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//===- MipsOptimizePICCall.cpp - Optimize PIC Calls -----------------------===//
// 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
// This pass eliminates unnecessary instructions that set up $gp and replace
// instructions that load target function addresses with copy instructions.
#include "MCTargetDesc/MipsBaseInfo.h"
#include "Mips.h"
#include "MipsRegisterInfo.h"
#include "MipsSubtarget.h"
#include "llvm/ADT/PointerUnion.h"
#include "llvm/ADT/ScopedHashTable.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/MachineValueType.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/CodeGen/TargetOpcodes.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/RecyclingAllocator.h"
#include <cassert>
#include <utility>
#include <vector>
using namespace llvm;
#define DEBUG_TYPE "optimize-mips-pic-call"
static cl::opt<bool> LoadTargetFromGOT("mips-load-target-from-got",
cl::desc("Load target address from GOT"),
static cl::opt<bool> EraseGPOpnd("mips-erase-gp-opnd",
cl::init(true), cl::desc("Erase GP Operand"),
namespace {
using ValueType = PointerUnion<const Value *, const PseudoSourceValue *>;
using CntRegP = std::pair<unsigned, unsigned>;
using AllocatorTy = RecyclingAllocator<BumpPtrAllocator,
ScopedHashTableVal<ValueType, CntRegP>>;
using ScopedHTType = ScopedHashTable<ValueType, CntRegP,
DenseMapInfo<ValueType>, AllocatorTy>;
class MBBInfo {
MBBInfo(MachineDomTreeNode *N);
const MachineDomTreeNode *getNode() const;
bool isVisited() const;
void preVisit(ScopedHTType &ScopedHT);
void postVisit();
MachineDomTreeNode *Node;
ScopedHTType::ScopeTy *HTScope;
class OptimizePICCall : public MachineFunctionPass {
OptimizePICCall() : MachineFunctionPass(ID) {}
StringRef getPassName() const override { return "Mips OptimizePICCall"; }
bool runOnMachineFunction(MachineFunction &F) override;
void getAnalysisUsage(AnalysisUsage &AU) const override {
/// Visit MBB.
bool visitNode(MBBInfo &MBBI);
/// Test if MI jumps to a function via a register.
/// Also, return the virtual register containing the target function's address
/// and the underlying object in Reg and Val respectively, if the function's
/// address can be resolved lazily.
bool isCallViaRegister(MachineInstr &MI, unsigned &Reg,
ValueType &Val) const;
/// Return the number of instructions that dominate the current
/// instruction and load the function address from object Entry.
unsigned getCount(ValueType Entry);
/// Return the destination virtual register of the last instruction
/// that loads from object Entry.
unsigned getReg(ValueType Entry);
/// Update ScopedHT.
void incCntAndSetReg(ValueType Entry, unsigned Reg);
ScopedHTType ScopedHT;
static char ID;
} // end of anonymous namespace
char OptimizePICCall::ID = 0;
/// Return the first MachineOperand of MI if it is a used virtual register.
static MachineOperand *getCallTargetRegOpnd(MachineInstr &MI) {
if (MI.getNumOperands() == 0)
return nullptr;
MachineOperand &MO = MI.getOperand(0);
if (!MO.isReg() || !MO.isUse() || !MO.getReg().isVirtual())
return nullptr;
return &MO;
/// Return type of register Reg.
static MVT::SimpleValueType getRegTy(unsigned Reg, MachineFunction &MF) {
const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
const TargetRegisterClass *RC = MF.getRegInfo().getRegClass(Reg);
assert(TRI.legalclasstypes_end(*RC) - TRI.legalclasstypes_begin(*RC) == 1);
return *TRI.legalclasstypes_begin(*RC);
/// Do the following transformation:
/// jalr $vreg
/// =>
/// copy $t9, $vreg
/// jalr $t9
static void setCallTargetReg(MachineBasicBlock *MBB,
MachineBasicBlock::iterator I) {
MachineFunction &MF = *MBB->getParent();
const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();
Register SrcReg = I->getOperand(0).getReg();
unsigned DstReg = getRegTy(SrcReg, MF) == MVT::i32 ? Mips::T9 : Mips::T9_64;
BuildMI(*MBB, I, I->getDebugLoc(), TII.get(TargetOpcode::COPY), DstReg)
/// Search MI's operands for register GP and erase it.
