//===- AMDGPUTargetTransformInfo.cpp - AMDGPU specific TTI pass -----------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // \file // This file implements a TargetTransformInfo analysis pass specific to the // AMDGPU target machine. It uses the target's detailed information to provide // more precise answers to certain TTI queries, while letting the target // independent and default TTI implementations handle the rest. // //===----------------------------------------------------------------------===// #include "AMDGPUTargetTransformInfo.h" #include "AMDGPUSubtarget.h" #include "llvm/ADT/STLExtras.h" #include "llvm/Analysis/LoopInfo.h" #include "llvm/Analysis/TargetTransformInfo.h" #include "llvm/Analysis/ValueTracking.h" #include "llvm/CodeGen/ISDOpcodes.h" #include "llvm/CodeGen/MachineValueType.h" #include "llvm/CodeGen/ValueTypes.h" #include "llvm/IR/Argument.h" #include "llvm/IR/Attributes.h" #include "llvm/IR/BasicBlock.h" #include "llvm/IR/CallingConv.h" #include "llvm/IR/DataLayout.h" #include "llvm/IR/DerivedTypes.h" #include "llvm/IR/Function.h" #include "llvm/IR/Instruction.h" #include "llvm/IR/Instructions.h" #include "llvm/IR/IntrinsicInst.h" #include "llvm/IR/Module.h" #include "llvm/IR/PatternMatch.h" #include "llvm/IR/Type.h" #include "llvm/IR/Value.h" #include "llvm/MC/SubtargetFeature.h" #include "llvm/Support/Casting.h" #include "llvm/Support/CommandLine.h" #include "llvm/Support/Debug.h" #include "llvm/Support/ErrorHandling.h" #include "llvm/Support/raw_ostream.h" #include "llvm/Target/TargetMachine.h" #include #include #include #include using namespace llvm; #define DEBUG_TYPE "AMDGPUtti" static cl::opt UnrollThresholdPrivate( "amdgpu-unroll-threshold-private", cl::desc("Unroll threshold for AMDGPU if private memory used in a loop"), cl::init(2500), cl::Hidden); static cl::opt UnrollThresholdLocal( "amdgpu-unroll-threshold-local", cl::desc("Unroll threshold for AMDGPU if local memory used in a loop"), cl::init(1000), cl::Hidden); static cl::opt UnrollThresholdIf( "amdgpu-unroll-threshold-if", cl::desc("Unroll threshold increment for AMDGPU for each if statement inside loop"), cl::init(150), cl::Hidden); static bool dependsOnLocalPhi(const Loop *L, const Value *Cond, unsigned Depth = 0) { const Instruction *I = dyn_cast(Cond); if (!I) return false; for (const Value *V : I->operand_values()) { if (!L->contains(I)) continue; if (const PHINode *PHI = dyn_cast(V)) { if (llvm::none_of(L->getSubLoops(), [PHI](const Loop* SubLoop) { return SubLoop->contains(PHI); })) return true; } else if (Depth < 10 && dependsOnLocalPhi(L, V, Depth+1)) return true; } return false; } void AMDGPUTTIImpl::getUnrollingPreferences(Loop *L, ScalarEvolution &SE, TTI::UnrollingPreferences &UP) { UP.Threshold = 300; // Twice the default. UP.MaxCount = std::numeric_limits::max(); UP.Partial = true; // TODO: Do we want runtime unrolling? // Maximum alloca size than can fit registers. Reserve 16 registers. const unsigned MaxAlloca = (256 - 16) * 4; unsigned ThresholdPrivate = UnrollThresholdPrivate; unsigned ThresholdLocal = UnrollThresholdLocal; unsigned MaxBoost = std::max(ThresholdPrivate, ThresholdLocal); AMDGPUAS ASST = ST->getAMDGPUAS(); for (const BasicBlock *BB : L->getBlocks()) { const DataLayout &DL = BB->getModule()->getDataLayout(); unsigned LocalGEPsSeen = 0; if (llvm::any_of(L->getSubLoops(), [BB](const Loop* SubLoop) { return SubLoop->contains(BB); })) continue; // Block belongs to an inner loop. for (const Instruction &I : *BB) { // Unroll a loop which contains an "if" statement whose condition // defined by a PHI belonging to the loop. This may help to eliminate // if region and potentially even PHI itself, saving on both divergence // and registers used for the