[Bug middle-end/68122] ICE in gcc/toplev.c:353 with -fsanitize=undefined and -fgnu-tm

["torvald at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68122

--- Comment #9 from torvald at gcc dot gnu.org ---
Marek, just skipping handling of internal functions is not correct I think.  In
the worst case, it should treat them as txn-unsafe, unless they are considered
txn-pure.  Do we have some idea of how many built-ins would be affected?  For
example I believe it wouldn't be critical if TM wouldn't be compatible with
UBSan for now, but if there are builtins for code that would be intuitively
txn-safe, supporting them would be good.

Regarding UBSan specifically, I believe many of the checks could be handled in
a straight-forward way: All values returned by transactional memory accesses
will form a consistent snapshot, always.  So, for example, an
addition-with-check call that takes values as arguments should be tm_pure
because it will check values that could have happened in some execution, even
if the transaction has to be rolled back later on.