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/*========================== begin_copyright_notice ============================
Copyright (C) 2017-2021 Intel Corporation
SPDX-License-Identifier: MIT
============================= end_copyright_notice ===========================*/
#include "PullConstantHeuristics.hpp"
#include "Platform.hpp"
using namespace llvm;
using namespace IGC;
static const unsigned EUInstCycleCount = 2;
static const unsigned SendInstCycleCount = 190;
static const unsigned RTWriteInstCycleCount = 190;
char PullConstantHeuristics::ID = 0;
#define PASS_FLAG "Analyse shader to determine push const threshold"
#define PASS_DESCRIPTION "This is an analysis pass for pulling constants for short shaders "
#define PASS_CFG_ONLY true
#define PASS_ANALYSIS true
IGC_INITIALIZE_PASS_BEGIN(PullConstantHeuristics, PASS_FLAG, PASS_DESCRIPTION, PASS_CFG_ONLY, PASS_ANALYSIS)
IGC_INITIALIZE_PASS_DEPENDENCY(CodeGenContextWrapper)
IGC_INITIALIZE_PASS_END(PullConstantHeuristics, PASS_FLAG, PASS_DESCRIPTION, PASS_CFG_ONLY, PASS_ANALYSIS)
//needs to be fine-tuned after obtaining feedback from visa
static unsigned estimateShaderLifetime(unsigned int EUCnt, unsigned SendMsgCnt, unsigned RTWriteCnt)
{
return EUCnt * EUInstCycleCount + SendMsgCnt * SendInstCycleCount + RTWriteCnt * RTWriteInstCycleCount;
}
static bool isSendMessage(GenIntrinsicInst* inst)
{
if (isSampleInstruction(inst) || isSampleLoadGather4InfoInstruction(inst))
{
return true;
}
return false;
}
//approximating EU insts count - TODO: need a better way to do this
static unsigned getEUInstEstimate(Instruction* inst)
{
//handle ALU, Logical, and load-store insts
//Presently we're restricting to shaders with 1 BB only, i.e, short shaders
//But this handles branch insts as well (in case of multiple BB support in future)
if (inst->getOpcode() <= Instruction::Fence)
{
return 1;
}
//handling remaining inst types
switch (inst->getOpcode())
{
case Instruction::FCmp:
case Instruction::ICmp:
case Instruction::Select:
case Instruction::Ret:
return 1;
default:
//bitcast insts don't make an EU inst in visa
return 0;
}
}
//estimate EU, SendMsg and RTWrite insts required by the PS
static std::tuple<unsigned, unsigned, unsigned> getInstStats(const Function& F) {
unsigned EUInstCnt = 0;
unsigned int SendMsgInstCnt = 0;
unsigned int RTWriteInstCnt = 0;
for (auto BBI = F.getBasicBlockList().begin(); BBI != F.getBasicBlockList().end(); BBI++)
{
llvm::BasicBlock* BB = const_cast<llvm::BasicBlock*>(&*BBI);
for (auto II = BB->begin(); II != BB->end(); II++)
{
if (llvm::GenIntrinsicInst * pIntrinsic = llvm::dyn_cast<llvm::GenIntrinsicInst>(II))
{
if (isSendMessage(pIntrinsic))
SendMsgInstCnt++;
else if (pIntrinsic->getIntrinsicID() == GenISAIntrinsic::GenISA_RTWrite)
RTWriteInstCnt++;
}
else
{
EUInstCnt += getEUInstEstimate(&*II);
}
}
}
return std::make_tuple(EUInstCnt, SendMsgInstCnt, RTWriteInstCnt);
}
//Pixel Shader Dispatch can be bottleneck if
// thread_payload_size > max(simd4_sample_instr, simd4_eu_instr / 16, simd4_rt_write * 2, shader_lifetime / 56)
unsigned int PullConstantHeuristics::getPSDBottleNeckThreshold(const Function& F)
{
CodeGenContext* ctx = nullptr;
