| //===-- PPCCTRLoops.cpp - Identify and generate CTR loops -----------------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This pass identifies loops where we can generate the PPC branch instructions |
| // that decrement and test the count register (CTR) (bdnz and friends). |
| // |
| // The pattern that defines the induction variable can changed depending on |
| // prior optimizations. For example, the IndVarSimplify phase run by 'opt' |
| // normalizes induction variables, and the Loop Strength Reduction pass |
| // run by 'llc' may also make changes to the induction variable. |
| // |
| // Criteria for CTR loops: |
| // - Countable loops (w/ ind. var for a trip count) |
| // - Try inner-most loops first |
| // - No nested CTR loops. |
| // - No function calls in loops. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "PPC.h" |
| #include "PPCSubtarget.h" |
| #include "PPCTargetMachine.h" |
| #include "PPCTargetTransformInfo.h" |
| #include "llvm/ADT/STLExtras.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/Analysis/AssumptionCache.h" |
| #include "llvm/Analysis/CFG.h" |
| #include "llvm/Analysis/CodeMetrics.h" |
| #include "llvm/Analysis/LoopInfo.h" |
| #include "llvm/Analysis/LoopIterator.h" |
| #include "llvm/Analysis/ScalarEvolutionExpander.h" |
| #include "llvm/Analysis/TargetLibraryInfo.h" |
| #include "llvm/Analysis/TargetTransformInfo.h" |
| #include "llvm/Transforms/Utils/Local.h" |
| #include "llvm/CodeGen/TargetPassConfig.h" |
| #include "llvm/CodeGen/TargetSchedule.h" |
| #include "llvm/IR/Constants.h" |
| #include "llvm/IR/DerivedTypes.h" |
| #include "llvm/IR/Dominators.h" |
| #include "llvm/IR/InlineAsm.h" |
| #include "llvm/IR/Instructions.h" |
| #include "llvm/IR/IntrinsicInst.h" |
| #include "llvm/IR/Module.h" |
| #include "llvm/IR/ValueHandle.h" |
| #include "llvm/PassSupport.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" |
| |
| #ifndef NDEBUG |
| #include "llvm/CodeGen/MachineDominators.h" |
| #include "llvm/CodeGen/MachineFunction.h" |
| #include "llvm/CodeGen/MachineFunctionPass.h" |
| #include "llvm/CodeGen/MachineRegisterInfo.h" |
| #endif |
| |
| using namespace llvm; |
| |
| #define DEBUG_TYPE "ctrloops" |
| |
| #ifndef NDEBUG |
| static cl::opt<int> CTRLoopLimit("ppc-max-ctrloop", cl::Hidden, cl::init(-1)); |
| #endif |
| |
| // The latency of mtctr is only justified if there are more than 4 |
| // comparisons that will be removed as a result. |
| static cl::opt<unsigned> |
| SmallCTRLoopThreshold("min-ctr-loop-threshold", cl::init(4), cl::Hidden, |
| cl::desc("Loops with a constant trip count smaller than " |
| "this value will not use the count register.")); |
| |
| STATISTIC(NumCTRLoops, "Number of loops converted to CTR loops"); |
| |
| namespace llvm { |
| void initializePPCCTRLoopsPass(PassRegistry&); |
| #ifndef NDEBUG |
| void initializePPCCTRLoopsVerifyPass(PassRegistry&); |
| #endif |
| } |
| |
| namespace { |
| struct PPCCTRLoops : public FunctionPass { |
| |
| #ifndef NDEBUG |
| static int Counter; |
| #endif |
| |
| public: |
| static char ID; |
| |
| PPCCTRLoops() : FunctionPass(ID) { |
| initializePPCCTRLoopsPass(*PassRegistry::getPassRegistry()); |
| } |
| |
| bool runOnFunction(Function &F) override; |
