[llvm-branch-commits] [llvm] [ThinLTO] Generate import status in per-module combined summary (PR #88024)

Mingming Liu via llvm-branch-commits llvm-branch-commits at lists.llvm.org
Fri May 10 17:01:49 PDT 2024


https://github.com/minglotus-6 updated https://github.com/llvm/llvm-project/pull/88024

>From cfb63d775d43a28b560d938346f1dd4b2dddc765 Mon Sep 17 00:00:00 2001
From: mingmingl <mingmingl at google.com>
Date: Thu, 4 Apr 2024 11:54:17 -0700
Subject: [PATCH 01/10] function import changes

---
 llvm/include/llvm/IR/ModuleSummaryIndex.h     |  24 ++++
 .../llvm/Transforms/IPO/FunctionImport.h      |  18 ++-
 llvm/lib/LTO/LTO.cpp                          |  13 +-
 llvm/lib/LTO/LTOBackend.cpp                   |   5 +-
 llvm/lib/LTO/ThinLTOCodeGenerator.cpp         |   9 +-
 llvm/lib/Transforms/IPO/FunctionImport.cpp    | 130 ++++++++++++------
 llvm/tools/llvm-link/llvm-link.cpp            |   2 +-
 7 files changed, 146 insertions(+), 55 deletions(-)

diff --git a/llvm/include/llvm/IR/ModuleSummaryIndex.h b/llvm/include/llvm/IR/ModuleSummaryIndex.h
index 286b51bda0e2c..259fe56ce5f63 100644
--- a/llvm/include/llvm/IR/ModuleSummaryIndex.h
+++ b/llvm/include/llvm/IR/ModuleSummaryIndex.h
@@ -296,6 +296,30 @@ template <> struct DenseMapInfo<ValueInfo> {
   static unsigned getHashValue(ValueInfo I) { return (uintptr_t)I.getRef(); }
 };
 
+struct SummaryImportInfo {
+  enum class ImportType : uint8_t {
+    NotImported = 0,
+    Declaration = 1,
+    Definition = 2,
+  };
+  unsigned Type : 3;
+  SummaryImportInfo() : Type(static_cast<unsigned>(ImportType::NotImported)) {}
+  SummaryImportInfo(ImportType Type) : Type(static_cast<unsigned>(Type)) {}
+
+  // FIXME: delete the first two set* helper function.
+  void updateType(ImportType InputType) {
+    Type = std::max(Type, static_cast<unsigned>(InputType));
+  }
+
+  bool isDefinition() const {
+    return static_cast<ImportType>(Type) == ImportType::Definition;
+  }
+
+  bool isDeclaration() const {
+    return static_cast<ImportType>(Type) == ImportType::Declaration;
+  }
+};
+
 /// Summary of memprof callsite metadata.
 struct CallsiteInfo {
   // Actual callee function.
diff --git a/llvm/include/llvm/Transforms/IPO/FunctionImport.h b/llvm/include/llvm/Transforms/IPO/FunctionImport.h
index c4d19e8641eca..9adc0c31eed43 100644
--- a/llvm/include/llvm/Transforms/IPO/FunctionImport.h
+++ b/llvm/include/llvm/Transforms/IPO/FunctionImport.h
@@ -33,7 +33,14 @@ class FunctionImporter {
 public:
   /// Set of functions to import from a source module. Each entry is a set
   /// containing all the GUIDs of all functions to import for a source module.
-  using FunctionsToImportTy = std::unordered_set<GlobalValue::GUID>;
+  using FunctionsToImportTy = DenseMap<GlobalValue::GUID, SummaryImportInfo>;
+
+  // FIXME: Remove this.
+  enum ImportStatus {
+    NotImported,
+    ImportDeclaration,
+    ImportDefinition,
+  };
 
   /// The different reasons selectCallee will chose not to import a
   /// candidate.
@@ -99,8 +106,10 @@ class FunctionImporter {
   /// index's module path string table).
   using ImportMapTy = DenseMap<StringRef, FunctionsToImportTy>;
 
-  /// The set contains an entry for every global value the module exports.
-  using ExportSetTy = DenseSet<ValueInfo>;
+  /// The map contains an entry for every global value the module exports, the
+  /// key being the value info, and the value is the summary-based import info.
+  /// FIXME: Does this set need to be a map?
+  using ExportSetTy = DenseMap<ValueInfo, SummaryImportInfo>;
 
   /// A function of this type is used to load modules referenced by the index.
   using ModuleLoaderTy =
@@ -211,7 +220,8 @@ void gatherImportedSummariesForModule(
     StringRef ModulePath,
     const DenseMap<StringRef, GVSummaryMapTy> &ModuleToDefinedGVSummaries,
     const FunctionImporter::ImportMapTy &ImportList,
-    std::map<std::string, GVSummaryMapTy> &ModuleToSummariesForIndex);
+    std::map<std::string, GVSummaryMapTy> &ModuleToSummariesForIndex,
+    ModuleToGVSummaryPtrSet &ModuleToDecSummaries);
 
 /// Emit into \p OutputFilename the files module \p ModulePath will import from.
 std::error_code EmitImportsFiles(
diff --git a/llvm/lib/LTO/LTO.cpp b/llvm/lib/LTO/LTO.cpp
index 53060df7f503e..ace533fe28c92 100644
--- a/llvm/lib/LTO/LTO.cpp
+++ b/llvm/lib/LTO/LTO.cpp
@@ -159,7 +159,7 @@ void llvm::computeLTOCacheKey(
   std::vector<uint64_t> ExportsGUID;
   ExportsGUID.reserve(ExportList.size());
   for (const auto &VI : ExportList) {
-    auto GUID = VI.getGUID();
+    auto GUID = VI.first.getGUID();
     ExportsGUID.push_back(GUID);
   }
 
@@ -205,7 +205,7 @@ void llvm::computeLTOCacheKey(
 
     AddUint64(Entry.getFunctions().size());
     for (auto &Fn : Entry.getFunctions())
-      AddUint64(Fn);
+      AddUint64(Fn.first);
   }
 
   // Include the hash for the resolved ODR.
@@ -277,7 +277,7 @@ void llvm::computeLTOCacheKey(
   for (const ImportModule &ImpM : ImportModulesVector)
     for (auto &ImpF : ImpM.getFunctions()) {
       GlobalValueSummary *S =
-          Index.findSummaryInModule(ImpF, ImpM.getIdentifier());
+          Index.findSummaryInModule(ImpF.first, ImpM.getIdentifier());
       AddUsedThings(S);
       // If this is an alias, we also care about any types/etc. that the aliasee
       // may reference.
@@ -1389,15 +1389,18 @@ class lto::ThinBackendProc {
                   llvm::StringRef ModulePath,
                   const std::string &NewModulePath) {
     std::map<std::string, GVSummaryMapTy> ModuleToSummariesForIndex;
+    ModuleToGVSummaryPtrSet ModuleToDeclarationSummaries;
     std::error_code EC;
     gatherImportedSummariesForModule(ModulePath, ModuleToDefinedGVSummaries,
-                                     ImportList, ModuleToSummariesForIndex);
+                                     ImportList, ModuleToSummariesForIndex,
+                                     ModuleToDeclarationSummaries);
 
     raw_fd_ostream OS(NewModulePath + ".thinlto.bc", EC,
                       sys::fs::OpenFlags::OF_None);
     if (EC)
       return errorCodeToError(EC);
-    writeIndexToFile(CombinedIndex, OS, &ModuleToSummariesForIndex);
+    writeIndexToFile(CombinedIndex, OS, &ModuleToSummariesForIndex,
+                     &ModuleToDeclarationSummaries);
 
     if (ShouldEmitImportsFiles) {
       EC = EmitImportsFiles(ModulePath, NewModulePath + ".imports",
diff --git a/llvm/lib/LTO/LTOBackend.cpp b/llvm/lib/LTO/LTOBackend.cpp
index 71e8849dc3cc9..6bb514d3d24e7 100644
--- a/llvm/lib/LTO/LTOBackend.cpp
+++ b/llvm/lib/LTO/LTOBackend.cpp
@@ -716,7 +716,10 @@ bool lto::initImportList(const Module &M,
       if (Summary->modulePath() == M.getModuleIdentifier())
         continue;
       // Add an entry to provoke importing by thinBackend.
-      ImportList[Summary->modulePath()].insert(GUID);
+      ImportList[Summary->modulePath()][GUID].updateType(
+          Summary->flags().ImportAsDec
+              ? SummaryImportInfo::ImportType::Declaration
+              : SummaryImportInfo::ImportType::Definition);
     }
   }
   return true;
diff --git a/llvm/lib/LTO/ThinLTOCodeGenerator.cpp b/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
index 8f517eb50dc76..75aecc95e789f 100644
--- a/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
+++ b/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
@@ -794,9 +794,11 @@ void ThinLTOCodeGenerator::gatherImportedSummariesForModule(
                            IsPrevailing(PrevailingCopy), ImportLists,
                            ExportLists);
 
+  ModuleToGVSummaryPtrSet ModuleToDecSummaries;
   llvm::gatherImportedSummariesForModule(
       ModuleIdentifier, ModuleToDefinedGVSummaries,
-      ImportLists[ModuleIdentifier], ModuleToSummariesForIndex);
+      ImportLists[ModuleIdentifier], ModuleToSummariesForIndex,
+      ModuleToDecSummaries);
 }
 
 /**
@@ -833,9 +835,12 @@ void ThinLTOCodeGenerator::emitImports(Module &TheModule, StringRef OutputName,
                            ExportLists);
 
   std::map<std::string, GVSummaryMapTy> ModuleToSummariesForIndex;
+  // FIXME: Pass on `ModuleToDecSummaries` to `EmitImportFiles` below.
+  ModuleToGVSummaryPtrSet ModuleToDecSummaries;
   llvm::gatherImportedSummariesForModule(
       ModuleIdentifier, ModuleToDefinedGVSummaries,
-      ImportLists[ModuleIdentifier], ModuleToSummariesForIndex);
+      ImportLists[ModuleIdentifier], ModuleToSummariesForIndex,
+      ModuleToDecSummaries);
 
   std::error_code EC;
   if ((EC = EmitImportsFiles(ModuleIdentifier, OutputName,
diff --git a/llvm/lib/Transforms/IPO/FunctionImport.cpp b/llvm/lib/Transforms/IPO/FunctionImport.cpp
index 68f9799616ae6..042fc285128b1 100644
--- a/llvm/lib/Transforms/IPO/FunctionImport.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionImport.cpp
@@ -358,17 +358,23 @@ class GlobalsImporter final {
         if (!GVS || !Index.canImportGlobalVar(GVS, /* AnalyzeRefs */ true) ||
             LocalNotInModule(GVS))
           continue;
-        auto ILI = ImportList[RefSummary->modulePath()].insert(VI.getGUID());
+        auto [Iter, Inserted] =
+            ImportList[RefSummary->modulePath()].try_emplace(
+                VI.getGUID(),
+                SummaryImportInfo(SummaryImportInfo::ImportType::Definition));
         // Only update stat and exports if we haven't already imported this
         // variable.
-        if (!ILI.second)
+        if (!Inserted) {
+          Iter->second.updateType(SummaryImportInfo::ImportType::Definition);
           break;
+        }
         NumImportedGlobalVarsThinLink++;
         // Any references made by this variable will be marked exported
         // later, in ComputeCrossModuleImport, after import decisions are
         // complete, which is more efficient than adding them here.
         if (ExportLists)
-          (*ExportLists)[RefSummary->modulePath()].insert(VI);
+          (*ExportLists)[RefSummary->modulePath()][VI].updateType(
+              SummaryImportInfo::ImportType::Definition);
 
         // If variable is not writeonly we attempt to recursively analyze
         // its references in order to import referenced constants.
@@ -545,10 +551,12 @@ class WorkloadImportsManager : public ModuleImportsManager {
       LLVM_DEBUG(dbgs() << "[Workload][Including]" << VI.name() << " from "
                         << ExportingModule << " : "
                         << Function::getGUID(VI.name()) << "\n");
-      ImportList[ExportingModule].insert(VI.getGUID());
+      ImportList[ExportingModule][VI.getGUID()].updateType(
+          SummaryImportInfo::ImportType::Definition);
       GVI.onImportingSummary(*GVS);
       if (ExportLists)
-        (*ExportLists)[ExportingModule].insert(VI);
+        (*ExportLists)[ExportingModule][VI].updateType(
+            SummaryImportInfo::ImportType::Definition);
     }
     LLVM_DEBUG(dbgs() << "[Workload] Done\n");
   }
@@ -816,23 +824,27 @@ static void computeImportForFunction(
              "selectCallee() didn't honor the threshold");
 
       auto ExportModulePath = ResolvedCalleeSummary->modulePath();
-      auto ILI = ImportList[ExportModulePath].insert(VI.getGUID());
+      auto [Iter, Inserted] =
+          ImportList[ExportModulePath].insert(std::make_pair(
+              VI.getGUID(),
+              SummaryImportInfo(SummaryImportInfo::ImportType::Definition)));
       // We previously decided to import this GUID definition if it was already
       // inserted in the set of imports from the exporting module.
-      bool PreviouslyImported = !ILI.second;
-      if (!PreviouslyImported) {
+      if (Inserted) {
         NumImportedFunctionsThinLink++;
         if (IsHotCallsite)
           NumImportedHotFunctionsThinLink++;
         if (IsCriticalCallsite)
           NumImportedCriticalFunctionsThinLink++;
-      }
+      } else
+        Iter->second.updateType(SummaryImportInfo::ImportType::Definition);
 
       // Any calls/references made by this function will be marked exported
       // later, in ComputeCrossModuleImport, after import decisions are
       // complete, which is more efficient than adding them here.
       if (ExportLists)
-        (*ExportLists)[ExportModulePath].insert(VI);
+        (*ExportLists)[ExportModulePath][VI].updateType(
+            SummaryImportInfo::ImportType::Definition);
     }
 
     auto GetAdjustedThreshold = [](unsigned Threshold, bool IsHotCallsite) {
@@ -942,9 +954,11 @@ template <class T>
 static unsigned numGlobalVarSummaries(const ModuleSummaryIndex &Index,
                                       T &Cont) {
   unsigned NumGVS = 0;
-  for (auto &V : Cont)
-    if (isGlobalVarSummary(Index, V))
+  for (auto &[GUID, Type] : Cont) {
+    assert(Type.isDefinition() && "Declaration type doesn't exist yet");
+    if (isGlobalVarSummary(Index, GUID))
       ++NumGVS;
+  }
   return NumGVS;
 }
 #endif
@@ -959,8 +973,8 @@ static bool checkVariableImport(
 
   for (auto &ImportPerModule : ImportLists)
     for (auto &ExportPerModule : ImportPerModule.second)
-      FlattenedImports.insert(ExportPerModule.second.begin(),
-                              ExportPerModule.second.end());
+      for (auto &[GUID, Type] : ExportPerModule.second)
+        FlattenedImports.insert(GUID);
 
   // Checks that all GUIDs of read/writeonly vars we see in export lists
   // are also in the import lists. Otherwise we my face linker undefs,
@@ -979,7 +993,7 @@ static bool checkVariableImport(
   };
 
