MergeFunctions.cpp revision b0104e1bb56cde925d91a5b2432a18f87214484a
1//===- MergeFunctions.cpp - Merge identical functions ---------------------===//
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 pass looks for equivalent functions that are mergable and folds them.
11//
12// A hash is computed from the function, based on its type and number of
13// basic blocks.
14//
15// Once all hashes are computed, we perform an expensive equality comparison
16// on each function pair. This takes n^2/2 comparisons per bucket, so it's
17// important that the hash function be high quality. The equality comparison
18// iterates through each instruction in each basic block.
19//
20// When a match is found the functions are folded. If both functions are
21// overridable, we move the functionality into a new internal function and
22// leave two overridable thunks to it.
23//
24//===----------------------------------------------------------------------===//
25//
26// Future work:
27//
28// * virtual functions.
29//
30// Many functions have their address taken by the virtual function table for
31// the object they belong to. However, as long as it's only used for a lookup
32// and call, this is irrelevant, and we'd like to fold such functions.
33//
34// * switch from n^2 pair-wise comparisons to an n-way comparison for each
35// bucket.
36//
37// * be smarter about bitcasts.
38//
39// In order to fold functions, we will sometimes add either bitcast instructions
40// or bitcast constant expressions. Unfortunately, this can confound further
41// analysis since the two functions differ where one has a bitcast and the
42// other doesn't. We should learn to look through bitcasts.
43//
44//===----------------------------------------------------------------------===//
45
46#define DEBUG_TYPE "mergefunc"
47#include "llvm/Transforms/IPO.h"
48#include "llvm/ADT/DenseSet.h"
49#include "llvm/ADT/FoldingSet.h"
50#include "llvm/ADT/SmallSet.h"
51#include "llvm/ADT/Statistic.h"
52#include "llvm/ADT/STLExtras.h"
53#include "llvm/Constants.h"
54#include "llvm/InlineAsm.h"
55#include "llvm/Instructions.h"
56#include "llvm/LLVMContext.h"
57#include "llvm/Module.h"
58#include "llvm/Pass.h"
59#include "llvm/Support/CallSite.h"
60#include "llvm/Support/Debug.h"
61#include "llvm/Support/ErrorHandling.h"
62#include "llvm/Support/IRBuilder.h"
63#include "llvm/Support/ValueHandle.h"
64#include "llvm/Support/raw_ostream.h"
65#include "llvm/Target/TargetData.h"
66#include <vector>
67using namespace llvm;
68
69STATISTIC(NumFunctionsMerged, "Number of functions merged");
70
71namespace {
72
73static unsigned ProfileFunction(const Function *F) {
74  const FunctionType *FTy = F->getFunctionType();
75
76  FoldingSetNodeID ID;
77  ID.AddInteger(F->size());
78  ID.AddInteger(F->getCallingConv());
79  ID.AddBoolean(F->hasGC());
80  ID.AddBoolean(FTy->isVarArg());
81  ID.AddInteger(FTy->getReturnType()->getTypeID());
82  for (unsigned i = 0, e = FTy->getNumParams(); i != e; ++i)
83    ID.AddInteger(FTy->getParamType(i)->getTypeID());
84  return ID.ComputeHash();
85}
86
87class ComparableFunction {
88public:
89  ComparableFunction(Function *Func, TargetData *TD)
90    : Func(Func), Hash(ProfileFunction(Func)), TD(TD) {}
91
92  AssertingVH<Function> const Func;
93  const unsigned Hash;
94  TargetData * const TD;
95};
96
97struct MergeFunctionsEqualityInfo {
98  static ComparableFunction *getEmptyKey() {
99    return reinterpret_cast<ComparableFunction*>(0);
100  }
101  static ComparableFunction *getTombstoneKey() {
102    return reinterpret_cast<ComparableFunction*>(-1);
103  }
104  static unsigned getHashValue(const ComparableFunction *CF) {
105    return CF->Hash;
106  }
107  static bool isEqual(const ComparableFunction *LHS,
108                      const ComparableFunction *RHS);
109};
110
111/// MergeFunctions finds functions which will generate identical machine code,
112/// by considering all pointer types to be equivalent. Once identified,
113/// MergeFunctions will fold them by replacing a call to one to a call to a
114/// bitcast of the other.