| |
| void getAnalysisUsage(AnalysisUsage &AU) const override { |
| AU.addRequired<LoopInfoWrapperPass>(); |
| AU.addPreserved<LoopInfoWrapperPass>(); |
| AU.addRequired<DominatorTreeWrapperPass>(); |
| AU.addPreserved<DominatorTreeWrapperPass>(); |
| AU.addRequired<ScalarEvolutionWrapperPass>(); |
| AU.addRequired<AssumptionCacheTracker>(); |
| AU.addRequired<TargetTransformInfoWrapperPass>(); |
| } |
| |
| private: |
| bool mightUseCTR(BasicBlock *BB); |
| bool convertToCTRLoop(Loop *L); |
| |
| private: |
| const PPCTargetMachine *TM; |
| const PPCSubtarget *STI; |
| const PPCTargetLowering *TLI; |
| const DataLayout *DL; |
| const TargetLibraryInfo *LibInfo; |
| const TargetTransformInfo *TTI; |
| LoopInfo *LI; |
| ScalarEvolution *SE; |
| DominatorTree *DT; |
| bool PreserveLCSSA; |
| TargetSchedModel SchedModel; |
| }; |
| |
| char PPCCTRLoops::ID = 0; |
| #ifndef NDEBUG |
| int PPCCTRLoops::Counter = 0; |
| #endif |
| |
| #ifndef NDEBUG |
| struct PPCCTRLoopsVerify : public MachineFunctionPass { |
| public: |
| static char ID; |
| |
| PPCCTRLoopsVerify() : MachineFunctionPass(ID) { |
| initializePPCCTRLoopsVerifyPass(*PassRegistry::getPassRegistry()); |
| } |
| |
| void getAnalysisUsage(AnalysisUsage &AU) const override { |
| AU.addRequired<MachineDominatorTree>(); |
| MachineFunctionPass::getAnalysisUsage(AU); |
| } |
| |
| bool runOnMachineFunction(MachineFunction &MF) override; |
| |
| private: |
| MachineDominatorTree *MDT; |
| }; |
| |
| char PPCCTRLoopsVerify::ID = 0; |
| #endif // NDEBUG |
| } // end anonymous namespace |
| |
| INITIALIZE_PASS_BEGIN(PPCCTRLoops, "ppc-ctr-loops", "PowerPC CTR Loops", |
| false, false) |
| INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) |
| INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass) |
| INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass) |
| INITIALIZE_PASS_END(PPCCTRLoops, "ppc-ctr-loops", "PowerPC CTR Loops", |
| false, false) |
| |
| FunctionPass *llvm::createPPCCTRLoops() { return new PPCCTRLoops(); } |
| |
| #ifndef NDEBUG |
| INITIALIZE_PASS_BEGIN(PPCCTRLoopsVerify, "ppc-ctr-loops-verify", |
| "PowerPC CTR Loops Verify", false, false) |
| INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree) |
| INITIALIZE_PASS_END(PPCCTRLoopsVerify, "ppc-ctr-loops-verify", |
| "PowerPC CTR Loops Verify", false, false) |
| |
| FunctionPass *llvm::createPPCCTRLoopsVerify() { |
| return new PPCCTRLoopsVerify(); |
| } |
| #endif // NDEBUG |
| |
| bool PPCCTRLoops::runOnFunction(Function &F) { |
| if (skipFunction(F)) |
| return false; |
| |
| auto *TPC = getAnalysisIfAvailable<TargetPassConfig>(); |
| if (!TPC) |
| return false; |
| |
| TM = &TPC->getTM<PPCTargetMachine>(); |
| STI = TM->getSubtargetImpl(F); |
| TLI = STI->getTargetLowering(); |
| |
| LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo(); |
| SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE(); |
| DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree(); |
| TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F); |
| DL = &F.getParent()->getDataLayout(); |
| auto *TLIP = getAnalysisIfAvailable<TargetLibraryInfoWrapperPass>(); |
| LibInfo = TLIP ? &TLIP->getTLI() : nullptr; |
