//===- IndVarSimplify.cpp - Induction Variable Elimination ----------------===//
+//
+// The LLVM Compiler Infrastructure
//
-// InductionVariableSimplify - Transform induction variables in a program
-// to all use a single cannonical induction variable per loop.
+// This file was developed by the LLVM research group and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This transformation analyzes and transforms the induction variables (and
+// computations derived from them) into simpler forms suitable for subsequent
+// analysis and transformation.
+//
+// This transformation make the following changes to each loop with an
+// identifiable induction variable:
+// 1. All loops are transformed to have a SINGLE canonical induction variable
+// which starts at zero and steps by one.
+// 2. The canonical induction variable is guaranteed to be the first PHI node
+// in the loop header block.
+// 3. Any pointer arithmetic recurrences are raised to use array subscripts.
+//
+// If the trip count of a loop is computable, this pass also makes the following
+// changes:
+// 1. The exit condition for the loop is canonicalized to compare the
+// induction value against the exit value. This turns loops like:
+// 'for (i = 7; i*i < 1000; ++i)' into 'for (i = 0; i != 25; ++i)'
+// 2. Any use outside of the loop of an expression derived from the indvar
+// is changed to compute the derived value outside of the loop, eliminating
+// the dependence on the exit value of the induction variable. If the only
+// purpose of the loop is to compute the exit value of some derived
+// expression, this transformation will make the loop dead.
+//
+// This transformation should be followed by strength reduction after all of the
+// desired loop transformations have been performed. Additionally, on targets
+// where it is profitable, the loop could be transformed to count down to zero
+// (the "do loop" optimization).
//
//===----------------------------------------------------------------------===//
-#include "llvm/Transforms/Scalar/IndVarSimplify.h"
-#include "llvm/Analysis/InductionVariable.h"
-#include "llvm/Analysis/LoopInfo.h"
-#include "llvm/iPHINode.h"
-#include "llvm/iOther.h"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/BasicBlock.h"
+#include "llvm/Constant.h"
+#include "llvm/Instructions.h"
#include "llvm/Type.h"
-#include "llvm/ConstantVals.h"
-#include "Support/STLExtras.h"
+#include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Support/CFG.h"
+#include "llvm/Transforms/Utils/Local.h"
+#include "Support/CommandLine.h"
+#include "Support/Statistic.h"
+using namespace llvm;
-#if 0
-#define DEBUG
-#include "llvm/Analysis/Writer.h"
-#endif
+namespace {
+ Statistic<> NumRemoved ("indvars", "Number of aux indvars removed");
+ Statistic<> NumPointer ("indvars", "Number of pointer indvars promoted");
+ Statistic<> NumInserted("indvars", "Number of canonical indvars added");
+ Statistic<> NumReplaced("indvars", "Number of exit values replaced");
+ Statistic<> NumLFTR ("indvars", "Number of loop exit tests replaced");
-// InsertCast - Cast Val to Ty, setting a useful name on the cast if Val has a
-// name...
-//
-static Instruction *InsertCast(Instruction *Val, const Type *Ty,
- BasicBlock::iterator It) {
- Instruction *Cast = new CastInst(Val, Ty);
- if (Val->hasName()) Cast->setName(Val->getName()+"-casted");
- Val->getParent()->getInstList().insert(It, Cast);
- return Cast;
+ class IndVarSimplify : public FunctionPass {
+ LoopInfo *LI;
+ ScalarEvolution *SE;
+ bool Changed;
+ public:
+ virtual bool runOnFunction(Function &) {
+ LI = &getAnalysis<LoopInfo>();
+ SE = &getAnalysis<ScalarEvolution>();
+ Changed = false;
+
+ // Induction Variables live in the header nodes of loops
+ for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
+ runOnLoop(*I);
+ return Changed;
+ }
+
+ virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.addRequiredID(LoopSimplifyID);
+ AU.addRequired<ScalarEvolution>();
+ AU.addRequired<LoopInfo>();
+ AU.addPreservedID(LoopSimplifyID);
+ AU.setPreservesCFG();
+ }
+ private:
+ void runOnLoop(Loop *L);
+ void EliminatePointerRecurrence(PHINode *PN, BasicBlock *Preheader,
+ std::set<Instruction*> &DeadInsts);
+ void LinearFunctionTestReplace(Loop *L, SCEV *IterationCount,
+ Value *IndVar, ScalarEvolutionRewriter &RW);
+ void RewriteLoopExitValues(Loop *L);
+
+ void DeleteTriviallyDeadInstructions(std::set<Instruction*> &Insts);
+ };
+ RegisterOpt<IndVarSimplify> X("indvars", "Canonicalize Induction Variables");
}
-static bool TransformLoop(cfg::LoopInfo *Loops, cfg::Loop *Loop) {
- // Transform all subloops before this loop...
