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/LegacyPassManager.h"
33 #include "llvm/IR/Mangler.h"
34 #include "llvm/IR/Module.h"
35 #include "llvm/IR/PassTimingInfo.h"
36 #include "llvm/IR/RemarkStreamer.h"
37 #include "llvm/IR/Verifier.h"
38 #include "llvm/InitializePasses.h"
39 #include "llvm/LTO/LTO.h"
40 #include "llvm/LTO/legacy/LTOModule.h"
41 #include "llvm/LTO/legacy/UpdateCompilerUsed.h"
42 #include "llvm/Linker/Linker.h"
43 #include "llvm/MC/MCAsmInfo.h"
44 #include "llvm/MC/MCContext.h"
45 #include "llvm/MC/SubtargetFeature.h"
46 #include "llvm/Support/CommandLine.h"
47 #include "llvm/Support/FileSystem.h"
48 #include "llvm/Support/Host.h"
49 #include "llvm/Support/MemoryBuffer.h"
50 #include "llvm/Support/Signals.h"
51 #include "llvm/Support/TargetRegistry.h"
52 #include "llvm/Support/TargetSelect.h"
53 #include "llvm/Support/ToolOutputFile.h"
54 #include "llvm/Support/YAMLTraits.h"
55 #include "llvm/Support/raw_ostream.h"
56 #include "llvm/Target/TargetOptions.h"
57 #include "llvm/Transforms/IPO.h"
58 #include "llvm/Transforms/IPO/Internalize.h"
59 #include "llvm/Transforms/IPO/PassManagerBuilder.h"
60 #include "llvm/Transforms/ObjCARC.h"
61 #include "llvm/Transforms/Utils/ModuleUtils.h"
62 #include <system_error>
63 using namespace llvm;
64 
65 const char* LTOCodeGenerator::getVersionString() {
66 #ifdef LLVM_VERSION_INFO
67   return PACKAGE_NAME " version " PACKAGE_VERSION ", " LLVM_VERSION_INFO;
68 #else
69   return PACKAGE_NAME " version " PACKAGE_VERSION;
70 #endif
71 }
72 
73 namespace llvm {
74 cl::opt<bool> LTODiscardValueNames(
75     "lto-discard-value-names",
76     cl::desc("Strip names from Value during LTO (other than GlobalValue)."),
77 #ifdef NDEBUG
78     cl::init(true),
79 #else
80     cl::init(false),
81 #endif
82     cl::Hidden);
83 
84 cl::opt<bool> RemarksWithHotness(
85     "lto-pass-remarks-with-hotness",
86     cl::desc("With PGO, include profile count in optimization remarks"),
87     cl::Hidden);
88 
89 cl::opt<std::string>
90     RemarksFilename("lto-pass-remarks-output",
91                     cl::desc("Output filename for pass remarks"),
92                     cl::value_desc("filename"));
93 
94 cl::opt<std::string>
95     RemarksPasses("lto-pass-remarks-filter",
96                   cl::desc("Only record optimization remarks from passes whose "
97                            "names match the given regular expression"),
98                   cl::value_desc("regex"));
99 
100 cl::opt<std::string> RemarksFormat(
101     "lto-pass-remarks-format",
102     cl::desc("The format used for serializing remarks (default: YAML)"),
103     cl::value_desc("format"), cl::init("yaml"));
104 
105 cl::opt<std::string> LTOStatsFile(
106     "lto-stats-file",
107     cl::desc("Save statistics to the specified file"),
108     cl::Hidden);
109 }
110 
111 LTOCodeGenerator::LTOCodeGenerator(LLVMContext &Context)
112     : Context(Context), MergedModule(new Module("ld-temp.o", Context)),
113       TheLinker(new Linker(*MergedModule)) {
114   Context.setDiscardValueNames(LTODiscardValueNames);
115   Context.enableDebugTypeODRUniquing();
116   initializeLTOPasses();
117 }
118 
119 LTOCodeGenerator::~LTOCodeGenerator() {}
120 
121 // Initialize LTO passes. Please keep this function in sync with
122 // PassManagerBuilder::populateLTOPassManager(), and make sure all LTO
123 // passes are initialized.
