--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lib/Transforms/IPO/DeadArgumentElimination.cpp	Thu Dec 12 13:56:28 2013 +0900
@@ -0,0 +1,1144 @@
+//===-- DeadArgumentElimination.cpp - Eliminate dead arguments ------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass deletes dead arguments from internal functions.  Dead argument
+// elimination removes arguments which are directly dead, as well as arguments
+// only passed into function calls as dead arguments of other functions.  This
+// pass also deletes dead return values in a similar way.
+//
+// This pass is often useful as a cleanup pass to run after aggressive
+// interprocedural passes, which add possibly-dead arguments or return values.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "deadargelim"
+#include "llvm/Transforms/IPO.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/DIBuilder.h"
+#include "llvm/DebugInfo.h"
+#include "llvm/IR/CallingConv.h"
+#include "llvm/IR/Constant.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/CallSite.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+#include <map>
+#include <set>
+using namespace llvm;
+
+STATISTIC(NumArgumentsEliminated, "Number of unread args removed");
+STATISTIC(NumRetValsEliminated  , "Number of unused return values removed");
+STATISTIC(NumArgumentsReplacedWithUndef, 
+          "Number of unread args replaced with undef");
+namespace {
+  /// DAE - The dead argument elimination pass.
+  ///
+  class DAE : public ModulePass {
+  public:
+
+    /// Struct that represents (part of) either a return value or a function
+    /// argument.  Used so that arguments and return values can be used
+    /// interchangeably.
+    struct RetOrArg {
+      RetOrArg(const Function *F, unsigned Idx, bool IsArg) : F(F), Idx(Idx),
+               IsArg(IsArg) {}
+      const Function *F;
+      unsigned Idx;
+      bool IsArg;
+
+      /// Make RetOrArg comparable, so we can put it into a map.
+      bool operator<(const RetOrArg &O) const {
+        if (F != O.F)
+          return F < O.F;
+        else if (Idx != O.Idx)
+          return Idx < O.Idx;
+        else
+          return IsArg < O.IsArg;
+      }
+
+      /// Make RetOrArg comparable, so we can easily iterate the multimap.
+      bool operator==(const RetOrArg &O) const {
+        return F == O.F && Idx == O.Idx && IsArg == O.IsArg;
+      }
+
+      std::string getDescription() const {
+        return std::string((IsArg ? "Argument #" : "Return value #"))
+               + utostr(Idx) + " of function " + F->getName().str();
+      }
+    };
+
+    /// Liveness enum - During our initial pass over the program, we determine
+    /// that things are either alive or maybe alive. We don't mark anything
+    /// explicitly dead (even if we know they are), since anything not alive
+    /// with no registered uses (in Uses) will never be marked alive and will
+    /// thus become dead in the end.
+    enum Liveness { Live, MaybeLive };
+
+    /// Convenience wrapper
+    RetOrArg CreateRet(const Function *F, unsigned Idx) {
+      return RetOrArg(F, Idx, false);
+    }
+    /// Convenience wrapper
+    RetOrArg CreateArg(const Function *F, unsigned Idx) {
+      return RetOrArg(F, Idx, true);
+    }
+
+    typedef std::multimap<RetOrArg, RetOrArg> UseMap;
+    /// This maps a return value or argument to any MaybeLive return values or
+    /// arguments it uses. This allows the MaybeLive values to be marked live
+    /// when any of its users is marked live.
+    /// For example (indices are left out for clarity):
+    ///  - Uses[ret F] = ret G
+    ///    This means that F calls G, and F returns the value returned by G.
+    ///  - Uses[arg F] = ret G
+    ///    This means that some function calls G and passes its result as an
+    ///    argument to F.
+    ///  - Uses[ret F] = arg F
+    ///    This means that F returns one of its own arguments.
+    ///  - Uses[arg F] = arg G
+    ///    This means that G calls F and passes one of its own (G's) arguments
+    ///    directly to F.
+    UseMap Uses;
+
+    typedef std::set<RetOrArg> LiveSet;
+    typedef std::set<const Function*> LiveFuncSet;
+
+    /// This set contains all values that have been determined to be live.
+    LiveSet LiveValues;
+    /// This set contains all values that are cannot be changed in any way.
+    LiveFuncSet LiveFunctions;
+
+    typedef SmallVector<RetOrArg, 5> UseVector;
+
+    // Map each LLVM function to corresponding metadata with debug info. If
+    // the function is replaced with another one, we should patch the pointer
+    // to LLVM function in metadata.
+    // As the code generation for module is finished (and DIBuilder is
+    // finalized) we assume that subprogram descriptors won't be changed, and
+    // they are stored in map for short duration anyway.
+    typedef DenseMap<Function*, DISubprogram> FunctionDIMap;
+    FunctionDIMap FunctionDIs;
+
+  protected:
+    // DAH uses this to specify a different ID.
+    explicit DAE(char &ID) : ModulePass(ID) {}
+
+  public:
+    static char ID; // Pass identification, replacement for typeid
+    DAE() : ModulePass(ID) {
+      initializeDAEPass(*PassRegistry::getPassRegistry());
+    }
+
+    bool runOnModule(Module &M);
+
+    virtual bool ShouldHackArguments() const { return false; }
+
+  private:
+    Liveness MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses);
+    Liveness SurveyUse(Value::const_use_iterator U, UseVector &MaybeLiveUses,
+                       unsigned RetValNum = 0);
+    Liveness SurveyUses(const Value *V, UseVector &MaybeLiveUses);
+
+    void CollectFunctionDIs(Module &M);
+    void SurveyFunction(const Function &F);
+    void MarkValue(const RetOrArg &RA, Liveness L,
+                   const UseVector &MaybeLiveUses);
+    void MarkLive(const RetOrArg &RA);
+    void MarkLive(const Function &F);
+    void PropagateLiveness(const RetOrArg &RA);
+    bool RemoveDeadStuffFromFunction(Function *F);
+    bool DeleteDeadVarargs(Function &Fn);
+    bool RemoveDeadArgumentsFromCallers(Function &Fn);
+  };
+}
+
+
+char DAE::ID = 0;
+INITIALIZE_PASS(DAE, "deadargelim", "Dead Argument Elimination", false, false)
+
+namespace {
+  /// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but
+  /// deletes arguments to functions which are external.  This is only for use
+  /// by bugpoint.