- bool Changed = reduce_apply_bool(Loop->getSubLoops().begin(),
- Loop->getSubLoops().end(),
- std::bind1st(std::ptr_fun(TransformLoop), Loops));
- // Get the header node for this loop. All of the phi nodes that could be
- // induction variables must live in this basic block.
- BasicBlock *Header = (BasicBlock*)Loop->getBlocks().front();
-
- // Loop over all of the PHI nodes in the basic block, calculating the
- // induction variables that they represent... stuffing the induction variable
- // info into a vector...
- //
- std::vector<InductionVariable> IndVars; // Induction variables for block
- for (BasicBlock::iterator I = Header->begin();
- PHINode *PN = dyn_cast<PHINode>(*I); ++I)
- IndVars.push_back(InductionVariable(PN, Loops));
+Pass *llvm::createIndVarSimplifyPass() {
+ return new IndVarSimplify();
+}
- // If there are no phi nodes in this basic block, there can't be indvars...
- if (IndVars.empty()) return Changed;
-
- // Loop over the induction variables, looking for a cannonical induction
- // variable, and checking to make sure they are not all unknown induction
- // variables.
- //
- bool FoundIndVars = false;
- InductionVariable *Cannonical = 0;
- for (unsigned i = 0; i < IndVars.size(); ++i) {
- if (IndVars[i].InductionType == InductionVariable::Cannonical)
- Cannonical = &IndVars[i];
- if (IndVars[i].InductionType != InductionVariable::Unknown)
- FoundIndVars = true;
- }
- // No induction variables, bail early... don't add a cannonnical indvar
- if (!FoundIndVars) return Changed;
-
- // Okay, we want to convert other induction variables to use a cannonical
- // indvar. If we don't have one, add one now...
- if (!Cannonical) {
- // Create the PHI node for the new induction variable
- PHINode *PN = new PHINode(Type::UIntTy, "cann-indvar");
-
- // Insert the phi node at the end of the other phi nodes...
- Header->getInstList().insert(Header->begin()+IndVars.size(), PN);
-
- // Create the increment instruction to add one to the counter...
- Instruction *Add = BinaryOperator::create(Instruction::Add, PN,
- ConstantUInt::get(Type::UIntTy,1),
- "add1-indvar");
-
- // Insert the add instruction after all of the PHI nodes...
- Header->getInstList().insert(Header->begin()+(IndVars.size()+1), Add);
-
- // Figure out which block is incoming and which is the backedge for the loop
- BasicBlock *Incoming, *BackEdgeBlock;
- BasicBlock::pred_iterator PI = Header->pred_begin();
- assert(PI != Header->pred_end() && "Loop headers should have 2 preds!");
- if (Loop->contains(*PI)) { // First pred is back edge...
- BackEdgeBlock = *PI++;
- Incoming = *PI++;
- } else {
- Incoming = *PI++;
- BackEdgeBlock = *PI++;
+/// DeleteTriviallyDeadInstructions - If any of the instructions is the
+/// specified set are trivially dead, delete them and see if this makes any of
+/// their operands subsequently dead.
+void IndVarSimplify::
+DeleteTriviallyDeadInstructions(std::set<Instruction*> &Insts) {
+ while (!Insts.empty()) {
+ Instruction *I = *Insts.begin();
+ Insts.erase(Insts.begin());
+ if (isInstructionTriviallyDead(I)) {
+ for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
+ if (Instruction *U = dyn_cast<Instruction>(I->getOperand(i)))
+ Insts.insert(U);
+ SE->deleteInstructionFromRecords(I);
+ I->getParent()->getInstList().erase(I);
+ Changed = true;
}
- assert(PI == Header->pred_end() && "Loop headers should have 2 preds!");
-
- // Add incoming values for the PHI node...
- PN->addIncoming(Constant::getNullConstant(Type::UIntTy), Incoming);
- PN->addIncoming(Add, BackEdgeBlock);
-
- // Analyze the new induction variable...
