summaryrefslogtreecommitdiff
path: root/lib/LTO/LTOModule.cpp
blob: f7f6a3c4b8c2bac15942814c6dea8303f944ff73 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
//===-- LTOModule.cpp - LLVM Link Time Optimizer --------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the Link Time Optimization library. This library is
// intended to be used by linker to optimize code at link time.
//
//===----------------------------------------------------------------------===//

#include "llvm/LTO/LTOModule.h"
#include "llvm/ADT/Triple.h"
#include "llvm/Bitcode/ReaderWriter.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Metadata.h"
#include "llvm/IR/Module.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCInst.h"
#include "llvm/MC/MCInstrInfo.h"
#include "llvm/MC/MCParser/MCAsmParser.h"
#include "llvm/MC/MCSection.h"
#include "llvm/MC/MCStreamer.h"
#include "llvm/MC/MCSubtargetInfo.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/MC/MCTargetAsmParser.h"
#include "llvm/MC/SubtargetFeature.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/Host.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/SourceMgr.h"
#include "llvm/Support/TargetRegistry.h"
#include "llvm/Support/TargetSelect.h"
#include "llvm/Support/system_error.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Target/TargetLoweringObjectFile.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Transforms/Utils/GlobalStatus.h"
using namespace llvm;

LTOModule::LTOModule(llvm::Module *m, llvm::TargetMachine *t)
  : _module(m), _target(t),
    _context(_target->getMCAsmInfo(), _target->getRegisterInfo(), &ObjFileInfo),
    _mangler(t->getDataLayout()) {
  ObjFileInfo.InitMCObjectFileInfo(t->getTargetTriple(),
                                   t->getRelocationModel(), t->getCodeModel(),
                                   _context);
}

/// isBitcodeFile - Returns 'true' if the file (or memory contents) is LLVM
/// bitcode.
bool LTOModule::isBitcodeFile(const void *mem, size_t length) {
  return sys::fs::identify_magic(StringRef((const char *)mem, length)) ==
         sys::fs::file_magic::bitcode;
}

bool LTOModule::isBitcodeFile(const char *path) {
  sys::fs::file_magic type;
  if (sys::fs::identify_magic(path, type))
    return false;
  return type == sys::fs::file_magic::bitcode;
}

/// isBitcodeFileForTarget - Returns 'true' if the file (or memory contents) is
/// LLVM bitcode for the specified triple.
bool LTOModule::isBitcodeFileForTarget(const void *mem, size_t length,
                                       const char *triplePrefix) {
  MemoryBuffer *buffer = makeBuffer(mem, length);
  if (!buffer)
    return false;
  return isTargetMatch(buffer, triplePrefix);
}

bool LTOModule::isBitcodeFileForTarget(const char *path,
                                       const char *triplePrefix) {
  std::unique_ptr<MemoryBuffer> buffer;
  if (MemoryBuffer::getFile(path, buffer))
    return false;
  return isTargetMatch(buffer.release(), triplePrefix);
}

/// isTargetMatch - Returns 'true' if the memory buffer is for the specified
/// target triple.
bool LTOModule::isTargetMatch(MemoryBuffer *buffer, const char *triplePrefix) {
  std::string Triple = getBitcodeTargetTriple(buffer, getGlobalContext());
  delete buffer;
  return strncmp(Triple.c_str(), triplePrefix, strlen(triplePrefix)) == 0;
}

/// makeLTOModule - Create an LTOModule. N.B. These methods take ownership of
/// the buffer.
LTOModule *LTOModule::makeLTOModule(const char *path, TargetOptions options,
                                    std::string &errMsg) {
  std::unique_ptr<MemoryBuffer> buffer;
  if (error_code ec = MemoryBuffer::getFile(path, buffer)) {
    errMsg = ec.message();
    return nullptr;
  }
  return makeLTOModule(buffer.release(), options, errMsg);
}

LTOModule *LTOModule::makeLTOModule(int fd, const char *path,
                                    size_t size, TargetOptions options,
                                    std::string &errMsg) {
  return makeLTOModule(fd, path, size, 0, options, errMsg);
}

