1 files changed, 431 insertions, 215 deletions
diff --git a/contrib/llvm/lib/Transforms/IPO/MergeFunctions.cpp b/contrib/llvm/lib/Transforms/IPO/MergeFunctions.cpp
index 5d838f9..cccffca 100644
--- a/contrib/llvm/lib/Transforms/IPO/MergeFunctions.cpp
+++ b/contrib/llvm/lib/Transforms/IPO/MergeFunctions.cpp
@@ -67,42 +67,87 @@
 using namespace llvm;
 
 STATISTIC(NumFunctionsMerged, "Number of functions merged");
+STATISTIC(NumThunksWritten, "Number of thunks generated");
+STATISTIC(NumAliasesWritten, "Number of aliases generated");
+STATISTIC(NumDoubleWeak, "Number of new functions created");
+
+/// Creates a hash-code for the function which is the same for any two
+/// functions that will compare equal, without looking at the instructions
+/// inside the function.
+static unsigned profileFunction(const Function *F) {
+  const FunctionType *FTy = F->getFunctionType();
 
-namespace {
-  /// MergeFunctions finds functions which will generate identical machine code,
-  /// by considering all pointer types to be equivalent. Once identified,
-  /// MergeFunctions will fold them by replacing a call to one to a call to a
-  /// bitcast of the other.
-  ///
-  class MergeFunctions : public ModulePass {
-  public:
-    static char ID;
-    MergeFunctions() : ModulePass(ID) {}
-
-    bool runOnModule(Module &M);
-
-  private:
-    /// MergeTwoFunctions - Merge two equivalent functions. Upon completion, G
-    /// may be deleted, or may be converted into a thunk. In either case, it
-    /// should never be visited again.
-    void MergeTwoFunctions(Function *F, Function *G) const;
-
-    /// WriteThunk - Replace G with a simple tail call to bitcast(F). Also
-    /// replace direct uses of G with bitcast(F).
-    void WriteThunk(Function *F, Function *G) const;
-
-    TargetData *TD;
-  };
+  FoldingSetNodeID ID;
+  ID.AddInteger(F->size());
+  ID.AddInteger(F->getCallingConv());
+  ID.AddBoolean(F->hasGC());
+  ID.AddBoolean(FTy->isVarArg());
+  ID.AddInteger(FTy->getReturnType()->getTypeID());
+  for (unsigned i = 0, e = FTy->getNumParams(); i != e; ++i)
+    ID.AddInteger(FTy->getParamType(i)->getTypeID());
+  return ID.ComputeHash();
 }
 
-char MergeFunctions::ID = 0;
-INITIALIZE_PASS(MergeFunctions, "mergefunc", "Merge Functions", false, false);
+namespace {
+
+/// ComparableFunction - A struct that pairs together functions with a
+/// TargetData so that we can keep them together as elements in the DenseSet.
+class ComparableFunction {
+public:
+  static const ComparableFunction EmptyKey;
+  static const ComparableFunction TombstoneKey;
+  static TargetData * const LookupOnly;
+
+  ComparableFunction(Function *Func, TargetData *TD)
+    : Func(Func), Hash(profileFunction(Func)), TD(TD) {}
+
+  Function *getFunc() const { return Func; }
+  unsigned getHash() const { return Hash; }
+  TargetData *getTD() const { return TD; }
+
+  // Drops AssertingVH reference to the function. Outside of debug mode, this
+  // does nothing.
+  void release() {
+    assert(Func &&
+           "Attempted to release function twice, or release empty/tombstone!");
+    Func = NULL;
+  }
+
+private:
+  explicit ComparableFunction(unsigned Hash)
+    : Func(NULL), Hash(Hash), TD(NULL) {}
+
+  AssertingVH<Function> Func;
+  unsigned Hash;
+  TargetData *TD;
+};
+
+const ComparableFunction ComparableFunction::EmptyKey = ComparableFunction(0);
+const ComparableFunction ComparableFunction::TombstoneKey =
+    ComparableFunction(1);
+TargetData * const ComparableFunction::LookupOnly = (TargetData*)(-1);
 
