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

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//===-- X86FixupLEAs.cpp - use or replace LEA instructions -----------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines the pass that finds instructions that can be
// re-written as LEA instructions in order to reduce pipeline delays.
// When optimizing for size it replaces suitable LEAs with INC or DEC.
//
//===----------------------------------------------------------------------===//
#include "X86.h"
#include "X86InstrInfo.h"
#include "X86Subtarget.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.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;
namespace llvm {
void initializeFixupLEAPassPass(PassRegistry &);
}
#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 };
/// \brief Loop over all of the instructions in the basic block
/// replacing applicable instructions with LEA instructions,
/// where appropriate.
bool processBasicBlock(MachineFunction &MF, MachineFunction::iterator MFI);
/// \brief 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,
MachineFunction::iterator MFI);
/// \brief 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,
MachineFunction::iterator MFI);
/// \brief Given a LEA instruction which is unprofitable
/// on Silvermont try to replace it with an equivalent ADD instruction
void processInstructionForSLM(MachineBasicBlock::iterator &I,
MachineFunction::iterator MFI);
/// \brief 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.
MachineInstr *processInstrForSlow3OpLEA(MachineInstr &MI,
MachineFunction::iterator MFI);
/// \brief Look for LEAs that add 1 to reg or subtract 1 from reg
/// and convert them to INC or DEC respectively.
bool fixupIncDec(MachineBasicBlock::iterator &I,
MachineFunction::iterator MFI) const;
/// \brief 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);
/// \brief 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,
MachineFunction::iterator MFI);
/// \brief 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(MachineFunction::iterator &MFI,
MachineBasicBlock::iterator &MBBI) const;
public:
static char ID;
StringRef getPassName() const override { return FIXUPLEA_DESC; }
FixupLEAPass() : MachineFunctionPass(ID) {
initializeFixupLEAPassPass(*PassRegistry::getPassRegistry());
}
/// \brief 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);
}
private:
TargetSchedModel TSM;
MachineFunction *MF;
const X86InstrInfo *TII; // Machine instruction info.
bool OptIncDec;
bool OptLEA;
};
}
char FixupLEAPass::ID = 0;
INITIALIZE_PASS(FixupLEAPass, FIXUPLEA_NAME, FIXUPLEA_DESC, false, false)
MachineInstr *
FixupLEAPass::postRAConvertToLEA(MachineFunction::iterator &MFI,
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(*MF, MI.getDebugLoc(),
TII->get(MI.getOpcode() == X86::MOV32rr ? X86::LEA32r
: X86::LEA64r))
.add(Dest)
.add(Src)
.addImm(1)
.addReg(0)
.addImm(0)
.addReg(0);
MFI->insert(MBBI, NewMI); // Insert the new inst
return NewMI;
}
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:
case X86::ADD16ri:
case X86::ADD16ri8:
case X86::ADD16ri_DB:
case X86::ADD16ri8_DB:
if (!MI.getOperand(2).isImm()) {
// convertToThreeAddress will call getImm()
// which requires isImm() to be true
return nullptr;
}
break;
case X86::ADD16rr:
case X86::ADD16rr_DB:
if (MI.getOperand(1).getReg() != MI.getOperand(2).getReg()) {
// if src1 != src2, then convertToThreeAddress will
// need to create a Virtual register, which we cannot do
// after register allocation.
return nullptr;
}
}
return TII->convertToThreeAddress(MFI, MI, nullptr);
}
FunctionPass *llvm::createX86FixupLEAs() { return new FixupLEAPass(); }
bool FixupLEAPass::runOnMachineFunction(MachineFunction &Func) {
if (skipFunction(Func.getFunction()))
return false;
MF = &Func;
const X86Subtarget &ST = Func.getSubtarget<X86Subtarget>();
OptIncDec = !ST.slowIncDec() || Func.getFunction().optForMinSize();
OptLEA = ST.LEAusesAG() || ST.slowLEA() || ST.slow3OpsLEA();
if (!OptLEA && !OptIncDec)
return false;
TSM.init(&Func.getSubtarget());
TII = ST.getInstrInfo();
DEBUG(dbgs() << "Start X86FixupLEAs\n";);
// Process all basic blocks.
