1 //===-LTOCodeGenerator.cpp - LLVM Link Time Optimizer ---------------------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements the Link Time Optimization library. This library is
11 // intended to be used by linker to optimize code at link time.
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #include "llvm/LTO/LTOCodeGenerator.h"
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/ReaderWriter.h"
22 #include "llvm/CodeGen/ParallelCG.h"
23 #include "llvm/CodeGen/RuntimeLibcalls.h"
24 #include "llvm/Config/config.h"
25 #include "llvm/IR/Constants.h"
26 #include "llvm/IR/DataLayout.h"
27 #include "llvm/IR/DerivedTypes.h"
28 #include "llvm/IR/DiagnosticInfo.h"
29 #include "llvm/IR/DiagnosticPrinter.h"
30 #include "llvm/IR/LLVMContext.h"
31 #include "llvm/IR/LegacyPassManager.h"
32 #include "llvm/IR/Mangler.h"
33 #include "llvm/IR/Module.h"
34 #include "llvm/IR/Verifier.h"
35 #include "llvm/InitializePasses.h"
36 #include "llvm/LTO/LTOModule.h"
37 #include "llvm/Linker/Linker.h"
38 #include "llvm/MC/MCAsmInfo.h"
39 #include "llvm/MC/MCContext.h"
40 #include "llvm/MC/SubtargetFeature.h"
41 #include "llvm/Support/CommandLine.h"
42 #include "llvm/Support/FileSystem.h"
43 #include "llvm/Support/Host.h"
44 #include "llvm/Support/MemoryBuffer.h"
45 #include "llvm/Support/Signals.h"
46 #include "llvm/Support/TargetRegistry.h"
47 #include "llvm/Support/TargetSelect.h"
48 #include "llvm/Support/ToolOutputFile.h"
49 #include "llvm/Support/raw_ostream.h"
50 #include "llvm/Target/TargetLowering.h"
51 #include "llvm/Target/TargetOptions.h"
52 #include "llvm/Target/TargetRegisterInfo.h"
53 #include "llvm/Target/TargetSubtargetInfo.h"
54 #include "llvm/Transforms/IPO.h"
55 #include "llvm/Transforms/IPO/PassManagerBuilder.h"
56 #include "llvm/Transforms/ObjCARC.h"
57 #include <system_error>
58 using namespace llvm;
59 
60 const char* LTOCodeGenerator::getVersionString() {
61 #ifdef LLVM_VERSION_INFO
62   return PACKAGE_NAME " version " PACKAGE_VERSION ", " LLVM_VERSION_INFO;
63 #else
64   return PACKAGE_NAME " version " PACKAGE_VERSION;
65 #endif
66 }
67 
68 LTOCodeGenerator::LTOCodeGenerator(LLVMContext &Context)
69     : Context(Context), MergedModule(new Module("ld-temp.o", Context)),
70       TheLinker(new Linker(*MergedModule)) {
71   initializeLTOPasses();
72 }
73 
74 LTOCodeGenerator::~LTOCodeGenerator() {}
75 
76 // Initialize LTO passes. Please keep this function in sync with
77 // PassManagerBuilder::populateLTOPassManager(), and make sure all LTO
78 // passes are initialized.
