handle DetachNode pointing to dead BB

Author: vchuravy

base/compiler/typeinfer.jl

@@ -321,13 +321,21 @@ function type_annotate!(sv::InferenceState)
     nexpr = length(body)
 
     # replace gotoifnot with its condition if the branch target is unreachable
+    # use serial projection to turn DetachNode into branch
     for i = 1:nexpr
         expr = body[i]
         if isa(expr, Expr) && expr.head === :gotoifnot
             tgt = expr.args[2]::Int
             if !isa(states[tgt], VarTable)
                 body[i] = expr.args[1]
             end
+        elseif isa(expr, DetachNode)
+            # Unecessary for ReattachNode since if that points to a dead BB
+            # if will get automatically removed.
+            tgt = expr.reattach
+            if !isa(states[tgt], VarTable)
+                body[i] = GotoNode(expr.label)
+            end
         end
     end