PHI. // Add a small bonus for each of such "if" statements. if (const BranchInst *Br = dyn_cast(&I)) { if (UP.Threshold < MaxBoost && Br->isConditional()) { if (L->isLoopExiting(Br->getSuccessor(0)) || L->isLoopExiting(Br->getSuccessor(1))) continue; if (dependsOnLocalPhi(L, Br->getCondition())) { UP.Threshold += UnrollThresholdIf; DEBUG(dbgs() << "Set unroll threshold " << UP.Threshold << " for loop:\n" << *L << " due to " << *Br << '\n'); if (UP.Threshold >= MaxBoost) return; } } continue; } const GetElementPtrInst *GEP = dyn_cast(&I); if (!GEP) continue; unsigned AS = GEP->getAddressSpace(); unsigned Threshold = 0; if (AS == ASST.PRIVATE_ADDRESS) Threshold = ThresholdPrivate; else if (AS == ASST.LOCAL_ADDRESS) Threshold = ThresholdLocal; else continue; if (UP.Threshold >= Threshold) continue; if (AS == ASST.PRIVATE_ADDRESS) { const Value *Ptr = GEP->getPointerOperand(); const AllocaInst *Alloca = dyn_cast(GetUnderlyingObject(Ptr, DL)); if (!Alloca || !Alloca->isStaticAlloca()) continue; Type *Ty = Alloca->getAllocatedType(); unsigned AllocaSize = Ty->isSized() ? DL.getTypeAllocSize(Ty) : 0; if (AllocaSize > MaxAlloca) continue; } else if (AS == ASST.LOCAL_ADDRESS) { LocalGEPsSeen++; // Inhibit unroll for local memory if we have seen addressing not to // a variable, most likely we will be unable to combine it. // Do not unroll too deep inner loops for local memory to give a chance // to unroll an outer loop for a more important reason. if (LocalGEPsSeen > 1 || L->getLoopDepth() > 2 || (!isa(GEP->getPointerOperand()) && !isa(GEP->getPointerOperand()))) continue; } // Check if GEP depends on a value defined by this loop itself. bool HasLoopDef = false; for (const Value *Op : GEP->operands()) { const Instruction *Inst = dyn_cast(Op); if (!Inst || L->isLoopInvariant(Op)) continue; if (llvm::any_of(L->getSubLoops(), [Inst](const Loop* SubLoop) { return SubLoop->contains(Inst); })) continue; HasLoopDef = true; break; } if (!HasLoopDef) continue; // We want to do whatever we can to limit the number of alloca // instructions that make it through to the code generator. allocas // require us to use indirect addressing, which is slow and prone to // compiler bugs. If this loop does an address calculation on an // alloca ptr, then we want to use a higher than normal loop unroll // threshold. This will give SROA a better chance to eliminate these // allocas. // // We also want to have more unrolling for local memory to let ds // instructions with different offsets combine. // // Don't use the maximum allowed value here as it will make some // programs way too big. UP.Threshold = Threshold; DEBUG(dbgs() << "Set unroll threshold " << Threshold << " for loop:\n" << *L << " due to " << *GEP << '\n'); if (UP.Threshold >= MaxBoost) return; } } } unsigned AMDGPUTTIImpl::getHardwareNumberOfRegisters(bool Vec) const { // The concept of vector registers doesn't really exist. Some packed vector // operations operate on the normal 32-bit registers. // Number of VGPRs on SI. if (ST->getGeneration() >= AMDGPUSubtarget::SOUTHERN_ISLANDS) return 256; return 4 * 128; // XXX - 4 channels. Should these count as vector instead? } unsigned AMDGPUTTIImpl::getNumberOfRegisters(bool Vec) const { // This is really the number of registers to fill when vectorizing / // interleaving loops, so we lie to avoid trying to use all registers. return getHardwareNumberOfRegisters(Vec) >> 3; } unsigned AMDGPUTTIImpl::getRegisterBitWidth(bool Vector) const { return 32; } unsigned AMDGPUTTIImpl::getMinVectorRegisterBitWidth() const { return 32; } unsigned AMDGPUTTIImpl::getLoadStoreVecRegBitWidth(unsigned AddrSpace) const { AMDGPUAS AS = ST->getAMDGPUAS(); if (AddrSpace == AS.GLOBAL_ADDRESS || AddrSpace == AS.CONSTANT_ADDRESS || AddrSpace == AS.FLAT_ADDRESS) return 128; if (AddrSpace == AS.LOCAL_ADDRESS || AddrSpace == AS.REGION_ADDRESS) return 64; if (AddrSpace == AS.PRIVATE_ADDRESS) return 8 * ST->getMaxPrivateElementSize(); if (ST->getGeneration() <= AMDGPUSubtarget::NORTHERN_ISLANDS && (AddrSpace == AS.PARAM_D_ADDRESS || AddrSpace == AS.PARAM_I_ADDRESS || (AddrSpace >= AS.CONSTANT_BUFFER_0 && AddrSpace <= AS.CONSTANT_BUFFER_15))) return 128; llvm_unreachable("unhandled address space"); } bool AMDGPUTTIImpl::isLegalToVectorizeMemChain(unsigned ChainSizeInBytes, unsigned Alignment, unsigned AddrSpace) const { // We allow vectorization of flat stores, even though we may need to decompose // them later if they may access private memory. We don't have enough context // here, and legalization can handle it. if (AddrSpace == ST->getAMDGPUAS().PRIVATE_ADDRESS) { return (Alignment >= 4 || ST->hasUnalignedScratchAccess()) && ChainSizeInBytes <= ST->getMaxPrivateElementSize(); } return true; } bool AMDGPUTTIImpl::isLegalToVectorizeLoadChain(unsigned ChainSizeInBytes, unsigned Alignment, unsigned AddrSpace) const { return isLegalToVectorizeMemChain(ChainSizeInBytes, Alignment, AddrSpace); } bool AMDGPUTTIImpl::isLegalToVectorizeStoreChain(unsigned ChainSizeInBytes, unsigned Alignment, unsigned AddrSpace) const { return isLegalToVectorizeMemChain(ChainSizeInBytes, Alignment, AddrSpace); } unsigned AMDGPUTTIImpl::getMaxInterleaveFactor(unsigned VF) { // Disable unrolling if the loop is not vectorized. // TODO: Enable this again. if (VF == 1) return 1; return 8; } bool AMDGPUTTIImpl::getTgtMemIntrinsic(IntrinsicInst *Inst, MemIntrinsicInfo &Info) const { switch (Inst->getIntrinsicID()) { case Intrinsic::amdgcn_atomic_inc: case Intrinsic::amdgcn_atomic_dec: { auto *Ordering = dyn_cast(Inst->getArgOperand(2)); auto *Volatile = dyn_cast(Inst->getArgOperand(4)); if (!Ordering || !Volatile) return false; // Invalid. unsigned OrderingVal = Ordering->getZExtValue(); if (OrderingVal > static_cast(AtomicOrdering::SequentiallyConsistent)) return false; Info.PtrVal = Inst->getArgOperand(0); Info.Ordering = static_cast(OrderingVal); Info.ReadMem = true; Info.WriteMem = true; Info.IsVolatile = !Volatile->isNullValue(); return true; } default: return false; } } int AMDGPUTTIImpl::getArithmeticInstrCost( unsigned Opcode, Type *Ty, TTI::OperandValueKind Opd1Info, TTI::OperandValueKind Opd2Info, TTI::OperandValueProperties Opd1PropInfo, TTI::OperandValueProperties Opd2PropInfo, ArrayRef Args ) { EVT OrigTy = TLI->getValueType(DL, Ty); if (!OrigTy.isSimple()) { return BaseT::getArithmeticInstrCost(Opcode, Ty, Opd1Info, Opd2Info, Opd1PropInfo, Opd2PropInfo); } // Legalize the type. std::pair LT = TLI->getTypeLegalizationCost(DL, Ty); int ISD = TLI->InstructionOpcodeToISD(Opcode); // Because we don't have any legal vector operations, but the legal types, we // need to account for split vectors. unsigned NElts = LT.second.isVector() ? LT.second.getVectorNumElements() : 1; MVT::SimpleValueType SLT = LT.second.getScalarType().SimpleTy; switch (ISD) { case ISD::SHL: case ISD::SRL: case ISD::SRA: if (SLT == MVT::i64) return get64BitInstrCost() * LT.first * NElts; // i32 return getFullRateInstrCost() * LT.first * NElts; case ISD::ADD: case ISD::SUB: case ISD::AND: case ISD::OR: case ISD::XOR: if (SLT == MVT::i64){ // and, or and xor are typically split into 2 VALU instructions. return 2 * getFullRateInstrCost() * LT.first * NElts; } return LT.first * NElts * getFullRateInstrCost(); case ISD::MUL: { const int QuarterRateCost = getQuarterRateInstrCost(); if (SLT == MVT::i64) { const int FullRateCost = getFullRateInstrCost(); return (4 * QuarterRateCost + (2 * 2) * FullRateCost) * LT.first * NElts; } // i32 return QuarterRateCost * NElts * LT.first; } case ISD::FADD: case ISD::FSUB: case ISD::FMUL: if (SLT == MVT::f64) return LT.first * NElts * get64BitInstrCost(); if (SLT == MVT::f32 || SLT == MVT::f16) return LT.first * NElts * getFullRateInstrCost(); break; case ISD::FDIV: case ISD::FREM: // FIXME: frem should be handled separately. The fdiv in it is most of it, // but the current lowering is also not entirely correct. if (SLT == MVT::f64) { int Cost = 4 * get64BitInstrCost() + 7 * getQuarterRateInstrCost(); // Add cost of workaround. if (ST->getGeneration() == AMDGPUSubtarget::SOUTHERN_ISLANDS) Cost += 3 * getFullRateInstrCost(); return LT.first * Cost * NElts; } if (!Args.empty() && match(Args[0], PatternMatch::m_FPOne())) { // TODO: This is more complicated, unsafe flags etc. if ((SLT == MVT::f32 && !ST->hasFP32Denormals()) || (SLT == MVT::f16 && ST->has16BitInsts())) { return LT.first * getQuarterRateInstrCost() * NElts; } } if (SLT == MVT::f16 && ST->has16BitInsts()) { // 2 x v_cvt_f32_f16 // f32 rcp // f32 fmul // v_cvt_f16_f32 // f16 div_fixup int Cost = 4 * getFullRateInstrCost() + 2 * getQuarterRateInstrCost(); return LT.first * Cost * NElts; } if (SLT == MVT::f32 || SLT == MVT::f16) { int Cost = 7 * getFullRateInstrCost() + 1 * getQuarterRateInstrCost(); if (!ST->hasFP32Denormals()) { // FP mode switches. Cost += 2 * getFullRateInstrCost(); } return LT.first * NElts * Cost; } break; default: break; } return BaseT::getArithmeticInstrCost(Opcode, Ty, Opd1Info, Opd2Info, Opd1PropInfo, Opd2PropInfo); } unsigned AMDGPUTTIImpl::getCFInstrCost(unsigned Opcode) { // XXX - For some reason this isn't called for switch. switch (Opcode) { case Instruction::Br: case Instruction::Ret: return 10; default: return BaseT::getCFInstrCost(Opcode); } } int AMDGPUTTIImpl::getVectorInstrCost(unsigned Opcode, Type *ValTy, unsigned Index) { switch (Opcode) { case Instruction::ExtractElement: case Instruction::InsertElement: { unsigned EltSize = DL.getTypeSizeInBits(cast(ValTy)->getElementType()); if (EltSize < 32) { if (EltSize == 16 && Index == 0 && ST->has16BitInsts()) return 0; return BaseT::getVectorInstrCost(Opcode, ValTy, Index); } // Extracts are just reads of a subregister, so are free. Inserts are // considered free because we don't want to have any cost for scalarizing // operations, and we don't have to copy into a different register class. // Dynamic indexing isn't free and is best avoided. return Index == ~0u ? 2 : 0; } default: return BaseT::getVectorInstrCost(Opcode, ValTy, Index); } } static bool isIntrinsicSourceOfDivergence(const IntrinsicInst *I) { switch (I->getIntrinsicID()) { case Intrinsic::amdgcn_workitem_id_x: case Intrinsic::amdgcn_workitem_id_y: case Intrinsic::amdgcn_workitem_id_z: case Intrinsic::amdgcn_interp_mov: case Intrinsic::amdgcn_interp_p1: case Intrinsic::amdgcn_interp_p2: case Intrinsic::amdgcn_mbcnt_hi: case Intrinsic::amdgcn_mbcnt_lo: case Intrinsic::r600_read_tidig_x: case Intrinsic::r600_read_tidig_y: case Intrinsic::r600_read_tidig_z: case Intrinsic::amdgcn_atomic_inc: case Intrinsic::amdgcn_atomic_dec: case Intrinsic::amdgcn_image_atomic_swap: case Intrinsic::amdgcn_image_atomic_add: case Intrinsic::amdgcn_image_atomic_sub: case Intrinsic::amdgcn_image_atomic_smin: case Intrinsic::amdgcn_image_atomic_umin: case Intrinsic::amdgcn_image_atomic_smax: case Intrinsic::amdgcn_image_atomic_umax: case Intrinsic::amdgcn_image_atomic_and: case Intrinsic::amdgcn_image_atomic_or: case Intrinsic::amdgcn_image_atomic_xor: case Intrinsic::amdgcn_image_atomic_inc: case Intrinsic::amdgcn_image_atomic_dec: case Intrinsic::amdgcn_image_atomic_cmpswap: case Intrinsic::amdgcn_buffer_atomic_swap: case Intrinsic::amdgcn_buffer_atomic_add: case Intrinsic::amdgcn_buffer_atomic_sub: case