[creduce-dev] unifdef

[John Regehr <regehr@cs.utah.edu>]

I just merged the new pass that does partial resolution of ifdefs.

For the 196 transitive include files that come from a C++ hello world on 
OS X (not making this up) the unifdef pass by itself gives a 57% 
reduction (in 352 seconds) if we choose -D first and -U second for each 
CPP symbol.  Reduction is only 45% for -U first (in 518 seconds).  I 
have no idea if this generalizes but I'm going with -D first for now.

Also I'm putting the unifdef and comment removal passes right up at the 
front of the phase ordering on the idea that they work well for 
non-preprocessed code and terminate very quickly if there aren't any 
ifdefs / comments to remove.  We can revisit this if my idea isn't right.

John