X-Git-Url: http://plrg.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FTransforms%2FScalar%2FIndVarSimplify.cpp;h=ff2b9939c70cdd952207c5e893a63ccad91d81d2;hb=7cbd8a3e92221437048b484d5ef9c0a22d0f8c58;hp=411ab11fece088c2fc009ce7faf2cd356426aea9;hpb=a6275ccdf5e1aa208afde56c498e2b13e16442f0;p=oota-llvm.git diff --git a/lib/Transforms/Scalar/IndVarSimplify.cpp b/lib/Transforms/Scalar/IndVarSimplify.cpp index 411ab11fece..ed377658932 100644 --- a/lib/Transforms/Scalar/IndVarSimplify.cpp +++ b/lib/Transforms/Scalar/IndVarSimplify.cpp @@ -1,207 +1,608 @@ //===- IndVarSimplify.cpp - Induction Variable Elimination ----------------===// // -// InductionVariableSimplify - Transform induction variables in a program -// to all use a single cannonical induction variable per loop. +// The LLVM Compiler Infrastructure +// +// This file 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 makes 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). // //===----------------------------------------------------------------------===// +#define DEBUG_TYPE "indvars" #include "llvm/Transforms/Scalar.h" -#include "llvm/Analysis/InductionVariable.h" -#include "llvm/Analysis/LoopInfo.h" -#include "llvm/Analysis/Writer.h" -#include "llvm/iPHINode.h" -#include "llvm/iOther.h" -#include "llvm/Type.h" +#include "llvm/BasicBlock.h" #include "llvm/Constants.h" +#include "llvm/Instructions.h" +#include "llvm/Type.h" +#include "llvm/Analysis/ScalarEvolutionExpander.h" +#include "llvm/Analysis/LoopInfo.h" +#include "llvm/Analysis/LoopPass.h" #include "llvm/Support/CFG.h" -#include "Support/STLExtras.h" -#include "Support/StatisticReporter.h" +#include "llvm/Support/Compiler.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/GetElementPtrTypeIterator.h" +#include "llvm/Transforms/Utils/Local.h" +#include "llvm/Support/CommandLine.h" +#include "llvm/ADT/SmallVector.h" +#include "llvm/ADT/Statistic.h" +using namespace llvm; -static Statistic<> NumRemoved ("indvars\t\t- Number of aux indvars removed"); -static Statistic<> NumInserted("indvars\t\t- Number of cannonical indvars added"); +STATISTIC(NumRemoved , "Number of aux indvars removed"); +STATISTIC(NumPointer , "Number of pointer indvars promoted"); +STATISTIC(NumInserted, "Number of canonical indvars added"); +STATISTIC(NumReplaced, "Number of exit values replaced"); +STATISTIC(NumLFTR , "Number of loop exit tests replaced"); +namespace { + class VISIBILITY_HIDDEN IndVarSimplify : public LoopPass { + LoopInfo *LI; + ScalarEvolution *SE; + bool Changed; + public: -// 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; + static char ID; // Pass identification, replacement for typeid + IndVarSimplify() : LoopPass((intptr_t)&ID) {} + + bool runOnLoop(Loop *L, LPPassManager &LPM); + bool doInitialization(Loop *L, LPPassManager &LPM); + virtual void getAnalysisUsage(AnalysisUsage &AU) const { + AU.addRequired(); + AU.addRequiredID(LCSSAID); + AU.addRequiredID(LoopSimplifyID); + AU.addRequired(); + AU.addPreservedID(LoopSimplifyID); + AU.addPreservedID(LCSSAID); + AU.setPreservesCFG(); + } + + private: + + void EliminatePointerRecurrence(PHINode *PN, BasicBlock *Preheader, + std::set &DeadInsts); + Instruction *LinearFunctionTestReplace(Loop *L, SCEV *IterationCount, + SCEVExpander &RW); + void RewriteLoopExitValues(Loop *L); + + void DeleteTriviallyDeadInstructions(std::set &Insts); + }; } -static bool TransformLoop(LoopInfo *Loops, 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 = 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 IndVars; // Induction variables for block - BasicBlock::iterator AfterPHIIt = Header->begin(); - for (; PHINode *PN = dyn_cast(&*AfterPHIIt); ++AfterPHIIt) - IndVars.push_back(InductionVariable(PN, Loops)); - // AfterPHIIt now points to first nonphi instruction... - - // 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; - } +char IndVarSimplify::ID = 0; +static RegisterPass +X("indvars", "Canonicalize Induction Variables"); - // 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... - AfterPHIIt = ++Header->getInstList().insert(AfterPHIIt, 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(AfterPHIIt, Add); - - // Figure out which block is incoming and which is the backedge for the loop - BasicBlock *Incoming, *BackEdgeBlock; - pred_iterator PI = pred_begin(Header); - assert(PI != pred_end(Header) && "Loop headers should have 2 preds!"); - if (Loop->contains(*PI)) { // First pred is back edge... - BackEdgeBlock = *PI++; - Incoming = *PI++; - } else { - Incoming = *PI++; - BackEdgeBlock = *PI++; +LoopPass *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 &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(I->getOperand(i))) + Insts.insert(U); + SE->deleteValueFromRecords(I); + DOUT << "INDVARS: Deleting: " << *I; + I->eraseFromParent(); + Changed = true; } - assert(PI == pred_end(Header) && "Loop headers should have 2 preds!"); - - // Add incoming values for the PHI node... - PN->addIncoming(Constant::getNullValue(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(); - ++NumInserted; - Changed = true; } +} - DEBUG(std::cerr << "Induction variables:\n"); - // 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 &DeadInsts) { + assert(PN->getNumIncomingValues() == 2 && "Noncanonicalized loop!"); + unsigned PreheaderIdx = PN->getBasicBlockIndex(Preheader); + unsigned BackedgeIdx = PreheaderIdx^1; + if (GetElementPtrInst *GEPI = + dyn_cast(PN->getIncomingValue(BackedgeIdx))) + if (GEPI->getOperand(0) == PN) { + assert(GEPI->getNumOperands() == 2 && "GEP types must match!"); + DOUT << "INDVARS: Eliminating pointer recurrence: " << *GEPI; + + // 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... - // - for (unsigned i = 0; i < IndVars.size(); ++i) { - InductionVariable *IV = &IndVars[i]; - - DEBUG(std::cerr << IV); - - // Don't modify the cannonical indvar or unrecognized indvars... - if (IV != Cannonical && IV->InductionType != InductionVariable::Unknown) { - Instruction *Val = IterCount; - if (!isa(IV->Step) || // If the step != 1 - !cast(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(), AfterPHIIt); - - Val = BinaryOperator::create(Instruction::Mul, Val, IV->Step, Name); - // Insert the phi node at the end of the other phi nodes... - Header->getInstList().insert(AfterPHIIt, Val); - } + // Insert a new integer PHI node into the top of the block. + PHINode *NewPhi = PHINode::Create(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)); - if (!isa(IV->Start) || // If the start != 0 - !cast(IV->Start)->isNullValue()) { - std::string Name; // Create a offset by the start value... - if (IV->Phi->hasName()) Name = IV->Phi->getName()+"-offset"; + // Update the existing GEP to use the recurrence. + GEPI->setOperand(0, PN->getIncomingValue(PreheaderIdx)); - // If the types are not compatible, insert a cast now... - if (Val->getType() != IV->Start->getType()) - Val = InsertCast(Val, IV->Start->getType(), AfterPHIIt); + // Update the GEP to use the new recurrence we just inserted. + GEPI->setOperand(1, NewAdd); - Val = BinaryOperator::create(Instruction::Add, Val, IV->Start, Name); - // Insert the phi node at the end of the other phi nodes... - Header->getInstList().insert(AfterPHIIt, Val); + // If the incoming value is a constant expr GEP, try peeling out the array + // 0 index if possible to make things simpler. + if (ConstantExpr *CE = dyn_cast(GEPI->getOperand(0))) + if (CE->getOpcode() == Instruction::GetElementPtr) { + unsigned NumOps = CE->getNumOperands(); + assert(NumOps > 1 && "CE folding didn't work!"); + if (CE->getOperand(NumOps-1)->isNullValue()) { + // Check to make sure the last index really is an array index. + gep_type_iterator GTI = gep_type_begin(CE); + for (unsigned i = 1, e = CE->getNumOperands()-1; + i != e; ++i, ++GTI) + /*empty*/; + if (isa(*GTI)) { + // Pull the last index out of the constant expr GEP. + SmallVector CEIdxs(CE->op_begin()+1, CE->op_end()-1); + Constant *NCE = ConstantExpr::getGetElementPtr(CE->getOperand(0), + &CEIdxs[0], + CEIdxs.size()); + Value *Idx[2]; + Idx[0] = Constant::getNullValue(Type::Int32Ty); + Idx[1] = NewAdd; + GetElementPtrInst *NGEPI = GetElementPtrInst::Create( + NCE, Idx, Idx + 2, + GEPI->getName(), GEPI); + SE->deleteValueFromRecords(GEPI); + GEPI->replaceAllUsesWith(NGEPI); + GEPI->eraseFromParent(); + GEPI = NGEPI; + } + } + } + + + // 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(InsertPos)) ++InsertPos; + Value *PreInc = + GetElementPtrInst::Create(PN->getIncomingValue(PreheaderIdx), + NewPhi, "", InsertPos); + PreInc->takeName(PN); + PN->replaceAllUsesWith(PreInc); } - // 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(), AfterPHIIt); + // 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. +/// +/// This method returns a "potentially dead" instruction whose computation chain +/// should be deleted when convenient. +Instruction *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. + SmallVector ExitBlocks; + L->getExitBlocks(ExitBlocks); + if (ExitBlocks.size() != 1) return 0; + 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 0; // Multiple exits from loop to this block. + } + assert(ExitingBlock && "Loop info is broken"); + + if (!isa(ExitingBlock->getTerminator())) + return 0; // Can't rewrite non-branch yet + BranchInst *BI = cast(ExitingBlock->getTerminator()); + assert(BI->isConditional() && "Must be conditional to be part of loop!"); + + Instruction *PotentiallyDeadInst = dyn_cast(BI->getCondition()); + + // 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. + ConstantInt *OneC = ConstantInt::get(IterationCount->getType(), 1); + TripCount = SE->getAddExpr(IterationCount, SE->getConstant(OneC)); + IndVar = L->getCanonicalInductionVariableIncrement(); + } else { + // We have to use the preincremented value... + IndVar = L->getCanonicalInductionVariable(); + } + + DOUT << "INDVARS: LFTR: TripCount = " << *TripCount + << " IndVar = " << *IndVar << "\n"; + + // Expand the code for the iteration count into the preheader of the loop. + BasicBlock *Preheader = L->getLoopPreheader(); + Value *ExitCnt = RW.expandCodeFor(TripCount, Preheader->getTerminator()); + + // Insert a new icmp_ne or icmp_eq instruction before the branch. + ICmpInst::Predicate Opcode; + if (L->contains(BI->getSuccessor(0))) + Opcode = ICmpInst::ICMP_NE; + else + Opcode = ICmpInst::ICMP_EQ; + + Value *Cond = new ICmpInst(Opcode, IndVar, ExitCnt, "exitcond", BI); + BI->setCondition(Cond); + ++NumLFTR; + Changed = true; + return PotentiallyDeadInst; +} + + +/// 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; + SmallVector ExitBlocks; + L->getUniqueExitBlocks(ExitBlocks); + if (ExitBlocks.size() == 1) + BlockToInsertInto = ExitBlocks[0]; + else + BlockToInsertInto = Preheader; + BasicBlock::iterator InsertPt = BlockToInsertInto->begin(); + while (isa(InsertPt)) ++InsertPt; + + bool HasConstantItCount = isa(SE->getIterationCount(L)); + + std::set InstructionsToDelete; + std::map ExitValues; + + // Find all values that are computed inside the loop, but used outside of it. + // Because of LCSSA, these values will only occur in LCSSA PHI Nodes. Scan + // the exit blocks of the loop to find them. + for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) { + BasicBlock *ExitBB = ExitBlocks[i]; + + // If there are no PHI nodes in this exit block, then no values defined + // inside the loop are used on this path, skip it. + PHINode *PN = dyn_cast(ExitBB->begin()); + if (!PN) continue; + + unsigned NumPreds = PN->getNumIncomingValues(); + + // Iterate over all of the PHI nodes. + BasicBlock::iterator BBI = ExitBB->begin(); + while ((PN = dyn_cast(BBI++))) { - // Replace