More Liveness

Yesterday, and the plan for today

Well, yesterday was the weekend, but on Friday I got a bit of work done on the liveness analysis. In particular, I implemented much of the gen function. Today, the plan is to clarify those few questions I had about gen, and to write kill.

Questions about gen


For now, I think it's easiest not to do any special handling of opaque. I can always change it later, and I'm more afraid of messing up the liveness analysis than I am of accidentally un-opqaueing something.


I'm still not quite sure what the correct way to handle blocks are. Perhaps gen and kill are not quite sufficient in their current incarnations? In fact, perhaps gen and kill should only be called on blocks themselves, and not the nested blocks. Then in and out are responsible for bridging the two?

Enter FreeIn

Of course, I'm not the first one to be needing this kind of information in the Futhark compiler, and so I just realized that the FreeIn type class provides me with everything I need. I knew about it before, but didn't understand exactly what it was that it did. Looking at it now, I can see that it returns the list of VName in some IR thing. This makes gen and kill much easier to make.

Indeed, after deciding to use freeIn, I was able to do the actual liveness analysis for most of the constructs in Futhark quite easily. The only major things left hanging are the Op instructions.


A day at DIKU!