Observed on the releases/gcc-6 branch of https://github.com/gcc-mirror/gcc . 
There is a commit backported from the main branch, which looks like the 
attached file when extracting it with "git format-patch -1 
c86135dec7521ca3a877fa455b449dd8aa068a9c".

When trying to apply that patch with "git am", you get an error message:

error: config/rs6000/rs6000.md (working copy): does not exist in index

Apparently git tries to apply the diff from the git commit message, instead of 
the real diff.