| PreserveLCSSA = mustPreserveAnalysisID(LCSSAID); |
| |
| bool MadeChange = false; |
| |
| for (LoopInfo::iterator I = LI->begin(), E = LI->end(); |
| I != E; ++I) { |
| Loop *L = *I; |
| if (!L->getParentLoop()) |
| MadeChange |= convertToCTRLoop(L); |
| } |
| |
| return MadeChange; |
| } |
| |
| static bool isLargeIntegerTy(bool Is32Bit, Type *Ty) { |
| if (IntegerType *ITy = dyn_cast<IntegerType>(Ty)) |
| return ITy->getBitWidth() > (Is32Bit ? 32U : 64U); |
| |
| return false; |
| } |
| |
| // Determining the address of a TLS variable results in a function call in |
| // certain TLS models. |
| static bool memAddrUsesCTR(const PPCTargetMachine &TM, const Value *MemAddr) { |
| const auto *GV = dyn_cast<GlobalValue>(MemAddr); |
| if (!GV) { |
| // Recurse to check for constants that refer to TLS global variables. |
| if (const auto *CV = dyn_cast<Constant>(MemAddr)) |
| for (const auto &CO : CV->operands()) |
| if (memAddrUsesCTR(TM, CO)) |
| return true; |
| |
| return false; |
| } |
| |
| if (!GV->isThreadLocal()) |
| return false; |
| TLSModel::Model Model = TM.getTLSModel(GV); |
| return Model == TLSModel::GeneralDynamic || Model == TLSModel::LocalDynamic; |
| } |
| |
| // Loop through the inline asm constraints and look for something that clobbers |
| // ctr. |
| static bool asmClobbersCTR(InlineAsm *IA) { |
| InlineAsm::ConstraintInfoVector CIV = IA->ParseConstraints(); |
| for (unsigned i = 0, ie = CIV.size(); i < ie; ++i) { |
| InlineAsm::ConstraintInfo &C = CIV[i]; |
| if (C.Type != InlineAsm::isInput) |
| for (unsigned j = 0, je = C.Codes.size(); j < je; ++j) |
| if (StringRef(C.Codes[j]).equals_lower("{ctr}")) |
| return true; |
| } |
| return false; |
| } |
| |
| bool PPCCTRLoops::mightUseCTR(BasicBlock *BB) { |
| for (BasicBlock::iterator J = BB->begin(), JE = BB->end(); |
| J != JE; ++J) { |
| if (CallInst *CI = dyn_cast<CallInst>(J)) { |
| // Inline ASM is okay, unless it clobbers the ctr register. |
| if (InlineAsm *IA = dyn_cast<InlineAsm>(CI->getCalledValue())) { |
| if (asmClobbersCTR(IA)) |
| return true; |
| continue; |
| } |
| |
| if (Function *F = CI->getCalledFunction()) { |
| // Most intrinsics don't become function calls, but some might. |
| // sin, cos, exp and log are always calls. |
| unsigned Opcode = 0; |
| if (F->getIntrinsicID() != Intrinsic::not_intrinsic) { |
| switch (F->getIntrinsicID()) { |
| default: continue; |
| // If we have a call to ppc_is_decremented_ctr_nonzero, or ppc_mtctr |
| // we're definitely using CTR. |
| case Intrinsic::ppc_is_decremented_ctr_nonzero: |
| case Intrinsic::ppc_mtctr: |
| return true; |
| |
| // VisualStudio defines setjmp as _setjmp |
| #if defined(_MSC_VER) && defined(setjmp) && \ |
| !defined(setjmp_undefined_for_msvc) |
| # pragma push_macro("setjmp") |
| # undef setjmp |
| # define setjmp_undefined_for_msvc |
| #endif |
| |
| case Intrinsic::setjmp: |
| |
| #if defined(_MSC_VER) && defined(setjmp_undefined_for_msvc) |
| // let's return it to _setjmp state |
| # pragma pop_macro("setjmp") |
| # undef setjmp_undefined_for_msvc |
| #endif |
| |
| case Intrinsic::longjmp: |
| |
| // Exclude eh_sjlj_setjmp; we don't need to exclude eh_sjlj_longjmp |
| // because, although it does clobber the counter register, the |
