Type coercion into scalar fails with internal compiler error

[sndels]

Implicit narrowing conversions into a scalar type seem to cause Internal Compiler error: llvm::cast<X>() argument of incompatible type!. Doesn't appear to happen when coercing into a vector type.

Minimal example, reproduces with dndxc.exe from de6a8ed's AppVeyor build
Fails: -enable-templates -DFAILURE_CASE
Compiles: -enable-templates

#ifdef FAILURE_CASE
template<typename T>
T Fn(T input)
{
    T ret = input - 1.f;

    return ret;
}

#else

template<typename T>
T Fn(T input)
{
    T ret = input - (T)1.f;

    return ret;
}

#endif

void main()
{
    Fn(1.0);
}

[llvm-beanz]

Actually... never mind on that... After PR #3991, this code causes a different error to arise in the compiler. I'll get on that too.