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//===-- LanaiMemAluCombiner.cpp - Pass to combine memory & ALU operations -===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// Simple pass to combine memory and ALU operations
// The Lanai ISA supports instructions where a load/store modifies the base
// register used in the load/store operation. This pass finds suitable
// load/store and ALU instructions and combines them into one instruction.
// For example,
// ld [ %r6 -- ], %r12
// is a supported instruction that is not currently generated by the instruction
// selection pass of this backend. This pass generates these instructions by
// merging
// add %r6, -4, %r6
// followed by
// ld [ %r6 ], %r12
// in the same machine basic block into one machine instruction.
#include "LanaiAluCode.h"
#include "LanaiTargetMachine.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/RegisterScavenging.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/Support/CommandLine.h"
using namespace llvm;
#include ""
#define DEBUG_TYPE "lanai-mem-alu-combiner"
STATISTIC(NumLdStAluCombined, "Number of memory and ALU instructions combined");
static llvm::cl::opt<bool> DisableMemAluCombiner(
"disable-lanai-mem-alu-combiner", llvm::cl::init(false),
llvm::cl::desc("Do not combine ALU and memory operators"),
namespace llvm {
void initializeLanaiMemAluCombinerPass(PassRegistry &);
} // namespace llvm
namespace {
typedef MachineBasicBlock::iterator MbbIterator;
typedef MachineFunction::iterator MfIterator;
class LanaiMemAluCombiner : public MachineFunctionPass {
static char ID;
explicit LanaiMemAluCombiner() : MachineFunctionPass(ID) {
StringRef getPassName() const override {
return "Lanai load / store optimization pass";
bool runOnMachineFunction(MachineFunction &F) override;
MachineFunctionProperties getRequiredProperties() const override {
return MachineFunctionProperties().set(
MbbIterator findClosestSuitableAluInstr(MachineBasicBlock *BB,
const MbbIterator &MemInstr,
bool Decrement);
void insertMergedInstruction(MachineBasicBlock *BB,
const MbbIterator &MemInstr,
const MbbIterator &AluInstr, bool Before);
bool combineMemAluInBasicBlock(MachineBasicBlock *BB);
// Target machine description which we query for register names, data
// layout, etc.
const TargetInstrInfo *TII;
} // namespace
char LanaiMemAluCombiner::ID = 0;
"Lanai memory ALU combiner pass", false, false)
namespace {
bool isSpls(uint16_t Opcode) { return Lanai::splsIdempotent(Opcode) == Opcode; }
// Determine the opcode for the merged instruction created by considering the
// old memory operation's opcode and whether the merged opcode will have an
// immediate offset.
unsigned mergedOpcode(unsigned OldOpcode, bool ImmediateOffset) {
switch (OldOpcode) {
case Lanai::LDW_RI:
case Lanai::LDW_RR:
if (ImmediateOffset)
return Lanai::LDW_RI;
return Lanai::LDW_RR;
case Lanai::LDHs_RI:
case Lanai::LDHs_RR:
if (ImmediateOffset)
return Lanai::LDHs_RI;
return Lanai::LDHs_RR;
case Lanai::LDHz_RI:
case Lanai::LDHz_RR:
if (ImmediateOffset)
return Lanai::LDHz_RI;
return Lanai::LDHz_RR;
case Lanai::LDBs_RI:
case Lanai::LDBs_RR:
if (ImmediateOffset)
return Lanai::LDBs_RI;
return Lanai::LDBs_RR;
case Lanai::LDBz_RI:
case Lanai::LDBz_RR:
if (ImmediateOffset)
return Lanai::LDBz_RI;
return Lanai::LDBz_RR;
case Lanai::SW_RI:
case Lanai::SW_RR:
if (ImmediateOffset)
return Lanai::SW_RI;
return Lanai::SW_RR;
case Lanai::STB_RI:
case Lanai::STB_RR:
if (ImmediateOffset)
return Lanai::STB_RI;
return Lanai::STB_RR;
case Lanai::STH_RI:
case Lanai::STH_RR:
if (ImmediateOffset)
return Lanai::STH_RI;
return Lanai::STH_RR;
return 0;
// Check if the machine instruction has non-volatile memory operands of the type
// supported for combining with ALU instructions.
bool isNonVolatileMemoryOp(const MachineInstr &MI) {
if (!MI.hasOneMemOperand())
return false;
// Determine if the machine instruction is a supported memory operation by
// testing if the computed merge opcode is a valid memory operation opcode.