   for (auto &ExportPerModule : ExportLists)
-    for (auto &VI : ExportPerModule.second)
+    for (auto &[VI, Unused] : ExportPerModule.second)
       if (!FlattenedImports.count(VI.getGUID()) &&
           IsReadOrWriteOnlyVarNeedingImporting(ExportPerModule.first, VI))
         return false;
@@ -1015,7 +1029,8 @@ void llvm::ComputeCrossModuleImport(
     FunctionImporter::ExportSetTy NewExports;
     const auto &DefinedGVSummaries =
         ModuleToDefinedGVSummaries.lookup(ELI.first);
-    for (auto &EI : ELI.second) {
+    for (auto &[EI, Type] : ELI.second) {
+      assert(Type.isDefinition() && "Declaration type doesn't exist yet");
       // Find the copy defined in the exporting module so that we can mark the
       // values it references in that specific definition as exported.
       // Below we will add all references and called values, without regard to
@@ -1035,13 +1050,16 @@ void llvm::ComputeCrossModuleImport(
         // See processGlobalForThinLTO.
         if (!Index.isWriteOnly(GVS))
           for (const auto &VI : GVS->refs())
-            NewExports.insert(VI);
+            NewExports[VI].updateType(
+                SummaryImportInfo::ImportType::Declaration);
       } else {
         auto *FS = cast<FunctionSummary>(S);
         for (const auto &Edge : FS->calls())
-          NewExports.insert(Edge.first);
+          NewExports[Edge.first].updateType(
+              SummaryImportInfo::ImportType::Declaration);
         for (const auto &Ref : FS->refs())
-          NewExports.insert(Ref);
+          NewExports[Ref].updateType(
+              SummaryImportInfo::ImportType::Declaration);
       }
     }
     // Prune list computed above to only include values defined in the exporting
@@ -1049,7 +1067,7 @@ void llvm::ComputeCrossModuleImport(
     // ref/call target multiple times in above loop, and it is more efficient to
     // avoid a set lookup each time.
     for (auto EI = NewExports.begin(); EI != NewExports.end();) {
-      if (!DefinedGVSummaries.count(EI->getGUID()))
+      if (!DefinedGVSummaries.count(EI->first.getGUID()))
         NewExports.erase(EI++);
       else
         ++EI;
@@ -1149,7 +1167,10 @@ static void ComputeCrossModuleImportForModuleFromIndexForTest(
     if (Summary->modulePath() == ModulePath)
       continue;
     // Add an entry to provoke importing by thinBackend.
-    ImportList[Summary->modulePath()].insert(GUID);
+    ImportList[Summary->modulePath()][GUID].updateType(
+        Summary->flags().ImportAsDec
+            ? SummaryImportInfo::ImportType::Declaration
+            : SummaryImportInfo::ImportType::Definition);
   }
 #ifndef NDEBUG
   dumpImportListForModule(Index, ModulePath, ImportList);
@@ -1332,20 +1353,25 @@ void llvm::gatherImportedSummariesForModule(
     StringRef ModulePath,
     const DenseMap<StringRef, GVSummaryMapTy> &ModuleToDefinedGVSummaries,
     const FunctionImporter::ImportMapTy &ImportList,
-    std::map<std::string, GVSummaryMapTy> &ModuleToSummariesForIndex) {
+    std::map<std::string, GVSummaryMapTy> &ModuleToSummariesForIndex,
+    ModuleToGVSummaryPtrSet &ModuleToDecSummaries) {
   // Include all summaries from the importing module.
   ModuleToSummariesForIndex[std::string(ModulePath)] =
       ModuleToDefinedGVSummaries.lookup(ModulePath);
   // Include summaries for imports.
   for (const auto &ILI : ImportList) {
-    auto &SummariesForIndex = ModuleToSummariesForIndex[std::string(ILI.first)];
+    std::string ModulePath(ILI.first);
+    auto &SummariesForIndex = ModuleToSummariesForIndex[ModulePath];
+    auto &DecSummaries = ModuleToDecSummaries[ModulePath];
     const auto &DefinedGVSummaries =
         ModuleToDefinedGVSummaries.lookup(ILI.first);
-    for (const auto &GI : ILI.second) {
-      const auto &DS = DefinedGVSummaries.find(GI);
+    for (const auto &[GUID, Type] : ILI.second) {
+      const auto &DS = DefinedGVSummaries.find(GUID);
       assert(DS != DefinedGVSummaries.end() &&
              "Expected a defined summary for imported global value");
-      SummariesForIndex[GI] = DS->second;
+      SummariesForIndex[GUID] = DS->second;
+      if (Type.isDeclaration())
+        DecSummaries.insert(DS->second);
     }
   }
 }
@@ -1617,6 +1643,16 @@ Expected<bool> FunctionImporter::importFunctions(
   for (const auto &FunctionsToImportPerModule : ImportList) {
     ModuleNameOrderedList.insert(FunctionsToImportPerModule.first);
   }
+
+  auto getImportStatus = [&](const FunctionsToImportTy &GUIDToImportType,
+                             GlobalValue::GUID GUID) -> ImportStatus {
+    auto Iter = GUIDToImportType.find(GUID);
+    if (Iter == GUIDToImportType.end())
+      return ImportStatus::NotImported;
+    return Iter->second.isDefinition() ? ImportStatus::ImportDefinition
+                                       : ImportStatus::ImportDeclaration;
+  };
+
   for (const auto &Name : ModuleNameOrderedList) {
     // Get the module for the import
     const auto &FunctionsToImportPerModule = ImportList.find(Name);
@@ -1634,17 +1670,21 @@ Expected<bool> FunctionImporter::importFunctions(
       return std::move(Err);
 
     auto &ImportGUIDs = FunctionsToImportPerModule->second;
+
     // Find the globals to import
     SetVector<GlobalValue *> GlobalsToImport;
+    SetVector<GlobalValue *> GlobalDeclsToImport;
     for (Function &F : *SrcModule) {
       if (!F.hasName())
         continue;
       auto GUID = F.getGUID();
-      auto Import = ImportGUIDs.count(GUID);
-      LLVM_DEBUG(dbgs() << (Import ? "Is" : "Not") << " importing function "
-                        << GUID << " " << F.getName() << " from "
-                        << SrcModule->getSourceFileName() << "\n");
-      if (Import) {
+      auto ImportStatus = getImportStatus(ImportGUIDs, GUID);
+      const bool ImportDefinition =
+          ImportStatus == ImportStatus::ImportDefinition;
+      LLVM_DEBUG(dbgs() << (ImportDefinition ? "Is" : "Not")
+                        << " importing function " << GUID << " " << F.getName()
+                        << " from " << SrcModule->getSourceFileName() << "\n");
+      if (ImportDefinition) {
         if (Error Err = F.materialize())
           return std::move(Err);
         // MemProf should match function's definition and summary,
@@ -1664,17 +1704,20 @@ Expected<bool> FunctionImporter::importFunctions(
                                          SrcModule->getSourceFileName())}));
         }
         GlobalsToImport.insert(&F);
-      }
+      } else if (ImportStatus == ImportDeclaration)
+        GlobalDeclsToImport.insert(&F);
     }
     for (GlobalVariable &GV : SrcModule->globals()) {
       if (!GV.hasName())
         continue;
       auto GUID = GV.getGUID();
-      auto Import = ImportGUIDs.count(GUID);
-      LLVM_DEBUG(dbgs() << (Import ? "Is" : "Not") << " importing global "
-                        << GUID << " " << GV.getName() << " from "
-                        << SrcModule->getSourceFileName() << "\n");
-      if (Import) {
+      auto ImportStatus = getImportStatus(ImportGUIDs, GUID);
+      const bool ImportDefinition =
+          (ImportStatus == ImportStatus::ImportDefinition);
+      LLVM_DEBUG(dbgs() << (ImportDefinition ? "Is" : "Not")
+                        << " importing global " << GUID << " " << GV.getName()
+                        << " from " << SrcModule->getSourceFileName() << "\n");
+      if (ImportDefinition) {
         if (Error Err = GV.materialize())
           return std::move(Err);
         ImportedGVCount += GlobalsToImport.insert(&GV);
@@ -1684,11 +1727,13 @@ Expected<bool> FunctionImporter::importFunctions(
       if (!GA.hasName() || isa<GlobalIFunc>(GA.getAliaseeObject()))
         continue;
       auto GUID = GA.getGUID();
-      auto Import = ImportGUIDs.count(GUID);
-      LLVM_DEBUG(dbgs() << (Import ? "Is" : "Not") << " importing alias "
-                        << GUID << " " << GA.getName() << " from "
-                        << SrcModule->getSourceFileName() << "\n");
-      if (Import) {
+      auto ImportStatus = getImportStatus(ImportGUIDs, GUID);
+      const bool ImportDefinition =
+          (ImportStatus == ImportStatus::ImportDefinition);
+      LLVM_DEBUG(dbgs() << (ImportDefinition ? "Is" : "Not")
+                        << " importing alias " << GUID << " " << GA.getName()
+                        << " from " << SrcModule->getSourceFileName() << "\n");
+      if (ImportDefinition) {
         if (Error Err = GA.materialize())
           return std::move(Err);
         // Import alias as a copy of its aliasee.
@@ -1738,6 +1783,7 @@ Expected<bool> FunctionImporter::importFunctions(
                << " from " << SrcModule->getSourceFileName() << "\n";
     }
 
+    // FIXME: A later change will pass on GlobalDeclsToImport to IRMover.
     if (Error Err = Mover.move(std::move(SrcModule),
                                GlobalsToImport.getArrayRef(), nullptr,
                                /*IsPerformingImport=*/true))
diff --git a/llvm/tools/llvm-link/llvm-link.cpp b/llvm/tools/llvm-link/llvm-link.cpp
index 9049cb5e85800..0a60b1e3d8f5d 100644
--- a/llvm/tools/llvm-link/llvm-link.cpp
+++ b/llvm/tools/llvm-link/llvm-link.cpp
@@ -376,7 +376,7 @@ static bool importFunctions(const char *argv0, Module &DestModule) {
 
     auto &Entry =
         ImportList[FileNameStringCache.insert(FileName).first->getKey()];
-    Entry.insert(F->getGUID());
+    Entry[F->getGUID()].updateType(SummaryImportInfo::ImportType::Definition);
   }
   auto CachedModuleLoader = [&](StringRef Identifier) {
     return ModuleLoaderCache.takeModule(std::string(Identifier));

>From 23a3fa4d3d124a2525f20e3a58da6d5e7740e7df Mon Sep 17 00:00:00 2001
From: mingmingl <mingmingl at google.com>
Date: Tue, 16 Apr 2024 21:12:34 -0700
Subject: [PATCH 02/10] simplify code

---
 llvm/include/llvm/IR/ModuleSummaryIndex.h     | 30 ++-----
 .../llvm/Transforms/IPO/FunctionImport.h      | 16 ++--
 llvm/lib/LTO/LTOBackend.cpp                   | 10 ++-
 llvm/lib/Transforms/IPO/FunctionImport.cpp    | 90 +++++++++----------
 llvm/tools/llvm-link/llvm-link.cpp            |  2 +-
 5 files changed, 62 insertions(+), 86 deletions(-)

diff --git a/llvm/include/llvm/IR/ModuleSummaryIndex.h b/llvm/include/llvm/IR/ModuleSummaryIndex.h
index 7f6f7446e0962..29d13cf4f4fae 100644
--- a/llvm/include/llvm/IR/ModuleSummaryIndex.h
+++ b/llvm/include/llvm/IR/ModuleSummaryIndex.h
@@ -296,30 +296,6 @@ template <> struct DenseMapInfo<ValueInfo> {
   static unsigned getHashValue(ValueInfo I) { return (uintptr_t)I.getRef(); }
 };
 
-struct SummaryImportInfo {
-  enum class ImportType : uint8_t {
-    NotImported = 0,
-    Declaration = 1,
-    Definition = 2,
-  };
-  unsigned Type : 3;
-  SummaryImportInfo() : Type(static_cast<unsigned>(ImportType::NotImported)) {}
-  SummaryImportInfo(ImportType Type) : Type(static_cast<unsigned>(Type)) {}
-
-  // FIXME: delete the first two set* helper function.
-  void updateType(ImportType InputType) {
-    Type = std::max(Type, static_cast<unsigned>(InputType));
-  }
-
-  bool isDefinition() const {
-    return static_cast<ImportType>(Type) == ImportType::Definition;
-  }
-
-  bool isDeclaration() const {
-    return static_cast<ImportType>(Type) == ImportType::Declaration;
-  }
-};
-
 /// Summary of memprof callsite metadata.
 struct CallsiteInfo {
   // Actual callee function.
@@ -609,7 +585,11 @@ class GlobalValueSummary {
     return Flags.ImportType == GlobalValueSummary::ImportKind::Declaration;
   }
 
-  void setImportKind(ImportKind IK) { Flags.ImportType = IK; }
+  GlobalValueSummary::ImportKind importType() const {
+    return static_cast<ImportKind>(Flags.ImportType);
+  }
+
+  void setImportType(ImportKind IK) { Flags.ImportType = IK; }
 
   GlobalValue::VisibilityTypes getVisibility() const {
     return (GlobalValue::VisibilityTypes)Flags.Visibility;
diff --git a/llvm/include/llvm/Transforms/IPO/FunctionImport.h b/llvm/include/llvm/Transforms/IPO/FunctionImport.h
index 9adc0c31eed43..6729fcc420a6e 100644
--- a/llvm/include/llvm/Transforms/IPO/FunctionImport.h
+++ b/llvm/include/llvm/Transforms/IPO/FunctionImport.h
@@ -33,14 +33,8 @@ class FunctionImporter {
 public:
   /// Set of functions to import from a source module. Each entry is a set
   /// containing all the GUIDs of all functions to import for a source module.
-  using FunctionsToImportTy = DenseMap<GlobalValue::GUID, SummaryImportInfo>;
-
-  // FIXME: Remove this.
-  enum ImportStatus {
-    NotImported,
-    ImportDeclaration,
-    ImportDefinition,
-  };
+  using FunctionsToImportTy =
+      DenseMap<GlobalValue::GUID, GlobalValueSummary::ImportKind>;
 
   /// The different reasons selectCallee will chose not to import a
   /// candidate.
@@ -107,9 +101,9 @@ class FunctionImporter {
   using ImportMapTy = DenseMap<StringRef, FunctionsToImportTy>;
 
   /// The map contains an entry for every global value the module exports, the
-  /// key being the value info, and the value is the summary-based import info.
-  /// FIXME: Does this set need to be a map?
-  using ExportSetTy = DenseMap<ValueInfo, SummaryImportInfo>;
+  /// key being the value info, and the value indicates whether the definition
+  /// or declaration is visible to another module.
+  using ExportSetTy = DenseMap<ValueInfo, GlobalValueSummary::ImportKind>;
 
   /// A function of this type is used to load modules referenced by the index.
   using ModuleLoaderTy =
diff --git a/llvm/lib/LTO/LTOBackend.cpp b/llvm/lib/LTO/LTOBackend.cpp
index 6bb514d3d24e7..23d75c238fc29 100644
--- a/llvm/lib/LTO/LTOBackend.cpp
+++ b/llvm/lib/LTO/LTOBackend.cpp
@@ -715,11 +715,13 @@ bool lto::initImportList(const Module &M,
       // e.g. record required linkage changes.
       if (Summary->modulePath() == M.getModuleIdentifier())
         continue;
+
       // Add an entry to provoke importing by thinBackend.
-      ImportList[Summary->modulePath()][GUID].updateType(
-          Summary->flags().ImportAsDec
-              ? SummaryImportInfo::ImportType::Declaration
-              : SummaryImportInfo::ImportType::Definition);
+      auto [Iter, Inserted] = ImportList[Summary->modulePath()].try_emplace(
+          GUID, Summary->importType());
+
+      if (!Inserted)
+        Iter->second = std::min(Iter->second, Summary->importType());
     }
   }
   return true;
diff --git a/llvm/lib/Transforms/IPO/FunctionImport.cpp b/llvm/lib/Transforms/IPO/FunctionImport.cpp
index 042fc285128b1..1485259e642a0 100644
--- a/llvm/lib/Transforms/IPO/FunctionImport.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionImport.cpp
@@ -358,14 +358,14 @@ class GlobalsImporter final {
         if (!GVS || !Index.canImportGlobalVar(GVS, /* AnalyzeRefs */ true) ||
             LocalNotInModule(GVS))
           continue;
+
         auto [Iter, Inserted] =
             ImportList[RefSummary->modulePath()].try_emplace(
-                VI.getGUID(),
-                SummaryImportInfo(SummaryImportInfo::ImportType::Definition));
+                VI.getGUID(), GlobalValueSummary::Definition);
         // Only update stat and exports if we haven't already imported this
         // variable.
         if (!Inserted) {
-          Iter->second.updateType(SummaryImportInfo::ImportType::Definition);
+          Iter->second = std::min(GlobalValueSummary::Definition, Iter->second);
           break;
         }
         NumImportedGlobalVarsThinLink++;
@@ -373,8 +373,8 @@ class GlobalsImporter final {
         // later, in ComputeCrossModuleImport, after import decisions are
         // complete, which is more efficient than adding them here.
         if (ExportLists)
-          (*ExportLists)[RefSummary->modulePath()][VI].updateType(
-              SummaryImportInfo::ImportType::Definition);
+          (*ExportLists)[RefSummary->modulePath()][VI] =
+              GlobalValueSummary::Definition;
 
         // If variable is not writeonly we attempt to recursively analyze
         // its references in order to import referenced constants.
@@ -551,12 +551,11 @@ class WorkloadImportsManager : public ModuleImportsManager {
       LLVM_DEBUG(dbgs() << "[Workload][Including]" << VI.name() << " from "
                         << ExportingModule << " : "
                         << Function::getGUID(VI.name()) << "\n");
-      ImportList[ExportingModule][VI.getGUID()].updateType(
-          SummaryImportInfo::ImportType::Definition);
+      ImportList[ExportingModule][VI.getGUID()] =
+          GlobalValueSummary::Definition;
       GVI.onImportingSummary(*GVS);
       if (ExportLists)
-        (*ExportLists)[ExportingModule][VI].updateType(
-            SummaryImportInfo::ImportType::Definition);
+        (*ExportLists)[ExportingModule][VI] = GlobalValueSummary::Definition;
     }
     LLVM_DEBUG(dbgs() << "[Workload] Done\n");
   }
@@ -824,10 +823,8 @@ static void computeImportForFunction(
              "selectCallee() didn't honor the threshold");
 
       auto ExportModulePath = ResolvedCalleeSummary->modulePath();
-      auto [Iter, Inserted] =
-          ImportList[ExportModulePath].insert(std::make_pair(
-              VI.getGUID(),
-              SummaryImportInfo(SummaryImportInfo::ImportType::Definition)));
+      auto [Iter, Inserted] = ImportList[ExportModulePath].insert(
+          std::make_pair(VI.getGUID(), GlobalValueSummary::Definition));
       // We previously decided to import this GUID definition if it was already
       // inserted in the set of imports from the exporting module.
       if (Inserted) {
@@ -837,14 +834,13 @@ static void computeImportForFunction(
         if (IsCriticalCallsite)
           NumImportedCriticalFunctionsThinLink++;
       } else
-        Iter->second.updateType(SummaryImportInfo::ImportType::Definition);
+        Iter->second = GlobalValueSummary::Definition;
 
