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llvm-project/llvm/lib/Target/X86/X86FixupLEAs.cpp

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//===-- X86FixupLEAs.cpp - use or replace LEA instructions -----------===//
//
// 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 defines the pass that finds instructions that can be
// re-written as LEA instructions in order to reduce pipeline delays.
// It replaces LEAs with ADD/INC/DEC when that is better for size/speed.
//
//===----------------------------------------------------------------------===//
#include "X86.h"
#include "X86InstrInfo.h"
#include "X86Subtarget.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/ProfileSummaryInfo.h"
#include "llvm/CodeGen/LazyMachineBlockFrequencyInfo.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineSizeOpts.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/TargetSchedule.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
#define FIXUPLEA_DESC "X86 LEA Fixup"
#define FIXUPLEA_NAME "x86-fixup-LEAs"
#define DEBUG_TYPE FIXUPLEA_NAME
STATISTIC(NumLEAs, "Number of LEA instructions created");
namespace {
class FixupLEAPass : public MachineFunctionPass {
enum RegUsageState { RU_NotUsed, RU_Write, RU_Read };
/// Given a machine register, look for the instruction
/// which writes it in the current basic block. If found,
/// try to replace it with an equivalent LEA instruction.
/// If replacement succeeds, then also process the newly created
/// instruction.
void seekLEAFixup(MachineOperand &p, MachineBasicBlock::iterator &I,
MachineBasicBlock &MBB);
/// Given a memory access or LEA instruction
/// whose address mode uses a base and/or index register, look for
/// an opportunity to replace the instruction which sets the base or index
/// register with an equivalent LEA instruction.
void processInstruction(MachineBasicBlock::iterator &I,
MachineBasicBlock &MBB);
/// Given a LEA instruction which is unprofitable
/// on SlowLEA targets try to replace it with an equivalent ADD instruction.
void processInstructionForSlowLEA(MachineBasicBlock::iterator &I,
MachineBasicBlock &MBB);
/// Given a LEA instruction which is unprofitable
/// on SNB+ try to replace it with other instructions.
/// According to Intel's Optimization Reference Manual:
/// " For LEA instructions with three source operands and some specific
/// situations, instruction latency has increased to 3 cycles, and must
/// dispatch via port 1:
/// - LEA that has all three source operands: base, index, and offset
/// - LEA that uses base and index registers where the base is EBP, RBP,
/// or R13
/// - LEA that uses RIP relative addressing mode
/// - LEA that uses 16-bit addressing mode "
/// This function currently handles the first 2 cases only.
void processInstrForSlow3OpLEA(MachineBasicBlock::iterator &I,
MachineBasicBlock &MBB, bool OptIncDec);
/// Look for LEAs that are really two address LEAs that we might be able to
/// turn into regular ADD instructions.
bool optTwoAddrLEA(MachineBasicBlock::iterator &I,
MachineBasicBlock &MBB, bool OptIncDec,
bool UseLEAForSP) const;
/// Look for and transform the sequence
/// lea (reg1, reg2), reg3
/// sub reg3, reg4
/// to
/// sub reg1, reg4
/// sub reg2, reg4
/// It can also optimize the sequence lea/add similarly.
bool optLEAALU(MachineBasicBlock::iterator &I, MachineBasicBlock &MBB) const;
/// Step forwards in MBB, looking for an ADD/SUB instruction which uses
/// the dest register of LEA instruction I.
MachineBasicBlock::iterator searchALUInst(MachineBasicBlock::iterator &I,
MachineBasicBlock &MBB) const;
/// Check instructions between LeaI and AluI (exclusively).
/// Set BaseIndexDef to true if base or index register from LeaI is defined.
/// Set AluDestRef to true if the dest register of AluI is used or defined.
void checkRegUsage(MachineBasicBlock::iterator &LeaI,
MachineBasicBlock::iterator &AluI, bool &BaseIndexDef,
bool &AluDestRef) const;
/// Determine if an instruction references a machine register
/// and, if so, whether it reads or writes the register.
RegUsageState usesRegister(MachineOperand &p, MachineBasicBlock::iterator I);
/// Step backwards through a basic block, looking
/// for an instruction which writes a register within
/// a maximum of INSTR_DISTANCE_THRESHOLD instruction latency cycles.
MachineBasicBlock::iterator searchBackwards(MachineOperand &p,
MachineBasicBlock::iterator &I,
MachineBasicBlock &MBB);
/// if an instruction can be converted to an
/// equivalent LEA, insert the new instruction into the basic block
/// and return a pointer to it. Otherwise, return zero.
