CodeGen: Replace ThinLTO backend implementation with a client of LTO/Resolution.

[pcc]

Summary

This changes clang to use the llvm::lto::thinBackend function instead of
its own less comprehensive ThinLTO backend implementation.

Depends on D20268

Depends on D21537

Depends on D21542

[tejohnson]

Sorry for the delay, comments below.

lib/CodeGen/BackendUtil.cpp

740

Use ComputeCrossModuleImportForModule instead, since this is only for a single module and we don't need the ExportLists (and is the same routine invoked currently by the FunctionImportPass).

756

OwnedImports is never read from.

lib/Driver/Tools.cpp

3894 ↗

(On Diff #61332)

This change and the associated test change seem independent of the rest of the patch and could be submitted now independently.

[pcc]

• Use ComputeCrossModuleImportForModule

lib/CodeGen/BackendUtil.cpp

756

Yes, but it is needed to preserve ownership of the module's memory buffer until we exit the function scope.

lib/Driver/Tools.cpp

3894 ↗

(On Diff #61332)

D21825

[tejohnson]

LGTM

lib/CodeGen/BackendUtil.cpp

756

Ok, please add a comment.

[tejohnson]

lib/CodeGen/BackendUtil.cpp

757

Can we pass along -save-temps here (i.e. invoke Conf.addSaveTemps)?

[pcc]

Refresh

[tejohnson]

Note that this will have the side effect of enabling linkonce/weak resolution and internalization for the distributed backends.

I had just sent a separate patch (D22356) to do the former, which includes a fix for a subtle linking issue in the distributed backend case. I was planning to follow that up with another patch to add the internalization, after first removing the forced linkonce linking. However, I like having the weak resolution and internalization outside of the FunctionImporter pass, as is done here. So I think the best thing is to change my D22356 to not add weak resolution to the pass, but just have it address the linker issue requiring the new PreserveNonPrevailing flag and the test case. It should probably go in immediately after this one (or my distributed backend testing will start getting failures).

[mehdi_amini]

lib/CodeGen/BackendUtil.cpp

740

This should go away at some point right?
Just to double check if my memory is correct: the linker plugin will emit the import decision and the backend will take it as an input instead of recomputing anything?

[tejohnson]

lib/CodeGen/BackendUtil.cpp

740

The way they are passed down is via the individual combined index. So it simply computes via what is in the index, which will only include summaries for what should be imported. I suppose we could make the logic even simpler tho and just blindly import what is in the index.

Peter, can you add a fixme?

[pcc]

• Add a FIXME

[mehdi_amini]

(I didn't mark it as accepted because Teresa did, but in case you're waiting for me, don't)

lib/CodeGen/BackendUtil.cpp

 #include "llvm/CodeGen/RegAllocRegistry.h"
 #include "llvm/CodeGen/SchedulerRegistry.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/ModuleSummaryIndex.h"
 #include "llvm/IR/IRPrintingPasses.h"
 #include "llvm/IR/LegacyPassManager.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/Verifier.h"
+#include "llvm/LTO/LTOBackend.h"
 #include "llvm/MC/SubtargetFeature.h"
 #include "llvm/Object/ModuleSummaryIndexObjectFile.h"
 #include "llvm/Support/CommandLine.h"
+#include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/PrettyStackTrace.h"
 #include "llvm/Support/TargetRegistry.h"
 #include "llvm/Support/Timer.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Target/TargetMachine.h"
 #include "llvm/Target/TargetOptions.h"
 #include "llvm/Target/TargetSubtargetInfo.h"
 #include "llvm/Transforms/IPO.h"
if (TM)
       return TM->getTargetIRAnalysis();
 
     return TargetIRAnalysis();
   }
 
   /// Set LLVM command line options passed through -backend-option.
   void setCommandLineOpts();
 
-  void CreatePasses(legacy::PassManager &MPM, legacy::FunctionPassManager &FPM,
-                    ModuleSummaryIndex *ModuleSummary);
+  void CreatePasses(legacy::PassManager &MPM, legacy::FunctionPassManager &FPM);
 
