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//===- MipsDelaySlotFiller.cpp - Mips Delay Slot Filler -------------------===//
// 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 fill delay slots with useful instructions.
#include "MCTargetDesc/MipsMCNaCl.h"
#include "Mips.h"
#include "MipsInstrInfo.h"
#include "MipsRegisterInfo.h"
#include "MipsSubtarget.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/PointerUnion.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineBranchProbabilityInfo.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/PseudoSourceValue.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/MC/MCInstrDesc.h"
#include "llvm/MC/MCRegisterInfo.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CodeGen.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Target/TargetMachine.h"
#include <algorithm>
#include <cassert>
#include <iterator>
#include <memory>
#include <utility>
using namespace llvm;
#define DEBUG_TYPE "mips-delay-slot-filler"
STATISTIC(FilledSlots, "Number of delay slots filled");
STATISTIC(UsefulSlots, "Number of delay slots filled with instructions that"
" are not NOP.");
static cl::opt<bool> DisableDelaySlotFiller(
cl::desc("Fill all delay slots with NOPs."),
static cl::opt<bool> DisableForwardSearch(
cl::desc("Disallow MIPS delay filler to search forward."),
static cl::opt<bool> DisableSuccBBSearch(
cl::desc("Disallow MIPS delay filler to search successor basic blocks."),
static cl::opt<bool> DisableBackwardSearch(
cl::desc("Disallow MIPS delay filler to search backward."),
enum CompactBranchPolicy {
CB_Never, ///< The policy 'never' may in some circumstances or for some
///< ISAs not be absolutely adhered to.
CB_Optimal, ///< Optimal is the default and will produce compact branches
///< when delay slots cannot be filled.
CB_Always ///< 'always' may in some circumstances may not be
///< absolutely adhered to there may not be a corresponding
///< compact form of a branch.
static cl::opt<CompactBranchPolicy> MipsCompactBranchPolicy(
"mips-compact-branches", cl::Optional, cl::init(CB_Optimal),
cl::desc("MIPS Specific: Compact branch policy."),
cl::values(clEnumValN(CB_Never, "never",
"Do not use compact branches if possible."),
clEnumValN(CB_Optimal, "optimal",
"Use compact branches where appropiate (default)."),
clEnumValN(CB_Always, "always",
"Always use compact branches if possible.")));
namespace {
using Iter = MachineBasicBlock::iterator;
using ReverseIter = MachineBasicBlock::reverse_iterator;
using BB2BrMap = SmallDenseMap<MachineBasicBlock *, MachineInstr *, 2>;
class RegDefsUses {
RegDefsUses(const TargetRegisterInfo &TRI);
void init(const MachineInstr &MI);
/// This function sets all caller-saved registers in Defs.
void setCallerSaved(const MachineInstr &MI);
/// This function sets all unallocatable registers in Defs.
void setUnallocatableRegs(const MachineFunction &MF);
/// Set bits in Uses corresponding to MBB's live-out registers except for
/// the registers that are live-in to SuccBB.
void addLiveOut(const MachineBasicBlock &MBB,
const MachineBasicBlock &SuccBB);
bool update(const MachineInstr &MI, unsigned Begin, unsigned End);
bool checkRegDefsUses(BitVector &NewDefs, BitVector &NewUses, unsigned Reg,
bool IsDef) const;
/// Returns true if Reg or its alias is in RegSet.
bool isRegInSet(const BitVector &RegSet, unsigned Reg) const;
const TargetRegisterInfo &TRI;
BitVector Defs, Uses;
/// Base class for inspecting loads and stores.
class InspectMemInstr {
InspectMemInstr(bool ForbidMemInstr_) : ForbidMemInstr(ForbidMemInstr_) {}
virtual ~InspectMemInstr() = default;
/// Return true if MI cannot be moved to delay slot.
bool hasHazard(const MachineInstr &MI);
/// Flags indicating whether loads or stores have been seen.
bool OrigSeenLoad = false;
bool OrigSeenStore = false;
bool SeenLoad = false;
bool SeenStore = false;
/// Memory instructions are not allowed to move to delay slot if this flag
/// is true.