LTOModule *LTOModule::makeLTOModule(int fd, const char *path,
                                    size_t map_size,
                                    off_t offset,
                                    TargetOptions options,
                                    std::string &errMsg) {
  std::unique_ptr<MemoryBuffer> buffer;
  if (error_code ec =
          MemoryBuffer::getOpenFileSlice(fd, path, buffer, map_size, offset)) {
    errMsg = ec.message();
    return nullptr;
  }
  return makeLTOModule(buffer.release(), options, errMsg);
}

LTOModule *LTOModule::makeLTOModule(const void *mem, size_t length,
                                    TargetOptions options,
                                    std::string &errMsg, StringRef path) {
  std::unique_ptr<MemoryBuffer> buffer(makeBuffer(mem, length, path));
  if (!buffer)
    return nullptr;
  return makeLTOModule(buffer.release(), options, errMsg);
}

LTOModule *LTOModule::makeLTOModule(MemoryBuffer *buffer,
                                    TargetOptions options,
                                    std::string &errMsg) {
  // parse bitcode buffer
  ErrorOr<Module *> ModuleOrErr =
      getLazyBitcodeModule(buffer, getGlobalContext());
  if (error_code EC = ModuleOrErr.getError()) {
    errMsg = EC.message();
    delete buffer;
    return nullptr;
  }
  std::unique_ptr<Module> m(ModuleOrErr.get());

  std::string TripleStr = m->getTargetTriple();
  if (TripleStr.empty())
    TripleStr = sys::getDefaultTargetTriple();
  llvm::Triple Triple(TripleStr);

  // find machine architecture for this module
  const Target *march = TargetRegistry::lookupTarget(TripleStr, errMsg);
  if (!march)
    return nullptr;

  // construct LTOModule, hand over ownership of module and target
  SubtargetFeatures Features;
  Features.getDefaultSubtargetFeatures(Triple);
  std::string FeatureStr = Features.getString();
  // Set a default CPU for Darwin triples.
  std::string CPU;
  if (Triple.isOSDarwin()) {
    if (Triple.getArch() == llvm::Triple::x86_64)
      CPU = "core2";
    else if (Triple.getArch() == llvm::Triple::x86)
      CPU = "yonah";
    else if (Triple.getArch() == llvm::Triple::arm64 ||
             Triple.getArch() == llvm::Triple::aarch64)
      CPU = "cyclone";
  }

  TargetMachine *target = march->createTargetMachine(TripleStr, CPU, FeatureStr,
                                                     options);
  m->materializeAllPermanently();

  LTOModule *Ret = new LTOModule(m.release(), target);

  // We need a MCContext set up in order to get mangled names of private
  // symbols. It is a bit odd that we need to report uses and definitions
  // of private symbols, but it does look like ld64 expects to be informed
  // of at least the ones with an 'l' prefix.
  MCContext &Context = Ret->_context;
  const TargetLoweringObjectFile &TLOF =
      target->getTargetLowering()->getObjFileLowering();
  const_cast<TargetLoweringObjectFile &>(TLOF).Initialize(Context, *target);

  if (Ret->parseSymbols(errMsg)) {
    delete Ret;
    return nullptr;
  }

  Ret->parseMetadata();

  return Ret;
}

/// Create a MemoryBuffer from a memory range with an optional name.
MemoryBuffer *LTOModule::makeBuffer(const void *mem, size_t length,
                                    StringRef name) {
  const char *startPtr = (const char*)mem;
  return MemoryBuffer::getMemBuffer(StringRef(startPtr, length), name, false);
}

/// objcClassNameFromExpression - Get string that the data pointer points to.
bool
LTOModule::objcClassNameFromExpression(const Constant *c, std::string &name) {
  if (const ConstantExpr *ce = dyn_cast<ConstantExpr>(c)) {
    Constant *op = ce->getOperand(0);
    if (GlobalVariable *gvn = dyn_cast<GlobalVariable>(op)) {
      Constant *cn = gvn->getInitializer();
      if (ConstantDataArray *ca = dyn_cast<ConstantDataArray>(cn)) {
        if (ca->isCString()) {
          name = ".objc_class_name_" + ca->getAsCString().str();
          return true;
        }
      }
    }
  }
  return false;
}

/// addObjCClass - Parse i386/ppc ObjC class data structure.
void LTOModule::addObjCClass(const GlobalVariable *clgv) {
  const ConstantStruct *c = dyn_cast<ConstantStruct>(clgv->getInitializer());
  if (!c) return;

