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 private:
77   TargetIRAnalysis getTargetIRAnalysis() const {
78     if (TM)
79       return TM->getTargetIRAnalysis();
80 
81     return TargetIRAnalysis();
82   }
83 
84   /// Set LLVM command line options passed through -backend-option.
85   void setCommandLineOpts();
86 
87   void CreatePasses(legacy::PassManager &MPM, legacy::FunctionPassManager &FPM);
88 
89   /// Generates the TargetMachine.
90   /// Leaves TM unchanged if it is unable to create the target machine.
91   /// Some of our clang tests specify triples which are not built
92   /// into clang. This is okay because these tests check the generated
93   /// IR, and they require DataLayout which depends on the triple.
94   /// In this case, we allow this method to fail and not report an error.
95   /// When MustCreateTM is used, we print an error if we are unable to load
96   /// the requested target.
97   void CreateTargetMachine(bool MustCreateTM);
98 
99   /// Add passes necessary to emit assembly or LLVM IR.
100   ///
101   /// \return True on success.
102   bool AddEmitPasses(legacy::PassManager &CodeGenPasses, BackendAction Action,
103                      raw_pwrite_stream &OS);
104 
105 public:
106   EmitAssemblyHelper(DiagnosticsEngine &_Diags,
107                      const HeaderSearchOptions &HeaderSearchOpts,
108                      const CodeGenOptions &CGOpts,
109                      const clang::TargetOptions &TOpts,
110                      const LangOptions &LOpts, Module *M)
111       : Diags(_Diags), HSOpts(HeaderSearchOpts), CodeGenOpts(CGOpts),
112         TargetOpts(TOpts), LangOpts(LOpts), TheModule(M),
113         CodeGenerationTime("codegen", "Code Generation Time") {}
114 
115   ~EmitAssemblyHelper() {
116     if (CodeGenOpts.DisableFree)
117       BuryPointer(std::move(TM));
118   }
119 
120   std::unique_ptr<TargetMachine> TM;
121 
122   void EmitAssembly(BackendAction Action,
123                     std::unique_ptr<raw_pwrite_stream> OS);
124 
125   void EmitAssemblyWithNewPassManager(BackendAction Action,
126                                       std::unique_ptr<raw_pwrite_stream> OS);
127 };
128 
129 // We need this wrapper to access LangOpts and CGOpts from extension functions
130 // that we add to the PassManagerBuilder.
131 class PassManagerBuilderWrapper : public PassManagerBuilder {
132 public:
133   PassManagerBuilderWrapper(const CodeGenOptions &CGOpts,
134                             const LangOptions &LangOpts)
135       : PassManagerBuilder(), CGOpts(CGOpts), LangOpts(LangOpts) {}
136   const CodeGenOptions &getCGOpts() const { return CGOpts; }
137   const LangOptions &getLangOpts() const { return LangOpts; }
138 private:
139   const CodeGenOptions &CGOpts;
140   const LangOptions &LangOpts;
141 };
142 
143 }
144 
145 static void addObjCARCAPElimPass(const PassManagerBuilder &Builder, PassManagerBase &PM) {
146   if (Builder.OptLevel > 0)
147     PM.add(createObjCARCAPElimPass());
148 }
149 
150 static void addObjCARCExpandPass(const PassManagerBuilder &Builder, PassManagerBase &PM) {
151   if (Builder.OptLevel > 0)
152     PM.add(createObjCARCExpandPass());
153 }
154 
155 static void addObjCARCOptPass(const PassManagerBuilder &Builder, PassManagerBase &PM) {
156   if (Builder.OptLevel > 0)
157     PM.add(createObjCARCOptPass());
158 }
159 
160 static void addAddDiscriminatorsPass(const PassManagerBuilder &Builder,
161                                      legacy::PassManagerBase &PM) {
162   PM.add(createAddDiscriminatorsPass());
163 }
164 
165 static void addBoundsCheckingPass(const PassManagerBuilder &Builder,
166                                   legacy::PassManagerBase &PM) {
167   PM.add(createBoundsCheckingPass());
168 }
169 
170 static void addSanitizerCoveragePass(const PassManagerBuilder &Builder,
171                                      legacy::PassManagerBase &PM) {
172   const PassManagerBuilderWrapper &BuilderWrapper =
173       static_cast<const PassManagerBuilderWrapper&>(Builder);
174   const CodeGenOptions &CGOpts = BuilderWrapper.getCGOpts();
175   SanitizerCoverageOptions Opts;
176   Opts.CoverageType =
177       static_cast<SanitizerCoverageOptions::Type>(CGOpts.SanitizeCoverageType);
178   Opts.IndirectCalls = CGOpts.SanitizeCoverageIndirectCalls;
179   Opts.TraceBB = CGOpts.SanitizeCoverageTraceBB;
180   Opts.TraceCmp = CGOpts.SanitizeCoverageTraceCmp;
181   Opts.TraceDiv = CGOpts.SanitizeCoverageTraceDiv;
182   Opts.TraceGep = CGOpts.SanitizeCoverageTraceGep;
183   Opts.Use8bitCounters = CGOpts.SanitizeCoverage8bitCounters;
184   Opts.TracePC = CGOpts.SanitizeCoverageTracePC;
185   Opts.TracePCGuard = CGOpts.SanitizeCoverageTracePCGuard;
186   PM.add(createSanitizerCoverageModulePass(Opts));
187 }
188 
189 static void addAddressSanitizerPasses(const PassManagerBuilder &Builder,
190                                       legacy::PassManagerBase &PM) {
191   const PassManagerBuilderWrapper &BuilderWrapper =
192       static_cast<const PassManagerBuilderWrapper&>(Builder);
193   const CodeGenOptions &CGOpts = BuilderWrapper.getCGOpts();
194   bool Recover = CGOpts.SanitizeRecover.has(SanitizerKind::Address);
195   bool UseAfterScope = CGOpts.SanitizeAddressUseAfterScope;
196   PM.add(createAddressSanitizerFunctionPass(/*CompileKernel*/ false, Recover,
197                                             UseAfterScope));
198   PM.add(createAddressSanitizerModulePass(/*CompileKernel*/false, Recover));
199 }
200 
201 static void addKernelAddressSanitizerPasses(const PassManagerBuilder &Builder,
202                                             legacy::PassManagerBase &PM) {
203   PM.add(createAddressSanitizerFunctionPass(
204       /*CompileKernel*/ true,
205       /*Recover*/ true, /*UseAfterScope*/ false));
206   PM.add(createAddressSanitizerModulePass(/*CompileKernel*/true,
207                                           /*Recover*/true));
208 }
209 
210 static void addMemorySanitizerPass(const PassManagerBuilder &Builder,
211                                    legacy::PassManagerBase &PM) {
212   const PassManagerBuilderWrapper &BuilderWrapper =
213       static_cast<const PassManagerBuilderWrapper&>(Builder);
214   const CodeGenOptions &CGOpts = BuilderWrapper.getCGOpts();
215   int TrackOrigins = CGOpts.SanitizeMemoryTrackOrigins;
216   bool Recover = CGOpts.SanitizeRecover.has(SanitizerKind::Memory);
217   PM.add(createMemorySanitizerPass(TrackOrigins, Recover));
218 
219   // MemorySanitizer inserts complex instrumentation that mostly follows
220   // the logic of the original code, but operates on "shadow" values.
