1 //===-LTOCodeGenerator.cpp - LLVM Link Time Optimizer ---------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements the Link Time Optimization library. This library is
10 // intended to be used by linker to optimize code at link time.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "llvm/LTO/legacy/LTOCodeGenerator.h"
15 
16 #include "llvm/ADT/Statistic.h"
17 #include "llvm/ADT/StringExtras.h"
18 #include "llvm/Analysis/Passes.h"
19 #include "llvm/Analysis/TargetLibraryInfo.h"
20 #include "llvm/Analysis/TargetTransformInfo.h"
21 #include "llvm/Bitcode/BitcodeWriter.h"
22 #include "llvm/CodeGen/ParallelCG.h"
23 #include "llvm/CodeGen/TargetSubtargetInfo.h"
24 #include "llvm/Config/config.h"
25 #include "llvm/IR/Constants.h"
26 #include "llvm/IR/DataLayout.h"
27 #include "llvm/IR/DebugInfo.h"
28 #include "llvm/IR/DerivedTypes.h"
29 #include "llvm/IR/DiagnosticInfo.h"
30 #include "llvm/IR/DiagnosticPrinter.h"
31 #include "llvm/IR/LLVMContext.h"
32 #include "llvm/IR/LLVMRemarkStreamer.h"
33 #include "llvm/IR/LegacyPassManager.h"
34 #include "llvm/IR/Mangler.h"
35 #include "llvm/IR/Module.h"
36 #include "llvm/IR/PassTimingInfo.h"
37 #include "llvm/IR/Verifier.h"
38 #include "llvm/InitializePasses.h"
39 #include "llvm/LTO/LTO.h"
40 #include "llvm/LTO/LTOBackend.h"
41 #include "llvm/LTO/legacy/LTOModule.h"
42 #include "llvm/LTO/legacy/UpdateCompilerUsed.h"
43 #include "llvm/Linker/Linker.h"
44 #include "llvm/MC/MCAsmInfo.h"
45 #include "llvm/MC/MCContext.h"
46 #include "llvm/MC/SubtargetFeature.h"
47 #include "llvm/Remarks/HotnessThresholdParser.h"
48 #include "llvm/Support/CommandLine.h"
49 #include "llvm/Support/FileSystem.h"
50 #include "llvm/Support/Host.h"
51 #include "llvm/Support/MemoryBuffer.h"
52 #include "llvm/Support/Signals.h"
53 #include "llvm/Support/TargetRegistry.h"
54 #include "llvm/Support/TargetSelect.h"
55 #include "llvm/Support/ToolOutputFile.h"
56 #include "llvm/Support/YAMLTraits.h"
57 #include "llvm/Support/raw_ostream.h"
58 #include "llvm/Target/TargetOptions.h"
59 #include "llvm/Transforms/IPO.h"
60 #include "llvm/Transforms/IPO/Internalize.h"
61 #include "llvm/Transforms/IPO/PassManagerBuilder.h"
62 #include "llvm/Transforms/IPO/WholeProgramDevirt.h"
63 #include "llvm/Transforms/ObjCARC.h"
64 #include "llvm/Transforms/Utils/ModuleUtils.h"
65 #include <system_error>
66 using namespace llvm;
67 
68 const char* LTOCodeGenerator::getVersionString() {
69 #ifdef LLVM_VERSION_INFO
70   return PACKAGE_NAME " version " PACKAGE_VERSION ", " LLVM_VERSION_INFO;
71 #else
72   return PACKAGE_NAME " version " PACKAGE_VERSION;
73 #endif
74 }
75 
76 namespace llvm {
77 cl::opt<bool> LTODiscardValueNames(
78     "lto-discard-value-names",
79     cl::desc("Strip names from Value during LTO (other than GlobalValue)."),
80 #ifdef NDEBUG
81     cl::init(true),
82 #else
83     cl::init(false),
84 #endif
85     cl::Hidden);
86 
87 cl::opt<bool> RemarksWithHotness(
88     "lto-pass-remarks-with-hotness",
89     cl::desc("With PGO, include profile count in optimization remarks"),
90     cl::Hidden);
91 
92 cl::opt<Optional<uint64_t>, false, remarks::HotnessThresholdParser>
93     RemarksHotnessThreshold(
94         "lto-pass-remarks-hotness-threshold",
95         cl::desc("Minimum profile count required for an "
96                  "optimization remark to be output."