-ModulePass *llvm::createMergeFunctionsPass() {
-  return new MergeFunctions();
+}
+
+namespace llvm {
+  template <>
+  struct DenseMapInfo<ComparableFunction> {
+    static ComparableFunction getEmptyKey() {
+      return ComparableFunction::EmptyKey;
+    }
+    static ComparableFunction getTombstoneKey() {
+      return ComparableFunction::TombstoneKey;
+    }
+    static unsigned getHashValue(const ComparableFunction &CF) {
+      return CF.getHash();
+    }
+    static bool isEqual(const ComparableFunction &LHS,
+                        const ComparableFunction &RHS);
+  };
 }
 
 namespace {
+
 /// FunctionComparator - Compares two functions to determine whether or not
 /// they will generate machine code with the same behaviour. TargetData is
 /// used if available. The comparator always fails conservatively (erring on the
@@ -111,34 +156,34 @@ class FunctionComparator {
 public:
   FunctionComparator(const TargetData *TD, const Function *F1,
                      const Function *F2)
-    : F1(F1), F2(F2), TD(TD), IDMap1Count(0), IDMap2Count(0) {}
+    : F1(F1), F2(F2), TD(TD) {}
 
-  /// Compare - test whether the two functions have equivalent behaviour.
-  bool Compare();
+  /// Test whether the two functions have equivalent behaviour.
+  bool compare();
 
 private:
-  /// Compare - test whether two basic blocks have equivalent behaviour.
-  bool Compare(const BasicBlock *BB1, const BasicBlock *BB2);
+  /// Test whether two basic blocks have equivalent behaviour.
+  bool compare(const BasicBlock *BB1, const BasicBlock *BB2);
 
-  /// Enumerate - Assign or look up previously assigned numbers for the two
-  /// values, and return whether the numbers are equal. Numbers are assigned in
-  /// the order visited.
-  bool Enumerate(const Value *V1, const Value *V2);
+  /// Assign or look up previously assigned numbers for the two values, and
+  /// return whether the numbers are equal. Numbers are assigned in the order
+  /// visited.
+  bool enumerate(const Value *V1, const Value *V2);
 
-  /// isEquivalentOperation - Compare two Instructions for equivalence, similar
-  /// to Instruction::isSameOperationAs but with modifications to the type
+  /// Compare two Instructions for equivalence, similar to
+  /// Instruction::isSameOperationAs but with modifications to the type
   /// comparison.
   bool isEquivalentOperation(const Instruction *I1,
                              const Instruction *I2) const;
 
-  /// isEquivalentGEP - Compare two GEPs for equivalent pointer arithmetic.
+  /// Compare two GEPs for equivalent pointer arithmetic.
   bool isEquivalentGEP(const GEPOperator *GEP1, const GEPOperator *GEP2);
   bool isEquivalentGEP(const GetElementPtrInst *GEP1,
                        const GetElementPtrInst *GEP2) {
     return isEquivalentGEP(cast<GEPOperator>(GEP1), cast<GEPOperator>(GEP2));
   }
 
-  /// isEquivalentType - Compare two Types, treating all pointer types as equal.
+  /// Compare two Types, treating all pointer types as equal.
   bool isEquivalentType(const Type *Ty1, const Type *Ty2) const;
 
   // The two functions undergoing comparison.
@@ -146,20 +191,26 @@ private:
 
   const TargetData *TD;
 
-  typedef DenseMap<const Value *, unsigned long> IDMap;
-  IDMap Map1, Map2;
-  unsigned long IDMap1Count, IDMap2Count;
+  DenseMap<const Value *, const Value *> id_map;
+  DenseSet<const Value *> seen_values;
 };
+
 }
 
-/// isEquivalentType - any two pointers in the same address space are
-/// equivalent. Otherwise, standard type equivalence rules apply.
+// Any two pointers in the same address space are equivalent, intptr_t and
+// pointers are equivalent. Otherwise, standard type equivalence rules apply.
 bool FunctionComparator::isEquivalentType(const Type *Ty1,
                                           const Type *Ty2) const {
   if (Ty1 == Ty2)
     return true;
-  if (Ty1->getTypeID() != Ty2->getTypeID())
+  if (Ty1->getTypeID() != Ty2->getTypeID()) {
+    if (TD) {
+      LLVMContext &Ctx = Ty1->getContext();
+      if (isa<PointerType>(Ty1) && Ty2 == TD->getIntPtrType(Ctx)) return true;
+      if (isa<PointerType>(Ty2) && Ty1 == TD->getIntPtrType(Ctx)) return true;
+    }
     return false;
+  }
 
   switch(Ty1->getTypeID()) {
   default:
@@ -167,6 +218,7 @@ bool FunctionComparator::isEquivalentType(const Type *Ty1,
     // Fall through in Release mode.
   case Type::IntegerTyID:
   case Type::OpaqueTyID:
+  case Type::VectorTyID:
     // Ty1 == Ty2 would have returned true earlier.
     return false;
 
