lib/Analysis/LoopInfo.cpp - platform/external/llvm - Gitiles

 //===- LoopInfo.cpp - Natural Loop Calculator -------------------------------=//
 //
 // This file defines the LoopInfo class that is used to identify natural loops
 // and determine the loop depth of various nodes of the CFG.  Note that the
 // loops identified may actually be several natural loops that share the same
 // header node... not just a single natural loop.
 //
 //===----------------------------------------------------------------------===//

 #include "llvm/Analysis/LoopInfo.h"
 #include "llvm/Analysis/Dominators.h"
 #include "llvm/Support/CFG.h"
 #include "llvm/Assembly/Writer.h"
 #include "Support/DepthFirstIterator.h"
 #include <algorithm>

 static RegisterAnalysis<LoopInfo>
 X("loops", "Natural Loop Construction", true);

 //===----------------------------------------------------------------------===//
 // Loop implementation
 //
 bool Loop::contains(const BasicBlock *BB) const {
   return find(Blocks.begin(), Blocks.end(), BB) != Blocks.end();
 }

 bool Loop::isLoopExit(const BasicBlock *BB) const {
   for (BasicBlock::succ_const_iterator SI = succ_begin(BB), SE = succ_end(BB);
        SI != SE; ++SI) {
     if (!contains(*SI))
       return true;
   }
   return false;
 }

 unsigned Loop::getNumBackEdges() const {
   unsigned NumBackEdges = 0;
   BasicBlock *H = getHeader();

   for (std::vector<BasicBlock*>::const_iterator I = Blocks.begin(),
          E = Blocks.end(); I != E; ++I)
     for (BasicBlock::succ_iterator SI = succ_begin(*I), SE = succ_end(*I);
          SI != SE; ++SI)
       if (*SI == H)
 	++NumBackEdges;

   return NumBackEdges;
 }

 void Loop::print(std::ostream &OS, unsigned Depth) const {
   OS << std::string(Depth*2, ' ') << "Loop Containing: ";

   for (unsigned i = 0; i < getBlocks().size(); ++i) {
     if (i) OS << ",";
     WriteAsOperand(OS, getBlocks()[i], false);
   }
   if (!ExitBlocks.empty()) {
     OS << "\tExitBlocks: ";
     for (unsigned i = 0; i < getExitBlocks().size(); ++i) {
       if (i) OS << ",";
       WriteAsOperand(OS, getExitBlocks()[i], false);
     }
   }

   OS << "\n";

   for (unsigned i = 0, e = getSubLoops().size(); i != e; ++i)
     getSubLoops()[i]->print(OS, Depth+2);
 }

 void Loop::dump() const {
   print(std::cerr);
 }


 //===----------------------------------------------------------------------===//
 // LoopInfo implementation
 //
 void LoopInfo::stub() {}

 bool LoopInfo::runOnFunction(Function &) {
   releaseMemory();
   Calculate(getAnalysis<DominatorSet>());    // Update
   return false;
 }

 void LoopInfo::releaseMemory() {
   for (std::vector<Loop*>::iterator I = TopLevelLoops.begin(),
          E = TopLevelLoops.end(); I != E; ++I)
     delete *I;   // Delete all of the loops...

   BBMap.clear();                             // Reset internal state of analysis
   TopLevelLoops.clear();
 }


 void LoopInfo::Calculate(const DominatorSet &DS) {
   BasicBlock *RootNode = DS.getRoot();

   for (df_iterator<BasicBlock*> NI = df_begin(RootNode),
 	 NE = df_end(RootNode); NI != NE; ++NI)
     if (Loop *L = ConsiderForLoop(*NI, DS))
       TopLevelLoops.push_back(L);

   for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
     TopLevelLoops[i]->setLoopDepth(1);
 }

 void LoopInfo::getAnalysisUsage(AnalysisUsage &AU) const {
   AU.setPreservesAll();
   AU.addRequired<DominatorSet>();
 }

 void LoopInfo::print(std::ostream &OS) const {
   for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
     TopLevelLoops[i]->print(OS);
 #if 0
   for (std::map<BasicBlock*, Loop*>::const_iterator I = BBMap.begin(),
          E = BBMap.end(); I != E; ++I)
     OS << "BB '" << I->first->getName() << "' level = "
        << I->second->LoopDepth << "\n";
 #endif
 }

 static bool isNotAlreadyContainedIn(Loop *SubLoop, Loop *ParentLoop) {
   if (SubLoop == 0) return true;
   if (SubLoop == ParentLoop) return false;
   return isNotAlreadyContainedIn(SubLoop->getParentLoop(), ParentLoop);
 }