MachineInstr *postRAConvertToLEA(MachineBasicBlock &MBB,
MachineBasicBlock::iterator &MBBI) const;
public:
static char ID;
StringRef getPassName() const override { return FIXUPLEA_DESC; }
FixupLEAPass() : MachineFunctionPass(ID) { }
/// Loop over all of the basic blocks,
/// replacing instructions by equivalent LEA instructions
/// if needed and when possible.
bool runOnMachineFunction(MachineFunction &MF) override;
// This pass runs after regalloc and doesn't support VReg operands.
MachineFunctionProperties getRequiredProperties() const override {
return MachineFunctionProperties().set(
MachineFunctionProperties::Property::NoVRegs);
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<ProfileSummaryInfoWrapperPass>();
AU.addRequired<LazyMachineBlockFrequencyInfoPass>();
MachineFunctionPass::getAnalysisUsage(AU);
}
private:
TargetSchedModel TSM;
const X86InstrInfo *TII = nullptr;
const X86RegisterInfo *TRI = nullptr;
};
}
char FixupLEAPass::ID = 0;
INITIALIZE_PASS(FixupLEAPass, FIXUPLEA_NAME, FIXUPLEA_DESC, false, false)
MachineInstr *
FixupLEAPass::postRAConvertToLEA(MachineBasicBlock &MBB,
MachineBasicBlock::iterator &MBBI) const {
MachineInstr &MI = *MBBI;
switch (MI.getOpcode()) {
case X86::MOV32rr:
case X86::MOV64rr: {
const MachineOperand &Src = MI.getOperand(1);
const MachineOperand &Dest = MI.getOperand(0);
MachineInstr *NewMI =
BuildMI(MBB, MBBI, MI.getDebugLoc(),
TII->get(MI.getOpcode() == X86::MOV32rr ? X86::LEA32r
: X86::LEA64r))
.add(Dest)
.add(Src)
.addImm(1)
.addReg(0)
.addImm(0)
.addReg(0);
return NewMI;
}
}
if (!MI.isConvertibleTo3Addr())
return nullptr;
switch (MI.getOpcode()) {
default:
// Only convert instructions that we've verified are safe.
return nullptr;
case X86::ADD64ri32:
case X86::ADD64ri8:
case X86::ADD64ri32_DB:
case X86::ADD64ri8_DB:
case X86::ADD32ri:
case X86::ADD32ri8:
case X86::ADD32ri_DB:
case X86::ADD32ri8_DB:
if (!MI.getOperand(2).isImm()) {
// convertToThreeAddress will call getImm()
// which requires isImm() to be true
return nullptr;
}
break;
case X86::SHL64ri:
case X86::SHL32ri:
case X86::INC64r:
case X86::INC32r:
case X86::DEC64r:
case X86::DEC32r:
case X86::ADD64rr:
case X86::ADD64rr_DB:
case X86::ADD32rr:
case X86::ADD32rr_DB:
// These instructions are all fine to convert.
break;
}
MachineFunction::iterator MFI = MBB.getIterator();
return TII->convertToThreeAddress(MFI, MI, nullptr);
}
FunctionPass *llvm::createX86FixupLEAs() { return new FixupLEAPass(); }
static bool isLEA(unsigned Opcode) {
return Opcode == X86::LEA32r || Opcode == X86::LEA64r ||
Opcode == X86::LEA64_32r;
}
bool FixupLEAPass::runOnMachineFunction(MachineFunction &MF) {
if (skipFunction(MF.getFunction()))
return false;
const X86Subtarget &ST = MF.getSubtarget<X86Subtarget>();
bool IsSlowLEA = ST.slowLEA();
bool IsSlow3OpsLEA = ST.slow3OpsLEA();
bool LEAUsesAG = ST.LEAusesAG();
bool OptIncDec = !ST.slowIncDec() || MF.getFunction().hasOptSize();
bool UseLEAForSP = ST.useLeaForSP();
TSM.init(&ST);
TII = ST.getInstrInfo();
TRI = ST.getRegisterInfo();
auto *PSI = &getAnalysis<ProfileSummaryInfoWrapperPass>().getPSI();
auto *MBFI = (PSI && PSI->hasProfileSummary())
? &getAnalysis<LazyMachineBlockFrequencyInfoPass>().getBFI()
: nullptr;
LLVM_DEBUG(dbgs() << "Start X86FixupLEAs\n";);
for (MachineBasicBlock &MBB : MF) {
// First pass. Try to remove or optimize existing LEAs.
