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 "llvm/Analysis/Verifier.h"
17 #include "llvm/Assembly/PrintModulePass.h"
18 #include "llvm/Bitcode/ReaderWriter.h"
19 #include "llvm/CodeGen/RegAllocRegistry.h"
20 #include "llvm/CodeGen/SchedulerRegistry.h"
21 #include "llvm/IR/DataLayout.h"
22 #include "llvm/IR/Module.h"
23 #include "llvm/MC/SubtargetFeature.h"
24 #include "llvm/PassManager.h"
25 #include "llvm/Support/CommandLine.h"
26 #include "llvm/Support/FormattedStream.h"
27 #include "llvm/Support/PrettyStackTrace.h"
28 #include "llvm/Support/TargetRegistry.h"
29 #include "llvm/Support/Timer.h"
30 #include "llvm/Support/raw_ostream.h"
31 #include "llvm/Target/TargetLibraryInfo.h"
32 #include "llvm/Target/TargetMachine.h"
33 #include "llvm/Target/TargetOptions.h"
34 #include "llvm/Transforms/IPO.h"
35 #include "llvm/Transforms/IPO/PassManagerBuilder.h"
36 #include "llvm/Transforms/Instrumentation.h"
37 #include "llvm/Transforms/ObjCARC.h"
38 #include "llvm/Transforms/Scalar.h"
39 using namespace clang;
40 using namespace llvm;
41 
42 namespace {
43 
44 class EmitAssemblyHelper {
45   DiagnosticsEngine &Diags;
46   const CodeGenOptions &CodeGenOpts;
47   const clang::TargetOptions &TargetOpts;
48   const LangOptions &LangOpts;
49   Module *TheModule;
50 
51   Timer CodeGenerationTime;
52 
53   mutable PassManager *CodeGenPasses;
54   mutable PassManager *PerModulePasses;
55   mutable FunctionPassManager *PerFunctionPasses;
56 
57 private:
58   PassManager *getCodeGenPasses(TargetMachine *TM) const {
59     if (!CodeGenPasses) {
60       CodeGenPasses = new PassManager();
61       CodeGenPasses->add(new DataLayout(TheModule));
62       if (TM)
63         TM->addAnalysisPasses(*CodeGenPasses);
64     }
65     return CodeGenPasses;
66   }
67 
68   PassManager *getPerModulePasses(TargetMachine *TM) const {
69     if (!PerModulePasses) {
70       PerModulePasses = new PassManager();
71       PerModulePasses->add(new DataLayout(TheModule));
72       if (TM)
73         TM->addAnalysisPasses(*PerModulePasses);
74     }
75     return PerModulePasses;
76   }
77 
78   FunctionPassManager *getPerFunctionPasses(TargetMachine *TM) const {
79     if (!PerFunctionPasses) {
80       PerFunctionPasses = new FunctionPassManager(TheModule);
81       PerFunctionPasses->add(new DataLayout(TheModule));
82       if (TM)
83         TM->addAnalysisPasses(*PerFunctionPasses);
84     }
85     return PerFunctionPasses;
86   }
87 
88 
89   void CreatePasses(TargetMachine *TM);
90 
91   /// CreateTargetMachine - Generates the TargetMachine.
92   /// Returns Null if it is unable to create the target machine.
93   /// Some of our clang tests specify triples which are not built
94   /// into clang. This is okay because these tests check the generated
95   /// IR, and they require DataLayout which depends on the triple.
96   /// In this case, we allow this method to fail and not report an error.
97   /// When MustCreateTM is used, we print an error if we are unable to load
98   /// the requested target.
99   TargetMachine *CreateTargetMachine(bool MustCreateTM);
100 
101   /// AddEmitPasses - Add passes necessary to emit assembly or LLVM IR.
102   ///
103   /// \return True on success.