@@ -225,21 +277,18 @@ bool FunctionComparator::isEquivalentType(const Type *Ty1,
     return ATy1->getNumElements() == ATy2->getNumElements() &&
            isEquivalentType(ATy1->getElementType(), ATy2->getElementType());
   }
-
-  case Type::VectorTyID: {
-    const VectorType *VTy1 = cast<VectorType>(Ty1);
-    const VectorType *VTy2 = cast<VectorType>(Ty2);
-    return VTy1->getNumElements() == VTy2->getNumElements() &&
-           isEquivalentType(VTy1->getElementType(), VTy2->getElementType());
-  }
   }
 }
 
-/// isEquivalentOperation - determine whether the two operations are the same
-/// except that pointer-to-A and pointer-to-B are equivalent. This should be
-/// kept in sync with Instruction::isSameOperationAs.
+// Determine whether the two operations are the same except that pointer-to-A
+// and pointer-to-B are equivalent. This should be kept in sync with
+// Instruction::isSameOperationAs.
 bool FunctionComparator::isEquivalentOperation(const Instruction *I1,
                                                const Instruction *I2) const {
+  // Differences from Instruction::isSameOperationAs:
+  //  * replace type comparison with calls to isEquivalentType.
+  //  * we test for I->hasSameSubclassOptionalData (nuw/nsw/tail) at the top
+  //  * because of the above, we don't test for the tail bit on calls later on
   if (I1->getOpcode() != I2->getOpcode() ||
       I1->getNumOperands() != I2->getNumOperands() ||
       !isEquivalentType(I1->getType(), I2->getType()) ||
@@ -263,14 +312,11 @@ bool FunctionComparator::isEquivalentOperation(const Instruction *I1,
   if (const CmpInst *CI = dyn_cast<CmpInst>(I1))
     return CI->getPredicate() == cast<CmpInst>(I2)->getPredicate();
   if (const CallInst *CI = dyn_cast<CallInst>(I1))
-    return CI->isTailCall() == cast<CallInst>(I2)->isTailCall() &&
-           CI->getCallingConv() == cast<CallInst>(I2)->getCallingConv() &&
-           CI->getAttributes().getRawPointer() ==
-             cast<CallInst>(I2)->getAttributes().getRawPointer();
+    return CI->getCallingConv() == cast<CallInst>(I2)->getCallingConv() &&
+           CI->getAttributes() == cast<CallInst>(I2)->getAttributes();
   if (const InvokeInst *CI = dyn_cast<InvokeInst>(I1))
     return CI->getCallingConv() == cast<InvokeInst>(I2)->getCallingConv() &&
-           CI->getAttributes().getRawPointer() ==
-             cast<InvokeInst>(I2)->getAttributes().getRawPointer();
+           CI->getAttributes() == cast<InvokeInst>(I2)->getAttributes();
   if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(I1)) {
     if (IVI->getNumIndices() != cast<InsertValueInst>(I2)->getNumIndices())
       return false;
@@ -291,8 +337,7 @@ bool FunctionComparator::isEquivalentOperation(const Instruction *I1,
   return true;
 }
 
-/// isEquivalentGEP - determine whether two GEP operations perform the same
-/// underlying arithmetic.
+// Determine whether two GEP operations perform the same underlying arithmetic.
 bool FunctionComparator::isEquivalentGEP(const GEPOperator *GEP1,
                                          const GEPOperator *GEP2) {
   // When we have target data, we can reduce the GEP down to the value in bytes
@@ -315,17 +360,17 @@ bool FunctionComparator::isEquivalentGEP(const GEPOperator *GEP1,
     return false;
 
   for (unsigned i = 0, e = GEP1->getNumOperands(); i != e; ++i) {
-    if (!Enumerate(GEP1->getOperand(i), GEP2->getOperand(i)))
+    if (!enumerate(GEP1->getOperand(i), GEP2->getOperand(i)))
       return false;
   }
 
   return true;
 }
 
-/// Enumerate - Compare two values used by the two functions under pair-wise
-/// comparison. If this is the first time the values are seen, they're added to
-/// the mapping so that we will detect mismatches on next use.
-bool FunctionComparator::Enumerate(const Value *V1, const Value *V2) {
+// Compare two values used by the two functions under pair-wise comparison. If
+// this is the first time the values are seen, they're added to the mapping so
+// that we will detect mismatches on next use.
+bool FunctionComparator::enumerate(const Value *V1, const Value *V2) {
   // Check for function @f1 referring to itself and function @f2 referring to
   // itself, or referring to each other, or both referring to either of them.
   // They're all equivalent if the two functions are otherwise equivalent.
@@ -334,35 +379,44 @@ bool FunctionComparator::Enumerate(const Value *V1, const Value *V2) {
   if (V1 == F2 && V2 == F1)
     return true;
 