+  struct DAH : public DAE {
+    static char ID;
+    DAH() : DAE(ID) {}
+
+    virtual bool ShouldHackArguments() const { return true; }
+  };
+}
+
+char DAH::ID = 0;
+INITIALIZE_PASS(DAH, "deadarghaX0r", 
+                "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)",
+                false, false)
+
+/// createDeadArgEliminationPass - This pass removes arguments from functions
+/// which are not used by the body of the function.
+///
+ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); }
+ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); }
+
+/// CollectFunctionDIs - Map each function in the module to its debug info
+/// descriptor.
+void DAE::CollectFunctionDIs(Module &M) {
+  FunctionDIs.clear();
+
+  for (Module::named_metadata_iterator I = M.named_metadata_begin(),
+       E = M.named_metadata_end(); I != E; ++I) {
+    NamedMDNode &NMD = *I;
+    for (unsigned MDIndex = 0, MDNum = NMD.getNumOperands();
+         MDIndex < MDNum; ++MDIndex) {
+      MDNode *Node = NMD.getOperand(MDIndex);
+      if (!DIDescriptor(Node).isCompileUnit())
+        continue;
+      DICompileUnit CU(Node);
+      const DIArray &SPs = CU.getSubprograms();
+      for (unsigned SPIndex = 0, SPNum = SPs.getNumElements();
+           SPIndex < SPNum; ++SPIndex) {
+        DISubprogram SP(SPs.getElement(SPIndex));
+        assert((!SP || SP.isSubprogram()) &&
+          "A MDNode in subprograms of a CU should be null or a DISubprogram.");
+        if (!SP)
+          continue;
+        if (Function *F = SP.getFunction())
+          FunctionDIs[F] = SP;
+      }
+    }
+  }
+}
+
+/// DeleteDeadVarargs - If this is an function that takes a ... list, and if
+/// llvm.vastart is never called, the varargs list is dead for the function.
+bool DAE::DeleteDeadVarargs(Function &Fn) {
+  assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!");
+  if (Fn.isDeclaration() || !Fn.hasLocalLinkage()) return false;
+
+  // Ensure that the function is only directly called.
+  if (Fn.hasAddressTaken())
+    return false;
+
+  // Okay, we know we can transform this function if safe.  Scan its body
+  // looking for calls to llvm.vastart.
+  for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) {
+    for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
+      if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
+        if (II->getIntrinsicID() == Intrinsic::vastart)
+          return false;
+      }
+    }
+  }
+
+  // If we get here, there are no calls to llvm.vastart in the function body,
+  // remove the "..." and adjust all the calls.
+
+  // Start by computing a new prototype for the function, which is the same as
+  // the old function, but doesn't have isVarArg set.
+  FunctionType *FTy = Fn.getFunctionType();
+
+  std::vector<Type*> Params(FTy->param_begin(), FTy->param_end());
+  FunctionType *NFTy = FunctionType::get(FTy->getReturnType(),
+                                                Params, false);
+  unsigned NumArgs = Params.size();
+
+  // Create the new function body and insert it into the module...
+  Function *NF = Function::Create(NFTy, Fn.getLinkage());
+  NF->copyAttributesFrom(&Fn);
+  Fn.getParent()->getFunctionList().insert(&Fn, NF);
+  NF->takeName(&Fn);
+
+  // Loop over all of the callers of the function, transforming the call sites
+  // to pass in a smaller number of arguments into the new function.
+  //
+  std::vector<Value*> Args;
+  for (Value::use_iterator I = Fn.use_begin(), E = Fn.use_end(); I != E; ) {
+    CallSite CS(*I++);
+    if (!CS)
+      continue;
+    Instruction *Call = CS.getInstruction();
+
+    // Pass all the same arguments.
+    Args.assign(CS.arg_begin(), CS.arg_begin() + NumArgs);
+
+    // Drop any attributes that were on the vararg arguments.
+    AttributeSet PAL = CS.getAttributes();
+    if (!PAL.isEmpty() && PAL.getSlotIndex(PAL.getNumSlots() - 1) > NumArgs) {
+      SmallVector<AttributeSet, 8> AttributesVec;
+      for (unsigned i = 0; PAL.getSlotIndex(i) <= NumArgs; ++i)
+        AttributesVec.push_back(PAL.getSlotAttributes(i));
+      if (PAL.hasAttributes(AttributeSet::FunctionIndex))
+        AttributesVec.push_back(AttributeSet::get(Fn.getContext(),
+                                                  PAL.getFnAttributes()));
+      PAL = AttributeSet::get(Fn.getContext(), AttributesVec);
+    }
+
+    Instruction *New;
+    if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
+      New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
+                               Args, "", Call);
+      cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
+      cast<InvokeInst>(New)->setAttributes(PAL);
+    } else {
+      New = CallInst::Create(NF, Args, "", Call);
+      cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
+      cast<CallInst>(New)->setAttributes(PAL);
+      if (cast<CallInst>(Call)->isTailCall())
+        cast<CallInst>(New)->setTailCall();
+    }
+    New->setDebugLoc(Call->getDebugLoc());
+
+    Args.clear();
+
+    if (!Call->use_empty())
+      Call->replaceAllUsesWith(New);
+
+    New->takeName(Call);
+
+    // Finally, remove the old call from the program, reducing the use-count of
+    // F.
