//===-- HexagonHardwareLoops.cpp - Identify and generate hardware loops ---===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass identifies loops where we can generate the Hexagon hardware
// loop instruction. The hardware loop can perform loop branches with a
// zero-cycle overhead.
//
// The pattern that defines the induction variable can changed depending on
// prior optimizations. For example, the IndVarSimplify phase run by 'opt'
// normalizes induction variables, and the Loop Strength Reduction pass
// run by 'llc' may also make changes to the induction variable.
// The pattern detected by this phase is due to running Strength Reduction.
//
// Criteria for hardware loops:
// - Countable loops (w/ ind. var for a trip count)
// - Assumes loops are normalized by IndVarSimplify
// - Try inner-most loops first
// - No nested hardware loops.
// - No function calls in loops.
//
//===----------------------------------------------------------------------===//
#include "llvm/ADT/SmallSet.h"
#include "Hexagon.h"
#include "HexagonSubtarget.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/PassSupport.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
#include <algorithm>
#include <vector>
using namespace llvm;
#define DEBUG_TYPE "hwloops"
#ifndef NDEBUG
static cl::opt<int> HWLoopLimit("max-hwloop", cl::Hidden, cl::init(-1));
#endif
STATISTIC(NumHWLoops, "Number of loops converted to hardware loops");
namespace llvm {
void initializeHexagonHardwareLoopsPass(PassRegistry&);
}
namespace {
class CountValue;
struct HexagonHardwareLoops : public MachineFunctionPass {
MachineLoopInfo *MLI;
MachineRegisterInfo *MRI;
MachineDominatorTree *MDT;
const HexagonInstrInfo *TII;
#ifndef NDEBUG
static int Counter;
#endif
public:
static char ID;
HexagonHardwareLoops() : MachineFunctionPass(ID) {
initializeHexagonHardwareLoopsPass(*PassRegistry::getPassRegistry());
}
bool runOnMachineFunction(MachineFunction &MF) override;
const char *getPassName() const override { return "Hexagon Hardware Loops"; }
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<MachineDominatorTree>();
AU.addRequired<MachineLoopInfo>();
MachineFunctionPass::getAnalysisUsage(AU);
}
private:
/// Kinds of comparisons in the compare instructions.
struct Comparison {
enum Kind {
EQ = 0x01,
NE = 0x02,
L = 0x04, // Less-than property.
G = 0x08, // Greater-than property.
U = 0x40, // Unsigned property.
LTs = L,
LEs = L | EQ,
GTs = G,
GEs = G | EQ,
LTu = L | U,
LEu = L | EQ | U,
GTu = G | U,
GEu = G | EQ | U
};
static Kind getSwappedComparison(Kind Cmp) {
assert ((!((Cmp & L) && (Cmp & G))) && "Malformed comparison operator");
if ((Cmp & L) || (Cmp & G))
return (Kind)(Cmp ^ (L|G));
return Cmp;
}
};
/// \brief Find the register that contains the loop controlling
/// induction variable.
/// If successful, it will return true and set the \p Reg, \p IVBump
/// and \p IVOp arguments. Otherwise it will return false.
/// The returned induction register is the register R that follows the
/// following induction pattern:
/// loop:
/// R = phi ..., [ R.next, LatchBlock ]
/// R.next = R + #bump
/// if (R.next < #N) goto loop
/// IVBump is the immediate value added to R, and IVOp is the instruction
/// "R.next = R + #bump".
bool findInductionRegister(MachineLoop *L, unsigned &Reg,
int64_t &IVBump, MachineInstr *&IVOp) const;
/// \brief Analyze the statements in a loop to determine if the loop
/// has a computable trip count and, if so, return a value that represents
/// the trip count expression.
CountValue *getLoopTripCount(MachineLoop *L,
SmallVectorImpl<MachineInstr *> &OldInsts);
/// \brief Return the expression that represents the number of times
/// a loop iterates. The function takes the operands that represent the
/// loop start value, loop end value, and induction value. Based upon
/// these operands, the function attempts to compute the trip count.
/// If the trip count is not directly available (as an immediate value,
/// or a register), the function will attempt to insert computation of it
/// to the loop's preheader.
CountValue *computeCount(MachineLoop *Loop,
const MachineOperand *Start,
const MachineOperand *End,
unsigned IVReg,
int64_t IVBump,
Comparison::Kind Cmp) const;
/// \brief Return true if the instruction is not valid within a hardware
/// loop.
bool isInvalidLoopOperation(const MachineInstr *MI) const;
/// \brief Return true if the loop contains an instruction that inhibits
/// using the hardware loop.
bool containsInvalidInstruction(MachineLoop *L) const;
/// \brief Given a loop, check if we can convert it to a hardware loop.
/// If so, then perform the conversion and return true.
bool convertToHardwareLoop(MachineLoop *L);
/// \brief Return true if the instruction is now dead.
bool isDead(const MachineInstr *MI,
SmallVectorImpl<MachineInstr *> &DeadPhis) const;
/// \brief Remove the instruction if it is now dead.
void removeIfDead(MachineInstr *MI);
/// \brief Make sure that the "bump" instruction executes before the
/// compare. We need that for the IV fixup, so that the compare
/// instruction would not use a bumped value that has not yet been
/// defined. If the instructions are out of order, try to reorder them.
bool orderBumpCompare(MachineInstr *BumpI, MachineInstr *CmpI);
/// \brief Get the instruction that loads an immediate value into \p R,
/// or 0 if such an instruction does not exist.
