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//===- HexagonExpandCondsets.cpp ------------------------------------------===//
// 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
// Replace mux instructions with the corresponding legal instructions.
// It is meant to work post-SSA, but still on virtual registers. It was
// originally placed between register coalescing and machine instruction
// scheduler.
// In this place in the optimization sequence, live interval analysis had
// been performed, and the live intervals should be preserved. A large part
// of the code deals with preserving the liveness information.
// Liveness tracking aside, the main functionality of this pass is divided
// into two steps. The first step is to replace an instruction
// %0 = C2_mux %1, %2, %3
// with a pair of conditional transfers
// %0 = A2_tfrt %1, %2
// %0 = A2_tfrf %1, %3
// It is the intention that the execution of this pass could be terminated
// after this step, and the code generated would be functionally correct.
// If the uses of the source values %1 and %2 are kills, and their
// definitions are predicable, then in the second step, the conditional
// transfers will then be rewritten as predicated instructions. E.g.
// %0 = A2_or %1, %2
// %3 = A2_tfrt %99, killed %0
// will be rewritten as
// %3 = A2_port %99, %1, %2
// This replacement has two variants: "up" and "down". Consider this case:
// %0 = A2_or %1, %2
// ... [intervening instructions] ...
// %3 = A2_tfrt %99, killed %0
// variant "up":
// %3 = A2_port %99, %1, %2
// ... [intervening instructions, %0->vreg3] ...
// [deleted]
// variant "down":
// [deleted]
// ... [intervening instructions] ...
// %3 = A2_port %99, %1, %2
// Both, one or none of these variants may be valid, and checks are made
// to rule out inapplicable variants.
// As an additional optimization, before either of the two steps above is
// executed, the pass attempts to coalesce the target register with one of
// the source registers, e.g. given an instruction
// %3 = C2_mux %0, %1, %2
// %3 will be coalesced with either %1 or %2. If this succeeds,
// the instruction would then be (for example)
// %3 = C2_mux %0, %3, %2
// and, under certain circumstances, this could result in only one predicated
// instruction:
// %3 = A2_tfrf %0, %2
// Splitting a definition of a register into two predicated transfers
// creates a complication in liveness tracking. Live interval computation
// will see both instructions as actual definitions, and will mark the
// first one as dead. The definition is not actually dead, and this
// situation will need to be fixed. For example:
// dead %1 = A2_tfrt ... ; marked as dead
// %1 = A2_tfrf ...
// Since any of the individual predicated transfers may end up getting
// removed (in case it is an identity copy), some pre-existing def may
// be marked as dead after live interval recomputation:
// dead %1 = ... ; marked as dead
// ...
// %1 = A2_tfrf ... ; if A2_tfrt is removed
// This case happens if %1 was used as a source in A2_tfrt, which means
// that is it actually live at the A2_tfrf, and so the now dead definition
// of %1 will need to be updated to non-dead at some point.
// This issue could be remedied by adding implicit uses to the predicated
// transfers, but this will create a problem with subsequent predication,
// since the transfers will no longer be possible to reorder. To avoid
// that, the initial splitting will not add any implicit uses. These
// implicit uses will be added later, after predication. The extra price,
// however, is that finding the locations where the implicit uses need
// to be added, and updating the live ranges will be more involved.
#include "HexagonInstrInfo.h"
#include "HexagonRegisterInfo.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/CodeGen/LiveInterval.h"
#include "llvm/CodeGen/LiveIntervals.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/SlotIndexes.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/IR/Function.h"
#include "llvm/InitializePasses.h"
#include "llvm/MC/LaneBitmask.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include <cassert>
#include <iterator>
#include <set>
#include <utility>
#define DEBUG_TYPE "expand-condsets"
using namespace llvm;
static cl::opt<unsigned> OptTfrLimit("expand-condsets-tfr-limit",
cl::init(~0U), cl::Hidden, cl::desc("Max number of mux expansions"));
static cl::opt<unsigned> OptCoaLimit("expand-condsets-coa-limit",
cl::init(~0U), cl::Hidden, cl::desc("Max number of segment coalescings"));
namespace llvm {
void initializeHexagonExpandCondsetsPass(PassRegistry&);
FunctionPass *createHexagonExpandCondsets();
} // end namespace llvm
namespace {
class HexagonExpandCondsets : public MachineFunctionPass {
static char ID;
HexagonExpandCondsets() : MachineFunctionPass(ID) {
if (OptCoaLimit.getPosition())
CoaLimitActive = true, CoaLimit = OptCoaLimit;
if (OptTfrLimit.getPosition())
TfrLimitActive = true, TfrLimit = OptTfrLimit;
StringRef getPassName() const override { return "Hexagon Expand Condsets"; }
void getAnalysisUsage(AnalysisUsage &AU) const override {