97                  " Use 'auto' to apply the threshold from profile summary."),
98         cl::value_desc("uint or 'auto'"), cl::init(0), cl::Hidden);
99 
100 cl::opt<std::string>
101     RemarksFilename("lto-pass-remarks-output",
102                     cl::desc("Output filename for pass remarks"),
103                     cl::value_desc("filename"));
104 
105 cl::opt<std::string>
106     RemarksPasses("lto-pass-remarks-filter",
107                   cl::desc("Only record optimization remarks from passes whose "
108                            "names match the given regular expression"),
109                   cl::value_desc("regex"));
110 
111 cl::opt<std::string> RemarksFormat(
112     "lto-pass-remarks-format",
113     cl::desc("The format used for serializing remarks (default: YAML)"),
114     cl::value_desc("format"), cl::init("yaml"));
115 
116 cl::opt<std::string> LTOStatsFile(
117     "lto-stats-file",
118     cl::desc("Save statistics to the specified file"),
119     cl::Hidden);
120 }
121 
122 LTOCodeGenerator::LTOCodeGenerator(LLVMContext &Context)
123     : Context(Context), MergedModule(new Module("ld-temp.o", Context)),
124       TheLinker(new Linker(*MergedModule)) {
125   Context.setDiscardValueNames(LTODiscardValueNames);
126   Context.enableDebugTypeODRUniquing();
127 
128   Config.CodeModel = None;
129   Config.StatsFile = LTOStatsFile;
130   Config.PreCodeGenPassesHook = [](legacy::PassManager &PM) {
131     PM.add(createObjCARCContractPass());
132   };
133 }
134 
135 LTOCodeGenerator::~LTOCodeGenerator() {}
136 
137 void LTOCodeGenerator::setAsmUndefinedRefs(LTOModule *Mod) {
138   const std::vector<StringRef> &undefs = Mod->getAsmUndefinedRefs();
139   for (int i = 0, e = undefs.size(); i != e; ++i)
140     AsmUndefinedRefs.insert(undefs[i]);
141 }
142 
143 bool LTOCodeGenerator::addModule(LTOModule *Mod) {
144   assert(&Mod->getModule().getContext() == &Context &&
145          "Expected module in same context");
146 
147   bool ret = TheLinker->linkInModule(Mod->takeModule());
148   setAsmUndefinedRefs(Mod);
149 
150   // We've just changed the input, so let's make sure we verify it.
151   HasVerifiedInput = false;
152 
153   return !ret;
154 }
155 
156 void LTOCodeGenerator::setModule(std::unique_ptr<LTOModule> Mod) {
157   assert(&Mod->getModule().getContext() == &Context &&
158          "Expected module in same context");
159 
160   AsmUndefinedRefs.clear();
161 
162   MergedModule = Mod->takeModule();
163   TheLinker = std::make_unique<Linker>(*MergedModule);
164   setAsmUndefinedRefs(&*Mod);
165 
166   // We've just changed the input, so let's make sure we verify it.
