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IndVarSimplify.cpp

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00001 //===- IndVarSimplify.cpp - Induction Variable Elimination ----------------===//
00002 //
00003 //                     The LLVM Compiler Infrastructure
00004 //
00005 // This file was developed by the LLVM research group and is distributed under
00006 // the University of Illinois Open Source License. See LICENSE.TXT for details.
00007 //
00008 //===----------------------------------------------------------------------===//
00009 //
00010 // This transformation analyzes and transforms the induction variables (and
00011 // computations derived from them) into simpler forms suitable for subsequent
00012 // analysis and transformation.
00013 //
00014 // This transformation make the following changes to each loop with an
00015 // identifiable induction variable:
00016 //   1. All loops are transformed to have a SINGLE canonical induction variable
00017 //      which starts at zero and steps by one.
00018 //   2. The canonical induction variable is guaranteed to be the first PHI node
00019 //      in the loop header block.
00020 //   3. Any pointer arithmetic recurrences are raised to use array subscripts.
00021 //
00022 // If the trip count of a loop is computable, this pass also makes the following
00023 // changes:
00024 //   1. The exit condition for the loop is canonicalized to compare the
00025 //      induction value against the exit value.  This turns loops like:
00026 //        'for (i = 7; i*i < 1000; ++i)' into 'for (i = 0; i != 25; ++i)'
00027 //   2. Any use outside of the loop of an expression derived from the indvar
00028 //      is changed to compute the derived value outside of the loop, eliminating
00029 //      the dependence on the exit value of the induction variable.  If the only
00030 //      purpose of the loop is to compute the exit value of some derived
00031 //      expression, this transformation will make the loop dead.
00032 //
00033 // This transformation should be followed by strength reduction after all of the
00034 // desired loop transformations have been performed.  Additionally, on targets
00035 // where it is profitable, the loop could be transformed to count down to zero
00036 // (the "do loop" optimization).
00037 //
00038 //===----------------------------------------------------------------------===//
00039 
00040 #include "llvm/Transforms/Scalar.h"
00041 #include "llvm/BasicBlock.h"
00042 #include "llvm/Constants.h"
00043 #include "llvm/Instructions.h"
00044 #include "llvm/Type.h"
00045 #include "llvm/Analysis/ScalarEvolutionExpander.h"
00046 #include "llvm/Analysis/LoopInfo.h"
00047 #include "llvm/Support/CFG.h"
00048 #include "llvm/Support/GetElementPtrTypeIterator.h"
00049 #include "llvm/Transforms/Utils/Local.h"
00050 #include "llvm/Support/CommandLine.h"
00051 #include "llvm/ADT/Statistic.h"
00052 using namespace llvm;
00053 
00054 namespace {
00055   Statistic<> NumRemoved ("indvars", "Number of aux indvars removed");
00056   Statistic<> NumPointer ("indvars", "Number of pointer indvars promoted");
00057   Statistic<> NumInserted("indvars", "Number of canonical indvars added");
00058   Statistic<> NumReplaced("indvars", "Number of exit values replaced");
00059   Statistic<> NumLFTR    ("indvars", "Number of loop exit tests replaced");
00060 
00061   class IndVarSimplify : public FunctionPass {
00062     LoopInfo        *LI;
00063     ScalarEvolution *SE;
00064     bool Changed;
00065   public:
00066     virtual bool runOnFunction(Function &) {
00067       LI = &getAnalysis<LoopInfo>();
00068       SE = &getAnalysis<ScalarEvolution>();
00069       Changed = false;
00070 
00071       // Induction Variables live in the header nodes of loops
00072       for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
00073         runOnLoop(*I);
00074       return Changed;
00075     }
00076 
00077     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
00078       AU.addRequiredID(LoopSimplifyID);
00079       AU.addRequired<ScalarEvolution>();
00080       AU.addRequired<LoopInfo>();
00081       AU.addPreservedID(LoopSimplifyID);
00082       AU.setPreservesCFG();
00083     }
00084   private:
00085     void runOnLoop(Loop *L);
00086     void EliminatePointerRecurrence(PHINode *PN, BasicBlock *Preheader,
00087                                     std::set<Instruction*> &DeadInsts);
00088     void LinearFunctionTestReplace(Loop *L, SCEV *IterationCount,
00089                                    SCEVExpander &RW);
00090     void RewriteLoopExitValues(Loop *L);
00091 
00092     void DeleteTriviallyDeadInstructions(std::set<Instruction*> &Insts);
00093   };
00094   RegisterOpt<IndVarSimplify> X("indvars", "Canonicalize Induction Variables");
00095 }
00096 
00097 FunctionPass *llvm::createIndVarSimplifyPass() {
00098   return new IndVarSimplify();
00099 }
00100 
00101 /// DeleteTriviallyDeadInstructions - If any of the instructions is the
00102 /// specified set are trivially dead, delete them and see if this makes any of
00103 /// their operands subsequently dead.