104   bool AddEmitPasses(BackendAction Action, formatted_raw_ostream &OS,
105                      TargetMachine *TM);
106 
107 public:
108   EmitAssemblyHelper(DiagnosticsEngine &_Diags,
109                      const CodeGenOptions &CGOpts,
110                      const clang::TargetOptions &TOpts,
111                      const LangOptions &LOpts,
112                      Module *M)
113     : Diags(_Diags), CodeGenOpts(CGOpts), TargetOpts(TOpts), LangOpts(LOpts),
114       TheModule(M), CodeGenerationTime("Code Generation Time"),
115       CodeGenPasses(0), PerModulePasses(0), PerFunctionPasses(0) {}
116 
117   ~EmitAssemblyHelper() {
118     delete CodeGenPasses;
119     delete PerModulePasses;
120     delete PerFunctionPasses;
121   }
122 
123   void EmitAssembly(BackendAction Action, raw_ostream *OS);
124 };
125 
126 // We need this wrapper to access LangOpts and CGOpts from extension functions
127 // that we add to the PassManagerBuilder.
128 class PassManagerBuilderWrapper : public PassManagerBuilder {
129 public:
130   PassManagerBuilderWrapper(const CodeGenOptions &CGOpts,
131                             const LangOptions &LangOpts)
132       : PassManagerBuilder(), CGOpts(CGOpts), LangOpts(LangOpts) {}
133   const CodeGenOptions &getCGOpts() const { return CGOpts; }
134   const LangOptions &getLangOpts() const { return LangOpts; }
135 private:
136   const CodeGenOptions &CGOpts;
137   const LangOptions &LangOpts;
138 };
139 
140 }
141 
142 static void addObjCARCAPElimPass(const PassManagerBuilder &Builder, PassManagerBase &PM) {
143   if (Builder.OptLevel > 0)
144     PM.add(createObjCARCAPElimPass());
145 }
146 
147 static void addObjCARCExpandPass(const PassManagerBuilder &Builder, PassManagerBase &PM) {
148   if (Builder.OptLevel > 0)
149     PM.add(createObjCARCExpandPass());
150 }
151 
152 static void addObjCARCOptPass(const PassManagerBuilder &Builder, PassManagerBase &PM) {
153   if (Builder.OptLevel > 0)
154     PM.add(createObjCARCOptPass());
155 }
156 
157 static void addBoundsCheckingPass(const PassManagerBuilder &Builder,
158                                     PassManagerBase &PM) {
159   PM.add(createBoundsCheckingPass());
160 }
161 
162 static void addAddressSanitizerPasses(const PassManagerBuilder &Builder,
163                                       PassManagerBase &PM) {
164   const PassManagerBuilderWrapper &BuilderWrapper =
165       static_cast<const PassManagerBuilderWrapper&>(Builder);
166   const CodeGenOptions &CGOpts = BuilderWrapper.getCGOpts();
167   const LangOptions &LangOpts = BuilderWrapper.getLangOpts();
168   PM.add(createAddressSanitizerFunctionPass(
169       LangOpts.Sanitize.InitOrder,
170       LangOpts.Sanitize.UseAfterReturn,
171       LangOpts.Sanitize.UseAfterScope,
172       CGOpts.SanitizerBlacklistFile,
173       CGOpts.SanitizeAddressZeroBaseShadow));
174   PM.add(createAddressSanitizerModulePass(
175       LangOpts.Sanitize.InitOrder,
176       CGOpts.SanitizerBlacklistFile,
177       CGOpts.SanitizeAddressZeroBaseShadow));
178 }
179 
180 static void addMemorySanitizerPass(const PassManagerBuilder &Builder,
181                                    PassManagerBase &PM) {
182   const PassManagerBuilderWrapper &BuilderWrapper =
183       static_cast<const PassManagerBuilderWrapper&>(Builder);
184   const CodeGenOptions &CGOpts = BuilderWrapper.getCGOpts();
185   PM.add(createMemorySanitizerPass(CGOpts.SanitizeMemoryTrackOrigins,
186                                    CGOpts.SanitizerBlacklistFile));
187 
188   // MemorySanitizer inserts complex instrumentation that mostly follows
189   // the logic of the original code, but operates on "shadow" values.