       // Any calls/references made by this function will be marked exported
       // later, in ComputeCrossModuleImport, after import decisions are
       // complete, which is more efficient than adding them here.
       if (ExportLists)
-        (*ExportLists)[ExportModulePath][VI].updateType(
-            SummaryImportInfo::ImportType::Definition);
+        (*ExportLists)[ExportModulePath][VI] = GlobalValueSummary::Definition;
     }
 
     auto GetAdjustedThreshold = [](unsigned Threshold, bool IsHotCallsite) {
@@ -955,7 +951,8 @@ static unsigned numGlobalVarSummaries(const ModuleSummaryIndex &Index,
                                       T &Cont) {
   unsigned NumGVS = 0;
   for (auto &[GUID, Type] : Cont) {
-    assert(Type.isDefinition() && "Declaration type doesn't exist yet");
+    assert(Type == GlobalValueSummary::Definition &&
+           "Declaration type doesn't exist yet");
     if (isGlobalVarSummary(Index, GUID))
       ++NumGVS;
   }
@@ -1030,7 +1027,8 @@ void llvm::ComputeCrossModuleImport(
     const auto &DefinedGVSummaries =
         ModuleToDefinedGVSummaries.lookup(ELI.first);
     for (auto &[EI, Type] : ELI.second) {
-      assert(Type.isDefinition() && "Declaration type doesn't exist yet");
+      assert(Type == GlobalValueSummary::Definition &&
+             "Declaration type doesn't exist yet");
       // Find the copy defined in the exporting module so that we can mark the
       // values it references in that specific definition as exported.
       // Below we will add all references and called values, without regard to
@@ -1049,17 +1047,15 @@ void llvm::ComputeCrossModuleImport(
         // we convert such variables initializers to "zeroinitializer".
         // See processGlobalForThinLTO.
         if (!Index.isWriteOnly(GVS))
-          for (const auto &VI : GVS->refs())
-            NewExports[VI].updateType(
-                SummaryImportInfo::ImportType::Declaration);
+          for (const auto &VI : GVS->refs()) {
+            NewExports.try_emplace(VI, GlobalValueSummary::Declaration);
+          }
       } else {
         auto *FS = cast<FunctionSummary>(S);
         for (const auto &Edge : FS->calls())
-          NewExports[Edge.first].updateType(
-              SummaryImportInfo::ImportType::Declaration);
+          NewExports.try_emplace(Edge.first, GlobalValueSummary::Declaration);
         for (const auto &Ref : FS->refs())
-          NewExports[Ref].updateType(
-              SummaryImportInfo::ImportType::Declaration);
+          NewExports.try_emplace(Ref, GlobalValueSummary::Declaration);
       }
     }
     // Prune list computed above to only include values defined in the exporting
@@ -1167,10 +1163,10 @@ static void ComputeCrossModuleImportForModuleFromIndexForTest(
     if (Summary->modulePath() == ModulePath)
       continue;
     // Add an entry to provoke importing by thinBackend.
-    ImportList[Summary->modulePath()][GUID].updateType(
-        Summary->flags().ImportAsDec
-            ? SummaryImportInfo::ImportType::Declaration
-            : SummaryImportInfo::ImportType::Definition);
+    auto [Iter, Inserted] = ImportList[Summary->modulePath()].try_emplace(
+        GUID, Summary->importType());
+    if (!Inserted)
+      Iter->second = std::min(Iter->second, Summary->importType());
   }
 #ifndef NDEBUG
   dumpImportListForModule(Index, ModulePath, ImportList);
@@ -1370,7 +1366,7 @@ void llvm::gatherImportedSummariesForModule(
       assert(DS != DefinedGVSummaries.end() &&
              "Expected a defined summary for imported global value");
       SummariesForIndex[GUID] = DS->second;
-      if (Type.isDeclaration())
+      if (Type == GlobalValueSummary::Declaration)
         DecSummaries.insert(DS->second);
     }
   }
@@ -1644,13 +1640,13 @@ Expected<bool> FunctionImporter::importFunctions(
     ModuleNameOrderedList.insert(FunctionsToImportPerModule.first);
   }
 
-  auto getImportStatus = [&](const FunctionsToImportTy &GUIDToImportType,
-                             GlobalValue::GUID GUID) -> ImportStatus {
+  auto maybeGetImportType = [&](const FunctionsToImportTy &GUIDToImportType,
+                                GlobalValue::GUID GUID)
+      -> std::optional<GlobalValueSummary::ImportKind> {
     auto Iter = GUIDToImportType.find(GUID);
     if (Iter == GUIDToImportType.end())
-      return ImportStatus::NotImported;
-    return Iter->second.isDefinition() ? ImportStatus::ImportDefinition
-                                       : ImportStatus::ImportDeclaration;
+      return std::nullopt;
+    return Iter->second;
   };
 
   for (const auto &Name : ModuleNameOrderedList) {
@@ -1673,14 +1669,15 @@ Expected<bool> FunctionImporter::importFunctions(
 
     // Find the globals to import
     SetVector<GlobalValue *> GlobalsToImport;
-    SetVector<GlobalValue *> GlobalDeclsToImport;
     for (Function &F : *SrcModule) {
       if (!F.hasName())
         continue;
       auto GUID = F.getGUID();
-      auto ImportStatus = getImportStatus(ImportGUIDs, GUID);
+      auto ImportType = maybeGetImportType(ImportGUIDs, GUID);
+      if (!ImportType)
+        continue;
       const bool ImportDefinition =
-          ImportStatus == ImportStatus::ImportDefinition;
+          *ImportType == GlobalValueSummary::Definition;
       LLVM_DEBUG(dbgs() << (ImportDefinition ? "Is" : "Not")
                         << " importing function " << GUID << " " << F.getName()
                         << " from " << SrcModule->getSourceFileName() << "\n");
@@ -1704,16 +1701,17 @@ Expected<bool> FunctionImporter::importFunctions(
                                          SrcModule->getSourceFileName())}));
         }
         GlobalsToImport.insert(&F);
-      } else if (ImportStatus == ImportDeclaration)
-        GlobalDeclsToImport.insert(&F);
+      }
     }
     for (GlobalVariable &GV : SrcModule->globals()) {
       if (!GV.hasName())
         continue;
       auto GUID = GV.getGUID();
-      auto ImportStatus = getImportStatus(ImportGUIDs, GUID);
+      auto ImportType = maybeGetImportType(ImportGUIDs, GUID);
+      if (!ImportType)
+        continue;
       const bool ImportDefinition =
-          (ImportStatus == ImportStatus::ImportDefinition);
+          (*ImportType == GlobalValueSummary::Definition);
       LLVM_DEBUG(dbgs() << (ImportDefinition ? "Is" : "Not")
                         << " importing global " << GUID << " " << GV.getName()
                         << " from " << SrcModule->getSourceFileName() << "\n");
@@ -1727,9 +1725,12 @@ Expected<bool> FunctionImporter::importFunctions(
       if (!GA.hasName() || isa<GlobalIFunc>(GA.getAliaseeObject()))
         continue;
       auto GUID = GA.getGUID();
-      auto ImportStatus = getImportStatus(ImportGUIDs, GUID);
+      auto ImportType = maybeGetImportType(ImportGUIDs, GUID);
+      if (!ImportType)
+        continue;
+
       const bool ImportDefinition =
-          (ImportStatus == ImportStatus::ImportDefinition);
+          (*ImportType == GlobalValueSummary::Definition);
       LLVM_DEBUG(dbgs() << (ImportDefinition ? "Is" : "Not")
                         << " importing alias " << GUID << " " << GA.getName()
                         << " from " << SrcModule->getSourceFileName() << "\n");
@@ -1783,7 +1784,6 @@ Expected<bool> FunctionImporter::importFunctions(
                << " from " << SrcModule->getSourceFileName() << "\n";
     }
 
-    // FIXME: A later change will pass on GlobalDeclsToImport to IRMover.
     if (Error Err = Mover.move(std::move(SrcModule),
                                GlobalsToImport.getArrayRef(), nullptr,
                                /*IsPerformingImport=*/true))
diff --git a/llvm/tools/llvm-link/llvm-link.cpp b/llvm/tools/llvm-link/llvm-link.cpp
index 9e28b3a217f8b..a6bee02b1302d 100644
--- a/llvm/tools/llvm-link/llvm-link.cpp
+++ b/llvm/tools/llvm-link/llvm-link.cpp
@@ -377,7 +377,7 @@ static bool importFunctions(const char *argv0, Module &DestModule) {
 
     auto &Entry =
         ImportList[FileNameStringCache.insert(FileName).first->getKey()];
-    Entry[F->getGUID()].updateType(SummaryImportInfo::ImportType::Definition);
+    Entry[F->getGUID()] = GlobalValueSummary::Definition;
   }
   auto CachedModuleLoader = [&](StringRef Identifier) {
     return ModuleLoaderCache.takeModule(std::string(Identifier));

>From a0277b43faf515c3aa21b290c09e51501fa796ac Mon Sep 17 00:00:00 2001
From: mingmingl <mingmingl at google.com>
Date: Tue, 16 Apr 2024 23:44:18 -0700
Subject: [PATCH 03/10] Flag gate the import-declaration change.

---
 .../llvm/Transforms/IPO/FunctionImport.h      |  3 +-
 llvm/lib/Transforms/IPO/FunctionImport.cpp    | 55 +++++++++++++++++--
 2 files changed, 51 insertions(+), 7 deletions(-)

diff --git a/llvm/include/llvm/Transforms/IPO/FunctionImport.h b/llvm/include/llvm/Transforms/IPO/FunctionImport.h
index 6729fcc420a6e..fcf51ed5a4edd 100644
--- a/llvm/include/llvm/Transforms/IPO/FunctionImport.h
+++ b/llvm/include/llvm/Transforms/IPO/FunctionImport.h
@@ -31,8 +31,7 @@ class Module;
 /// based on the provided summary informations.
 class FunctionImporter {
 public:
-  /// Set of functions to import from a source module. Each entry is a set
-  /// containing all the GUIDs of all functions to import for a source module.
+  /// The functions to import from a source module and their import type.
   using FunctionsToImportTy =
       DenseMap<GlobalValue::GUID, GlobalValueSummary::ImportKind>;
 
diff --git a/llvm/lib/Transforms/IPO/FunctionImport.cpp b/llvm/lib/Transforms/IPO/FunctionImport.cpp
index 1485259e642a0..eb0bf36ab26d1 100644
--- a/llvm/lib/Transforms/IPO/FunctionImport.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionImport.cpp
@@ -140,6 +140,16 @@ static cl::opt<bool>
     ImportAllIndex("import-all-index",
                    cl::desc("Import all external functions in index."));
 
+/// Test-only option.
+/// TODO: Implement selective import (based on combined summary analysis) to
+/// ensure the imported function has a use case in the postlink pipeline.
+/// Import each function declaration as a fallback in real build may grow map
+/// size unnecessarily in the indexing step.
+static cl::opt<bool> ImportDeclaration(
+    "import-declaration", cl::init(false), cl::Hidden,
+    cl::desc("If true, import function declaration as fallback if the function "
+             "definition is not imported."));
+
 /// Pass a workload description file - an example of workload would be the
 /// functions executed to satisfy a RPC request. A workload is defined by a root
 /// function and the list of functions that are (frequently) needed to satisfy
@@ -245,8 +255,10 @@ static auto qualifyCalleeCandidates(
 }
 
 /// Given a list of possible callee implementation for a call site, select one
-/// that fits the \p Threshold. If none are found, the Reason will give the last
-/// reason for the failure (last, in the order of CalleeSummaryList entries).
+/// that fits the \p Threshold for function definition import. If none are
+/// found, the Reason will give the last reason for the failure (last, in the
+/// order of CalleeSummaryList entries). If caller wants to select eligible
+/// summary
 ///
 /// FIXME: select "best" instead of first that fits. But what is "best"?
 /// - The smallest: more likely to be inlined.
@@ -259,24 +271,32 @@ static const GlobalValueSummary *
 selectCallee(const ModuleSummaryIndex &Index,
              ArrayRef<std::unique_ptr<GlobalValueSummary>> CalleeSummaryList,
              unsigned Threshold, StringRef CallerModulePath,
+             const GlobalValueSummary *&TooLargeOrNoInlineSummary,
              FunctionImporter::ImportFailureReason &Reason) {
+  // Records the last summary with reason noinline or too-large.
+  TooLargeOrNoInlineSummary = nullptr;
   auto QualifiedCandidates =
       qualifyCalleeCandidates(Index, CalleeSummaryList, CallerModulePath);
   for (auto QualifiedValue : QualifiedCandidates) {
     Reason = QualifiedValue.first;
+    // Skip a summary if its import is not (proved to be) legal.
     if (Reason != FunctionImporter::ImportFailureReason::None)
       continue;
     auto *Summary =
         cast<FunctionSummary>(QualifiedValue.second->getBaseObject());
 
+    // Don't bother importing the definition if the chance of inlining it is
+    // not high enough (except under `--force-import-all`).
     if ((Summary->instCount() > Threshold) && !Summary->fflags().AlwaysInline &&
         !ForceImportAll) {
+      TooLargeOrNoInlineSummary = Summary;
       Reason = FunctionImporter::ImportFailureReason::TooLarge;
       continue;
     }
 
-    // Don't bother importing if we can't inline it anyway.
+    // Don't bother importing the definition if we can't inline it anyway.
     if (Summary->fflags().NoInline && !ForceImportAll) {
+      TooLargeOrNoInlineSummary = Summary;
       Reason = FunctionImporter::ImportFailureReason::NoInline;
       continue;
     }
@@ -359,12 +379,17 @@ class GlobalsImporter final {
             LocalNotInModule(GVS))
           continue;
 
+        // If there isn't an entry for GUID, insert <GUID, Definition> pair.
+        // Otherwise, definition should take precedence  over declaration.
         auto [Iter, Inserted] =
             ImportList[RefSummary->modulePath()].try_emplace(
                 VI.getGUID(), GlobalValueSummary::Definition);
         // Only update stat and exports if we haven't already imported this
         // variable.
         if (!Inserted) {
+          // FIXME: Introduce a wrapper struct around ImportType, and provide
+          // an `updateType` method for better readability, just like how we
+          // update the hotness of a call edge.
           Iter->second = std::min(GlobalValueSummary::Definition, Iter->second);
           break;
         }
@@ -776,9 +801,28 @@ static void computeImportForFunction(
       }
 
       FunctionImporter::ImportFailureReason Reason{};
-      CalleeSummary = selectCallee(Index, VI.getSummaryList(), NewThreshold,
-                                   Summary.modulePath(), Reason);
+
+      // `SummaryForDeclImport` is an summary eligible for declaration import.
+      const GlobalValueSummary *SummaryForDeclImport = nullptr;
+      CalleeSummary =
+          selectCallee(Index, VI.getSummaryList(), NewThreshold,
+                       Summary.modulePath(), SummaryForDeclImport, Reason);
       if (!CalleeSummary) {
+        // There isn't a callee for definition import but one for declaration
+        // import.
+        if (ImportDeclaration && SummaryForDeclImport) {
+          StringRef DeclSourceModule = SummaryForDeclImport->modulePath();
+
+          // Since definition takes precedence over declaration for the same VI,
+          // try emplace <VI, declaration> pair without checking insert result.
+          // If insert doesn't happen, there must be an existing entry keyed by
+          // VI.
+          if (ExportLists)
+            (*ExportLists)[DeclSourceModule].try_emplace(
+                VI, GlobalValueSummary::Declaration);
+          ImportList[DeclSourceModule].try_emplace(
+              VI.getGUID(), GlobalValueSummary::Declaration);
+        }
         // Update with new larger threshold if this was a retry (otherwise
         // we would have already inserted with NewThreshold above). Also
         // update failure info if requested.
@@ -798,6 +842,7 @@ static void computeImportForFunction(
           FailureInfo = std::make_unique<FunctionImporter::ImportFailureInfo>(
               VI, Edge.second.getHotness(), Reason, 1);
         }
+
         if (ForceImportAll) {
           std::string Msg = std::string("Failed to import function ") +
                             VI.name().str() + " due to " +

>From 5edecccb0fb4dc4d6da54b2533484c7c176314c6 Mon Sep 17 00:00:00 2001
From: mingmingl <mingmingl at google.com>
Date: Tue, 23 Apr 2024 09:16:57 -0700
Subject: [PATCH 04/10] stage changes

---
 llvm/lib/Transforms/IPO/FunctionImport.cpp | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/llvm/lib/Transforms/IPO/FunctionImport.cpp b/llvm/lib/Transforms/IPO/FunctionImport.cpp
index eb0bf36ab26d1..bc139e5a905bb 100644
--- a/llvm/lib/Transforms/IPO/FunctionImport.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionImport.cpp
@@ -996,8 +996,6 @@ static unsigned numGlobalVarSummaries(const ModuleSummaryIndex &Index,
                                       T &Cont) {
   unsigned NumGVS = 0;
   for (auto &[GUID, Type] : Cont) {
-    assert(Type == GlobalValueSummary::Definition &&
-           "Declaration type doesn't exist yet");
     if (isGlobalVarSummary(Index, GUID))
       ++NumGVS;
   }
@@ -1092,9 +1090,8 @@ void llvm::ComputeCrossModuleImport(
         // we convert such variables initializers to "zeroinitializer".
         // See processGlobalForThinLTO.
         if (!Index.isWriteOnly(GVS))
-          for (const auto &VI : GVS->refs()) {
+          for (const auto &VI : GVS->refs())
             NewExports.try_emplace(VI, GlobalValueSummary::Declaration);
-          }
       } else {
         auto *FS = cast<FunctionSummary>(S);
         for (const auto &Edge : FS->calls())

>From a139e4afc02c1e9f5dfae86f2f4a540cd97d8e87 Mon Sep 17 00:00:00 2001
From: mingmingl <mingmingl at google.com>
Date: Thu, 2 May 2024 16:15:19 -0700
Subject: [PATCH 05/10] Add test coverage for import delcaration

---
 llvm/lib/Transforms/IPO/FunctionImport.cpp    |  16 ++-
 .../ThinLTO/X86/import_callee_declaration.ll  | 111 ++++++++++++++++++
 llvm/tools/llvm-link/llvm-link.cpp            |   4 +
 3 files changed, 125 insertions(+), 6 deletions(-)
 create mode 100644 llvm/test/ThinLTO/X86/import_callee_declaration.ll

diff --git a/llvm/lib/Transforms/IPO/FunctionImport.cpp b/llvm/lib/Transforms/IPO/FunctionImport.cpp
index bc139e5a905bb..b13770ed49d83 100644
--- a/llvm/lib/Transforms/IPO/FunctionImport.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionImport.cpp
@@ -140,11 +140,12 @@ static cl::opt<bool>
     ImportAllIndex("import-all-index",
                    cl::desc("Import all external functions in index."));
 