bool ForbidMemInstr;
virtual bool hasHazard_(const MachineInstr &MI) = 0;
/// This subclass rejects any memory instructions.
class NoMemInstr : public InspectMemInstr {
NoMemInstr() : InspectMemInstr(true) {}
bool hasHazard_(const MachineInstr &MI) override { return true; }
/// This subclass accepts loads from stacks and constant loads.
class LoadFromStackOrConst : public InspectMemInstr {
LoadFromStackOrConst() : InspectMemInstr(false) {}
bool hasHazard_(const MachineInstr &MI) override;
/// This subclass uses memory dependence information to determine whether a
/// memory instruction can be moved to a delay slot.
class MemDefsUses : public InspectMemInstr {
MemDefsUses(const DataLayout &DL, const MachineFrameInfo *MFI);
using ValueType = PointerUnion<const Value *, const PseudoSourceValue *>;
bool hasHazard_(const MachineInstr &MI) override;
/// Update Defs and Uses. Return true if there exist dependences that
/// disqualify the delay slot candidate between V and values in Uses and
/// Defs.
bool updateDefsUses(ValueType V, bool MayStore);
/// Get the list of underlying objects of MI's memory operand.
bool getUnderlyingObjects(const MachineInstr &MI,
SmallVectorImpl<ValueType> &Objects) const;
const MachineFrameInfo *MFI;
SmallPtrSet<ValueType, 4> Uses, Defs;
const DataLayout &DL;
/// Flags indicating whether loads or stores with no underlying objects have
/// been seen.
bool SeenNoObjLoad = false;
bool SeenNoObjStore = false;
class MipsDelaySlotFiller : public MachineFunctionPass {
MipsDelaySlotFiller() : MachineFunctionPass(ID) {
StringRef getPassName() const override { return "Mips Delay Slot Filler"; }
bool runOnMachineFunction(MachineFunction &F) override {
TM = &F.getTarget();
bool Changed = false;
for (MachineFunction::iterator FI = F.begin(), FE = F.end();
FI != FE; ++FI)
Changed |= runOnMachineBasicBlock(*FI);
// This pass invalidates liveness information when it reorders
// instructions to fill delay slot. Without this, -verify-machineinstrs
// will fail.
if (Changed)
return Changed;
MachineFunctionProperties getRequiredProperties() const override {
return MachineFunctionProperties().set(
void getAnalysisUsage(AnalysisUsage &AU) const override {
static char ID;
bool runOnMachineBasicBlock(MachineBasicBlock &MBB);
Iter replaceWithCompactBranch(MachineBasicBlock &MBB, Iter Branch,
const DebugLoc &DL);
/// This function checks if it is valid to move Candidate to the delay slot
/// and returns true if it isn't. It also updates memory and register
/// dependence information.
bool delayHasHazard(const MachineInstr &Candidate, RegDefsUses &RegDU,
InspectMemInstr &IM) const;
/// This function searches range [Begin, End) for an instruction that can be
/// moved to the delay slot. Returns true on success.
template<typename IterTy>
bool searchRange(MachineBasicBlock &MBB, IterTy Begin, IterTy End,
RegDefsUses &RegDU, InspectMemInstr &IM, Iter Slot,
IterTy &Filler) const;
/// This function searches in the backward direction for an instruction that
/// can be moved to the delay slot. Returns true on success.
bool searchBackward(MachineBasicBlock &MBB, MachineInstr &Slot) const;
/// This function searches MBB in the forward direction for an instruction
/// that can be moved to the delay slot. Returns true on success.
bool searchForward(MachineBasicBlock &MBB, Iter Slot) const;
/// This function searches one of MBB's successor blocks for an instruction
/// that can be moved to the delay slot and inserts clones of the
/// instruction into the successor's predecessor blocks.
bool searchSuccBBs(MachineBasicBlock &MBB, Iter Slot) const;
/// Pick a successor block of MBB. Return NULL if MBB doesn't have a
/// successor block that is not a landing pad.
