gold-plugin: Implement parallel LTO code generation using llvm::LinkedCodeGen.

[pcc]

Summary

Parallelism can be enabled using a new plugin option, jobs=N, where N is
the number of code generation threads.

Depends on D12260

[mehdi_amini]

Few comment (I never used gold)

tools/gold/gold-plugin.cpp

134

any reason not re-using the same -j that is used by most tool for the jobs?
(Maybe it is more coherent with gold, I don't know).

135

strtol?

786

Is the .get() useful here?

789

same

803

Same question as for llvm-lto, what about tool_output_file?

[pcc]

Address review comments

tools/gold/gold-plugin.cpp

134

-j is fine for the testing tools. But for user-facing tools I think a more descriptive flag would be more appropriate.

135

Seems that StringRef::getAsInteger is the canonical way to do this.

786

Removed

789

Removed

803

I believe that tool_output_file cannot be used with temporary files.

[• rafael]

Needs a testcase. Do include one test using save-temps or obj-path showing the mulitple .o files that are created.

tools/gold/gold-plugin.cpp

109

Why do you need to change this? All the errors in here still fail the build, no?

[pcc]

In D12308#237283, @rafael wrote:

Needs a testcase. Do include one test using save-temps or obj-path showing the mulitple .o files that are created.

This would be test/tools/gold/X86/parallel.ll, no?

tools/gold/gold-plugin.cpp

109

I suppose it doesn't really matter much, but I think it is more appropriate to use the linker callbacks here rather than report_fatal_error which should only really be used for LLVM internal errors.

test/tools/gold/parallel.ll

+; RUN: llvm-as -o %t.bc %s
+; RUN: %gold -plugin %llvmshlibdir/LLVMgold.so -u foo -u bar -plugin-opt jobs=2 -plugin-opt save-temps -o %t %t.bc
+; RUN: llvm-nm %t.o0 | FileCheck --check-prefix=CHECK0 %s
+; RUN: llvm-nm %t.o1 | FileCheck --check-prefix=CHECK1 %s
+
+target triple = "x86_64-unknown-linux-gnu"
+
+; CHECK0-NOT: bar
+; CHECK0: T foo
+; CHECK0-NOT: bar
+define void @foo() {
+  call void @bar()
+  ret void
+}
+
+; CHECK1-NOT: foo
+; CHECK1: T bar
+; CHECK1-NOT: foo
+define void @bar() {
+  call void @foo()
+  ret void
+}

tools/gold/gold-plugin.cpp

 #include "llvm/Config/config.h" // plugin-api.h requires HAVE_STDINT_H
 #include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/StringSet.h"
 #include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
 #include "llvm/Bitcode/ReaderWriter.h"
 #include "llvm/CodeGen/Analysis.h"
 #include "llvm/CodeGen/CommandFlags.h"
+#include "llvm/CodeGen/Parallel.h"
 #include "llvm/IR/AutoUpgrade.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DiagnosticInfo.h"
 #include "llvm/IR/DiagnosticPrinter.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/LegacyPassManager.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/Verifier.h"
enum OutputType {
     OT_NORMAL,
     OT_DISABLE,
     OT_BC_ONLY,
     OT_SAVE_TEMPS
   };
   static bool generate_api_file = false;
   static OutputType TheOutputType = OT_NORMAL;
   static unsigned OptLevel = 2;
+  static unsigned Parallelism = 1;
   static std::string obj_path;
   static std::string extra_library_path;
   static std::string triple;
   static std::string mcpu;
   // Additional options to pass into the code generator.
   // Note: This array will contain all plugin options which are not claimed
   // as plugin exclusive to pass to the code generator.
   // For example, "generate-api-file" and "as"options are for the plugin
   // use only and will not be passed.
   static std::vector<const char *> extra;
 
   static void process_plugin_option(const char *opt_)
   {
     if (opt_ == nullptr)
       return;
     llvm::StringRef opt = opt_;
 
     if (opt == "generate-api-file") {
       generate_api_file = true;
     } else if (opt.startswith("mcpu=")) {
       mcpu = opt.substr(strlen("mcpu="));
     } else if (opt.startswith("extra-library-path=")) {
       extra_library_path = opt.substr(strlen("extra_library_path="));
     } else if (opt.startswith("mtriple=")) {
       triple = opt.substr(strlen("mtriple="));
     } else if (opt.startswith("obj-path=")) {
       obj_path = opt.substr(strlen("obj-path="));
     } else if (opt == "emit-llvm") {
       TheOutputType = OT_BC_ONLY;
     } else if (opt == "save-temps") {
       TheOutputType = OT_SAVE_TEMPS;
     } else if (opt == "disable-output") {
       TheOutputType = OT_DISABLE;
     } else if (opt.size() == 2 && opt[0] == 'O') {
       if (opt[1] < '0' || opt[1] > '3')
         report_fatal_error("Optimization level must be between 0 and 3");
       OptLevel = opt[1] - '0';
+    } else if (opt.startswith("jobs=")) {
+      Parallelism = atoi(opt_ + 5);
     } else {
       // Save this option to pass to the code generator.
       // ParseCommandLineOptions() expects argv[0] to be program name. Lazily
       // add that.
       if (extra.empty())
         extra.push_back("LLVMgold");
 
       extra.push_back(opt_);

 static void saveBCFile(StringRef Path, Module &M) {
   std::error_code EC;
   raw_fd_ostream OS(Path, EC, sys::fs::OpenFlags::F_None);
   if (EC)
     message(LDPL_FATAL, "Failed to write the output file.");
   WriteBitcodeToFile(&M, OS, /* ShouldPreserveUseListOrder */ true);
 }
 