+    Call->eraseFromParent();
+  }
+
+  // Since we have now created the new function, splice the body of the old
+  // function right into the new function, leaving the old rotting hulk of the
+  // function empty.
+  NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList());
+
+  // Loop over the argument list, transferring uses of the old arguments over to
+  // the new arguments, also transferring over the names as well.  While we're at
+  // it, remove the dead arguments from the DeadArguments list.
+  //
+  for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(),
+       I2 = NF->arg_begin(); I != E; ++I, ++I2) {
+    // Move the name and users over to the new version.
+    I->replaceAllUsesWith(I2);
+    I2->takeName(I);
+  }
+
+  // Patch the pointer to LLVM function in debug info descriptor.
+  FunctionDIMap::iterator DI = FunctionDIs.find(&Fn);
+  if (DI != FunctionDIs.end())
+    DI->second.replaceFunction(NF);
+
+  // Fix up any BlockAddresses that refer to the function.
+  Fn.replaceAllUsesWith(ConstantExpr::getBitCast(NF, Fn.getType()));
+  // Delete the bitcast that we just created, so that NF does not
+  // appear to be address-taken.
+  NF->removeDeadConstantUsers();
+  // Finally, nuke the old function.
+  Fn.eraseFromParent();
+  return true;
+}
+
+/// RemoveDeadArgumentsFromCallers - Checks if the given function has any 
+/// arguments that are unused, and changes the caller parameters to be undefined
+/// instead.
+bool DAE::RemoveDeadArgumentsFromCallers(Function &Fn)
+{
+  if (Fn.isDeclaration() || Fn.mayBeOverridden())
+    return false;
+
+  // Functions with local linkage should already have been handled, except the
+  // fragile (variadic) ones which we can improve here.
+  if (Fn.hasLocalLinkage() && !Fn.getFunctionType()->isVarArg())
+    return false;
+
+  // If a function seen at compile time is not necessarily the one linked to
+  // the binary being built, it is illegal to change the actual arguments
+  // passed to it. These functions can be captured by isWeakForLinker().
+  // *NOTE* that mayBeOverridden() is insufficient for this purpose as it
+  // doesn't include linkage types like AvailableExternallyLinkage and
+  // LinkOnceODRLinkage. Take link_odr* as an example, it indicates a set of
+  // *EQUIVALENT* globals that can be merged at link-time. However, the
+  // semantic of *EQUIVALENT*-functions includes parameters. Changing
+  // parameters breaks this assumption.
+  //
+  if (Fn.isWeakForLinker())
+    return false;
+
+  if (Fn.use_empty())
+    return false;
+
+  SmallVector<unsigned, 8> UnusedArgs;
+  for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(); 
+       I != E; ++I) {
+    Argument *Arg = I;
+
+    if (Arg->use_empty() && !Arg->hasByValAttr())
+      UnusedArgs.push_back(Arg->getArgNo());
+  }
+
+  if (UnusedArgs.empty())
+    return false;
+
+  bool Changed = false;
+
+  for (Function::use_iterator I = Fn.use_begin(), E = Fn.use_end(); 
+       I != E; ++I) {
+    CallSite CS(*I);
+    if (!CS || !CS.isCallee(I))
+      continue;
+
+    // Now go through all unused args and replace them with "undef".
+    for (unsigned I = 0, E = UnusedArgs.size(); I != E; ++I) {
+      unsigned ArgNo = UnusedArgs[I];
+
+      Value *Arg = CS.getArgument(ArgNo);
+      CS.setArgument(ArgNo, UndefValue::get(Arg->getType()));
+      ++NumArgumentsReplacedWithUndef;
+      Changed = true;
+    }
+  }
+
+  return Changed;
+}
+
+/// Convenience function that returns the number of return values. It returns 0
+/// for void functions and 1 for functions not returning a struct. It returns
+/// the number of struct elements for functions returning a struct.
+static unsigned NumRetVals(const Function *F) {
+  if (F->getReturnType()->isVoidTy())
+    return 0;
+  else if (StructType *STy = dyn_cast<StructType>(F->getReturnType()))
+    return STy->getNumElements();
+  else
+    return 1;
+}
+
+/// MarkIfNotLive - This checks Use for liveness in LiveValues. If Use is not
+/// live, it adds Use to the MaybeLiveUses argument. Returns the determined
+/// liveness of Use.
+DAE::Liveness DAE::MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses) {
+  // We're live if our use or its Function is already marked as live.
+  if (LiveFunctions.count(Use.F) || LiveValues.count(Use))
+    return Live;
+
+  // We're maybe live otherwise, but remember that we must become live if
+  // Use becomes live.
+  MaybeLiveUses.push_back(Use);
+  return MaybeLive;
+}
+
+
+/// SurveyUse - This looks at a single use of an argument or return value
+/// and determines if it should be alive or not. Adds this use to MaybeLiveUses
+/// if it causes the used value to become MaybeLive.
+///
+/// RetValNum is the return value number to use when this use is used in a
+/// return instruction. This is used in the recursion, you should always leave
+/// it at 0.