00104 void IndVarSimplify::
00105 DeleteTriviallyDeadInstructions(std::set<Instruction*> &Insts) {
00106   while (!Insts.empty()) {
00107     Instruction *I = *Insts.begin();
00108     Insts.erase(Insts.begin());
00109     if (isInstructionTriviallyDead(I)) {
00110       for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
00111         if (Instruction *U = dyn_cast<Instruction>(I->getOperand(i)))
00112           Insts.insert(U);
00113       SE->deleteInstructionFromRecords(I);
00114       I->eraseFromParent();
00115       Changed = true;
00116     }
00117   }
00118 }
00119 
00120 
00121 /// EliminatePointerRecurrence - Check to see if this is a trivial GEP pointer
00122 /// recurrence.  If so, change it into an integer recurrence, permitting
00123 /// analysis by the SCEV routines.
00124 void IndVarSimplify::EliminatePointerRecurrence(PHINode *PN,
00125                                                 BasicBlock *Preheader,
00126                                             std::set<Instruction*> &DeadInsts) {
00127   assert(PN->getNumIncomingValues() == 2 && "Noncanonicalized loop!");
00128   unsigned PreheaderIdx = PN->getBasicBlockIndex(Preheader);
00129   unsigned BackedgeIdx = PreheaderIdx^1;
00130   if (GetElementPtrInst *GEPI =
00131           dyn_cast<GetElementPtrInst>(PN->getIncomingValue(BackedgeIdx)))
00132     if (GEPI->getOperand(0) == PN) {
00133       assert(GEPI->getNumOperands() == 2 && "GEP types must match!");
00134 
00135       // Okay, we found a pointer recurrence.  Transform this pointer
00136       // recurrence into an integer recurrence.  Compute the value that gets
00137       // added to the pointer at every iteration.
00138       Value *AddedVal = GEPI->getOperand(1);
00139 
00140       // Insert a new integer PHI node into the top of the block.
00141       PHINode *NewPhi = new PHINode(AddedVal->getType(),
00142                                     PN->getName()+".rec", PN);
00143       NewPhi->addIncoming(Constant::getNullValue(NewPhi->getType()), Preheader);
00144 
00145       // Create the new add instruction.
00146       Value *NewAdd = BinaryOperator::createAdd(NewPhi, AddedVal,
00147                                                 GEPI->getName()+".rec", GEPI);
00148       NewPhi->addIncoming(NewAdd, PN->getIncomingBlock(BackedgeIdx));
00149 
00150       // Update the existing GEP to use the recurrence.
00151       GEPI->setOperand(0, PN->getIncomingValue(PreheaderIdx));
00152 
00153       // Update the GEP to use the new recurrence we just inserted.
00154       GEPI->setOperand(1, NewAdd);
00155 
00156       // If the incoming value is a constant expr GEP, try peeling out the array
00157       // 0 index if possible to make things simpler.