-static void codegen(Module &M) {
-  const std::string &TripleStr = M.getTargetTriple();
+static void codegen(std::unique_ptr<Module> M) {
+  const std::string &TripleStr = M->getTargetTriple();
   Triple TheTriple(TripleStr);
 
   std::string ErrMsg;
   const Target *TheTarget = TargetRegistry::lookupTarget(TripleStr, ErrMsg);
   if (!TheTarget)
     message(LDPL_FATAL, "Target not found: %s", ErrMsg.c_str());
 
   if (unsigned NumOpts = options::extra.size())
static void codegen(std::unique_ptr<Module> M) {
   case 3:
     CGOptLevel = CodeGenOpt::Aggressive;
     break;
   }
   std::unique_ptr<TargetMachine> TM(TheTarget->createTargetMachine(
       TripleStr, options::mcpu, Features.getString(), Options, RelocationModel,
       CodeModel::Default, CGOptLevel));
 
-  runLTOPasses(M, *TM);
+  runLTOPasses(*M.get(), *TM);
 
   if (options::TheOutputType == options::OT_SAVE_TEMPS)
-    saveBCFile(output_name + ".opt.bc", M);
-
-  legacy::PassManager CodeGenPasses;
+    saveBCFile(output_name + ".opt.bc", *M.get());
 
   SmallString<128> Filename;
   if (!options::obj_path.empty())
     Filename = options::obj_path;
   else if (options::TheOutputType == options::OT_SAVE_TEMPS)
     Filename = output_name + ".o";
 
-  int FD;
+  std::vector<SmallString<128>> Filenames(options::Parallelism);
   bool TempOutFile = Filename.empty();
+  {
+    // Open a file descriptor for each backend thread. This is done in a block
+    // so that the output file descriptors are closed before gold opens them.
+    std::list<llvm::raw_fd_ostream> OSs;
+    std::vector<llvm::raw_pwrite_stream *> OSPtrs(options::Parallelism);
+    for (unsigned I = 0; I != options::Parallelism; ++I) {
+      int FD;
       if (TempOutFile) {
         std::error_code EC =
-        sys::fs::createTemporaryFile("lto-llvm", "o", FD, Filename);
+            sys::fs::createTemporaryFile("lto-llvm", "o", FD, Filenames[I]);
         if (EC)
           message(LDPL_FATAL, "Could not create temporary file: %s",
                   EC.message().c_str());
       } else {
+        Filenames[I] = Filename;
+        if (options::Parallelism != 1)
+          Filenames[I] += utostr(I);
         std::error_code EC =
-        sys::fs::openFileForWrite(Filename.c_str(), FD, sys::fs::F_None);
+            sys::fs::openFileForWrite(Filenames[I], FD, sys::fs::F_None);
         if (EC)
           message(LDPL_FATAL, "Could not open file: %s", EC.message().c_str());
       }
+      OSs.emplace_back(FD, true);
+      OSPtrs[I] = &OSs.back();
+    }
 
-  {
-    raw_fd_ostream OS(FD, true);
-
-    if (TM->addPassesToEmitFile(CodeGenPasses, OS,
-                                TargetMachine::CGFT_ObjectFile))
-      message(LDPL_FATAL, "Failed to setup codegen");
-    CodeGenPasses.run(M);
+    // Run backend threads.
+    LinkedCodeGen(std::move(M), OSPtrs, options::mcpu, Features.getString(),
+                  Options, RelocationModel, CodeModel::Default, CGOptLevel);
   }
 
+  for (auto &Filename : Filenames) {
     if (add_input_file(Filename.c_str()) != LDPS_OK)
       message(LDPL_FATAL,
               "Unable to add .o file to the link. File left behind in: %s",
               Filename.c_str());
-
     if (TempOutFile)
       Cleanup.push_back(Filename.c_str());
   }
+}
 
 /// gold informs us that all symbols have been read. At this point, we use
 /// get_symbols to see if any of our definitions have been overridden by a
 /// native object file. Then, perform optimization and codegen.
 static ld_plugin_status allSymbolsReadHook(raw_fd_ostream *ApiFile) {
   if (Modules.empty())
     return LDPS_OK;
 
if (options::TheOutputType == options::OT_BC_ONLY)
       path = output_name;
     else
       path = output_name + ".bc";
     saveBCFile(path, *L.getModule());
     if (options::TheOutputType == options::OT_BC_ONLY)
       return LDPS_OK;
   }
 
-  codegen(*L.getModule());
+  codegen(std::move(Combined));
 
   if (!options::extra_library_path.empty() &&
       set_extra_library_path(options::extra_library_path.c_str()) != LDPS_OK)
     message(LDPL_FATAL, "Unable to set the extra library path.");
 
   return LDPS_OK;
 }