lto.cpp revision 5e563c326490207ebd58d47935fb9efda7638aa2 
1//===-lto.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/Module.h"
16#include "llvm/PassManager.h"
17#include "llvm/Linker.h"
18#include "llvm/Constants.h"
19#include "llvm/DerivedTypes.h"
20#include "llvm/ModuleProvider.h"
21#include "llvm/Bitcode/ReaderWriter.h"
22#include "llvm/Support/CommandLine.h"
23#include "llvm/Support/FileUtilities.h"
24#include "llvm/Support/SystemUtils.h"
25#include "llvm/Support/Mangler.h"
26#include "llvm/Support/MemoryBuffer.h"
27#include "llvm/System/Program.h"
28#include "llvm/System/Signals.h"
29#include "llvm/Analysis/Passes.h"
30#include "llvm/Analysis/LoopPass.h"
31#include "llvm/Analysis/Verifier.h"
32#include "llvm/CodeGen/FileWriters.h"
33#include "llvm/Target/SubtargetFeature.h"
34#include "llvm/Target/TargetData.h"
35#include "llvm/Target/TargetMachine.h"
36#include "llvm/Target/TargetMachineRegistry.h"
37#include "llvm/Target/TargetAsmInfo.h"
38#include "llvm/Transforms/IPO.h"
39#include "llvm/Transforms/Scalar.h"
40#include "llvm/Analysis/LoadValueNumbering.h"
41#include "llvm/Support/MathExtras.h"
42#include "llvm/LinkTimeOptimizer.h"
43#include <fstream>
44#include <ostream>
45using namespace llvm;
46
47extern "C"
48llvm::LinkTimeOptimizer *createLLVMOptimizer(unsigned VERSION)
49{
50  // Linker records LLVM_LTO_VERSION based on llvm optimizer available
51  // during linker build. Match linker's recorded LTO VERSION number
52  // with installed llvm optimizer version. If these numbers do not match
53  // then linker may not be able to use llvm optimizer dynamically.
54  if (VERSION != LLVM_LTO_VERSION)
55    return NULL;
56
57  llvm::LTO *l = new llvm::LTO();
58  return l;
59}
60
61/// If symbol is not used then make it internal and let optimizer takes
62/// care of it.
63void LLVMSymbol::mayBeNotUsed() {
64  gv->setLinkage(GlobalValue::InternalLinkage);
65}
66
67// Map LLVM LinkageType to LTO LinakgeType
68static LTOLinkageTypes
69getLTOLinkageType(GlobalValue *v)
70{
71  LTOLinkageTypes lt;
72  if (v->hasExternalLinkage())
73    lt = LTOExternalLinkage;
74  else if (v->hasLinkOnceLinkage())
75    lt = LTOLinkOnceLinkage;
76  else if (v->hasWeakLinkage())
77    lt = LTOWeakLinkage;
78  else
79    // Otherwise it is internal linkage for link time optimizer
80    lt = LTOInternalLinkage;
81  return lt;
82}
83
84// MAP LLVM VisibilityType to LTO VisibilityType
85static LTOVisibilityTypes
86getLTOVisibilityType(GlobalValue *v)
87{
88  LTOVisibilityTypes vis;
89  if (v->hasHiddenVisibility())
90    vis = LTOHiddenVisibility;
91  else if (v->hasProtectedVisibility())
92    vis = LTOProtectedVisibility;
93  else
94    vis = LTODefaultVisibility;
95  return vis;
96}
97
98// Find exeternal symbols referenced by VALUE. This is a recursive function.
99static void
100findExternalRefs(Value *value, std::set<std::string> &references,
101                 Mangler &mangler) {
102
103  if (GlobalValue *gv = dyn_cast<GlobalValue>(value)) {
104    LTOLinkageTypes lt = getLTOLinkageType(gv);
105    if (lt != LTOInternalLinkage && strncmp (gv->getName().c_str(), "llvm.", 5))
106      references.insert(mangler.getValueName(gv));
107  }
108
109  // GlobalValue, even with InternalLinkage type, may have operands with
110  // ExternalLinkage type. Do not ignore these operands.