| // control can't then return to inside the loop unless there is also |
| // an eh_sjlj_setjmp. |
| case Intrinsic::eh_sjlj_setjmp: |
| |
| case Intrinsic::memcpy: |
| case Intrinsic::memmove: |
| case Intrinsic::memset: |
| case Intrinsic::powi: |
| case Intrinsic::log: |
| case Intrinsic::log2: |
| case Intrinsic::log10: |
| case Intrinsic::exp: |
| case Intrinsic::exp2: |
| case Intrinsic::pow: |
| case Intrinsic::sin: |
| case Intrinsic::cos: |
| return true; |
| case Intrinsic::copysign: |
| if (CI->getArgOperand(0)->getType()->getScalarType()-> |
| isPPC_FP128Ty()) |
| return true; |
| else |
| continue; // ISD::FCOPYSIGN is never a library call. |
| case Intrinsic::sqrt: Opcode = ISD::FSQRT; break; |
| case Intrinsic::floor: Opcode = ISD::FFLOOR; break; |
| case Intrinsic::ceil: Opcode = ISD::FCEIL; break; |
| case Intrinsic::trunc: Opcode = ISD::FTRUNC; break; |
| case Intrinsic::rint: Opcode = ISD::FRINT; break; |
| case Intrinsic::nearbyint: Opcode = ISD::FNEARBYINT; break; |
| case Intrinsic::round: Opcode = ISD::FROUND; break; |
| case Intrinsic::minnum: Opcode = ISD::FMINNUM; break; |
| case Intrinsic::maxnum: Opcode = ISD::FMAXNUM; break; |
| case Intrinsic::umul_with_overflow: Opcode = ISD::UMULO; break; |
| case Intrinsic::smul_with_overflow: Opcode = ISD::SMULO; break; |
| } |
| } |
| |
| // PowerPC does not use [US]DIVREM or other library calls for |
| // operations on regular types which are not otherwise library calls |
| // (i.e. soft float or atomics). If adapting for targets that do, |
| // additional care is required here. |
| |
| LibFunc Func; |
| if (!F->hasLocalLinkage() && F->hasName() && LibInfo && |
| LibInfo->getLibFunc(F->getName(), Func) && |
| LibInfo->hasOptimizedCodeGen(Func)) { |
| // Non-read-only functions are never treated as intrinsics. |
| if (!CI->onlyReadsMemory()) |
| return true; |
| |
| // Conversion happens only for FP calls. |
| if (!CI->getArgOperand(0)->getType()->isFloatingPointTy()) |
| return true; |
| |
| switch (Func) { |
| default: return true; |
| case LibFunc_copysign: |
| case LibFunc_copysignf: |
| continue; // ISD::FCOPYSIGN is never a library call. |
| case LibFunc_copysignl: |
| return true; |
| case LibFunc_fabs: |
| case LibFunc_fabsf: |
| case LibFunc_fabsl: |
| continue; // ISD::FABS is never a library call. |
| case LibFunc_sqrt: |
| case LibFunc_sqrtf: |
| case LibFunc_sqrtl: |
| Opcode = ISD::FSQRT; break; |
| case LibFunc_floor: |
| case LibFunc_floorf: |
| case LibFunc_floorl: |
| Opcode = ISD::FFLOOR; break; |
| case LibFunc_nearbyint: |
| case LibFunc_nearbyintf: |
| case LibFunc_nearbyintl: |
| Opcode = ISD::FNEARBYINT; break; |
| case LibFunc_ceil: |
| case LibFunc_ceilf: |
| case LibFunc_ceill: |
| Opcode = ISD::FCEIL; break; |
| case LibFunc_rint: |
| case LibFunc_rintf: |
| case LibFunc_rintl: |
| Opcode = ISD::FRINT; break; |
| case LibFunc_round: |
| case LibFunc_roundf: |
| case LibFunc_roundl: |
| Opcode = ISD::FROUND; break; |
| case LibFunc_trunc: |
| case LibFunc_truncf: |
| case LibFunc_truncl: |
| Opcode = ISD::FTRUNC; break; |
| case LibFunc_fmin: |
| case LibFunc_fminf: |
| case LibFunc_fminl: |
| Opcode = ISD::FMINNUM; break; |
| case LibFunc_fmax: |