MachineBasicBlock *selectSuccBB(MachineBasicBlock &B) const;
/// This function analyzes MBB and returns an instruction with an unoccupied
/// slot that branches to Dst.
std::pair<MipsInstrInfo::BranchType, MachineInstr *>
getBranch(MachineBasicBlock &MBB, const MachineBasicBlock &Dst) const;
/// Examine Pred and see if it is possible to insert an instruction into
/// one of its branches delay slot or its end.
bool examinePred(MachineBasicBlock &Pred, const MachineBasicBlock &Succ,
RegDefsUses &RegDU, bool &HasMultipleSuccs,
BB2BrMap &BrMap) const;
bool terminateSearch(const MachineInstr &Candidate) const;
const TargetMachine *TM = nullptr;
} // end anonymous namespace
char MipsDelaySlotFiller::ID = 0;
static bool hasUnoccupiedSlot(const MachineInstr *MI) {
return MI->hasDelaySlot() && !MI->isBundledWithSucc();
"Fill delay slot for MIPS", false, false)
/// This function inserts clones of Filler into predecessor blocks.
static void insertDelayFiller(Iter Filler, const BB2BrMap &BrMap) {
MachineFunction *MF = Filler->getParent()->getParent();
for (BB2BrMap::const_iterator I = BrMap.begin(); I != BrMap.end(); ++I) {
if (I->second) {
} else {
I->first->insert(I->first->end(), MF->CloneMachineInstr(&*Filler));
/// This function adds registers Filler defines to MBB's live-in register list.
static void addLiveInRegs(Iter Filler, MachineBasicBlock &MBB) {
for (unsigned I = 0, E = Filler->getNumOperands(); I != E; ++I) {
const MachineOperand &MO = Filler->getOperand(I);
unsigned R;
if (!MO.isReg() || !MO.isDef() || !(R = MO.getReg()))
#ifndef NDEBUG
const MachineFunction &MF = *MBB.getParent();
assert(MF.getSubtarget().getRegisterInfo()->getAllocatableSet(MF).test(R) &&
"Shouldn't move an instruction with unallocatable registers across "
"basic block boundaries.");
if (!MBB.isLiveIn(R))
RegDefsUses::RegDefsUses(const TargetRegisterInfo &TRI)
: TRI(TRI), Defs(TRI.getNumRegs(), false), Uses(TRI.getNumRegs(), false) {}
void RegDefsUses::init(const MachineInstr &MI) {
// Add all register operands which are explicit and non-variadic.
update(MI, 0, MI.getDesc().getNumOperands());
// If MI is a call, add RA to Defs to prevent users of RA from going into
// delay slot.
if (MI.isCall())
// Add all implicit register operands of branch instructions except
// register AT.
if (MI.isBranch()) {
update(MI, MI.getDesc().getNumOperands(), MI.getNumOperands());
void RegDefsUses::setCallerSaved(const MachineInstr &MI) {
// Add RA/RA_64 to Defs to prevent users of RA/RA_64 from going into
// the delay slot. The reason is that RA/RA_64 must not be changed
// in the delay slot so that the callee can return to the caller.
if (MI.definesRegister(Mips::RA) || MI.definesRegister(Mips::RA_64)) {
// If MI is a call, add all caller-saved registers to Defs.
