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/StringExtras.h"
17 #include "llvm/Analysis/Passes.h"
18 #include "llvm/Analysis/TargetLibraryInfo.h"
19 #include "llvm/Analysis/TargetTransformInfo.h"
20 #include "llvm/Bitcode/ReaderWriter.h"
21 #include "llvm/CodeGen/ParallelCG.h"
22 #include "llvm/CodeGen/RuntimeLibcalls.h"
23 #include "llvm/Config/config.h"
24 #include "llvm/IR/Constants.h"
25 #include "llvm/IR/DataLayout.h"
26 #include "llvm/IR/DerivedTypes.h"
27 #include "llvm/IR/DiagnosticInfo.h"
28 #include "llvm/IR/DiagnosticPrinter.h"
29 #include "llvm/IR/LLVMContext.h"
30 #include "llvm/IR/LegacyPassManager.h"
31 #include "llvm/IR/Mangler.h"
32 #include "llvm/IR/Module.h"
33 #include "llvm/IR/Verifier.h"
34 #include "llvm/InitializePasses.h"
35 #include "llvm/LTO/LTOModule.h"
36 #include "llvm/Linker/Linker.h"
37 #include "llvm/MC/MCAsmInfo.h"
38 #include "llvm/MC/MCContext.h"
39 #include "llvm/MC/SubtargetFeature.h"
40 #include "llvm/Support/CommandLine.h"
41 #include "llvm/Support/FileSystem.h"
42 #include "llvm/Support/Host.h"
43 #include "llvm/Support/MemoryBuffer.h"
44 #include "llvm/Support/Signals.h"
45 #include "llvm/Support/TargetRegistry.h"
46 #include "llvm/Support/TargetSelect.h"
47 #include "llvm/Support/ToolOutputFile.h"
48 #include "llvm/Support/raw_ostream.h"
49 #include "llvm/Target/TargetLowering.h"
50 #include "llvm/Target/TargetOptions.h"
51 #include "llvm/Target/TargetRegisterInfo.h"
52 #include "llvm/Target/TargetSubtargetInfo.h"
53 #include "llvm/Transforms/IPO.h"
54 #include "llvm/Transforms/IPO/PassManagerBuilder.h"
55 #include "llvm/Transforms/ObjCARC.h"
56 #include <system_error>
57 using namespace llvm;
58 
getVersionString()59 const char* LTOCodeGenerator::getVersionString() {
60 #ifdef LLVM_VERSION_INFO
61   return PACKAGE_NAME " version " PACKAGE_VERSION ", " LLVM_VERSION_INFO;
62 #else
63   return PACKAGE_NAME " version " PACKAGE_VERSION;
64 #endif
65 }
66 
LTOCodeGenerator(LLVMContext & Context)67 LTOCodeGenerator::LTOCodeGenerator(LLVMContext &Context)
68     : Context(Context), MergedModule(new Module("ld-temp.o", Context)),
69       TheLinker(new Linker(*MergedModule)) {
70   initializeLTOPasses();
71 }
72 
~LTOCodeGenerator()73 LTOCodeGenerator::~LTOCodeGenerator() {}
74 
75 // Initialize LTO passes. Please keep this function in sync with
76 // PassManagerBuilder::populateLTOPassManager(), and make sure all LTO
77 // passes are initialized.
