Hello. I found that llvm-diff reports difference in the same input if the source contains specific constants (or instruction).
I reported this to llvm’s bugzilla ( https://bugs.llvm.org/show_bug.cgi?id=33623 ), and also
uploaded a patch for fix ( https://reviews.llvm.org/D34856 ).
It would be great for me if somebody confirms this.
I like llvm-diff. 
It helps me a lot when I’m investigating the optimized part of source code.
Best Regards,
Juneyoung Lee