Re: [PATCH 1/2] Implementation of new RISCV optimizations pass: fold-mem-offsets.

[Jeff Law <jeffreyalaw@gmail.com>]

On 6/12/23 01:41, Manolis Tsamis wrote:

> 
> I also think that's where this should end up since most of the pass is
> target independent anyway.
> I just couldn't figure out what would be a proper way to model the
> propagation rules for each target.
> Is a target hook necessary for that?
No hook should be necessary.  You're already checking that the result is 
recognized.  In theory you shouldn't have to, but checking the 
constraints seems advisable as well.

Costing is a different matter.  You might end changing an offset in such 
a way as to create a longer instruction on targets that have variable 
length encoding.  If we see that we'll likely have to add some rtx cost 
calls and compare the before/after.

But I suspect those cases are going to be limited in practice and in 
general if we're able to delete an earlier instruction we going to win 
even if the offset in the MEM changes and perhaps even results in a 
longer instruction.

Jeff