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llvm-project/llvm/lib/Target/X86/X86PeepholeOpt.cpp

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//===-- X86PeepholeOpt.cpp - X86 Peephole Optimizer -----------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains a peephole optimizer for the X86.
//
//===----------------------------------------------------------------------===//
#include "X86.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/Target/MRegisterInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
using namespace llvm;
namespace {
Statistic<> NumPHOpts("x86-peephole",
"Number of peephole optimization performed");
Statistic<> NumPHMoves("x86-peephole", "Number of peephole moves folded");
struct PH : public MachineFunctionPass {
virtual bool runOnMachineFunction(MachineFunction &MF);
bool PeepholeOptimize(MachineBasicBlock &MBB,
MachineBasicBlock::iterator &I);
virtual const char *getPassName() const { return "X86 Peephole Optimizer"; }
};
}
FunctionPass *llvm::createX86PeepholeOptimizerPass() { return new PH(); }
bool PH::runOnMachineFunction(MachineFunction &MF) {
bool Changed = false;
for (MachineFunction::iterator BI = MF.begin(), E = MF.end(); BI != E; ++BI)
for (MachineBasicBlock::iterator I = BI->begin(); I != BI->end(); )
if (PeepholeOptimize(*BI, I)) {
Changed = true;
++NumPHOpts;
} else
++I;
return Changed;
}
bool PH::PeepholeOptimize(MachineBasicBlock &MBB,
MachineBasicBlock::iterator &I) {
assert(I != MBB.end());
MachineBasicBlock::iterator NextI = next(I);
MachineInstr *MI = I;
MachineInstr *Next = (NextI != MBB.end()) ? &*NextI : (MachineInstr*)0;
unsigned Size = 0;
switch (MI->getOpcode()) {
case X86::MOV8rr:
case X86::MOV16rr:
case X86::MOV32rr: // Destroy X = X copies...
if (MI->getOperand(0).getReg() == MI->getOperand(1).getReg()) {
I = MBB.erase(I);
return true;
}
return false;
// A large number of X86 instructions have forms which take an 8-bit
// immediate despite the fact that the operands are 16 or 32 bits. Because
// this can save three bytes of code size (and icache space), we want to
// shrink them if possible.
case X86::IMUL16rri: case X86::IMUL32rri:
assert(MI->getNumOperands() == 3 && "These should all have 3 operands!");
if (MI->getOperand(2).isImmediate()) {
int Val = MI->getOperand(2).getImmedValue();
// If the value is the same when signed extended from 8 bits...
if (Val == (signed int)(signed char)Val) {
unsigned Opcode;
switch (MI->getOpcode()) {
default: assert(0 && "Unknown opcode value!");
case X86::IMUL16rri: Opcode = X86::IMUL16rri8; break;
case X86::IMUL32rri: Opcode = X86::IMUL32rri8; break;
}
unsigned R0 = MI->getOperand(0).getReg();
unsigned R1 = MI->getOperand(1).getReg();
I = MBB.insert(MBB.erase(I),
BuildMI(Opcode, 2, R0).addReg(R1).addZImm((char)Val));
return true;
}
}
return false;
#if 0
case X86::IMUL16rmi: case X86::IMUL32rmi:
assert(MI->getNumOperands() == 6 && "These should all have 6 operands!");
if (MI->getOperand(5).isImmediate()) {
int Val = MI->getOperand(5).getImmedValue();
// If the value is the same when signed extended from 8 bits...
if (Val == (signed int)(signed char)Val) {
unsigned Opcode;
switch (MI->getOpcode()) {
default: assert(0 && "Unknown opcode value!");
case X86::IMUL16rmi: Opcode = X86::IMUL16rmi8; break;
case X86::IMUL32rmi: Opcode = X86::IMUL32rmi8; break;
}
unsigned R0 = MI->getOperand(0).getReg();
unsigned R1 = MI->getOperand(1).getReg();
unsigned Scale = MI->getOperand(2).getImmedValue();
unsigned R2 = MI->getOperand(3).getReg();
unsigned Offset = MI->getOperand(4).getImmedValue();
I = MBB.insert(MBB.erase(I),
BuildMI(Opcode, 5, R0).addReg(R1).addZImm(Scale).