bool runOnMachineFunction(MachineFunction &MF) override;
const HexagonInstrInfo *HII = nullptr;
const TargetRegisterInfo *TRI = nullptr;
MachineDominatorTree *MDT;
MachineRegisterInfo *MRI = nullptr;
LiveIntervals *LIS = nullptr;
bool CoaLimitActive = false;
bool TfrLimitActive = false;
unsigned CoaLimit;
unsigned TfrLimit;
unsigned CoaCounter = 0;
unsigned TfrCounter = 0;
// FIXME: Consolidate duplicate definitions of RegisterRef
struct RegisterRef {
RegisterRef(const MachineOperand &Op) : Reg(Op.getReg()),
Sub(Op.getSubReg()) {}
RegisterRef(unsigned R = 0, unsigned S = 0) : Reg(R), Sub(S) {}
bool operator== (RegisterRef RR) const {
return Reg == RR.Reg && Sub == RR.Sub;
bool operator!= (RegisterRef RR) const { return !operator==(RR); }
bool operator< (RegisterRef RR) const {
return Reg < RR.Reg || (Reg == RR.Reg && Sub < RR.Sub);
Register Reg;
unsigned Sub;
using ReferenceMap = DenseMap<unsigned, unsigned>;
enum { Sub_Low = 0x1, Sub_High = 0x2, Sub_None = (Sub_Low | Sub_High) };
enum { Exec_Then = 0x10, Exec_Else = 0x20 };
unsigned getMaskForSub(unsigned Sub);
bool isCondset(const MachineInstr &MI);
LaneBitmask getLaneMask(Register Reg, unsigned Sub);
void addRefToMap(RegisterRef RR, ReferenceMap &Map, unsigned Exec);
bool isRefInMap(RegisterRef, ReferenceMap &Map, unsigned Exec);
void updateDeadsInRange(Register Reg, LaneBitmask LM, LiveRange &Range);
void updateKillFlags(Register Reg);
void updateDeadFlags(Register Reg);
void recalculateLiveInterval(Register Reg);
void removeInstr(MachineInstr &MI);
void updateLiveness(std::set<Register> &RegSet, bool Recalc,
bool UpdateKills, bool UpdateDeads);
unsigned getCondTfrOpcode(const MachineOperand &SO, bool Cond);
MachineInstr *genCondTfrFor(MachineOperand &SrcOp,
MachineBasicBlock::iterator At, unsigned DstR,
unsigned DstSR, const MachineOperand &PredOp, bool PredSense,
bool ReadUndef, bool ImpUse);
bool split(MachineInstr &MI, std::set<Register> &UpdRegs);
bool isPredicable(MachineInstr *MI);
MachineInstr *getReachingDefForPred(RegisterRef RD,
MachineBasicBlock::iterator UseIt, unsigned PredR, bool Cond);
bool canMoveOver(MachineInstr &MI, ReferenceMap &Defs, ReferenceMap &Uses);
bool canMoveMemTo(MachineInstr &MI, MachineInstr &ToI, bool IsDown);
void predicateAt(const MachineOperand &DefOp, MachineInstr &MI,
MachineBasicBlock::iterator Where,
const MachineOperand &PredOp, bool Cond,
std::set<Register> &UpdRegs);
void renameInRange(RegisterRef RO, RegisterRef RN, unsigned PredR,
bool Cond, MachineBasicBlock::iterator First,
MachineBasicBlock::iterator Last);
bool predicate(MachineInstr &TfrI, bool Cond, std::set<Register> &UpdRegs);
bool predicateInBlock(MachineBasicBlock &B, std::set<Register> &UpdRegs);
bool isIntReg(RegisterRef RR, unsigned &BW);
bool isIntraBlocks(LiveInterval &LI);
bool coalesceRegisters(RegisterRef R1, RegisterRef R2);
bool coalesceSegments(const SmallVectorImpl<MachineInstr *> &Condsets,
std::set<Register> &UpdRegs);
} // end anonymous namespace
char HexagonExpandCondsets::ID = 0;
namespace llvm {
char &HexagonExpandCondsetsID = HexagonExpandCondsets::ID;
} // end namespace llvm
INITIALIZE_PASS_BEGIN(HexagonExpandCondsets, "expand-condsets",
"Hexagon Expand Condsets", false, false)
INITIALIZE_PASS_END(HexagonExpandCondsets, "expand-condsets",
"Hexagon Expand Condsets", false, false)
unsigned HexagonExpandCondsets::getMaskForSub(unsigned Sub) {
switch (Sub) {
case Hexagon::isub_lo:
case Hexagon::vsub_lo:
return Sub_Low;
case Hexagon::isub_hi:
case Hexagon::vsub_hi:
return Sub_High;
case Hexagon::NoSubRegister:
return Sub_None;
llvm_unreachable("Invalid subregister");
bool HexagonExpandCondsets::isCondset(const MachineInstr &MI) {
unsigned Opc = MI.getOpcode();
switch (Opc) {
case Hexagon::C2_mux:
case Hexagon::C2_muxii:
case Hexagon::C2_muxir:
case Hexagon::C2_muxri:
case Hexagon::PS_pselect:
return true;
return false;
LaneBitmask HexagonExpandCondsets::getLaneMask(Register Reg, unsigned Sub) {
return Sub != 0 ? TRI->getSubRegIndexLaneMask(Sub)
: MRI->getMaxLaneMaskForVReg(Reg);
void HexagonExpandCondsets::addRefToMap(RegisterRef RR, ReferenceMap &Map,
unsigned Exec) {
unsigned Mask = getMaskForSub(RR.Sub) | Exec;
ReferenceMap::iterator F = Map.find(RR.Reg);
if (F == Map.end())
Map.insert(std::make_pair(RR.Reg, Mask));
F->second |= Mask;
bool HexagonExpandCondsets::isRefInMap(RegisterRef RR, ReferenceMap &Map,
unsigned Exec) {
ReferenceMap::iterator F = Map.find(RR.Reg);
if (F == Map.end())
return false;
unsigned Mask = getMaskForSub(RR.Sub) | Exec;
if (Mask & F->second)
return true;
return false;
void HexagonExpandCondsets::updateKillFlags(Register Reg) {
auto KillAt = [this,Reg] (SlotIndex K, LaneBitmask LM) -> void {
// Set the <kill> flag on a use of Reg whose lane mask is contained in LM.
MachineInstr *MI = LIS->getInstructionFromIndex(K);
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &Op = MI->getOperand(i);
if (!Op.isReg() || !Op.isUse() || Op.getReg() != Reg ||
LaneBitmask SLM = getLaneMask(Reg, Op.getSubReg());
if ((SLM & LM) == SLM) {
// Only set the kill flag on the first encountered use of Reg in this
// instruction.
