Index: llvm/trunk/include/llvm/ProfileData/InstrProf.h
===================================================================
--- llvm/trunk/include/llvm/ProfileData/InstrProf.h
+++ llvm/trunk/include/llvm/ProfileData/InstrProf.h
@@ -598,6 +598,28 @@
   InstrProfRecord() = default;
   InstrProfRecord(StringRef Name, uint64_t Hash, std::vector<uint64_t> Counts)
       : Name(Name), Hash(Hash), Counts(std::move(Counts)) {}
+  InstrProfRecord(InstrProfRecord &&) = default;
+  InstrProfRecord(const InstrProfRecord &RHS)
+      : Name(RHS.Name), Hash(RHS.Hash), Counts(RHS.Counts), SIPE(RHS.SIPE),
+        ValueData(RHS.ValueData
+                      ? llvm::make_unique<ValueProfData>(*RHS.ValueData)
+                      : nullptr) {}
+  InstrProfRecord &operator=(InstrProfRecord &&) = default;
+  InstrProfRecord &operator=(const InstrProfRecord &RHS) {
+    Name = RHS.Name;
+    Hash = RHS.Hash;
+    Counts = RHS.Counts;
+    SIPE = RHS.SIPE;
+    if (!RHS.ValueData) {
+      ValueData = nullptr;
+      return *this;
+    }
+    if (!ValueData)
+      ValueData = llvm::make_unique<ValueProfData>(*RHS.ValueData);
+    else
+      *ValueData = *RHS.ValueData;
+    return *this;
+  }
 
   using ValueMapType = std::vector<std::pair<uint64_t, uint64_t>>;
 
@@ -647,12 +669,9 @@
 
   /// Sort value profile data (per site) by count.
   void sortValueData() {
-    for (uint32_t Kind = IPVK_First; Kind <= IPVK_Last; ++Kind) {
-      std::vector<InstrProfValueSiteRecord> &SiteRecords =
-          getValueSitesForKind(Kind);
-      for (auto &SR : SiteRecords)
+    for (uint32_t Kind = IPVK_First; Kind <= IPVK_Last; ++Kind)
+      for (auto &SR : getValueSitesForKind(Kind))
         SR.sortByCount();
-    }
   }
 
   /// Clear value data entries and edge counters.
@@ -662,36 +681,54 @@
   }
 
   /// Clear value data entries
-  void clearValueData() {
-    for (uint32_t Kind = IPVK_First; Kind <= IPVK_Last; ++Kind)
-      getValueSitesForKind(Kind).clear();
-  }
+  void clearValueData() { ValueData = nullptr; }
 
   /// Get the error contained within the record's soft error counter.
   Error takeError() { return SIPE.takeError(); }
 
 private:
-  std::vector<InstrProfValueSiteRecord> IndirectCallSites;
-  std::vector<InstrProfValueSiteRecord> MemOPSizes;
+  struct ValueProfData {
+    std::vector<InstrProfValueSiteRecord> IndirectCallSites;
+    std::vector<InstrProfValueSiteRecord> MemOPSizes;
+  };
+  std::unique_ptr<ValueProfData> ValueData;
 
-  const std::vector<InstrProfValueSiteRecord> &
+  MutableArrayRef<InstrProfValueSiteRecord>
+  getValueSitesForKind(uint32_t ValueKind) {
+    // Cast to /add/ const (should be an implicit_cast, ideally, if that's ever
+    // implemented in LLVM) to call the const overload of this function, then
+    // cast away the constness from the result.
+    auto AR = const_cast<const InstrProfRecord *>(this)->getValueSitesForKind(
+        ValueKind);
+    return makeMutableArrayRef(
+        const_cast<InstrProfValueSiteRecord *>(AR.data()), AR.size());
+  }
+  ArrayRef<InstrProfValueSiteRecord>
   getValueSitesForKind(uint32_t ValueKind) const {
+    if (!ValueData)
+      return None;
     switch (ValueKind) {
     case IPVK_IndirectCallTarget:
-      return IndirectCallSites;
+      return ValueData->IndirectCallSites;
     case IPVK_MemOPSize:
-      return MemOPSizes;
+      return ValueData->MemOPSizes;
     default:
       llvm_unreachable("Unknown value kind!");
     }
-    return IndirectCallSites;
   }
 
   std::vector<InstrProfValueSiteRecord> &
-  getValueSitesForKind(uint32_t ValueKind) {
-    return const_cast<std::vector<InstrProfValueSiteRecord> &>(
-        const_cast<const InstrProfRecord *>(this)
-            ->getValueSitesForKind(ValueKind));
+  getOrCreateValueSitesForKind(uint32_t ValueKind) {
+    if (!ValueData)
+      ValueData = llvm::make_unique<ValueProfData>();
+    switch (ValueKind) {
+    case IPVK_IndirectCallTarget:
+      return ValueData->IndirectCallSites;
+    case IPVK_MemOPSize:
+      return ValueData->MemOPSizes;
+    default:
+      llvm_unreachable("Unknown value kind!");
+    }
   }
 
   // Map indirect call target name hash to name string.
@@ -765,9 +802,9 @@
 }
 
 void InstrProfRecord::reserveSites(uint32_t ValueKind, uint32_t NumValueSites) {
-  std::vector<InstrProfValueSiteRecord> &ValueSites =
-      getValueSitesForKind(ValueKind);
-  ValueSites.reserve(NumValueSites);
+  if (!NumValueSites)
+    return;
+  getOrCreateValueSitesForKind(ValueKind).reserve(NumValueSites);
 }
 
 inline support::endianness getHostEndianness() {
Index: llvm/trunk/lib/ProfileData/InstrProf.cpp
===================================================================
--- llvm/trunk/lib/ProfileData/InstrProf.cpp
+++ llvm/trunk/lib/ProfileData/InstrProf.cpp
@@ -504,9 +504,11 @@
     SIPE.addError(instrprof_error::value_site_count_mismatch);
     return;
   }
+  if (!ThisNumValueSites)
+    return;
   std::vector<InstrProfValueSiteRecord> &ThisSiteRecords =
-      getValueSitesForKind(ValueKind);
-  std::vector<InstrProfValueSiteRecord> &OtherSiteRecords =
+      getOrCreateValueSitesForKind(ValueKind);
+  MutableArrayRef<InstrProfValueSiteRecord> OtherSiteRecords =
       Src.getValueSitesForKind(ValueKind);
   for (uint32_t I = 0; I < ThisNumValueSites; I++)
     ThisSiteRecords[I].merge(SIPE, OtherSiteRecords[I], Weight);
@@ -533,11 +535,8 @@
 }
 
 void InstrProfRecord::scaleValueProfData(uint32_t ValueKind, uint64_t Weight) {
-  uint32_t ThisNumValueSites = getNumValueSites(ValueKind);
-  std::vector<InstrProfValueSiteRecord> &ThisSiteRecords =
-      getValueSitesForKind(ValueKind);
-  for (uint32_t I = 0; I < ThisNumValueSites; I++)
-    ThisSiteRecords[I].scale(SIPE, Weight);
+  for (auto &R : getValueSitesForKind(ValueKind))
+    R.scale(SIPE, Weight);
 }
 
 void InstrProfRecord::scale(uint64_t Weight) {
@@ -583,7 +582,7 @@
     VData[I].Value = remapValue(VData[I].Value, ValueKind, ValueMap);
   }
   std::vector<InstrProfValueSiteRecord> &ValueSites =
-      getValueSitesForKind(ValueKind);
+      getOrCreateValueSitesForKind(ValueKind);
   if (N == 0)
     ValueSites.emplace_back();
   else