124 void LTOCodeGenerator::initializeLTOPasses() {
125   PassRegistry &R = *PassRegistry::getPassRegistry();
126 
127   initializeInternalizeLegacyPassPass(R);
128   initializeIPSCCPLegacyPassPass(R);
129   initializeGlobalOptLegacyPassPass(R);
130   initializeConstantMergeLegacyPassPass(R);
131   initializeDAHPass(R);
132   initializeInstructionCombiningPassPass(R);
133   initializeSimpleInlinerPass(R);
134   initializePruneEHPass(R);
135   initializeGlobalDCELegacyPassPass(R);
136   initializeArgPromotionPass(R);
137   initializeJumpThreadingPass(R);
138   initializeSROALegacyPassPass(R);
139   initializeAttributorLegacyPassPass(R);
140   initializePostOrderFunctionAttrsLegacyPassPass(R);
141   initializeReversePostOrderFunctionAttrsLegacyPassPass(R);
142   initializeGlobalsAAWrapperPassPass(R);
143   initializeLegacyLICMPassPass(R);
144   initializeMergedLoadStoreMotionLegacyPassPass(R);
145   initializeGVNLegacyPassPass(R);
146   initializeMemCpyOptLegacyPassPass(R);
147   initializeDCELegacyPassPass(R);
148   initializeCFGSimplifyPassPass(R);
149 }
150 
151 void LTOCodeGenerator::setAsmUndefinedRefs(LTOModule *Mod) {
152   const std::vector<StringRef> &undefs = Mod->getAsmUndefinedRefs();
153   for (int i = 0, e = undefs.size(); i != e; ++i)
154     AsmUndefinedRefs.insert(undefs[i]);
155 }
156 
157 bool LTOCodeGenerator::addModule(LTOModule *Mod) {
158   assert(&Mod->getModule().getContext() == &Context &&
159          "Expected module in same context");
160 
161   bool ret = TheLinker->linkInModule(Mod->takeModule());
162   setAsmUndefinedRefs(Mod);
163 
164   // We've just changed the input, so let's make sure we verify it.
165   HasVerifiedInput = false;
166 
167   return !ret;
168 }
169 
170 void LTOCodeGenerator::setModule(std::unique_ptr<LTOModule> Mod) {
171   assert(&Mod->getModule().getContext() == &Context &&
172          "Expected module in same context");
173 
174   AsmUndefinedRefs.clear();
175 
176   MergedModule = Mod->takeModule();
177   TheLinker = std::make_unique<Linker>(*MergedModule);
178   setAsmUndefinedRefs(&*Mod);
179 
180   // We've just changed the input, so let's make sure we verify it.
181   HasVerifiedInput = false;
182 }
183 
184 void LTOCodeGenerator::setTargetOptions(const TargetOptions &Options) {
185   this->Options = Options;
186 }
187 
188 void LTOCodeGenerator::setDebugInfo(lto_debug_model Debug) {
189   switch (Debug) {
190   case LTO_DEBUG_MODEL_NONE:
191     EmitDwarfDebugInfo = false;
192     return;
193 
194   case LTO_DEBUG_MODEL_DWARF:
195     EmitDwarfDebugInfo = true;
196     return;
197   }
198   llvm_unreachable("Unknown debug format!");
199 }
200 
201 void LTOCodeGenerator::setOptLevel(unsigned Level) {
202   OptLevel = Level;
203   switch (OptLevel) {
204   case 0:
205     CGOptLevel = CodeGenOpt::None;
206     return;
207   case 1:
208     CGOptLevel = CodeGenOpt::Less;
209     return;
210   case 2:
211     CGOptLevel = CodeGenOpt::Default;
212     return;
213   case 3:
214     CGOptLevel = CodeGenOpt::Aggressive;
215     return;
216   }
217   llvm_unreachable("Unknown optimization level!");
218 }
219 
220 bool LTOCodeGenerator::writeMergedModules(StringRef Path) {
221   if (!determineTarget())
222     return false;
223 
224   // We always run the verifier once on the merged module.