111  if (Constant *c = dyn_cast<Constant>(value))
112    // Handle ConstantExpr, ConstantStruct, ConstantArry etc..
113    for (unsigned i = 0, e = c->getNumOperands(); i != e; ++i)
114      findExternalRefs(c->getOperand(i), references, mangler);
115}
116
117/// If Module with InputFilename is available then remove it from allModules
118/// and call delete on it.
119void
120LTO::removeModule (const std::string &InputFilename)
121{
122  NameToModuleMap::iterator pos = allModules.find(InputFilename.c_str());
123  if (pos == allModules.end())
124    return;
125
126  Module *m = pos->second;
127  allModules.erase(pos);
128  delete m;
129}
130
131/// InputFilename is a LLVM bitcode file. If Module with InputFilename is
132/// available then return it. Otherwise parseInputFilename.
133Module *
134LTO::getModule(const std::string &InputFilename)
135{
136  Module *m = NULL;
137
138  NameToModuleMap::iterator pos = allModules.find(InputFilename.c_str());
139  if (pos != allModules.end())
140    m = allModules[InputFilename.c_str()];
141  else {
142    if (MemoryBuffer *Buffer
143        = MemoryBuffer::getFile(&InputFilename[0], InputFilename.size())) {
144      m = ParseBitcodeFile(Buffer);
145      delete Buffer;
146    }
147    allModules[InputFilename.c_str()] = m;
148  }
149  return m;
150}
151
152/// InputFilename is a LLVM bitcode file. Reade this bitcode file and
153/// set corresponding target triplet string.
154void
155LTO::getTargetTriple(const std::string &InputFilename,
156                     std::string &targetTriple)
157{
158  Module *m = getModule(InputFilename);
159  if (m)
160    targetTriple = m->getTargetTriple();
161}
162
163/// InputFilename is a LLVM bitcode file. Read it using bitcode reader.
164/// Collect global functions and symbol names in symbols vector.
165/// Collect external references in references vector.
166/// Return LTO_READ_SUCCESS if there is no error.
167enum LTOStatus
168LTO::readLLVMObjectFile(const std::string &InputFilename,
169                        NameToSymbolMap &symbols,
170                        std::set<std::string> &references)
171{
172  Module *m = getModule(InputFilename);
173  if (!m)
174    return LTO_READ_FAILURE;
175
176  // Collect Target info
177  getTarget(m);
178
179  if (!Target)
180    return LTO_READ_FAILURE;
181
182  // Use mangler to add GlobalPrefix to names to match linker names.
183  // FIXME : Instead of hard coding "-" use GlobalPrefix.
184  Mangler mangler(*m, Target->getTargetAsmInfo()->getGlobalPrefix());
185  modules.push_back(m);
186
187  for (Module::iterator f = m->begin(), e = m->end(); f != e; ++f) {
188    LTOLinkageTypes lt = getLTOLinkageType(f);
189    LTOVisibilityTypes vis = getLTOVisibilityType(f);
190    if (!f->isDeclaration() && lt != LTOInternalLinkage
191        && strncmp (f->getName().c_str(), "llvm.", 5)) {
192      int alignment = ( 16 > f->getAlignment() ? 16 : f->getAlignment());
193      LLVMSymbol *newSymbol = new LLVMSymbol(lt, vis, f, f->getName(),
194                                             mangler.getValueName(f),
195                                             Log2_32(alignment));
196      symbols[newSymbol->getMangledName()] = newSymbol;
197      allSymbols[newSymbol->getMangledName()] = newSymbol;
198    }
199
200    // Collect external symbols referenced by this function.
