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//===- HexagonNewValueJump.cpp - Hexagon Backend New Value Jump -----------===//
// 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 implements NewValueJump pass in Hexagon.
// Ideally, we should merge this as a Peephole pass prior to register
// allocation, but because we have a spill in between the feeder and new value
// jump instructions, we are forced to write after register allocation.
// Having said that, we should re-attempt to pull this earlier at some point
// in future.
// The basic approach looks for sequence of predicated jump, compare instruciton
// that genereates the predicate and, the feeder to the predicate. Once it finds
// all, it collapses compare and jump instruction into a new value jump
// intstructions.
#include "llvm/InitializePasses.h"
#include "Hexagon.h"
#include "HexagonInstrInfo.h"
#include "HexagonRegisterInfo.h"
#include "HexagonSubtarget.h"
#include "llvm/ADT/Statistic.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/TargetOpcodes.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/MC/MCInstrDesc.h"
#include "llvm/Pass.h"
#include "llvm/Support/BranchProbability.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include <cassert>
#include <cstdint>
#include <iterator>
using namespace llvm;
#define DEBUG_TYPE "hexagon-nvj"
STATISTIC(NumNVJGenerated, "Number of New Value Jump Instructions created");
static cl::opt<int> DbgNVJCount("nvj-count", cl::init(-1), cl::Hidden,
cl::desc("Maximum number of predicated jumps to be converted to "
"New Value Jump"));
static cl::opt<bool> DisableNewValueJumps("disable-nvjump", cl::Hidden,
cl::ZeroOrMore, cl::init(false),
cl::desc("Disable New Value Jumps"));
namespace llvm {
FunctionPass *createHexagonNewValueJump();
void initializeHexagonNewValueJumpPass(PassRegistry&);
} // end namespace llvm
namespace {
struct HexagonNewValueJump : public MachineFunctionPass {
static char ID;
HexagonNewValueJump() : MachineFunctionPass(ID) {}
void getAnalysisUsage(AnalysisUsage &AU) const override {
StringRef getPassName() const override { return "Hexagon NewValueJump"; }
bool runOnMachineFunction(MachineFunction &Fn) override;
MachineFunctionProperties getRequiredProperties() const override {
return MachineFunctionProperties().set(
const HexagonInstrInfo *QII;
const HexagonRegisterInfo *QRI;
/// A handle to the branch probability pass.
const MachineBranchProbabilityInfo *MBPI;
bool isNewValueJumpCandidate(const MachineInstr &MI) const;
} // end anonymous namespace
char HexagonNewValueJump::ID = 0;
INITIALIZE_PASS_BEGIN(HexagonNewValueJump, "hexagon-nvj",
"Hexagon NewValueJump", false, false)
INITIALIZE_PASS_END(HexagonNewValueJump, "hexagon-nvj",
"Hexagon NewValueJump", false, false)
// We have identified this II could be feeder to NVJ,
// verify that it can be.
static bool canBeFeederToNewValueJump(const HexagonInstrInfo *QII,
const TargetRegisterInfo *TRI,
MachineBasicBlock::iterator II,
MachineBasicBlock::iterator end,
MachineBasicBlock::iterator skip,
MachineFunction &MF) {
// Predicated instruction can not be feeder to NVJ.
if (QII->isPredicated(*II))
return false;
// Bail out if feederReg is a paired register (double regs in
// our case). One would think that we can check to see if a given
// register cmpReg1 or cmpReg2 is a sub register of feederReg
// using -- if (QRI->isSubRegister(feederReg, cmpReg1) logic
// before the callsite of this function
// But we can not as it comes in the following fashion.
