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//===---- HexagonFixupHwLoops.cpp - Fixup HW loops too far from LOOPn. ----===//
// 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
// The loop start address in the LOOPn instruction is encoded as a distance
// from the LOOPn instruction itself. If the start address is too far from
// the LOOPn instruction, the instruction needs to use a constant extender.
// This pass will identify and convert such LOOPn instructions to a proper
// form.
#include "Hexagon.h"
#include "HexagonTargetMachine.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Pass.h"
using namespace llvm;
static cl::opt<unsigned> MaxLoopRange(
"hexagon-loop-range", cl::Hidden, cl::init(200),
cl::desc("Restrict range of loopN instructions (testing only)"));
namespace llvm {
FunctionPass *createHexagonFixupHwLoops();
void initializeHexagonFixupHwLoopsPass(PassRegistry&);
namespace {
struct HexagonFixupHwLoops : public MachineFunctionPass {
static char ID;
HexagonFixupHwLoops() : MachineFunctionPass(ID) {
bool runOnMachineFunction(MachineFunction &MF) override;
MachineFunctionProperties getRequiredProperties() const override {
return MachineFunctionProperties().set(
StringRef getPassName() const override {
return "Hexagon Hardware Loop Fixup";
void getAnalysisUsage(AnalysisUsage &AU) const override {
/// Check the offset between each loop instruction and
/// the loop basic block to determine if we can use the LOOP instruction
/// or if we need to set the LC/SA registers explicitly.
bool fixupLoopInstrs(MachineFunction &MF);
/// Replace loop instruction with the constant extended
/// version if the loop label is too far from the loop instruction.
void useExtLoopInstr(MachineFunction &MF,
MachineBasicBlock::iterator &MII);
char HexagonFixupHwLoops::ID = 0;
INITIALIZE_PASS(HexagonFixupHwLoops, "hwloopsfixup",
"Hexagon Hardware Loops Fixup", false, false)
FunctionPass *llvm::createHexagonFixupHwLoops() {
return new HexagonFixupHwLoops();
/// Returns true if the instruction is a hardware loop instruction.
static bool isHardwareLoop(const MachineInstr &MI) {
return MI.getOpcode() == Hexagon::J2_loop0r ||
MI.getOpcode() == Hexagon::J2_loop0i ||
MI.getOpcode() == Hexagon::J2_loop1r ||
MI.getOpcode() == Hexagon::J2_loop1i;
bool HexagonFixupHwLoops::runOnMachineFunction(MachineFunction &MF) {
if (skipFunction(MF.getFunction()))
return false;
return fixupLoopInstrs(MF);
/// For Hexagon, if the loop label is to far from the
/// loop instruction then we need to set the LC0 and SA0 registers
/// explicitly instead of using LOOP(start,count). This function
/// checks the distance, and generates register assignments if needed.
/// This function makes two passes over the basic blocks. The first
/// pass computes the offset of the basic block from the start.
/// The second pass checks all the loop instructions.
bool HexagonFixupHwLoops::fixupLoopInstrs(MachineFunction &MF) {
// Offset of the current instruction from the start.
unsigned InstOffset = 0;
// Map for each basic block to it's first instruction.
DenseMap<const MachineBasicBlock *, unsigned> BlockToInstOffset;
const HexagonInstrInfo *HII =
static_cast<const HexagonInstrInfo *>(MF.getSubtarget().getInstrInfo());
// First pass - compute the offset of each basic block.
for (const MachineBasicBlock &MBB : MF) {
if (MBB.getAlignment() != Align(1)) {
// Although we don't know the exact layout of the final code, we need
// to account for alignment padding somehow. This heuristic pads each
// aligned basic block according to the alignment value.
InstOffset = alignTo(InstOffset, MBB.getAlignment());
BlockToInstOffset[&MBB] = InstOffset;
for (const MachineInstr &MI : MBB)
InstOffset += HII->getSize(MI);
// Second pass - check each loop instruction to see if it needs to be
// converted.
bool Changed = false;
for (MachineBasicBlock &MBB : MF) {
InstOffset = BlockToInstOffset[&MBB];
// Loop over all the instructions.
MachineBasicBlock::iterator MII = MBB.begin();
MachineBasicBlock::iterator MIE = MBB.end();
while (MII != MIE) {
unsigned InstSize = HII->getSize(*MII);
if (MII->isMetaInstruction()) {
if (isHardwareLoop(*MII)) {
assert(MII->getOperand(0).isMBB() &&
"Expect a basic block as loop operand");
MachineBasicBlock *TargetBB = MII->getOperand(0).getMBB();
unsigned Diff = AbsoluteDifference(InstOffset,
if (Diff > MaxLoopRange) {
useExtLoopInstr(MF, MII);
MII = MBB.erase(MII);
Changed = true;
} else {
} else {
InstOffset += InstSize;
return Changed;
/// Replace loop instructions with the constant extended version.
void HexagonFixupHwLoops::useExtLoopInstr(MachineFunction &MF,
MachineBasicBlock::iterator &MII) {
const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo();
MachineBasicBlock *MBB = MII->getParent();
DebugLoc DL = MII->getDebugLoc();
MachineInstrBuilder MIB;
unsigned newOp;
switch (MII->getOpcode()) {
case Hexagon::J2_loop0r:
newOp = Hexagon::J2_loop0rext;
case Hexagon::J2_loop0i:
newOp = Hexagon::J2_loop0iext;
case Hexagon::J2_loop1r:
newOp = Hexagon::J2_loop1rext;
case Hexagon::J2_loop1i:
newOp = Hexagon::J2_loop1iext;
llvm_unreachable("Invalid Hardware Loop Instruction.");
MIB = BuildMI(*MBB, MII, DL, TII->get(newOp));
for (unsigned i = 0; i < MII->getNumOperands(); ++i)