Recommit "[ThinLTO] Add correctness check for RO/WO variable import"

ValueInfo has user-defined 'operator bool' which allows incorrect implicit conversion
to GlobalValue::GUID (which is unsigned long). This causes bugs which are hard to
track and should be removed in future.

llvm/include/llvm/LTO/LTO.h

@@ -59,7 +59,7 @@ void thinLTOResolvePrevailingInIndex(
 /// must apply the changes to the Module via thinLTOInternalizeModule.
 void thinLTOInternalizeAndPromoteInIndex(
     ModuleSummaryIndex &Index,
-    function_ref<bool(StringRef, GlobalValue::GUID)> isExported,
+    function_ref<bool(StringRef, ValueInfo)> isExported,
     function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
         isPrevailing);
 

llvm/include/llvm/Transforms/IPO/FunctionImport.h

@@ -98,7 +98,7 @@ public:
   using ImportMapTy = StringMap<FunctionsToImportTy>;
 
   /// The set contains an entry for every global value the module exports.
-  using ExportSetTy = std::unordered_set<GlobalValue::GUID>;
+  using ExportSetTy = DenseSet<ValueInfo>;
 
   /// A function of this type is used to load modules referenced by the index.
   using ModuleLoaderTy =

llvm/include/llvm/Transforms/IPO/WholeProgramDevirt.h

@@ -251,7 +251,7 @@ void runWholeProgramDevirtOnIndex(
 /// devirt target names for any locals that were exported.
 void updateIndexWPDForExports(
     ModuleSummaryIndex &Summary,
-    function_ref<bool(StringRef, GlobalValue::GUID)> isExported,
+    function_ref<bool(StringRef, ValueInfo)> isExported,
     std::map<ValueInfo, std::vector<VTableSlotSummary>> &LocalWPDTargetsMap);
 
 } // end namespace llvm

llvm/lib/LTO/LTO.cpp

@@ -147,9 +147,11 @@ void llvm::computeLTOCacheKey(
   // Include the hash for the current module
   auto ModHash = Index.getModuleHash(ModuleID);
   Hasher.update(ArrayRef<uint8_t>((uint8_t *)&ModHash[0], sizeof(ModHash)));
-  for (auto F : ExportList)
+  for (const auto &VI : ExportList) {
+    auto GUID = VI.getGUID();
     // The export list can impact the internalization, be conservative here
-    Hasher.update(ArrayRef<uint8_t>((uint8_t *)&F, sizeof(F)));
+    Hasher.update(ArrayRef<uint8_t>((uint8_t *)&GUID, sizeof(GUID)));
+  }
 
   // Include the hash for every module we import functions from. The set of
   // imported symbols for each module may affect code generation and is
@@ -384,12 +386,12 @@ static bool isWeakObjectWithRWAccess(GlobalValueSummary *GVS) {
 }
 
 static void thinLTOInternalizeAndPromoteGUID(
-    GlobalValueSummaryList &GVSummaryList, GlobalValue::GUID GUID,
+    GlobalValueSummaryList &GVSummaryList, ValueInfo VI,
-    function_ref<bool(StringRef, GlobalValue::GUID)> isExported,
+    function_ref<bool(StringRef, ValueInfo)> isExported,
     function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
         isPrevailing) {
   for (auto &S : GVSummaryList) {
-    if (isExported(S->modulePath(), GUID)) {
+    if (isExported(S->modulePath(), VI)) {
       if (GlobalValue::isLocalLinkage(S->linkage()))
         S->setLinkage(GlobalValue::ExternalLinkage);
     } else if (EnableLTOInternalization &&
@@ -397,7 +399,7 @@ static void thinLTOInternalizeAndPromoteGUID(
                // doesn't resolve them.
                !GlobalValue::isLocalLinkage(S->linkage()) &&
                (!GlobalValue::isInterposableLinkage(S->linkage()) ||
-                isPrevailing(GUID, S.get())) &&
+                isPrevailing(VI.getGUID(), S.get())) &&
                S->linkage() != GlobalValue::AppendingLinkage &&
                // We can't internalize available_externally globals because this
                // can break function pointer equality.
@@ -416,12 +418,12 @@ static void thinLTOInternalizeAndPromoteGUID(
 // as external and non-exported values as internal.
 void llvm::thinLTOInternalizeAndPromoteInIndex(
     ModuleSummaryIndex &Index,
-    function_ref<bool(StringRef, GlobalValue::GUID)> isExported,
+    function_ref<bool(StringRef, ValueInfo)> isExported,
     function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
         isPrevailing) {
   for (auto &I : Index)
-    thinLTOInternalizeAndPromoteGUID(I.second.SummaryList, I.first, isExported,
+    thinLTOInternalizeAndPromoteGUID(
-                                     isPrevailing);
+        I.second.SummaryList, Index.getValueInfo(I), isExported, isPrevailing);
 }
 
