1 //===--- BackendUtil.cpp - LLVM Backend Utilities -------------------------===//
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 #include "clang/CodeGen/BackendUtil.h"
11 #include "clang/Basic/Diagnostic.h"
12 #include "clang/Basic/LangOptions.h"
13 #include "clang/Basic/TargetOptions.h"
14 #include "clang/Frontend/CodeGenOptions.h"
15 #include "clang/Frontend/FrontendDiagnostic.h"
16 #include "clang/Frontend/Utils.h"
17 #include "clang/Lex/HeaderSearchOptions.h"
18 #include "llvm/ADT/SmallSet.h"
19 #include "llvm/ADT/StringExtras.h"
20 #include "llvm/ADT/StringSwitch.h"
21 #include "llvm/ADT/Triple.h"
22 #include "llvm/Analysis/TargetLibraryInfo.h"
23 #include "llvm/Analysis/TargetTransformInfo.h"
24 #include "llvm/Bitcode/BitcodeReader.h"
25 #include "llvm/Bitcode/BitcodeWriter.h"
26 #include "llvm/Bitcode/BitcodeWriterPass.h"
27 #include "llvm/CodeGen/RegAllocRegistry.h"
28 #include "llvm/CodeGen/SchedulerRegistry.h"
29 #include "llvm/IR/DataLayout.h"
30 #include "llvm/IR/IRPrintingPasses.h"
31 #include "llvm/IR/LegacyPassManager.h"
32 #include "llvm/IR/Module.h"
33 #include "llvm/IR/ModuleSummaryIndex.h"
34 #include "llvm/IR/Verifier.h"
35 #include "llvm/LTO/LTOBackend.h"
36 #include "llvm/MC/MCAsmInfo.h"
37 #include "llvm/MC/SubtargetFeature.h"
38 #include "llvm/Object/ModuleSummaryIndexObjectFile.h"
39 #include "llvm/Passes/PassBuilder.h"
40 #include "llvm/Support/CommandLine.h"
41 #include "llvm/Support/MemoryBuffer.h"
42 #include "llvm/Support/PrettyStackTrace.h"
43 #include "llvm/Support/TargetRegistry.h"
44 #include "llvm/Support/Timer.h"
45 #include "llvm/Support/raw_ostream.h"
46 #include "llvm/Target/TargetMachine.h"
47 #include "llvm/Target/TargetOptions.h"
48 #include "llvm/Target/TargetSubtargetInfo.h"
49 #include "llvm/Transforms/Coroutines.h"
50 #include "llvm/Transforms/IPO.h"
51 #include "llvm/Transforms/IPO/AlwaysInliner.h"
52 #include "llvm/Transforms/IPO/PassManagerBuilder.h"
53 #include "llvm/Transforms/Instrumentation.h"
54 #include "llvm/Transforms/ObjCARC.h"
55 #include "llvm/Transforms/Scalar.h"
56 #include "llvm/Transforms/Scalar/GVN.h"
57 #include "llvm/Transforms/Utils/SymbolRewriter.h"
58 #include <memory>
59 using namespace clang;
60 using namespace llvm;
61 
62 namespace {
63 
64 class EmitAssemblyHelper {
65   DiagnosticsEngine &Diags;
66   const HeaderSearchOptions &HSOpts;
67   const CodeGenOptions &CodeGenOpts;
68   const clang::TargetOptions &TargetOpts;
69   const LangOptions &LangOpts;
70   Module *TheModule;
71 
72   Timer CodeGenerationTime;
73 
74   std::unique_ptr<raw_pwrite_stream> OS;
75 
76   TargetIRAnalysis getTargetIRAnalysis() const {
77     if (TM)
78       return TM->getTargetIRAnalysis();
79 
80     return TargetIRAnalysis();
81   }
82 
83   /// Set LLVM command line options passed through -backend-option.
84   void setCommandLineOpts();
85 
86   void CreatePasses(legacy::PassManager &MPM, legacy::FunctionPassManager &FPM);
87 
88   /// Generates the TargetMachine.
89   /// Leaves TM unchanged if it is unable to create the target machine.
90   /// Some of our clang tests specify triples which are not built
91   /// into clang. This is okay because these tests check the generated
92   /// IR, and they require DataLayout which depends on the triple.
93   /// In this case, we allow this method to fail and not report an error.
94   /// When MustCreateTM is used, we print an error if we are unable to load
95   /// the requested target.
96   void CreateTargetMachine(bool MustCreateTM);
97 
98   /// Add passes necessary to emit assembly or LLVM IR.
99   ///
100   /// \return True on success.
101   bool AddEmitPasses(legacy::PassManager &CodeGenPasses, BackendAction Action,
102                      raw_pwrite_stream &OS);
103 
104 public:
105   EmitAssemblyHelper(DiagnosticsEngine &_Diags,
106                      const HeaderSearchOptions &HeaderSearchOpts,
107                      const CodeGenOptions &CGOpts,
108                      const clang::TargetOptions &TOpts,
109                      const LangOptions &LOpts, Module *M)
110       : Diags(_Diags), HSOpts(HeaderSearchOpts), CodeGenOpts(CGOpts),
111         TargetOpts(TOpts), LangOpts(LOpts), TheModule(M),
112         CodeGenerationTime("codegen", "Code Generation Time") {}
113 
114   ~EmitAssemblyHelper() {
115     if (CodeGenOpts.DisableFree)
116       BuryPointer(std::move(TM));
117   }
118 
119   std::unique_ptr<TargetMachine> TM;
120 
121   void EmitAssembly(BackendAction Action,
122                     std::unique_ptr<raw_pwrite_stream> OS);
123 
124   void EmitAssemblyWithNewPassManager(BackendAction Action,
125                                       std::unique_ptr<raw_pwrite_stream> OS);
126 };
127 
128 // We need this wrapper to access LangOpts and CGOpts from extension functions
129 // that we add to the PassManagerBuilder.