BitVector CallerSavedRegs(TRI.getNumRegs(), true);
for (const MCPhysReg *R = TRI.getCalleeSavedRegs(MI.getParent()->getParent());
*R; ++R)
for (MCRegAliasIterator AI(*R, &TRI, true); AI.isValid(); ++AI)
Defs |= CallerSavedRegs;
void RegDefsUses::setUnallocatableRegs(const MachineFunction &MF) {
BitVector AllocSet = TRI.getAllocatableSet(MF);
for (unsigned R : AllocSet.set_bits())
for (MCRegAliasIterator AI(R, &TRI, false); AI.isValid(); ++AI)
Defs |= AllocSet.flip();
void RegDefsUses::addLiveOut(const MachineBasicBlock &MBB,
const MachineBasicBlock &SuccBB) {
for (MachineBasicBlock::const_succ_iterator SI = MBB.succ_begin(),
SE = MBB.succ_end(); SI != SE; ++SI)
if (*SI != &SuccBB)
for (const auto &LI : (*SI)->liveins())
bool RegDefsUses::update(const MachineInstr &MI, unsigned Begin, unsigned End) {
BitVector NewDefs(TRI.getNumRegs()), NewUses(TRI.getNumRegs());
bool HasHazard = false;
for (unsigned I = Begin; I != End; ++I) {
const MachineOperand &MO = MI.getOperand(I);
if (MO.isReg() && MO.getReg()) {
if (checkRegDefsUses(NewDefs, NewUses, MO.getReg(), MO.isDef())) {
LLVM_DEBUG(dbgs() << DEBUG_TYPE ": found register hazard for operand "
<< I << ": ";
HasHazard = true;
Defs |= NewDefs;
Uses |= NewUses;
return HasHazard;
bool RegDefsUses::checkRegDefsUses(BitVector &NewDefs, BitVector &NewUses,
unsigned Reg, bool IsDef) const {
if (IsDef) {
// check whether Reg has already been defined or used.
return (isRegInSet(Defs, Reg) || isRegInSet(Uses, Reg));
// check whether Reg has already been defined.
return isRegInSet(Defs, Reg);
bool RegDefsUses::isRegInSet(const BitVector &RegSet, unsigned Reg) const {
// Check Reg and all aliased Registers.
for (MCRegAliasIterator AI(Reg, &TRI, true); AI.isValid(); ++AI)
if (RegSet.test(*AI))
return true;
return false;
bool InspectMemInstr::hasHazard(const MachineInstr &MI) {
if (!MI.mayStore() && !MI.mayLoad())
return false;
if (ForbidMemInstr)
return true;
OrigSeenLoad = SeenLoad;
OrigSeenStore = SeenStore;
SeenLoad |= MI.mayLoad();
SeenStore |= MI.mayStore();
// If MI is an ordered or volatile memory reference, disallow moving
// subsequent loads and stores to delay slot.
if (MI.hasOrderedMemoryRef() && (OrigSeenLoad || OrigSeenStore)) {
ForbidMemInstr = true;
return true;
return hasHazard_(MI);
bool LoadFromStackOrConst::hasHazard_(const MachineInstr &MI) {
if (MI.mayStore())
return true;
if (!MI.hasOneMemOperand() || !(*MI.memoperands_begin())->getPseudoValue())
return true;
if (const PseudoSourceValue *PSV =
(*MI.memoperands_begin())->getPseudoValue()) {
if (isa<FixedStackPseudoSourceValue>(PSV))
return false;
return !PSV->isConstant(nullptr) && !PSV->isStack();
return true;
MemDefsUses::MemDefsUses(const DataLayout &DL, const MachineFrameInfo *MFI_)
: InspectMemInstr(false), MFI(MFI_), DL(DL) {}
bool MemDefsUses::hasHazard_(const MachineInstr &MI) {
bool HasHazard = false;
// Check underlying object list.
SmallVector<ValueType, 4> Objs;
if (getUnderlyingObjects(MI, Objs)) {
for (ValueType VT : Objs)
HasHazard |= updateDefsUses(VT, MI.mayStore());
return HasHazard;
// No underlying objects found.
