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BinaryPasses.cpp
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//===--- BinaryPasses.cpp - Binary-level analysis/optimization passes -----===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
//===----------------------------------------------------------------------===//
#include "bolt/Passes/BinaryPasses.h"
#include "bolt/Core/ParallelUtilities.h"
#include "bolt/Passes/ReorderAlgorithm.h"
#include "bolt/Passes/ReorderFunctions.h"
#include "llvm/Support/CommandLine.h"
#include <numeric>
#include <vector>
#define DEBUG_TYPE "bolt-opts"
using namespace llvm;
using namespace bolt;
namespace {
const char* dynoStatsOptName(const bolt::DynoStats::Category C) {
if (C == bolt::DynoStats::FIRST_DYNO_STAT)
return "none";
else if (C == bolt::DynoStats::LAST_DYNO_STAT)
return "all";
static std::string OptNames[bolt::DynoStats::LAST_DYNO_STAT+1];
OptNames[C] = bolt::DynoStats::Description(C);
std::replace(OptNames[C].begin(), OptNames[C].end(), ' ', '-');
return OptNames[C].c_str();
}
const char* dynoStatsOptDesc(const bolt::DynoStats::Category C) {
if (C == bolt::DynoStats::FIRST_DYNO_STAT)
return "unsorted";
else if (C == bolt::DynoStats::LAST_DYNO_STAT)
return "sorted by all stats";
return bolt::DynoStats::Description(C);
}
}
namespace opts {
extern cl::OptionCategory BoltCategory;
extern cl::OptionCategory BoltOptCategory;
extern cl::opt<bolt::MacroFusionType> AlignMacroOpFusion;
extern cl::opt<unsigned> Verbosity;
extern cl::opt<bool> EnableBAT;
extern cl::opt<unsigned> ExecutionCountThreshold;
extern cl::opt<bool> UpdateDebugSections;
extern cl::opt<bolt::ReorderFunctions::ReorderType> ReorderFunctions;
enum DynoStatsSortOrder : char {
Ascending,
Descending
};
static cl::opt<DynoStatsSortOrder>
DynoStatsSortOrderOpt("print-sorted-by-order",
cl::desc("use ascending or descending order when printing functions "
"ordered by dyno stats"),
cl::ZeroOrMore,
cl::init(DynoStatsSortOrder::Descending),
cl::cat(BoltOptCategory));
cl::list<std::string>
HotTextMoveSections("hot-text-move-sections",
cl::desc("list of sections containing functions used for hugifying hot text. "
"BOLT makes sure these functions are not placed on the same page as "
"the hot text. (default=\'.stub,.mover\')."),
cl::value_desc("sec1,sec2,sec3,..."),
cl::CommaSeparated,
cl::ZeroOrMore,
cl::cat(BoltCategory));
bool isHotTextMover(const BinaryFunction &Function) {
for (std::string &SectionName : opts::HotTextMoveSections) {
if (Function.getOriginSectionName() &&
*Function.getOriginSectionName() == SectionName)
return true;
}
return false;
}
static cl::opt<bool>
MinBranchClusters("min-branch-clusters",
cl::desc("use a modified clustering algorithm geared towards minimizing "
"branches"),
cl::ZeroOrMore,
cl::Hidden,
cl::cat(BoltOptCategory));
enum PeepholeOpts : char {
PEEP_NONE = 0x0,
PEEP_SHORTEN = 0x1,
PEEP_DOUBLE_JUMPS = 0x2,
PEEP_TAILCALL_TRAPS = 0x4,
PEEP_USELESS_BRANCHES = 0x8,
PEEP_ALL = 0xf
};
static cl::list<PeepholeOpts>
Peepholes("peepholes",
cl::CommaSeparated,
cl::desc("enable peephole optimizations"),
cl::value_desc("opt1,opt2,opt3,..."),
cl::values(
clEnumValN(PEEP_NONE, "none", "disable peepholes"),
clEnumValN(PEEP_SHORTEN, "shorten", "perform instruction shortening"),
clEnumValN(PEEP_DOUBLE_JUMPS, "double-jumps",
"remove double jumps when able"),
clEnumValN(PEEP_TAILCALL_TRAPS, "tailcall-traps", "insert tail call traps"),
clEnumValN(PEEP_USELESS_BRANCHES, "useless-branches",
"remove useless conditional branches"),
clEnumValN(PEEP_ALL, "all", "enable all peephole optimizations")),
cl::ZeroOrMore,
cl::cat(BoltOptCategory));
static cl::opt<unsigned>
PrintFuncStat("print-function-statistics",
cl::desc("print statistics about basic block ordering"),
cl::init(0),
cl::ZeroOrMore,
cl::cat(BoltOptCategory));
static cl::list<bolt::DynoStats::Category>
PrintSortedBy("print-sorted-by",
cl::CommaSeparated,
cl::desc("print functions sorted by order of dyno stats"),
cl::value_desc("key1,key2,key3,..."),
cl::values(
#define D(name, ...) \
clEnumValN(bolt::DynoStats::name, \
dynoStatsOptName(bolt::DynoStats::name), \
dynoStatsOptDesc(bolt::DynoStats::name)),
DYNO_STATS
#undef D
clEnumValN(0xffff, ".", ".")
