On 6/29/23 19:14, juzhe.zh...@rivai.ai wrote:
No, reduction patterns won't help.
As I said in vfwmul patch. You should make sure your environment is
working then try again.
I've triple checked this already.
I checked it again and your patch does not impact behavior, nor should
it. I checked it on top of these trunk commits:
14bfda6084eaca07c842566a34316974907958e2
e714af12e3bee0032d8d226f87d92c9bc46f0269
I checked it with the code from the godbolt links you suggested with the
options shown in those links.
More importantly, your explanation of what the pattern is supposed to do
shows a misunderstanding of what combine's capabilities actually are. A
bridge or intermediate pattern is not needed here, combine can
substitute multiple sources in combination attempts as can be clearly
seen from the dump fragments I posted.
The only reason I didn't reject the patch at the outset was the
possibility that maybe we were trying to combine more than 4
instructions or that possibility something about the number of operands,
unspecs, whatever were getting in the way.
This patch is not needed and does not affect code generation.
I would strongly suggest looking at a dependency height reduction
pattern if you want to optimize that code further.
Jeff
