[clang] [llvm] [CGData][ThinLTO] Global Outlining with Two-CodeGen Rounds (PR #90933)

[Teresa Johnson via cfe-commits]

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@@ -1513,6 +1522,171 @@ class InProcessThinBackend : public ThinBackendProc {
     return Error::success();
   }
 };
+
+/// This backend is utilized in the first round of a two-codegen round process.
+/// It first saves optimized bitcode files to disk before the codegen process
+/// begins. After codegen, it stores the resulting object files in a scratch
+/// buffer. Note the codegen data stored in the scratch buffer will be extracted
+/// and merged in the subsequent step.
+class FirstRoundThinBackend : public InProcessThinBackend {
+  AddStreamFn IRAddStream;
+  FileCache IRCache;
+
+public:
+  FirstRoundThinBackend(
+      const Config &Conf, ModuleSummaryIndex &CombinedIndex,
+      ThreadPoolStrategy ThinLTOParallelism,
+      const DenseMap<StringRef, GVSummaryMapTy> &ModuleToDefinedGVSummaries,
+      AddStreamFn CGAddStream, FileCache CGCache, AddStreamFn IRAddStream,
+      FileCache IRCache)
+      : InProcessThinBackend(Conf, CombinedIndex, ThinLTOParallelism,
+                             ModuleToDefinedGVSummaries, std::move(CGAddStream),
+                             std::move(CGCache), /*OnWrite=*/nullptr,
+                             /*ShouldEmitIndexFiles=*/false,
+                             /*ShouldEmitImportsFiles=*/false),
+        IRAddStream(std::move(IRAddStream)), IRCache(std::move(IRCache)) {}
+
+  Error runThinLTOBackendThread(
+      AddStreamFn CGAddStream, FileCache CGCache, unsigned Task,
+      BitcodeModule BM, ModuleSummaryIndex &CombinedIndex,
+      const FunctionImporter::ImportMapTy &ImportList,
+      const FunctionImporter::ExportSetTy &ExportList,
+      const std::map<GlobalValue::GUID, GlobalValue::LinkageTypes> &ResolvedODR,
+      const GVSummaryMapTy &DefinedGlobals,
+      MapVector<StringRef, BitcodeModule> &ModuleMap) override {
+    auto RunThinBackend = [&](AddStreamFn CGAddStream,
+                              AddStreamFn IRAddStream) {
+      LTOLLVMContext BackendContext(Conf);
+      Expected<std::unique_ptr<Module>> MOrErr = BM.parseModule(BackendContext);
+      if (!MOrErr)
+        return MOrErr.takeError();
+
+      return thinBackend(Conf, Task, CGAddStream, **MOrErr, CombinedIndex,
+                         ImportList, DefinedGlobals, &ModuleMap,
+                         Conf.CodeGenOnly, IRAddStream);
+    };
+
+    auto ModuleID = BM.getModuleIdentifier();
+    // Like InProcessThinBackend, we produce index files as needed for
+    // FirstRoundThinBackend. However, these files are not generated for
+    // SecondRoundThinBackend.
+    if (ShouldEmitIndexFiles) {
+      if (auto E = emitFiles(ImportList, ModuleID, ModuleID.str()))
+        return E;
+    }
+
+    assert((CGCache.isValid() == IRCache.isValid()) &&
+           "Both caches for CG and IR should have matching availability");
+    if (!CGCache.isValid() || !CombinedIndex.modulePaths().count(ModuleID) ||
+        all_of(CombinedIndex.getModuleHash(ModuleID),
+               [](uint32_t V) { return V == 0; }))
+      // Cache disabled or no entry for this module in the combined index or
+      // no module hash.
+      return RunThinBackend(CGAddStream, IRAddStream);
+
+    // Get CGKey for caching object in CGCache.
+    std::string CGKey = computeLTOCacheKey(
+        Conf, CombinedIndex, ModuleID, ImportList, ExportList, ResolvedODR,
+        DefinedGlobals, CfiFunctionDefs, CfiFunctionDecls);
+    Expected<AddStreamFn> CacheCGAddStreamOrErr =
+        CGCache(Task, CGKey, ModuleID);
+    if (Error Err = CacheCGAddStreamOrErr.takeError())
+      return Err;
+    AddStreamFn &CacheCGAddStream = *CacheCGAddStreamOrErr;
+
+    // Get IRKey for caching (optimized) IR in IRCache with an extra ID.
+    std::string IRKey = computeLTOCacheKey(
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teresajohnson wrote:

It's a bit unfortunate to have to compute the whole cache key again but just with one extra ID added. I suppose an alternative would be to just rehash the CGKey with "IR".

https://github.com/llvm/llvm-project/pull/90933