),
cl::ZeroOrMore,
cl::cat(BoltOptCategory));
static cl::opt<bool>
PrintUnknown("print-unknown",
cl::desc("print names of functions with unknown control flow"),
cl::init(false),
cl::ZeroOrMore,
cl::cat(BoltCategory),
cl::Hidden);
static cl::opt<bool>
PrintUnknownCFG("print-unknown-cfg",
cl::desc("dump CFG of functions with unknown control flow"),
cl::init(false),
cl::ZeroOrMore,
cl::cat(BoltCategory),
cl::ReallyHidden);
cl::opt<bolt::ReorderBasicBlocks::LayoutType> ReorderBlocks(
"reorder-blocks", cl::desc("change layout of basic blocks in a function"),
cl::init(bolt::ReorderBasicBlocks::LT_NONE),
cl::values(
clEnumValN(bolt::ReorderBasicBlocks::LT_NONE, "none",
"do not reorder basic blocks"),
clEnumValN(bolt::ReorderBasicBlocks::LT_REVERSE, "reverse",
"layout blocks in reverse order"),
clEnumValN(bolt::ReorderBasicBlocks::LT_OPTIMIZE, "normal",
"perform optimal layout based on profile"),
clEnumValN(bolt::ReorderBasicBlocks::LT_OPTIMIZE_BRANCH,
"branch-predictor",
"perform optimal layout prioritizing branch "
"predictions"),
clEnumValN(bolt::ReorderBasicBlocks::LT_OPTIMIZE_CACHE, "cache",
"perform optimal layout prioritizing I-cache "
"behavior"),
clEnumValN(bolt::ReorderBasicBlocks::LT_OPTIMIZE_EXT_TSP, "cache+",
"perform layout optimizing I-cache behavior"),
clEnumValN(bolt::ReorderBasicBlocks::LT_OPTIMIZE_EXT_TSP, "ext-tsp",
"perform layout optimizing I-cache behavior"),
clEnumValN(bolt::ReorderBasicBlocks::LT_OPTIMIZE_SHUFFLE,
"cluster-shuffle", "perform random layout of clusters")),
cl::ZeroOrMore, cl::cat(BoltOptCategory));
static cl::opt<unsigned>
ReportBadLayout("report-bad-layout",
cl::desc("print top <uint> functions with suboptimal code layout on input"),
cl::init(0),
cl::ZeroOrMore,
cl::Hidden,
cl::cat(BoltOptCategory));
static cl::opt<bool>
ReportStaleFuncs("report-stale",
cl::desc("print the list of functions with stale profile"),
cl::init(false),
cl::ZeroOrMore,
cl::Hidden,
cl::cat(BoltOptCategory));
enum SctcModes : char {
SctcAlways,
SctcPreserveDirection,
SctcHeuristic
};
static cl::opt<SctcModes>
SctcMode("sctc-mode",
cl::desc("mode for simplify conditional tail calls"),
cl::init(SctcAlways),
cl::values(clEnumValN(SctcAlways, "always", "always perform sctc"),
clEnumValN(SctcPreserveDirection,
"preserve",
"only perform sctc when branch direction is "
"preserved"),
clEnumValN(SctcHeuristic,
"heuristic",
"use branch prediction data to control sctc")),
cl::ZeroOrMore,
cl::cat(BoltOptCategory));
static cl::opt<unsigned>
StaleThreshold("stale-threshold",
cl::desc(
"maximum percentage of stale functions to tolerate (default: 100)"),
cl::init(100),
cl::Hidden,
cl::cat(BoltOptCategory));
static cl::opt<unsigned>
TSPThreshold("tsp-threshold",
cl::desc("maximum number of hot basic blocks in a function for which to use "
"a precise TSP solution while re-ordering basic blocks"),
cl::init(10),
cl::ZeroOrMore,
cl::Hidden,
cl::cat(BoltOptCategory));
static cl::opt<unsigned>
TopCalledLimit("top-called-limit",
cl::desc("maximum number of functions to print in top called "
"functions section"),
cl::init(100),
cl::ZeroOrMore,
cl::Hidden,
cl::cat(BoltCategory));
} // namespace opts
namespace llvm {
namespace bolt {
bool BinaryFunctionPass::shouldOptimize(const BinaryFunction &BF) const {
return BF.isSimple() &&
BF.getState() == BinaryFunction::State::CFG &&
!BF.isIgnored();
}
bool BinaryFunctionPass::shouldPrint(const BinaryFunction &BF) const {
return BF.isSimple() && !BF.isIgnored();
}
void EliminateUnreachableBlocks::runOnFunction(BinaryFunction& Function) {
if (Function.layout_size() > 0) {
unsigned Count;
uint64_t Bytes;
Function.markUnreachableBlocks();
LLVM_DEBUG({