00158       if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GEPI->getOperand(0)))
00159         if (CE->getOpcode() == Instruction::GetElementPtr) {
00160           unsigned NumOps = CE->getNumOperands();
00161           assert(NumOps > 1 && "CE folding didn't work!");
00162           if (CE->getOperand(NumOps-1)->isNullValue()) {
00163             // Check to make sure the last index really is an array index.
00164             gep_type_iterator GTI = gep_type_begin(CE);
00165             for (unsigned i = 1, e = CE->getNumOperands()-1;
00166                  i != e; ++i, ++GTI)
00167               /*empty*/;
00168             if (isa<SequentialType>(*GTI)) {
00169               // Pull the last index out of the constant expr GEP.
00170               std::vector<Value*> CEIdxs(CE->op_begin()+1, CE->op_end()-1);
00171               Constant *NCE = ConstantExpr::getGetElementPtr(CE->getOperand(0),
00172                                                              CEIdxs);
00173               GetElementPtrInst *NGEPI =
00174                 new GetElementPtrInst(NCE, Constant::getNullValue(Type::IntTy),
00175                                       NewAdd, GEPI->getName(), GEPI);
00176               GEPI->replaceAllUsesWith(NGEPI);
00177               GEPI->eraseFromParent();
00178               GEPI = NGEPI;
00179             }
00180           }
00181         }
00182 
00183 
00184       // Finally, if there are any other users of the PHI node, we must
00185       // insert a new GEP instruction that uses the pre-incremented version
00186       // of the induction amount.
00187       if (!PN->use_empty()) {
00188         BasicBlock::iterator InsertPos = PN; ++InsertPos;
00189         while (isa<PHINode>(InsertPos)) ++InsertPos;
00190         std::string Name = PN->getName(); PN->setName("");
00191         Value *PreInc =
00192           new GetElementPtrInst(PN->getIncomingValue(PreheaderIdx),
00193                                 std::vector<Value*>(1, NewPhi), Name,
00194                                 InsertPos);
00195         PN->replaceAllUsesWith(PreInc);
00196       }
00197 
00198       // Delete the old PHI for sure, and the GEP if its otherwise unused.
00199       DeadInsts.insert(PN);
00200 
00201       ++NumPointer;
00202       Changed = true;
00203     }
00204 }
00205 
00206 /// LinearFunctionTestReplace - This method rewrites the exit condition of the
00207 /// loop to be a canonical != comparison against the incremented loop induction
00208 /// variable.  This pass is able to rewrite the exit tests of any loop where the
00209 /// SCEV analysis can determine a loop-invariant trip count of the loop, which
00210 /// is actually a much broader range than just linear tests.
00211 void IndVarSimplify::LinearFunctionTestReplace(Loop *L, SCEV *IterationCount,
00212                                                SCEVExpander &RW) {
00213   // Find the exit block for the loop.  We can currently only handle loops with
00214   // a single exit.
00215   std::vector<BasicBlock*> ExitBlocks;
00216   L->getExitBlocks(ExitBlocks);
00217   if (ExitBlocks.size() != 1) return;
00218   BasicBlock *ExitBlock = ExitBlocks[0];
00219 
00220   // Make sure there is only one predecessor block in the loop.
00221   BasicBlock *ExitingBlock = 0;
00222   for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock);
00223        PI != PE; ++PI)
00224     if (L->contains(*PI)) {
00225       if (ExitingBlock == 0)
00226         ExitingBlock = *PI;
00227       else
00228         return;  // Multiple exits from loop to this block.
00229     }
00230   assert(ExitingBlock && "Loop info is broken");
00231 
00232   if (!isa<BranchInst>(ExitingBlock->getTerminator()))
00233     return;  // Can't rewrite non-branch yet
00234   BranchInst *BI = cast<BranchInst>(ExitingBlock->getTerminator());
00235   assert(BI->isConditional() && "Must be conditional to be part of loop!");
00236 
00237   std::set<Instruction*> InstructionsToDelete;
00238   if (Instruction *Cond = dyn_cast<Instruction>(BI->getCondition()))
00239     InstructionsToDelete.insert(Cond);
00240 
00241   // If the exiting block is not the same as the backedge block, we must compare
00242   // against the preincremented value, otherwise we prefer to compare against
00243   // the post-incremented value.