   /// Generates the TargetMachine.
   /// Leaves TM unchanged if it is unable to create the target machine.
   /// Some of our clang tests specify triples which are not built
   /// into clang. This is okay because these tests check the generated
   /// IR, and they require DataLayout which depends on the triple.
   /// In this case, we allow this method to fail and not report an error.
   /// When MustCreateTM is used, we print an error if we are unable to load
static void addSymbolRewriterPass(const CodeGenOptions &Opts,
   llvm::SymbolRewriter::RewriteMapParser MapParser;
   for (const auto &MapFile : Opts.RewriteMapFiles)
     MapParser.parse(MapFile, &DL);
 
   MPM->add(createRewriteSymbolsPass(DL));
 }
 
 void EmitAssemblyHelper::CreatePasses(legacy::PassManager &MPM,
-                                      legacy::FunctionPassManager &FPM,
-                                      ModuleSummaryIndex *ModuleSummary) {
+                                      legacy::FunctionPassManager &FPM) {
   if (CodeGenOpts.DisableLLVMPasses)
     return;
 
   unsigned OptLevel = CodeGenOpts.OptimizationLevel;
   CodeGenOptions::InliningMethod Inlining = CodeGenOpts.getInlining();
 
   // Handle disabling of LLVM optimization, where we want to preserve the
   // internal module before any optimization.
void EmitAssemblyHelper::CreatePasses(legacy::PassManager &MPM,
   PMBuilder.LoopVectorize = CodeGenOpts.VectorizeLoop;
 
   PMBuilder.DisableUnrollLoops = !CodeGenOpts.UnrollLoops;
   PMBuilder.MergeFunctions = CodeGenOpts.MergeFunctions;
   PMBuilder.PrepareForThinLTO = CodeGenOpts.EmitSummaryIndex;
   PMBuilder.PrepareForLTO = CodeGenOpts.PrepareForLTO;
   PMBuilder.RerollLoops = CodeGenOpts.RerollLoops;
 
-  // If we are performing a ThinLTO importing compile, invoke the LTO
-  // pipeline and pass down the in-memory module summary index.
-  if (ModuleSummary) {
-    PMBuilder.ModuleSummary = ModuleSummary;
-    PMBuilder.populateThinLTOPassManager(MPM);
-    return;
-  }
-
   // Add target-specific passes that need to run as early as possible.
   if (TM)
     PMBuilder.addExtension(
         PassManagerBuilder::EP_EarlyAsPossible,
         [&](const PassManagerBuilder &, legacy::PassManagerBase &PM) {
           TM->addEarlyAsPossiblePasses(PM);
         });
 
bool UsesCodeGen = (Action != Backend_EmitNothing &&
                       Action != Backend_EmitLL);
   CreateTargetMachine(UsesCodeGen);
 
   if (UsesCodeGen && !TM)
     return;
   if (TM)
     TheModule->setDataLayout(TM->createDataLayout());
 
-  // If we are performing a ThinLTO importing compile, load the function
-  // index into memory and pass it into CreatePasses, which will add it
-  // to the PassManagerBuilder and invoke LTO passes.
-  std::unique_ptr<ModuleSummaryIndex> ModuleSummary;
-  if (!CodeGenOpts.ThinLTOIndexFile.empty()) {
-    ErrorOr<std::unique_ptr<ModuleSummaryIndex>> IndexOrErr =
-        llvm::getModuleSummaryIndexForFile(
-            CodeGenOpts.ThinLTOIndexFile, [&](const DiagnosticInfo &DI) {
-              TheModule->getContext().diagnose(DI);
-            });
-    if (std::error_code EC = IndexOrErr.getError()) {
-      std::string Error = EC.message();
-      errs() << "Error loading index file '" << CodeGenOpts.ThinLTOIndexFile
-             << "': " << Error << "\n";
-      return;
-    }
-    ModuleSummary = std::move(IndexOrErr.get());
-    assert(ModuleSummary && "Expected non-empty module summary index");
-  }
-
   legacy::PassManager PerModulePasses;
   PerModulePasses.add(
       createTargetTransformInfoWrapperPass(getTargetIRAnalysis()));
 
   legacy::FunctionPassManager PerFunctionPasses(TheModule);
   PerFunctionPasses.add(
       createTargetTransformInfoWrapperPass(getTargetIRAnalysis()));
 