// %d0 = Hexagon_S2_lsr_r_p killed %d0, killed %r2
// %r0 = KILL %r0, implicit killed %d0
// %p0 = CMPEQri killed %r0, 0
// Hence, we need to check if it's a KILL instruction.
if (II->getOpcode() == TargetOpcode::KILL)
return false;
if (II->isImplicitDef())
return false;
if (QII->isSolo(*II))
return false;
if (QII->isFloat(*II))
return false;
// Make sure that the (unique) def operand is a register from IntRegs.
bool HadDef = false;
for (const MachineOperand &Op : II->operands()) {
if (!Op.isReg() || !Op.isDef())
if (HadDef)
return false;
HadDef = true;
if (!Hexagon::IntRegsRegClass.contains(Op.getReg()))
return false;
// Make sure there is no 'def' or 'use' of any of the uses of
// feeder insn between its definition, this MI and jump, jmpInst
// skipping compare, cmpInst.
// Here's the example.
// r21=memub(r22+r24<<#0)
// p0 = cmp.eq(r21, #0)
// r4=memub(r3+r21<<#0)
// if ( jump:t .LBB29_45
// Without this check, it will be converted into
// r4=memub(r3+r21<<#0)
// r21=memub(r22+r24<<#0)
// p0 = cmp.eq(r21, #0)
// if ( jump:t .LBB29_45
// and result WAR hazards if converted to New Value Jump.
for (unsigned i = 0; i < II->getNumOperands(); ++i) {
if (II->getOperand(i).isReg() &&
(II->getOperand(i).isUse() || II->getOperand(i).isDef())) {
MachineBasicBlock::iterator localII = II;
Register Reg = II->getOperand(i).getReg();
for (MachineBasicBlock::iterator localBegin = localII; localBegin != end;
++localBegin) {
if (localBegin == skip)
// Check for Subregisters too.
if (localBegin->modifiesRegister(Reg, TRI) ||
localBegin->readsRegister(Reg, TRI))
return false;
return true;
// These are the common checks that need to performed
// to determine if
// 1. compare instruction can be moved before jump.
// 2. feeder to the compare instruction can be moved before jump.
static bool commonChecksToProhibitNewValueJump(bool afterRA,
MachineBasicBlock::iterator MII) {
// If store in path, bail out.
if (MII->mayStore())
return false;
// if call in path, bail out.
if (MII->isCall())
return false;
// if NVJ is running prior to RA, do the following checks.
if (!afterRA) {
// The following Target Opcode instructions are spurious
// to new value jump. If they are in the path, bail out.
// KILL sets kill flag on the opcode. It also sets up a
// single register, out of pair.
// %d0 = S2_lsr_r_p killed %d0, killed %r2
// %r0 = KILL %r0, implicit killed %d0
// %p0 = C2_cmpeqi killed %r0, 0
// PHI can be anything after RA.
// COPY can remateriaze things in between feeder, compare and nvj.
if (MII->getOpcode() == TargetOpcode::KILL ||
MII->getOpcode() == TargetOpcode::PHI ||
MII->getOpcode() == TargetOpcode::COPY)
return false;
// The following pseudo Hexagon instructions sets "use" and "def"
// of registers by individual passes in the backend. At this time,
// we don't know the scope of usage and definitions of these
// instructions.
if (MII->getOpcode() == Hexagon::LDriw_pred ||
MII->getOpcode() == Hexagon::STriw_pred)
return false;
return true;
static bool canCompareBeNewValueJump(const HexagonInstrInfo *QII,
const TargetRegisterInfo *TRI,
MachineBasicBlock::iterator II,
unsigned pReg,
bool secondReg,
bool optLocation,
MachineBasicBlock::iterator end,
MachineFunction &MF) {
MachineInstr &MI = *II;
// If the second operand of the compare is an imm, make sure it's in the
// range specified by the arch.
if (!secondReg) {
const MachineOperand &Op2 = MI.getOperand(2);
if (!Op2.isImm())
return false;
int64_t v = Op2.getImm();
bool Valid = false;
switch (MI.getOpcode()) {
case Hexagon::C2_cmpeqi:
case Hexagon::C4_cmpneqi:
case Hexagon::C2_cmpgti:
case Hexagon::C4_cmpltei:
Valid = (isUInt<5>(v) || v == -1);
case Hexagon::C2_cmpgtui:
case Hexagon::C4_cmplteui:
Valid = isUInt<5>(v);
case Hexagon::S2_tstbit_i:
case Hexagon::S4_ntstbit_i:
Valid = (v == 0);
if (!Valid)
return false;
unsigned cmpReg1, cmpOp2 = 0; // cmpOp2 assignment silences compiler warning.
