lib/Transforms/Scalar/DCE.cpp - platform/external/llvm - Gitiles

 //===- DCE.cpp - Code to perform dead code elimination --------------------===//
 //
 // This file implements dead code elimination and basic block merging.
 //
 // Specifically, this:
 //   * removes definitions with no uses
 //   * removes basic blocks with no predecessors
 //   * merges a basic block into its predecessor if there is only one and the
 //     predecessor only has one successor.
 //   * Eliminates PHI nodes for basic blocks with a single predecessor
 //   * Eliminates a basic block that only contains an unconditional branch
 //   * Eliminates function prototypes that are not referenced
 //
 // TODO: This should REALLY be worklist driven instead of iterative.  Right now,
 // we scan linearly through values, removing unused ones as we go.  The problem
 // is that this may cause other earlier values to become unused.  To make sure
 // that we get them all, we iterate until things stop changing.  Instead, when
 // removing a value, recheck all of its operands to see if they are now unused.
 // Piece of cake, and more efficient as well.
 //
 // Note, this is not trivial, because we have to worry about invalidating
 // iterators.  :(
 //
 //===----------------------------------------------------------------------===//

 #include "llvm/Transforms/Scalar/DCE.h"
 #include "llvm/Module.h"
 #include "llvm/GlobalVariable.h"
 #include "llvm/Function.h"
 #include "llvm/BasicBlock.h"
 #include "llvm/iTerminators.h"
 #include "llvm/iPHINode.h"
 #include "llvm/ConstantVals.h"
 #include "llvm/Support/CFG.h"
 #include "llvm/Pass.h"
 #include "Support/STLExtras.h"
 #include <algorithm>

 // dceInstruction - Inspect the instruction at *BBI and figure out if it's
 // [trivially] dead.  If so, remove the instruction and update the iterator
 // to point to the instruction that immediately succeeded the original
 // instruction.
 //
 bool dceInstruction(BasicBlock::InstListType &BBIL,
                     BasicBlock::iterator &BBI) {
   // Look for un"used" definitions...
   if ((*BBI)->use_empty() && !(*BBI)->hasSideEffects() &&
       !isa<TerminatorInst>(*BBI)) {
     delete BBIL.remove(BBI);   // Bye bye
     return true;
   }
   return false;
 }

 static inline bool RemoveUnusedDefs(BasicBlock::InstListType &Vals) {
   bool Changed = false;
   for (BasicBlock::InstListType::iterator DI = Vals.begin();
        DI != Vals.end(); )
     if (dceInstruction(Vals, DI))
       Changed = true;
     else
       ++DI;
   return Changed;
 }

 struct DeadInstElimination : public BasicBlockPass {
   virtual bool runOnBasicBlock(BasicBlock *BB) {
     return RemoveUnusedDefs(BB->getInstList());
   }
 };

 Pass *createDeadInstEliminationPass() {
   return new DeadInstElimination();
 }

 // RemoveSingularPHIs - This removes PHI nodes from basic blocks that have only
 // a single predecessor.  This means that the PHI node must only have a single
 // RHS value and can be eliminated.
 //
 // This routine is very simple because we know that PHI nodes must be the first
 // things in a basic block, if they are present.
 //
 static bool RemoveSingularPHIs(BasicBlock *BB) {
   pred_iterator PI(pred_begin(BB));
   if (PI == pred_end(BB) || ++PI != pred_end(BB))
     return false;   // More than one predecessor...

   Instruction *I = BB->front();
   if (!isa<PHINode>(I)) return false;  // No PHI nodes

   //cerr << "Killing PHIs from " << BB;
   //cerr << "Pred #0 = " << *pred_begin(BB);

   //cerr << "Function == " << BB->getParent();

   do {
     PHINode *PN = cast<PHINode>(I);
     assert(PN->getNumOperands() == 2 && "PHI node should only have one value!");
     Value *V = PN->getOperand(0);

     PN->replaceAllUsesWith(V);      // Replace PHI node with its single value.
     delete BB->getInstList().remove(BB->begin());

     I = BB->front();
   } while (isa<PHINode>(I));

   return true;  // Yes, we nuked at least one phi node
 }

 static void ReplaceUsesWithConstant(Instruction *I) {
   // Make all users of this instruction reference the constant instead
   I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
 }

