| //===- 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. |
| // |
| // 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. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Transforms/Scalar.h" |
| #include "llvm/ADT/DenseMap.h" |
| #include "llvm/ADT/SmallVector.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/Analysis/LoopInfo.h" |
| #include "llvm/Analysis/LoopPass.h" |
| #include "llvm/Analysis/ScalarEvolutionExpander.h" |
| #include "llvm/Analysis/TargetLibraryInfo.h" |
| #include "llvm/Analysis/TargetTransformInfo.h" |
| #include "llvm/IR/BasicBlock.h" |
| #include "llvm/IR/CFG.h" |
| #include "llvm/IR/Constants.h" |
| #include "llvm/IR/DataLayout.h" |
| #include "llvm/IR/Dominators.h" |
| #include "llvm/IR/Instructions.h" |
| #include "llvm/IR/IntrinsicInst.h" |
| #include "llvm/IR/LLVMContext.h" |
| #include "llvm/IR/PatternMatch.h" |
| #include "llvm/IR/Type.h" |
| #include "llvm/Support/CommandLine.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/raw_ostream.h" |
| #include "llvm/Transforms/Utils/BasicBlockUtils.h" |
| #include "llvm/Transforms/Utils/Local.h" |
| #include "llvm/Transforms/Utils/SimplifyIndVar.h" |
| using namespace llvm; |
| |
| #define DEBUG_TYPE "indvars" |
| |
| STATISTIC(NumWidened , "Number of indvars widened"); |
| STATISTIC(NumReplaced , "Number of exit values replaced"); |
| STATISTIC(NumLFTR , "Number of loop exit tests replaced"); |
| STATISTIC(NumElimExt , "Number of IV sign/zero extends eliminated"); |
| STATISTIC(NumElimIV , "Number of congruent IVs eliminated"); |
| |
| // Trip count verification can be enabled by default under NDEBUG if we |
| // implement a strong expression equivalence checker in SCEV. Until then, we |
| // use the verify-indvars flag, which may assert in some cases. |
| static cl::opt<bool> VerifyIndvars( |
| "verify-indvars", cl::Hidden, |
| cl::desc("Verify the ScalarEvolution result after running indvars")); |
| |
| static cl::opt<bool> ReduceLiveIVs("liv-reduce", cl::Hidden, |
| cl::desc("Reduce live induction variables.")); |
| |
| enum ReplaceExitVal { NeverRepl, OnlyCheapRepl, AlwaysRepl }; |
| |
| static cl::opt<ReplaceExitVal> ReplaceExitValue( |
| "replexitval", cl::Hidden, cl::init(OnlyCheapRepl), |
| cl::desc("Choose the strategy to replace exit value in IndVarSimplify"), |
| cl::values(clEnumValN(NeverRepl, "never", "never replace exit value"), |
| clEnumValN(OnlyCheapRepl, "cheap", |
| "only replace exit value when the cost is cheap"), |
| clEnumValN(AlwaysRepl, "always", |
| "always replace exit value whenever possible"), |
| clEnumValEnd)); |
| |
| namespace { |
| struct RewritePhi; |
| } |
| |
| namespace { |
| class IndVarSimplify : public LoopPass { |
| LoopInfo *LI; |
| ScalarEvolution *SE; |
| DominatorTree *DT; |
| TargetLibraryInfo *TLI; |
| const TargetTransformInfo *TTI; |
| |
| SmallVector<WeakVH, 16> DeadInsts; |
| bool Changed; |
| public: |
| |
| static char ID; // Pass identification, replacement for typeid |
| IndVarSimplify() |
| : LoopPass(ID), LI(nullptr), SE(nullptr), DT(nullptr), Changed(false) { |
| initializeIndVarSimplifyPass(*PassRegistry::getPassRegistry()); |
| } |
| |
| bool runOnLoop(Loop *L, LPPassManager &LPM) override; |
| |
| void getAnalysisUsage(AnalysisUsage &AU) const override { |
| AU.addRequired<DominatorTreeWrapperPass>(); |
| AU.addRequired<LoopInfoWrapperPass>(); |
| AU.addRequired<ScalarEvolution>(); |
| AU.addRequiredID(LoopSimplifyID); |
| AU.addRequiredID(LCSSAID); |
| AU.addPreserved<ScalarEvolution>(); |
| AU.addPreservedID(LoopSimplifyID); |
| AU.addPreservedID(LCSSAID); |
| AU.setPreservesCFG(); |
| } |
| |
| private: |
| void releaseMemory() override { |
| DeadInsts.clear(); |
| } |
| |
| bool isValidRewrite(Value *FromVal, Value *ToVal); |
| |
| void HandleFloatingPointIV(Loop *L, PHINode *PH); |
| void RewriteNonIntegerIVs(Loop *L); |
| |
| void SimplifyAndExtend(Loop *L, SCEVExpander &Rewriter, LPPassManager &LPM); |
| |
| bool CanLoopBeDeleted(Loop *L, SmallVector<RewritePhi, 8> &RewritePhiSet); |
| void RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter); |
| |
| Value *LinearFunctionTestReplace(Loop *L, const SCEV *BackedgeTakenCount, |
| PHINode *IndVar, SCEVExpander &Rewriter); |
| |
| void SinkUnusedInvariants(Loop *L); |
| |
| Value *ExpandSCEVIfNeeded(SCEVExpander &Rewriter, const SCEV *S, Loop *L, |
| Instruction *InsertPt, Type *Ty, |
| bool &IsHighCostExpansion); |
| }; |
| } |
| |
| char IndVarSimplify::ID = 0; |
| INITIALIZE_PASS_BEGIN(IndVarSimplify, "indvars", |
| "Induction Variable Simplification", false, false) |
| INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) |
| INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass) |
| INITIALIZE_PASS_DEPENDENCY(ScalarEvolution) |
| INITIALIZE_PASS_DEPENDENCY(LoopSimplify) |
| INITIALIZE_PASS_DEPENDENCY(LCSSA) |
| INITIALIZE_PASS_END(IndVarSimplify, "indvars", |
| "Induction Variable Simplification", false, false) |
| |
| Pass *llvm::createIndVarSimplifyPass() { |
| return new IndVarSimplify(); |
| } |
| |
| /// isValidRewrite - Return true if the SCEV expansion generated by the |
| /// rewriter can replace the original value. SCEV guarantees that it |
| /// produces the same value, but the way it is produced may be illegal IR. |
| /// Ideally, this function will only be called for verification. |
| bool IndVarSimplify::isValidRewrite(Value *FromVal, Value *ToVal) { |
| // If an SCEV expression subsumed multiple pointers, its expansion could |
| // reassociate the GEP changing the base pointer. This is illegal because the |
| // final address produced by a GEP chain must be inbounds relative to its |
| // underlying object. Otherwise basic alias analysis, among other things, |
| // could fail in a dangerous way. Ultimately, SCEV will be improved to avoid |
| // producing an expression involving multiple pointers. Until then, we must |
| // bail out here. |
| // |
| // Retrieve the pointer operand of the GEP. Don't use GetUnderlyingObject |
| // because it understands lcssa phis while SCEV does not. |
| Value *FromPtr = FromVal; |
| Value *ToPtr = ToVal; |
| if (GEPOperator *GEP = dyn_cast<GEPOperator>(FromVal)) { |
| FromPtr = GEP->getPointerOperand(); |
| } |
| if (GEPOperator *GEP = dyn_cast<GEPOperator>(ToVal)) { |
| ToPtr = GEP->getPointerOperand(); |
| } |
| if (FromPtr != FromVal || ToPtr != ToVal) { |
| // Quickly check the common case |
| if (FromPtr == ToPtr) |
| return true; |
| |
| // SCEV may have rewritten an expression that produces the GEP's pointer |
| // operand. That's ok as long as the pointer operand has the same base |
| // pointer. Unlike GetUnderlyingObject(), getPointerBase() will find the |
| // base of a recurrence. This handles the case in which SCEV expansion |
| // converts a pointer type recurrence into a nonrecurrent pointer base |
| // indexed by an integer recurrence. |
| |
| // If the GEP base pointer is a vector of pointers, abort. |
| if (!FromPtr->getType()->isPointerTy() || !ToPtr->getType()->isPointerTy()) |
| return false; |
| |
| const SCEV *FromBase = SE->getPointerBase(SE->getSCEV(FromPtr)); |
| const SCEV *ToBase = SE->getPointerBase(SE->getSCEV(ToPtr)); |
| if (FromBase == ToBase) |
| return true; |
| |
| DEBUG(dbgs() << "INDVARS: GEP rewrite bail out " |
| << *FromBase << " != " << *ToBase << "\n"); |
| |
| return false; |
| } |
| return true; |
| } |
| |
| /// Determine the insertion point for this user. By default, insert immediately |
| /// before the user. SCEVExpander or LICM will 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. |
| static Instruction *getInsertPointForUses(Instruction *User, Value *Def, |
| DominatorTree *DT) { |
| PHINode *PHI = dyn_cast<PHINode>(User); |
| if (!PHI) |
| return User; |
| |
| Instruction *InsertPt = nullptr; |
| for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i) { |
| if (PHI->getIncomingValue(i) != Def) |
| continue; |
| |
| BasicBlock *InsertBB = PHI->getIncomingBlock(i); |
| if (!InsertPt) { |
| InsertPt = InsertBB->getTerminator(); |
| continue; |
| } |
| InsertBB = DT->findNearestCommonDominator(InsertPt->getParent(), InsertBB); |
| InsertPt = InsertBB->getTerminator(); |
| } |
| assert(InsertPt && "Missing phi operand"); |
| assert((!isa<Instruction>(Def) || |
| DT->dominates(cast<Instruction>(Def), InsertPt)) && |
| "def does not dominate all uses"); |
| return InsertPt; |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // RewriteNonIntegerIVs and helpers. Prefer integer IVs. |
