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Diffstat (limited to 'gnu/llvm/lib/Transforms/Scalar/LoopRerollPass.cpp')
| -rw-r--r-- | gnu/llvm/lib/Transforms/Scalar/LoopRerollPass.cpp | 1689 |
1 files changed, 0 insertions, 1689 deletions
diff --git a/gnu/llvm/lib/Transforms/Scalar/LoopRerollPass.cpp b/gnu/llvm/lib/Transforms/Scalar/LoopRerollPass.cpp deleted file mode 100644 index 9a99e592557..00000000000 --- a/gnu/llvm/lib/Transforms/Scalar/LoopRerollPass.cpp +++ /dev/null @@ -1,1689 +0,0 @@ -//===- LoopReroll.cpp - Loop rerolling pass -------------------------------===// -// -// The LLVM Compiler Infrastructure -// -// This file is distributed under the University of Illinois Open Source -// License. See LICENSE.TXT for details. -// -//===----------------------------------------------------------------------===// -// -// 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; - 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; - - 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(); - 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; -} |