inference: correctly handle rare cases when Const wraps extended lattice objects

[aviatesk]

Otherwise, in rare cases, we may see this sort of weird behavior:

julia> @eval edgecase(_) = $(Core.Compiler.InterConditional(2, Int, Any))
edgecase (generic function with 1 method)

julia> code_typed((Any,)) do x
           edgecase(x) ? x : nothing
       end
1-element Vector{Any}:
 CodeInfo(
1 ─     goto #3 if not $(QuoteNode(Core.InterConditional(2, Int64, Any)))
2 ─     return x
3 ─     return Main.nothing
) => Any

julia> code_typed((Any,)) do x
           edgecase(x) ? x : nothing
       end
1-element Vector{Any}:
 CodeInfo(
1 ─      goto #3 if not $(QuoteNode(Core.InterConditional(2, Int64, Any)))
2 ─ %2 = π (x, Int64)
└──      return %2
3 ─      return Main.nothing
) => Union{Nothing, Int64}

[aviatesk]

@vtjnash I also found we actually never pass Const into the global cache:

julia/base/compiler/typeinfer.jl

Lines 298 to 300 in dc627e7

	if isa(result_type, Const)
	rettype_const = result_type.val
	const_flags = 0x2

So I wonder there is actually no external consumer of those extended lattice objects, and we can just move them to Core.Compiler (except PartialOpaque, which is observed in C) ?

[vtjnash]

Const (and other extended lattice types) get passed in as the sub-lattice fields of other lattice types

[vtjnash]

Though I would note that the commit/issue title is misleading, as only InterConditional had this issue, whereas we already previously handled it for the other extended lattice types

[aviatesk]

Const (and other extended lattice types) get passed in as the sub-lattice fields of other lattice types

Do you mean cases like PartialStruct(T, Any[Const(42), ...]) and InterConditional(n, Const(42), PartialStruct(...)) ?
I'm still not sure if there is any external consumer that wants to use jl_const_type etc. for such cases.