move two functions up higher in the file. Delete a useless argument

to EmitGEPOffset.  

Implement some new transforms for optimizing 
subtracts of two pointer to ints into the same vector.  This happens
for C++ iterator idioms for example, stringmap takes a const char*
that points to the start and end of a string.  Once inlined, we want
the pointer difference to turn back into a length.

This is rdar://7362831.

llvm-svn: 86021