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Diffstat (limited to 'llvm/lib/Transforms/Scalar/LoopRerollPass.cpp')
| -rw-r--r-- | llvm/lib/Transforms/Scalar/LoopRerollPass.cpp | 1699 |
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diff --git a/llvm/lib/Transforms/Scalar/LoopRerollPass.cpp b/llvm/lib/Transforms/Scalar/LoopRerollPass.cpp new file mode 100644 index 000000000000..96e2c2a3ac6b --- /dev/null +++ b/llvm/lib/Transforms/Scalar/LoopRerollPass.cpp @@ -0,0 +1,1699 @@ +//===- LoopReroll.cpp - Loop rerolling pass -------------------------------===// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +//===----------------------------------------------------------------------===// +// +// This pass implements a simple loop reroller. +// +//===----------------------------------------------------------------------===// + +#include "llvm/ADT/APInt.h" +#include "llvm/ADT/BitVector.h" +#include "llvm/ADT/DenseMap.h" +#include "llvm/ADT/DenseSet.h" +#include "llvm/ADT/MapVector.h" +#include "llvm/ADT/STLExtras.h" +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/ADT/SmallVector.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/Analysis/AliasAnalysis.h" +#include "llvm/Analysis/AliasSetTracker.h" +#include "llvm/Analysis/LoopInfo.h" +#include "llvm/Analysis/LoopPass.h" +#include "llvm/Analysis/ScalarEvolution.h" +#include "llvm/Analysis/ScalarEvolutionExpander.h" +#include "llvm/Analysis/ScalarEvolutionExpressions.h" +#include "llvm/Analysis/TargetLibraryInfo.h" +#include "llvm/Transforms/Utils/Local.h" +#include "llvm/Analysis/ValueTracking.h" +#include "llvm/IR/BasicBlock.h" +#include "llvm/IR/Constants.h" +#include "llvm/IR/DataLayout.h" +#include "llvm/IR/DerivedTypes.h" +#include "llvm/IR/Dominators.h" +#include "llvm/IR/IRBuilder.h" +#include "llvm/IR/InstrTypes.h" +#include "llvm/IR/Instruction.h" +#include "llvm/IR/Instructions.h" +#include "llvm/IR/IntrinsicInst.h" +#include "llvm/IR/Intrinsics.h" +#include "llvm/IR/Module.h" +#include "llvm/IR/Type.h" +#include "llvm/IR/Use.h" +#include "llvm/IR/User.h" +#include "llvm/IR/Value.h" +#include "llvm/Pass.h" +#include "llvm/Support/Casting.h" +#include "llvm/Support/CommandLine.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/raw_ostream.h" +#include "llvm/Transforms/Scalar.h" +#include "llvm/Transforms/Utils.h" +#include "llvm/Transforms/Utils/BasicBlockUtils.h" +#include "llvm/Transforms/Utils/LoopUtils.h" +#include <cassert> +#include <cstddef> +#include <cstdint> +#include <cstdlib> +#include <iterator> +#include <map> +#include <utility> + +using namespace llvm; + +#define DEBUG_TYPE "loop-reroll" + +STATISTIC(NumRerolledLoops, "Number of rerolled loops"); + +static cl::opt<unsigned> +NumToleratedFailedMatches("reroll-num-tolerated-failed-matches", cl::init(400), + cl::Hidden, + cl::desc("The maximum number of failures to tolerate" + " during fuzzy matching. (default: 400)")); + +// This loop re-rolling transformation aims to transform loops like this: +// +// int foo(int a); +// void bar(int *x) { +// for (int i = 0; i < 500; i += 3) { +// foo(i); +// foo(i+1); +// foo(i+2); +// } +// } +// +// into a loop like this: +// +// void bar(int *x) { +// for (int i = 0; i < 500; ++i) +// foo(i); +// } +// +// It does this by looking for loops that, besides the latch code, are composed +// of isomorphic DAGs of instructions, with each DAG rooted at some increment +// to the induction variable, and where each DAG is isomorphic to the DAG +// rooted at the induction variable (excepting the sub-DAGs which root the +// other induction-variable increments). In other words, we're looking for loop +// bodies of the form: +// +// %iv = phi [ (preheader, ...), (body, %iv.next) ] +// f(%iv) +// %iv.1 = add %iv, 1 <-- a root increment +// f(%iv.1) +// %iv.2 = add %iv, 2 <-- a root increment +// f(%iv.2) +// %iv.scale_m_1 = add %iv, scale-1 <-- a root increment +// f(%iv.scale_m_1) +// ... +// %iv.next = add %iv, scale +// %cmp = icmp(%iv, ...) +// br %cmp, header, exit +// +// where each f(i) is a set of instructions that, collectively, are a function +// only of i (and other loop-invariant values). +// +// As a special case, we can also reroll loops like this: +// +// int foo(int); +// void bar(int *x) { +// for (int i = 0; i < 500; ++i) { +// x[3*i] = foo(0); +// x[3*i+1] = foo(0); +// x[3*i+2] = foo(0); +// } +// } +// +// into this: +// +// void bar(int *x) { +// for (int i = 0; i < 1500; ++i) +// x[i] = foo(0); +// } +// +// in which case, we're looking for inputs like this: +// +// %iv = phi [ (preheader, ...), (body, %iv.next) ] +// %scaled.iv = mul %iv, scale +// f(%scaled.iv) +// %scaled.iv.1 = add %scaled.iv, 1 +// f(%scaled.iv.1) +// %scaled.iv.2 = add %scaled.iv, 2 +// f(%scaled.iv.2) +// %scaled.iv.scale_m_1 = add %scaled.iv, scale-1 +// f(%scaled.iv.scale_m_1) +// ... +// %iv.next = add %iv, 1 +// %cmp = icmp(%iv, ...) +// br %cmp, header, exit + +namespace { + + enum IterationLimits { + /// The maximum number of iterations that we'll try and reroll. + IL_MaxRerollIterations = 32, + /// The bitvector index used by loop induction variables and other + /// instructions that belong to all iterations. + IL_All, + IL_End + }; + + class LoopReroll : public LoopPass { + public: + static char ID; // Pass ID, replacement for typeid + + LoopReroll() : LoopPass(ID) { + initializeLoopRerollPass(*PassRegistry::getPassRegistry()); + } + + bool runOnLoop(Loop *L, LPPassManager &LPM) override; + + void getAnalysisUsage(AnalysisUsage &AU) const override { + AU.addRequired<TargetLibraryInfoWrapperPass>(); + getLoopAnalysisUsage(AU); + } + + protected: + AliasAnalysis *AA; + LoopInfo *LI; + ScalarEvolution *SE; + TargetLibraryInfo *TLI; + DominatorTree *DT; + bool PreserveLCSSA; + + using SmallInstructionVector = SmallVector<Instruction *, 16>; + using SmallInstructionSet = SmallPtrSet<Instruction *, 16>; + + // Map between induction variable and its increment + DenseMap<Instruction *, int64_t> IVToIncMap; + + // For loop with multiple induction variable, remember the one used only to + // control the loop. + Instruction *LoopControlIV; + + // A chain of isomorphic instructions, identified by a single-use PHI + // representing a reduction. Only the last value may be used outside the + // loop. + struct SimpleLoopReduction { + SimpleLoopReduction(Instruction *P, Loop *L) : Instructions(1, P) { + assert(isa<PHINode>(P) && "First reduction instruction must be a PHI"); + add(L); + } + + bool valid() const { + return Valid; + } + + Instruction *getPHI() const { + assert(Valid && "Using invalid reduction"); + return Instructions.front(); + } + + Instruction *getReducedValue() const { + assert(Valid && "Using invalid reduction"); + return Instructions.back(); + } + + Instruction *get(size_t i) const { + assert(Valid && "Using invalid reduction"); + return