[LLVMdev] Flow-Sensitive AA

David Greene dag at cray.com
Mon Aug 18 15:48:27 PDT 2008

On Monday 18 August 2008 17:21, Chris Lattner wrote:
> On Aug 18, 2008, at 3:19 PM, David Greene wrote:
> > I'm not quite understanding how one would use the existing alias
> > analysis
> > framework to represent a flow-sensitive analysis.
> Yep, the current infrastructure isn't set up to support this.
> I haven't seen a real world case where flow sensitive AA is useful.

Yes, in the general case, flow-sensitive AA isn't worth it.

> Normally, the conversion to SSA form is sufficient.  Can you talk
> about cases where this matters to you?

Mostly it involves tying into our memory dependence analysis which
annotates things on program points.  I need a way to translate back 
to our optimizer data structures.

So it's not "flow-sensitive AA" in the strictest sense but it does require
program point information.

I looked at MemoryDependenceAnalysis and it's not quite what I want.
I need to know things like "does this load and store pair interfere," not
"give me the most recent instruction that interferes with this memory 
operation."  It's the kinds of things you'd want to ask for scheduling 
purposes, where no particular instruction ordering is assumed.


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