for (BinaryBasicBlock *BB : Function.layout()) {
if (!BB->isValid()) {
dbgs() << "BOLT-INFO: UCE found unreachable block " << BB->getName()
<< " in function " << Function << "\n";
Function.dump();
}
}
});
std::tie(Count, Bytes) = Function.eraseInvalidBBs();
DeletedBlocks += Count;
DeletedBytes += Bytes;
if (Count) {
Modified.insert(&Function);
if (opts::Verbosity > 0) {
outs() << "BOLT-INFO: Removed " << Count
<< " dead basic block(s) accounting for " << Bytes
<< " bytes in function " << Function << '\n';
}
}
}
}
void EliminateUnreachableBlocks::runOnFunctions(BinaryContext &BC) {
for (auto &It : BC.getBinaryFunctions()) {
BinaryFunction &Function = It.second;
if (shouldOptimize(Function)) {
runOnFunction(Function);
}
}
outs() << "BOLT-INFO: UCE removed " << DeletedBlocks << " blocks and "
<< DeletedBytes << " bytes of code.\n";
}
bool ReorderBasicBlocks::shouldPrint(const BinaryFunction &BF) const {
return (BinaryFunctionPass::shouldPrint(BF) &&
opts::ReorderBlocks != ReorderBasicBlocks::LT_NONE);
}
bool ReorderBasicBlocks::shouldOptimize(const BinaryFunction &BF) const {
// Apply execution count threshold
if (BF.getKnownExecutionCount() < opts::ExecutionCountThreshold)
return false;
return BinaryFunctionPass::shouldOptimize(BF);
}
void ReorderBasicBlocks::runOnFunctions(BinaryContext &BC) {
if (opts::ReorderBlocks == ReorderBasicBlocks::LT_NONE)
return;
std::atomic<uint64_t> ModifiedFuncCount{0};
ParallelUtilities::WorkFuncTy WorkFun = [&](BinaryFunction &BF) {
modifyFunctionLayout(BF, opts::ReorderBlocks, opts::MinBranchClusters);
if (BF.hasLayoutChanged()) {
++ModifiedFuncCount;
}
};
ParallelUtilities::PredicateTy SkipFunc = [&](const BinaryFunction &BF) {
return !shouldOptimize(BF);
};
ParallelUtilities::runOnEachFunction(
BC, ParallelUtilities::SchedulingPolicy::SP_BB_LINEAR, WorkFun, SkipFunc,
"ReorderBasicBlocks");
outs() << "BOLT-INFO: basic block reordering modified layout of "
<< format("%zu (%.2lf%%) functions\n", ModifiedFuncCount.load(),
100.0 * ModifiedFuncCount.load() /
BC.getBinaryFunctions().size());
if (opts::PrintFuncStat > 0) {
raw_ostream &OS = outs();
// Copy all the values into vector in order to sort them
std::map<uint64_t, BinaryFunction &> ScoreMap;
auto &BFs = BC.getBinaryFunctions();
for (auto It = BFs.begin(); It != BFs.end(); ++It) {
ScoreMap.insert(std::pair<uint64_t, BinaryFunction &>(
It->second.getFunctionScore(), It->second));
}
OS << "\nBOLT-INFO: Printing Function Statistics:\n\n";
OS << " There are " << BFs.size() << " functions in total. \n";
OS << " Number of functions being modified: "
<< ModifiedFuncCount.load() << "\n";
OS << " User asks for detailed information on top "
<< opts::PrintFuncStat << " functions. (Ranked by function score)"
<< "\n\n";
uint64_t I = 0;
for (std::map<uint64_t, BinaryFunction &>::reverse_iterator
Rit = ScoreMap.rbegin();
Rit != ScoreMap.rend() && I < opts::PrintFuncStat; ++Rit, ++I) {
BinaryFunction &Function = Rit->second;
OS << " Information for function of top: " << (I + 1) << ": \n";
OS << " Function Score is: " << Function.getFunctionScore()
<< "\n";
OS << " There are " << Function.size()
<< " number of blocks in this function.\n";
OS << " There are " << Function.getInstructionCount()
<< " number of instructions in this function.\n";
OS << " The edit distance for this function is: "
<< Function.getEditDistance() << "\n\n";
}
}
}
void ReorderBasicBlocks::modifyFunctionLayout(BinaryFunction &BF,
LayoutType Type, bool MinBranchClusters) const {
if (BF.size() == 0 || Type == LT_NONE)
return;
BinaryFunction::BasicBlockOrderType NewLayout;
std::unique_ptr<ReorderAlgorithm> Algo;
// Cannot do optimal layout without profile.
