diff --git a/hphp/runtime/vm/translator/hopt/codegen.cpp b/hphp/runtime/vm/translator/hopt/codegen.cpp
index 3dfbc82bb..38bcd5250 100644
--- a/hphp/runtime/vm/translator/hopt/codegen.cpp
+++ b/hphp/runtime/vm/translator/hopt/codegen.cpp
@@ -4255,6 +4255,59 @@ void CodeGenerator::cgLookupClsCns(IRInstruction* inst) {
                inst->getDst(), kSyncPoint, args, DestType::TV);
 }
 
+void CodeGenerator::cgLdCns(IRInstruction* inst) {
+  const StringData* cnsName = inst->getSrc(0)->getValStr();
+
+  TargetCache::CacheHandle ch = StringData::DefCnsHandle(cnsName, false);
+  // Has an unlikely branch to a LookupCns
+  cgLoad(rVmTl, ch, inst);
+}
+
+static TypedValue lookupCnsHelper(const TypedValue* tv, StringData* nm) {
+  assert(tv->m_type == KindOfUninit);
+  TypedValue *cns = nullptr;
+  TypedValue c1;
+  if (UNLIKELY(tv->m_data.pref != nullptr)) {
+    ClassInfo::ConstantInfo* ci =
+      (ClassInfo::ConstantInfo*)(void*)tv->m_data.pref;
+    cns = const_cast<Variant&>(ci->getDeferredValue()).asTypedValue();
+    tvReadCell(cns, &c1);
+  } else {
+    if (UNLIKELY(TargetCache::s_constants != nullptr)) {
+      cns = TargetCache::s_constants->HphpArray::nvGet(nm);
+    }
+    if (!cns) {
+      cns = Unit::loadCns(const_cast<StringData*>(nm));
+    }
+    if (UNLIKELY(!cns)) {
+      raise_notice(Strings::UNDEFINED_CONSTANT, nm->data(), nm->data());
+      c1.m_data.pstr = const_cast<StringData*>(nm);
+      c1.m_type = KindOfStaticString;
+    } else {
+      c1.m_type = cns->m_type;
+      c1.m_data = cns->m_data;
+    }
+  }
+  return c1;
+}
+
+void CodeGenerator::cgLookupCns(IRInstruction* inst) {
+  SSATmp* cnsNameTmp = inst->getSrc(0);
+
+  assert(inst->getTypeParam() == Type::Cell);
+  assert(cnsNameTmp->isConst() && cnsNameTmp->getType() == Type::StaticStr);
+
+  const StringData* cnsName = cnsNameTmp->getValStr();
+  TargetCache::CacheHandle ch = StringData::DefCnsHandle(cnsName, false);
+
+  ArgGroup args;
+  args.addr(rVmTl, ch)
+      .immPtr(cnsName);
+
+  cgCallHelper(m_as, TCA(lookupCnsHelper),
+               inst->getDst(), kSyncPoint, args, DestType::TV);
+}
+
 HOT_FUNC_VM
 static inline int64_t ak_exist_string_helper(StringData* key, ArrayData* arr) {
   int64_t n;
diff --git a/hphp/runtime/vm/translator/hopt/hhbctranslator.cpp b/hphp/runtime/vm/translator/hopt/hhbctranslator.cpp
index c00aabe50..cd6332c4f 100644
--- a/hphp/runtime/vm/translator/hopt/hhbctranslator.cpp
+++ b/hphp/runtime/vm/translator/hopt/hhbctranslator.cpp
@@ -341,7 +341,51 @@ void HhbcTranslator::emitColAddNewElemC() {
 }
 
 void HhbcTranslator::emitCns(uint32_t id) {
-  emitInterpOneOrPunt(Type::Cell, 0);
+  StringData* name = curUnit()->lookupLitstrId(id);
+  SSATmp* cnsNameTmp = m_tb->genDefConst(name);
+  const TypedValue* tv = Unit::lookupPersistentCns(name);
+  SSATmp* result = nullptr;
+  Type cnsType = Type::Cell;
+  if (tv) {
+    switch (tv->m_type) {
+      case KindOfUninit:
+        // a dynamic system constant. always a slow lookup
+        result = m_tb->gen(LookupCns, cnsType, cnsNameTmp);
+        break;
+      case KindOfBoolean:
+        result = m_tb->genDefConst((bool)tv->m_data.num);
+        break;
+      case KindOfInt64:
+        result = m_tb->genDefConst(tv->m_data.num);
+        break;
+      case KindOfDouble:
+        result = m_tb->genDefConst(tv->m_data.dbl);
+        break;
+      case KindOfString:
+      case KindOfStaticString:
+        result = m_tb->genDefConst(tv->m_data.pstr);
+        break;
+      default:
+        not_reached();
+    }
+  } else {
+    spillStack(); // do this on main trace so we update stack tracking once.
+    SSATmp* c1 = m_tb->gen(LdCns, cnsType, cnsNameTmp);
+    result = m_tb->cond(
+      getCurFunc(),
+      [&] (Block* taken) { // branch
+        m_tb->gen(CheckInit, taken, c1);
+      },
+      [&] { // Next: LdCns hit in TC
+        return c1;
+      },
+      [&] { // Taken: miss in TC, do lookup & init
+        m_tb->hint(Block::Unlikely);
+        return m_tb->gen(LookupCns, cnsType, cnsNameTmp);
+      }
+    );
+  }
+  push(result);
 }
 
 void HhbcTranslator::emitDefCns(uint32_t id) {
diff --git a/hphp/runtime/vm/translator/hopt/ir.h b/hphp/runtime/vm/translator/hopt/ir.h
index 01bfb0301..0089b80a8 100644
--- a/hphp/runtime/vm/translator/hopt/ir.h
+++ b/hphp/runtime/vm/translator/hopt/ir.h
@@ -277,6 +277,8 @@ O(LdClsCtx,                     D(Cls), S(Ctx),                            C) \
 O(LdClsCctx,                    D(Cls), S(Cctx),                           C) \
 O(LdClsCns,                     DParam, CStr CStr,                         C) \
 O(LookupClsCns,                 DParam, CStr CStr,           E|Refs|Er|N|Mem) \
+O(LdCns,                        DParam, CStr,                              C) \
+O(LookupCns,                    DParam, CStr,                E|Refs|Er|N|Mem) \
 O(LdClsMethodCache,         D(FuncCls), SUnk,              N|C|E|Refs|Er|Mem) \
 O(LdClsMethodFCache,        D(FuncCtx), C(Cls) CStr S(Obj,Cls,Ctx), N|C|E|Er) \
 O(GetCtxFwdCall,                D(Ctx), S(Ctx) S(Func),                    C) \