00244   BasicBlock *Header = L->getHeader();
00245   pred_iterator HPI = pred_begin(Header);
00246   assert(HPI != pred_end(Header) && "Loop with zero preds???");
00247   if (!L->contains(*HPI)) ++HPI;
00248   assert(HPI != pred_end(Header) && L->contains(*HPI) &&
00249          "No backedge in loop?");
00250 
00251   SCEVHandle TripCount = IterationCount;
00252   Value *IndVar;
00253   if (*HPI == ExitingBlock) {
00254     // The IterationCount expression contains the number of times that the
00255     // backedge actually branches to the loop header.  This is one less than the
00256     // number of times the loop executes, so add one to it.
00257     Constant *OneC = ConstantInt::get(IterationCount->getType(), 1);
00258     TripCount = SCEVAddExpr::get(IterationCount, SCEVUnknown::get(OneC));
00259     IndVar = L->getCanonicalInductionVariableIncrement();
00260   } else {
00261     // We have to use the preincremented value...
00262     IndVar = L->getCanonicalInductionVariable();
00263   }
00264 
00265   // Expand the code for the iteration count into the preheader of the loop.
00266   BasicBlock *Preheader = L->getLoopPreheader();
00267   Value *ExitCnt = RW.expandCodeFor(TripCount, Preheader->getTerminator(),
00268                                     IndVar->getType());
00269 
00270   // Insert a new setne or seteq instruction before the branch.
00271   Instruction::BinaryOps Opcode;
00272   if (L->contains(BI->getSuccessor(0)))
00273     Opcode = Instruction::SetNE;
00274   else
00275     Opcode = Instruction::SetEQ;
00276 
00277   Value *Cond = new SetCondInst(Opcode, IndVar, ExitCnt, "exitcond", BI);
00278   BI->setCondition(Cond);
00279   ++NumLFTR;
00280   Changed = true;
00281 
00282   DeleteTriviallyDeadInstructions(InstructionsToDelete);
00283 }
00284 
00285 
00286 /// RewriteLoopExitValues - Check to see if this loop has a computable
00287 /// loop-invariant execution count.  If so, this means that we can compute the
00288 /// final value of any expressions that are recurrent in the loop, and
00289 /// substitute the exit values from the loop into any instructions outside of
00290 /// the loop that use the final values of the current expressions.
00291 void IndVarSimplify::RewriteLoopExitValues(Loop *L) {
00292   BasicBlock *Preheader = L->getLoopPreheader();
00293 
00294   // Scan all of the instructions in the loop, looking at those that have
00295   // extra-loop users and which are recurrences.
00296   SCEVExpander Rewriter(*SE, *LI);
00297 
00298   // We insert the code into the preheader of the loop if the loop contains
00299   // multiple exit blocks, or in the exit block if there is exactly one.
00300   BasicBlock *BlockToInsertInto;
00301   std::vector<BasicBlock*> ExitBlocks;
00302   L->getExitBlocks(ExitBlocks);
00303   if (ExitBlocks.size() == 1)
00304     BlockToInsertInto = ExitBlocks[0];
00305   else
00306     BlockToInsertInto = Preheader;
00307   BasicBlock::iterator InsertPt = BlockToInsertInto->begin();
00308   while (isa<PHINode>(InsertPt)) ++InsertPt;
00309 
00310   bool HasConstantItCount = isa<SCEVConstant>(SE->getIterationCount(L));
00311 
00312   std::set<Instruction*> InstructionsToDelete;
00313 
00314   for (unsigned i = 0, e = L->getBlocks().size(); i != e; ++i)
00315     if (LI->getLoopFor(L->getBlocks()[i]) == L) {  // Not in a subloop...