 // PropogatePredecessors - This gets "Succ" ready to have the predecessors from
 // "BB".  This is a little tricky because "Succ" has PHI nodes, which need to
 // have extra slots added to them to hold the merge edges from BB's
 // predecessors.  This function returns true (failure) if the Succ BB already
 // has a predecessor that is a predecessor of BB.
 //
 // Assumption: Succ is the single successor for BB.
 //
 static bool PropogatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
   assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
   assert(isa<PHINode>(Succ->front()) && "Only works on PHId BBs!");

   // If there is more than one predecessor, and there are PHI nodes in
   // the successor, then we need to add incoming edges for the PHI nodes
   //
   const std::vector<BasicBlock*> BBPreds(pred_begin(BB), pred_end(BB));

   // Check to see if one of the predecessors of BB is already a predecessor of
   // Succ.  If so, we cannot do the transformation!
   //
   for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ);
        PI != PE; ++PI) {
     if (find(BBPreds.begin(), BBPreds.end(), *PI) != BBPreds.end())
       return true;
   }

   BasicBlock::iterator I = Succ->begin();
   do {                     // Loop over all of the PHI nodes in the successor BB
     PHINode *PN = cast<PHINode>(*I);
     Value *OldVal = PN->removeIncomingValue(BB);
     assert(OldVal && "No entry in PHI for Pred BB!");

     for (std::vector<BasicBlock*>::const_iterator PredI = BBPreds.begin(),
 	   End = BBPreds.end(); PredI != End; ++PredI) {
       // Add an incoming value for each of the new incoming values...
       PN->addIncoming(OldVal, *PredI);
     }

     ++I;
   } while (isa<PHINode>(*I));
   return false;
 }


 // SimplifyCFG - This function is used to do simplification of a CFG.  For
 // example, it adjusts branches to branches to eliminate the extra hop, it
 // eliminates unreachable basic blocks, and does other "peephole" optimization
 // of the CFG.  It returns true if a modification was made, and returns an
 // iterator that designates the first element remaining after the block that
 // was deleted.
 //
 // WARNING:  The entry node of a function may not be simplified.
 //
 bool SimplifyCFG(Function::iterator &BBIt) {
   BasicBlock *BB = *BBIt;
   Function *M = BB->getParent();

   assert(BB && BB->getParent() && "Block not embedded in function!");
   assert(BB->getTerminator() && "Degenerate basic block encountered!");
   assert(BB->getParent()->front() != BB && "Can't Simplify entry block!");


   // Remove basic blocks that have no predecessors... which are unreachable.
   if (pred_begin(BB) == pred_end(BB) &&
       !BB->hasConstantReferences()) {
     //cerr << "Removing BB: \n" << BB;

     // Loop through all of our successors and make sure they know that one
     // of their predecessors is going away.
     for_each(succ_begin(BB), succ_end(BB),
 	     std::bind2nd(std::mem_fun(&BasicBlock::removePredecessor), BB));

     while (!BB->empty()) {
       Instruction *I = BB->back();
       // If this instruction is used, replace uses with an arbitrary
       // constant value.  Because control flow can't get here, we don't care
       // what we replace the value with.  Note that since this block is
       // unreachable, and all values contained within it must dominate their
       // uses, that all uses will eventually be removed.
       if (!I->use_empty()) ReplaceUsesWithConstant(I);

       // Remove the instruction from the basic block
       delete BB->getInstList().pop_back();
     }
     delete M->getBasicBlocks().remove(BBIt);
     return true;
   }

   // Check to see if this block has no instructions and only a single
   // successor.  If so, replace block references with successor.
   succ_iterator SI(succ_begin(BB));
   if (SI != succ_end(BB) && ++SI == succ_end(BB)) {  // One succ?
     if (BB->front()->isTerminator()) {   // Terminator is the only instruction!
       BasicBlock *Succ = *succ_begin(BB); // There is exactly one successor
       //cerr << "Killing Trivial BB: \n" << BB;

       if (Succ != BB) {   // Arg, don't hurt infinite loops!
         // If our successor has PHI nodes, then we need to update them to
         // include entries for BB's predecessors, not for BB itself.
         // Be careful though, if this transformation fails (returns true) then
         // we cannot do this transformation!
         //
 	if (!isa<PHINode>(Succ->front()) ||
             !PropogatePredecessorsForPHIs(BB, Succ)) {

           BB->replaceAllUsesWith(Succ);
           BB = M->getBasicBlocks().remove(BBIt);

           if (BB->hasName() && !Succ->hasName())  // Transfer name if we can
             Succ->setName(BB->getName());
           delete BB;                              // Delete basic block