-  // TODO: constant expressions with GEP or references to F1 or F2.
-  if (isa<Constant>(V1))
-    return V1 == V2;
-
-  if (isa<InlineAsm>(V1) && isa<InlineAsm>(V2)) {
-    const InlineAsm *IA1 = cast<InlineAsm>(V1);
-    const InlineAsm *IA2 = cast<InlineAsm>(V2);
-    return IA1->getAsmString() == IA2->getAsmString() &&
-           IA1->getConstraintString() == IA2->getConstraintString();
+  if (const Constant *C1 = dyn_cast<Constant>(V1)) {
+    if (V1 == V2) return true;
+    const Constant *C2 = dyn_cast<Constant>(V2);
+    if (!C2) return false;
+    // TODO: constant expressions with GEP or references to F1 or F2.
+    if (C1->isNullValue() && C2->isNullValue() &&
+	isEquivalentType(C1->getType(), C2->getType()))
+      return true;
+    // Try bitcasting C2 to C1's type. If the bitcast is legal and returns C1
+    // then they must have equal bit patterns.
+    return C1->getType()->canLosslesslyBitCastTo(C2->getType()) &&
+      C1 == ConstantExpr::getBitCast(const_cast<Constant*>(C2), C1->getType());
   }
 
-  unsigned long &ID1 = Map1[V1];
-  if (!ID1)
-    ID1 = ++IDMap1Count;
+  if (isa<InlineAsm>(V1) || isa<InlineAsm>(V2))
+    return V1 == V2;
 
-  unsigned long &ID2 = Map2[V2];
-  if (!ID2)
-    ID2 = ++IDMap2Count;
+  // Check that V1 maps to V2. If we find a value that V1 maps to then we simply
+  // check whether it's equal to V2. When there is no mapping then we need to
+  // ensure that V2 isn't already equivalent to something else. For this
+  // purpose, we track the V2 values in a set.
 
-  return ID1 == ID2;
+  const Value *&map_elem = id_map[V1];
+  if (map_elem)
+    return map_elem == V2;
+  if (!seen_values.insert(V2).second)
+    return false;
+  map_elem = V2;
+  return true;
 }
 
-/// Compare - test whether two basic blocks have equivalent behaviour.
-bool FunctionComparator::Compare(const BasicBlock *BB1, const BasicBlock *BB2) {
+// Test whether two basic blocks have equivalent behaviour.
+bool FunctionComparator::compare(const BasicBlock *BB1, const BasicBlock *BB2) {
   BasicBlock::const_iterator F1I = BB1->begin(), F1E = BB1->end();
   BasicBlock::const_iterator F2I = BB2->begin(), F2E = BB2->end();
 
   do {
-    if (!Enumerate(F1I, F2I))
+    if (!enumerate(F1I, F2I))
       return false;
 
     if (const GetElementPtrInst *GEP1 = dyn_cast<GetElementPtrInst>(F1I)) {
@@ -370,7 +424,7 @@ bool FunctionComparator::Compare(const BasicBlock *BB1, const BasicBlock *BB2) {
       if (!GEP2)
         return false;
 
-      if (!Enumerate(GEP1->getPointerOperand(), GEP2->getPointerOperand()))
+      if (!enumerate(GEP1->getPointerOperand(), GEP2->getPointerOperand()))
         return false;
 
       if (!isEquivalentGEP(GEP1, GEP2))
@@ -384,7 +438,7 @@ bool FunctionComparator::Compare(const BasicBlock *BB1, const BasicBlock *BB2) {
         Value *OpF1 = F1I->getOperand(i);
         Value *OpF2 = F2I->getOperand(i);
 
-        if (!Enumerate(OpF1, OpF2))
+        if (!enumerate(OpF1, OpF2))
           return false;
 
         if (OpF1->getValueID() != OpF2->getValueID() ||
@@ -399,8 +453,8 @@ bool FunctionComparator::Compare(const BasicBlock *BB1, const BasicBlock *BB2) {
   return F1I == F1E && F2I == F2E;
 }
 
-/// Compare - test whether the two functions have equivalent behaviour.
-bool FunctionComparator::Compare() {
+// Test whether the two functions have equivalent behaviour.
+bool FunctionComparator::compare() {
   // We need to recheck everything, but check the things that weren't included
   // in the hash first.
 