221   // It can benefit from re-running some general purpose optimization passes.
222   if (Builder.OptLevel > 0) {
223     PM.add(createEarlyCSEPass());
224     PM.add(createReassociatePass());
225     PM.add(createLICMPass());
226     PM.add(createGVNPass());
227     PM.add(createInstructionCombiningPass());
228     PM.add(createDeadStoreEliminationPass());
229   }
230 }
231 
232 static void addThreadSanitizerPass(const PassManagerBuilder &Builder,
233                                    legacy::PassManagerBase &PM) {
234   PM.add(createThreadSanitizerPass());
235 }
236 
237 static void addDataFlowSanitizerPass(const PassManagerBuilder &Builder,
238                                      legacy::PassManagerBase &PM) {
239   const PassManagerBuilderWrapper &BuilderWrapper =
240       static_cast<const PassManagerBuilderWrapper&>(Builder);
241   const LangOptions &LangOpts = BuilderWrapper.getLangOpts();
242   PM.add(createDataFlowSanitizerPass(LangOpts.SanitizerBlacklistFiles));
243 }
244 
245 static void addEfficiencySanitizerPass(const PassManagerBuilder &Builder,
246                                        legacy::PassManagerBase &PM) {
247   const PassManagerBuilderWrapper &BuilderWrapper =
248       static_cast<const PassManagerBuilderWrapper&>(Builder);
249   const LangOptions &LangOpts = BuilderWrapper.getLangOpts();
250   EfficiencySanitizerOptions Opts;
251   if (LangOpts.Sanitize.has(SanitizerKind::EfficiencyCacheFrag))
252     Opts.ToolType = EfficiencySanitizerOptions::ESAN_CacheFrag;
253   else if (LangOpts.Sanitize.has(SanitizerKind::EfficiencyWorkingSet))
254     Opts.ToolType = EfficiencySanitizerOptions::ESAN_WorkingSet;
255   PM.add(createEfficiencySanitizerPass(Opts));
256 }
257 
258 static TargetLibraryInfoImpl *createTLII(llvm::Triple &TargetTriple,
259                                          const CodeGenOptions &CodeGenOpts) {
260   TargetLibraryInfoImpl *TLII = new TargetLibraryInfoImpl(TargetTriple);
261   if (!CodeGenOpts.SimplifyLibCalls)
262     TLII->disableAllFunctions();
263   else {
264     // Disable individual libc/libm calls in TargetLibraryInfo.
265     LibFunc F;
266     for (auto &FuncName : CodeGenOpts.getNoBuiltinFuncs())
267       if (TLII->getLibFunc(FuncName, F))
268         TLII->setUnavailable(F);
269   }
270 
271   switch (CodeGenOpts.getVecLib()) {
272   case CodeGenOptions::Accelerate:
273     TLII->addVectorizableFunctionsFromVecLib(TargetLibraryInfoImpl::Accelerate);
274     break;
275   case CodeGenOptions::SVML:
276     TLII->addVectorizableFunctionsFromVecLib(TargetLibraryInfoImpl::SVML);
277     break;
278   default:
279     break;
280   }
281   return TLII;
282 }
283 
284 static void addSymbolRewriterPass(const CodeGenOptions &Opts,
285                                   legacy::PassManager *MPM) {
286   llvm::SymbolRewriter::RewriteDescriptorList DL;
287 
288   llvm::SymbolRewriter::RewriteMapParser MapParser;
289   for (const auto &MapFile : Opts.RewriteMapFiles)
290     MapParser.parse(MapFile, &DL);
291 
292   MPM->add(createRewriteSymbolsPass(DL));
293 }
294 
295 void EmitAssemblyHelper::CreatePasses(legacy::PassManager &MPM,
296                                       legacy::FunctionPassManager &FPM) {
297   // Handle disabling of all LLVM passes, where we want to preserve the
298   // internal module before any optimization.
299   if (CodeGenOpts.DisableLLVMPasses)
300     return;
301 
302   PassManagerBuilderWrapper PMBuilder(CodeGenOpts, LangOpts);
303 
304   // Figure out TargetLibraryInfo.  This needs to be added to MPM and FPM
305   // manually (and not via PMBuilder), since some passes (eg. InstrProfiling)
306   // are inserted before PMBuilder ones - they'd get the default-constructed
307   // TLI with an unknown target otherwise.
308   Triple TargetTriple(TheModule->getTargetTriple());
309   std::unique_ptr<TargetLibraryInfoImpl> TLII(
310       createTLII(TargetTriple, CodeGenOpts));
311 
312   // At O0 and O1 we only run the always inliner which is more efficient. At
313   // higher optimization levels we run the normal inliner.