HasHazard = MI.mayStore() && (OrigSeenLoad || OrigSeenStore);
HasHazard |= MI.mayLoad() || OrigSeenStore;
SeenNoObjLoad |= MI.mayLoad();
SeenNoObjStore |= MI.mayStore();
return HasHazard;
bool MemDefsUses::updateDefsUses(ValueType V, bool MayStore) {
if (MayStore)
return !Defs.insert(V).second || Uses.count(V) || SeenNoObjStore ||
return Defs.count(V) || SeenNoObjStore;
bool MemDefsUses::
getUnderlyingObjects(const MachineInstr &MI,
SmallVectorImpl<ValueType> &Objects) const {
if (!MI.hasOneMemOperand())
return false;
auto & MMO = **MI.memoperands_begin();
if (const PseudoSourceValue *PSV = MMO.getPseudoValue()) {
if (!PSV->isAliased(MFI))
return false;
return true;
if (const Value *V = MMO.getValue()) {
SmallVector<const Value *, 4> Objs;
GetUnderlyingObjects(V, Objs, DL);
for (const Value *UValue : Objs) {
if (!isIdentifiedObject(V))
return false;
return true;
return false;
// Replace Branch with the compact branch instruction.
Iter MipsDelaySlotFiller::replaceWithCompactBranch(MachineBasicBlock &MBB,
Iter Branch,
const DebugLoc &DL) {
const MipsSubtarget &STI = MBB.getParent()->getSubtarget<MipsSubtarget>();
const MipsInstrInfo *TII = STI.getInstrInfo();
unsigned NewOpcode = TII->getEquivalentCompactForm(Branch);
Branch = TII->genInstrWithNewOpc(NewOpcode, Branch);
return Branch;
// For given opcode returns opcode of corresponding instruction with short
// delay slot.
// For the pseudo TAILCALL*_MM instructions return the short delay slot
// form. Unfortunately, TAILCALL<->b16 is denied as b16 has a limited range
// that is too short to make use of for tail calls.
static int getEquivalentCallShort(int Opcode) {
switch (Opcode) {
case Mips::BGEZAL:
return Mips::BGEZALS_MM;
case Mips::BLTZAL:
return Mips::BLTZALS_MM;
case Mips::JAL:
case Mips::JAL_MM:
return Mips::JALS_MM;
case Mips::JALR:
return Mips::JALRS_MM;
case Mips::JALR16_MM:
return Mips::JALRS16_MM;
case Mips::TAILCALL_MM:
llvm_unreachable("Attempting to shorten the TAILCALL_MM pseudo!");
return Mips::JR16_MM;
llvm_unreachable("Unexpected call instruction for microMIPS.");
/// runOnMachineBasicBlock - Fill in delay slots for the given basic block.
/// We assume there is only one delay slot per delayed instruction.
bool MipsDelaySlotFiller::runOnMachineBasicBlock(MachineBasicBlock &MBB) {
bool Changed = false;
const MipsSubtarget &STI = MBB.getParent()->getSubtarget<MipsSubtarget>();
bool InMicroMipsMode = STI.inMicroMipsMode();
const MipsInstrInfo *TII = STI.getInstrInfo();
for (Iter I = MBB.begin(); I != MBB.end(); ++I) {
if (!hasUnoccupiedSlot(&*I))
// Delay slot filling is disabled at -O0, or in microMIPS32R6.
if (!DisableDelaySlotFiller && (TM->getOptLevel() != CodeGenOpt::None) &&
!(InMicroMipsMode && STI.hasMips32r6())) {
bool Filled = false;
if (MipsCompactBranchPolicy.getValue() != CB_Always ||
!TII->getEquivalentCompactForm(I)) {
if (searchBackward(MBB, *I)) {
LLVM_DEBUG(dbgs() << DEBUG_TYPE ": found instruction for delay slot"
" in backwards search.\n");
Filled = true;
} else if (I->isTerminator()) {
if (searchSuccBBs(MBB, I)) {
Filled = true;
LLVM_DEBUG(dbgs() << DEBUG_TYPE ": found instruction for delay slot"
" in successor BB search.\n");
} else if (searchForward(MBB, I)) {
LLVM_DEBUG(dbgs() << DEBUG_TYPE ": found instruction for delay slot"
" in forwards search.\n");
Filled = true;
if (Filled) {
// Get instruction with delay slot.
MachineBasicBlock::instr_iterator DSI = I.getInstrIterator();
if (InMicroMipsMode && TII->getInstSizeInBytes(*std::next(DSI)) == 2 &&
DSI->isCall()) {
// If instruction in delay slot is 16b change opcode to
// corresponding instruction with short delay slot.