190   // It can benefit from re-running some general purpose optimization passes.
191   if (Builder.OptLevel > 0) {
192     PM.add(createEarlyCSEPass());
193     PM.add(createReassociatePass());
194     PM.add(createLICMPass());
195     PM.add(createGVNPass());
196     PM.add(createInstructionCombiningPass());
197     PM.add(createDeadStoreEliminationPass());
198   }
199 }
200 
201 static void addThreadSanitizerPass(const PassManagerBuilder &Builder,
202                                    PassManagerBase &PM) {
203   const PassManagerBuilderWrapper &BuilderWrapper =
204       static_cast<const PassManagerBuilderWrapper&>(Builder);
205   const CodeGenOptions &CGOpts = BuilderWrapper.getCGOpts();
206   PM.add(createThreadSanitizerPass(CGOpts.SanitizerBlacklistFile));
207 }
208 
209 void EmitAssemblyHelper::CreatePasses(TargetMachine *TM) {
210   unsigned OptLevel = CodeGenOpts.OptimizationLevel;
211   CodeGenOptions::InliningMethod Inlining = CodeGenOpts.getInlining();
212 
213   // Handle disabling of LLVM optimization, where we want to preserve the
214   // internal module before any optimization.
215   if (CodeGenOpts.DisableLLVMOpts) {
216     OptLevel = 0;
217     Inlining = CodeGenOpts.NoInlining;
218   }
219 
220   PassManagerBuilderWrapper PMBuilder(CodeGenOpts, LangOpts);
221   PMBuilder.OptLevel = OptLevel;
222   PMBuilder.SizeLevel = CodeGenOpts.OptimizeSize;
223 
224   PMBuilder.DisableUnitAtATime = !CodeGenOpts.UnitAtATime;
225   PMBuilder.DisableUnrollLoops = !CodeGenOpts.UnrollLoops;
226 
227   // In ObjC ARC mode, add the main ARC optimization passes.
228   if (LangOpts.ObjCAutoRefCount) {
229     PMBuilder.addExtension(PassManagerBuilder::EP_EarlyAsPossible,
230                            addObjCARCExpandPass);
231     PMBuilder.addExtension(PassManagerBuilder::EP_ModuleOptimizerEarly,
232                            addObjCARCAPElimPass);
233     PMBuilder.addExtension(PassManagerBuilder::EP_ScalarOptimizerLate,
234                            addObjCARCOptPass);
235   }
236 
237   if (LangOpts.Sanitize.Bounds) {
238     PMBuilder.addExtension(PassManagerBuilder::EP_ScalarOptimizerLate,
239                            addBoundsCheckingPass);
240     PMBuilder.addExtension(PassManagerBuilder::EP_EnabledOnOptLevel0,
241                            addBoundsCheckingPass);
242   }
243 
244   if (LangOpts.Sanitize.Address) {
245     PMBuilder.addExtension(PassManagerBuilder::EP_OptimizerLast,
246                            addAddressSanitizerPasses);
247     PMBuilder.addExtension(PassManagerBuilder::EP_EnabledOnOptLevel0,
248                            addAddressSanitizerPasses);
249   }
250 
251   if (LangOpts.Sanitize.Memory) {
252     PMBuilder.addExtension(PassManagerBuilder::EP_OptimizerLast,
253                            addMemorySanitizerPass);
254     PMBuilder.addExtension(PassManagerBuilder::EP_EnabledOnOptLevel0,
255                            addMemorySanitizerPass);
256   }
257 
258   if (LangOpts.Sanitize.Thread) {
259     PMBuilder.addExtension(PassManagerBuilder::EP_OptimizerLast,
260                            addThreadSanitizerPass);
261     PMBuilder.addExtension(PassManagerBuilder::EP_EnabledOnOptLevel0,
262                            addThreadSanitizerPass);
263   }
264 
265   // Figure out TargetLibraryInfo.
