| //===- IndVarSimplify.cpp - Induction Variable Elimination ----------------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // 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.h" |
| #include "llvm/BasicBlock.h" |
| #include "llvm/Constants.h" |
| #include "llvm/Instructions.h" |
| #include "llvm/Type.h" |
| #include "llvm/Analysis/ScalarEvolutionExpressions.h" |
| #include "llvm/Analysis/LoopInfo.h" |
| #include "llvm/Support/CFG.h" |
| #include "llvm/Transforms/Utils/Local.h" |
| #include "llvm/Support/CommandLine.h" |
| #include "llvm/ADT/Statistic.h" |
| using namespace llvm; |
| |
| namespace { |
| /// SCEVExpander - This class uses information about analyze scalars to |
| /// rewrite expressions in canonical form. |
| /// |
| /// Clients should create an instance of this class when rewriting is needed, |
| /// and destroying it when finished to allow the release of the associated |
| /// memory. |
| struct SCEVExpander : public SCEVVisitor<SCEVExpander, Value*> { |
| ScalarEvolution &SE; |
| LoopInfo &LI; |
| std::map<SCEVHandle, Value*> InsertedExpressions; |
| std::set<Instruction*> InsertedInstructions; |
| |
| Instruction *InsertPt; |
| |
| friend class SCEVVisitor<SCEVExpander, Value*>; |
| public: |
| SCEVExpander(ScalarEvolution &se, LoopInfo &li) : SE(se), LI(li) {} |
| |
| /// isInsertedInstruction - Return true if the specified instruction was |
| /// inserted by the code rewriter. If so, the client should not modify the |
| /// instruction. |
| bool isInsertedInstruction(Instruction *I) const { |
| return InsertedInstructions.count(I); |
| } |
| |
| /// getOrInsertCanonicalInductionVariable - This method returns the |
| /// canonical induction variable of the specified type for the specified |
| /// loop (inserting one if there is none). A canonical induction variable |
| /// starts at zero and steps by one on each iteration. |
| Value *getOrInsertCanonicalInductionVariable(const Loop *L, const Type *Ty){ |
| assert((Ty->isInteger() || Ty->isFloatingPoint()) && |
| "Can only insert integer or floating point induction variables!"); |
| SCEVHandle H = SCEVAddRecExpr::get(SCEVUnknown::getIntegerSCEV(0, Ty), |
| SCEVUnknown::getIntegerSCEV(1, Ty), L); |
| return expand(H); |
| } |
| |
| /// addInsertedValue - Remember the specified instruction as being the |
| /// canonical form for the specified SCEV. |
| void addInsertedValue(Instruction *I, SCEV *S) { |
| InsertedExpressions[S] = (Value*)I; |
| InsertedInstructions.insert(I); |
| } |
| |
| /// expandCodeFor - Insert code to directly compute the specified SCEV |
| /// expression into the program. The inserted code is inserted into the |
| /// specified block. |
| /// |
| /// If a particular value sign is required, a type may be specified for the |
| /// result. |
| Value *expandCodeFor(SCEVHandle SH, Instruction *IP, const Type *Ty = 0) { |
| // Expand the code for this SCEV. |
| this->InsertPt = IP; |
| return expandInTy(SH, Ty); |
| } |
| |
| protected: |
| Value *expand(SCEV *S) { |
| // Check to see if we already expanded this. |
| std::map<SCEVHandle, Value*>::iterator I = InsertedExpressions.find(S); |
| if (I != InsertedExpressions.end()) |
| return I->second; |
| |
| Value *V = visit(S); |
| InsertedExpressions[S] = V; |
| return V; |
| } |
| |
| Value *expandInTy(SCEV *S, const Type *Ty) { |
| Value *V = expand(S); |
| if (Ty && V->getType() != Ty) { |
| // FIXME: keep track of the cast instruction. |
| if (Constant *C = dyn_cast<Constant>(V)) |
| return ConstantExpr::getCast(C, Ty); |
| else if (Instruction *I = dyn_cast<Instruction>(V)) { |
| // Check to see if there is already a cast. If there is, use it. |
| for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); |
| UI != E; ++UI) { |
| if ((*UI)->getType() == Ty) |
| if (CastInst *CI = dyn_cast<CastInst>(cast<Instruction>(*UI))) { |
| BasicBlock::iterator It = I; ++It; |
| while (isa<PHINode>(It)) ++It; |
| if (It != BasicBlock::iterator(CI)) { |
| // Splice the cast immediately after the operand in question. |
| I->getParent()->getInstList().splice(It, |