cmpReg1 = MI.getOperand(1).getReg();
if (secondReg) {
cmpOp2 = MI.getOperand(2).getReg();
// If the same register appears as both operands, we cannot generate a new
// value compare. Only one operand may use the .new suffix.
if (cmpReg1 == cmpOp2)
return false;
// Make sure that the second register is not from COPY
// at machine code level, we don't need this, but if we decide
// to move new value jump prior to RA, we would be needing this.
MachineRegisterInfo &MRI = MF.getRegInfo();
if (!Register::isPhysicalRegister(cmpOp2)) {
MachineInstr *def = MRI.getVRegDef(cmpOp2);
if (def->getOpcode() == TargetOpcode::COPY)
return false;
// Walk the instructions after the compare (predicate def) to the jump,
// and satisfy the following conditions.
for (MachineBasicBlock::iterator localII = II; localII != end; ++localII) {
if (localII->isDebugInstr())
// Check 1.
// If "common" checks fail, bail out.
if (!commonChecksToProhibitNewValueJump(optLocation, localII))
return false;
// Check 2.
// If there is a def or use of predicate (result of compare), bail out.
if (localII->modifiesRegister(pReg, TRI) ||
localII->readsRegister(pReg, TRI))
return false;
// Check 3.
// If there is a def of any of the use of the compare (operands of compare),
// bail out.
// Eg.
// p0 = cmp.eq(r2, r0)
// r2 = r4
// if ( jump:t .LBB28_3
if (localII->modifiesRegister(cmpReg1, TRI) ||
(secondReg && localII->modifiesRegister(cmpOp2, TRI)))
return false;
return true;
// Given a compare operator, return a matching New Value Jump compare operator.
// Make sure that MI here is included in isNewValueJumpCandidate.
static unsigned getNewValueJumpOpcode(MachineInstr *MI, int reg,
bool secondRegNewified,
MachineBasicBlock *jmpTarget,
const MachineBranchProbabilityInfo
*MBPI) {
bool taken = false;
MachineBasicBlock *Src = MI->getParent();
const BranchProbability Prediction =
MBPI->getEdgeProbability(Src, jmpTarget);
if (Prediction >= BranchProbability(1,2))
taken = true;
switch (MI->getOpcode()) {
case Hexagon::C2_cmpeq:
return taken ? Hexagon::J4_cmpeq_t_jumpnv_t
: Hexagon::J4_cmpeq_t_jumpnv_nt;
case Hexagon::C2_cmpeqi:
if (reg >= 0)
return taken ? Hexagon::J4_cmpeqi_t_jumpnv_t
: Hexagon::J4_cmpeqi_t_jumpnv_nt;
return taken ? Hexagon::J4_cmpeqn1_t_jumpnv_t
: Hexagon::J4_cmpeqn1_t_jumpnv_nt;
case Hexagon::C4_cmpneqi:
if (reg >= 0)
return taken ? Hexagon::J4_cmpeqi_f_jumpnv_t
: Hexagon::J4_cmpeqi_f_jumpnv_nt;
return taken ? Hexagon::J4_cmpeqn1_f_jumpnv_t :
case Hexagon::C2_cmpgt:
if (secondRegNewified)
return taken ? Hexagon::J4_cmplt_t_jumpnv_t
: Hexagon::J4_cmplt_t_jumpnv_nt;
return taken ? Hexagon::J4_cmpgt_t_jumpnv_t
: Hexagon::J4_cmpgt_t_jumpnv_nt;
case Hexagon::C2_cmpgti:
if (reg >= 0)
return taken ? Hexagon::J4_cmpgti_t_jumpnv_t
: Hexagon::J4_cmpgti_t_jumpnv_nt;
return taken ? Hexagon::J4_cmpgtn1_t_jumpnv_t