// TODO: Implement an instruction mapping table of 16bit opcodes to
// 32bit opcodes so that an instruction can be expanded. This would
// save 16 bits as a TAILCALL_MM pseudo requires a fullsized nop.
// TODO: Permit b16 when branching backwards to the same function
// if it is in range.
Changed = true;
// For microMIPS if instruction is BEQ or BNE with one ZERO register, then
// instead of adding NOP replace this instruction with the corresponding
// compact branch instruction, i.e. BEQZC or BNEZC. Additionally
// PseudoReturn and PseudoIndirectBranch are expanded to JR_MM, so they can
// be replaced with JRC16_MM.
// For MIPSR6 attempt to produce the corresponding compact (no delay slot)
// form of the CTI. For indirect jumps this will not require inserting a
// NOP and for branches will hopefully avoid requiring a NOP.
if ((InMicroMipsMode ||
(STI.hasMips32r6() && MipsCompactBranchPolicy != CB_Never)) &&
TII->getEquivalentCompactForm(I)) {
I = replaceWithCompactBranch(MBB, I, I->getDebugLoc());
Changed = true;
// Bundle the NOP to the instruction with the delay slot.
LLVM_DEBUG(dbgs() << DEBUG_TYPE << ": could not fill delay slot for ";
BuildMI(MBB, std::next(I), I->getDebugLoc(), TII->get(Mips::NOP));
MIBundleBuilder(MBB, I, std::next(I, 2));
Changed = true;
return Changed;
template <typename IterTy>
bool MipsDelaySlotFiller::searchRange(MachineBasicBlock &MBB, IterTy Begin,
IterTy End, RegDefsUses &RegDU,
InspectMemInstr &IM, Iter Slot,
IterTy &Filler) const {
for (IterTy I = Begin; I != End;) {
IterTy CurrI = I;
LLVM_DEBUG(dbgs() << DEBUG_TYPE ": checking instruction: "; CurrI->dump());
// skip debug value
if (CurrI->isDebugInstr()) {
LLVM_DEBUG(dbgs() << DEBUG_TYPE ": ignoring debug instruction: ";
if (CurrI->isBundle()) {
LLVM_DEBUG(dbgs() << DEBUG_TYPE ": ignoring BUNDLE instruction: ";
// However, we still need to update the register def-use information.
RegDU.update(*CurrI, 0, CurrI->getNumOperands());
if (terminateSearch(*CurrI)) {
LLVM_DEBUG(dbgs() << DEBUG_TYPE ": should terminate search: ";
assert((!CurrI->isCall() && !CurrI->isReturn() && !CurrI->isBranch()) &&
"Cannot put calls, returns or branches in delay slot.");
if (CurrI->isKill()) {
if (delayHasHazard(*CurrI, RegDU, IM))
const MipsSubtarget &STI = MBB.getParent()->getSubtarget<MipsSubtarget>();
if (STI.isTargetNaCl()) {
// In NaCl, instructions that must be masked are forbidden in delay slots.
// We only check for loads, stores and SP changes. Calls, returns and
// branches are not checked because non-NaCl targets never put them in
// delay slots.
unsigned AddrIdx;
if ((isBasePlusOffsetMemoryAccess(CurrI->getOpcode(), &AddrIdx) &&
baseRegNeedsLoadStoreMask(CurrI->getOperand(AddrIdx).getReg())) ||
CurrI->modifiesRegister(Mips::SP, STI.getRegisterInfo()))
bool InMicroMipsMode = STI.inMicroMipsMode();
const MipsInstrInfo *TII = STI.getInstrInfo();
unsigned Opcode = (*Slot).getOpcode();
// This is complicated by the tail call optimization. For non-PIC code
// there is only a 32bit sized unconditional branch which can be assumed
// to be able to reach the target. b16 only has a range of +/- 1 KB.