for (MachineFunction::iterator I = Func.begin(), E = Func.end(); I != E; ++I)
processBasicBlock(Func, I);
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 int 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,
MachineFunction::iterator MFI) {
if (I == MFI->begin()) {
if (MFI->isPredecessor(&*MFI)) {
I = --MFI->end();
return true;
} else
return false;
}
--I;
return true;
}
MachineBasicBlock::iterator
FixupLEAPass::searchBackwards(MachineOperand &p, MachineBasicBlock::iterator &I,
MachineFunction::iterator MFI) {
int InstrDistance = 1;
MachineBasicBlock::iterator CurInst;
static const int INSTR_DISTANCE_THRESHOLD = 5;
CurInst = I;
bool Found;
Found = getPreviousInstr(CurInst, MFI);
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, MFI);
}
return MachineBasicBlock::iterator();
}
static inline bool isLEA(const int Opcode) {
return Opcode == X86::LEA16r || Opcode == X86::LEA32r ||
Opcode == X86::LEA64r || Opcode == X86::LEA64_32r;
}
static inline bool isInefficientLEAReg(unsigned int Reg) {
return Reg == X86::EBP || Reg == X86::RBP || Reg == X86::R13;
}
static inline bool isRegOperand(const MachineOperand &Op) {
return Op.isReg() && Op.getReg() != X86::NoRegister;
}
/// hasIneffecientLEARegs - LEA that uses base and index registers
/// where the base is EBP, RBP, or R13
static inline bool hasInefficientLEABaseReg(const MachineOperand &Base,
const MachineOperand &Index) {
return Base.isReg() && isInefficientLEAReg(Base.getReg()) &&
isRegOperand(Index);
}
static inline bool hasLEAOffset(const MachineOperand &Offset) {
return (Offset.isImm() && Offset.getImm() != 0) || Offset.isGlobal();
}
// LEA instruction that has all three operands: offset, base and index
static inline bool isThreeOperandsLEA(const MachineOperand &Base,
const MachineOperand &Index,
const MachineOperand &Offset) {
return isRegOperand(Base) && isRegOperand(Index) && hasLEAOffset(Offset);
}
static inline int getADDrrFromLEA(int LEAOpcode) {
switch (LEAOpcode) {
default:
llvm_unreachable("Unexpected LEA instruction");
case X86::LEA16r:
return X86::ADD16rr;
case X86::LEA32r:
return X86::ADD32rr;
case X86::LEA64_32r:
case X86::LEA64r:
return X86::ADD64rr;
}
}
static inline int getADDriFromLEA(int LEAOpcode, const MachineOperand &Offset) {
bool IsInt8 = Offset.isImm() && isInt<8>(Offset.getImm());
switch (LEAOpcode) {
default:
llvm_unreachable("Unexpected LEA instruction");
case X86::LEA16r:
return IsInt8 ? X86::ADD16ri8 : X86::ADD16ri;
case X86::LEA32r:
case X86::LEA64_32r:
return IsInt8 ? X86::ADD32ri8 : X86::ADD32ri;
case X86::LEA64r:
return IsInt8 ? X86::ADD64ri8 : X86::ADD64ri32;
}
}
/// isLEASimpleIncOrDec - Does this LEA have one these forms:
/// lea %reg, 1(%reg)
/// lea %reg, -1(%reg)
static inline bool isLEASimpleIncOrDec(MachineInstr &LEA) {
unsigned SrcReg = LEA.getOperand(1 + X86::AddrBaseReg).getReg();
unsigned DstReg = LEA.getOperand(0).getReg();
unsigned AddrDispOp = 1 + X86::AddrDisp;
return SrcReg == DstReg &&
LEA.getOperand(1 + X86::AddrIndexReg).getReg() == 0 &&
LEA.getOperand(1 + X86::AddrSegmentReg).getReg() == 0 &&
LEA.getOperand(AddrDispOp).isImm() &&
(LEA.getOperand(AddrDispOp).getImm() == 1 ||
LEA.getOperand(AddrDispOp).getImm() == -1);
}
bool FixupLEAPass::fixupIncDec(MachineBasicBlock::iterator &I,
MachineFunction::iterator MFI) const {
MachineInstr &MI = *I;
int Opcode = MI.getOpcode();
if (!isLEA(Opcode))
return false;
if (isLEASimpleIncOrDec(MI) && TII->isSafeToClobberEFLAGS(*MFI, I)) {
int NewOpcode;
bool isINC = MI.getOperand(4).getImm() == 1;
switch (Opcode) {
case X86::LEA16r:
NewOpcode = isINC ? X86::INC16r : X86::DEC16r;
break;
case X86::LEA32r:
