Refactor HType to get rid of various hacks.

src/x64/lithium-x64.cc

Index: src/x64/lithium-x64.cc
diff --git a/src/x64/lithium-x64.cc b/src/x64/lithium-x64.cc
index e1b9e5f159095eccedde4ea3da55f89173e5b131..3989db2580ede5ab19f3fd9496ad022439c337a1 100644
--- a/src/x64/lithium-x64.cc
+++ b/src/x64/lithium-x64.cc
@@ -1918,7 +1918,9 @@ LInstruction* LChunkBuilder::DoChange(HChange* instr) {
 LInstruction* LChunkBuilder::DoCheckHeapObject(HCheckHeapObject* instr) {
   LOperand* value = UseRegisterAtStart(instr->value());
   LInstruction* result = new(zone()) LCheckNonSmi(value);
-  if (!instr->value()->IsHeapObject()) result = AssignEnvironment(result);
+  if (!instr->value()->type().IsHeapObject()) {
+    result = AssignEnvironment(result);
+  }
   return result;
 }