// It's entirely possible that the target function is reachable with b16
// but we don't have enough information to make that decision.
if (InMicroMipsMode && TII->getInstSizeInBytes(*CurrI) == 2 &&
(Opcode == Mips::JR || Opcode == Mips::PseudoIndirectBranch ||
Opcode == Mips::PseudoIndirectBranch_MM ||
Opcode == Mips::PseudoReturn || Opcode == Mips::TAILCALL))
// Instructions LWP/SWP and MOVEP should not be in a delay slot as that
// results in unpredictable behaviour
if (InMicroMipsMode && (Opcode == Mips::LWP_MM || Opcode == Mips::SWP_MM ||
Opcode == Mips::MOVEP_MM))
Filler = CurrI;
LLVM_DEBUG(dbgs() << DEBUG_TYPE ": found instruction for delay slot: ";
return true;
return false;
bool MipsDelaySlotFiller::searchBackward(MachineBasicBlock &MBB,
MachineInstr &Slot) const {
if (DisableBackwardSearch)
return false;
auto *Fn = MBB.getParent();
RegDefsUses RegDU(*Fn->getSubtarget().getRegisterInfo());
MemDefsUses MemDU(Fn->getDataLayout(), &Fn->getFrameInfo());
ReverseIter Filler;
MachineBasicBlock::iterator SlotI = Slot;
if (!searchRange(MBB, ++SlotI.getReverse(), MBB.rend(), RegDU, MemDU, Slot,
Filler)) {
LLVM_DEBUG(dbgs() << DEBUG_TYPE ": could not find instruction for delay "
"slot using backwards search.\n");
return false;
MBB.splice(std::next(SlotI), &MBB, Filler.getReverse());
MIBundleBuilder(MBB, SlotI, std::next(SlotI, 2));
return true;
bool MipsDelaySlotFiller::searchForward(MachineBasicBlock &MBB,
Iter Slot) const {
// Can handle only calls.
if (DisableForwardSearch || !Slot->isCall())
return false;
RegDefsUses RegDU(*MBB.getParent()->getSubtarget().getRegisterInfo());
NoMemInstr NM;
Iter Filler;
if (!searchRange(MBB, std::next(Slot), MBB.end(), RegDU, NM, Slot, Filler)) {
LLVM_DEBUG(dbgs() << DEBUG_TYPE ": could not find instruction for delay "
"slot using forwards search.\n");
return false;
MBB.splice(std::next(Slot), &MBB, Filler);
MIBundleBuilder(MBB, Slot, std::next(Slot, 2));
return true;
bool MipsDelaySlotFiller::searchSuccBBs(MachineBasicBlock &MBB,
Iter Slot) const {
if (DisableSuccBBSearch)
return false;
MachineBasicBlock *SuccBB = selectSuccBB(MBB);
if (!SuccBB)
return false;
RegDefsUses RegDU(*MBB.getParent()->getSubtarget().getRegisterInfo());
bool HasMultipleSuccs = false;
BB2BrMap BrMap;
std::unique_ptr<InspectMemInstr> IM;
Iter Filler;
auto *Fn = MBB.getParent();
// Iterate over SuccBB's predecessor list.
for (MachineBasicBlock::pred_iterator PI = SuccBB->pred_begin(),
PE = SuccBB->pred_end(); PI != PE; ++PI)
if (!examinePred(**PI, *SuccBB, RegDU, HasMultipleSuccs, BrMap))
return false;
// Do not allow moving instructions which have unallocatable register operands
// across basic block boundaries.
// Only allow moving loads from stack or constants if any of the SuccBB's
// predecessors have multiple successors.
if (HasMultipleSuccs) {
IM.reset(new LoadFromStackOrConst());
} else {
const MachineFrameInfo &MFI = Fn->getFrameInfo();
IM.reset(new MemDefsUses(Fn->getDataLayout(), &MFI));
if (!searchRange(MBB, SuccBB->begin(), SuccBB->end(), RegDU, *IM, Slot,
return false;
insertDelayFiller(Filler, BrMap);
addLiveInRegs(Filler, *SuccBB);
return true;
MachineBasicBlock *
MipsDelaySlotFiller::selectSuccBB(MachineBasicBlock &B) const {
if (B.succ_empty())
return nullptr;
// Select the successor with the larget edge weight.