| //===----------------------------------------------------------------------===// |
| |
| /// ConvertToSInt - Convert APF to an integer, if possible. |
| static bool ConvertToSInt(const APFloat &APF, int64_t &IntVal) { |
| bool isExact = 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 == nullptr || 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 == nullptr || 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::user_iterator IncrUse = Incr->user_begin(); |
| Instruction *U1 = cast<Instruction>(*IncrUse++); |
| if (IncrUse == Incr->user_end()) return; |
| Instruction *U2 = cast<Instruction>(*IncrUse++); |
| if (IncrUse != Incr->user_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 || !Compare->hasOneUse() || |
| !isa<BranchInst>(Compare->user_back())) |
| return; |
| |
| BranchInst *TheBr = cast<BranchInst>(Compare->user_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 == nullptr || |
| !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. |
| if (InitValue >= ExitValue) |
| return; |
| |
| uint32_t Range = uint32_t(ExitValue-InitValue); |
| // Check for infinite loop, either: |
| // while (i <= Exit) or until (i > Exit) |
| if (NewPred == CmpInst::ICMP_SLE || NewPred == CmpInst::ICMP_SGT) { |
| 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. |
| if (InitValue <= ExitValue) |
| return; |
| |
| uint32_t Range = uint32_t(InitValue-ExitValue); |
| // Check for infinite loop, either: |
| // while (i >= Exit) or until (i < Exit) |
| if (NewPred == CmpInst::ICMP_SGE || NewPred == CmpInst::ICMP_SLT) { |
| 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; |
| } |
| |
| IntegerType *Int32Ty = Type::getInt32Ty(PN->getContext()); |
| |
| // Insert new integer induction variable. |
| PHINode *NewPHI = PHINode::Create(Int32Ty, 2, 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, TLI); |
| |
| // Delete the old floating point increment. |
| Incr->replaceAllUsesWith(UndefValue::get(Incr->getType())); |
| RecursivelyDeleteTriviallyDeadInstructions(Incr, TLI); |
| |
| // 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()->getFirstInsertionPt()); |
| PN->replaceAllUsesWith(Conv); |
| RecursivelyDeleteTriviallyDeadInstructions(PN, TLI); |
| } |
| Changed = true; |
| } |
| |
| 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); |
| } |
| |
| namespace { |
| // Collect information about PHI nodes which can be transformed in |
| // RewriteLoopExitValues. |
| struct RewritePhi { |
| PHINode *PN; |
| unsigned Ith; // Ith incoming value. |
| Value *Val; // Exit value after expansion. |
| bool HighCost; // High Cost when expansion. |
| bool SafePhi; // LCSSASafePhiForRAUW. |
| |
| RewritePhi(PHINode *P, unsigned I, Value *V, bool H, bool S) |
| : PN(P), Ith(I), Val(V), HighCost(H), SafePhi(S) {} |
| }; |
| } |
| |
| Value *IndVarSimplify::ExpandSCEVIfNeeded(SCEVExpander &Rewriter, const SCEV *S, |
| Loop *L, Instruction *InsertPt, |
| Type *ResultTy, |
| bool &IsHighCostExpansion) { |
| using namespace llvm::PatternMatch; |
| |
| if (!Rewriter.isHighCostExpansion(S, L)) { |
| IsHighCostExpansion = false; |
| return Rewriter.expandCodeFor(S, ResultTy, InsertPt); |
| } |
| |
| // Before expanding S into an expensive LLVM expression, see if we can use an |
| // already existing value as the expansion for S. There is potential to make |
| // this significantly smarter, but this simple heuristic already gets some |
| // interesting cases. |
| |
| SmallVector<BasicBlock *, 4> Latches; |
| L->getLoopLatches(Latches); |
| |
| for (BasicBlock *BB : Latches) { |
| ICmpInst::Predicate Pred; |
| Instruction *LHS, *RHS; |
| BasicBlock *TrueBB, *FalseBB; |
| |
| if (!match(BB->getTerminator(), |
| m_Br(m_ICmp(Pred, m_Instruction(LHS), m_Instruction(RHS)), |
| TrueBB, FalseBB))) |
| continue; |
| |
| if (SE->getSCEV(LHS) == S && DT->dominates(LHS, InsertPt)) { |
| IsHighCostExpansion = false; |
| return LHS; |
| } |
| |
| if (SE->getSCEV(RHS) == S && DT->dominates(RHS, InsertPt)) { |
| IsHighCostExpansion = false; |
| return RHS; |
| } |
| } |
| |
| // We didn't find anything, fall back to using SCEVExpander. |
| assert(Rewriter.isHighCostExpansion(S, L) && "this should not have changed!"); |
| IsHighCostExpansion = true; |
| return Rewriter.expandCodeFor(S, ResultTy, InsertPt); |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // RewriteLoopExitValues - Optimize IV users outside the loop. |
| // As a side effect, reduces the amount of IV processing within the loop. |
| //===----------------------------------------------------------------------===// |
| |
| /// 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); |
| |
| SmallVector<RewritePhi, 8> RewritePhiSet; |
| // 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(); |
| |
| // We would like to be able to RAUW single-incoming value PHI nodes. We |
| // have to be certain this is safe even when this is an LCSSA PHI node. |
| // While the computed exit value is no longer varying in *this* loop, the |
| // exit block may be an exit block for an outer containing loop as well, |
| // the exit value may be varying in the outer loop, and thus it may still |
| // require an LCSSA PHI node. The safe case is when this is |
| // single-predecessor PHI node (LCSSA) and the exit block containing it is |
| // part of the enclosing loop, or this is the outer most loop of the nest. |
| // In either case the exit value could (at most) be varying in the same |
| // loop body as the phi node itself. Thus if it is in turn used outside of |
| // an enclosing loop it will only be via a separate LCSSA node. |
| bool LCSSASafePhiForRAUW = |
| NumPreds == 1 && |
| (!L->getParentLoop() || L->getParentLoop() == LI->getLoopFor(ExitBB)); |
| |
| // 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) || |
| !isSafeToExpand(ExitValue, *SE)) |
| continue; |
| |
| // Computing the value outside of the loop brings no benefit if : |
| // - it is definitely used inside the loop in a way which can not be |
| // optimized away. |
| // - no use outside of the loop can take advantage of hoisting the |
| // computation out of the loop |
| if (ExitValue->getSCEVType()>=scMulExpr) { |
| unsigned NumHardInternalUses = 0; |
| unsigned NumSoftExternalUses = 0; |
| unsigned NumUses = 0; |
| for (auto IB = Inst->user_begin(), IE = Inst->user_end(); |
| IB != IE && NumUses <= 6; ++IB) { |
| Instruction *UseInstr = cast<Instruction>(*IB); |
| unsigned Opc = UseInstr->getOpcode(); |
| NumUses++; |
| if (L->contains(UseInstr)) { |
| if (Opc == Instruction::Call || Opc == Instruction::Ret) |
| NumHardInternalUses++; |
| } else { |
| if (Opc == Instruction::PHI) { |
| // Do not count the Phi as a use. LCSSA may have inserted |
| // plenty of trivial ones. |
| NumUses--; |
| for (auto PB = UseInstr->user_begin(), |
| PE = UseInstr->user_end(); |
| PB != PE && NumUses <= 6; ++PB, ++NumUses) { |
| unsigned PhiOpc = cast<Instruction>(*PB)->getOpcode(); |
| if (PhiOpc != Instruction::Call && PhiOpc != Instruction::Ret) |
| NumSoftExternalUses++; |
| } |
| continue; |
| } |
| if (Opc != Instruction::Call && Opc != Instruction::Ret) |
| NumSoftExternalUses++; |
| } |
| } |
| if (NumUses <= 6 && NumHardInternalUses && !NumSoftExternalUses) |
| continue; |
| } |
| |
| bool HighCost = false; |
| Value *ExitVal = ExpandSCEVIfNeeded(Rewriter, ExitValue, L, Inst, |
| PN->getType(), HighCost); |
| |
| DEBUG(dbgs() << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal << '\n' |
| << " LoopVal = " << *Inst << "\n"); |
| |
| if (!isValidRewrite(Inst, ExitVal)) { |
| DeadInsts.push_back(ExitVal); |
| continue; |
| } |
| |
| // Collect all the candidate PHINodes to be rewritten. |
| RewritePhiSet.push_back( |
| RewritePhi(PN, i, ExitVal, HighCost, LCSSASafePhiForRAUW)); |
| } |
| } |
| } |
| |
| bool LoopCanBeDel = CanLoopBeDeleted(L, RewritePhiSet); |
| |
| // Transformation. |
| for (const RewritePhi &Phi : RewritePhiSet) { |
| PHINode *PN = Phi.PN; |
| Value *ExitVal = Phi.Val; |
| |
| // Only do the rewrite when the ExitValue can be expanded cheaply. |
| // If LoopCanBeDel is true, rewrite exit value aggressively. |
| if (ReplaceExitValue == OnlyCheapRepl && !LoopCanBeDel && Phi.HighCost) { |
| DeadInsts.push_back(ExitVal); |
| continue; |
| } |
| |
| Changed = true; |
| ++NumReplaced; |
| Instruction *Inst = cast<Instruction>(PN->getIncomingValue(Phi.Ith)); |
| PN->setIncomingValue(Phi.Ith, ExitVal); |
| |
| // If this instruction is dead now, delete it. Don't do it now to avoid |