130 class PassManagerBuilderWrapper : public PassManagerBuilder {
131 public:
132   PassManagerBuilderWrapper(const CodeGenOptions &CGOpts,
133                             const LangOptions &LangOpts)
134       : PassManagerBuilder(), CGOpts(CGOpts), LangOpts(LangOpts) {}
135   const CodeGenOptions &getCGOpts() const { return CGOpts; }
136   const LangOptions &getLangOpts() const { return LangOpts; }
137 private:
138   const CodeGenOptions &CGOpts;
139   const LangOptions &LangOpts;
140 };
141 
142 }
143 
144 static void addObjCARCAPElimPass(const PassManagerBuilder &Builder, PassManagerBase &PM) {
145   if (Builder.OptLevel > 0)
146     PM.add(createObjCARCAPElimPass());
147 }
148 
149 static void addObjCARCExpandPass(const PassManagerBuilder &Builder, PassManagerBase &PM) {
150   if (Builder.OptLevel > 0)
151     PM.add(createObjCARCExpandPass());
152 }
153 
154 static void addObjCARCOptPass(const PassManagerBuilder &Builder, PassManagerBase &PM) {
155   if (Builder.OptLevel > 0)
156     PM.add(createObjCARCOptPass());
157 }
158 
159 static void addAddDiscriminatorsPass(const PassManagerBuilder &Builder,
160                                      legacy::PassManagerBase &PM) {
161   PM.add(createAddDiscriminatorsPass());
162 }
163 
164 static void addBoundsCheckingPass(const PassManagerBuilder &Builder,
165                                   legacy::PassManagerBase &PM) {
166   PM.add(createBoundsCheckingPass());
167 }
168 
169 static void addSanitizerCoveragePass(const PassManagerBuilder &Builder,
170                                      legacy::PassManagerBase &PM) {
171   const PassManagerBuilderWrapper &BuilderWrapper =
172       static_cast<const PassManagerBuilderWrapper&>(Builder);
173   const CodeGenOptions &CGOpts = BuilderWrapper.getCGOpts();
174   SanitizerCoverageOptions Opts;
175   Opts.CoverageType =
176       static_cast<SanitizerCoverageOptions::Type>(CGOpts.SanitizeCoverageType);
177   Opts.IndirectCalls = CGOpts.SanitizeCoverageIndirectCalls;
178   Opts.TraceBB = CGOpts.SanitizeCoverageTraceBB;
179   Opts.TraceCmp = CGOpts.SanitizeCoverageTraceCmp;
180   Opts.TraceDiv = CGOpts.SanitizeCoverageTraceDiv;
181   Opts.TraceGep = CGOpts.SanitizeCoverageTraceGep;
182   Opts.Use8bitCounters = CGOpts.SanitizeCoverage8bitCounters;
183   Opts.TracePC = CGOpts.SanitizeCoverageTracePC;
184   Opts.TracePCGuard = CGOpts.SanitizeCoverageTracePCGuard;
185   PM.add(createSanitizerCoverageModulePass(Opts));
186 }
187 
188 static void addAddressSanitizerPasses(const PassManagerBuilder &Builder,
189                                       legacy::PassManagerBase &PM) {
190   const PassManagerBuilderWrapper &BuilderWrapper =
191       static_cast<const PassManagerBuilderWrapper&>(Builder);
192   const CodeGenOptions &CGOpts = BuilderWrapper.getCGOpts();
193   bool Recover = CGOpts.SanitizeRecover.has(SanitizerKind::Address);
194   bool UseAfterScope = CGOpts.SanitizeAddressUseAfterScope;
195   PM.add(createAddressSanitizerFunctionPass(/*CompileKernel*/ false, Recover,
196                                             UseAfterScope));
197   PM.add(createAddressSanitizerModulePass(/*CompileKernel*/false, Recover));
198 }
199 
200 static void addKernelAddressSanitizerPasses(const PassManagerBuilder &Builder,
201                                             legacy::PassManagerBase &PM) {
202   PM.add(createAddressSanitizerFunctionPass(
203       /*CompileKernel*/ true,
204       /*Recover*/ true, /*UseAfterScope*/ false));
205   PM.add(createAddressSanitizerModulePass(/*CompileKernel*/true,
206                                           /*Recover*/true));
207 }
208 
209 static void addMemorySanitizerPass(const PassManagerBuilder &Builder,
210                                    legacy::PassManagerBase &PM) {
211   const PassManagerBuilderWrapper &BuilderWrapper =
212       static_cast<const PassManagerBuilderWrapper&>(Builder);
213   const CodeGenOptions &CGOpts = BuilderWrapper.getCGOpts();
214   int TrackOrigins = CGOpts.SanitizeMemoryTrackOrigins;
215   bool Recover = CGOpts.SanitizeRecover.has(SanitizerKind::Memory);
216   PM.add(createMemorySanitizerPass(TrackOrigins, Recover));
217 
218   // MemorySanitizer inserts complex instrumentation that mostly follows
219   // the logic of the original code, but operates on "shadow" values.
220   // It can benefit from re-running some general purpose optimization passes.
221   if (Builder.OptLevel > 0) {
222     PM.add(createEarlyCSEPass());
223     PM.add(createReassociatePass());
224     PM.add(createLICMPass());
225     PM.add(createGVNPass());
226     PM.add(createInstructionCombiningPass());
227     PM.add(createDeadStoreEliminationPass());
228   }
229 }
230 
231 static void addThreadSanitizerPass(const PassManagerBuilder &Builder,
232                                    legacy::PassManagerBase &PM) {
233   PM.add(createThreadSanitizerPass());
234 }
235 
236 static void addDataFlowSanitizerPass(const PassManagerBuilder &Builder,
237                                      legacy::PassManagerBase &PM) {
238   const PassManagerBuilderWrapper &BuilderWrapper =
239       static_cast<const PassManagerBuilderWrapper&>(Builder);
240   const LangOptions &LangOpts = BuilderWrapper.getLangOpts();
241   PM.add(createDataFlowSanitizerPass(LangOpts.SanitizerBlacklistFiles));
242 }
243 
244 static void addEfficiencySanitizerPass(const PassManagerBuilder &Builder,
245                                        legacy::PassManagerBase &PM) {
246   const PassManagerBuilderWrapper &BuilderWrapper =
247       static_cast<const PassManagerBuilderWrapper&>(Builder);
248   const LangOptions &LangOpts = BuilderWrapper.getLangOpts();
249   EfficiencySanitizerOptions Opts;
250   if (LangOpts.Sanitize.has(SanitizerKind::EfficiencyCacheFrag))
251     Opts.ToolType = EfficiencySanitizerOptions::ESAN_CacheFrag;
252   else if (LangOpts.Sanitize.has(SanitizerKind::EfficiencyWorkingSet))
253     Opts.ToolType = EfficiencySanitizerOptions::ESAN_WorkingSet;
254   PM.add(createEfficiencySanitizerPass(Opts));
255 }
256 
257 static TargetLibraryInfoImpl *createTLII(llvm::Triple &TargetTriple,
258                                          const CodeGenOptions &CodeGenOpts) {
259   TargetLibraryInfoImpl *TLII = new TargetLibraryInfoImpl(TargetTriple);
260   if (!CodeGenOpts.SimplifyLibCalls)
261     TLII->disableAllFunctions();
262   else {
263     // Disable individual libc/libm calls in TargetLibraryInfo.