LiveInterval &LI = LIS->getInterval(Reg);
for (auto I = LI.begin(), E = LI.end(); I != E; ++I) {
if (!I->end.isRegister())
// Do not mark the end of the segment as <kill>, if the next segment
// starts with a predicated instruction.
auto NextI = std::next(I);
if (NextI != E && NextI->start.isRegister()) {
MachineInstr *DefI = LIS->getInstructionFromIndex(NextI->start);
if (HII->isPredicated(*DefI))
bool WholeReg = true;
if (LI.hasSubRanges()) {
auto EndsAtI = [I] (LiveInterval::SubRange &S) -> bool {
LiveRange::iterator F = S.find(I->end);
return F != S.end() && I->end == F->end;
// Check if all subranges end at I->end. If so, make sure to kill
// the whole register.
for (LiveInterval::SubRange &S : LI.subranges()) {
if (EndsAtI(S))
KillAt(I->end, S.LaneMask);
WholeReg = false;
if (WholeReg)
KillAt(I->end, MRI->getMaxLaneMaskForVReg(Reg));
void HexagonExpandCondsets::updateDeadsInRange(Register Reg, LaneBitmask LM,
LiveRange &Range) {
if (Range.empty())
// Return two booleans: { def-modifes-reg, def-covers-reg }.
auto IsRegDef = [this,Reg,LM] (MachineOperand &Op) -> std::pair<bool,bool> {
if (!Op.isReg() || !Op.isDef())
return { false, false };
Register DR = Op.getReg(), DSR = Op.getSubReg();
if (!DR.isVirtual() || DR != Reg)
return { false, false };
LaneBitmask SLM = getLaneMask(DR, DSR);
LaneBitmask A = SLM & LM;
return { A.any(), A == SLM };
// The splitting step will create pairs of predicated definitions without
// any implicit uses (since implicit uses would interfere with predication).
// This can cause the reaching defs to become dead after live range
// recomputation, even though they are not really dead.
// We need to identify predicated defs that need implicit uses, and
// dead defs that are not really dead, and correct both problems.
auto Dominate = [this] (SetVector<MachineBasicBlock*> &Defs,
MachineBasicBlock *Dest) -> bool {
for (MachineBasicBlock *D : Defs)
if (D != Dest && MDT->dominates(D, Dest))
return true;
MachineBasicBlock *Entry = &Dest->getParent()->front();
SetVector<MachineBasicBlock*> Work(Dest->pred_begin(), Dest->pred_end());
for (unsigned i = 0; i < Work.size(); ++i) {
MachineBasicBlock *B = Work[i];
if (Defs.count(B))
if (B == Entry)
return false;
for (auto *P : B->predecessors())
return true;
// First, try to extend live range within individual basic blocks. This
// will leave us only with dead defs that do not reach any predicated
// defs in the same block.
SetVector<MachineBasicBlock*> Defs;
SmallVector<SlotIndex,4> PredDefs;
for (auto &Seg : Range) {
if (!Seg.start.isRegister())
MachineInstr *DefI = LIS->getInstructionFromIndex(Seg.start);
if (HII->isPredicated(*DefI))
SmallVector<SlotIndex,8> Undefs;
LiveInterval &LI = LIS->getInterval(Reg);
LI.computeSubRangeUndefs(Undefs, LM, *MRI, *LIS->getSlotIndexes());
for (auto &SI : PredDefs) {
MachineBasicBlock *BB = LIS->getMBBFromIndex(SI);
auto P = Range.extendInBlock(Undefs, LIS->getMBBStartIdx(BB), SI);
if (P.first != nullptr || P.second)
SI = SlotIndex();
// Calculate reachability for those predicated defs that were not handled
// by the in-block extension.
SmallVector<SlotIndex,4> ExtTo;
for (auto &SI : PredDefs) {
if (!SI.isValid())
MachineBasicBlock *BB = LIS->getMBBFromIndex(SI);
if (BB->pred_empty())
// If the defs from this range reach SI via all predecessors, it is live.
// It can happen that SI is reached by the defs through some paths, but
// not all. In the IR coming into this optimization, SI would not be
// considered live, since the defs would then not jointly dominate SI.
// That means that SI is an overwriting def, and no implicit use is
// needed at this point. Do not add SI to the extension points, since
// extendToIndices will abort if there is no joint dominance.
// If the abort was avoided by adding extra undefs added to Undefs,
// extendToIndices could actually indicate that SI is live, contrary
// to the original IR.
if (Dominate(Defs, BB))
if (!ExtTo.empty())
LIS->extendToIndices(Range, ExtTo, Undefs);
// Remove <dead> flags from all defs that are not dead after live range
// extension, and collect all def operands. They will be used to generate
// the necessary implicit uses.
// At the same time, add <dead> flag to all defs that are actually dead.
// This can happen, for example, when a mux with identical inputs is
// replaced with a COPY: the use of the predicate register disappears and
// the dead can become dead.
std::set<RegisterRef> DefRegs;
for (auto &Seg : Range) {
if (!Seg.start.isRegister())
MachineInstr *DefI = LIS->getInstructionFromIndex(Seg.start);
for (auto &Op : DefI->operands()) {
auto P = IsRegDef(Op);
if (P.second && Seg.end.isDead()) {
} else if (P.first) {
// Now, add implicit uses to each predicated def that is reached
// by other defs.
for (auto &Seg : Range) {
if (!Seg.start.isRegister() || !Range.liveAt(Seg.start.getPrevSlot()))
MachineInstr *DefI = LIS->getInstructionFromIndex(Seg.start);
if (!HII->isPredicated(*DefI))
// Construct the set of all necessary implicit uses, based on the def
// operands in the instruction. We need to tie the implicit uses to
// the corresponding defs.
std::map<RegisterRef,unsigned> ImpUses;
for (unsigned i = 0, e = DefI->getNumOperands(); i != e; ++i) {
MachineOperand &Op = DefI->getOperand(i);
if (!Op.isReg() || !DefRegs.count(Op))
if (Op.isDef()) {
// Tied defs will always have corresponding uses, so no extra
// implicit uses are needed.