| case LibFunc_fmaxf: |
| case LibFunc_fmaxl: |
| Opcode = ISD::FMAXNUM; break; |
| } |
| } |
| |
| if (Opcode) { |
| EVT EVTy = |
| TLI->getValueType(*DL, CI->getArgOperand(0)->getType(), true); |
| |
| if (EVTy == MVT::Other) |
| return true; |
| |
| if (TLI->isOperationLegalOrCustom(Opcode, EVTy)) |
| continue; |
| else if (EVTy.isVector() && |
| TLI->isOperationLegalOrCustom(Opcode, EVTy.getScalarType())) |
| continue; |
| |
| return true; |
| } |
| } |
| |
| return true; |
| } else if (isa<BinaryOperator>(J) && |
| J->getType()->getScalarType()->isPPC_FP128Ty()) { |
| // Most operations on ppc_f128 values become calls. |
| return true; |
| } else if (isa<UIToFPInst>(J) || isa<SIToFPInst>(J) || |
| isa<FPToUIInst>(J) || isa<FPToSIInst>(J)) { |
| CastInst *CI = cast<CastInst>(J); |
| if (CI->getSrcTy()->getScalarType()->isPPC_FP128Ty() || |
| CI->getDestTy()->getScalarType()->isPPC_FP128Ty() || |
| isLargeIntegerTy(!TM->isPPC64(), CI->getSrcTy()->getScalarType()) || |
| isLargeIntegerTy(!TM->isPPC64(), CI->getDestTy()->getScalarType())) |
| return true; |
| } else if (isLargeIntegerTy(!TM->isPPC64(), |
| J->getType()->getScalarType()) && |
| (J->getOpcode() == Instruction::UDiv || |
| J->getOpcode() == Instruction::SDiv || |
| J->getOpcode() == Instruction::URem || |
| J->getOpcode() == Instruction::SRem)) { |
| return true; |
| } else if (!TM->isPPC64() && |
| isLargeIntegerTy(false, J->getType()->getScalarType()) && |
| (J->getOpcode() == Instruction::Shl || |
| J->getOpcode() == Instruction::AShr || |
| J->getOpcode() == Instruction::LShr)) { |
| // Only on PPC32, for 128-bit integers (specifically not 64-bit |
| // integers), these might be runtime calls. |
| return true; |
| } else if (isa<IndirectBrInst>(J) || isa<InvokeInst>(J)) { |
| // On PowerPC, indirect jumps use the counter register. |
| return true; |
| } else if (SwitchInst *SI = dyn_cast<SwitchInst>(J)) { |
| if (SI->getNumCases() + 1 >= (unsigned)TLI->getMinimumJumpTableEntries()) |
| return true; |
| } |
| |
| // FREM is always a call. |
| if (J->getOpcode() == Instruction::FRem) |
| return true; |
| |
| if (STI->useSoftFloat()) { |
| switch(J->getOpcode()) { |
| case Instruction::FAdd: |
| case Instruction::FSub: |
| case Instruction::FMul: |
| case Instruction::FDiv: |
| case Instruction::FPTrunc: |
| case Instruction::FPExt: |
| case Instruction::FPToUI: |
| case Instruction::FPToSI: |
| case Instruction::UIToFP: |
| case Instruction::SIToFP: |
| case Instruction::FCmp: |
| return true; |
| } |
| } |
| |
| for (Value *Operand : J->operands()) |
| if (memAddrUsesCTR(*TM, Operand)) |
| return true; |
| } |
| |
| return false; |
| } |
| bool PPCCTRLoops::convertToCTRLoop(Loop *L) { |
| bool MadeChange = false; |
| |
| // Do not convert small short loops to CTR loop. |
| unsigned ConstTripCount = SE->getSmallConstantTripCount(L); |
| if (ConstTripCount && ConstTripCount < SmallCTRLoopThreshold) { |
| SmallPtrSet<const Value *, 32> EphValues; |
| auto AC = getAnalysis<AssumptionCacheTracker>().getAssumptionCache( |
| *L->getHeader()->getParent()); |
| CodeMetrics::collectEphemeralValues(L, &AC, EphValues); |
| CodeMetrics Metrics; |
| for (BasicBlock *BB : L->blocks()) |