MachineInstr *defWithImmediate(unsigned R);
/// \brief Get the immediate value referenced to by \p MO, either for
/// immediate operands, or for register operands, where the register
/// was defined with an immediate value.
int64_t getImmediate(MachineOperand &MO);
/// \brief Reset the given machine operand to now refer to a new immediate
/// value. Assumes that the operand was already referencing an immediate
/// value, either directly, or via a register.
void setImmediate(MachineOperand &MO, int64_t Val);
/// \brief Fix the data flow of the induction varible.
/// The desired flow is: phi ---> bump -+-> comparison-in-latch.
/// |
/// +-> back to phi
/// where "bump" is the increment of the induction variable:
/// iv = iv + #const.
/// Due to some prior code transformations, the actual flow may look
/// like this:
/// phi -+-> bump ---> back to phi
/// |
/// +-> comparison-in-latch (against upper_bound-bump),
/// i.e. the comparison that controls the loop execution may be using
/// the value of the induction variable from before the increment.
///
/// Return true if the loop's flow is the desired one (i.e. it's
/// either been fixed, or no fixing was necessary).
/// Otherwise, return false. This can happen if the induction variable
/// couldn't be identified, or if the value in the latch's comparison
/// cannot be adjusted to reflect the post-bump value.
bool fixupInductionVariable(MachineLoop *L);
/// \brief Given a loop, if it does not have a preheader, create one.
/// Return the block that is the preheader.
MachineBasicBlock *createPreheaderForLoop(MachineLoop *L);
};
char HexagonHardwareLoops::ID = 0;
#ifndef NDEBUG
int HexagonHardwareLoops::Counter = 0;
#endif
/// \brief Abstraction for a trip count of a loop. A smaller version
/// of the MachineOperand class without the concerns of changing the
/// operand representation.
class CountValue {
public:
enum CountValueType {
CV_Register,
CV_Immediate
};
private:
CountValueType Kind;
union Values {
struct {
unsigned Reg;
unsigned Sub;
} R;
unsigned ImmVal;
} Contents;
public:
explicit CountValue(CountValueType t, unsigned v, unsigned u = 0) {
Kind = t;
if (Kind == CV_Register) {
Contents.R.Reg = v;
Contents.R.Sub = u;
} else {
Contents.ImmVal = v;
}
}
bool isReg() const { return Kind == CV_Register; }
bool isImm() const { return Kind == CV_Immediate; }
unsigned getReg() const {
assert(isReg() && "Wrong CountValue accessor");
return Contents.R.Reg;
}
unsigned getSubReg() const {
assert(isReg() && "Wrong CountValue accessor");
return Contents.R.Sub;
}
unsigned getImm() const {
assert(isImm() && "Wrong CountValue accessor");
return Contents.ImmVal;
}
void print(raw_ostream &OS, const TargetRegisterInfo *TRI = nullptr) const {
if (isReg()) { OS << PrintReg(Contents.R.Reg, TRI, Contents.R.Sub); }
if (isImm()) { OS << Contents.ImmVal; }
}
};
} // end anonymous namespace
INITIALIZE_PASS_BEGIN(HexagonHardwareLoops, "hwloops",
"Hexagon Hardware Loops", false, false)
INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
INITIALIZE_PASS_END(HexagonHardwareLoops, "hwloops",
"Hexagon Hardware Loops", false, false)
/// \brief 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;
}
FunctionPass *llvm::createHexagonHardwareLoops() {
return new HexagonHardwareLoops();
}
bool HexagonHardwareLoops::runOnMachineFunction(MachineFunction &MF) {
DEBUG(dbgs() << "********* Hexagon Hardware Loops *********\n");
bool Changed = false;
MLI = &getAnalysis<MachineLoopInfo>();
MRI = &MF.getRegInfo();
MDT = &getAnalysis<MachineDominatorTree>();
TII = MF.getSubtarget<HexagonSubtarget>().getInstrInfo();
for (MachineLoopInfo::iterator I = MLI->begin(), E = MLI->end();
I != E; ++I) {
MachineLoop *L = *I;
if (!L->getParentLoop())
Changed |= convertToHardwareLoop(L);
}
return Changed;
}
bool HexagonHardwareLoops::findInductionRegister(MachineLoop *L,
unsigned &Reg,
int64_t &IVBump,
MachineInstr *&IVOp
) const {
MachineBasicBlock *Header = L->getHeader();
MachineBasicBlock *Preheader = L->getLoopPreheader();
MachineBasicBlock *Latch = L->getLoopLatch();
if (!Header || !Preheader || !Latch)
return false;
// This pair represents an induction register together with an immediate
// value that will be added to it in each loop iteration.
typedef std::pair<unsigned,int64_t> RegisterBump;
// Mapping: R.next -> (R, bump), where R, R.next and bump are derived
// from an induction operation
// R.next = R + bump
// where bump is an immediate value.
