//===------ PPCLoopPreIncPrep.cpp - Loop Pre-Inc. AM Prep. Pass -----------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // This file implements a pass to prepare loops for pre-increment addressing // modes. Additional PHIs are created for loop induction variables used by // load/store instructions so that the pre-increment forms can be used. // Generically, this means transforming loops like this: // for (int i = 0; i < n; ++i) // array[i] = c; // to look like this: // T *p = array[-1]; // for (int i = 0; i < n; ++i) // *++p = c; //===----------------------------------------------------------------------===// #define DEBUG_TYPE "ppc-loop-preinc-prep" #include "PPC.h" #include "PPCTargetMachine.h" #include "llvm/ADT/DepthFirstIterator.h" #include "llvm/ADT/STLExtras.h" #include "llvm/ADT/SmallSet.h" #include "llvm/ADT/Statistic.h" #include "llvm/Analysis/CodeMetrics.h" #include "llvm/Analysis/InstructionSimplify.h" #include "llvm/Analysis/LoopInfo.h" #include "llvm/Analysis/ScalarEvolution.h" #include "llvm/Analysis/ScalarEvolutionExpander.h" #include "llvm/Analysis/ScalarEvolutionExpressions.h" #include "llvm/Analysis/ValueTracking.h" #include "llvm/IR/CFG.h" #include "llvm/IR/Dominators.h" #include "llvm/IR/Function.h" #include "llvm/IR/IntrinsicInst.h" #include "llvm/IR/Module.h" #include "llvm/Support/CommandLine.h" #include "llvm/Support/Debug.h" #include "llvm/Transforms/Scalar.h" #include "llvm/Transforms/Utils/BasicBlockUtils.h" #include "llvm/Transforms/Utils/Local.h" #include "llvm/Transforms/Utils/LoopUtils.h" #include "llvm/Transforms/Utils/ValueMapper.h" using namespace llvm; // By default, we limit this to creating 16 PHIs (which is a little over half // of the allocatable register set). static cl::opt<unsigned> MaxVars("ppc-preinc-prep-max-vars", cl::Hidden, cl::init(16), cl::desc("Potential PHI threshold for PPC preinc loop prep")); namespace llvm { void initializePPCLoopPreIncPrepPass(PassRegistry&); } namespace { class PPCLoopPreIncPrep : public FunctionPass { public: static char ID; // Pass ID, replacement for typeid PPCLoopPreIncPrep() : FunctionPass(ID), TM(nullptr) { initializePPCLoopPreIncPrepPass(*PassRegistry::getPassRegistry()); } PPCLoopPreIncPrep(PPCTargetMachine &TM) : FunctionPass(ID), TM(&TM) { initializePPCLoopPreIncPrepPass(*PassRegistry::getPassRegistry()); } void getAnalysisUsage(AnalysisUsage &AU) const override { AU.addPreserved<DominatorTreeWrapperPass>(); AU.addRequired<LoopInfoWrapperPass>(); AU.addPreserved<LoopInfoWrapperPass>(); AU.addRequired<ScalarEvolutionWrapperPass>(); } bool runOnFunction(Function &F) override; bool runOnLoop(Loop *L); void simplifyLoopLatch(Loop *L); bool rotateLoop(Loop *L); private: PPCTargetMachine *TM; DominatorTree *DT; LoopInfo *LI; ScalarEvolution *SE; bool PreserveLCSSA; }; } char PPCLoopPreIncPrep::ID = 0; static const char *name = "Prepare loop for pre-inc. addressing modes"; INITIALIZE_PASS_BEGIN(PPCLoopPreIncPrep, DEBUG_TYPE, name, false, false) INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass) INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass) INITIALIZE_PASS_END(PPCLoopPreIncPrep, DEBUG_TYPE, name, false, false) FunctionPass *llvm::createPPCLoopPreIncPrepPass(PPCTargetMachine &TM) { return new PPCLoopPreIncPrep(TM); } namespace { struct BucketElement { BucketElement(const