115///
116class MergeFunctions : public ModulePass {
117public:
118  static char ID;
119  MergeFunctions() : ModulePass(ID) {}
120
121  bool runOnModule(Module &M);
122
123private:
124  typedef DenseSet<ComparableFunction *, MergeFunctionsEqualityInfo> FnSetType;
125
126
127  /// Insert a ComparableFunction into the FnSet, or merge it away if it's
128  /// equal to one that's already present.
129  bool Insert(FnSetType &FnSet, ComparableFunction *NewF);
130
131  /// MergeTwoFunctions - Merge two equivalent functions. Upon completion, G
132  /// may be deleted, or may be converted into a thunk. In either case, it
133  /// should never be visited again.
134  void MergeTwoFunctions(Function *F, Function *G) const;
135
136  /// WriteThunk - Replace G with a simple tail call to bitcast(F). Also
137  /// replace direct uses of G with bitcast(F). Deletes G.
138  void WriteThunk(Function *F, Function *G) const;
139
140  TargetData *TD;
141};
142
143}  // end anonymous namespace
144
145char MergeFunctions::ID = 0;
146INITIALIZE_PASS(MergeFunctions, "mergefunc", "Merge Functions", false, false);
147
148ModulePass *llvm::createMergeFunctionsPass() {
149  return new MergeFunctions();
150}
151
152namespace {
153/// FunctionComparator - Compares two functions to determine whether or not
154/// they will generate machine code with the same behaviour. TargetData is
155/// used if available. The comparator always fails conservatively (erring on the
156/// side of claiming that two functions are different).
157class FunctionComparator {
158public:
159  FunctionComparator(const TargetData *TD, const Function *F1,
160                     const Function *F2)
161    : F1(F1), F2(F2), TD(TD), IDMap1Count(0), IDMap2Count(0) {}
162
163  /// Compare - test whether the two functions have equivalent behaviour.
164  bool Compare();
165
166private:
167  /// Compare - test whether two basic blocks have equivalent behaviour.
168  bool Compare(const BasicBlock *BB1, const BasicBlock *BB2);
169
170  /// Enumerate - Assign or look up previously assigned numbers for the two
171  /// values, and return whether the numbers are equal. Numbers are assigned in
172  /// the order visited.
173  bool Enumerate(const Value *V1, const Value *V2);
174
175  /// isEquivalentOperation - Compare two Instructions for equivalence, similar
176  /// to Instruction::isSameOperationAs but with modifications to the type
177  /// comparison.
178  bool isEquivalentOperation(const Instruction *I1,
179                             const Instruction *I2) const;
180
181  /// isEquivalentGEP - Compare two GEPs for equivalent pointer arithmetic.
182  bool isEquivalentGEP(const GEPOperator *GEP1, const GEPOperator *GEP2);
183  bool isEquivalentGEP(const GetElementPtrInst *GEP1,
184                       const GetElementPtrInst *GEP2) {
185    return isEquivalentGEP(cast<GEPOperator>(GEP1), cast<GEPOperator>(GEP2));
186  }
187
188  /// isEquivalentType - Compare two Types, treating all pointer types as equal.
189  bool isEquivalentType(const Type *Ty1, const Type *Ty2) const;
190
191  // The two functions undergoing comparison.
192  const Function *F1, *F2;
193
194  const TargetData *TD;
195
196  typedef DenseMap<const Value *, unsigned long> IDMap;
197  IDMap Map1, Map2;
198  unsigned long IDMap1Count, IDMap2Count;
199};
200}
201
202/// isEquivalentType - any two pointers in the same address space are
203/// equivalent. Otherwise, standard type equivalence rules apply.