266   Triple TargetTriple(TheModule->getTargetTriple());
267   PMBuilder.LibraryInfo = new TargetLibraryInfo(TargetTriple);
268   if (!CodeGenOpts.SimplifyLibCalls)
269     PMBuilder.LibraryInfo->disableAllFunctions();
270 
271   switch (Inlining) {
272   case CodeGenOptions::NoInlining: break;
273   case CodeGenOptions::NormalInlining: {
274     // FIXME: Derive these constants in a principled fashion.
275     unsigned Threshold = 225;
276     if (CodeGenOpts.OptimizeSize == 1)      // -Os
277       Threshold = 75;
278     else if (CodeGenOpts.OptimizeSize == 2) // -Oz
279       Threshold = 25;
280     else if (OptLevel > 2)
281       Threshold = 275;
282     PMBuilder.Inliner = createFunctionInliningPass(Threshold);
283     break;
284   }
285   case CodeGenOptions::OnlyAlwaysInlining:
286     // Respect always_inline.
287     if (OptLevel == 0)
288       // Do not insert lifetime intrinsics at -O0.
289       PMBuilder.Inliner = createAlwaysInlinerPass(false);
290     else
291       PMBuilder.Inliner = createAlwaysInlinerPass();
292     break;
293   }
294 
295   // Set up the per-function pass manager.
296   FunctionPassManager *FPM = getPerFunctionPasses(TM);
297   if (CodeGenOpts.VerifyModule)
298     FPM->add(createVerifierPass());
299   PMBuilder.populateFunctionPassManager(*FPM);
300 
301   // Set up the per-module pass manager.
302   PassManager *MPM = getPerModulePasses(TM);
303 
304   if (!CodeGenOpts.DisableGCov &&
305       (CodeGenOpts.EmitGcovArcs || CodeGenOpts.EmitGcovNotes)) {
306     // Not using 'GCOVOptions::getDefault' allows us to avoid exiting if
307     // LLVM's -default-gcov-version flag is set to something invalid.
308     GCOVOptions Options;
309     Options.EmitNotes = CodeGenOpts.EmitGcovNotes;
310     Options.EmitData = CodeGenOpts.EmitGcovArcs;
311     memcpy(Options.Version, CodeGenOpts.CoverageVersion, 4);
312     Options.UseCfgChecksum = CodeGenOpts.CoverageExtraChecksum;
313     Options.NoRedZone = CodeGenOpts.DisableRedZone;
314     Options.FunctionNamesInData =
315         !CodeGenOpts.CoverageNoFunctionNamesInData;
316     MPM->add(createGCOVProfilerPass(Options));
317     if (CodeGenOpts.getDebugInfo() == CodeGenOptions::NoDebugInfo)
318       MPM->add(createStripSymbolsPass(true));
319   }
320 
321   PMBuilder.populateModulePassManager(*MPM);
322 }
323 
324 TargetMachine *EmitAssemblyHelper::CreateTargetMachine(bool MustCreateTM) {
325   // Create the TargetMachine for generating code.
326   std::string Error;
327   std::string Triple = TheModule->getTargetTriple();
328   const llvm::Target *TheTarget = TargetRegistry::lookupTarget(Triple, Error);
329   if (!TheTarget) {
330     if (MustCreateTM)
331       Diags.Report(diag::err_fe_unable_to_create_target) << Error;
332     return 0;
333   }
334 
335   // FIXME: Expose these capabilities via actual APIs!!!! Aside from just
336   // being gross, this is also totally broken if we ever care about
337   // concurrency.
