Move ShareZeroVec later in SSA simplify order

mlton/ssa/simplify.fun

@@ -1,4 +1,4 @@
-(* Copyright (C) 2009 Matthew Fluet.
+(* Copyright (C) 2009,2017 Matthew Fluet.
  * Copyright (C) 1999-2008 Henry Cejtin, Matthew Fluet, Suresh
  *    Jagannathan, and Stephen Weeks.
  * Copyright (C) 1997-2000 NEC Research Institute.
@@ -63,7 +63,6 @@ val ssaPassesDefault =
    {name = "loopUnroll1", doit = LoopUnroll.transform, execute = false} ::
    {name = "removeUnused2", doit = RemoveUnused.transform, execute = true} ::
    {name = "simplifyTypes", doit = SimplifyTypes.transform, execute = true} ::
-   {name = "shareZeroVec", doit = ShareZeroVec.transform, execute = true} ::
    (* polyEqual should run
     *   - after types are simplified so that many equals are turned into eqs
     *   - before inlining so that equality functions can be inlined
@@ -97,6 +96,16 @@ val ssaPassesDefault =
    {name = "commonArg", doit = CommonArg.transform, execute = true} ::
    {name = "commonSubexp1", doit = CommonSubexp.transform, execute = true} ::
    {name = "commonBlock", doit = CommonBlock.transform, execute = true} ::
+   (* shareZeroVec should run
+    *  - after useless because sharing of zero-length array inhibits
+    *    changing type of flow-disjoint vector data
+    *  - after simplifyTypes because it may make previously distinct
+    *    types equal and allow more sharing of zero-length arrays
+    *  - after inlining because shareZeroVec (slightly) increases size
+    *  - before redundantTests because shareZeroVec introduces
+    *    comparisons with zero
+    *)
+   {name = "shareZeroVec", doit = ShareZeroVec.transform, execute = true} ::
    {name = "redundantTests", doit = RedundantTests.transform, execute = true} ::
    {name = "redundant", doit = Redundant.transform, execute = true} ::
    {name = "loopUnswitch2", doit = LoopUnswitch.transform, execute = false} ::