- IndVars.push_back(InductionVariable(PN, Loops));
- assert(IndVars.back().InductionType == InductionVariable::Cannonical &&
- "Just inserted cannonical indvar that is not cannonical!");
- Cannonical = &IndVars.back();
- Changed = true;
}
+}
-#ifdef DEBUG
- cerr << "Induction variables:\n";
-#endif
- // Get the current loop iteration count, which is always the value of the
- // cannonical phi node...
- //
- PHINode *IterCount = Cannonical->Phi;
+/// EliminatePointerRecurrence - Check to see if this is a trivial GEP pointer
+/// recurrence. If so, change it into an integer recurrence, permitting
+/// analysis by the SCEV routines.
+void IndVarSimplify::EliminatePointerRecurrence(PHINode *PN,
+ BasicBlock *Preheader,
+ std::set<Instruction*> &DeadInsts) {
+ assert(PN->getNumIncomingValues() == 2 && "Noncanonicalized loop!");
+ unsigned PreheaderIdx = PN->getBasicBlockIndex(Preheader);
+ unsigned BackedgeIdx = PreheaderIdx^1;
+ if (GetElementPtrInst *GEPI =
+ dyn_cast<GetElementPtrInst>(PN->getIncomingValue(BackedgeIdx)))
+ if (GEPI->getOperand(0) == PN) {
+ assert(GEPI->getNumOperands() == 2 && "GEP types must mismatch!");
+
+ // Okay, we found a pointer recurrence. Transform this pointer
+ // recurrence into an integer recurrence. Compute the value that gets
+ // added to the pointer at every iteration.
+ Value *AddedVal = GEPI->getOperand(1);
- // Loop through and replace all of the auxillary induction variables with
- // references to the primary induction variable...
- //
- unsigned InsertPos = IndVars.size();
- for (unsigned i = 0; i < IndVars.size(); ++i) {
- InductionVariable *IV = &IndVars[i];
-#ifdef DEBUG
- cerr << IndVars[i];
-#endif
- // Don't modify the cannonical indvar or unrecognized indvars...
- if (IV != Cannonical && IV->InductionType != InductionVariable::Unknown) {
- Instruction *Val = IterCount;
- if (!isa<ConstantInt>(IV->Step) || // If the step != 1
- !cast<ConstantInt>(IV->Step)->equalsInt(1)) {
- std::string Name; // Create a scale by the step value...
- if (IV->Phi->hasName()) Name = IV->Phi->getName()+"-scale";
-
- // If the types are not compatible, insert a cast now...
- if (Val->getType() != IV->Step->getType())
- Val = InsertCast(Val, IV->Step->getType(),
- Header->begin()+InsertPos++);
-
- Val = BinaryOperator::create(Instruction::Mul, Val, IV->Step, Name);
- // Insert the phi node at the end of the other phi nodes...
- Header->getInstList().insert(Header->begin()+InsertPos++, Val);
+ // Insert a new integer PHI node into the top of the block.
+ PHINode *NewPhi = new PHINode(AddedVal->getType(),
+ PN->getName()+".rec", PN);
+ NewPhi->addIncoming(Constant::getNullValue(NewPhi->getType()),
+ Preheader);
+ // Create the new add instruction.
+ Value *NewAdd = BinaryOperator::create(Instruction::Add, NewPhi,
+ AddedVal,
+ GEPI->getName()+".rec", GEPI);
+ NewPhi->addIncoming(NewAdd, PN->getIncomingBlock(BackedgeIdx));
+
+ // Update the existing GEP to use the recurrence.
+ GEPI->setOperand(0, PN->getIncomingValue(PreheaderIdx));
+
+ // Update the GEP to use the new recurrence we just inserted.
+ GEPI->setOperand(1, NewAdd);
+
+ // Finally, if there are any other users of the PHI node, we must
+ // insert a new GEP instruction that uses the pre-incremented version
+ // of the induction amount.
+ if (!PN->use_empty()) {
+ BasicBlock::iterator InsertPos = PN; ++InsertPos;
+ while (isa<PHINode>(InsertPos)) ++InsertPos;
+ std::string Name = PN->getName(); PN->setName("");
+ Value *PreInc =
+ new GetElementPtrInst(PN->getIncomingValue(PreheaderIdx),
+ std::vector<Value*>(1, NewPhi), Name,
+ InsertPos);
+ PN->replaceAllUsesWith(PreInc);
}
- if (!isa<Constant>(IV->Start) || // If the start != 0
- !cast<Constant>(IV->Start)->isNullValue()) {
- std::string Name; // Create a offset by the start value...