314   if (CodeGenOpts.OptimizationLevel <= 1) {
315     bool InsertLifetimeIntrinsics = (CodeGenOpts.OptimizationLevel != 0 &&
316                                      !CodeGenOpts.DisableLifetimeMarkers);
317     PMBuilder.Inliner = createAlwaysInlinerLegacyPass(InsertLifetimeIntrinsics);
318   } else {
319     PMBuilder.Inliner = createFunctionInliningPass(
320         CodeGenOpts.OptimizationLevel, CodeGenOpts.OptimizeSize);
321   }
322 
323   PMBuilder.OptLevel = CodeGenOpts.OptimizationLevel;
324   PMBuilder.SizeLevel = CodeGenOpts.OptimizeSize;
325   PMBuilder.BBVectorize = CodeGenOpts.VectorizeBB;
326   PMBuilder.SLPVectorize = CodeGenOpts.VectorizeSLP;
327   PMBuilder.LoopVectorize = CodeGenOpts.VectorizeLoop;
328 
329   PMBuilder.DisableUnrollLoops = !CodeGenOpts.UnrollLoops;
330   PMBuilder.MergeFunctions = CodeGenOpts.MergeFunctions;
331   PMBuilder.PrepareForThinLTO = CodeGenOpts.EmitSummaryIndex;
332   PMBuilder.PrepareForLTO = CodeGenOpts.PrepareForLTO;
333   PMBuilder.RerollLoops = CodeGenOpts.RerollLoops;
334 
335   MPM.add(new TargetLibraryInfoWrapperPass(*TLII));
336 
337   if (TM)
338     TM->adjustPassManager(PMBuilder);
339 
340   PMBuilder.addExtension(PassManagerBuilder::EP_EarlyAsPossible,
341                          addAddDiscriminatorsPass);
342 
343   // In ObjC ARC mode, add the main ARC optimization passes.
344   if (LangOpts.ObjCAutoRefCount) {
345     PMBuilder.addExtension(PassManagerBuilder::EP_EarlyAsPossible,
346                            addObjCARCExpandPass);
347     PMBuilder.addExtension(PassManagerBuilder::EP_ModuleOptimizerEarly,
348                            addObjCARCAPElimPass);
349     PMBuilder.addExtension(PassManagerBuilder::EP_ScalarOptimizerLate,
350                            addObjCARCOptPass);
351   }
352 
353   if (LangOpts.Sanitize.has(SanitizerKind::LocalBounds)) {
354     PMBuilder.addExtension(PassManagerBuilder::EP_ScalarOptimizerLate,
355                            addBoundsCheckingPass);
356     PMBuilder.addExtension(PassManagerBuilder::EP_EnabledOnOptLevel0,
357                            addBoundsCheckingPass);
358   }
359 
360   if (CodeGenOpts.SanitizeCoverageType ||
361       CodeGenOpts.SanitizeCoverageIndirectCalls ||
362       CodeGenOpts.SanitizeCoverageTraceCmp) {
363     PMBuilder.addExtension(PassManagerBuilder::EP_OptimizerLast,
364                            addSanitizerCoveragePass);
365     PMBuilder.addExtension(PassManagerBuilder::EP_EnabledOnOptLevel0,
366                            addSanitizerCoveragePass);
367   }
368 
369   if (LangOpts.Sanitize.has(SanitizerKind::Address)) {
370     PMBuilder.addExtension(PassManagerBuilder::EP_OptimizerLast,
371                            addAddressSanitizerPasses);
372     PMBuilder.addExtension(PassManagerBuilder::EP_EnabledOnOptLevel0,
373                            addAddressSanitizerPasses);
374   }
375 
376   if (LangOpts.Sanitize.has(SanitizerKind::KernelAddress)) {
377     PMBuilder.addExtension(PassManagerBuilder::EP_OptimizerLast,
378                            addKernelAddressSanitizerPasses);
379     PMBuilder.addExtension(PassManagerBuilder::EP_EnabledOnOptLevel0,
380                            addKernelAddressSanitizerPasses);
381   }
382 
383   if (LangOpts.Sanitize.has(SanitizerKind::Memory)) {
384     PMBuilder.addExtension(PassManagerBuilder::EP_OptimizerLast,
385                            addMemorySanitizerPass);
386     PMBuilder.addExtension(PassManagerBuilder::EP_EnabledOnOptLevel0,
387                            addMemorySanitizerPass);
388   }
389 
390   if (LangOpts.Sanitize.has(SanitizerKind::Thread)) {
391     PMBuilder.addExtension(PassManagerBuilder::EP_OptimizerLast,
392                            addThreadSanitizerPass);
393     PMBuilder.addExtension(PassManagerBuilder::EP_EnabledOnOptLevel0,
394                            addThreadSanitizerPass);
395   }
396 
397   if (LangOpts.Sanitize.has(SanitizerKind::DataFlow)) {
398     PMBuilder.addExtension(PassManagerBuilder::EP_OptimizerLast,
399                            addDataFlowSanitizerPass);
400     PMBuilder.addExtension(PassManagerBuilder::EP_EnabledOnOptLevel0,
401                            addDataFlowSanitizerPass);
402   }
403 
404   if (LangOpts.CoroutinesTS)
405     addCoroutinePassesToExtensionPoints(PMBuilder);
406 
407   if (LangOpts.Sanitize.hasOneOf(SanitizerKind::Efficiency)) {
408     PMBuilder.addExtension(PassManagerBuilder::EP_OptimizerLast,
409                            addEfficiencySanitizerPass);
410     PMBuilder.addExtension(PassManagerBuilder::EP_EnabledOnOptLevel0,
411                            addEfficiencySanitizerPass);
412   }
413 
414   // Set up the per-function pass manager.
415   FPM.add(new TargetLibraryInfoWrapperPass(*TLII));
416   if (CodeGenOpts.VerifyModule)
417     FPM.add(createVerifierPass());
418 
419   // Set up the per-module pass manager.
420   if (!CodeGenOpts.RewriteMapFiles.empty())
421     addSymbolRewriterPass(CodeGenOpts, &MPM);
422 
423   if (!CodeGenOpts.DisableGCov &&
424       (CodeGenOpts.EmitGcovArcs || CodeGenOpts.EmitGcovNotes)) {
425     // Not using 'GCOVOptions::getDefault' allows us to avoid exiting if
426     // LLVM's -default-gcov-version flag is set to something invalid.
