On 01/24/2017 03:15 AM, Richard Biener wrote:
The more I look at our SCCVN implementation, the more I want to explore
trying to re-use that infrastructure to simplify DOM.
Certainly having a single way to hash/record stmts/expressions on GIMPLE would
be nice. Not sure if the SCCVN one is perfect (enhancing the memory
part further is on my TODO list).
It doesn't have to be perfect. From my wanderings in its code I think
it's probably sufficient to replace 90% of the non-path specific DOM
optimizations.
The idea is to do value numbering as an independent step (SCCVN, RPO
walk, whatever). Then use a scheduler similar to Click's 95 work to
place statements where they belong. The result is far simpler than what
DOM does and re-uses the VN framework.
In that world DOM morphs away from generic CSE/simplifications and
focuses on path specific stuff. And *that* should be reimplemented as
backwards walk with value numbering. It's hard to tease that out right
now given how we depend on DOM for generic CSE/simplifications.
Jeff