225   verifyMergedModuleOnce();
226 
227   // mark which symbols can not be internalized
228   applyScopeRestrictions();
229 
230   // create output file
231   std::error_code EC;
232   ToolOutputFile Out(Path, EC, sys::fs::OF_None);
233   if (EC) {
234     std::string ErrMsg = "could not open bitcode file for writing: ";
235     ErrMsg += Path.str() + ": " + EC.message();
236     emitError(ErrMsg);
237     return false;
238   }
239 
240   // write bitcode to it
241   WriteBitcodeToFile(*MergedModule, Out.os(), ShouldEmbedUselists);
242   Out.os().close();
243 
244   if (Out.os().has_error()) {
245     std::string ErrMsg = "could not write bitcode file: ";
246     ErrMsg += Path.str() + ": " + Out.os().error().message();
247     emitError(ErrMsg);
248     Out.os().clear_error();
249     return false;
250   }
251 
252   Out.keep();
253   return true;
254 }
255 
256 bool LTOCodeGenerator::compileOptimizedToFile(const char **Name) {
257   // make unique temp output file to put generated code
258   SmallString<128> Filename;
259   int FD;
260 
261   StringRef Extension
262       (FileType == TargetMachine::CGFT_AssemblyFile ? "s" : "o");
263 
264   std::error_code EC =
265       sys::fs::createTemporaryFile("lto-llvm", Extension, FD, Filename);
266   if (EC) {
267     emitError(EC.message());
268     return false;
269   }
270 
271   // generate object file
272   ToolOutputFile objFile(Filename, FD);
273 
274   bool genResult = compileOptimized(&objFile.os());
275   objFile.os().close();
276   if (objFile.os().has_error()) {
277     emitError((Twine("could not write object file: ") + Filename + ": " +
278                objFile.os().error().message())
279                   .str());
280     objFile.os().clear_error();
281     sys::fs::remove(Twine(Filename));
282     return false;
283   }
284 
285   objFile.keep();
286   if (!genResult) {
287     sys::fs::remove(Twine(Filename));
288     return false;
289   }
290 
291   NativeObjectPath = Filename.c_str();
292   *Name = NativeObjectPath.c_str();
293   return true;
294 }
295 
296 std::unique_ptr<MemoryBuffer>
297 LTOCodeGenerator::compileOptimized() {
298   const char *name;
299   if (!compileOptimizedToFile(&name))
300     return nullptr;
301 
302   // read .o file into memory buffer
303   ErrorOr<std::unique_ptr<MemoryBuffer>> BufferOrErr =
304       MemoryBuffer::getFile(name, -1, false);
305   if (std::error_code EC = BufferOrErr.getError()) {
306     emitError(EC.message());
307     sys::fs::remove(NativeObjectPath);
308     return nullptr;
309   }
310 
311   // remove temp files
312   sys::fs::remove(NativeObjectPath);
313 
314   return std::move(*BufferOrErr);
315 }
316 
317 bool LTOCodeGenerator::compile_to_file(const char **Name, bool DisableVerify,
318                                        bool DisableInline,
319                                        bool DisableGVNLoadPRE,
320                                        bool DisableVectorization) {
321   if (!optimize(DisableVerify, DisableInline, DisableGVNLoadPRE,
322                 DisableVectorization))
323     return false;
324 
325   return compileOptimizedToFile(Name);
326 }
327 
328 std::unique_ptr<MemoryBuffer>
329 LTOCodeGenerator::compile(bool DisableVerify, bool DisableInline,
330                           bool DisableGVNLoadPRE, bool DisableVectorization) {
331   if (!optimize(DisableVerify, DisableInline, DisableGVNLoadPRE,
332                 DisableVectorization))
333     return nullptr;
334 
335   return compileOptimized();
336 }
337 
338 bool LTOCodeGenerator::determineTarget() {
339   if (TargetMach)
340     return true;
341 
342   TripleStr = MergedModule->getTargetTriple();
343   if (TripleStr.empty()) {
344     TripleStr = sys::getDefaultTargetTriple();
345     MergedModule->setTargetTriple(TripleStr);
346   }
347   llvm::Triple Triple(TripleStr);
348 
349   // create target machine from info for merged modules
350   std::string ErrMsg;
351   MArch = TargetRegistry::lookupTarget(TripleStr, ErrMsg);
352   if (!MArch) {
353     emitError(ErrMsg);
354     return false;
355   }
356 
357   // Construct LTOModule, hand over ownership of module and target. Use MAttr as
358   // the default set of features.
