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.
I had a patch for this... 20 years ago. It was in pgcc for a while but apparently it had some bookkeeping problems. It would be nice to solve this at some point.
Bernd
