I never
really investigated why.

Hopefully someone with more knowledge of the DMD backend code can
chime in with a firmer assessment, but I think an ARM port would wind
up taking much longer than the 64 bit port did, and that efforts are
probably better spent elsewhere at the moment.