| // invalidating iterators. |
| if (isInstructionTriviallyDead(Inst, TLI)) |
| DeadInsts.push_back(Inst); |
| |
| // If we determined that this PHI is safe to replace even if an LCSSA |
| // PHI, do so. |
| if (Phi.SafePhi) { |
| PN->replaceAllUsesWith(ExitVal); |
| 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(); |
| } |
| |
| /// CanLoopBeDeleted - Check whether it is possible to delete the loop after |
| /// rewriting exit value. If it is possible, ignore ReplaceExitValue and |
| /// do rewriting aggressively. |
| bool IndVarSimplify::CanLoopBeDeleted( |
| Loop *L, SmallVector<RewritePhi, 8> &RewritePhiSet) { |
| |
| BasicBlock *Preheader = L->getLoopPreheader(); |
| // If there is no preheader, the loop will not be deleted. |
| if (!Preheader) |
| return false; |
| |
| // In LoopDeletion pass Loop can be deleted when ExitingBlocks.size() > 1. |
| // We obviate multiple ExitingBlocks case for simplicity. |
| // TODO: If we see testcase with multiple ExitingBlocks can be deleted |
| // after exit value rewriting, we can enhance the logic here. |
| SmallVector<BasicBlock *, 4> ExitingBlocks; |
| L->getExitingBlocks(ExitingBlocks); |
| SmallVector<BasicBlock *, 8> ExitBlocks; |
| L->getUniqueExitBlocks(ExitBlocks); |
| if (ExitBlocks.size() > 1 || ExitingBlocks.size() > 1) |
| return false; |
| |
| BasicBlock *ExitBlock = ExitBlocks[0]; |
| BasicBlock::iterator BI = ExitBlock->begin(); |
| while (PHINode *P = dyn_cast<PHINode>(BI)) { |
| Value *Incoming = P->getIncomingValueForBlock(ExitingBlocks[0]); |
| |
| // If the Incoming value of P is found in RewritePhiSet, we know it |
| // could be rewritten to use a loop invariant value in transformation |
| // phase later. Skip it in the loop invariant check below. |
| bool found = false; |
| for (const RewritePhi &Phi : RewritePhiSet) { |
| unsigned i = Phi.Ith; |
| if (Phi.PN == P && (Phi.PN)->getIncomingValue(i) == Incoming) { |
| found = true; |
| break; |
| } |
| } |
| |
| Instruction *I; |
| if (!found && (I = dyn_cast<Instruction>(Incoming))) |
| if (!L->hasLoopInvariantOperands(I)) |
| return false; |
| |
| ++BI; |
| } |
| |
| for (Loop::block_iterator LI = L->block_begin(), LE = L->block_end(); |
| LI != LE; ++LI) { |
| for (BasicBlock::iterator BI = (*LI)->begin(), BE = (*LI)->end(); BI != BE; |
| ++BI) { |
| if (BI->mayHaveSideEffects()) |
| return false; |
| } |
| } |
| |
| return true; |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // IV Widening - Extend the width of an IV to cover its widest uses. |
| //===----------------------------------------------------------------------===// |
| |
| namespace { |
| // Collect information about induction variables that are used by sign/zero |
| // extend operations. This information is recorded by CollectExtend and |
| // provides the input to WidenIV. |
| struct WideIVInfo { |
| PHINode *NarrowIV; |
| Type *WidestNativeType; // Widest integer type created [sz]ext |
| bool IsSigned; // Was a sext user seen before a zext? |
| |
| WideIVInfo() : NarrowIV(nullptr), WidestNativeType(nullptr), |
| IsSigned(false) {} |
| }; |
| } |
| |
| /// visitCast - Update information about the induction variable that is |
| /// extended by this sign or zero extend operation. This is used to determine |
| /// the final width of the IV before actually widening it. |
| static void visitIVCast(CastInst *Cast, WideIVInfo &WI, ScalarEvolution *SE, |
| const TargetTransformInfo *TTI) { |
| bool IsSigned = Cast->getOpcode() == Instruction::SExt; |
| if (!IsSigned && Cast->getOpcode() != Instruction::ZExt) |
| return; |
| |
| Type *Ty = Cast->getType(); |
| uint64_t Width = SE->getTypeSizeInBits(Ty); |
| if (!Cast->getModule()->getDataLayout().isLegalInteger(Width)) |
| return; |
| |
| // Cast is either an sext or zext up to this point. |
| // We should not widen an indvar if arithmetics on the wider indvar are more |
| // expensive than those on the narrower indvar. We check only the cost of ADD |
| // because at least an ADD is required to increment the induction variable. We |
| // could compute more comprehensively the cost of all instructions on the |
| // induction variable when necessary. |
| if (TTI && |
| TTI->getArithmeticInstrCost(Instruction::Add, Ty) > |
| TTI->getArithmeticInstrCost(Instruction::Add, |
| Cast->getOperand(0)->getType())) { |
| return; |
| } |
| |
| if (!WI.WidestNativeType) { |
| WI.WidestNativeType = SE->getEffectiveSCEVType(Ty); |
| WI.IsSigned = IsSigned; |
| return; |
| } |
| |
| // We extend the IV to satisfy the sign of its first user, arbitrarily. |
| if (WI.IsSigned != IsSigned) |
| return; |
| |
| if (Width > SE->getTypeSizeInBits(WI.WidestNativeType)) |
| WI.WidestNativeType = SE->getEffectiveSCEVType(Ty); |
| } |
| |
| namespace { |
| |
| /// NarrowIVDefUse - Record a link in the Narrow IV def-use chain along with the |
| /// WideIV that computes the same value as the Narrow IV def. This avoids |
| /// caching Use* pointers. |
| struct NarrowIVDefUse { |
| Instruction *NarrowDef; |
| Instruction *NarrowUse; |
| Instruction *WideDef; |
| |
| NarrowIVDefUse(): NarrowDef(nullptr), NarrowUse(nullptr), WideDef(nullptr) {} |
| |
| NarrowIVDefUse(Instruction *ND, Instruction *NU, Instruction *WD): |
| NarrowDef(ND), NarrowUse(NU), WideDef(WD) {} |
| }; |
| |
| /// WidenIV - The goal of this transform is to remove sign and zero extends |
| /// without creating any new induction variables. To do this, it creates a new |
| /// phi of the wider type and redirects all users, either removing extends or |
| /// inserting truncs whenever we stop propagating the type. |
| /// |
| class WidenIV { |
| // Parameters |
| PHINode *OrigPhi; |
| Type *WideType; |
| bool IsSigned; |
| |
| // Context |
| LoopInfo *LI; |
| Loop *L; |
| ScalarEvolution *SE; |
| DominatorTree *DT; |
| |
| // Result |
| PHINode *WidePhi; |
| Instruction *WideInc; |
| const SCEV *WideIncExpr; |
| SmallVectorImpl<WeakVH> &DeadInsts; |
| |
| SmallPtrSet<Instruction*,16> Widened; |
| SmallVector<NarrowIVDefUse, 8> NarrowIVUsers; |
| |
| public: |
| WidenIV(const WideIVInfo &WI, LoopInfo *LInfo, |
| ScalarEvolution *SEv, DominatorTree *DTree, |
| SmallVectorImpl<WeakVH> &DI) : |
| OrigPhi(WI.NarrowIV), |
| WideType(WI.WidestNativeType), |
| IsSigned(WI.IsSigned), |
| LI(LInfo), |
| L(LI->getLoopFor(OrigPhi->getParent())), |
| SE(SEv), |
| DT(DTree), |
| WidePhi(nullptr), |
| WideInc(nullptr), |
| WideIncExpr(nullptr), |
| DeadInsts(DI) { |
| assert(L->getHeader() == OrigPhi->getParent() && "Phi must be an IV"); |
| } |
| |
| PHINode *CreateWideIV(SCEVExpander &Rewriter); |
| |
| protected: |
| Value *getExtend(Value *NarrowOper, Type *WideType, bool IsSigned, |
| Instruction *Use); |
| |
| Instruction *CloneIVUser(NarrowIVDefUse DU); |
| |
| const SCEVAddRecExpr *GetWideRecurrence(Instruction *NarrowUse); |
| |
| const SCEVAddRecExpr* GetExtendedOperandRecurrence(NarrowIVDefUse DU); |
| |
| const SCEV *GetSCEVByOpCode(const SCEV *LHS, const SCEV *RHS, |
| unsigned OpCode) const; |
| |
| Instruction *WidenIVUse(NarrowIVDefUse DU, SCEVExpander &Rewriter); |
| |
| bool WidenLoopCompare(NarrowIVDefUse DU); |
| |
| void pushNarrowIVUsers(Instruction *NarrowDef, Instruction *WideDef); |
| }; |
| } // anonymous namespace |
| |
| /// isLoopInvariant - Perform a quick domtree based check for loop invariance |
| /// assuming that V is used within the loop. LoopInfo::isLoopInvariant() seems |
| /// gratuitous for this purpose. |
| static bool isLoopInvariant(Value *V, const Loop *L, const DominatorTree *DT) { |
| Instruction *Inst = dyn_cast<Instruction>(V); |
| if (!Inst) |
| return true; |
| |
| return DT->properlyDominates(Inst->getParent(), L->getHeader()); |
| } |
| |
| Value *WidenIV::getExtend(Value *NarrowOper, Type *WideType, bool IsSigned, |
| Instruction *Use) { |
| // Set the debug location and conservative insertion point. |
| IRBuilder<> Builder(Use); |
| // Hoist the insertion point into loop preheaders as far as possible. |
| for (const Loop *L = LI->getLoopFor(Use->getParent()); |
| L && L->getLoopPreheader() && isLoopInvariant(NarrowOper, L, DT); |
| L = L->getParentLoop()) |
| Builder.SetInsertPoint(L->getLoopPreheader()->getTerminator()); |
| |
| return IsSigned ? Builder.CreateSExt(NarrowOper, WideType) : |
| Builder.CreateZExt(NarrowOper, WideType); |
| } |
| |
| /// CloneIVUser - Instantiate a wide operation to replace a narrow |
| /// operation. This only needs to handle operations that can evaluation to |