- if (IV->Phi->hasName()) Name = IV->Phi->getName()+"-offset";
+ // Delete the old PHI for sure, and the GEP if its otherwise unused.
+ DeadInsts.insert(PN);
- // If the types are not compatible, insert a cast now...
- if (Val->getType() != IV->Start->getType())
- Val = InsertCast(Val, IV->Start->getType(),
- Header->begin()+InsertPos++);
+ ++NumPointer;
+ Changed = true;
+ }
+}
- Val = BinaryOperator::create(Instruction::Add, Val, IV->Start, Name);
- // Insert the phi node at the end of the other phi nodes...
- Header->getInstList().insert(Header->begin()+InsertPos++, Val);
- }
+/// LinearFunctionTestReplace - This method rewrites the exit condition of the
+/// loop to be a canonical != comparison against the loop induction variable.
+/// This pass is able to rewrite the exit tests of any loop where the SCEV
+/// analysis can determine the trip count of the loop, which is actually a much
+/// broader range than just linear tests.
+void IndVarSimplify::LinearFunctionTestReplace(Loop *L, SCEV *IterationCount,
+ Value *IndVar,
+ ScalarEvolutionRewriter &RW) {
+ // Find the exit block for the loop. We can currently only handle loops with
+ // a single exit.
+ if (L->getExitBlocks().size() != 1) return;
+ BasicBlock *ExitBlock = L->getExitBlocks()[0];
- // If the PHI node has a different type than val is, insert a cast now...
- if (Val->getType() != IV->Phi->getType())
- Val = InsertCast(Val, IV->Phi->getType(),
- Header->begin()+InsertPos++);
-
- // Replace all uses of the old PHI node with the new computed value...
- IV->Phi->replaceAllUsesWith(Val);
-
- // Move the PHI name to it's new equivalent value...
- std::string OldName = IV->Phi->getName();
- IV->Phi->setName("");
- Val->setName(OldName);
-
- // Delete the old, now unused, phi node...
- Header->getInstList().remove(IV->Phi);
- delete IV->Phi;
- InsertPos--; // Deleted an instr, decrement insert position
- Changed = true;
+ // Make sure there is only one predecessor block in the loop.
+ BasicBlock *ExitingBlock = 0;
+ for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock);
+ PI != PE; ++PI)
+ if (L->contains(*PI)) {
+ if (ExitingBlock == 0)
+ ExitingBlock = *PI;
+ else
+ return; // Multiple exits from loop to this block.
}
- }
+ assert(ExitingBlock && "Loop info is broken");
- return Changed;
-}
+ if (!isa<BranchInst>(ExitingBlock->getTerminator()))
+ return; // Can't rewrite non-branch yet
+ BranchInst *BI = cast<BranchInst>(ExitingBlock->getTerminator());
+ assert(BI->isConditional() && "Must be conditional to be part of loop!");
+
+ std::set<Instruction*> InstructionsToDelete;
+ if (Instruction *Cond = dyn_cast<Instruction>(BI->getCondition()))
+ InstructionsToDelete.insert(Cond);
+
+ // Expand the code for the iteration count into the preheader of the loop.
+ BasicBlock *Preheader = L->getLoopPreheader();
+ Value *ExitCnt = RW.ExpandCodeFor(IterationCount, Preheader->getTerminator(),
+ IndVar->getType());
+
+ // Insert a new setne or seteq instruction before the branch.
+ Instruction::BinaryOps Opcode;
+ if (L->contains(BI->getSuccessor(0)))
+ Opcode = Instruction::SetNE;
+ else
+ Opcode = Instruction::SetEQ;
+
+ Value *Cond = new SetCondInst(Opcode, IndVar, ExitCnt, "exitcond", BI);
+ BI->setCondition(Cond);
+ ++NumLFTR;
+ Changed = true;
-bool InductionVariableSimplify::doit(Method *M, cfg::LoopInfo &Loops) {
- // Induction Variables live in the header nodes of the loops of the method...
- return reduce_apply_bool(Loops.getTopLevelLoops().begin(),
- Loops.getTopLevelLoops().end(),
- std::bind1st(std::ptr_fun(TransformLoop), &Loops));
+ DeleteTriviallyDeadInstructions(InstructionsToDelete);
}
-bool InductionVariableSimplify::runOnMethod(Method *M) {
- return doit(M, getAnalysis<cfg::LoopInfo>());
+
+/// RewriteLoopExitValues - Check to see if this loop has a computable
+/// loop-invariant execution count. If so, this means that we can compute the
+/// final value of any expressions that are recurrent in the loop, and
+/// substitute the exit values from the loop into any instructions outside of
+/// the loop that use the final values of the current expressions.