if (Type != LT_REVERSE && !BF.hasValidProfile())
return;
if (Type == LT_REVERSE) {
Algo.reset(new ReverseReorderAlgorithm());
} else if (BF.size() <= opts::TSPThreshold && Type != LT_OPTIMIZE_SHUFFLE) {
// Work on optimal solution if problem is small enough
LLVM_DEBUG(dbgs() << "finding optimal block layout for " << BF << "\n");
Algo.reset(new TSPReorderAlgorithm());
} else {
LLVM_DEBUG(dbgs() << "running block layout heuristics on " << BF << "\n");
std::unique_ptr<ClusterAlgorithm> CAlgo;
if (MinBranchClusters)
CAlgo.reset(new MinBranchGreedyClusterAlgorithm());
else
CAlgo.reset(new PHGreedyClusterAlgorithm());
switch(Type) {
case LT_OPTIMIZE:
Algo.reset(new OptimizeReorderAlgorithm(std::move(CAlgo)));
break;
case LT_OPTIMIZE_BRANCH:
Algo.reset(new OptimizeBranchReorderAlgorithm(std::move(CAlgo)));
break;
case LT_OPTIMIZE_CACHE:
Algo.reset(new OptimizeCacheReorderAlgorithm(std::move(CAlgo)));
break;
case LT_OPTIMIZE_EXT_TSP:
Algo.reset(new ExtTSPReorderAlgorithm());
break;
case LT_OPTIMIZE_SHUFFLE:
Algo.reset(new RandomClusterReorderAlgorithm(std::move(CAlgo)));
break;
default:
llvm_unreachable("unexpected layout type");
}
}
Algo->reorderBasicBlocks(BF, NewLayout);
BF.updateBasicBlockLayout(NewLayout);
}
void FixupBranches::runOnFunctions(BinaryContext &BC) {
for (auto &It : BC.getBinaryFunctions()) {
BinaryFunction &Function = It.second;
if (!BC.shouldEmit(Function) || !Function.isSimple())
continue;
Function.fixBranches();
}
}
void FinalizeFunctions::runOnFunctions(BinaryContext &BC) {
ParallelUtilities::WorkFuncTy WorkFun = [&](BinaryFunction &BF) {
if (!BF.finalizeCFIState()) {
if (BC.HasRelocations) {
errs() << "BOLT-ERROR: unable to fix CFI state for function " << BF
<< ". Exiting.\n";
exit(1);
}
BF.setSimple(false);
return;
}
BF.setFinalized();
// Update exception handling information.
BF.updateEHRanges();
};
ParallelUtilities::PredicateTy SkipPredicate = [&](const BinaryFunction &BF) {
return !BC.shouldEmit(BF);
};
ParallelUtilities::runOnEachFunction(
BC, ParallelUtilities::SchedulingPolicy::SP_CONSTANT, WorkFun,
SkipPredicate, "FinalizeFunctions");
}
void CheckLargeFunctions::runOnFunctions(BinaryContext &BC) {
if (BC.HasRelocations)
return;
if (!opts::UpdateDebugSections)
return;
// If the function wouldn't fit, mark it as non-simple. Otherwise, we may emit
// incorrect debug info.
ParallelUtilities::WorkFuncTy WorkFun = [&](BinaryFunction &BF) {
uint64_t HotSize, ColdSize;
std::tie(HotSize, ColdSize) =
BC.calculateEmittedSize(BF, /*FixBranches=*/false);
if (HotSize > BF.getMaxSize())
BF.setSimple(false);
};
ParallelUtilities::PredicateTy SkipFunc = [&](const BinaryFunction &BF) {
return !shouldOptimize(BF);
};
ParallelUtilities::runOnEachFunction(
BC, ParallelUtilities::SchedulingPolicy::SP_INST_LINEAR, WorkFun,
SkipFunc, "CheckLargeFunctions");
}
bool CheckLargeFunctions::shouldOptimize(const BinaryFunction &BF) const {
// Unlike other passes, allow functions in non-CFG state.