@@ -431,14 +485,14 @@ bool FunctionComparator::Compare() {
     return false;
 
   assert(F1->arg_size() == F2->arg_size() &&
-         "Identical functions have a different number of args.");
+         "Identically typed functions have different numbers of args!");
 
   // Visit the arguments so that they get enumerated in the order they're
   // passed in.
   for (Function::const_arg_iterator f1i = F1->arg_begin(),
          f2i = F2->arg_begin(), f1e = F1->arg_end(); f1i != f1e; ++f1i, ++f2i) {
-    if (!Enumerate(f1i, f2i))
-      llvm_unreachable("Arguments repeat");
+    if (!enumerate(f1i, f2i))
+      llvm_unreachable("Arguments repeat!");
   }
 
   // We do a CFG-ordered walk since the actual ordering of the blocks in the
@@ -456,7 +510,7 @@ bool FunctionComparator::Compare() {
     const BasicBlock *F1BB = F1BBs.pop_back_val();
     const BasicBlock *F2BB = F2BBs.pop_back_val();
 
-    if (!Enumerate(F1BB, F2BB) || !Compare(F1BB, F2BB))
+    if (!enumerate(F1BB, F2BB) || !compare(F1BB, F2BB))
       return false;
 
     const TerminatorInst *F1TI = F1BB->getTerminator();
@@ -474,23 +528,190 @@ bool FunctionComparator::Compare() {
   return true;
 }
 