-/// Test-only option.
+/// This is a test-only option.
+/// If this option is enabled, the ThinLTO indexing step will import each
+/// function declaration as a fallback. In a real build this may increase ram
+/// usage of the indexing step unnecessarily.
 /// TODO: Implement selective import (based on combined summary analysis) to
 /// ensure the imported function has a use case in the postlink pipeline.
-/// Import each function declaration as a fallback in real build may grow map
-/// size unnecessarily in the indexing step.
 static cl::opt<bool> ImportDeclaration(
     "import-declaration", cl::init(false), cl::Hidden,
     cl::desc("If true, import function declaration as fallback if the function "
@@ -1070,8 +1071,6 @@ void llvm::ComputeCrossModuleImport(
     const auto &DefinedGVSummaries =
         ModuleToDefinedGVSummaries.lookup(ELI.first);
     for (auto &[EI, Type] : ELI.second) {
-      assert(Type == GlobalValueSummary::Definition &&
-             "Declaration type doesn't exist yet");
       // Find the copy defined in the exporting module so that we can mark the
       // values it references in that specific definition as exported.
       // Below we will add all references and called values, without regard to
@@ -1716,8 +1715,13 @@ Expected<bool> FunctionImporter::importFunctions(
         continue;
       auto GUID = F.getGUID();
       auto ImportType = maybeGetImportType(ImportGUIDs, GUID);
-      if (!ImportType)
+
+      if (!ImportType) {
+        LLVM_DEBUG(dbgs() << "Not importing function " << GUID << " "
+                          << F.getName() << " from "
+                          << SrcModule->getSourceFileName() << "\n");
         continue;
+      }
       const bool ImportDefinition =
           *ImportType == GlobalValueSummary::Definition;
       LLVM_DEBUG(dbgs() << (ImportDefinition ? "Is" : "Not")
diff --git a/llvm/test/ThinLTO/X86/import_callee_declaration.ll b/llvm/test/ThinLTO/X86/import_callee_declaration.ll
new file mode 100644
index 0000000000000..344bde1a1a07d
--- /dev/null
+++ b/llvm/test/ThinLTO/X86/import_callee_declaration.ll
@@ -0,0 +1,111 @@
+; RUN: rm -rf %t && split-file %s %t && cd %t
+
+; Generate per-module summaries.
+; RUN: opt -module-summary main.ll -o main.bc
+; RUN: opt -module-summary lib.ll -o lib.bc
+
+; Generate the combined summary using per-module summaries.
+; For function import, set 'import-instr-limit' to 5 and fall back to import
+; function declarations.
+;
+; RUN: llvm-lto2 run \
+; RUN:   -import-instr-limit=5 \
+; RUN:   -import-declaration \
+; RUN:   -thinlto-distributed-indexes \
+; RUN:   -thinlto-emit-imports \
+; RUN:   -r=main.bc,main,px \
+; RUN:   -r=main.bc,small_func, \
+; RUN:   -r=main.bc,large_func, \
+; RUN:   -r=lib.bc,callee,px \
+; RUN:   -r=lib.bc,large_indirect_callee,px \
+; RUN:   -r=lib.bc,small_func,px \
+; RUN:   -r=lib.bc,large_func,px \
+; RUN:   -r=lib.bc,calleeAddrs,px -o summary main.bc lib.bc
+
+; main.ll should import {large_func, large_indirect_callee} as declarations.
+; 
+; First disassemble per-module summary and find out the GUID for {large_func, large_indirect_callee}.
+;
+; RUN: llvm-dis lib.bc -o - | FileCheck %s --check-prefix=LIB-DIS
+; LIB-DIS: [[LIBMOD:\^[0-9]+]] = module: (path: "lib.bc", hash: (0, 0, 0, 0, 0))
+; LIB-DIS: [[LARGEFUNC:\^[0-9]+]] = gv: (name: "large_func", summaries: {{.*}}) ; guid = 2418497564662708935
+; LIB-DIS: [[LARGEINDIRECT:\^[0-9]+]] = gv: (name: "large_indirect_callee", summaries: {{.*}}) ; guid = 14343440786664691134
+;
+; Secondly disassemble main's combined summary and verify the import type of
+; these two GUIDs are declaration.
+;
+; RUN: llvm-dis main.bc.thinlto.bc -o - | FileCheck %s --check-prefix=MAIN-DIS
+;
+; MAIN-DIS: [[LIBMOD:\^[0-9]+]] = module: (path: "lib.bc", hash: (0, 0, 0, 0, 0))
+; MAIN-DIS: [[LARGEFUNC:\^[0-9]+]] = gv: (guid: 2418497564662708935, summaries: (function: (module: [[LIBMOD]], flags: ({{.*}} importType: declaration), insts: 6, {{.*}})))
+; MAIN-DIS: [[LARGEINDIRECT:\^[0-9]+]] = gv: (guid: 14343440786664691134, summaries: (function: (module: [[LIBMOD]], flags: ({{.*}} importType: declaration), insts: 7, {{.*}})))
+
+; TODO: Add test coverage for function alias.
+
+;--- main.ll
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define i32 @main() {
+  call void @small_func()
+  call void @large_func()
+  ret i32 0
+}
+
+declare void @small_func()
+
+; large_func without attributes
+declare void @large_func()
+
+;--- lib.ll
+source_filename = "lib.cc"
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+ at calleeAddrs = global [2 x ptr] [ptr @large_indirect_callee, ptr @small_indirect_callee]
+
+define void @callee() #1 {
+  ret void
+}
+
+define void @large_indirect_callee()#2 {
+  call void @callee()
+  call void @callee()
+  call void @callee()
+  call void @callee()
+  call void @callee()
+  call void @callee()
+  ret void
+}
+
+define internal void @small_indirect_callee() #0 {
+  ret void
+}
+
+define void @small_func() {
+entry:
+  %0 = load ptr, ptr @calleeAddrs
+  call void %0(), !prof !0
+  %1 = load ptr, ptr getelementptr inbounds ([2 x ptr], ptr @calleeAddrs, i64 0, i64 1)
+  call void %1(), !prof !1
+  ret void
+}
+
+define void @large_func() #0 {
+entry:
+  call void @callee()
+  call void @callee()
+  call void @callee()
+  call void @callee()
+  call void @callee()
+  ret void
+}
+
+attributes #0 = { nounwind norecurse }
+
+attributes #1 = { noinline }
+
+attributes #2 = { norecurse }
+
+!0 = !{!"VP", i32 0, i64 1, i64 14343440786664691134, i64 1}
+!1 = !{!"VP", i32 0, i64 2, i64 13568239288960714650, i64 1}
diff --git a/llvm/tools/llvm-link/llvm-link.cpp b/llvm/tools/llvm-link/llvm-link.cpp
index a6bee02b1302d..3a20103135152 100644
--- a/llvm/tools/llvm-link/llvm-link.cpp
+++ b/llvm/tools/llvm-link/llvm-link.cpp
@@ -375,6 +375,10 @@ static bool importFunctions(const char *argv0, Module &DestModule) {
     if (Verbose)
       errs() << "Importing " << FunctionName << " from " << FileName << "\n";
 
+    // `-import` specifies the `<filename,function-name>` pairs to import as
+    // definition, so make the import type definition directly.
+    // FIXME: A follow-up patch should add test coverage for import declaration
+    // in `llvm-link` CLI (e.g., by introducing a new command line option).
     auto &Entry =
         ImportList[FileNameStringCache.insert(FileName).first->getKey()];
     Entry[F->getGUID()] = GlobalValueSummary::Definition;

>From 916dc96a66a1809ef2c6f5511e697489efbb505d Mon Sep 17 00:00:00 2001
From: mingmingl <mingmingl at google.com>
Date: Fri, 3 May 2024 14:30:10 -0700
Subject: [PATCH 06/10] add test coverage for function alias

---
 .../ThinLTO/X86/import_callee_declaration.ll  | 46 ++++++++++++++-----
 1 file changed, 35 insertions(+), 11 deletions(-)

diff --git a/llvm/test/ThinLTO/X86/import_callee_declaration.ll b/llvm/test/ThinLTO/X86/import_callee_declaration.ll
index 344bde1a1a07d..9854e42494535 100644
--- a/llvm/test/ThinLTO/X86/import_callee_declaration.ll
+++ b/llvm/test/ThinLTO/X86/import_callee_declaration.ll
@@ -4,15 +4,29 @@
 ; RUN: opt -module-summary main.ll -o main.bc
 ; RUN: opt -module-summary lib.ll -o lib.bc
 
-; Generate the combined summary using per-module summaries.
-; For function import, set 'import-instr-limit' to 5 and fall back to import
-; function declarations.
+; Generate the combined summary and distributed indices.
+
+; - For function import, set 'import-instr-limit' to 7 and fall back to import
+;   function declarations.
+; - In main.ll, function 'main' calls 'small_func' and 'large_func'. Both callees
+;   are defined in lib.ll. 'small_func' has two indirect callees, one is smaller
+;   and the other one is larger. Both callees of 'small_func' are defined in lib.ll.
+; - Given the import limit, in main's combined summary, the import type of 'small_func'
+;   and 'small_indirect_callee' will be 'definition', and the import type of
+;   'large_func' and 'large_indirect_callee' will be 'declaration'.
+;
+; The test will disassemble combined summaries and check the import type is
+; correct. Right now postlink optimizer pipeline doesn't do anything (e.g.,
+; import the declaration or de-serialize summary attributes yet) so there is
+; nothing to test more than the summary content.
+;
+; TODO: Extend this test case to test IR once postlink optimizer makes use of
+; the import type for declarations, and add test coverage for in-process thinlto.
 ;
 ; RUN: llvm-lto2 run \
-; RUN:   -import-instr-limit=5 \
+; RUN:   -import-instr-limit=7 \
 ; RUN:   -import-declaration \
 ; RUN:   -thinlto-distributed-indexes \
-; RUN:   -thinlto-emit-imports \
 ; RUN:   -r=main.bc,main,px \
 ; RUN:   -r=main.bc,small_func, \
 ; RUN:   -r=main.bc,large_func, \
@@ -20,6 +34,7 @@
 ; RUN:   -r=lib.bc,large_indirect_callee,px \
 ; RUN:   -r=lib.bc,small_func,px \
 ; RUN:   -r=lib.bc,large_func,px \
+; RUN:   -r=lib.bc,large_indirect_callee_alias,px \
 ; RUN:   -r=lib.bc,calleeAddrs,px -o summary main.bc lib.bc
 
 ; main.ll should import {large_func, large_indirect_callee} as declarations.
@@ -37,10 +52,11 @@
 ; RUN: llvm-dis main.bc.thinlto.bc -o - | FileCheck %s --check-prefix=MAIN-DIS
 ;
 ; MAIN-DIS: [[LIBMOD:\^[0-9]+]] = module: (path: "lib.bc", hash: (0, 0, 0, 0, 0))
-; MAIN-DIS: [[LARGEFUNC:\^[0-9]+]] = gv: (guid: 2418497564662708935, summaries: (function: (module: [[LIBMOD]], flags: ({{.*}} importType: declaration), insts: 6, {{.*}})))
-; MAIN-DIS: [[LARGEINDIRECT:\^[0-9]+]] = gv: (guid: 14343440786664691134, summaries: (function: (module: [[LIBMOD]], flags: ({{.*}} importType: declaration), insts: 7, {{.*}})))
+; MAIN-DIS: [[LARGEFUNC:\^[0-9]+]] = gv: (guid: 2418497564662708935, summaries: (function: (module: [[LIBMOD]], flags: ({{.*}} importType: declaration), insts: 8, {{.*}})))
+; MAIN-DIS: [[LARGEINDIRECT:\^[0-9]+]] = gv: (guid: 14343440786664691134, summaries: (function: (module: [[LIBMOD]], flags: ({{.*}} importType: declaration), insts: 8, {{.*}})))
+; MAIN-DIS: [[LARGEINDIRECTALIAS:\^[0-9]+]] = gv: (guid: 16730173943625350469, summaries: (alias: (module: [[LIBMOD]], flags: ({{.*}} importType: declaration), aliasee: [[LARGEINDIRECT]])))
 
-; TODO: Add test coverage for function alias.
+; TODO: add test coverage for llvm-lto.
 
 ;--- main.ll
 target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
@@ -62,7 +78,7 @@ source_filename = "lib.cc"
 target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
- at calleeAddrs = global [2 x ptr] [ptr @large_indirect_callee, ptr @small_indirect_callee]
+ at calleeAddrs = global [3 x ptr] [ptr @large_indirect_callee, ptr @small_indirect_callee, ptr @large_indirect_callee_alias]
 
 define void @callee() #1 {
   ret void
@@ -75,6 +91,7 @@ define void @large_indirect_callee()#2 {
   call void @callee()
   call void @callee()
   call void @callee()
+  call void @callee()
   ret void
 }
 
@@ -82,12 +99,16 @@ define internal void @small_indirect_callee() #0 {
   ret void
 }
 
+ at large_indirect_callee_alias = alias void(), ptr @large_indirect_callee
+
 define void @small_func() {
 entry:
   %0 = load ptr, ptr @calleeAddrs
   call void %0(), !prof !0
-  %1 = load ptr, ptr getelementptr inbounds ([2 x ptr], ptr @calleeAddrs, i64 0, i64 1)
+  %1 = load ptr, ptr getelementptr inbounds ([3 x ptr], ptr @calleeAddrs, i64 0, i64 1)
   call void %1(), !prof !1
+  %2 = load ptr, ptr getelementptr inbounds ([3 x ptr], ptr @calleeAddrs, i64 0, i64 2)
+  call void %2(), !prof !2
   ret void
 }
 
@@ -98,6 +119,8 @@ entry:
   call void @callee()
   call void @callee()
   call void @callee()
+  call void @callee()
+  call void @callee()
   ret void
 }
 
@@ -108,4 +131,5 @@ attributes #1 = { noinline }
 attributes #2 = { norecurse }
 
 !0 = !{!"VP", i32 0, i64 1, i64 14343440786664691134, i64 1}
-!1 = !{!"VP", i32 0, i64 2, i64 13568239288960714650, i64 1}
+!1 = !{!"VP", i32 0, i64 1, i64 13568239288960714650, i64 1}
+!2 = !{!"VP", i32 0, i64 1, i64 16730173943625350469, i64 1}

>From 248fbfb3de943ef056bf2ca430d4b4d485a60691 Mon Sep 17 00:00:00 2001
From: mingmingl <mingmingl at google.com>
Date: Sun, 5 May 2024 11:39:11 -0700
Subject: [PATCH 07/10] llvm-lto test coverage

---
 llvm/include/llvm/LTO/legacy/ThinLTOCodeGenerator.h |  3 ++-
 llvm/include/llvm/Transforms/IPO/FunctionImport.h   | 12 +++++++++---
 llvm/lib/LTO/LTO.cpp                                | 12 ++++++------
 llvm/lib/LTO/LTOBackend.cpp                         |  4 +++-
 llvm/lib/LTO/ThinLTOCodeGenerator.cpp               |  3 +--
 llvm/test/ThinLTO/X86/import_callee_declaration.ll  |  6 +++++-
 llvm/tools/llvm-lto/llvm-lto.cpp                    |  7 +++++--
 7 files changed, 31 insertions(+), 16 deletions(-)

diff --git a/llvm/include/llvm/LTO/legacy/ThinLTOCodeGenerator.h b/llvm/include/llvm/LTO/legacy/ThinLTOCodeGenerator.h
index c450acda82ad0..6e197ae2f279c 100644
--- a/llvm/include/llvm/LTO/legacy/ThinLTOCodeGenerator.h
+++ b/llvm/include/llvm/LTO/legacy/ThinLTOCodeGenerator.h
@@ -276,7 +276,8 @@ class ThinLTOCodeGenerator {
   void gatherImportedSummariesForModule(
       Module &Module, ModuleSummaryIndex &Index,
       std::map<std::string, GVSummaryMapTy> &ModuleToSummariesForIndex,
-      const lto::InputFile &File);
+      const lto::InputFile &File,
+      ModuleToGVSummaryPtrSet &ModuleToDecSummaries);
 
   /**
    * Perform internalization. Index is updated to reflect linkage changes.
diff --git a/llvm/include/llvm/Transforms/IPO/FunctionImport.h b/llvm/include/llvm/Transforms/IPO/FunctionImport.h
index fcf51ed5a4edd..fb38c68b56df0 100644
--- a/llvm/include/llvm/Transforms/IPO/FunctionImport.h
+++ b/llvm/include/llvm/Transforms/IPO/FunctionImport.h
@@ -99,9 +99,11 @@ class FunctionImporter {
   /// index's module path string table).
   using ImportMapTy = DenseMap<StringRef, FunctionsToImportTy>;
 
-  /// The map contains an entry for every global value the module exports, the
-  /// key being the value info, and the value indicates whether the definition
-  /// or declaration is visible to another module.
+  /// The map contains an entry for every global value the module exports.
+  /// The key is ValueInfo, and the value indicates whether the definition
+  /// or declaration is visible to another module. If a function's definition is
+  /// visible to other modules, the global values this function referenced are
+  /// visible and shouldn't be internalized.
   using ExportSetTy = DenseMap<ValueInfo, GlobalValueSummary::ImportKind>;
 
   /// A function of this type is used to load modules referenced by the index.
@@ -209,6 +211,10 @@ bool convertToDeclaration(GlobalValue &GV);
 /// \p ModuleToSummariesForIndex will be populated with the needed summaries
 /// from each required module path. Use a std::map instead of StringMap to get
 /// stable order for bitcode emission.
+///
+/// \p ModuleToDecSummaries will be populated with the set of declarations \p
+/// ModulePath need from other modules. They key is module path, and the value
+/// is a set of summary pointers.
 void gatherImportedSummariesForModule(
     StringRef ModulePath,
     const DenseMap<StringRef, GVSummaryMapTy> &ModuleToDefinedGVSummaries,
diff --git a/llvm/lib/LTO/LTO.cpp b/llvm/lib/LTO/LTO.cpp
index ace533fe28c92..e2a765d0d52fa 100644
--- a/llvm/lib/LTO/LTO.cpp
+++ b/llvm/lib/LTO/LTO.cpp
@@ -158,8 +158,8 @@ void llvm::computeLTOCacheKey(
 
   std::vector<uint64_t> ExportsGUID;
   ExportsGUID.reserve(ExportList.size());
-  for (const auto &VI : ExportList) {
-    auto GUID = VI.first.getGUID();
+  for (const auto &[VI, UnusedImportType] : ExportList) {
+    auto GUID = VI.getGUID();
     ExportsGUID.push_back(GUID);
   }
 
