[LLVMdev] LiveIntervalAnalysis

[Jakob Stoklund Olesen]

On May 18, 2012, at 12:42 PM, dag at cray.com wrote:

> I'm debugging a problem with a custom pass and I was surprised to
> discover that LiveIntervalAnalysis depends on PHIElimination.  Why is
> that so?  Intervals could be useful for all sorts of things beyond
> register allocation.
> 
> Just curious.  Is there something about the design of LiveIntervals that
> it needs the out-of-SSA conversion?

The LiveIntervals analysis currently requires the MIs to be in SSA form + whatever specific transforms 2-addr and phi-elim do to the instructions and LiveVariables. There are no attempts to make it work anywhere else in the pipeline.

For example, it doesn't understand PHI instructions.

I would like for LiveIntervals to be independent of LiveVariables and any other passes.

/jakob