-/// WriteThunk - Replace G with a simple tail call to bitcast(F). Also replace
-/// direct uses of G with bitcast(F).
-void MergeFunctions::WriteThunk(Function *F, Function *G) const {
+namespace {
+
+/// MergeFunctions finds functions which will generate identical machine code,
+/// by considering all pointer types to be equivalent. Once identified,
+/// MergeFunctions will fold them by replacing a call to one to a call to a
+/// bitcast of the other.
+///
+class MergeFunctions : public ModulePass {
+public:
+  static char ID;
+  MergeFunctions()
+    : ModulePass(ID), HasGlobalAliases(false) {
+    initializeMergeFunctionsPass(*PassRegistry::getPassRegistry());
+  }
+
+  bool runOnModule(Module &M);
+
+private:
+  typedef DenseSet<ComparableFunction> FnSetType;
+
+  /// A work queue of functions that may have been modified and should be
+  /// analyzed again.
+  std::vector<WeakVH> Deferred;
+
+  /// Insert a ComparableFunction into the FnSet, or merge it away if it's
+  /// equal to one that's already present.
+  bool insert(ComparableFunction &NewF);
+
+  /// Remove a Function from the FnSet and queue it up for a second sweep of
+  /// analysis.
+  void remove(Function *F);
+
+  /// Find the functions that use this Value and remove them from FnSet and
+  /// queue the functions.
+  void removeUsers(Value *V);
+
+  /// Replace all direct calls of Old with calls of New. Will bitcast New if
+  /// necessary to make types match.
+  void replaceDirectCallers(Function *Old, Function *New);
+
+  /// Merge two equivalent functions. Upon completion, G may be deleted, or may
+  /// be converted into a thunk. In either case, it should never be visited
+  /// again.
+  void mergeTwoFunctions(Function *F, Function *G);
+
+  /// Replace G with a thunk or an alias to F. Deletes G.
+  void writeThunkOrAlias(Function *F, Function *G);
+
+  /// Replace G with a simple tail call to bitcast(F). Also replace direct uses
+  /// of G with bitcast(F). Deletes G.
+  void writeThunk(Function *F, Function *G);
+
+  /// Replace G with an alias to F. Deletes G.
+  void writeAlias(Function *F, Function *G);
+
+  /// The set of all distinct functions. Use the insert() and remove() methods
+  /// to modify it.
+  FnSetType FnSet;
+
+  /// TargetData for more accurate GEP comparisons. May be NULL.
+  TargetData *TD;
+
+  /// Whether or not the target supports global aliases.
+  bool HasGlobalAliases;
+};
+
+}  // end anonymous namespace
+
+char MergeFunctions::ID = 0;
+INITIALIZE_PASS(MergeFunctions, "mergefunc", "Merge Functions", false, false)
+
+ModulePass *llvm::createMergeFunctionsPass() {
+  return new MergeFunctions();
+}
+
+bool MergeFunctions::runOnModule(Module &M) {
+  bool Changed = false;
+  TD = getAnalysisIfAvailable<TargetData>();
+
+  for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
+    if (!I->isDeclaration() && !I->hasAvailableExternallyLinkage())
+      Deferred.push_back(WeakVH(I));
+  }
+  FnSet.resize(Deferred.size());
+
+  do {
+    std::vector<WeakVH> Worklist;
+    Deferred.swap(Worklist);
+
+    DEBUG(dbgs() << "size of module: " << M.size() << '\n');
+    DEBUG(dbgs() << "size of worklist: " << Worklist.size() << '\n');
+
+    // Insert only strong functions and merge them. Strong function merging
+    // always deletes one of them.
+    for (std::vector<WeakVH>::iterator I = Worklist.begin(),
+           E = Worklist.end(); I != E; ++I) {
+      if (!*I) continue;
+      Function *F = cast<Function>(*I);
+      if (!F->isDeclaration() && !F->hasAvailableExternallyLinkage() &&
+          !F->mayBeOverridden()) {
+        ComparableFunction CF = ComparableFunction(F, TD);
+        Changed |= insert(CF);
+      }
+    }
+
+    // Insert only weak functions and merge them. By doing these second we
+    // create thunks to the strong function when possible. When two weak
+    // functions are identical, we create a new strong function with two weak
+    // weak thunks to it which are identical but not mergable.
+    for (std::vector<WeakVH>::iterator I = Worklist.begin(),
+           E = Worklist.end(); I != E; ++I) {
+      if (!*I) continue;
+      Function *F = cast<Function>(*I);
+      if (!F->isDeclaration() && !F->hasAvailableExternallyLinkage() &&
+          F->mayBeOverridden()) {
+        ComparableFunction CF = ComparableFunction(F, TD);
+        Changed |= insert(CF);
+      }
+    }
+    DEBUG(dbgs() << "size of FnSet: " << FnSet.size() << '\n');
+  } while (!Deferred.empty());
+
+  FnSet.clear();
+
+  return Changed;
+}
+
+bool DenseMapInfo<ComparableFunction>::isEqual(const ComparableFunction &LHS,
+                                               const ComparableFunction &RHS) {
+  if (LHS.getFunc() == RHS.getFunc() &&
+      LHS.getHash() == RHS.getHash())
+    return true;
+  if (!LHS.getFunc() || !RHS.getFunc())
+    return false;
+
+  // One of these is a special "underlying pointer comparison only" object.
+  if (LHS.getTD() == ComparableFunction::LookupOnly ||
+      RHS.getTD() == ComparableFunction::LookupOnly)
+    return false;
+
+  assert(LHS.getTD() == RHS.getTD() &&
+         "Comparing functions for different targets");
+
+  return FunctionComparator(LHS.getTD(), LHS.getFunc(),
+                            RHS.getFunc()).compare();
+}
+
+// Replace direct callers of Old with New.
+void MergeFunctions::replaceDirectCallers(Function *Old, Function *New) {
+  Constant *BitcastNew = ConstantExpr::getBitCast(New, Old->getType());
+  for (Value::use_iterator UI = Old->use_begin(), UE = Old->use_end();
+       UI != UE;) {
+    Value::use_iterator TheIter = UI;
+    ++UI;
+    CallSite CS(*TheIter);
+    if (CS && CS.isCallee(TheIter)) {
+      remove(CS.getInstruction()->getParent()->getParent());
+      TheIter.getUse().set(BitcastNew);
+    }
+  }
+}
+
+// Replace G with an alias to F if possible, or else a thunk to F. Deletes G.
+void MergeFunctions::writeThunkOrAlias(Function *F, Function *G) {
+  if (HasGlobalAliases && G->hasUnnamedAddr()) {
+    if (G->hasExternalLinkage() || G->hasLocalLinkage() ||
+        G->hasWeakLinkage()) {
+      writeAlias(F, G);
+      return;
+    }
+  }
+
+  writeThunk(F, G);
+}
+
+// Replace G with a simple tail call to bitcast(F). Also replace direct uses
+// of G with bitcast(F). Deletes G.
+void MergeFunctions::writeThunk(Function *F, Function *G) {
   if (!G->mayBeOverridden()) {
     // Redirect direct callers of G to F.
-    Constant *BitcastF = ConstantExpr::getBitCast(F, G->getType());
-    for (Value::use_iterator UI = G->use_begin(), UE = G->use_end();
-         UI != UE;) {
-      Value::use_iterator TheIter = UI;
-      ++UI;
-      CallSite CS(*TheIter);
-      if (CS && CS.isCallee(TheIter))
-        TheIter.getUse().set(BitcastF);
-    }
+    replaceDirectCallers(G, F);
   }
 
-  // If G was internal then we may have replaced all uses if G with F. If so,
+  // If G was internal then we may have replaced all uses of G with F. If so,
   // stop here and delete G. There's no need for a thunk.
   if (G->hasLocalLinkage() && G->use_empty()) {
     G->eraseFromParent();
@@ -522,131 +743,126 @@ void MergeFunctions::WriteThunk(Function *F, Function *G) const {
 
   NewG->copyAttributesFrom(G);
   NewG->takeName(G);
+  removeUsers(G);
   G->replaceAllUsesWith(NewG);
   G->eraseFromParent();
+
+  DEBUG(dbgs() << "writeThunk: " << NewG->getName() << '\n');
+  ++NumThunksWritten;
 }
 