264     LibFunc F;
265     for (auto &FuncName : CodeGenOpts.getNoBuiltinFuncs())
266       if (TLII->getLibFunc(FuncName, F))
267         TLII->setUnavailable(F);
268   }
269 
270   switch (CodeGenOpts.getVecLib()) {
271   case CodeGenOptions::Accelerate:
272     TLII->addVectorizableFunctionsFromVecLib(TargetLibraryInfoImpl::Accelerate);
273     break;
274   case CodeGenOptions::SVML:
275     TLII->addVectorizableFunctionsFromVecLib(TargetLibraryInfoImpl::SVML);
276     break;
277   default:
278     break;
279   }
280   return TLII;
281 }
282 
283 static void addSymbolRewriterPass(const CodeGenOptions &Opts,
284                                   legacy::PassManager *MPM) {
285   llvm::SymbolRewriter::RewriteDescriptorList DL;
286 
287   llvm::SymbolRewriter::RewriteMapParser MapParser;
288   for (const auto &MapFile : Opts.RewriteMapFiles)
289     MapParser.parse(MapFile, &DL);
290 
291   MPM->add(createRewriteSymbolsPass(DL));
292 }
293 
294 void EmitAssemblyHelper::CreatePasses(legacy::PassManager &MPM,
295                                       legacy::FunctionPassManager &FPM) {
296   // Handle disabling of all LLVM passes, where we want to preserve the
297   // internal module before any optimization.
298   if (CodeGenOpts.DisableLLVMPasses)
299     return;
300 
301   PassManagerBuilderWrapper PMBuilder(CodeGenOpts, LangOpts);
302 
303   // Figure out TargetLibraryInfo.  This needs to be added to MPM and FPM
304   // manually (and not via PMBuilder), since some passes (eg. InstrProfiling)
305   // are inserted before PMBuilder ones - they'd get the default-constructed
306   // TLI with an unknown target otherwise.
307   Triple TargetTriple(TheModule->getTargetTriple());
308   std::unique_ptr<TargetLibraryInfoImpl> TLII(
309       createTLII(TargetTriple, CodeGenOpts));
310 
311   // At O0 and O1 we only run the always inliner which is more efficient. At
312   // higher optimization levels we run the normal inliner.
313   if (CodeGenOpts.OptimizationLevel <= 1) {
314     bool InsertLifetimeIntrinsics = (CodeGenOpts.OptimizationLevel != 0 &&
315                                      !CodeGenOpts.DisableLifetimeMarkers);
316     PMBuilder.Inliner = createAlwaysInlinerLegacyPass(InsertLifetimeIntrinsics);
317   } else {
318     PMBuilder.Inliner = createFunctionInliningPass(
319         CodeGenOpts.OptimizationLevel, CodeGenOpts.OptimizeSize);
320   }
321 
322   PMBuilder.OptLevel = CodeGenOpts.OptimizationLevel;
323   PMBuilder.SizeLevel = CodeGenOpts.OptimizeSize;
324   PMBuilder.BBVectorize = CodeGenOpts.VectorizeBB;
325   PMBuilder.SLPVectorize = CodeGenOpts.VectorizeSLP;
326   PMBuilder.LoopVectorize = CodeGenOpts.VectorizeLoop;
327 
328   PMBuilder.DisableUnrollLoops = !CodeGenOpts.UnrollLoops;
329   PMBuilder.MergeFunctions = CodeGenOpts.MergeFunctions;
330   PMBuilder.PrepareForThinLTO = CodeGenOpts.EmitSummaryIndex;
331   PMBuilder.PrepareForLTO = CodeGenOpts.PrepareForLTO;
332   PMBuilder.RerollLoops = CodeGenOpts.RerollLoops;
333 
334   MPM.add(new TargetLibraryInfoWrapperPass(*TLII));
335 
336   if (TM)
337     TM->adjustPassManager(PMBuilder);
338 
339   PMBuilder.addExtension(PassManagerBuilder::EP_EarlyAsPossible,
340                          addAddDiscriminatorsPass);
341 
342   // In ObjC ARC mode, add the main ARC optimization passes.
343   if (LangOpts.ObjCAutoRefCount) {
344     PMBuilder.addExtension(PassManagerBuilder::EP_EarlyAsPossible,
345                            addObjCARCExpandPass);
346     PMBuilder.addExtension(PassManagerBuilder::EP_ModuleOptimizerEarly,
347                            addObjCARCAPElimPass);
348     PMBuilder.addExtension(PassManagerBuilder::EP_ScalarOptimizerLate,
349                            addObjCARCOptPass);
350   }
351 
352   if (LangOpts.Sanitize.has(SanitizerKind::LocalBounds)) {
353     PMBuilder.addExtension(PassManagerBuilder::EP_ScalarOptimizerLate,
354                            addBoundsCheckingPass);
355     PMBuilder.addExtension(PassManagerBuilder::EP_EnabledOnOptLevel0,
356                            addBoundsCheckingPass);
357   }
358 
359   if (CodeGenOpts.SanitizeCoverageType ||
360       CodeGenOpts.SanitizeCoverageIndirectCalls ||
361       CodeGenOpts.SanitizeCoverageTraceCmp) {
362     PMBuilder.addExtension(PassManagerBuilder::EP_OptimizerLast,
363                            addSanitizerCoveragePass);
364     PMBuilder.addExtension(PassManagerBuilder::EP_EnabledOnOptLevel0,
365                            addSanitizerCoveragePass);
366   }
367 
368   if (LangOpts.Sanitize.has(SanitizerKind::Address)) {
369     PMBuilder.addExtension(PassManagerBuilder::EP_OptimizerLast,
370                            addAddressSanitizerPasses);
371     PMBuilder.addExtension(PassManagerBuilder::EP_EnabledOnOptLevel0,
372                            addAddressSanitizerPasses);
373   }
374 
375   if (LangOpts.Sanitize.has(SanitizerKind::KernelAddress)) {
376     PMBuilder.addExtension(PassManagerBuilder::EP_OptimizerLast,
377                            addKernelAddressSanitizerPasses);
378     PMBuilder.addExtension(PassManagerBuilder::EP_EnabledOnOptLevel0,
379                            addKernelAddressSanitizerPasses);
380   }
381 
382   if (LangOpts.Sanitize.has(SanitizerKind::Memory)) {
383     PMBuilder.addExtension(PassManagerBuilder::EP_OptimizerLast,
384                            addMemorySanitizerPass);
385     PMBuilder.addExtension(PassManagerBuilder::EP_EnabledOnOptLevel0,
386                            addMemorySanitizerPass);
387   }
388 
389   if (LangOpts.Sanitize.has(SanitizerKind::Thread)) {
390     PMBuilder.addExtension(PassManagerBuilder::EP_OptimizerLast,
391                            addThreadSanitizerPass);
392     PMBuilder.addExtension(PassManagerBuilder::EP_EnabledOnOptLevel0,
393                            addThreadSanitizerPass);
394   }
395 
396   if (LangOpts.Sanitize.has(SanitizerKind::DataFlow)) {
397     PMBuilder.addExtension(PassManagerBuilder::EP_OptimizerLast,
398                            addDataFlowSanitizerPass);
399     PMBuilder.addExtension(PassManagerBuilder::EP_EnabledOnOptLevel0,
400                            addDataFlowSanitizerPass);
401   }
402 
403   if (LangOpts.CoroutinesTS)
404     addCoroutinePassesToExtensionPoints(PMBuilder);
405 
406   if (LangOpts.Sanitize.hasOneOf(SanitizerKind::Efficiency)) {
407     PMBuilder.addExtension(PassManagerBuilder::EP_OptimizerLast,
408                            addEfficiencySanitizerPass);
409     PMBuilder.addExtension(PassManagerBuilder::EP_EnabledOnOptLevel0,
410                            addEfficiencySanitizerPass);
411   }
412 
413   // Set up the per-function pass manager.