typedef std::map<unsigned,RegisterBump> InductionMap;
InductionMap IndMap;
typedef MachineBasicBlock::instr_iterator instr_iterator;
for (instr_iterator I = Header->instr_begin(), E = Header->instr_end();
I != E && I->isPHI(); ++I) {
MachineInstr *Phi = &*I;
// Have a PHI instruction. Get the operand that corresponds to the
// latch block, and see if is a result of an addition of form "reg+imm",
// where the "reg" is defined by the PHI node we are looking at.
for (unsigned i = 1, n = Phi->getNumOperands(); i < n; i += 2) {
if (Phi->getOperand(i+1).getMBB() != Latch)
continue;
unsigned PhiOpReg = Phi->getOperand(i).getReg();
MachineInstr *DI = MRI->getVRegDef(PhiOpReg);
unsigned UpdOpc = DI->getOpcode();
bool isAdd = (UpdOpc == Hexagon::A2_addi);
if (isAdd) {
// If the register operand to the add is the PHI we're
// looking at, this meets the induction pattern.
unsigned IndReg = DI->getOperand(1).getReg();
if (MRI->getVRegDef(IndReg) == Phi) {
unsigned UpdReg = DI->getOperand(0).getReg();
int64_t V = DI->getOperand(2).getImm();
IndMap.insert(std::make_pair(UpdReg, std::make_pair(IndReg, V)));
}
}
} // for (i)
} // for (instr)
SmallVector<MachineOperand,2> Cond;
MachineBasicBlock *TB = nullptr, *FB = nullptr;
bool NotAnalyzed = TII->AnalyzeBranch(*Latch, TB, FB, Cond, false);
if (NotAnalyzed)
return false;
unsigned CSz = Cond.size();
assert (CSz == 1 || CSz == 2);
unsigned PredR = Cond[CSz-1].getReg();
MachineInstr *PredI = MRI->getVRegDef(PredR);
if (!PredI->isCompare())
return false;
unsigned CmpReg1 = 0, CmpReg2 = 0;
int CmpImm = 0, CmpMask = 0;
bool CmpAnalyzed = TII->analyzeCompare(PredI, CmpReg1, CmpReg2,
CmpMask, CmpImm);
// Fail if the compare was not analyzed, or it's not comparing a register
// with an immediate value. Not checking the mask here, since we handle
// the individual compare opcodes (including CMPb) later on.
if (!CmpAnalyzed)
return false;
// Exactly one of the input registers to the comparison should be among
// the induction registers.
InductionMap::iterator IndMapEnd = IndMap.end();
InductionMap::iterator F = IndMapEnd;
if (CmpReg1 != 0) {
InductionMap::iterator F1 = IndMap.find(CmpReg1);
if (F1 != IndMapEnd)
F = F1;
}
if (CmpReg2 != 0) {
InductionMap::iterator F2 = IndMap.find(CmpReg2);
if (F2 != IndMapEnd) {
if (F != IndMapEnd)
return false;
F = F2;
}
}
if (F == IndMapEnd)
return false;
Reg = F->second.first;
IVBump = F->second.second;
IVOp = MRI->getVRegDef(F->first);
return true;
}
/// \brief Analyze the statements in a loop to determine if the loop has
/// a computable trip count and, if so, return a value that represents
/// the trip count expression.
///
/// This function iterates over the phi nodes in the loop to check for
/// induction variable patterns that are used in the calculation for
/// the number of time the loop is executed.
CountValue *HexagonHardwareLoops::getLoopTripCount(MachineLoop *L,
SmallVectorImpl<MachineInstr *> &OldInsts) {
MachineBasicBlock *TopMBB = L->getTopBlock();
MachineBasicBlock::pred_iterator PI = TopMBB->pred_begin();
assert(PI != TopMBB->pred_end() &&
"Loop must have more than one incoming edge!");
MachineBasicBlock *Backedge = *PI++;
if (PI == TopMBB->pred_end()) // dead loop?
return nullptr;
MachineBasicBlock *Incoming = *PI++;
if (PI != TopMBB->pred_end()) // multiple backedges?
return nullptr;
// Make sure there is one incoming and one backedge and determine which
// is which.
if (L->contains(Incoming)) {
if (L->contains(Backedge))
return nullptr;
std::swap(Incoming, Backedge);
} else if (!L->contains(Backedge))
return nullptr;
// Look for the cmp instruction to determine if we can get a useful trip
// count. The trip count can be either a register or an immediate. The
// location of the value depends upon the type (reg or imm).
MachineBasicBlock *Latch = L->getLoopLatch();
if (!Latch)
return nullptr;
unsigned IVReg = 0;
int64_t IVBump = 0;
MachineInstr *IVOp;
bool FoundIV = findInductionRegister(L, IVReg, IVBump, IVOp);
if (!FoundIV)
return nullptr;
MachineBasicBlock *Preheader = L->getLoopPreheader();
MachineOperand *InitialValue = nullptr;
MachineInstr *IV_Phi = MRI->getVRegDef(IVReg);
for (unsigned i = 1, n = IV_Phi->getNumOperands(); i < n; i += 2) {
MachineBasicBlock *MBB = IV_Phi->getOperand(i+1).getMBB();
if (MBB == Preheader)
InitialValue = &IV_Phi->getOperand(i);
else if (MBB == Latch)
IVReg = IV_Phi->getOperand(i).getReg(); // Want IV reg after bump.