| Metrics.analyzeBasicBlock(BB, *TTI, EphValues); |
| // 6 is an approximate latency for the mtctr instruction. |
| if (Metrics.NumInsts <= (6 * SchedModel.getIssueWidth())) |
| return false; |
| } |
| |
| // Process nested loops first. |
| for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I) { |
| MadeChange |= convertToCTRLoop(*I); |
| LLVM_DEBUG(dbgs() << "Nested loop converted\n"); |
| } |
| |
| // If a nested loop has been converted, then we can't convert this loop. |
| if (MadeChange) |
| return MadeChange; |
| |
| // Bail out if the loop has irreducible control flow. |
| LoopBlocksRPO RPOT(L); |
| RPOT.perform(LI); |
| if (containsIrreducibleCFG<const BasicBlock *>(RPOT, *LI)) |
| return false; |
| |
| #ifndef NDEBUG |
| // Stop trying after reaching the limit (if any). |
| int Limit = CTRLoopLimit; |
| if (Limit >= 0) { |
| if (Counter >= CTRLoopLimit) |
| return false; |
| Counter++; |
| } |
| #endif |
| |
| // We don't want to spill/restore the counter register, and so we don't |
| // want to use the counter register if the loop contains calls. |
| for (Loop::block_iterator I = L->block_begin(), IE = L->block_end(); |
| I != IE; ++I) |
| if (mightUseCTR(*I)) |
| return MadeChange; |
| |
| SmallVector<BasicBlock*, 4> ExitingBlocks; |
| L->getExitingBlocks(ExitingBlocks); |
| |
| // If there is an exit edge known to be frequently taken, |
| // we should not transform this loop. |
| for (auto &BB : ExitingBlocks) { |
| Instruction *TI = BB->getTerminator(); |
| if (!TI) continue; |
| |
| if (BranchInst *BI = dyn_cast<BranchInst>(TI)) { |
| uint64_t TrueWeight = 0, FalseWeight = 0; |
| if (!BI->isConditional() || |
| !BI->extractProfMetadata(TrueWeight, FalseWeight)) |
| continue; |
| |
| // If the exit path is more frequent than the loop path, |
| // we return here without further analysis for this loop. |
| bool TrueIsExit = !L->contains(BI->getSuccessor(0)); |
| if (( TrueIsExit && FalseWeight < TrueWeight) || |
| (!TrueIsExit && FalseWeight > TrueWeight)) |
| return MadeChange; |
| } |
| } |
| |
| BasicBlock *CountedExitBlock = nullptr; |
| const SCEV *ExitCount = nullptr; |
| BranchInst *CountedExitBranch = nullptr; |
| for (SmallVectorImpl<BasicBlock *>::iterator I = ExitingBlocks.begin(), |
| IE = ExitingBlocks.end(); I != IE; ++I) { |
| const SCEV *EC = SE->getExitCount(L, *I); |
| LLVM_DEBUG(dbgs() << "Exit Count for " << *L << " from block " |
| << (*I)->getName() << ": " << *EC << "\n"); |
| if (isa<SCEVCouldNotCompute>(EC)) |
| continue; |
| if (const SCEVConstant *ConstEC = dyn_cast<SCEVConstant>(EC)) { |
| if (ConstEC->getValue()->isZero()) |
| continue; |
| } else if (!SE->isLoopInvariant(EC, L)) |
| continue; |
| |
| if (SE->getTypeSizeInBits(EC->getType()) > (TM->isPPC64() ? 64 : 32)) |
| continue; |
| |
| // If this exiting block is contained in a nested loop, it is not eligible |
| // for insertion of the branch-and-decrement since the inner loop would |
| // end up messing up the value in the CTR. |
| if (LI->getLoopFor(*I) != L) |
| continue; |
| |
| // We now have a loop-invariant count of loop iterations (which is not the |
| // constant zero) for which we know that this loop will not exit via this |
| // existing block. |
| |