167   HasVerifiedInput = false;
168 }
169 
170 void LTOCodeGenerator::setTargetOptions(const TargetOptions &Options) {
171   Config.Options = Options;
172 }
173 
174 void LTOCodeGenerator::setDebugInfo(lto_debug_model Debug) {
175   switch (Debug) {
176   case LTO_DEBUG_MODEL_NONE:
177     EmitDwarfDebugInfo = false;
178     return;
179 
180   case LTO_DEBUG_MODEL_DWARF:
181     EmitDwarfDebugInfo = true;
182     return;
183   }
184   llvm_unreachable("Unknown debug format!");
185 }
186 
187 void LTOCodeGenerator::setOptLevel(unsigned Level) {
188   Config.OptLevel = Level;
189   Config.PTO.LoopVectorization = Config.OptLevel > 1;
190   Config.PTO.SLPVectorization = Config.OptLevel > 1;
191   switch (Config.OptLevel) {
192   case 0:
193     Config.CGOptLevel = CodeGenOpt::None;
194     return;
195   case 1:
196     Config.CGOptLevel = CodeGenOpt::Less;
197     return;
198   case 2:
199     Config.CGOptLevel = CodeGenOpt::Default;
200     return;
201   case 3:
202     Config.CGOptLevel = CodeGenOpt::Aggressive;
203     return;
204   }
205   llvm_unreachable("Unknown optimization level!");
206 }
207 
208 bool LTOCodeGenerator::writeMergedModules(StringRef Path) {
209   if (!determineTarget())
210     return false;
211 
212   // We always run the verifier once on the merged module.
213   verifyMergedModuleOnce();
214 
215   // mark which symbols can not be internalized
216   applyScopeRestrictions();
217 
218   // create output file
219   std::error_code EC;
220   ToolOutputFile Out(Path, EC, sys::fs::OF_None);
221   if (EC) {
222     std::string ErrMsg = "could not open bitcode file for writing: ";
223     ErrMsg += Path.str() + ": " + EC.message();
224     emitError(ErrMsg);
225     return false;
226   }
227 
228   // write bitcode to it
229   WriteBitcodeToFile(*MergedModule, Out.os(), ShouldEmbedUselists);
230   Out.os().close();
231 
232   if (Out.os().has_error()) {
233     std::string ErrMsg = "could not write bitcode file: ";
234     ErrMsg += Path.str() + ": " + Out.os().error().message();
235     emitError(ErrMsg);
236     Out.os().clear_error();
237     return false;
238   }
239 
240   Out.keep();
241   return true;
242 }
243 
244 bool LTOCodeGenerator::compileOptimizedToFile(const char **Name) {
245   // make unique temp output file to put generated code
246   SmallString<128> Filename;
247 
248   auto AddStream =
249       [&](size_t Task) -> std::unique_ptr<lto::NativeObjectStream> {
250     StringRef Extension(Config.CGFileType == CGFT_AssemblyFile ? "s" : "o");
251 
252     int FD;
253     std::error_code EC =
254         sys::fs::createTemporaryFile("lto-llvm", Extension, FD, Filename);
255     if (EC)
256       emitError(EC.message());
257 
258     return std::make_unique<lto::NativeObjectStream>(
259         std::make_unique<llvm::raw_fd_ostream>(FD, true));
260   };
261 
262   bool genResult = compileOptimized(AddStream, 1);
263 
264   if (!genResult) {
265     sys::fs::remove(Twine(Filename));
266     return false;
267   }
268 
269   // If statistics were requested, save them to the specified file or
270   // print them out after codegen.