static void eraseGPOpnd(MachineInstr &MI) {
if (!EraseGPOpnd)
MachineFunction &MF = *MI.getParent()->getParent();
MVT::SimpleValueType Ty = getRegTy(MI.getOperand(0).getReg(), MF);
unsigned Reg = Ty == MVT::i32 ? Mips::GP : Mips::GP_64;
for (unsigned I = 0; I < MI.getNumOperands(); ++I) {
MachineOperand &MO = MI.getOperand(I);
if (MO.isReg() && MO.getReg() == Reg) {
MBBInfo::MBBInfo(MachineDomTreeNode *N) : Node(N), HTScope(nullptr) {}
const MachineDomTreeNode *MBBInfo::getNode() const { return Node; }
bool MBBInfo::isVisited() const { return HTScope; }
void MBBInfo::preVisit(ScopedHTType &ScopedHT) {
HTScope = new ScopedHTType::ScopeTy(ScopedHT);
void MBBInfo::postVisit() {
delete HTScope;
// OptimizePICCall methods.
bool OptimizePICCall::runOnMachineFunction(MachineFunction &F) {
if (F.getSubtarget<MipsSubtarget>().inMips16Mode())
return false;
// Do a pre-order traversal of the dominator tree.
MachineDominatorTree *MDT = &getAnalysis<MachineDominatorTree>();
bool Changed = false;
SmallVector<MBBInfo, 8> WorkList(1, MBBInfo(MDT->getRootNode()));
while (!WorkList.empty()) {
MBBInfo &MBBI = WorkList.back();
// If this MBB has already been visited, destroy the scope for the MBB and
// pop it from the work list.
if (MBBI.isVisited()) {
// Visit the MBB and add its children to the work list.
Changed |= visitNode(MBBI);
const MachineDomTreeNode *Node = MBBI.getNode();
WorkList.append(Node->begin(), Node->end());
return Changed;
bool OptimizePICCall::visitNode(MBBInfo &MBBI) {
bool Changed = false;
MachineBasicBlock *MBB = MBBI.getNode()->getBlock();
for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); I != E;
++I) {
unsigned Reg;
ValueType Entry;
// Skip instructions that are not call instructions via registers.
if (!isCallViaRegister(*I, Reg, Entry))
Changed = true;
unsigned N = getCount(Entry);
if (N != 0) {
// If a function has been called more than twice, we do not have to emit a
// load instruction to get the function address from the GOT, but can
// instead reuse the address that has been loaded before.
if (N >= 2 && !LoadTargetFromGOT)
// Erase the $gp operand if this isn't the first time a function has
// been called. $gp needs to be set up only if the function call can go
// through a lazy binding stub.
if (Entry)
incCntAndSetReg(Entry, Reg);
setCallTargetReg(MBB, I);
return Changed;
bool OptimizePICCall::isCallViaRegister(MachineInstr &MI, unsigned &Reg,
ValueType &Val) const {
if (!MI.isCall())
return false;
MachineOperand *MO = getCallTargetRegOpnd(MI);
// Return if MI is not a function call via a register.
if (!MO)
return false;
// Get the instruction that loads the function address from the GOT.
Reg = MO->getReg();
Val = nullptr;
MachineRegisterInfo &MRI = MI.getParent()->getParent()->getRegInfo();
MachineInstr *DefMI = MRI.getVRegDef(Reg);
// See if DefMI is an instruction that loads from a GOT entry that holds the
// address of a lazy binding stub.
if (!DefMI->mayLoad() || DefMI->getNumOperands() < 3)
return true;
unsigned Flags = DefMI->getOperand(2).getTargetFlags();
if (Flags != MipsII::MO_GOT_CALL && Flags != MipsII::MO_CALL_LO16)
return true;
// Return the underlying object for the GOT entry in Val.
Val = (*DefMI->memoperands_begin())->getValue();
if (!Val)
Val = (*DefMI->memoperands_begin())->getPseudoValue();
return true;
unsigned OptimizePICCall::getCount(ValueType Entry) {
return ScopedHT.lookup(Entry).first;
unsigned OptimizePICCall::getReg(ValueType Entry) {
unsigned Reg = ScopedHT.lookup(Entry).second;
return Reg;
void OptimizePICCall::incCntAndSetReg(ValueType Entry, unsigned Reg) {
CntRegP P = ScopedHT.lookup(Entry);
ScopedHT.insert(Entry, std::make_pair(P.first + 1, Reg));
/// Return an OptimizeCall object.
FunctionPass *llvm::createMipsOptimizePICCallPass() {
return new OptimizePICCall();