+DAE::Liveness DAE::SurveyUse(Value::const_use_iterator U,
+                             UseVector &MaybeLiveUses, unsigned RetValNum) {
+    const User *V = *U;
+    if (const ReturnInst *RI = dyn_cast<ReturnInst>(V)) {
+      // The value is returned from a function. It's only live when the
+      // function's return value is live. We use RetValNum here, for the case
+      // that U is really a use of an insertvalue instruction that uses the
+      // original Use.
+      RetOrArg Use = CreateRet(RI->getParent()->getParent(), RetValNum);
+      // We might be live, depending on the liveness of Use.
+      return MarkIfNotLive(Use, MaybeLiveUses);
+    }
+    if (const InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) {
+      if (U.getOperandNo() != InsertValueInst::getAggregateOperandIndex()
+          && IV->hasIndices())
+        // The use we are examining is inserted into an aggregate. Our liveness
+        // depends on all uses of that aggregate, but if it is used as a return
+        // value, only index at which we were inserted counts.
+        RetValNum = *IV->idx_begin();
+
+      // Note that if we are used as the aggregate operand to the insertvalue,
+      // we don't change RetValNum, but do survey all our uses.
+
+      Liveness Result = MaybeLive;
+      for (Value::const_use_iterator I = IV->use_begin(),
+           E = V->use_end(); I != E; ++I) {
+        Result = SurveyUse(I, MaybeLiveUses, RetValNum);
+        if (Result == Live)
+          break;
+      }
+      return Result;
+    }
+
+    if (ImmutableCallSite CS = V) {
+      const Function *F = CS.getCalledFunction();
+      if (F) {
+        // Used in a direct call.
+
+        // Find the argument number. We know for sure that this use is an
+        // argument, since if it was the function argument this would be an
+        // indirect call and the we know can't be looking at a value of the
+        // label type (for the invoke instruction).
+        unsigned ArgNo = CS.getArgumentNo(U);
+
+        if (ArgNo >= F->getFunctionType()->getNumParams())
+          // The value is passed in through a vararg! Must be live.
+          return Live;
+
+        assert(CS.getArgument(ArgNo)
+               == CS->getOperand(U.getOperandNo())
+               && "Argument is not where we expected it");
+
+        // Value passed to a normal call. It's only live when the corresponding
+        // argument to the called function turns out live.
+        RetOrArg Use = CreateArg(F, ArgNo);
+        return MarkIfNotLive(Use, MaybeLiveUses);
+      }
+    }
+    // Used in any other way? Value must be live.
+    return Live;
+}
+
+/// SurveyUses - This looks at all the uses of the given value
+/// Returns the Liveness deduced from the uses of this value.
+///
+/// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. If
+/// the result is Live, MaybeLiveUses might be modified but its content should
+/// be ignored (since it might not be complete).
+DAE::Liveness DAE::SurveyUses(const Value *V, UseVector &MaybeLiveUses) {
+  // Assume it's dead (which will only hold if there are no uses at all..).
+  Liveness Result = MaybeLive;
+  // Check each use.
+  for (Value::const_use_iterator I = V->use_begin(),
+       E = V->use_end(); I != E; ++I) {
+    Result = SurveyUse(I, MaybeLiveUses);
+    if (Result == Live)
+      break;
+  }
+  return Result;
+}
+
+// SurveyFunction - This performs the initial survey of the specified function,
+// checking out whether or not it uses any of its incoming arguments or whether
+// any callers use the return value.  This fills in the LiveValues set and Uses
+// map.
+//
+// We consider arguments of non-internal functions to be intrinsically alive as
+// well as arguments to functions which have their "address taken".
+//
+void DAE::SurveyFunction(const Function &F) {
+  unsigned RetCount = NumRetVals(&F);
+  // Assume all return values are dead
+  typedef SmallVector<Liveness, 5> RetVals;
+  RetVals RetValLiveness(RetCount, MaybeLive);
+
+  typedef SmallVector<UseVector, 5> RetUses;
+  // These vectors map each return value to the uses that make it MaybeLive, so
+  // we can add those to the Uses map if the return value really turns out to be
+  // MaybeLive. Initialized to a list of RetCount empty lists.
+  RetUses MaybeLiveRetUses(RetCount);
+
+  for (Function::const_iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
+    if (const ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
+      if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType()
+          != F.getFunctionType()->getReturnType()) {
+        // We don't support old style multiple return values.
+        MarkLive(F);
+        return;
+      }
+
+  if (!F.hasLocalLinkage() && (!ShouldHackArguments() || F.isIntrinsic())) {
+    MarkLive(F);
+    return;
+  }
+
+  DEBUG(dbgs() << "DAE - Inspecting callers for fn: " << F.getName() << "\n");
+  // Keep track of the number of live retvals, so we can skip checks once all
+  // of them turn out to be live.
+  unsigned NumLiveRetVals = 0;
+  Type *STy = dyn_cast<StructType>(F.getReturnType());
+  // Loop all uses of the function.
+  for (Value::const_use_iterator I = F.use_begin(), E = F.use_end();
+       I != E; ++I) {
+    // If the function is PASSED IN as an argument, its address has been
+    // taken.
+    ImmutableCallSite CS(*I);
+    if (!CS || !CS.isCallee(I)) {
+      MarkLive(F);
+      return;
+    }
+
+    // If this use is anything other than a call site, the function is alive.
+    const Instruction *TheCall = CS.getInstruction();
+    if (!TheCall) {   // Not a direct call site?
+      MarkLive(F);
+      return;
+    }
+
+    // If we end up here, we are looking at a direct call to our function.
+
+    // Now, check how our return value(s) is/are used in this caller. Don't
+    // bother checking return values if all of them are live already.
+    if (NumLiveRetVals != RetCount) {
+      if (STy) {
+        // Check all uses of the return value.