ctx = getAnalysis<CodeGenContextWrapper>().getCodeGenContext();
const unsigned numThreadsPerSubslice = ctx->platform.getMaxNumberThreadPerSubslice(); //read from ctx.platform
const unsigned roofLineIPC = 16;
const unsigned pixelRate = 2;
unsigned EstimatedEUInstCnt = 0;
unsigned SendMsgInstCnt = 0;
unsigned RTWriteInstCnt = 0;
std::tie(EstimatedEUInstCnt, SendMsgInstCnt, RTWriteInstCnt) = getInstStats(F);
unsigned shaderLifetime = estimateShaderLifetime(EstimatedEUInstCnt, SendMsgInstCnt, RTWriteInstCnt);
//calculate payload size threshold assuming SIMD16 to stop pushing constants
unsigned SIMD4_EU_Cnt = EstimatedEUInstCnt * 4;
unsigned SIMD4_Sample_Cnt = SendMsgInstCnt * 4;
unsigned SIMD4_RT_Write_Cnt = RTWriteInstCnt * 4;
unsigned payloadThreshold = std::max(std::max(SIMD4_Sample_Cnt, SIMD4_EU_Cnt / roofLineIPC),
std::max(SIMD4_RT_Write_Cnt * pixelRate, shaderLifetime / numThreadsPerSubslice));
return payloadThreshold;
}
//currentPayloadSize = payloadHeaderSIMD16 + payloadBarySIMD16 + inputSize;
//
static unsigned getCurrentPayloadSizeEstimate(const Function& F)
{
unsigned payloadHeaderSIMD16 = 3;
unsigned payloadBarySIMD16 = 4;
unsigned inputGRFSize = 1;
//helper variables
unsigned maxValueFromInputVec = 0;
std::set<unsigned> countOfDifferentBary;
for (auto BBI = F.getBasicBlockList().begin(); BBI != F.getBasicBlockList().end(); BBI++)
{
llvm::BasicBlock* BB = const_cast<llvm::BasicBlock*>(&*BBI);
for (auto II = BB->begin(); II != BB->end(); II++)
{
if (llvm::GenIntrinsicInst * pIntrinsic = llvm::dyn_cast<llvm::GenIntrinsicInst>(II))
{
if (pIntrinsic->getIntrinsicID() == GenISAIntrinsic::GenISA_DCL_inputVec)
{
countOfDifferentBary.insert((unsigned)llvm::cast<llvm::ConstantInt>(II->getOperand(1))->getZExtValue());
maxValueFromInputVec = std::max(maxValueFromInputVec, (unsigned)llvm::cast<llvm::ConstantInt>(II->getOperand(0))->getZExtValue());
}
}
}
}
payloadBarySIMD16 = countOfDifferentBary.size() * 4;
inputGRFSize = (unsigned)(maxValueFromInputVec / 2) % 2 == 0 ? (maxValueFromInputVec / 2) : ((maxValueFromInputVec / 2) + 1);
return payloadHeaderSIMD16 + payloadBarySIMD16 + inputGRFSize;
}
bool PullConstantHeuristics::runOnModule(Module& M)
{
if (IGC_IS_FLAG_ENABLED(DisablePullConstantHeuristics))
{
return false;
}
CodeGenContext* ctx = nullptr;
ctx = getAnalysis<CodeGenContextWrapper>().getCodeGenContext();
if (ctx->type == ShaderType::PIXEL_SHADER && ctx->platform.hasPSDBottleneck())
{
for (auto& F : M)
{
if (F.getBasicBlockList().size() == 1)
{
BasicBlock* BB = &(*F.begin());
if (BB->getInstList().size() < 200)
{//short shaders
int PSDBottleNeckThreshold = getPSDBottleNeckThreshold(F);
int PayloadWithoutConstants = getCurrentPayloadSizeEstimate(F);
int maxPayload_Regkey = (IGC_GET_FLAG_VALUE(PayloadSizeThreshold));
PSDBottleNeckThreshold = PSDBottleNeckThreshold > maxPayload_Regkey ?
maxPayload_Regkey : PSDBottleNeckThreshold;
int threshold = PSDBottleNeckThreshold - PayloadWithoutConstants;
threshold = threshold < 0 ? 0 : threshold;
thresholdMap.insert(std::make_pair(&F, threshold));
}
}
}
}
return false;//does not modify IR
}
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