427     GCOVOptions Options;
428     Options.EmitNotes = CodeGenOpts.EmitGcovNotes;
429     Options.EmitData = CodeGenOpts.EmitGcovArcs;
430     memcpy(Options.Version, CodeGenOpts.CoverageVersion, 4);
431     Options.UseCfgChecksum = CodeGenOpts.CoverageExtraChecksum;
432     Options.NoRedZone = CodeGenOpts.DisableRedZone;
433     Options.FunctionNamesInData =
434         !CodeGenOpts.CoverageNoFunctionNamesInData;
435     Options.ExitBlockBeforeBody = CodeGenOpts.CoverageExitBlockBeforeBody;
436     MPM.add(createGCOVProfilerPass(Options));
437     if (CodeGenOpts.getDebugInfo() == codegenoptions::NoDebugInfo)
438       MPM.add(createStripSymbolsPass(true));
439   }
440 
441   if (CodeGenOpts.hasProfileClangInstr()) {
442     InstrProfOptions Options;
443     Options.NoRedZone = CodeGenOpts.DisableRedZone;
444     Options.InstrProfileOutput = CodeGenOpts.InstrProfileOutput;
445     MPM.add(createInstrProfilingLegacyPass(Options));
446   }
447   if (CodeGenOpts.hasProfileIRInstr()) {
448     PMBuilder.EnablePGOInstrGen = true;
449     if (!CodeGenOpts.InstrProfileOutput.empty())
450       PMBuilder.PGOInstrGen = CodeGenOpts.InstrProfileOutput;
451     else
452       PMBuilder.PGOInstrGen = "default_%m.profraw";
453   }
454   if (CodeGenOpts.hasProfileIRUse())
455     PMBuilder.PGOInstrUse = CodeGenOpts.ProfileInstrumentUsePath;
456 
457   if (!CodeGenOpts.SampleProfileFile.empty())
458     PMBuilder.PGOSampleUse = CodeGenOpts.SampleProfileFile;
459 
460   PMBuilder.populateFunctionPassManager(FPM);
461   PMBuilder.populateModulePassManager(MPM);
462 }
463 
464 void EmitAssemblyHelper::setCommandLineOpts() {
465   SmallVector<const char *, 16> BackendArgs;
466   BackendArgs.push_back("clang"); // Fake program name.
467   if (!CodeGenOpts.DebugPass.empty()) {
468     BackendArgs.push_back("-debug-pass");
469     BackendArgs.push_back(CodeGenOpts.DebugPass.c_str());
470   }
471   if (!CodeGenOpts.LimitFloatPrecision.empty()) {
472     BackendArgs.push_back("-limit-float-precision");
473     BackendArgs.push_back(CodeGenOpts.LimitFloatPrecision.c_str());
474   }
475   for (const std::string &BackendOption : CodeGenOpts.BackendOptions)
476     BackendArgs.push_back(BackendOption.c_str());
477   BackendArgs.push_back(nullptr);
478   llvm::cl::ParseCommandLineOptions(BackendArgs.size() - 1,
479                                     BackendArgs.data());
480 }
481 
482 void EmitAssemblyHelper::CreateTargetMachine(bool MustCreateTM) {
483   // Create the TargetMachine for generating code.
484   std::string Error;
485   std::string Triple = TheModule->getTargetTriple();
486   const llvm::Target *TheTarget = TargetRegistry::lookupTarget(Triple, Error);
487   if (!TheTarget) {
488     if (MustCreateTM)
489       Diags.Report(diag::err_fe_unable_to_create_target) << Error;
490     return;
491   }
492 
493   unsigned CodeModel =
494     llvm::StringSwitch<unsigned>(CodeGenOpts.CodeModel)
495       .Case("small", llvm::CodeModel::Small)
496       .Case("kernel", llvm::CodeModel::Kernel)
497       .Case("medium", llvm::CodeModel::Medium)
498       .Case("large", llvm::CodeModel::Large)
499       .Case("default", llvm::CodeModel::Default)
500       .Default(~0u);
501   assert(CodeModel != ~0u && "invalid code model!");
502   llvm::CodeModel::Model CM = static_cast<llvm::CodeModel::Model>(CodeModel);
503 
504   std::string FeaturesStr =
505       llvm::join(TargetOpts.Features.begin(), TargetOpts.Features.end(), ",");
506 
507   // Keep this synced with the equivalent code in tools/driver/cc1as_main.cpp.
508   llvm::Optional<llvm::Reloc::Model> RM;
509   RM = llvm::StringSwitch<llvm::Reloc::Model>(CodeGenOpts.RelocationModel)
510            .Case("static", llvm::Reloc::Static)
511            .Case("pic", llvm::Reloc::PIC_)
512            .Case("ropi", llvm::Reloc::ROPI)
513            .Case("rwpi", llvm::Reloc::RWPI)
514            .Case("ropi-rwpi", llvm::Reloc::ROPI_RWPI)
515            .Case("dynamic-no-pic", llvm::Reloc::DynamicNoPIC);
516   assert(RM.hasValue() && "invalid PIC model!");
517 
518   CodeGenOpt::Level OptLevel;
519   switch (CodeGenOpts.OptimizationLevel) {
520   default:
521     llvm_unreachable("Invalid optimization level!");
522   case 0:
523     OptLevel = CodeGenOpt::None;
524     break;
525   case 1:
526     OptLevel = CodeGenOpt::Less;
527     break;
528   case 2:
529     OptLevel = CodeGenOpt::Default;
530     break; // O2/Os/Oz
531   case 3:
532     OptLevel = CodeGenOpt::Aggressive;
533     break;
534   }
535 
536   llvm::TargetOptions Options;
537 
538   Options.ThreadModel =
539     llvm::StringSwitch<llvm::ThreadModel::Model>(CodeGenOpts.ThreadModel)
540       .Case("posix", llvm::ThreadModel::POSIX)
541       .Case("single", llvm::ThreadModel::Single);
542 
543   // Set float ABI type.
544   assert((CodeGenOpts.FloatABI == "soft" || CodeGenOpts.FloatABI == "softfp" ||
545           CodeGenOpts.FloatABI == "hard" || CodeGenOpts.FloatABI.empty()) &&
546          "Invalid Floating Point ABI!");
547   Options.FloatABIType =
548       llvm::StringSwitch<llvm::FloatABI::ABIType>(CodeGenOpts.FloatABI)
549           .Case("soft", llvm::FloatABI::Soft)
550           .Case("softfp", llvm::FloatABI::Soft)
551           .Case("hard", llvm::FloatABI::Hard)
552           .Default(llvm::FloatABI::Default);
553 
554   // Set FP fusion mode.
555   switch (CodeGenOpts.getFPContractMode()) {
556   case CodeGenOptions::FPC_Off:
557     Options.AllowFPOpFusion = llvm::FPOpFusion::Strict;
558     break;
559   case CodeGenOptions::FPC_On:
560     Options.AllowFPOpFusion = llvm::FPOpFusion::Standard;
561     break;
562   case CodeGenOptions::FPC_Fast:
563     Options.AllowFPOpFusion = llvm::FPOpFusion::Fast;
564     break;
565   }
566 
567   Options.UseInitArray = CodeGenOpts.UseInitArray;
568   Options.DisableIntegratedAS = CodeGenOpts.DisableIntegratedAS;
569   Options.CompressDebugSections = CodeGenOpts.CompressDebugSections;
570   Options.RelaxELFRelocations = CodeGenOpts.RelaxELFRelocations;
571 
572   // Set EABI version.
