fwd_demand: Fix handling of SSAValue in stmt position (#138)

Author: Keno

src/codegen/forward_demand.jl

@@ -268,7 +268,7 @@ function forward_diff_no_inf!(ir::IRCode, to_diff::Vector{Pair{SSAValue, Int}};
                 # TODO: New PiNode that discriminates based on primal?
                 inst[:inst] = maparg(stmt.val, SSAValue(ssa), order)
                 inst[:type] = Any
-            elseif isa(stmt, GlobalRef)
+            elseif isa(stmt, GlobalRef) || isa(stmt, SSAValue)
                 inst[:inst] = maparg(stmt, SSAValue(ssa), order)
                 inst[:type] = Any
             elseif isa(stmt, Expr) || isa(stmt, PhiNode) || isa(stmt, PhiCNode) ||