bool OptIncDecPerBB =
OptIncDec || llvm::shouldOptimizeForSize(&MBB, PSI, MBFI);
for (MachineBasicBlock::iterator I = MBB.begin(); I != MBB.end(); ++I) {
if (!isLEA(I->getOpcode()))
continue;
if (optTwoAddrLEA(I, MBB, OptIncDecPerBB, UseLEAForSP))
continue;
if (IsSlowLEA)
processInstructionForSlowLEA(I, MBB);
else if (IsSlow3OpsLEA)
processInstrForSlow3OpLEA(I, MBB, OptIncDecPerBB);
}
// Second pass for creating LEAs. This may reverse some of the
// transformations above.
if (LEAUsesAG) {
for (MachineBasicBlock::iterator I = MBB.begin(); I != MBB.end(); ++I)
processInstruction(I, MBB);
}
}
LLVM_DEBUG(dbgs() << "End X86FixupLEAs\n";);
return true;
}
FixupLEAPass::RegUsageState
FixupLEAPass::usesRegister(MachineOperand &p, MachineBasicBlock::iterator I) {
RegUsageState RegUsage = RU_NotUsed;
MachineInstr &MI = *I;
for (unsigned i = 0; i < MI.getNumOperands(); ++i) {
MachineOperand &opnd = MI.getOperand(i);
if (opnd.isReg() && opnd.getReg() == p.getReg()) {
if (opnd.isDef())
return RU_Write;
RegUsage = RU_Read;
}
}
return RegUsage;
}
/// getPreviousInstr - Given a reference to an instruction in a basic
/// block, return a reference to the previous instruction in the block,
/// wrapping around to the last instruction of the block if the block
/// branches to itself.
static inline bool getPreviousInstr(MachineBasicBlock::iterator &I,
MachineBasicBlock &MBB) {
if (I == MBB.begin()) {
if (MBB.isPredecessor(&MBB)) {
I = --MBB.end();
return true;
} else
return false;
}
--I;
return true;
}
MachineBasicBlock::iterator
FixupLEAPass::searchBackwards(MachineOperand &p, MachineBasicBlock::iterator &I,
MachineBasicBlock &MBB) {
int InstrDistance = 1;
MachineBasicBlock::iterator CurInst;
static const int INSTR_DISTANCE_THRESHOLD = 5;
CurInst = I;
bool Found;
Found = getPreviousInstr(CurInst, MBB);
while (Found && I != CurInst) {
if (CurInst->isCall() || CurInst->isInlineAsm())
break;
if (InstrDistance > INSTR_DISTANCE_THRESHOLD)
break; // too far back to make a difference
if (usesRegister(p, CurInst) == RU_Write) {
return CurInst;
}
InstrDistance += TSM.computeInstrLatency(&*CurInst);
Found = getPreviousInstr(CurInst, MBB);
}
return MachineBasicBlock::iterator();
}
static inline bool isInefficientLEAReg(unsigned Reg) {
return Reg == X86::EBP || Reg == X86::RBP ||
Reg == X86::R13D || Reg == X86::R13;
}
/// Returns true if this LEA uses base an index registers, and the base register
/// is known to be inefficient for the subtarget.
// TODO: use a variant scheduling class to model the latency profile
// of LEA instructions, and implement this logic as a scheduling predicate.