338 
339   TargetMachine::setAsmVerbosityDefault(CodeGenOpts.AsmVerbose);
340 
341   TargetMachine::setFunctionSections(CodeGenOpts.FunctionSections);
342   TargetMachine::setDataSections    (CodeGenOpts.DataSections);
343 
344   // FIXME: Parse this earlier.
345   llvm::CodeModel::Model CM;
346   if (CodeGenOpts.CodeModel == "small") {
347     CM = llvm::CodeModel::Small;
348   } else if (CodeGenOpts.CodeModel == "kernel") {
349     CM = llvm::CodeModel::Kernel;
350   } else if (CodeGenOpts.CodeModel == "medium") {
351     CM = llvm::CodeModel::Medium;
352   } else if (CodeGenOpts.CodeModel == "large") {
353     CM = llvm::CodeModel::Large;
354   } else {
355     assert(CodeGenOpts.CodeModel.empty() && "Invalid code model!");
356     CM = llvm::CodeModel::Default;
357   }
358 
359   SmallVector<const char *, 16> BackendArgs;
360   BackendArgs.push_back("clang"); // Fake program name.
361   if (!CodeGenOpts.DebugPass.empty()) {
362     BackendArgs.push_back("-debug-pass");
363     BackendArgs.push_back(CodeGenOpts.DebugPass.c_str());
364   }
365   if (!CodeGenOpts.LimitFloatPrecision.empty()) {
366     BackendArgs.push_back("-limit-float-precision");
367     BackendArgs.push_back(CodeGenOpts.LimitFloatPrecision.c_str());
368   }
369   if (llvm::TimePassesIsEnabled)
370     BackendArgs.push_back("-time-passes");
371   for (unsigned i = 0, e = CodeGenOpts.BackendOptions.size(); i != e; ++i)
372     BackendArgs.push_back(CodeGenOpts.BackendOptions[i].c_str());
373   if (CodeGenOpts.NoGlobalMerge)
374     BackendArgs.push_back("-global-merge=false");
375   BackendArgs.push_back(0);
376   llvm::cl::ParseCommandLineOptions(BackendArgs.size() - 1,
377                                     BackendArgs.data());
378 
379   std::string FeaturesStr;
380   if (TargetOpts.Features.size()) {
381     SubtargetFeatures Features;
382     for (std::vector<std::string>::const_iterator
383            it = TargetOpts.Features.begin(),
384            ie = TargetOpts.Features.end(); it != ie; ++it)
385       Features.AddFeature(*it);
386     FeaturesStr = Features.getString();
387   }
388 
389   llvm::Reloc::Model RM = llvm::Reloc::Default;
390   if (CodeGenOpts.RelocationModel == "static") {
391     RM = llvm::Reloc::Static;
392   } else if (CodeGenOpts.RelocationModel == "pic") {
393     RM = llvm::Reloc::PIC_;
394   } else {
395     assert(CodeGenOpts.RelocationModel == "dynamic-no-pic" &&
396            "Invalid PIC model!");
397     RM = llvm::Reloc::DynamicNoPIC;
398   }
399 
400   CodeGenOpt::Level OptLevel = CodeGenOpt::Default;
401   switch (CodeGenOpts.OptimizationLevel) {
402   default: break;
403   case 0: OptLevel = CodeGenOpt::None; break;
404   case 3: OptLevel = CodeGenOpt::Aggressive; break;
405   }
406 
407   llvm::TargetOptions Options;
408 
409   // Set frame pointer elimination mode.
410   if (!CodeGenOpts.DisableFPElim) {
411     Options.NoFramePointerElim = false;
412     Options.NoFramePointerElimNonLeaf = false;
413   } else if (CodeGenOpts.OmitLeafFramePointer) {
414     Options.NoFramePointerElim = false;
415     Options.NoFramePointerElimNonLeaf = true;
416   } else {
417     Options.NoFramePointerElim = true;
418     Options.NoFramePointerElimNonLeaf = true;
419   }
420 
421   if (CodeGenOpts.UseInitArray)
422     Options.UseInitArray = true;
423 
424   // Set float ABI type.