: Hexagon::J4_cmpgtn1_t_jumpnv_nt;
case Hexagon::C2_cmpgtu:
if (secondRegNewified)
return taken ? Hexagon::J4_cmpltu_t_jumpnv_t
: Hexagon::J4_cmpltu_t_jumpnv_nt;
return taken ? Hexagon::J4_cmpgtu_t_jumpnv_t
: Hexagon::J4_cmpgtu_t_jumpnv_nt;
case Hexagon::C2_cmpgtui:
return taken ? Hexagon::J4_cmpgtui_t_jumpnv_t
: Hexagon::J4_cmpgtui_t_jumpnv_nt;
case Hexagon::C4_cmpneq:
return taken ? Hexagon::J4_cmpeq_f_jumpnv_t
: Hexagon::J4_cmpeq_f_jumpnv_nt;
case Hexagon::C4_cmplte:
if (secondRegNewified)
return taken ? Hexagon::J4_cmplt_f_jumpnv_t
: Hexagon::J4_cmplt_f_jumpnv_nt;
return taken ? Hexagon::J4_cmpgt_f_jumpnv_t
: Hexagon::J4_cmpgt_f_jumpnv_nt;
case Hexagon::C4_cmplteu:
if (secondRegNewified)
return taken ? Hexagon::J4_cmpltu_f_jumpnv_t
: Hexagon::J4_cmpltu_f_jumpnv_nt;
return taken ? Hexagon::J4_cmpgtu_f_jumpnv_t
: Hexagon::J4_cmpgtu_f_jumpnv_nt;
case Hexagon::C4_cmpltei:
if (reg >= 0)
return taken ? Hexagon::J4_cmpgti_f_jumpnv_t
: Hexagon::J4_cmpgti_f_jumpnv_nt;
return taken ? Hexagon::J4_cmpgtn1_f_jumpnv_t
: Hexagon::J4_cmpgtn1_f_jumpnv_nt;
case Hexagon::C4_cmplteui:
return taken ? Hexagon::J4_cmpgtui_f_jumpnv_t
: Hexagon::J4_cmpgtui_f_jumpnv_nt;
llvm_unreachable("Could not find matching New Value Jump instruction.");
// return *some value* to avoid compiler warning
return 0;
bool HexagonNewValueJump::isNewValueJumpCandidate(
const MachineInstr &MI) const {
switch (MI.getOpcode()) {
case Hexagon::C2_cmpeq:
case Hexagon::C2_cmpeqi:
case Hexagon::C2_cmpgt:
case Hexagon::C2_cmpgti:
case Hexagon::C2_cmpgtu:
case Hexagon::C2_cmpgtui:
case Hexagon::C4_cmpneq:
case Hexagon::C4_cmpneqi:
case Hexagon::C4_cmplte:
case Hexagon::C4_cmplteu:
case Hexagon::C4_cmpltei:
case Hexagon::C4_cmplteui:
return true;
return false;
bool HexagonNewValueJump::runOnMachineFunction(MachineFunction &MF) {
LLVM_DEBUG(dbgs() << "********** Hexagon New Value Jump **********\n"
<< "********** Function: " << MF.getName() << "\n");
if (skipFunction(MF.getFunction()))
return false;
// If we move NewValueJump before register allocation we'll need live variable
// analysis here too.
QII = static_cast<const HexagonInstrInfo *>(MF.getSubtarget().getInstrInfo());
QRI = static_cast<const HexagonRegisterInfo *>(
MBPI = &getAnalysis<MachineBranchProbabilityInfo>();
if (DisableNewValueJumps ||
return false;
int nvjCount = DbgNVJCount;
int nvjGenerated = 0;
// Loop through all the bb's of the function
for (MachineFunction::iterator MBBb = MF.begin(), MBBe = MF.end();
MBBb != MBBe; ++MBBb) {
MachineBasicBlock *MBB = &*MBBb;
LLVM_DEBUG(dbgs() << "** dumping bb ** " << MBB->getNumber() << "\n");
LLVM_DEBUG(dbgs() << "\n"
<< "********** dumping instr bottom up **********\n");
bool foundJump = false;
bool foundCompare = false;
bool invertPredicate = false;
unsigned predReg = 0; // predicate reg of the jump.