 Loop *LoopInfo::ConsiderForLoop(BasicBlock *BB, const DominatorSet &DS) {
   if (BBMap.find(BB) != BBMap.end()) return 0;   // Haven't processed this node?

   std::vector<BasicBlock *> TodoStack;

   // Scan the predecessors of BB, checking to see if BB dominates any of
   // them.  This identifies backedges which target this node...
   for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I)
     if (DS.dominates(BB, *I))   // If BB dominates it's predecessor...
       TodoStack.push_back(*I);

   if (TodoStack.empty()) return 0;  // No backedges to this block...

   // Create a new loop to represent this basic block...
   Loop *L = new Loop(BB);
   BBMap[BB] = L;

   while (!TodoStack.empty()) {  // Process all the nodes in the loop
     BasicBlock *X = TodoStack.back();
     TodoStack.pop_back();

     if (!L->contains(X)) {         // As of yet unprocessed??
       // Check to see if this block already belongs to a loop.  If this occurs
       // then we have a case where a loop that is supposed to be a child of the
       // current loop was processed before the current loop.  When this occurs,
       // this child loop gets added to a part of the current loop, making it a
       // sibling to the current loop.  We have to reparent this loop.
       if (Loop *SubLoop = const_cast<Loop*>(getLoopFor(X)))
         if (SubLoop->getHeader() == X && isNotAlreadyContainedIn(SubLoop, L)) {
           // Remove the subloop from it's current parent...
           assert(SubLoop->ParentLoop && SubLoop->ParentLoop != L);
           Loop *SLP = SubLoop->ParentLoop;  // SubLoopParent
           std::vector<Loop*>::iterator I =
             std::find(SLP->SubLoops.begin(), SLP->SubLoops.end(), SubLoop);
           assert(I != SLP->SubLoops.end() && "SubLoop not a child of parent?");
           SLP->SubLoops.erase(I);   // Remove from parent...

           // Add the subloop to THIS loop...
           SubLoop->ParentLoop = L;
           L->SubLoops.push_back(SubLoop);
         }

       // Normal case, add the block to our loop...
       L->Blocks.push_back(X);

       // Add all of the predecessors of X to the end of the work stack...
       TodoStack.insert(TodoStack.end(), pred_begin(X), pred_end(X));
     }
   }

   // If there are any loops nested within this loop, create them now!
   for (std::vector<BasicBlock*>::iterator I = L->Blocks.begin(),
 	 E = L->Blocks.end(); I != E; ++I)
     if (Loop *NewLoop = ConsiderForLoop(*I, DS)) {
       L->SubLoops.push_back(NewLoop);
       NewLoop->ParentLoop = L;
     }

   // Add the basic blocks that comprise this loop to the BBMap so that this
   // loop can be found for them.
   //
   for (std::vector<BasicBlock*>::iterator I = L->Blocks.begin(),
 	 E = L->Blocks.end(); I != E; ++I) {
     std::map<BasicBlock*, Loop*>::iterator BBMI = BBMap.lower_bound(*I);
     if (BBMI == BBMap.end() || BBMI->first != *I)  // Not in map yet...
       BBMap.insert(BBMI, std::make_pair(*I, L));   // Must be at this level
   }