00316       BasicBlock *BB = L->getBlocks()[i];
00317       for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;) {
00318         if (I->getType()->isInteger()) {      // Is an integer instruction
00319           SCEVHandle SH = SE->getSCEV(I);
00320           if (SH->hasComputableLoopEvolution(L) ||    // Varies predictably
00321               HasConstantItCount) {
00322             // Find out if this predictably varying value is actually used
00323             // outside of the loop.  "extra" as opposed to "intra".
00324             std::vector<Instruction*> ExtraLoopUsers;
00325             for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
00326                  UI != E; ++UI) {
00327               Instruction *User = cast<Instruction>(*UI);
00328               if (!L->contains(User->getParent())) {
00329                 // If this is a PHI node in the exit block and we're inserting,
00330                 // into the exit block, it must have a single entry.  In this
00331                 // case, we can't insert the code after the PHI and have the PHI
00332                 // still use it.  Instead, don't insert the the PHI.
00333                 if (PHINode *PN = dyn_cast<PHINode>(User)) {
00334                   // FIXME: This is a case where LCSSA pessimizes code, this
00335                   // should be fixed better.
00336                   if (PN->getNumOperands() == 2 && 
00337                       PN->getParent() == BlockToInsertInto)
00338                     continue;
00339                 }
00340                 ExtraLoopUsers.push_back(User);
00341               }
00342             }
00343             
00344             if (!ExtraLoopUsers.empty()) {
00345               // Okay, this instruction has a user outside of the current loop
00346               // and varies predictably in this loop.  Evaluate the value it
00347               // contains when the loop exits, and insert code for it.
00348               SCEVHandle ExitValue = SE->getSCEVAtScope(I, L->getParentLoop());
00349               if (!isa<SCEVCouldNotCompute>(ExitValue)) {
00350                 Changed = true;
00351                 ++NumReplaced;
00352                 // Remember the next instruction.  The rewriter can move code
00353                 // around in some cases.
00354                 BasicBlock::iterator NextI = I; ++NextI;
00355 
00356                 Value *NewVal = Rewriter.expandCodeFor(ExitValue, InsertPt,
00357                                                        I->getType());
00358 
00359                 // Rewrite any users of the computed value outside of the loop
00360                 // with the newly computed value.
00361                 for (unsigned i = 0, e = ExtraLoopUsers.size(); i != e; ++i) {
00362                   PHINode* PN = dyn_cast<PHINode>(ExtraLoopUsers[i]);
00363                   if (PN && PN->getNumOperands() == 2 &&
00364                       !L->contains(PN->getParent())) {
00365                     // We're dealing with an LCSSA Phi.  Handle it specially.
00366                     Instruction* LCSSAInsertPt = BlockToInsertInto->begin();
00367                     
00368                     Instruction* NewInstr = dyn_cast<Instruction>(NewVal);
00369                     if (NewInstr && !isa<PHINode>(NewInstr) &&
00370                         !L->contains(NewInstr->getParent()))
00371                       for (unsigned j = 0; j < NewInstr->getNumOperands(); ++j){
00372                         Instruction* PredI = 
00373                                  dyn_cast<Instruction>(NewInstr->getOperand(j));
00374                         if (PredI && L->contains(PredI->getParent())) {
00375                           PHINode* NewLCSSA = new PHINode(PredI->getType(),
00376                                                     PredI->getName() + ".lcssa",
00377                                                     LCSSAInsertPt);
00378                           NewLCSSA->addIncoming(PredI, 
00379                                      BlockToInsertInto->getSinglePredecessor());
00380                         
00381                           NewInstr->replaceUsesOfWith(PredI, NewLCSSA);
00382                         }
00383                       }
00384                     
00385                     PN->replaceAllUsesWith(NewVal);
00386                     PN->eraseFromParent();
00387                   } else {
00388                     ExtraLoopUsers[i]->replaceUsesOfWith(I, NewVal);
00389                   }
00390                 }
00391 
00392                 // If this instruction is dead now, schedule it to be removed.