addReg(R2).addSImm(Offset).addZImm((char)Val));
return true;
}
}
return false;
#endif
case X86::ADD16ri: case X86::ADD32ri: case X86::ADC32ri:
case X86::SUB16ri: case X86::SUB32ri:
case X86::SBB16ri: case X86::SBB32ri:
case X86::AND16ri: case X86::AND32ri:
case X86::OR16ri: case X86::OR32ri:
case X86::XOR16ri: case X86::XOR32ri:
assert(MI->getNumOperands() == 2 && "These should all have 2 operands!");
if (MI->getOperand(1).isImmediate()) {
int Val = MI->getOperand(1).getImmedValue();
// If the value is the same when signed extended from 8 bits...
if (Val == (signed int)(signed char)Val) {
unsigned Opcode;
switch (MI->getOpcode()) {
default: assert(0 && "Unknown opcode value!");
case X86::ADD16ri: Opcode = X86::ADD16ri8; break;
case X86::ADD32ri: Opcode = X86::ADD32ri8; break;
case X86::ADC32ri: Opcode = X86::ADC32ri8; break;
case X86::SUB16ri: Opcode = X86::SUB16ri8; break;
case X86::SUB32ri: Opcode = X86::SUB32ri8; break;
case X86::SBB16ri: Opcode = X86::SBB16ri8; break;
case X86::SBB32ri: Opcode = X86::SBB32ri8; break;
case X86::AND16ri: Opcode = X86::AND16ri8; break;
case X86::AND32ri: Opcode = X86::AND32ri8; break;
case X86::OR16ri: Opcode = X86::OR16ri8; break;
case X86::OR32ri: Opcode = X86::OR32ri8; break;
case X86::XOR16ri: Opcode = X86::XOR16ri8; break;
case X86::XOR32ri: Opcode = X86::XOR32ri8; break;
}
unsigned R0 = MI->getOperand(0).getReg();
I = MBB.insert(MBB.erase(I),
BuildMI(Opcode, 1, R0, MachineOperand::UseAndDef)
.addZImm((char)Val));
return true;
}
}
return false;
case X86::ADD16mi: case X86::ADD32mi: case X86::ADC32mi:
case X86::SUB16mi: case X86::SUB32mi:
case X86::SBB16mi: case X86::SBB32mi:
case X86::AND16mi: case X86::AND32mi:
case X86::OR16mi: case X86::OR32mi:
case X86::XOR16mi: case X86::XOR32mi:
assert(MI->getNumOperands() == 5 && "These should all have 5 operands!");
if (MI->getOperand(4).isImmediate()) {
int Val = MI->getOperand(4).getImmedValue();
// If the value is the same when signed extended from 8 bits...
if (Val == (signed int)(signed char)Val) {
unsigned Opcode;
switch (MI->getOpcode()) {
default: assert(0 && "Unknown opcode value!");
case X86::ADD16mi: Opcode = X86::ADD16mi8; break;
case X86::ADD32mi: Opcode = X86::ADD32mi8; break;
case X86::ADC32mi: Opcode = X86::ADC32mi8; break;
case X86::SUB16mi: Opcode = X86::SUB16mi8; break;
case X86::SUB32mi: Opcode = X86::SUB32mi8; break;
case X86::SBB16mi: Opcode = X86::SBB16mi8; break;
case X86::SBB32mi: Opcode = X86::SBB32mi8; break;
case X86::AND16mi: Opcode = X86::AND16mi8; break;
case X86::AND32mi: Opcode = X86::AND32mi8; break;
case X86::OR16mi: Opcode = X86::OR16mi8; break;
case X86::OR32mi: Opcode = X86::OR32mi8; break;
case X86::XOR16mi: Opcode = X86::XOR16mi8; break;
case X86::XOR32mi: Opcode = X86::XOR32mi8; break;
}
unsigned R0 = MI->getOperand(0).getReg();
unsigned Scale = MI->getOperand(1).getImmedValue();
unsigned R1 = MI->getOperand(2).getReg();
unsigned Offset = MI->getOperand(3).getImmedValue();
I = MBB.insert(MBB.erase(I),
BuildMI(Opcode, 5).addReg(R0).addZImm(Scale).