79 void LTOCodeGenerator::initializeLTOPasses() {
80   PassRegistry &R = *PassRegistry::getPassRegistry();
81 
82   initializeInternalizePassPass(R);
83   initializeIPSCCPPass(R);
84   initializeGlobalOptPass(R);
85   initializeConstantMergePass(R);
86   initializeDAHPass(R);
87   initializeInstructionCombiningPassPass(R);
88   initializeSimpleInlinerPass(R);
89   initializePruneEHPass(R);
90   initializeGlobalDCEPass(R);
91   initializeArgPromotionPass(R);
92   initializeJumpThreadingPass(R);
93   initializeSROALegacyPassPass(R);
94   initializeSROA_DTPass(R);
95   initializeSROA_SSAUpPass(R);
96   initializePostOrderFunctionAttrsLegacyPassPass(R);
97   initializeReversePostOrderFunctionAttrsPass(R);
98   initializeGlobalsAAWrapperPassPass(R);
99   initializeLICMPass(R);
100   initializeMergedLoadStoreMotionPass(R);
101   initializeGVNPass(R);
102   initializeMemCpyOptPass(R);
103   initializeDCEPass(R);
104   initializeCFGSimplifyPassPass(R);
105 }
106 
107 bool LTOCodeGenerator::addModule(LTOModule *Mod) {
108   assert(&Mod->getModule().getContext() == &Context &&
109          "Expected module in same context");
110 
111   bool ret = TheLinker->linkInModule(Mod->takeModule());
112 
113   const std::vector<const char *> &undefs = Mod->getAsmUndefinedRefs();
114   for (int i = 0, e = undefs.size(); i != e; ++i)
115     AsmUndefinedRefs[undefs[i]] = 1;
116 
117   return !ret;
118 }
119 
120 void LTOCodeGenerator::setModule(std::unique_ptr<LTOModule> Mod) {
121   assert(&Mod->getModule().getContext() == &Context &&
122          "Expected module in same context");
123 
124   AsmUndefinedRefs.clear();
125 
126   MergedModule = Mod->takeModule();
127   TheLinker = make_unique<Linker>(*MergedModule);
128 
129   const std::vector<const char*> &Undefs = Mod->getAsmUndefinedRefs();
130   for (int I = 0, E = Undefs.size(); I != E; ++I)
131     AsmUndefinedRefs[Undefs[I]] = 1;
132 }
133 
134 void LTOCodeGenerator::setTargetOptions(TargetOptions Options) {
135   this->Options = Options;
136 }
137 
138 void LTOCodeGenerator::setDebugInfo(lto_debug_model Debug) {
139   switch (Debug) {
140   case LTO_DEBUG_MODEL_NONE:
141     EmitDwarfDebugInfo = false;
142     return;
143 
144   case LTO_DEBUG_MODEL_DWARF:
145     EmitDwarfDebugInfo = true;
146     return;
147   }
148   llvm_unreachable("Unknown debug format!");
149 }
150 
151 void LTOCodeGenerator::setOptLevel(unsigned Level) {
152   OptLevel = Level;
153   switch (OptLevel) {
154   case 0:
155     CGOptLevel = CodeGenOpt::None;
156     break;
157   case 1:
158     CGOptLevel = CodeGenOpt::Less;
159     break;
160   case 2:
161     CGOptLevel = CodeGenOpt::Default;
162     break;
163   case 3:
164     CGOptLevel = CodeGenOpt::Aggressive;
165     break;
166   }
167 }
168 
169 bool LTOCodeGenerator::writeMergedModules(const char *Path) {
170   if (!determineTarget())
171     return false;
172 
173   // mark which symbols can not be internalized
174   applyScopeRestrictions();
175 
176   // create output file
177   std::error_code EC;
178   tool_output_file Out(Path, EC, sys::fs::F_None);
179   if (EC) {
180     std::string ErrMsg = "could not open bitcode file for writing: ";
181     ErrMsg += Path;
182     emitError(ErrMsg);
183     return false;
184   }
185 
186   // write bitcode to it
187   WriteBitcodeToFile(MergedModule.get(), Out.os(), ShouldEmbedUselists);
188   Out.os().close();
189 
190   if (Out.os().has_error()) {
191     std::string ErrMsg = "could not write bitcode file: ";
192     ErrMsg += Path;
193     emitError(ErrMsg);
194     Out.os().clear_error();
195     return false;
196   }
197 
198   Out.keep();
199   return true;
200 }
201 
202 bool LTOCodeGenerator::compileOptimizedToFile(const char **Name) {
203   // make unique temp output file to put generated code
204   SmallString<128> Filename;
205   int FD;
206 
207   const char *Extension =
208       (FileType == TargetMachine::CGFT_AssemblyFile ? "s" : "o");
209 
210   std::error_code EC =
211       sys::fs::createTemporaryFile("lto-llvm", Extension, FD, Filename);
212   if (EC) {
213     emitError(EC.message());
214     return false;
215   }
216 
217   // generate object file
218   tool_output_file objFile(Filename.c_str(), FD);
219 
220   bool genResult = compileOptimized(&objFile.os());
221   objFile.os().close();
222   if (objFile.os().has_error()) {
223     objFile.os().clear_error();
224     sys::fs::remove(Twine(Filename));