| CI->getParent()->getInstList(), |
| CI); |
| } |
| return CI; |
| } |
| } |
| BasicBlock::iterator IP = I; ++IP; |
| if (InvokeInst *II = dyn_cast<InvokeInst>(I)) |
| IP = II->getNormalDest()->begin(); |
| while (isa<PHINode>(IP)) ++IP; |
| return new CastInst(V, Ty, V->getName(), IP); |
| } else { |
| // FIXME: check to see if there is already a cast! |
| return new CastInst(V, Ty, V->getName(), InsertPt); |
| } |
| } |
| return V; |
| } |
| |
| Value *visitConstant(SCEVConstant *S) { |
| return S->getValue(); |
| } |
| |
| Value *visitTruncateExpr(SCEVTruncateExpr *S) { |
| Value *V = expand(S->getOperand()); |
| return new CastInst(V, S->getType(), "tmp.", InsertPt); |
| } |
| |
| Value *visitZeroExtendExpr(SCEVZeroExtendExpr *S) { |
| Value *V = expandInTy(S->getOperand(),S->getType()->getUnsignedVersion()); |
| return new CastInst(V, S->getType(), "tmp.", InsertPt); |
| } |
| |
| Value *visitAddExpr(SCEVAddExpr *S) { |
| const Type *Ty = S->getType(); |
| Value *V = expandInTy(S->getOperand(S->getNumOperands()-1), Ty); |
| |
| // Emit a bunch of add instructions |
| for (int i = S->getNumOperands()-2; i >= 0; --i) |
| V = BinaryOperator::createAdd(V, expandInTy(S->getOperand(i), Ty), |
| "tmp.", InsertPt); |
| return V; |
| } |
| |
| Value *visitMulExpr(SCEVMulExpr *S); |
| |
| Value *visitUDivExpr(SCEVUDivExpr *S) { |
| const Type *Ty = S->getType(); |
| Value *LHS = expandInTy(S->getLHS(), Ty); |
| Value *RHS = expandInTy(S->getRHS(), Ty); |
| return BinaryOperator::createDiv(LHS, RHS, "tmp.", InsertPt); |
| } |
| |
| Value *visitAddRecExpr(SCEVAddRecExpr *S); |
| |
| Value *visitUnknown(SCEVUnknown *S) { |
| return S->getValue(); |
| } |
| }; |
| } |
| |
| Value *SCEVExpander::visitMulExpr(SCEVMulExpr *S) { |
| const Type *Ty = S->getType(); |
| int FirstOp = 0; // Set if we should emit a subtract. |
| if (SCEVConstant *SC = dyn_cast<SCEVConstant>(S->getOperand(0))) |
| if (SC->getValue()->isAllOnesValue()) |
| FirstOp = 1; |
| |
| int i = S->getNumOperands()-2; |
| Value *V = expandInTy(S->getOperand(i+1), Ty); |
| |
| // Emit a bunch of multiply instructions |
| for (; i >= FirstOp; --i) |
| V = BinaryOperator::createMul(V, expandInTy(S->getOperand(i), Ty), |
| "tmp.", InsertPt); |
| // -1 * ... ---> 0 - ... |
| if (FirstOp == 1) |
| V = BinaryOperator::createNeg(V, "tmp.", InsertPt); |
| return V; |
| } |
| |
| Value *SCEVExpander::visitAddRecExpr(SCEVAddRecExpr *S) { |
| const Type *Ty = S->getType(); |
| const Loop *L = S->getLoop(); |
| // We cannot yet do fp recurrences, e.g. the xform of {X,+,F} --> X+{0,+,F} |
| assert(Ty->isIntegral() && "Cannot expand fp recurrences yet!"); |
| |
| // {X,+,F} --> X + {0,+,F} |
| if (!isa<SCEVConstant>(S->getStart()) || |
| !cast<SCEVConstant>(S->getStart())->getValue()->isNullValue()) { |
| Value *Start = expandInTy(S->getStart(), Ty); |
| std::vector<SCEVHandle> NewOps(S->op_begin(), S->op_end()); |
| NewOps[0] = SCEVUnknown::getIntegerSCEV(0, Ty); |
| Value *Rest = expandInTy(SCEVAddRecExpr::get(NewOps, L), Ty); |
| |
| // FIXME: look for an existing add to use. |
| return BinaryOperator::createAdd(Rest, Start, "tmp.", InsertPt); |
| } |
| |
| // {0,+,1} --> Insert a canonical induction variable into the loop! |
| if (S->getNumOperands() == 2 && |
| S->getOperand(1) == SCEVUnknown::getIntegerSCEV(1, Ty)) { |
| // Create and insert the PHI node for the induction variable in the |
| // specified loop. |
| BasicBlock *Header = L->getHeader(); |
| PHINode *PN = new PHINode(Ty, "indvar", Header->begin()); |
| PN->addIncoming(Constant::getNullValue(Ty), L->getLoopPreheader()); |
| |
| pred_iterator HPI = pred_begin(Header); |
| assert(HPI != pred_end(Header) && "Loop with zero preds???"); |
| if (!L->contains(*HPI)) ++HPI; |
| assert(HPI != pred_end(Header) && L->contains(*HPI) && |
| "No backedge in loop?"); |
| |
| // Insert a unit add instruction right before the terminator corresponding |
| // to the back-edge. |
| Constant *One = Ty->isFloatingPoint() ? (Constant*)ConstantFP::get(Ty, 1.0) |
| : ConstantInt::get(Ty, 1); |
| Instruction *Add = BinaryOperator::createAdd(PN, One, "indvar.next", |