573   Options.EABIVersion = llvm::StringSwitch<llvm::EABI>(TargetOpts.EABIVersion)
574                             .Case("4", llvm::EABI::EABI4)
575                             .Case("5", llvm::EABI::EABI5)
576                             .Case("gnu", llvm::EABI::GNU)
577                             .Default(llvm::EABI::Default);
578 
579   if (LangOpts.SjLjExceptions)
580     Options.ExceptionModel = llvm::ExceptionHandling::SjLj;
581 
582   Options.LessPreciseFPMADOption = CodeGenOpts.LessPreciseFPMAD;
583   Options.NoInfsFPMath = CodeGenOpts.NoInfsFPMath;
584   Options.NoNaNsFPMath = CodeGenOpts.NoNaNsFPMath;
585   Options.NoZerosInBSS = CodeGenOpts.NoZeroInitializedInBSS;
586   Options.UnsafeFPMath = CodeGenOpts.UnsafeFPMath;
587   Options.StackAlignmentOverride = CodeGenOpts.StackAlignment;
588   Options.FunctionSections = CodeGenOpts.FunctionSections;
589   Options.DataSections = CodeGenOpts.DataSections;
590   Options.UniqueSectionNames = CodeGenOpts.UniqueSectionNames;
591   Options.EmulatedTLS = CodeGenOpts.EmulatedTLS;
592   Options.DebuggerTuning = CodeGenOpts.getDebuggerTuning();
593 
594   Options.MCOptions.MCRelaxAll = CodeGenOpts.RelaxAll;
595   Options.MCOptions.MCSaveTempLabels = CodeGenOpts.SaveTempLabels;
596   Options.MCOptions.MCUseDwarfDirectory = !CodeGenOpts.NoDwarfDirectoryAsm;
597   Options.MCOptions.MCNoExecStack = CodeGenOpts.NoExecStack;
598   Options.MCOptions.MCIncrementalLinkerCompatible =
599       CodeGenOpts.IncrementalLinkerCompatible;
600   Options.MCOptions.MCPIECopyRelocations = CodeGenOpts.PIECopyRelocations;
601   Options.MCOptions.MCFatalWarnings = CodeGenOpts.FatalWarnings;
602   Options.MCOptions.AsmVerbose = CodeGenOpts.AsmVerbose;
603   Options.MCOptions.PreserveAsmComments = CodeGenOpts.PreserveAsmComments;
604   Options.MCOptions.ABIName = TargetOpts.ABI;
605   for (const auto &Entry : HSOpts.UserEntries)
606     if (!Entry.IsFramework &&
607         (Entry.Group == frontend::IncludeDirGroup::Quoted ||
608          Entry.Group == frontend::IncludeDirGroup::Angled ||
609          Entry.Group == frontend::IncludeDirGroup::System))
610       Options.MCOptions.IASSearchPaths.push_back(
611           Entry.IgnoreSysRoot ? Entry.Path : HSOpts.Sysroot + Entry.Path);
612 
613   TM.reset(TheTarget->createTargetMachine(Triple, TargetOpts.CPU, FeaturesStr,
614                                           Options, RM, CM, OptLevel));
615 }
616 
617 bool EmitAssemblyHelper::AddEmitPasses(legacy::PassManager &CodeGenPasses,
618                                        BackendAction Action,
619                                        raw_pwrite_stream &OS) {
620   // Add LibraryInfo.
621   llvm::Triple TargetTriple(TheModule->getTargetTriple());
622   std::unique_ptr<TargetLibraryInfoImpl> TLII(
623       createTLII(TargetTriple, CodeGenOpts));
624   CodeGenPasses.add(new TargetLibraryInfoWrapperPass(*TLII));
625 
626   // Normal mode, emit a .s or .o file by running the code generator. Note,
627   // this also adds codegenerator level optimization passes.
628   TargetMachine::CodeGenFileType CGFT = TargetMachine::CGFT_AssemblyFile;
629   if (Action == Backend_EmitObj)
630     CGFT = TargetMachine::CGFT_ObjectFile;
631   else if (Action == Backend_EmitMCNull)
632     CGFT = TargetMachine::CGFT_Null;
633   else
634     assert(Action == Backend_EmitAssembly && "Invalid action!");
635 
636   // Add ObjC ARC final-cleanup optimizations. This is done as part of the
637   // "codegen" passes so that it isn't run multiple times when there is
638   // inlining happening.
639   if (CodeGenOpts.OptimizationLevel > 0)
640     CodeGenPasses.add(createObjCARCContractPass());
641 
642   if (TM->addPassesToEmitFile(CodeGenPasses, OS, CGFT,
643                               /*DisableVerify=*/!CodeGenOpts.VerifyModule)) {
644     Diags.Report(diag::err_fe_unable_to_interface_with_target);
645     return false;
646   }
647 
648   return true;
649 }
650 
651 void EmitAssemblyHelper::EmitAssembly(BackendAction Action,
652                                       std::unique_ptr<raw_pwrite_stream> OS) {
653   TimeRegion Region(llvm::TimePassesIsEnabled ? &CodeGenerationTime : nullptr);
654 
655   setCommandLineOpts();
656 
657   bool UsesCodeGen = (Action != Backend_EmitNothing &&
658                       Action != Backend_EmitBC &&
659                       Action != Backend_EmitLL);
660   CreateTargetMachine(UsesCodeGen);
661 
662   if (UsesCodeGen && !TM)
663     return;
664   if (TM)
665     TheModule->setDataLayout(TM->createDataLayout());
666 
667   legacy::PassManager PerModulePasses;
668   PerModulePasses.add(
669       createTargetTransformInfoWrapperPass(getTargetIRAnalysis()));
670 
671   legacy::FunctionPassManager PerFunctionPasses(TheModule);
672   PerFunctionPasses.add(
673       createTargetTransformInfoWrapperPass(getTargetIRAnalysis()));
674 
675   CreatePasses(PerModulePasses, PerFunctionPasses);
676 
677   legacy::PassManager CodeGenPasses;
678   CodeGenPasses.add(
679       createTargetTransformInfoWrapperPass(getTargetIRAnalysis()));
680 
681   switch (Action) {
682   case Backend_EmitNothing:
683     break;
684 
685   case Backend_EmitBC:
686     if (CodeGenOpts.EmitSummaryIndex)
687       PerModulePasses.add(createWriteThinLTOBitcodePass(*OS));
688     else
689       PerModulePasses.add(
690           createBitcodeWriterPass(*OS, CodeGenOpts.EmitLLVMUseLists));
691     break;
692 
693   case Backend_EmitLL:
694     PerModulePasses.add(
695         createPrintModulePass(*OS, "", CodeGenOpts.EmitLLVMUseLists));
696     break;
697 
698   default:
699     if (!AddEmitPasses(CodeGenPasses, Action, *OS))
700       return;
701   }
702 
703   // Before executing passes, print the final values of the LLVM options.