 // Requires a destructor for std::vector<InputModule>.
@@ -1331,11 +1333,10 @@ Error LTO::runThinLTO(AddStreamFn AddStream, NativeObjectCache Cache,
     ExportedGUIDs.insert(
         GlobalValue::getGUID(GlobalValue::dropLLVMManglingEscape(Def)));
 
-  auto isExported = [&](StringRef ModuleIdentifier, GlobalValue::GUID GUID) {
+  auto isExported = [&](StringRef ModuleIdentifier, ValueInfo VI) {
     const auto &ExportList = ExportLists.find(ModuleIdentifier);
-    return (ExportList != ExportLists.end() &&
+    return (ExportList != ExportLists.end() && ExportList->second.count(VI)) ||
-            ExportList->second.count(GUID)) ||
+           ExportedGUIDs.count(VI.getGUID());
-           ExportedGUIDs.count(GUID);
   };
 
   // Update local devirtualized targets that were exported by cross-module

llvm/lib/LTO/ThinLTOCodeGenerator.cpp

@@ -590,11 +590,10 @@ struct IsExported {
              const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols)
       : ExportLists(ExportLists), GUIDPreservedSymbols(GUIDPreservedSymbols) {}
 
-  bool operator()(StringRef ModuleIdentifier, GlobalValue::GUID GUID) const {
+  bool operator()(StringRef ModuleIdentifier, ValueInfo VI) const {
     const auto &ExportList = ExportLists.find(ModuleIdentifier);
-    return (ExportList != ExportLists.end() &&
+    return (ExportList != ExportLists.end() && ExportList->second.count(VI)) ||
-            ExportList->second.count(GUID)) ||
+           GUIDPreservedSymbols.count(VI.getGUID());
-           GUIDPreservedSymbols.count(GUID);
   }
 };
 

llvm/lib/Transforms/IPO/FunctionImport.cpp

@@ -308,7 +308,7 @@ static void computeImportForReferencedGlobals(
 
     auto MarkExported = [&](const ValueInfo &VI, const GlobalValueSummary *S) {
       if (ExportLists)
-        (*ExportLists)[S->modulePath()].insert(VI.getGUID());
+        (*ExportLists)[S->modulePath()].insert(VI);
     };
 
     for (auto &RefSummary : VI.getSummaryList())
@@ -497,7 +497,7 @@ static void computeImportForFunction(
       // Make exports in the source module.
       if (ExportLists) {
         auto &ExportList = (*ExportLists)[ExportModulePath];
-        ExportList.insert(VI.getGUID());
+        ExportList.insert(VI);
         if (!PreviouslyImported) {
           // This is the first time this function was exported from its source
           // module, so mark all functions and globals it references as exported
@@ -505,14 +505,11 @@ static void computeImportForFunction(
           // For efficiency, we unconditionally add all the referenced GUIDs
           // to the ExportList for this module, and will prune out any not
           // defined in the module later in a single pass.
-          for (auto &Edge : ResolvedCalleeSummary->calls()) {
+          for (auto &Edge : ResolvedCalleeSummary->calls())
-            auto CalleeGUID = Edge.first.getGUID();
+            ExportList.insert(Edge.first);
-            ExportList.insert(CalleeGUID);
+
-          }
+          for (auto &Ref : ResolvedCalleeSummary->refs())
-          for (auto &Ref : ResolvedCalleeSummary->refs()) {
+            ExportList.insert(Ref);
-            auto GUID = Ref.getGUID();
-            ExportList.insert(GUID);
-          }
         }
       }
     }
@@ -630,6 +627,37 @@ static unsigned numGlobalVarSummaries(const ModuleSummaryIndex &Index,
 }
 #endif
 
