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//===- llvm/CodeGen/BasicBlockMatchingAndInference.cpp ----------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// In Propeller's profile, we have already read the hash values of basic blocks,
// as well as the weights of basic blocks and edges in the CFG. In this file,
// we first match the basic blocks in the profile with those in the current
// MachineFunction using the basic block hash, thereby obtaining the weights of
// some basic blocks and edges. Subsequently, we infer the weights of all basic
// blocks using an inference algorithm.
//
// TODO: Integrate part of the code in this file with BOLT's implementation into
// the LLVM infrastructure, enabling both BOLT and Propeller to reuse it.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/BasicBlockMatchingAndInference.h"
#include "llvm/CodeGen/BasicBlockSectionsProfileReader.h"
#include "llvm/CodeGen/MachineBlockHashInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/InitializePasses.h"
#include <llvm/Support/CommandLine.h>
#include <unordered_map>
using namespace llvm;
static cl::opt<float>
PropellerInferThreshold("propeller-infer-threshold",
cl::desc("Threshold for infer stale profile"),
cl::init(0.6), cl::Optional);
/// The object is used to identify and match basic blocks given their hashes.
class StaleMatcher {
public:
/// Initialize stale matcher.
void init(const std::vector<MachineBasicBlock *> &Blocks,
const std::vector<BlendedBlockHash> &Hashes) {
assert(Blocks.size() == Hashes.size() &&
"incorrect matcher initialization");
for (size_t I = 0; I < Blocks.size(); I++) {
MachineBasicBlock *Block = Blocks[I];
uint16_t OpHash = Hashes[I].getOpcodeHash();
OpHashToBlocks[OpHash].push_back(std::make_pair(Hashes[I], Block));
}
}
/// Find the most similar block for a given hash.
MachineBasicBlock *matchBlock(BlendedBlockHash BlendedHash) const {
auto BlockIt = OpHashToBlocks.find(BlendedHash.getOpcodeHash());
if (BlockIt == OpHashToBlocks.end()) {
return nullptr;
}
MachineBasicBlock *BestBlock = nullptr;
uint64_t BestDist = std::numeric_limits<uint64_t>::max();
for (auto It : BlockIt->second) {
MachineBasicBlock *Block = It.second;
BlendedBlockHash Hash = It.first;
uint64_t Dist = Hash.distance(BlendedHash);
if (BestBlock == nullptr || Dist < BestDist) {
BestDist = Dist;
BestBlock = Block;
}
}
return BestBlock;
}
private:
using HashBlockPairType = std::pair<BlendedBlockHash, MachineBasicBlock *>;
std::unordered_map<uint16_t, std::vector<HashBlockPairType>> OpHashToBlocks;
};
INITIALIZE_PASS_BEGIN(BasicBlockMatchingAndInference,
"machine-block-match-infer",
"Machine Block Matching and Inference Analysis", true,
true)
INITIALIZE_PASS_DEPENDENCY(MachineBlockHashInfo)
INITIALIZE_PASS_DEPENDENCY(BasicBlockSectionsProfileReaderWrapperPass)
INITIALIZE_PASS_END(BasicBlockMatchingAndInference, "machine-block-match-infer",
"Machine Block Matching and Inference Analysis", true, true)
char BasicBlockMatchingAndInference::ID = 0;
BasicBlockMatchingAndInference::BasicBlockMatchingAndInference()
: MachineFunctionPass(ID) {
initializeBasicBlockMatchingAndInferencePass(
*PassRegistry::getPassRegistry());
}
void BasicBlockMatchingAndInference::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<MachineBlockHashInfo>();
AU.addRequired<BasicBlockSectionsProfileReaderWrapperPass>();
AU.setPreservesAll();
MachineFunctionPass::getAnalysisUsage(AU);
}
