| //===- 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/ScalarEvolutionExpressions.h" |
| #include "llvm/Analysis/TargetLibraryInfo.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/InitializePasses.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/Scalar/LoopReroll.h" |
| #include "llvm/Transforms/Utils.h" |
| #include "llvm/Transforms/Utils/BasicBlockUtils.h" |
| #include "llvm/Transforms/Utils/Local.h" |
| #include "llvm/Transforms/Utils/LoopUtils.h" |
| #include "llvm/Transforms/Utils/ScalarEvolutionExpander.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 LoopRerollLegacyPass : public LoopPass { |
| public: |
| static char ID; // Pass ID, replacement for typeid |
| |
| LoopRerollLegacyPass() : LoopPass(ID) { |
| initializeLoopRerollLegacyPassPass(*PassRegistry::getPassRegistry()); |
| } |
| |
| bool runOnLoop(Loop *L, LPPassManager &LPM) override; |
| |
| void getAnalysisUsage(AnalysisUsage &AU) const override { |
| AU.addRequired<TargetLibraryInfoWrapperPass>(); |
| getLoopAnalysisUsage(AU); |
| } |
| }; |
| |
| class LoopReroll { |
| public: |
| LoopReroll(AliasAnalysis *AA, LoopInfo *LI, ScalarEvolution *SE, |
| TargetLibraryInfo *TLI, DominatorTree *DT, bool PreserveLCSSA) |
| : AA(AA), LI(LI), SE(SE), TLI(TLI), DT(DT), |
| PreserveLCSSA(PreserveLCSSA) {} |
| bool runOnLoop(Loop *L); |
| |
| 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 LoopRerollLegacyPass::ID = 0; |
| |
| INITIALIZE_PASS_BEGIN(LoopRerollLegacyPass, "loop-reroll", "Reroll loops", |
| false, false) |
| INITIALIZE_PASS_DEPENDENCY(LoopPass) |
| INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) |
| INITIALIZE_PASS_END(LoopRerollLegacyPass, "loop-reroll", "Reroll loops", false, |
| false) |
| |
| Pass *llvm::createLoopRerollPass() { return new LoopRerollLegacyPass; } |
| |
| // 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 (Use &U : I->operands()) { |
| if (Instruction *Op = dyn_cast<Instruction>(U)) |
| 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; |
| |
| // If the value of the base instruction is used outside the loop, we cannot |
| // reroll the loop. Check for other root instructions is unnecessary because |
| // they don't match any base instructions if their values are used outside. |
| if (hasUsesOutsideLoop(DRS.BaseInst, L)) |
| 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); |
| if (isa<SCEVCouldNotCompute>(StepSCEV) || StepSCEV->getType()->isPointerTy()) |
| return false; |
| 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) { |
| if (I->mayHaveSideEffects()) { |
| LLVM_DEBUG(dbgs() << "LRR: Aborting - " |
| << "An instruction which does not belong to any root " |
| << "sets must not have side effects: " << *I); |
| return false; |
| } |
| 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.contains(I->first))) |
| ++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 allowed: |
| // 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) { |
| 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; |
| } |
| |
| bool LoopRerollLegacyPass::runOnLoop(Loop *L, LPPassManager &LPM) { |
| if (skipLoop(L)) |
| return false; |
| |
| auto *AA = &getAnalysis<AAResultsWrapperPass>().getAAResults(); |
| auto *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo(); |
| auto *SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE(); |
| auto *TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI( |
| *L->getHeader()->getParent()); |
| auto *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree(); |
| bool PreserveLCSSA = mustPreserveAnalysisID(LCSSAID); |
| |
| return LoopReroll(AA, LI, SE, TLI, DT, PreserveLCSSA).runOnLoop(L); |
| } |
| |
| PreservedAnalyses LoopRerollPass::run(Loop &L, LoopAnalysisManager &AM, |
| LoopStandardAnalysisResults &AR, |
| LPMUpdater &U) { |
| return LoopReroll(&AR.AA, &AR.LI, &AR.SE, &AR.TLI, &AR.DT, true).runOnLoop(&L) |
| ? getLoopPassPreservedAnalyses() |
| : PreservedAnalyses::all(); |
| } |