//===- HexagonVectorLoopCarriedReuse.cpp ----------------------------------===// // // 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 removes the computation of provably redundant expressions that have // been computed earlier in a previous iteration. It relies on the use of PHIs // to identify loop carried dependences. This is scalar replacement for vector // types. // //===----------------------------------------------------------------------===// #include "HexagonVectorLoopCarriedReuse.h" #include "llvm/ADT/SetVector.h" #include "llvm/ADT/SmallVector.h" #include "llvm/ADT/Statistic.h" #include "llvm/Analysis/LoopInfo.h" #include "llvm/Analysis/LoopPass.h" #include "llvm/IR/BasicBlock.h" #include "llvm/IR/DerivedTypes.h" #include "llvm/IR/IRBuilder.h" #include "llvm/IR/Instruction.h" #include "llvm/IR/Instructions.h" #include "llvm/IR/IntrinsicInst.h" #include "llvm/IR/Intrinsics.h" #include "llvm/IR/IntrinsicsHexagon.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/Compiler.h" #include "llvm/Support/Debug.h" #include "llvm/Support/raw_ostream.h" #include "llvm/Transforms/Scalar.h" #include "llvm/Transforms/Utils.h" #include #include #include #include #include #include using namespace llvm; #define DEBUG_TYPE "hexagon-vlcr" STATISTIC(HexagonNumVectorLoopCarriedReuse, "Number of values that were reused from a previous iteration."); static cl::opt HexagonVLCRIterationLim( "hexagon-vlcr-iteration-lim", cl::Hidden, cl::desc("Maximum distance of loop carried dependences that are handled"), cl::init(2)); namespace llvm { void initializeHexagonVectorLoopCarriedReuseLegacyPassPass(PassRegistry &); Pass *createHexagonVectorLoopCarriedReuseLegacyPass(); } // end namespace llvm namespace { // See info about DepChain in the comments at the top of this file. using ChainOfDependences = SmallVector; class DepChain { ChainOfDependences Chain; public: bool isIdentical(DepChain &Other) const { if (Other.size() != size()) return false; ChainOfDependences &OtherChain = Other.getChain(); for (int i = 0; i < size(); ++i) { if (Chain[i] != OtherChain[i]) return false; } return true; } ChainOfDependences &getChain() { return Chain; } int size() const { return Chain.size(); } void clear() { Chain.clear(); } void push_back(Instruction *I) { Chain.push_back(I); } int iterations() const { return size() - 1; } Instruction *front() const { return Chain.front(); } Instruction *back() const { return Chain.back(); } Instruction *&operator[](const int index) { return Chain[index]; } friend raw_ostream &operator<< (raw_ostream &OS, const DepChain &D); }; LLVM_ATTRIBUTE_UNUSED raw_ostream &operator<<(raw_ostream &OS, const DepChain &D) { const ChainOfDependences &CD = D.Chain; int ChainSize = CD.size(); OS << "**DepChain Start::**\n"; for (int i = 0; i < ChainSize -1; ++i) { OS << *(CD[i]) << " -->\n"; } OS << *CD[ChainSize-1] << "\n"; return OS; } struct ReuseValue { Instruction *Inst2Replace = nullptr; // In the new PHI node that we'll construct this is the value that'll be // used over the backedge. This is the value that gets reused from a // previous iteration. Instruction *BackedgeInst = nullptr; std::map DepChains; int Iterations = -1; ReuseValue() = default; void reset() { Inst2Replace = nullptr; BackedgeInst = nullptr; DepChains.clear(); Iterations = -1; } bool isDefined() { return Inst2Replace != nullptr; } }; LLVM_ATTRIBUTE_UNUSED raw_ostream &operator<<(raw_ostream &OS, const ReuseValue &RU) { OS << "** ReuseValue ***\n"; OS << "Instruction to Replace: " << *(RU.Inst2Replace) << "\n"; OS << "Backedge Instruction: " << *(RU.BackedgeInst) << "\n"; return OS; } class HexagonVectorLoopCarriedReuseLegacyPass : public LoopPass { public: static char ID; explicit HexagonVectorLoopCarriedReuseLegacyPass() : LoopPass(ID) { PassRegistry *PR = PassRegistry::getPassRegistry(); initializeHexagonVectorLoopCarriedReuseLegacyPassPass(*PR); } StringRef getPassName() const override { return "Hexagon-specific loop carried reuse for HVX vectors"; } void getAnalysisUsage(AnalysisUsage &AU) const override { AU.addRequiredID(LoopSimplifyID); AU.addRequiredID(LCSSAID); AU.addPreservedID(LCSSAID); AU.setPreservesCFG(); } bool runOnLoop(Loop *L, LPPassManager &LPM) override; }; class HexagonVectorLoopCarriedReuse { public: HexagonVectorLoopCarriedReuse(Loop *L) : CurLoop(L){}; bool run(); private: SetVector Dependences; std::set ReplacedInsts; Loop *CurLoop; ReuseValue ReuseCandidate; bool doVLCR(); void findLoopCarriedDeps(); void findValueToReuse(); void findDepChainFromPHI(Instruction *I, DepChain &D); void reuseValue(); Value *findValueInBlock(Value *Op, BasicBlock *BB); DepChain *getDepChainBtwn(Instruction *I1, Instruction *I2, int Iters); bool isEquivalentOperation(Instruction *I1, Instruction *I2); bool canReplace(Instruction *I); bool isCallInstCommutative(CallInst *C); }; } // end anonymous namespace char HexagonVectorLoopCarriedReuseLegacyPass::ID = 0; INITIALIZE_PASS_BEGIN(HexagonVectorLoopCarriedReuseLegacyPass, "hexagon-vlcr", "Hexagon-specific predictive commoning for HVX vectors", false, false) INITIALIZE_PASS_DEPENDENCY(LoopSimplify) INITIALIZE_PASS_DEPENDENCY(LCSSAWrapperPass) INITIALIZE_PASS_END(HexagonVectorLoopCarriedReuseLegacyPass, "hexagon-vlcr", "Hexagon-specific predictive commoning for HVX vectors", false, false) PreservedAnalyses HexagonVectorLoopCarriedReusePass::run(Loop &L, LoopAnalysisManager &LAM, LoopStandardAnalysisResults &AR, LPMUpdater &U) { HexagonVectorLoopCarriedReuse Vlcr(&L); if (!Vlcr.run()) return PreservedAnalyses::all(); PreservedAnalyses PA; PA.preserveSet(); return PA; } bool HexagonVectorLoopCarriedReuseLegacyPass::runOnLoop(Loop *L, LPPassManager &LPM) { if (skipLoop(L)) return false; HexagonVectorLoopCarriedReuse Vlcr(L); return Vlcr.run(); } bool HexagonVectorLoopCarriedReuse::run() { if (!CurLoop->getLoopPreheader()) return false; // Work only on innermost loops. if (!CurLoop->getSubLoops().empty()) return false; // Work only on single basic blocks loops. if (CurLoop->getNumBlocks() != 1) return false; return doVLCR(); } bool HexagonVectorLoopCarriedReuse::isCallInstCommutative(CallInst *C) { switch (C->getCalledFunction()->getIntrinsicID()) { case Intrinsic::hexagon_V6_vaddb: case Intrinsic::hexagon_V6_vaddb_128B: case Intrinsic::hexagon_V6_vaddh: case Intrinsic::hexagon_V6_vaddh_128B: case Intrinsic::hexagon_V6_vaddw: case Intrinsic::hexagon_V6_vaddw_128B: case Intrinsic::hexagon_V6_vaddubh: case Intrinsic::hexagon_V6_vaddubh_128B: case Intrinsic::hexagon_V6_vadduhw: case Intrinsic::hexagon_V6_vadduhw_128B: case Intrinsic::hexagon_V6_vaddhw: case Intrinsic::hexagon_V6_vaddhw_128B: case Intrinsic::hexagon_V6_vmaxb: case Intrinsic::hexagon_V6_vmaxb_128B: case Intrinsic::hexagon_V6_vmaxh: case Intrinsic::hexagon_V6_vmaxh_128B: case Intrinsic::hexagon_V6_vmaxw: case Intrinsic::hexagon_V6_vmaxw_128B: case Intrinsic::hexagon_V6_vmaxub: case Intrinsic::hexagon_V6_vmaxub_128B: case Intrinsic::hexagon_V6_vmaxuh: case Intrinsic::hexagon_V6_vmaxuh_128B: case Intrinsic::hexagon_V6_vminub: case Intrinsic::hexagon_V6_vminub_128B: case Intrinsic::hexagon_V6_vminuh: case Intrinsic::hexagon_V6_vminuh_128B: case