| /// SCEVAddRec. It can safely return 0 for any operation we decide not to clone. |
| Instruction *WidenIV::CloneIVUser(NarrowIVDefUse DU) { |
| unsigned Opcode = DU.NarrowUse->getOpcode(); |
| switch (Opcode) { |
| default: |
| return nullptr; |
| case Instruction::Add: |
| case Instruction::Mul: |
| case Instruction::UDiv: |
| case Instruction::Sub: |
| case Instruction::And: |
| case Instruction::Or: |
| case Instruction::Xor: |
| case Instruction::Shl: |
| case Instruction::LShr: |
| case Instruction::AShr: |
| DEBUG(dbgs() << "Cloning IVUser: " << *DU.NarrowUse << "\n"); |
| |
| // Replace NarrowDef operands with WideDef. Otherwise, we don't know |
| // anything about the narrow operand yet so must insert a [sz]ext. It is |
| // probably loop invariant and will be folded or hoisted. If it actually |
| // comes from a widened IV, it should be removed during a future call to |
| // WidenIVUse. |
| Value *LHS = (DU.NarrowUse->getOperand(0) == DU.NarrowDef) ? DU.WideDef : |
| getExtend(DU.NarrowUse->getOperand(0), WideType, IsSigned, DU.NarrowUse); |
| Value *RHS = (DU.NarrowUse->getOperand(1) == DU.NarrowDef) ? DU.WideDef : |
| getExtend(DU.NarrowUse->getOperand(1), WideType, IsSigned, DU.NarrowUse); |
| |
| BinaryOperator *NarrowBO = cast<BinaryOperator>(DU.NarrowUse); |
| BinaryOperator *WideBO = BinaryOperator::Create(NarrowBO->getOpcode(), |
| LHS, RHS, |
| NarrowBO->getName()); |
| IRBuilder<> Builder(DU.NarrowUse); |
| Builder.Insert(WideBO); |
| if (const OverflowingBinaryOperator *OBO = |
| dyn_cast<OverflowingBinaryOperator>(NarrowBO)) { |
| if (OBO->hasNoUnsignedWrap()) WideBO->setHasNoUnsignedWrap(); |
| if (OBO->hasNoSignedWrap()) WideBO->setHasNoSignedWrap(); |
| } |
| return WideBO; |
| } |
| } |
| |
| const SCEV *WidenIV::GetSCEVByOpCode(const SCEV *LHS, const SCEV *RHS, |
| unsigned OpCode) const { |
| if (OpCode == Instruction::Add) |
| return SE->getAddExpr(LHS, RHS); |
| if (OpCode == Instruction::Sub) |
| return SE->getMinusSCEV(LHS, RHS); |
| if (OpCode == Instruction::Mul) |
| return SE->getMulExpr(LHS, RHS); |
| |
| llvm_unreachable("Unsupported opcode."); |
| } |
| |
| /// No-wrap operations can transfer sign extension of their result to their |
| /// operands. Generate the SCEV value for the widened operation without |
| /// actually modifying the IR yet. If the expression after extending the |
| /// operands is an AddRec for this loop, return it. |
| const SCEVAddRecExpr* WidenIV::GetExtendedOperandRecurrence(NarrowIVDefUse DU) { |
| |
| // Handle the common case of add<nsw/nuw> |
| const unsigned OpCode = DU.NarrowUse->getOpcode(); |
| // Only Add/Sub/Mul instructions supported yet. |
| if (OpCode != Instruction::Add && OpCode != Instruction::Sub && |
| OpCode != Instruction::Mul) |
| return nullptr; |
| |
| // One operand (NarrowDef) has already been extended to WideDef. Now determine |
| // if extending the other will lead to a recurrence. |
| const unsigned ExtendOperIdx = |
| DU.NarrowUse->getOperand(0) == DU.NarrowDef ? 1 : 0; |
| assert(DU.NarrowUse->getOperand(1-ExtendOperIdx) == DU.NarrowDef && "bad DU"); |
| |
| const SCEV *ExtendOperExpr = nullptr; |
| const OverflowingBinaryOperator *OBO = |
| cast<OverflowingBinaryOperator>(DU.NarrowUse); |
| if (IsSigned && OBO->hasNoSignedWrap()) |
| ExtendOperExpr = SE->getSignExtendExpr( |
| SE->getSCEV(DU.NarrowUse->getOperand(ExtendOperIdx)), WideType); |
| else if(!IsSigned && OBO->hasNoUnsignedWrap()) |
| ExtendOperExpr = SE->getZeroExtendExpr( |
| SE->getSCEV(DU.NarrowUse->getOperand(ExtendOperIdx)), WideType); |
| else |
| return nullptr; |
| |
| // When creating this SCEV expr, don't apply the current operations NSW or NUW |
| // flags. This instruction may be guarded by control flow that the no-wrap |
| // behavior depends on. Non-control-equivalent instructions can be mapped to |
| // the same SCEV expression, and it would be incorrect to transfer NSW/NUW |
| // semantics to those operations. |
| const SCEV *lhs = SE->getSCEV(DU.WideDef); |
| const SCEV *rhs = ExtendOperExpr; |
| |
| // Let's swap operands to the initial order for the case of non-commutative |
| // operations, like SUB. See PR21014. |
| if (ExtendOperIdx == 0) |
| std::swap(lhs, rhs); |
| const SCEVAddRecExpr *AddRec = |
| dyn_cast<SCEVAddRecExpr>(GetSCEVByOpCode(lhs, rhs, OpCode)); |
| |
| if (!AddRec || AddRec->getLoop() != L) |
| return nullptr; |
| return AddRec; |
| } |
| |
| /// GetWideRecurrence - Is this instruction potentially interesting for further |
| /// simplification after widening it's type? In other words, can the |
| /// extend be safely hoisted out of the loop with SCEV reducing the value to a |
| /// recurrence on the same loop. If so, return the sign or zero extended |
| /// recurrence. Otherwise return NULL. |
| const SCEVAddRecExpr *WidenIV::GetWideRecurrence(Instruction *NarrowUse) { |
| if (!SE->isSCEVable(NarrowUse->getType())) |
| return nullptr; |
| |
| const SCEV *NarrowExpr = SE->getSCEV(NarrowUse); |
| if (SE->getTypeSizeInBits(NarrowExpr->getType()) |
| >= SE->getTypeSizeInBits(WideType)) { |
| // NarrowUse implicitly widens its operand. e.g. a gep with a narrow |
| // index. So don't follow this use. |
| return nullptr; |
| } |
| |
| const SCEV *WideExpr = IsSigned ? |
| SE->getSignExtendExpr(NarrowExpr, WideType) : |
| SE->getZeroExtendExpr(NarrowExpr, WideType); |
| const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(WideExpr); |
| if (!AddRec || AddRec->getLoop() != L) |
| return nullptr; |
| return AddRec; |
| } |
| |
| /// This IV user cannot be widen. Replace this use of the original narrow IV |
| /// with a truncation of the new wide IV to isolate and eliminate the narrow IV. |
| static void truncateIVUse(NarrowIVDefUse DU, DominatorTree *DT) { |
| DEBUG(dbgs() << "INDVARS: Truncate IV " << *DU.WideDef |
| << " for user " << *DU.NarrowUse << "\n"); |
| IRBuilder<> Builder(getInsertPointForUses(DU.NarrowUse, DU.NarrowDef, DT)); |
| Value *Trunc = Builder.CreateTrunc(DU.WideDef, DU.NarrowDef->getType()); |
| DU.NarrowUse->replaceUsesOfWith(DU.NarrowDef, Trunc); |
| } |
| |
| /// If the narrow use is a compare instruction, then widen the compare |
| // (and possibly the other operand). The extend operation is hoisted into the |
| // loop preheader as far as possible. |
| bool WidenIV::WidenLoopCompare(NarrowIVDefUse DU) { |
| ICmpInst *Cmp = dyn_cast<ICmpInst>(DU.NarrowUse); |
| if (!Cmp) |
| return false; |
| |
| // Sign of IV user and compare must match. |
| if (IsSigned != CmpInst::isSigned(Cmp->getPredicate())) |
| return false; |
| |
| Value *Op = Cmp->getOperand(Cmp->getOperand(0) == DU.NarrowDef ? 1 : 0); |
| unsigned CastWidth = SE->getTypeSizeInBits(Op->getType()); |
| unsigned IVWidth = SE->getTypeSizeInBits(WideType); |
| assert (CastWidth <= IVWidth && "Unexpected width while widening compare."); |
| |
| // Widen the compare instruction. |
| IRBuilder<> Builder(getInsertPointForUses(DU.NarrowUse, DU.NarrowDef, DT)); |
| DU.NarrowUse->replaceUsesOfWith(DU.NarrowDef, DU.WideDef); |
| |
| // Widen the other operand of the compare, if necessary. |
| if (CastWidth < IVWidth) { |
| Value *ExtOp = getExtend(Op, WideType, IsSigned, Cmp); |
| DU.NarrowUse->replaceUsesOfWith(Op, ExtOp); |
| } |
| return true; |
| } |
| |
| /// WidenIVUse - Determine whether an individual user of the narrow IV can be |
| /// widened. If so, return the wide clone of the user. |
| Instruction *WidenIV::WidenIVUse(NarrowIVDefUse DU, SCEVExpander &Rewriter) { |
| |
| // Stop traversing the def-use chain at inner-loop phis or post-loop phis. |
| if (PHINode *UsePhi = dyn_cast<PHINode>(DU.NarrowUse)) { |
| if (LI->getLoopFor(UsePhi->getParent()) != L) { |
| // For LCSSA phis, sink the truncate outside the loop. |
| // After SimplifyCFG most loop exit targets have a single predecessor. |
| // Otherwise fall back to a truncate within the loop. |
| if (UsePhi->getNumOperands() != 1) |
| truncateIVUse(DU, DT); |
| else { |
| PHINode *WidePhi = |
| PHINode::Create(DU.WideDef->getType(), 1, UsePhi->getName() + ".wide", |
| UsePhi); |
| WidePhi->addIncoming(DU.WideDef, UsePhi->getIncomingBlock(0)); |
| IRBuilder<> Builder(WidePhi->getParent()->getFirstInsertionPt()); |
| Value *Trunc = Builder.CreateTrunc(WidePhi, DU.NarrowDef->getType()); |
| UsePhi->replaceAllUsesWith(Trunc); |
| DeadInsts.emplace_back(UsePhi); |
| DEBUG(dbgs() << "INDVARS: Widen lcssa phi " << *UsePhi |
| << " to " << *WidePhi << "\n"); |
| } |
| return nullptr; |
| } |
| } |