initializeLTOPasses()78 void LTOCodeGenerator::initializeLTOPasses() {
79   PassRegistry &R = *PassRegistry::getPassRegistry();
80 
81   initializeInternalizePassPass(R);
82   initializeIPSCCPPass(R);
83   initializeGlobalOptPass(R);
84   initializeConstantMergePass(R);
85   initializeDAHPass(R);
86   initializeInstructionCombiningPassPass(R);
87   initializeSimpleInlinerPass(R);
88   initializePruneEHPass(R);
89   initializeGlobalDCEPass(R);
90   initializeArgPromotionPass(R);
91   initializeJumpThreadingPass(R);
92   initializeSROALegacyPassPass(R);
93   initializeSROA_DTPass(R);
94   initializeSROA_SSAUpPass(R);
95   initializeFunctionAttrsPass(R);
96   initializeGlobalsAAWrapperPassPass(R);
97   initializeLICMPass(R);
98   initializeMergedLoadStoreMotionPass(R);
99   initializeGVNPass(R);
100   initializeMemCpyOptPass(R);
101   initializeDCEPass(R);
102   initializeCFGSimplifyPassPass(R);
103 }
104 
addModule(LTOModule * Mod)105 bool LTOCodeGenerator::addModule(LTOModule *Mod) {
106   assert(&Mod->getModule().getContext() == &Context &&
107          "Expected module in same context");
108 
109   bool ret = TheLinker->linkInModule(Mod->takeModule());
110 
111   const std::vector<const char *> &undefs = Mod->getAsmUndefinedRefs();
112   for (int i = 0, e = undefs.size(); i != e; ++i)
113     AsmUndefinedRefs[undefs[i]] = 1;
114 
115   return !ret;
116 }
117 
setModule(std::unique_ptr<LTOModule> Mod)118 void LTOCodeGenerator::setModule(std::unique_ptr<LTOModule> Mod) {
119   assert(&Mod->getModule().getContext() == &Context &&
120          "Expected module in same context");
121 
122   AsmUndefinedRefs.clear();
123 
124   MergedModule = Mod->takeModule();
125   TheLinker = make_unique<Linker>(*MergedModule);
126 
127   const std::vector<const char*> &Undefs = Mod->getAsmUndefinedRefs();
128   for (int I = 0, E = Undefs.size(); I != E; ++I)
129     AsmUndefinedRefs[Undefs[I]] = 1;
130 }
131 
setTargetOptions(TargetOptions Options)132 void LTOCodeGenerator::setTargetOptions(TargetOptions Options) {
133   this->Options = Options;
134 }
135 
setDebugInfo(lto_debug_model Debug)136 void LTOCodeGenerator::setDebugInfo(lto_debug_model Debug) {
137   switch (Debug) {
138   case LTO_DEBUG_MODEL_NONE:
139     EmitDwarfDebugInfo = false;
140     return;
141 
142   case LTO_DEBUG_MODEL_DWARF:
143     EmitDwarfDebugInfo = true;
144     return;
145   }
146   llvm_unreachable("Unknown debug format!");
147 }
148 
setOptLevel(unsigned Level)149 void LTOCodeGenerator::setOptLevel(unsigned Level) {
150   OptLevel = Level;
151   switch (OptLevel) {
152   case 0:
153     CGOptLevel = CodeGenOpt::None;
154     break;
155   case 1:
156     CGOptLevel = CodeGenOpt::Less;
157     break;
158   case 2:
159     CGOptLevel = CodeGenOpt::Default;
160     break;
161   case 3:
162     CGOptLevel = CodeGenOpt::Aggressive;
163     break;
164   }
165 }
166 
writeMergedModules(const char * Path)167 bool LTOCodeGenerator::writeMergedModules(const char *Path) {
168   if (!determineTarget())
169     return false;
170 
171   // mark which symbols can not be internalized
172   applyScopeRestrictions();
173 
174   // create output file
175   std::error_code EC;
176   tool_output_file Out(Path, EC, sys::fs::F_None);
177   if (EC) {
178     std::string ErrMsg = "could not open bitcode file for writing: ";
179     ErrMsg += Path;
180     emitError(ErrMsg);
181     return false;
182   }
183 
184   // write bitcode to it
185   WriteBitcodeToFile(MergedModule.get(), Out.os(), ShouldEmbedUselists);
186   Out.os().close();
187 
188   if (Out.os().has_error()) {
189     std::string ErrMsg = "could not write bitcode file: ";
190     ErrMsg += Path;
191     emitError(ErrMsg);
192     Out.os().clear_error();
193     return false;
194   }
195 
196   Out.keep();
197   return true;
198 }
199 
compileOptimizedToFile(const char ** Name)200 bool LTOCodeGenerator::compileOptimizedToFile(const char **Name) {
201   // make unique temp output file to put generated code
202   SmallString<128> Filename;
203   int FD;
204 
205   const char *Extension =
206       (FileType == TargetMachine::CGFT_AssemblyFile ? "s" : "o");
207 
208   std::error_code EC =
209       sys::fs::createTemporaryFile("lto-llvm", Extension, FD, Filename);
210   if (EC) {
211     emitError(EC.message());
212     return false;
213   }
214 
215   // generate object file
