The current splicing behavior dates back to when all blocks had terminators,
so we would "helpfully" splice before the terminator. This doesn't make sense
anymore, and leads to somewhat unexpected results when parsing multiple
pieces of IR into the same block.
Differential Revision: https://reviews.llvm.org/D135096
This is very useful when you want to parse IR even if
its invalid (e.g. bytecode). It's also useful if you don't
want to pay the cost of verification in certain situations.
Differential Revision: https://reviews.llvm.org/D134847