| //===- IndVarSimplify.cpp - Induction Variable Elimination ----------------===// |
| // |
| // 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. The canonical induction variable is guaranteed to be in a wide enough |
| // type so that IV expressions need not be (directly) zero-extended or |
| // sign-extended. |
| // 4. 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. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #define DEBUG_TYPE "indvars" |
| #include "llvm/Transforms/Scalar.h" |
| #include "llvm/BasicBlock.h" |
| #include "llvm/Constants.h" |
| #include "llvm/Instructions.h" |
| #include "llvm/IntrinsicInst.h" |
| #include "llvm/LLVMContext.h" |
| #include "llvm/Type.h" |
| #include "llvm/Analysis/Dominators.h" |
| #include "llvm/Analysis/IVUsers.h" |
| #include "llvm/Analysis/ScalarEvolutionExpander.h" |
| #include "llvm/Analysis/LoopInfo.h" |
| #include "llvm/Analysis/LoopPass.h" |
| #include "llvm/Support/CFG.h" |
| #include "llvm/Support/CommandLine.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/raw_ostream.h" |
| #include "llvm/Transforms/Utils/Local.h" |
| #include "llvm/Transforms/Utils/BasicBlockUtils.h" |
| #include "llvm/ADT/SmallVector.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/ADT/STLExtras.h" |
| using namespace llvm; |
| |
| STATISTIC(NumRemoved , "Number of aux indvars removed"); |
| STATISTIC(NumInserted, "Number of canonical indvars added"); |
| STATISTIC(NumReplaced, "Number of exit values replaced"); |
| STATISTIC(NumLFTR , "Number of loop exit tests replaced"); |
| |
| namespace { |
| class IndVarSimplify : public LoopPass { |
| IVUsers *IU; |
| LoopInfo *LI; |
| ScalarEvolution *SE; |
| DominatorTree *DT; |
| bool Changed; |
| public: |
| |
| static char ID; // Pass identification, replacement for typeid |
| IndVarSimplify() : LoopPass(ID) { |
| initializeIndVarSimplifyPass(*PassRegistry::getPassRegistry()); |
| } |
| |
| virtual bool runOnLoop(Loop *L, LPPassManager &LPM); |
| |
| virtual void getAnalysisUsage(AnalysisUsage &AU) const { |
| AU.addRequired<DominatorTree>(); |
| AU.addRequired<LoopInfo>(); |
| AU.addRequired<ScalarEvolution>(); |
| AU.addRequiredID(LoopSimplifyID); |
| AU.addRequiredID(LCSSAID); |
| AU.addRequired<IVUsers>(); |
| AU.addPreserved<ScalarEvolution>(); |
| AU.addPreservedID(LoopSimplifyID); |
| AU.addPreservedID(LCSSAID); |
| AU.addPreserved<IVUsers>(); |
| AU.setPreservesCFG(); |
| } |
| |
| private: |
| |
| void EliminateIVComparisons(); |
| void EliminateIVRemainders(); |
| void RewriteNonIntegerIVs(Loop *L); |
| |
| ICmpInst *LinearFunctionTestReplace(Loop *L, const SCEV *BackedgeTakenCount, |
| PHINode *IndVar, |
| BasicBlock *ExitingBlock, |
| BranchInst *BI, |
| SCEVExpander &Rewriter); |
| void RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter); |
| |
| void RewriteIVExpressions(Loop *L, SCEVExpander &Rewriter); |
| |
| void SinkUnusedInvariants(Loop *L); |
| |
| void HandleFloatingPointIV(Loop *L, PHINode *PH); |
| }; |
| } |
| |
| char IndVarSimplify::ID = 0; |
| INITIALIZE_PASS_BEGIN(IndVarSimplify, "indvars", |
| "Canonicalize Induction Variables", false, false) |
| INITIALIZE_PASS_DEPENDENCY(DominatorTree) |
| INITIALIZE_PASS_DEPENDENCY(LoopInfo) |
| INITIALIZE_PASS_DEPENDENCY(ScalarEvolution) |
| INITIALIZE_PASS_DEPENDENCY(LoopSimplify) |
| INITIALIZE_PASS_DEPENDENCY(LCSSA) |
| INITIALIZE_PASS_DEPENDENCY(IVUsers) |
| INITIALIZE_PASS_END(IndVarSimplify, "indvars", |
| "Canonicalize Induction Variables", false, false) |
| |
| Pass *llvm::createIndVarSimplifyPass() { |
| return new IndVarSimplify(); |
| } |
| |
| /// 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. |
| ICmpInst *IndVarSimplify::LinearFunctionTestReplace(Loop *L, |
| const SCEV *BackedgeTakenCount, |
| PHINode *IndVar, |
| BasicBlock *ExitingBlock, |
| BranchInst *BI, |
| SCEVExpander &Rewriter) { |
| // Special case: If the backedge-taken count is a UDiv, it's very likely a |
| // UDiv that ScalarEvolution produced in order to compute a precise |
| // expression, rather than a UDiv from the user's code. If we can't find a |
| // UDiv in the code with some simple searching, assume the former and forego |
| // rewriting the loop. |
| if (isa<SCEVUDivExpr>(BackedgeTakenCount)) { |
| ICmpInst *OrigCond = dyn_cast<ICmpInst>(BI->getCondition()); |
| if (!OrigCond) return 0; |
| const SCEV *R = SE->getSCEV(OrigCond->getOperand(1)); |
| R = SE->getMinusSCEV(R, SE->getConstant(R->getType(), 1)); |
| if (R != BackedgeTakenCount) { |
| const SCEV *L = SE->getSCEV(OrigCond->getOperand(0)); |