   // Now that we have a list of all of the child loops of this loop, check to
   // see if any of them should actually be nested inside of each other.  We can
   // accidentally pull loops our of their parents, so we must make sure to
   // organize the loop nests correctly now.
   {
     std::map<BasicBlock*, Loop*> ContainingLoops;
     for (unsigned i = 0; i != L->SubLoops.size(); ++i) {
       Loop *Child = L->SubLoops[i];
       assert(Child->getParentLoop() == L && "Not proper child loop?");

       if (Loop *ContainingLoop = ContainingLoops[Child->getHeader()]) {
         // If there is already a loop which contains this loop, move this loop
         // into the containing loop.
         MoveSiblingLoopInto(Child, ContainingLoop);
         --i;  // The loop got removed from the SubLoops list.
       } else {
         // This is currently considered to be a top-level loop.  Check to see if
         // any of the contained blocks are loop headers for subloops we have
         // already processed.
         for (unsigned b = 0, e = Child->Blocks.size(); b != e; ++b) {
           Loop *&BlockLoop = ContainingLoops[Child->Blocks[b]];
           if (BlockLoop == 0) {   // Child block not processed yet...
             BlockLoop = Child;
           } else if (BlockLoop != Child) {
             Loop *SubLoop = BlockLoop;
             // Reparent all of the blocks which used to belong to BlockLoops
             for (unsigned j = 0, e = SubLoop->Blocks.size(); j != e; ++j)
               ContainingLoops[SubLoop->Blocks[j]] = Child;

             // There is already a loop which contains this block, that means
             // that we should reparent the loop which the block is currently
             // considered to belong to to be a child of this loop.
             MoveSiblingLoopInto(SubLoop, Child);
             --i;  // We just shrunk the SubLoops list.
           }
         }
       }
     }
   }

   // Now that we know all of the blocks that make up this loop, see if there are
   // any branches to outside of the loop... building the ExitBlocks list.
   for (std::vector<BasicBlock*>::iterator BI = L->Blocks.begin(),
          BE = L->Blocks.end(); BI != BE; ++BI)
     for (succ_iterator I = succ_begin(*BI), E = succ_end(*BI); I != E; ++I)
       if (!L->contains(*I))               // Not in current loop?
         L->ExitBlocks.push_back(*I);      // It must be an exit block...

   return L;
 }

 /// MoveSiblingLoopInto - This method moves the NewChild loop to live inside of
 /// the NewParent Loop, instead of being a sibling of it.
 void LoopInfo::MoveSiblingLoopInto(Loop *NewChild, Loop *NewParent) {
   Loop *OldParent = NewChild->getParentLoop();
   assert(OldParent && OldParent == NewParent->getParentLoop() &&
          NewChild != NewParent && "Not sibling loops!");

   // Remove NewChild from being a child of OldParent
   std::vector<Loop*>::iterator I =
     std::find(OldParent->SubLoops.begin(), OldParent->SubLoops.end(), NewChild);
   assert(I != OldParent->SubLoops.end() && "Parent fields incorrect??");
   OldParent->SubLoops.erase(I);   // Remove from parent's subloops list
   NewChild->ParentLoop = 0;

   InsertLoopInto(NewChild, NewParent);
 }

 /// InsertLoopInto - This inserts loop L into the specified parent loop.  If the
 /// parent loop contains a loop which should contain L, the loop gets inserted
 /// into L instead.
 void LoopInfo::InsertLoopInto(Loop *L, Loop *Parent) {
   BasicBlock *LHeader = L->getHeader();
   assert(Parent->contains(LHeader) && "This loop should not be inserted here!");

   // Check to see if it belongs in a child loop...
   for (unsigned i = 0, e = Parent->SubLoops.size(); i != e; ++i)
     if (Parent->SubLoops[i]->contains(LHeader)) {
       InsertLoopInto(L, Parent->SubLoops[i]);
       return;
     }

   // If not, insert it here!
   Parent->SubLoops.push_back(L);
   L->ParentLoop = Parent;
 }


 /// getLoopPreheader - If there is a preheader for this loop, return it.  A
 /// loop has a preheader if there is only one edge to the header of the loop
 /// from outside of the loop.  If this is the case, the block branching to the
 /// header of the loop is the preheader node.  The "preheaders" pass can be
 /// "Required" to ensure that there is always a preheader node for every loop.
 ///
 /// This method returns null if there is no preheader for the loop (either
 /// because the loop is dead or because multiple blocks branch to the header
 /// node of this loop).
 ///
 BasicBlock *Loop::getLoopPreheader() const {
   // Keep track of nodes outside the loop branching to the header...
   BasicBlock *Out = 0;

   // Loop over the predecessors of the header node...
   BasicBlock *Header = getHeader();
   for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
        PI != PE; ++PI)
     if (!contains(*PI)) {     // If the block is not in the loop...
       if (Out && Out != *PI)
         return 0;             // Multiple predecessors outside the loop
       Out = *PI;
     }

   // Make sure there is only one exit out of the preheader...
   succ_iterator SI = succ_begin(Out);
   ++SI;
   if (SI != succ_end(Out))
     return 0;  // Multiple exits from the block, must not be a preheader.