std::optional<BasicBlockMatchingAndInference::WeightInfo>
BasicBlockMatchingAndInference::getWeightInfo(StringRef FuncName) const {
auto It = ProgramWeightInfo.find(FuncName);
if (It == ProgramWeightInfo.end()) {
return std::nullopt;
}
return It->second;
}
BasicBlockMatchingAndInference::WeightInfo
BasicBlockMatchingAndInference::initWeightInfoByMatching(MachineFunction &MF) {
std::vector<MachineBasicBlock *> Blocks;
std::vector<BlendedBlockHash> Hashes;
auto BSPR = &getAnalysis<BasicBlockSectionsProfileReaderWrapperPass>();
auto MBHI = &getAnalysis<MachineBlockHashInfo>();
for (auto &Block : MF) {
Blocks.push_back(&Block);
Hashes.push_back(BlendedBlockHash(MBHI->getMBBHash(Block)));
}
StaleMatcher Matcher;
Matcher.init(Blocks, Hashes);
BasicBlockMatchingAndInference::WeightInfo MatchWeight;
auto [IsValid, PathAndClusterInfo] =
BSPR->getFunctionPathAndClusterInfo(MF.getName());
if (!IsValid)
return MatchWeight;
for (auto &BlockCount : PathAndClusterInfo.NodeCounts) {
if (PathAndClusterInfo.BBHashes.count(BlockCount.first.BaseID)) {
auto Hash = PathAndClusterInfo.BBHashes[BlockCount.first.BaseID];
MachineBasicBlock *Block = Matcher.matchBlock(BlendedBlockHash(Hash));
// When a basic block has clone copies, sum their counts.
if (Block != nullptr)
MatchWeight.BlockWeights[Block] += BlockCount.second;
}
}
for (auto &PredItem : PathAndClusterInfo.EdgeCounts) {
auto PredID = PredItem.first.BaseID;
if (!PathAndClusterInfo.BBHashes.count(PredID))
continue;
auto PredHash = PathAndClusterInfo.BBHashes[PredID];
MachineBasicBlock *PredBlock =
Matcher.matchBlock(BlendedBlockHash(PredHash));
if (PredBlock == nullptr)
continue;
for (auto &SuccItem : PredItem.second) {
auto SuccID = SuccItem.first.BaseID;
auto EdgeWeight = SuccItem.second;
if (PathAndClusterInfo.BBHashes.count(SuccID)) {
auto SuccHash = PathAndClusterInfo.BBHashes[SuccID];
MachineBasicBlock *SuccBlock =
Matcher.matchBlock(BlendedBlockHash(SuccHash));
// When an edge has clone copies, sum their counts.
if (SuccBlock != nullptr)
MatchWeight.EdgeWeights[std::make_pair(PredBlock, SuccBlock)] +=
EdgeWeight;
}
}
}
return MatchWeight;
}
void BasicBlockMatchingAndInference::generateWeightInfoByInference(
MachineFunction &MF,
BasicBlockMatchingAndInference::WeightInfo &MatchWeight) {
BlockEdgeMap Successors;
for (auto &Block : MF) {
for (auto *Succ : Block.successors())
Successors[&Block].push_back(Succ);
}
SampleProfileInference<MachineFunction> SPI(
MF, Successors, MatchWeight.BlockWeights, MatchWeight.EdgeWeights);
BlockWeightMap BlockWeights;
EdgeWeightMap EdgeWeights;
SPI.apply(BlockWeights, EdgeWeights);
ProgramWeightInfo.try_emplace(
MF.getName(), BasicBlockMatchingAndInference::WeightInfo{
std::move(BlockWeights), std::move(EdgeWeights)});
}
bool BasicBlockMatchingAndInference::runOnMachineFunction(MachineFunction &MF) {
if (MF.empty())
return false;
auto MatchWeight = initWeightInfoByMatching(MF);
// If the ratio of the number of MBBs in matching to the total number of MBBs
// in the function is less than the threshold value, the processing should be
// abandoned.
if (static_cast<float>(MatchWeight.BlockWeights.size()) / MF.size() <
PropellerInferThreshold) {
return false;
}
generateWeightInfoByInference(MF, MatchWeight);
return false;
}
MachineFunctionPass *llvm::createBasicBlockMatchingAndInferencePass() {
return new BasicBlockMatchingAndInference();
}
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