| L = SE->getMinusSCEV(L, SE->getConstant(L->getType(), 1)); |
| if (L != BackedgeTakenCount) |
| return 0; |
| } |
| } |
| |
| // 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. |
| Value *CmpIndVar; |
| const SCEV *RHS = BackedgeTakenCount; |
| if (ExitingBlock == L->getLoopLatch()) { |
| // Add one to the "backedge-taken" count to get the trip count. |
| // If this addition may overflow, we have to be more pessimistic and |
| // cast the induction variable before doing the add. |
| const SCEV *Zero = SE->getConstant(BackedgeTakenCount->getType(), 0); |
| const SCEV *N = |
| SE->getAddExpr(BackedgeTakenCount, |
| SE->getConstant(BackedgeTakenCount->getType(), 1)); |
| if ((isa<SCEVConstant>(N) && !N->isZero()) || |
| SE->isLoopEntryGuardedByCond(L, ICmpInst::ICMP_NE, N, Zero)) { |
| // No overflow. Cast the sum. |
| RHS = SE->getTruncateOrZeroExtend(N, IndVar->getType()); |
| } else { |
| // Potential overflow. Cast before doing the add. |
| RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount, |
| IndVar->getType()); |
| RHS = SE->getAddExpr(RHS, |
| SE->getConstant(IndVar->getType(), 1)); |
| } |
| |
| // The BackedgeTaken expression contains the number of times that the |
| // backedge branches to the loop header. This is one less than the |
| // number of times the loop executes, so use the incremented indvar. |
| CmpIndVar = IndVar->getIncomingValueForBlock(ExitingBlock); |
| } else { |
| // We have to use the preincremented value... |
| RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount, |
| IndVar->getType()); |
| CmpIndVar = IndVar; |
| } |
| |
| // Expand the code for the iteration count. |
| assert(SE->isLoopInvariant(RHS, L) && |
| "Computed iteration count is not loop invariant!"); |
| Value *ExitCnt = Rewriter.expandCodeFor(RHS, IndVar->getType(), BI); |
| |
| // 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; |
| |
| DEBUG(dbgs() << "INDVARS: Rewriting loop exit condition to:\n" |
| << " LHS:" << *CmpIndVar << '\n' |
| << " op:\t" |
| << (Opcode == ICmpInst::ICMP_NE ? "!=" : "==") << "\n" |
| << " RHS:\t" << *RHS << "\n"); |
| |
| ICmpInst *Cond = new ICmpInst(BI, Opcode, CmpIndVar, ExitCnt, "exitcond"); |
| |
| Value *OrigCond = BI->getCondition(); |
| // It's tempting to use replaceAllUsesWith here to fully replace the old |
| // comparison, but that's not immediately safe, since users of the old |
| // comparison may not be dominated by the new comparison. Instead, just |
| // update the branch to use the new comparison; in the common case this |
| // will make old comparison dead. |
| BI->setCondition(Cond); |
| RecursivelyDeleteTriviallyDeadInstructions(OrigCond); |
| |
| ++NumLFTR; |
| Changed = true; |
| return Cond; |
| } |
| |
| /// 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. |
| /// |
| /// This is mostly redundant with the regular IndVarSimplify activities that |
| /// happen later, except that it's more powerful in some cases, because it's |
| /// able to brute-force evaluate arbitrary instructions as long as they have |
| /// constant operands at the beginning of the loop. |
| void IndVarSimplify::RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter) { |
| // Verify the input to the pass in already in LCSSA form. |
| assert(L->isLCSSAForm(*DT)); |
| |
| SmallVector<BasicBlock*, 8> ExitBlocks; |
| L->getUniqueExitBlocks(ExitBlocks); |
| |
| // 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<PHINode>(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<PHINode>(BBI++))) { |
| if (PN->use_empty()) |
| continue; // dead use, don't replace it |
| |
| // SCEV only supports integer expressions for now. |
| if (!PN->getType()->isIntegerTy() && !PN->getType()->isPointerTy()) |
| continue; |
| |
| // It's necessary to tell ScalarEvolution about this explicitly so that |
| // it can walk the def-use list and forget all SCEVs, as it may not be |
| // watching the PHI itself. Once the new exit value is in place, there |
| // may not be a def-use connection between the loop and every instruction |
| // which got a SCEVAddRecExpr for that loop. |
| SE->forgetValue(PN); |
| |
| // 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<Instruction>(InVal)) |
| continue; |
| |
| // 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. |
| |
| // Check that InVal is defined in the loop. |
| Instruction *Inst = cast<Instruction>(InVal); |
| if (!L->contains(Inst)) |
| continue; |
| |
| // 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. |
| const SCEV *ExitValue = SE->getSCEVAtScope(Inst, L->getParentLoop()); |