  // second slot in __OBJC,__class is pointer to superclass name
  std::string superclassName;
  if (objcClassNameFromExpression(c->getOperand(1), superclassName)) {
    NameAndAttributes info;
    StringMap<NameAndAttributes>::value_type &entry =
      _undefines.GetOrCreateValue(superclassName);
    if (!entry.getValue().name) {
      const char *symbolName = entry.getKey().data();
      info.name = symbolName;
      info.attributes = LTO_SYMBOL_DEFINITION_UNDEFINED;
      info.isFunction = false;
      info.symbol = clgv;
      entry.setValue(info);
    }
  }

  // third slot in __OBJC,__class is pointer to class name
  std::string className;
  if (objcClassNameFromExpression(c->getOperand(2), className)) {
    StringSet::value_type &entry = _defines.GetOrCreateValue(className);
    entry.setValue(1);

    NameAndAttributes info;
    info.name = entry.getKey().data();
    info.attributes = LTO_SYMBOL_PERMISSIONS_DATA |
      LTO_SYMBOL_DEFINITION_REGULAR | LTO_SYMBOL_SCOPE_DEFAULT;
    info.isFunction = false;
    info.symbol = clgv;
    _symbols.push_back(info);
  }
}

/// addObjCCategory - Parse i386/ppc ObjC category data structure.
void LTOModule::addObjCCategory(const GlobalVariable *clgv) {
  const ConstantStruct *c = dyn_cast<ConstantStruct>(clgv->getInitializer());
  if (!c) return;

  // second slot in __OBJC,__category is pointer to target class name
  std::string targetclassName;
  if (!objcClassNameFromExpression(c->getOperand(1), targetclassName))
    return;

  NameAndAttributes info;
  StringMap<NameAndAttributes>::value_type &entry =
    _undefines.GetOrCreateValue(targetclassName);

  if (entry.getValue().name)
    return;

  const char *symbolName = entry.getKey().data();
  info.name = symbolName;
  info.attributes = LTO_SYMBOL_DEFINITION_UNDEFINED;
  info.isFunction = false;
  info.symbol = clgv;
  entry.setValue(info);
}

/// addObjCClassRef - Parse i386/ppc ObjC class list data structure.
void LTOModule::addObjCClassRef(const GlobalVariable *clgv) {
  std::string targetclassName;
  if (!objcClassNameFromExpression(clgv->getInitializer(), targetclassName))
    return;

  NameAndAttributes info;
  StringMap<NameAndAttributes>::value_type &entry =
    _undefines.GetOrCreateValue(targetclassName);
  if (entry.getValue().name)
    return;

  const char *symbolName = entry.getKey().data();
  info.name = symbolName;
  info.attributes = LTO_SYMBOL_DEFINITION_UNDEFINED;
  info.isFunction = false;
  info.symbol = clgv;
  entry.setValue(info);
}

/// addDefinedDataSymbol - Add a data symbol as defined to the list.
void LTOModule::addDefinedDataSymbol(const GlobalValue *v) {
  // Add to list of defined symbols.
  addDefinedSymbol(v, false);

  if (!v->hasSection() /* || !isTargetDarwin */)
    return;

  // Special case i386/ppc ObjC data structures in magic sections:
  // The issue is that the old ObjC object format did some strange
  // contortions to avoid real linker symbols.  For instance, the
  // ObjC class data structure is allocated statically in the executable
  // that defines that class.  That data structures contains a pointer to
  // its superclass.  But instead of just initializing that part of the
  // struct to the address of its superclass, and letting the static and
  // dynamic linkers do the rest, the runtime works by having that field
  // instead point to a C-string that is the name of the superclass.
  // At runtime the objc initialization updates that pointer and sets
  // it to point to the actual super class.  As far as the linker
  // knows it is just a pointer to a string.  But then someone wanted the
  // linker to issue errors at build time if the superclass was not found.
  // So they figured out a way in mach-o object format to use an absolute
  // symbols (.objc_class_name_Foo = 0) and a floating reference
  // (.reference .objc_class_name_Bar) to cause the linker into erroring when
  // a class was missing.
  // The following synthesizes the implicit .objc_* symbols for the linker
  // from the ObjC data structures generated by the front end.

