When run under valgrind, or with a malloc that poisons freed memory,
this can lead to segfaults or other problems.
To avoid modifying the AdditionalUsers DenseMap while still iterating,
save the instructions to be notified in a separate SmallPtrSet, and use
this to later call OperandChangedState on each instruction.
Fixes PR49582.
Reviewed By: fhahn
Differential Revision: https://reviews.llvm.org/D98602
Dimitry Andric