Simplify building the @generated function by returning the CodeInfo

[NHDaly]

Apparently using an actual return code_info line, instead of just having the code_info as the final expression, prevents Julia lowering pass from wrapping the return value in an Expr(:block, ...), meaning it can be used by Julia to build the generated function.

Here is an example showing that difference:

With return:

julia> Meta.@lower @generated function f() return 2 end
...
    $(Expr(:meta, :nospecialize, :(@_2)))
    return 2
    Core._expr(:block, $(QuoteNode(:(#= REPL[107]:1 =#))), nothing)
    return %3
...

Without return:

julia> Meta.@lower @generated function f() 2 end
...
    $(Expr(:meta, :nospecialize, :(@_2)))
    Core._expr(:block, $(QuoteNode(:(#= REPL[108]:1 =#))), 2)
    return %2
...

As far as I can tell, it's been like this since Julia 0.7.

Before this PR, I was manually lowering the function and unwrapping the return value to allow it to pass-through unmodified. Now, this syntax change somehow stops the lowering-pass from wrapping it in the first place.

---

That said, this seems like maybe a bug in Julia's lowering logic... I'm leaving a big note in the code, and we may need to re-evaluate this if that lowering logic changes in the future.

[NHDaly]

Haha, this PR is so ridiculous. CC: @vchuravy @oxinabox

[vchuravy]

That said, this seems like maybe a bug in Julia's lowering logic... I'm leaving a big note in the code, and we may need to re-evaluate this if that lowering logic changes in the future.

Maybe ask Jeff whether this is intended :P

[oxinabox]

It certainly took me a back when I realized that was the difference between my code and @NHDaly's