}
if (!InitialValue)
return nullptr;
SmallVector<MachineOperand,2> Cond;
MachineBasicBlock *TB = nullptr, *FB = nullptr;
bool NotAnalyzed = TII->AnalyzeBranch(*Latch, TB, FB, Cond, false);
if (NotAnalyzed)
return nullptr;
MachineBasicBlock *Header = L->getHeader();
// TB must be non-null. If FB is also non-null, one of them must be
// the header. Otherwise, branch to TB could be exiting the loop, and
// the fall through can go to the header.
assert (TB && "Latch block without a branch?");
assert ((!FB || TB == Header || FB == Header) && "Branches not to header?");
if (!TB || (FB && TB != Header && FB != Header))
return nullptr;
// Branches of form "if (!P) ..." cause HexagonInstrInfo::AnalyzeBranch
// to put imm(0), followed by P in the vector Cond.
// If TB is not the header, it means that the "not-taken" path must lead
// to the header.
bool Negated = (Cond.size() > 1) ^ (TB != Header);
unsigned PredReg = Cond[Cond.size()-1].getReg();
MachineInstr *CondI = MRI->getVRegDef(PredReg);
unsigned CondOpc = CondI->getOpcode();
unsigned CmpReg1 = 0, CmpReg2 = 0;
int Mask = 0, ImmValue = 0;
bool AnalyzedCmp = TII->analyzeCompare(CondI, CmpReg1, CmpReg2,
Mask, ImmValue);
if (!AnalyzedCmp)
return nullptr;
// The comparison operator type determines how we compute the loop
// trip count.
OldInsts.push_back(CondI);
OldInsts.push_back(IVOp);
// Sadly, the following code gets information based on the position
// of the operands in the compare instruction. This has to be done
// this way, because the comparisons check for a specific relationship
// between the operands (e.g. is-less-than), rather than to find out
// what relationship the operands are in (as on PPC).
Comparison::Kind Cmp;
bool isSwapped = false;
const MachineOperand &Op1 = CondI->getOperand(1);
const MachineOperand &Op2 = CondI->getOperand(2);
const MachineOperand *EndValue = nullptr;
if (Op1.isReg()) {
if (Op2.isImm() || Op1.getReg() == IVReg)
EndValue = &Op2;
else {
EndValue = &Op1;
isSwapped = true;
}
}
if (!EndValue)
return nullptr;
switch (CondOpc) {
case Hexagon::C2_cmpeqi:
case Hexagon::C2_cmpeq:
Cmp = !Negated ? Comparison::EQ : Comparison::NE;
break;
case Hexagon::C2_cmpgtui:
case Hexagon::C2_cmpgtu:
Cmp = !Negated ? Comparison::GTu : Comparison::LEu;
break;
case Hexagon::C2_cmpgti:
case Hexagon::C2_cmpgt:
Cmp = !Negated ? Comparison::GTs : Comparison::LEs;
break;
// Very limited support for byte/halfword compares.
case Hexagon::A4_cmpbeqi:
case Hexagon::A4_cmpheqi: {
if (IVBump != 1)
return nullptr;
int64_t InitV, EndV;
// Since the comparisons are "ri", the EndValue should be an
// immediate. Check it just in case.
assert(EndValue->isImm() && "Unrecognized latch comparison");
EndV = EndValue->getImm();
// Allow InitialValue to be a register defined with an immediate.
if (InitialValue->isReg()) {
if (!defWithImmediate(InitialValue->getReg()))
return nullptr;
InitV = getImmediate(*InitialValue);
} else {
assert(InitialValue->isImm());
InitV = InitialValue->getImm();
}
if (InitV >= EndV)
return nullptr;
if (CondOpc == Hexagon::A4_cmpbeqi) {
if (!isInt<8>(InitV) || !isInt<8>(EndV))
return nullptr;
} else { // Hexagon::CMPhEQri_V4
if (!isInt<16>(InitV) || !isInt<16>(EndV))
return nullptr;
}
Cmp = !Negated ? Comparison::EQ : Comparison::NE;
break;
}
default:
return nullptr;
}
if (isSwapped)
Cmp = Comparison::getSwappedComparison(Cmp);
if (InitialValue->isReg()) {
unsigned R = InitialValue->getReg();
MachineBasicBlock *DefBB = MRI->getVRegDef(R)->getParent();
if (!MDT->properlyDominates(DefBB, Header))
return nullptr;
OldInsts.push_back(MRI->getVRegDef(R));
}
if (EndValue->isReg()) {
unsigned R = EndValue->getReg();
MachineBasicBlock *DefBB = MRI->getVRegDef(R)->getParent();
if (!MDT->properlyDominates(DefBB, Header))
return nullptr;
}
return computeCount(L, InitialValue, EndValue, IVReg, IVBump, Cmp);
}
/// \brief Helper function that returns the expression that represents the
/// number of times a loop iterates. The function takes the operands that
/// represent the loop start value, loop end value, and induction value.
/// Based upon these operands, the function attempts to compute the trip count.
CountValue *HexagonHardwareLoops::computeCount(MachineLoop *Loop,
const MachineOperand *Start,
const MachineOperand *End,
unsigned IVReg,
int64_t IVBump,
Comparison::Kind Cmp) const {
// Cannot handle comparison EQ, i.e. while (A == B).
if (Cmp == Comparison::EQ)
return nullptr;
// Check if either the start or end values are an assignment of an immediate.