00393                 if (I->use_empty())
00394                   InstructionsToDelete.insert(I);
00395                 I = NextI;
00396                 continue;  // Skip the ++I
00397               }
00398             }
00399           }
00400         }
00401 
00402         // Next instruction.  Continue instruction skips this.
00403         ++I;
00404       }
00405     }
00406 
00407   DeleteTriviallyDeadInstructions(InstructionsToDelete);
00408 }
00409 
00410 
00411 void IndVarSimplify::runOnLoop(Loop *L) {
00412   // First step.  Check to see if there are any trivial GEP pointer recurrences.
00413   // If there are, change them into integer recurrences, permitting analysis by
00414   // the SCEV routines.
00415   //
00416   BasicBlock *Header    = L->getHeader();
00417   BasicBlock *Preheader = L->getLoopPreheader();
00418 
00419   std::set<Instruction*> DeadInsts;
00420   for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
00421     PHINode *PN = cast<PHINode>(I);
00422     if (isa<PointerType>(PN->getType()))
00423       EliminatePointerRecurrence(PN, Preheader, DeadInsts);
00424   }
00425 
00426   if (!DeadInsts.empty())
00427     DeleteTriviallyDeadInstructions(DeadInsts);
00428 
00429 
00430   // Next, transform all loops nesting inside of this loop.
00431   for (LoopInfo::iterator I = L->begin(), E = L->end(); I != E; ++I)
00432     runOnLoop(*I);
00433 
00434   // Check to see if this loop has a computable loop-invariant execution count.
00435   // If so, this means that we can compute the final value of any expressions
00436   // that are recurrent in the loop, and substitute the exit values from the
00437   // loop into any instructions outside of the loop that use the final values of
00438   // the current expressions.
00439   //
00440   SCEVHandle IterationCount = SE->getIterationCount(L);
00441   if (!isa<SCEVCouldNotCompute>(IterationCount))
00442     RewriteLoopExitValues(L);
00443 
00444   // Next, analyze all of the induction variables in the loop, canonicalizing
00445   // auxillary induction variables.
00446   std::vector<std::pair<PHINode*, SCEVHandle> > IndVars;
00447 
00448   for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
00449     PHINode *PN = cast<PHINode>(I);
00450     if (PN->getType()->isInteger()) {  // FIXME: when we have fast-math, enable!
00451       SCEVHandle SCEV = SE->getSCEV(PN);
00452       if (SCEV->hasComputableLoopEvolution(L))
00453         // FIXME: It is an extremely bad idea to indvar substitute anything more
00454         // complex than affine induction variables.  Doing so will put expensive
00455         // polynomial evaluations inside of the loop, and the str reduction pass
00456         // currently can only reduce affine polynomials.  For now just disable
00457         // indvar subst on anything more complex than an affine addrec.
00458         if (SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(SCEV))
00459           if (AR->isAffine())
00460             IndVars.push_back(std::make_pair(PN, SCEV));
00461     }
00462   }
00463 
00464   // If there are no induction variables in the loop, there is nothing more to
00465   // do.
00466   if (IndVars.empty()) {
00467     // Actually, if we know how many times the loop iterates, lets insert a
00468     // canonical induction variable to help subsequent passes.
00469     if (!isa<SCEVCouldNotCompute>(IterationCount)) {
00470       SCEVExpander Rewriter(*SE, *LI);
00471       Rewriter.getOrInsertCanonicalInductionVariable(L,
00472                                                      IterationCount->getType());
00473       LinearFunctionTestReplace(L, IterationCount, Rewriter);
00474     }
00475     return;
00476   }
00477 
00478   // Compute the type of the largest recurrence expression.
00479   //
00480   const Type *LargestType = IndVars[0].first->getType();
00481   bool DifferingSizes = false;
00482   for (unsigned i = 1, e = IndVars.size(); i != e; ++i) {
00483     const Type *Ty = IndVars[i].first->getType();
00484     DifferingSizes |= Ty->getPrimitiveSize() != LargestType->getPrimitiveSize();
00485     if (Ty->getPrimitiveSize() > LargestType->getPrimitiveSize())
00486       LargestType = Ty;
00487   }
00488 
00489   // Create a rewriter object which we'll use to transform the code with.