| if (!SE->isLoopInvariant(ExitValue, L)) |
| continue; |
| |
| Changed = true; |
| ++NumReplaced; |
| |
| Value *ExitVal = Rewriter.expandCodeFor(ExitValue, PN->getType(), Inst); |
| |
| DEBUG(dbgs() << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal << '\n' |
| << " LoopVal = " << *Inst << "\n"); |
| |
| PN->setIncomingValue(i, ExitVal); |
| |
| // If this instruction is dead now, delete it. |
| RecursivelyDeleteTriviallyDeadInstructions(Inst); |
| |
| if (NumPreds == 1) { |
| // Completely replace a single-pred PHI. This is safe, because the |
| // NewVal won't be variant in the loop, so we don't need an LCSSA phi |
| // node anymore. |
| PN->replaceAllUsesWith(ExitVal); |
| RecursivelyDeleteTriviallyDeadInstructions(PN); |
| } |
| } |
| if (NumPreds != 1) { |
| // Clone the PHI and delete the original one. This lets IVUsers and |
| // any other maps purge the original user from their records. |
| PHINode *NewPN = cast<PHINode>(PN->clone()); |
| NewPN->takeName(PN); |
| NewPN->insertBefore(PN); |
| PN->replaceAllUsesWith(NewPN); |
| PN->eraseFromParent(); |
| } |
| } |
| } |
| |
| // The insertion point instruction may have been deleted; clear it out |
| // so that the rewriter doesn't trip over it later. |
| Rewriter.clearInsertPoint(); |
| } |
| |
| void IndVarSimplify::RewriteNonIntegerIVs(Loop *L) { |
| // First step. Check to see if there are any floating-point recurrences. |
| // If there are, change them into integer recurrences, permitting analysis by |
| // the SCEV routines. |
| // |
| BasicBlock *Header = L->getHeader(); |
| |
| SmallVector<WeakVH, 8> PHIs; |
| for (BasicBlock::iterator I = Header->begin(); |
| PHINode *PN = dyn_cast<PHINode>(I); ++I) |
| PHIs.push_back(PN); |
| |
| for (unsigned i = 0, e = PHIs.size(); i != e; ++i) |
| if (PHINode *PN = dyn_cast_or_null<PHINode>(&*PHIs[i])) |
| HandleFloatingPointIV(L, PN); |
| |
| // If the loop previously had floating-point IV, ScalarEvolution |
| // may not have been able to compute a trip count. Now that we've done some |
| // re-writing, the trip count may be computable. |
| if (Changed) |
| SE->forgetLoop(L); |
| } |
| |
| void IndVarSimplify::EliminateIVComparisons() { |
| SmallVector<WeakVH, 16> DeadInsts; |
| |
| // Look for ICmp users. |
| for (IVUsers::iterator I = IU->begin(), E = IU->end(); I != E; ++I) { |
| IVStrideUse &UI = *I; |
| ICmpInst *ICmp = dyn_cast<ICmpInst>(UI.getUser()); |
| if (!ICmp) continue; |
| |
| bool Swapped = UI.getOperandValToReplace() == ICmp->getOperand(1); |
| ICmpInst::Predicate Pred = ICmp->getPredicate(); |
| if (Swapped) Pred = ICmpInst::getSwappedPredicate(Pred); |
| |
| // Get the SCEVs for the ICmp operands. |
| const SCEV *S = IU->getReplacementExpr(UI); |
| const SCEV *X = SE->getSCEV(ICmp->getOperand(!Swapped)); |
| |
| // Simplify unnecessary loops away. |
| const Loop *ICmpLoop = LI->getLoopFor(ICmp->getParent()); |
| S = SE->getSCEVAtScope(S, ICmpLoop); |
| X = SE->getSCEVAtScope(X, ICmpLoop); |
| |
| // If the condition is always true or always false, replace it with |
| // a constant value. |
| if (SE->isKnownPredicate(Pred, S, X)) |
| ICmp->replaceAllUsesWith(ConstantInt::getTrue(ICmp->getContext())); |
| else if (SE->isKnownPredicate(ICmpInst::getInversePredicate(Pred), S, X)) |
| ICmp->replaceAllUsesWith(ConstantInt::getFalse(ICmp->getContext())); |
| else |
| continue; |
| |
| DEBUG(dbgs() << "INDVARS: Eliminated comparison: " << *ICmp << '\n'); |
| DeadInsts.push_back(ICmp); |
| } |
| |
| // Now that we're done iterating through lists, clean up any instructions |
| // which are now dead. |
| while (!DeadInsts.empty()) |
| if (Instruction *Inst = |
| dyn_cast_or_null<Instruction>(&*DeadInsts.pop_back_val())) |
| RecursivelyDeleteTriviallyDeadInstructions(Inst); |
| } |
| |
| void IndVarSimplify::EliminateIVRemainders() { |
| SmallVector<WeakVH, 16> DeadInsts; |
| |
| // Look for SRem and URem users. |
| for (IVUsers::iterator I = IU->begin(), E = IU->end(); I != E; ++I) { |
| IVStrideUse &UI = *I; |
| BinaryOperator *Rem = dyn_cast<BinaryOperator>(UI.getUser()); |
| if (!Rem) continue; |
| |
| bool isSigned = Rem->getOpcode() == Instruction::SRem; |
| if (!isSigned && Rem->getOpcode() != Instruction::URem) |
| continue; |
| |
| // We're only interested in the case where we know something about |
| // the numerator. |
| if (UI.getOperandValToReplace() != Rem->getOperand(0)) |
| continue; |
| |
| // Get the SCEVs for the ICmp operands. |
| const SCEV *S = SE->getSCEV(Rem->getOperand(0)); |
| const SCEV *X = SE->getSCEV(Rem->getOperand(1)); |
| |
| // Simplify unnecessary loops away. |