if (mergedOpcode(MI.getOpcode(), false) == 0)
return false;
const MachineMemOperand *MemOperand = *MI.memoperands_begin();
// Don't move volatile memory accesses
// TODO: unclear if we need to be as conservative about atomics
if (MemOperand->isVolatile() || MemOperand->isAtomic())
return false;
return true;
// Test to see if two machine operands are of the same type. This test is less
// strict than the MachineOperand::isIdenticalTo function.
bool isSameOperand(const MachineOperand &Op1, const MachineOperand &Op2) {
if (Op1.getType() != Op2.getType())
return false;
switch (Op1.getType()) {
case MachineOperand::MO_Register:
return Op1.getReg() == Op2.getReg();
case MachineOperand::MO_Immediate:
return Op1.getImm() == Op2.getImm();
return false;
bool isZeroOperand(const MachineOperand &Op) {
return ((Op.isReg() && Op.getReg() == Lanai::R0) ||
(Op.isImm() && Op.getImm() == 0));
// Determines whether a register is used by an instruction.
bool InstrUsesReg(const MbbIterator &Instr, const MachineOperand *Reg) {
for (MachineInstr::const_mop_iterator Mop = Instr->operands_begin();
Mop != Instr->operands_end(); ++Mop) {
if (isSameOperand(*Mop, *Reg))
return true;
return false;
// Converts between machine opcode and AluCode.
// Flag using/modifying ALU operations should not be considered for merging and
// are omitted from this list.
LPAC::AluCode mergedAluCode(unsigned AluOpcode) {
switch (AluOpcode) {
case Lanai::ADD_I_LO:
case Lanai::ADD_R:
return LPAC::ADD;
case Lanai::SUB_I_LO:
case Lanai::SUB_R:
return LPAC::SUB;
case Lanai::AND_I_LO:
case Lanai::AND_R:
return LPAC::AND;
case Lanai::OR_I_LO:
case Lanai::OR_R:
return LPAC::OR;
case Lanai::XOR_I_LO:
case Lanai::XOR_R:
return LPAC::XOR;
case Lanai::SHL_R:
return LPAC::SHL;
case Lanai::SRL_R:
return LPAC::SRL;
case Lanai::SRA_R:
return LPAC::SRA;
case Lanai::SA_I:
case Lanai::SL_I:
// Insert a new combined memory and ALU operation instruction.
// This function builds a new machine instruction using the MachineInstrBuilder
// class and inserts it before the memory instruction.
void LanaiMemAluCombiner::insertMergedInstruction(MachineBasicBlock *BB,
const MbbIterator &MemInstr,
const MbbIterator &AluInstr,
bool Before) {
// Insert new combined load/store + alu operation
MachineOperand Dest = MemInstr->getOperand(0);
MachineOperand Base = MemInstr->getOperand(1);
MachineOperand MemOffset = MemInstr->getOperand(2);
MachineOperand AluOffset = AluInstr->getOperand(2);
// Abort if ALU offset is not a register or immediate
assert((AluOffset.isReg() || AluOffset.isImm()) &&
"Unsupported operand type in merge");
// Determined merged instructions opcode and ALU code
LPAC::AluCode AluOpcode = mergedAluCode(AluInstr->getOpcode());
unsigned NewOpc = mergedOpcode(MemInstr->getOpcode(), AluOffset.isImm());
assert(AluOpcode != LPAC::UNKNOWN && "Unknown ALU code in merging");
assert(NewOpc != 0 && "Unknown merged node opcode");
// Build and insert new machine instruction
MachineInstrBuilder InstrBuilder =
BuildMI(*BB, MemInstr, MemInstr->getDebugLoc(), TII->get(NewOpc));
InstrBuilder.addReg(Dest.getReg(), getDefRegState(true));
InstrBuilder.addReg(Base.getReg(), getKillRegState(true));
// Add offset to machine instruction
if (AluOffset.isReg())
else if (AluOffset.isImm())
llvm_unreachable("Unsupported ld/st ALU merge.");
// Create a pre-op if the ALU operation preceded the memory operation or the
// MemOffset is non-zero (i.e. the memory value should be adjusted before
// accessing it), else create a post-op.
if (Before || !isZeroOperand(MemOffset))
// Transfer memory operands.