-/// MergeTwoFunctions - Merge two equivalent functions. Upon completion,
-/// Function G is deleted.
-void MergeFunctions::MergeTwoFunctions(Function *F, Function *G) const {
-  if (F->isWeakForLinker()) {
-    assert(G->isWeakForLinker());
+// Replace G with an alias to F and delete G.
+void MergeFunctions::writeAlias(Function *F, Function *G) {
+  Constant *BitcastF = ConstantExpr::getBitCast(F, G->getType());
+  GlobalAlias *GA = new GlobalAlias(G->getType(), G->getLinkage(), "",
+                                    BitcastF, G->getParent());
+  F->setAlignment(std::max(F->getAlignment(), G->getAlignment()));
+  GA->takeName(G);
+  GA->setVisibility(G->getVisibility());
+  removeUsers(G);
+  G->replaceAllUsesWith(GA);
+  G->eraseFromParent();
+
+  DEBUG(dbgs() << "writeAlias: " << GA->getName() << '\n');
+  ++NumAliasesWritten;
+}
+
+// Merge two equivalent functions. Upon completion, Function G is deleted.
+void MergeFunctions::mergeTwoFunctions(Function *F, Function *G) {
+  if (F->mayBeOverridden()) {
+    assert(G->mayBeOverridden());
+
+    if (HasGlobalAliases) {
+      // Make them both thunks to the same internal function.
+      Function *H = Function::Create(F->getFunctionType(), F->getLinkage(), "",
+                                     F->getParent());
+      H->copyAttributesFrom(F);
+      H->takeName(F);
+      removeUsers(F);
+      F->replaceAllUsesWith(H);
 
-    // Make them both thunks to the same internal function.
-    Function *H = Function::Create(F->getFunctionType(), F->getLinkage(), "",
-                                   F->getParent());
-    H->copyAttributesFrom(F);
-    H->takeName(F);
-    F->replaceAllUsesWith(H);
+      unsigned MaxAlignment = std::max(G->getAlignment(), H->getAlignment());
 
-    unsigned MaxAlignment = std::max(G->getAlignment(), H->getAlignment());
+      writeAlias(F, G);
+      writeAlias(F, H);
 
-    WriteThunk(F, G);
-    WriteThunk(F, H);
+      F->setAlignment(MaxAlignment);
+      F->setLinkage(GlobalValue::PrivateLinkage);
+    } else {
+      // We can't merge them. Instead, pick one and update all direct callers
+      // to call it and hope that we improve the instruction cache hit rate.
+      replaceDirectCallers(G, F);
+    }
 
-    F->setAlignment(MaxAlignment);
-    F->setLinkage(GlobalValue::InternalLinkage);
+    ++NumDoubleWeak;
   } else {
-    WriteThunk(F, G);
+    writeThunkOrAlias(F, G);
   }
 
   ++NumFunctionsMerged;
 }
 
-static unsigned ProfileFunction(const Function *F) {
-  const FunctionType *FTy = F->getFunctionType();
-
-  FoldingSetNodeID ID;
-  ID.AddInteger(F->size());
-  ID.AddInteger(F->getCallingConv());
-  ID.AddBoolean(F->hasGC());
-  ID.AddBoolean(FTy->isVarArg());
-  ID.AddInteger(FTy->getReturnType()->getTypeID());
-  for (unsigned i = 0, e = FTy->getNumParams(); i != e; ++i)
-    ID.AddInteger(FTy->getParamType(i)->getTypeID());
-  return ID.ComputeHash();
-}
-
-class ComparableFunction {
-public:
-  ComparableFunction(Function *Func, TargetData *TD)
-    : Func(Func), Hash(ProfileFunction(Func)), TD(TD) {}
+// Insert a ComparableFunction into the FnSet, or merge it away if equal to one
+// that was already inserted.
+bool MergeFunctions::insert(ComparableFunction &NewF) {
+  std::pair<FnSetType::iterator, bool> Result = FnSet.insert(NewF);
+  if (Result.second) {
+    DEBUG(dbgs() << "Inserting as unique: " << NewF.getFunc()->getName() << '\n');
+    return false;
+  }
 
-  AssertingVH<Function> const Func;
-  const unsigned Hash;
-  TargetData * const TD;
-};
+  const ComparableFunction &OldF = *Result.first;
 