204bool FunctionComparator::isEquivalentType(const Type *Ty1,
205                                          const Type *Ty2) const {
206  if (Ty1 == Ty2)
207    return true;
208  if (Ty1->getTypeID() != Ty2->getTypeID())
209    return false;
210
211  switch(Ty1->getTypeID()) {
212  default:
213    llvm_unreachable("Unknown type!");
214    // Fall through in Release mode.
215  case Type::IntegerTyID:
216  case Type::OpaqueTyID:
217    // Ty1 == Ty2 would have returned true earlier.
218    return false;
219
220  case Type::VoidTyID:
221  case Type::FloatTyID:
222  case Type::DoubleTyID:
223  case Type::X86_FP80TyID:
224  case Type::FP128TyID:
225  case Type::PPC_FP128TyID:
226  case Type::LabelTyID:
227  case Type::MetadataTyID:
228    return true;
229
230  case Type::PointerTyID: {
231    const PointerType *PTy1 = cast<PointerType>(Ty1);
232    const PointerType *PTy2 = cast<PointerType>(Ty2);
233    return PTy1->getAddressSpace() == PTy2->getAddressSpace();
234  }
235
236  case Type::StructTyID: {
237    const StructType *STy1 = cast<StructType>(Ty1);
238    const StructType *STy2 = cast<StructType>(Ty2);
239    if (STy1->getNumElements() != STy2->getNumElements())
240      return false;
241
242    if (STy1->isPacked() != STy2->isPacked())
243      return false;
244
245    for (unsigned i = 0, e = STy1->getNumElements(); i != e; ++i) {
246      if (!isEquivalentType(STy1->getElementType(i), STy2->getElementType(i)))
247        return false;
248    }
249    return true;
250  }
251
252  case Type::FunctionTyID: {
253    const FunctionType *FTy1 = cast<FunctionType>(Ty1);
254    const FunctionType *FTy2 = cast<FunctionType>(Ty2);
255    if (FTy1->getNumParams() != FTy2->getNumParams() ||
256        FTy1->isVarArg() != FTy2->isVarArg())
257      return false;
258
259    if (!isEquivalentType(FTy1->getReturnType(), FTy2->getReturnType()))
260      return false;
261
262    for (unsigned i = 0, e = FTy1->getNumParams(); i != e; ++i) {
263      if (!isEquivalentType(FTy1->getParamType(i), FTy2->getParamType(i)))
264        return false;
265    }
266    return true;
267  }
268
269  case Type::ArrayTyID: {
270    const ArrayType *ATy1 = cast<ArrayType>(Ty1);
271    const ArrayType *ATy2 = cast<ArrayType>(Ty2);
272    return ATy1->getNumElements() == ATy2->getNumElements() &&
273           isEquivalentType(ATy1->getElementType(), ATy2->getElementType());
274  }
275
276  case Type::VectorTyID: {
277    const VectorType *VTy1 = cast<VectorType>(Ty1);
278    const VectorType *VTy2 = cast<VectorType>(Ty2);
279    return VTy1->getNumElements() == VTy2->getNumElements() &&
280           isEquivalentType(VTy1->getElementType(), VTy2->getElementType());
281  }
282  }
283}
284
285/// isEquivalentOperation - determine whether the two operations are the same
286/// except that pointer-to-A and pointer-to-B are equivalent. This should be
287/// kept in sync with Instruction::isSameOperationAs.