   // If there is exactly one preheader, return it.  If there was zero, then Out
   // is still null.
   return Out;
 }

 /// addBasicBlockToLoop - This function is used by other analyses to update loop
 /// information.  NewBB is set to be a new member of the current loop.  Because
 /// of this, it is added as a member of all parent loops, and is added to the
 /// specified LoopInfo object as being in the current basic block.  It is not
 /// valid to replace the loop header with this method.
 ///
 void Loop::addBasicBlockToLoop(BasicBlock *NewBB, LoopInfo &LI) {
   assert(LI[getHeader()] == this && "Incorrect LI specified for this loop!");
   assert(NewBB && "Cannot add a null basic block to the loop!");
   assert(LI[NewBB] == 0 && "BasicBlock already in the loop!");

   // Add the loop mapping to the LoopInfo object...
   LI.BBMap[NewBB] = this;

   // Add the basic block to this loop and all parent loops...
   Loop *L = this;
   while (L) {
     L->Blocks.push_back(NewBB);
     L = L->getParentLoop();
   }
 }

 /// changeExitBlock - This method is used to update loop information.  All
 /// instances of the specified Old basic block are removed from the exit list
 /// and replaced with New.
 ///
 void Loop::changeExitBlock(BasicBlock *Old, BasicBlock *New) {
   assert(Old != New && "Cannot changeExitBlock to the same thing!");
   assert(Old && New && "Cannot changeExitBlock to or from a null node!");
   assert(hasExitBlock(Old) && "Old exit block not found!");
   std::vector<BasicBlock*>::iterator
     I = std::find(ExitBlocks.begin(), ExitBlocks.end(), Old);
   while (I != ExitBlocks.end()) {
     *I = New;
     I = std::find(I+1, ExitBlocks.end(), Old);
   }
 }
	//===- LoopInfo.cpp - Natural Loop Calculator -------------------------------=//
	//
	// This file defines the LoopInfo class that is used to identify natural loops
	// and determine the loop depth of various nodes of the CFG. Note that the
	// loops identified may actually be several natural loops that share the same
	// header node... not just a single natural loop.
	//
	//===----------------------------------------------------------------------===//

	#include "llvm/Analysis/LoopInfo.h"
	#include "llvm/Analysis/Dominators.h"
	#include "llvm/Support/CFG.h"
	#include "llvm/Assembly/Writer.h"
	#include "Support/DepthFirstIterator.h"
	#include <algorithm>

	static RegisterAnalysis<LoopInfo>
	X("loops", "Natural Loop Construction", true);

	//===----------------------------------------------------------------------===//
	// Loop implementation
	//
	bool Loop::contains(const BasicBlock *BB) const {
	return find(Blocks.begin(), Blocks.end(), BB) != Blocks.end();
	}

	bool Loop::isLoopExit(const BasicBlock *BB) const {
	for (BasicBlock::succ_const_iterator SI = succ_begin(BB), SE = succ_end(BB);
	SI != SE; ++SI) {
	if (!contains(*SI))
	return true;
	}
	return false;
	}

	unsigned Loop::getNumBackEdges() const {
	unsigned NumBackEdges = 0;
	BasicBlock *H = getHeader();

	for (std::vector<BasicBlock*>::const_iterator I = Blocks.begin(),
	E = Blocks.end(); I != E; ++I)
	for (BasicBlock::succ_iterator SI = succ_begin(I), SE = succ_end(I);
	SI != SE; ++SI)
	if (*SI == H)
	++NumBackEdges;

	return NumBackEdges;
	}

	void Loop::print(std::ostream &OS, unsigned Depth) const {
	OS << std::string(Depth*2, ' ') << "Loop Containing: ";

	for (unsigned i = 0; i < getBlocks().size(); ++i) {
	if (i) OS << ",";
	WriteAsOperand(OS, getBlocks()[i], false);
	}
	if (!ExitBlocks.empty()) {
	OS << "\tExitBlocks: ";
	for (unsigned i = 0; i < getExitBlocks().size(); ++i) {
	if (i) OS << ",";
	WriteAsOperand(OS, getExitBlocks()[i], false);
	}
	}

