define_split

[Paolo Bonzini]

On 11/09/2010 10:22 AM, Joern Rennecke wrote:
> Quoting roy rosen <roy.1rosen@gmail.com>:
>
>> What is the difference when writing define_insn_and_split?
>> From what I understood from the docs then if there is such an insn
>> then the split does not occur so it would simply match it as an insn
>> without splitting and at the end would print the #?
>> Can you please elaborate?
>
> The combiner (and other passes) would match it as an insn, but ordinary
> splitter passes, e.g. before scheduling, will still split it.

As I understand it, this will also give combine the ability to do 
two->two (and two->N) transformations, though indirectly through the 
temporary insn.  Given this, could you explain further the benefits of 
combiner-split define_split vs. define_insn_and_split.

Paolo