225     return false;
226   }
227 
228   objFile.keep();
229   if (!genResult) {
230     sys::fs::remove(Twine(Filename));
231     return false;
232   }
233 
234   NativeObjectPath = Filename.c_str();
235   *Name = NativeObjectPath.c_str();
236   return true;
237 }
238 
239 std::unique_ptr<MemoryBuffer>
240 LTOCodeGenerator::compileOptimized() {
241   const char *name;
242   if (!compileOptimizedToFile(&name))
243     return nullptr;
244 
245   // read .o file into memory buffer
246   ErrorOr<std::unique_ptr<MemoryBuffer>> BufferOrErr =
247       MemoryBuffer::getFile(name, -1, false);
248   if (std::error_code EC = BufferOrErr.getError()) {
249     emitError(EC.message());
250     sys::fs::remove(NativeObjectPath);
251     return nullptr;
252   }
253 
254   // remove temp files
255   sys::fs::remove(NativeObjectPath);
256 
257   return std::move(*BufferOrErr);
258 }
259 
260 bool LTOCodeGenerator::compile_to_file(const char **Name, bool DisableVerify,
261                                        bool DisableInline,
262                                        bool DisableGVNLoadPRE,
263                                        bool DisableVectorization) {
264   if (!optimize(DisableVerify, DisableInline, DisableGVNLoadPRE,
265                 DisableVectorization))
266     return false;
267 
268   return compileOptimizedToFile(Name);
269 }
270 
271 std::unique_ptr<MemoryBuffer>
272 LTOCodeGenerator::compile(bool DisableVerify, bool DisableInline,
273                           bool DisableGVNLoadPRE, bool DisableVectorization) {
274   if (!optimize(DisableVerify, DisableInline, DisableGVNLoadPRE,
275                 DisableVectorization))
276     return nullptr;
277 
278   return compileOptimized();
279 }
280 
281 bool LTOCodeGenerator::determineTarget() {
282   if (TargetMach)
283     return true;
284 
285   std::string TripleStr = MergedModule->getTargetTriple();
286   if (TripleStr.empty()) {
287     TripleStr = sys::getDefaultTargetTriple();
288     MergedModule->setTargetTriple(TripleStr);
289   }
290   llvm::Triple Triple(TripleStr);
291 
292   // create target machine from info for merged modules
293   std::string ErrMsg;
294   const Target *march = TargetRegistry::lookupTarget(TripleStr, ErrMsg);
295   if (!march) {
296     emitError(ErrMsg);
297     return false;
298   }
299 
300   // Construct LTOModule, hand over ownership of module and target. Use MAttr as
301   // the default set of features.
302   SubtargetFeatures Features(MAttr);
303   Features.getDefaultSubtargetFeatures(Triple);
304   FeatureStr = Features.getString();
305   // Set a default CPU for Darwin triples.
306   if (MCpu.empty() && Triple.isOSDarwin()) {
307     if (Triple.getArch() == llvm::Triple::x86_64)
308       MCpu = "core2";
309     else if (Triple.getArch() == llvm::Triple::x86)
310       MCpu = "yonah";
311     else if (Triple.getArch() == llvm::Triple::aarch64)
312       MCpu = "cyclone";
313   }
314 
315   TargetMach.reset(march->createTargetMachine(TripleStr, MCpu, FeatureStr,
316                                               Options, RelocModel,
317                                               CodeModel::Default, CGOptLevel));
318   return true;
319 }
320 
321 void LTOCodeGenerator::
322 applyRestriction(GlobalValue &GV,
323                  ArrayRef<StringRef> Libcalls,
324                  std::vector<const char*> &MustPreserveList,
325                  SmallPtrSetImpl<GlobalValue*> &AsmUsed,
326                  Mangler &Mangler) {
327   // There are no restrictions to apply to declarations.
328   if (GV.isDeclaration())
329     return;
330 
331   // There is nothing more restrictive than private linkage.
332   if (GV.hasPrivateLinkage())
333     return;
334 
335   SmallString<64> Buffer;
336   TargetMach->getNameWithPrefix(Buffer, &GV, Mangler);
337 
338   if (MustPreserveSymbols.count(Buffer))
339     MustPreserveList.push_back(GV.getName().data());
340   if (AsmUndefinedRefs.count(Buffer))
341     AsmUsed.insert(&GV);
342 
343   // Conservatively append user-supplied runtime library functions to
344   // llvm.compiler.used.  These could be internalized and deleted by
345   // optimizations like -globalopt, causing problems when later optimizations
346   // add new library calls (e.g., llvm.memset => memset and printf => puts).
347   // Leave it to the linker to remove any dead code (e.g. with -dead_strip).
