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llvm-project/llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp

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//===-- 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 "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/CodeGen/BasicTTIImpl.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/Debug.h"
#include "llvm/Target/CostTable.h"
#include "llvm/Target/TargetLowering.h"
using namespace llvm;
#define DEBUG_TYPE "AMDGPUtti"
static cl::opt<unsigned> 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<unsigned> 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<unsigned> 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<Instruction>(Cond);
if (!I)
return false;
for (const Value *V : I->operand_values()) {
if (!L->contains(I))
continue;
if (const PHINode *PHI = dyn_cast<PHINode>(V)) {
if (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,
TTI::UnrollingPreferences &UP) {
UP.Threshold = 300; // Twice the default.
UP.MaxCount = UINT_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 (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<BranchInst>(&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<GetElementPtrInst>(&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<AllocaInst>(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<GlobalVariable>(GEP->getPointerOperand()) &&
!isa<Argument>(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<Instruction>(Op);
if (!Inst || L->isLoopInvariant(Op))
continue;
if (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;
}
int AMDGPUTTIImpl::getArithmeticInstrCost(
unsigned Opcode, Type *Ty, TTI::OperandValueKind Opd1Info,
TTI::OperandValueKind Opd2Info, TTI::OperandValueProperties Opd1PropInfo,
TTI::OperandValueProperties Opd2PropInfo, ArrayRef<const Value *> Args ) {
EVT OrigTy = TLI->getValueType(DL, Ty);
if (!OrigTy.isSimple()) {
return BaseT::getArithmeticInstrCost(Opcode, Ty, Opd1Info, Opd2Info,
Opd1PropInfo, Opd2PropInfo);
}
// Legalize the type.
std::pair<int, MVT> 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;
}
// Assuming no fp32 denormals lowering.
if (SLT == MVT::f32 || SLT == MVT::f16) {
assert(!ST->hasFP32Denormals() && "will change when supported");
int Cost = 7 * getFullRateInstrCost() + 1 * getQuarterRateInstrCost();
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<VectorType>(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_HS:
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<Argument>(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<LoadInst>(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<AtomicRMWInst>(V) || isa<AtomicCmpXchgInst>(V))
return true;
if (const IntrinsicInst *Intrinsic = dyn_cast<IntrinsicInst>(V))
return isIntrinsicSourceOfDivergence(Intrinsic);
// Assume all function calls are a source of divergence.
if (isa<CallInst>(V) || isa<InvokeInst>(V))
return true;
return false;
}
bool AMDGPUTTIImpl::isAlwaysUniform(const Value *V) const {
if (const IntrinsicInst *Intrinsic = dyn_cast<IntrinsicInst>(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<VectorType>(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);
}
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