[PATCH] D71578: [CodeMoverUtils] Improve IsControlFlowEquivalent.

[Florian Hahn via Phabricator via llvm-commits]

fhahn added inline comments.


================
Comment at: llvm/lib/Transforms/Utils/CodeMoverUtils.cpp:38
+
+// FIXME: Reuse GVN/CSE logic to check for equivalence between Values.
+bool llvm::ControlConditionsComparator::isEquivalent(const Value &V1,
----------------
jdoerfert wrote:
> fhahn wrote:
> > I guess we could just use SCEV here to check for equivalence. I don't think re-using GVN logic will be feasible, unless you want to value number the whole function
> > I guess we could just use SCEV here to check for equivalence. 
> 
> "Just use SCEV" is maybe the wrong wording, at least for what I had in mind. My thinking was:
> We have probably quite a few "equivalence" checker in the code base. Which one to reuse depends at the end of the day on the properties you need.
> It becomes interesting as soon as you actually have condition sets that do not match 1-1 but are still equivalent. As I mentioned earlier, other relations, e.g., subset, will also be interesting. This is all "future work" where though.
> 
> 
> > I don't think re-using GVN logic will be feasible, unless you want to value number the whole function
> 
> If that turns out to help normalizing complex control conditions, why not. I will hopefully have a GSoC student to revive the PolyhedralValueAnalysis, that is even more expensive ;)
> 
> 
> "Just use SCEV" is maybe the wrong wording, at least for what I had in mind.
I should have been more specific. I meant by using SCEV we would be able to handle more general conditions, benefit from normalization and probably do all that with less code and benefit from the existing caching.


> My thinking was:
> We have probably quite a few "equivalence" checker in the code base. Which one to reuse depends at the end of the day on the properties you need.
> It becomes interesting as soon as you actually have condition sets that do not match 1-1 but are still equivalent. As I mentioned earlier, other relations, e.g., subset, will also be interesting. This is all "future work" where though.

That makes a lot of sense to me.

>> I don't think re-using GVN logic will be feasible, unless you want to value number the whole function
> If that turns out to help normalizing complex control conditions, why not. I will hopefully have a GSoC student to revive the PolyhedralValueAnalysis, that is even more expensive ;)

Sure, those are things we can decide on driven by data. 



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