348   if (isa<Function>(GV) &&
349       std::binary_search(Libcalls.begin(), Libcalls.end(), GV.getName()))
350     AsmUsed.insert(&GV);
351 
352   // Record the linkage type of non-local symbols so they can be restored prior
353   // to module splitting.
354   if (ShouldRestoreGlobalsLinkage && !GV.hasAvailableExternallyLinkage() &&
355       !GV.hasLocalLinkage() && GV.hasName())
356     ExternalSymbols.insert(std::make_pair(GV.getName(), GV.getLinkage()));
357 }
358 
359 static void findUsedValues(GlobalVariable *LLVMUsed,
360                            SmallPtrSetImpl<GlobalValue*> &UsedValues) {
361   if (!LLVMUsed) return;
362 
363   ConstantArray *Inits = cast<ConstantArray>(LLVMUsed->getInitializer());
364   for (unsigned i = 0, e = Inits->getNumOperands(); i != e; ++i)
365     if (GlobalValue *GV =
366         dyn_cast<GlobalValue>(Inits->getOperand(i)->stripPointerCasts()))
367       UsedValues.insert(GV);
368 }
369 
370 // Collect names of runtime library functions. User-defined functions with the
371 // same names are added to llvm.compiler.used to prevent them from being
372 // deleted by optimizations.
373 static void accumulateAndSortLibcalls(std::vector<StringRef> &Libcalls,
374                                       const TargetLibraryInfo& TLI,
375                                       const Module &Mod,
376                                       const TargetMachine &TM) {
377   // TargetLibraryInfo has info on C runtime library calls on the current
378   // target.
379   for (unsigned I = 0, E = static_cast<unsigned>(LibFunc::NumLibFuncs);
380        I != E; ++I) {
381     LibFunc::Func F = static_cast<LibFunc::Func>(I);
382     if (TLI.has(F))
383       Libcalls.push_back(TLI.getName(F));
384   }
385 
386   SmallPtrSet<const TargetLowering *, 1> TLSet;
387 
388   for (const Function &F : Mod) {
389     const TargetLowering *Lowering =
390         TM.getSubtargetImpl(F)->getTargetLowering();
391 
392     if (Lowering && TLSet.insert(Lowering).second)
393       // TargetLowering has info on library calls that CodeGen expects to be
394       // available, both from the C runtime and compiler-rt.
395       for (unsigned I = 0, E = static_cast<unsigned>(RTLIB::UNKNOWN_LIBCALL);
396            I != E; ++I)
397         if (const char *Name =
398                 Lowering->getLibcallName(static_cast<RTLIB::Libcall>(I)))
399           Libcalls.push_back(Name);
400   }
401 
402   array_pod_sort(Libcalls.begin(), Libcalls.end());
403   Libcalls.erase(std::unique(Libcalls.begin(), Libcalls.end()),
404                  Libcalls.end());
405 }
406 
407 void LTOCodeGenerator::applyScopeRestrictions() {
408   if (ScopeRestrictionsDone || !ShouldInternalize)
409     return;
410 
411   // Start off with a verification pass.
412   legacy::PassManager passes;
413   passes.add(createVerifierPass());
414 
415   // mark which symbols can not be internalized
416   Mangler Mangler;
417   std::vector<const char*> MustPreserveList;
418   SmallPtrSet<GlobalValue*, 8> AsmUsed;
419   std::vector<StringRef> Libcalls;
420   TargetLibraryInfoImpl TLII(Triple(TargetMach->getTargetTriple()));
421   TargetLibraryInfo TLI(TLII);
422 
423   accumulateAndSortLibcalls(Libcalls, TLI, *MergedModule, *TargetMach);
424 
425   for (Function &f : *MergedModule)
426     applyRestriction(f, Libcalls, MustPreserveList, AsmUsed, Mangler);
427   for (GlobalVariable &v : MergedModule->globals())
428     applyRestriction(v, Libcalls, MustPreserveList, AsmUsed, Mangler);
429   for (GlobalAlias &a : MergedModule->aliases())
430     applyRestriction(a, Libcalls, MustPreserveList, AsmUsed, Mangler);
431 
432   GlobalVariable *LLVMCompilerUsed =
433     MergedModule->getGlobalVariable("llvm.compiler.used");
434   findUsedValues(LLVMCompilerUsed, AsmUsed);
435   if (LLVMCompilerUsed)
436     LLVMCompilerUsed->eraseFromParent();
437 
438   if (!AsmUsed.empty()) {
439     llvm::Type *i8PTy = llvm::Type::getInt8PtrTy(Context);
440     std::vector<Constant*> asmUsed2;
441     for (auto *GV : AsmUsed) {
442       Constant *c = ConstantExpr::getBitCast(GV, i8PTy);
