Convert between tagged and untagged kSimd128 values.

src/compiler/representation-change.cc

Index: src/compiler/representation-change.cc
diff --git a/src/compiler/representation-change.cc b/src/compiler/representation-change.cc
index 2f7720beb3705599929416c442e2f1ab910677dc..073f03632d32876ef83daf82129c0a1fc5f53d03 100644
--- a/src/compiler/representation-change.cc
+++ b/src/compiler/representation-change.cc
@@ -137,6 +137,8 @@ Node* RepresentationChanger::GetRepresentationFor(
     case MachineRepresentation::kFloat64:
       return GetFloat64RepresentationFor(node, output_rep, output_type,
                                          truncation);
+    case MachineRepresentation::kSimd128:
+      return GetSimd128RepresentationFor(node, output_rep, output_type);
     case MachineRepresentation::kBit:
       return GetBitRepresentationFor(node, output_rep, output_type);
     case MachineRepresentation::kWord8:
@@ -145,9 +147,6 @@ Node* RepresentationChanger::GetRepresentationFor(
       return GetWord32RepresentationFor(node, output_rep, output_type);
     case MachineRepresentation::kWord64:
       return GetWord64RepresentationFor(node, output_rep, output_type);
-    case MachineRepresentation::kSimd128:  // Fall through.
-      // TODO(bbudge) Handle conversions between tagged and untagged.
-      break;
     case MachineRepresentation::kNone:
       return node;
   }
@@ -314,12 +313,23 @@ Node* RepresentationChanger::GetFloat64RepresentationFor(
   return jsgraph()->graph()->NewNode(op, node);
 }
 
+Node* RepresentationChanger::GetSimd128RepresentationFor(
+    Node* node, MachineRepresentation output_rep, Type* output_type) {
+  // Select the correct X -> Simd128 operator.
+  const Operator* op;
+  if (output_rep == MachineRepresentation::kTagged) {
+    op = nullptr;
+  } else {
+    return TypeError(node, output_rep, output_type,
+                     MachineRepresentation::kFloat64);
+  }
+  return jsgraph()->graph()->NewNode(op, node);
+}
 
 Node* RepresentationChanger::MakeTruncatedInt32Constant(double value) {
   return jsgraph()->Int32Constant(DoubleToInt32(value));
 }
 
-
 Node* RepresentationChanger::GetWord32RepresentationFor(
     Node* node, MachineRepresentation output_rep, Type* output_type) {
   // Eagerly fold representation changes for constants.