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

[Weddington, Eric]

> -----Original Message-----
> From: John Regehr [mailto:address@hidden 
> Sent: Thursday, November 13, 2008 9:15 PM
> To: Weddington, Eric
> Cc: David Brown; address@hidden
> Subject: RE: [avr-gcc-list] Re: AVR LLVM backend?
> 
> > My experience with -fwhole-program -fcombine has been less 
> than stellar. 
> > I have seen a 25% code reduction, which is great! But I 
> have also seen 
> > up to 25% code *increase*, which is really bad. I would 
> have thought 
> > that, at the very least, they would ensure that the code 
> size would not 
> > increase. But because of this wide range of results, I 
> can't always rely 
> > on those switches, which is a real shame.
> 
> I think that ad hoc and embedded-inappropriate inlining 
> heuristics are 
> entirely to blame here.  Both llvm and gcc use speed-focused inlining 
> where code bloat is an afterthought.  For a target like AVR 
> it won't be 
> hard to improve this.

Sure, and other AVR toolchain developers have also pointed this out. GCC's 
inlining heuristics need to be tuned for the AVR backend. They have 
particularly gotten worse in th 4.x series.