           //cerr << "Function after removal: \n" << M;
           return true;
 	}
       }
     }
   }

   // Merge basic blocks into their predecessor if there is only one pred,
   // and if there is only one successor of the predecessor.
   pred_iterator PI(pred_begin(BB));
   if (PI != pred_end(BB) && *PI != BB &&    // Not empty?  Not same BB?
       ++PI == pred_end(BB) && !BB->hasConstantReferences()) {
     BasicBlock *Pred = *pred_begin(BB);
     TerminatorInst *Term = Pred->getTerminator();
     assert(Term != 0 && "malformed basic block without terminator!");

     // Does the predecessor block only have a single successor?
     succ_iterator SI(succ_begin(Pred));
     if (++SI == succ_end(Pred)) {
       //cerr << "Merging: " << BB << "into: " << Pred;

       // Delete the unconditianal branch from the predecessor...
       BasicBlock::iterator DI = Pred->end();
       assert(Pred->getTerminator() &&
 	     "Degenerate basic block encountered!");  // Empty bb???
       delete Pred->getInstList().remove(--DI);        // Destroy uncond branch

       // Move all definitions in the succecessor to the predecessor...
       while (!BB->empty()) {
 	DI = BB->begin();
 	Instruction *Def = BB->getInstList().remove(DI); // Remove from front
 	Pred->getInstList().push_back(Def);              // Add to end...
       }

       // Remove basic block from the function... and advance iterator to the
       // next valid block...
       BB = M->getBasicBlocks().remove(BBIt);

       // Make all PHI nodes that refered to BB now refer to Pred as their
       // source...
       BB->replaceAllUsesWith(Pred);

       // Inherit predecessors name if it exists...
       if (BB->hasName() && !Pred->hasName()) Pred->setName(BB->getName());

       delete BB; // You ARE the weakest link... goodbye
       return true;
     }
   }

   return false;
 }

 static bool DoDCEPass(Function *F) {
   Function::iterator BBIt, BBEnd = F->end();
   if (F->begin() == BBEnd) return false;  // Nothing to do
   bool Changed = false;

   // Loop through now and remove instructions that have no uses...
   for (BBIt = F->begin(); BBIt != BBEnd; ++BBIt) {
     Changed |= RemoveUnusedDefs((*BBIt)->getInstList());
     Changed |= RemoveSingularPHIs(*BBIt);
   }

   // Loop over all of the basic blocks (except the first one) and remove them
   // if they are unneeded...
   //
   for (BBIt = F->begin(), ++BBIt; BBIt != F->end(); ) {
     if (SimplifyCFG(BBIt)) {
       Changed = true;
     } else {
       ++BBIt;
     }
   }

   return Changed;
 }

 // Remove unused global values - This removes unused global values of no
 // possible value.  This currently includes unused function prototypes and
 // unitialized global variables.
 //
 static bool RemoveUnusedGlobalValues(Module *Mod) {
   bool Changed = false;

   for (Module::iterator MI = Mod->begin(); MI != Mod->end(); ) {
     Function *Meth = *MI;
     if (Meth->isExternal() && Meth->use_size() == 0) {
       // No references to prototype?
       //cerr << "Removing function proto: " << Meth->getName() << endl;
       delete Mod->getFunctionList().remove(MI);  // Remove prototype
       // Remove moves iterator to point to the next one automatically
       Changed = true;
     } else {
       ++MI;                                    // Skip prototype in use.
     }
   }

   for (Module::giterator GI = Mod->gbegin(); GI != Mod->gend(); ) {
     GlobalVariable *GV = *GI;
     if (!GV->hasInitializer() && GV->use_size() == 0) {
       // No references to uninitialized global variable?
       //cerr << "Removing global var: " << GV->getName() << endl;
       delete Mod->getGlobalList().remove(GI);
       // Remove moves iterator to point to the next one automatically
       Changed = true;
     } else {
       ++GI;
     }
   }

   return Changed;
 }

 namespace {
   struct DeadCodeElimination : public FunctionPass {

     // Pass Interface...
     virtual bool doInitialization(Module *M) {
       return RemoveUnusedGlobalValues(M);
     }

     // It is possible that we may require multiple passes over the code to fully
     // eliminate dead code.  Iterate until we are done.
     //
     virtual bool runOnFunction(Function *F) {
       bool Changed = false;
       while (DoDCEPass(F)) Changed = true;
       return Changed;
     }

     virtual bool doFinalization(Module *M) {
       return RemoveUnusedGlobalValues(M);
     }
   };
 }