static inline bool hasInefficientLEABaseReg(const MachineOperand &Base,
const MachineOperand &Index) {
return Base.isReg() && isInefficientLEAReg(Base.getReg()) && Index.isReg() &&
Index.getReg() != X86::NoRegister;
}
static inline bool hasLEAOffset(const MachineOperand &Offset) {
return (Offset.isImm() && Offset.getImm() != 0) || Offset.isGlobal();
}
static inline unsigned getADDrrFromLEA(unsigned LEAOpcode) {
switch (LEAOpcode) {
default:
llvm_unreachable("Unexpected LEA instruction");
case X86::LEA32r:
case X86::LEA64_32r:
return X86::ADD32rr;
case X86::LEA64r:
return X86::ADD64rr;
}
}
static inline unsigned getSUBrrFromLEA(unsigned LEAOpcode) {
switch (LEAOpcode) {
default:
llvm_unreachable("Unexpected LEA instruction");
case X86::LEA32r:
case X86::LEA64_32r:
return X86::SUB32rr;
case X86::LEA64r:
return X86::SUB64rr;
}
}
static inline unsigned getADDriFromLEA(unsigned LEAOpcode,
const MachineOperand &Offset) {
bool IsInt8 = Offset.isImm() && isInt<8>(Offset.getImm());
switch (LEAOpcode) {
default:
llvm_unreachable("Unexpected LEA instruction");
case X86::LEA32r:
case X86::LEA64_32r:
return IsInt8 ? X86::ADD32ri8 : X86::ADD32ri;
case X86::LEA64r:
return IsInt8 ? X86::ADD64ri8 : X86::ADD64ri32;
}
}
static inline unsigned getINCDECFromLEA(unsigned LEAOpcode, bool IsINC) {
switch (LEAOpcode) {
default:
llvm_unreachable("Unexpected LEA instruction");
case X86::LEA32r:
case X86::LEA64_32r:
return IsINC ? X86::INC32r : X86::DEC32r;
case X86::LEA64r:
return IsINC ? X86::INC64r : X86::DEC64r;
}
}
MachineBasicBlock::iterator
FixupLEAPass::searchALUInst(MachineBasicBlock::iterator &I,
MachineBasicBlock &MBB) const {
const int InstrDistanceThreshold = 5;
int InstrDistance = 1;
MachineBasicBlock::iterator CurInst = std::next(I);
unsigned LEAOpcode = I->getOpcode();
unsigned AddOpcode = getADDrrFromLEA(LEAOpcode);
unsigned SubOpcode = getSUBrrFromLEA(LEAOpcode);
Register DestReg = I->getOperand(0).getReg();
while (CurInst != MBB.end()) {
if (CurInst->isCall() || CurInst->isInlineAsm())
break;
if (InstrDistance > InstrDistanceThreshold)
break;
// Check if the lea dest register is used in an add/sub instruction only.
for (unsigned I = 0, E = CurInst->getNumOperands(); I != E; ++I) {
MachineOperand &Opnd = CurInst->getOperand(I);
if (Opnd.isReg() && Opnd.getReg() == DestReg) {
if (Opnd.isDef() || !Opnd.isKill())
return MachineBasicBlock::iterator();
unsigned AluOpcode = CurInst->getOpcode();
if (AluOpcode != AddOpcode && AluOpcode != SubOpcode)
return MachineBasicBlock::iterator();
MachineOperand &Opnd2 = CurInst->getOperand(3 - I);
MachineOperand AluDest = CurInst->getOperand(0);
if (Opnd2.getReg() != AluDest.getReg())
return MachineBasicBlock::iterator();
// X - (Y + Z) may generate different flags than (X - Y) - Z when there
// is overflow. So we can't change the alu instruction if the flags
// register is live.
if (!CurInst->registerDefIsDead(X86::EFLAGS, TRI))
return MachineBasicBlock::iterator();
return CurInst;
}
}
InstrDistance++;
++CurInst;
}
return MachineBasicBlock::iterator();
}
void FixupLEAPass::checkRegUsage(MachineBasicBlock::iterator &LeaI,
MachineBasicBlock::iterator &AluI,
bool &BaseIndexDef, bool &AluDestRef) const {
BaseIndexDef = AluDestRef = false;
Register BaseReg = LeaI->getOperand(1 + X86::AddrBaseReg).getReg();
Register IndexReg = LeaI->getOperand(1 + X86::AddrIndexReg).getReg();
Register AluDestReg = AluI->getOperand(0).getReg();
MachineBasicBlock::iterator CurInst = std::next(LeaI);
while (CurInst != AluI) {
for (unsigned I = 0, E = CurInst->getNumOperands(); I != E; ++I) {
MachineOperand &Opnd = CurInst->getOperand(I);
if (!Opnd.isReg())
continue;
Register Reg = Opnd.getReg();
if (TRI->regsOverlap(Reg, AluDestReg))
AluDestRef = true;
if (Opnd.isDef() &&
(TRI->regsOverlap(Reg, BaseReg) || TRI->regsOverlap(Reg, IndexReg))) {
BaseIndexDef = true;
}
}
++CurInst;
}
}
bool FixupLEAPass::optLEAALU(MachineBasicBlock::iterator &I,
MachineBasicBlock &MBB) const {
// Look for an add/sub instruction which uses the result of lea.
MachineBasicBlock::iterator AluI = searchALUInst(I, MBB);
if (AluI == MachineBasicBlock::iterator())
return false;
// Check if there are any related register usage between lea and alu.
bool BaseIndexDef, AluDestRef;
checkRegUsage(I, AluI, BaseIndexDef, AluDestRef);
MachineBasicBlock::iterator InsertPos = AluI;
if (BaseIndexDef) {
if (AluDestRef)
return false;
InsertPos = I;
}
// Check if there are same registers.