443       asmUsed2.push_back(c);
444     }
445 
446     llvm::ArrayType *ATy = llvm::ArrayType::get(i8PTy, asmUsed2.size());
447     LLVMCompilerUsed =
448       new llvm::GlobalVariable(*MergedModule, ATy, false,
449                                llvm::GlobalValue::AppendingLinkage,
450                                llvm::ConstantArray::get(ATy, asmUsed2),
451                                "llvm.compiler.used");
452 
453     LLVMCompilerUsed->setSection("llvm.metadata");
454   }
455 
456   passes.add(createInternalizePass(MustPreserveList));
457 
458   // apply scope restrictions
459   passes.run(*MergedModule);
460 
461   ScopeRestrictionsDone = true;
462 }
463 
464 /// Restore original linkage for symbols that may have been internalized
465 void LTOCodeGenerator::restoreLinkageForExternals() {
466   if (!ShouldInternalize || !ShouldRestoreGlobalsLinkage)
467     return;
468 
469   assert(ScopeRestrictionsDone &&
470          "Cannot externalize without internalization!");
471 
472   if (ExternalSymbols.empty())
473     return;
474 
475   auto externalize = [this](GlobalValue &GV) {
476     if (!GV.hasLocalLinkage() || !GV.hasName())
477       return;
478 
479     auto I = ExternalSymbols.find(GV.getName());
480     if (I == ExternalSymbols.end())
481       return;
482 
483     GV.setLinkage(I->second);
484   };
485 
486   std::for_each(MergedModule->begin(), MergedModule->end(), externalize);
487   std::for_each(MergedModule->global_begin(), MergedModule->global_end(),
488                 externalize);
489   std::for_each(MergedModule->alias_begin(), MergedModule->alias_end(),
490                 externalize);
491 }
492 
493 /// Optimize merged modules using various IPO passes
494 bool LTOCodeGenerator::optimize(bool DisableVerify, bool DisableInline,
495                                 bool DisableGVNLoadPRE,
496                                 bool DisableVectorization) {
497   if (!this->determineTarget())
498     return false;
499 
500   // Mark which symbols can not be internalized
501   this->applyScopeRestrictions();
502 
503   // Instantiate the pass manager to organize the passes.
504   legacy::PassManager passes;
505 
506   // Add an appropriate DataLayout instance for this module...
507   MergedModule->setDataLayout(TargetMach->createDataLayout());
508 
509   passes.add(
510       createTargetTransformInfoWrapperPass(TargetMach->getTargetIRAnalysis()));
511 
512   Triple TargetTriple(TargetMach->getTargetTriple());
513   PassManagerBuilder PMB;
514   PMB.DisableGVNLoadPRE = DisableGVNLoadPRE;
515   PMB.LoopVectorize = !DisableVectorization;
516   PMB.SLPVectorize = !DisableVectorization;
517   if (!DisableInline)
518     PMB.Inliner = createFunctionInliningPass();
519   PMB.LibraryInfo = new TargetLibraryInfoImpl(TargetTriple);
520   PMB.OptLevel = OptLevel;
521   PMB.VerifyInput = !DisableVerify;
522   PMB.VerifyOutput = !DisableVerify;
523 
524   PMB.populateLTOPassManager(passes);
525 
526   // Run our queue of passes all at once now, efficiently.
527   passes.run(*MergedModule);
528 
529   return true;
530 }
531 
532 bool LTOCodeGenerator::compileOptimized(ArrayRef<raw_pwrite_stream *> Out) {
533   if (!this->determineTarget())
534     return false;
535 
536   legacy::PassManager preCodeGenPasses;
537 
538   // If the bitcode files contain ARC code and were compiled with optimization,
539   // the ObjCARCContractPass must be run, so do it unconditionally here.
540   preCodeGenPasses.add(createObjCARCContractPass());
541   preCodeGenPasses.run(*MergedModule);
542 
543   // Re-externalize globals that may have been internalized to increase scope
544   // for splitting
545   restoreLinkageForExternals();
546 
547   // Do code generation. We need to preserve the module in case the client calls
548   // writeMergedModules() after compilation, but we only need to allow this at
549   // parallelism level 1. This is achieved by having splitCodeGen return the
550   // original module at parallelism level 1 which we then assign back to
551   // MergedModule.