 Pass *createDeadCodeEliminationPass() {
   return new DeadCodeElimination();
 }
	//===- DCE.cpp - Code to perform dead code elimination --------------------===//
	//
	// This file implements dead code elimination and basic block merging.
	//
	// Specifically, this:
	// * removes definitions with no uses
	// * removes basic blocks with no predecessors
	// * merges a basic block into its predecessor if there is only one and the
	// predecessor only has one successor.
	// * Eliminates PHI nodes for basic blocks with a single predecessor
	// * Eliminates a basic block that only contains an unconditional branch
	// * Eliminates function prototypes that are not referenced
	//
	// TODO: This should REALLY be worklist driven instead of iterative. Right now,
	// we scan linearly through values, removing unused ones as we go. The problem
	// is that this may cause other earlier values to become unused. To make sure
	// that we get them all, we iterate until things stop changing. Instead, when
	// removing a value, recheck all of its operands to see if they are now unused.
	// Piece of cake, and more efficient as well.
	//
	// Note, this is not trivial, because we have to worry about invalidating
	// iterators. :(
	//
	//===----------------------------------------------------------------------===//

	#include "llvm/Transforms/Scalar/DCE.h"
	#include "llvm/Module.h"
	#include "llvm/GlobalVariable.h"
	#include "llvm/Function.h"
	#include "llvm/BasicBlock.h"
	#include "llvm/iTerminators.h"
	#include "llvm/iPHINode.h"
	#include "llvm/ConstantVals.h"
	#include "llvm/Support/CFG.h"
	#include "llvm/Pass.h"
	#include "Support/STLExtras.h"
	#include <algorithm>

	// dceInstruction - Inspect the instruction at *BBI and figure out if it's
	// [trivially] dead. If so, remove the instruction and update the iterator
	// to point to the instruction that immediately succeeded the original
	// instruction.
	//
	bool dceInstruction(BasicBlock::InstListType &BBIL,
	BasicBlock::iterator &BBI) {
	// Look for un"used" definitions...
	if ((BBI)->use_empty() && !(BBI)->hasSideEffects() &&
	!isa<TerminatorInst>(*BBI)) {
	delete BBIL.remove(BBI); // Bye bye
	return true;
	}
	return false;
	}

	static inline bool RemoveUnusedDefs(BasicBlock::InstListType &Vals) {
	bool Changed = false;
	for (BasicBlock::InstListType::iterator DI = Vals.begin();
	DI != Vals.end(); )
	if (dceInstruction(Vals, DI))
	Changed = true;
	else
	++DI;
	return Changed;
	}

	struct DeadInstElimination : public BasicBlockPass {
	virtual bool runOnBasicBlock(BasicBlock *BB) {
	return RemoveUnusedDefs(BB->getInstList());
	}
	};

	Pass *createDeadInstEliminationPass() {
	return new DeadInstElimination();
	}

	// RemoveSingularPHIs - This removes PHI nodes from basic blocks that have only
	// a single predecessor. This means that the PHI node must only have a single
	// RHS value and can be eliminated.
	//
	// This routine is very simple because we know that PHI nodes must be the first
	// things in a basic block, if they are present.
	//
	static bool RemoveSingularPHIs(BasicBlock *BB) {
	pred_iterator PI(pred_begin(BB));
	if (PI == pred_end(BB) \|\| ++PI != pred_end(BB))
	return false; // More than one predecessor...

	Instruction *I = BB->front();
	if (!isa<PHINode>(I)) return false; // No PHI nodes

	//cerr << "Killing PHIs from " << BB;
	//cerr << "Pred #0 = " << *pred_begin(BB);

	//cerr << "Function == " << BB->getParent();

	do {
	PHINode *PN = cast<PHINode>(I);
	assert(PN->getNumOperands() == 2 && "PHI node should only have one value!");
	Value *V = PN->getOperand(0);

	PN->replaceAllUsesWith(V); // Replace PHI node with its single value.
	delete BB->getInstList().remove(BB->begin());

	I = BB->front();
	} while (isa<PHINode>(I));

	return true; // Yes, we nuked at least one phi node
	}

	static void ReplaceUsesWithConstant(Instruction *I) {
	// Make all users of this instruction reference the constant instead
	I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
	}