288bool FunctionComparator::isEquivalentOperation(const Instruction *I1,
289                                               const Instruction *I2) const {
290  if (I1->getOpcode() != I2->getOpcode() ||
291      I1->getNumOperands() != I2->getNumOperands() ||
292      !isEquivalentType(I1->getType(), I2->getType()) ||
293      !I1->hasSameSubclassOptionalData(I2))
294    return false;
295
296  // We have two instructions of identical opcode and #operands.  Check to see
297  // if all operands are the same type
298  for (unsigned i = 0, e = I1->getNumOperands(); i != e; ++i)
299    if (!isEquivalentType(I1->getOperand(i)->getType(),
300                          I2->getOperand(i)->getType()))
301      return false;
302
303  // Check special state that is a part of some instructions.
304  if (const LoadInst *LI = dyn_cast<LoadInst>(I1))
305    return LI->isVolatile() == cast<LoadInst>(I2)->isVolatile() &&
306           LI->getAlignment() == cast<LoadInst>(I2)->getAlignment();
307  if (const StoreInst *SI = dyn_cast<StoreInst>(I1))
308    return SI->isVolatile() == cast<StoreInst>(I2)->isVolatile() &&
309           SI->getAlignment() == cast<StoreInst>(I2)->getAlignment();
310  if (const CmpInst *CI = dyn_cast<CmpInst>(I1))
311    return CI->getPredicate() == cast<CmpInst>(I2)->getPredicate();
312  if (const CallInst *CI = dyn_cast<CallInst>(I1))
313    return CI->isTailCall() == cast<CallInst>(I2)->isTailCall() &&
314           CI->getCallingConv() == cast<CallInst>(I2)->getCallingConv() &&
315           CI->getAttributes().getRawPointer() ==
316             cast<CallInst>(I2)->getAttributes().getRawPointer();
317  if (const InvokeInst *CI = dyn_cast<InvokeInst>(I1))
318    return CI->getCallingConv() == cast<InvokeInst>(I2)->getCallingConv() &&
319           CI->getAttributes().getRawPointer() ==
320             cast<InvokeInst>(I2)->getAttributes().getRawPointer();
321  if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(I1)) {
322    if (IVI->getNumIndices() != cast<InsertValueInst>(I2)->getNumIndices())
323      return false;
324    for (unsigned i = 0, e = IVI->getNumIndices(); i != e; ++i)
325      if (IVI->idx_begin()[i] != cast<InsertValueInst>(I2)->idx_begin()[i])
326        return false;
327    return true;
328  }
329  if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(I1)) {
330    if (EVI->getNumIndices() != cast<ExtractValueInst>(I2)->getNumIndices())
331      return false;
332    for (unsigned i = 0, e = EVI->getNumIndices(); i != e; ++i)
333      if (EVI->idx_begin()[i] != cast<ExtractValueInst>(I2)->idx_begin()[i])
334        return false;
335    return true;
336  }
337
338  return true;
339}
340
341/// isEquivalentGEP - determine whether two GEP operations perform the same
342/// underlying arithmetic.
343bool FunctionComparator::isEquivalentGEP(const GEPOperator *GEP1,
344                                         const GEPOperator *GEP2) {
345  // When we have target data, we can reduce the GEP down to the value in bytes
346  // added to the address.
347  if (TD && GEP1->hasAllConstantIndices() && GEP2->hasAllConstantIndices()) {
348    SmallVector<Value *, 8> Indices1(GEP1->idx_begin(), GEP1->idx_end());
349    SmallVector<Value *, 8> Indices2(GEP2->idx_begin(), GEP2->idx_end());
350    uint64_t Offset1 = TD->getIndexedOffset(GEP1->getPointerOperandType(),
351                                            Indices1.data(), Indices1.size());
352    uint64_t Offset2 = TD->getIndexedOffset(GEP2->getPointerOperandType(),
353                                            Indices2.data(), Indices2.size());
354    return Offset1 == Offset2;
355  }
356
357  if (GEP1->getPointerOperand()->getType() !=
358      GEP2->getPointerOperand()->getType())
359    return false;
360
361  if (GEP1->getNumOperands() != GEP2->getNumOperands())
362    return false;
363
364  for (unsigned i = 0, e = GEP1->getNumOperands(); i != e; ++i) {
365    if (!Enumerate(GEP1->getOperand(i), GEP2->getOperand(i)))
366      return false;
367  }
368
369  return true;
370}
371
372/// Enumerate - Compare two values used by the two functions under pair-wise
373/// comparison. If this is the first time the values are seen, they're added to
374/// the mapping so that we will detect mismatches on next use.