414   FPM.add(new TargetLibraryInfoWrapperPass(*TLII));
415   if (CodeGenOpts.VerifyModule)
416     FPM.add(createVerifierPass());
417 
418   // Set up the per-module pass manager.
419   if (!CodeGenOpts.RewriteMapFiles.empty())
420     addSymbolRewriterPass(CodeGenOpts, &MPM);
421 
422   if (!CodeGenOpts.DisableGCov &&
423       (CodeGenOpts.EmitGcovArcs || CodeGenOpts.EmitGcovNotes)) {
424     // Not using 'GCOVOptions::getDefault' allows us to avoid exiting if
425     // LLVM's -default-gcov-version flag is set to something invalid.
426     GCOVOptions Options;
427     Options.EmitNotes = CodeGenOpts.EmitGcovNotes;
428     Options.EmitData = CodeGenOpts.EmitGcovArcs;
429     memcpy(Options.Version, CodeGenOpts.CoverageVersion, 4);
430     Options.UseCfgChecksum = CodeGenOpts.CoverageExtraChecksum;
431     Options.NoRedZone = CodeGenOpts.DisableRedZone;
432     Options.FunctionNamesInData =
433         !CodeGenOpts.CoverageNoFunctionNamesInData;
434     Options.ExitBlockBeforeBody = CodeGenOpts.CoverageExitBlockBeforeBody;
435     MPM.add(createGCOVProfilerPass(Options));
436     if (CodeGenOpts.getDebugInfo() == codegenoptions::NoDebugInfo)
437       MPM.add(createStripSymbolsPass(true));
438   }
439 
440   if (CodeGenOpts.hasProfileClangInstr()) {
441     InstrProfOptions Options;
442     Options.NoRedZone = CodeGenOpts.DisableRedZone;
443     Options.InstrProfileOutput = CodeGenOpts.InstrProfileOutput;
444     MPM.add(createInstrProfilingLegacyPass(Options));
445   }
446   if (CodeGenOpts.hasProfileIRInstr()) {
447     PMBuilder.EnablePGOInstrGen = true;
448     if (!CodeGenOpts.InstrProfileOutput.empty())
449       PMBuilder.PGOInstrGen = CodeGenOpts.InstrProfileOutput;
450     else
451       PMBuilder.PGOInstrGen = "default_%m.profraw";
452   }
453   if (CodeGenOpts.hasProfileIRUse())
454     PMBuilder.PGOInstrUse = CodeGenOpts.ProfileInstrumentUsePath;
455 
456   if (!CodeGenOpts.SampleProfileFile.empty())
457     PMBuilder.PGOSampleUse = CodeGenOpts.SampleProfileFile;
458 
459   PMBuilder.populateFunctionPassManager(FPM);
460   PMBuilder.populateModulePassManager(MPM);
461 }
462 
463 void EmitAssemblyHelper::setCommandLineOpts() {
464   SmallVector<const char *, 16> BackendArgs;
465   BackendArgs.push_back("clang"); // Fake program name.
466   if (!CodeGenOpts.DebugPass.empty()) {
467     BackendArgs.push_back("-debug-pass");
468     BackendArgs.push_back(CodeGenOpts.DebugPass.c_str());
469   }
470   if (!CodeGenOpts.LimitFloatPrecision.empty()) {
471     BackendArgs.push_back("-limit-float-precision");
472     BackendArgs.push_back(CodeGenOpts.LimitFloatPrecision.c_str());
473   }
474   for (const std::string &BackendOption : CodeGenOpts.BackendOptions)
475     BackendArgs.push_back(BackendOption.c_str());
476   BackendArgs.push_back(nullptr);
477   llvm::cl::ParseCommandLineOptions(BackendArgs.size() - 1,
478                                     BackendArgs.data());
479 }
480 
481 void EmitAssemblyHelper::CreateTargetMachine(bool MustCreateTM) {
482   // Create the TargetMachine for generating code.
483   std::string Error;
484   std::string Triple = TheModule->getTargetTriple();
485   const llvm::Target *TheTarget = TargetRegistry::lookupTarget(Triple, Error);
486   if (!TheTarget) {
487     if (MustCreateTM)
488       Diags.Report(diag::err_fe_unable_to_create_target) << Error;
489     return;
490   }
491 
492   unsigned CodeModel =
493     llvm::StringSwitch<unsigned>(CodeGenOpts.CodeModel)
494       .Case("small", llvm::CodeModel::Small)
495       .Case("kernel", llvm::CodeModel::Kernel)
496       .Case("medium", llvm::CodeModel::Medium)
497       .Case("large", llvm::CodeModel::Large)
498       .Case("default", llvm::CodeModel::Default)
499       .Default(~0u);
500   assert(CodeModel != ~0u && "invalid code model!");
501   llvm::CodeModel::Model CM = static_cast<llvm::CodeModel::Model>(CodeModel);
502 
503   std::string FeaturesStr =
504       llvm::join(TargetOpts.Features.begin(), TargetOpts.Features.end(), ",");
505 
506   // Keep this synced with the equivalent code in tools/driver/cc1as_main.cpp.
507   llvm::Optional<llvm::Reloc::Model> RM;
508   RM = llvm::StringSwitch<llvm::Reloc::Model>(CodeGenOpts.RelocationModel)
509            .Case("static", llvm::Reloc::Static)
510            .Case("pic", llvm::Reloc::PIC_)
511            .Case("ropi", llvm::Reloc::ROPI)
512            .Case("rwpi", llvm::Reloc::RWPI)
513            .Case("ropi-rwpi", llvm::Reloc::ROPI_RWPI)
514            .Case("dynamic-no-pic", llvm::Reloc::DynamicNoPIC);
515   assert(RM.hasValue() && "invalid PIC model!");
516 
517   CodeGenOpt::Level OptLevel;
518   switch (CodeGenOpts.OptimizationLevel) {
519   default:
520     llvm_unreachable("Invalid optimization level!");
521   case 0:
522     OptLevel = CodeGenOpt::None;
523     break;
524   case 1:
525     OptLevel = CodeGenOpt::Less;
526     break;
527   case 2:
528     OptLevel = CodeGenOpt::Default;
529     break; // O2/Os/Oz
530   case 3:
531     OptLevel = CodeGenOpt::Aggressive;
532     break;
533   }
534 
535   llvm::TargetOptions Options;
536 
537   Options.ThreadModel =
538     llvm::StringSwitch<llvm::ThreadModel::Model>(CodeGenOpts.ThreadModel)
539       .Case("posix", llvm::ThreadModel::POSIX)
540       .Case("single", llvm::ThreadModel::Single);
541 
542   // Set float ABI type.