	// PropogatePredecessors - This gets "Succ" ready to have the predecessors from
	// "BB". This is a little tricky because "Succ" has PHI nodes, which need to
	// have extra slots added to them to hold the merge edges from BB's
	// predecessors. This function returns true (failure) if the Succ BB already
	// has a predecessor that is a predecessor of BB.
	//
	// Assumption: Succ is the single successor for BB.
	//
	static bool PropogatePredecessorsForPHIs(BasicBlock BB, BasicBlock Succ) {
	assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
	assert(isa<PHINode>(Succ->front()) && "Only works on PHId BBs!");

	// If there is more than one predecessor, and there are PHI nodes in
	// the successor, then we need to add incoming edges for the PHI nodes
	//
	const std::vector<BasicBlock*> BBPreds(pred_begin(BB), pred_end(BB));

	// Check to see if one of the predecessors of BB is already a predecessor of
	// Succ. If so, we cannot do the transformation!
	//
	for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ);
	PI != PE; ++PI) {
	if (find(BBPreds.begin(), BBPreds.end(), *PI) != BBPreds.end())
	return true;
	}

	BasicBlock::iterator I = Succ->begin();
	do { // Loop over all of the PHI nodes in the successor BB
	PHINode PN = cast<PHINode>(I);
	Value *OldVal = PN->removeIncomingValue(BB);
	assert(OldVal && "No entry in PHI for Pred BB!");

	for (std::vector<BasicBlock*>::const_iterator PredI = BBPreds.begin(),
	End = BBPreds.end(); PredI != End; ++PredI) {
	// Add an incoming value for each of the new incoming values...
	PN->addIncoming(OldVal, *PredI);
	}

	++I;
	} while (isa<PHINode>(*I));
	return false;
	}


	// SimplifyCFG - This function is used to do simplification of a CFG. For
	// example, it adjusts branches to branches to eliminate the extra hop, it
	// eliminates unreachable basic blocks, and does other "peephole" optimization
	// of the CFG. It returns true if a modification was made, and returns an
	// iterator that designates the first element remaining after the block that
	// was deleted.
	//
	// WARNING: The entry node of a function may not be simplified.
	//
	bool SimplifyCFG(Function::iterator &BBIt) {
	BasicBlock BB = BBIt;
	Function *M = BB->getParent();

	assert(BB && BB->getParent() && "Block not embedded in function!");
	assert(BB->getTerminator() && "Degenerate basic block encountered!");
	assert(BB->getParent()->front() != BB && "Can't Simplify entry block!");


	// Remove basic blocks that have no predecessors... which are unreachable.
	if (pred_begin(BB) == pred_end(BB) &&
	!BB->hasConstantReferences()) {
	//cerr << "Removing BB: \n" << BB;

	// Loop through all of our successors and make sure they know that one
	// of their predecessors is going away.
	for_each(succ_begin(BB), succ_end(BB),
	std::bind2nd(std::mem_fun(&BasicBlock::removePredecessor), BB));

	while (!BB->empty()) {
	Instruction *I = BB->back();
	// If this instruction is used, replace uses with an arbitrary
	// constant value. Because control flow can't get here, we don't care
	// what we replace the value with. Note that since this block is
	// unreachable, and all values contained within it must dominate their
	// uses, that all uses will eventually be removed.
	if (!I->use_empty()) ReplaceUsesWithConstant(I);

	// Remove the instruction from the basic block
	delete BB->getInstList().pop_back();
	}
	delete M->getBasicBlocks().remove(BBIt);
	return true;
	}

	// Check to see if this block has no instructions and only a single
	// successor. If so, replace block references with successor.
	succ_iterator SI(succ_begin(BB));
	if (SI != succ_end(BB) && ++SI == succ_end(BB)) { // One succ?
	if (BB->front()->isTerminator()) { // Terminator is the only instruction!
	BasicBlock Succ = succ_begin(BB); // There is exactly one successor
	//cerr << "Killing Trivial BB: \n" << BB;

	if (Succ != BB) { // Arg, don't hurt infinite loops!
	// If our successor has PHI nodes, then we need to update them to
	// include entries for BB's predecessors, not for BB itself.
	// Be careful though, if this transformation fails (returns true) then
	// we cannot do this transformation!
	//
	if (!isa<PHINode>(Succ->front()) \|\|
	!PropogatePredecessorsForPHIs(BB, Succ)) {

	BB->replaceAllUsesWith(Succ);
	BB = M->getBasicBlocks().remove(BBIt);

	if (BB->hasName() && !Succ->hasName()) // Transfer name if we can
	Succ->setName(BB->getName());
	delete BB; // Delete basic block