| const Loop *ICmpLoop = LI->getLoopFor(Rem->getParent()); |
| S = SE->getSCEVAtScope(S, ICmpLoop); |
| X = SE->getSCEVAtScope(X, ICmpLoop); |
| |
| // i % n --> i if i is in [0,n). |
| if ((!isSigned || SE->isKnownNonNegative(S)) && |
| SE->isKnownPredicate(isSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT, |
| S, X)) |
| Rem->replaceAllUsesWith(Rem->getOperand(0)); |
| else { |
| // (i+1) % n --> (i+1)==n?0:(i+1) if i is in [0,n). |
| const SCEV *LessOne = |
| SE->getMinusSCEV(S, SE->getConstant(S->getType(), 1)); |
| if ((!isSigned || SE->isKnownNonNegative(LessOne)) && |
| SE->isKnownPredicate(isSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT, |
| LessOne, X)) { |
| ICmpInst *ICmp = new ICmpInst(Rem, ICmpInst::ICMP_EQ, |
| Rem->getOperand(0), Rem->getOperand(1), |
| "tmp"); |
| SelectInst *Sel = |
| SelectInst::Create(ICmp, |
| ConstantInt::get(Rem->getType(), 0), |
| Rem->getOperand(0), "tmp", Rem); |
| Rem->replaceAllUsesWith(Sel); |
| } else |
| continue; |
| } |
| |
| // Inform IVUsers about the new users. |
| if (Instruction *I = dyn_cast<Instruction>(Rem->getOperand(0))) |
| IU->AddUsersIfInteresting(I); |
| |
| DEBUG(dbgs() << "INDVARS: Simplified rem: " << *Rem << '\n'); |
| DeadInsts.push_back(Rem); |
| } |
| |
| // Now that we're done iterating through lists, clean up any instructions |
| // which are now dead. |
| while (!DeadInsts.empty()) |
| if (Instruction *Inst = |
| dyn_cast_or_null<Instruction>(&*DeadInsts.pop_back_val())) |
| RecursivelyDeleteTriviallyDeadInstructions(Inst); |
| } |
| |
| bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) { |
| // If LoopSimplify form is not available, stay out of trouble. Some notes: |
| // - LSR currently only supports LoopSimplify-form loops. Indvars' |
| // canonicalization can be a pessimization without LSR to "clean up" |
| // afterwards. |
| // - We depend on having a preheader; in particular, |
| // Loop::getCanonicalInductionVariable only supports loops with preheaders, |
| // and we're in trouble if we can't find the induction variable even when |
| // we've manually inserted one. |
| if (!L->isLoopSimplifyForm()) |
| return false; |
| |
| IU = &getAnalysis<IVUsers>(); |
| LI = &getAnalysis<LoopInfo>(); |
| SE = &getAnalysis<ScalarEvolution>(); |
| DT = &getAnalysis<DominatorTree>(); |
| Changed = false; |
| |
| // If there are any floating-point recurrences, attempt to |
| // transform them to use integer recurrences. |
| RewriteNonIntegerIVs(L); |
| |
| BasicBlock *ExitingBlock = L->getExitingBlock(); // may be null |
| const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L); |
| |
| // Create a rewriter object which we'll use to transform the code with. |
| SCEVExpander Rewriter(*SE); |
| |
| // 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. |
| // |
| if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount)) |
| RewriteLoopExitValues(L, Rewriter); |
| |
| // Simplify ICmp IV users. |
| EliminateIVComparisons(); |
| |
| // Simplify SRem and URem IV users. |
| EliminateIVRemainders(); |
| |
| // Compute the type of the largest recurrence expression, and decide whether |
| // a canonical induction variable should be inserted. |
| const Type *LargestType = 0; |
| bool NeedCannIV = false; |
| if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount)) { |
| LargestType = BackedgeTakenCount->getType(); |
| LargestType = SE->getEffectiveSCEVType(LargestType); |
| // If we have a known trip count and a single exit block, we'll be |
| // rewriting the loop exit test condition below, which requires a |
| // canonical induction variable. |
| if (ExitingBlock) |
| NeedCannIV = true; |
| } |
| for (IVUsers::const_iterator I = IU->begin(), E = IU->end(); I != E; ++I) { |
| const Type *Ty = |
| SE->getEffectiveSCEVType(I->getOperandValToReplace()->getType()); |
| if (!LargestType || |
| SE->getTypeSizeInBits(Ty) > |
| SE->getTypeSizeInBits(LargestType)) |
| LargestType = Ty; |
| NeedCannIV = true; |
| } |
| |
| // Now that we know the largest of the induction variable expressions |
| // in this loop, insert a canonical induction variable of the largest size. |
| PHINode *IndVar = 0; |
| if (NeedCannIV) { |
| // Check to see if the loop already has any canonical-looking induction |
| // variables. If any are present and wider than the planned canonical |
| // induction variable, temporarily remove them, so that the Rewriter |
| // doesn't attempt to reuse them. |
| SmallVector<PHINode *, 2> OldCannIVs; |
| while (PHINode *OldCannIV = L->getCanonicalInductionVariable()) { |
