Truncation from 64-bit is not a `NOP`.
Oh, right, I got confused.
Minimum precision is a bit messy in DXIL. While FXC emits 32-bit types and flags them as only requiring 16 bits of precision, DXC emits them as 16-bit which are allowed to be implemented as 32-bit. Transparently remapping them is apparently acceptable. We must remap them in SPIR-V since they work much the same there as in TPF.
Ok, thanks for the explanation.