271   if (StatsFile)
272     PrintStatisticsJSON(StatsFile->os());
273   else if (AreStatisticsEnabled())
274     PrintStatistics();
275 
276   NativeObjectPath = Filename.c_str();
277   *Name = NativeObjectPath.c_str();
278   return true;
279 }
280 
281 std::unique_ptr<MemoryBuffer>
282 LTOCodeGenerator::compileOptimized() {
283   const char *name;
284   if (!compileOptimizedToFile(&name))
285     return nullptr;
286 
287   // read .o file into memory buffer
288   ErrorOr<std::unique_ptr<MemoryBuffer>> BufferOrErr = MemoryBuffer::getFile(
289       name, /*IsText=*/false, /*RequiresNullTerminator=*/false);
290   if (std::error_code EC = BufferOrErr.getError()) {
291     emitError(EC.message());
292     sys::fs::remove(NativeObjectPath);
293     return nullptr;
294   }
295 
296   // remove temp files
297   sys::fs::remove(NativeObjectPath);
298 
299   return std::move(*BufferOrErr);
300 }
301 
302 bool LTOCodeGenerator::compile_to_file(const char **Name) {
303   if (!optimize())
304     return false;
305 
306   return compileOptimizedToFile(Name);
307 }
308 
309 std::unique_ptr<MemoryBuffer> LTOCodeGenerator::compile() {
310   if (!optimize())
311     return nullptr;
312 
313   return compileOptimized();
314 }
315 
316 bool LTOCodeGenerator::determineTarget() {
317   if (TargetMach)
318     return true;
319 
320   TripleStr = MergedModule->getTargetTriple();
321   if (TripleStr.empty()) {
322     TripleStr = sys::getDefaultTargetTriple();
323     MergedModule->setTargetTriple(TripleStr);
324   }
325   llvm::Triple Triple(TripleStr);
326 
327   // create target machine from info for merged modules
328   std::string ErrMsg;
329   MArch = TargetRegistry::lookupTarget(TripleStr, ErrMsg);
330   if (!MArch) {
331     emitError(ErrMsg);
332     return false;
333   }
334 
335   // Construct LTOModule, hand over ownership of module and target. Use MAttr as
336   // the default set of features.
337   SubtargetFeatures Features(join(Config.MAttrs, ""));
338   Features.getDefaultSubtargetFeatures(Triple);
339   FeatureStr = Features.getString();
340   // Set a default CPU for Darwin triples.
341   if (Config.CPU.empty() && Triple.isOSDarwin()) {
342     if (Triple.getArch() == llvm::Triple::x86_64)
343       Config.CPU = "core2";
344     else if (Triple.getArch() == llvm::Triple::x86)
345       Config.CPU = "yonah";
346     else if (Triple.isArm64e())
347       Config.CPU = "apple-a12";
348     else if (Triple.getArch() == llvm::Triple::aarch64 ||
349              Triple.getArch() == llvm::Triple::aarch64_32)
350       Config.CPU = "cyclone";
351   }
352 
353   TargetMach = createTargetMachine();
354   assert(TargetMach && "Unable to create target machine");
355 
356   return true;
357 }
358 
359 std::unique_ptr<TargetMachine> LTOCodeGenerator::createTargetMachine() {
360   assert(MArch && "MArch is not set!");
361   return std::unique_ptr<TargetMachine>(MArch->createTargetMachine(
362       TripleStr, Config.CPU, FeatureStr, Config.Options, Config.RelocModel,
363       None, Config.CGOptLevel));
364 }
365 
366 // If a linkonce global is present in the MustPreserveSymbols, we need to make
367 // sure we honor this. To force the compiler to not drop it, we add it to the
368 // "llvm.compiler.used" global.
369 void LTOCodeGenerator::preserveDiscardableGVs(
370     Module &TheModule,
371     llvm::function_ref<bool(const GlobalValue &)> mustPreserveGV) {
372   std::vector<GlobalValue *> Used;
373   auto mayPreserveGlobal = [&](GlobalValue &GV) {
374     if (!GV.isDiscardableIfUnused() || GV.isDeclaration() ||
375         !mustPreserveGV(GV))
376       return;
377     if (GV.hasAvailableExternallyLinkage())
378       return emitWarning(
379           (Twine("Linker asked to preserve available_externally global: '") +
380            GV.getName() + "'").str());
381     if (GV.hasInternalLinkage())
382       return emitWarning((Twine("Linker asked to preserve internal global: '") +
383                    GV.getName() + "'").str());
384     Used.push_back(&GV);
385   };
386   for (auto &GV : TheModule)
387     mayPreserveGlobal(GV);
388   for (auto &GV : TheModule.globals())
389     mayPreserveGlobal(GV);
390   for (auto &GV : TheModule.aliases())
391     mayPreserveGlobal(GV);
392 
393   if (Used.empty())
394     return;
395 
396   appendToCompilerUsed(TheModule, Used);
397 }
398 
399 void LTOCodeGenerator::applyScopeRestrictions() {
400   if (ScopeRestrictionsDone)
401     return;
402 
403   // Declare a callback for the internalize pass that will ask for every
404   // candidate GlobalValue if it can be internalized or not.