216   tool_output_file objFile(Filename.c_str(), FD);
217 
218   bool genResult = compileOptimized(&objFile.os());
219   objFile.os().close();
220   if (objFile.os().has_error()) {
221     objFile.os().clear_error();
222     sys::fs::remove(Twine(Filename));
223     return false;
224   }
225 
226   objFile.keep();
227   if (!genResult) {
228     sys::fs::remove(Twine(Filename));
229     return false;
230   }
231 
232   NativeObjectPath = Filename.c_str();
233   *Name = NativeObjectPath.c_str();
234   return true;
235 }
236 
237 std::unique_ptr<MemoryBuffer>
compileOptimized()238 LTOCodeGenerator::compileOptimized() {
239   const char *name;
240   if (!compileOptimizedToFile(&name))
241     return nullptr;
242 
243   // read .o file into memory buffer
244   ErrorOr<std::unique_ptr<MemoryBuffer>> BufferOrErr =
245       MemoryBuffer::getFile(name, -1, false);
246   if (std::error_code EC = BufferOrErr.getError()) {
247     emitError(EC.message());
248     sys::fs::remove(NativeObjectPath);
249     return nullptr;
250   }
251 
252   // remove temp files
253   sys::fs::remove(NativeObjectPath);
254 
255   return std::move(*BufferOrErr);
256 }
257 
compile_to_file(const char ** Name,bool DisableVerify,bool DisableInline,bool DisableGVNLoadPRE,bool DisableVectorization)258 bool LTOCodeGenerator::compile_to_file(const char **Name, bool DisableVerify,
259                                        bool DisableInline,
260                                        bool DisableGVNLoadPRE,
261                                        bool DisableVectorization) {
262   if (!optimize(DisableVerify, DisableInline, DisableGVNLoadPRE,
263                 DisableVectorization))
264     return false;
265 
266   return compileOptimizedToFile(Name);
267 }
268 
269 std::unique_ptr<MemoryBuffer>
compile(bool DisableVerify,bool DisableInline,bool DisableGVNLoadPRE,bool DisableVectorization)270 LTOCodeGenerator::compile(bool DisableVerify, bool DisableInline,
271                           bool DisableGVNLoadPRE, bool DisableVectorization) {
272   if (!optimize(DisableVerify, DisableInline, DisableGVNLoadPRE,
273                 DisableVectorization))
274     return nullptr;
275 
276   return compileOptimized();
277 }
278 
determineTarget()279 bool LTOCodeGenerator::determineTarget() {
280   if (TargetMach)
281     return true;
282 
283   std::string TripleStr = MergedModule->getTargetTriple();
284   if (TripleStr.empty()) {
285     TripleStr = sys::getDefaultTargetTriple();
286     MergedModule->setTargetTriple(TripleStr);
287   }
288   llvm::Triple Triple(TripleStr);
289 
290   // create target machine from info for merged modules
291   std::string ErrMsg;
292   const Target *march = TargetRegistry::lookupTarget(TripleStr, ErrMsg);
293   if (!march) {
294     emitError(ErrMsg);
295     return false;
296   }
297 
298   // Construct LTOModule, hand over ownership of module and target. Use MAttr as
299   // the default set of features.
300   SubtargetFeatures Features(MAttr);
301   Features.getDefaultSubtargetFeatures(Triple);
302   FeatureStr = Features.getString();
303   // Set a default CPU for Darwin triples.
304   if (MCpu.empty() && Triple.isOSDarwin()) {
305     if (Triple.getArch() == llvm::Triple::x86_64)
306       MCpu = "core2";
307     else if (Triple.getArch() == llvm::Triple::x86)
308       MCpu = "yonah";
309     else if (Triple.getArch() == llvm::Triple::aarch64)
310       MCpu = "cyclone";
311   }
312 
313   TargetMach.reset(march->createTargetMachine(TripleStr, MCpu, FeatureStr,
314                                               Options, RelocModel,
315                                               CodeModel::Default, CGOptLevel));
316   return true;
317 }
318 
319 void LTOCodeGenerator::
applyRestriction(GlobalValue & GV,ArrayRef<StringRef> Libcalls,std::vector<const char * > & MustPreserveList,SmallPtrSetImpl<GlobalValue * > & AsmUsed,Mangler & Mangler)320 applyRestriction(GlobalValue &GV,
321                  ArrayRef<StringRef> Libcalls,
322                  std::vector<const char*> &MustPreserveList,
323                  SmallPtrSetImpl<GlobalValue*> &AsmUsed,
324                  Mangler &Mangler) {
325   // There are no restrictions to apply to declarations.
326   if (GV.isDeclaration())
327     return;
328 
329   // There is nothing more restrictive than private linkage.
