[turbofan] Always defer replacement in simplified lowering.

Since we do negative type checks, the current shortcut might still affect
the lowering choices, possibly leading to inconsistent results.

This CL gets rid of the shortcut.

Review-Url: https://codereview.chromium.org/2101943005
Cr-Commit-Position: refs/heads/master@{#37412}

src/compiler/simplified-lowering.cc

@@ -2102,20 +2102,9 @@ class RepresentationSelector {
       DCHECK_EQ(0, node->op()->ControlInputCount());
     }
 
-    if (replacement->id() < count_ &&
-        GetUpperBound(node)->Is(GetUpperBound(replacement)) &&
-        TypeOf(node)->Is(TypeOf(replacement))) {
-      // Replace with a previously existing node eagerly only if the type is the
-      // same.
-      node->ReplaceUses(replacement);
-    } else {
-      // Otherwise, we are replacing a node with a representation change.
-      // Such a substitution must be done after all lowering is done, because
-      // changing the type could confuse the representation change
-      // insertion for uses of the node.
     replacements_.push_back(node);
     replacements_.push_back(replacement);
-    }
+
     node->NullAllInputs();  // Node is now dead.
   }