Currently ConstantExpr::getWithOperands does not handle FNeg and
subsequently treats FNeg as binary operator, leading to an assertion
failure or segmentation fault if built without assertions.
Originally I reproduced this with llvm-dis on a bitcode file, which I
unfortunately cannot share and also cannot really reduce.
But PR45426 describes the same issue and has a reproducer with Clang, so
I'll go with that.