unsigned cmpReg1 = 0;
int cmpOp2 = 0;
MachineBasicBlock::iterator jmpPos;
MachineBasicBlock::iterator cmpPos;
MachineInstr *cmpInstr = nullptr, *jmpInstr = nullptr;
MachineBasicBlock *jmpTarget = nullptr;
bool afterRA = false;
bool isSecondOpReg = false;
bool isSecondOpNewified = false;
// Traverse the basic block - bottom up
for (MachineBasicBlock::iterator MII = MBB->end(), E = MBB->begin();
MII != E;) {
MachineInstr &MI = *--MII;
if (MI.isDebugInstr()) {
if ((nvjCount == 0) || (nvjCount > -1 && nvjCount <= nvjGenerated))
LLVM_DEBUG(dbgs() << "Instr: "; MI.dump(); dbgs() << "\n");
if (!foundJump && (MI.getOpcode() == Hexagon::J2_jumpt ||
MI.getOpcode() == Hexagon::J2_jumptpt ||
MI.getOpcode() == Hexagon::J2_jumpf ||
MI.getOpcode() == Hexagon::J2_jumpfpt ||
MI.getOpcode() == Hexagon::J2_jumptnewpt ||
MI.getOpcode() == Hexagon::J2_jumptnew ||
MI.getOpcode() == Hexagon::J2_jumpfnewpt ||
MI.getOpcode() == Hexagon::J2_jumpfnew)) {
// This is where you would insert your compare and
// instr that feeds compare
jmpPos = MII;
jmpInstr = &MI;
predReg = MI.getOperand(0).getReg();
afterRA = Register::isPhysicalRegister(predReg);
// If ifconverter had not messed up with the kill flags of the
// operands, the following check on the kill flag would suffice.
// if(!jmpInstr->getOperand(0).isKill()) break;
// This predicate register is live out of BB
// this would only work if we can actually use Live
// variable analysis on phy regs - but LLVM does not
// provide LV analysis on phys regs.
//if(LVs.isLiveOut(predReg, *MBB)) break;
// Get all the successors of this block - which will always
// be 2. Check if the predicate register is live-in in those
// successor. If yes, we can not delete the predicate -
// I am doing this only because LLVM does not provide LiveOut
// at the BB level.
bool predLive = false;
for (const MachineBasicBlock *SuccMBB : MBB->successors())
if (SuccMBB->isLiveIn(predReg))
predLive = true;
if (predLive)
if (!MI.getOperand(1).isMBB())
jmpTarget = MI.getOperand(1).getMBB();
foundJump = true;
if (MI.getOpcode() == Hexagon::J2_jumpf ||
MI.getOpcode() == Hexagon::J2_jumpfnewpt ||
MI.getOpcode() == Hexagon::J2_jumpfnew) {
invertPredicate = true;
// No new value jump if there is a barrier. A barrier has to be in its
// own packet. A barrier has zero operands. We conservatively bail out
// here if we see any instruction with zero operands.
if (foundJump && MI.getNumOperands() == 0)
if (foundJump && !foundCompare && MI.getOperand(0).isReg() &&
MI.getOperand(0).getReg() == predReg) {
// Not all compares can be new value compare. Arch Spec:
if (isNewValueJumpCandidate(MI)) {
(MI.getDesc().isCompare()) &&
"Only compare instruction can be collapsed into New Value Jump");
isSecondOpReg = MI.getOperand(2).isReg();
if (!canCompareBeNewValueJump(QII, QRI, MII, predReg, isSecondOpReg,
afterRA, jmpPos, MF))
cmpInstr = &MI;
cmpPos = MII;
foundCompare = true;
// We need cmpReg1 and cmpOp2(imm or reg) while building
// new value jump instruction.
cmpReg1 = MI.getOperand(1).getReg();
if (isSecondOpReg)
cmpOp2 = MI.getOperand(2).getReg();
cmpOp2 = MI.getOperand(2).getImm();
if (foundCompare && foundJump) {
// If "common" checks fail, bail out on this BB.