	OS << "\n";

	for (unsigned i = 0, e = getSubLoops().size(); i != e; ++i)
	getSubLoops()[i]->print(OS, Depth+2);
	}

	void Loop::dump() const {
	print(std::cerr);
	}


	//===----------------------------------------------------------------------===//
	// LoopInfo implementation
	//
	void LoopInfo::stub() {}

	bool LoopInfo::runOnFunction(Function &) {
	releaseMemory();
	Calculate(getAnalysis<DominatorSet>()); // Update
	return false;
	}

	void LoopInfo::releaseMemory() {
	for (std::vector<Loop*>::iterator I = TopLevelLoops.begin(),
	E = TopLevelLoops.end(); I != E; ++I)
	delete *I; // Delete all of the loops...

	BBMap.clear(); // Reset internal state of analysis
	TopLevelLoops.clear();
	}


	void LoopInfo::Calculate(const DominatorSet &DS) {
	BasicBlock *RootNode = DS.getRoot();

	for (df_iterator<BasicBlock*> NI = df_begin(RootNode),
	NE = df_end(RootNode); NI != NE; ++NI)
	if (Loop L = ConsiderForLoop(NI, DS))
	TopLevelLoops.push_back(L);

	for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
	TopLevelLoops[i]->setLoopDepth(1);
	}

	void LoopInfo::getAnalysisUsage(AnalysisUsage &AU) const {
	AU.setPreservesAll();
	AU.addRequired<DominatorSet>();
	}

	void LoopInfo::print(std::ostream &OS) const {
	for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
	TopLevelLoops[i]->print(OS);
	#if 0
	for (std::map<BasicBlock, Loop>::const_iterator I = BBMap.begin(),
	E = BBMap.end(); I != E; ++I)
	OS << "BB '" << I->first->getName() << "' level = "
	<< I->second->LoopDepth << "\n";
	#endif
	}

	static bool isNotAlreadyContainedIn(Loop SubLoop, Loop ParentLoop) {
	if (SubLoop == 0) return true;
	if (SubLoop == ParentLoop) return false;
	return isNotAlreadyContainedIn(SubLoop->getParentLoop(), ParentLoop);
	}

	Loop LoopInfo::ConsiderForLoop(BasicBlock BB, const DominatorSet &DS) {
	if (BBMap.find(BB) != BBMap.end()) return 0; // Haven't processed this node?

	std::vector<BasicBlock *> TodoStack;

	// Scan the predecessors of BB, checking to see if BB dominates any of
	// them. This identifies backedges which target this node...
	for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I)
	if (DS.dominates(BB, *I)) // If BB dominates it's predecessor...
	TodoStack.push_back(*I);

	if (TodoStack.empty()) return 0; // No backedges to this block...

	// Create a new loop to represent this basic block...
	Loop *L = new Loop(BB);
	BBMap[BB] = L;

	while (!TodoStack.empty()) { // Process all the nodes in the loop
	BasicBlock *X = TodoStack.back();
	TodoStack.pop_back();

	if (!L->contains(X)) { // As of yet unprocessed??
	// Check to see if this block already belongs to a loop. If this occurs
	// then we have a case where a loop that is supposed to be a child of the
	// current loop was processed before the current loop. When this occurs,
	// this child loop gets added to a part of the current loop, making it a
	// sibling to the current loop. We have to reparent this loop.
	if (Loop SubLoop = const_cast<Loop>(getLoopFor(X)))
	if (SubLoop->getHeader() == X && isNotAlreadyContainedIn(SubLoop, L)) {
	// Remove the subloop from it's current parent...
	assert(SubLoop->ParentLoop && SubLoop->ParentLoop != L);
	Loop *SLP = SubLoop->ParentLoop; // SubLoopParent
	std::vector<Loop*>::iterator I =
	std::find(SLP->SubLoops.begin(), SLP->SubLoops.end(), SubLoop);
	assert(I != SLP->SubLoops.end() && "SubLoop not a child of parent?");
	SLP->SubLoops.erase(I); // Remove from parent...