// Function determines if ALU operation (in alu_iter) can be combined with
// a load/store with base and offset.
bool isSuitableAluInstr(bool IsSpls, const MbbIterator &AluIter,
const MachineOperand &Base,
const MachineOperand &Offset) {
// ALU operations have 3 operands
if (AluIter->getNumOperands() != 3)
return false;
MachineOperand &Dest = AluIter->getOperand(0);
MachineOperand &Op1 = AluIter->getOperand(1);
MachineOperand &Op2 = AluIter->getOperand(2);
// Only match instructions using the base register as destination and with the
// base and first operand equal
if (!isSameOperand(Dest, Base) || !isSameOperand(Dest, Op1))
return false;
if (Op2.isImm()) {
// It is not a match if the 2nd operand in the ALU operation is an
// immediate but the ALU operation is not an addition.
if (AluIter->getOpcode() != Lanai::ADD_I_LO)
return false;
if (Offset.isReg() && Offset.getReg() == Lanai::R0)
return true;
if (Offset.isImm() &&
((Offset.getImm() == 0 &&
// Check that the Op2 would fit in the immediate field of the
// memory operation.
((IsSpls && isInt<10>(Op2.getImm())) ||
(!IsSpls && isInt<16>(Op2.getImm())))) ||
Offset.getImm() == Op2.getImm()))
return true;
} else if (Op2.isReg()) {
// The Offset and 2nd operand are both registers and equal
if (Offset.isReg() && Op2.getReg() == Offset.getReg())
return true;
} else
// Only consider operations with register or immediate values
return false;
return false;
MbbIterator LanaiMemAluCombiner::findClosestSuitableAluInstr(
MachineBasicBlock *BB, const MbbIterator &MemInstr, const bool Decrement) {
MachineOperand *Base = &MemInstr->getOperand(1);
MachineOperand *Offset = &MemInstr->getOperand(2);
bool IsSpls = isSpls(MemInstr->getOpcode());
MbbIterator First = MemInstr;
MbbIterator Last = Decrement ? BB->begin() : BB->end();
while (First != Last) {
Decrement ? --First : ++First;
if (First == Last)
// Skip over debug instructions
if (First->isDebugInstr())
if (isSuitableAluInstr(IsSpls, First, *Base, *Offset)) {
return First;
// Usage of the base or offset register is not a form suitable for merging.
if (First != Last) {
if (InstrUsesReg(First, Base))
if (Offset->isReg() && InstrUsesReg(First, Offset))
return MemInstr;
bool LanaiMemAluCombiner::combineMemAluInBasicBlock(MachineBasicBlock *BB) {
bool Modified = false;
MbbIterator MBBIter = BB->begin(), End = BB->end();
while (MBBIter != End) {
bool IsMemOp = isNonVolatileMemoryOp(*MBBIter);
if (IsMemOp) {
MachineOperand AluOperand = MBBIter->getOperand(3);
unsigned int DestReg = MBBIter->getOperand(0).getReg(),
BaseReg = MBBIter->getOperand(1).getReg();
assert(AluOperand.isImm() && "Unexpected memory operator type");
LPAC::AluCode AluOpcode = static_cast<LPAC::AluCode>(AluOperand.getImm());
// Skip memory operations that already modify the base register or if
// the destination and base register are the same
if (!LPAC::modifiesOp(AluOpcode) && DestReg != BaseReg) {
for (int Inc = 0; Inc <= 1; ++Inc) {
MbbIterator AluIter =
findClosestSuitableAluInstr(BB, MBBIter, Inc == 0);
if (AluIter != MBBIter) {
insertMergedInstruction(BB, MBBIter, AluIter, Inc == 0);
Modified = true;
// Erase the matching ALU instruction
// Erase old load/store instruction
if (MBBIter == End)
return Modified;
// Driver function that iterates over the machine basic building blocks of a
// machine function
bool LanaiMemAluCombiner::runOnMachineFunction(MachineFunction &MF) {
if (DisableMemAluCombiner)
return false;
TII = MF.getSubtarget<LanaiSubtarget>().getInstrInfo();
bool Modified = false;
for (MfIterator MFI = MF.begin(); MFI != MF.end(); ++MFI) {
Modified |= combineMemAluInBasicBlock(&*MFI);
return Modified;
} // namespace
FunctionPass *llvm::createLanaiMemAluCombinerPass() {
return new LanaiMemAluCombiner();