all uses of the old PHI node with the new computed value... - IV->Phi->replaceAllUsesWith(Val); + // Iterate over all of the values in all the PHI nodes. + for (unsigned i = 0; i != NumPreds; ++i) { + // If the value being merged in is not integer or is not defined + // in the loop, skip it. + Value *InVal = PN->getIncomingValue(i); + if (!isa(InVal) || + // SCEV only supports integer expressions for now. + !isa(InVal->getType())) + continue; - // Move the PHI name to it's new equivalent value... - std::string OldName = IV->Phi->getName(); - IV->Phi->setName(""); - Val->setName(OldName); + // If this pred is for a subloop, not L itself, skip it. + if (LI->getLoopFor(PN->getIncomingBlock(i)) != L) + continue; // The Block is in a subloop, skip it. - // Delete the old, now unused, phi node... - Header->getInstList().erase(IV->Phi); - Changed = true; - ++NumRemoved; + // Check that InVal is defined in the loop. + Instruction *Inst = cast(InVal); + if (!L->contains(Inst->getParent())) + continue; + + // We require that this value either have a computable evolution or that + // the loop have a constant iteration count. In the case where the loop + // has a constant iteration count, we can sometimes force evaluation of + // the exit value through brute force. + SCEVHandle SH = SE->getSCEV(Inst); + if (!SH->hasComputableLoopEvolution(L) && !HasConstantItCount) + continue; // Cannot get exit evolution for the loop value. + + // Okay, this instruction has a user outside of the current loop + // and varies predictably *inside* the loop. Evaluate the value it + // contains when the loop exits, if possible. + SCEVHandle ExitValue = SE->getSCEVAtScope(Inst, L->getParentLoop()); + if (isa(ExitValue) || + !ExitValue->isLoopInvariant(L)) + continue; + + Changed = true; + ++NumReplaced; + + // See if we already computed the exit value for the instruction, if so, + // just reuse it. + Value *&ExitVal = ExitValues[Inst]; + if (!ExitVal) + ExitVal = Rewriter.expandCodeFor(ExitValue, InsertPt); + + DOUT << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal + << " LoopVal = " << *Inst << "\n"; + + PN->setIncomingValue(i, ExitVal); + + // If this instruction is dead now, schedule it to be removed. + if (Inst->use_empty()) + InstructionsToDelete.insert(Inst); + + // See if this is a single-entry LCSSA PHI node. If so, we can (and + // have to) remove + // the PHI entirely. This is safe, because the NewVal won't be variant + // in the loop, so we don't need an LCSSA phi node anymore. + if (NumPreds == 1) { + SE->deleteValueFromRecords(PN); + PN->replaceAllUsesWith(ExitVal); + PN->eraseFromParent(); + break; + } + } } } + + DeleteTriviallyDeadInstructions(InstructionsToDelete); +} + +bool IndVarSimplify::doInitialization(Loop *L, LPPassManager &LPM) { + + Changed = false; + // 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(); + SE = &LPM.getAnalysis(); + + std::set DeadInsts; + for (BasicBlock::iterator I = Header->begin(); isa(I); ++I) { + PHINode *PN = cast(I); + if (isa(PN->getType())) + EliminatePointerRecurrence(PN, Preheader, DeadInsts); + } + + if (!DeadInsts.empty()) + DeleteTriviallyDeadInstructions(DeadInsts); return Changed; } -namespace { - struct InductionVariableSimplify : public FunctionPass { - virtual bool runOnFunction(Function &) { - LoopInfo &LI = getAnalysis(); - - // Induction Variables live in the header nodes of loops - return reduce_apply_bool(LI.getTopLevelLoops().begin(), - LI.getTopLevelLoops().end(), - std::bind1st(std::ptr_fun(TransformLoop), &LI)); +bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) { + + + LI = &getAnalysis(); + SE = &getAnalysis(); + + Changed = false; + BasicBlock *Header = L->getHeader(); + std::set DeadInsts; + + // Verify the input to the pass in already in LCSSA form. + assert(L->isLCSSAForm()); + + // 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(IterationCount)) + RewriteLoopExitValues(L); + + // Next, analyze