Don't error on empty pass managers. (#488)

Author: maleadt

src/newpm.jl

@@ -57,11 +57,9 @@ Base.string(pm::NewPMPassManager) = "$(pm.type)($(join(pm.passes, ",")))"
 
 function add!(f::Base.Callable, parent::AbstractPassManager, nested::AbstractPassManager)
     f(nested)
-    if isempty(nested.passes)
-        # LLVM errors when doing `module()` etc, so catch this early
-        error("Cannot add an empty pass manager; did you forget to add passes?")
+    if !isempty(nested.passes)
+        add!(parent, nested)
     end
-    add!(parent, nested)
 end
 
 @doc (@doc NewPMPassManager)