-struct MergeFunctionsEqualityInfo {
-  static ComparableFunction *getEmptyKey() {
-    return reinterpret_cast<ComparableFunction*>(0);
-  }
-  static ComparableFunction *getTombstoneKey() {
-    return reinterpret_cast<ComparableFunction*>(-1);
-  }
-  static unsigned getHashValue(const ComparableFunction *CF) {
-    return CF->Hash;
-  }
-  static bool isEqual(const ComparableFunction *LHS,
-                      const ComparableFunction *RHS) {
-    if (LHS == RHS)
-      return true;
-    if (LHS == getEmptyKey() || LHS == getTombstoneKey() ||
-        RHS == getEmptyKey() || RHS == getTombstoneKey())
-      return false;
-    assert(LHS->TD == RHS->TD && "Comparing functions for different targets");
-    return FunctionComparator(LHS->TD, LHS->Func, RHS->Func).Compare();
-  }
-};
+  // Never thunk a strong function to a weak function.
+  assert(!OldF.getFunc()->mayBeOverridden() ||
+         NewF.getFunc()->mayBeOverridden());
 
-bool MergeFunctions::runOnModule(Module &M) {
-  typedef DenseSet<ComparableFunction *, MergeFunctionsEqualityInfo> FnSetType;
+  DEBUG(dbgs() << "  " << OldF.getFunc()->getName() << " == "
+               << NewF.getFunc()->getName() << '\n');
 
-  bool Changed = false;
-  TD = getAnalysisIfAvailable<TargetData>();
+  Function *DeleteF = NewF.getFunc();
+  NewF.release();
+  mergeTwoFunctions(OldF.getFunc(), DeleteF);
+  return true;
+}
 
-  std::vector<Function *> Funcs;
-  for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
-    if (!F->isDeclaration() && !F->hasAvailableExternallyLinkage())
-      Funcs.push_back(F);
+// Remove a function from FnSet. If it was already in FnSet, add it to Deferred
+// so that we'll look at it in the next round.
+void MergeFunctions::remove(Function *F) {
+  // We need to make sure we remove F, not a function "equal" to F per the
+  // function equality comparator.
+  //
+  // The special "lookup only" ComparableFunction bypasses the expensive
+  // function comparison in favour of a pointer comparison on the underlying
+  // Function*'s.
+  ComparableFunction CF = ComparableFunction(F, ComparableFunction::LookupOnly);
+  if (FnSet.erase(CF)) {
+    DEBUG(dbgs() << "Removed " << F->getName() << " from set and deferred it.\n");
+    Deferred.push_back(F);
   }
+}
 
-  bool LocalChanged;
-  do {
-    LocalChanged = false;
-
-    FnSetType FnSet;
-    for (unsigned i = 0, e = Funcs.size(); i != e;) {
-      Function *F = Funcs[i];
-      ComparableFunction *NewF = new ComparableFunction(F, TD);
-      std::pair<FnSetType::iterator, bool> Result = FnSet.insert(NewF);
-      if (!Result.second) {
-        ComparableFunction *&OldF = *Result.first;
-        assert(OldF && "Expected a hash collision");
-
-        // NewF will be deleted in favour of OldF unless NewF is strong and
-        // OldF is weak in which case swap them to keep the strong definition.
-
-        if (OldF->Func->isWeakForLinker() && !NewF->Func->isWeakForLinker())
-          std::swap(OldF, NewF);
-
-        DEBUG(dbgs() << "  " << OldF->Func->getName() << " == "
-                     << NewF->Func->getName() << '\n');
-
-	Funcs.erase(Funcs.begin() + i);
-	--e;
-
-        Function *DeleteF = NewF->Func;
-        delete NewF;
-        MergeTwoFunctions(OldF->Func, DeleteF);
-	LocalChanged = true;
-        Changed = true;
-      } else {
-	++i;
+// For each instruction used by the value, remove() the function that contains
+// the instruction. This should happen right before a call to RAUW.
+void MergeFunctions::removeUsers(Value *V) {
+  std::vector<Value *> Worklist;
+  Worklist.push_back(V);
+  while (!Worklist.empty()) {
+    Value *V = Worklist.back();
+    Worklist.pop_back();
+
+    for (Value::use_iterator UI = V->use_begin(), UE = V->use_end();
+         UI != UE; ++UI) {
+      Use &U = UI.getUse();
+      if (Instruction *I = dyn_cast<Instruction>(U.getUser())) {
+        remove(I->getParent()->getParent());
+      } else if (isa<GlobalValue>(U.getUser())) {
+        // do nothing
+      } else if (Constant *C = dyn_cast<Constant>(U.getUser())) {
+        for (Value::use_iterator CUI = C->use_begin(), CUE = C->use_end();
+             CUI != CUE; ++CUI)
+          Worklist.push_back(*CUI);
       }
     }
-    DeleteContainerPointers(FnSet);
-  } while (LocalChanged);
-
-  return Changed;
+  }
 }