201    for (Function::iterator b = f->begin(), fe = f->end(); b != fe; ++b)
202      for (BasicBlock::iterator i = b->begin(), be = b->end();
203           i != be; ++i) {
204        for (unsigned count = 0, total = i->getNumOperands();
205             count != total; ++count)
206          findExternalRefs(i->getOperand(count), references, mangler);
207      }
208  }
209
210  for (Module::global_iterator v = m->global_begin(), e = m->global_end();
211       v !=  e; ++v) {
212    LTOLinkageTypes lt = getLTOLinkageType(v);
213    LTOVisibilityTypes vis = getLTOVisibilityType(v);
214    if (!v->isDeclaration() && lt != LTOInternalLinkage
215        && strncmp (v->getName().c_str(), "llvm.", 5)) {
216      const TargetData *TD = Target->getTargetData();
217      LLVMSymbol *newSymbol = new LLVMSymbol(lt, vis, v, v->getName(),
218                                             mangler.getValueName(v),
219                                             TD->getPreferredAlignmentLog(v));
220      symbols[newSymbol->getMangledName()] = newSymbol;
221      allSymbols[newSymbol->getMangledName()] = newSymbol;
222
223      for (unsigned count = 0, total = v->getNumOperands();
224           count != total; ++count)
225        findExternalRefs(v->getOperand(count), references, mangler);
226
227    }
228  }
229
230  return LTO_READ_SUCCESS;
231}
232
233/// Get TargetMachine.
234/// Use module M to find appropriate Target.
235void
236LTO::getTarget (Module *M) {
237
238  if (Target)
239    return;
240
241  std::string Err;
242  const TargetMachineRegistry::entry* March =
243    TargetMachineRegistry::getClosestStaticTargetForModule(*M, Err);
244
245  if (March == 0)
246    return;
247
248  // Create target
249  std::string Features;
250  Target = March->CtorFn(*M, Features);
251}
252
253/// Optimize module M using various IPO passes. Use exportList to
254/// internalize selected symbols. Target platform is selected
255/// based on information available to module M. No new target
256/// features are selected.
257enum LTOStatus
258LTO::optimize(Module *M, std::ostream &Out,
259              std::vector<const char *> &exportList)
260{
261  // Instantiate the pass manager to organize the passes.
262  PassManager Passes;
263
264  // Collect Target info
265  getTarget(M);
266
267  if (!Target)
268    return LTO_NO_TARGET;
269
270  // Start off with a verification pass.
271  Passes.add(createVerifierPass());
272
273  // Add an appropriate TargetData instance for this module...
274  Passes.add(new TargetData(*Target->getTargetData()));
275
276  // Internalize symbols if export list is nonemty
277  if (!exportList.empty())
278    Passes.add(createInternalizePass(exportList));
279
280  // Now that we internalized some globals, see if we can hack on them!
281  Passes.add(createGlobalOptimizerPass());
282
283  // Linking modules together can lead to duplicated global constants, only
284  // keep one copy of each constant...
285  Passes.add(createConstantMergePass());
286
287  // If the -s command line option was specified, strip the symbols out of the
288  // resulting program to make it smaller.  -s is a GLD option that we are
289  // supporting.
290  Passes.add(createStripSymbolsPass());
291
292  // Propagate constants at call sites into the functions they call.
293  Passes.add(createIPConstantPropagationPass());
294
295  // Remove unused arguments from functions...
296  Passes.add(createDeadArgEliminationPass());
297
298  Passes.add(createFunctionInliningPass()); // Inline small functions
299
300  Passes.add(createPruneEHPass());            // Remove dead EH info
301
302  Passes.add(createGlobalDCEPass());          // Remove dead functions
303
304  // If we didn't decide to inline a function, check to see if we can
305  // transform it to pass arguments by value instead of by reference.
306  Passes.add(createArgumentPromotionPass());
307
308  // The IPO passes may leave cruft around.  Clean up after them.
309  Passes.add(createInstructionCombiningPass());
310
311  Passes.add(createScalarReplAggregatesPass()); // Break up allocas
312
313  // Run a few AA driven optimizations here and now, to cleanup the code.
314  Passes.add(createGlobalsModRefPass());      // IP alias analysis
315
316  Passes.add(createLICMPass());               // Hoist loop invariants
317  Passes.add(createLoadValueNumberingPass()); // GVN for load instrs
318  Passes.add(createGCSEPass());               // Remove common subexprs
319  Passes.add(createDeadStoreEliminationPass()); // Nuke dead stores
320
321  // Cleanup and simplify the code after the scalar optimizations.