| if (SE->getTypeSizeInBits(OldCannIV->getType()) > |
| SE->getTypeSizeInBits(LargestType)) |
| OldCannIV->removeFromParent(); |
| else |
| break; |
| OldCannIVs.push_back(OldCannIV); |
| } |
| |
| IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L, LargestType); |
| |
| ++NumInserted; |
| Changed = true; |
| DEBUG(dbgs() << "INDVARS: New CanIV: " << *IndVar << '\n'); |
| |
| // Now that the official induction variable is established, reinsert |
| // any old canonical-looking variables after it so that the IR remains |
| // consistent. They will be deleted as part of the dead-PHI deletion at |
| // the end of the pass. |
| while (!OldCannIVs.empty()) { |
| PHINode *OldCannIV = OldCannIVs.pop_back_val(); |
| OldCannIV->insertBefore(L->getHeader()->getFirstNonPHI()); |
| } |
| } |
| |
| // If we have a trip count expression, rewrite the loop's exit condition |
| // using it. We can currently only handle loops with a single exit. |
| ICmpInst *NewICmp = 0; |
| if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount) && |
| !BackedgeTakenCount->isZero() && |
| ExitingBlock) { |
| assert(NeedCannIV && |
| "LinearFunctionTestReplace requires a canonical induction variable"); |
| // Can't rewrite non-branch yet. |
| if (BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator())) |
| NewICmp = LinearFunctionTestReplace(L, BackedgeTakenCount, IndVar, |
| ExitingBlock, BI, Rewriter); |
| } |
| |
| // Rewrite IV-derived expressions. Clears the rewriter cache. |
| RewriteIVExpressions(L, Rewriter); |
| |
| // The Rewriter may not be used from this point on. |
| |
| // Loop-invariant instructions in the preheader that aren't used in the |
| // loop may be sunk below the loop to reduce register pressure. |
| SinkUnusedInvariants(L); |
| |
| // For completeness, inform IVUsers of the IV use in the newly-created |
| // loop exit test instruction. |
| if (NewICmp) |
| IU->AddUsersIfInteresting(cast<Instruction>(NewICmp->getOperand(0))); |
| |
| // Clean up dead instructions. |
| Changed |= DeleteDeadPHIs(L->getHeader()); |
| // Check a post-condition. |
| assert(L->isLCSSAForm(*DT) && "Indvars did not leave the loop in lcssa form!"); |
| return Changed; |
| } |
| |
| // 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, unless |
| // it can be expanded to a trivial value. |
| static bool isSafe(const SCEV *S, const Loop *L, ScalarEvolution *SE) { |
| // Loop-invariant values are safe. |
| if (SE->isLoopInvariant(S, L)) return true; |
| |
| // Affine addrecs are safe. Non-affine are not, because LSR doesn't know how |
| // to transform them into efficient code. |
| if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) |
| return AR->isAffine(); |
| |
| // An add is safe it all its operands are safe. |
| if (const SCEVCommutativeExpr *Commutative = dyn_cast<SCEVCommutativeExpr>(S)) { |
| for (SCEVCommutativeExpr::op_iterator I = Commutative->op_begin(), |
| E = Commutative->op_end(); I != E; ++I) |
| if (!isSafe(*I, L, SE)) return false; |
| return true; |
| } |
| |
| // A cast is safe if its operand is. |
| if (const SCEVCastExpr *C = dyn_cast<SCEVCastExpr>(S)) |
| return isSafe(C->getOperand(), L, SE); |
| |
| // A udiv is safe if its operands are. |
| if (const SCEVUDivExpr *UD = dyn_cast<SCEVUDivExpr>(S)) |
| return isSafe(UD->getLHS(), L, SE) && |
| isSafe(UD->getRHS(), L, SE); |
| |
| // SCEVUnknown is always safe. |
| if (isa<SCEVUnknown>(S)) |
| return true; |
| |
| // Nothing else is safe. |
| return false; |
| } |
| |
| void IndVarSimplify::RewriteIVExpressions(Loop *L, SCEVExpander &Rewriter) { |
| SmallVector<WeakVH, 16> DeadInsts; |
| |
| // Rewrite all induction variable expressions in terms of the canonical |
| // induction variable. |
| // |
| // If there were induction variables of other sizes or offsets, manually |
| // add the offsets to the primary induction variable and cast, avoiding |
| // the need for the code evaluation methods to insert induction variables |
| // of different sizes. |
| for (IVUsers::iterator UI = IU->begin(), E = IU->end(); UI != E; ++UI) { |
| Value *Op = UI->getOperandValToReplace(); |
| const Type *UseTy = Op->getType(); |
| Instruction *User = UI->getUser(); |
| |
| // Compute the final addrec to expand into code. |
| const SCEV *AR = IU->getReplacementExpr(*UI); |
| |
| // Evaluate the expression out of the loop, if possible. |
| if (!L->contains(UI->getUser())) { |
| const SCEV *ExitVal = SE->getSCEVAtScope(AR, L->getParentLoop()); |
| if (SE->isLoopInvariant(ExitVal, L)) |
| AR = ExitVal; |
| } |
| |