@@ -204,8 +204,8 @@ void llvm::computeLTOCacheKey(
     Hasher.update(ArrayRef<uint8_t>((uint8_t *)&ModHash[0], sizeof(ModHash)));
 
     AddUint64(Entry.getFunctions().size());
-    for (auto &Fn : Entry.getFunctions())
-      AddUint64(Fn.first);
+    for (auto &[GUID, UnusedImportType] : Entry.getFunctions())
+      AddUint64(GUID);
   }
 
   // Include the hash for the resolved ODR.
@@ -275,9 +275,9 @@ void llvm::computeLTOCacheKey(
   // Imported functions may introduce new uses of type identifier resolutions,
   // so we need to collect their used resolutions as well.
   for (const ImportModule &ImpM : ImportModulesVector)
-    for (auto &ImpF : ImpM.getFunctions()) {
+    for (auto &[GUID, UnusedImportType] : ImpM.getFunctions()) {
       GlobalValueSummary *S =
-          Index.findSummaryInModule(ImpF.first, ImpM.getIdentifier());
+          Index.findSummaryInModule(GUID, ImpM.getIdentifier());
       AddUsedThings(S);
       // If this is an alias, we also care about any types/etc. that the aliasee
       // may reference.
diff --git a/llvm/lib/LTO/LTOBackend.cpp b/llvm/lib/LTO/LTOBackend.cpp
index 23d75c238fc29..a2cd672e0f0a1 100644
--- a/llvm/lib/LTO/LTOBackend.cpp
+++ b/llvm/lib/LTO/LTOBackend.cpp
@@ -715,8 +715,10 @@ bool lto::initImportList(const Module &M,
       // e.g. record required linkage changes.
       if (Summary->modulePath() == M.getModuleIdentifier())
         continue;
-
       // Add an entry to provoke importing by thinBackend.
+      // Try emplace the entry first. If an entry with the same key already
+      // exists, set the value to 'std::min(existing-value, new-value)' to make
+      // sure a definition takes precedence over a declaration.
       auto [Iter, Inserted] = ImportList[Summary->modulePath()].try_emplace(
           GUID, Summary->importType());
 
diff --git a/llvm/lib/LTO/ThinLTOCodeGenerator.cpp b/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
index 75aecc95e789f..0e6660133cce0 100644
--- a/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
+++ b/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
@@ -766,7 +766,7 @@ void ThinLTOCodeGenerator::crossModuleImport(Module &TheModule,
 void ThinLTOCodeGenerator::gatherImportedSummariesForModule(
     Module &TheModule, ModuleSummaryIndex &Index,
     std::map<std::string, GVSummaryMapTy> &ModuleToSummariesForIndex,
-    const lto::InputFile &File) {
+    const lto::InputFile &File, ModuleToGVSummaryPtrSet &ModuleToDecSummaries) {
   auto ModuleCount = Index.modulePaths().size();
   auto ModuleIdentifier = TheModule.getModuleIdentifier();
 
@@ -794,7 +794,6 @@ void ThinLTOCodeGenerator::gatherImportedSummariesForModule(
                            IsPrevailing(PrevailingCopy), ImportLists,
                            ExportLists);
 
-  ModuleToGVSummaryPtrSet ModuleToDecSummaries;
   llvm::gatherImportedSummariesForModule(
       ModuleIdentifier, ModuleToDefinedGVSummaries,
       ImportLists[ModuleIdentifier], ModuleToSummariesForIndex,
diff --git a/llvm/test/ThinLTO/X86/import_callee_declaration.ll b/llvm/test/ThinLTO/X86/import_callee_declaration.ll
index 9854e42494535..cdfaa67729619 100644
--- a/llvm/test/ThinLTO/X86/import_callee_declaration.ll
+++ b/llvm/test/ThinLTO/X86/import_callee_declaration.ll
@@ -56,7 +56,11 @@
 ; MAIN-DIS: [[LARGEINDIRECT:\^[0-9]+]] = gv: (guid: 14343440786664691134, summaries: (function: (module: [[LIBMOD]], flags: ({{.*}} importType: declaration), insts: 8, {{.*}})))
 ; MAIN-DIS: [[LARGEINDIRECTALIAS:\^[0-9]+]] = gv: (guid: 16730173943625350469, summaries: (alias: (module: [[LIBMOD]], flags: ({{.*}} importType: declaration), aliasee: [[LARGEINDIRECT]])))
 
-; TODO: add test coverage for llvm-lto.
+; TODO: add test coverage for lto indexing stats.
+
+; RUN: llvm-lto -thinlto-action=thinlink -import-declaration -import-instr-limit=7  -o combined.index.bc main.bc lib.bc
+; RUN: llvm-lto -thinlto-action=distributedindexes -import-declaration -import-instr-limit=7 -thinlto-index combined.index.bc main.bc lib.bc
+; RUN: llvm-dis main.bc.thinlto.bc -o - | FileCheck %s --check-prefix=MAIN-DIS
 
 ;--- main.ll
 target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
diff --git a/llvm/tools/llvm-lto/llvm-lto.cpp b/llvm/tools/llvm-lto/llvm-lto.cpp
index f310097eec634..ce32799150313 100644
--- a/llvm/tools/llvm-lto/llvm-lto.cpp
+++ b/llvm/tools/llvm-lto/llvm-lto.cpp
@@ -692,8 +692,10 @@ class ThinLTOProcessing {
       // Build a map of module to the GUIDs and summary objects that should
       // be written to its index.
       std::map<std::string, GVSummaryMapTy> ModuleToSummariesForIndex;
+      ModuleToGVSummaryPtrSet ModuleToDecSummaries;
       ThinGenerator.gatherImportedSummariesForModule(
-          *TheModule, *Index, ModuleToSummariesForIndex, *Input);
+          *TheModule, *Index, ModuleToSummariesForIndex, *Input,
+          ModuleToDecSummaries);
 
       std::string OutputName = OutputFilename;
       if (OutputName.empty()) {
@@ -703,7 +705,8 @@ class ThinLTOProcessing {
       std::error_code EC;
       raw_fd_ostream OS(OutputName, EC, sys::fs::OpenFlags::OF_None);
       error(EC, "error opening the file '" + OutputName + "'");
-      writeIndexToFile(*Index, OS, &ModuleToSummariesForIndex);
+      writeIndexToFile(*Index, OS, &ModuleToSummariesForIndex,
+                       &ModuleToDecSummaries);
     }
   }
 

>From 5e731ec0b4285f1a0ebbf9cc57cee75f13258c42 Mon Sep 17 00:00:00 2001
From: mingmingl <mingmingl at google.com>
Date: Mon, 6 May 2024 15:51:44 -0700
Subject: [PATCH 08/10] add test coverage for debugging log, and a RUN line for
 internalization

---
 llvm/lib/LTO/LTO.cpp                          |   1 +
 llvm/lib/LTO/ThinLTOCodeGenerator.cpp         |   5 +-
 llvm/lib/Transforms/IPO/FunctionImport.cpp    | 109 +++++++++++++-----
 llvm/test/ThinLTO/X86/funcimport-stats.ll     |   4 +-
 .../ThinLTO/X86/import_callee_declaration.ll  |  38 +++++-
 .../Transforms/FunctionImport/funcimport.ll   |   8 +-
 6 files changed, 122 insertions(+), 43 deletions(-)

diff --git a/llvm/lib/LTO/LTO.cpp b/llvm/lib/LTO/LTO.cpp
index e2a765d0d52fa..e7e5a6ab39277 100644
--- a/llvm/lib/LTO/LTO.cpp
+++ b/llvm/lib/LTO/LTO.cpp
@@ -1399,6 +1399,7 @@ class lto::ThinBackendProc {
                       sys::fs::OpenFlags::OF_None);
     if (EC)
       return errorCodeToError(EC);
+
     writeIndexToFile(CombinedIndex, OS, &ModuleToSummariesForIndex,
                      &ModuleToDeclarationSummaries);
 
diff --git a/llvm/lib/LTO/ThinLTOCodeGenerator.cpp b/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
index 0e6660133cce0..1227f26cc4280 100644
--- a/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
+++ b/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
@@ -834,7 +834,10 @@ void ThinLTOCodeGenerator::emitImports(Module &TheModule, StringRef OutputName,
                            ExportLists);
 
   std::map<std::string, GVSummaryMapTy> ModuleToSummariesForIndex;
-  // FIXME: Pass on `ModuleToDecSummaries` to `EmitImportFiles` below.
+  // 'EmitImportsFiles' emits the list of modules from which to import from, and
+  // the set of keys in `ModuleToSummariesForIndex` should be a superset of keys
+  // in `ModuleToDecSummaries`, so no need to use `ModuleToDecSummaries` in
+  // `EmitImportFiles`.
   ModuleToGVSummaryPtrSet ModuleToDecSummaries;
   llvm::gatherImportedSummariesForModule(
       ModuleIdentifier, ModuleToDefinedGVSummaries,
diff --git a/llvm/lib/Transforms/IPO/FunctionImport.cpp b/llvm/lib/Transforms/IPO/FunctionImport.cpp
index b13770ed49d83..77d644dc97ab7 100644
--- a/llvm/lib/Transforms/IPO/FunctionImport.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionImport.cpp
@@ -381,7 +381,7 @@ class GlobalsImporter final {
           continue;
 
         // If there isn't an entry for GUID, insert <GUID, Definition> pair.
-        // Otherwise, definition should take precedence  over declaration.
+        // Otherwise, definition should take precedence over declaration.
         auto [Iter, Inserted] =
             ImportList[RefSummary->modulePath()].try_emplace(
                 VI.getGUID(), GlobalValueSummary::Definition);
@@ -869,17 +869,23 @@ static void computeImportForFunction(
              "selectCallee() didn't honor the threshold");
 
       auto ExportModulePath = ResolvedCalleeSummary->modulePath();
-      auto [Iter, Inserted] = ImportList[ExportModulePath].insert(
-          std::make_pair(VI.getGUID(), GlobalValueSummary::Definition));
+
+      // Try emplace the definition entry, and update stats based on insertion
+      // status.
+      auto [Iter, Inserted] = ImportList[ExportModulePath].try_emplace(
+          VI.getGUID(), GlobalValueSummary::Definition);
+
       // We previously decided to import this GUID definition if it was already
       // inserted in the set of imports from the exporting module.
-      if (Inserted) {
+      if (Inserted || Iter->second == GlobalValueSummary::Declaration) {
         NumImportedFunctionsThinLink++;
         if (IsHotCallsite)
           NumImportedHotFunctionsThinLink++;
         if (IsCriticalCallsite)
           NumImportedCriticalFunctionsThinLink++;
-      } else
+      }
+
+      if (Iter->second == GlobalValueSummary::Declaration)
         Iter->second = GlobalValueSummary::Definition;
 
       // Any calls/references made by this function will be marked exported
@@ -993,12 +999,19 @@ static bool isGlobalVarSummary(const ModuleSummaryIndex &Index,
 }
 
 template <class T>
-static unsigned numGlobalVarSummaries(const ModuleSummaryIndex &Index,
-                                      T &Cont) {
+static unsigned numGlobalVarSummaries(const ModuleSummaryIndex &Index, T &Cont,
+                                      unsigned &DefinedGVS,
+                                      unsigned &DefinedFS) {
   unsigned NumGVS = 0;
+  DefinedGVS = 0;
+  DefinedFS = 0;
   for (auto &[GUID, Type] : Cont) {
-    if (isGlobalVarSummary(Index, GUID))
+    if (isGlobalVarSummary(Index, GUID)) {
+      if (Type == GlobalValueSummary::Definition)
+        ++DefinedGVS;
       ++NumGVS;
+    } else if (Type == GlobalValueSummary::Definition)
+      ++DefinedFS;
   }
   return NumGVS;
 }
@@ -1009,7 +1022,6 @@ static bool checkVariableImport(
     const ModuleSummaryIndex &Index,
     DenseMap<StringRef, FunctionImporter::ImportMapTy> &ImportLists,
     DenseMap<StringRef, FunctionImporter::ExportSetTy> &ExportLists) {
-
   DenseSet<GlobalValue::GUID> FlattenedImports;
 
   for (auto &ImportPerModule : ImportLists)
@@ -1071,6 +1083,10 @@ void llvm::ComputeCrossModuleImport(
     const auto &DefinedGVSummaries =
         ModuleToDefinedGVSummaries.lookup(ELI.first);
     for (auto &[EI, Type] : ELI.second) {
+      // If a variable is exported as a declaration, its 'refs' and 'calls' are
+      // not further exported.
+      if (Type == GlobalValueSummary::Declaration)
+        continue;
       // Find the copy defined in the exporting module so that we can mark the
       // values it references in that specific definition as exported.
       // Below we will add all references and called values, without regard to
@@ -1089,20 +1105,29 @@ void llvm::ComputeCrossModuleImport(
         // we convert such variables initializers to "zeroinitializer".
         // See processGlobalForThinLTO.
         if (!Index.isWriteOnly(GVS))
-          for (const auto &VI : GVS->refs())
+          for (const auto &VI : GVS->refs()) {
+            // Try to emplace the declaration entry. If a definition entry
+            // already exists for key `VI`, this is a no-op.
             NewExports.try_emplace(VI, GlobalValueSummary::Declaration);
+          }
       } else {
         auto *FS = cast<FunctionSummary>(S);
-        for (const auto &Edge : FS->calls())
+        for (const auto &Edge : FS->calls()) {
+          // Try to emplace the declaration entry. If a definition entry
+          // already exists for key `VI`, this is a no-op.
           NewExports.try_emplace(Edge.first, GlobalValueSummary::Declaration);
-        for (const auto &Ref : FS->refs())
+        }
+        for (const auto &Ref : FS->refs()) {
+          // Try to emplace the declaration entry. If a definition entry
+          // already exists for key `VI`, this is a no-op.
           NewExports.try_emplace(Ref, GlobalValueSummary::Declaration);
+        }
       }
     }
-    // Prune list computed above to only include values defined in the exporting
-    // module. We do this after the above insertion since we may hit the same
-    // ref/call target multiple times in above loop, and it is more efficient to
-    // avoid a set lookup each time.
+    //  Prune list computed above to only include values defined in the
+    //  exporting module. We do this after the above insertion since we may hit
+    //  the same ref/call target multiple times in above loop, and it is more
+    //  efficient to avoid a set lookup each time.
     for (auto EI = NewExports.begin(); EI != NewExports.end();) {
       if (!DefinedGVSummaries.count(EI->first.getGUID()))
         NewExports.erase(EI++);
@@ -1119,18 +1144,29 @@ void llvm::ComputeCrossModuleImport(
   for (auto &ModuleImports : ImportLists) {
     auto ModName = ModuleImports.first;
     auto &Exports = ExportLists[ModName];
-    unsigned NumGVS = numGlobalVarSummaries(Index, Exports);
-    LLVM_DEBUG(dbgs() << "* Module " << ModName << " exports "
-                      << Exports.size() - NumGVS << " functions and " << NumGVS
-                      << " vars. Imports from " << ModuleImports.second.size()
-                      << " modules.\n");
+    unsigned DefinedGVS = 0, DefinedFS = 0;
+    unsigned NumGVS =
+        numGlobalVarSummaries(Index, Exports, DefinedGVS, DefinedFS);
+    LLVM_DEBUG(dbgs() << "* Module " << ModName << " exports " << DefinedFS
+                      << " function as definitions, "
+                      << Exports.size() - NumGVS - DefinedFS
+                      << " functions as declarations, " << DefinedGVS
+                      << " var definitions and " << NumGVS - DefinedGVS
+                      << " var declarations. Imports from "
+                      << ModuleImports.second.size() << " modules.\n");
     for (auto &Src : ModuleImports.second) {
       auto SrcModName = Src.first;
-      unsigned NumGVSPerMod = numGlobalVarSummaries(Index, Src.second);
-      LLVM_DEBUG(dbgs() << " - " << Src.second.size() - NumGVSPerMod
-                        << " functions imported from " << SrcModName << "\n");
-      LLVM_DEBUG(dbgs() << " - " << NumGVSPerMod
-                        << " global vars imported from " << SrcModName << "\n");
+      unsigned DefinedGVS = 0, DefinedFS = 0;
+      unsigned NumGVSPerMod =
+          numGlobalVarSummaries(Index, Src.second, DefinedGVS, DefinedFS);
+      LLVM_DEBUG(dbgs() << " - " << DefinedFS << " function definitions and "
+                        << Src.second.size() - NumGVSPerMod - DefinedFS
+                        << " function declarations imported from " << SrcModName
+                        << "\n");
+      LLVM_DEBUG(dbgs() << " - " << DefinedGVS << " global vars definition and "
+                        << NumGVSPerMod - DefinedGVS
+                        << " global vars declaration imported from "
+                        << SrcModName << "\n");
     }
   }
 #endif
@@ -1144,11 +1180,17 @@ static void dumpImportListForModule(const ModuleSummaryIndex &Index,
                     << ImportList.size() << " modules.\n");
   for (auto &Src : ImportList) {
     auto SrcModName = Src.first;
-    unsigned NumGVSPerMod = numGlobalVarSummaries(Index, Src.second);
-    LLVM_DEBUG(dbgs() << " - " << Src.second.size() - NumGVSPerMod
-                      << " functions imported from " << SrcModName << "\n");
-    LLVM_DEBUG(dbgs() << " - " << NumGVSPerMod << " vars imported from "
-                      << SrcModName << "\n");
+    unsigned DefinedGVS = 0, DefinedFS = 0;
+    unsigned NumGVSPerMod =
+        numGlobalVarSummaries(Index, Src.second, DefinedGVS, DefinedFS);
+    LLVM_DEBUG(dbgs() << " - " << DefinedFS << " function definitions and "
+                      << Src.second.size() - DefinedFS - NumGVSPerMod
+                      << " function declarations imported from " << SrcModName
+                      << "\n");
+    LLVM_DEBUG(dbgs() << " - " << DefinedGVS << " var definitions and "
+                      << NumGVSPerMod - DefinedGVS
+                      << " var declarations imported from " << SrcModName
+                      << "\n");
   }
 }
 #endif
@@ -1206,8 +1248,11 @@ static void ComputeCrossModuleImportForModuleFromIndexForTest(
     // Add an entry to provoke importing by thinBackend.
     auto [Iter, Inserted] = ImportList[Summary->modulePath()].try_emplace(
         GUID, Summary->importType());
-    if (!Inserted)
+    if (!Inserted) {
+      // Use 'std::min' to make sure definition (with enum value 0) takes
+      // precedence over declaration (with enum value 1).
       Iter->second = std::min(Iter->second, Summary->importType());
+    }
   }
 #ifndef NDEBUG
   dumpImportListForModule(Index, ModulePath, ImportList);
diff --git a/llvm/test/ThinLTO/X86/funcimport-stats.ll b/llvm/test/ThinLTO/X86/funcimport-stats.ll
index 913b13004c1c2..7fcd33855fe1a 100644
--- a/llvm/test/ThinLTO/X86/funcimport-stats.ll
+++ b/llvm/test/ThinLTO/X86/funcimport-stats.ll
@@ -9,8 +9,8 @@
 ; RUN: cat %t4 | grep 'Is importing aliasee' | count 1
 ; RUN: cat %t4 | FileCheck %s
 