// If so, use the immediate value rather than the register.
if (Start->isReg()) {
const MachineInstr *StartValInstr = MRI->getVRegDef(Start->getReg());
if (StartValInstr && StartValInstr->getOpcode() == Hexagon::A2_tfrsi)
Start = &StartValInstr->getOperand(1);
}
if (End->isReg()) {
const MachineInstr *EndValInstr = MRI->getVRegDef(End->getReg());
if (EndValInstr && EndValInstr->getOpcode() == Hexagon::A2_tfrsi)
End = &EndValInstr->getOperand(1);
}
assert (Start->isReg() || Start->isImm());
assert (End->isReg() || End->isImm());
bool CmpLess = Cmp & Comparison::L;
bool CmpGreater = Cmp & Comparison::G;
bool CmpHasEqual = Cmp & Comparison::EQ;
// Avoid certain wrap-arounds. This doesn't detect all wrap-arounds.
// If loop executes while iv is "less" with the iv value going down, then
// the iv must wrap.
if (CmpLess && IVBump < 0)
return nullptr;
// If loop executes while iv is "greater" with the iv value going up, then
// the iv must wrap.
if (CmpGreater && IVBump > 0)
return nullptr;
if (Start->isImm() && End->isImm()) {
// Both, start and end are immediates.
int64_t StartV = Start->getImm();
int64_t EndV = End->getImm();
int64_t Dist = EndV - StartV;
if (Dist == 0)
return nullptr;
bool Exact = (Dist % IVBump) == 0;
if (Cmp == Comparison::NE) {
if (!Exact)
return nullptr;
if ((Dist < 0) ^ (IVBump < 0))
return nullptr;
}
// For comparisons that include the final value (i.e. include equality
// with the final value), we need to increase the distance by 1.
if (CmpHasEqual)
Dist = Dist > 0 ? Dist+1 : Dist-1;
// assert (CmpLess => Dist > 0);
assert ((!CmpLess || Dist > 0) && "Loop should never iterate!");
// assert (CmpGreater => Dist < 0);
assert ((!CmpGreater || Dist < 0) && "Loop should never iterate!");
// "Normalized" distance, i.e. with the bump set to +-1.
int64_t Dist1 = (IVBump > 0) ? (Dist + (IVBump-1)) / IVBump
: (-Dist + (-IVBump-1)) / (-IVBump);
assert (Dist1 > 0 && "Fishy thing. Both operands have the same sign.");
uint64_t Count = Dist1;
if (Count > 0xFFFFFFFFULL)
return nullptr;
return new CountValue(CountValue::CV_Immediate, Count);
}
// A general case: Start and End are some values, but the actual
// iteration count may not be available. If it is not, insert
// a computation of it into the preheader.
// If the induction variable bump is not a power of 2, quit.
// Othwerise we'd need a general integer division.
if (!isPowerOf2_64(std::abs(IVBump)))
return nullptr;
MachineBasicBlock *PH = Loop->getLoopPreheader();
assert (PH && "Should have a preheader by now");
MachineBasicBlock::iterator InsertPos = PH->getFirstTerminator();
DebugLoc DL = (InsertPos != PH->end()) ? InsertPos->getDebugLoc()
: DebugLoc();
// If Start is an immediate and End is a register, the trip count
// will be "reg - imm". Hexagon's "subtract immediate" instruction
// is actually "reg + -imm".
// If the loop IV is going downwards, i.e. if the bump is negative,
// then the iteration count (computed as End-Start) will need to be
// negated. To avoid the negation, just swap Start and End.
if (IVBump < 0) {
std::swap(Start, End);
IVBump = -IVBump;
}
// Cmp may now have a wrong direction, e.g. LEs may now be GEs.
// Signedness, and "including equality" are preserved.
bool RegToImm = Start->isReg() && End->isImm(); // for (reg..imm)
bool RegToReg = Start->isReg() && End->isReg(); // for (reg..reg)
int64_t StartV = 0, EndV = 0;
if (Start->isImm())
StartV = Start->getImm();
if (End->isImm())
EndV = End->getImm();
int64_t AdjV = 0;
// To compute the iteration count, we would need this computation:
// Count = (End - Start + (IVBump-1)) / IVBump
// or, when CmpHasEqual:
// Count = (End - Start + (IVBump-1)+1) / IVBump
// The "IVBump-1" part is the adjustment (AdjV). We can avoid
// generating an instruction specifically to add it if we can adjust
// the immediate values for Start or End.
if (CmpHasEqual) {
// Need to add 1 to the total iteration count.
if (Start->isImm())
StartV--;
else if (End->isImm())
EndV++;
else
AdjV += 1;
}
if (Cmp != Comparison::NE) {
if (Start->isImm())
StartV -= (IVBump-1);
else if (End->isImm())
EndV += (IVBump-1);
else
AdjV += (IVBump-1);
}
unsigned R = 0, SR = 0;
if (Start->isReg()) {
R = Start->getReg();
SR = Start->getSubReg();
} else {
R = End->getReg();
SR = End->getSubReg();
}
const TargetRegisterClass *RC = MRI->getRegClass(R);
// Hardware loops cannot handle 64-bit registers. If it's a double
// register, it has to have a subregister.