  // special case if this data blob is an ObjC class definition
  std::string Section = v->getSection();
  if (Section.compare(0, 15, "__OBJC,__class,") == 0) {
    if (const GlobalVariable *gv = dyn_cast<GlobalVariable>(v)) {
      addObjCClass(gv);
    }
  }

  // special case if this data blob is an ObjC category definition
  else if (Section.compare(0, 18, "__OBJC,__category,") == 0) {
    if (const GlobalVariable *gv = dyn_cast<GlobalVariable>(v)) {
      addObjCCategory(gv);
    }
  }

  // special case if this data blob is the list of referenced classes
  else if (Section.compare(0, 18, "__OBJC,__cls_refs,") == 0) {
    if (const GlobalVariable *gv = dyn_cast<GlobalVariable>(v)) {
      addObjCClassRef(gv);
    }
  }
}

/// addDefinedFunctionSymbol - Add a function symbol as defined to the list.
void LTOModule::addDefinedFunctionSymbol(const Function *f) {
  // add to list of defined symbols
  addDefinedSymbol(f, true);
}

static bool canBeHidden(const GlobalValue *GV) {
  // FIXME: this is duplicated with another static function in AsmPrinter.cpp
  GlobalValue::LinkageTypes L = GV->getLinkage();

  if (L != GlobalValue::LinkOnceODRLinkage)
    return false;

  if (GV->hasUnnamedAddr())
    return true;

  // If it is a non constant variable, it needs to be uniqued across shared
  // objects.
  if (const GlobalVariable *Var = dyn_cast<GlobalVariable>(GV)) {
    if (!Var->isConstant())
      return false;
  }

  GlobalStatus GS;
  if (GlobalStatus::analyzeGlobal(GV, GS))
    return false;

  return !GS.IsCompared;
}

/// addDefinedSymbol - Add a defined symbol to the list.
void LTOModule::addDefinedSymbol(const GlobalValue *def, bool isFunction) {
  // ignore all llvm.* symbols
  if (def->getName().startswith("llvm."))
    return;

  // string is owned by _defines
  SmallString<64> Buffer;
  _target->getNameWithPrefix(Buffer, def, _mangler);

  // set alignment part log2() can have rounding errors
  uint32_t align = def->getAlignment();
  uint32_t attr = align ? countTrailingZeros(align) : 0;

  // set permissions part
  if (isFunction) {
    attr |= LTO_SYMBOL_PERMISSIONS_CODE;
  } else {
    const GlobalVariable *gv = dyn_cast<GlobalVariable>(def);
    if (gv && gv->isConstant())
      attr |= LTO_SYMBOL_PERMISSIONS_RODATA;
    else
      attr |= LTO_SYMBOL_PERMISSIONS_DATA;
  }

  // set definition part
  if (def->hasWeakLinkage() || def->hasLinkOnceLinkage())
    attr |= LTO_SYMBOL_DEFINITION_WEAK;
  else if (def->hasCommonLinkage())
    attr |= LTO_SYMBOL_DEFINITION_TENTATIVE;
  else
    attr |= LTO_SYMBOL_DEFINITION_REGULAR;

  // set scope part
  if (def->hasLocalLinkage())
    // Ignore visibility if linkage is local.
    attr |= LTO_SYMBOL_SCOPE_INTERNAL;
  else if (def->hasHiddenVisibility())
    attr |= LTO_SYMBOL_SCOPE_HIDDEN;
  else if (def->hasProtectedVisibility())
    attr |= LTO_SYMBOL_SCOPE_PROTECTED;
  else if (canBeHidden(def))
    attr |= LTO_SYMBOL_SCOPE_DEFAULT_CAN_BE_HIDDEN;
  else
    attr |= LTO_SYMBOL_SCOPE_DEFAULT;

  StringSet::value_type &entry = _defines.GetOrCreateValue(Buffer);
  entry.setValue(1);

  // fill information structure
  NameAndAttributes info;
  StringRef Name = entry.getKey();
  info.name = Name.data();
  assert(info.name[Name.size()] == '\0');
  info.attributes = attr;
  info.isFunction = isFunction;
  info.symbol = def;

  // add to table of symbols
  _symbols.push_back(info);
}

/// addAsmGlobalSymbol - Add a global symbol from module-level ASM to the
/// defined list.
void LTOModule::addAsmGlobalSymbol(const char *name,
                                   lto_symbol_attributes scope) {
  StringSet::value_type &entry = _defines.GetOrCreateValue(name);

  // only add new define if not already defined
  if (entry.getValue())
    return;

  entry.setValue(1);

  NameAndAttributes &info = _undefines[entry.getKey().data()];

  if (info.symbol == nullptr) {
    // FIXME: This is trying to take care of module ASM like this:
    //
    //   module asm ".zerofill __FOO, __foo, _bar_baz_qux, 0"
    //
    // but is gross and its mother dresses it funny. Have the ASM parser give us
    // more details for this type of situation so that we're not guessing so
    // much.