359   SubtargetFeatures Features(MAttr);
360   Features.getDefaultSubtargetFeatures(Triple);
361   FeatureStr = Features.getString();
362   // Set a default CPU for Darwin triples.
363   if (MCpu.empty() && Triple.isOSDarwin()) {
364     if (Triple.getArch() == llvm::Triple::x86_64)
365       MCpu = "core2";
366     else if (Triple.getArch() == llvm::Triple::x86)
367       MCpu = "yonah";
368     else if (Triple.getArch() == llvm::Triple::aarch64 ||
369              Triple.getArch() == llvm::Triple::aarch64_32)
370       MCpu = "cyclone";
371   }
372 
373   TargetMach = createTargetMachine();
374   return true;
375 }
376 
377 std::unique_ptr<TargetMachine> LTOCodeGenerator::createTargetMachine() {
378   return std::unique_ptr<TargetMachine>(MArch->createTargetMachine(
379       TripleStr, MCpu, FeatureStr, Options, RelocModel, None, CGOptLevel));
380 }
381 
382 // If a linkonce global is present in the MustPreserveSymbols, we need to make
383 // sure we honor this. To force the compiler to not drop it, we add it to the
384 // "llvm.compiler.used" global.
385 void LTOCodeGenerator::preserveDiscardableGVs(
386     Module &TheModule,
387     llvm::function_ref<bool(const GlobalValue &)> mustPreserveGV) {
388   std::vector<GlobalValue *> Used;
389   auto mayPreserveGlobal = [&](GlobalValue &GV) {
390     if (!GV.isDiscardableIfUnused() || GV.isDeclaration() ||
391         !mustPreserveGV(GV))
392       return;
393     if (GV.hasAvailableExternallyLinkage())
394       return emitWarning(
395           (Twine("Linker asked to preserve available_externally global: '") +
396            GV.getName() + "'").str());
397     if (GV.hasInternalLinkage())
398       return emitWarning((Twine("Linker asked to preserve internal global: '") +
399                    GV.getName() + "'").str());
400     Used.push_back(&GV);
401   };
402   for (auto &GV : TheModule)
403     mayPreserveGlobal(GV);
404   for (auto &GV : TheModule.globals())
405     mayPreserveGlobal(GV);
406   for (auto &GV : TheModule.aliases())
407     mayPreserveGlobal(GV);
408 
409   if (Used.empty())
410     return;
411 
412   appendToCompilerUsed(TheModule, Used);
413 }
414 
415 void LTOCodeGenerator::applyScopeRestrictions() {
416   if (ScopeRestrictionsDone)
417     return;
418 
419   // Declare a callback for the internalize pass that will ask for every
420   // candidate GlobalValue if it can be internalized or not.
421   Mangler Mang;
422   SmallString<64> MangledName;
423   auto mustPreserveGV = [&](const GlobalValue &GV) -> bool {
424     // Unnamed globals can't be mangled, but they can't be preserved either.
425     if (!GV.hasName())
426       return false;
427 
428     // Need to mangle the GV as the "MustPreserveSymbols" StringSet is filled
429     // with the linker supplied name, which on Darwin includes a leading
430     // underscore.