Register AluDestReg = AluI->getOperand(0).getReg();
Register BaseReg = I->getOperand(1 + X86::AddrBaseReg).getReg();
Register IndexReg = I->getOperand(1 + X86::AddrIndexReg).getReg();
if (I->getOpcode() == X86::LEA64_32r) {
BaseReg = TRI->getSubReg(BaseReg, X86::sub_32bit);
IndexReg = TRI->getSubReg(IndexReg, X86::sub_32bit);
}
if (AluDestReg == IndexReg) {
if (BaseReg == IndexReg)
return false;
std::swap(BaseReg, IndexReg);
}
// Now it's safe to change instructions.
MachineInstr *NewMI1, *NewMI2;
unsigned NewOpcode = AluI->getOpcode();
NewMI1 = BuildMI(MBB, InsertPos, AluI->getDebugLoc(), TII->get(NewOpcode),
AluDestReg)
.addReg(AluDestReg)
.addReg(BaseReg);
NewMI1->addRegisterDead(X86::EFLAGS, TRI);
NewMI2 = BuildMI(MBB, InsertPos, AluI->getDebugLoc(), TII->get(NewOpcode),
AluDestReg)
.addReg(AluDestReg)
.addReg(IndexReg);
NewMI2->addRegisterDead(X86::EFLAGS, TRI);
MBB.getParent()->substituteDebugValuesForInst(*AluI, *NewMI1, 1);
MBB.getParent()->substituteDebugValuesForInst(*AluI, *NewMI2, 1);
MBB.erase(I);
MBB.erase(AluI);
I = NewMI1;
return true;
}
bool FixupLEAPass::optTwoAddrLEA(MachineBasicBlock::iterator &I,
MachineBasicBlock &MBB, bool OptIncDec,
bool UseLEAForSP) const {
MachineInstr &MI = *I;
const MachineOperand &Base = MI.getOperand(1 + X86::AddrBaseReg);
const MachineOperand &Scale = MI.getOperand(1 + X86::AddrScaleAmt);
const MachineOperand &Index = MI.getOperand(1 + X86::AddrIndexReg);
const MachineOperand &Disp = MI.getOperand(1 + X86::AddrDisp);
const MachineOperand &Segment = MI.getOperand(1 + X86::AddrSegmentReg);
if (Segment.getReg() != 0 || !Disp.isImm() || Scale.getImm() > 1 ||
MBB.computeRegisterLiveness(TRI, X86::EFLAGS, I) !=
MachineBasicBlock::LQR_Dead)
return false;
Register DestReg = MI.getOperand(0).getReg();
Register BaseReg = Base.getReg();
Register IndexReg = Index.getReg();
// Don't change stack adjustment LEAs.
if (UseLEAForSP && (DestReg == X86::ESP || DestReg == X86::RSP))
return false;
// LEA64_32 has 64-bit operands but 32-bit result.
if (MI.getOpcode() == X86::LEA64_32r) {
if (BaseReg != 0)
BaseReg = TRI->getSubReg(BaseReg, X86::sub_32bit);
if (IndexReg != 0)
IndexReg = TRI->getSubReg(IndexReg, X86::sub_32bit);
}
MachineInstr *NewMI = nullptr;
// Case 1.
// Look for lea(%reg1, %reg2), %reg1 or lea(%reg2, %reg1), %reg1
// which can be turned into add %reg2, %reg1
if (BaseReg != 0 && IndexReg != 0 && Disp.getImm() == 0 &&
(DestReg == BaseReg || DestReg == IndexReg)) {
unsigned NewOpcode = getADDrrFromLEA(MI.getOpcode());
if (DestReg != BaseReg)
std::swap(BaseReg, IndexReg);
if (MI.getOpcode() == X86::LEA64_32r) {
// TODO: Do we need the super register implicit use?
NewMI = BuildMI(MBB, I, MI.getDebugLoc(), TII->get(NewOpcode), DestReg)
.addReg(BaseReg).addReg(IndexReg)
.addReg(Base.getReg(), RegState::Implicit)
.addReg(Index.getReg(), RegState::Implicit);
} else {
NewMI = BuildMI(MBB, I, MI.getDebugLoc(), TII->get(NewOpcode), DestReg)
.addReg(BaseReg).addReg(IndexReg);
}
} else if (DestReg == BaseReg && IndexReg == 0) {
// Case 2.
