Re: Implementing VMX128 AltiVec Variant

[Gordan Bobic <gordan at bobich dot net>]

On Wed, 22 Aug 2007, Paolo Bonzini wrote:

> > > >  With the modifications I made, GCC still compiled fine. However,
> > > >  libgcc and libstdc++ DO still get build with the missing instructions
> > > >  (according to objdump -D). Why is that? Is that a consequence of the
> > > >  ADA files? Or something else? Where should I look? Is the it ada files
> > > >  that are the cause of the problem I'm seeing?
> > > 
> > >  It must be something else.  I'm not sure what, though.  It might be
> > >  something as simple as an instruction built from substrings.  For
> > >  example, search for altivec_vmsumu<VI_char>m in altivec.md.
> >
> >  I just re-checked for that and I can't find any. I have attached a diff
> >  for my modified altivec.h, altivec.md and rs6000.c files. Patch in
> >  gcc/config/rs6000 subtree with -p1.
> >
> >  Can anyone think of anywhere else I should be looking? Where else could
> >  these instructions be coming from?
>
> This is really not relevant to the posted patch; however, I'll still post it 
> here.
>
> The proper way to disable Altivec instructions is to leave altivec.h and 
> rs6000.c aside, and just change the "TARGET_ALTIVEC" to something like 
> "(TARGET_ALTIVEC && 0)".  The remaining code will automagically be disabled.
>
> Later, you can add your option and the corresponding TARGET_VMX128 mask, and 
> go back replacing the "TARGET_ALTIVEC && 0" with "TARGET_ALTIVEC && 
> !TARGET_VMX128".

Thanks for that. This is the sort of thing I was hoping to eventually 
implement (rather than re-implementing vmx128.h and vmx128.md from scratch 
with 90% overlap with altivec.h and altivec.md). But I'd really like to go 
with a quick and dirty proof of concept first, which is to just cut out 
the offending instructions from altivec support, just to make sure that it 
would work.

Gordan