704   cl::PrintOptionValues();
705 
706   // Run passes. For now we do all passes at once, but eventually we
707   // would like to have the option of streaming code generation.
708 
709   {
710     PrettyStackTraceString CrashInfo("Per-function optimization");
711 
712     PerFunctionPasses.doInitialization();
713     for (Function &F : *TheModule)
714       if (!F.isDeclaration())
715         PerFunctionPasses.run(F);
716     PerFunctionPasses.doFinalization();
717   }
718 
719   {
720     PrettyStackTraceString CrashInfo("Per-module optimization passes");
721     PerModulePasses.run(*TheModule);
722   }
723 
724   {
725     PrettyStackTraceString CrashInfo("Code generation");
726     CodeGenPasses.run(*TheModule);
727   }
728 }
729 
730 static PassBuilder::OptimizationLevel mapToLevel(const CodeGenOptions &Opts) {
731   switch (Opts.OptimizationLevel) {
732   default:
733     llvm_unreachable("Invalid optimization level!");
734 
735   case 1:
736     return PassBuilder::O1;
737 
738   case 2:
739     switch (Opts.OptimizeSize) {
740     default:
741       llvm_unreachable("Invalide optimization level for size!");
742 
743     case 0:
744       return PassBuilder::O2;
745 
746     case 1:
747       return PassBuilder::Os;
748 
749     case 2:
750       return PassBuilder::Oz;
751     }
752 
753   case 3:
754     return PassBuilder::O3;
755   }
756 }
757 
758 /// A clean version of `EmitAssembly` that uses the new pass manager.
759 ///
760 /// Not all features are currently supported in this system, but where
761 /// necessary it falls back to the legacy pass manager to at least provide
762 /// basic functionality.
763 ///
764 /// This API is planned to have its functionality finished and then to replace
765 /// `EmitAssembly` at some point in the future when the default switches.
766 void EmitAssemblyHelper::EmitAssemblyWithNewPassManager(
767     BackendAction Action, std::unique_ptr<raw_pwrite_stream> OS) {
768   TimeRegion Region(llvm::TimePassesIsEnabled ? &CodeGenerationTime : nullptr);
769   setCommandLineOpts();
770 
771   // The new pass manager always makes a target machine available to passes
772   // during construction.
773   CreateTargetMachine(/*MustCreateTM*/ true);
774   if (!TM)
775     // This will already be diagnosed, just bail.
776     return;
777   TheModule->setDataLayout(TM->createDataLayout());
778 
779   PassBuilder PB(TM.get());
780 
781   LoopAnalysisManager LAM;
782   FunctionAnalysisManager FAM;
783   CGSCCAnalysisManager CGAM;
784   ModuleAnalysisManager MAM;
785 
786   // Register the AA manager first so that our version is the one used.
787   FAM.registerPass([&] { return PB.buildDefaultAAPipeline(); });
788 
789   // Register all the basic analyses with the managers.
790   PB.registerModuleAnalyses(MAM);
791   PB.registerCGSCCAnalyses(CGAM);
792   PB.registerFunctionAnalyses(FAM);
793   PB.registerLoopAnalyses(LAM);
794   PB.crossRegisterProxies(LAM, FAM, CGAM, MAM);
795 
796   ModulePassManager MPM;
797 
798   if (!CodeGenOpts.DisableLLVMPasses) {
799     if (CodeGenOpts.OptimizationLevel == 0) {
800       // Build a minimal pipeline based on the semantics required by Clang,
801       // which is just that always inlining occurs.
802       MPM.addPass(AlwaysInlinerPass());
803     } else {
804       // Otherwise, use the default pass pipeline. We also have to map our
805       // optimization levels into one of the distinct levels used to configure
806       // the pipeline.
807       PassBuilder::OptimizationLevel Level = mapToLevel(CodeGenOpts);
808 
809       MPM = PB.buildPerModuleDefaultPipeline(Level);
810     }
811   }
812 
813   // FIXME: We still use the legacy pass manager to do code generation. We
814   // create that pass manager here and use it as needed below.
815   legacy::PassManager CodeGenPasses;
816   bool NeedCodeGen = false;
817 
818   // Append any output we need to the pass manager.
819   switch (Action) {
820   case Backend_EmitNothing:
821     break;
822 
823   case Backend_EmitBC:
824     MPM.addPass(BitcodeWriterPass(*OS, CodeGenOpts.EmitLLVMUseLists,
825                                   CodeGenOpts.EmitSummaryIndex,
826                                   CodeGenOpts.EmitSummaryIndex));
827     break;
828 
829   case Backend_EmitLL:
830     MPM.addPass(PrintModulePass(*OS, "", CodeGenOpts.EmitLLVMUseLists));
831     break;
832 
833   case Backend_EmitAssembly:
834   case Backend_EmitMCNull:
835   case Backend_EmitObj:
836     NeedCodeGen = true;
837     CodeGenPasses.add(
838         createTargetTransformInfoWrapperPass(getTargetIRAnalysis()));
839     if (!AddEmitPasses(CodeGenPasses, Action, *OS))
840       // FIXME: Should we handle this error differently?
841       return;
842     break;
843   }
844 
845   // Before executing passes, print the final values of the LLVM options.
846   cl::PrintOptionValues();
847 
848   // Now that we have all of the passes ready, run them.
849   {
850     PrettyStackTraceString CrashInfo("Optimizer");
851     MPM.run(*TheModule, MAM);
852   }
853 
854   // Now if needed, run the legacy PM for codegen.