| // 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, unless |
| // it can be expanded to a trivial value. |
| if (!isSafe(AR, L, SE)) |
| continue; |
| |
| // Determine the insertion point for this user. By default, insert |
| // immediately before the user. The SCEVExpander class will automatically |
| // hoist loop invariants out of the loop. For PHI nodes, there may be |
| // multiple uses, so compute the nearest common dominator for the |
| // incoming blocks. |
| Instruction *InsertPt = User; |
| if (PHINode *PHI = dyn_cast<PHINode>(InsertPt)) |
| for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i) |
| if (PHI->getIncomingValue(i) == Op) { |
| if (InsertPt == User) |
| InsertPt = PHI->getIncomingBlock(i)->getTerminator(); |
| else |
| InsertPt = |
| DT->findNearestCommonDominator(InsertPt->getParent(), |
| PHI->getIncomingBlock(i)) |
| ->getTerminator(); |
| } |
| |
| // Now expand it into actual Instructions and patch it into place. |
| Value *NewVal = Rewriter.expandCodeFor(AR, UseTy, InsertPt); |
| |
| // Inform ScalarEvolution that this value is changing. The change doesn't |
| // affect its value, but it does potentially affect which use lists the |
| // value will be on after the replacement, which affects ScalarEvolution's |
| // ability to walk use lists and drop dangling pointers when a value is |
| // deleted. |
| SE->forgetValue(User); |
| |
| // Patch the new value into place. |
| if (Op->hasName()) |
| NewVal->takeName(Op); |
| User->replaceUsesOfWith(Op, NewVal); |
| UI->setOperandValToReplace(NewVal); |
| DEBUG(dbgs() << "INDVARS: Rewrote IV '" << *AR << "' " << *Op << '\n' |
| << " into = " << *NewVal << "\n"); |
| ++NumRemoved; |
| Changed = true; |
| |
| // The old value may be dead now. |
| DeadInsts.push_back(Op); |
| } |
| |
| // Clear the rewriter cache, because values that are in the rewriter's cache |
| // can be deleted in the loop below, causing the AssertingVH in the cache to |
| // trigger. |
| Rewriter.clear(); |
| // Now that we're done iterating through lists, clean up any instructions |
| // which are now dead. |
| while (!DeadInsts.empty()) |
| if (Instruction *Inst = |
| dyn_cast_or_null<Instruction>(&*DeadInsts.pop_back_val())) |
| RecursivelyDeleteTriviallyDeadInstructions(Inst); |
| } |
| |
| /// If there's a single exit block, sink any loop-invariant values that |
| /// were defined in the preheader but not used inside the loop into the |
| /// exit block to reduce register pressure in the loop. |
| void IndVarSimplify::SinkUnusedInvariants(Loop *L) { |
| BasicBlock *ExitBlock = L->getExitBlock(); |
| if (!ExitBlock) return; |
| |
| BasicBlock *Preheader = L->getLoopPreheader(); |
| if (!Preheader) return; |
| |
| Instruction *InsertPt = ExitBlock->getFirstNonPHI(); |
| BasicBlock::iterator I = Preheader->getTerminator(); |
| while (I != Preheader->begin()) { |
| --I; |
| // New instructions were inserted at the end of the preheader. |
| if (isa<PHINode>(I)) |
| break; |
| |
| // Don't move instructions which might have side effects, since the side |
| // effects need to complete before instructions inside the loop. Also don't |
| // move instructions which might read memory, since the loop may modify |
| // memory. Note that it's okay if the instruction might have undefined |
| // behavior: LoopSimplify guarantees that the preheader dominates the exit |
| // block. |
| if (I->mayHaveSideEffects() || I->mayReadFromMemory()) |
| continue; |
| |
| // Skip debug info intrinsics. |
| if (isa<DbgInfoIntrinsic>(I)) |
| continue; |
| |
| // Don't sink static AllocaInsts out of the entry block, which would |
| // turn them into dynamic allocas! |
| if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) |
| if (AI->isStaticAlloca()) |
| continue; |
| |
| // Determine if there is a use in or before the loop (direct or |
| // otherwise). |
| bool UsedInLoop = false; |
| for (Value::use_iterator UI = I->use_begin(), UE = I->use_end(); |
| UI != UE; ++UI) { |
| User *U = *UI; |
| BasicBlock *UseBB = cast<Instruction>(U)->getParent(); |
| if (PHINode *P = dyn_cast<PHINode>(U)) { |
| unsigned i = |
| PHINode::getIncomingValueNumForOperand(UI.getOperandNo()); |
| UseBB = P->getIncomingBlock(i); |
| } |
| if (UseBB == Preheader || L->contains(UseBB)) { |
| UsedInLoop = true; |
| break; |
| } |
| } |
| |
| // If there is, the def must remain in the preheader. |
| if (UsedInLoop) |
| continue; |
| |
| // Otherwise, sink it to the exit block. |
| Instruction *ToMove = I; |
| bool Done = false; |
| |
| if (I != Preheader->begin()) { |
| // Skip debug info intrinsics. |