+void IndVarSimplify::RewriteLoopExitValues(Loop *L) {
+ BasicBlock *Preheader = L->getLoopPreheader();
+
+ // Scan all of the instructions in the loop, looking at those that have
+ // extra-loop users and which are recurrences.
+ ScalarEvolutionRewriter Rewriter(*SE, *LI);
+
+ // We insert the code into the preheader of the loop if the loop contains
+ // multiple exit blocks, or in the exit block if there is exactly one.
+ BasicBlock *BlockToInsertInto;
+ if (L->getExitBlocks().size() == 1)
+ BlockToInsertInto = L->getExitBlocks()[0];
+ else
+ BlockToInsertInto = Preheader;
+ BasicBlock::iterator InsertPt = BlockToInsertInto->begin();
+ while (isa<PHINode>(InsertPt)) ++InsertPt;
+
+ std::set<Instruction*> InstructionsToDelete;
+
+ for (unsigned i = 0, e = L->getBlocks().size(); i != e; ++i)
+ if (LI->getLoopFor(L->getBlocks()[i]) == L) { // Not in a subloop...
+ BasicBlock *BB = L->getBlocks()[i];
+ for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
+ if (I->getType()->isInteger()) { // Is an integer instruction
+ SCEVHandle SH = SE->getSCEV(I);
+ if (SH->hasComputableLoopEvolution(L)) { // Varies predictably
+ // Find out if this predictably varying value is actually used
+ // outside of the loop. "extra" as opposed to "intra".
+ std::vector<User*> ExtraLoopUsers;
+ for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
+ UI != E; ++UI)
+ if (!L->contains(cast<Instruction>(*UI)->getParent()))
+ ExtraLoopUsers.push_back(*UI);
+ if (!ExtraLoopUsers.empty()) {
+ // Okay, this instruction has a user outside of the current loop
+ // and varies predictably in this loop. Evaluate the value it
+ // contains when the loop exits, and insert code for it.
+ SCEVHandle ExitValue = SE->getSCEVAtScope(I,L->getParentLoop());
+ if (!isa<SCEVCouldNotCompute>(ExitValue)) {
+ Changed = true;
+ ++NumReplaced;
+ Value *NewVal = Rewriter.ExpandCodeFor(ExitValue, InsertPt,
+ I->getType());
+
+ // Rewrite any users of the computed value outside of the loop
+ // with the newly computed value.
+ for (unsigned i = 0, e = ExtraLoopUsers.size(); i != e; ++i)
+ ExtraLoopUsers[i]->replaceUsesOfWith(I, NewVal);
+
+ // If this instruction is dead now, schedule it to be removed.
+ if (I->use_empty())
+ InstructionsToDelete.insert(I);
+ }
+ }
+ }
+ }
+ }
+
+ DeleteTriviallyDeadInstructions(InstructionsToDelete);
}
-void InductionVariableSimplify::getAnalysisUsageInfo(Pass::AnalysisSet &Req,
- Pass::AnalysisSet &Dest,
- Pass::AnalysisSet &Prov) {
- Req.push_back(cfg::LoopInfo::ID);
+
+void IndVarSimplify::runOnLoop(Loop *L) {
+ // First step. Check to see if there are any trivial GEP pointer recurrences.
+ // If there are, change them into integer recurrences, permitting analysis by
+ // the SCEV routines.
+ //
+ BasicBlock *Header = L->getHeader();
+ BasicBlock *Preheader = L->getLoopPreheader();
+
+ std::set<Instruction*> DeadInsts;
+ for (BasicBlock::iterator I = Header->begin();
+ PHINode *PN = dyn_cast<PHINode>(I); ++I)
+ if (isa<PointerType>(PN->getType()))
+ EliminatePointerRecurrence(PN, Preheader, DeadInsts);
+
+ if (!DeadInsts.empty())
+ DeleteTriviallyDeadInstructions(DeadInsts);
+
+
+ // Next, transform all loops nesting inside of this loop.
+ for (LoopInfo::iterator I = L->begin(), E = L->end(); I != E; ++I)
+ runOnLoop(*I);
+
+ // Check to see if this loop has a computable loop-invariant execution count.