Instructions[i+1]; + } + + Instruction *operator [] (size_t i) const { return get(i); } + + // The size, ignoring the initial PHI. + size_t size() const { + assert(Valid && "Using invalid reduction"); + return Instructions.size()-1; + } + + using iterator = SmallInstructionVector::iterator; + using const_iterator = SmallInstructionVector::const_iterator; + + iterator begin() { + assert(Valid && "Using invalid reduction"); + return std::next(Instructions.begin()); + } + + const_iterator begin() const { + assert(Valid && "Using invalid reduction"); + return std::next(Instructions.begin()); + } + + iterator end() { return Instructions.end(); } + const_iterator end() const { return Instructions.end(); } + + protected: + bool Valid = false; + SmallInstructionVector Instructions; + + void add(Loop *L); + }; + + // The set of all reductions, and state tracking of possible reductions + // during loop instruction processing. + struct ReductionTracker { + using SmallReductionVector = SmallVector<SimpleLoopReduction, 16>; + + // Add a new possible reduction. + void addSLR(SimpleLoopReduction &SLR) { PossibleReds.push_back(SLR); } + + // Setup to track possible reductions corresponding to the provided + // rerolling scale. Only reductions with a number of non-PHI instructions + // that is divisible by the scale are considered. Three instructions sets + // are filled in: + // - A set of all possible instructions in eligible reductions. + // - A set of all PHIs in eligible reductions + // - A set of all reduced values (last instructions) in eligible + // reductions. + void restrictToScale(uint64_t Scale, + SmallInstructionSet &PossibleRedSet, + SmallInstructionSet &PossibleRedPHISet, + SmallInstructionSet &PossibleRedLastSet) { + PossibleRedIdx.clear(); + PossibleRedIter.clear(); + Reds.clear(); + + for (unsigned i = 0, e = PossibleReds.size(); i != e; ++i) + if (PossibleReds[i].size() % Scale == 0) { + PossibleRedLastSet.insert(PossibleReds[i].getReducedValue()); + PossibleRedPHISet.insert(PossibleReds[i].getPHI()); + + PossibleRedSet.insert(PossibleReds[i].getPHI()); + PossibleRedIdx[PossibleReds[i].getPHI()] = i; + for (Instruction *J : PossibleReds[i]) { + PossibleRedSet.insert(J); + PossibleRedIdx[J] = i; + } + } + } + + // The functions below are used while processing the loop instructions. + + // Are the two instructions both from reductions, and furthermore, from + // the same reduction? + bool isPairInSame(Instruction *J1, Instruction *J2) { + DenseMap<Instruction *, int>::iterator J1I = PossibleRedIdx.find(J1); + if (J1I != PossibleRedIdx.end()) { + DenseMap<Instruction *, int>::iterator J2I = PossibleRedIdx.find(J2); + if (J2I != PossibleRedIdx.end() && J1I->second == J2I->second) + return true; + } + + return false; + } + + // The two provided instructions, the first from the base iteration, and + // the second from iteration i, form a matched pair. If these are part of + // a reduction, record that fact. + void recordPair(Instruction *J1, Instruction *J2, unsigned i) { + if (PossibleRedIdx.count(J1)) { + assert(PossibleRedIdx.count(J2) && + "Recording reduction vs. non-reduction instruction?"); + + PossibleRedIter[J1] = 0; + PossibleRedIter[J2] = i; + + int Idx = PossibleRedIdx[J1]; + assert(Idx == PossibleRedIdx[J2] && + "Recording pair from different reductions?"); + Reds.insert(Idx); + } + } + + // The functions below can be called after we've finished processing all + // instructions in the loop, and we know which reductions were selected. + + bool validateSelected(); + void replaceSelected(); + + protected: + // The vector of all possible reductions (for any scale). + SmallReductionVector PossibleReds; + + DenseMap<Instruction *, int> PossibleRedIdx; + DenseMap<Instruction *, int> PossibleRedIter; + DenseSet<int> Reds; + }; + + // A DAGRootSet models an induction variable being used in a rerollable + // loop. For example, + // + // x[i*3+0] = y1 + // x[i*3+1] = y2 + // x[i*3+2] = y3 + // + // Base instruction -> i*3 + // +---+----+ + // / | \ + // ST[y1] +1 +2 <-- Roots + // | | + // ST[y2] ST[y3] + // + // There may be multiple DAGRoots, for example: + // + // x[i*2+0] = ... (1) + // x[i*2+1] = ... (1) + // x[i*2+4] = ... (2) + // x[i*2+5] = ... (2) + // x[(i+1234)*2+5678] = ... (3) + // x[(i+1234)*2+5679] = ... (3) + // + // The loop will be rerolled by adding a new loop induction variable, + // one for the Base instruction in each DAGRootSet. + // + struct DAGRootSet { + Instruction *BaseInst; + SmallInstructionVector Roots; + + // The instructions between IV and BaseInst (but not including BaseInst). + SmallInstructionSet SubsumedInsts; + }; + + // The set of all DAG roots, and state tracking of all roots + // for a particular induction variable. + struct DAGRootTracker { + DAGRootTracker(LoopReroll *Parent, Loop *L, Instruction *IV, + ScalarEvolution *SE, AliasAnalysis *AA, + TargetLibraryInfo *TLI, DominatorTree *DT, LoopInfo *LI, + bool PreserveLCSSA, + DenseMap<Instruction *, int64_t> &IncrMap, + Instruction *LoopCtrlIV) + : Parent(Parent), L(L), SE(SE), AA(AA), TLI(TLI), DT(DT), LI(LI), + PreserveLCSSA(PreserveLCSSA), IV(IV), IVToIncMap(IncrMap), + LoopControlIV(LoopCtrlIV) {} + + /// Stage 1: Find all the DAG roots for the induction variable. + bool findRoots(); + + /// Stage 2: Validate if the found roots are valid. + bool validate(ReductionTracker &Reductions); + + /// Stage 3: Assuming validate() returned true, perform the + /// replacement. + /// @param BackedgeTakenCount The backedge-taken count of L. + void replace(const SCEV *BackedgeTakenCount); + + protected: + using UsesTy = MapVector<Instruction *, BitVector>; + + void findRootsRecursive(Instruction *IVU, + SmallInstructionSet SubsumedInsts); + bool findRootsBase(Instruction *IVU, SmallInstructionSet SubsumedInsts); + bool collectPossibleRoots(Instruction *Base, + std::map<int64_t,Instruction*> &Roots); + bool validateRootSet(DAGRootSet &DRS); + + bool collectUsedInstructions(SmallInstructionSet &PossibleRedSet); + void collectInLoopUserSet(const SmallInstructionVector &Roots, + const SmallInstructionSet &Exclude, + const SmallInstructionSet &Final, + DenseSet<Instruction *> &Users); + void collectInLoopUserSet(Instruction *Root, + const SmallInstructionSet &Exclude, + const SmallInstructionSet &Final, + DenseSet<Instruction *> &Users); + + UsesTy::iterator nextInstr(int Val, UsesTy &In, + const SmallInstructionSet &Exclude, + UsesTy::iterator *StartI=nullptr); + bool isBaseInst(Instruction *I); + bool isRootInst(Instruction *I); + bool instrDependsOn(Instruction *I, + UsesTy::iterator Start, + UsesTy::iterator End); + void replaceIV(DAGRootSet &DRS, const SCEV *Start, const SCEV *IncrExpr); + + LoopReroll *Parent; + + // Members of Parent, replicated here for brevity. + Loop *L; + ScalarEvolution *SE; + AliasAnalysis *AA; + TargetLibraryInfo *TLI; + DominatorTree *DT; + LoopInfo *LI; + bool PreserveLCSSA; + + // The loop induction variable. + Instruction *IV; + + // Loop step amount. + int64_t Inc; + + // Loop reroll count; if Inc == 1, this records the scaling applied + // to the indvar: a[i*2+0] = ...; a[i*2+1] = ... ; + // If Inc is not 1, Scale = Inc. + uint64_t Scale; + + // The roots themselves. + SmallVector<DAGRootSet,16> RootSets; + + // All increment instructions for IV. + SmallInstructionVector LoopIncs; + + // Map of all instructions in the loop (in order) to the iterations + // they are used in (or specially, IL_All for instructions + // used in the loop increment mechanism). + UsesTy Uses; + + // Map between induction variable and its increment + DenseMap<Instruction *, int64_t> &IVToIncMap; + + Instruction *LoopControlIV; + }; + + // Check if it is a compare-like instruction whose user is a branch + bool isCompareUsedByBranch(Instruction *I) { + auto *TI = I->getParent()->getTerminator(); + if (!isa<BranchInst>(TI) || !isa<CmpInst>(I)) + return false; + return I->hasOneUse() && TI->getOperand(0) == I; + }; + + bool isLoopControlIV(Loop *L, Instruction *IV); + void collectPossibleIVs(Loop *L, SmallInstructionVector &PossibleIVs); + void collectPossibleReductions(Loop *L, + ReductionTracker &Reductions); + bool reroll(Instruction *IV, Loop *L, BasicBlock *Header, + const SCEV *BackedgeTakenCount, ReductionTracker &Reductions); + }; + +} // end anonymous namespace + +char LoopReroll::ID = 0; + +INITIALIZE_PASS_BEGIN(LoopReroll, "loop-reroll", "Reroll loops", false, false) +INITIALIZE_PASS_DEPENDENCY(LoopPass) +INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) +INITIALIZE_PASS_END(LoopReroll, "loop-reroll", "Reroll loops", false, false) + +Pass *llvm::createLoopRerollPass() { + return new LoopReroll; +} + +// Returns true if the provided instruction is used outside the given loop. +// This operates like Instruction::isUsedOutsideOfBlock, but considers PHIs in +// non-loop blocks to be outside the loop. +static bool hasUsesOutsideLoop(Instruction *I, Loop *L) { + for (User *U : I->users()) { + if (!L->contains(cast<Instruction>(U))) + return true; + } + return false; +} + +// Check if an IV is only used to control the loop. There are two cases: +// 1. It only has one use which is loop increment, and the increment is only +// used by comparison and the PHI (could has sext with nsw in between), and the +// comparison is only used by branch. +// 2. It is used by loop increment and the comparison, the loop increment is +// only used by the PHI, and the comparison is used only by the branch. +bool LoopReroll::isLoopControlIV(Loop *L, Instruction *IV) { + unsigned IVUses = IV->getNumUses(); + if (IVUses != 2 && IVUses != 1) + return false; + + for (auto *User : IV->users()) { + int32_t IncOrCmpUses = User->getNumUses(); + bool IsCompInst = isCompareUsedByBranch(cast<Instruction>(User)); + + // User can only have one or two uses. + if (IncOrCmpUses != 2 && IncOrCmpUses != 1) + return false; + + // Case 1 + if (IVUses == 1) { + // The only user must be the loop increment. + // The loop increment must have two uses. + if (IsCompInst || IncOrCmpUses != 2) + return false; + } + + // Case 2 + if (IVUses == 2 && IncOrCmpUses != 1) + return false; + + // The users of the IV must be a binary operation or a comparison + if (auto *BO = dyn_cast<BinaryOperator>(User)) { + if (BO->getOpcode() == Instruction::Add) { + // Loop Increment + // User of Loop Increment should be either PHI or CMP + for (auto *UU : User->users()) { + if (PHINode *PN = dyn_cast<PHINode>(UU)) { + if (PN != IV) + return false; + } + // Must be a CMP or an ext (of a value with nsw) then CMP + else { + Instruction *UUser = dyn_cast<Instruction>(UU); + // Skip SExt if we are extending an nsw value + // TODO: Allow ZExt too + if (BO->hasNoSignedWrap() && UUser && UUser->hasOneUse() && + isa<SExtInst>(UUser)) + UUser = dyn_cast<Instruction>(*(UUser->user_begin())); + if (!isCompareUsedByBranch(UUser)) + return false; + } + } + } else + return false; + // Compare : can only have one use, and must be branch + } else if (!IsCompInst) + return false; + } + return true; +} + +// Collect the list of loop induction variables with respect to which it might +// be possible to reroll the loop. +void LoopReroll::collectPossibleIVs(Loop *L, + SmallInstructionVector &PossibleIVs) { + BasicBlock *Header = L->getHeader(); + for (BasicBlock::iterator I = Header->begin(), + IE = Header->getFirstInsertionPt(); I != IE; ++I) { + if (!isa<PHINode>(I)) + continue; + if (!I->getType()->isIntegerTy() && !I->getType()->isPointerTy()) + continue; + + if (const SCEVAddRecExpr *PHISCEV = + dyn_cast<SCEVAddRecExpr>(SE->getSCEV(&*I))) { + if (PHISCEV->getLoop() != L) + continue; + if (!PHISCEV->isAffine()) + continue; + auto IncSCEV = dyn_cast<SCEVConstant>(PHISCEV->getStepRecurrence(*SE)); + if (IncSCEV) { + IVToIncMap[&*I] = IncSCEV->getValue()->getSExtValue(); + LLVM_DEBUG(dbgs() << "LRR: Possible IV: " << *I << " = " << *PHISCEV + << "\n"); + + if (isLoopControlIV(L, &*I)) { + assert(!LoopControlIV && "Found two loop control only IV"); + LoopControlIV = &(*I); + LLVM_DEBUG(dbgs() << "LRR: Possible loop control only IV: " << *I + << " = " << *PHISCEV << "\n"); + } else + PossibleIVs.push_back(&*I); + } + } + } +} + +// Add the remainder of the reduction-variable chain to the instruction vector +// (the initial PHINode has already been added). If successful, the object is +// marked as valid. +void LoopReroll::SimpleLoopReduction::add(Loop *L) { + assert(!Valid && "Cannot add to an already-valid chain"); + + // The reduction variable must be a chain of single-use instructions + // (including the PHI), except for the last value (which is used by the PHI + // and also outside the loop). + Instruction *C = Instructions.front(); + if (C->user_empty()) + return; + + do { + C = cast<Instruction>(*C->user_begin()); + if (C->hasOneUse()) { + if (!C->isBinaryOp()) + return; + + if (!