405   Mangler Mang;
406   SmallString<64> MangledName;
407   auto mustPreserveGV = [&](const GlobalValue &GV) -> bool {
408     // Unnamed globals can't be mangled, but they can't be preserved either.
409     if (!GV.hasName())
410       return false;
411 
412     // Need to mangle the GV as the "MustPreserveSymbols" StringSet is filled
413     // with the linker supplied name, which on Darwin includes a leading
414     // underscore.
415     MangledName.clear();
416     MangledName.reserve(GV.getName().size() + 1);
417     Mang.getNameWithPrefix(MangledName, &GV, /*CannotUsePrivateLabel=*/false);
418     return MustPreserveSymbols.count(MangledName);
419   };
420 
421   // Preserve linkonce value on linker request
422   preserveDiscardableGVs(*MergedModule, mustPreserveGV);
423 
424   if (!ShouldInternalize)
425     return;
426 
427   if (ShouldRestoreGlobalsLinkage) {
428     // Record the linkage type of non-local symbols so they can be restored
429     // prior
430     // to module splitting.
431     auto RecordLinkage = [&](const GlobalValue &GV) {
432       if (!GV.hasAvailableExternallyLinkage() && !GV.hasLocalLinkage() &&
433           GV.hasName())
434         ExternalSymbols.insert(std::make_pair(GV.getName(), GV.getLinkage()));
435     };
436     for (auto &GV : *MergedModule)
437       RecordLinkage(GV);
438     for (auto &GV : MergedModule->globals())
439       RecordLinkage(GV);
440     for (auto &GV : MergedModule->aliases())
441       RecordLinkage(GV);
442   }
443 
444   // Update the llvm.compiler_used globals to force preserving libcalls and
445   // symbols referenced from asm
446   updateCompilerUsed(*MergedModule, *TargetMach, AsmUndefinedRefs);
447 
448   internalizeModule(*MergedModule, mustPreserveGV);
449 
450   ScopeRestrictionsDone = true;
451 }
452 
453 /// Restore original linkage for symbols that may have been internalized
454 void LTOCodeGenerator::restoreLinkageForExternals() {
455   if (!ShouldInternalize || !ShouldRestoreGlobalsLinkage)
456     return;
457 
458   assert(ScopeRestrictionsDone &&
459          "Cannot externalize without internalization!");
460 
461   if (ExternalSymbols.empty())
462     return;
463 
464   auto externalize = [this](GlobalValue &GV) {
465     if (!GV.hasLocalLinkage() || !GV.hasName())
466       return;
467 
468     auto I = ExternalSymbols.find(GV.getName());
469     if (I == ExternalSymbols.end())
470       return;
471 
472     GV.setLinkage(I->second);
473   };
474 
475   llvm::for_each(MergedModule->functions(), externalize);
476   llvm::for_each(MergedModule->globals(), externalize);
477   llvm::for_each(MergedModule->aliases(), externalize);
478 }
479 
480 void LTOCodeGenerator::verifyMergedModuleOnce() {
481   // Only run on the first call.
482   if (HasVerifiedInput)
483     return;
484   HasVerifiedInput = true;
485 
486   bool BrokenDebugInfo = false;
487   if (verifyModule(*MergedModule, &dbgs(), &BrokenDebugInfo))
488     report_fatal_error("Broken module found, compilation aborted!");
489   if (BrokenDebugInfo) {
490     emitWarning("Invalid debug info found, debug info will be stripped");
491     StripDebugInfo(*MergedModule);
492   }
493 }
494 
495 void LTOCodeGenerator::finishOptimizationRemarks() {
496   if (DiagnosticOutputFile) {
497     DiagnosticOutputFile->keep();
498     // FIXME: LTOCodeGenerator dtor is not invoked on Darwin
499     DiagnosticOutputFile->os().flush();
500   }
501 }
502 
503 /// Optimize merged modules using various IPO passes
504 bool LTOCodeGenerator::optimize() {
505   if (!this->determineTarget())
506     return false;
507 
508   auto DiagFileOrErr = lto::setupLLVMOptimizationRemarks(
509       Context, RemarksFilename, RemarksPasses, RemarksFormat,
510       RemarksWithHotness, RemarksHotnessThreshold);
511   if (!DiagFileOrErr) {
512     errs() << "Error: " << toString(DiagFileOrErr.takeError()) << "\n";
513     report_fatal_error("Can't get an output file for the remarks");
514   }
515   DiagnosticOutputFile = std::move(*DiagFileOrErr);
516 
517   // Setup output file to emit statistics.
