[ThinLTO] AliasSummary should not have any references

[tejohnson]

Summary

References should only be on the aliasee.

[pcc]

LGTM

include/llvm/IR/ModuleSummaryIndex.h

private:
   /// from within a function). This does not include functions called, which
   /// are listed in the derived FunctionSummary object.
   std::vector<ValueInfo> RefEdgeList;
 
   bool isLive() const { return Flags.Live; }
 
 protected:
   GlobalValueSummary(SummaryKind K, GVFlags Flags, std::vector<ValueInfo> Refs)
-      : Kind(K), Flags(Flags), RefEdgeList(std::move(Refs)) {}
+      : Kind(K), Flags(Flags), RefEdgeList(std::move(Refs)) {
+    assert((K != AliasKind || Refs.empty()) &&
+           "Expect no references for AliasSummary");
+  }
 
 public:
   virtual ~GlobalValueSummary() = default;
 
   /// Returns the hash of the original name, it is identical to the GUID for
   /// externally visible symbols, but not for local ones.
   GlobalValue::GUID getOriginalName() { return OriginalName; }
 
friend void computeDeadSymbols(class ModuleSummaryIndex &,
                                  const DenseSet<GlobalValue::GUID> &);
 };
 
 /// \brief Alias summary information.
 class AliasSummary : public GlobalValueSummary {
   GlobalValueSummary *AliaseeSummary;
 
 public:
-  AliasSummary(GVFlags Flags, std::vector<ValueInfo> Refs)
-      : GlobalValueSummary(AliasKind, Flags, std::move(Refs)) {}
+  AliasSummary(GVFlags Flags)
+      : GlobalValueSummary(AliasKind, Flags, ArrayRef<ValueInfo>{}) {}
 
   /// Check if this is an alias summary.
   static bool classof(const GlobalValueSummary *GVS) {
     return GVS->getSummaryKind() == AliasKind;
   }
 
   void setAliasee(GlobalValueSummary *Aliasee) { AliaseeSummary = Aliasee; }
 

lib/Analysis/ModuleSummaryAnalysis.cpp

 }
 
 static void
 computeAliasSummary(ModuleSummaryIndex &Index, const GlobalAlias &A,
                     DenseSet<GlobalValue::GUID> &CantBePromoted) {
   bool NonRenamableLocal = isNonRenamableLocal(A);
   GlobalValueSummary::GVFlags Flags(A.getLinkage(), NonRenamableLocal,
                                     /* Live = */ false);
-  auto AS = llvm::make_unique<AliasSummary>(Flags, ArrayRef<ValueInfo>{});
+  auto AS = llvm::make_unique<AliasSummary>(Flags);
   auto *Aliasee = A.getBaseObject();
   auto *AliaseeSummary = Index.getGlobalValueSummary(*Aliasee);
   assert(AliaseeSummary && "Alias expects aliasee summary to be parsed");
   AS->setAliasee(AliaseeSummary);
   if (NonRenamableLocal)
     CantBePromoted.insert(A.getGUID());
   Index.addGlobalValueSummary(A.getName(), std::move(AS));
 }

lib/Bitcode/Reader/BitcodeReader.cpp

while (true) {
     // FS_ALIAS: [valueid, flags, valueid]
     // Aliases must be emitted (and parsed) after all FS_PERMODULE entries, as
     // they expect all aliasee summaries to be available.
     case bitc::FS_ALIAS: {
       unsigned ValueID = Record[0];
       uint64_t RawFlags = Record[1];
       unsigned AliaseeID = Record[2];
       auto Flags = getDecodedGVSummaryFlags(RawFlags, Version);
-      auto AS =
-          llvm::make_unique<AliasSummary>(Flags, std::vector<ValueInfo>{});
+      auto AS = llvm::make_unique<AliasSummary>(Flags);
       // The module path string ref set in the summary must be owned by the
       // index's module string table. Since we don't have a module path
       // string table section in the per-module index, we create a single
       // module path string table entry with an empty (0) ID to take
       // ownership.
       AS->setModulePath(addThisModule()->first());
 
       GlobalValue::GUID AliaseeGUID =
while (true) {
     // Aliases must be emitted (and parsed) after all FS_COMBINED entries, as
     // they expect all aliasee summaries to be available.
     case bitc::FS_COMBINED_ALIAS: {
       unsigned ValueID = Record[0];
       uint64_t ModuleId = Record[1];
       uint64_t RawFlags = Record[2];
       unsigned AliaseeValueId = Record[3];
       auto Flags = getDecodedGVSummaryFlags(RawFlags, Version);
-      auto AS = llvm::make_unique<AliasSummary>(Flags, std::vector<ValueInfo>{});
+      auto AS = llvm::make_unique<AliasSummary>(Flags);
       LastSeenSummary = AS.get();
       AS->setModulePath(ModuleIdMap[ModuleId]);
 
       auto AliaseeGUID =
           getValueInfoFromValueId(AliaseeValueId).first.getGUID();
       auto AliaseeInModule =
           TheIndex.findSummaryInModule(AliaseeGUID, AS->modulePath());
       if (!AliaseeInModule)