case X86::LEA64_32r:
NewOpcode = isINC ? X86::INC32r : X86::DEC32r;
break;
case X86::LEA64r:
NewOpcode = isINC ? X86::INC64r : X86::DEC64r;
break;
}
MachineInstr *NewMI =
BuildMI(*MFI, I, MI.getDebugLoc(), TII->get(NewOpcode))
.add(MI.getOperand(0))
.add(MI.getOperand(1));
MFI->erase(I);
I = static_cast<MachineBasicBlock::iterator>(NewMI);
return true;
}
return false;
}
void FixupLEAPass::processInstruction(MachineBasicBlock::iterator &I,
MachineFunction::iterator MFI) {
// 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, MFI);
}
MachineOperand &q = MI.getOperand(AddrOffset + X86::AddrIndexReg);
if (q.isReg() && q.getReg() != X86::ESP) {
seekLEAFixup(q, I, MFI);
}
}
}
void FixupLEAPass::seekLEAFixup(MachineOperand &p,
MachineBasicBlock::iterator &I,
MachineFunction::iterator MFI) {
MachineBasicBlock::iterator MBI = searchBackwards(p, I, MFI);
if (MBI != MachineBasicBlock::iterator()) {
MachineInstr *NewMI = postRAConvertToLEA(MFI, MBI);
if (NewMI) {
++NumLEAs;
DEBUG(dbgs() << "FixLEA: Candidate to replace:"; MBI->dump(););
// now to replace with an equivalent LEA...
DEBUG(dbgs() << "FixLEA: Replaced by: "; NewMI->dump(););
MFI->erase(MBI);
MachineBasicBlock::iterator J =
static_cast<MachineBasicBlock::iterator>(NewMI);
processInstruction(J, MFI);
}
}
}
void FixupLEAPass::processInstructionForSLM(MachineBasicBlock::iterator &I,
MachineFunction::iterator MFI) {
MachineInstr &MI = *I;
const int Opcode = MI.getOpcode();
if (!isLEA(Opcode))
return;
if (MI.getOperand(5).getReg() != 0 || !MI.getOperand(4).isImm() ||
!TII->isSafeToClobberEFLAGS(*MFI, I))
return;
const unsigned DstR = MI.getOperand(0).getReg();
const unsigned SrcR1 = MI.getOperand(1).getReg();
const unsigned SrcR2 = MI.getOperand(3).getReg();
if ((SrcR1 == 0 || SrcR1 != DstR) && (SrcR2 == 0 || SrcR2 != DstR))
return;
if (MI.getOperand(2).getImm() > 1)
return;
DEBUG(dbgs() << "FixLEA: Candidate to replace:"; I->dump(););
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 = MI.getOperand(SrcR1 == DstR ? 3 : 1);
NewMI =
BuildMI(*MFI, I, MI.getDebugLoc(), ADDrr, DstR).addReg(DstR).add(Src);
DEBUG(NewMI->dump(););
}
// Make ADD instruction for immediate
if (MI.getOperand(4).getImm() != 0) {
const MCInstrDesc &ADDri =
TII->get(getADDriFromLEA(Opcode, MI.getOperand(4)));
const MachineOperand &SrcR = MI.getOperand(SrcR1 == DstR ? 1 : 3);
NewMI = BuildMI(*MFI, I, MI.getDebugLoc(), ADDri, DstR)
.add(SrcR)
.addImm(MI.getOperand(4).getImm());
DEBUG(NewMI->dump(););
}
if (NewMI) {
MFI->erase(I);
I = NewMI;
}
}
MachineInstr *
FixupLEAPass::processInstrForSlow3OpLEA(MachineInstr &MI,
MachineFunction::iterator MFI) {
const int LEAOpcode = MI.getOpcode();
if (!isLEA(LEAOpcode))
return nullptr;
const MachineOperand &Dst = MI.getOperand(0);
const MachineOperand &Base = MI.getOperand(1);
const MachineOperand &Scale = MI.getOperand(2);
const MachineOperand &Index = MI.getOperand(3);
const MachineOperand &Offset = MI.getOperand(4);
const MachineOperand &Segment = MI.getOperand(5);
if (!(isThreeOperandsLEA(Base, Index, Offset) ||
hasInefficientLEABaseReg(Base, Index)) ||
!TII->isSafeToClobberEFLAGS(*MFI, MI) ||
Segment.getReg() != X86::NoRegister)
return nullptr;
unsigned int DstR = Dst.getReg();
unsigned int BaseR = Base.getReg();
unsigned int IndexR = Index.getReg();
unsigned SSDstR =
(LEAOpcode == X86::LEA64_32r) ? getX86SubSuperRegister(DstR, 64) : DstR;
bool IsScale1 = Scale.getImm() == 1;
bool IsInefficientBase = isInefficientLEAReg(BaseR);
bool IsInefficientIndex = isInefficientLEAReg(IndexR);
// Skip these cases since it takes more than 2 instructions
// to replace the LEA instruction.