330   if (GV.hasPrivateLinkage())
331     return;
332 
333   SmallString<64> Buffer;
334   TargetMach->getNameWithPrefix(Buffer, &GV, Mangler);
335 
336   if (MustPreserveSymbols.count(Buffer))
337     MustPreserveList.push_back(GV.getName().data());
338   if (AsmUndefinedRefs.count(Buffer))
339     AsmUsed.insert(&GV);
340 
341   // Conservatively append user-supplied runtime library functions to
342   // llvm.compiler.used.  These could be internalized and deleted by
343   // optimizations like -globalopt, causing problems when later optimizations
344   // add new library calls (e.g., llvm.memset => memset and printf => puts).
345   // Leave it to the linker to remove any dead code (e.g. with -dead_strip).
346   if (isa<Function>(GV) &&
347       std::binary_search(Libcalls.begin(), Libcalls.end(), GV.getName()))
348     AsmUsed.insert(&GV);
349 }
350 
findUsedValues(GlobalVariable * LLVMUsed,SmallPtrSetImpl<GlobalValue * > & UsedValues)351 static void findUsedValues(GlobalVariable *LLVMUsed,
352                            SmallPtrSetImpl<GlobalValue*> &UsedValues) {
353   if (!LLVMUsed) return;
354 
355   ConstantArray *Inits = cast<ConstantArray>(LLVMUsed->getInitializer());
356   for (unsigned i = 0, e = Inits->getNumOperands(); i != e; ++i)
357     if (GlobalValue *GV =
358         dyn_cast<GlobalValue>(Inits->getOperand(i)->stripPointerCasts()))
359       UsedValues.insert(GV);
360 }
361 
362 // Collect names of runtime library functions. User-defined functions with the
363 // same names are added to llvm.compiler.used to prevent them from being
364 // deleted by optimizations.
accumulateAndSortLibcalls(std::vector<StringRef> & Libcalls,const TargetLibraryInfo & TLI,const Module & Mod,const TargetMachine & TM)365 static void accumulateAndSortLibcalls(std::vector<StringRef> &Libcalls,
366                                       const TargetLibraryInfo& TLI,
367                                       const Module &Mod,
368                                       const TargetMachine &TM) {
369   // TargetLibraryInfo has info on C runtime library calls on the current
370   // target.
371   for (unsigned I = 0, E = static_cast<unsigned>(LibFunc::NumLibFuncs);
372        I != E; ++I) {
373     LibFunc::Func F = static_cast<LibFunc::Func>(I);
374     if (TLI.has(F))
375       Libcalls.push_back(TLI.getName(F));
376   }
377 
378   SmallPtrSet<const TargetLowering *, 1> TLSet;
379 
380   for (const Function &F : Mod) {
381     const TargetLowering *Lowering =
382         TM.getSubtargetImpl(F)->getTargetLowering();
383 
384     if (Lowering && TLSet.insert(Lowering).second)
385       // TargetLowering has info on library calls that CodeGen expects to be
386       // available, both from the C runtime and compiler-rt.
387       for (unsigned I = 0, E = static_cast<unsigned>(RTLIB::UNKNOWN_LIBCALL);
388            I != E; ++I)
389         if (const char *Name =
390                 Lowering->getLibcallName(static_cast<RTLIB::Libcall>(I)))
391           Libcalls.push_back(Name);
392   }
393 
394   array_pod_sort(Libcalls.begin(), Libcalls.end());
395   Libcalls.erase(std::unique(Libcalls.begin(), Libcalls.end()),
396                  Libcalls.end());
397 }
398 
applyScopeRestrictions()399 void LTOCodeGenerator::applyScopeRestrictions() {
400   if (ScopeRestrictionsDone || !ShouldInternalize)
401     return;
402 
403   // Start off with a verification pass.