SCEVConstant *O, Instruction *I) : Offset(O), Instr(I) {} BucketElement(Instruction *I) : Offset(nullptr), Instr(I) {} const SCEVConstant *Offset; Instruction *Instr; }; struct Bucket { Bucket(const SCEV *B, Instruction *I) : BaseSCEV(B), Elements(1, BucketElement(I)) {} const SCEV *BaseSCEV; SmallVector<BucketElement, 16> Elements; }; } static bool IsPtrInBounds(Value *BasePtr) { Value *StrippedBasePtr = BasePtr; while (BitCastInst *BC = dyn_cast<BitCastInst>(StrippedBasePtr)) StrippedBasePtr = BC->getOperand(0); if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(StrippedBasePtr)) return GEP->isInBounds(); return false; } static Value *GetPointerOperand(Value *MemI) { if (LoadInst *LMemI = dyn_cast<LoadInst>(MemI)) { return LMemI->getPointerOperand(); } else if (StoreInst *SMemI = dyn_cast<StoreInst>(MemI)) { return SMemI->getPointerOperand(); } else if (IntrinsicInst *IMemI = dyn_cast<IntrinsicInst>(MemI)) { if (IMemI->getIntrinsicID() == Intrinsic::prefetch) return IMemI->getArgOperand(0); } return 0; } bool PPCLoopPreIncPrep::runOnFunction(Function &F) { LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo(); SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE(); auto *DTWP = getAnalysisIfAvailable<DominatorTreeWrapperPass>(); DT = DTWP ? &DTWP->getDomTree() : nullptr; PreserveLCSSA = mustPreserveAnalysisID(LCSSAID); bool MadeChange = false; for (auto I = LI->begin(), IE = LI->end(); I != IE; ++I) for (auto L = df_begin(*I), LE = df_end(*I); L != LE; ++L) MadeChange |= runOnLoop(*L); return MadeChange; } bool PPCLoopPreIncPrep::runOnLoop(Loop *L) { bool MadeChange = false; // Only prep. the inner-most loop if (!L->empty()) return MadeChange; DEBUG(dbgs() << "PIP: Examining: " << *L << "\n"); BasicBlock *Header = L->getHeader(); const PPCSubtarget *ST = TM ? TM->getSubtargetImpl(*Header->getParent()) : nullptr; unsigned HeaderLoopPredCount = std::distance(pred_begin(Header), pred_end(Header)); // Collect buckets of comparable addresses used by loads and stores. SmallVector<Bucket, 16> Buckets; for (Loop::block_iterator I = L->block_begin(), IE = L->block_end(); I != IE; ++I) { for (BasicBlock::iterator J = (*I)->begin(), JE = (*I)->end(); J != JE; ++J) { Value *PtrValue; Instruction *MemI; if (LoadInst *LMemI = dyn_cast<LoadInst>(J)) { MemI = LMemI; PtrValue = LMemI->getPointerOperand(); } else if (StoreInst *SMemI = dyn_cast<StoreInst>(J)) { MemI = SMemI; PtrValue = SMemI->getPointerOperand(); } else if (IntrinsicInst *IMemI = dyn_cast<IntrinsicInst>(J)) { if (IMemI->getIntrinsicID() == Intrinsic::prefetch) { MemI = IMemI; PtrValue = IMemI->getArgOperand(0); } else continue; } else continue; unsigned PtrAddrSpace = PtrValue->getType()->getPointerAddressSpace(); if (PtrAddrSpace) continue; // There are no update forms for Altivec vector load/stores. if (ST && ST->hasAltivec() && PtrValue->getType()->getPointerElementType()->isVectorTy()) continue; if (L->isLoopInvariant(PtrValue)) continue; const SCEV *LSCEV = SE->getSCEVAtScope(PtrValue, L); if (const SCEVAddRecExpr *LARSCEV = dyn_cast<SCEVAddRecExpr>(LSCEV)) { if (LARSCEV->getLoop() != L) continue; } else { continue; } bool FoundBucket = false; for (auto &B : Buckets) { const SCEV *Diff = SE->getMinusSCEV(LSCEV, B.BaseSCEV); if (const auto *CDiff = dyn_cast<SCEVConstant>(Diff)) { B.Elements.push_back(BucketElement(CDiff, MemI)); FoundBucket = true; break; } } if (!FoundBucket) { if (Buckets.size() == MaxVars) return MadeChange; Buckets.push_back(Bucket(LSCEV, MemI)); } } } if (Buckets.empty()) return MadeChange; BasicBlock *LoopPredecessor = L->getLoopPredecessor(); // If there is no loop predecessor, or the loop predecessor's terminator // returns a value (which might contribute to determining the loop's // iteration space), insert a new preheader for the loop. if (!LoopPredecessor || !LoopPredecessor->getTerminator()->getType()->isVoidTy()) { LoopPredecessor = InsertPreheaderForLoop(L, DT, LI, PreserveLCSSA); if (LoopPredecessor) MadeChange = true; } if (!LoopPredecessor) return MadeChange; DEBUG(dbgs() << "PIP: Found " << Buckets.size() << " buckets\n"); SmallSet<BasicBlock *, 16> BBChanged; for (unsigned i = 0, e = Buckets.size(); i != e; ++i) { // The base address of each bucket is transformed into a phi and the others // are rewritten as offsets of that variable. // We have a choice now of which instruction's memory operand we use as the // base for the generated PHI. Always picking the first instruction in each // bucket does not work well, specifically because that instruction might // be a prefetch (and there are no pre-increment dcbt variants). Otherwise, // the choice is somewhat arbitrary, because the backend will happily // generate direct offsets from both the pre-incremented and // post-incremented pointer values. Thus, we'll pick the first non-prefetch // instruction in each bucket, and adjust the recurrence and other offsets // accordingly. for (int j = 0, je = Buckets[i].Elements.size(); j != je; ++j) { if (auto *II = dyn_cast<IntrinsicInst>(Buckets[i].Elements[j].Instr)) if (II->getIntrinsicID() == Intrinsic::prefetch) continue; // If we'd otherwise pick the first element anyway, there's nothing to do. if (j == 0) break; // If our chosen element has no offset from the base pointer, there's // nothing to do. if (!Buckets[i].Elements[j].Offset || Buckets[i].Elements[j].Offset->isZero()) break; const SCEV *Offset = Buckets[i].Elements[j].Offset; Buckets[i].BaseSCEV = SE->getAddExpr(Buckets[i].BaseSCEV, Offset); for (auto &E : Buckets[i].Elements) { if (E.Offset) E.Offset = cast<SCEVConstant>(SE->getMinusSCEV(E.Offset, Offset)); else E.Offset = cast<SCEVConstant>(SE->getNegativeSCEV(Offset)); } std::swap(Buckets[i].Elements[j], Buckets[i].Elements[0]); break; } const SCEVAddRecExpr *BasePtrSCEV = cast<SCEVAddRecExpr>(Buckets[i].BaseSCEV); if (!BasePtrSCEV->isAffine()) continue; DEBUG(dbgs() << "PIP: Transforming: " << *BasePtrSCEV << "\n"); assert(BasePtrSCEV->getLoop() == L && "AddRec for the wrong loop?"); // The instruction corresponding to the Bucket's BaseSCEV must be the first // in the vector of elements. Instruction *MemI = Buckets[i].Elements.begin()->Instr; Value *BasePtr = GetPointerOperand(MemI); assert(BasePtr && "No pointer operand"); Type *I8Ty = Type::getInt8Ty(MemI->getParent()->getContext()); Type *I8PtrTy = Type::getInt8PtrTy(MemI->getParent()->getContext(), BasePtr->getType()->getPointerAddressSpace()); const SCEV *BasePtrStartSCEV = BasePtrSCEV->getStart(); if (!SE->isLoopInvariant(BasePtrStartSCEV, L)) continue; const SCEVConstant *BasePtrIncSCEV = dyn_cast<SCEVConstant>(BasePtrSCEV->getStepRecurrence(*SE)); if (!BasePtrIncSCEV) continue; BasePtrStartSCEV = SE->getMinusSCEV(BasePtrStartSCEV, BasePtrIncSCEV); if (!isSafeToExpand(BasePtrStartSCEV, *SE)) continue; DEBUG(dbgs() << "PIP: New start is: " << *BasePtrStartSCEV << "\n"); PHINode *NewPHI = PHINode::Create(I8PtrTy, HeaderLoopPredCount, MemI->hasName() ? MemI->getName() + ".phi" : "", Header->getFirstNonPHI()); SCEVExpander SCEVE(*SE, Header->getModule()->getDataLayout(), "pistart"); Value *BasePtrStart = SCEVE.expandCodeFor(BasePtrStartSCEV, I8PtrTy, LoopPredecessor->getTerminator()); // Note that LoopPredecessor might occur in the predecessor list multiple // times, and we need to add it the right number of times. for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header); PI != PE; ++PI) { if (*PI != LoopPredecessor) continue; NewPHI->addIncoming(BasePtrStart, LoopPredecessor); } Instruction *InsPoint = &*Header->getFirstInsertionPt(); GetElementPtrInst *PtrInc = GetElementPtrInst::Create( I8Ty, NewPHI, BasePtrIncSCEV->getValue(), MemI->hasName() ? MemI->getName() + ".inc" : "", InsPoint); PtrInc->setIsInBounds(IsPtrInBounds(BasePtr)); for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header); PI != PE; ++PI) { if (*PI == LoopPredecessor) continue; NewPHI->addIncoming(PtrInc, *PI); } Instruction *NewBasePtr; if (PtrInc->getType() != BasePtr->getType()) NewBasePtr = new BitCastInst(PtrInc, BasePtr->getType(), PtrInc->hasName() ? PtrInc->getName() + ".cast" : "", InsPoint); else NewBasePtr = PtrInc; if (Instruction *IDel = dyn_cast<Instruction>(BasePtr)) BBChanged.insert(IDel->getParent()); BasePtr->replaceAllUsesWith(NewBasePtr); RecursivelyDeleteTriviallyDeadInstructions(BasePtr); // Keep track of the replacement pointer values we've inserted so that we // don't generate more pointer values than necessary. SmallPtrSet<Value *, 16> NewPtrs; NewPtrs.insert( NewBasePtr); for (auto I = std::next(Buckets[i].Elements.begin()), IE = Buckets[i].Elements.end(); I != IE; ++I) { Value *Ptr = GetPointerOperand(I->Instr); assert(Ptr && "No pointer operand"); if (NewPtrs.count(Ptr)) continue; Instruction *RealNewPtr; if (!I->Offset || I->Offset->getValue()->isZero()) { RealNewPtr = NewBasePtr; } else { Instruction *PtrIP = dyn_cast<Instruction>(Ptr); if (PtrIP && isa<Instruction>(NewBasePtr) && cast<Instruction>(NewBasePtr)->getParent() == PtrIP->getParent()) PtrIP = 0; else if (isa<PHINode>(PtrIP)) PtrIP = &*PtrIP->getParent()->getFirstInsertionPt(); else if (!PtrIP) PtrIP = I->Instr; GetElementPtrInst *NewPtr = GetElementPtrInst::Create( I8Ty, PtrInc, I->Offset->getValue(), I->Instr->hasName() ? I->Instr->getName() + ".off" : "", PtrIP); if (!PtrIP) NewPtr->insertAfter(cast<Instruction>(PtrInc)); NewPtr->setIsInBounds(IsPtrInBounds(Ptr)); RealNewPtr = NewPtr; } if (Instruction *IDel = dyn_cast<Instruction>(Ptr)) BBChanged.insert(IDel->getParent()); Instruction *ReplNewPtr; if (Ptr->getType() != RealNewPtr->getType()) { ReplNewPtr = new BitCastInst(RealNewPtr, Ptr->getType(), Ptr->hasName() ? Ptr->getName() + ".cast" : ""); ReplNewPtr->insertAfter(RealNewPtr); } else ReplNewPtr = RealNewPtr; Ptr->replaceAllUsesWith(ReplNewPtr); RecursivelyDeleteTriviallyDeadInstructions(Ptr); NewPtrs.insert(RealNewPtr); } MadeChange = true; } for (Loop::block_iterator I = L->block_begin(), IE = L->block_end(); I != IE; ++I) { if (BBChanged.count(*I)) DeleteDeadPHIs(*I); } return MadeChange; }