518   auto StatsFileOrErr = lto::setupStatsFile(LTOStatsFile);
519   if (!StatsFileOrErr) {
520     errs() << "Error: " << toString(StatsFileOrErr.takeError()) << "\n";
521     report_fatal_error("Can't get an output file for the statistics");
522   }
523   StatsFile = std::move(StatsFileOrErr.get());
524 
525   // Currently there is no support for enabling whole program visibility via a
526   // linker option in the old LTO API, but this call allows it to be specified
527   // via the internal option. Must be done before WPD invoked via the optimizer
528   // pipeline run below.
529   updateVCallVisibilityInModule(*MergedModule,
530                                 /* WholeProgramVisibilityEnabledInLTO */ false,
531                                 // FIXME: This needs linker information via a
532                                 // TBD new interface.
533                                 /* DynamicExportSymbols */ {});
534 
535   // We always run the verifier once on the merged module, the `DisableVerify`
536   // parameter only applies to subsequent verify.
537   verifyMergedModuleOnce();
538 
539   // Mark which symbols can not be internalized
540   this->applyScopeRestrictions();
541 
542   // Write LTOPostLink flag for passes that require all the modules.
543   MergedModule->addModuleFlag(Module::Error, "LTOPostLink", 1);
544 
545   // Add an appropriate DataLayout instance for this module...
546   MergedModule->setDataLayout(TargetMach->createDataLayout());
547 
548   ModuleSummaryIndex CombinedIndex(false);
549   TargetMach = createTargetMachine();
550   if (!opt(Config, TargetMach.get(), 0, *MergedModule, /*IsThinLTO=*/false,
551            /*ExportSummary=*/&CombinedIndex, /*ImportSummary=*/nullptr,
552            /*CmdArgs*/ std::vector<uint8_t>())) {
553     emitError("LTO middle-end optimizations failed");
554     return false;
555   }
556 
557   return true;
558 }
559 
560 bool LTOCodeGenerator::compileOptimized(lto::AddStreamFn AddStream,
561                                         unsigned ParallelismLevel) {
562   if (!this->determineTarget())
563     return false;
564 
565   // We always run the verifier once on the merged module.  If it has already
566   // been called in optimize(), this call will return early.
567   verifyMergedModuleOnce();
568 
569   // Re-externalize globals that may have been internalized to increase scope
570   // for splitting
571   restoreLinkageForExternals();
572 
573   ModuleSummaryIndex CombinedIndex(false);
574 
575   Config.CodeGenOnly = true;
576   Error Err = backend(Config, AddStream, ParallelismLevel, *MergedModule,
577                       CombinedIndex);
578   assert(!Err && "unexpected code-generation failure");
579   (void)Err;
580 
581   // If statistics were requested, save them to the specified file or
582   // print them out after codegen.
583   if (StatsFile)
584     PrintStatisticsJSON(StatsFile->os());
585   else if (AreStatisticsEnabled())
586     PrintStatistics();
587 
588   reportAndResetTimings();
589 
590   finishOptimizationRemarks();
591 
592   return true;
593 }
594 
595 void LTOCodeGenerator::setCodeGenDebugOptions(ArrayRef<StringRef> Options) {
596   for (StringRef Option : Options)
597     CodegenOptions.push_back(Option.str());
598 }
599 
600 void LTOCodeGenerator::parseCodeGenDebugOptions() {
601   if (!CodegenOptions.empty())
602     llvm::parseCommandLineOptions(CodegenOptions);
603 }
604 
605 void llvm::parseCommandLineOptions(std::vector<std::string> &Options) {
606   if (!Options.empty()) {
607     // ParseCommandLineOptions() expects argv[0] to be program name.
