[LLVMdev] PredicateSimplifier questions

[John Regehr]

PredicateSimplifier is a pretty interesting pass, but it doesn't look 
like opt invokes it at any standard -Ox level, and so I assume that 
llvm-gcc also does not use this pass?  If that is right, I'm curious 
about why this is the case -- does it simply not provide enough code 
speedup to compensate for the increase in compile time?

Also, a colleague and I (we both teach advanced compiler courses) would 
like to have a relatively easy way for students to try out various 
abstract interpretation techniques on LLVM code.  Writing an abstract 
interpreter from scratch has too much overhead.  Of the LLVM passes that 
we know of, PredicateSimplifier seems the best starting point for making 
a more generic abstract interpreter into which collections of transfer 
functions could be plugged.  Does that seem right or can anyone suggest 
a better starting point?  It would be pretty cool, for example, to see 
what the Octagon domain could learn about LLVM programs.

John Regehr