| // Our raison d'etre! Eliminate sign and zero extension. |
| if (IsSigned ? isa<SExtInst>(DU.NarrowUse) : isa<ZExtInst>(DU.NarrowUse)) { |
| Value *NewDef = DU.WideDef; |
| if (DU.NarrowUse->getType() != WideType) { |
| unsigned CastWidth = SE->getTypeSizeInBits(DU.NarrowUse->getType()); |
| unsigned IVWidth = SE->getTypeSizeInBits(WideType); |
| if (CastWidth < IVWidth) { |
| // The cast isn't as wide as the IV, so insert a Trunc. |
| IRBuilder<> Builder(DU.NarrowUse); |
| NewDef = Builder.CreateTrunc(DU.WideDef, DU.NarrowUse->getType()); |
| } |
| else { |
| // A wider extend was hidden behind a narrower one. This may induce |
| // another round of IV widening in which the intermediate IV becomes |
| // dead. It should be very rare. |
| DEBUG(dbgs() << "INDVARS: New IV " << *WidePhi |
| << " not wide enough to subsume " << *DU.NarrowUse << "\n"); |
| DU.NarrowUse->replaceUsesOfWith(DU.NarrowDef, DU.WideDef); |
| NewDef = DU.NarrowUse; |
| } |
| } |
| if (NewDef != DU.NarrowUse) { |
| DEBUG(dbgs() << "INDVARS: eliminating " << *DU.NarrowUse |
| << " replaced by " << *DU.WideDef << "\n"); |
| ++NumElimExt; |
| DU.NarrowUse->replaceAllUsesWith(NewDef); |
| DeadInsts.emplace_back(DU.NarrowUse); |
| } |
| // Now that the extend is gone, we want to expose it's uses for potential |
| // further simplification. We don't need to directly inform SimplifyIVUsers |
| // of the new users, because their parent IV will be processed later as a |
| // new loop phi. If we preserved IVUsers analysis, we would also want to |
| // push the uses of WideDef here. |
| |
| // No further widening is needed. The deceased [sz]ext had done it for us. |
| return nullptr; |
| } |
| |
| // Does this user itself evaluate to a recurrence after widening? |
| const SCEVAddRecExpr *WideAddRec = GetWideRecurrence(DU.NarrowUse); |
| if (!WideAddRec) |
| WideAddRec = GetExtendedOperandRecurrence(DU); |
| |
| if (!WideAddRec) { |
| // If use is a loop condition, try to promote the condition instead of |
| // truncating the IV first. |
| if (WidenLoopCompare(DU)) |
| return nullptr; |
| |
| // This user does not evaluate to a recurence after widening, so don't |
| // follow it. Instead insert a Trunc to kill off the original use, |
| // eventually isolating the original narrow IV so it can be removed. |
| truncateIVUse(DU, DT); |
| return nullptr; |
| } |
| // Assume block terminators cannot evaluate to a recurrence. We can't to |
| // insert a Trunc after a terminator if there happens to be a critical edge. |
| assert(DU.NarrowUse != DU.NarrowUse->getParent()->getTerminator() && |
| "SCEV is not expected to evaluate a block terminator"); |
| |
| // Reuse the IV increment that SCEVExpander created as long as it dominates |
| // NarrowUse. |
| Instruction *WideUse = nullptr; |
| if (WideAddRec == WideIncExpr |
| && Rewriter.hoistIVInc(WideInc, DU.NarrowUse)) |
| WideUse = WideInc; |
| else { |
| WideUse = CloneIVUser(DU); |
| if (!WideUse) |
| return nullptr; |
| } |
| // Evaluation of WideAddRec ensured that the narrow expression could be |
| // extended outside the loop without overflow. This suggests that the wide use |
| // evaluates to the same expression as the extended narrow use, but doesn't |
| // absolutely guarantee it. Hence the following failsafe check. In rare cases |
| // where it fails, we simply throw away the newly created wide use. |
| if (WideAddRec != SE->getSCEV(WideUse)) { |
| DEBUG(dbgs() << "Wide use expression mismatch: " << *WideUse |
| << ": " << *SE->getSCEV(WideUse) << " != " << *WideAddRec << "\n"); |
| DeadInsts.emplace_back(WideUse); |
| return nullptr; |
| } |
| |
| // Returning WideUse pushes it on the worklist. |
| return WideUse; |
| } |
| |
| /// pushNarrowIVUsers - Add eligible users of NarrowDef to NarrowIVUsers. |
| /// |
| void WidenIV::pushNarrowIVUsers(Instruction *NarrowDef, Instruction *WideDef) { |
| for (User *U : NarrowDef->users()) { |
| Instruction *NarrowUser = cast<Instruction>(U); |
| |
| // Handle data flow merges and bizarre phi cycles. |
| if (!Widened.insert(NarrowUser).second) |
| continue; |
| |
| NarrowIVUsers.push_back(NarrowIVDefUse(NarrowDef, NarrowUser, WideDef)); |
| } |
| } |
| |
| /// CreateWideIV - Process a single induction variable. First use the |
| /// SCEVExpander to create a wide induction variable that evaluates to the same |
| /// recurrence as the original narrow IV. Then use a worklist to forward |
| /// traverse the narrow IV's def-use chain. After WidenIVUse has processed all |
| /// interesting IV users, the narrow IV will be isolated for removal by |
| /// DeleteDeadPHIs. |
| /// |
| /// It would be simpler to delete uses as they are processed, but we must avoid |
| /// invalidating SCEV expressions. |
| /// |
| PHINode *WidenIV::CreateWideIV(SCEVExpander &Rewriter) { |
| // Is this phi an induction variable? |
| const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(OrigPhi)); |
| if (!AddRec) |
| return nullptr; |
| |
| // Widen the induction variable expression. |
| const SCEV *WideIVExpr = IsSigned ? |
| SE->getSignExtendExpr(AddRec, WideType) : |
| SE->getZeroExtendExpr(AddRec, WideType); |
| |
| assert(SE->getEffectiveSCEVType(WideIVExpr->getType()) == WideType && |
| "Expect the new IV expression to preserve its type"); |
| |
| // Can the IV be extended outside the loop without overflow? |
| AddRec = dyn_cast<SCEVAddRecExpr>(WideIVExpr); |
| if (!AddRec || AddRec->getLoop() != L) |
| return nullptr; |
| |
| // An AddRec must have loop-invariant operands. Since this AddRec is |
| // materialized by a loop header phi, the expression cannot have any post-loop |
| // operands, so they must dominate the loop header. |
| assert(SE->properlyDominates(AddRec->getStart(), L->getHeader()) && |
| SE->properlyDominates(AddRec->getStepRecurrence(*SE), L->getHeader()) |
| && "Loop header phi recurrence inputs do not dominate the loop"); |
| |
| // The rewriter provides a value for the desired IV expression. This may |
| // either find an existing phi or materialize a new one. Either way, we |
| // expect a well-formed cyclic phi-with-increments. i.e. any operand not part |
| // of the phi-SCC dominates the loop entry. |
| Instruction *InsertPt = L->getHeader()->begin(); |
| WidePhi = cast<PHINode>(Rewriter.expandCodeFor(AddRec, WideType, InsertPt)); |
| |
| // Remembering the WideIV increment generated by SCEVExpander allows |
| // WidenIVUse to reuse it when widening the narrow IV's increment. We don't |
| // employ a general reuse mechanism because the call above is the only call to |
| // SCEVExpander. Henceforth, we produce 1-to-1 narrow to wide uses. |
| if (BasicBlock *LatchBlock = L->getLoopLatch()) { |
| WideInc = |
| cast<Instruction>(WidePhi->getIncomingValueForBlock(LatchBlock)); |
| WideIncExpr = SE->getSCEV(WideInc); |
| } |
| |
| DEBUG(dbgs() << "Wide IV: " << *WidePhi << "\n"); |
| ++NumWidened; |
| |
| // Traverse the def-use chain using a worklist starting at the original IV. |
| assert(Widened.empty() && NarrowIVUsers.empty() && "expect initial state" ); |
| |
| Widened.insert(OrigPhi); |
| pushNarrowIVUsers(OrigPhi, WidePhi); |
| |
| while (!NarrowIVUsers.empty()) { |
| NarrowIVDefUse DU = NarrowIVUsers.pop_back_val(); |
| |
| // Process a def-use edge. This may replace the use, so don't hold a |
| // use_iterator across it. |
| Instruction *WideUse = WidenIVUse(DU, Rewriter); |
| |
| // Follow all def-use edges from the previous narrow use. |
| if (WideUse) |
| pushNarrowIVUsers(DU.NarrowUse, WideUse); |
| |
| // WidenIVUse may have removed the def-use edge. |
| if (DU.NarrowDef->use_empty()) |
| DeadInsts.emplace_back(DU.NarrowDef); |
| } |
| return WidePhi; |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // Live IV Reduction - Minimize IVs live across the loop. |
| //===----------------------------------------------------------------------===// |
| |
| |
| //===----------------------------------------------------------------------===// |
| // Simplification of IV users based on SCEV evaluation. |
| //===----------------------------------------------------------------------===// |
| |
| namespace { |
| class IndVarSimplifyVisitor : public IVVisitor { |
| ScalarEvolution *SE; |
| const TargetTransformInfo *TTI; |
| PHINode *IVPhi; |
| |
| public: |
| WideIVInfo WI; |
| |
| IndVarSimplifyVisitor(PHINode *IV, ScalarEvolution *SCEV, |
| const TargetTransformInfo *TTI, |
| const DominatorTree *DTree) |
| : SE(SCEV), TTI(TTI), IVPhi(IV) { |
| DT = DTree; |
| WI.NarrowIV = IVPhi; |