Intrinsic::amdgcn_buffer_atomic_smin: case Intrinsic::amdgcn_buffer_atomic_umin: case Intrinsic::amdgcn_buffer_atomic_smax: case Intrinsic::amdgcn_buffer_atomic_umax: case Intrinsic::amdgcn_buffer_atomic_and: case Intrinsic::amdgcn_buffer_atomic_or: case Intrinsic::amdgcn_buffer_atomic_xor: case Intrinsic::amdgcn_buffer_atomic_cmpswap: case Intrinsic::amdgcn_ps_live: case Intrinsic::amdgcn_ds_swizzle: return true; default: return false; } } static bool isArgPassedInSGPR(const Argument *A) { const Function *F = A->getParent(); // Arguments to compute shaders are never a source of divergence. CallingConv::ID CC = F->getCallingConv(); switch (CC) { case CallingConv::AMDGPU_KERNEL: case CallingConv::SPIR_KERNEL: return true; case CallingConv::AMDGPU_VS: case CallingConv::AMDGPU_LS: case CallingConv::AMDGPU_HS: case CallingConv::AMDGPU_ES: case CallingConv::AMDGPU_GS: case CallingConv::AMDGPU_PS: case CallingConv::AMDGPU_CS: // For non-compute shaders, SGPR inputs are marked with either inreg or byval. // Everything else is in VGPRs. return F->getAttributes().hasParamAttribute(A->getArgNo(), Attribute::InReg) || F->getAttributes().hasParamAttribute(A->getArgNo(), Attribute::ByVal); default: // TODO: Should calls support inreg for SGPR inputs? return false; } } /// \returns true if the result of the value could potentially be /// different across workitems in a wavefront. bool AMDGPUTTIImpl::isSourceOfDivergence(const Value *V) const { if (const Argument *A = dyn_cast(V)) return !isArgPassedInSGPR(A); // Loads from the private address space are divergent, because threads // can execute the load instruction with the same inputs and get different // results. // // All other loads are not divergent, because if threads issue loads with the // same arguments, they will always get the same result. if (const LoadInst *Load = dyn_cast(V)) return Load->getPointerAddressSpace() == ST->getAMDGPUAS().PRIVATE_ADDRESS; // Atomics are divergent because they are executed sequentially: when an // atomic operation refers to the same address in each thread, then each // thread after the first sees the value written by the previous thread as // original value. if (isa(V) || isa(V)) return true; if (const IntrinsicInst *Intrinsic = dyn_cast(V)) return isIntrinsicSourceOfDivergence(Intrinsic); // Assume all function calls are a source of divergence. if (isa(V) || isa(V)) return true; return false; } bool AMDGPUTTIImpl::isAlwaysUniform(const Value *V) const { if (const IntrinsicInst *Intrinsic = dyn_cast(V)) { switch (Intrinsic->getIntrinsicID()) { default: return false; case Intrinsic::amdgcn_readfirstlane: case Intrinsic::amdgcn_readlane: return true; } } return false; } unsigned AMDGPUTTIImpl::getShuffleCost(TTI::ShuffleKind Kind, Type *Tp, int Index, Type *SubTp) { if (ST->hasVOP3PInsts()) { VectorType *VT = cast(Tp); if (VT->getNumElements() == 2 && DL.getTypeSizeInBits(VT->getElementType()) == 16) { // With op_sel VOP3P instructions freely can access the low half or high // half of a register, so any swizzle is free. switch (Kind) { case TTI::SK_Broadcast: case TTI::SK_Reverse: case TTI::SK_PermuteSingleSrc: return 0; default: break; } } } return BaseT::getShuffleCost(Kind, Tp, Index, SubTp); } bool AMDGPUTTIImpl::areInlineCompatible(const Function *Caller, const Function *Callee) const { const TargetMachine &TM = getTLI()->getTargetMachine(); const FeatureBitset &CallerBits = TM.getSubtargetImpl(*Caller)->getFeatureBits(); const FeatureBitset &CalleeBits = TM.getSubtargetImpl(*Callee)->getFeatureBits(); FeatureBitset RealCallerBits = CallerBits & ~InlineFeatureIgnoreList; FeatureBitset RealCalleeBits = CalleeBits & ~InlineFeatureIgnoreList; return ((RealCallerBits & RealCalleeBits) == RealCalleeBits); }