404   legacy::PassManager passes;
405   passes.add(createVerifierPass());
406 
407   // mark which symbols can not be internalized
408   Mangler Mangler;
409   std::vector<const char*> MustPreserveList;
410   SmallPtrSet<GlobalValue*, 8> AsmUsed;
411   std::vector<StringRef> Libcalls;
412   TargetLibraryInfoImpl TLII(Triple(TargetMach->getTargetTriple()));
413   TargetLibraryInfo TLI(TLII);
414 
415   accumulateAndSortLibcalls(Libcalls, TLI, *MergedModule, *TargetMach);
416 
417   for (Function &f : *MergedModule)
418     applyRestriction(f, Libcalls, MustPreserveList, AsmUsed, Mangler);
419   for (GlobalVariable &v : MergedModule->globals())
420     applyRestriction(v, Libcalls, MustPreserveList, AsmUsed, Mangler);
421   for (GlobalAlias &a : MergedModule->aliases())
422     applyRestriction(a, Libcalls, MustPreserveList, AsmUsed, Mangler);
423 
424   GlobalVariable *LLVMCompilerUsed =
425     MergedModule->getGlobalVariable("llvm.compiler.used");
426   findUsedValues(LLVMCompilerUsed, AsmUsed);
427   if (LLVMCompilerUsed)
428     LLVMCompilerUsed->eraseFromParent();
429 
430   if (!AsmUsed.empty()) {
431     llvm::Type *i8PTy = llvm::Type::getInt8PtrTy(Context);
432     std::vector<Constant*> asmUsed2;
433     for (auto *GV : AsmUsed) {
434       Constant *c = ConstantExpr::getBitCast(GV, i8PTy);
435       asmUsed2.push_back(c);
436     }
437 
438     llvm::ArrayType *ATy = llvm::ArrayType::get(i8PTy, asmUsed2.size());
439     LLVMCompilerUsed =
440       new llvm::GlobalVariable(*MergedModule, ATy, false,
441                                llvm::GlobalValue::AppendingLinkage,
442                                llvm::ConstantArray::get(ATy, asmUsed2),
443                                "llvm.compiler.used");
444 
445     LLVMCompilerUsed->setSection("llvm.metadata");
446   }
447 
448   passes.add(createInternalizePass(MustPreserveList));
449 
450   // apply scope restrictions
451   passes.run(*MergedModule);
452 
453   ScopeRestrictionsDone = true;
454 }
455 
456 /// Optimize merged modules using various IPO passes
optimize(bool DisableVerify,bool DisableInline,bool DisableGVNLoadPRE,bool DisableVectorization)457 bool LTOCodeGenerator::optimize(bool DisableVerify, bool DisableInline,
458                                 bool DisableGVNLoadPRE,
459                                 bool DisableVectorization) {
460   if (!this->determineTarget())
461     return false;
462 
463   // Mark which symbols can not be internalized
464   this->applyScopeRestrictions();
465 
466   // Instantiate the pass manager to organize the passes.
467   legacy::PassManager passes;
468 
469   // Add an appropriate DataLayout instance for this module...
470   MergedModule->setDataLayout(TargetMach->createDataLayout());
471 
472   passes.add(
473       createTargetTransformInfoWrapperPass(TargetMach->getTargetIRAnalysis()));
474 
475   Triple TargetTriple(TargetMach->getTargetTriple());
476   PassManagerBuilder PMB;
477   PMB.DisableGVNLoadPRE = DisableGVNLoadPRE;
478   PMB.LoopVectorize = !DisableVectorization;
479   PMB.SLPVectorize = !DisableVectorization;
480   if (!DisableInline)
481     PMB.Inliner = createFunctionInliningPass();
482   PMB.LibraryInfo = new TargetLibraryInfoImpl(TargetTriple);
483   PMB.OptLevel = OptLevel;
484   PMB.VerifyInput = !DisableVerify;
485   PMB.VerifyOutput = !DisableVerify;
486 
487   PMB.populateLTOPassManager(passes);
488 
489   // Run our queue of passes all at once now, efficiently.
490   passes.run(*MergedModule);
491 
492   return true;
493 }
494 
compileOptimized(ArrayRef<raw_pwrite_stream * > Out)495 bool LTOCodeGenerator::compileOptimized(ArrayRef<raw_pwrite_stream *> Out) {
496   if (!this->determineTarget())
497     return false;
498 
499   legacy::PassManager preCodeGenPasses;
500 
501   // If the bitcode files contain ARC code and were compiled with optimization,
502   // the ObjCARCContractPass must be run, so do it unconditionally here.
503   preCodeGenPasses.add(createObjCARCContractPass());
504   preCodeGenPasses.run(*MergedModule);
505 
506   // Do code generation. We need to preserve the module in case the client calls
507   // writeMergedModules() after compilation, but we only need to allow this at
508   // parallelism level 1. This is achieved by having splitCodeGen return the
509   // original module at parallelism level 1 which we then assign back to
510   // MergedModule.