| (*HPI)->getTerminator()); |
| |
| pred_iterator PI = pred_begin(Header); |
| if (*PI == L->getLoopPreheader()) |
| ++PI; |
| PN->addIncoming(Add, *PI); |
| return PN; |
| } |
| |
| // Get the canonical induction variable I for this loop. |
| Value *I = getOrInsertCanonicalInductionVariable(L, Ty); |
| |
| if (S->getNumOperands() == 2) { // {0,+,F} --> i*F |
| Value *F = expandInTy(S->getOperand(1), Ty); |
| return BinaryOperator::createMul(I, F, "tmp.", InsertPt); |
| } |
| |
| // If this is a chain of recurrences, turn it into a closed form, using the |
| // folders, then expandCodeFor the closed form. This allows the folders to |
| // simplify the expression without having to build a bunch of special code |
| // into this folder. |
| SCEVHandle IH = SCEVUnknown::get(I); // Get I as a "symbolic" SCEV. |
| |
| SCEVHandle V = S->evaluateAtIteration(IH); |
| //std::cerr << "Evaluated: " << *this << "\n to: " << *V << "\n"; |
| |
| return expandInTy(V, Ty); |
| } |
| |
| |
| 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"); |
| |
| 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, |
| SCEVExpander &RW); |
| void RewriteLoopExitValues(Loop *L); |
| |
| void DeleteTriviallyDeadInstructions(std::set<Instruction*> &Insts); |
| }; |
| RegisterOpt<IndVarSimplify> X("indvars", "Canonicalize Induction Variables"); |
| } |
| |
| Pass *llvm::createIndVarSimplifyPass() { |
| return new IndVarSimplify(); |
| } |
| |
| /// 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; |
| } |
| } |
| } |
| |
| |
| /// 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); |
| |
| // 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::createAdd(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); |
| } |
| |
| // Delete the old PHI for sure, and the GEP if its otherwise unused. |
| DeadInsts.insert(PN); |
| |
| ++NumPointer; |
| Changed = true; |
| } |
| } |
| |
| /// LinearFunctionTestReplace - This method rewrites the exit condition of the |
| /// loop to be a canonical != comparison against the incremented loop induction |
| /// variable. This pass is able to rewrite the exit tests of any loop where the |
| /// SCEV analysis can determine a loop-invariant trip count of the loop, which |
| /// is actually a much broader range than just linear tests. |
| void IndVarSimplify::LinearFunctionTestReplace(Loop *L, SCEV *IterationCount, |
| SCEVExpander &RW) { |
| // Find the exit block for the loop. We can currently only handle loops with |
| // a single exit. |
| std::vector<BasicBlock*> ExitBlocks; |
| L->getExitBlocks(ExitBlocks); |
| if (ExitBlocks.size() != 1) return; |
| BasicBlock *ExitBlock = ExitBlocks[0]; |
| |
| // 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"); |
| |
| 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); |
| |
| // If the exiting block is not the same as the backedge block, we must compare |
| // against the preincremented value, otherwise we prefer to compare against |
| // the post-incremented value. |
| BasicBlock *Header = L->getHeader(); |
| pred_iterator HPI = pred_begin(Header); |
| assert(HPI != pred_end(Header) && "Loop with zero preds???"); |
| if (!L->contains(*HPI)) ++HPI; |
| assert(HPI != pred_end(Header) && L->contains(*HPI) && |
| "No backedge in loop?"); |
| |
| SCEVHandle TripCount = IterationCount; |
| Value *IndVar; |
| if (*HPI == ExitingBlock) { |
| // The IterationCount expression contains the number of times that the |
| // backedge actually branches to the loop header. This is one less than the |
| // number of times the loop executes, so add one to it. |
| Constant *OneC = ConstantInt::get(IterationCount->getType(), 1); |
| TripCount = SCEVAddExpr::get(IterationCount, SCEVUnknown::get(OneC)); |
| IndVar = L->getCanonicalInductionVariableIncrement(); |
| } else { |
| // We have to use the preincremented value... |
| IndVar = L->getCanonicalInductionVariable(); |
| } |
| |
| // Expand the code for the iteration count into the preheader of the loop. |
| BasicBlock *Preheader = L->getLoopPreheader(); |
