following amusing sequence:
- AST writing schedules writing a type X* that it had never seen
before
- AST writing starts writing another declaration, ends up
deserializing X* from a prior AST file. Now we have two type IDs for
the same type!
- AST writer tries to write X*. It only has the lower-numbered ID
from the the prior AST file, so references to the higher-numbered ID
that was scheduled for writing go off into lalaland.
To fix this, keep the higher-numbered ID so we end up writing the type
twice. Since this issue occurs so rarely, and type records are
generally rather small, I deemed this better than the alternative: to
keep a separate mapping from the higher-numbered IDs to the
lower-numbered IDs, which we would end up having to check whenever we
want to deserialize any type.
Fixes <rdar://problem/8511624>, I think.
llvm-svn: 115647
9b3932c0bc