375bool FunctionComparator::Enumerate(const Value *V1, const Value *V2) {
376  // Check for function @f1 referring to itself and function @f2 referring to
377  // itself, or referring to each other, or both referring to either of them.
378  // They're all equivalent if the two functions are otherwise equivalent.
379  if (V1 == F1 && V2 == F2)
380    return true;
381  if (V1 == F2 && V2 == F1)
382    return true;
383
384  // TODO: constant expressions with GEP or references to F1 or F2.
385  if (isa<Constant>(V1))
386    return V1 == V2;
387
388  if (isa<InlineAsm>(V1) && isa<InlineAsm>(V2)) {
389    const InlineAsm *IA1 = cast<InlineAsm>(V1);
390    const InlineAsm *IA2 = cast<InlineAsm>(V2);
391    return IA1->getAsmString() == IA2->getAsmString() &&
392           IA1->getConstraintString() == IA2->getConstraintString();
393  }
394
395  unsigned long &ID1 = Map1[V1];
396  if (!ID1)
397    ID1 = ++IDMap1Count;
398
399  unsigned long &ID2 = Map2[V2];
400  if (!ID2)
401    ID2 = ++IDMap2Count;
402
403  return ID1 == ID2;
404}
405
406/// Compare - test whether two basic blocks have equivalent behaviour.
407bool FunctionComparator::Compare(const BasicBlock *BB1, const BasicBlock *BB2) {
408  BasicBlock::const_iterator F1I = BB1->begin(), F1E = BB1->end();
409  BasicBlock::const_iterator F2I = BB2->begin(), F2E = BB2->end();
410
411  do {
412    if (!Enumerate(F1I, F2I))
413      return false;
414
415    if (const GetElementPtrInst *GEP1 = dyn_cast<GetElementPtrInst>(F1I)) {
416      const GetElementPtrInst *GEP2 = dyn_cast<GetElementPtrInst>(F2I);
417      if (!GEP2)
418        return false;
419
420      if (!Enumerate(GEP1->getPointerOperand(), GEP2->getPointerOperand()))
421        return false;
422
423      if (!isEquivalentGEP(GEP1, GEP2))
424        return false;
425    } else {
426      if (!isEquivalentOperation(F1I, F2I))
427        return false;
428
429      assert(F1I->getNumOperands() == F2I->getNumOperands());
430      for (unsigned i = 0, e = F1I->getNumOperands(); i != e; ++i) {
431        Value *OpF1 = F1I->getOperand(i);
432        Value *OpF2 = F2I->getOperand(i);
433
434        if (!Enumerate(OpF1, OpF2))
435          return false;
436
437        if (OpF1->getValueID() != OpF2->getValueID() ||
438            !isEquivalentType(OpF1->getType(), OpF2->getType()))
439          return false;
440      }
441    }
442
443    ++F1I, ++F2I;
444  } while (F1I != F1E && F2I != F2E);
445
446  return F1I == F1E && F2I == F2E;
447}
448
449/// Compare - test whether the two functions have equivalent behaviour.
450bool FunctionComparator::Compare() {
451  // We need to recheck everything, but check the things that weren't included
452  // in the hash first.
