0fcff69bcb
The first attempt at this missed a validity check. This version includes a test of the narrow source type for modulo-16-bits. Original commit message: This is the IR counterpart to 370ebc9d9a573d6 which provided a bswap narrowing fix for issue #53867. Here we can be more general (although I'm not sure yet what would happen for illegal types in codegen - too rare to worry about?): https://alive2.llvm.org/ce/z/3-CPfo This will be more effective if we have moved the shift after the bswap as proposed in D122010, but it is independent of that patch. Differential Revision: https://reviews.llvm.org/D122166