855   if (NeedCodeGen) {
856     PrettyStackTraceString CrashInfo("Code generation");
857     CodeGenPasses.run(*TheModule);
858   }
859 }
860 
861 Expected<BitcodeModule> clang::FindThinLTOModule(MemoryBufferRef MBRef) {
862   Expected<std::vector<BitcodeModule>> BMsOrErr = getBitcodeModuleList(MBRef);
863   if (!BMsOrErr)
864     return BMsOrErr.takeError();
865 
866   // The bitcode file may contain multiple modules, we want the one with a
867   // summary.
868   for (BitcodeModule &BM : *BMsOrErr) {
869     Expected<bool> HasSummary = BM.hasSummary();
870     if (HasSummary && *HasSummary)
871       return BM;
872   }
873 
874   return make_error<StringError>("Could not find module summary",
875                                  inconvertibleErrorCode());
876 }
877 
878 static void runThinLTOBackend(ModuleSummaryIndex *CombinedIndex, Module *M,
879                               std::unique_ptr<raw_pwrite_stream> OS,
880                               std::string SampleProfile) {
881   StringMap<std::map<GlobalValue::GUID, GlobalValueSummary *>>
882       ModuleToDefinedGVSummaries;
883   CombinedIndex->collectDefinedGVSummariesPerModule(ModuleToDefinedGVSummaries);
884 
885   // We can simply import the values mentioned in the combined index, since
886   // we should only invoke this using the individual indexes written out
887   // via a WriteIndexesThinBackend.
888   FunctionImporter::ImportMapTy ImportList;
889   for (auto &GlobalList : *CombinedIndex) {
890     auto GUID = GlobalList.first;
891     assert(GlobalList.second.size() == 1 &&
892            "Expected individual combined index to have one summary per GUID");
893     auto &Summary = GlobalList.second[0];
894     // Skip the summaries for the importing module. These are included to
895     // e.g. record required linkage changes.
896     if (Summary->modulePath() == M->getModuleIdentifier())
897       continue;
898     // Doesn't matter what value we plug in to the map, just needs an entry
899     // to provoke importing by thinBackend.
900     ImportList[Summary->modulePath()][GUID] = 1;
901   }
902 
903   std::vector<std::unique_ptr<llvm::MemoryBuffer>> OwnedImports;
904   MapVector<llvm::StringRef, llvm::BitcodeModule> ModuleMap;
905 
906   for (auto &I : ImportList) {
907     ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> MBOrErr =
908         llvm::MemoryBuffer::getFile(I.first());
909     if (!MBOrErr) {
910       errs() << "Error loading imported file '" << I.first()
911              << "': " << MBOrErr.getError().message() << "\n";
912       return;
913     }
914 
915     Expected<BitcodeModule> BMOrErr = FindThinLTOModule(**MBOrErr);
916     if (!BMOrErr) {
917       handleAllErrors(BMOrErr.takeError(), [&](ErrorInfoBase &EIB) {
918         errs() << "Error loading imported file '" << I.first()
919                << "': " << EIB.message() << '\n';
920       });
921       return;
922     }
923     ModuleMap.insert({I.first(), *BMOrErr});
924 
925     OwnedImports.push_back(std::move(*MBOrErr));
926   }
927   auto AddStream = [&](size_t Task) {
928     return llvm::make_unique<lto::NativeObjectStream>(std::move(OS));
929   };
930   lto::Config Conf;
931   Conf.SampleProfile = SampleProfile;
932   if (Error E = thinBackend(
933           Conf, 0, AddStream, *M, *CombinedIndex, ImportList,
934           ModuleToDefinedGVSummaries[M->getModuleIdentifier()], ModuleMap)) {
935     handleAllErrors(std::move(E), [&](ErrorInfoBase &EIB) {
936       errs() << "Error running ThinLTO backend: " << EIB.message() << '\n';
937     });
938   }
939 }
940 
941 void clang::EmitBackendOutput(DiagnosticsEngine &Diags,
942                               const HeaderSearchOptions &HeaderOpts,
943                               const CodeGenOptions &CGOpts,
944                               const clang::TargetOptions &TOpts,
945                               const LangOptions &LOpts,
946                               const llvm::DataLayout &TDesc, Module *M,
947                               BackendAction Action,
948                               std::unique_ptr<raw_pwrite_stream> OS) {
949   if (!CGOpts.ThinLTOIndexFile.empty()) {
950     // If we are performing a ThinLTO importing compile, load the function index
951     // into memory and pass it into runThinLTOBackend, which will run the
952     // function importer and invoke LTO passes.
953     Expected<std::unique_ptr<ModuleSummaryIndex>> IndexOrErr =
954         llvm::getModuleSummaryIndexForFile(CGOpts.ThinLTOIndexFile);
955     if (!IndexOrErr) {
956       logAllUnhandledErrors(IndexOrErr.takeError(), errs(),
957                             "Error loading index file '" +
958                             CGOpts.ThinLTOIndexFile + "': ");
959       return;
960     }
961     std::unique_ptr<ModuleSummaryIndex> CombinedIndex = std::move(*IndexOrErr);
962     // A null CombinedIndex means we should skip ThinLTO compilation
963     // (LLVM will optionally ignore empty index files, returning null instead
964     // of an error).
965     bool DoThinLTOBackend = CombinedIndex != nullptr;
966     if (DoThinLTOBackend) {
967       runThinLTOBackend(CombinedIndex.get(), M, std::move(OS),
968                         CGOpts.SampleProfileFile);
969       return;
970     }
971   }
972 
973   EmitAssemblyHelper AsmHelper(Diags, HeaderOpts, CGOpts, TOpts, LOpts, M);
974 
975   if (CGOpts.ExperimentalNewPassManager)
976     AsmHelper.EmitAssemblyWithNewPassManager(Action, std::move(OS));
977   else
978     AsmHelper.EmitAssembly(Action, std::move(OS));
979 
980   // Verify clang's TargetInfo DataLayout against the LLVM TargetMachine's
981   // DataLayout.