| if (ReduceLiveIVs) |
| setSplitOverflowIntrinsics(); |
| } |
| |
| // Implement the interface used by simplifyUsersOfIV. |
| void visitCast(CastInst *Cast) override { visitIVCast(Cast, WI, SE, TTI); } |
| }; |
| } |
| |
| /// SimplifyAndExtend - Iteratively perform simplification on a worklist of IV |
| /// users. Each successive simplification may push more users which may |
| /// themselves be candidates for simplification. |
| /// |
| /// Sign/Zero extend elimination is interleaved with IV simplification. |
| /// |
| void IndVarSimplify::SimplifyAndExtend(Loop *L, |
| SCEVExpander &Rewriter, |
| LPPassManager &LPM) { |
| SmallVector<WideIVInfo, 8> WideIVs; |
| |
| SmallVector<PHINode*, 8> LoopPhis; |
| for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I) { |
| LoopPhis.push_back(cast<PHINode>(I)); |
| } |
| // Each round of simplification iterates through the SimplifyIVUsers worklist |
| // for all current phis, then determines whether any IVs can be |
| // widened. Widening adds new phis to LoopPhis, inducing another round of |
| // simplification on the wide IVs. |
| while (!LoopPhis.empty()) { |
| // Evaluate as many IV expressions as possible before widening any IVs. This |
| // forces SCEV to set no-wrap flags before evaluating sign/zero |
| // extension. The first time SCEV attempts to normalize sign/zero extension, |
| // the result becomes final. So for the most predictable results, we delay |
| // evaluation of sign/zero extend evaluation until needed, and avoid running |
| // other SCEV based analysis prior to SimplifyAndExtend. |
| do { |
| PHINode *CurrIV = LoopPhis.pop_back_val(); |
| |
| // Information about sign/zero extensions of CurrIV. |
| IndVarSimplifyVisitor Visitor(CurrIV, SE, TTI, DT); |
| |
| Changed |= simplifyUsersOfIV(CurrIV, SE, &LPM, DeadInsts, &Visitor); |
| |
| if (Visitor.WI.WidestNativeType) { |
| WideIVs.push_back(Visitor.WI); |
| } |
| } while(!LoopPhis.empty()); |
| |
| for (; !WideIVs.empty(); WideIVs.pop_back()) { |
| WidenIV Widener(WideIVs.back(), LI, SE, DT, DeadInsts); |
| if (PHINode *WidePhi = Widener.CreateWideIV(Rewriter)) { |
| Changed = true; |
| LoopPhis.push_back(WidePhi); |
| } |
| } |
| } |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // LinearFunctionTestReplace and its kin. Rewrite the loop exit condition. |
| //===----------------------------------------------------------------------===// |
| |
| /// canExpandBackedgeTakenCount - Return true if this loop's backedge taken |
| /// count expression can be safely and cheaply expanded into an instruction |
| /// sequence that can be used by LinearFunctionTestReplace. |
| /// |
| /// TODO: This fails for pointer-type loop counters with greater than one byte |
| /// strides, consequently preventing LFTR from running. For the purpose of LFTR |
| /// we could skip this check in the case that the LFTR loop counter (chosen by |
| /// FindLoopCounter) is also pointer type. Instead, we could directly convert |
| /// the loop test to an inequality test by checking the target data's alignment |
| /// of element types (given that the initial pointer value originates from or is |
| /// used by ABI constrained operation, as opposed to inttoptr/ptrtoint). |
| /// However, we don't yet have a strong motivation for converting loop tests |
| /// into inequality tests. |
| static bool canExpandBackedgeTakenCount(Loop *L, ScalarEvolution *SE, |
| SCEVExpander &Rewriter) { |
| const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L); |
| if (isa<SCEVCouldNotCompute>(BackedgeTakenCount) || |
| BackedgeTakenCount->isZero()) |
| return false; |
| |
| if (!L->getExitingBlock()) |
| return false; |
| |
| // Can't rewrite non-branch yet. |
| if (!isa<BranchInst>(L->getExitingBlock()->getTerminator())) |
| return false; |
| |
| if (Rewriter.isHighCostExpansion(BackedgeTakenCount, L)) |
| return false; |
| |
| return true; |
| } |
| |
| /// getLoopPhiForCounter - Return the loop header phi IFF IncV adds a loop |
| /// invariant value to the phi. |
| static PHINode *getLoopPhiForCounter(Value *IncV, Loop *L, DominatorTree *DT) { |
| Instruction *IncI = dyn_cast<Instruction>(IncV); |
| if (!IncI) |
| return nullptr; |
| |
| switch (IncI->getOpcode()) { |
| case Instruction::Add: |
| case Instruction::Sub: |
| break; |
| case Instruction::GetElementPtr: |
| // An IV counter must preserve its type. |
| if (IncI->getNumOperands() == 2) |
| break; |
| default: |
| return nullptr; |
| } |
| |
| PHINode *Phi = dyn_cast<PHINode>(IncI->getOperand(0)); |
| if (Phi && Phi->getParent() == L->getHeader()) { |
| if (isLoopInvariant(IncI->getOperand(1), L, DT)) |
| return Phi; |
| return nullptr; |
| } |
| if (IncI->getOpcode() == Instruction::GetElementPtr) |
| return nullptr; |
| |
| // Allow add/sub to be commuted. |
| Phi = dyn_cast<PHINode>(IncI->getOperand(1)); |
| if (Phi && Phi->getParent() == L->getHeader()) { |
| if (isLoopInvariant(IncI->getOperand(0), L, DT)) |
| return Phi; |
| } |
| return nullptr; |
| } |
| |
| /// Return the compare guarding the loop latch, or NULL for unrecognized tests. |
| static ICmpInst *getLoopTest(Loop *L) { |
| assert(L->getExitingBlock() && "expected loop exit"); |
| |
| BasicBlock *LatchBlock = L->getLoopLatch(); |
| // Don't bother with LFTR if the loop is not properly simplified. |
| if (!LatchBlock) |
| return nullptr; |
| |
| BranchInst *BI = dyn_cast<BranchInst>(L->getExitingBlock()->getTerminator()); |
| assert(BI && "expected exit branch"); |
| |
| return dyn_cast<ICmpInst>(BI->getCondition()); |
| } |
| |
| /// needsLFTR - LinearFunctionTestReplace policy. Return true unless we can show |
| /// that the current exit test is already sufficiently canonical. |
| static bool needsLFTR(Loop *L, DominatorTree *DT) { |
| // Do LFTR to simplify the exit condition to an ICMP. |
| ICmpInst *Cond = getLoopTest(L); |
| if (!Cond) |
| return true; |
| |
| // Do LFTR to simplify the exit ICMP to EQ/NE |
| ICmpInst::Predicate Pred = Cond->getPredicate(); |
| if (Pred != ICmpInst::ICMP_NE && Pred != ICmpInst::ICMP_EQ) |
| return true; |
| |
| // Look for a loop invariant RHS |
| Value *LHS = Cond->getOperand(0); |
| Value *RHS = Cond->getOperand(1); |
| if (!isLoopInvariant(RHS, L, DT)) { |
| if (!isLoopInvariant(LHS, L, DT)) |
| return true; |
| std::swap(LHS, RHS); |
| } |
| // Look for a simple IV counter LHS |
| PHINode *Phi = dyn_cast<PHINode>(LHS); |
| if (!Phi) |
| Phi = getLoopPhiForCounter(LHS, L, DT); |
| |
| if (!Phi) |
| return true; |
| |
| // Do LFTR if PHI node is defined in the loop, but is *not* a counter. |
| int Idx = Phi->getBasicBlockIndex(L->getLoopLatch()); |
| if (Idx < 0) |
| return true; |
| |
| // Do LFTR if the exit condition's IV is *not* a simple counter. |
| Value *IncV = Phi->getIncomingValue(Idx); |
| return Phi != getLoopPhiForCounter(IncV, L, DT); |
| } |
| |
| /// Recursive helper for hasConcreteDef(). Unfortunately, this currently boils |
| /// down to checking that all operands are constant and listing instructions |
| /// that may hide undef. |
| static bool hasConcreteDefImpl(Value *V, SmallPtrSetImpl<Value*> &Visited, |
| unsigned Depth) { |
| if (isa<Constant>(V)) |
| return !isa<UndefValue>(V); |
| |
| if (Depth >= 6) |
| return false; |
| |
| // Conservatively handle non-constant non-instructions. For example, Arguments |
| // may be undef. |
| Instruction *I = dyn_cast<Instruction>(V); |
| if (!I) |
| return false; |
| |
| // Load and return values may be undef. |
| if(I->mayReadFromMemory() || isa<CallInst>(I) || isa<InvokeInst>(I)) |
| return false; |
| |
| // Optimistically handle other instructions. |
| for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI) { |
| if (!Visited.insert(*OI).second) |
| continue; |
| if (!hasConcreteDefImpl(*OI, Visited, Depth+1)) |
| return false; |
| } |
| return true; |
| } |
| |
| /// Return true if the given value is concrete. We must prove that undef can |
| /// never reach it. |
| /// |
| /// TODO: If we decide that this is a good approach to checking for undef, we |
| /// may factor it into a common location. |
| static bool hasConcreteDef(Value *V) { |
| SmallPtrSet<Value*, 8> Visited; |
| Visited.insert(V); |
| return hasConcreteDefImpl(V, Visited, 0); |
| } |
| |
| /// AlmostDeadIV - Return true if this IV has any uses other than the (soon to |
| /// be rewritten) loop exit test. |
| static bool AlmostDeadIV(PHINode *Phi, BasicBlock *LatchBlock, Value *Cond) { |
| int LatchIdx = Phi->getBasicBlockIndex(LatchBlock); |