    // fill information structure
    info.name = entry.getKey().data();
    info.attributes =
      LTO_SYMBOL_PERMISSIONS_DATA | LTO_SYMBOL_DEFINITION_REGULAR | scope;
    info.isFunction = false;
    info.symbol = nullptr;

    // add to table of symbols
    _symbols.push_back(info);
    return;
  }

  if (info.isFunction)
    addDefinedFunctionSymbol(cast<Function>(info.symbol));
  else
    addDefinedDataSymbol(info.symbol);

  _symbols.back().attributes &= ~LTO_SYMBOL_SCOPE_MASK;
  _symbols.back().attributes |= scope;
}

/// addAsmGlobalSymbolUndef - Add a global symbol from module-level ASM to the
/// undefined list.
void LTOModule::addAsmGlobalSymbolUndef(const char *name) {
  StringMap<NameAndAttributes>::value_type &entry =
    _undefines.GetOrCreateValue(name);

  _asm_undefines.push_back(entry.getKey().data());

  // we already have the symbol
  if (entry.getValue().name)
    return;

  uint32_t attr = LTO_SYMBOL_DEFINITION_UNDEFINED;
  attr |= LTO_SYMBOL_SCOPE_DEFAULT;
  NameAndAttributes info;
  info.name = entry.getKey().data();
  info.attributes = attr;
  info.isFunction = false;
  info.symbol = nullptr;

  entry.setValue(info);
}

/// addPotentialUndefinedSymbol - Add a symbol which isn't defined just yet to a
/// list to be resolved later.
void
LTOModule::addPotentialUndefinedSymbol(const GlobalValue *decl, bool isFunc) {
  // ignore all llvm.* symbols
  if (decl->getName().startswith("llvm."))
    return;

  // ignore all aliases
  if (isa<GlobalAlias>(decl))
    return;

  SmallString<64> name;
  _target->getNameWithPrefix(name, decl, _mangler);

  StringMap<NameAndAttributes>::value_type &entry =
    _undefines.GetOrCreateValue(name);

  // we already have the symbol
  if (entry.getValue().name)
    return;

  NameAndAttributes info;

  info.name = entry.getKey().data();

  if (decl->hasExternalWeakLinkage())
    info.attributes = LTO_SYMBOL_DEFINITION_WEAKUNDEF;
  else
    info.attributes = LTO_SYMBOL_DEFINITION_UNDEFINED;

  info.isFunction = isFunc;
  info.symbol = decl;

  entry.setValue(info);
}

namespace {

  class RecordStreamer : public MCStreamer {
  public:
    enum State { NeverSeen, Global, Defined, DefinedGlobal, Used };

  private:
    StringMap<State> Symbols;

    void markDefined(const MCSymbol &Symbol) {
      State &S = Symbols[Symbol.getName()];
      switch (S) {
      case DefinedGlobal:
      case Global:
        S = DefinedGlobal;
        break;
      case NeverSeen:
      case Defined:
      case Used:
        S = Defined;
        break;
      }
    }
    void markGlobal(const MCSymbol &Symbol) {
      State &S = Symbols[Symbol.getName()];
      switch (S) {
      case DefinedGlobal:
      case Defined:
        S = DefinedGlobal;
        break;

      case NeverSeen:
      case Global:
      case Used:
        S = Global;
        break;
      }
    }
    void markUsed(const MCSymbol &Symbol) {
      State &S = Symbols[Symbol.getName()];
      switch (S) {
      case DefinedGlobal:
      case Defined:
      case Global:
        break;

      case NeverSeen:
      case Used:
        S = Used;
        break;
      }
    }

    // FIXME: mostly copied for the obj streamer.
    void AddValueSymbols(const MCExpr *Value) {
      switch (Value->getKind()) {
      case MCExpr::Target:
        // FIXME: What should we do in here?
        break;

      case MCExpr::Constant:
        break;