addReg(R1).addSImm(Offset).addZImm((char)Val));
return true;
}
}
return false;
#if 0
case X86::MOV32ri: Size++;
case X86::MOV16ri: Size++;
case X86::MOV8ri:
// FIXME: We can only do this transformation if we know that flags are not
// used here, because XOR clobbers the flags!
if (MI->getOperand(1).isImmediate()) { // avoid mov EAX, <value>
int Val = MI->getOperand(1).getImmedValue();
if (Val == 0) { // mov EAX, 0 -> xor EAX, EAX
static const unsigned Opcode[] ={X86::XOR8rr,X86::XOR16rr,X86::XOR32rr};
unsigned Reg = MI->getOperand(0).getReg();
I = MBB.insert(MBB.erase(I),
BuildMI(Opcode[Size], 2, Reg).addReg(Reg).addReg(Reg));
return true;
} else if (Val == -1) { // mov EAX, -1 -> or EAX, -1
// TODO: 'or Reg, -1' has a smaller encoding than 'mov Reg, -1'
}
}
return false;
#endif
case X86::BSWAP32r: // Change bswap EAX, bswap EAX into nothing
if (Next->getOpcode() == X86::BSWAP32r &&
MI->getOperand(0).getReg() == Next->getOperand(0).getReg()) {
I = MBB.erase(MBB.erase(I));
return true;
}
return false;
default:
return false;
}
}
namespace {
class UseDefChains : public MachineFunctionPass {
std::vector<MachineInstr*> DefiningInst;
public:
// getDefinition - Return the machine instruction that defines the specified
// SSA virtual register.
MachineInstr *getDefinition(unsigned Reg) {
assert(MRegisterInfo::isVirtualRegister(Reg) &&
"use-def chains only exist for SSA registers!");
assert(Reg - MRegisterInfo::FirstVirtualRegister < DefiningInst.size() &&
"Unknown register number!");
assert(DefiningInst[Reg-MRegisterInfo::FirstVirtualRegister] &&
"Unknown register number!");
return DefiningInst[Reg-MRegisterInfo::FirstVirtualRegister];
}
// setDefinition - Update the use-def chains to indicate that MI defines
// register Reg.
void setDefinition(unsigned Reg, MachineInstr *MI) {
if (Reg-MRegisterInfo::FirstVirtualRegister >= DefiningInst.size())
DefiningInst.resize(Reg-MRegisterInfo::FirstVirtualRegister+1);
DefiningInst[Reg-MRegisterInfo::FirstVirtualRegister] = MI;
}
// removeDefinition - Update the use-def chains to forget about Reg
// entirely.
void removeDefinition(unsigned Reg) {
assert(getDefinition(Reg)); // Check validity
DefiningInst[Reg-MRegisterInfo::FirstVirtualRegister] = 0;
}
virtual bool runOnMachineFunction(MachineFunction &MF) {
for (MachineFunction::iterator BI = MF.begin(), E = MF.end(); BI!=E; ++BI)
for (MachineBasicBlock::iterator I = BI->begin(); I != BI->end(); ++I) {
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
MachineOperand &MO = I->getOperand(i);
if (MO.isRegister() && MO.isDef() && !MO.isUse() &&
MRegisterInfo::isVirtualRegister(MO.getReg()))
setDefinition(MO.getReg(), I);
}
}
return false;
}
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesAll();
MachineFunctionPass::getAnalysisUsage(AU);
}
virtual void releaseMemory() {
std::vector<MachineInstr*>().swap(DefiningInst);
}
};
RegisterAnalysis<UseDefChains> X("use-def-chains",
"use-def chain construction for machine code");
}
namespace {
Statistic<> NumSSAPHOpts("x86-ssa-peephole",
"Number of SSA peephole optimization performed");
/// SSAPH - This pass is an X86-specific, SSA-based, peephole optimizer. This
/// pass is really a bad idea: a better instruction selector should completely
/// supersume it. However, that will take some time to develop, and the
/// simple things this can do are important now.