543   assert((CodeGenOpts.FloatABI == "soft" || CodeGenOpts.FloatABI == "softfp" ||
544           CodeGenOpts.FloatABI == "hard" || CodeGenOpts.FloatABI.empty()) &&
545          "Invalid Floating Point ABI!");
546   Options.FloatABIType =
547       llvm::StringSwitch<llvm::FloatABI::ABIType>(CodeGenOpts.FloatABI)
548           .Case("soft", llvm::FloatABI::Soft)
549           .Case("softfp", llvm::FloatABI::Soft)
550           .Case("hard", llvm::FloatABI::Hard)
551           .Default(llvm::FloatABI::Default);
552 
553   // Set FP fusion mode.
554   switch (CodeGenOpts.getFPContractMode()) {
555   case CodeGenOptions::FPC_Off:
556     Options.AllowFPOpFusion = llvm::FPOpFusion::Strict;
557     break;
558   case CodeGenOptions::FPC_On:
559     Options.AllowFPOpFusion = llvm::FPOpFusion::Standard;
560     break;
561   case CodeGenOptions::FPC_Fast:
562     Options.AllowFPOpFusion = llvm::FPOpFusion::Fast;
563     break;
564   }
565 
566   Options.UseInitArray = CodeGenOpts.UseInitArray;
567   Options.DisableIntegratedAS = CodeGenOpts.DisableIntegratedAS;
568   Options.CompressDebugSections = CodeGenOpts.CompressDebugSections;
569   Options.RelaxELFRelocations = CodeGenOpts.RelaxELFRelocations;
570 
571   // Set EABI version.
572   Options.EABIVersion = llvm::StringSwitch<llvm::EABI>(TargetOpts.EABIVersion)
573                             .Case("4", llvm::EABI::EABI4)
574                             .Case("5", llvm::EABI::EABI5)
575                             .Case("gnu", llvm::EABI::GNU)
576                             .Default(llvm::EABI::Default);
577 
578   if (LangOpts.SjLjExceptions)
579     Options.ExceptionModel = llvm::ExceptionHandling::SjLj;
580 
581   Options.LessPreciseFPMADOption = CodeGenOpts.LessPreciseFPMAD;
582   Options.NoInfsFPMath = CodeGenOpts.NoInfsFPMath;
583   Options.NoNaNsFPMath = CodeGenOpts.NoNaNsFPMath;
584   Options.NoZerosInBSS = CodeGenOpts.NoZeroInitializedInBSS;
585   Options.UnsafeFPMath = CodeGenOpts.UnsafeFPMath;
586   Options.StackAlignmentOverride = CodeGenOpts.StackAlignment;
587   Options.FunctionSections = CodeGenOpts.FunctionSections;
588   Options.DataSections = CodeGenOpts.DataSections;
589   Options.UniqueSectionNames = CodeGenOpts.UniqueSectionNames;
590   Options.EmulatedTLS = CodeGenOpts.EmulatedTLS;
591   Options.DebuggerTuning = CodeGenOpts.getDebuggerTuning();
592 
593   Options.MCOptions.MCRelaxAll = CodeGenOpts.RelaxAll;
594   Options.MCOptions.MCSaveTempLabels = CodeGenOpts.SaveTempLabels;
595   Options.MCOptions.MCUseDwarfDirectory = !CodeGenOpts.NoDwarfDirectoryAsm;
596   Options.MCOptions.MCNoExecStack = CodeGenOpts.NoExecStack;
597   Options.MCOptions.MCIncrementalLinkerCompatible =
598       CodeGenOpts.IncrementalLinkerCompatible;
599   Options.MCOptions.MCPIECopyRelocations = CodeGenOpts.PIECopyRelocations;
600   Options.MCOptions.MCFatalWarnings = CodeGenOpts.FatalWarnings;
601   Options.MCOptions.AsmVerbose = CodeGenOpts.AsmVerbose;
602   Options.MCOptions.PreserveAsmComments = CodeGenOpts.PreserveAsmComments;
603   Options.MCOptions.ABIName = TargetOpts.ABI;
604   for (const auto &Entry : HSOpts.UserEntries)
605     if (!Entry.IsFramework &&
606         (Entry.Group == frontend::IncludeDirGroup::Quoted ||
607          Entry.Group == frontend::IncludeDirGroup::Angled ||
608          Entry.Group == frontend::IncludeDirGroup::System))
609       Options.MCOptions.IASSearchPaths.push_back(
610           Entry.IgnoreSysRoot ? Entry.Path : HSOpts.Sysroot + Entry.Path);
611 
612   TM.reset(TheTarget->createTargetMachine(Triple, TargetOpts.CPU, FeaturesStr,
613                                           Options, RM, CM, OptLevel));
614 }
615 
616 bool EmitAssemblyHelper::AddEmitPasses(legacy::PassManager &CodeGenPasses,
617                                        BackendAction Action,
618                                        raw_pwrite_stream &OS) {
619   // Add LibraryInfo.
620   llvm::Triple TargetTriple(TheModule->getTargetTriple());
621   std::unique_ptr<TargetLibraryInfoImpl> TLII(
622       createTLII(TargetTriple, CodeGenOpts));
623   CodeGenPasses.add(new TargetLibraryInfoWrapperPass(*TLII));
624 
625   // Normal mode, emit a .s or .o file by running the code generator. Note,
626   // this also adds codegenerator level optimization passes.
627   TargetMachine::CodeGenFileType CGFT = TargetMachine::CGFT_AssemblyFile;
628   if (Action == Backend_EmitObj)
629     CGFT = TargetMachine::CGFT_ObjectFile;
630   else if (Action == Backend_EmitMCNull)
631     CGFT = TargetMachine::CGFT_Null;
632   else
633     assert(Action == Backend_EmitAssembly && "Invalid action!");
634 
635   // Add ObjC ARC final-cleanup optimizations. This is done as part of the
636   // "codegen" passes so that it isn't run multiple times when there is
637   // inlining happening.