if (!Op.isTied())
ImpUses.insert({Op, i});
} else {
// This function can be called for the same register with different
// lane masks. If the def in this instruction was for the whole
// register, we can get here more than once. Avoid adding multiple
// implicit uses (or adding an implicit use when an explicit one is
// present).
if (Op.isTied())
if (ImpUses.empty())
MachineFunction &MF = *DefI->getParent()->getParent();
for (std::pair<RegisterRef, unsigned> P : ImpUses) {
RegisterRef R = P.first;
MachineInstrBuilder(MF, DefI).addReg(R.Reg, RegState::Implicit, R.Sub);
DefI->tieOperands(P.second, DefI->getNumOperands()-1);
void HexagonExpandCondsets::updateDeadFlags(Register Reg) {
LiveInterval &LI = LIS->getInterval(Reg);
if (LI.hasSubRanges()) {
for (LiveInterval::SubRange &S : LI.subranges()) {
updateDeadsInRange(Reg, S.LaneMask, S);
LIS->shrinkToUses(S, Reg);
} else {
updateDeadsInRange(Reg, MRI->getMaxLaneMaskForVReg(Reg), LI);
void HexagonExpandCondsets::recalculateLiveInterval(Register Reg) {
void HexagonExpandCondsets::removeInstr(MachineInstr &MI) {
void HexagonExpandCondsets::updateLiveness(std::set<Register> &RegSet,
bool Recalc, bool UpdateKills,
bool UpdateDeads) {
UpdateKills |= UpdateDeads;
for (Register R : RegSet) {
if (!R.isVirtual()) {
// There shouldn't be any physical registers as operands, except
// possibly reserved registers.
if (Recalc)
if (UpdateKills)
if (UpdateDeads)
// Fixing <dead> flags may extend live ranges, so reset <kill> flags
// after that.
if (UpdateKills)
/// Get the opcode for a conditional transfer of the value in SO (source
/// operand). The condition (true/false) is given in Cond.
unsigned HexagonExpandCondsets::getCondTfrOpcode(const MachineOperand &SO,
bool IfTrue) {
using namespace Hexagon;
if (SO.isReg()) {
MCRegister PhysR;
RegisterRef RS = SO;
if (RS.Reg.isVirtual()) {
const TargetRegisterClass *VC = MRI->getRegClass(RS.Reg);
assert(VC->begin() != VC->end() && "Empty register class");
PhysR = *VC->begin();
} else {
PhysR = RS.Reg;
MCRegister PhysS = (RS.Sub == 0) ? PhysR : TRI->getSubReg(PhysR, RS.Sub);
const TargetRegisterClass *RC = TRI->getMinimalPhysRegClass(PhysS);
switch (TRI->getRegSizeInBits(*RC)) {
case 32:
return IfTrue ? A2_tfrt : A2_tfrf;
case 64:
return IfTrue ? A2_tfrpt : A2_tfrpf;
llvm_unreachable("Invalid register operand");
switch (SO.getType()) {
case MachineOperand::MO_Immediate:
case MachineOperand::MO_FPImmediate:
case MachineOperand::MO_ConstantPoolIndex:
case MachineOperand::MO_TargetIndex:
case MachineOperand::MO_JumpTableIndex:
case MachineOperand::MO_ExternalSymbol:
case MachineOperand::MO_GlobalAddress:
case MachineOperand::MO_BlockAddress:
return IfTrue ? C2_cmoveit : C2_cmoveif;
llvm_unreachable("Unexpected source operand");
/// Generate a conditional transfer, copying the value SrcOp to the
/// destination register DstR:DstSR, and using the predicate register from
/// PredOp. The Cond argument specifies whether the predicate is to be
/// if(PredOp), or if(!PredOp).
MachineInstr *HexagonExpandCondsets::genCondTfrFor(MachineOperand &SrcOp,
MachineBasicBlock::iterator At,
unsigned DstR, unsigned DstSR, const MachineOperand &PredOp,
bool PredSense, bool ReadUndef, bool ImpUse) {
MachineInstr *MI = SrcOp.getParent();
MachineBasicBlock &B = *At->getParent();
const DebugLoc &DL = MI->getDebugLoc();
// Don't avoid identity copies here (i.e. if the source and the destination
// are the same registers). It is actually better to generate them here,
// since this would cause the copy to potentially be predicated in the next
// step. The predication will remove such a copy if it is unable to
/// predicate.
unsigned Opc = getCondTfrOpcode(SrcOp, PredSense);
unsigned DstState = RegState::Define | (ReadUndef ? RegState::Undef : 0);
unsigned PredState = getRegState(PredOp) & ~RegState::Kill;
MachineInstrBuilder MIB;
if (SrcOp.isReg()) {
unsigned SrcState = getRegState(SrcOp);
if (RegisterRef(SrcOp) == RegisterRef(DstR, DstSR))
SrcState &= ~RegState::Kill;
MIB = BuildMI(B, At, DL, HII->get(Opc))
.addReg(DstR, DstState, DstSR)
.addReg(PredOp.getReg(), PredState, PredOp.getSubReg())
.addReg(SrcOp.getReg(), SrcState, SrcOp.getSubReg());
} else {
MIB = BuildMI(B, At, DL, HII->get(Opc))
.addReg(DstR, DstState, DstSR)
.addReg(PredOp.getReg(), PredState, PredOp.getSubReg())
LLVM_DEBUG(dbgs() << "created an initial copy: " << *MIB);
return &*MIB;
/// Replace a MUX instruction MI with a pair A2_tfrt/A2_tfrf. This function
/// performs all necessary changes to complete the replacement.
bool HexagonExpandCondsets::split(MachineInstr &MI,
std::set<Register> &UpdRegs) {
if (TfrLimitActive) {
if (TfrCounter >= TfrLimit)
return false;
LLVM_DEBUG(dbgs() << "\nsplitting " << printMBBReference(*MI.getParent())
<< ": " << MI);
MachineOperand &MD = MI.getOperand(0); // Definition
MachineOperand &MP = MI.getOperand(1); // Predicate register
Register DR = MD.getReg(), DSR = MD.getSubReg();
bool ReadUndef = MD.isUndef();
MachineBasicBlock::iterator At = MI;
auto updateRegs = [&UpdRegs] (const MachineInstr &MI) -> void {
for (auto &Op : MI.operands())
if (Op.isReg())
// If this is a mux of the same register, just replace it with COPY.
