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Diffstat (limited to 'contrib/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp')
| -rw-r--r-- | contrib/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp | 1022 |
1 files changed, 1022 insertions, 0 deletions
diff --git a/contrib/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp b/contrib/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp new file mode 100644 index 0000000..36bea67 --- /dev/null +++ b/contrib/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp @@ -0,0 +1,1022 @@ +//===- 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) {} + + 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, + Value *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; +static RegisterPass<IndVarSimplify> +X("indvars", "Canonicalize Induction Variables"); + +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, + Value *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 = L->getCanonicalInductionVariableIncrement(); + } else { + // We have to use the preincremented value... + RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount, + IndVar->getType()); + CmpIndVar = IndVar; + } + + // Expand the code for the iteration count. + assert(RHS->isLoopInvariant(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 (!ExitValue->isLoopInvariant(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) { + 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. + Value *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) { + // Loop-invariant values are safe. + if (S->isLoopInvariant(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)) 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); + + // A udiv is safe if its operands are. + if (const SCEVUDivExpr *UD = dyn_cast<SCEVUDivExpr>(S)) + return isSafe(UD->getLHS(), L) && + isSafe(UD->getRHS(), L); + + // 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 (ExitVal->isLoopInvariant(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)) + 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) { + BasicBlock *UseBB = cast<Instruction>(UI)->getParent(); + if (PHINode *P = dyn_cast<PHINode>(UI)) { + 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); +} |