class SSAPH : public MachineFunctionPass {
UseDefChains *UDC;
public:
virtual bool runOnMachineFunction(MachineFunction &MF);
bool PeepholeOptimize(MachineBasicBlock &MBB,
MachineBasicBlock::iterator &I);
virtual const char *getPassName() const {
return "X86 SSA-based Peephole Optimizer";
}
/// Propagate - Set MI[DestOpNo] = Src[SrcOpNo], optionally change the
/// opcode of the instruction, then return true.
bool Propagate(MachineInstr *MI, unsigned DestOpNo,
MachineInstr *Src, unsigned SrcOpNo, unsigned NewOpcode = 0){
MI->getOperand(DestOpNo) = Src->getOperand(SrcOpNo);
if (NewOpcode) MI->setOpcode(NewOpcode);
return true;
}
/// OptimizeAddress - If we can fold the addressing arithmetic for this
/// memory instruction into the instruction itself, do so and return true.
bool OptimizeAddress(MachineInstr *MI, unsigned OpNo);
/// getDefininingInst - If the specified operand is a read of an SSA
/// register, return the machine instruction defining it, otherwise, return
/// null.
MachineInstr *getDefiningInst(MachineOperand &MO) {
if (MO.isDef() || !MO.isRegister() ||
!MRegisterInfo::isVirtualRegister(MO.getReg())) return 0;
return UDC->getDefinition(MO.getReg());
}
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<UseDefChains>();
AU.addPreserved<UseDefChains>();
MachineFunctionPass::getAnalysisUsage(AU);
}
};
}
FunctionPass *llvm::createX86SSAPeepholeOptimizerPass() { return new SSAPH(); }
bool SSAPH::runOnMachineFunction(MachineFunction &MF) {
bool Changed = false;
bool LocalChanged;
UDC = &getAnalysis<UseDefChains>();
do {
LocalChanged = false;
for (MachineFunction::iterator BI = MF.begin(), E = MF.end(); BI != E; ++BI)
for (MachineBasicBlock::iterator I = BI->begin(); I != BI->end(); )
if (PeepholeOptimize(*BI, I)) {
LocalChanged = true;
++NumSSAPHOpts;
} else
++I;
Changed |= LocalChanged;
} while (LocalChanged);
return Changed;
}
static bool isValidScaleAmount(unsigned Scale) {
return Scale == 1 || Scale == 2 || Scale == 4 || Scale == 8;
}
/// OptimizeAddress - If we can fold the addressing arithmetic for this
/// memory instruction into the instruction itself, do so and return true.
bool SSAPH::OptimizeAddress(MachineInstr *MI, unsigned OpNo) {
MachineOperand &BaseRegOp = MI->getOperand(OpNo+0);
MachineOperand &ScaleOp = MI->getOperand(OpNo+1);
MachineOperand &IndexRegOp = MI->getOperand(OpNo+2);
MachineOperand &DisplacementOp = MI->getOperand(OpNo+3);
unsigned BaseReg = BaseRegOp.hasAllocatedReg() ? BaseRegOp.getReg() : 0;
unsigned Scale = ScaleOp.getImmedValue();
unsigned IndexReg = IndexRegOp.hasAllocatedReg() ? IndexRegOp.getReg() : 0;
bool Changed = false;
// If the base register is unset, and the index register is set with a scale
// of 1, move it to be the base register.
if (BaseRegOp.hasAllocatedReg() && BaseReg == 0 &&
Scale == 1 && IndexReg != 0) {
BaseRegOp.setReg(IndexReg);
IndexRegOp.setReg(0);
return true;
}
// Attempt to fold instructions used by the base register into the instruction
if (MachineInstr *DefInst = getDefiningInst(BaseRegOp)) {
switch (DefInst->getOpcode()) {
case X86::MOV32ri:
// If there is no displacement set for this instruction set one now.