// Ideally, this would happen earlier, so that register coalescing would
// see it.
MachineOperand &ST = MI.getOperand(2);
MachineOperand &SF = MI.getOperand(3);
if (ST.isReg() && SF.isReg()) {
RegisterRef RT(ST);
if (RT == RegisterRef(SF)) {
// Copy regs to update first.
unsigned S = getRegState(ST);
while (MI.getNumOperands() > 1)
MachineFunction &MF = *MI.getParent()->getParent();
MachineInstrBuilder(MF, MI).addReg(RT.Reg, S, RT.Sub);
return true;
// First, create the two invididual conditional transfers, and add each
// of them to the live intervals information. Do that first and then remove
// the old instruction from live intervals.
MachineInstr *TfrT =
genCondTfrFor(ST, At, DR, DSR, MP, true, ReadUndef, false);
MachineInstr *TfrF =
genCondTfrFor(SF, At, DR, DSR, MP, false, ReadUndef, true);
// Will need to recalculate live intervals for all registers in MI.
return true;
bool HexagonExpandCondsets::isPredicable(MachineInstr *MI) {
if (HII->isPredicated(*MI) || !HII->isPredicable(*MI))
return false;
if (MI->hasUnmodeledSideEffects() || MI->mayStore())
return false;
// Reject instructions with multiple defs (e.g. post-increment loads).
bool HasDef = false;
for (auto &Op : MI->operands()) {
if (!Op.isReg() || !Op.isDef())
if (HasDef)
return false;
HasDef = true;
for (auto &Mo : MI->memoperands())
if (Mo->isVolatile() || Mo->isAtomic())
return false;
return true;
/// Find the reaching definition for a predicated use of RD. The RD is used
/// under the conditions given by PredR and Cond, and this function will ignore
/// definitions that set RD under the opposite conditions.
MachineInstr *HexagonExpandCondsets::getReachingDefForPred(RegisterRef RD,
MachineBasicBlock::iterator UseIt, unsigned PredR, bool Cond) {
MachineBasicBlock &B = *UseIt->getParent();
MachineBasicBlock::iterator I = UseIt, S = B.begin();
if (I == S)
return nullptr;
bool PredValid = true;
do {
MachineInstr *MI = &*I;
// Check if this instruction can be ignored, i.e. if it is predicated
// on the complementary condition.
if (PredValid && HII->isPredicated(*MI)) {
if (MI->readsRegister(PredR) && (Cond != HII->isPredicatedTrue(*MI)))
// Check the defs. If the PredR is defined, invalidate it. If RD is
// defined, return the instruction or 0, depending on the circumstances.
for (auto &Op : MI->operands()) {
if (!Op.isReg() || !Op.isDef())
RegisterRef RR = Op;
if (RR.Reg == PredR) {
PredValid = false;
if (RR.Reg != RD.Reg)
// If the "Reg" part agrees, there is still the subregister to check.
// If we are looking for %1:loreg, we can skip %1:hireg, but
// not %1 (w/o subregisters).
if (RR.Sub == RD.Sub)
return MI;
if (RR.Sub == 0 || RD.Sub == 0)
return nullptr;
// We have different subregisters, so we can continue looking.
} while (I != S);
return nullptr;
/// Check if the instruction MI can be safely moved over a set of instructions
/// whose side-effects (in terms of register defs and uses) are expressed in
/// the maps Defs and Uses. These maps reflect the conditional defs and uses
/// that depend on the same predicate register to allow moving instructions
/// over instructions predicated on the opposite condition.
bool HexagonExpandCondsets::canMoveOver(MachineInstr &MI, ReferenceMap &Defs,
ReferenceMap &Uses) {
// In order to be able to safely move MI over instructions that define
// "Defs" and use "Uses", no def operand from MI can be defined or used
// and no use operand can be defined.
for (auto &Op : MI.operands()) {
if (!Op.isReg())
RegisterRef RR = Op;
// For physical register we would need to check register aliases, etc.
// and we don't want to bother with that. It would be of little value
// before the actual register rewriting (from virtual to physical).
if (!RR.Reg.isVirtual())
return false;
// No redefs for any operand.
if (isRefInMap(RR, Defs, Exec_Then))
return false;
// For defs, there cannot be uses.
if (Op.isDef() && isRefInMap(RR, Uses, Exec_Then))
return false;
return true;
/// Check if the instruction accessing memory (TheI) can be moved to the
/// location ToI.
bool HexagonExpandCondsets::canMoveMemTo(MachineInstr &TheI, MachineInstr &ToI,
bool IsDown) {
bool IsLoad = TheI.mayLoad(), IsStore = TheI.mayStore();
if (!IsLoad && !IsStore)
return true;
if (HII->areMemAccessesTriviallyDisjoint(TheI, ToI))
return true;
if (TheI.hasUnmodeledSideEffects())
return false;
MachineBasicBlock::iterator StartI = IsDown ? TheI : ToI;
MachineBasicBlock::iterator EndI = IsDown ? ToI : TheI;
bool Ordered = TheI.hasOrderedMemoryRef();
// Search for aliased memory reference in (StartI, EndI).
for (MachineBasicBlock::iterator I = std::next(StartI); I != EndI; ++I) {
MachineInstr *MI = &*I;
if (MI->hasUnmodeledSideEffects())
return false;
bool L = MI->mayLoad(), S = MI->mayStore();
if (!L && !S)
if (Ordered && MI->hasOrderedMemoryRef())
return false;
bool Conflict = (L && IsStore) || S;
if (Conflict)
return false;
return true;
/// Generate a predicated version of MI (where the condition is given via
/// PredR and Cond) at the point indicated by Where.