Intrinsic::hexagon_V6_vminb: case Intrinsic::hexagon_V6_vminb_128B: case Intrinsic::hexagon_V6_vminh: case Intrinsic::hexagon_V6_vminh_128B: case Intrinsic::hexagon_V6_vminw: case Intrinsic::hexagon_V6_vminw_128B: case Intrinsic::hexagon_V6_vmpyub: case Intrinsic::hexagon_V6_vmpyub_128B: case Intrinsic::hexagon_V6_vmpyuh: case Intrinsic::hexagon_V6_vmpyuh_128B: case Intrinsic::hexagon_V6_vavgub: case Intrinsic::hexagon_V6_vavgub_128B: case Intrinsic::hexagon_V6_vavgh: case Intrinsic::hexagon_V6_vavgh_128B: case Intrinsic::hexagon_V6_vavguh: case Intrinsic::hexagon_V6_vavguh_128B: case Intrinsic::hexagon_V6_vavgw: case Intrinsic::hexagon_V6_vavgw_128B: case Intrinsic::hexagon_V6_vavgb: case Intrinsic::hexagon_V6_vavgb_128B: case Intrinsic::hexagon_V6_vavguw: case Intrinsic::hexagon_V6_vavguw_128B: case Intrinsic::hexagon_V6_vabsdiffh: case Intrinsic::hexagon_V6_vabsdiffh_128B: case Intrinsic::hexagon_V6_vabsdiffub: case Intrinsic::hexagon_V6_vabsdiffub_128B: case Intrinsic::hexagon_V6_vabsdiffuh: case Intrinsic::hexagon_V6_vabsdiffuh_128B: case Intrinsic::hexagon_V6_vabsdiffw: case Intrinsic::hexagon_V6_vabsdiffw_128B: return true; default: return false; } } bool HexagonVectorLoopCarriedReuse::isEquivalentOperation(Instruction *I1, Instruction *I2) { if (!I1->isSameOperationAs(I2)) return false; // This check is in place specifically for intrinsics. isSameOperationAs will // return two for any two hexagon intrinsics because they are essentially the // same instruciton (CallInst). We need to scratch the surface to see if they // are calls to the same function. if (CallInst *C1 = dyn_cast(I1)) { if (CallInst *C2 = dyn_cast(I2)) { if (C1->getCalledFunction() != C2->getCalledFunction()) return false; } } // If both the Instructions are of Vector Type and any of the element // is integer constant, check their values too for equivalence. if (I1->getType()->isVectorTy() && I2->getType()->isVectorTy()) { unsigned NumOperands = I1->getNumOperands(); for (unsigned i = 0; i < NumOperands; ++i) { ConstantInt *C1 = dyn_cast(I1->getOperand(i)); ConstantInt *C2 = dyn_cast(I2->getOperand(i)); if(!C1) continue; assert(C2); if (C1->getSExtValue() != C2->getSExtValue()) return false; } } return true; } bool HexagonVectorLoopCarriedReuse::canReplace(Instruction *I) { const IntrinsicInst *II = dyn_cast(I); if (!II) return true; switch (II->getIntrinsicID()) { case Intrinsic::hexagon_V6_hi: case Intrinsic::hexagon_V6_lo: case Intrinsic::hexagon_V6_hi_128B: case Intrinsic::hexagon_V6_lo_128B: LLVM_DEBUG(dbgs() << "Not considering for reuse: " << *II << "\n"); return false; default: return true; } } void HexagonVectorLoopCarriedReuse::findValueToReuse() { for (auto *D : Dependences) { LLVM_DEBUG(dbgs() << "Processing dependence " << *(D->front()) << "\n"); if (D->iterations() > HexagonVLCRIterationLim) { LLVM_DEBUG( dbgs() << ".. Skipping because number of iterations > than the limit\n"); continue; } PHINode *PN = cast(D->front()); Instruction *BEInst = D->back(); int Iters = D->iterations(); BasicBlock *BB = PN->getParent(); LLVM_DEBUG(dbgs() << "Checking if any uses of " << *PN << " can be reused\n"); SmallVector PNUsers; for (Use &U : PN->uses()) { Instruction *User = cast(U.getUser()); if (User->getParent() != BB) continue; if (ReplacedInsts.count(User)) { LLVM_DEBUG(dbgs() << *User << " has already been replaced. Skipping...