453
454  if (F1->getAttributes() != F2->getAttributes())
455    return false;
456
457  if (F1->hasGC() != F2->hasGC())
458    return false;
459
460  if (F1->hasGC() && F1->getGC() != F2->getGC())
461    return false;
462
463  if (F1->hasSection() != F2->hasSection())
464    return false;
465
466  if (F1->hasSection() && F1->getSection() != F2->getSection())
467    return false;
468
469  if (F1->isVarArg() != F2->isVarArg())
470    return false;
471
472  // TODO: if it's internal and only used in direct calls, we could handle this
473  // case too.
474  if (F1->getCallingConv() != F2->getCallingConv())
475    return false;
476
477  if (!isEquivalentType(F1->getFunctionType(), F2->getFunctionType()))
478    return false;
479
480  assert(F1->arg_size() == F2->arg_size() &&
481         "Identical functions have a different number of args.");
482
483  // Visit the arguments so that they get enumerated in the order they're
484  // passed in.
485  for (Function::const_arg_iterator f1i = F1->arg_begin(),
486         f2i = F2->arg_begin(), f1e = F1->arg_end(); f1i != f1e; ++f1i, ++f2i) {
487    if (!Enumerate(f1i, f2i))
488      llvm_unreachable("Arguments repeat");
489  }
490
491  // We do a CFG-ordered walk since the actual ordering of the blocks in the
492  // linked list is immaterial. Our walk starts at the entry block for both
493  // functions, then takes each block from each terminator in order. As an
494  // artifact, this also means that unreachable blocks are ignored.
495  SmallVector<const BasicBlock *, 8> F1BBs, F2BBs;
496  SmallSet<const BasicBlock *, 128> VisitedBBs; // in terms of F1.
497
498  F1BBs.push_back(&F1->getEntryBlock());
499  F2BBs.push_back(&F2->getEntryBlock());
500
501  VisitedBBs.insert(F1BBs[0]);
502  while (!F1BBs.empty()) {
503    const BasicBlock *F1BB = F1BBs.pop_back_val();
504    const BasicBlock *F2BB = F2BBs.pop_back_val();
505
506    if (!Enumerate(F1BB, F2BB) || !Compare(F1BB, F2BB))
507      return false;
508
509    const TerminatorInst *F1TI = F1BB->getTerminator();
510    const TerminatorInst *F2TI = F2BB->getTerminator();
511
512    assert(F1TI->getNumSuccessors() == F2TI->getNumSuccessors());
513    for (unsigned i = 0, e = F1TI->getNumSuccessors(); i != e; ++i) {
514      if (!VisitedBBs.insert(F1TI->getSuccessor(i)))
515        continue;
516
517      F1BBs.push_back(F1TI->getSuccessor(i));
518      F2BBs.push_back(F2TI->getSuccessor(i));
519    }
520  }
521  return true;
522}
523
524/// WriteThunk - Replace G with a simple tail call to bitcast(F). Also replace
525/// direct uses of G with bitcast(F). Deletes G.
526void MergeFunctions::WriteThunk(Function *F, Function *G) const {
527  if (!G->mayBeOverridden()) {
528    // Redirect direct callers of G to F.
529    Constant *BitcastF = ConstantExpr::getBitCast(F, G->getType());
530    for (Value::use_iterator UI = G->use_begin(), UE = G->use_end();
531         UI != UE;) {
532      Value::use_iterator TheIter = UI;
533      ++UI;
534      CallSite CS(*TheIter);
535      if (CS && CS.isCallee(TheIter))
536        TheIter.getUse().set(BitcastF);
537    }
538  }
539
540  // If G was internal then we may have replaced all uses if G with F. If so,
541  // stop here and delete G. There's no need for a thunk.
