RE: [avr-gcc-list] AVR LLVM backend?

[John Regehr]

In my opinion the advantage of llvm-avr-gcc wouldn't so much be better 
code (though it may be a bit better) but rather decreased compiler 
maintenance effort.  The LLVM interfaces seem (1) pretty stable and (2) 
relatively narrow compared to gcc's.

Someone should just do it.  A hacky backend supporting only the megas is 
probably less than a month effort for a reasonable hacker.  Then if 
initial results are promising, others will jump in to help and eventually 
perhaps an avr-gcc replacement would emerge.

In my opinion LLVM needs a few tweaks before it's a really strong embedded 
compiler.  For example its inliner can cause significant bloat even at 
-Os.  But overall it is quite good.  On the other hand there are the 
advantages above plus the developers are extremely responsive.  For 
example in the past year I've been reporting lots of bugs in compilers' 
implementations of volatile.  The LLVM people almost always fix bugs in a 
few days whereas there's at least one volatile bug that has sat in the gcc 
bugzilla for 6 months without even being confirmed.  As a result LLVM is 
at present almost totally volatile-correct, gcc has a ways to go.

John Regehr


--
John Regehr, address@hidden
Assistant Professor, School of Computing, University of Utah
http://www.cs.utah.edu/~regehr/

On Tue, 11 Nov 2008, Weddington, Eric wrote:

> > -----Original Message-----
> > From:
> > address@hidden
> > [mailto:address@hidden
> > org] On Behalf Of Arnim Littek
> > Sent: Tuesday, November 11, 2008 8:32 PM
> > To: address@hidden
> > Subject: Re: [avr-gcc-list] AVR LLVM backend?
> >
> > On Wed, 12 Nov 2008 16:14:10 Weddington, Eric wrote:
> > > > Sorry if this is off-topic, but I was wondering whether anyone has
> > > > considered adding an AVR backend to the LLVM compiler.
> > >
> > > Yes.
> <snip>
> >   considered adding an AVR back end to LLVM?
> >
> > If the latter, can this be talked about?
>
> Yes, I have been aware of LLVM and I have considered looking into what it would 
> take to create an AVR backend for that tool.
>
> The problem is that there are so few people right now who volunteer to help on 
> the AVR GCC toolchain, that it's not worth the time and effort to splinter off 
> to see if LLVM can produce smaller code for the AVR than GCC.
>
> We need so much help right now on the AVR GCC toolchain, I can't afford the 
> time and energy to even look into LLVM.
>
>
>
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