void HexagonExpandCondsets::predicateAt(const MachineOperand &DefOp,
MachineInstr &MI,
MachineBasicBlock::iterator Where,
const MachineOperand &PredOp, bool Cond,
std::set<Register> &UpdRegs) {
// The problem with updating live intervals is that we can move one def
// past another def. In particular, this can happen when moving an A2_tfrt
// over an A2_tfrf defining the same register. From the point of view of
// live intervals, these two instructions are two separate definitions,
// and each one starts another live segment. LiveIntervals's "handleMove"
// does not allow such moves, so we need to handle it ourselves. To avoid
// invalidating liveness data while we are using it, the move will be
// implemented in 4 steps: (1) add a clone of the instruction MI at the
// target location, (2) update liveness, (3) delete the old instruction,
// and (4) update liveness again.
MachineBasicBlock &B = *MI.getParent();
DebugLoc DL = Where->getDebugLoc(); // "Where" points to an instruction.
unsigned Opc = MI.getOpcode();
unsigned PredOpc = HII->getCondOpcode(Opc, !Cond);
MachineInstrBuilder MB = BuildMI(B, Where, DL, HII->get(PredOpc));
unsigned Ox = 0, NP = MI.getNumOperands();
// Skip all defs from MI first.
while (Ox < NP) {
MachineOperand &MO = MI.getOperand(Ox);
if (!MO.isReg() || !MO.isDef())
// Add the new def, then the predicate register, then the rest of the
// operands.
MB.addReg(DefOp.getReg(), getRegState(DefOp), DefOp.getSubReg());
MB.addReg(PredOp.getReg(), PredOp.isUndef() ? RegState::Undef : 0,
while (Ox < NP) {
MachineOperand &MO = MI.getOperand(Ox);
if (!MO.isReg() || !MO.isImplicit())
MachineInstr *NewI = MB;
for (auto &Op : NewI->operands())
if (Op.isReg())
/// In the range [First, Last], rename all references to the "old" register RO
/// to the "new" register RN, but only in instructions predicated on the given
/// condition.
void HexagonExpandCondsets::renameInRange(RegisterRef RO, RegisterRef RN,
unsigned PredR, bool Cond, MachineBasicBlock::iterator First,
MachineBasicBlock::iterator Last) {
MachineBasicBlock::iterator End = std::next(Last);
for (MachineBasicBlock::iterator I = First; I != End; ++I) {
MachineInstr *MI = &*I;
// Do not touch instructions that are not predicated, or are predicated
// on the opposite condition.
if (!HII->isPredicated(*MI))
if (!MI->readsRegister(PredR) || (Cond != HII->isPredicatedTrue(*MI)))
for (auto &Op : MI->operands()) {
if (!Op.isReg() || RO != RegisterRef(Op))
// In practice, this isn't supposed to see any defs.
assert(!Op.isDef() && "Not expecting a def");
/// For a given conditional copy, predicate the definition of the source of
/// the copy under the given condition (using the same predicate register as
/// the copy).
bool HexagonExpandCondsets::predicate(MachineInstr &TfrI, bool Cond,
std::set<Register> &UpdRegs) {
// TfrI - A2_tfr[tf] Instruction (not A2_tfrsi).
unsigned Opc = TfrI.getOpcode();
assert(Opc == Hexagon::A2_tfrt || Opc == Hexagon::A2_tfrf);
LLVM_DEBUG(dbgs() << "\nattempt to predicate if-" << (Cond ? "true" : "false")
<< ": " << TfrI);
MachineOperand &MD = TfrI.getOperand(0);
MachineOperand &MP = TfrI.getOperand(1);
MachineOperand &MS = TfrI.getOperand(2);
// The source operand should be a <kill>. This is not strictly necessary,
// but it makes things a lot simpler. Otherwise, we would need to rename
// some registers, which would complicate the transformation considerably.
if (!MS.isKill())
return false;
// Avoid predicating instructions that define a subregister if subregister
// liveness tracking is not enabled.
if (MD.getSubReg() && !MRI->shouldTrackSubRegLiveness(MD.getReg()))
return false;
RegisterRef RT(MS);
Register PredR = MP.getReg();
MachineInstr *DefI = getReachingDefForPred(RT, TfrI, PredR, Cond);
if (!DefI || !isPredicable(DefI))
return false;
LLVM_DEBUG(dbgs() << "Source def: " << *DefI);
// Collect the information about registers defined and used between the
// DefI and the TfrI.
// Map: reg -> bitmask of subregs
ReferenceMap Uses, Defs;
MachineBasicBlock::iterator DefIt = DefI, TfrIt = TfrI;
// Check if the predicate register is valid between DefI and TfrI.
// If it is, we can then ignore instructions predicated on the negated
// conditions when collecting def and use information.
bool PredValid = true;
for (MachineBasicBlock::iterator I = std::next(DefIt); I != TfrIt; ++I) {
if (!I->modifiesRegister(PredR, nullptr))
PredValid = false;
for (MachineBasicBlock::iterator I = std::next(DefIt); I != TfrIt; ++I) {
MachineInstr *MI = &*I;
// If this instruction is predicated on the same register, it could
// potentially be ignored.
// By default assume that the instruction executes on the same condition
// as TfrI (Exec_Then), and also on the opposite one (Exec_Else).
unsigned Exec = Exec_Then | Exec_Else;
if (PredValid && HII->isPredicated(*MI) && MI->readsRegister(PredR))
Exec = (Cond == HII->isPredicatedTrue(*MI)) ? Exec_Then : Exec_Else;
for (auto &Op : MI->operands()) {
if (!Op.isReg())
// We don't want to deal with physical registers. The reason is that
// they can be aliased with other physical registers. Aliased virtual
// registers must share the same register number, and can only differ
// in the subregisters, which we are keeping track of. Physical
// registers ters no longer have subregisters---their super- and
// subregisters are other physical registers, and we are not checking
// that.