// This is an LEA with only a base register and a displacement,
// We can use ADDri or INC/DEC.
// Does this LEA have one these forms:
// lea %reg, 1(%reg)
// lea %reg, -1(%reg)
if (OptIncDec && (Disp.getImm() == 1 || Disp.getImm() == -1)) {
bool IsINC = Disp.getImm() == 1;
unsigned NewOpcode = getINCDECFromLEA(MI.getOpcode(), IsINC);
if (MI.getOpcode() == X86::LEA64_32r) {
// TODO: Do we need the super register implicit use?
NewMI = BuildMI(MBB, I, MI.getDebugLoc(), TII->get(NewOpcode), DestReg)
.addReg(BaseReg).addReg(Base.getReg(), RegState::Implicit);
} else {
NewMI = BuildMI(MBB, I, MI.getDebugLoc(), TII->get(NewOpcode), DestReg)
.addReg(BaseReg);
}
} else {
unsigned NewOpcode = getADDriFromLEA(MI.getOpcode(), Disp);
if (MI.getOpcode() == X86::LEA64_32r) {
// TODO: Do we need the super register implicit use?
NewMI = BuildMI(MBB, I, MI.getDebugLoc(), TII->get(NewOpcode), DestReg)
.addReg(BaseReg).addImm(Disp.getImm())
.addReg(Base.getReg(), RegState::Implicit);
} else {
NewMI = BuildMI(MBB, I, MI.getDebugLoc(), TII->get(NewOpcode), DestReg)
.addReg(BaseReg).addImm(Disp.getImm());
}
}
} else if (BaseReg != 0 && IndexReg != 0 && Disp.getImm() == 0) {
// Case 3.
// Look for and transform the sequence
// lea (reg1, reg2), reg3
// sub reg3, reg4
return optLEAALU(I, MBB);
} else
return false;
MBB.getParent()->substituteDebugValuesForInst(*I, *NewMI, 1);
MBB.erase(I);
I = NewMI;
return true;
}
void FixupLEAPass::processInstruction(MachineBasicBlock::iterator &I,
MachineBasicBlock &MBB) {
// Process a load, store, or LEA instruction.
MachineInstr &MI = *I;
const MCInstrDesc &Desc = MI.getDesc();
int AddrOffset = X86II::getMemoryOperandNo(Desc.TSFlags);
if (AddrOffset >= 0) {
AddrOffset += X86II::getOperandBias(Desc);
MachineOperand &p = MI.getOperand(AddrOffset + X86::AddrBaseReg);
if (p.isReg() && p.getReg() != X86::ESP) {
seekLEAFixup(p, I, MBB);
}
MachineOperand &q = MI.getOperand(AddrOffset + X86::AddrIndexReg);
if (q.isReg() && q.getReg() != X86::ESP) {
seekLEAFixup(q, I, MBB);
}
}
}
void FixupLEAPass::seekLEAFixup(MachineOperand &p,
MachineBasicBlock::iterator &I,
MachineBasicBlock &MBB) {
MachineBasicBlock::iterator MBI = searchBackwards(p, I, MBB);
if (MBI != MachineBasicBlock::iterator()) {
MachineInstr *NewMI = postRAConvertToLEA(MBB, MBI);
if (NewMI) {
++NumLEAs;
LLVM_DEBUG(dbgs() << "FixLEA: Candidate to replace:"; MBI->dump(););
// now to replace with an equivalent LEA...
