Fix cfg_simplify! for empty preds and succs

[tkf]

Before this patch, cfg_simplify! relied on the conversion for handling empty preds and succs

julia> Vector{Int}(Union{}[])
Int64[]

which is not available inside the compiler:

julia> Base.invoke_in_world(UInt(4526), Vector{Int}, Union{}[])
ERROR: MethodError: no method matching Vector{Int64}(::Vector{Union{}})
The applicable method may be too new: running in world age 4526, while current world is 31202.

(I get 4526 via gdb)

This PR fixes it and also calls cfg_simplify! in the compiler's world age during the test. I think it's also good for improving inferrability. This is extracted from #39773.

[tkf]

Is this OK since jl_typeinf_world is serialized? Or should I add a C function jl_get_typeinf_world?

[Keno]

I don't think this will work. You'll need to ask C what the world age of inference is.

[tkf]

jl_typeinf_world is set by jl_set_typeinf_func just above. IIUC, this jl_typeinf_world is baked in the sysimage. So, isn't this age correct (though off by one) unless jl_set_typeinf_func is called again?

Of course, I'm fine with adding a proper C function but I'm curious when/how it'd be wrong.

[Keno]

I suppose you're right. World ages do persist across sysimage serialization (but not incremental serialization), so this should be ok.

[vtjnash]

We could pontially replace jl_call_in_typeinf_world with this too. While normally preserving these values would be risky, this is Core.Compiler, and is loaded early enough it is often not too important, but Revise expects to be able to change this, so it might still be a bit of a nuisance.

So might be better to write this as:

function invoke_in_compiler(args...)
    return ccall(:jl_call_in_typeinf_world, Any, (Ptr{Ptr{Cvoid}}, Cint), Any[args...], length(args))
end

[vtjnash]

I fixed this bug already in a different PR, and I don't think the test change is particularly necessary here

[tkf]

The fix part of it was already in master after #42172.