431     MangledName.clear();
432     MangledName.reserve(GV.getName().size() + 1);
433     Mang.getNameWithPrefix(MangledName, &GV, /*CannotUsePrivateLabel=*/false);
434     return MustPreserveSymbols.count(MangledName);
435   };
436 
437   // Preserve linkonce value on linker request
438   preserveDiscardableGVs(*MergedModule, mustPreserveGV);
439 
440   if (!ShouldInternalize)
441     return;
442 
443   if (ShouldRestoreGlobalsLinkage) {
444     // Record the linkage type of non-local symbols so they can be restored
445     // prior
446     // to module splitting.
447     auto RecordLinkage = [&](const GlobalValue &GV) {
448       if (!GV.hasAvailableExternallyLinkage() && !GV.hasLocalLinkage() &&
449           GV.hasName())
450         ExternalSymbols.insert(std::make_pair(GV.getName(), GV.getLinkage()));
451     };
452     for (auto &GV : *MergedModule)
453       RecordLinkage(GV);
454     for (auto &GV : MergedModule->globals())
455       RecordLinkage(GV);
456     for (auto &GV : MergedModule->aliases())
457       RecordLinkage(GV);
458   }
459 
460   // Update the llvm.compiler_used globals to force preserving libcalls and
461   // symbols referenced from asm
462   updateCompilerUsed(*MergedModule, *TargetMach, AsmUndefinedRefs);
463 
464   internalizeModule(*MergedModule, mustPreserveGV);
465 
466   ScopeRestrictionsDone = true;
467 }
468 
469 /// Restore original linkage for symbols that may have been internalized
470 void LTOCodeGenerator::restoreLinkageForExternals() {
471   if (!ShouldInternalize || !ShouldRestoreGlobalsLinkage)
472     return;
473 
474   assert(ScopeRestrictionsDone &&
475          "Cannot externalize without internalization!");
476 
477   if (ExternalSymbols.empty())
478     return;
479 
480   auto externalize = [this](GlobalValue &GV) {
481     if (!GV.hasLocalLinkage() || !GV.hasName())
482       return;
483 
484     auto I = ExternalSymbols.find(GV.getName());
485     if (I == ExternalSymbols.end())
486       return;
487 
488     GV.setLinkage(I->second);
489   };
490 
491   llvm::for_each(MergedModule->functions(), externalize);
492   llvm::for_each(MergedModule->globals(), externalize);
493   llvm::for_each(MergedModule->aliases(), externalize);
494 }
495 
496 void LTOCodeGenerator::verifyMergedModuleOnce() {
497   // Only run on the first call.
498   if (HasVerifiedInput)
499     return;
500   HasVerifiedInput = true;
501 
502   bool BrokenDebugInfo = false;
503   if (verifyModule(*MergedModule, &dbgs(), &BrokenDebugInfo))
504     report_fatal_error("Broken module found, compilation aborted!");
505   if (BrokenDebugInfo) {
506     emitWarning("Invalid debug info found, debug info will be stripped");
507     StripDebugInfo(*MergedModule);
508   }
509 }
510 
511 void LTOCodeGenerator::finishOptimizationRemarks() {
512   if (DiagnosticOutputFile) {
513     DiagnosticOutputFile->keep();
514     // FIXME: LTOCodeGenerator dtor is not invoked on Darwin
515     DiagnosticOutputFile->os().flush();
516   }
517 }
518 
519 /// Optimize merged modules using various IPO passes
520 bool LTOCodeGenerator::optimize(bool DisableVerify, bool DisableInline,
521                                 bool DisableGVNLoadPRE,
522                                 bool DisableVectorization) {
523   if (!this->determineTarget())
524     return false;
525 
526   auto DiagFileOrErr =
527       lto::setupOptimizationRemarks(Context, RemarksFilename, RemarksPasses,
528                                     RemarksFormat, RemarksWithHotness);
529   if (!DiagFileOrErr) {
530     errs() << "Error: " << toString(DiagFileOrErr.takeError()) << "\n";
531     report_fatal_error("Can't get an output file for the remarks");
532   }
533   DiagnosticOutputFile = std::move(*DiagFileOrErr);
534 
535   // Setup output file to emit statistics.