RegisterRef RR = Op;
if (!RR.Reg.isVirtual())
return false;
ReferenceMap &Map = Op.isDef() ? Defs : Uses;
if (Op.isDef() && Op.isUndef()) {
assert(RR.Sub && "Expecting a subregister on <def,read-undef>");
// If this is a <def,read-undef>, then it invalidates the non-written
// part of the register. For the purpose of checking the validity of
// the move, assume that it modifies the whole register.
RR.Sub = 0;
addRefToMap(RR, Map, Exec);
// The situation:
// RT = DefI
// ...
// RD = TfrI ..., RT
// If the register-in-the-middle (RT) is used or redefined between
// DefI and TfrI, we may not be able proceed with this transformation.
// We can ignore a def that will not execute together with TfrI, and a
// use that will. If there is such a use (that does execute together with
// TfrI), we will not be able to move DefI down. If there is a use that
// executed if TfrI's condition is false, then RT must be available
// unconditionally (cannot be predicated).
// Essentially, we need to be able to rename RT to RD in this segment.
if (isRefInMap(RT, Defs, Exec_Then) || isRefInMap(RT, Uses, Exec_Else))
return false;
RegisterRef RD = MD;
// If the predicate register is defined between DefI and TfrI, the only
// potential thing to do would be to move the DefI down to TfrI, and then
// predicate. The reaching def (DefI) must be movable down to the location
// of the TfrI.
// If the target register of the TfrI (RD) is not used or defined between
// DefI and TfrI, consider moving TfrI up to DefI.
bool CanUp = canMoveOver(TfrI, Defs, Uses);
bool CanDown = canMoveOver(*DefI, Defs, Uses);
// The TfrI does not access memory, but DefI could. Check if it's safe
// to move DefI down to TfrI.
if (DefI->mayLoadOrStore())
if (!canMoveMemTo(*DefI, TfrI, true))
CanDown = false;
LLVM_DEBUG(dbgs() << "Can move up: " << (CanUp ? "yes" : "no")
<< ", can move down: " << (CanDown ? "yes\n" : "no\n"));
MachineBasicBlock::iterator PastDefIt = std::next(DefIt);
if (CanUp)
predicateAt(MD, *DefI, PastDefIt, MP, Cond, UpdRegs);
else if (CanDown)
predicateAt(MD, *DefI, TfrIt, MP, Cond, UpdRegs);
return false;
if (RT != RD) {
renameInRange(RT, RD, PredR, Cond, PastDefIt, TfrIt);
return true;
/// Predicate all cases of conditional copies in the specified block.
bool HexagonExpandCondsets::predicateInBlock(MachineBasicBlock &B,
std::set<Register> &UpdRegs) {
bool Changed = false;
for (MachineInstr &MI : llvm::make_early_inc_range(B)) {
unsigned Opc = MI.getOpcode();
if (Opc == Hexagon::A2_tfrt || Opc == Hexagon::A2_tfrf) {
bool Done = predicate(MI, (Opc == Hexagon::A2_tfrt), UpdRegs);
if (!Done) {
// If we didn't predicate I, we may need to remove it in case it is
// an "identity" copy, e.g. %1 = A2_tfrt %2, %1.
if (RegisterRef(MI.getOperand(0)) == RegisterRef(MI.getOperand(2))) {
for (auto &Op : MI.operands())
if (Op.isReg())
Changed |= Done;
return Changed;
bool HexagonExpandCondsets::isIntReg(RegisterRef RR, unsigned &BW) {
if (!RR.Reg.isVirtual())
return false;
const TargetRegisterClass *RC = MRI->getRegClass(RR.Reg);
if (RC == &Hexagon::IntRegsRegClass) {
BW = 32;
return true;
if (RC == &Hexagon::DoubleRegsRegClass) {
BW = (RR.Sub != 0) ? 32 : 64;
return true;
return false;
bool HexagonExpandCondsets::isIntraBlocks(LiveInterval &LI) {
for (LiveInterval::iterator I = LI.begin(), E = LI.end(); I != E; ++I) {
LiveRange::Segment &LR = *I;
// Range must start at a register...
if (!LR.start.isRegister())
return false;
// ...and end in a register or in a dead slot.
if (!LR.end.isRegister() && !LR.end.isDead())
return false;
return true;
bool HexagonExpandCondsets::coalesceRegisters(RegisterRef R1, RegisterRef R2) {
if (CoaLimitActive) {
if (CoaCounter >= CoaLimit)
return false;
unsigned BW1, BW2;
if (!isIntReg(R1, BW1) || !isIntReg(R2, BW2) || BW1 != BW2)
return false;
if (MRI->isLiveIn(R1.Reg))
return false;
if (MRI->isLiveIn(R2.Reg))
return false;
LiveInterval &L1 = LIS->getInterval(R1.Reg);
LiveInterval &L2 = LIS->getInterval(R2.Reg);
if (L2.empty())
return false;
if (L1.hasSubRanges() || L2.hasSubRanges())
return false;
bool Overlap = L1.overlaps(L2);
LLVM_DEBUG(dbgs() << "compatible registers: ("
<< (Overlap ? "overlap" : "disjoint") << ")\n "
<< printReg(R1.Reg, TRI, R1.Sub) << " " << L1 << "\n "
<< printReg(R2.Reg, TRI, R2.Sub) << " " << L2 << "\n");
if (R1.Sub || R2.Sub)
return false;
if (Overlap)
return false;
// Coalescing could have a negative impact on scheduling, so try to limit
// to some reasonable extent. Only consider coalescing segments, when one
// of them does not cross basic block boundaries.
if (!isIntraBlocks(L1) && !isIntraBlocks(L2))
return false;
MRI->replaceRegWith(R2.Reg, R1.Reg);
// Move all live segments from L2 to L1.