return BF.isSimple() && !BF.isIgnored();
}
void LowerAnnotations::runOnFunctions(BinaryContext &BC) {
std::vector<std::pair<MCInst *, uint32_t>> PreservedOffsetAnnotations;
for (auto &It : BC.getBinaryFunctions()) {
BinaryFunction &BF = It.second;
int64_t CurrentGnuArgsSize = 0;
// Have we crossed hot/cold border for split functions?
bool SeenCold = false;
for (BinaryBasicBlock *BB : BF.layout()) {
if (BB->isCold() && !SeenCold) {
SeenCold = true;
CurrentGnuArgsSize = 0;
}
// First convert GnuArgsSize annotations into CFIs. This may change instr
// pointers, so do it before recording ptrs for preserved annotations
if (BF.usesGnuArgsSize()) {
for (auto II = BB->begin(); II != BB->end(); ++II) {
if (!BC.MIB->isInvoke(*II))
continue;
const int64_t NewGnuArgsSize = BC.MIB->getGnuArgsSize(*II);
assert(NewGnuArgsSize >= 0 && "expected non-negative GNU_args_size");
if (NewGnuArgsSize != CurrentGnuArgsSize) {
auto InsertII = BF.addCFIInstruction(BB, II,
MCCFIInstruction::createGnuArgsSize(nullptr, NewGnuArgsSize));
CurrentGnuArgsSize = NewGnuArgsSize;
II = std::next(InsertII);
}
}
}
// Now record preserved annotations separately and then strip annotations.
for (auto II = BB->begin(); II != BB->end(); ++II) {
if (BF.requiresAddressTranslation() &&
BC.MIB->hasAnnotation(*II, "Offset")) {
PreservedOffsetAnnotations.emplace_back(
&(*II), BC.MIB->getAnnotationAs<uint32_t>(*II, "Offset"));
}
BC.MIB->stripAnnotations(*II);
}
}
}
for (BinaryFunction *BF : BC.getInjectedBinaryFunctions()) {
for (BinaryBasicBlock &BB : *BF) {
for (MCInst &Instruction : BB) {
BC.MIB->stripAnnotations(Instruction);
}
}
}
// Release all memory taken by annotations
BC.MIB->freeAnnotations();
// Reinsert preserved annotations we need during code emission.
for (const std::pair<MCInst *, uint32_t> &Item : PreservedOffsetAnnotations)
BC.MIB->addAnnotation<uint32_t>(*Item.first, "Offset", Item.second);
}
namespace {
// This peephole fixes jump instructions that jump to another basic
// block with a single jump instruction, e.g.
//
// B0: ...
// jmp B1 (or jcc B1)
//
// B1: jmp B2
//
// ->
//
// B0: ...
// jmp B2 (or jcc B2)
//
uint64_t fixDoubleJumps(BinaryFunction &Function, bool MarkInvalid) {
uint64_t NumDoubleJumps = 0;
MCContext *Ctx = Function.getBinaryContext().Ctx.get();
MCPlusBuilder *MIB = Function.getBinaryContext().MIB.get();
for (BinaryBasicBlock &BB : Function) {
auto checkAndPatch = [&](BinaryBasicBlock *Pred,
BinaryBasicBlock *Succ,
const MCSymbol *SuccSym) {
// Ignore infinite loop jumps or fallthrough tail jumps.
if (Pred == Succ || Succ == &BB)
return false;
if (Succ) {
const MCSymbol *TBB = nullptr;
const MCSymbol *FBB = nullptr;
MCInst *CondBranch = nullptr;
MCInst *UncondBranch = nullptr;
bool Res = Pred->analyzeBranch(TBB, FBB, CondBranch, UncondBranch);
if(!Res) {
LLVM_DEBUG(dbgs() << "analyzeBranch failed in peepholes in block:\n";
Pred->dump());
return false;
}
Pred->replaceSuccessor(&BB, Succ);
// We must patch up any existing branch instructions to match up
// with the new successor.
assert((CondBranch || (!CondBranch && Pred->succ_size() == 1)) &&
"Predecessor block has inconsistent number of successors");
if (CondBranch && MIB->getTargetSymbol(*CondBranch) == BB.getLabel()) {
MIB->replaceBranchTarget(*CondBranch, Succ->getLabel(), Ctx);
} else if (UncondBranch &&
MIB->getTargetSymbol(*UncondBranch) == BB.getLabel()) {
MIB->replaceBranchTarget(*UncondBranch, Succ->getLabel(), Ctx);
} else if (!UncondBranch) {
assert(Function.getBasicBlockAfter(Pred, false) != Succ &&
"Don't add an explicit jump to a fallthrough block.");
Pred->addBranchInstruction(Succ);
}
} else {
// Succ will be null in the tail call case. In this case we
// need to explicitly add a tail call instruction.