LLVM_DEBUG(dbgs() << "FixLEA: Replaced by: "; NewMI->dump(););
MBB.getParent()->substituteDebugValuesForInst(*MBI, *NewMI, 1);
MBB.erase(MBI);
MachineBasicBlock::iterator J =
static_cast<MachineBasicBlock::iterator>(NewMI);
processInstruction(J, MBB);
}
}
}
void FixupLEAPass::processInstructionForSlowLEA(MachineBasicBlock::iterator &I,
MachineBasicBlock &MBB) {
MachineInstr &MI = *I;
const unsigned Opcode = MI.getOpcode();
const MachineOperand &Dst = MI.getOperand(0);
const MachineOperand &Base = MI.getOperand(1 + X86::AddrBaseReg);
const MachineOperand &Scale = MI.getOperand(1 + X86::AddrScaleAmt);
const MachineOperand &Index = MI.getOperand(1 + X86::AddrIndexReg);
const MachineOperand &Offset = MI.getOperand(1 + X86::AddrDisp);
const MachineOperand &Segment = MI.getOperand(1 + X86::AddrSegmentReg);
if (Segment.getReg() != 0 || !Offset.isImm() ||
MBB.computeRegisterLiveness(TRI, X86::EFLAGS, I, 4) !=
MachineBasicBlock::LQR_Dead)
return;
const Register DstR = Dst.getReg();
const Register SrcR1 = Base.getReg();
const Register SrcR2 = Index.getReg();
if ((SrcR1 == 0 || SrcR1 != DstR) && (SrcR2 == 0 || SrcR2 != DstR))
return;
if (Scale.getImm() > 1)
return;
LLVM_DEBUG(dbgs() << "FixLEA: Candidate to replace:"; I->dump(););
LLVM_DEBUG(dbgs() << "FixLEA: Replaced by: ";);
MachineInstr *NewMI = nullptr;
// Make ADD instruction for two registers writing to LEA's destination
if (SrcR1 != 0 && SrcR2 != 0) {
const MCInstrDesc &ADDrr = TII->get(getADDrrFromLEA(Opcode));
const MachineOperand &Src = SrcR1 == DstR ? Index : Base;
NewMI =
BuildMI(MBB, I, MI.getDebugLoc(), ADDrr, DstR).addReg(DstR).add(Src);
LLVM_DEBUG(NewMI->dump(););
}
// Make ADD instruction for immediate
if (Offset.getImm() != 0) {
const MCInstrDesc &ADDri =
TII->get(getADDriFromLEA(Opcode, Offset));
const MachineOperand &SrcR = SrcR1 == DstR ? Base : Index;
NewMI = BuildMI(MBB, I, MI.getDebugLoc(), ADDri, DstR)
.add(SrcR)
.addImm(Offset.getImm());
LLVM_DEBUG(NewMI->dump(););
}
if (NewMI) {
MBB.getParent()->substituteDebugValuesForInst(*I, *NewMI, 1);
MBB.erase(I);
I = NewMI;
}
}
void FixupLEAPass::processInstrForSlow3OpLEA(MachineBasicBlock::iterator &I,
MachineBasicBlock &MBB,
bool OptIncDec) {
MachineInstr &MI = *I;
const unsigned LEAOpcode = MI.getOpcode();
const MachineOperand &Dest = MI.getOperand(0);
const MachineOperand &Base = MI.getOperand(1 + X86::AddrBaseReg);
const MachineOperand &Scale = MI.getOperand(1 + X86::AddrScaleAmt);
const MachineOperand &Index = MI.getOperand(1 + X86::AddrIndexReg);
const MachineOperand &Offset = MI.getOperand(1 + X86::AddrDisp);
const MachineOperand &Segment = MI.getOperand(1 + X86::AddrSegmentReg);
if (!(TII->isThreeOperandsLEA(MI) || hasInefficientLEABaseReg(Base, Index)) ||
MBB.computeRegisterLiveness(TRI, X86::EFLAGS, I, 4) !=
MachineBasicBlock::LQR_Dead ||
Segment.getReg() != X86::NoRegister)
return;
Register DestReg = Dest.getReg();
Register BaseReg = Base.getReg();
Register IndexReg = Index.getReg();
if (MI.getOpcode() == X86::LEA64_32r) {
if (BaseReg != 0)
BaseReg = TRI->getSubReg(BaseReg, X86::sub_32bit);
if (IndexReg != 0)
IndexReg = TRI->getSubReg(IndexReg, X86::sub_32bit);
}
bool IsScale1 = Scale.getImm() == 1;
bool IsInefficientBase = isInefficientLEAReg(BaseReg);
bool IsInefficientIndex = isInefficientLEAReg(IndexReg);
// Skip these cases since it takes more than 2 instructions
// to replace the LEA instruction.
if (IsInefficientBase && DestReg == BaseReg && !IsScale1)
return;
LLVM_DEBUG(dbgs() << "FixLEA: Candidate to replace:"; MI.dump(););
LLVM_DEBUG(dbgs() << "FixLEA: Replaced by: ";);
MachineInstr *NewMI = nullptr;
// First try to replace LEA with one or two (for the 3-op LEA case)
// add instructions:
// 1.lea (%base,%index,1), %base => add %index,%base
// 2.lea (%base,%index,1), %index => add %base,%index
if (IsScale1 && (DestReg == BaseReg || DestReg == IndexReg)) {
unsigned NewOpc = getADDrrFromLEA(MI.getOpcode());
if (DestReg != BaseReg)
std::swap(BaseReg, IndexReg);
if (MI.getOpcode() == X86::LEA64_32r) {
// TODO: Do we need the super register implicit use?