00490   SCEVExpander Rewriter(*SE, *LI);
00491 
00492   // Now that we know the largest of of the induction variables in this loop,
00493   // insert a canonical induction variable of the largest size.
00494   LargestType = LargestType->getUnsignedVersion();
00495   Value *IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L,LargestType);
00496   ++NumInserted;
00497   Changed = true;
00498 
00499   if (!isa<SCEVCouldNotCompute>(IterationCount))
00500     LinearFunctionTestReplace(L, IterationCount, Rewriter);
00501 
00502   // Now that we have a canonical induction variable, we can rewrite any
00503   // recurrences in terms of the induction variable.  Start with the auxillary
00504   // induction variables, and recursively rewrite any of their uses.
00505   BasicBlock::iterator InsertPt = Header->begin();
00506   while (isa<PHINode>(InsertPt)) ++InsertPt;
00507 
00508   // If there were induction variables of other sizes, cast the primary
00509   // induction variable to the right size for them, avoiding the need for the
00510   // code evaluation methods to insert induction variables of different sizes.
00511   if (DifferingSizes) {
00512     bool InsertedSizes[17] = { false };
00513     InsertedSizes[LargestType->getPrimitiveSize()] = true;
00514     for (unsigned i = 0, e = IndVars.size(); i != e; ++i)
00515       if (!InsertedSizes[IndVars[i].first->getType()->getPrimitiveSize()]) {
00516         PHINode *PN = IndVars[i].first;
00517         InsertedSizes[PN->getType()->getPrimitiveSize()] = true;
00518         Instruction *New = new CastInst(IndVar,
00519                                         PN->getType()->getUnsignedVersion(),
00520                                         "indvar", InsertPt);
00521         Rewriter.addInsertedValue(New, SE->getSCEV(New));
00522       }
00523   }
00524 
00525   // If there were induction variables of other sizes, cast the primary
00526   // induction variable to the right size for them, avoiding the need for the
00527   // code evaluation methods to insert induction variables of different sizes.
00528   std::map<unsigned, Value*> InsertedSizes;
00529   while (!IndVars.empty()) {
00530     PHINode *PN = IndVars.back().first;
00531     Value *NewVal = Rewriter.expandCodeFor(IndVars.back().second, InsertPt,
00532                                            PN->getType());
00533     std::string Name = PN->getName();
00534     PN->setName("");
00535     NewVal->setName(Name);
00536 
00537     // Replace the old PHI Node with the inserted computation.
00538     PN->replaceAllUsesWith(NewVal);
00539     DeadInsts.insert(PN);
00540     IndVars.pop_back();
00541     ++NumRemoved;
00542     Changed = true;
00543   }
00544 
00545 #if 0
00546   // Now replace all derived expressions in the loop body with simpler
00547   // expressions.
00548   for (unsigned i = 0, e = L->getBlocks().size(); i != e; ++i)
00549     if (LI->getLoopFor(L->getBlocks()[i]) == L) {  // Not in a subloop...
00550       BasicBlock *BB = L->getBlocks()[i];
00551       for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
00552         if (I->getType()->isInteger() &&      // Is an integer instruction
00553             !I->use_empty() &&
00554             !Rewriter.isInsertedInstruction(I)) {
00555           SCEVHandle SH = SE->getSCEV(I);
00556           Value *V = Rewriter.expandCodeFor(SH, I, I->getType());
00557           if (V != I) {
00558             if (isa<Instruction>(V)) {
00559               std::string Name = I->getName();
00560               I->setName("");
00561               V->setName(Name);
00562             }
00563             I->replaceAllUsesWith(V);
00564             DeadInsts.insert(I);
00565             ++NumRemoved;
00566             Changed = true;
00567           }
00568         }
00569     }
00570 #endif
00571 
00572   DeleteTriviallyDeadInstructions(DeadInsts);
00573 }