\n"); continue; } if (isa(User)) continue; if (User->mayHaveSideEffects()) continue; if (!canReplace(User)) continue; PNUsers.push_back(User); } LLVM_DEBUG(dbgs() << PNUsers.size() << " use(s) of the PHI in the block\n"); // For each interesting use I of PN, find an Instruction BEUser that // performs the same operation as I on BEInst and whose other operands, // if any, can also be rematerialized in OtherBB. We stop when we find the // first such Instruction BEUser. This is because once BEUser is // rematerialized in OtherBB, we may find more such "fixup" opportunities // in this block. So, we'll start over again. for (Instruction *I : PNUsers) { for (Use &U : BEInst->uses()) { Instruction *BEUser = cast(U.getUser()); if (BEUser->getParent() != BB) continue; if (!isEquivalentOperation(I, BEUser)) continue; int NumOperands = I->getNumOperands(); // Take operands of each PNUser one by one and try to find DepChain // with every operand of the BEUser. If any of the operands of BEUser // has DepChain with current operand of the PNUser, break the matcher // loop. Keep doing this for Every PNUser operand. If PNUser operand // does not have DepChain with any of the BEUser operand, break the // outer matcher loop, mark the BEUser as null and reset the ReuseCandidate. // This ensures that DepChain exist for all the PNUser operand with // BEUser operand. This also ensures that DepChains are independent of // the positions in PNUser and BEUser. std::map DepChains; CallInst *C1 = dyn_cast(I); if ((I && I->isCommutative()) || (C1 && isCallInstCommutative(C1))) { bool Found = false; for (int OpNo = 0; OpNo < NumOperands; ++OpNo) { Value *Op = I->getOperand(OpNo); Instruction *OpInst = dyn_cast(Op); Found = false; for (int T = 0; T < NumOperands; ++T) { Value *BEOp = BEUser->getOperand(T); Instruction *BEOpInst = dyn_cast(BEOp); if (!OpInst && !BEOpInst) { if (Op == BEOp) { Found = true; break; } } if ((OpInst && !BEOpInst) || (!OpInst && BEOpInst)) continue; DepChain *D = getDepChainBtwn(OpInst, BEOpInst, Iters); if (D) { Found = true; DepChains[OpInst] = D; break; } } if (!Found) { BEUser = nullptr; break; } } } else { for (int OpNo = 0; OpNo < NumOperands; ++OpNo) { Value *Op = I->getOperand(OpNo); Value *BEOp = BEUser->getOperand(OpNo); Instruction *OpInst = dyn_cast(Op); if (!OpInst) { if (Op == BEOp) continue; // Do not allow reuse to occur when the operands may be different // values. BEUser = nullptr; break; } Instruction *BEOpInst = dyn_cast(BEOp); DepChain *D = getDepChainBtwn(OpInst, BEOpInst, Iters); if (D) { DepChains[OpInst] = D; } else { BEUser = nullptr; break; } } } if (BEUser) { LLVM_DEBUG(dbgs() << "Found Value for reuse.\n"); ReuseCandidate.Inst2Replace = I; ReuseCandidate.BackedgeInst = BEUser; ReuseCandidate.DepChains = DepChains; ReuseCandidate.Iterations = Iters; return; } ReuseCandidate.reset(); } } } ReuseCandidate.reset(); } Value *HexagonVectorLoopCarriedReuse::findValueInBlock(Value *Op, BasicBlock *BB) { PHINode *PN = dyn_cast(Op); assert(PN); Value *ValueInBlock = PN->getIncomingValueForBlock(BB); return ValueInBlock; } void HexagonVectorLoopCarriedReuse::reuseValue() { LLVM_DEBUG(dbgs() << ReuseCandidate); Instruction *Inst2Replace = ReuseCandidate.Inst2Replace; Instruction *BEInst = ReuseCandidate.BackedgeInst; int NumOperands = Inst2Replace->getNumOperands(); std::map &DepChains = ReuseCandidate.DepChains; int Iterations = ReuseCandidate.Iterations; BasicBlock *LoopPH = CurLoop->getLoopPreheader(); assert(!DepChains.empty() && "No DepChains"); LLVM_DEBUG(dbgs() << "reuseValue is making the following changes\n"); SmallVector InstsInPreheader; for (int i = 0; i < Iterations; ++i) { Instruction *InstInPreheader = Inst2Replace->clone(); SmallVector Ops; for (int j = 0; j < NumOperands; ++j) { Instruction *I = dyn_cast(Inst2Replace->getOperand(j)); if (!I) continue; // Get the DepChain corresponding to this operand. DepChain &D = *DepChains[I]; // Get the PHI for the iteration number and find // the incoming value from the Loop Preheader for // that PHI. Value *ValInPreheader = findValueInBlock(D[i], LoopPH); InstInPreheader->setOperand(j, ValInPreheader); } InstsInPreheader.push_back(InstInPreheader); InstInPreheader->setName(Inst2Replace->getName() + ".hexagon.vlcr"); InstInPreheader->insertBefore(LoopPH->getTerminator()); LLVM_DEBUG(dbgs() << "Added " << *InstInPreheader << " to " << LoopPH->getName() << "\n"); } BasicBlock *BB = BEInst->getParent(); IRBuilder<> IRB(BB); IRB.SetInsertPoint(BB->getFirstNonPHI()); Value *BEVal = BEInst; PHINode *NewPhi; for (int i = Iterations-1; i >=0 ; --i) { Instruction *InstInPreheader = InstsInPreheader[i]; NewPhi = IRB.CreatePHI(InstInPreheader->getType(), 2); NewPhi->addIncoming(InstInPreheader, LoopPH); NewPhi->addIncoming(BEVal, BB); LLVM_DEBUG(dbgs() << "Adding " << *NewPhi << " to " << BB->getName() << "\n"); BEVal = NewPhi; } // We are in LCSSA form. So, a value defined inside the Loop is used only // inside the loop. So, the following is safe. Inst2Replace->replaceAllUsesWith(NewPhi); ReplacedInsts.insert(Inst2Replace); ++HexagonNumVectorLoopCarriedReuse; } bool HexagonVectorLoopCarriedReuse::doVLCR() { assert(CurLoop->getSubLoops().empty() && "Can do VLCR on the innermost loop only"); assert((CurLoop->getNumBlocks() == 1) && "Can do VLCR only on single block loops"); bool Changed = false; bool Continue; LLVM_DEBUG(dbgs() << "Working on Loop: " << *CurLoop->getHeader() << "\n"); do { // Reset datastructures. Dependences.clear(); Continue = false; findLoopCarriedDeps(); findValueToReuse(); if (ReuseCandidate.isDefined()) { reuseValue(); Changed = true; Continue = true; } llvm::for_each(Dependences, std::default_delete()); } while (Continue); return Changed; } void HexagonVectorLoopCarriedReuse::findDepChainFromPHI(Instruction *I, DepChain &D) { PHINode *PN = dyn_cast(I); if (!PN) { D.push_back(I); return; } else { auto NumIncomingValues = PN->getNumIncomingValues(); if (NumIncomingValues != 2) { D.clear(); return; } BasicBlock *BB = PN->getParent(); if (BB != CurLoop->getHeader()) { D.clear(); return; } Value *BEVal = PN->getIncomingValueForBlock(BB); Instruction *BEInst = dyn_cast(BEVal); // This is a single block loop with a preheader, so at least // one value should come over the backedge. assert(BEInst && "There should be a value over the backedge"); Value *PreHdrVal = PN->getIncomingValueForBlock(CurLoop->getLoopPreheader()); if(!PreHdrVal || !isa(PreHdrVal)) { D.clear(); return; } D.push_back(PN); findDepChainFromPHI(BEInst, D); } } DepChain *HexagonVectorLoopCarriedReuse::getDepChainBtwn(Instruction *I1, Instruction *I2, int Iters) { for (auto *D : Dependences) { if (D->front() == I1 && D->back() == I2 && D->iterations() == Iters) return D; } return nullptr; } void HexagonVectorLoopCarriedReuse::findLoopCarriedDeps() { BasicBlock *BB = CurLoop->getHeader(); for (auto I = BB->begin(), E = BB->end(); I != E && isa(I); ++I) { auto *PN = cast(I); if (!isa(PN->getType())) continue; DepChain *D = new DepChain(); findDepChainFromPHI(PN, *D); if (D->size() != 0) Dependences.insert(D); else delete D; } LLVM_DEBUG(dbgs() << "Found " << Dependences.size() << " dependences\n"); LLVM_DEBUG(for (const DepChain *D : Dependences) dbgs() << *D << "\n";); } Pass *llvm::createHexagonVectorLoopCarriedReuseLegacyPass() { return new HexagonVectorLoopCarriedReuseLegacyPass(); }