C++: Fix join order

Author: jbj

cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/internal/SSAConstruction.qll

@@ -569,17 +569,18 @@ module DefUse {
   ) {
     exists(OldInstruction oldInstr, int oldOffset |
       oldInstr = defBlock.getInstruction(oldOffset) and
-      hasNonPhiDefinition(_, defLocation, defBlock, defOffset) and
       oldOffset >= 0
     |
       // An odd offset corresponds to the `Chi` instruction.
       defOffset = oldOffset * 2 + 1 and
       result = Chi(oldInstr) and
+      hasNonPhiDefinition(_, defLocation, defBlock, defOffset) and
       actualDefLocation = defLocation.getVirtualVariable()
       or
       // An even offset corresponds to the original instruction.
       defOffset = oldOffset * 2 and
       result = getNewInstruction(oldInstr) and
+      hasNonPhiDefinition(_, defLocation, defBlock, defOffset) and
       actualDefLocation = defLocation
     )
     or