diff --git a/src/compiler/simplified-lowering.cc b/src/compiler/simplified-lowering.cc
index d1bea0a119..c2e8e97e23 100644
--- a/src/compiler/simplified-lowering.cc
+++ b/src/compiler/simplified-lowering.cc
@@ -128,54 +128,6 @@ void ChangeToPureOp(Node* node, const Operator* new_op) {
 
 #ifdef DEBUG
 // Helpers for monotonicity checking.
-bool MachineRepresentationIsSubtype(MachineRepresentation r1,
-                                    MachineRepresentation r2) {
-  switch (r1) {
-    case MachineRepresentation::kNone:
-      return true;
-    case MachineRepresentation::kBit:
-      return r2 == MachineRepresentation::kBit ||
-             r2 == MachineRepresentation::kTagged;
-    case MachineRepresentation::kWord8:
-      return r2 == MachineRepresentation::kWord8 ||
-             r2 == MachineRepresentation::kWord16 ||
-             r2 == MachineRepresentation::kWord32 ||
-             r2 == MachineRepresentation::kWord64 ||
-             r2 == MachineRepresentation::kFloat32 ||
-             r2 == MachineRepresentation::kFloat64 ||
-             r2 == MachineRepresentation::kTagged;
-    case MachineRepresentation::kWord16:
-      return r2 == MachineRepresentation::kWord16 ||
-             r2 == MachineRepresentation::kWord32 ||
-             r2 == MachineRepresentation::kWord64 ||
-             r2 == MachineRepresentation::kFloat32 ||
-             r2 == MachineRepresentation::kFloat64 ||
-             r2 == MachineRepresentation::kTagged;
-    case MachineRepresentation::kWord32:
-      return r2 == MachineRepresentation::kWord32 ||
-             r2 == MachineRepresentation::kWord64 ||
-             r2 == MachineRepresentation::kFloat64 ||
-             r2 == MachineRepresentation::kTagged;
-    case MachineRepresentation::kWord64:
-      return r2 == MachineRepresentation::kWord64;
-    case MachineRepresentation::kFloat32:
-      return r2 == MachineRepresentation::kFloat32 ||
-             r2 == MachineRepresentation::kFloat64 ||
-             r2 == MachineRepresentation::kTagged;
-    case MachineRepresentation::kFloat64:
-      return r2 == MachineRepresentation::kFloat64 ||
-             r2 == MachineRepresentation::kTagged;
-    case MachineRepresentation::kSimd128:
-      return r2 == MachineRepresentation::kSimd128 ||
-             r2 == MachineRepresentation::kTagged;
-    case MachineRepresentation::kTagged:
-      return r2 == MachineRepresentation::kTagged;
-  }
-  UNREACHABLE();
-  return false;
-}
-
-
 class InputUseInfos {
  public:
   explicit InputUseInfos(Zone* zone) : input_use_infos_(zone) {}
@@ -194,9 +146,7 @@ class InputUseInfos {
   ZoneVector<UseInfo> input_use_infos_;
 
   static bool IsUseLessGeneral(UseInfo use1, UseInfo use2) {
-    return MachineRepresentationIsSubtype(use1.representation(),
-                                          use2.representation()) &&
-           use1.truncation().IsLessGeneralThan(use2.truncation());
+    return use1.truncation().IsLessGeneralThan(use2.truncation());
   }
 };
 
diff --git a/test/mjsunit/regress/regress-crbug-630952.js b/test/mjsunit/regress/regress-crbug-630952.js
new file mode 100644
index 0000000000..42d30a3ec1
--- /dev/null
+++ b/test/mjsunit/regress/regress-crbug-630952.js
@@ -0,0 +1,25 @@
+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --always-opt
+try {
+function __f_4(sign_bit,
+                          mantissa_29_bits) {
+}
+__f_4.prototype.returnSpecial = function() {
+                     this.mantissa_29_bits * mantissa_29_shift;
+}
+__f_4.prototype.toSingle = function() {
+  if (-65535) return this.toSingleSubnormal();
+}
+__f_4.prototype.toSingleSubnormal = function() {
+  if (__v_15) {
+      var __v_7 = this.mantissa_29_bits == -1 &&
+                 (__v_13 & __v_10 ) == 0;
+    }
+  __v_8 >>= __v_7;
+}
+__v_14 = new __f_4();
+__v_14.toSingle();
+} catch(e) {}