(isa<PHINode>(Instructions.back()) || + C->isSameOperationAs(Instructions.back()))) + return; + + Instructions.push_back(C); + } + } while (C->hasOneUse()); + + if (Instructions.size() < 2 || + !C->isSameOperationAs(Instructions.back()) || + C->use_empty()) + return; + + // C is now the (potential) last instruction in the reduction chain. + for (User *U : C->users()) { + // The only in-loop user can be the initial PHI. + if (L->contains(cast<Instruction>(U))) + if (cast<Instruction>(U) != Instructions.front()) + return; + } + + Instructions.push_back(C); + Valid = true; +} + +// Collect the vector of possible reduction variables. +void LoopReroll::collectPossibleReductions(Loop *L, + ReductionTracker &Reductions) { + BasicBlock *Header = L->getHeader(); + for (BasicBlock::iterator I = Header->begin(), + IE = Header->getFirstInsertionPt(); I != IE; ++I) { + if (!isa<PHINode>(I)) + continue; + if (!I->getType()->isSingleValueType()) + continue; + + SimpleLoopReduction SLR(&*I, L); + if (!SLR.valid()) + continue; + + LLVM_DEBUG(dbgs() << "LRR: Possible reduction: " << *I << " (with " + << SLR.size() << " chained instructions)\n"); + Reductions.addSLR(SLR); + } +} + +// Collect the set of all users of the provided root instruction. This set of +// users contains not only the direct users of the root instruction, but also +// all users of those users, and so on. There are two exceptions: +// +// 1. Instructions in the set of excluded instructions are never added to the +// use set (even if they are users). This is used, for example, to exclude +// including root increments in the use set of the primary IV. +// +// 2. Instructions in the set of final instructions are added to the use set +// if they are users, but their users are not added. This is used, for +// example, to prevent a reduction update from forcing all later reduction +// updates into the use set. +void LoopReroll::DAGRootTracker::collectInLoopUserSet( + Instruction *Root, const SmallInstructionSet &Exclude, + const SmallInstructionSet &Final, + DenseSet<Instruction *> &Users) { + SmallInstructionVector Queue(1, Root); + while (!Queue.empty()) { + Instruction *I = Queue.pop_back_val(); + if (!Users.insert(I).second) + continue; + + if (!Final.count(I)) + for (Use &U : I->uses()) { + Instruction *User = cast<Instruction>(U.getUser()); + if (PHINode *PN = dyn_cast<PHINode>(User)) { + // Ignore "wrap-around" uses to PHIs of this loop's header. + if (PN->getIncomingBlock(U) == L->getHeader()) + continue; + } + + if (L->contains(User) && !Exclude.count(User)) { + Queue.push_back(User); + } + } + + // We also want to collect single-user "feeder" values. + for (User::op_iterator OI = I->op_begin(), + OIE = I->op_end(); OI != OIE; ++OI) { + if (Instruction *Op = dyn_cast<Instruction>(*OI)) + if (Op->hasOneUse() && L->contains(Op) && !Exclude.count(Op) && + !Final.count(Op)) + Queue.push_back(Op); + } + } +} + +// Collect all of the users of all of the provided root instructions (combined +// into a single set). +void LoopReroll::DAGRootTracker::collectInLoopUserSet( + const SmallInstructionVector &Roots, + const SmallInstructionSet &Exclude, + const SmallInstructionSet &Final, + DenseSet<Instruction *> &Users) { + for (Instruction *Root : Roots) + collectInLoopUserSet(Root, Exclude, Final, Users); +} + +static bool isUnorderedLoadStore(Instruction *I) { + if (LoadInst *LI = dyn_cast<LoadInst>(I)) + return LI->isUnordered(); + if (StoreInst *SI = dyn_cast<StoreInst>(I)) + return SI->isUnordered(); + if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) + return !MI->isVolatile(); + return false; +} + +/// Return true if IVU is a "simple" arithmetic operation. +/// This is used for narrowing the search space for DAGRoots; only arithmetic +/// and GEPs can be part of a DAGRoot. +static bool isSimpleArithmeticOp(User *IVU) { + if (Instruction *I = dyn_cast<Instruction>(IVU)) { + switch (I->getOpcode()) { + default: return false; + case Instruction::Add: + case Instruction::Sub: + case Instruction::Mul: + case Instruction::Shl: + case Instruction::AShr: + case Instruction::LShr: + case Instruction::GetElementPtr: + case Instruction::Trunc: + case Instruction::ZExt: + case Instruction::SExt: + return true; + } + } + return false; +} + +static bool isLoopIncrement(User *U, Instruction *IV) { + BinaryOperator *BO = dyn_cast<BinaryOperator>(U); + + if ((BO && BO->getOpcode() != Instruction::Add) || + (!BO && !isa<GetElementPtrInst>(U))) + return false; + + for (auto *UU : U->users()) { + PHINode *PN = dyn_cast<PHINode>(UU); + if (PN && PN == IV) + return true; + } + return false; +} + +bool LoopReroll::DAGRootTracker:: +collectPossibleRoots(Instruction *Base, std::map<int64_t,Instruction*> &Roots) { + SmallInstructionVector BaseUsers; + + for (auto *I : Base->users()) { + ConstantInt *CI = nullptr; + + if (isLoopIncrement(I, IV)) { + LoopIncs.push_back(cast<Instruction>(I)); + continue; + } + + // The root nodes must be either GEPs, ORs or ADDs. + if (auto *BO = dyn_cast<BinaryOperator>(I)) { + if (BO->getOpcode() == Instruction::Add || + BO->getOpcode() == Instruction::Or) + CI = dyn_cast<ConstantInt>(BO->getOperand(1)); + } else if (auto *GEP = dyn_cast<GetElementPtrInst>(I)) { + Value *LastOperand = GEP->getOperand(GEP->getNumOperands()-1); + CI = dyn_cast<ConstantInt>(LastOperand); + } + + if (!CI) { + if (Instruction *II = dyn_cast<Instruction>(I)) { + BaseUsers.push_back(II); + continue; + } else { + LLVM_DEBUG(dbgs() << "LRR: Aborting due to non-instruction: " << *I + << "\n"); + return false; + } + } + + int64_t V = std::abs(CI->getValue().getSExtValue()); + if (Roots.find(V) != Roots.end()) + // No duplicates, please. + return false; + + Roots[V] = cast<Instruction>(I); + } + + // Make sure we have at least two roots. + if (Roots.empty() || (Roots.size() == 1 && BaseUsers.empty())) + return false; + + // If we found non-loop-inc, non-root users of Base, assume they are + // for the zeroth root index. This is because "add %a, 0" gets optimized + // away. + if (BaseUsers.size()) { + if (Roots.find(0) != Roots.end()) { + LLVM_DEBUG(dbgs() << "LRR: Multiple roots found for base - aborting!\n"); + return false; + } + Roots[0] = Base; + } + + // Calculate the number of users of the base, or lowest indexed, iteration. + unsigned NumBaseUses = BaseUsers.size(); + if (NumBaseUses == 0) + NumBaseUses = Roots.begin()->second->getNumUses(); + + // Check that every node has the same number of users. + for (auto &KV : Roots) { + if (KV.first == 0) + continue; + if (!KV.second->hasNUses(NumBaseUses)) { + LLVM_DEBUG(dbgs() << "LRR: Aborting - Root and Base #users not the same: " + << "#Base=" << NumBaseUses + << ", #Root=" << KV.second->getNumUses() << "\n"); + return false; + } + } + + return true; +} + +void LoopReroll::DAGRootTracker:: +findRootsRecursive(Instruction *I, SmallInstructionSet SubsumedInsts) { + // Does the user look like it could be part of a root set? + // All its users must be simple arithmetic ops. + if (I->hasNUsesOrMore(IL_MaxRerollIterations + 1)) + return; + + if (I != IV && findRootsBase(I, SubsumedInsts)) + return; + + SubsumedInsts.insert(I); + + for (User *V : I->users()) { + Instruction *I = cast<Instruction>(V); + if (is_contained(LoopIncs, I)) + continue; + + if (!isSimpleArithmeticOp(I)) + continue; + + // The recursive call makes a copy of SubsumedInsts. + findRootsRecursive(I, SubsumedInsts); + } +} + +bool LoopReroll::DAGRootTracker::validateRootSet(DAGRootSet &DRS) { + if (DRS.Roots.empty()) + return false; + + // Consider a DAGRootSet with N-1 roots (so N different values including + // BaseInst). + // Define d = Roots[0] - BaseInst, which