542  if (G->hasLocalLinkage() && G->use_empty()) {
543    G->eraseFromParent();
544    return;
545  }
546
547  Function *NewG = Function::Create(G->getFunctionType(), G->getLinkage(), "",
548                                    G->getParent());
549  BasicBlock *BB = BasicBlock::Create(F->getContext(), "", NewG);
550  IRBuilder<false> Builder(BB);
551
552  SmallVector<Value *, 16> Args;
553  unsigned i = 0;
554  const FunctionType *FFTy = F->getFunctionType();
555  for (Function::arg_iterator AI = NewG->arg_begin(), AE = NewG->arg_end();
556       AI != AE; ++AI) {
557    Args.push_back(Builder.CreateBitCast(AI, FFTy->getParamType(i)));
558    ++i;
559  }
560
561  CallInst *CI = Builder.CreateCall(F, Args.begin(), Args.end());
562  CI->setTailCall();
563  CI->setCallingConv(F->getCallingConv());
564  if (NewG->getReturnType()->isVoidTy()) {
565    Builder.CreateRetVoid();
566  } else {
567    Builder.CreateRet(Builder.CreateBitCast(CI, NewG->getReturnType()));
568  }
569
570  NewG->copyAttributesFrom(G);
571  NewG->takeName(G);
572  G->replaceAllUsesWith(NewG);
573  G->eraseFromParent();
574}
575
576/// MergeTwoFunctions - Merge two equivalent functions. Upon completion,
577/// Function G is deleted.
578void MergeFunctions::MergeTwoFunctions(Function *F, Function *G) const {
579  if (F->isWeakForLinker()) {
580    assert(G->isWeakForLinker());
581
582    // Make them both thunks to the same internal function.
583    Function *H = Function::Create(F->getFunctionType(), F->getLinkage(), "",
584                                   F->getParent());
585    H->copyAttributesFrom(F);
586    H->takeName(F);
587    F->replaceAllUsesWith(H);
588
589    unsigned MaxAlignment = std::max(G->getAlignment(), H->getAlignment());
590
591    WriteThunk(F, G);
592    WriteThunk(F, H);
593
594    F->setAlignment(MaxAlignment);
595    F->setLinkage(GlobalValue::InternalLinkage);
596  } else {
597    WriteThunk(F, G);
598  }
599
600  ++NumFunctionsMerged;
601}
602
603// Insert - Insert a ComparableFunction into the FnSet, or merge it away if
604// equal to one that's already inserted.
605bool MergeFunctions::Insert(FnSetType &FnSet, ComparableFunction *NewF) {
606  std::pair<FnSetType::iterator, bool> Result = FnSet.insert(NewF);
607  if (Result.second)
608    return false;
609
610  ComparableFunction *OldF = *Result.first;
611  assert(OldF && "Expected a hash collision");
612
613  // Never thunk a strong function to a weak function.
614  assert(!OldF->Func->isWeakForLinker() || NewF->Func->isWeakForLinker());
615
616  DEBUG(dbgs() << "  " << OldF->Func->getName() << " == "
617               << NewF->Func->getName() << '\n');
618
619  Function *DeleteF = NewF->Func;
620  delete NewF;
621  MergeTwoFunctions(OldF->Func, DeleteF);
622  return true;
623}
624
625// IsThunk - This method determines whether or not a given Function is a thunk\// like the ones emitted by this pass and therefore not subject to further
626// merging.
627static bool IsThunk(const Function *F) {
628  // The safe direction to fail is to return true. In that case, the function
629  // will be removed from merging analysis. If we failed to including functions
630  // then we may try to merge unmergable thing (ie., identical weak functions)
631  // which will push us into an infinite loop.
632
633  if (F->size() != 1)
634    return false;
635
636  const BasicBlock *BB = &F->front();
637  // A thunk is:
638  //   bitcast-inst*
639  //   optional-reg tail call @thunkee(args...*)
640  //   ret void|optional-reg
641  // where the args are in the same order as the arguments.
642
643  // Verify that the sequence of bitcast-inst's are all casts of arguments and
644  // that there aren't any extras (ie. no repeated casts).