+ // If so, this means that we can compute the final value of any expressions
+ // that are recurrent in the loop, and substitute the exit values from the
+ // loop into any instructions outside of the loop that use the final values of
+ // the current expressions.
+ //
+ SCEVHandle IterationCount = SE->getIterationCount(L);
+ if (!isa<SCEVCouldNotCompute>(IterationCount))
+ RewriteLoopExitValues(L);
+
+ // Next, analyze all of the induction variables in the loop, canonicalizing
+ // auxillary induction variables.
+ std::vector<std::pair<PHINode*, SCEVHandle> > IndVars;
+
+ for (BasicBlock::iterator I = Header->begin();
+ PHINode *PN = dyn_cast<PHINode>(I); ++I)
+ if (PN->getType()->isInteger()) { // FIXME: when we have fast-math, enable!
+ SCEVHandle SCEV = SE->getSCEV(PN);
+ if (SCEV->hasComputableLoopEvolution(L))
+ if (SE->shouldSubstituteIndVar(SCEV)) // HACK!
+ IndVars.push_back(std::make_pair(PN, SCEV));
+ }
+
+ // If there are no induction variables in the loop, there is nothing more to
+ // do.
+ if (IndVars.empty()) return;
+
+ // Compute the type of the largest recurrence expression.
+ //
+ const Type *LargestType = IndVars[0].first->getType();
+ bool DifferingSizes = false;
+ for (unsigned i = 1, e = IndVars.size(); i != e; ++i) {
+ const Type *Ty = IndVars[i].first->getType();
+ DifferingSizes |= Ty->getPrimitiveSize() != LargestType->getPrimitiveSize();
+ if (Ty->getPrimitiveSize() > LargestType->getPrimitiveSize())
+ LargestType = Ty;
+ }
+
+ // Create a rewriter object which we'll use to transform the code with.
+ ScalarEvolutionRewriter Rewriter(*SE, *LI);
+
+ // Now that we know the largest of of the induction variables in this loop,
+ // insert a canonical induction variable of the largest size.
+ Value *IndVar = Rewriter.GetOrInsertCanonicalInductionVariable(L,LargestType);
+ ++NumInserted;
+ Changed = true;
+
+ if (!isa<SCEVCouldNotCompute>(IterationCount))
+ LinearFunctionTestReplace(L, IterationCount, IndVar, Rewriter);
+
+#if 0
+ // If there were induction variables of other sizes, cast the primary
+ // induction variable to the right size for them, avoiding the need for the
+ // code evaluation methods to insert induction variables of different sizes.
+ // FIXME!
+ if (DifferingSizes) {
+ std::map<unsigned, Value*> InsertedSizes;
+ for (unsigned i = 0, e = IndVars.size(); i != e; ++i) {
+ }
+ }
+#endif
+
+ // Now that we have a canonical induction variable, we can rewrite any
+ // recurrences in terms of the induction variable. Start with the auxillary
+ // induction variables, and recursively rewrite any of their uses.
+ BasicBlock::iterator InsertPt = Header->begin();
+ while (isa<PHINode>(InsertPt)) ++InsertPt;
+
+ while (!IndVars.empty()) {
+ PHINode *PN = IndVars.back().first;
+ Value *NewVal = Rewriter.ExpandCodeFor(IndVars.back().second, InsertPt,
+ PN->getType());
+ // Replace the old PHI Node with the inserted computation.
+ PN->replaceAllUsesWith(NewVal);
+ DeadInsts.insert(PN);
+ IndVars.pop_back();
+ ++NumRemoved;
+ Changed = true;
+ }
+
+ DeleteTriviallyDeadInstructions(DeadInsts);
+
+ // TODO: In the future we could replace all instructions in the loop body with
+ // simpler expressions. It's not clear how useful this would be though or if
+ // the code expansion cost would be worth it! We probably shouldn't do this
+ // until we have a way to reuse expressions already in the code.
+#if 0
+ for (unsigned i = 0, e = L->getBlocks().size(); i != e; ++i)
+ if (LI->getLoopFor(L->getBlocks()[i]) == L) { // Not in a subloop...
+ BasicBlock *BB = L->getBlocks()[i];
+ for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
+ if (I->getType()->isInteger() && // Is an integer instruction
+ !Rewriter.isInsertedInstruction(I)) {
+ SCEVHandle SH = SE->getSCEV(I);
+ }
+ }
+#endif
}
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