+        for (Value::const_use_iterator I = TheCall->use_begin(),
+             E = TheCall->use_end(); I != E; ++I) {
+          const ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(*I);
+          if (Ext && Ext->hasIndices()) {
+            // This use uses a part of our return value, survey the uses of
+            // that part and store the results for this index only.
+            unsigned Idx = *Ext->idx_begin();
+            if (RetValLiveness[Idx] != Live) {
+              RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]);
+              if (RetValLiveness[Idx] == Live)
+                NumLiveRetVals++;
+            }
+          } else {
+            // Used by something else than extractvalue. Mark all return
+            // values as live.
+            for (unsigned i = 0; i != RetCount; ++i )
+              RetValLiveness[i] = Live;
+            NumLiveRetVals = RetCount;
+            break;
+          }
+        }
+      } else {
+        // Single return value
+        RetValLiveness[0] = SurveyUses(TheCall, MaybeLiveRetUses[0]);
+        if (RetValLiveness[0] == Live)
+          NumLiveRetVals = RetCount;
+      }
+    }
+  }
+
+  // Now we've inspected all callers, record the liveness of our return values.
+  for (unsigned i = 0; i != RetCount; ++i)
+    MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]);
+
+  DEBUG(dbgs() << "DAE - Inspecting args for fn: " << F.getName() << "\n");
+
+  // Now, check all of our arguments.
+  unsigned i = 0;
+  UseVector MaybeLiveArgUses;
+  for (Function::const_arg_iterator AI = F.arg_begin(),
+       E = F.arg_end(); AI != E; ++AI, ++i) {
+    Liveness Result;
+    if (F.getFunctionType()->isVarArg()) {
+      // Variadic functions will already have a va_arg function expanded inside
+      // them, making them potentially very sensitive to ABI changes resulting
+      // from removing arguments entirely, so don't. For example AArch64 handles
+      // register and stack HFAs very differently, and this is reflected in the
+      // IR which has already been generated.
+      Result = Live;
+    } else {
+      // See what the effect of this use is (recording any uses that cause
+      // MaybeLive in MaybeLiveArgUses). 
+      Result = SurveyUses(AI, MaybeLiveArgUses);
+    }
+
+    // Mark the result.
+    MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses);
+    // Clear the vector again for the next iteration.
+    MaybeLiveArgUses.clear();
+  }
+}
+
+/// MarkValue - This function marks the liveness of RA depending on L. If L is
+/// MaybeLive, it also takes all uses in MaybeLiveUses and records them in Uses,
+/// such that RA will be marked live if any use in MaybeLiveUses gets marked
+/// live later on.
+void DAE::MarkValue(const RetOrArg &RA, Liveness L,
+                    const UseVector &MaybeLiveUses) {
+  switch (L) {
+    case Live: MarkLive(RA); break;
+    case MaybeLive:
+    {
+      // Note any uses of this value, so this return value can be
+      // marked live whenever one of the uses becomes live.
+      for (UseVector::const_iterator UI = MaybeLiveUses.begin(),
+           UE = MaybeLiveUses.end(); UI != UE; ++UI)
+        Uses.insert(std::make_pair(*UI, RA));
+      break;
+    }
+  }
+}
+
+/// MarkLive - Mark the given Function as alive, meaning that it cannot be
+/// changed in any way. Additionally,
+/// mark any values that are used as this function's parameters or by its return
+/// values (according to Uses) live as well.
+void DAE::MarkLive(const Function &F) {
+  DEBUG(dbgs() << "DAE - Intrinsically live fn: " << F.getName() << "\n");
+  // Mark the function as live.
+  LiveFunctions.insert(&F);
+  // Mark all arguments as live.
+  for (unsigned i = 0, e = F.arg_size(); i != e; ++i)
+    PropagateLiveness(CreateArg(&F, i));
+  // Mark all return values as live.
+  for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i)
+    PropagateLiveness(CreateRet(&F, i));
+}
+
+/// MarkLive - Mark the given return value or argument as live. Additionally,
+/// mark any values that are used by this value (according to Uses) live as
+/// well.
+void DAE::MarkLive(const RetOrArg &RA) {
+  if (LiveFunctions.count(RA.F))
+    return; // Function was already marked Live.
+
+  if (!LiveValues.insert(RA).second)
+    return; // We were already marked Live.
+
+  DEBUG(dbgs() << "DAE - Marking " << RA.getDescription() << " live\n");
+  PropagateLiveness(RA);
+}
+
+/// PropagateLiveness - Given that RA is a live value, propagate it's liveness
+/// to any other values it uses (according to Uses).
+void DAE::PropagateLiveness(const RetOrArg &RA) {
+  // We don't use upper_bound (or equal_range) here, because our recursive call
+  // to ourselves is likely to cause the upper_bound (which is the first value
+  // not belonging to RA) to become erased and the iterator invalidated.
+  UseMap::iterator Begin = Uses.lower_bound(RA);
+  UseMap::iterator E = Uses.end();
+  UseMap::iterator I;
+  for (I = Begin; I != E && I->first == RA; ++I)
+    MarkLive(I->second);
+
+  // Erase RA from the Uses map (from the lower bound to wherever we ended up
+  // after the loop).
+  Uses.erase(Begin, I);
+}
+
+// RemoveDeadStuffFromFunction - Remove any arguments and return values from F
+// that are not in LiveValues. Transform the function and all of the callees of
+// the function to not have these arguments and return values.
+//
+bool DAE::RemoveDeadStuffFromFunction(Function *F) {
+  // Don't modify fully live functions
+  if (LiveFunctions.count(F))
+    return false;
+
+  // Start by computing a new prototype for the function, which is the same as
+  // the old function, but has fewer arguments and a different return type.