638   if (CodeGenOpts.OptimizationLevel > 0)
639     CodeGenPasses.add(createObjCARCContractPass());
640 
641   if (TM->addPassesToEmitFile(CodeGenPasses, OS, CGFT,
642                               /*DisableVerify=*/!CodeGenOpts.VerifyModule)) {
643     Diags.Report(diag::err_fe_unable_to_interface_with_target);
644     return false;
645   }
646 
647   return true;
648 }
649 
650 void EmitAssemblyHelper::EmitAssembly(BackendAction Action,
651                                       std::unique_ptr<raw_pwrite_stream> OS) {
652   TimeRegion Region(llvm::TimePassesIsEnabled ? &CodeGenerationTime : nullptr);
653 
654   setCommandLineOpts();
655 
656   bool UsesCodeGen = (Action != Backend_EmitNothing &&
657                       Action != Backend_EmitBC &&
658                       Action != Backend_EmitLL);
659   CreateTargetMachine(UsesCodeGen);
660 
661   if (UsesCodeGen && !TM)
662     return;
663   if (TM)
664     TheModule->setDataLayout(TM->createDataLayout());
665 
666   legacy::PassManager PerModulePasses;
667   PerModulePasses.add(
668       createTargetTransformInfoWrapperPass(getTargetIRAnalysis()));
669 
670   legacy::FunctionPassManager PerFunctionPasses(TheModule);
671   PerFunctionPasses.add(
672       createTargetTransformInfoWrapperPass(getTargetIRAnalysis()));
673 
674   CreatePasses(PerModulePasses, PerFunctionPasses);
675 
676   legacy::PassManager CodeGenPasses;
677   CodeGenPasses.add(
678       createTargetTransformInfoWrapperPass(getTargetIRAnalysis()));
679 
680   switch (Action) {
681   case Backend_EmitNothing:
682     break;
683 
684   case Backend_EmitBC:
685     if (CodeGenOpts.EmitSummaryIndex)
686       PerModulePasses.add(createWriteThinLTOBitcodePass(*OS));
687     else
688       PerModulePasses.add(
689           createBitcodeWriterPass(*OS, CodeGenOpts.EmitLLVMUseLists));
690     break;
691 
692   case Backend_EmitLL:
693     PerModulePasses.add(
694         createPrintModulePass(*OS, "", CodeGenOpts.EmitLLVMUseLists));
695     break;
696 
697   default:
698     if (!AddEmitPasses(CodeGenPasses, Action, *OS))
699       return;
700   }
701 
702   // Before executing passes, print the final values of the LLVM options.
703   cl::PrintOptionValues();
704 
705   // Run passes. For now we do all passes at once, but eventually we
706   // would like to have the option of streaming code generation.
707 
708   {
709     PrettyStackTraceString CrashInfo("Per-function optimization");
710 
711     PerFunctionPasses.doInitialization();
712     for (Function &F : *TheModule)
713       if (!F.isDeclaration())
714         PerFunctionPasses.run(F);
715     PerFunctionPasses.doFinalization();
716   }
717 
718   {
719     PrettyStackTraceString CrashInfo("Per-module optimization passes");
720     PerModulePasses.run(*TheModule);
721   }
722 
723   {
724     PrettyStackTraceString CrashInfo("Code generation");
725     CodeGenPasses.run(*TheModule);
726   }
727 }
728 
729 static PassBuilder::OptimizationLevel mapToLevel(const CodeGenOptions &Opts) {
730   switch (Opts.OptimizationLevel) {
731   default:
732     llvm_unreachable("Invalid optimization level!");
733 
734   case 1:
735     return PassBuilder::O1;
736 
737   case 2:
738     switch (Opts.OptimizeSize) {
739     default:
740       llvm_unreachable("Invalide optimization level for size!");
741 
742     case 0:
743       return PassBuilder::O2;
744 
745     case 1:
746       return PassBuilder::Os;
747 
748     case 2:
749       return PassBuilder::Oz;
750     }
751 
752   case 3:
753     return PassBuilder::O3;
754   }
755 }
756 
757 /// A clean version of `EmitAssembly` that uses the new pass manager.
758 ///
759 /// Not all features are currently supported in this system, but where
760 /// necessary it falls back to the legacy pass manager to at least provide
761 /// basic functionality.
762 ///
763 /// This API is planned to have its functionality finished and then to replace
764 /// `EmitAssembly` at some point in the future when the default switches.
765 void EmitAssemblyHelper::EmitAssemblyWithNewPassManager(
766     BackendAction Action, std::unique_ptr<raw_pwrite_stream> OS) {
767   TimeRegion Region(llvm::TimePassesIsEnabled ? &CodeGenerationTime : nullptr);
768   setCommandLineOpts();
769 
770   // The new pass manager always makes a target machine available to passes
771   // during construction.
772   CreateTargetMachine(/*MustCreateTM*/ true);
773   if (!TM)
774     // This will already be diagnosed, just bail.
775     return;
776   TheModule->setDataLayout(TM->createDataLayout());
777 
778   PassBuilder PB(TM.get());
779 
780   LoopAnalysisManager LAM;
781   FunctionAnalysisManager FAM;
782   CGSCCAnalysisManager CGAM;
783   ModuleAnalysisManager MAM;
784 
785   // Register the AA manager first so that our version is the one used.
786   FAM.registerPass([&] { return PB.buildDefaultAAPipeline(); });
787 
788   // Register all the basic analyses with the managers.
789   PB.registerModuleAnalyses(MAM);
790   PB.registerCGSCCAnalyses(CGAM);
791   PB.registerFunctionAnalyses(FAM);
792   PB.registerLoopAnalyses(LAM);
793   PB.crossRegisterProxies(LAM, FAM, CGAM, MAM);
794 
795   ModulePassManager MPM;
796 
797   if (!CodeGenOpts.DisableLLVMPasses) {
798     if (CodeGenOpts.OptimizationLevel == 0) {
799       // Build a minimal pipeline based on the semantics required by Clang,
800       // which is just that always inlining occurs.
801       MPM.addPass(AlwaysInlinerPass());
802     } else {
803       // Otherwise, use the default pass pipeline. We also have to map our
804       // optimization levels into one of the distinct levels used to configure
805       // the pipeline.
806       PassBuilder::OptimizationLevel Level = mapToLevel(CodeGenOpts);
807 
808       MPM = PB.buildPerModuleDefaultPipeline(Level);
809     }
810   }
811 
812   // FIXME: We still use the legacy pass manager to do code generation. We
813   // create that pass manager here and use it as needed below.
814   legacy::PassManager CodeGenPasses;
815   bool NeedCodeGen = false;
816 
817   // Append any output we need to the pass manager.