| do { |
| --I; |
| } while (isa<DbgInfoIntrinsic>(I) && I != Preheader->begin()); |
| |
| if (isa<DbgInfoIntrinsic>(I) && I == Preheader->begin()) |
| Done = true; |
| } else { |
| Done = true; |
| } |
| |
| ToMove->moveBefore(InsertPt); |
| if (Done) break; |
| InsertPt = ToMove; |
| } |
| } |
| |
| /// ConvertToSInt - Convert APF to an integer, if possible. |
| static bool ConvertToSInt(const APFloat &APF, int64_t &IntVal) { |
| bool isExact = false; |
| if (&APF.getSemantics() == &APFloat::PPCDoubleDouble) |
| return false; |
| // See if we can convert this to an int64_t |
| uint64_t UIntVal; |
| if (APF.convertToInteger(&UIntVal, 64, true, APFloat::rmTowardZero, |
| &isExact) != APFloat::opOK || !isExact) |
| return false; |
| IntVal = UIntVal; |
| return true; |
| } |
| |
| /// HandleFloatingPointIV - If the loop has floating induction variable |
| /// then insert corresponding integer induction variable if possible. |
| /// For example, |
| /// for(double i = 0; i < 10000; ++i) |
| /// bar(i) |
| /// is converted into |
| /// for(int i = 0; i < 10000; ++i) |
| /// bar((double)i); |
| /// |
| void IndVarSimplify::HandleFloatingPointIV(Loop *L, PHINode *PN) { |
| unsigned IncomingEdge = L->contains(PN->getIncomingBlock(0)); |
| unsigned BackEdge = IncomingEdge^1; |
| |
| // Check incoming value. |
| ConstantFP *InitValueVal = |
| dyn_cast<ConstantFP>(PN->getIncomingValue(IncomingEdge)); |
| |
| int64_t InitValue; |
| if (!InitValueVal || !ConvertToSInt(InitValueVal->getValueAPF(), InitValue)) |
| return; |
| |
| // Check IV increment. Reject this PN if increment operation is not |
| // an add or increment value can not be represented by an integer. |
| BinaryOperator *Incr = |
| dyn_cast<BinaryOperator>(PN->getIncomingValue(BackEdge)); |
| if (Incr == 0 || Incr->getOpcode() != Instruction::FAdd) return; |
| |
| // If this is not an add of the PHI with a constantfp, or if the constant fp |
| // is not an integer, bail out. |
| ConstantFP *IncValueVal = dyn_cast<ConstantFP>(Incr->getOperand(1)); |
| int64_t IncValue; |
| if (IncValueVal == 0 || Incr->getOperand(0) != PN || |
| !ConvertToSInt(IncValueVal->getValueAPF(), IncValue)) |
| return; |
| |
| // Check Incr uses. One user is PN and the other user is an exit condition |
| // used by the conditional terminator. |
| Value::use_iterator IncrUse = Incr->use_begin(); |
| Instruction *U1 = cast<Instruction>(*IncrUse++); |
| if (IncrUse == Incr->use_end()) return; |
| Instruction *U2 = cast<Instruction>(*IncrUse++); |
| if (IncrUse != Incr->use_end()) return; |
| |
| // Find exit condition, which is an fcmp. If it doesn't exist, or if it isn't |
| // only used by a branch, we can't transform it. |
| FCmpInst *Compare = dyn_cast<FCmpInst>(U1); |
| if (!Compare) |
| Compare = dyn_cast<FCmpInst>(U2); |
| if (Compare == 0 || !Compare->hasOneUse() || |
| !isa<BranchInst>(Compare->use_back())) |
| return; |
| |
| BranchInst *TheBr = cast<BranchInst>(Compare->use_back()); |
| |
| // We need to verify that the branch actually controls the iteration count |
| // of the loop. If not, the new IV can overflow and no one will notice. |
| // The branch block must be in the loop and one of the successors must be out |
| // of the loop. |
| assert(TheBr->isConditional() && "Can't use fcmp if not conditional"); |
| if (!L->contains(TheBr->getParent()) || |
| (L->contains(TheBr->getSuccessor(0)) && |
| L->contains(TheBr->getSuccessor(1)))) |
| return; |
| |
| |
| // If it isn't a comparison with an integer-as-fp (the exit value), we can't |
| // transform it. |
| ConstantFP *ExitValueVal = dyn_cast<ConstantFP>(Compare->getOperand(1)); |
| int64_t ExitValue; |
| if (ExitValueVal == 0 || |
| !ConvertToSInt(ExitValueVal->getValueAPF(), ExitValue)) |
| return; |
| |
| // Find new predicate for integer comparison. |
| CmpInst::Predicate NewPred = CmpInst::BAD_ICMP_PREDICATE; |
| switch (Compare->getPredicate()) { |
| default: return; // Unknown comparison. |
| case CmpInst::FCMP_OEQ: |
| case CmpInst::FCMP_UEQ: NewPred = CmpInst::ICMP_EQ; break; |
| case CmpInst::FCMP_ONE: |
| case CmpInst::FCMP_UNE: NewPred = CmpInst::ICMP_NE; break; |
| case CmpInst::FCMP_OGT: |
| case CmpInst::FCMP_UGT: NewPred = CmpInst::ICMP_SGT; break; |
| case CmpInst::FCMP_OGE: |
| case CmpInst::FCMP_UGE: NewPred = CmpInst::ICMP_SGE; break; |
| case CmpInst::FCMP_OLT: |
| case CmpInst::FCMP_ULT: NewPred = CmpInst::ICMP_SLT; break; |
| case CmpInst::FCMP_OLE: |
| case CmpInst::FCMP_ULE: NewPred = CmpInst::ICMP_SLE; break; |
| } |
| |