auto &Prob = getAnalysis<MachineBranchProbabilityInfo>();
MachineBasicBlock *S = *std::max_element(
B.succ_begin(), B.succ_end(),
[&](const MachineBasicBlock *Dst0, const MachineBasicBlock *Dst1) {
return Prob.getEdgeProbability(&B, Dst0) <
Prob.getEdgeProbability(&B, Dst1);
return S->isEHPad() ? nullptr : S;
std::pair<MipsInstrInfo::BranchType, MachineInstr *>
MipsDelaySlotFiller::getBranch(MachineBasicBlock &MBB,
const MachineBasicBlock &Dst) const {
const MipsInstrInfo *TII =
MachineBasicBlock *TrueBB = nullptr, *FalseBB = nullptr;
SmallVector<MachineInstr*, 2> BranchInstrs;
SmallVector<MachineOperand, 2> Cond;
MipsInstrInfo::BranchType R =
TII->analyzeBranch(MBB, TrueBB, FalseBB, Cond, false, BranchInstrs);
if ((R == MipsInstrInfo::BT_None) || (R == MipsInstrInfo::BT_NoBranch))
return std::make_pair(R, nullptr);
if (R != MipsInstrInfo::BT_CondUncond) {
if (!hasUnoccupiedSlot(BranchInstrs[0]))
return std::make_pair(MipsInstrInfo::BT_None, nullptr);
assert(((R != MipsInstrInfo::BT_Uncond) || (TrueBB == &Dst)));
return std::make_pair(R, BranchInstrs[0]);
assert((TrueBB == &Dst) || (FalseBB == &Dst));
// Examine the conditional branch. See if its slot is occupied.
if (hasUnoccupiedSlot(BranchInstrs[0]))
return std::make_pair(MipsInstrInfo::BT_Cond, BranchInstrs[0]);
// If that fails, try the unconditional branch.
if (hasUnoccupiedSlot(BranchInstrs[1]) && (FalseBB == &Dst))
return std::make_pair(MipsInstrInfo::BT_Uncond, BranchInstrs[1]);
return std::make_pair(MipsInstrInfo::BT_None, nullptr);
bool MipsDelaySlotFiller::examinePred(MachineBasicBlock &Pred,
const MachineBasicBlock &Succ,
RegDefsUses &RegDU,
bool &HasMultipleSuccs,
BB2BrMap &BrMap) const {
std::pair<MipsInstrInfo::BranchType, MachineInstr *> P =
getBranch(Pred, Succ);
// Return if either getBranch wasn't able to analyze the branches or there
// were no branches with unoccupied slots.
if (P.first == MipsInstrInfo::BT_None)
return false;
if ((P.first != MipsInstrInfo::BT_Uncond) &&
(P.first != MipsInstrInfo::BT_NoBranch)) {
HasMultipleSuccs = true;
RegDU.addLiveOut(Pred, Succ);
BrMap[&Pred] = P.second;
return true;
bool MipsDelaySlotFiller::delayHasHazard(const MachineInstr &Candidate,
RegDefsUses &RegDU,
InspectMemInstr &IM) const {
assert(!Candidate.isKill() &&
"KILL instructions should have been eliminated at this point.");
bool HasHazard = Candidate.isImplicitDef();
HasHazard |= IM.hasHazard(Candidate);
HasHazard |= RegDU.update(Candidate, 0, Candidate.getNumOperands());
return HasHazard;
bool MipsDelaySlotFiller::terminateSearch(const MachineInstr &Candidate) const {
return (Candidate.isTerminator() || Candidate.isCall() ||
Candidate.isPosition() || Candidate.isInlineAsm() ||
/// createMipsDelaySlotFillerPass - Returns a pass that fills in delay
/// slots in Mips MachineFunctions
FunctionPass *llvm::createMipsDelaySlotFillerPass() {
return new MipsDelaySlotFiller();