608     std::vector<const char *> CodegenArgv(1, "libLLVMLTO");
609     for (std::string &Arg : Options)
610       CodegenArgv.push_back(Arg.c_str());
611     cl::ParseCommandLineOptions(CodegenArgv.size(), CodegenArgv.data());
612   }
613 }
614 
615 void LTOCodeGenerator::DiagnosticHandler(const DiagnosticInfo &DI) {
616   // Map the LLVM internal diagnostic severity to the LTO diagnostic severity.
617   lto_codegen_diagnostic_severity_t Severity;
618   switch (DI.getSeverity()) {
619   case DS_Error:
620     Severity = LTO_DS_ERROR;
621     break;
622   case DS_Warning:
623     Severity = LTO_DS_WARNING;
624     break;
625   case DS_Remark:
626     Severity = LTO_DS_REMARK;
627     break;
628   case DS_Note:
629     Severity = LTO_DS_NOTE;
630     break;
631   }
632   // Create the string that will be reported to the external diagnostic handler.
633   std::string MsgStorage;
634   raw_string_ostream Stream(MsgStorage);
635   DiagnosticPrinterRawOStream DP(Stream);
636   DI.print(DP);
637   Stream.flush();
638 
639   // If this method has been called it means someone has set up an external
640   // diagnostic handler. Assert on that.
641   assert(DiagHandler && "Invalid diagnostic handler");
642   (*DiagHandler)(Severity, MsgStorage.c_str(), DiagContext);
643 }
644 
645 namespace {
646 struct LTODiagnosticHandler : public DiagnosticHandler {
647   LTOCodeGenerator *CodeGenerator;
648   LTODiagnosticHandler(LTOCodeGenerator *CodeGenPtr)
649       : CodeGenerator(CodeGenPtr) {}
650   bool handleDiagnostics(const DiagnosticInfo &DI) override {
651     CodeGenerator->DiagnosticHandler(DI);
652     return true;
653   }
654 };
655 }
656 
657 void
658 LTOCodeGenerator::setDiagnosticHandler(lto_diagnostic_handler_t DiagHandler,
659                                        void *Ctxt) {
660   this->DiagHandler = DiagHandler;
661   this->DiagContext = Ctxt;
662   if (!DiagHandler)
663     return Context.setDiagnosticHandler(nullptr);
664   // Register the LTOCodeGenerator stub in the LLVMContext to forward the
665   // diagnostic to the external DiagHandler.
666   Context.setDiagnosticHandler(std::make_unique<LTODiagnosticHandler>(this),
667                                true);
668 }
669 
670 namespace {
671 class LTODiagnosticInfo : public DiagnosticInfo {
672   const Twine &Msg;
673 public:
674   LTODiagnosticInfo(const Twine &DiagMsg, DiagnosticSeverity Severity=DS_Error)
675       : DiagnosticInfo(DK_Linker, Severity), Msg(DiagMsg) {}
676   void print(DiagnosticPrinter &DP) const override { DP << Msg; }
677 };
678 }
679 
680 void LTOCodeGenerator::emitError(const std::string &ErrMsg) {
681   if (DiagHandler)
682     (*DiagHandler)(LTO_DS_ERROR, ErrMsg.c_str(), DiagContext);
683   else
684     Context.diagnose(LTODiagnosticInfo(ErrMsg));
685 }
686 
687 void LTOCodeGenerator::emitWarning(const std::string &ErrMsg) {
688   if (DiagHandler)
689     (*DiagHandler)(LTO_DS_WARNING, ErrMsg.c_str(), DiagContext);
690   else
691     Context.diagnose(LTODiagnosticInfo(ErrMsg, DS_Warning));
692 }
693