982   if (AsmHelper.TM) {
983     std::string DLDesc = M->getDataLayout().getStringRepresentation();
984     if (DLDesc != TDesc.getStringRepresentation()) {
985       unsigned DiagID = Diags.getCustomDiagID(
986           DiagnosticsEngine::Error, "backend data layout '%0' does not match "
987                                     "expected target description '%1'");
988       Diags.Report(DiagID) << DLDesc << TDesc.getStringRepresentation();
989     }
990   }
991 }
992 
993 static const char* getSectionNameForBitcode(const Triple &T) {
994   switch (T.getObjectFormat()) {
995   case Triple::MachO:
996     return "__LLVM,__bitcode";
997   case Triple::COFF:
998   case Triple::ELF:
999   case Triple::Wasm:
1000   case Triple::UnknownObjectFormat:
1001     return ".llvmbc";
1002   }
1003   llvm_unreachable("Unimplemented ObjectFormatType");
1004 }
1005 
1006 static const char* getSectionNameForCommandline(const Triple &T) {
1007   switch (T.getObjectFormat()) {
1008   case Triple::MachO:
1009     return "__LLVM,__cmdline";
1010   case Triple::COFF:
1011   case Triple::ELF:
1012   case Triple::Wasm:
1013   case Triple::UnknownObjectFormat:
1014     return ".llvmcmd";
1015   }
1016   llvm_unreachable("Unimplemented ObjectFormatType");
1017 }
1018 
1019 // With -fembed-bitcode, save a copy of the llvm IR as data in the
1020 // __LLVM,__bitcode section.
1021 void clang::EmbedBitcode(llvm::Module *M, const CodeGenOptions &CGOpts,
1022                          llvm::MemoryBufferRef Buf) {
1023   if (CGOpts.getEmbedBitcode() == CodeGenOptions::Embed_Off)
1024     return;
1025 
1026   // Save llvm.compiler.used and remote it.
1027   SmallVector<Constant*, 2> UsedArray;
1028   SmallSet<GlobalValue*, 4> UsedGlobals;
1029   Type *UsedElementType = Type::getInt8Ty(M->getContext())->getPointerTo(0);
1030   GlobalVariable *Used = collectUsedGlobalVariables(*M, UsedGlobals, true);
1031   for (auto *GV : UsedGlobals) {
1032     if (GV->getName() != "llvm.embedded.module" &&
1033         GV->getName() != "llvm.cmdline")
1034       UsedArray.push_back(
1035           ConstantExpr::getPointerBitCastOrAddrSpaceCast(GV, UsedElementType));
1036   }
1037   if (Used)
1038     Used->eraseFromParent();
1039 
1040   // Embed the bitcode for the llvm module.
1041   std::string Data;
1042   ArrayRef<uint8_t> ModuleData;
1043   Triple T(M->getTargetTriple());
1044   // Create a constant that contains the bitcode.
1045   // In case of embedding a marker, ignore the input Buf and use the empty
1046   // ArrayRef. It is also legal to create a bitcode marker even Buf is empty.
1047   if (CGOpts.getEmbedBitcode() != CodeGenOptions::Embed_Marker) {
1048     if (!isBitcode((const unsigned char *)Buf.getBufferStart(),
1049                    (const unsigned char *)Buf.getBufferEnd())) {
1050       // If the input is LLVM Assembly, bitcode is produced by serializing
1051       // the module. Use-lists order need to be perserved in this case.
1052       llvm::raw_string_ostream OS(Data);
1053       llvm::WriteBitcodeToFile(M, OS, /* ShouldPreserveUseListOrder */ true);
1054       ModuleData =
1055           ArrayRef<uint8_t>((const uint8_t *)OS.str().data(), OS.str().size());
1056     } else
1057       // If the input is LLVM bitcode, write the input byte stream directly.
1058       ModuleData = ArrayRef<uint8_t>((const uint8_t *)Buf.getBufferStart(),
1059                                      Buf.getBufferSize());
1060   }
1061   llvm::Constant *ModuleConstant =
1062       llvm::ConstantDataArray::get(M->getContext(), ModuleData);
1063   llvm::GlobalVariable *GV = new llvm::GlobalVariable(
1064       *M, ModuleConstant->getType(), true, llvm::GlobalValue::PrivateLinkage,
1065       ModuleConstant);
1066   GV->setSection(getSectionNameForBitcode(T));
1067   UsedArray.push_back(
1068       ConstantExpr::getPointerBitCastOrAddrSpaceCast(GV, UsedElementType));
1069   if (llvm::GlobalVariable *Old =
1070           M->getGlobalVariable("llvm.embedded.module", true)) {
1071     assert(Old->hasOneUse() &&
1072            "llvm.embedded.module can only be used once in llvm.compiler.used");
1073     GV->takeName(Old);
1074     Old->eraseFromParent();
1075   } else {
1076     GV->setName("llvm.embedded.module");
1077   }
1078 
1079   // Skip if only bitcode needs to be embedded.
1080   if (CGOpts.getEmbedBitcode() != CodeGenOptions::Embed_Bitcode) {
1081     // Embed command-line options.
1082     ArrayRef<uint8_t> CmdData(const_cast<uint8_t *>(CGOpts.CmdArgs.data()),
1083                               CGOpts.CmdArgs.size());
1084     llvm::Constant *CmdConstant =
1085       llvm::ConstantDataArray::get(M->getContext(), CmdData);
1086     GV = new llvm::GlobalVariable(*M, CmdConstant->getType(), true,
1087                                   llvm::GlobalValue::PrivateLinkage,
1088                                   CmdConstant);
1089     GV->setSection(getSectionNameForCommandline(T));
1090     UsedArray.push_back(
1091         ConstantExpr::getPointerBitCastOrAddrSpaceCast(GV, UsedElementType));
1092     if (llvm::GlobalVariable *Old =
1093             M->getGlobalVariable("llvm.cmdline", true)) {
1094       assert(Old->hasOneUse() &&
1095              "llvm.cmdline can only be used once in llvm.compiler.used");
1096       GV->takeName(Old);
1097       Old->eraseFromParent();
1098     } else {
1099       GV->setName("llvm.cmdline");
1100     }
1101   }
1102 
1103   if (UsedArray.empty())
1104     return;
1105 
1106   // Recreate llvm.compiler.used.
1107   ArrayType *ATy = ArrayType::get(UsedElementType, UsedArray.size());
1108   auto *NewUsed = new GlobalVariable(
1109       *M, ATy, false, llvm::GlobalValue::AppendingLinkage,
1110       llvm::ConstantArray::get(ATy, UsedArray), "llvm.compiler.used");
1111   NewUsed->setSection("llvm.metadata");
1112 }
1113