-; CHECK:      - [[NUM_FUNCS:[0-9]+]] functions imported from
-; CHECK-NEXT: - [[NUM_VARS:[0-9]+]] global vars imported from
+; CHECK:      - [[NUM_FUNCS:[0-9]+]] function definitions and 0 function declarations imported from
+; CHECK-NEXT: - [[NUM_VARS:[0-9]+]] global vars definition and 0 global vars declaration imported from
 
 ; CHECK:      [[NUM_FUNCS]] function-import - Number of functions imported in backend
 ; CHECK-NEXT: [[NUM_FUNCS]] function-import - Number of functions thin link decided to import
diff --git a/llvm/test/ThinLTO/X86/import_callee_declaration.ll b/llvm/test/ThinLTO/X86/import_callee_declaration.ll
index cdfaa67729619..12286e5eb7a2f 100644
--- a/llvm/test/ThinLTO/X86/import_callee_declaration.ll
+++ b/llvm/test/ThinLTO/X86/import_callee_declaration.ll
@@ -1,3 +1,5 @@
+; "-debug-only" requires asserts.
+; REQUIRES: asserts
 ; RUN: rm -rf %t && split-file %s %t && cd %t
 
 ; Generate per-module summaries.
@@ -24,18 +26,25 @@
 ; the import type for declarations, and add test coverage for in-process thinlto.
 ;
 ; RUN: llvm-lto2 run \
+; RUN:   -debug-only=function-import \
 ; RUN:   -import-instr-limit=7 \
 ; RUN:   -import-declaration \
 ; RUN:   -thinlto-distributed-indexes \
 ; RUN:   -r=main.bc,main,px \
 ; RUN:   -r=main.bc,small_func, \
 ; RUN:   -r=main.bc,large_func, \
-; RUN:   -r=lib.bc,callee,px \
+; RUN:   -r=lib.bc,callee,pl \
 ; RUN:   -r=lib.bc,large_indirect_callee,px \
 ; RUN:   -r=lib.bc,small_func,px \
 ; RUN:   -r=lib.bc,large_func,px \
 ; RUN:   -r=lib.bc,large_indirect_callee_alias,px \
-; RUN:   -r=lib.bc,calleeAddrs,px -o summary main.bc lib.bc
+; RUN:   -r=lib.bc,calleeAddrs,px -o summary main.bc lib.bc 2>&1 | FileCheck %s --check-prefix=DUMP
+;
+; RUN: llvm-lto -thinlto-action=thinlink -import-declaration -import-instr-limit=7  -o combined.index.bc main.bc lib.bc
+; RUN: llvm-lto -thinlto-action=distributedindexes -debug-only=function-import -import-declaration -import-instr-limit=7 -thinlto-index combined.index.bc main.bc lib.bc 2>&1 | FileCheck %s --check-prefix=DUMP
+; RUN: llvm-dis main.bc.thinlto.bc -o - | FileCheck %s --check-prefix=MAIN-DIS
+
+; DUMP: - 2 function definitions and 3 function declarations imported from lib.bc
 
 ; main.ll should import {large_func, large_indirect_callee} as declarations.
 ; 
@@ -56,11 +65,28 @@
 ; MAIN-DIS: [[LARGEINDIRECT:\^[0-9]+]] = gv: (guid: 14343440786664691134, summaries: (function: (module: [[LIBMOD]], flags: ({{.*}} importType: declaration), insts: 8, {{.*}})))
 ; MAIN-DIS: [[LARGEINDIRECTALIAS:\^[0-9]+]] = gv: (guid: 16730173943625350469, summaries: (alias: (module: [[LIBMOD]], flags: ({{.*}} importType: declaration), aliasee: [[LARGEINDIRECT]])))
 
-; TODO: add test coverage for lto indexing stats.
+; TODO: add test coverage for lto indexing stats (-debug-only=function-import, and 'reqasserts').
 
-; RUN: llvm-lto -thinlto-action=thinlink -import-declaration -import-instr-limit=7  -o combined.index.bc main.bc lib.bc
-; RUN: llvm-lto -thinlto-action=distributedindexes -import-declaration -import-instr-limit=7 -thinlto-index combined.index.bc main.bc lib.bc
-; RUN: llvm-dis main.bc.thinlto.bc -o - | FileCheck %s --check-prefix=MAIN-DIS
+; Run in-process ThinLTO and tests that `callee` remains internalized even if
+; the symbols of its callers (large_func and large_indirect_callee) are exported
+; and visible to main module.
+
+; RUN: llvm-lto2 run \
+; RUN:   -save-temps \
+; RUN:   -import-instr-limit=7 \
+; RUN:   -import-declaration \
+; RUN:   -r=main.bc,main,px \
+; RUN:   -r=main.bc,small_func, \
+; RUN:   -r=main.bc,large_func, \
+; RUN:   -r=lib.bc,callee,pl \
+; RUN:   -r=lib.bc,large_indirect_callee,px \
+; RUN:   -r=lib.bc,small_func,px \
+; RUN:   -r=lib.bc,large_func,px \
+; RUN:   -r=lib.bc,large_indirect_callee_alias,px \
+; RUN:   -r=lib.bc,calleeAddrs,px -o in-process main.bc lib.bc
+
+; RUN: llvm-dis in-process.2.2.internalize.bc -o - | FileCheck %s --check-prefix=INTERNALIZE
+; INTERNALIZE: define internal void @callee()
 
 ;--- main.ll
 target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
diff --git a/llvm/test/Transforms/FunctionImport/funcimport.ll b/llvm/test/Transforms/FunctionImport/funcimport.ll
index a0968a67f5ce8..4b8bcec2a18fb 100644
--- a/llvm/test/Transforms/FunctionImport/funcimport.ll
+++ b/llvm/test/Transforms/FunctionImport/funcimport.ll
@@ -166,7 +166,11 @@ declare void @variadic_va_start(...)
 ; GUID-DAG: GUID {{.*}} is linkoncefunc
 
 ; DUMP:       Module [[M1:.*]] imports from 1 module
-; DUMP-NEXT:  15 functions imported from [[M2:.*]]
-; DUMP-NEXT:  4 vars imported from [[M2]]
+; DUMP-NEXT:  15 function definitions and 0 function declarations imported from [[M2:.*]]
+; DUMP-NEXT:  4 var definitions and 0 var declarations imported from [[M2]]
+
+; The following information are printed from `FunctionImporter::importFunctions`
+; in the postlink pipeline.
+; TODO: Update debug information for postlink pipeline.
 ; DUMP:       Imported 15 functions for Module [[M1]]
 ; DUMP-NEXT:  Imported 4 global variables for Module [[M1]]

>From f1d22e1d7ec2fbe8822658bb4b9a2ea0284cf3ce Mon Sep 17 00:00:00 2001
From: mingmingl <mingmingl at google.com>
Date: Tue, 7 May 2024 14:21:43 -0700
Subject: [PATCH 09/10] Diffbase is updated
 (https://github.com/llvm/llvm-project/pull/87600/commits/2c38b47e4526686a2353a1cdd282352a2927f055).
 Update this one accordingly

---
 llvm/include/llvm/LTO/legacy/ThinLTOCodeGenerator.h |  3 +--
 llvm/include/llvm/Transforms/IPO/FunctionImport.h   |  2 +-
 llvm/lib/LTO/LTO.cpp                                |  6 +++---
 llvm/lib/LTO/ThinLTOCodeGenerator.cpp               | 10 ++++------
 llvm/lib/Transforms/IPO/FunctionImport.cpp          |  4 ++--
 llvm/tools/llvm-lto/llvm-lto.cpp                    |  8 +++-----
 6 files changed, 14 insertions(+), 19 deletions(-)

diff --git a/llvm/include/llvm/LTO/legacy/ThinLTOCodeGenerator.h b/llvm/include/llvm/LTO/legacy/ThinLTOCodeGenerator.h
index 6e197ae2f279c..750d09b65bf90 100644
--- a/llvm/include/llvm/LTO/legacy/ThinLTOCodeGenerator.h
+++ b/llvm/include/llvm/LTO/legacy/ThinLTOCodeGenerator.h
@@ -276,8 +276,7 @@ class ThinLTOCodeGenerator {
   void gatherImportedSummariesForModule(
       Module &Module, ModuleSummaryIndex &Index,
       std::map<std::string, GVSummaryMapTy> &ModuleToSummariesForIndex,
-      const lto::InputFile &File,
-      ModuleToGVSummaryPtrSet &ModuleToDecSummaries);
+      const lto::InputFile &File, GVSummaryPtrSet &DecSummaries);
 
   /**
    * Perform internalization. Index is updated to reflect linkage changes.
diff --git a/llvm/include/llvm/Transforms/IPO/FunctionImport.h b/llvm/include/llvm/Transforms/IPO/FunctionImport.h
index fb38c68b56df0..bc4deb29ba8d2 100644
--- a/llvm/include/llvm/Transforms/IPO/FunctionImport.h
+++ b/llvm/include/llvm/Transforms/IPO/FunctionImport.h
@@ -220,7 +220,7 @@ void gatherImportedSummariesForModule(
     const DenseMap<StringRef, GVSummaryMapTy> &ModuleToDefinedGVSummaries,
     const FunctionImporter::ImportMapTy &ImportList,
     std::map<std::string, GVSummaryMapTy> &ModuleToSummariesForIndex,
-    ModuleToGVSummaryPtrSet &ModuleToDecSummaries);
+    GVSummaryPtrSet &DecSummaries);
 
 /// Emit into \p OutputFilename the files module \p ModulePath will import from.
 std::error_code EmitImportsFiles(
diff --git a/llvm/lib/LTO/LTO.cpp b/llvm/lib/LTO/LTO.cpp
index e3ab5c738cfd9..fd252acb3909a 100644
--- a/llvm/lib/LTO/LTO.cpp
+++ b/llvm/lib/LTO/LTO.cpp
@@ -1389,11 +1389,11 @@ class lto::ThinBackendProc {
                   llvm::StringRef ModulePath,
                   const std::string &NewModulePath) {
     std::map<std::string, GVSummaryMapTy> ModuleToSummariesForIndex;
-    ModuleToGVSummaryPtrSet ModuleToDeclarationSummaries;
+    GVSummaryPtrSet DeclarationSummaries;
     std::error_code EC;
     gatherImportedSummariesForModule(ModulePath, ModuleToDefinedGVSummaries,
                                      ImportList, ModuleToSummariesForIndex,
-                                     ModuleToDeclarationSummaries);
+                                     DeclarationSummaries);
 
     raw_fd_ostream OS(NewModulePath + ".thinlto.bc", EC,
                       sys::fs::OpenFlags::OF_None);
@@ -1401,7 +1401,7 @@ class lto::ThinBackendProc {
       return errorCodeToError(EC);
 
     writeIndexToFile(CombinedIndex, OS, &ModuleToSummariesForIndex,
-                     &ModuleToDeclarationSummaries);
+                     &DeclarationSummaries);
 
     if (ShouldEmitImportsFiles) {
       EC = EmitImportsFiles(ModulePath, NewModulePath + ".imports",
diff --git a/llvm/lib/LTO/ThinLTOCodeGenerator.cpp b/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
index 1227f26cc4280..507c7e4048c79 100644
--- a/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
+++ b/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
@@ -766,7 +766,7 @@ void ThinLTOCodeGenerator::crossModuleImport(Module &TheModule,
 void ThinLTOCodeGenerator::gatherImportedSummariesForModule(
     Module &TheModule, ModuleSummaryIndex &Index,
     std::map<std::string, GVSummaryMapTy> &ModuleToSummariesForIndex,
-    const lto::InputFile &File, ModuleToGVSummaryPtrSet &ModuleToDecSummaries) {
+    const lto::InputFile &File, GVSummaryPtrSet &DecSummaries) {
   auto ModuleCount = Index.modulePaths().size();
   auto ModuleIdentifier = TheModule.getModuleIdentifier();
 
@@ -796,8 +796,7 @@ void ThinLTOCodeGenerator::gatherImportedSummariesForModule(
 
   llvm::gatherImportedSummariesForModule(
       ModuleIdentifier, ModuleToDefinedGVSummaries,
-      ImportLists[ModuleIdentifier], ModuleToSummariesForIndex,
-      ModuleToDecSummaries);
+      ImportLists[ModuleIdentifier], ModuleToSummariesForIndex, DecSummaries);
 }
 
 /**
@@ -838,11 +837,10 @@ void ThinLTOCodeGenerator::emitImports(Module &TheModule, StringRef OutputName,
   // the set of keys in `ModuleToSummariesForIndex` should be a superset of keys
   // in `ModuleToDecSummaries`, so no need to use `ModuleToDecSummaries` in
   // `EmitImportFiles`.
-  ModuleToGVSummaryPtrSet ModuleToDecSummaries;
+  GVSummaryPtrSet DecSummaries;
   llvm::gatherImportedSummariesForModule(
       ModuleIdentifier, ModuleToDefinedGVSummaries,
-      ImportLists[ModuleIdentifier], ModuleToSummariesForIndex,
-      ModuleToDecSummaries);
+      ImportLists[ModuleIdentifier], ModuleToSummariesForIndex, DecSummaries);
 
   std::error_code EC;
   if ((EC = EmitImportsFiles(ModuleIdentifier, OutputName,
diff --git a/llvm/lib/Transforms/IPO/FunctionImport.cpp b/llvm/lib/Transforms/IPO/FunctionImport.cpp
index 77d644dc97ab7..069a4e62a12ae 100644
--- a/llvm/lib/Transforms/IPO/FunctionImport.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionImport.cpp
@@ -1436,7 +1436,7 @@ void llvm::gatherImportedSummariesForModule(
     const DenseMap<StringRef, GVSummaryMapTy> &ModuleToDefinedGVSummaries,
     const FunctionImporter::ImportMapTy &ImportList,
     std::map<std::string, GVSummaryMapTy> &ModuleToSummariesForIndex,
-    ModuleToGVSummaryPtrSet &ModuleToDecSummaries) {
+    GVSummaryPtrSet &DecSummaries) {
   // Include all summaries from the importing module.
   ModuleToSummariesForIndex[std::string(ModulePath)] =
       ModuleToDefinedGVSummaries.lookup(ModulePath);
@@ -1444,7 +1444,7 @@ void llvm::gatherImportedSummariesForModule(
   for (const auto &ILI : ImportList) {
     std::string ModulePath(ILI.first);
     auto &SummariesForIndex = ModuleToSummariesForIndex[ModulePath];
-    auto &DecSummaries = ModuleToDecSummaries[ModulePath];
+
     const auto &DefinedGVSummaries =
         ModuleToDefinedGVSummaries.lookup(ILI.first);
     for (const auto &[GUID, Type] : ILI.second) {
diff --git a/llvm/tools/llvm-lto/llvm-lto.cpp b/llvm/tools/llvm-lto/llvm-lto.cpp
index ce32799150313..4bda7f10c00ef 100644
--- a/llvm/tools/llvm-lto/llvm-lto.cpp
+++ b/llvm/tools/llvm-lto/llvm-lto.cpp
@@ -692,10 +692,9 @@ class ThinLTOProcessing {
       // Build a map of module to the GUIDs and summary objects that should
       // be written to its index.
       std::map<std::string, GVSummaryMapTy> ModuleToSummariesForIndex;
-      ModuleToGVSummaryPtrSet ModuleToDecSummaries;
+      GVSummaryPtrSet DecSummaries;
       ThinGenerator.gatherImportedSummariesForModule(
-          *TheModule, *Index, ModuleToSummariesForIndex, *Input,
-          ModuleToDecSummaries);
+          *TheModule, *Index, ModuleToSummariesForIndex, *Input, DecSummaries);
 
       std::string OutputName = OutputFilename;
       if (OutputName.empty()) {
@@ -705,8 +704,7 @@ class ThinLTOProcessing {
       std::error_code EC;
       raw_fd_ostream OS(OutputName, EC, sys::fs::OpenFlags::OF_None);
       error(EC, "error opening the file '" + OutputName + "'");
-      writeIndexToFile(*Index, OS, &ModuleToSummariesForIndex,
-                       &ModuleToDecSummaries);
+      writeIndexToFile(*Index, OS, &ModuleToSummariesForIndex, &DecSummaries);
     }
   }
 