+static bool
+checkVariableImport(const ModuleSummaryIndex &Index,
+                    StringMap<FunctionImporter::ImportMapTy> &ImportLists,
+                    StringMap<FunctionImporter::ExportSetTy> &ExportLists) {
+
+  DenseSet<GlobalValue::GUID> FlattenedImports;
+
+  for (auto &ImportPerModule : ImportLists)
+    for (auto &ExportPerModule : ImportPerModule.second)
+      FlattenedImports.insert(ExportPerModule.second.begin(),
+                              ExportPerModule.second.end());
+
+  // 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,
+  // because readonly and writeonly vars are internalized in their
+  // source modules.
+  auto IsReadOrWriteOnlyVar = [&](StringRef ModulePath, const ValueInfo &VI) {
+    auto *GVS = dyn_cast_or_null<GlobalVarSummary>(
+        Index.findSummaryInModule(VI, ModulePath));
+    return GVS && (Index.isReadOnly(GVS) || Index.isWriteOnly(GVS));
+  };
+
+  for (auto &ExportPerModule : ExportLists)
+    for (auto &VI : ExportPerModule.second)
+      if (!FlattenedImports.count(VI.getGUID()) &&
+          IsReadOrWriteOnlyVar(ExportPerModule.first(), VI))
+        return false;
+
+  return true;
+}
+
 /// Compute all the import and export for every module using the Index.
 void llvm::ComputeCrossModuleImport(
     const ModuleSummaryIndex &Index,
@@ -655,13 +683,14 @@ void llvm::ComputeCrossModuleImport(
     const auto &DefinedGVSummaries =
         ModuleToDefinedGVSummaries.lookup(ELI.first());
     for (auto EI = ELI.second.begin(); EI != ELI.second.end();) {
-      if (!DefinedGVSummaries.count(*EI))
+      if (!DefinedGVSummaries.count(EI->getGUID()))
-        EI = ELI.second.erase(EI);
+        ELI.second.erase(EI++);
       else
         ++EI;
     }
   }
 
+  assert(checkVariableImport(Index, ImportLists, ExportLists));
 #ifndef NDEBUG
   LLVM_DEBUG(dbgs() << "Import/Export lists for " << ImportLists.size()
                     << " modules:\n");

llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp

@@ -711,7 +711,7 @@ void runWholeProgramDevirtOnIndex(
 
 void updateIndexWPDForExports(
     ModuleSummaryIndex &Summary,
-    function_ref<bool(StringRef, GlobalValue::GUID)> isExported,
+    function_ref<bool(StringRef, ValueInfo)> isExported,
     std::map<ValueInfo, std::vector<VTableSlotSummary>> &LocalWPDTargetsMap) {
   for (auto &T : LocalWPDTargetsMap) {
     auto &VI = T.first;
@@ -719,7 +719,7 @@ void updateIndexWPDForExports(
     assert(VI.getSummaryList().size() == 1 &&
            "Devirt of local target has more than one copy");
     auto &S = VI.getSummaryList()[0];
-    if (!isExported(S->modulePath(), VI.getGUID()))
+    if (!isExported(S->modulePath(), VI))
       continue;
 
     // It's been exported by a cross module import.

llvm/lib/Transforms/Utils/FunctionImportUtils.cpp

@@ -250,12 +250,12 @@ void FunctionImportGlobalProcessing::processGlobalForThinLTO(GlobalValue &GV) {
       // contains summaries from the source modules if they are being imported.
       // We might have a non-null VI and get here even in that case if the name
       // matches one in this module (e.g. weak or appending linkage).
-      auto* GVS = dyn_cast_or_null<GlobalVarSummary>(
+      auto *GVS = dyn_cast_or_null<GlobalVarSummary>(
-          ImportIndex.findSummaryInModule(VI, M.getModuleIdentifier()));      
+          ImportIndex.findSummaryInModule(VI, M.getModuleIdentifier()));
       if (GVS &&
           (ImportIndex.isReadOnly(GVS) || ImportIndex.isWriteOnly(GVS))) {
         V->addAttribute("thinlto-internalize");
-        // Objects referenced by writeonly GV initializer should not be 
+        // Objects referenced by writeonly GV initializer should not be
         // promoted, because there is no any kind of read access to them
         // on behalf of this writeonly GV. To avoid promotion we convert
         // GV initializer to 'zeroinitializer'. This effectively drops