	// Add the subloop to THIS loop...
	SubLoop->ParentLoop = L;
	L->SubLoops.push_back(SubLoop);
	}

	// Normal case, add the block to our loop...
	L->Blocks.push_back(X);

	// Add all of the predecessors of X to the end of the work stack...
	TodoStack.insert(TodoStack.end(), pred_begin(X), pred_end(X));
	}
	}

	// If there are any loops nested within this loop, create them now!
	for (std::vector<BasicBlock*>::iterator I = L->Blocks.begin(),
	E = L->Blocks.end(); I != E; ++I)
	if (Loop NewLoop = ConsiderForLoop(I, DS)) {
	L->SubLoops.push_back(NewLoop);
	NewLoop->ParentLoop = L;
	}

	// Add the basic blocks that comprise this loop to the BBMap so that this
	// loop can be found for them.
	//
	for (std::vector<BasicBlock*>::iterator I = L->Blocks.begin(),
	E = L->Blocks.end(); I != E; ++I) {
	std::map<BasicBlock, Loop>::iterator BBMI = BBMap.lower_bound(*I);
	if (BBMI == BBMap.end() \|\| BBMI->first != *I) // Not in map yet...
	BBMap.insert(BBMI, std::make_pair(*I, L)); // Must be at this level
	}

	// Now that we have a list of all of the child loops of this loop, check to
	// see if any of them should actually be nested inside of each other. We can
	// accidentally pull loops our of their parents, so we must make sure to
	// organize the loop nests correctly now.
	{
	std::map<BasicBlock, Loop> ContainingLoops;
	for (unsigned i = 0; i != L->SubLoops.size(); ++i) {
	Loop *Child = L->SubLoops[i];
	assert(Child->getParentLoop() == L && "Not proper child loop?");

	if (Loop *ContainingLoop = ContainingLoops[Child->getHeader()]) {
	// If there is already a loop which contains this loop, move this loop
	// into the containing loop.
	MoveSiblingLoopInto(Child, ContainingLoop);
	--i; // The loop got removed from the SubLoops list.
	} else {
	// This is currently considered to be a top-level loop. Check to see if
	// any of the contained blocks are loop headers for subloops we have
	// already processed.
	for (unsigned b = 0, e = Child->Blocks.size(); b != e; ++b) {
	Loop *&BlockLoop = ContainingLoops[Child->Blocks[b]];
	if (BlockLoop == 0) { // Child block not processed yet...
	BlockLoop = Child;
	} else if (BlockLoop != Child) {
	Loop *SubLoop = BlockLoop;
	// Reparent all of the blocks which used to belong to BlockLoops
	for (unsigned j = 0, e = SubLoop->Blocks.size(); j != e; ++j)
	ContainingLoops[SubLoop->Blocks[j]] = Child;

	// There is already a loop which contains this block, that means
	// that we should reparent the loop which the block is currently
	// considered to belong to to be a child of this loop.
	MoveSiblingLoopInto(SubLoop, Child);
	--i; // We just shrunk the SubLoops list.
	}
	}
	}
	}
	}

	// Now that we know all of the blocks that make up this loop, see if there are
	// any branches to outside of the loop... building the ExitBlocks list.
	for (std::vector<BasicBlock*>::iterator BI = L->Blocks.begin(),
	BE = L->Blocks.end(); BI != BE; ++BI)
	for (succ_iterator I = succ_begin(BI), E = succ_end(BI); I != E; ++I)
	if (!L->contains(*I)) // Not in current loop?
	L->ExitBlocks.push_back(*I); // It must be an exit block...

	return L;
	}

	/// MoveSiblingLoopInto - This method moves the NewChild loop to live inside of
	/// the NewParent Loop, instead of being a sibling of it.
	void LoopInfo::MoveSiblingLoopInto(Loop NewChild, Loop NewParent) {
	Loop *OldParent = NewChild->getParentLoop();
	assert(OldParent && OldParent == NewParent->getParentLoop() &&
	NewChild != NewParent && "Not sibling loops!");