>From 86f3f445b4f5b14b19d5f23791e16906582bfc13 Mon Sep 17 00:00:00 2001
From: mingmingl <mingmingl at google.com>
Date: Fri, 10 May 2024 12:00:59 -0700
Subject: [PATCH 10/10] resolve review feedback

---
 llvm/include/llvm/Bitcode/BitcodeWriter.h     |  9 +-
 llvm/include/llvm/IR/ModuleSummaryIndex.h     |  4 +-
 .../llvm/LTO/legacy/ThinLTOCodeGenerator.h    |  2 +-
 .../llvm/Transforms/IPO/FunctionImport.h      |  8 +-
 llvm/lib/Bitcode/Writer/BitcodeWriter.cpp     | 38 ++------
 llvm/lib/LTO/LTO.cpp                          | 35 ++++---
 llvm/lib/LTO/ThinLTOCodeGenerator.cpp         | 11 +--
 llvm/lib/Transforms/IPO/FunctionImport.cpp    | 91 ++++++++++---------
 .../ThinLTO/X86/import_callee_declaration.ll  | 47 ++++++----
 llvm/tools/llvm-lto/llvm-lto.cpp              |  5 +-
 10 files changed, 124 insertions(+), 126 deletions(-)

diff --git a/llvm/include/llvm/Bitcode/BitcodeWriter.h b/llvm/include/llvm/Bitcode/BitcodeWriter.h
index a343f0e057631..248d33f4502ef 100644
--- a/llvm/include/llvm/Bitcode/BitcodeWriter.h
+++ b/llvm/include/llvm/Bitcode/BitcodeWriter.h
@@ -102,8 +102,7 @@ class raw_ostream;
 
     void writeIndex(
         const ModuleSummaryIndex *Index,
-        const std::map<std::string, GVSummaryMapTy> *ModuleToSummariesForIndex,
-        const GVSummaryPtrSet *DecSummaries);
+        const std::map<std::string, GVSummaryMapTy> *ModuleToSummariesForIndex);
   };
 
   /// Write the specified module to the specified raw output stream.
@@ -148,12 +147,10 @@ class raw_ostream;
   /// where it will be written in a new bitcode block. This is used when
   /// writing the combined index file for ThinLTO. When writing a subset of the
   /// index for a distributed backend, provide the \p ModuleToSummariesForIndex
-  /// map. \p DecSummaries specifies the set of summaries for which the
-  /// corresponding value should be imported as a declaration (prototype).
+  /// map.
   void writeIndexToFile(const ModuleSummaryIndex &Index, raw_ostream &Out,
                         const std::map<std::string, GVSummaryMapTy>
-                            *ModuleToSummariesForIndex = nullptr,
-                        const GVSummaryPtrSet *DecSummaries = nullptr);
+                            *ModuleToSummariesForIndex = nullptr);
 
   /// If EmbedBitcode is set, save a copy of the llvm IR as data in the
   ///  __LLVM,__bitcode section (.llvmbc on non-MacOS).
diff --git a/llvm/include/llvm/IR/ModuleSummaryIndex.h b/llvm/include/llvm/IR/ModuleSummaryIndex.h
index a13c0ad5c5795..a6bb261af7522 100644
--- a/llvm/include/llvm/IR/ModuleSummaryIndex.h
+++ b/llvm/include/llvm/IR/ModuleSummaryIndex.h
@@ -585,12 +585,12 @@ class GlobalValueSummary {
     return Flags.ImportType == GlobalValueSummary::ImportKind::Declaration;
   }
 
+  void setImportKind(ImportKind IK) { Flags.ImportType = IK; }
+
   GlobalValueSummary::ImportKind importType() const {
     return static_cast<ImportKind>(Flags.ImportType);
   }
 
-  void setImportType(ImportKind IK) { Flags.ImportType = IK; }
-
   GlobalValue::VisibilityTypes getVisibility() const {
     return (GlobalValue::VisibilityTypes)Flags.Visibility;
   }
diff --git a/llvm/include/llvm/LTO/legacy/ThinLTOCodeGenerator.h b/llvm/include/llvm/LTO/legacy/ThinLTOCodeGenerator.h
index 750d09b65bf90..c450acda82ad0 100644
--- a/llvm/include/llvm/LTO/legacy/ThinLTOCodeGenerator.h
+++ b/llvm/include/llvm/LTO/legacy/ThinLTOCodeGenerator.h
@@ -276,7 +276,7 @@ class ThinLTOCodeGenerator {
   void gatherImportedSummariesForModule(
       Module &Module, ModuleSummaryIndex &Index,
       std::map<std::string, GVSummaryMapTy> &ModuleToSummariesForIndex,
-      const lto::InputFile &File, GVSummaryPtrSet &DecSummaries);
+      const lto::InputFile &File);
 
   /**
    * Perform internalization. Index is updated to reflect linkage changes.
diff --git a/llvm/include/llvm/Transforms/IPO/FunctionImport.h b/llvm/include/llvm/Transforms/IPO/FunctionImport.h
index bc4deb29ba8d2..024bba8105b89 100644
--- a/llvm/include/llvm/Transforms/IPO/FunctionImport.h
+++ b/llvm/include/llvm/Transforms/IPO/FunctionImport.h
@@ -104,6 +104,7 @@ class FunctionImporter {
   /// or declaration is visible to another module. If a function's definition is
   /// visible to other modules, the global values this function referenced are
   /// visible and shouldn't be internalized.
+  /// TODO: Rename to `ExportMapTy`.
   using ExportSetTy = DenseMap<ValueInfo, GlobalValueSummary::ImportKind>;
 
   /// A function of this type is used to load modules referenced by the index.
@@ -211,16 +212,11 @@ bool convertToDeclaration(GlobalValue &GV);
 /// \p ModuleToSummariesForIndex will be populated with the needed summaries
 /// from each required module path. Use a std::map instead of StringMap to get
 /// stable order for bitcode emission.
-///
-/// \p ModuleToDecSummaries will be populated with the set of declarations \p
-/// ModulePath need from other modules. They key is module path, and the value
-/// is a set of summary pointers.
 void gatherImportedSummariesForModule(
     StringRef ModulePath,
     const DenseMap<StringRef, GVSummaryMapTy> &ModuleToDefinedGVSummaries,
     const FunctionImporter::ImportMapTy &ImportList,
-    std::map<std::string, GVSummaryMapTy> &ModuleToSummariesForIndex,
-    GVSummaryPtrSet &DecSummaries);
+    std::map<std::string, GVSummaryMapTy> &ModuleToSummariesForIndex);
 
 /// Emit into \p OutputFilename the files module \p ModulePath will import from.
 std::error_code EmitImportsFiles(
diff --git a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
index 7b89424194f9b..6d01e3b4d8218 100644
--- a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
+++ b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -428,11 +428,6 @@ class IndexBitcodeWriter : public BitcodeWriterBase {
   /// The combined index to write to bitcode.
   const ModuleSummaryIndex &Index;
 
-  /// When writing combined summaries, provides the set of global value
-  /// summaries for which the value (function, function alias, etc) should be
-  /// imported as a declaration.
-  const GVSummaryPtrSet *DecSummaries = nullptr;
-
   /// When writing a subset of the index for distributed backends, client
   /// provides a map of modules to the corresponding GUIDs/summaries to write.
   const std::map<std::string, GVSummaryMapTy> *ModuleToSummariesForIndex;
@@ -457,16 +452,11 @@ class IndexBitcodeWriter : public BitcodeWriterBase {
   /// Constructs a IndexBitcodeWriter object for the given combined index,
   /// writing to the provided \p Buffer. When writing a subset of the index
   /// for a distributed backend, provide a \p ModuleToSummariesForIndex map.
-  /// If provided, \p ModuleToDecSummaries specifies the set of summaries for
-  /// which the corresponding functions or aliased functions should be imported
-  /// as a declaration (but not definition) for each module.
   IndexBitcodeWriter(BitstreamWriter &Stream, StringTableBuilder &StrtabBuilder,
                      const ModuleSummaryIndex &Index,
-                     const GVSummaryPtrSet *DecSummaries = nullptr,
                      const std::map<std::string, GVSummaryMapTy>
                          *ModuleToSummariesForIndex = nullptr)
       : BitcodeWriterBase(Stream, StrtabBuilder), Index(Index),
-        DecSummaries(DecSummaries),
         ModuleToSummariesForIndex(ModuleToSummariesForIndex) {
     // Assign unique value ids to all summaries to be written, for use
     // in writing out the call graph edges. Save the mapping from GUID
@@ -1212,8 +1202,7 @@ static uint64_t getEncodedFFlags(FunctionSummary::FFlags Flags) {
 
 // Decode the flags for GlobalValue in the summary. See getDecodedGVSummaryFlags
 // in BitcodeReader.cpp.
-static uint64_t getEncodedGVSummaryFlags(GlobalValueSummary::GVFlags Flags,
-                                         bool ImportAsDecl = false) {
+static uint64_t getEncodedGVSummaryFlags(GlobalValueSummary::GVFlags Flags) {
   uint64_t RawFlags = 0;
 
   RawFlags |= Flags.NotEligibleToImport; // bool
@@ -1228,8 +1217,7 @@ static uint64_t getEncodedGVSummaryFlags(GlobalValueSummary::GVFlags Flags,
 
   RawFlags |= (Flags.Visibility << 8); // 2 bits
 
-  unsigned ImportType = Flags.ImportType | ImportAsDecl;
-  RawFlags |= (ImportType << 10); // 1 bit
+  RawFlags |= (Flags.ImportType << 10); // 1 bit
 
   return RawFlags;
 }
@@ -4555,12 +4543,6 @@ void IndexBitcodeWriter::writeCombinedGlobalValueSummary() {
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
   unsigned AllocAbbrev = Stream.EmitAbbrev(std::move(Abbv));
 
-  auto shouldImportValueAsDecl = [&](GlobalValueSummary *GVS) -> bool {
-    if (DecSummaries == nullptr)
-      return false;
-    return DecSummaries->contains(GVS);
-  };
-
   // The aliases are emitted as a post-pass, and will point to the value
   // id of the aliasee. Save them in a vector for post-processing.
   SmallVector<AliasSummary *, 64> Aliases;
@@ -4671,8 +4653,7 @@ void IndexBitcodeWriter::writeCombinedGlobalValueSummary() {
     NameVals.push_back(*ValueId);
     assert(ModuleIdMap.count(FS->modulePath()));
     NameVals.push_back(ModuleIdMap[FS->modulePath()]);
-    NameVals.push_back(
-        getEncodedGVSummaryFlags(FS->flags(), shouldImportValueAsDecl(FS)));
+    NameVals.push_back(getEncodedGVSummaryFlags(FS->flags()));
     NameVals.push_back(FS->instCount());
     NameVals.push_back(getEncodedFFlags(FS->fflags()));
     NameVals.push_back(FS->entryCount());
@@ -4721,8 +4702,7 @@ void IndexBitcodeWriter::writeCombinedGlobalValueSummary() {
     NameVals.push_back(AliasValueId);
     assert(ModuleIdMap.count(AS->modulePath()));
     NameVals.push_back(ModuleIdMap[AS->modulePath()]);
-    NameVals.push_back(
-        getEncodedGVSummaryFlags(AS->flags(), shouldImportValueAsDecl(AS)));
+    NameVals.push_back(getEncodedGVSummaryFlags(AS->flags()));
     auto AliaseeValueId = SummaryToValueIdMap[&AS->getAliasee()];
     assert(AliaseeValueId);
     NameVals.push_back(AliaseeValueId);
@@ -5056,9 +5036,8 @@ void BitcodeWriter::writeModule(const Module &M,
 
 void BitcodeWriter::writeIndex(
     const ModuleSummaryIndex *Index,
-    const std::map<std::string, GVSummaryMapTy> *ModuleToSummariesForIndex,
-    const GVSummaryPtrSet *DecSummaries) {
-  IndexBitcodeWriter IndexWriter(*Stream, StrtabBuilder, *Index, DecSummaries,
+    const std::map<std::string, GVSummaryMapTy> *ModuleToSummariesForIndex) {
+  IndexBitcodeWriter IndexWriter(*Stream, StrtabBuilder, *Index,
                                  ModuleToSummariesForIndex);
   IndexWriter.write();
 }
@@ -5111,13 +5090,12 @@ void IndexBitcodeWriter::write() {
 // index for a distributed backend, provide a \p ModuleToSummariesForIndex map.
 void llvm::writeIndexToFile(
     const ModuleSummaryIndex &Index, raw_ostream &Out,
-    const std::map<std::string, GVSummaryMapTy> *ModuleToSummariesForIndex,
-    const GVSummaryPtrSet *DecSummaries) {
+    const std::map<std::string, GVSummaryMapTy> *ModuleToSummariesForIndex) {
   SmallVector<char, 0> Buffer;
   Buffer.reserve(256 * 1024);
 
   BitcodeWriter Writer(Buffer);
-  Writer.writeIndex(&Index, ModuleToSummariesForIndex, DecSummaries);
+  Writer.writeIndex(&Index, ModuleToSummariesForIndex);
   Writer.writeStrtab();
 
   Out.write((char *)&Buffer.front(), Buffer.size());
diff --git a/llvm/lib/LTO/LTO.cpp b/llvm/lib/LTO/LTO.cpp
index fd252acb3909a..2bdfd03580145 100644
--- a/llvm/lib/LTO/LTO.cpp
+++ b/llvm/lib/LTO/LTO.cpp
@@ -121,6 +121,9 @@ void llvm::computeLTOCacheKey(
     support::endian::write64le(Data, I);
     Hasher.update(Data);
   };
+  auto AddUint8 = [&](const uint8_t &I) {
+    Hasher.update(ArrayRef<uint8_t>((const uint8_t *)&I, 1));
+  };
   AddString(Conf.CPU);
   // FIXME: Hash more of Options. For now all clients initialize Options from
   // command-line flags (which is unsupported in production), but may set
@@ -156,18 +159,23 @@ void llvm::computeLTOCacheKey(
   auto ModHash = Index.getModuleHash(ModuleID);
   Hasher.update(ArrayRef<uint8_t>((uint8_t *)&ModHash[0], sizeof(ModHash)));
 
-  std::vector<uint64_t> ExportsGUID;
+  std::vector<std::pair<uint64_t, uint8_t>> ExportsGUID;
   ExportsGUID.reserve(ExportList.size());
-  for (const auto &[VI, UnusedImportType] : ExportList) {
-    auto GUID = VI.getGUID();
-    ExportsGUID.push_back(GUID);
-  }
+  for (const auto &[VI, ExportType] : ExportList)
+    ExportsGUID.push_back(
+        std::make_pair(VI.getGUID(), static_cast<uint8_t>(ExportType)));
 
   // Sort the export list elements GUIDs.
-  llvm::sort(ExportsGUID);
-  for (uint64_t GUID : ExportsGUID) {
+  llvm::sort(ExportsGUID, [](const std::pair<uint64_t, uint8_t> &LHS,
+                             const std::pair<uint64_t, uint8_t> &RHS) {
+    if (LHS.first != RHS.first)
+      return LHS.first < RHS.first;
+    return LHS.second < RHS.second;
+  });
+  for (auto [GUID, ExportType] : ExportsGUID) {
     // The export list can impact the internalization, be conservative here
     Hasher.update(ArrayRef<uint8_t>((uint8_t *)&GUID, sizeof(GUID)));
+    AddUint8(ExportType);
   }
 
   // Include the hash for every module we import functions from. The set of
@@ -204,8 +212,10 @@ void llvm::computeLTOCacheKey(
     Hasher.update(ArrayRef<uint8_t>((uint8_t *)&ModHash[0], sizeof(ModHash)));
 
     AddUint64(Entry.getFunctions().size());
-    for (auto &[GUID, UnusedImportType] : Entry.getFunctions())
+    for (auto &[GUID, ImportType] : Entry.getFunctions()) {
       AddUint64(GUID);
+      AddUint8(ImportType);
+    }
   }
 
   // Include the hash for the resolved ODR.
@@ -1389,19 +1399,18 @@ class lto::ThinBackendProc {
                   llvm::StringRef ModulePath,
                   const std::string &NewModulePath) {
     std::map<std::string, GVSummaryMapTy> ModuleToSummariesForIndex;
-    GVSummaryPtrSet DeclarationSummaries;
+
     std::error_code EC;
     gatherImportedSummariesForModule(ModulePath, ModuleToDefinedGVSummaries,
-                                     ImportList, ModuleToSummariesForIndex,
-                                     DeclarationSummaries);
+                                     ImportList, ModuleToSummariesForIndex);
 
     raw_fd_ostream OS(NewModulePath + ".thinlto.bc", EC,
                       sys::fs::OpenFlags::OF_None);
     if (EC)
       return errorCodeToError(EC);
 
-    writeIndexToFile(CombinedIndex, OS, &ModuleToSummariesForIndex,
-                     &DeclarationSummaries);
+    // TODO: Serialize declaration bits to bitcode.
+    writeIndexToFile(CombinedIndex, OS, &ModuleToSummariesForIndex);
 
     if (ShouldEmitImportsFiles) {
       EC = EmitImportsFiles(ModulePath, NewModulePath + ".imports",
diff --git a/llvm/lib/LTO/ThinLTOCodeGenerator.cpp b/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
index 507c7e4048c79..8f517eb50dc76 100644
--- a/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
+++ b/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
@@ -766,7 +766,7 @@ void ThinLTOCodeGenerator::crossModuleImport(Module &TheModule,
 void ThinLTOCodeGenerator::gatherImportedSummariesForModule(
     Module &TheModule, ModuleSummaryIndex &Index,
     std::map<std::string, GVSummaryMapTy> &ModuleToSummariesForIndex,
-    const lto::InputFile &File, GVSummaryPtrSet &DecSummaries) {
+    const lto::InputFile &File) {
   auto ModuleCount = Index.modulePaths().size();
   auto ModuleIdentifier = TheModule.getModuleIdentifier();
 