      case MCExpr::Binary: {
        const MCBinaryExpr *BE = cast<MCBinaryExpr>(Value);
        AddValueSymbols(BE->getLHS());
        AddValueSymbols(BE->getRHS());
        break;
      }

      case MCExpr::SymbolRef:
        markUsed(cast<MCSymbolRefExpr>(Value)->getSymbol());
        break;

      case MCExpr::Unary:
        AddValueSymbols(cast<MCUnaryExpr>(Value)->getSubExpr());
        break;
      }
    }

  public:
    typedef StringMap<State>::const_iterator const_iterator;

    const_iterator begin() {
      return Symbols.begin();
    }

    const_iterator end() {
      return Symbols.end();
    }

    RecordStreamer(MCContext &Context) : MCStreamer(Context) {}

    void EmitInstruction(const MCInst &Inst,
                         const MCSubtargetInfo &STI) override {
      // Scan for values.
      for (unsigned i = Inst.getNumOperands(); i--; )
        if (Inst.getOperand(i).isExpr())
          AddValueSymbols(Inst.getOperand(i).getExpr());
    }
    void EmitLabel(MCSymbol *Symbol) override {
      Symbol->setSection(*getCurrentSection().first);
      markDefined(*Symbol);
    }
    void EmitDebugLabel(MCSymbol *Symbol) override {
      EmitLabel(Symbol);
    }
    void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) override {
      // FIXME: should we handle aliases?
      markDefined(*Symbol);
      AddValueSymbols(Value);
    }
    bool EmitSymbolAttribute(MCSymbol *Symbol,
                             MCSymbolAttr Attribute) override {
      if (Attribute == MCSA_Global)
        markGlobal(*Symbol);
      return true;
    }
    void EmitZerofill(const MCSection *Section, MCSymbol *Symbol,
                      uint64_t Size , unsigned ByteAlignment) override {
      markDefined(*Symbol);
    }
    void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
                          unsigned ByteAlignment) override {
      markDefined(*Symbol);
    }

    void EmitBundleAlignMode(unsigned AlignPow2) override {}
    void EmitBundleLock(bool AlignToEnd) override {}
    void EmitBundleUnlock() override {}

    // Noop calls.
    void ChangeSection(const MCSection *Section,
                       const MCExpr *Subsection) override {}
    void EmitAssemblerFlag(MCAssemblerFlag Flag) override {}
    void EmitThumbFunc(MCSymbol *Func) override {}
    void EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) override {}
    void EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) override {}
    void BeginCOFFSymbolDef(const MCSymbol *Symbol) override {}
    void EmitCOFFSymbolStorageClass(int StorageClass) override {}
    void EmitCOFFSymbolType(int Type) override {}
    void EndCOFFSymbolDef() override {}
    void EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) override {}
    void EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
                               unsigned ByteAlignment) override {}
    void EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
                        uint64_t Size, unsigned ByteAlignment) override {}
    void EmitBytes(StringRef Data) override {}
    void EmitValueImpl(const MCExpr *Value, unsigned Size,
                       const SMLoc &Loc) override {}
    void EmitULEB128Value(const MCExpr *Value) override {}
    void EmitSLEB128Value(const MCExpr *Value) override {}
    void EmitValueToAlignment(unsigned ByteAlignment, int64_t Value,
                              unsigned ValueSize,
                              unsigned MaxBytesToEmit) override {}
    void EmitCodeAlignment(unsigned ByteAlignment,
                           unsigned MaxBytesToEmit) override {}
    bool EmitValueToOffset(const MCExpr *Offset,
                           unsigned char Value) override { return false; }
    void EmitFileDirective(StringRef Filename) override {}
    void FinishImpl() override {}
    void EmitCFIEndProcImpl(MCDwarfFrameInfo &Frame) override {
      RecordProcEnd(Frame);
    }
  };
} // end anonymous namespace