645  int LastArgNo = -1;
646  BasicBlock::const_iterator I = BB->begin();
647  while (const BitCastInst *BCI = dyn_cast<BitCastInst>(I)) {
648    const Argument *A = dyn_cast<Argument>(BCI->getOperand(0));
649    if (!A) return false;
650    if ((int)A->getArgNo() >= LastArgNo) return false;
651    LastArgNo = A->getArgNo();
652    ++I;
653  }
654
655  // Verify that the call instruction has the same arguments as this function
656  // and that they're all either the incoming argument or a cast of the right
657  // argument.
658  const CallInst *CI = dyn_cast<CallInst>(I++);
659  if (!CI || !CI->isTailCall() ||
660      CI->getNumArgOperands() != F->arg_size()) return false;
661
662  for (unsigned i = 0, e = CI->getNumArgOperands(); i != e; ++i) {
663    const Value *V = CI->getArgOperand(i);
664    const Argument *A = dyn_cast<Argument>(V);
665    if (!A) {
666      const BitCastInst *BCI = dyn_cast<BitCastInst>(V);
667      if (!BCI) return false;
668      A = cast<Argument>(BCI->getOperand(0));
669    }
670    if (A->getArgNo() != i) return false;
671  }
672
673  // Verify that the terminator is a ret void (if we're void) or a ret of the
674  // call's return, or a ret of a bitcast of the call's return.
675  const Value *RetOp = CI;
676  if (const BitCastInst *BCI = dyn_cast<BitCastInst>(I)) {
677    ++I;
678    if (BCI->getOperand(0) != CI) return false;
679    RetOp = BCI;
680  }
681  const ReturnInst *RI = dyn_cast<ReturnInst>(I);
682  if (!RI) return false;
683  if (RI->getNumOperands() == 0)
684    return CI->getType()->isVoidTy();
685  return RI->getReturnValue() == CI;
686}
687
688bool MergeFunctions::runOnModule(Module &M) {
689  bool Changed = false;
690  TD = getAnalysisIfAvailable<TargetData>();
691
692  bool LocalChanged;
693  do {
694    DEBUG(dbgs() << "size: " << M.size() << '\n');
695    LocalChanged = false;
696    FnSetType FnSet;
697
698    // Insert only strong functions and merge them. Strong function merging
699    // always deletes one of them.
700    for (Module::iterator I = M.begin(), E = M.end(); I != E;) {
701      Function *F = I++;
702      if (!F->isDeclaration() && !F->hasAvailableExternallyLinkage() &&
703          !F->isWeakForLinker() && !IsThunk(F)) {
704        ComparableFunction *CF = new ComparableFunction(F, TD);
705        LocalChanged |= Insert(FnSet, CF);
706      }
707    }
708
709    // Insert only weak functions and merge them. By doing these second we
710    // create thunks to the strong function when possible. When two weak
711    // functions are identical, we create a new strong function with two weak
712    // weak thunks to it which are identical but not mergable.
713    for (Module::iterator I = M.begin(), E = M.end(); I != E;) {
714      Function *F = I++;
715      if (!F->isDeclaration() && !F->hasAvailableExternallyLinkage() &&
716          F->isWeakForLinker() && !IsThunk(F)) {
717        ComparableFunction *CF = new ComparableFunction(F, TD);
718        LocalChanged |= Insert(FnSet, CF);
719      }
720    }
721    DeleteContainerPointers(FnSet);
722    Changed |= LocalChanged;
723  } while (LocalChanged);
724
725  return Changed;
726}
727
728bool MergeFunctionsEqualityInfo::isEqual(const ComparableFunction *LHS,
729                                         const ComparableFunction *RHS) {
730  if (LHS == RHS)
731    return true;
732  if (LHS == getEmptyKey() || LHS == getTombstoneKey() ||
733      RHS == getEmptyKey() || RHS == getTombstoneKey())
734    return false;
735  assert(LHS->TD == RHS->TD && "Comparing functions for different targets");
736  return FunctionComparator(LHS->TD, LHS->Func, RHS->Func).Compare();
737}
738