@@ -796,7 +796,7 @@ void ThinLTOCodeGenerator::gatherImportedSummariesForModule(
 
   llvm::gatherImportedSummariesForModule(
       ModuleIdentifier, ModuleToDefinedGVSummaries,
-      ImportLists[ModuleIdentifier], ModuleToSummariesForIndex, DecSummaries);
+      ImportLists[ModuleIdentifier], ModuleToSummariesForIndex);
 }
 
 /**
@@ -833,14 +833,9 @@ void ThinLTOCodeGenerator::emitImports(Module &TheModule, StringRef OutputName,
                            ExportLists);
 
   std::map<std::string, GVSummaryMapTy> ModuleToSummariesForIndex;
-  // 'EmitImportsFiles' emits the list of modules from which to import from, and
-  // the set of keys in `ModuleToSummariesForIndex` should be a superset of keys
-  // in `ModuleToDecSummaries`, so no need to use `ModuleToDecSummaries` in
-  // `EmitImportFiles`.
-  GVSummaryPtrSet DecSummaries;
   llvm::gatherImportedSummariesForModule(
       ModuleIdentifier, ModuleToDefinedGVSummaries,
-      ImportLists[ModuleIdentifier], ModuleToSummariesForIndex, DecSummaries);
+      ImportLists[ModuleIdentifier], ModuleToSummariesForIndex);
 
   std::error_code EC;
   if ((EC = EmitImportsFiles(ModuleIdentifier, OutputName,
diff --git a/llvm/lib/Transforms/IPO/FunctionImport.cpp b/llvm/lib/Transforms/IPO/FunctionImport.cpp
index 069a4e62a12ae..e99fb554cd654 100644
--- a/llvm/lib/Transforms/IPO/FunctionImport.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionImport.cpp
@@ -258,8 +258,10 @@ static auto qualifyCalleeCandidates(
 /// Given a list of possible callee implementation for a call site, select one
 /// that fits the \p Threshold for function definition import. If none are
 /// found, the Reason will give the last reason for the failure (last, in the
-/// order of CalleeSummaryList entries). If caller wants to select eligible
-/// summary
+/// order of CalleeSummaryList entries). While looking for a callee definition,
+/// sets \p TooLargeOrNoInlineSummary to the last seen too-large or noinline
+/// candidate; other modules may want to know the function summary or
+/// declaration even if a definition is not needed.
 ///
 /// FIXME: select "best" instead of first that fits. But what is "best"?
 /// - The smallest: more likely to be inlined.
@@ -843,7 +845,6 @@ static void computeImportForFunction(
           FailureInfo = std::make_unique<FunctionImporter::ImportFailureInfo>(
               VI, Edge.second.getHotness(), Reason, 1);
         }
-
         if (ForceImportAll) {
           std::string Msg = std::string("Failed to import function ") +
                             VI.name().str() + " due to " +
@@ -1435,15 +1436,13 @@ void llvm::gatherImportedSummariesForModule(
     StringRef ModulePath,
     const DenseMap<StringRef, GVSummaryMapTy> &ModuleToDefinedGVSummaries,
     const FunctionImporter::ImportMapTy &ImportList,
-    std::map<std::string, GVSummaryMapTy> &ModuleToSummariesForIndex,
-    GVSummaryPtrSet &DecSummaries) {
+    std::map<std::string, GVSummaryMapTy> &ModuleToSummariesForIndex) {
   // Include all summaries from the importing module.
   ModuleToSummariesForIndex[std::string(ModulePath)] =
       ModuleToDefinedGVSummaries.lookup(ModulePath);
   // Include summaries for imports.
   for (const auto &ILI : ImportList) {
-    std::string ModulePath(ILI.first);
-    auto &SummariesForIndex = ModuleToSummariesForIndex[ModulePath];
+    auto &SummariesForIndex = ModuleToSummariesForIndex[std::string(ILI.first)];
 
     const auto &DefinedGVSummaries =
         ModuleToDefinedGVSummaries.lookup(ILI.first);
@@ -1451,9 +1450,10 @@ void llvm::gatherImportedSummariesForModule(
       const auto &DS = DefinedGVSummaries.find(GUID);
       assert(DS != DefinedGVSummaries.end() &&
              "Expected a defined summary for imported global value");
-      SummariesForIndex[GUID] = DS->second;
       if (Type == GlobalValueSummary::Declaration)
-        DecSummaries.insert(DS->second);
+        continue;
+
+      SummariesForIndex[GUID] = DS->second;
     }
   }
 }
@@ -1726,8 +1726,8 @@ Expected<bool> FunctionImporter::importFunctions(
     ModuleNameOrderedList.insert(FunctionsToImportPerModule.first);
   }
 
-  auto maybeGetImportType = [&](const FunctionsToImportTy &GUIDToImportType,
-                                GlobalValue::GUID GUID)
+  auto getImportType = [&](const FunctionsToImportTy &GUIDToImportType,
+                           GlobalValue::GUID GUID)
       -> std::optional<GlobalValueSummary::ImportKind> {
     auto Iter = GUIDToImportType.find(GUID);
     if (Iter == GUIDToImportType.end())
@@ -1759,19 +1759,19 @@ Expected<bool> FunctionImporter::importFunctions(
       if (!F.hasName())
         continue;
       auto GUID = F.getGUID();
-      auto ImportType = maybeGetImportType(ImportGUIDs, GUID);
-
-      if (!ImportType) {
-        LLVM_DEBUG(dbgs() << "Not importing function " << GUID << " "
-                          << F.getName() << " from "
-                          << SrcModule->getSourceFileName() << "\n");
-        continue;
-      }
-      const bool ImportDefinition =
-          *ImportType == GlobalValueSummary::Definition;
-      LLVM_DEBUG(dbgs() << (ImportDefinition ? "Is" : "Not")
-                        << " importing function " << GUID << " " << F.getName()
-                        << " from " << SrcModule->getSourceFileName() << "\n");
+      auto MaybeImportType = getImportType(ImportGUIDs, GUID);
+
+      bool ImportDefinition =
+          (MaybeImportType &&
+           (*MaybeImportType == GlobalValueSummary::Definition));
+
+      LLVM_DEBUG(dbgs() << (MaybeImportType ? "Is" : "Not")
+                        << " importing function"
+                        << (ImportDefinition
+                                ? " definition "
+                                : (MaybeImportType ? " declaration " : " "))
+                        << GUID << " " << F.getName() << " from "
+                        << SrcModule->getSourceFileName() << "\n");
       if (ImportDefinition) {
         if (Error Err = F.materialize())
           return std::move(Err);
@@ -1798,14 +1798,19 @@ Expected<bool> FunctionImporter::importFunctions(
       if (!GV.hasName())
         continue;
       auto GUID = GV.getGUID();
-      auto ImportType = maybeGetImportType(ImportGUIDs, GUID);
-      if (!ImportType)
-        continue;
-      const bool ImportDefinition =
-          (*ImportType == GlobalValueSummary::Definition);
-      LLVM_DEBUG(dbgs() << (ImportDefinition ? "Is" : "Not")
-                        << " importing global " << GUID << " " << GV.getName()
-                        << " from " << SrcModule->getSourceFileName() << "\n");
+      auto MaybeImportType = getImportType(ImportGUIDs, GUID);
+
+      bool ImportDefinition =
+          (MaybeImportType &&
+           (*MaybeImportType == GlobalValueSummary::Definition));
+
+      LLVM_DEBUG(dbgs() << (MaybeImportType ? "Is" : "Not")
+                        << " importing global"
+                        << (ImportDefinition
+                                ? " definition "
+                                : (MaybeImportType ? " declaration " : " "))
+                        << GUID << " " << GV.getName() << " from "
+                        << SrcModule->getSourceFileName() << "\n");
       if (ImportDefinition) {
         if (Error Err = GV.materialize())
           return std::move(Err);
@@ -1816,15 +1821,19 @@ Expected<bool> FunctionImporter::importFunctions(
       if (!GA.hasName() || isa<GlobalIFunc>(GA.getAliaseeObject()))
         continue;
       auto GUID = GA.getGUID();
-      auto ImportType = maybeGetImportType(ImportGUIDs, GUID);
-      if (!ImportType)
-        continue;
-
-      const bool ImportDefinition =
-          (*ImportType == GlobalValueSummary::Definition);
-      LLVM_DEBUG(dbgs() << (ImportDefinition ? "Is" : "Not")
-                        << " importing alias " << GUID << " " << GA.getName()
-                        << " from " << SrcModule->getSourceFileName() << "\n");
+      auto MaybeImportType = getImportType(ImportGUIDs, GUID);
+
+      bool ImportDefinition =
+          (MaybeImportType &&
+           (*MaybeImportType == GlobalValueSummary::Definition));
+
+      LLVM_DEBUG(dbgs() << (MaybeImportType ? "Is" : "Not")
+                        << " importing alias"
+                        << (ImportDefinition
+                                ? " definition "
+                                : (MaybeImportType ? " declaration " : " "))
+                        << GUID << " " << GA.getName() << " from "
+                        << SrcModule->getSourceFileName() << "\n");
       if (ImportDefinition) {
         if (Error Err = GA.materialize())
           return std::move(Err);
diff --git a/llvm/test/ThinLTO/X86/import_callee_declaration.ll b/llvm/test/ThinLTO/X86/import_callee_declaration.ll
index 12286e5eb7a2f..b4ce10270e026 100644
--- a/llvm/test/ThinLTO/X86/import_callee_declaration.ll
+++ b/llvm/test/ThinLTO/X86/import_callee_declaration.ll
@@ -23,7 +23,7 @@
 ; nothing to test more than the summary content.
 ;
 ; TODO: Extend this test case to test IR once postlink optimizer makes use of
-; the import type for declarations, and add test coverage for in-process thinlto.
+; the import type for declarations.
 ;
 ; RUN: llvm-lto2 run \
 ; RUN:   -debug-only=function-import \
@@ -42,36 +42,34 @@
 ;
 ; RUN: llvm-lto -thinlto-action=thinlink -import-declaration -import-instr-limit=7  -o combined.index.bc main.bc lib.bc
 ; RUN: llvm-lto -thinlto-action=distributedindexes -debug-only=function-import -import-declaration -import-instr-limit=7 -thinlto-index combined.index.bc main.bc lib.bc 2>&1 | FileCheck %s --check-prefix=DUMP
-; RUN: llvm-dis main.bc.thinlto.bc -o - | FileCheck %s --check-prefix=MAIN-DIS
 
 ; DUMP: - 2 function definitions and 3 function declarations imported from lib.bc
 
-; main.ll should import {large_func, large_indirect_callee} as declarations.
-; 
 ; First disassemble per-module summary and find out the GUID for {large_func, large_indirect_callee}.
 ;
 ; RUN: llvm-dis lib.bc -o - | FileCheck %s --check-prefix=LIB-DIS
-; LIB-DIS: [[LIBMOD:\^[0-9]+]] = module: (path: "lib.bc", hash: (0, 0, 0, 0, 0))
 ; LIB-DIS: [[LARGEFUNC:\^[0-9]+]] = gv: (name: "large_func", summaries: {{.*}}) ; guid = 2418497564662708935
 ; LIB-DIS: [[LARGEINDIRECT:\^[0-9]+]] = gv: (name: "large_indirect_callee", summaries: {{.*}}) ; guid = 14343440786664691134
+; LIB-DIS: [[LARGEINDIRECTALIAS:\^[0-9]+]] = gv: (name: "large_indirect_callee_alias", summaries: {{.*}}, aliasee: [[LARGEINDIRECT]]
 ;
-; Secondly disassemble main's combined summary and verify the import type of
-; these two GUIDs are declaration.
+; Secondly disassemble main's combined summary and test that large callees are
+; not imported as declarations yet.
+; TODO: Serialize declaration bit and test declaration bits are correctly set.
 ;
 ; RUN: llvm-dis main.bc.thinlto.bc -o - | FileCheck %s --check-prefix=MAIN-DIS
 ;
 ; MAIN-DIS: [[LIBMOD:\^[0-9]+]] = module: (path: "lib.bc", hash: (0, 0, 0, 0, 0))
-; MAIN-DIS: [[LARGEFUNC:\^[0-9]+]] = gv: (guid: 2418497564662708935, summaries: (function: (module: [[LIBMOD]], flags: ({{.*}} importType: declaration), insts: 8, {{.*}})))
-; MAIN-DIS: [[LARGEINDIRECT:\^[0-9]+]] = gv: (guid: 14343440786664691134, summaries: (function: (module: [[LIBMOD]], flags: ({{.*}} importType: declaration), insts: 8, {{.*}})))
-; MAIN-DIS: [[LARGEINDIRECTALIAS:\^[0-9]+]] = gv: (guid: 16730173943625350469, summaries: (alias: (module: [[LIBMOD]], flags: ({{.*}} importType: declaration), aliasee: [[LARGEINDIRECT]])))
-
-; TODO: add test coverage for lto indexing stats (-debug-only=function-import, and 'reqasserts').
+; MAIN-DIS-NOT: [[LARGEFUNC:\^[0-9]+]] = gv: (guid: 2418497564662708935, summaries: (function: (module: [[LIBMOD]], flags: ({{.*}} importType: declaration), insts: 8, {{.*}})))
+; MAIN-DIS-NOT: [[LARGEINDIRECT:\^[0-9]+]] = gv: (guid: 14343440786664691134, summaries: (function: (module: [[LIBMOD]], flags: ({{.*}} importType: declaration), insts: 8, {{.*}})))
+; MAIN-DIS-NOT: [[LARGEINDIRECTALIAS:\^[0-9]+]] = gv: (guid: 16730173943625350469, summaries: (alias: (module: [[LIBMOD]], flags: ({{.*}} importType: declaration)
 
-; Run in-process ThinLTO and tests that `callee` remains internalized even if
-; the symbols of its callers (large_func and large_indirect_callee) are exported
-; and visible to main module.
+; Run in-process ThinLTO and tests that
+; 1. `callee` remains internalized even if the symbols of its callers
+; (large_func and large_indirect_callee) are exported as declarations and visible to main module.
+; 2. the debugging logs from `function-import` pass are expected.
 
 ; RUN: llvm-lto2 run \
+; RUN:   -debug-only=function-import \
 ; RUN:   -save-temps \
 ; RUN:   -import-instr-limit=7 \
 ; RUN:   -import-declaration \
@@ -83,9 +81,26 @@
 ; RUN:   -r=lib.bc,small_func,px \
 ; RUN:   -r=lib.bc,large_func,px \
 ; RUN:   -r=lib.bc,large_indirect_callee_alias,px \
-; RUN:   -r=lib.bc,calleeAddrs,px -o in-process main.bc lib.bc
+; RUN:   -r=lib.bc,calleeAddrs,px -o in-process main.bc lib.bc 2>&1 | FileCheck %s --check-prefix=IMPORTDUMP
+
+; IMPORTDUMP: Not importing function 11825436545918268459 callee from lib.cc
+; IMPORTDUMP: Is importing function declaration 14343440786664691134 large_indirect_callee from lib.cc
+; IMPORTDUMP: Is importing function definition 13568239288960714650 small_indirect_callee from lib.cc
+; IMPORTDUMP: Is importing function definition 6976996067367342685 small_func from lib.cc
+; IMPORTDUMP: Is importing function declaration 2418497564662708935 large_func from lib.cc
+; IMPORTDUMP: Not importing global 7680325410415171624 calleeAddrs from lib.cc
+; IMPORTDUMP: Is importing alias declaration 16730173943625350469 large_indirect_callee_alias from lib.cc
+
+; RUN: llvm-dis in-process.1.3.import.bc -o - | FileCheck %s --check-prefix=IMPORT
 
 ; RUN: llvm-dis in-process.2.2.internalize.bc -o - | FileCheck %s --check-prefix=INTERNALIZE
+
+; IMPORT-DAG: define available_externally void @small_func
+; IMPORT-DAG: define available_externally hidden void @small_indirect_callee
+; IMPORT-DAG: declare void @large_func
+; IMPORT-NOT: large_indirect_callee
+; IMPORT-NOT: large_indirect_callee_alias
+
 ; INTERNALIZE: define internal void @callee()
 
 ;--- main.ll
diff --git a/llvm/tools/llvm-lto/llvm-lto.cpp b/llvm/tools/llvm-lto/llvm-lto.cpp
index 4bda7f10c00ef..f310097eec634 100644
--- a/llvm/tools/llvm-lto/llvm-lto.cpp
+++ b/llvm/tools/llvm-lto/llvm-lto.cpp
@@ -692,9 +692,8 @@ class ThinLTOProcessing {
       // Build a map of module to the GUIDs and summary objects that should
       // be written to its index.
       std::map<std::string, GVSummaryMapTy> ModuleToSummariesForIndex;
-      GVSummaryPtrSet DecSummaries;
       ThinGenerator.gatherImportedSummariesForModule(
-          *TheModule, *Index, ModuleToSummariesForIndex, *Input, DecSummaries);
+          *TheModule, *Index, ModuleToSummariesForIndex, *Input);
 
       std::string OutputName = OutputFilename;
       if (OutputName.empty()) {
@@ -704,7 +703,7 @@ class ThinLTOProcessing {
       std::error_code EC;
       raw_fd_ostream OS(OutputName, EC, sys::fs::OpenFlags::OF_None);
       error(EC, "error opening the file '" + OutputName + "'");
-      writeIndexToFile(*Index, OS, &ModuleToSummariesForIndex, &DecSummaries);
+      writeIndexToFile(*Index, OS, &ModuleToSummariesForIndex);
     }
   }
 



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