if (!SR && RC == &Hexagon::DoubleRegsRegClass)
return nullptr;
const TargetRegisterClass *IntRC = &Hexagon::IntRegsRegClass;
// Compute DistR (register with the distance between Start and End).
unsigned DistR, DistSR;
// Avoid special case, where the start value is an imm(0).
if (Start->isImm() && StartV == 0) {
DistR = End->getReg();
DistSR = End->getSubReg();
} else {
const MCInstrDesc &SubD = RegToReg ? TII->get(Hexagon::A2_sub) :
(RegToImm ? TII->get(Hexagon::A2_subri) :
TII->get(Hexagon::A2_addi));
unsigned SubR = MRI->createVirtualRegister(IntRC);
MachineInstrBuilder SubIB =
BuildMI(*PH, InsertPos, DL, SubD, SubR);
if (RegToReg) {
SubIB.addReg(End->getReg(), 0, End->getSubReg())
.addReg(Start->getReg(), 0, Start->getSubReg());
} else if (RegToImm) {
SubIB.addImm(EndV)
.addReg(Start->getReg(), 0, Start->getSubReg());
} else { // ImmToReg
SubIB.addReg(End->getReg(), 0, End->getSubReg())
.addImm(-StartV);
}
DistR = SubR;
DistSR = 0;
}
// From DistR, compute AdjR (register with the adjusted distance).
unsigned AdjR, AdjSR;
if (AdjV == 0) {
AdjR = DistR;
AdjSR = DistSR;
} else {
// Generate CountR = ADD DistR, AdjVal
unsigned AddR = MRI->createVirtualRegister(IntRC);
MCInstrDesc const &AddD = TII->get(Hexagon::A2_addi);
BuildMI(*PH, InsertPos, DL, AddD, AddR)
.addReg(DistR, 0, DistSR)
.addImm(AdjV);
AdjR = AddR;
AdjSR = 0;
}
// From AdjR, compute CountR (register with the final count).
unsigned CountR, CountSR;
if (IVBump == 1) {
CountR = AdjR;
CountSR = AdjSR;
} else {
// The IV bump is a power of two. Log_2(IV bump) is the shift amount.
unsigned Shift = Log2_32(IVBump);
// Generate NormR = LSR DistR, Shift.
unsigned LsrR = MRI->createVirtualRegister(IntRC);
const MCInstrDesc &LsrD = TII->get(Hexagon::S2_lsr_i_r);
BuildMI(*PH, InsertPos, DL, LsrD, LsrR)
.addReg(AdjR, 0, AdjSR)
.addImm(Shift);
CountR = LsrR;
CountSR = 0;
}
return new CountValue(CountValue::CV_Register, CountR, CountSR);
}
/// \brief Return true if the operation is invalid within hardware loop.
bool HexagonHardwareLoops::isInvalidLoopOperation(
const MachineInstr *MI) const {
// call is not allowed because the callee may use a hardware loop
if (MI->getDesc().isCall())
return true;
// do not allow nested hardware loops
if (isHardwareLoop(MI))
return true;
// check if the instruction defines a hardware loop register
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg() || !MO.isDef())
continue;
unsigned R = MO.getReg();
if (R == Hexagon::LC0 || R == Hexagon::LC1 ||
R == Hexagon::SA0 || R == Hexagon::SA1)
return true;
}
return false;
}
/// \brief - Return true if the loop contains an instruction that inhibits
/// the use of the hardware loop function.
bool HexagonHardwareLoops::containsInvalidInstruction(MachineLoop *L) const {
const std::vector<MachineBasicBlock *> &Blocks = L->getBlocks();
for (unsigned i = 0, e = Blocks.size(); i != e; ++i) {
MachineBasicBlock *MBB = Blocks[i];
for (MachineBasicBlock::iterator
MII = MBB->begin(), E = MBB->end(); MII != E; ++MII) {
const MachineInstr *MI = &*MII;
if (isInvalidLoopOperation(MI))
return true;
}
}
return false;
}
/// \brief Returns true if the instruction is dead. This was essentially
/// copied from DeadMachineInstructionElim::isDead, but with special cases
/// for inline asm, physical registers and instructions with side effects
/// removed.
bool HexagonHardwareLoops::isDead(const MachineInstr *MI,
SmallVectorImpl<MachineInstr *> &DeadPhis) const {
// Examine each operand.
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg() || !MO.isDef())
continue;
unsigned Reg = MO.getReg();
if (MRI->use_nodbg_empty(Reg))
continue;
typedef MachineRegisterInfo::use_nodbg_iterator use_nodbg_iterator;
// This instruction has users, but if the only user is the phi node for the
// parent block, and the only use of that phi node is this instruction, then
// this instruction is dead: both it (and the phi node) can be removed.
use_nodbg_iterator I = MRI->use_nodbg_begin(Reg);
use_nodbg_iterator End = MRI->use_nodbg_end();
if (std::next(I) != End || !I->getParent()->isPHI())
return false;
MachineInstr *OnePhi = I->getParent();
for (unsigned j = 0, f = OnePhi->getNumOperands(); j != f; ++j) {
const MachineOperand &OPO = OnePhi->getOperand(j);
if (!OPO.isReg() || !OPO.isDef())
continue;
unsigned OPReg = OPO.getReg();
use_nodbg_iterator nextJ;
for (use_nodbg_iterator J = MRI->use_nodbg_begin(OPReg);
J != End; J = nextJ) {
nextJ = std::next(J);
MachineOperand &Use = *J;
MachineInstr *UseMI = Use.getParent();
// If the phi node has a user that is not MI, bail...
if (MI != UseMI)
return false;
}
}
DeadPhis.push_back(OnePhi);
}
// If there are no defs with uses, the instruction is dead.
return true;
}
void HexagonHardwareLoops::removeIfDead(MachineInstr *MI) {
// This procedure was essentially copied from DeadMachineInstructionElim.
