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|
//===- bolt/Passes/JTFootprintReduction.cpp -------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// This file implements JTFootprintReduction class.
//
//===----------------------------------------------------------------------===//
#include "bolt/Passes/JTFootprintReduction.h"
#include "bolt/Passes/BinaryFunctionCallGraph.h"
#include "bolt/Passes/DataflowInfoManager.h"
#include "llvm/Support/CommandLine.h"
#define DEBUG_TYPE "JT"
using namespace llvm;
using namespace bolt;
namespace opts {
extern cl::OptionCategory BoltOptCategory;
extern cl::opt<unsigned> Verbosity;
extern cl::opt<JumpTableSupportLevel> JumpTables;
static cl::opt<bool> JTFootprintOnlyPIC(
"jt-footprint-optimize-for-icache",
cl::desc("with jt-footprint-reduction, only process PIC jumptables and turn"
" off other transformations that increase code size"),
cl::init(false), cl::ZeroOrMore, cl::cat(BoltOptCategory));
} // namespace opts
namespace llvm {
namespace bolt {
void JTFootprintReduction::checkOpportunities(BinaryFunction &Function,
DataflowInfoManager &Info) {
BinaryContext &BC = Function.getBinaryContext();
std::map<JumpTable *, uint64_t> AllJTs;
for (BinaryBasicBlock &BB : Function) {
for (MCInst &Inst : BB) {
JumpTable *JumpTable = Function.getJumpTable(Inst);
if (!JumpTable)
continue;
AllJTs[JumpTable] += BB.getKnownExecutionCount();
++IndJmps;
if (BlacklistedJTs.count(JumpTable)) {
++IndJmpsDenied;
continue;
}
uint64_t Scale;
// Try a standard indirect jump matcher
std::unique_ptr<MCPlusBuilder::MCInstMatcher> IndJmpMatcher =
BC.MIB->matchIndJmp(BC.MIB->matchAnyOperand(),
BC.MIB->matchImm(Scale), BC.MIB->matchReg(),
BC.MIB->matchAnyOperand());
if (!opts::JTFootprintOnlyPIC &&
IndJmpMatcher->match(*BC.MRI, *BC.MIB,
MutableArrayRef<MCInst>(&*BB.begin(), &Inst + 1),
-1) &&
Scale == 8) {
if (Info.getLivenessAnalysis().scavengeRegAfter(&Inst))
continue;
BlacklistedJTs.insert(JumpTable);
++IndJmpsDenied;
++NumJTsNoReg;
continue;
}
// Try a PIC matcher. The pattern we are looking for is a PIC JT ind jmp:
// addq %rdx, %rsi
// addq %rdx, %rdi
// leaq DATAat0x402450(%rip), %r11
// movslq (%r11,%rdx,4), %rcx
// addq %r11, %rcx
// jmpq *%rcx # JUMPTABLE @0x402450
MCPhysReg BaseReg1;
MCPhysReg BaseReg2;
uint64_t Offset;
std::unique_ptr<MCPlusBuilder::MCInstMatcher> PICIndJmpMatcher =
BC.MIB->matchIndJmp(BC.MIB->matchAdd(
BC.MIB->matchReg(BaseReg1),
BC.MIB->matchLoad(BC.MIB->matchReg(BaseReg2),
BC.MIB->matchImm(Scale), BC.MIB->matchReg(),
BC.MIB->matchImm(Offset))));
std::unique_ptr<MCPlusBuilder::MCInstMatcher> PICBaseAddrMatcher =
BC.MIB->matchIndJmp(
BC.MIB->matchAdd(BC.MIB->matchLoadAddr(BC.MIB->matchSymbol()),
BC.MIB->matchAnyOperand()));
if (!PICIndJmpMatcher->match(