536   auto StatsFileOrErr = lto::setupStatsFile(LTOStatsFile);
537   if (!StatsFileOrErr) {
538     errs() << "Error: " << toString(StatsFileOrErr.takeError()) << "\n";
539     report_fatal_error("Can't get an output file for the statistics");
540   }
541   StatsFile = std::move(StatsFileOrErr.get());
542 
543   // We always run the verifier once on the merged module, the `DisableVerify`
544   // parameter only applies to subsequent verify.
545   verifyMergedModuleOnce();
546 
547   // Mark which symbols can not be internalized
548   this->applyScopeRestrictions();
549 
550   // Instantiate the pass manager to organize the passes.
551   legacy::PassManager passes;
552 
553   // Add an appropriate DataLayout instance for this module...
554   MergedModule->setDataLayout(TargetMach->createDataLayout());
555 
556   passes.add(
557       createTargetTransformInfoWrapperPass(TargetMach->getTargetIRAnalysis()));
558 
559   Triple TargetTriple(TargetMach->getTargetTriple());
560   PassManagerBuilder PMB;
561   PMB.DisableGVNLoadPRE = DisableGVNLoadPRE;
562   PMB.LoopVectorize = !DisableVectorization;
563   PMB.SLPVectorize = !DisableVectorization;
564   if (!DisableInline)
565     PMB.Inliner = createFunctionInliningPass();
566   PMB.LibraryInfo = new TargetLibraryInfoImpl(TargetTriple);
567   if (Freestanding)
568     PMB.LibraryInfo->disableAllFunctions();
569   PMB.OptLevel = OptLevel;
570   PMB.VerifyInput = !DisableVerify;
571   PMB.VerifyOutput = !DisableVerify;
572 
573   PMB.populateLTOPassManager(passes);
574 
575   // Run our queue of passes all at once now, efficiently.
576   passes.run(*MergedModule);
577 
578   return true;
579 }
580 
581 bool LTOCodeGenerator::compileOptimized(ArrayRef<raw_pwrite_stream *> Out) {
582   if (!this->determineTarget())
583     return false;
584 
585   // We always run the verifier once on the merged module.  If it has already
586   // been called in optimize(), this call will return early.
587   verifyMergedModuleOnce();
588 
589   legacy::PassManager preCodeGenPasses;
590 
591   // If the bitcode files contain ARC code and were compiled with optimization,
592   // the ObjCARCContractPass must be run, so do it unconditionally here.
593   preCodeGenPasses.add(createObjCARCContractPass());
594   preCodeGenPasses.run(*MergedModule);
595 
596   // Re-externalize globals that may have been internalized to increase scope
597   // for splitting
598   restoreLinkageForExternals();
599 
600   // Do code generation. We need to preserve the module in case the client calls
601   // writeMergedModules() after compilation, but we only need to allow this at
602   // parallelism level 1. This is achieved by having splitCodeGen return the
603   // original module at parallelism level 1 which we then assign back to
604   // MergedModule.
605   MergedModule = splitCodeGen(std::move(MergedModule), Out, {},
606                               [&]() { return createTargetMachine(); }, FileType,
607                               ShouldRestoreGlobalsLinkage);
608 
609   // If statistics were requested, save them to the specified file or
610   // print them out after codegen.
611   if (StatsFile)
612     PrintStatisticsJSON(StatsFile->os());
613   else if (AreStatisticsEnabled())
614     PrintStatistics();
615 
616   reportAndResetTimings();
617 
618   finishOptimizationRemarks();
619 
620   return true;
621 }
622 
623 /// setCodeGenDebugOptions - Set codegen debugging options to aid in debugging
624 /// LTO problems.