| // We need to make sure that this block will run on every loop iteration. |
| // For this to be true, we must dominate all blocks with backedges. Such |
| // blocks are in-loop predecessors to the header block. |
| bool NotAlways = false; |
| for (pred_iterator PI = pred_begin(L->getHeader()), |
| PIE = pred_end(L->getHeader()); PI != PIE; ++PI) { |
| if (!L->contains(*PI)) |
| continue; |
| |
| if (!DT->dominates(*I, *PI)) { |
| NotAlways = true; |
| break; |
| } |
| } |
| |
| if (NotAlways) |
| continue; |
| |
| // Make sure this blocks ends with a conditional branch. |
| Instruction *TI = (*I)->getTerminator(); |
| if (!TI) |
| continue; |
| |
| if (BranchInst *BI = dyn_cast<BranchInst>(TI)) { |
| if (!BI->isConditional()) |
| continue; |
| |
| CountedExitBranch = BI; |
| } else |
| continue; |
| |
| // Note that this block may not be the loop latch block, even if the loop |
| // has a latch block. |
| CountedExitBlock = *I; |
| ExitCount = EC; |
| break; |
| } |
| |
| if (!CountedExitBlock) |
| return MadeChange; |
| |
| BasicBlock *Preheader = L->getLoopPreheader(); |
| |
| // If we don't have a preheader, then insert one. If we already have a |
| // preheader, then we can use it (except if the preheader contains a use of |
| // the CTR register because some such uses might be reordered by the |
| // selection DAG after the mtctr instruction). |
| if (!Preheader || mightUseCTR(Preheader)) |
| Preheader = InsertPreheaderForLoop(L, DT, LI, PreserveLCSSA); |
| if (!Preheader) |
| return MadeChange; |
| |
| LLVM_DEBUG(dbgs() << "Preheader for exit count: " << Preheader->getName() |
| << "\n"); |
| |
| // Insert the count into the preheader and replace the condition used by the |
| // selected branch. |
| MadeChange = true; |
| |
| SCEVExpander SCEVE(*SE, *DL, "loopcnt"); |
| LLVMContext &C = SE->getContext(); |
| Type *CountType = TM->isPPC64() ? Type::getInt64Ty(C) : Type::getInt32Ty(C); |
| if (!ExitCount->getType()->isPointerTy() && |
| ExitCount->getType() != CountType) |
| ExitCount = SE->getZeroExtendExpr(ExitCount, CountType); |
| ExitCount = SE->getAddExpr(ExitCount, SE->getOne(CountType)); |
| Value *ECValue = |
| SCEVE.expandCodeFor(ExitCount, CountType, Preheader->getTerminator()); |
| |
| IRBuilder<> CountBuilder(Preheader->getTerminator()); |
| Module *M = Preheader->getParent()->getParent(); |
| Value *MTCTRFunc = Intrinsic::getDeclaration(M, Intrinsic::ppc_mtctr, |
| CountType); |
| CountBuilder.CreateCall(MTCTRFunc, ECValue); |
| |
| IRBuilder<> CondBuilder(CountedExitBranch); |
| Value *DecFunc = |
| Intrinsic::getDeclaration(M, Intrinsic::ppc_is_decremented_ctr_nonzero); |
| Value *NewCond = CondBuilder.CreateCall(DecFunc, {}); |
| Value *OldCond = CountedExitBranch->getCondition(); |
| CountedExitBranch->setCondition(NewCond); |
| |
| // The false branch must exit the loop. |
| if (!L->contains(CountedExitBranch->getSuccessor(0))) |
| CountedExitBranch->swapSuccessors(); |
| |
| // The old condition may be dead now, and may have even created a dead PHI |
| // (the original induction variable). |
| RecursivelyDeleteTriviallyDeadInstructions(OldCond); |
| // Run through the basic blocks of the loop and see if any of them have dead |
| // PHIs that can be removed. |