using ValueInfoMap = DenseMap<VNInfo *, VNInfo *>;
ValueInfoMap VM;
for (LiveInterval::iterator I = L2.begin(), E = L2.end(); I != E; ++I) {
VNInfo *NewVN, *OldVN = I->valno;
ValueInfoMap::iterator F = VM.find(OldVN);
if (F == VM.end()) {
NewVN = L1.getNextValue(I->valno->def, LIS->getVNInfoAllocator());
VM.insert(std::make_pair(OldVN, NewVN));
} else {
NewVN = F->second;
L1.addSegment(LiveRange::Segment(I->start, I->end, NewVN));
while (!L2.empty())
LLVM_DEBUG(dbgs() << "coalesced: " << L1 << "\n");
return true;
/// Attempt to coalesce one of the source registers to a MUX instruction with
/// the destination register. This could lead to having only one predicated
/// instruction in the end instead of two.
bool HexagonExpandCondsets::coalesceSegments(
const SmallVectorImpl<MachineInstr *> &Condsets,
std::set<Register> &UpdRegs) {
SmallVector<MachineInstr*,16> TwoRegs;
for (MachineInstr *MI : Condsets) {
MachineOperand &S1 = MI->getOperand(2), &S2 = MI->getOperand(3);
if (!S1.isReg() && !S2.isReg())
bool Changed = false;
for (MachineInstr *CI : TwoRegs) {
RegisterRef RD = CI->getOperand(0);
RegisterRef RP = CI->getOperand(1);
MachineOperand &S1 = CI->getOperand(2), &S2 = CI->getOperand(3);
bool Done = false;
// Consider this case:
// %1 = instr1 ...
// %2 = instr2 ...
// %0 = C2_mux ..., %1, %2
// If %0 was coalesced with %1, we could end up with the following
// code:
// %0 = instr1 ...
// %2 = instr2 ...
// %0 = A2_tfrf ..., %2
// which will later become:
// %0 = instr1 ...
// %0 = instr2_cNotPt ...
// i.e. there will be an unconditional definition (instr1) of %0
// followed by a conditional one. The output dependency was there before
// and it unavoidable, but if instr1 is predicable, we will no longer be
// able to predicate it here.
// To avoid this scenario, don't coalesce the destination register with
// a source register that is defined by a predicable instruction.
if (S1.isReg()) {
RegisterRef RS = S1;
MachineInstr *RDef = getReachingDefForPred(RS, CI, RP.Reg, true);
if (!RDef || !HII->isPredicable(*RDef)) {
Done = coalesceRegisters(RD, RegisterRef(S1));
if (Done) {
if (!Done && S2.isReg()) {
RegisterRef RS = S2;
MachineInstr *RDef = getReachingDefForPred(RS, CI, RP.Reg, false);
if (!RDef || !HII->isPredicable(*RDef)) {
Done = coalesceRegisters(RD, RegisterRef(S2));
if (Done) {
Changed |= Done;
return Changed;
bool HexagonExpandCondsets::runOnMachineFunction(MachineFunction &MF) {
if (skipFunction(MF.getFunction()))
return false;
HII = static_cast<const HexagonInstrInfo*>(MF.getSubtarget().getInstrInfo());
TRI = MF.getSubtarget().getRegisterInfo();
MDT = &getAnalysis<MachineDominatorTree>();
LIS = &getAnalysis<LiveIntervals>();
MRI = &MF.getRegInfo();
LLVM_DEBUG(LIS->print(dbgs() << "Before expand-condsets\n",
bool Changed = false;
std::set<Register> CoalUpd, PredUpd;
SmallVector<MachineInstr*,16> Condsets;
for (auto &B : MF)
for (auto &I : B)
if (isCondset(I))
// Try to coalesce the target of a mux with one of its sources.
// This could eliminate a register copy in some circumstances.
Changed |= coalesceSegments(Condsets, CoalUpd);
// Update kill flags on all source operands. This is done here because
// at this moment (when expand-condsets runs), there are no kill flags
// in the IR (they have been removed by live range analysis).
// Updating them right before we split is the easiest, because splitting
// adds definitions which would interfere with updating kills afterwards.
std::set<Register> KillUpd;
for (MachineInstr *MI : Condsets)
for (MachineOperand &Op : MI->operands())
if (Op.isReg() && Op.isUse())
if (!CoalUpd.count(Op.getReg()))
updateLiveness(KillUpd, false, true, false);
LIS->print(dbgs() << "After coalescing\n", MF.getFunction().getParent()));
// First, simply split all muxes into a pair of conditional transfers
// and update the live intervals to reflect the new arrangement. The
// goal is to update the kill flags, since predication will rely on
// them.
for (MachineInstr *MI : Condsets)
Changed |= split(*MI, PredUpd);
Condsets.clear(); // The contents of Condsets are invalid here anyway.
// Do not update live ranges after splitting. Recalculation of live
// intervals removes kill flags, which were preserved by splitting on
// the source operands of condsets. These kill flags are needed by
// predication, and after splitting they are difficult to recalculate
// (because of predicated defs), so make sure they are left untouched.
// Predication does not use live intervals.
LIS->print(dbgs() << "After splitting\n", MF.getFunction().getParent()));
// Traverse all blocks and collapse predicable instructions feeding
// conditional transfers into predicated instructions.
// Walk over all the instructions again, so we may catch pre-existing
// cases that were not created in the previous step.
for (auto &B : MF)
Changed |= predicateInBlock(B, PredUpd);
LLVM_DEBUG(LIS->print(dbgs() << "After predicating\n",
PredUpd.insert(CoalUpd.begin(), CoalUpd.end());
updateLiveness(PredUpd, true, true, true);
if (Changed)
LIS->print(dbgs() << "After expand-condsets\n",
return Changed;
// Public Constructor Functions
FunctionPass *llvm::createHexagonExpandCondsets() {
return new HexagonExpandCondsets();