if (!commonChecksToProhibitNewValueJump(afterRA, MII))
bool foundFeeder = false;
MachineBasicBlock::iterator feederPos = MII;
if (MI.getOperand(0).isReg() && MI.getOperand(0).isDef() &&
(MI.getOperand(0).getReg() == cmpReg1 ||
(isSecondOpReg &&
MI.getOperand(0).getReg() == (unsigned)cmpOp2))) {
Register feederReg = MI.getOperand(0).getReg();
// First try to see if we can get the feeder from the first operand
// of the compare. If we can not, and if secondOpReg is true
// (second operand of the compare is also register), try that one.
// TODO: Try to come up with some heuristic to figure out which
// feeder would benefit.
if (feederReg == cmpReg1) {
if (!canBeFeederToNewValueJump(QII, QRI, MII, jmpPos, cmpPos, MF)) {
if (!isSecondOpReg)
} else
foundFeeder = true;
if (!foundFeeder && isSecondOpReg && feederReg == (unsigned)cmpOp2)
if (!canBeFeederToNewValueJump(QII, QRI, MII, jmpPos, cmpPos, MF))
if (isSecondOpReg) {
// In case of CMPLT, or CMPLTU, or EQ with the second register
// to newify, swap the operands.
unsigned COp = cmpInstr->getOpcode();
if ((COp == Hexagon::C2_cmpeq || COp == Hexagon::C4_cmpneq) &&
(feederReg == (unsigned)cmpOp2)) {
unsigned tmp = cmpReg1;
cmpReg1 = cmpOp2;
cmpOp2 = tmp;
// Now we have swapped the operands, all we need to check is,
// if the second operand (after swap) is the feeder.
// And if it is, make a note.
if (feederReg == (unsigned)cmpOp2)
isSecondOpNewified = true;
// Now that we are moving feeder close the jump,
// make sure we are respecting the kill values of
// the operands of the feeder.
auto TransferKills = [jmpPos,cmpPos] (MachineInstr &MI) {
for (MachineOperand &MO : MI.operands()) {
if (!MO.isReg() || !MO.isUse())
Register UseR = MO.getReg();
for (auto I = std::next(MI.getIterator()); I != jmpPos; ++I) {
if (I == cmpPos)
for (MachineOperand &Op : I->operands()) {
if (!Op.isReg() || !Op.isUse() || !Op.isKill())
if (Op.getReg() != UseR)
// We found that there is kill of a use register
// Set up a kill flag on the register
bool MO1IsKill = cmpPos->killsRegister(cmpReg1, QRI);
bool MO2IsKill = isSecondOpReg && cmpPos->killsRegister(cmpOp2, QRI);
MBB->splice(jmpPos, MI.getParent(), MI);
MBB->splice(jmpPos, MI.getParent(), cmpInstr);
DebugLoc dl = MI.getDebugLoc();
MachineInstr *NewMI;
assert((isNewValueJumpCandidate(*cmpInstr)) &&
"This compare is not a New Value Jump candidate.");
unsigned opc = getNewValueJumpOpcode(cmpInstr, cmpOp2,
jmpTarget, MBPI);
if (invertPredicate)
opc = QII->getInvertedPredicatedOpcode(opc);
if (isSecondOpReg)
NewMI = BuildMI(*MBB, jmpPos, dl, QII->get(opc))
.addReg(cmpReg1, getKillRegState(MO1IsKill))
.addReg(cmpOp2, getKillRegState(MO2IsKill))
NewMI = BuildMI(*MBB, jmpPos, dl, QII->get(opc))
.addReg(cmpReg1, getKillRegState(MO1IsKill))
assert(NewMI && "New Value Jump Instruction Not created!");
if (cmpInstr->getOperand(0).isReg() &&
if (cmpInstr->getOperand(1).isReg() &&
return true;
FunctionPass *llvm::createHexagonNewValueJump() {
return new HexagonNewValueJump();