[llvm] [ThinLTO] Allow importing based on a workload definition (PR #74545)

[Teresa Johnson via llvm-commits]

================
@@ -369,29 +387,273 @@ class GlobalsImporter final {
   }
 };
 
+static const char *getFailureName(FunctionImporter::ImportFailureReason Reason);
+
 /// Determine the list of imports and exports for each module.
-class ModuleImportsManager final {
+class ModuleImportsManager {
+protected:
   function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
       IsPrevailing;
   const ModuleSummaryIndex &Index;
   DenseMap<StringRef, FunctionImporter::ExportSetTy> *const ExportLists;
 
-public:
   ModuleImportsManager(
       function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
           IsPrevailing,
       const ModuleSummaryIndex &Index,
       DenseMap<StringRef, FunctionImporter::ExportSetTy> *ExportLists = nullptr)
       : IsPrevailing(IsPrevailing), Index(Index), ExportLists(ExportLists) {}
 
+public:
+  virtual ~ModuleImportsManager() = default;
+
   /// Given the list of globals defined in a module, compute the list of imports
   /// as well as the list of "exports", i.e. the list of symbols referenced from
   /// another module (that may require promotion).
-  void computeImportForModule(const GVSummaryMapTy &DefinedGVSummaries,
-                              StringRef ModName,
-                              FunctionImporter::ImportMapTy &ImportList);
+  virtual void
+  computeImportForModule(const GVSummaryMapTy &DefinedGVSummaries,
+                         StringRef ModName,
+                         FunctionImporter::ImportMapTy &ImportList);
+
+  static std::unique_ptr<ModuleImportsManager>
+  create(function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
+             IsPrevailing,
+         const ModuleSummaryIndex &Index,
+         DenseMap<StringRef, FunctionImporter::ExportSetTy> *ExportLists =
+             nullptr);
 };
 
+/// A ModuleImportsManager that operates based on a workload definition (see
+/// -thinlto-workload-def). For modules that do not define workload roots, it
+/// applies the base ModuleImportsManager import policy.
+class WorkloadImportsManager : public ModuleImportsManager {
+  // Keep a module name -> value infos to import association. We use it to
+  // determine if a module's import list should be done by the base
+  // ModuleImportsManager or by us.
+  StringMap<DenseSet<ValueInfo>> Workloads;
+
+  void
+  computeImportForModule(const GVSummaryMapTy &DefinedGVSummaries,
+                         StringRef ModName,
+                         FunctionImporter::ImportMapTy &ImportList) override {
+    auto SetIter = Workloads.find(ModName);
+    if (SetIter == Workloads.end()) {
+      LLVM_DEBUG(dbgs() << "[Workload] " << ModName
+                        << " does not contain the root of any context.\n");
+      return ModuleImportsManager::computeImportForModule(DefinedGVSummaries,
+                                                          ModName, ImportList);
+    }
+    LLVM_DEBUG(dbgs() << "[Workload] " << ModName
+                      << " contains the root(s) of context(s).\n");
+
+    GlobalsImporter GVI(Index, DefinedGVSummaries, IsPrevailing, ImportList,
+                        ExportLists);
+    auto &ValueInfos = SetIter->second;
+    SmallVector<EdgeInfo, 128> GlobWorklist;
+    for (auto &VI : llvm::make_early_inc_range(ValueInfos)) {
+      auto Candidates =
+          qualifyCalleeCandidates(Index, VI.getSummaryList(), ModName);
+
+      const GlobalValueSummary *GVS = nullptr;
+      FunctionImporter::ImportFailureReason LastReason =
+          FunctionImporter::ImportFailureReason::None;
+      for (const auto &Candidate : Candidates) {
+        /// We will prefer importing the prevailing candidate, if not, we'll
+        /// still pick the first available candidate. The reason we want to make
+        /// sure we do import the prevailing candidate is because the goal of
----------------
teresajohnson wrote:

Add note about this only being for interposable linkage, and why we don't do the same for non-interposable (e.g. linkonce_odr)

https://github.com/llvm/llvm-project/pull/74545