	// Remove NewChild from being a child of OldParent
	std::vector<Loop*>::iterator I =
	std::find(OldParent->SubLoops.begin(), OldParent->SubLoops.end(), NewChild);
	assert(I != OldParent->SubLoops.end() && "Parent fields incorrect??");
	OldParent->SubLoops.erase(I); // Remove from parent's subloops list
	NewChild->ParentLoop = 0;

	InsertLoopInto(NewChild, NewParent);
	}

	/// InsertLoopInto - This inserts loop L into the specified parent loop. If the
	/// parent loop contains a loop which should contain L, the loop gets inserted
	/// into L instead.
	void LoopInfo::InsertLoopInto(Loop L, Loop Parent) {
	BasicBlock *LHeader = L->getHeader();
	assert(Parent->contains(LHeader) && "This loop should not be inserted here!");

	// Check to see if it belongs in a child loop...
	for (unsigned i = 0, e = Parent->SubLoops.size(); i != e; ++i)
	if (Parent->SubLoops[i]->contains(LHeader)) {
	InsertLoopInto(L, Parent->SubLoops[i]);
	return;
	}

	// If not, insert it here!
	Parent->SubLoops.push_back(L);
	L->ParentLoop = Parent;
	}



	/// getLoopPreheader - If there is a preheader for this loop, return it. A
	/// loop has a preheader if there is only one edge to the header of the loop
	/// from outside of the loop. If this is the case, the block branching to the
	/// header of the loop is the preheader node. The "preheaders" pass can be
	/// "Required" to ensure that there is always a preheader node for every loop.
	///
	/// This method returns null if there is no preheader for the loop (either
	/// because the loop is dead or because multiple blocks branch to the header
	/// node of this loop).
	///
	BasicBlock *Loop::getLoopPreheader() const {
	// Keep track of nodes outside the loop branching to the header...
	BasicBlock *Out = 0;

	// Loop over the predecessors of the header node...
	BasicBlock *Header = getHeader();
	for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
	PI != PE; ++PI)
	if (!contains(*PI)) { // If the block is not in the loop...
	if (Out && Out != *PI)
	return 0; // Multiple predecessors outside the loop
	Out = *PI;
	}

	// Make sure there is only one exit out of the preheader...
	succ_iterator SI = succ_begin(Out);
	++SI;
	if (SI != succ_end(Out))
	return 0; // Multiple exits from the block, must not be a preheader.


	// If there is exactly one preheader, return it. If there was zero, then Out
	// is still null.
	return Out;
	}

	/// addBasicBlockToLoop - This function is used by other analyses to update loop
	/// information. NewBB is set to be a new member of the current loop. Because
	/// of this, it is added as a member of all parent loops, and is added to the
	/// specified LoopInfo object as being in the current basic block. It is not
	/// valid to replace the loop header with this method.
	///
	void Loop::addBasicBlockToLoop(BasicBlock *NewBB, LoopInfo &LI) {
	assert(LI[getHeader()] == this && "Incorrect LI specified for this loop!");
	assert(NewBB && "Cannot add a null basic block to the loop!");
	assert(LI[NewBB] == 0 && "BasicBlock already in the loop!");

	// Add the loop mapping to the LoopInfo object...
	LI.BBMap[NewBB] = this;

	// Add the basic block to this loop and all parent loops...
	Loop *L = this;
	while (L) {
	L->Blocks.push_back(NewBB);
	L = L->getParentLoop();
	}
	}

	/// changeExitBlock - This method is used to update loop information. All
	/// instances of the specified Old basic block are removed from the exit list
	/// and replaced with New.
	///
	void Loop::changeExitBlock(BasicBlock Old, BasicBlock New) {
	assert(Old != New && "Cannot changeExitBlock to the same thing!");
	assert(Old && New && "Cannot changeExitBlock to or from a null node!");
	assert(hasExitBlock(Old) && "Old exit block not found!");
	std::vector<BasicBlock*>::iterator
	I = std::find(ExitBlocks.begin(), ExitBlocks.end(), Old);
	while (I != ExitBlocks.end()) {
	*I = New;
	I = std::find(I+1, ExitBlocks.end(), Old);
	}
	}