[LLVMdev] AVX Shuffles & PatLeaf Help Needed
dag at cray.com
Thu Dec 17 18:12:48 CST 2009
On Thursday 17 December 2009 18:04, Anton Korobeynikov wrote:
> Hello, David
> > Can you expand on this with an example? There seems to be an awful lot
> > of shuffle patterns and predicates in PPCInstrAltivec.td. What do you
> > mean by, "Canonicalize to byte ops?" Can you walk me through how that
> > works with Altivec?
> The basic idea is quite simple - lower everything to vNi8 and write
> all the patterns using only these types.
Yeah, I figured that out after thinking a bit more. However, I think in this
case we only want to lower to vNi32 since there are no immediate-mask shuffles
in X86 that operate on smaller element types. Doing it at the byte level
would just be more confusing, I think.
PSHUFB is really a completely different instruction than PSHUFD, for example.
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