818   switch (Action) {
819   case Backend_EmitNothing:
820     break;
821 
822   case Backend_EmitBC:
823     MPM.addPass(BitcodeWriterPass(*OS, CodeGenOpts.EmitLLVMUseLists,
824                                   CodeGenOpts.EmitSummaryIndex,
825                                   CodeGenOpts.EmitSummaryIndex));
826     break;
827 
828   case Backend_EmitLL:
829     MPM.addPass(PrintModulePass(*OS, "", CodeGenOpts.EmitLLVMUseLists));
830     break;
831 
832   case Backend_EmitAssembly:
833   case Backend_EmitMCNull:
834   case Backend_EmitObj:
835     NeedCodeGen = true;
836     CodeGenPasses.add(
837         createTargetTransformInfoWrapperPass(getTargetIRAnalysis()));
838     if (!AddEmitPasses(CodeGenPasses, Action, *OS))
839       // FIXME: Should we handle this error differently?
840       return;
841     break;
842   }
843 
844   // Before executing passes, print the final values of the LLVM options.
845   cl::PrintOptionValues();
846 
847   // Now that we have all of the passes ready, run them.
848   {
849     PrettyStackTraceString CrashInfo("Optimizer");
850     MPM.run(*TheModule, MAM);
851   }
852 
853   // Now if needed, run the legacy PM for codegen.
854   if (NeedCodeGen) {
855     PrettyStackTraceString CrashInfo("Code generation");
856     CodeGenPasses.run(*TheModule);
857   }
858 }
859 
860 Expected<BitcodeModule> clang::FindThinLTOModule(MemoryBufferRef MBRef) {
861   Expected<std::vector<BitcodeModule>> BMsOrErr = getBitcodeModuleList(MBRef);
862   if (!BMsOrErr)
863     return BMsOrErr.takeError();
864 
865   // The bitcode file may contain multiple modules, we want the one with a
866   // summary.
867   for (BitcodeModule &BM : *BMsOrErr) {
868     Expected<bool> HasSummary = BM.hasSummary();
869     if (HasSummary && *HasSummary)
870       return BM;
871   }
872 
873   return make_error<StringError>("Could not find module summary",
874                                  inconvertibleErrorCode());
875 }
876 
877 static void runThinLTOBackend(ModuleSummaryIndex *CombinedIndex, Module *M,
878                               std::unique_ptr<raw_pwrite_stream> OS,
879                               std::string SampleProfile) {
880   StringMap<std::map<GlobalValue::GUID, GlobalValueSummary *>>
881       ModuleToDefinedGVSummaries;
882   CombinedIndex->collectDefinedGVSummariesPerModule(ModuleToDefinedGVSummaries);
883 
884   // We can simply import the values mentioned in the combined index, since
885   // we should only invoke this using the individual indexes written out
886   // via a WriteIndexesThinBackend.
887   FunctionImporter::ImportMapTy ImportList;
888   for (auto &GlobalList : *CombinedIndex) {
889     auto GUID = GlobalList.first;
890     assert(GlobalList.second.size() == 1 &&
891            "Expected individual combined index to have one summary per GUID");
892     auto &Summary = GlobalList.second[0];
893     // Skip the summaries for the importing module. These are included to
894     // e.g. record required linkage changes.
895     if (Summary->modulePath() == M->getModuleIdentifier())
896       continue;
897     // Doesn't matter what value we plug in to the map, just needs an entry
898     // to provoke importing by thinBackend.
899     ImportList[Summary->modulePath()][GUID] = 1;
900   }
901 
902   std::vector<std::unique_ptr<llvm::MemoryBuffer>> OwnedImports;
903   MapVector<llvm::StringRef, llvm::BitcodeModule> ModuleMap;
904 
905   for (auto &I : ImportList) {
906     ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> MBOrErr =
907         llvm::MemoryBuffer::getFile(I.first());
908     if (!MBOrErr) {
909       errs() << "Error loading imported file '" << I.first()
910              << "': " << MBOrErr.getError().message() << "\n";
911       return;
912     }
913 
914     Expected<BitcodeModule> BMOrErr = FindThinLTOModule(**MBOrErr);
915     if (!BMOrErr) {
916       handleAllErrors(BMOrErr.takeError(), [&](ErrorInfoBase &EIB) {
917         errs() << "Error loading imported file '" << I.first()
918                << "': " << EIB.message() << '\n';
919       });
920       return;
921     }
922     ModuleMap.insert({I.first(), *BMOrErr});
923 
924     OwnedImports.push_back(std::move(*MBOrErr));
925   }
926   auto AddStream = [&](size_t Task) {
927     return llvm::make_unique<lto::NativeObjectStream>(std::move(OS));
928   };
929   lto::Config Conf;
930   Conf.SampleProfile = SampleProfile;
931   if (Error E = thinBackend(
932           Conf, 0, AddStream, *M, *CombinedIndex, ImportList,
933           ModuleToDefinedGVSummaries[M->getModuleIdentifier()], ModuleMap)) {
934     handleAllErrors(std::move(E), [&](ErrorInfoBase &EIB) {
935       errs() << "Error running ThinLTO backend: " << EIB.message() << '\n';
936     });
937   }
938 }
939 
940 void clang::EmitBackendOutput(DiagnosticsEngine &Diags,
941                               const HeaderSearchOptions &HeaderOpts,
942                               const CodeGenOptions &CGOpts,
943                               const clang::TargetOptions &TOpts,
944                               const LangOptions &LOpts,
945                               const llvm::DataLayout &TDesc, Module *M,
946                               BackendAction Action,
947                               std::unique_ptr<raw_pwrite_stream> OS) {
948   if (!CGOpts.ThinLTOIndexFile.empty()) {
949     // If we are performing a ThinLTO importing compile, load the function index
950     // into memory and pass it into runThinLTOBackend, which will run the
951     // function importer and invoke LTO passes.
952     Expected<std::unique_ptr<ModuleSummaryIndex>> IndexOrErr =
953         llvm::getModuleSummaryIndexForFile(CGOpts.ThinLTOIndexFile);
954     if (!IndexOrErr) {
955       logAllUnhandledErrors(IndexOrErr.takeError(), errs(),
956                             "Error loading index file '" +
957                             CGOpts.ThinLTOIndexFile + "': ");
958       return;
959     }
960     std::unique_ptr<ModuleSummaryIndex> CombinedIndex = std::move(*IndexOrErr);
961     // A null CombinedIndex means we should skip ThinLTO compilation
962     // (LLVM will optionally ignore empty index files, returning null instead
963     // of an error).
964     bool DoThinLTOBackend = CombinedIndex != nullptr;
965     if (DoThinLTOBackend) {
966       runThinLTOBackend(CombinedIndex.get(), M, std::move(OS),
967                         CGOpts.SampleProfileFile);
968       return;
969     }
970   }
971 
972   EmitAssemblyHelper AsmHelper(Diags, HeaderOpts, CGOpts, TOpts, LOpts, M);
973 
974   if (CGOpts.ExperimentalNewPassManager)
975     AsmHelper.EmitAssemblyWithNewPassManager(Action, std::move(OS));
976   else
977     AsmHelper.EmitAssembly(Action, std::move(OS));
978 
979   // Verify clang's TargetInfo DataLayout against the LLVM TargetMachine's
980   // DataLayout.