+  FunctionType *FTy = F->getFunctionType();
+  std::vector<Type*> Params;
+
+  // Keep track of if we have a live 'returned' argument
+  bool HasLiveReturnedArg = false;
+
+  // Set up to build a new list of parameter attributes.
+  SmallVector<AttributeSet, 8> AttributesVec;
+  const AttributeSet &PAL = F->getAttributes();
+
+  // Remember which arguments are still alive.
+  SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false);
+  // Construct the new parameter list from non-dead arguments. Also construct
+  // a new set of parameter attributes to correspond. Skip the first parameter
+  // attribute, since that belongs to the return value.
+  unsigned i = 0;
+  for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
+       I != E; ++I, ++i) {
+    RetOrArg Arg = CreateArg(F, i);
+    if (LiveValues.erase(Arg)) {
+      Params.push_back(I->getType());
+      ArgAlive[i] = true;
+
+      // Get the original parameter attributes (skipping the first one, that is
+      // for the return value.
+      if (PAL.hasAttributes(i + 1)) {
+        AttrBuilder B(PAL, i + 1);
+        if (B.contains(Attribute::Returned))
+          HasLiveReturnedArg = true;
+        AttributesVec.
+          push_back(AttributeSet::get(F->getContext(), Params.size(), B));
+      }
+    } else {
+      ++NumArgumentsEliminated;
+      DEBUG(dbgs() << "DAE - Removing argument " << i << " (" << I->getName()
+            << ") from " << F->getName() << "\n");
+    }
+  }
+
+  // Find out the new return value.
+  Type *RetTy = FTy->getReturnType();
+  Type *NRetTy = NULL;
+  unsigned RetCount = NumRetVals(F);
+
+  // -1 means unused, other numbers are the new index
+  SmallVector<int, 5> NewRetIdxs(RetCount, -1);
+  std::vector<Type*> RetTypes;
+
+  // If there is a function with a live 'returned' argument but a dead return
+  // value, then there are two possible actions:
+  // 1) Eliminate the return value and take off the 'returned' attribute on the
+  //    argument.
+  // 2) Retain the 'returned' attribute and treat the return value (but not the
+  //    entire function) as live so that it is not eliminated.
+  // 
+  // It's not clear in the general case which option is more profitable because,
+  // even in the absence of explicit uses of the return value, code generation
+  // is free to use the 'returned' attribute to do things like eliding
+  // save/restores of registers across calls. Whether or not this happens is
+  // target and ABI-specific as well as depending on the amount of register
+  // pressure, so there's no good way for an IR-level pass to figure this out.
+  //
+  // Fortunately, the only places where 'returned' is currently generated by
+  // the FE are places where 'returned' is basically free and almost always a
+  // performance win, so the second option can just be used always for now.
+  //
+  // This should be revisited if 'returned' is ever applied more liberally.
+  if (RetTy->isVoidTy() || HasLiveReturnedArg) {
+    NRetTy = RetTy;
+  } else {
+    StructType *STy = dyn_cast<StructType>(RetTy);
+    if (STy)
+      // Look at each of the original return values individually.
+      for (unsigned i = 0; i != RetCount; ++i) {
+        RetOrArg Ret = CreateRet(F, i);
+        if (LiveValues.erase(Ret)) {
+          RetTypes.push_back(STy->getElementType(i));
+          NewRetIdxs[i] = RetTypes.size() - 1;
+        } else {
+          ++NumRetValsEliminated;
+          DEBUG(dbgs() << "DAE - Removing return value " << i << " from "
+                << F->getName() << "\n");
+        }
+      }
+    else
+      // We used to return a single value.
+      if (LiveValues.erase(CreateRet(F, 0))) {
+        RetTypes.push_back(RetTy);
+        NewRetIdxs[0] = 0;
+      } else {
+        DEBUG(dbgs() << "DAE - Removing return value from " << F->getName()
+              << "\n");
+        ++NumRetValsEliminated;
+      }
+    if (RetTypes.size() > 1)
+      // More than one return type? Return a struct with them. Also, if we used
+      // to return a struct and didn't change the number of return values,
+      // return a struct again. This prevents changing {something} into
+      // something and {} into void.
+      // Make the new struct packed if we used to return a packed struct
+      // already.
+      NRetTy = StructType::get(STy->getContext(), RetTypes, STy->isPacked());
+    else if (RetTypes.size() == 1)
+      // One return type? Just a simple value then, but only if we didn't use to
+      // return a struct with that simple value before.
+      NRetTy = RetTypes.front();
+    else if (RetTypes.size() == 0)
+      // No return types? Make it void, but only if we didn't use to return {}.
+      NRetTy = Type::getVoidTy(F->getContext());
+  }
+
+  assert(NRetTy && "No new return type found?");
+
+  // The existing function return attributes.
+  AttributeSet RAttrs = PAL.getRetAttributes();
+
+  // Remove any incompatible attributes, but only if we removed all return
+  // values. Otherwise, ensure that we don't have any conflicting attributes
+  // here. Currently, this should not be possible, but special handling might be
+  // required when new return value attributes are added.
+  if (NRetTy->isVoidTy())
+    RAttrs =
+      AttributeSet::get(NRetTy->getContext(), AttributeSet::ReturnIndex,
+                        AttrBuilder(RAttrs, AttributeSet::ReturnIndex).
+         removeAttributes(AttributeFuncs::
+                          typeIncompatible(NRetTy, AttributeSet::ReturnIndex),
+                          AttributeSet::ReturnIndex));
+  else
+    assert(!AttrBuilder(RAttrs, AttributeSet::ReturnIndex).