	//cerr << "Function after removal: \n" << M;
	return true;
	}
	}
	}
	}

	// Merge basic blocks into their predecessor if there is only one pred,
	// and if there is only one successor of the predecessor.
	pred_iterator PI(pred_begin(BB));
	if (PI != pred_end(BB) && *PI != BB && // Not empty? Not same BB?
	++PI == pred_end(BB) && !BB->hasConstantReferences()) {
	BasicBlock Pred = pred_begin(BB);
	TerminatorInst *Term = Pred->getTerminator();
	assert(Term != 0 && "malformed basic block without terminator!");

	// Does the predecessor block only have a single successor?
	succ_iterator SI(succ_begin(Pred));
	if (++SI == succ_end(Pred)) {
	//cerr << "Merging: " << BB << "into: " << Pred;

	// Delete the unconditianal branch from the predecessor...
	BasicBlock::iterator DI = Pred->end();
	assert(Pred->getTerminator() &&
	"Degenerate basic block encountered!"); // Empty bb???
	delete Pred->getInstList().remove(--DI); // Destroy uncond branch

	// Move all definitions in the succecessor to the predecessor...
	while (!BB->empty()) {
	DI = BB->begin();
	Instruction *Def = BB->getInstList().remove(DI); // Remove from front
	Pred->getInstList().push_back(Def); // Add to end...
	}

	// Remove basic block from the function... and advance iterator to the
	// next valid block...
	BB = M->getBasicBlocks().remove(BBIt);

	// Make all PHI nodes that refered to BB now refer to Pred as their
	// source...
	BB->replaceAllUsesWith(Pred);

	// Inherit predecessors name if it exists...
	if (BB->hasName() && !Pred->hasName()) Pred->setName(BB->getName());

	delete BB; // You ARE the weakest link... goodbye
	return true;
	}
	}

	return false;
	}

	static bool DoDCEPass(Function *F) {
	Function::iterator BBIt, BBEnd = F->end();
	if (F->begin() == BBEnd) return false; // Nothing to do
	bool Changed = false;

	// Loop through now and remove instructions that have no uses...
	for (BBIt = F->begin(); BBIt != BBEnd; ++BBIt) {
	Changed \|= RemoveUnusedDefs((*BBIt)->getInstList());
	Changed \|= RemoveSingularPHIs(*BBIt);
	}

	// Loop over all of the basic blocks (except the first one) and remove them
	// if they are unneeded...
	//
	for (BBIt = F->begin(), ++BBIt; BBIt != F->end(); ) {
	if (SimplifyCFG(BBIt)) {
	Changed = true;
	} else {
	++BBIt;
	}
	}

	return Changed;
	}

	// Remove unused global values - This removes unused global values of no
	// possible value. This currently includes unused function prototypes and
	// unitialized global variables.
	//
	static bool RemoveUnusedGlobalValues(Module *Mod) {
	bool Changed = false;

	for (Module::iterator MI = Mod->begin(); MI != Mod->end(); ) {
	Function Meth = MI;
	if (Meth->isExternal() && Meth->use_size() == 0) {
	// No references to prototype?
	//cerr << "Removing function proto: " << Meth->getName() << endl;
	delete Mod->getFunctionList().remove(MI); // Remove prototype
	// Remove moves iterator to point to the next one automatically
	Changed = true;
	} else {
	++MI; // Skip prototype in use.
	}
	}

	for (Module::giterator GI = Mod->gbegin(); GI != Mod->gend(); ) {
	GlobalVariable GV = GI;
	if (!GV->hasInitializer() && GV->use_size() == 0) {
	// No references to uninitialized global variable?
	//cerr << "Removing global var: " << GV->getName() << endl;
	delete Mod->getGlobalList().remove(GI);
	// Remove moves iterator to point to the next one automatically
	Changed = true;
	} else {
	++GI;
	}
	}

	return Changed;
	}

	namespace {
	struct DeadCodeElimination : public FunctionPass {

	// Pass Interface...
	virtual bool doInitialization(Module *M) {
	return RemoveUnusedGlobalValues(M);
	}

	// It is possible that we may require multiple passes over the code to fully
	// eliminate dead code. Iterate until we are done.
	//
	virtual bool runOnFunction(Function *F) {
	bool Changed = false;
	while (DoDCEPass(F)) Changed = true;
	return Changed;
	}

	virtual bool doFinalization(Module *M) {
	return RemoveUnusedGlobalValues(M);
	}
	};
	}

	Pass *createDeadCodeEliminationPass() {
	return new DeadCodeElimination();
	}