MCInst *Branch = Pred->getLastNonPseudoInstr();
if (Branch && MIB->isUnconditionalBranch(*Branch)) {
assert(MIB->getTargetSymbol(*Branch) == BB.getLabel());
Pred->removeSuccessor(&BB);
Pred->eraseInstruction(Pred->findInstruction(Branch));
Pred->addTailCallInstruction(SuccSym);
} else {
return false;
}
}
++NumDoubleJumps;
LLVM_DEBUG(dbgs() << "Removed double jump in " << Function << " from "
<< Pred->getName() << " -> " << BB.getName() << " to "
<< Pred->getName() << " -> " << SuccSym->getName()
<< (!Succ ? " (tail)\n" : "\n"));
return true;
};
if (BB.getNumNonPseudos() != 1 || BB.isLandingPad())
continue;
MCInst *Inst = BB.getFirstNonPseudoInstr();
const bool IsTailCall = MIB->isTailCall(*Inst);
if (!MIB->isUnconditionalBranch(*Inst) && !IsTailCall)
continue;
// If we operate after SCTC make sure it's not a conditional tail call.
if (IsTailCall && MIB->isConditionalBranch(*Inst))
continue;
const MCSymbol *SuccSym = MIB->getTargetSymbol(*Inst);
BinaryBasicBlock *Succ = BB.getSuccessor();
if (((!Succ || &BB == Succ) && !IsTailCall) || (IsTailCall && !SuccSym))
continue;
std::vector<BinaryBasicBlock *> Preds{BB.pred_begin(), BB.pred_end()};
for (BinaryBasicBlock *Pred : Preds) {
if (Pred->isLandingPad())
continue;
if (Pred->getSuccessor() == &BB ||
(Pred->getConditionalSuccessor(true) == &BB && !IsTailCall) ||
Pred->getConditionalSuccessor(false) == &BB) {
if (checkAndPatch(Pred, Succ, SuccSym) && MarkInvalid) {
BB.markValid(BB.pred_size() != 0 ||
BB.isLandingPad() ||
BB.isEntryPoint());
}
}
}
}
return NumDoubleJumps;
}
}
bool SimplifyConditionalTailCalls::shouldRewriteBranch(
const BinaryBasicBlock *PredBB,
const MCInst &CondBranch,
const BinaryBasicBlock *BB,
const bool DirectionFlag
) {
if (BeenOptimized.count(PredBB))
return false;
const bool IsForward = BinaryFunction::isForwardBranch(PredBB, BB);
if (IsForward)
++NumOrigForwardBranches;
else
++NumOrigBackwardBranches;
if (opts::SctcMode == opts::SctcAlways)
return true;
if (opts::SctcMode == opts::SctcPreserveDirection)
return IsForward == DirectionFlag;
const ErrorOr<std::pair<double, double>> Frequency =
PredBB->getBranchStats(BB);
// It's ok to rewrite the conditional branch if the new target will be
// a backward branch.
// If no data available for these branches, then it should be ok to
// do the optimization since it will reduce code size.
if (Frequency.getError())
return true;
// TODO: should this use misprediction frequency instead?
const bool Result =
(IsForward && Frequency.get().first >= 0.5) ||
(!IsForward && Frequency.get().first <= 0.5);
return Result == DirectionFlag;
}
uint64_t SimplifyConditionalTailCalls::fixTailCalls(BinaryFunction &BF) {
// Need updated indices to correctly detect branch' direction.
BF.updateLayoutIndices();
BF.markUnreachableBlocks();
MCPlusBuilder *MIB = BF.getBinaryContext().MIB.get();
MCContext *Ctx = BF.getBinaryContext().Ctx.get();
uint64_t NumLocalCTCCandidates = 0;
uint64_t NumLocalCTCs = 0;
uint64_t LocalCTCTakenCount = 0;
uint64_t LocalCTCExecCount = 0;
std::vector<std::pair<BinaryBasicBlock *,
const BinaryBasicBlock *>> NeedsUncondBranch;
// Will block be deleted by UCE?
auto isValid = [](const BinaryBasicBlock *BB) {
return (BB->pred_size() != 0 ||
BB->isLandingPad() ||
BB->isEntryPoint());
};
for (BinaryBasicBlock *BB : BF.layout()) {
// Locate BB with a single direct tail-call instruction.