+             hasAttributes(AttributeFuncs::
+                           typeIncompatible(NRetTy, AttributeSet::ReturnIndex),
+                           AttributeSet::ReturnIndex) &&
+           "Return attributes no longer compatible?");
+
+  if (RAttrs.hasAttributes(AttributeSet::ReturnIndex))
+    AttributesVec.push_back(AttributeSet::get(NRetTy->getContext(), RAttrs));
+
+  if (PAL.hasAttributes(AttributeSet::FunctionIndex))
+    AttributesVec.push_back(AttributeSet::get(F->getContext(),
+                                              PAL.getFnAttributes()));
+
+  // Reconstruct the AttributesList based on the vector we constructed.
+  AttributeSet NewPAL = AttributeSet::get(F->getContext(), AttributesVec);
+
+  // Create the new function type based on the recomputed parameters.
+  FunctionType *NFTy = FunctionType::get(NRetTy, Params, FTy->isVarArg());
+
+  // No change?
+  if (NFTy == FTy)
+    return false;
+
+  // Create the new function body and insert it into the module...
+  Function *NF = Function::Create(NFTy, F->getLinkage());
+  NF->copyAttributesFrom(F);
+  NF->setAttributes(NewPAL);
+  // Insert the new function before the old function, so we won't be processing
+  // it again.
+  F->getParent()->getFunctionList().insert(F, NF);
+  NF->takeName(F);
+
+  // Loop over all of the callers of the function, transforming the call sites
+  // to pass in a smaller number of arguments into the new function.
+  //
+  std::vector<Value*> Args;
+  while (!F->use_empty()) {
+    CallSite CS(F->use_back());
+    Instruction *Call = CS.getInstruction();
+
+    AttributesVec.clear();
+    const AttributeSet &CallPAL = CS.getAttributes();
+
+    // The call return attributes.
+    AttributeSet RAttrs = CallPAL.getRetAttributes();
+
+    // Adjust in case the function was changed to return void.
+    RAttrs =
+      AttributeSet::get(NF->getContext(), AttributeSet::ReturnIndex,
+                        AttrBuilder(RAttrs, AttributeSet::ReturnIndex).
+        removeAttributes(AttributeFuncs::
+                         typeIncompatible(NF->getReturnType(),
+                                          AttributeSet::ReturnIndex),
+                         AttributeSet::ReturnIndex));
+    if (RAttrs.hasAttributes(AttributeSet::ReturnIndex))
+      AttributesVec.push_back(AttributeSet::get(NF->getContext(), RAttrs));
+
+    // Declare these outside of the loops, so we can reuse them for the second
+    // loop, which loops the varargs.
+    CallSite::arg_iterator I = CS.arg_begin();
+    unsigned i = 0;
+    // Loop over those operands, corresponding to the normal arguments to the
+    // original function, and add those that are still alive.
+    for (unsigned e = FTy->getNumParams(); i != e; ++I, ++i)
+      if (ArgAlive[i]) {
+        Args.push_back(*I);
+        // Get original parameter attributes, but skip return attributes.
+        if (CallPAL.hasAttributes(i + 1)) {
+          AttrBuilder B(CallPAL, i + 1);
+          // If the return type has changed, then get rid of 'returned' on the
+          // call site. The alternative is to make all 'returned' attributes on
+          // call sites keep the return value alive just like 'returned'
+          // attributes on function declaration but it's less clearly a win
+          // and this is not an expected case anyway
+          if (NRetTy != RetTy && B.contains(Attribute::Returned))
+            B.removeAttribute(Attribute::Returned);
+          AttributesVec.
+            push_back(AttributeSet::get(F->getContext(), Args.size(), B));
+        }
+      }
+
+    // Push any varargs arguments on the list. Don't forget their attributes.
+    for (CallSite::arg_iterator E = CS.arg_end(); I != E; ++I, ++i) {
+      Args.push_back(*I);
+      if (CallPAL.hasAttributes(i + 1)) {
+        AttrBuilder B(CallPAL, i + 1);
+        AttributesVec.
+          push_back(AttributeSet::get(F->getContext(), Args.size(), B));
+      }
+    }
+
+    if (CallPAL.hasAttributes(AttributeSet::FunctionIndex))
+      AttributesVec.push_back(AttributeSet::get(Call->getContext(),
+                                                CallPAL.getFnAttributes()));
+
+    // Reconstruct the AttributesList based on the vector we constructed.
+    AttributeSet NewCallPAL = AttributeSet::get(F->getContext(), AttributesVec);
+
+    Instruction *New;
+    if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
+      New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
+                               Args, "", Call);
+      cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
+      cast<InvokeInst>(New)->setAttributes(NewCallPAL);
+    } else {
+      New = CallInst::Create(NF, Args, "", Call);
+      cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
+      cast<CallInst>(New)->setAttributes(NewCallPAL);
+      if (cast<CallInst>(Call)->isTailCall())
+        cast<CallInst>(New)->setTailCall();
+    }
+    New->setDebugLoc(Call->getDebugLoc());
+
+    Args.clear();
+
+    if (!Call->use_empty()) {
+      if (New->getType() == Call->getType()) {
+        // Return type not changed? Just replace users then.
+        Call->replaceAllUsesWith(New);
+        New->takeName(Call);
+      } else if (New->getType()->isVoidTy()) {
+        // Our return value has uses, but they will get removed later on.
+        // Replace by null for now.