511   MergedModule =
512       splitCodeGen(std::move(MergedModule), Out, MCpu, FeatureStr, Options,
513                    RelocModel, CodeModel::Default, CGOptLevel, FileType);
514 
515   return true;
516 }
517 
518 /// setCodeGenDebugOptions - Set codegen debugging options to aid in debugging
519 /// LTO problems.
setCodeGenDebugOptions(const char * Options)520 void LTOCodeGenerator::setCodeGenDebugOptions(const char *Options) {
521   for (std::pair<StringRef, StringRef> o = getToken(Options); !o.first.empty();
522        o = getToken(o.second))
523     CodegenOptions.push_back(o.first);
524 }
525 
parseCodeGenDebugOptions()526 void LTOCodeGenerator::parseCodeGenDebugOptions() {
527   // if options were requested, set them
528   if (!CodegenOptions.empty()) {
529     // ParseCommandLineOptions() expects argv[0] to be program name.
530     std::vector<const char *> CodegenArgv(1, "libLLVMLTO");
531     for (std::string &Arg : CodegenOptions)
532       CodegenArgv.push_back(Arg.c_str());
533     cl::ParseCommandLineOptions(CodegenArgv.size(), CodegenArgv.data());
534   }
535 }
536 
DiagnosticHandler(const DiagnosticInfo & DI,void * Context)537 void LTOCodeGenerator::DiagnosticHandler(const DiagnosticInfo &DI,
538                                          void *Context) {
539   ((LTOCodeGenerator *)Context)->DiagnosticHandler2(DI);
540 }
541 
DiagnosticHandler2(const DiagnosticInfo & DI)542 void LTOCodeGenerator::DiagnosticHandler2(const DiagnosticInfo &DI) {
543   // Map the LLVM internal diagnostic severity to the LTO diagnostic severity.
544   lto_codegen_diagnostic_severity_t Severity;
545   switch (DI.getSeverity()) {
546   case DS_Error:
547     Severity = LTO_DS_ERROR;
548     break;
549   case DS_Warning:
550     Severity = LTO_DS_WARNING;
551     break;
552   case DS_Remark:
553     Severity = LTO_DS_REMARK;
554     break;
555   case DS_Note:
556     Severity = LTO_DS_NOTE;
557     break;
558   }
559   // Create the string that will be reported to the external diagnostic handler.
560   std::string MsgStorage;
561   raw_string_ostream Stream(MsgStorage);
562   DiagnosticPrinterRawOStream DP(Stream);
563   DI.print(DP);
564   Stream.flush();
565 
566   // If this method has been called it means someone has set up an external
567   // diagnostic handler. Assert on that.
568   assert(DiagHandler && "Invalid diagnostic handler");
569   (*DiagHandler)(Severity, MsgStorage.c_str(), DiagContext);
570 }
571 
572 void
setDiagnosticHandler(lto_diagnostic_handler_t DiagHandler,void * Ctxt)573 LTOCodeGenerator::setDiagnosticHandler(lto_diagnostic_handler_t DiagHandler,
574                                        void *Ctxt) {
575   this->DiagHandler = DiagHandler;
576   this->DiagContext = Ctxt;
577   if (!DiagHandler)
578     return Context.setDiagnosticHandler(nullptr, nullptr);
579   // Register the LTOCodeGenerator stub in the LLVMContext to forward the
580   // diagnostic to the external DiagHandler.
581   Context.setDiagnosticHandler(LTOCodeGenerator::DiagnosticHandler, this,
582                                /* RespectFilters */ true);
583 }
584 
585 namespace {
586 class LTODiagnosticInfo : public DiagnosticInfo {
587   const Twine &Msg;
588 public:
LTODiagnosticInfo(const Twine & DiagMsg,DiagnosticSeverity Severity=DS_Error)589   LTODiagnosticInfo(const Twine &DiagMsg, DiagnosticSeverity Severity=DS_Error)
590       : DiagnosticInfo(DK_Linker, Severity), Msg(DiagMsg) {}
print(DiagnosticPrinter & DP) const591   void print(DiagnosticPrinter &DP) const override { DP << Msg; }
592 };
593 }
594 
emitError(const std::string & ErrMsg)595 void LTOCodeGenerator::emitError(const std::string &ErrMsg) {
596   if (DiagHandler)
597     (*DiagHandler)(LTO_DS_ERROR, ErrMsg.c_str(), DiagContext);
598   else
599     Context.diagnose(LTODiagnosticInfo(ErrMsg));
600 }
601