if (BB->getNumNonPseudos() != 1)
continue;
MCInst *Instr = BB->getFirstNonPseudoInstr();
if (!MIB->isTailCall(*Instr) || MIB->isConditionalBranch(*Instr))
continue;
const MCSymbol *CalleeSymbol = MIB->getTargetSymbol(*Instr);
if (!CalleeSymbol)
continue;
// Detect direction of the possible conditional tail call.
const bool IsForwardCTC = BF.isForwardCall(CalleeSymbol);
// Iterate through all predecessors.
for (BinaryBasicBlock *PredBB : BB->predecessors()) {
BinaryBasicBlock *CondSucc = PredBB->getConditionalSuccessor(true);
if (!CondSucc)
continue;
++NumLocalCTCCandidates;
const MCSymbol *TBB = nullptr;
const MCSymbol *FBB = nullptr;
MCInst *CondBranch = nullptr;
MCInst *UncondBranch = nullptr;
bool Result = PredBB->analyzeBranch(TBB, FBB, CondBranch, UncondBranch);
// analyzeBranch() can fail due to unusual branch instructions, e.g. jrcxz
if (!Result) {
LLVM_DEBUG(dbgs() << "analyzeBranch failed in SCTC in block:\n";
PredBB->dump());
continue;
}
assert(Result && "internal error analyzing conditional branch");
assert(CondBranch && "conditional branch expected");
// It's possible that PredBB is also a successor to BB that may have
// been processed by a previous iteration of the SCTC loop, in which
// case it may have been marked invalid. We should skip rewriting in
// this case.
if (!PredBB->isValid()) {
assert(PredBB->isSuccessor(BB) &&
"PredBB should be valid if it is not a successor to BB");
continue;
}
// We don't want to reverse direction of the branch in new order
// without further profile analysis.
const bool DirectionFlag = CondSucc == BB ? IsForwardCTC : !IsForwardCTC;
if (!shouldRewriteBranch(PredBB, *CondBranch, BB, DirectionFlag))
continue;
// Record this block so that we don't try to optimize it twice.
BeenOptimized.insert(PredBB);
uint64_t Count = 0;
if (CondSucc != BB) {
// Patch the new target address into the conditional branch.
MIB->reverseBranchCondition(*CondBranch, CalleeSymbol, Ctx);
// Since we reversed the condition on the branch we need to change
// the target for the unconditional branch or add a unconditional
// branch to the old target. This has to be done manually since
// fixupBranches is not called after SCTC.
NeedsUncondBranch.emplace_back(PredBB, CondSucc);
Count = PredBB->getFallthroughBranchInfo().Count;
} else {
// Change destination of the conditional branch.
MIB->replaceBranchTarget(*CondBranch, CalleeSymbol, Ctx);
Count = PredBB->getTakenBranchInfo().Count;
}
const uint64_t CTCTakenFreq =
Count == BinaryBasicBlock::COUNT_NO_PROFILE ? 0 : Count;
// Annotate it, so "isCall" returns true for this jcc
MIB->setConditionalTailCall(*CondBranch);
// Add info abount the conditional tail call frequency, otherwise this
// info will be lost when we delete the associated BranchInfo entry
auto &CTCAnnotation =
MIB->getOrCreateAnnotationAs<uint64_t>(*CondBranch, "CTCTakenCount");
CTCAnnotation = CTCTakenFreq;
// Remove the unused successor which may be eliminated later
// if there are no other users.
PredBB->removeSuccessor(BB);
// Update BB execution count
if (CTCTakenFreq && CTCTakenFreq <= BB->getKnownExecutionCount()) {
BB->setExecutionCount(BB->getExecutionCount() - CTCTakenFreq);
} else if (CTCTakenFreq > BB->getKnownExecutionCount()) {
BB->setExecutionCount(0);
}
++NumLocalCTCs;
LocalCTCTakenCount += CTCTakenFreq;
LocalCTCExecCount += PredBB->getKnownExecutionCount();
}
// Remove the block from CFG if all predecessors were removed.
BB->markValid(isValid(BB));
}
// Add unconditional branches at the end of BBs to new successors
// as long as the successor is not a fallthrough.
for (auto &Entry : NeedsUncondBranch) {
BinaryBasicBlock *PredBB = Entry.first;
const BinaryBasicBlock *CondSucc = Entry.second;
const MCSymbol *TBB = nullptr;
const MCSymbol *FBB = nullptr;
MCInst *CondBranch = nullptr;
MCInst *UncondBranch = nullptr;
PredBB->analyzeBranch(TBB, FBB, CondBranch, UncondBranch);
// Find the next valid block. Invalid blocks will be deleted
// so they shouldn't be considered fallthrough targets.
