[LLVMdev] Dependence Analysis [was: Flow-Sensitive AA]

[Chris Lattner]

On Aug 20, 2008, at 8:56 AM, David Greene wrote:
> What I really need is a dependence analysis interface.  I need to know
> about loop-carried dependencies and that sort of things, whether two  
> memory
> operations reference the same data, distance information, etc..  As  
> far as I
> can tell, there's no infrastructure for this in LLVM.

Right, this is something we've wanted for a long time, but noone has  
stepped up to add.

> I don't actually need the analysis because we have it in our  
> optimizer.  What
> I need is some kind of interface akin to AliasAnalysis that can chain
> analyses, etc.

Ok.

> I'm sure there are others working on this.  I believe Vikram  
> mentioned his
> group is working on a parallelizing compiler based on LLVM.

That project is just barely starting to get off the ground and will  
take awhile before it starts doing much, as far as I know.

> I would think it would be straightforward to taken the AliasAnalysis  
> interface
> and essentially duplicate it and call it DependenceAnalysis or some  
> such
> thing.  But if someone's already done this I'd rather not duplicate  
> the
> effort.

In theory, it should be pretty easy to create a new DependenceAnalysis  
analysis class and start piping it around.  It would be nice if there  
was a trivial implementation so that we can write regtests.

-Chris