| Value *IncV = Phi->getIncomingValue(LatchIdx); |
| |
| for (User *U : Phi->users()) |
| if (U != Cond && U != IncV) return false; |
| |
| for (User *U : IncV->users()) |
| if (U != Cond && U != Phi) return false; |
| return true; |
| } |
| |
| /// FindLoopCounter - Find an affine IV in canonical form. |
| /// |
| /// BECount may be an i8* pointer type. The pointer difference is already |
| /// valid count without scaling the address stride, so it remains a pointer |
| /// expression as far as SCEV is concerned. |
| /// |
| /// Currently only valid for LFTR. See the comments on hasConcreteDef below. |
| /// |
| /// FIXME: Accept -1 stride and set IVLimit = IVInit - BECount |
| /// |
| /// FIXME: Accept non-unit stride as long as SCEV can reduce BECount * Stride. |
| /// This is difficult in general for SCEV because of potential overflow. But we |
| /// could at least handle constant BECounts. |
| static PHINode *FindLoopCounter(Loop *L, const SCEV *BECount, |
| ScalarEvolution *SE, DominatorTree *DT) { |
| uint64_t BCWidth = SE->getTypeSizeInBits(BECount->getType()); |
| |
| Value *Cond = |
| cast<BranchInst>(L->getExitingBlock()->getTerminator())->getCondition(); |
| |
| // Loop over all of the PHI nodes, looking for a simple counter. |
| PHINode *BestPhi = nullptr; |
| const SCEV *BestInit = nullptr; |
| BasicBlock *LatchBlock = L->getLoopLatch(); |
| assert(LatchBlock && "needsLFTR should guarantee a loop latch"); |
| |
| for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I) { |
| PHINode *Phi = cast<PHINode>(I); |
| if (!SE->isSCEVable(Phi->getType())) |
| continue; |
| |
| // Avoid comparing an integer IV against a pointer Limit. |
| if (BECount->getType()->isPointerTy() && !Phi->getType()->isPointerTy()) |
| continue; |
| |
| const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(Phi)); |
| if (!AR || AR->getLoop() != L || !AR->isAffine()) |
| continue; |
| |
| // AR may be a pointer type, while BECount is an integer type. |
| // AR may be wider than BECount. With eq/ne tests overflow is immaterial. |
| // AR may not be a narrower type, or we may never exit. |
| uint64_t PhiWidth = SE->getTypeSizeInBits(AR->getType()); |
| if (PhiWidth < BCWidth || |
| !L->getHeader()->getModule()->getDataLayout().isLegalInteger(PhiWidth)) |
| continue; |
| |
| const SCEV *Step = dyn_cast<SCEVConstant>(AR->getStepRecurrence(*SE)); |
| if (!Step || !Step->isOne()) |
| continue; |
| |
| int LatchIdx = Phi->getBasicBlockIndex(LatchBlock); |
| Value *IncV = Phi->getIncomingValue(LatchIdx); |
| if (getLoopPhiForCounter(IncV, L, DT) != Phi) |
| continue; |
| |
| // Avoid reusing a potentially undef value to compute other values that may |
| // have originally had a concrete definition. |
| if (!hasConcreteDef(Phi)) { |
| // We explicitly allow unknown phis as long as they are already used by |
| // the loop test. In this case we assume that performing LFTR could not |
| // increase the number of undef users. |
| if (ICmpInst *Cond = getLoopTest(L)) { |
| if (Phi != getLoopPhiForCounter(Cond->getOperand(0), L, DT) |
| && Phi != getLoopPhiForCounter(Cond->getOperand(1), L, DT)) { |
| continue; |
| } |
| } |
| } |
| const SCEV *Init = AR->getStart(); |
| |
| if (BestPhi && !AlmostDeadIV(BestPhi, LatchBlock, Cond)) { |
| // Don't force a live loop counter if another IV can be used. |
| if (AlmostDeadIV(Phi, LatchBlock, Cond)) |
| continue; |
| |
| // Prefer to count-from-zero. This is a more "canonical" counter form. It |
| // also prefers integer to pointer IVs. |
| if (BestInit->isZero() != Init->isZero()) { |
| if (BestInit->isZero()) |
| continue; |
| } |
| // If two IVs both count from zero or both count from nonzero then the |
| // narrower is likely a dead phi that has been widened. Use the wider phi |
| // to allow the other to be eliminated. |
| else if (PhiWidth <= SE->getTypeSizeInBits(BestPhi->getType())) |
| continue; |
| } |
| BestPhi = Phi; |
| BestInit = Init; |
| } |
| return BestPhi; |
| } |
| |
| /// genLoopLimit - Help LinearFunctionTestReplace by generating a value that |
| /// holds the RHS of the new loop test. |
| static Value *genLoopLimit(PHINode *IndVar, const SCEV *IVCount, Loop *L, |
| SCEVExpander &Rewriter, ScalarEvolution *SE) { |
| const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(IndVar)); |
| assert(AR && AR->getLoop() == L && AR->isAffine() && "bad loop counter"); |
| const SCEV *IVInit = AR->getStart(); |
| |
| // IVInit may be a pointer while IVCount is an integer when FindLoopCounter |
| // finds a valid pointer IV. Sign extend BECount in order to materialize a |
| // GEP. Avoid running SCEVExpander on a new pointer value, instead reusing |
| // the existing GEPs whenever possible. |
| if (IndVar->getType()->isPointerTy() |
| && !IVCount->getType()->isPointerTy()) { |
| |
| // IVOffset will be the new GEP offset that is interpreted by GEP as a |
| // signed value. IVCount on the other hand represents the loop trip count, |
| // which is an unsigned value. FindLoopCounter only allows induction |
| // variables that have a positive unit stride of one. This means we don't |
| // have to handle the case of negative offsets (yet) and just need to zero |
| // extend IVCount. |
| Type *OfsTy = SE->getEffectiveSCEVType(IVInit->getType()); |
| const SCEV *IVOffset = SE->getTruncateOrZeroExtend(IVCount, OfsTy); |
| |
| // Expand the code for the iteration count. |
| assert(SE->isLoopInvariant(IVOffset, L) && |
| "Computed iteration count is not loop invariant!"); |
| BranchInst *BI = cast<BranchInst>(L->getExitingBlock()->getTerminator()); |
| Value *GEPOffset = Rewriter.expandCodeFor(IVOffset, OfsTy, BI); |
| |
| Value *GEPBase = IndVar->getIncomingValueForBlock(L->getLoopPreheader()); |
| assert(AR->getStart() == SE->getSCEV(GEPBase) && "bad loop counter"); |
| // We could handle pointer IVs other than i8*, but we need to compensate for |
| // gep index scaling. See canExpandBackedgeTakenCount comments. |
| assert(SE->getSizeOfExpr(IntegerType::getInt64Ty(IndVar->getContext()), |
| cast<PointerType>(GEPBase->getType())->getElementType())->isOne() |
| && "unit stride pointer IV must be i8*"); |
| |
| IRBuilder<> Builder(L->getLoopPreheader()->getTerminator()); |
| return Builder.CreateGEP(nullptr, GEPBase, GEPOffset, "lftr.limit"); |
| } |
| else { |
| // In any other case, convert both IVInit and IVCount to integers before |
| // comparing. This may result in SCEV expension of pointers, but in practice |
| // SCEV will fold the pointer arithmetic away as such: |
| // BECount = (IVEnd - IVInit - 1) => IVLimit = IVInit (postinc). |
| // |
| // Valid Cases: (1) both integers is most common; (2) both may be pointers |
| // for simple memset-style loops. |
| // |
| // IVInit integer and IVCount pointer would only occur if a canonical IV |
| // were generated on top of case #2, which is not expected. |
| |
| const SCEV *IVLimit = nullptr; |
| // For unit stride, IVCount = Start + BECount with 2's complement overflow. |
| // For non-zero Start, compute IVCount here. |
| if (AR->getStart()->isZero()) |
| IVLimit = IVCount; |
| else { |
| assert(AR->getStepRecurrence(*SE)->isOne() && "only handles unit stride"); |
| const SCEV *IVInit = AR->getStart(); |
| |
| // For integer IVs, truncate the IV before computing IVInit + BECount. |
| if (SE->getTypeSizeInBits(IVInit->getType()) |
| > SE->getTypeSizeInBits(IVCount->getType())) |
| IVInit = SE->getTruncateExpr(IVInit, IVCount->getType()); |
| |
| IVLimit = SE->getAddExpr(IVInit, IVCount); |
| } |
| // Expand the code for the iteration count. |
| BranchInst *BI = cast<BranchInst>(L->getExitingBlock()->getTerminator()); |
| IRBuilder<> Builder(BI); |
| assert(SE->isLoopInvariant(IVLimit, L) && |
| "Computed iteration count is not loop invariant!"); |
| // Ensure that we generate the same type as IndVar, or a smaller integer |
| // type. In the presence of null pointer values, we have an integer type |
| // SCEV expression (IVInit) for a pointer type IV value (IndVar). |
| Type *LimitTy = IVCount->getType()->isPointerTy() ? |
| IndVar->getType() : IVCount->getType(); |
| return Rewriter.expandCodeFor(IVLimit, LimitTy, BI); |
| } |
| } |
| |
| /// 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. |
| Value *IndVarSimplify:: |
| LinearFunctionTestReplace(Loop *L, |
| const SCEV *BackedgeTakenCount, |
| PHINode *IndVar, |
| SCEVExpander &Rewriter) { |
| assert(canExpandBackedgeTakenCount(L, SE, Rewriter) && "precondition"); |
| |
