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

This patch adds an assertion check for exported read/write-only
variables to be also in import list for module. If they aren't
we may face linker errors, because read/write-only variables are
internalized in their source modules. The patch also changes
export lists to store ValueInfo instead of GUID for performance
considerations.

Differential revision: https://reviews.llvm.org/D70128

1 files changed, 43 insertions, 16 deletions

diff --git a/llvm/lib/Transforms/IPO/FunctionImport.cpp b/llvm/lib/Transforms/IPO/FunctionImport.cpp
index b22cf47a797..d5419e1a1b9 100644
--- a/llvm/lib/Transforms/IPO/FunctionImport.cpp
+++ b/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()) {
-            auto CalleeGUID = Edge.first.getGUID();
-            ExportList.insert(CalleeGUID);
-          }
-          for (auto &Ref : ResolvedCalleeSummary->refs()) {
-            auto GUID = Ref.getGUID();
-            ExportList.insert(GUID);
-          }
+          for (auto &Edge : ResolvedCalleeSummary->calls())
+            ExportList.insert(Edge.first);
+
+          for (auto &Ref : ResolvedCalleeSummary->refs())
+            ExportList.insert(Ref);
         }
       }
     }
@@ -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,
@@ -654,14 +682,13 @@ void llvm::ComputeCrossModuleImport(
   for (auto &ELI : ExportLists) {
     const auto &DefinedGVSummaries =
         ModuleToDefinedGVSummaries.lookup(ELI.first());
-    for (auto EI = ELI.second.begin(); EI != ELI.second.end();) {
-      if (!DefinedGVSummaries.count(*EI))
-        EI = ELI.second.erase(EI);
-      else
-        ++EI;
-    }
+    std::remove_if(ELI.second.begin(), ELI.second.end(),
+                   [&](const ValueInfo &VI) {
+                     return !DefinedGVSummaries.count(VI.getGUID());
+                   });
   }
 
+  assert(checkVariableImport(Index, ImportLists, ExportLists));
 #ifndef NDEBUG
   LLVM_DEBUG(dbgs() << "Import/Export lists for " << ImportLists.size()
                     << " modules:\n");