Reorder/combine insns on superscalar arch

[Richard Henderson]

On 01/15/2016 06:06 AM, Bernd Schmidt wrote:
> On 01/15/2016 07:05 AM, Jeff Law wrote:
> 
>> Well, you have to write the pattern and a splitter.  But these days
>> there's define_insn_and_split to help with that.  Reusing Bernd's work
>> may ultimately be easier though.
> 
> Maybe, but maybe also not in the way you think. I've always wanted the ability
> to combine 2->2 insns, for cases like this. The parallel would be split into
> two separate insns if it doesn't match. This would allow more complicated forms
> to be used if they are equally cheap, and can lead to elimination of
> instructions if it triggers more combinations.

Maybe it's the same thing in the end, but I was thinking more in terms of 2->1
or 3->1, but without deleting some of the input instructions if their outputs
are still used.


r~