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Re: altivec triplets: comments?



The reason for the new altivec triplets needs some more explanation
than Aldy's brief note.

The powerpc-eabialtivec triplet parallels some of the other
powerpc-eabi* triplets, like powerpc-eabiaix (not to be confused with
powerpc-aix) or powerpc-eabisim, it just changes the compiler's
defaults.  It should need no special changes outside gcc, everything
else already uses -eabi*.

The powerpc-linux-gnualtivec triplet is because there will be two
completely different userspace powerpc linuxes; one will support
altivec, and one won't, and they'll be binary incompatible to some
degree, because the two ABIs are incompatible.  It's likely it will be
convenient to, for instance, build cross-compilers from one to the
other.  I don't think that in general people will want to use the
-altivec version, because it has disadvantages and it will be possible
to have Altivec code even in the regular ABI; the new triplet would be
used only for embedded applications that are targetting a specific
processor.

Daniel commented that

> For instance, there aren't triplets for every new MIPS
> processor supported by GCC

but actually, when we build a special version of Linux for some weird
MIPS ABI, a different triplet _is_ used.  For instance,

mips-linux-gnu
mipsisa32-linux-gnu

and in fact there are a bunch of triplets for particular MIPS
processors, although most of these don't change the ABI they just
change the ISA.

-- 
- Geoffrey Keating <geoffk@geoffk.org> <geoffk@redhat.com>


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