425   if (CodeGenOpts.FloatABI == "soft" || CodeGenOpts.FloatABI == "softfp")
426     Options.FloatABIType = llvm::FloatABI::Soft;
427   else if (CodeGenOpts.FloatABI == "hard")
428     Options.FloatABIType = llvm::FloatABI::Hard;
429   else {
430     assert(CodeGenOpts.FloatABI.empty() && "Invalid float abi!");
431     Options.FloatABIType = llvm::FloatABI::Default;
432   }
433 
434   // Set FP fusion mode.
435   switch (CodeGenOpts.getFPContractMode()) {
436   case CodeGenOptions::FPC_Off:
437     Options.AllowFPOpFusion = llvm::FPOpFusion::Strict;
438     break;
439   case CodeGenOptions::FPC_On:
440     Options.AllowFPOpFusion = llvm::FPOpFusion::Standard;
441     break;
442   case CodeGenOptions::FPC_Fast:
443     Options.AllowFPOpFusion = llvm::FPOpFusion::Fast;
444     break;
445   }
446 
447   Options.LessPreciseFPMADOption = CodeGenOpts.LessPreciseFPMAD;
448   Options.NoInfsFPMath = CodeGenOpts.NoInfsFPMath;
449   Options.NoNaNsFPMath = CodeGenOpts.NoNaNsFPMath;
450   Options.NoZerosInBSS = CodeGenOpts.NoZeroInitializedInBSS;
451   Options.UnsafeFPMath = CodeGenOpts.UnsafeFPMath;
452   Options.UseSoftFloat = CodeGenOpts.SoftFloat;
453   Options.StackAlignmentOverride = CodeGenOpts.StackAlignment;
454   Options.RealignStack = CodeGenOpts.StackRealignment;
455   Options.DisableTailCalls = CodeGenOpts.DisableTailCalls;
456   Options.TrapFuncName = CodeGenOpts.TrapFuncName;
457   Options.PositionIndependentExecutable = LangOpts.PIELevel != 0;
458   Options.SSPBufferSize = CodeGenOpts.SSPBufferSize;
459   Options.EnableSegmentedStacks = CodeGenOpts.EnableSegmentedStacks;
460 
461   TargetMachine *TM = TheTarget->createTargetMachine(Triple, TargetOpts.CPU,
462                                                      FeaturesStr, Options,
463                                                      RM, CM, OptLevel);
464 
465   if (CodeGenOpts.RelaxAll)
466     TM->setMCRelaxAll(true);
467   if (CodeGenOpts.SaveTempLabels)
468     TM->setMCSaveTempLabels(true);
469   if (CodeGenOpts.NoDwarf2CFIAsm)
470     TM->setMCUseCFI(false);
471   if (!CodeGenOpts.NoDwarfDirectoryAsm)
472     TM->setMCUseDwarfDirectory(true);
473   if (CodeGenOpts.NoExecStack)
474     TM->setMCNoExecStack(true);
475 
476   return TM;
477 }
478 
479 bool EmitAssemblyHelper::AddEmitPasses(BackendAction Action,
480                                        formatted_raw_ostream &OS,
481                                        TargetMachine *TM) {
482 
483   // Create the code generator passes.
484   PassManager *PM = getCodeGenPasses(TM);
485 
486   // Add LibraryInfo.
487   llvm::Triple TargetTriple(TheModule->getTargetTriple());
488   TargetLibraryInfo *TLI = new TargetLibraryInfo(TargetTriple);
489   if (!CodeGenOpts.SimplifyLibCalls)
490     TLI->disableAllFunctions();
491   PM->add(TLI);
492 
493   // Add Target specific analysis passes.
494   TM->addAnalysisPasses(*PM);
495 
496   // Normal mode, emit a .s or .o file by running the code generator. Note,
497   // this also adds codegenerator level optimization passes.