*BC.MRI, *BC.MIB,
MutableArrayRef<MCInst>(&*BB.begin(), &Inst + 1), -1) ||
Scale != 4 || BaseReg1 != BaseReg2 || Offset != 0 ||
!PICBaseAddrMatcher->match(
*BC.MRI, *BC.MIB,
MutableArrayRef<MCInst>(&*BB.begin(), &Inst + 1), -1)) {
BlacklistedJTs.insert(JumpTable);
++IndJmpsDenied;
++NumJTsBadMatch;
continue;
}
}
}
// Statistics only
for (const auto &JTFreq : AllJTs) {
JumpTable *JT = JTFreq.first;
uint64_t CurScore = JTFreq.second;
TotalJTScore += CurScore;
if (!BlacklistedJTs.count(JT)) {
OptimizedScore += CurScore;
if (JT->EntrySize == 8)
BytesSaved += JT->getSize() >> 1;
}
}
TotalJTs += AllJTs.size();
TotalJTsDenied += BlacklistedJTs.size();
}
bool JTFootprintReduction::tryOptimizeNonPIC(
BinaryContext &BC, BinaryBasicBlock &BB, BinaryBasicBlock::iterator Inst,
uint64_t JTAddr, JumpTable *JumpTable, DataflowInfoManager &Info) {
if (opts::JTFootprintOnlyPIC)
return false;
MCOperand Base;
uint64_t Scale;
MCPhysReg Index;
MCOperand Offset;
std::unique_ptr<MCPlusBuilder::MCInstMatcher> IndJmpMatcher =
BC.MIB->matchIndJmp(BC.MIB->matchAnyOperand(Base),
BC.MIB->matchImm(Scale), BC.MIB->matchReg(Index),
BC.MIB->matchAnyOperand(Offset));
if (!IndJmpMatcher->match(*BC.MRI, *BC.MIB,
MutableArrayRef<MCInst>(&*BB.begin(), &*Inst + 1),
-1))
return false;
assert(Scale == 8 && "Wrong scale");
Scale = 4;
IndJmpMatcher->annotate(*BC.MIB, "DeleteMe");
LivenessAnalysis &LA = Info.getLivenessAnalysis();
MCPhysReg Reg = LA.scavengeRegAfter(&*Inst);
assert(Reg != 0 && "Register scavenger failed!");
MCOperand RegOp = MCOperand::createReg(Reg);
SmallVector<MCInst, 4> NewFrag;
BC.MIB->createIJmp32Frag(NewFrag, Base, MCOperand::createImm(Scale),
MCOperand::createReg(Index), Offset, RegOp);
BC.MIB->setJumpTable(NewFrag.back(), JTAddr, Index);
JumpTable->OutputEntrySize = 4;
BB.replaceInstruction(Inst, NewFrag.begin(), NewFrag.end());
return true;
}
bool JTFootprintReduction::tryOptimizePIC(BinaryContext &BC,
BinaryBasicBlock &BB,
BinaryBasicBlock::iterator Inst,
uint64_t JTAddr, JumpTable *JumpTable,
DataflowInfoManager &Info) {
MCPhysReg BaseReg;
uint64_t Scale;
MCPhysReg Index;
MCOperand Offset;
MCOperand JumpTableRef;
std::unique_ptr<MCPlusBuilder::MCInstMatcher> PICIndJmpMatcher =
BC.MIB->matchIndJmp(BC.MIB->matchAdd(
BC.MIB->matchLoadAddr(BC.MIB->matchAnyOperand(JumpTableRef)),
BC.MIB->matchLoad(BC.MIB->matchReg(BaseReg), BC.MIB->matchImm(Scale),
BC.MIB->matchReg(Index),
BC.MIB->matchAnyOperand())));
if (!PICIndJmpMatcher->match(
*BC.MRI, *BC.MIB, MutableArrayRef<MCInst>(&*BB.begin(), &*Inst + 1),
-1))
return false;
assert(Scale == 4 && "Wrong scale");
PICIndJmpMatcher->annotate(*BC.MIB, "DeleteMe");
MCOperand RegOp = MCOperand::createReg(BaseReg);
SmallVector<MCInst, 4> NewFrag;
BC.MIB->createIJmp32Frag(NewFrag, MCOperand::createReg(0),