all of the induction variables in the loop, canonicalizing + // auxillary induction variables. + std::vector > IndVars; + + for (BasicBlock::iterator I = Header->begin(); isa(I); ++I) { + PHINode *PN = cast(I); + if (PN->getType()->isInteger()) { // FIXME: when we have fast-math, enable! + SCEVHandle SCEV = SE->getSCEV(PN); + if (SCEV->hasComputableLoopEvolution(L)) + // FIXME: It is an extremely bad idea to indvar substitute anything more + // complex than affine induction variables. Doing so will put expensive + // polynomial evaluations inside of the loop, and the str reduction pass + // currently can only reduce affine polynomials. For now just disable + // indvar subst on anything more complex than an affine addrec. + if (SCEVAddRecExpr *AR = dyn_cast(SCEV)) + if (AR->isAffine()) + IndVars.push_back(std::make_pair(PN, SCEV)); } - - virtual void getAnalysisUsage(AnalysisUsage &AU) const { - AU.addRequired(LoopInfo::ID); - AU.preservesCFG(); + } + + // 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(IterationCount)) { + SCEVExpander Rewriter(*SE, *LI); + Rewriter.getOrInsertCanonicalInductionVariable(L, + IterationCount->getType()); + if (Instruction *I = LinearFunctionTestReplace(L, IterationCount, + Rewriter)) { + std::set InstructionsToDelete; + InstructionsToDelete.insert(I); + DeleteTriviallyDeadInstructions(InstructionsToDelete); + } } - }; - RegisterOpt X("indvars", - "Cannonicalize Induction Variables"); -} + return Changed; + } + + // 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->getPrimitiveSizeInBits() != LargestType->getPrimitiveSizeInBits(); + if (Ty->getPrimitiveSizeInBits() > LargestType->getPrimitiveSizeInBits()) + 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. + Value *IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L,LargestType); + ++NumInserted; + Changed = true; + DOUT << "INDVARS: New CanIV: " << *IndVar; + + if (!isa(IterationCount)) { + if (IterationCount->getType()->getPrimitiveSizeInBits() < + LargestType->getPrimitiveSizeInBits()) + IterationCount = SE->getZeroExtendExpr(IterationCount, LargestType); + else if (IterationCount->getType() != LargestType) + IterationCount = SE->getTruncateExpr(IterationCount, LargestType); + if (Instruction *DI = LinearFunctionTestReplace(L, IterationCount,Rewriter)) + DeadInsts.insert(DI); + } + + // 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(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) { + SmallVector InsertedSizes; + InsertedSizes.push_back(LargestType->getPrimitiveSizeInBits()); + for (unsigned i = 0, e = IndVars.size(); i != e; ++i) { + unsigned ithSize = IndVars[i].first->getType()->getPrimitiveSizeInBits(); + if (std::find(InsertedSizes.begin(), InsertedSizes.end(), ithSize) + == InsertedSizes.end()) { + PHINode *PN = IndVars[i].first; + InsertedSizes.push_back(ithSize); + Instruction *New = new TruncInst(IndVar, PN->getType(), "indvar", + InsertPt); + Rewriter.addInsertedValue(New, SE->getSCEV(New)); + DOUT << "INDVARS: Made trunc IV for " << *PN + << " NewVal = " << *New << "\n"; + } + } + } + + // Rewrite all induction variables in terms of the canonical induction + // variable. + std::map InsertedSizes; + while (!IndVars.empty()) { + PHINode *PN = IndVars.back().first; + Value *NewVal = Rewriter.expandCodeFor(IndVars.back().second, InsertPt); + DOUT << "INDVARS: Rewrote IV '" << *IndVars.back().second << "' " << *PN + << " into = " << *NewVal << "\n"; + NewVal->takeName(PN); -Pass *createIndVarSimplifyPass() { - return new InductionVariableSimplify(); + // 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(V)) + V->takeName(I); + I->replaceAllUsesWith(V); + DeadInsts.insert(I); + ++NumRemoved; + Changed = true; + } + } + } +#endif + + DeleteTriviallyDeadInstructions(DeadInsts); + + assert(L->isLCSSAForm()); + return Changed; }