-  CreatePasses(PerModulePasses, PerFunctionPasses, ModuleSummary.get());
+  CreatePasses(PerModulePasses, PerFunctionPasses);
 
   legacy::PassManager CodeGenPasses;
   CodeGenPasses.add(
       createTargetTransformInfoWrapperPass(getTargetIRAnalysis()));
 
   switch (Action) {
   case Backend_EmitNothing:
     break;
void EmitAssemblyHelper::EmitAssembly(BackendAction Action,
   }
 
   {
     PrettyStackTraceString CrashInfo("Code generation");
     CodeGenPasses.run(*TheModule);
   }
 }
 
+static void runThinLTOBackend(const CodeGenOptions &CGOpts, Module *M,
+                              std::unique_ptr<raw_pwrite_stream> OS) {
+  // If we are performing a ThinLTO importing compile, load the function index
+  // into memory and pass it into thinBackend, which will run the function
+  // importer and invoke LTO passes.
+  ErrorOr<std::unique_ptr<ModuleSummaryIndex>> IndexOrErr =
+      llvm::getModuleSummaryIndexForFile(
+          CGOpts.ThinLTOIndexFile,
+          [&](const DiagnosticInfo &DI) { M->getContext().diagnose(DI); });
+  if (std::error_code EC = IndexOrErr.getError()) {
+    std::string Error = EC.message();
+    errs() << "Error loading index file '" << CGOpts.ThinLTOIndexFile
+           << "': " << Error << "\n";
+    return;
+  }
+  std::unique_ptr<ModuleSummaryIndex> CombinedIndex = std::move(*IndexOrErr);
+
+  auto AddStream = [&](size_t Task) { return std::move(OS); };
+
+  StringMap<std::map<GlobalValue::GUID, GlobalValueSummary *>>
+      ModuleToDefinedGVSummaries;
+  CombinedIndex->collectDefinedGVSummariesPerModule(ModuleToDefinedGVSummaries);
+
+  FunctionImporter::ImportMapTy ImportList;
+  ComputeCrossModuleImportForModule(M->getModuleIdentifier(), *CombinedIndex,
+                                    ImportList);
+
+  std::vector<std::unique_ptr<llvm::MemoryBuffer>> OwnedImports;
+  MapVector<llvm::StringRef, llvm::MemoryBufferRef> ModuleMap;
+
+  for (auto &I : ImportList) {
+    ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> MBOrErr =
+        llvm::MemoryBuffer::getFile(I.first());
+    if (!MBOrErr) {
+      errs() << "Error loading imported file '" << I.first()
+             << "': " << MBOrErr.getError().message() << "\n";
+      return;
+    }
+    ModuleMap[I.first()] = (*MBOrErr)->getMemBufferRef();
+    OwnedImports.push_back(std::move(*MBOrErr));
+  }
+
+  lto::Config Conf;
+  if (Error E = thinBackend(
+          Conf, 0, AddStream, *M, *CombinedIndex, ImportList,
+          ModuleToDefinedGVSummaries[M->getModuleIdentifier()], ModuleMap)) {
+    handleAllErrors(std::move(E), [&](ErrorInfoBase &EIB) {
+      errs() << "Error running ThinLTO backend: " << EIB.message() << '\n';
+    });
+  }
+}
+
 void clang::EmitBackendOutput(DiagnosticsEngine &Diags,
                               const CodeGenOptions &CGOpts,
                               const clang::TargetOptions &TOpts,
                               const LangOptions &LOpts, const llvm::DataLayout &TDesc,
                               Module *M, BackendAction Action,
                               std::unique_ptr<raw_pwrite_stream> OS) {
+  if (!CGOpts.ThinLTOIndexFile.empty()) {
+    runThinLTOBackend(CGOpts, M, std::move(OS));
+    return;
+  }
+
   EmitAssemblyHelper AsmHelper(Diags, CGOpts, TOpts, LOpts, M);
 
   AsmHelper.EmitAssembly(Action, std::move(OS));
 
   // Verify clang's TargetInfo DataLayout against the LLVM TargetMachine's
   // DataLayout.
   if (AsmHelper.TM) {
     std::string DLDesc = M->getDataLayout().getStringRepresentation();

lib/CodeGen/CMakeLists.txt

 set(LLVM_LINK_COMPONENTS
   Analysis
   BitReader
   BitWriter
   Core
   Coverage
   IPO
   IRReader
   InstCombine
   Instrumentation
+  LTO
   Linker
   MC
   ObjCARCOpts
   Object
   ProfileData
   ScalarOpts
   Support
   Target