// FIXME: If we can fold two immediates together, we should do so!
if (DisplacementOp.isImmediate() && !DisplacementOp.getImmedValue()) {
if (DefInst->getOperand(1).isImmediate()) {
BaseRegOp.setReg(0);
return Propagate(MI, OpNo+3, DefInst, 1);
}
}
break;
case X86::ADD32rr:
// If the source is a register-register add, and we do not yet have an
// index register, fold the add into the memory address.
if (IndexReg == 0) {
BaseRegOp = DefInst->getOperand(1);
IndexRegOp = DefInst->getOperand(2);
ScaleOp.setImmedValue(1);
return true;
}
break;
case X86::SHL32ri:
// If this shift could be folded into the index portion of the address if
// it were the index register, move it to the index register operand now,
// so it will be folded in below.
if ((Scale == 1 || (IndexReg == 0 && IndexRegOp.hasAllocatedReg())) &&
DefInst->getOperand(2).getImmedValue() < 4) {
std::swap(BaseRegOp, IndexRegOp);
ScaleOp.setImmedValue(1); Scale = 1;
std::swap(IndexReg, BaseReg);
Changed = true;
break;
}
}
}
// Attempt to fold instructions used by the index into the instruction
if (MachineInstr *DefInst = getDefiningInst(IndexRegOp)) {
switch (DefInst->getOpcode()) {
case X86::SHL32ri: {
// Figure out what the resulting scale would be if we folded this shift.
unsigned ResScale = Scale * (1 << DefInst->getOperand(2).getImmedValue());
if (isValidScaleAmount(ResScale)) {
IndexRegOp = DefInst->getOperand(1);
ScaleOp.setImmedValue(ResScale);
return true;
}
break;
}
}
}
return Changed;
}
bool SSAPH::PeepholeOptimize(MachineBasicBlock &MBB,
MachineBasicBlock::iterator &I) {
MachineBasicBlock::iterator NextI = next(I);
MachineInstr *MI = I;
MachineInstr *Next = (NextI != MBB.end()) ? &*NextI : (MachineInstr*)0;
bool Changed = false;
const TargetInstrInfo &TII = *MBB.getParent()->getTarget().getInstrInfo();
// Scan the operands of this instruction. If any operands are
// register-register copies, replace the operand with the source.
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i)
// Is this an SSA register use?
if (MachineInstr *DefInst = getDefiningInst(MI->getOperand(i))) {
// If the operand is a vreg-vreg copy, it is always safe to replace the
// source value with the input operand.
unsigned Source, Dest;
if (TII.isMoveInstr(*DefInst, Source, Dest)) {
// Don't propagate physical registers into any instructions.
if (DefInst->getOperand(1).isRegister() &&
MRegisterInfo::isVirtualRegister(Source)) {
MI->getOperand(i).setReg(Source);
Changed = true;
++NumPHMoves;
}
}
}
// Perform instruction specific optimizations.
switch (MI->getOpcode()) {
// Register to memory stores. Format: <base,scale,indexreg,immdisp>, srcreg
case X86::MOV32mr: case X86::MOV16mr: case X86::MOV8mr:
case X86::MOV32mi: case X86::MOV16mi: case X86::MOV8mi:
// Check to see if we can fold the source instruction into this one...
if (MachineInstr *SrcInst = getDefiningInst(MI->getOperand(4))) {
switch (SrcInst->getOpcode()) {
// Fold the immediate value into the store, if possible.
case X86::MOV8ri: return Propagate(MI, 4, SrcInst, 1, X86::MOV8mi);
case X86::MOV16ri: return Propagate(MI, 4, SrcInst, 1, X86::MOV16mi);
case X86::MOV32ri: return Propagate(MI, 4, SrcInst, 1, X86::MOV32mi);
default: break;
}
}
// If we can optimize the addressing expression, do so now.
if (OptimizeAddress(MI, 0))
return true;
break;
case X86::MOV32rm:
case X86::MOV16rm:
case X86::MOV8rm:
// If we can optimize the addressing expression, do so now.
if (OptimizeAddress(MI, 1))
return true;
break;
default: break;
}
return Changed;
}
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