Make the 'icmp pred trunc(ext(X)), CST --> icmp pred X, ext(trunc(CST))'

transformation much more careful. Truncating binary '01' to '1' sounds like it's
safe until you realize that it switched from positive to negative under a signed
interpretation, and that depends on the icmp predicate.

Also a few miscellaneous cleanups.

llvm-svn: 97721