981   if (AsmHelper.TM) {
982     std::string DLDesc = M->getDataLayout().getStringRepresentation();
983     if (DLDesc != TDesc.getStringRepresentation()) {
984       unsigned DiagID = Diags.getCustomDiagID(
985           DiagnosticsEngine::Error, "backend data layout '%0' does not match "
986                                     "expected target description '%1'");
987       Diags.Report(DiagID) << DLDesc << TDesc.getStringRepresentation();
988     }
989   }
990 }
991 
992 static const char* getSectionNameForBitcode(const Triple &T) {
993   switch (T.getObjectFormat()) {
994   case Triple::MachO:
995     return "__LLVM,__bitcode";
996   case Triple::COFF:
997   case Triple::ELF:
998   case Triple::Wasm:
999   case Triple::UnknownObjectFormat:
1000     return ".llvmbc";
1001   }
1002   llvm_unreachable("Unimplemented ObjectFormatType");
1003 }
1004 
1005 static const char* getSectionNameForCommandline(const Triple &T) {
1006   switch (T.getObjectFormat()) {
1007   case Triple::MachO:
1008     return "__LLVM,__cmdline";
1009   case Triple::COFF:
1010   case Triple::ELF:
1011   case Triple::Wasm:
1012   case Triple::UnknownObjectFormat:
1013     return ".llvmcmd";
1014   }
1015   llvm_unreachable("Unimplemented ObjectFormatType");
1016 }
1017 
1018 // With -fembed-bitcode, save a copy of the llvm IR as data in the
1019 // __LLVM,__bitcode section.
1020 void clang::EmbedBitcode(llvm::Module *M, const CodeGenOptions &CGOpts,
1021                          llvm::MemoryBufferRef Buf) {
1022   if (CGOpts.getEmbedBitcode() == CodeGenOptions::Embed_Off)
1023     return;
1024 
1025   // Save llvm.compiler.used and remote it.
1026   SmallVector<Constant*, 2> UsedArray;
1027   SmallSet<GlobalValue*, 4> UsedGlobals;
1028   Type *UsedElementType = Type::getInt8Ty(M->getContext())->getPointerTo(0);
1029   GlobalVariable *Used = collectUsedGlobalVariables(*M, UsedGlobals, true);
1030   for (auto *GV : UsedGlobals) {
1031     if (GV->getName() != "llvm.embedded.module" &&
1032         GV->getName() != "llvm.cmdline")
1033       UsedArray.push_back(
1034           ConstantExpr::getPointerBitCastOrAddrSpaceCast(GV, UsedElementType));
1035   }
1036   if (Used)
1037     Used->eraseFromParent();
1038 
1039   // Embed the bitcode for the llvm module.
1040   std::string Data;
1041   ArrayRef<uint8_t> ModuleData;
1042   Triple T(M->getTargetTriple());
1043   // Create a constant that contains the bitcode.
1044   // In case of embedding a marker, ignore the input Buf and use the empty
1045   // ArrayRef. It is also legal to create a bitcode marker even Buf is empty.
1046   if (CGOpts.getEmbedBitcode() != CodeGenOptions::Embed_Marker) {
1047     if (!isBitcode((const unsigned char *)Buf.getBufferStart(),
1048                    (const unsigned char *)Buf.getBufferEnd())) {
1049       // If the input is LLVM Assembly, bitcode is produced by serializing
1050       // the module. Use-lists order need to be perserved in this case.
1051       llvm::raw_string_ostream OS(Data);
1052       llvm::WriteBitcodeToFile(M, OS, /* ShouldPreserveUseListOrder */ true);
1053       ModuleData =
1054           ArrayRef<uint8_t>((const uint8_t *)OS.str().data(), OS.str().size());
1055     } else
1056       // If the input is LLVM bitcode, write the input byte stream directly.
1057       ModuleData = ArrayRef<uint8_t>((const uint8_t *)Buf.getBufferStart(),
1058                                      Buf.getBufferSize());
1059   }
1060   llvm::Constant *ModuleConstant =
1061       llvm::ConstantDataArray::get(M->getContext(), ModuleData);
1062   llvm::GlobalVariable *GV = new llvm::GlobalVariable(
1063       *M, ModuleConstant->getType(), true, llvm::GlobalValue::PrivateLinkage,
1064       ModuleConstant);
1065   GV->setSection(getSectionNameForBitcode(T));
1066   UsedArray.push_back(
1067       ConstantExpr::getPointerBitCastOrAddrSpaceCast(GV, UsedElementType));
1068   if (llvm::GlobalVariable *Old =
1069           M->getGlobalVariable("llvm.embedded.module", true)) {
1070     assert(Old->hasOneUse() &&
1071            "llvm.embedded.module can only be used once in llvm.compiler.used");
1072     GV->takeName(Old);
1073     Old->eraseFromParent();
1074   } else {
1075     GV->setName("llvm.embedded.module");
1076   }
1077 
1078   // Skip if only bitcode needs to be embedded.
1079   if (CGOpts.getEmbedBitcode() != CodeGenOptions::Embed_Bitcode) {
1080     // Embed command-line options.
1081     ArrayRef<uint8_t> CmdData(const_cast<uint8_t *>(CGOpts.CmdArgs.data()),
1082                               CGOpts.CmdArgs.size());
1083     llvm::Constant *CmdConstant =
1084       llvm::ConstantDataArray::get(M->getContext(), CmdData);
1085     GV = new llvm::GlobalVariable(*M, CmdConstant->getType(), true,
1086                                   llvm::GlobalValue::PrivateLinkage,
1087                                   CmdConstant);
1088     GV->setSection(getSectionNameForCommandline(T));
1089     UsedArray.push_back(
1090         ConstantExpr::getPointerBitCastOrAddrSpaceCast(GV, UsedElementType));
1091     if (llvm::GlobalVariable *Old =
1092             M->getGlobalVariable("llvm.cmdline", true)) {
1093       assert(Old->hasOneUse() &&
1094              "llvm.cmdline can only be used once in llvm.compiler.used");
1095       GV->takeName(Old);
1096       Old->eraseFromParent();
1097     } else {
1098       GV->setName("llvm.cmdline");
1099     }
1100   }
1101 
1102   if (UsedArray.empty())
1103     return;
1104 
1105   // Recreate llvm.compiler.used.
1106   ArrayType *ATy = ArrayType::get(UsedElementType, UsedArray.size());
1107   auto *NewUsed = new GlobalVariable(
1108       *M, ATy, false, llvm::GlobalValue::AppendingLinkage,
1109       llvm::ConstantArray::get(ATy, UsedArray), "llvm.compiler.used");
1110   NewUsed->setSection("llvm.metadata");
1111 }
1112