[LLVMdev] Machine Code for different architectures

[Matthew Gardiner]

Hi Johnny,

Thanks for this - particularly the tip about cfe-dev. I'm currently
trying to coerce lldb to debug these type of architectures (our
current toolchain already outputs good dwarf info). However, I'm
struggling since lldb has just assumes that the size of a byte is
universally 8-bits. At some stage, I *think* at some stage we'd like to
derive a compiler, from the "same code-base" (i.e. llvm) and I
wondered how tricky this would be.

Matt    

On Tue, 9 Sep 2014 11:49:01 +0100
Johnny Val <johnnydval at gmail.com> wrote:

> Hi Matthew,
> 
> The byte==8 bits is more of a Clang issue rather than an LLVM issue. I
> believe your bigger issue will be the fact that you would need to make
> i24's a legal type in your backend, which as far as I know (unless
> something has changed recently), is a _big_ job. I briefly looked
> into it at one point, and decided to leave it for another day.
> 
> I am also unsure how hard byte=8bits is backed into Clang. You might
> want to ask cfe-dev.
> 
> I hope that helps.
> 
> Johnny
> 
> On Tue, Sep 9, 2014 at 7:41 AM, Matthew Gardiner <mg11 at csr.com> wrote:
> 
> > Hi,
> >
> > We have some DSP architectures (kalimba) which have 24-bits as their
> > "minimum addressable unit". So this means that the sizeof a char
> > (and an int and a short for that matter) is 24-bits.
> >
> > I quickly read the posted link WritingAnLLVMBackend.html but did not
> > see an obvious answer to the following question:
> >
> > Is it possible to write a backend that faithfully represents these
> > architectures or is sizeof_byte==8 bits baked into to llvm?
> >
> > Does anyone have any views on the above?
> >
> > thanks
> > Matthew Gardiner
> >
> >
> > On Tue, 9 Sep 2014 18:21:01 +1200
> > Bruce Hoult <bruce at hoult.org> wrote:
> >
> > > http://llvm.org/docs/WritingAnLLVMBackend.html
> > >
> > >
> > > On Tue, Sep 9, 2014 at 6:09 PM, Prakash Premkumar
> > > <prakash.prax at gmail.com> wrote:
> > >
> > > > How does LLVM generate machine code for different architectures?
> > > > For example, the machine code for x86 and amd will vary.
> > > >
> > > > How does LLVM convert its IR to machine code for different
> > > > architectures.Can you please explain the approach? Is it just
> > > > write two different programs for two different architectures
> > > > and pass a flag to the compiler based on which machine code you
> > > > want to generate?
> > > >
> > > > Thanks a lot for your explanations.
> > > >
> > > > Thanks
> > > > Prakash
> > > >
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