should be the same as + // Roots[I] - Roots[I-1] for all I in [1..N). + // Define D = BaseInst@J - BaseInst@J-1, where "@J" means the value at the + // loop iteration J. + // + // Now, For the loop iterations to be consecutive: + // D = d * N + const auto *ADR = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(DRS.BaseInst)); + if (!ADR) + return false; + + // Check that the first root is evenly spaced. + unsigned N = DRS.Roots.size() + 1; + const SCEV *StepSCEV = SE->getMinusSCEV(SE->getSCEV(DRS.Roots[0]), ADR); + const SCEV *ScaleSCEV = SE->getConstant(StepSCEV->getType(), N); + if (ADR->getStepRecurrence(*SE) != SE->getMulExpr(StepSCEV, ScaleSCEV)) + return false; + + // Check that the remainling roots are evenly spaced. + for (unsigned i = 1; i < N - 1; ++i) { + const SCEV *NewStepSCEV = SE->getMinusSCEV(SE->getSCEV(DRS.Roots[i]), + SE->getSCEV(DRS.Roots[i-1])); + if (NewStepSCEV != StepSCEV) + return false; + } + + return true; +} + +bool LoopReroll::DAGRootTracker:: +findRootsBase(Instruction *IVU, SmallInstructionSet SubsumedInsts) { + // The base of a RootSet must be an AddRec, so it can be erased. + const auto *IVU_ADR = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(IVU)); + if (!IVU_ADR || IVU_ADR->getLoop() != L) + return false; + + std::map<int64_t, Instruction*> V; + if (!collectPossibleRoots(IVU, V)) + return false; + + // If we didn't get a root for index zero, then IVU must be + // subsumed. + if (V.find(0) == V.end()) + SubsumedInsts.insert(IVU); + + // Partition the vector into monotonically increasing indexes. + DAGRootSet DRS; + DRS.BaseInst = nullptr; + + SmallVector<DAGRootSet, 16> PotentialRootSets; + + for (auto &KV : V) { + if (!DRS.BaseInst) { + DRS.BaseInst = KV.second; + DRS.SubsumedInsts = SubsumedInsts; + } else if (DRS.Roots.empty()) { + DRS.Roots.push_back(KV.second); + } else if (V.find(KV.first - 1) != V.end()) { + DRS.Roots.push_back(KV.second); + } else { + // Linear sequence terminated. + if (!validateRootSet(DRS)) + return false; + + // Construct a new DAGRootSet with the next sequence. + PotentialRootSets.push_back(DRS); + DRS.BaseInst = KV.second; + DRS.Roots.clear(); + } + } + + if (!validateRootSet(DRS)) + return false; + + PotentialRootSets.push_back(DRS); + + RootSets.append(PotentialRootSets.begin(), PotentialRootSets.end()); + + return true; +} + +bool LoopReroll::DAGRootTracker::findRoots() { + Inc = IVToIncMap[IV]; + + assert(RootSets.empty() && "Unclean state!"); + if (std::abs(Inc) == 1) { + for (auto *IVU : IV->users()) { + if (isLoopIncrement(IVU, IV)) + LoopIncs.push_back(cast<Instruction>(IVU)); + } + findRootsRecursive(IV, SmallInstructionSet()); + LoopIncs.push_back(IV); + } else { + if (!findRootsBase(IV, SmallInstructionSet())) + return false; + } + + // Ensure all sets have the same size. + if (RootSets.empty()) { + LLVM_DEBUG(dbgs() << "LRR: Aborting because no root sets found!\n"); + return false; + } + for (auto &V : RootSets) { + if (V.Roots.empty() || V.Roots.size() != RootSets[0].Roots.size()) { + LLVM_DEBUG( + dbgs() + << "LRR: Aborting because not all root sets have the same size\n"); + return false; + } + } + + Scale = RootSets[0].Roots.size() + 1; + + if (Scale > IL_MaxRerollIterations) { + LLVM_DEBUG(dbgs() << "LRR: Aborting - too many iterations found. " + << "#Found=" << Scale + << ", #Max=" << IL_MaxRerollIterations << "\n"); + return false; + } + + LLVM_DEBUG(dbgs() << "LRR: Successfully found roots: Scale=" << Scale + << "\n"); + + return true; +} + +bool LoopReroll::DAGRootTracker::collectUsedInstructions(SmallInstructionSet &PossibleRedSet) { + // Populate the MapVector with all instructions in the block, in order first, + // so we can iterate over the contents later in perfect order. + for (auto &I : *L->getHeader()) { + Uses[&I].resize(IL_End); + } + + SmallInstructionSet Exclude; + for (auto &DRS : RootSets) { + Exclude.insert(DRS.Roots.begin(), DRS.Roots.end()); + Exclude.insert(DRS.SubsumedInsts.begin(), DRS.SubsumedInsts.end()); + Exclude.insert(DRS.BaseInst); + } + Exclude.insert(LoopIncs.begin(), LoopIncs.end()); + + for (auto &DRS : RootSets) { + DenseSet<Instruction*> VBase; + collectInLoopUserSet(DRS.BaseInst, Exclude, PossibleRedSet, VBase); + for (auto *I : VBase) { + Uses[I].set(0); + } + + unsigned Idx = 1; + for (auto *Root : DRS.Roots) { + DenseSet<Instruction*> V; + collectInLoopUserSet(Root, Exclude, PossibleRedSet, V); + + // While we're here, check the use sets are the same size. + if (V.size() != VBase.size()) { + LLVM_DEBUG(dbgs() << "LRR: Aborting - use sets are different sizes\n"); + return false; + } + + for (auto *I : V) { + Uses[I].set(Idx); + } + ++Idx; + } + + // Make sure our subsumed instructions are remembered too. + for (auto *I : DRS.SubsumedInsts) { + Uses[I].set(IL_All); + } + } + + // Make sure the loop increments are also accounted for. + + Exclude.clear(); + for (auto &DRS : RootSets) { + Exclude.insert(DRS.Roots.begin(), DRS.Roots.end()); + Exclude.insert(DRS.SubsumedInsts.begin(), DRS.SubsumedInsts.end()); + Exclude.insert(DRS.BaseInst); + } + + DenseSet<Instruction*> V; + collectInLoopUserSet(LoopIncs, Exclude, PossibleRedSet, V); + for (auto *I : V) { + Uses[I].set(IL_All); + } + + return true; +} + +/// Get the next instruction in "In" that is a member of set Val. +/// Start searching from StartI, and do not return anything in Exclude. +/// If StartI is not given, start from In.begin(). +LoopReroll::DAGRootTracker::UsesTy::iterator +LoopReroll::DAGRootTracker::nextInstr(int Val, UsesTy &In, + const SmallInstructionSet &Exclude, + UsesTy::iterator *StartI) { + UsesTy::iterator I = StartI ? *StartI : In.begin(); + while (I != In.end() && (I->second.test(Val) == 0 || + Exclude.count(I->first) != 0)) + ++I; + return I; +} + +bool LoopReroll::DAGRootTracker::isBaseInst(Instruction *I) { + for (auto &DRS : RootSets) { + if (DRS.BaseInst == I) + return true; + } + return false; +} + +bool LoopReroll::DAGRootTracker::isRootInst(Instruction *I) { + for (auto &DRS : RootSets) { + if (is_contained(DRS.Roots, I)) + return true; + } + return false; +} + +/// Return true if instruction I depends on any instruction between +/// Start and End. +bool LoopReroll::DAGRootTracker::instrDependsOn(Instruction *I, + UsesTy::iterator Start, + UsesTy::iterator End) { + for (auto *U : I->users()) { + for (auto It = Start; It != End; ++It) + if (U == It->first) + return true; + } + return false; +} + +static bool isIgnorableInst(const Instruction *I) { + if (isa<DbgInfoIntrinsic>(I)) + return true; + const IntrinsicInst* II = dyn_cast<IntrinsicInst>(I); + if (!II) + return false; + switch (II->getIntrinsicID()) { + default: + return false; + case Intrinsic::annotation: + case Intrinsic::ptr_annotation: + case Intrinsic::var_annotation: + // TODO: the following intrinsics may also be whitelisted: + // lifetime_start, lifetime_end, invariant_start, invariant_end + return true; + } + return false; +} + +bool LoopReroll::DAGRootTracker::validate(ReductionTracker &Reductions) { + // We now need to check for equivalence of the use graph of each root with + // that of the primary induction variable (excluding the roots). Our goal + // here is not to solve the full graph isomorphism problem, but rather to + // catch common cases without a lot of work. As a result, we will assume + // that the relative order of the instructions in each unrolled iteration + // is the same (although we will not make an assumption about how the + // different iterations are intermixed). Note that while the order must be + // the same, the instructions may not be in the same basic block. + + // An array of just the possible reductions for this scale factor. When we + // collect the set of all users of some root instructions, these reduction + // instructions are treated as 'final' (their uses are not considered). + // This is important because we don't want the root use set to search down + // the reduction chain. + SmallInstructionSet PossibleRedSet; + SmallInstructionSet PossibleRedLastSet; + SmallInstructionSet PossibleRedPHISet; + Reductions.restrictToScale(Scale, PossibleRedSet, + PossibleRedPHISet, PossibleRedLastSet); + + // Populate "Uses" with where each instruction is used. + if (!collectUsedInstructions(PossibleRedSet)) + return false; + + // Make sure we mark the reduction PHIs as used in all iterations. + for (auto *I : PossibleRedPHISet) { + Uses[I].set(IL_All); + } + + // Make sure we mark loop-control-only PHIs as used in all iterations. See + // comment above LoopReroll::isLoopControlIV for more information. + BasicBlock *Header = L->getHeader(); + if (LoopControlIV && LoopControlIV != IV) { + for (auto *U : LoopControlIV->users()) { + Instruction *IVUser = dyn_cast<Instruction>(U); + // IVUser could be loop increment or compare + Uses[IVUser].set(IL_All); + for (auto *UU : IVUser->users()) { + Instruction *UUser = dyn_cast<Instruction>(UU); + // UUser could be compare, PHI or branch + Uses[UUser].set(IL_All); + // Skip SExt + if (isa<SExtInst>(UUser)) { + UUser = dyn_cast<Instruction>(*(UUser->user_begin())); + Uses[UUser].set(IL_All); + } + // Is UUser a compare instruction? + if (UU->hasOneUse()) { + Instruction *BI = dyn_cast<BranchInst>(*UUser->user_begin()); + if (BI == cast<BranchInst>(Header->getTerminator())) + Uses[BI].set(IL_All); + } + } + } + } + + // Make sure all instructions in the loop are in one and only one + // set. + for (auto &KV : Uses) { + if (KV.second.count() != 1 && !isIgnorableInst(KV.first)) { + LLVM_DEBUG( + dbgs() << "LRR: Aborting - instruction is not used in 1 iteration: " + << *KV.first << " (#uses=" << KV.second.count() << ")\n"); + return false; + } + } + + LLVM_DEBUG(for (auto &KV + : Uses) { + dbgs() << "LRR: " << KV.second.find_first() << "\t" << *KV.first << "\n"; + }); + + for (unsigned Iter = 1; Iter < Scale; ++Iter) { + // In addition to regular aliasing information, we need to look for + // instructions from later (future) iterations that have side effects + // preventing us from reordering them past other instructions with side + // effects. + bool FutureSideEffects = false; + AliasSetTracker AST(*AA); + // The map between instructions in f(%iv.(i+1)) and f(%iv). + DenseMap<Value *, Value *> BaseMap; + + // Compare iteration Iter to the base. + SmallInstructionSet Visited; + auto BaseIt = nextInstr(0, Uses, Visited); + auto RootIt = nextInstr(Iter, Uses, Visited); + auto LastRootIt = Uses.begin(); + + while (BaseIt != Uses.end() && RootIt != Uses.end()) { + Instruction *BaseInst = BaseIt->first; + Instruction *RootInst = RootIt->first; + + // Skip over the IV or root instructions; only match their users. + bool Continue = false; + if (isBaseInst(BaseInst)) { + Visited.insert(BaseInst); + BaseIt = nextInstr(0, Uses, Visited); + Continue = true; + } + if (isRootInst(RootInst)) { + LastRootIt = RootIt; + Visited.insert(RootInst); + RootIt = nextInstr(Iter, Uses, Visited); + Continue = true; + } + if (Continue) continue; + + if (!BaseInst->isSameOperationAs(RootInst)) { + // Last chance saloon. We don't try and solve the full isomorphism + // problem, but try and at least catch the case where two instructions + // *of different types* are round the wrong way. We won't be able to + // efficiently tell, given two ADD instructions, which way around we + // should match them, but given an ADD and a SUB, we can at least infer + // which one is which. + // + // This should allow us to deal with a greater subset of the isomorphism + // problem. It does however change a linear algorithm into a quadratic + // one, so limit the number of probes we do. + auto TryIt = RootIt; + unsigned N = NumToleratedFailedMatches; + while (TryIt != Uses.end() && + !BaseInst->isSameOperationAs(TryIt->first) && + N--) { + ++TryIt; + TryIt = nextInstr(Iter, Uses, Visited, &TryIt); + } + + if (TryIt == Uses.end() || TryIt == RootIt || + instrDependsOn(TryIt->first, RootIt, TryIt)) { + LLVM_DEBUG(dbgs() << "LRR: iteration root match failed at " + << *BaseInst << " vs. " << *RootInst << "\n"); + return false; + } + + RootIt = TryIt; + RootInst = TryIt->first; + } + + // All instructions between the last root and this root + // may belong to some other iteration. If they belong to a + // future iteration, then they're dangerous to alias with. + // + // Note that because we allow a limited amount of flexibility in the order + // that we visit nodes, LastRootIt might be *before* RootIt, in which + // case we've already checked this set of instructions so we shouldn't + // do anything. + for (; LastRootIt < RootIt; ++LastRootIt) { + Instruction *I = LastRootIt->first; + if (LastRootIt->second.find_first() < (int)Iter) + continue; + if (I->mayWriteToMemory()) + AST.add(I); + // Note: This is specifically guarded by a check on isa<PHINode>, + // which while a valid (somewhat arbitrary) micro-optimization, is + // needed because otherwise isSafeToSpeculativelyExecute returns + // false on PHI nodes. + if (!isa<PHINode>(I) && !isUnorderedLoadStore(I) && + !isSafeToSpeculativelyExecute(I)) + // Intervening instructions cause side effects. + FutureSideEffects = true; + } + + // Make sure that this instruction, which is in the use set of this + // root instruction, does not also belong to the base set or the set of + // some other root instruction. + if (RootIt->second.count() > 1) { + LLVM_DEBUG(dbgs() << "LRR: iteration root match failed at " << *BaseInst + << " vs. " << *RootInst << " (prev. case overlap)\n"); + return false; + } + + // Make sure that we don't alias with any instruction in the alias set + // tracker. If we do, then we depend on a future iteration, and we + // can't reroll. + if (RootInst->mayReadFromMemory()) + for (auto &K : AST) { + if (K.aliasesUnknownInst(RootInst, *AA)) { + LLVM_DEBUG(dbgs() << "LRR: iteration root match failed at " + << *BaseInst << " vs. " << *RootInst + << " (depends on future store)\n"); + return false; + } + } + + // If we've past an instruction from a future iteration that may have + // side effects, and this instruction might also, then we can't reorder + // them, and this matching fails. As an exception, we allow the alias + // set tracker to handle regular (unordered) load/store dependencies. + if (FutureSideEffects && ((!isUnorderedLoadStore(BaseInst) && + !isSafeToSpeculativelyExecute(BaseInst)) || + (!isUnorderedLoadStore(RootInst) && + !isSafeToSpeculativelyExecute(RootInst)))) { + LLVM_DEBUG(dbgs() << "LRR: iteration root match failed at " << *BaseInst + << " vs. " << *RootInst + << " (side effects prevent reordering)\n"); + return false; + } + + // For instructions that are part of a reduction, if the operation is + // associative, then don't bother matching the operands (because we + // already know that the instructions are isomorphic, and the order + // within the iteration does not matter). For non-associative reductions, + // we do need to match the operands, because we need to reject + // out-of-order instructions within an iteration! + // For example (assume floating-point addition), we need to reject this: + // x += a[i]; x += b[i]; + // x += a[i+1]; x += b[i+1]; + // x += b[i+2]; x += a[i+2]; + bool InReduction = Reductions.isPairInSame(BaseInst, RootInst); + + if (!(InReduction && BaseInst->isAssociative())) { + bool Swapped = false, SomeOpMatched = false; + for (unsigned j = 0; j < BaseInst->getNumOperands(); ++j) { + Value *Op2 = RootInst->getOperand(j); + + // If this is part of a reduction (and the operation is not + // associatve), then we match all operands, but not those that are + // part of the reduction. + if (InReduction) + if (Instruction *Op2I = dyn_cast<Instruction>(Op2)) + if (Reductions.isPairInSame(RootInst, Op2I)) + continue; + + DenseMap<Value *, Value *>::iterator BMI = BaseMap.find(Op2); + if (BMI != BaseMap.end()) { + Op2 = BMI->second; + } else { + for (auto &DRS : RootSets) { + if (DRS.Roots[Iter-1] == (Instruction*) Op2) { + Op2 = DRS.BaseInst; + break; + } + } + } + + if (BaseInst->getOperand(Swapped ? unsigned(!j) : j) != Op2) { + // If we've not already decided to swap the matched operands, and + // we've not already matched our first operand (note that we could + // have skipped matching the first operand because it is part of a + // reduction above), and the instruction is commutative, then try + // the swapped match. + if (!Swapped && BaseInst->isCommutative() && !SomeOpMatched && + BaseInst->getOperand(!j) == Op2) { + Swapped = true; + } else { + LLVM_DEBUG(dbgs() + << "LRR: iteration root match failed at " << *BaseInst + << " vs. " << *RootInst << " (operand " << j << ")\n"); + return false; + } + } + + SomeOpMatched = true; + } + } + + if ((!PossibleRedLastSet.count(BaseInst) && + hasUsesOutsideLoop(BaseInst, L)) || + (!PossibleRedLastSet.count(RootInst) && + hasUsesOutsideLoop(RootInst, L))) { + LLVM_DEBUG(dbgs() << "LRR: iteration root match failed at " << *BaseInst + << " vs. " << *RootInst << " (uses outside loop)\n"); + return false; + } + + Reductions.recordPair(BaseInst, RootInst, Iter); + BaseMap.insert(std::make_pair(RootInst, BaseInst)); + + LastRootIt = RootIt; + Visited.insert(BaseInst); + Visited.insert(RootInst); + BaseIt = nextInstr(0, Uses, Visited); + RootIt = nextInstr(Iter, Uses, Visited); + } + assert(BaseIt == Uses.end() && RootIt == Uses.end() && + "Mismatched set sizes!"); + } + + LLVM_DEBUG(dbgs() << "LRR: Matched all iteration increments for " << *IV + << "\n"); + + return true; +} + +void LoopReroll::DAGRootTracker::replace(const SCEV *BackedgeTakenCount) { + BasicBlock *Header = L->getHeader(); + + // Compute the start and increment for each BaseInst before we start erasing + // instructions. + SmallVector<const SCEV *, 8> StartExprs; + SmallVector<const SCEV *, 8> IncrExprs; + for (auto &DRS : RootSets) { + const SCEVAddRecExpr *IVSCEV = + cast<SCEVAddRecExpr>(SE->getSCEV(DRS.BaseInst)); + StartExprs.push_back(IVSCEV->getStart()); + IncrExprs.push_back(SE->getMinusSCEV(SE->getSCEV(DRS.Roots[0]), IVSCEV)); + } + + // Remove instructions associated with non-base iterations. + for (BasicBlock::reverse_iterator J = Header->rbegin(), JE = Header->rend(); + J != JE;) { + unsigned I = Uses[&*J].find_first(); + if (I > 0 && I < IL_All) { + LLVM_DEBUG(dbgs() << "LRR: removing: " << *J << "\n"); + J++->eraseFromParent(); + continue; + } + + ++J; + } + + // Rewrite each BaseInst using SCEV. + for (size_t i = 0, e = RootSets.size(); i != e; ++i) + // Insert the new induction variable. + replaceIV(RootSets[i], StartExprs[i], IncrExprs[i]); + + { // Limit the lifetime of SCEVExpander. + BranchInst *BI = cast<BranchInst>(Header->getTerminator()); + const DataLayout &DL = Header->getModule()->getDataLayout(); + SCEVExpander Expander(*SE, DL, "reroll"); + auto Zero = SE->getZero(BackedgeTakenCount->getType()); + auto One = SE->getOne(BackedgeTakenCount->getType()); + auto NewIVSCEV = SE->getAddRecExpr(Zero, One, L, SCEV::FlagAnyWrap); + Value *NewIV = + Expander.expandCodeFor(NewIVSCEV, BackedgeTakenCount->getType(), + Header->getFirstNonPHIOrDbg()); + // FIXME: This arithmetic can overflow. + auto TripCount = SE->getAddExpr(BackedgeTakenCount, One); + auto ScaledTripCount = SE->getMulExpr( + TripCount, SE->getConstant(BackedgeTakenCount->getType(), Scale)); + auto ScaledBECount = SE->getMinusSCEV(ScaledTripCount, One); + Value *TakenCount = + Expander.expandCodeFor(ScaledBECount, BackedgeTakenCount->getType(), + Header->getFirstNonPHIOrDbg()); + Value *Cond = + new ICmpInst(BI, CmpInst::ICMP_EQ, NewIV, TakenCount, "exitcond"); + BI->setCondition(Cond); + + if (BI->getSuccessor(1) != Header) + BI->swapSuccessors(); + } + + SimplifyInstructionsInBlock(Header, TLI); + DeleteDeadPHIs(Header, TLI); +} + +void LoopReroll::DAGRootTracker::replaceIV(DAGRootSet &DRS, + const SCEV *Start, + const SCEV *IncrExpr) { + BasicBlock *Header = L->getHeader(); + Instruction *Inst = DRS.BaseInst; + + const SCEV *NewIVSCEV = + SE->getAddRecExpr(Start, IncrExpr, L, SCEV::FlagAnyWrap); + + { // Limit the lifetime of SCEVExpander. + const DataLayout &DL = Header->getModule()->getDataLayout(); + SCEVExpander Expander(*SE, DL, "reroll"); + Value *NewIV = Expander.expandCodeFor(NewIVSCEV, Inst->getType(), + Header->getFirstNonPHIOrDbg()); + + for (auto &KV : Uses) + if (KV.second.find_first() == 0) + KV.first->replaceUsesOfWith(Inst, NewIV); + } +} + +// Validate the selected reductions. All iterations must have an isomorphic +// part of the reduction chain and, for non-associative reductions, the chain +// entries must appear