This copies the text used in the #define statements to the code comments. The conflicting text comes from AMD manuals, but those are wrong. Sadly, this part has not been updated even after some docs were updated for Zen:
http://support.amd.com/en-us/search/tech-docs ( AMD64 Architecture Programmer's Manual Volume 4 )
See PR28110 for more discussion:
https://bugs.llvm.org/show_bug.cgi?id=28110