[ThinLTO] Create AliasSummary when building index

[tejohnson]

Summary

Previously we were creating the alias summary on the fly while writing
the summary to bitcode. This moves the creation of these summaries to
the module summary index builder where we build the rest of the summary
index.

[mehdi_amini]

Looks good. Can you add the motivation for doing this in the commit message when you push it?

lib/Analysis/ModuleSummaryAnalysis.cpp

static CalleeInfo::HotnessType getHotness(uint64_t ProfileCount,
   if (PSI->isColdCount(ProfileCount))
     return CalleeInfo::HotnessType::Cold;
   return CalleeInfo::HotnessType::None;
 }
 
 static void computeFunctionSummary(ModuleSummaryIndex &Index, const Module &M,
                                    const Function &F, BlockFrequencyInfo *BFI,
                                    ProfileSummaryInfo *PSI) {
-  // Summary not currently supported for anonymous functions, they must
-  // be renamed.
-  if (!F.hasName())
-    return;
+  // Summary not currently supported for anonymous functions, they should
+  // have been named.
+  assert(F.hasName());
 
   unsigned NumInsts = 0;
   // Map from callee ValueId to profile count. Used to accumulate profile
   // counts for all static calls to a given callee.
   DenseMap<const Value *, CalleeInfo> CallGraphEdges;
   DenseMap<GlobalValue::GUID, CalleeInfo> IndirectCallEdges;
   DenseSet<const Value *> RefEdges;
   ICallPromotionAnalysis ICallAnalysis;
for (const Instruction &I : BB) {
       // Check if this is an alias to a function. If so, get the
       // called aliasee for the checks below.
       if (auto *GA = dyn_cast<GlobalAlias>(CalledValue)) {
         assert(!CalledFunction && "Expected null called function in callsite for alias");
         CalledFunction = dyn_cast<Function>(GA->getBaseObject());
       }
       // Check if this is a direct call to a known function.
       if (CalledFunction) {
-        // Skip nameless and intrinsics.
-        if (!CalledFunction->hasName() || CalledFunction->isIntrinsic())
+        // Skip intrinsics.
+        if (CalledFunction->isIntrinsic())
           continue;
+        // We should have named any anonymous globals
+        assert(CalledFunction->hasName());
         auto ScaledCount = BFI ? BFI->getBlockProfileCount(&BB) : None;
         // Use the original CalledValue, in case it was an alias. We want
         // to record the call edge to the alias in that case. Eventually
         // an alias summary will be created to associate the alias and
         // aliasee.
         auto *CalleeId =
             M.getValueSymbolTable().lookup(CalledValue->getName());
 
static void computeVariableSummary(ModuleSummaryIndex &Index,
   findRefEdges(&V, RefEdges, Visited);
   GlobalValueSummary::GVFlags Flags(V);
   std::unique_ptr<GlobalVarSummary> GVarSummary =
       llvm::make_unique<GlobalVarSummary>(Flags);
   GVarSummary->addRefEdges(RefEdges);
   Index.addGlobalValueSummary(V.getName(), std::move(GVarSummary));
 }
 
+static void computeAliasSummary(ModuleSummaryIndex &Index,
+                                const GlobalAlias &A) {
+  GlobalValueSummary::GVFlags Flags(A);
+  std::unique_ptr<AliasSummary> 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);
+  Index.addGlobalValueSummary(A.getName(), std::move(AS));
+}
+
 ModuleSummaryIndex llvm::buildModuleSummaryIndex(
     const Module &M,
     std::function<BlockFrequencyInfo *(const Function &F)> GetBFICallback,
     ProfileSummaryInfo *PSI) {
   ModuleSummaryIndex Index;
   // Check if the module can be promoted, otherwise just disable importing from
   // it by not emitting any summary.
   // FIXME: we could still import *into* it most of the time.
ModuleSummaryIndex llvm::buildModuleSummaryIndex(
 
   // Compute summaries for all variables defined in module, and save in the
   // index.
   for (const GlobalVariable &G : M.globals()) {
     if (G.isDeclaration())
       continue;
     computeVariableSummary(Index, G);
   }
+
+  // Compute summaries for all aliases defined in module, and save in the
+  // index.
+  for (const GlobalAlias &A : M.aliases())
+    computeAliasSummary(Index, A);
+
   return Index;
 }
 
 char ModuleSummaryIndexAnalysis::PassID;
 
 ModuleSummaryIndex
 ModuleSummaryIndexAnalysis::run(Module &M, ModuleAnalysisManager &AM) {
   ProfileSummaryInfo &PSI = AM.getResult<ProfileSummaryAnalysis>(M);

lib/Bitcode/Writer/BitcodeWriter.cpp

void ModuleBitcodeWriter::writePerModuleGlobalValueSummary() {
   for (const GlobalAlias &A : M.aliases()) {
     auto *Aliasee = A.getBaseObject();
     if (!Aliasee->hasName())
       // Nameless function don't have an entry in the summary, skip it.
       continue;
     auto AliasId = VE.getValueID(&A);
     auto AliaseeId = VE.getValueID(Aliasee);
     NameVals.push_back(AliasId);
-    NameVals.push_back(getEncodedGVSummaryFlags(A));
+    auto *Summary = Index->getGlobalValueSummary(A);
+    AliasSummary *AS = cast<AliasSummary>(Summary);
+    NameVals.push_back(getEncodedGVSummaryFlags(AS->flags()));
     NameVals.push_back(AliaseeId);
     Stream.EmitRecord(bitc::FS_ALIAS, NameVals, FSAliasAbbrev);
     NameVals.clear();
   }
 
   Stream.ExitBlock();
 }