NewMI = BuildMI(MBB, I, MI.getDebugLoc(), TII->get(NewOpc), DestReg)
.addReg(BaseReg)
.addReg(IndexReg)
.addReg(Base.getReg(), RegState::Implicit)
.addReg(Index.getReg(), RegState::Implicit);
} else {
NewMI = BuildMI(MBB, I, MI.getDebugLoc(), TII->get(NewOpc), DestReg)
.addReg(BaseReg)
.addReg(IndexReg);
}
} else if (!IsInefficientBase || (!IsInefficientIndex && IsScale1)) {
// If the base is inefficient try switching the index and base operands,
// otherwise just break the 3-Ops LEA inst into 2-Ops LEA + ADD instruction:
// lea offset(%base,%index,scale),%dst =>
// lea (%base,%index,scale); add offset,%dst
NewMI = BuildMI(MBB, MI, MI.getDebugLoc(), TII->get(LEAOpcode))
.add(Dest)
.add(IsInefficientBase ? Index : Base)
.add(Scale)
.add(IsInefficientBase ? Base : Index)
.addImm(0)
.add(Segment);
LLVM_DEBUG(NewMI->dump(););
}
// If either replacement succeeded above, add the offset if needed, then
// replace the instruction.
if (NewMI) {
// Create ADD instruction for the Offset in case of 3-Ops LEA.
if (hasLEAOffset(Offset)) {
if (OptIncDec && Offset.isImm() &&
(Offset.getImm() == 1 || Offset.getImm() == -1)) {
unsigned NewOpc =
getINCDECFromLEA(MI.getOpcode(), Offset.getImm() == 1);
NewMI = BuildMI(MBB, I, MI.getDebugLoc(), TII->get(NewOpc), DestReg)
.addReg(DestReg);
LLVM_DEBUG(NewMI->dump(););
} else {
unsigned NewOpc = getADDriFromLEA(MI.getOpcode(), Offset);
NewMI = BuildMI(MBB, I, MI.getDebugLoc(), TII->get(NewOpc), DestReg)
.addReg(DestReg)
.add(Offset);
LLVM_DEBUG(NewMI->dump(););
}
}
MBB.getParent()->substituteDebugValuesForInst(*I, *NewMI, 1);
MBB.erase(I);
I = NewMI;
return;
}
// Handle the rest of the cases with inefficient base register:
assert(DestReg != BaseReg && "DestReg == BaseReg should be handled already!");
assert(IsInefficientBase && "efficient base should be handled already!");
// FIXME: Handle LEA64_32r.
if (LEAOpcode == X86::LEA64_32r)
return;
// lea (%base,%index,1), %dst => mov %base,%dst; add %index,%dst
if (IsScale1 && !hasLEAOffset(Offset)) {
bool BIK = Base.isKill() && BaseReg != IndexReg;
TII->copyPhysReg(MBB, MI, MI.getDebugLoc(), DestReg, BaseReg, BIK);
LLVM_DEBUG(MI.getPrevNode()->dump(););
unsigned NewOpc = getADDrrFromLEA(MI.getOpcode());
NewMI = BuildMI(MBB, MI, MI.getDebugLoc(), TII->get(NewOpc), DestReg)
.addReg(DestReg)
.add(Index);
LLVM_DEBUG(NewMI->dump(););
MBB.getParent()->substituteDebugValuesForInst(*I, *NewMI, 1);
MBB.erase(I);
I = NewMI;
return;
}
// lea offset(%base,%index,scale), %dst =>
// lea offset( ,%index,scale), %dst; add %base,%dst
NewMI = BuildMI(MBB, MI, MI.getDebugLoc(), TII->get(LEAOpcode))
.add(Dest)
.addReg(0)
.add(Scale)
.add(Index)
.add(Offset)
.add(Segment);
LLVM_DEBUG(NewMI->dump(););
unsigned NewOpc = getADDrrFromLEA(MI.getOpcode());
NewMI = BuildMI(MBB, MI, MI.getDebugLoc(), TII->get(NewOpc), DestReg)
.addReg(DestReg)
.add(Base);
LLVM_DEBUG(NewMI->dump(););
MBB.getParent()->substituteDebugValuesForInst(*I, *NewMI, 1);
MBB.erase(I);
I = NewMI;
}
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