| for (auto I : L->blocks()) |
| DeleteDeadPHIs(I); |
| |
| ++NumCTRLoops; |
| return MadeChange; |
| } |
| |
| #ifndef NDEBUG |
| static bool clobbersCTR(const MachineInstr &MI) { |
| for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) { |
| const MachineOperand &MO = MI.getOperand(i); |
| if (MO.isReg()) { |
| if (MO.isDef() && (MO.getReg() == PPC::CTR || MO.getReg() == PPC::CTR8)) |
| return true; |
| } else if (MO.isRegMask()) { |
| if (MO.clobbersPhysReg(PPC::CTR) || MO.clobbersPhysReg(PPC::CTR8)) |
| return true; |
| } |
| } |
| |
| return false; |
| } |
| |
| static bool verifyCTRBranch(MachineBasicBlock *MBB, |
| MachineBasicBlock::iterator I) { |
| MachineBasicBlock::iterator BI = I; |
| SmallSet<MachineBasicBlock *, 16> Visited; |
| SmallVector<MachineBasicBlock *, 8> Preds; |
| bool CheckPreds; |
| |
| if (I == MBB->begin()) { |
| Visited.insert(MBB); |
| goto queue_preds; |
| } else |
| --I; |
| |
| check_block: |
| Visited.insert(MBB); |
| if (I == MBB->end()) |
| goto queue_preds; |
| |
| CheckPreds = true; |
| for (MachineBasicBlock::iterator IE = MBB->begin();; --I) { |
| unsigned Opc = I->getOpcode(); |
| if (Opc == PPC::MTCTRloop || Opc == PPC::MTCTR8loop) { |
| CheckPreds = false; |
| break; |
| } |
| |
| if (I != BI && clobbersCTR(*I)) { |
| LLVM_DEBUG(dbgs() << printMBBReference(*MBB) << " (" << MBB->getFullName() |
| << ") instruction " << *I |
| << " clobbers CTR, invalidating " |
| << printMBBReference(*BI->getParent()) << " (" |
| << BI->getParent()->getFullName() << ") instruction " |
| << *BI << "\n"); |
| return false; |
| } |
| |
| if (I == IE) |
| break; |
| } |
| |
| if (!CheckPreds && Preds.empty()) |
| return true; |
| |
| if (CheckPreds) { |
| queue_preds: |
| if (MachineFunction::iterator(MBB) == MBB->getParent()->begin()) { |
| LLVM_DEBUG(dbgs() << "Unable to find a MTCTR instruction for " |
| << printMBBReference(*BI->getParent()) << " (" |
| << BI->getParent()->getFullName() << ") instruction " |
| << *BI << "\n"); |
| return false; |
| } |
| |
| for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(), |
| PIE = MBB->pred_end(); PI != PIE; ++PI) |
| Preds.push_back(*PI); |
| } |
| |
| do { |
| MBB = Preds.pop_back_val(); |
| if (!Visited.count(MBB)) { |
| I = MBB->getLastNonDebugInstr(); |
| goto check_block; |
| } |
| } while (!Preds.empty()); |
| |
| return true; |
| } |
| |
| bool PPCCTRLoopsVerify::runOnMachineFunction(MachineFunction &MF) { |
| MDT = &getAnalysis<MachineDominatorTree>(); |
| |
| // Verify that all bdnz/bdz instructions are dominated by a loop mtctr before |
| // any other instructions that might clobber the ctr register. |
| for (MachineFunction::iterator I = MF.begin(), IE = MF.end(); |
| I != IE; ++I) { |
| MachineBasicBlock *MBB = &*I; |
| if (!MDT->isReachableFromEntry(MBB)) |
| continue; |
| |
| for (MachineBasicBlock::iterator MII = MBB->getFirstTerminator(), |
| MIIE = MBB->end(); MII != MIIE; ++MII) { |
| unsigned Opc = MII->getOpcode(); |
| if (Opc == PPC::BDNZ8 || Opc == PPC::BDNZ || |
| Opc == PPC::BDZ8 || Opc == PPC::BDZ) |
| if (!verifyCTRBranch(MBB, MII)) |
| llvm_unreachable("Invalid PPC CTR loop!"); |
| } |
| } |
| |
| return false; |
| } |
| #endif // NDEBUG |