SmallVector<MachineInstr*, 1> DeadPhis;
if (isDead(MI, DeadPhis)) {
DEBUG(dbgs() << "HW looping will remove: " << *MI);
// It is possible that some DBG_VALUE instructions refer to this
// instruction. Examine each def operand for such references;
// if found, mark the DBG_VALUE as undef (but don't delete it).
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg() || !MO.isDef())
continue;
unsigned Reg = MO.getReg();
MachineRegisterInfo::use_iterator nextI;
for (MachineRegisterInfo::use_iterator I = MRI->use_begin(Reg),
E = MRI->use_end(); I != E; I = nextI) {
nextI = std::next(I); // I is invalidated by the setReg
MachineOperand &Use = *I;
MachineInstr *UseMI = I->getParent();
if (UseMI == MI)
continue;
if (Use.isDebug())
UseMI->getOperand(0).setReg(0U);
// This may also be a "instr -> phi -> instr" case which can
// be removed too.
}
}
MI->eraseFromParent();
for (unsigned i = 0; i < DeadPhis.size(); ++i)
DeadPhis[i]->eraseFromParent();
}
}
/// \brief Check if the loop is a candidate for converting to a hardware
/// loop. If so, then perform the transformation.
///
/// This function works on innermost loops first. A loop can be converted
/// if it is a counting loop; either a register value or an immediate.
///
/// The code makes several assumptions about the representation of the loop
/// in llvm.
bool HexagonHardwareLoops::convertToHardwareLoop(MachineLoop *L) {
// This is just for sanity.
assert(L->getHeader() && "Loop without a header?");
bool Changed = false;
// Process nested loops first.
for (MachineLoop::iterator I = L->begin(), E = L->end(); I != E; ++I)
Changed |= convertToHardwareLoop(*I);
// If a nested loop has been converted, then we can't convert this loop.
if (Changed)
return Changed;
#ifndef NDEBUG
// Stop trying after reaching the limit (if any).
int Limit = HWLoopLimit;
if (Limit >= 0) {
if (Counter >= HWLoopLimit)
return false;
Counter++;
}
#endif
// Does the loop contain any invalid instructions?
if (containsInvalidInstruction(L))
return false;
// Is the induction variable bump feeding the latch condition?
if (!fixupInductionVariable(L))
return false;
MachineBasicBlock *LastMBB = L->getExitingBlock();
// Don't generate hw loop if the loop has more than one exit.
if (!LastMBB)
return false;
MachineBasicBlock::iterator LastI = LastMBB->getFirstTerminator();
if (LastI == LastMBB->end())
return false;
// Ensure the loop has a preheader: the loop instruction will be
// placed there.
bool NewPreheader = false;
MachineBasicBlock *Preheader = L->getLoopPreheader();
if (!Preheader) {
Preheader = createPreheaderForLoop(L);
if (!Preheader)
return false;
NewPreheader = true;
}
MachineBasicBlock::iterator InsertPos = Preheader->getFirstTerminator();
SmallVector<MachineInstr*, 2> OldInsts;
// Are we able to determine the trip count for the loop?
CountValue *TripCount = getLoopTripCount(L, OldInsts);
if (!TripCount)
return false;
// Is the trip count available in the preheader?
if (TripCount->isReg()) {
// There will be a use of the register inserted into the preheader,
// so make sure that the register is actually defined at that point.
MachineInstr *TCDef = MRI->getVRegDef(TripCount->getReg());
MachineBasicBlock *BBDef = TCDef->getParent();
if (!NewPreheader) {
if (!MDT->dominates(BBDef, Preheader))
return false;
} else {
// If we have just created a preheader, the dominator tree won't be
// aware of it. Check if the definition of the register dominates
// the header, but is not the header itself.
if (!MDT->properlyDominates(BBDef, L->getHeader()))
return false;
}
}
// Determine the loop start.
MachineBasicBlock *LoopStart = L->getTopBlock();
if (L->getLoopLatch() != LastMBB) {
// When the exit and latch are not the same, use the latch block as the
// start.
// The loop start address is used only after the 1st iteration, and the
// loop latch may contains instrs. that need to be executed after the
// first iteration.
LoopStart = L->getLoopLatch();
// Make sure the latch is a successor of the exit, otherwise it won't work.
if (!LastMBB->isSuccessor(LoopStart))
return false;
}
// Convert the loop to a hardware loop.