498   TargetMachine::CodeGenFileType CGFT = TargetMachine::CGFT_AssemblyFile;
499   if (Action == Backend_EmitObj)
500     CGFT = TargetMachine::CGFT_ObjectFile;
501   else if (Action == Backend_EmitMCNull)
502     CGFT = TargetMachine::CGFT_Null;
503   else
504     assert(Action == Backend_EmitAssembly && "Invalid action!");
505 
506   // Add ObjC ARC final-cleanup optimizations. This is done as part of the
507   // "codegen" passes so that it isn't run multiple times when there is
508   // inlining happening.
509   if (LangOpts.ObjCAutoRefCount &&
510       CodeGenOpts.OptimizationLevel > 0)
511     PM->add(createObjCARCContractPass());
512 
513   if (TM->addPassesToEmitFile(*PM, OS, CGFT,
514                               /*DisableVerify=*/!CodeGenOpts.VerifyModule)) {
515     Diags.Report(diag::err_fe_unable_to_interface_with_target);
516     return false;
517   }
518 
519   return true;
520 }
521 
522 void EmitAssemblyHelper::EmitAssembly(BackendAction Action, raw_ostream *OS) {
523   TimeRegion Region(llvm::TimePassesIsEnabled ? &CodeGenerationTime : 0);
524   llvm::formatted_raw_ostream FormattedOS;
525 
526   bool UsesCodeGen = (Action != Backend_EmitNothing &&
527                       Action != Backend_EmitBC &&
528                       Action != Backend_EmitLL);
529   TargetMachine *TM = CreateTargetMachine(UsesCodeGen);
530   if (UsesCodeGen && !TM) return;
531   CreatePasses(TM);
532 
533   switch (Action) {
534   case Backend_EmitNothing:
535     break;
536 
537   case Backend_EmitBC:
538     getPerModulePasses(TM)->add(createBitcodeWriterPass(*OS));
539     break;
540 
541   case Backend_EmitLL:
542     FormattedOS.setStream(*OS, formatted_raw_ostream::PRESERVE_STREAM);
543     getPerModulePasses(TM)->add(createPrintModulePass(&FormattedOS));
544     break;
545 
546   default:
547     FormattedOS.setStream(*OS, formatted_raw_ostream::PRESERVE_STREAM);
548     if (!AddEmitPasses(Action, FormattedOS, TM))
549       return;
550   }
551 
552   // Before executing passes, print the final values of the LLVM options.
553   cl::PrintOptionValues();
554 
555   // Run passes. For now we do all passes at once, but eventually we
556   // would like to have the option of streaming code generation.
557 
558   if (PerFunctionPasses) {
559     PrettyStackTraceString CrashInfo("Per-function optimization");
560 
561     PerFunctionPasses->doInitialization();
562     for (Module::iterator I = TheModule->begin(),
563            E = TheModule->end(); I != E; ++I)
564       if (!I->isDeclaration())
565         PerFunctionPasses->run(*I);
566     PerFunctionPasses->doFinalization();
567   }
568 
569   if (PerModulePasses) {
570     PrettyStackTraceString CrashInfo("Per-module optimization passes");
571     PerModulePasses->run(*TheModule);
572   }
573 
574   if (CodeGenPasses) {
575     PrettyStackTraceString CrashInfo("Code generation");
576     CodeGenPasses->run(*TheModule);
577   }
578 }
579 
580 void clang::EmitBackendOutput(DiagnosticsEngine &Diags,
581                               const CodeGenOptions &CGOpts,
582                               const clang::TargetOptions &TOpts,
583                               const LangOptions &LOpts,
584                               Module *M,
585                               BackendAction Action, raw_ostream *OS) {
586   EmitAssemblyHelper AsmHelper(Diags, CGOpts, TOpts, LOpts, M);
587 
588   AsmHelper.EmitAssembly(Action, OS);
589 }
590