const BinaryBasicBlock *NextBlock = BF.getBasicBlockAfter(PredBB, false);
while (NextBlock && !isValid(NextBlock)) {
NextBlock = BF.getBasicBlockAfter(NextBlock, false);
}
// Get the unconditional successor to this block.
const BinaryBasicBlock *PredSucc = PredBB->getSuccessor();
assert(PredSucc && "The other branch should be a tail call");
const bool HasFallthrough = (NextBlock && PredSucc == NextBlock);
if (UncondBranch) {
if (HasFallthrough)
PredBB->eraseInstruction(PredBB->findInstruction(UncondBranch));
else
MIB->replaceBranchTarget(*UncondBranch, CondSucc->getLabel(), Ctx);
} else if (!HasFallthrough) {
MCInst Branch;
MIB->createUncondBranch(Branch, CondSucc->getLabel(), Ctx);
PredBB->addInstruction(Branch);
}
}
if (NumLocalCTCs > 0) {
NumDoubleJumps += fixDoubleJumps(BF, true);
// Clean-up unreachable tail-call blocks.
const std::pair<unsigned, uint64_t> Stats = BF.eraseInvalidBBs();
DeletedBlocks += Stats.first;
DeletedBytes += Stats.second;
assert(BF.validateCFG());
}
LLVM_DEBUG(dbgs() << "BOLT: created " << NumLocalCTCs
<< " conditional tail calls from a total of "
<< NumLocalCTCCandidates << " candidates in function " << BF
<< ". CTCs execution count for this function is "
<< LocalCTCExecCount << " and CTC taken count is "
<< LocalCTCTakenCount << "\n";);
NumTailCallsPatched += NumLocalCTCs;
NumCandidateTailCalls += NumLocalCTCCandidates;
CTCExecCount += LocalCTCExecCount;
CTCTakenCount += LocalCTCTakenCount;
return NumLocalCTCs > 0;
}
void SimplifyConditionalTailCalls::runOnFunctions(BinaryContext &BC) {
if (!BC.isX86())
return;
for (auto &It : BC.getBinaryFunctions()) {
BinaryFunction &Function = It.second;
if (!shouldOptimize(Function))
continue;
if (fixTailCalls(Function)) {
Modified.insert(&Function);
Function.setHasCanonicalCFG(false);
}
}
outs() << "BOLT-INFO: SCTC: patched " << NumTailCallsPatched
<< " tail calls (" << NumOrigForwardBranches << " forward)"
<< " tail calls (" << NumOrigBackwardBranches << " backward)"
<< " from a total of " << NumCandidateTailCalls << " while removing "
<< NumDoubleJumps << " double jumps"
<< " and removing " << DeletedBlocks << " basic blocks"
<< " totalling " << DeletedBytes
<< " bytes of code. CTCs total execution count is " << CTCExecCount
<< " and the number of times CTCs are taken is " << CTCTakenCount
<< ".\n";
}
uint64_t Peepholes::shortenInstructions(BinaryContext &BC,
BinaryFunction &Function) {
MCInst DebugInst;
uint64_t Count = 0;
for (BinaryBasicBlock &BB : Function) {
for (MCInst &Inst : BB) {
if (opts::Verbosity > 1) {
DebugInst = Inst;
}
if (BC.MIB->shortenInstruction(Inst)) {
if (opts::Verbosity > 1) {
outs() << "BOLT-INFO: peephole, shortening:\n"
<< "BOLT-INFO: ";
BC.printInstruction(outs(), DebugInst, 0, &Function);
outs() << "BOLT-INFO: to:";
BC.printInstruction(outs(), Inst, 0, &Function);
}
++Count;
}
}
}
return Count;
}
void Peepholes::addTailcallTraps(BinaryFunction &Function) {
MCPlusBuilder *MIB = Function.getBinaryContext().MIB.get();
for (BinaryBasicBlock &BB : Function) {
MCInst *Inst = BB.getLastNonPseudoInstr();
if (Inst && MIB->isTailCall(*Inst) && MIB->isIndirectBranch(*Inst)) {
MCInst Trap;
if (MIB->createTrap(Trap)) {
BB.addInstruction(Trap);
++TailCallTraps;
}
}
}
}
void Peepholes::removeUselessCondBranches(BinaryFunction &Function) {
for (BinaryBasicBlock &BB : Function) {
if (BB.succ_size() != 2)
continue;
BinaryBasicBlock *CondBB = BB.getConditionalSuccessor(true);
BinaryBasicBlock *UncondBB = BB.getConditionalSuccessor(false);
if (CondBB != UncondBB)
continue;
const MCSymbol *TBB = nullptr;
const MCSymbol *FBB = nullptr;