In tree-cfg.c, the function verify_gimple_assign_single reports several errors that cannot be triggered by ordinary GCC users. Therefore, these errors should call internal_error() instead of error(). See bug 79856 and bug 79857.
Two years later, nothing has changed. As the German translator, I refuse to translate these messages. There is really nothing a GCC user could take away from a message like "incorrect entry in label_to_block_map".
This predates pr90149 but that one has more detail so I'm resolving this as a dupe of the latter. *** This bug has been marked as a duplicate of bug 90149 ***