625 void LTOCodeGenerator::setCodeGenDebugOptions(StringRef Options) {
626   for (std::pair<StringRef, StringRef> o = getToken(Options); !o.first.empty();
627        o = getToken(o.second))
628     CodegenOptions.push_back(o.first);
629 }
630 
631 void LTOCodeGenerator::parseCodeGenDebugOptions() {
632   // if options were requested, set them
633   if (!CodegenOptions.empty()) {
634     // ParseCommandLineOptions() expects argv[0] to be program name.
635     std::vector<const char *> CodegenArgv(1, "libLLVMLTO");
636     for (std::string &Arg : CodegenOptions)
637       CodegenArgv.push_back(Arg.c_str());
638     cl::ParseCommandLineOptions(CodegenArgv.size(), CodegenArgv.data());
639   }
640 }
641 
642 
643 void LTOCodeGenerator::DiagnosticHandler(const DiagnosticInfo &DI) {
644   // Map the LLVM internal diagnostic severity to the LTO diagnostic severity.
645   lto_codegen_diagnostic_severity_t Severity;
646   switch (DI.getSeverity()) {
647   case DS_Error:
648     Severity = LTO_DS_ERROR;
649     break;
650   case DS_Warning:
651     Severity = LTO_DS_WARNING;
652     break;
653   case DS_Remark:
654     Severity = LTO_DS_REMARK;
655     break;
656   case DS_Note:
657     Severity = LTO_DS_NOTE;
658     break;
659   }
660   // Create the string that will be reported to the external diagnostic handler.
661   std::string MsgStorage;
662   raw_string_ostream Stream(MsgStorage);
663   DiagnosticPrinterRawOStream DP(Stream);
664   DI.print(DP);
665   Stream.flush();
666 
667   // If this method has been called it means someone has set up an external
668   // diagnostic handler. Assert on that.
669   assert(DiagHandler && "Invalid diagnostic handler");
670   (*DiagHandler)(Severity, MsgStorage.c_str(), DiagContext);
671 }
672 
673 namespace {
674 struct LTODiagnosticHandler : public DiagnosticHandler {
675   LTOCodeGenerator *CodeGenerator;
676   LTODiagnosticHandler(LTOCodeGenerator *CodeGenPtr)
677       : CodeGenerator(CodeGenPtr) {}
678   bool handleDiagnostics(const DiagnosticInfo &DI) override {
679     CodeGenerator->DiagnosticHandler(DI);
680     return true;
681   }
682 };
683 }
684 
685 void
686 LTOCodeGenerator::setDiagnosticHandler(lto_diagnostic_handler_t DiagHandler,
687                                        void *Ctxt) {
688   this->DiagHandler = DiagHandler;
689   this->DiagContext = Ctxt;
690   if (!DiagHandler)
691     return Context.setDiagnosticHandler(nullptr);
692   // Register the LTOCodeGenerator stub in the LLVMContext to forward the
693   // diagnostic to the external DiagHandler.
694   Context.setDiagnosticHandler(std::make_unique<LTODiagnosticHandler>(this),
695                                true);
696 }
697 
698 namespace {
699 class LTODiagnosticInfo : public DiagnosticInfo {
700   const Twine &Msg;
701 public:
702   LTODiagnosticInfo(const Twine &DiagMsg, DiagnosticSeverity Severity=DS_Error)
703       : DiagnosticInfo(DK_Linker, Severity), Msg(DiagMsg) {}
704   void print(DiagnosticPrinter &DP) const override { DP << Msg; }
705 };
706 }
707 
708 void LTOCodeGenerator::emitError(const std::string &ErrMsg) {
709   if (DiagHandler)
710     (*DiagHandler)(LTO_DS_ERROR, ErrMsg.c_str(), DiagContext);
711   else
712     Context.diagnose(LTODiagnosticInfo(ErrMsg));
713 }
714 
715 void LTOCodeGenerator::emitWarning(const std::string &ErrMsg) {
716   if (DiagHandler)
717     (*DiagHandler)(LTO_DS_WARNING, ErrMsg.c_str(), DiagContext);
718   else
719     Context.diagnose(LTODiagnosticInfo(ErrMsg, DS_Warning));
720 }
721