| // Initialize CmpIndVar and IVCount to their preincremented values. |
| Value *CmpIndVar = IndVar; |
| const SCEV *IVCount = BackedgeTakenCount; |
| |
| // If the exiting block is the same as the backedge block, we prefer to |
| // compare against the post-incremented value, otherwise we must compare |
| // against the preincremented value. |
| if (L->getExitingBlock() == L->getLoopLatch()) { |
| // Add one to the "backedge-taken" count to get the trip count. |
| // This addition may overflow, which is valid as long as the comparison is |
| // truncated to BackedgeTakenCount->getType(). |
| IVCount = SE->getAddExpr(BackedgeTakenCount, |
| SE->getConstant(BackedgeTakenCount->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(L->getExitingBlock()); |
| } |
| |
| Value *ExitCnt = genLoopLimit(IndVar, IVCount, L, Rewriter, SE); |
| assert(ExitCnt->getType()->isPointerTy() == IndVar->getType()->isPointerTy() |
| && "genLoopLimit missed a cast"); |
| |
| // Insert a new icmp_ne or icmp_eq instruction before the branch. |
| BranchInst *BI = cast<BranchInst>(L->getExitingBlock()->getTerminator()); |
| ICmpInst::Predicate P; |
| if (L->contains(BI->getSuccessor(0))) |
| P = ICmpInst::ICMP_NE; |
| else |
| P = ICmpInst::ICMP_EQ; |
| |
| DEBUG(dbgs() << "INDVARS: Rewriting loop exit condition to:\n" |
| << " LHS:" << *CmpIndVar << '\n' |
| << " op:\t" |
| << (P == ICmpInst::ICMP_NE ? "!=" : "==") << "\n" |
| << " RHS:\t" << *ExitCnt << "\n" |
| << " IVCount:\t" << *IVCount << "\n"); |
| |
| IRBuilder<> Builder(BI); |
| |
| // LFTR can ignore IV overflow and truncate to the width of |
| // BECount. This avoids materializing the add(zext(add)) expression. |
| unsigned CmpIndVarSize = SE->getTypeSizeInBits(CmpIndVar->getType()); |
| unsigned ExitCntSize = SE->getTypeSizeInBits(ExitCnt->getType()); |
| if (CmpIndVarSize > ExitCntSize) { |
| const SCEVAddRecExpr *AR = cast<SCEVAddRecExpr>(SE->getSCEV(IndVar)); |
| const SCEV *ARStart = AR->getStart(); |
| const SCEV *ARStep = AR->getStepRecurrence(*SE); |
| // For constant IVCount, avoid truncation. |
| if (isa<SCEVConstant>(ARStart) && isa<SCEVConstant>(IVCount)) { |
| const APInt &Start = cast<SCEVConstant>(ARStart)->getValue()->getValue(); |
| APInt Count = cast<SCEVConstant>(IVCount)->getValue()->getValue(); |
| // Note that the post-inc value of BackedgeTakenCount may have overflowed |
| // above such that IVCount is now zero. |
| if (IVCount != BackedgeTakenCount && Count == 0) { |
| Count = APInt::getMaxValue(Count.getBitWidth()).zext(CmpIndVarSize); |
| ++Count; |
| } |
| else |
| Count = Count.zext(CmpIndVarSize); |
| APInt NewLimit; |
| if (cast<SCEVConstant>(ARStep)->getValue()->isNegative()) |
| NewLimit = Start - Count; |
| else |
| NewLimit = Start + Count; |
| ExitCnt = ConstantInt::get(CmpIndVar->getType(), NewLimit); |
| |
| DEBUG(dbgs() << " Widen RHS:\t" << *ExitCnt << "\n"); |
| } else { |
| CmpIndVar = Builder.CreateTrunc(CmpIndVar, ExitCnt->getType(), |
| "lftr.wideiv"); |
| } |
| } |
| Value *Cond = Builder.CreateICmp(P, 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); |
| DeadInsts.push_back(OrigCond); |
| |
| ++NumLFTR; |
| Changed = true; |
| return Cond; |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // SinkUnusedInvariants. A late subpass to cleanup loop preheaders. |
| //===----------------------------------------------------------------------===// |
| |
| /// 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->getFirstInsertionPt(); |
| 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; |
| |
| // Skip landingpad instructions. |
| if (isa<LandingPadInst>(I)) |
| continue; |
| |
| // Don't sink alloca: we never want to sink static alloca's out of the |
| // entry block, and correctly sinking dynamic alloca's requires |
| // checks for stacksave/stackrestore intrinsics. |
| // FIXME: Refactor this check somehow? |
| if (isa<AllocaInst>(I)) |
| continue; |
| |
| // Determine if there is a use in or before the loop (direct or |
| // otherwise). |
| bool UsedInLoop = false; |
| for (Use &U : I->uses()) { |
| Instruction *User = cast<Instruction>(U.getUser()); |
| BasicBlock *UseBB = User->getParent(); |
| if (PHINode *P = dyn_cast<PHINode>(User)) { |
| unsigned i = |
| PHINode::getIncomingValueNumForOperand(U.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; |
| } |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // IndVarSimplify driver. Manage several subpasses of IV simplification. |
| //===----------------------------------------------------------------------===// |
| |
| bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) { |
| if (skipOptnoneFunction(L)) |
| return false; |
| |
| // 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; |
| |
| LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo(); |
| SE = &getAnalysis<ScalarEvolution>(); |
| DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree(); |
| auto *TLIP = getAnalysisIfAvailable<TargetLibraryInfoWrapperPass>(); |
| TLI = TLIP ? &TLIP->getTLI() : nullptr; |
| auto *TTIP = getAnalysisIfAvailable<TargetTransformInfoWrapperPass>(); |
| TTI = TTIP ? &TTIP->getTTI(*L->getHeader()->getParent()) : nullptr; |
| const DataLayout &DL = L->getHeader()->getModule()->getDataLayout(); |
| |
| DeadInsts.clear(); |
| Changed = false; |
| |
| // If there are any floating-point recurrences, attempt to |
| // transform them to use integer recurrences. |
| RewriteNonIntegerIVs(L); |
| |
| const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L); |
| |
| // Create a rewriter object which we'll use to transform the code with. |
| SCEVExpander Rewriter(*SE, DL, "indvars"); |
| #ifndef NDEBUG |
| Rewriter.setDebugType(DEBUG_TYPE); |
| #endif |
| |
| // Eliminate redundant IV users. |
| // |
| // Simplification works best when run before other consumers of SCEV. We |
| // attempt to avoid evaluating SCEVs for sign/zero extend operations until |
| // other expressions involving loop IVs have been evaluated. This helps SCEV |
| // set no-wrap flags before normalizing sign/zero extension. |
| Rewriter.disableCanonicalMode(); |
| SimplifyAndExtend(L, Rewriter, LPM); |
| |
| // 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 (ReplaceExitValue != NeverRepl && |
| !isa<SCEVCouldNotCompute>(BackedgeTakenCount)) |
| RewriteLoopExitValues(L, Rewriter); |
| |
| // Eliminate redundant IV cycles. |
| NumElimIV += Rewriter.replaceCongruentIVs(L, DT, DeadInsts); |
| |
| // 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. |
| if (canExpandBackedgeTakenCount(L, SE, Rewriter) && needsLFTR(L, DT)) { |
| PHINode *IndVar = FindLoopCounter(L, BackedgeTakenCount, SE, DT); |
| if (IndVar) { |
| // Check preconditions for proper SCEVExpander operation. SCEV does not |
| // express SCEVExpander's dependencies, such as LoopSimplify. Instead any |
| // pass that uses the SCEVExpander must do it. This does not work well for |
| // loop passes because SCEVExpander makes assumptions about all loops, |
| // while LoopPassManager only forces the current loop to be simplified. |
| // |
| // FIXME: SCEV expansion has no way to bail out, so the caller must |
| // explicitly check any assumptions made by SCEV. Brittle. |
| const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(BackedgeTakenCount); |
| if (!AR || AR->getLoop()->getLoopPreheader()) |
| (void)LinearFunctionTestReplace(L, BackedgeTakenCount, IndVar, |
| Rewriter); |
| } |
| } |
| // 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, TLI); |
| |
| // 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); |
| |
| // Clean up dead instructions. |
| Changed |= DeleteDeadPHIs(L->getHeader(), TLI); |
| // Check a post-condition. |
| assert(L->isLCSSAForm(*DT) && |
| "Indvars did not leave the loop in lcssa form!"); |
| |
| // Verify that LFTR, and any other change have not interfered with SCEV's |
| // ability to compute trip count. |
| #ifndef NDEBUG |
| if (VerifyIndvars && !isa<SCEVCouldNotCompute>(BackedgeTakenCount)) { |
| SE->forgetLoop(L); |
| const SCEV *NewBECount = SE->getBackedgeTakenCount(L); |
| if (SE->getTypeSizeInBits(BackedgeTakenCount->getType()) < |
| SE->getTypeSizeInBits(NewBECount->getType())) |
| NewBECount = SE->getTruncateOrNoop(NewBECount, |
| BackedgeTakenCount->getType()); |
| else |
| BackedgeTakenCount = SE->getTruncateOrNoop(BackedgeTakenCount, |
| NewBECount->getType()); |
| assert(BackedgeTakenCount == NewBECount && "indvars must preserve SCEV"); |
| } |
| #endif |
| |
| return Changed; |
| } |