322  Passes.add(createInstructionCombiningPass());
323
324  // Delete basic blocks, which optimization passes may have killed...
325  Passes.add(createCFGSimplificationPass());
326
327  // Now that we have optimized the program, discard unreachable functions...
328  Passes.add(createGlobalDCEPass());
329
330  // Make sure everything is still good.
331  Passes.add(createVerifierPass());
332
333  FunctionPassManager *CodeGenPasses =
334    new FunctionPassManager(new ExistingModuleProvider(M));
335
336  CodeGenPasses->add(new TargetData(*Target->getTargetData()));
337
338  MachineCodeEmitter *MCE = 0;
339
340  switch (Target->addPassesToEmitFile(*CodeGenPasses, Out,
341                                      TargetMachine::AssemblyFile, true)) {
342  default:
343  case FileModel::Error:
344    return LTO_WRITE_FAILURE;
345  case FileModel::AsmFile:
346    break;
347  case FileModel::MachOFile:
348    MCE = AddMachOWriter(*CodeGenPasses, Out, *Target);
349    break;
350  case FileModel::ElfFile:
351    MCE = AddELFWriter(*CodeGenPasses, Out, *Target);
352    break;
353  }
354
355  if (Target->addPassesToEmitFileFinish(*CodeGenPasses, MCE, true))
356    return LTO_WRITE_FAILURE;
357
358  // Run our queue of passes all at once now, efficiently.
359  Passes.run(*M);
360
361  // Run the code generator, if present.
362  CodeGenPasses->doInitialization();
363  for (Module::iterator I = M->begin(), E = M->end(); I != E; ++I) {
364    if (!I->isDeclaration())
365      CodeGenPasses->run(*I);
366  }
367  CodeGenPasses->doFinalization();
368
369  return LTO_OPT_SUCCESS;
370}
371
372///Link all modules together and optimize them using IPO. Generate
373/// native object file using OutputFilename
374/// Return appropriate LTOStatus.
375enum LTOStatus
376LTO::optimizeModules(const std::string &OutputFilename,
377                     std::vector<const char *> &exportList,
378                     std::string &targetTriple,
379                     bool saveTemps, const char *FinalOutputFilename)
380{
381  if (modules.empty())
382    return LTO_NO_WORK;
383
384  std::ios::openmode io_mode =
385    std::ios::out | std::ios::trunc | std::ios::binary;
386  std::string *errMsg = NULL;
387  Module *bigOne = modules[0];
388  Linker theLinker("LinkTimeOptimizer", bigOne, false);
389  for (unsigned i = 1, e = modules.size(); i != e; ++i)
390    if (theLinker.LinkModules(bigOne, modules[i], errMsg))
391      return LTO_MODULE_MERGE_FAILURE;
392  //  all modules have been handed off to the linker.
393  modules.clear();
394
395  sys::Path FinalOutputPath(FinalOutputFilename);
396  FinalOutputPath.eraseSuffix();
397
398  switch(CGModel) {
399  case LTO_CGM_Dynamic:
400    Target->setRelocationModel(Reloc::PIC_);
401    break;
402  case LTO_CGM_DynamicNoPIC:
403    Target->setRelocationModel(Reloc::DynamicNoPIC);
404    break;
405  case LTO_CGM_Static:
406    Target->setRelocationModel(Reloc::Static);
407    break;
408  }
409
410  if (saveTemps) {
411    std::string tempFileName(FinalOutputPath.c_str());
412    tempFileName += "0.bc";
413    std::ofstream Out(tempFileName.c_str(), io_mode);
414    WriteBitcodeToFile(bigOne, Out);
415  }
416
417  // Strip leading underscore because it was added to match names
418  // seen by linker.
