[LLVMdev] value tracking

[Nuno Lopes]

Hi,

I've been thinking about a (potentially lazy) value tracking analysis that 
could be reused by several optimization passes. I don't know if it exists in 
llvm or not, but to my better knowledge it does not. ok there exists the 
ValueTracking class, but it does not provide a function like e.g. 
MayHaveTheValue(Value* v, APSInt x) to check if a given var v may ever have 
the value x

My proposal:
 - create a value tracking analysis interface that can provide extensive 
info about vars (e.g. the set of possible values for a given vars, etc..)
 - implement that interface in several ways with different tradeoffs of 
preciseness vs speed (e.g. range analysis, value set tracking, path 
sensitive or not, interprocedural, etc..)

I believe this could reuse some code from PredSimplify and hopefully make it 
a very simple pass (as much of the work would then be hidden in the value 
tracking analysis).
Having this sort of readily available analysis would allow us to build other 
optimization more easily. I've already a few ideas in mind (I've implemented 
one of them, but I had to unnecessarily implement too much of this value 
tracking logic).

Any ideas, opinions, etc..?

Regards,
Nuno