MCOperand::createImm(Scale),
MCOperand::createReg(Index), JumpTableRef, RegOp);
BC.MIB->setJumpTable(NewFrag.back(), JTAddr, Index);
JumpTable->OutputEntrySize = 4;
// DePICify
JumpTable->Type = JumpTable::JTT_NORMAL;
BB.replaceInstruction(Inst, NewFrag.begin(), NewFrag.end());
return true;
}
void JTFootprintReduction::optimizeFunction(BinaryFunction &Function,
DataflowInfoManager &Info) {
BinaryContext &BC = Function.getBinaryContext();
for (BinaryBasicBlock &BB : Function) {
if (!BB.getNumNonPseudos())
continue;
auto IndJmpRI = BB.getLastNonPseudo();
auto IndJmp = std::prev(IndJmpRI.base());
const uint64_t JTAddr = BC.MIB->getJumpTable(*IndJmp);
if (!JTAddr)
continue;
JumpTable *JumpTable = Function.getJumpTable(*IndJmp);
if (BlacklistedJTs.count(JumpTable))
continue;
if (tryOptimizeNonPIC(BC, BB, IndJmp, JTAddr, JumpTable, Info) ||
tryOptimizePIC(BC, BB, IndJmp, JTAddr, JumpTable, Info)) {
Modified.insert(&Function);
continue;
}
llvm_unreachable("Should either optimize PIC or NonPIC successfuly");
}
if (!Modified.count(&Function))
return;
for (BinaryBasicBlock &BB : Function)
for (auto I = BB.begin(); I != BB.end();)
if (BC.MIB->hasAnnotation(*I, "DeleteMe"))
I = BB.eraseInstruction(I);
else
++I;
}
void JTFootprintReduction::runOnFunctions(BinaryContext &BC) {
if (opts::JumpTables == JTS_BASIC && BC.HasRelocations)
return;
std::unique_ptr<RegAnalysis> RA;
std::unique_ptr<BinaryFunctionCallGraph> CG;
if (!opts::JTFootprintOnlyPIC) {
CG.reset(new BinaryFunctionCallGraph(buildCallGraph(BC)));
RA.reset(new RegAnalysis(BC, &BC.getBinaryFunctions(), &*CG));
}
for (auto &BFIt : BC.getBinaryFunctions()) {
BinaryFunction &Function = BFIt.second;
if (!Function.isSimple() || Function.isIgnored())
continue;
if (Function.getKnownExecutionCount() == 0)
continue;
DataflowInfoManager Info(Function, RA.get(), nullptr);
BlacklistedJTs.clear();
checkOpportunities(Function, Info);
optimizeFunction(Function, Info);
}
if (TotalJTs == TotalJTsDenied) {
outs() << "BOLT-INFO: JT Footprint reduction: no changes were made.\n";
return;
}
outs() << "BOLT-INFO: JT Footprint reduction stats (simple funcs only):\n";
if (OptimizedScore)
outs() << format("\t %.2lf%%", (OptimizedScore * 100.0 / TotalJTScore))
<< " of dynamic JT entries were reduced.\n";
outs() << "\t " << TotalJTs - TotalJTsDenied << " of " << TotalJTs
<< " jump tables affected.\n";
outs() << "\t " << IndJmps - IndJmpsDenied << " of " << IndJmps
<< " indirect jumps to JTs affected.\n";
outs() << "\t " << NumJTsBadMatch
<< " JTs discarded due to unsupported jump pattern.\n";
outs() << "\t " << NumJTsNoReg
<< " JTs discarded due to register unavailability.\n";
outs() << "\t " << BytesSaved << " bytes saved.\n";
}
} // namespace bolt
} // namespace llvm
|
