[turbofan] Pick word representation for phis with Type::Internal().

src/compiler/simplified-lowering.cc

Index: src/compiler/simplified-lowering.cc
diff --git a/src/compiler/simplified-lowering.cc b/src/compiler/simplified-lowering.cc
index 050d6ce0873211d55f179b50b1f4c1e88ef39b67..929f8fdc405e2ba7fb45680d335cd2c7257cc43e 100644
--- a/src/compiler/simplified-lowering.cc
+++ b/src/compiler/simplified-lowering.cc
@@ -344,6 +344,8 @@ class RepresentationSelector {
     } else if (upper->Is(Type::Number())) {
       // multiple uses => pick kRepFloat64.
       return kRepFloat64;
+    } else if (upper->Is(Type::Internal())) {
+      return kMachPtr;
     }
     return kRepTagged;
   }