if (IsInefficientBase && SSDstR == BaseR && !IsScale1)
return nullptr;
if (LEAOpcode == X86::LEA64_32r && IsInefficientBase &&
(IsInefficientIndex || !IsScale1))
return nullptr;
const DebugLoc DL = MI.getDebugLoc();
const MCInstrDesc &ADDrr = TII->get(getADDrrFromLEA(LEAOpcode));
const MCInstrDesc &ADDri = TII->get(getADDriFromLEA(LEAOpcode, Offset));
DEBUG(dbgs() << "FixLEA: Candidate to replace:"; MI.dump(););
DEBUG(dbgs() << "FixLEA: Replaced by: ";);
// 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 && (DstR == BaseR || DstR == IndexR)) {
const MachineOperand &Src = DstR == BaseR ? Index : Base;
MachineInstr *NewMI =
BuildMI(*MFI, MI, DL, ADDrr, DstR).addReg(DstR).add(Src);
DEBUG(NewMI->dump(););
// Create ADD instruction for the Offset in case of 3-Ops LEA.
if (hasLEAOffset(Offset)) {
NewMI = BuildMI(*MFI, MI, DL, ADDri, DstR).addReg(DstR).add(Offset);
DEBUG(NewMI->dump(););
}
return NewMI;
}
// 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
if (!IsInefficientBase || (!IsInefficientIndex && IsScale1)) {
MachineInstr *NewMI = BuildMI(*MFI, MI, DL, TII->get(LEAOpcode))
.add(Dst)
.add(IsInefficientBase ? Index : Base)
.add(Scale)
.add(IsInefficientBase ? Base : Index)
.addImm(0)
.add(Segment);
DEBUG(NewMI->dump(););
// Create ADD instruction for the Offset in case of 3-Ops LEA.
if (hasLEAOffset(Offset)) {
NewMI = BuildMI(*MFI, MI, DL, ADDri, DstR).addReg(DstR).add(Offset);
DEBUG(NewMI->dump(););
}
return NewMI;
}
// Handle the rest of the cases with inefficient base register:
assert(SSDstR != BaseR && "SSDstR == BaseR should be handled already!");
assert(IsInefficientBase && "efficient base should be handled already!");
// lea (%base,%index,1), %dst => mov %base,%dst; add %index,%dst
if (IsScale1 && !hasLEAOffset(Offset)) {
bool BIK = Base.isKill() && BaseR != IndexR;
TII->copyPhysReg(*MFI, MI, DL, DstR, BaseR, BIK);
DEBUG(MI.getPrevNode()->dump(););
MachineInstr *NewMI =
BuildMI(*MFI, MI, DL, ADDrr, DstR).addReg(DstR).add(Index);
DEBUG(NewMI->dump(););
return NewMI;
}
// lea offset(%base,%index,scale), %dst =>
// lea offset( ,%index,scale), %dst; add %base,%dst
MachineInstr *NewMI = BuildMI(*MFI, MI, DL, TII->get(LEAOpcode))
.add(Dst)
.addReg(0)
.add(Scale)
.add(Index)
.add(Offset)
.add(Segment);
DEBUG(NewMI->dump(););
NewMI = BuildMI(*MFI, MI, DL, ADDrr, DstR).addReg(DstR).add(Base);
DEBUG(NewMI->dump(););
return NewMI;
}
bool FixupLEAPass::processBasicBlock(MachineFunction &MF,
MachineFunction::iterator MFI) {
for (MachineBasicBlock::iterator I = MFI->begin(); I != MFI->end(); ++I) {
if (OptIncDec)
if (fixupIncDec(I, MFI))
continue;
if (OptLEA) {
if (MF.getSubtarget<X86Subtarget>().isSLM())
processInstructionForSLM(I, MFI);
else {
if (MF.getSubtarget<X86Subtarget>().slow3OpsLEA()) {
if (auto *NewMI = processInstrForSlow3OpLEA(*I, MFI)) {
MFI->erase(I);
I = NewMI;
}
} else
processInstruction(I, MFI);
}
}
}
return false;
}
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