optimize primary constructors of Core types

[vtjnash]

this allows julia to optimize the Core type constructors

julia> f() = TopNode(:asdf)
f (generic function with 1 method)

julia> code_typed(f,())
1-element Array{Any,1}:
 :($(Expr(:lambda, Any[], Any[Any[],Any[],Any[]], :(begin  # none, line 1:
        return $(Expr(:new, :TopNode, :(:asdf)))
    end::TopNode))))

julia> code_llvm(f,())

define %jl_value_t* @julia_f_42804() {
top:
  %0 = call %jl_value_t* @allocobj(i64 16), !dbg !642
  %1 = getelementptr inbounds %jl_value_t* %0, i64 0, i32 0, !dbg !642
  store %jl_value_t* inttoptr (i64 19729664 to %jl_value_t*), %jl_value_t** %1, align 8, !dbg !642
  %2 = getelementptr inbounds %jl_value_t* %0, i64 1, i32 0, !dbg !642
  store %jl_value_t* inttoptr (i64 140523989960712 to %jl_value_t*), %jl_value_t** %2, align 8, !dbg !642
  ret %jl_value_t* %0, !dbg !642
}

julia> f(x) = GotoNode(x)
f (generic function with 2 methods)

julia> f(2)
:(goto 2)

julia> code_llvm(f,(Int,))

define %GotoNode @julia_f_42866(i64) {
top:
  %1 = insertvalue %GotoNode undef, i64 %0, 0, !dbg !822, !julia_type !824
  ret %GotoNode %1, !dbg !822
}

[JeffBezanson]

+1

[vtjnash]

i'll take that as a signal that this can be merged then (since CI finished now too)