+        if (!Call->getType()->isX86_MMXTy())
+          Call->replaceAllUsesWith(Constant::getNullValue(Call->getType()));
+      } else {
+        assert(RetTy->isStructTy() &&
+               "Return type changed, but not into a void. The old return type"
+               " must have been a struct!");
+        Instruction *InsertPt = Call;
+        if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
+          BasicBlock::iterator IP = II->getNormalDest()->begin();
+          while (isa<PHINode>(IP)) ++IP;
+          InsertPt = IP;
+        }
+
+        // We used to return a struct. Instead of doing smart stuff with all the
+        // uses of this struct, we will just rebuild it using
+        // extract/insertvalue chaining and let instcombine clean that up.
+        //
+        // Start out building up our return value from undef
+        Value *RetVal = UndefValue::get(RetTy);
+        for (unsigned i = 0; i != RetCount; ++i)
+          if (NewRetIdxs[i] != -1) {
+            Value *V;
+            if (RetTypes.size() > 1)
+              // We are still returning a struct, so extract the value from our
+              // return value
+              V = ExtractValueInst::Create(New, NewRetIdxs[i], "newret",
+                                           InsertPt);
+            else
+              // We are now returning a single element, so just insert that
+              V = New;
+            // Insert the value at the old position
+            RetVal = InsertValueInst::Create(RetVal, V, i, "oldret", InsertPt);
+          }
+        // Now, replace all uses of the old call instruction with the return
+        // struct we built
+        Call->replaceAllUsesWith(RetVal);
+        New->takeName(Call);
+      }
+    }
+
+    // Finally, remove the old call from the program, reducing the use-count of
+    // F.
+    Call->eraseFromParent();
+  }
+
+  // Since we have now created the new function, splice the body of the old
+  // function right into the new function, leaving the old rotting hulk of the
+  // function empty.
+  NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
+
+  // Loop over the argument list, transferring uses of the old arguments over to
+  // the new arguments, also transferring over the names as well.
+  i = 0;
+  for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(),
+       I2 = NF->arg_begin(); I != E; ++I, ++i)
+    if (ArgAlive[i]) {
+      // If this is a live argument, move the name and users over to the new
+      // version.
+      I->replaceAllUsesWith(I2);
+      I2->takeName(I);
+      ++I2;
+    } else {
+      // If this argument is dead, replace any uses of it with null constants
+      // (these are guaranteed to become unused later on).
+      if (!I->getType()->isX86_MMXTy())
+        I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
+    }
+
+  // If we change the return value of the function we must rewrite any return
+  // instructions.  Check this now.
+  if (F->getReturnType() != NF->getReturnType())
+    for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB)
+      if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
+        Value *RetVal;
+
+        if (NFTy->getReturnType()->isVoidTy()) {
+          RetVal = 0;
+        } else {
+          assert (RetTy->isStructTy());
+          // The original return value was a struct, insert
+          // extractvalue/insertvalue chains to extract only the values we need
+          // to return and insert them into our new result.
+          // This does generate messy code, but we'll let it to instcombine to
+          // clean that up.
+          Value *OldRet = RI->getOperand(0);
+          // Start out building up our return value from undef
+          RetVal = UndefValue::get(NRetTy);
+          for (unsigned i = 0; i != RetCount; ++i)
+            if (NewRetIdxs[i] != -1) {
+              ExtractValueInst *EV = ExtractValueInst::Create(OldRet, i,
+                                                              "oldret", RI);
+              if (RetTypes.size() > 1) {
+                // We're still returning a struct, so reinsert the value into
+                // our new return value at the new index
+
+                RetVal = InsertValueInst::Create(RetVal, EV, NewRetIdxs[i],
+                                                 "newret", RI);
+              } else {
+                // We are now only returning a simple value, so just return the
+                // extracted value.
+                RetVal = EV;
+              }
+            }
+        }
+        // Replace the return instruction with one returning the new return
+        // value (possibly 0 if we became void).
+        ReturnInst::Create(F->getContext(), RetVal, RI);
+        BB->getInstList().erase(RI);
+      }
+
+  // Patch the pointer to LLVM function in debug info descriptor.
+  FunctionDIMap::iterator DI = FunctionDIs.find(F);
+  if (DI != FunctionDIs.end())
+    DI->second.replaceFunction(NF);
+
+  // Now that the old function is dead, delete it.
+  F->eraseFromParent();
+
+  return true;
+}
+
+bool DAE::runOnModule(Module &M) {
+  bool Changed = false;
+
+  // Collect debug info descriptors for functions.
+  CollectFunctionDIs(M);
+
+  // First pass: Do a simple check to see if any functions can have their "..."
+  // removed.  We can do this if they never call va_start.  This loop cannot be
+  // fused with the next loop, because deleting a function invalidates
+  // information computed while surveying other functions.
+  DEBUG(dbgs() << "DAE - Deleting dead varargs\n");
+  for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
+    Function &F = *I++;
+    if (F.getFunctionType()->isVarArg())
+      Changed |= DeleteDeadVarargs(F);
+  }
+
+  // Second phase:loop through the module, determining which arguments are live.
+  // We assume all arguments are dead unless proven otherwise (allowing us to
+  // determine that dead arguments passed into recursive functions are dead).
+  //
+  DEBUG(dbgs() << "DAE - Determining liveness\n");
+  for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
+    SurveyFunction(*I);
+
+  // Now, remove all dead arguments and return values from each function in
+  // turn.
+  for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
+    // Increment now, because the function will probably get removed (ie.
+    // replaced by a new one).
+    Function *F = I++;
+    Changed |= RemoveDeadStuffFromFunction(F);
+  }
+
+  // Finally, look for any unused parameters in functions with non-local
+  // linkage and replace the passed in parameters with undef.
+  for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
+    Function& F = *I;
+
+    Changed |= RemoveDeadArgumentsFromCallers(F);
+  }
+
+  return Changed;
+}