/// addAsmGlobalSymbols - Add global symbols from module-level ASM to the
/// defined or undefined lists.
bool LTOModule::addAsmGlobalSymbols(std::string &errMsg) {
  const std::string &inlineAsm = _module->getModuleInlineAsm();
  if (inlineAsm.empty())
    return false;

  std::unique_ptr<RecordStreamer> Streamer(new RecordStreamer(_context));
  MemoryBuffer *Buffer = MemoryBuffer::getMemBuffer(inlineAsm);
  SourceMgr SrcMgr;
  SrcMgr.AddNewSourceBuffer(Buffer, SMLoc());
  std::unique_ptr<MCAsmParser> Parser(
      createMCAsmParser(SrcMgr, _context, *Streamer, *_target->getMCAsmInfo()));
  const Target &T = _target->getTarget();
  std::unique_ptr<MCInstrInfo> MCII(T.createMCInstrInfo());
  std::unique_ptr<MCSubtargetInfo> STI(T.createMCSubtargetInfo(
      _target->getTargetTriple(), _target->getTargetCPU(),
      _target->getTargetFeatureString()));
  std::unique_ptr<MCTargetAsmParser> TAP(
      T.createMCAsmParser(*STI, *Parser.get(), *MCII,
                          _target->Options.MCOptions));
  if (!TAP) {
    errMsg = "target " + std::string(T.getName()) +
      " does not define AsmParser.";
    return true;
  }

  Parser->setTargetParser(*TAP);
  if (Parser->Run(false))
    return true;

  for (RecordStreamer::const_iterator i = Streamer->begin(),
         e = Streamer->end(); i != e; ++i) {
    StringRef Key = i->first();
    RecordStreamer::State Value = i->second;
    if (Value == RecordStreamer::DefinedGlobal)
      addAsmGlobalSymbol(Key.data(), LTO_SYMBOL_SCOPE_DEFAULT);
    else if (Value == RecordStreamer::Defined)
      addAsmGlobalSymbol(Key.data(), LTO_SYMBOL_SCOPE_INTERNAL);
    else if (Value == RecordStreamer::Global ||
             Value == RecordStreamer::Used)
      addAsmGlobalSymbolUndef(Key.data());
  }

  return false;
}

/// isDeclaration - Return 'true' if the global value is a declaration.
static bool isDeclaration(const GlobalValue &V) {
  if (V.hasAvailableExternallyLinkage())
    return true;

  if (V.isMaterializable())
    return false;

  return V.isDeclaration();
}

/// parseSymbols - Parse the symbols from the module and model-level ASM and add
/// them to either the defined or undefined lists.
bool LTOModule::parseSymbols(std::string &errMsg) {
  // add functions
  for (Module::iterator f = _module->begin(), e = _module->end(); f != e; ++f) {
    if (isDeclaration(*f))
      addPotentialUndefinedSymbol(f, true);
    else
      addDefinedFunctionSymbol(f);
  }

  // add data
  for (Module::global_iterator v = _module->global_begin(),
         e = _module->global_end(); v !=  e; ++v) {
    if (isDeclaration(*v))
      addPotentialUndefinedSymbol(v, false);
    else
      addDefinedDataSymbol(v);
  }

  // add asm globals
  if (addAsmGlobalSymbols(errMsg))
    return true;

  // add aliases
  for (const auto &Alias : _module->aliases())
    addDefinedDataSymbol(&Alias);

  // make symbols for all undefines
  for (StringMap<NameAndAttributes>::iterator u =_undefines.begin(),
         e = _undefines.end(); u != e; ++u) {
    // If this symbol also has a definition, then don't make an undefine because
    // it is a tentative definition.
    if (_defines.count(u->getKey())) continue;
    NameAndAttributes info = u->getValue();
    _symbols.push_back(info);
  }

  return false;
}

/// parseMetadata - Parse metadata from the module
void LTOModule::parseMetadata() {
  // Linker Options
  if (Value *Val = _module->getModuleFlag("Linker Options")) {
    MDNode *LinkerOptions = cast<MDNode>(Val);
    for (unsigned i = 0, e = LinkerOptions->getNumOperands(); i != e; ++i) {
      MDNode *MDOptions = cast<MDNode>(LinkerOptions->getOperand(i));
      for (unsigned ii = 0, ie = MDOptions->getNumOperands(); ii != ie; ++ii) {
        MDString *MDOption = cast<MDString>(MDOptions->getOperand(ii));
        StringRef Op = _linkeropt_strings.
            GetOrCreateValue(MDOption->getString()).getKey();
        StringRef DepLibName = _target->getTargetLowering()->
            getObjFileLowering().getDepLibFromLinkerOpt(Op);
        if (!DepLibName.empty())
          _deplibs.push_back(DepLibName.data());
        else if (!Op.empty())
          _linkeropts.push_back(Op.data());
      }
    }
  }

  // Add other interesting metadata here.
}