419  for (unsigned i = 0, e = exportList.size(); i != e; ++i) {
420    const char *name = exportList[i];
421    NameToSymbolMap::iterator itr = allSymbols.find(name);
422    if (itr != allSymbols.end())
423      exportList[i] = allSymbols[name]->getName();
424  }
425
426
427  std::string ErrMsg;
428  sys::Path TempDir = sys::Path::GetTemporaryDirectory(&ErrMsg);
429  if (TempDir.isEmpty()) {
430    cerr << "lto: " << ErrMsg << "\n";
431    return LTO_WRITE_FAILURE;
432  }
433  sys::Path tmpAsmFilePath(TempDir);
434  if (!tmpAsmFilePath.appendComponent("lto")) {
435    cerr << "lto: " << ErrMsg << "\n";
436    TempDir.eraseFromDisk(true);
437    return LTO_WRITE_FAILURE;
438  }
439  if (tmpAsmFilePath.createTemporaryFileOnDisk(true, &ErrMsg)) {
440    cerr << "lto: " << ErrMsg << "\n";
441    TempDir.eraseFromDisk(true);
442    return LTO_WRITE_FAILURE;
443  }
444  sys::RemoveFileOnSignal(tmpAsmFilePath);
445
446  std::ofstream asmFile(tmpAsmFilePath.c_str(), io_mode);
447  if (!asmFile.is_open() || asmFile.bad()) {
448    if (tmpAsmFilePath.exists()) {
449      tmpAsmFilePath.eraseFromDisk();
450      TempDir.eraseFromDisk(true);
451    }
452    return LTO_WRITE_FAILURE;
453  }
454
455  enum LTOStatus status = optimize(bigOne, asmFile, exportList);
456  asmFile.close();
457  if (status != LTO_OPT_SUCCESS) {
458    tmpAsmFilePath.eraseFromDisk();
459    TempDir.eraseFromDisk(true);
460    return status;
461  }
462
463  if (saveTemps) {
464    std::string tempFileName(FinalOutputPath.c_str());
465    tempFileName += "1.bc";
466    std::ofstream Out(tempFileName.c_str(), io_mode);
467    WriteBitcodeToFile(bigOne, Out);
468  }
469
470  targetTriple = bigOne->getTargetTriple();
471
472  // Run GCC to assemble and link the program into native code.
473  //
474  // Note:
475  //  We can't just assemble and link the file with the system assembler
476  //  and linker because we don't know where to put the _start symbol.
477  //  GCC mysteriously knows how to do it.
478  const sys::Path gcc = sys::Program::FindProgramByName("gcc");
479  if (gcc.isEmpty()) {
480    tmpAsmFilePath.eraseFromDisk();
481    TempDir.eraseFromDisk(true);
482    return LTO_ASM_FAILURE;
483  }
484
485  std::vector<const char*> args;
486  args.push_back(gcc.c_str());
487  args.push_back("-c");
488  args.push_back("-x");
489  args.push_back("assembler");
490  args.push_back("-o");
491  args.push_back(OutputFilename.c_str());
492  args.push_back(tmpAsmFilePath.c_str());
493  args.push_back(0);
494
495  if (sys::Program::ExecuteAndWait(gcc, &args[0], 0, 0, 1, 0, &ErrMsg)) {
496    cerr << "lto: " << ErrMsg << "\n";
497    return LTO_ASM_FAILURE;
498  }
499
500  tmpAsmFilePath.eraseFromDisk();
501  TempDir.eraseFromDisk(true);
502
503  return LTO_OPT_SUCCESS;
504}
505
506void LTO::printVersion() {
507    cl::PrintVersionMessage();
508}
509
510/// Unused pure-virtual destructor. Must remain empty.
511LinkTimeOptimizer::~LinkTimeOptimizer() {}
512
513/// Destruct LTO. Delete all modules, symbols and target.
514LTO::~LTO() {
515
516  for (std::vector<Module *>::iterator itr = modules.begin(), e = modules.end();
517       itr != e; ++itr)
518    delete *itr;
519
520  modules.clear();
521
522  for (NameToSymbolMap::iterator itr = allSymbols.begin(), e = allSymbols.end();
523       itr != e; ++itr)
524    delete itr->second;
525
526  allSymbols.clear();
527
528  delete Target;
529}
530