| // We convert the floating point induction variable to a signed i32 value if |
| // we can. This is only safe if the comparison will not overflow in a way |
| // that won't be trapped by the integer equivalent operations. Check for this |
| // now. |
| // TODO: We could use i64 if it is native and the range requires it. |
| |
| // The start/stride/exit values must all fit in signed i32. |
| if (!isInt<32>(InitValue) || !isInt<32>(IncValue) || !isInt<32>(ExitValue)) |
| return; |
| |
| // If not actually striding (add x, 0.0), avoid touching the code. |
| if (IncValue == 0) |
| return; |
| |
| // Positive and negative strides have different safety conditions. |
| if (IncValue > 0) { |
| // If we have a positive stride, we require the init to be less than the |
| // exit value and an equality or less than comparison. |
| if (InitValue >= ExitValue || |
| NewPred == CmpInst::ICMP_SGT || NewPred == CmpInst::ICMP_SGE) |
| return; |
| |
| uint32_t Range = uint32_t(ExitValue-InitValue); |
| if (NewPred == CmpInst::ICMP_SLE) { |
| // Normalize SLE -> SLT, check for infinite loop. |
| if (++Range == 0) return; // Range overflows. |
| } |
| |
| unsigned Leftover = Range % uint32_t(IncValue); |
| |
| // If this is an equality comparison, we require that the strided value |
| // exactly land on the exit value, otherwise the IV condition will wrap |
| // around and do things the fp IV wouldn't. |
| if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) && |
| Leftover != 0) |
| return; |
| |
| // If the stride would wrap around the i32 before exiting, we can't |
| // transform the IV. |
| if (Leftover != 0 && int32_t(ExitValue+IncValue) < ExitValue) |
| return; |
| |
| } else { |
| // If we have a negative stride, we require the init to be greater than the |
| // exit value and an equality or greater than comparison. |
| if (InitValue >= ExitValue || |
| NewPred == CmpInst::ICMP_SLT || NewPred == CmpInst::ICMP_SLE) |
| return; |
| |
| uint32_t Range = uint32_t(InitValue-ExitValue); |
| if (NewPred == CmpInst::ICMP_SGE) { |
| // Normalize SGE -> SGT, check for infinite loop. |
| if (++Range == 0) return; // Range overflows. |
| } |
| |
| unsigned Leftover = Range % uint32_t(-IncValue); |
| |
| // If this is an equality comparison, we require that the strided value |
| // exactly land on the exit value, otherwise the IV condition will wrap |
| // around and do things the fp IV wouldn't. |
| if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) && |
| Leftover != 0) |
| return; |
| |
| // If the stride would wrap around the i32 before exiting, we can't |
| // transform the IV. |
| if (Leftover != 0 && int32_t(ExitValue+IncValue) > ExitValue) |
| return; |
| } |
| |
| const IntegerType *Int32Ty = Type::getInt32Ty(PN->getContext()); |
| |
| // Insert new integer induction variable. |
| PHINode *NewPHI = PHINode::Create(Int32Ty, PN->getName()+".int", PN); |
| NewPHI->addIncoming(ConstantInt::get(Int32Ty, InitValue), |
| PN->getIncomingBlock(IncomingEdge)); |
| |
| Value *NewAdd = |
| BinaryOperator::CreateAdd(NewPHI, ConstantInt::get(Int32Ty, IncValue), |
| Incr->getName()+".int", Incr); |
| NewPHI->addIncoming(NewAdd, PN->getIncomingBlock(BackEdge)); |
| |
| ICmpInst *NewCompare = new ICmpInst(TheBr, NewPred, NewAdd, |
| ConstantInt::get(Int32Ty, ExitValue), |
| Compare->getName()); |
| |
| // In the following deletions, PN may become dead and may be deleted. |
| // Use a WeakVH to observe whether this happens. |
| WeakVH WeakPH = PN; |
| |
| // Delete the old floating point exit comparison. The branch starts using the |
| // new comparison. |
| NewCompare->takeName(Compare); |
| Compare->replaceAllUsesWith(NewCompare); |
| RecursivelyDeleteTriviallyDeadInstructions(Compare); |
| |
| // Delete the old floating point increment. |
| Incr->replaceAllUsesWith(UndefValue::get(Incr->getType())); |
| RecursivelyDeleteTriviallyDeadInstructions(Incr); |
| |
| // If the FP induction variable still has uses, this is because something else |
| // in the loop uses its value. In order to canonicalize the induction |
| // variable, we chose to eliminate the IV and rewrite it in terms of an |
| // int->fp cast. |
| // |
| // We give preference to sitofp over uitofp because it is faster on most |
| // platforms. |
| if (WeakPH) { |
| Value *Conv = new SIToFPInst(NewPHI, PN->getType(), "indvar.conv", |
| PN->getParent()->getFirstNonPHI()); |
| PN->replaceAllUsesWith(Conv); |
| RecursivelyDeleteTriviallyDeadInstructions(PN); |
| } |
| |
| // Add a new IVUsers entry for the newly-created integer PHI. |
| IU->AddUsersIfInteresting(NewPHI); |
| } |