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