552   MergedModule =
553       splitCodeGen(std::move(MergedModule), Out, MCpu, FeatureStr, Options,
554                    RelocModel, CodeModel::Default, CGOptLevel, FileType,
555                    ShouldRestoreGlobalsLinkage);
556 
557   // If statistics were requested, print them out after codegen.
558   if (llvm::AreStatisticsEnabled())
559     llvm::PrintStatistics();
560 
561   return true;
562 }
563 
564 /// setCodeGenDebugOptions - Set codegen debugging options to aid in debugging
565 /// LTO problems.
566 void LTOCodeGenerator::setCodeGenDebugOptions(const char *Options) {
567   for (std::pair<StringRef, StringRef> o = getToken(Options); !o.first.empty();
568        o = getToken(o.second))
569     CodegenOptions.push_back(o.first);
570 }
571 
572 void LTOCodeGenerator::parseCodeGenDebugOptions() {
573   // if options were requested, set them
574   if (!CodegenOptions.empty()) {
575     // ParseCommandLineOptions() expects argv[0] to be program name.
576     std::vector<const char *> CodegenArgv(1, "libLLVMLTO");
577     for (std::string &Arg : CodegenOptions)
578       CodegenArgv.push_back(Arg.c_str());
579     cl::ParseCommandLineOptions(CodegenArgv.size(), CodegenArgv.data());
580   }
581 }
582 
583 void LTOCodeGenerator::DiagnosticHandler(const DiagnosticInfo &DI,
584                                          void *Context) {
585   ((LTOCodeGenerator *)Context)->DiagnosticHandler2(DI);
586 }
587 
588 void LTOCodeGenerator::DiagnosticHandler2(const DiagnosticInfo &DI) {
589   // Map the LLVM internal diagnostic severity to the LTO diagnostic severity.
590   lto_codegen_diagnostic_severity_t Severity;
591   switch (DI.getSeverity()) {
592   case DS_Error:
593     Severity = LTO_DS_ERROR;
594     break;
595   case DS_Warning:
596     Severity = LTO_DS_WARNING;
597     break;
598   case DS_Remark:
599     Severity = LTO_DS_REMARK;
600     break;
601   case DS_Note:
602     Severity = LTO_DS_NOTE;
603     break;
604   }
605   // Create the string that will be reported to the external diagnostic handler.
606   std::string MsgStorage;
607   raw_string_ostream Stream(MsgStorage);
608   DiagnosticPrinterRawOStream DP(Stream);
609   DI.print(DP);
610   Stream.flush();
611 
612   // If this method has been called it means someone has set up an external
613   // diagnostic handler. Assert on that.
614   assert(DiagHandler && "Invalid diagnostic handler");
615   (*DiagHandler)(Severity, MsgStorage.c_str(), DiagContext);
616 }
617 
618 void
619 LTOCodeGenerator::setDiagnosticHandler(lto_diagnostic_handler_t DiagHandler,
620                                        void *Ctxt) {
621   this->DiagHandler = DiagHandler;
622   this->DiagContext = Ctxt;
623   if (!DiagHandler)
624     return Context.setDiagnosticHandler(nullptr, nullptr);
625   // Register the LTOCodeGenerator stub in the LLVMContext to forward the
626   // diagnostic to the external DiagHandler.
627   Context.setDiagnosticHandler(LTOCodeGenerator::DiagnosticHandler, this,
628                                /* RespectFilters */ true);
629 }
630 
631 namespace {
632 class LTODiagnosticInfo : public DiagnosticInfo {
633   const Twine &Msg;
634 public:
635   LTODiagnosticInfo(const Twine &DiagMsg, DiagnosticSeverity Severity=DS_Error)
636       : DiagnosticInfo(DK_Linker, Severity), Msg(DiagMsg) {}
637   void print(DiagnosticPrinter &DP) const override { DP << Msg; }
638 };
639 }
640 
641 void LTOCodeGenerator::emitError(const std::string &ErrMsg) {
642   if (DiagHandler)
643     (*DiagHandler)(LTO_DS_ERROR, ErrMsg.c_str(), DiagContext);
644   else
645     Context.diagnose(LTODiagnosticInfo(ErrMsg));
646 }
647