in order. +bool LoopReroll::ReductionTracker::validateSelected() { + // For a non-associative reduction, the chain entries must appear in order. + for (int i : Reds) { + int PrevIter = 0, BaseCount = 0, Count = 0; + for (Instruction *J : PossibleReds[i]) { + // Note that all instructions in the chain must have been found because + // all instructions in the function must have been assigned to some + // iteration. + int Iter = PossibleRedIter[J]; + if (Iter != PrevIter && Iter != PrevIter + 1 && + !PossibleReds[i].getReducedValue()->isAssociative()) { + LLVM_DEBUG(dbgs() << "LRR: Out-of-order non-associative reduction: " + << J << "\n"); + return false; + } + + if (Iter != PrevIter) { + if (Count != BaseCount) { + LLVM_DEBUG(dbgs() + << "LRR: Iteration " << PrevIter << " reduction use count " + << Count << " is not equal to the base use count " + << BaseCount << "\n"); + return false; + } + + Count = 0; + } + + ++Count; + if (Iter == 0) + ++BaseCount; + + PrevIter = Iter; + } + } + + return true; +} + +// For all selected reductions, remove all parts except those in the first +// iteration (and the PHI). Replace outside uses of the reduced value with uses +// of the first-iteration reduced value (in other words, reroll the selected +// reductions). +void LoopReroll::ReductionTracker::replaceSelected() { + // Fixup reductions to refer to the last instruction associated with the + // first iteration (not the last). + for (int i : Reds) { + int j = 0; + for (int e = PossibleReds[i].size(); j != e; ++j) + if (PossibleRedIter[PossibleReds[i][j]] != 0) { + --j; + break; + } + + // Replace users with the new end-of-chain value. + SmallInstructionVector Users; + for (User *U : PossibleReds[i].getReducedValue()->users()) { + Users.push_back(cast<Instruction>(U)); + } + + for (Instruction *User : Users) + User->replaceUsesOfWith(PossibleReds[i].getReducedValue(), + PossibleReds[i][j]); + } +} + +// Reroll the provided loop with respect to the provided induction variable. +// Generally, we're looking for a loop like this: +// +// %iv = phi [ (preheader, ...), (body, %iv.next) ] +// f(%iv) +// %iv.1 = add %iv, 1 <-- a root increment +// f(%iv.1) +// %iv.2 = add %iv, 2 <-- a root increment +// f(%iv.2) +// %iv.scale_m_1 = add %iv, scale-1 <-- a root increment +// f(%iv.scale_m_1) +// ... +// %iv.next = add %iv, scale +// %cmp = icmp(%iv, ...) +// br %cmp, header, exit +// +// Notably, we do not require that f(%iv), f(%iv.1), etc. be isolated groups of +// instructions. In other words, the instructions in f(%iv), f(%iv.1), etc. can +// be intermixed with eachother. The restriction imposed by this algorithm is +// that the relative order of the isomorphic instructions in f(%iv), f(%iv.1), +// etc. be the same. +// +// First, we collect the use set of %iv, excluding the other increment roots. +// This gives us f(%iv). Then we iterate over the loop instructions (scale-1) +// times, having collected the use set of f(%iv.(i+1)), during which we: +// - Ensure that the next unmatched instruction in f(%iv) is isomorphic to +// the next unmatched instruction in f(%iv.(i+1)). +// - Ensure that both matched instructions don't have any external users +// (with the exception of last-in-chain reduction instructions). +// - Track the (aliasing) write set, and other side effects, of all +// instructions that belong to future iterations that come before the matched +// instructions. If the matched instructions read from that write set, then +// f(%iv) or f(%iv.(i+1)) has some dependency on instructions in +// f(%iv.(j+1)) for some j > i, and we cannot reroll the loop. Similarly, +// if any of these future instructions had side effects (could not be +// speculatively executed), and so do the matched instructions, when we +// cannot reorder those side-effect-producing instructions, and rerolling +// fails. +// +// Finally, we make sure that all loop instructions are either loop increment +// roots, belong to simple latch code, parts of validated reductions, part of +// f(%iv) or part of some f(%iv.i). If all of that is true (and all reductions +// have been validated), then we reroll the loop. +bool LoopReroll::reroll(Instruction *IV, Loop *L, BasicBlock *Header, + const SCEV *BackedgeTakenCount, + ReductionTracker &Reductions) { + DAGRootTracker DAGRoots(this, L, IV, SE, AA, TLI, DT, LI, PreserveLCSSA, + IVToIncMap, LoopControlIV); + + if (!DAGRoots.findRoots()) + return false; + LLVM_DEBUG(dbgs() << "LRR: Found all root induction increments for: " << *IV + << "\n"); + + if (!DAGRoots.validate(Reductions)) + return false; + if (!Reductions.validateSelected()) + return false; + // At this point, we've validated the rerolling, and we're committed to + // making changes! + + Reductions.replaceSelected(); + DAGRoots.replace(BackedgeTakenCount); + + ++NumRerolledLoops; + return true; +} + +bool LoopReroll::runOnLoop(Loop *L, LPPassManager &LPM) { + if (skipLoop(L)) + return false; + + AA = &getAnalysis<AAResultsWrapperPass>().getAAResults(); + LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo(); + SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE(); + TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI( + *L->getHeader()->getParent()); + DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree(); + PreserveLCSSA = mustPreserveAnalysisID(LCSSAID); + + BasicBlock *Header = L->getHeader(); + LLVM_DEBUG(dbgs() << "LRR: F[" << Header->getParent()->getName() << "] Loop %" + << Header->getName() << " (" << L->getNumBlocks() + << " block(s))\n"); + + // For now, we'll handle only single BB loops. + if (L->getNumBlocks() > 1) + return false; + + if (!SE->hasLoopInvariantBackedgeTakenCount(L)) + return false; + + const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L); + LLVM_DEBUG(dbgs() << "\n Before Reroll:\n" << *(L->getHeader()) << "\n"); + LLVM_DEBUG(dbgs() << "LRR: backedge-taken count = " << *BackedgeTakenCount + << "\n"); + + // First, we need to find the induction variable with respect to which we can + // reroll (there may be several possible options). + SmallInstructionVector PossibleIVs; + IVToIncMap.clear(); + LoopControlIV = nullptr; + collectPossibleIVs(L, PossibleIVs); + + if (PossibleIVs.empty()) { + LLVM_DEBUG(dbgs() << "LRR: No possible IVs found\n"); + return false; + } + + ReductionTracker Reductions; + collectPossibleReductions(L, Reductions); + bool Changed = false; + + // For each possible IV, collect the associated possible set of 'root' nodes + // (i+1, i+2, etc.). + for (Instruction *PossibleIV : PossibleIVs) + if (reroll(PossibleIV, L, Header, BackedgeTakenCount, Reductions)) { + Changed = true; + break; + } + LLVM_DEBUG(dbgs() << "\n After Reroll:\n" << *(L->getHeader()) << "\n"); + + // Trip count of L has changed so SE must be re-evaluated. + if (Changed) + SE->forgetLoop(L); + + return Changed; +} |