| Value *ExitCnt = RW.expandCodeFor(TripCount, 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; |
| |
| DeleteTriviallyDeadInstructions(InstructionsToDelete); |
| } |
| |
| |
| /// 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. |
| SCEVExpander 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; |
| std::vector<BasicBlock*> ExitBlocks; |
| L->getExitBlocks(ExitBlocks); |
| if (ExitBlocks.size() == 1) |
| BlockToInsertInto = ExitBlocks[0]; |
| else |
| BlockToInsertInto = Preheader; |
| BasicBlock::iterator InsertPt = BlockToInsertInto->begin(); |
| while (isa<PHINode>(InsertPt)) ++InsertPt; |
| |
| bool HasConstantItCount = isa<SCEVConstant>(SE->getIterationCount(L)); |
| |
| 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 |
| HasConstantItCount) { |
| // 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 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)) |
| // FIXME: Without a strength reduction pass, it is an extremely bad idea |
| // to indvar substitute anything more complex than a linear induction |
| // variable. Doing so will put expensive multiply instructions inside |
| // of the loop. For now just disable indvar subst on anything more |
| // complex than a linear addrec. |
| if (SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(SCEV)) |
| if (AR->getNumOperands() == 2 && isa<SCEVConstant>(AR->getOperand(1))) |
| 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()) { |
| // Actually, if we know how many times the loop iterates, lets insert a |
| // canonical induction variable to help subsequent passes. |
| if (!isa<SCEVCouldNotCompute>(IterationCount)) { |
| SCEVExpander Rewriter(*SE, *LI); |
| Rewriter.getOrInsertCanonicalInductionVariable(L, |
| IterationCount->getType()); |
| LinearFunctionTestReplace(L, IterationCount, Rewriter); |
| } |
| 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. |
| SCEVExpander 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. |
| LargestType = LargestType->getUnsignedVersion(); |
| Value *IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L,LargestType); |
| ++NumInserted; |
| Changed = true; |
| |
| if (!isa<SCEVCouldNotCompute>(IterationCount)) |
| LinearFunctionTestReplace(L, IterationCount, Rewriter); |
| |
| // 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; |
| |
| // 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. |
| if (DifferingSizes) { |
| bool InsertedSizes[17] = { false }; |
| InsertedSizes[LargestType->getPrimitiveSize()] = true; |
| for (unsigned i = 0, e = IndVars.size(); i != e; ++i) |
| if (!InsertedSizes[IndVars[i].first->getType()->getPrimitiveSize()]) { |
| PHINode *PN = IndVars[i].first; |
| InsertedSizes[PN->getType()->getPrimitiveSize()] = true; |
| Instruction *New = new CastInst(IndVar, |
| PN->getType()->getUnsignedVersion(), |
| "indvar", InsertPt); |
| Rewriter.addInsertedValue(New, SE->getSCEV(New)); |
| } |
| } |
| |
| // 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. |
| std::map<unsigned, Value*> InsertedSizes; |
| while (!IndVars.empty()) { |
| PHINode *PN = IndVars.back().first; |
| Value *NewVal = Rewriter.expandCodeFor(IndVars.back().second, InsertPt, |
| PN->getType()); |
| std::string Name = PN->getName(); |
| PN->setName(""); |
| NewVal->setName(Name); |
| |
| // Replace the old PHI Node with the inserted computation. |
| PN->replaceAllUsesWith(NewVal); |
| DeadInsts.insert(PN); |
| IndVars.pop_back(); |
| ++NumRemoved; |
| Changed = true; |
| } |
| |
| #if 0 |
| // Now replace all derived expressions in the loop body with simpler |
| // expressions. |
| 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 |
| !I->use_empty() && |
| !Rewriter.isInsertedInstruction(I)) { |
| SCEVHandle SH = SE->getSCEV(I); |
| Value *V = Rewriter.expandCodeFor(SH, I, I->getType()); |
| if (V != I) { |
| if (isa<Instruction>(V)) { |
| std::string Name = I->getName(); |
| I->setName(""); |
| V->setName(Name); |
| } |
| I->replaceAllUsesWith(V); |
| DeadInsts.insert(I); |
| ++NumRemoved; |
| Changed = true; |
| } |
| } |
| } |
| #endif |
| |
| DeleteTriviallyDeadInstructions(DeadInsts); |
| } |