DEBUG(dbgs() << "Change to hardware loop at "; L->dump());
DebugLoc DL;
if (InsertPos != Preheader->end())
DL = InsertPos->getDebugLoc();
if (TripCount->isReg()) {
// Create a copy of the loop count register.
unsigned CountReg = MRI->createVirtualRegister(&Hexagon::IntRegsRegClass);
BuildMI(*Preheader, InsertPos, DL, TII->get(TargetOpcode::COPY), CountReg)
.addReg(TripCount->getReg(), 0, TripCount->getSubReg());
// Add the Loop instruction to the beginning of the loop.
BuildMI(*Preheader, InsertPos, DL, TII->get(Hexagon::J2_loop0r))
.addMBB(LoopStart)
.addReg(CountReg);
} else {
assert(TripCount->isImm() && "Expecting immediate value for trip count");
// Add the Loop immediate instruction to the beginning of the loop,
// if the immediate fits in the instructions. Otherwise, we need to
// create a new virtual register.
int64_t CountImm = TripCount->getImm();
if (!TII->isValidOffset(Hexagon::J2_loop0i, CountImm)) {
unsigned CountReg = MRI->createVirtualRegister(&Hexagon::IntRegsRegClass);
BuildMI(*Preheader, InsertPos, DL, TII->get(Hexagon::A2_tfrsi), CountReg)
.addImm(CountImm);
BuildMI(*Preheader, InsertPos, DL, TII->get(Hexagon::J2_loop0r))
.addMBB(LoopStart).addReg(CountReg);
} else
BuildMI(*Preheader, InsertPos, DL, TII->get(Hexagon::J2_loop0i))
.addMBB(LoopStart).addImm(CountImm);
}
// Make sure the loop start always has a reference in the CFG. We need
// to create a BlockAddress operand to get this mechanism to work both the
// MachineBasicBlock and BasicBlock objects need the flag set.
LoopStart->setHasAddressTaken();
// This line is needed to set the hasAddressTaken flag on the BasicBlock
// object.
BlockAddress::get(const_cast<BasicBlock *>(LoopStart->getBasicBlock()));
// Replace the loop branch with an endloop instruction.
DebugLoc LastIDL = LastI->getDebugLoc();
BuildMI(*LastMBB, LastI, LastIDL,
TII->get(Hexagon::ENDLOOP0)).addMBB(LoopStart);
// The loop ends with either:
// - a conditional branch followed by an unconditional branch, or
// - a conditional branch to the loop start.
if (LastI->getOpcode() == Hexagon::J2_jumpt ||
LastI->getOpcode() == Hexagon::J2_jumpf) {
// Delete one and change/add an uncond. branch to out of the loop.
MachineBasicBlock *BranchTarget = LastI->getOperand(1).getMBB();
LastI = LastMBB->erase(LastI);
if (!L->contains(BranchTarget)) {
if (LastI != LastMBB->end())
LastI = LastMBB->erase(LastI);
SmallVector<MachineOperand, 0> Cond;
TII->InsertBranch(*LastMBB, BranchTarget, nullptr, Cond, LastIDL);
}
} else {
// Conditional branch to loop start; just delete it.
LastMBB->erase(LastI);
}
delete TripCount;
// The induction operation and the comparison may now be
// unneeded. If these are unneeded, then remove them.
for (unsigned i = 0; i < OldInsts.size(); ++i)
removeIfDead(OldInsts[i]);
++NumHWLoops;
return true;
}
bool HexagonHardwareLoops::orderBumpCompare(MachineInstr *BumpI,
MachineInstr *CmpI) {
assert (BumpI != CmpI && "Bump and compare in the same instruction?");
MachineBasicBlock *BB = BumpI->getParent();
if (CmpI->getParent() != BB)
return false;
typedef MachineBasicBlock::instr_iterator instr_iterator;
// Check if things are in order to begin with.
for (instr_iterator I = BumpI, E = BB->instr_end(); I != E; ++I)
if (&*I == CmpI)
return true;
// Out of order.
unsigned PredR = CmpI->getOperand(0).getReg();
bool FoundBump = false;
instr_iterator CmpIt = CmpI, NextIt = std::next(CmpIt);
for (instr_iterator I = NextIt, E = BB->instr_end(); I != E; ++I) {
MachineInstr *In = &*I;
for (unsigned i = 0, n = In->getNumOperands(); i < n; ++i) {
MachineOperand &MO = In->getOperand(i);
if (MO.isReg() && MO.isUse()) {
if (MO.getReg() == PredR) // Found an intervening use of PredR.
return false;
}
}
if (In == BumpI) {
instr_iterator After = BumpI;
instr_iterator From = CmpI;
BB->splice(std::next(After), BB, From);
FoundBump = true;
break;
}
}
assert (FoundBump && "Cannot determine instruction order");
return FoundBump;
}
MachineInstr *HexagonHardwareLoops::defWithImmediate(unsigned R) {
MachineInstr *DI = MRI->getVRegDef(R);
unsigned DOpc = DI->getOpcode();
switch (DOpc) {
case Hexagon::A2_tfrsi:
case Hexagon::A2_tfrpi:
case Hexagon::CONST32_Int_Real:
case Hexagon::CONST64_Int_Real:
return DI;
}
return nullptr;
}
int64_t HexagonHardwareLoops::getImmediate(MachineOperand &MO) {
if (MO.isImm())
return MO.getImm();
assert(MO.isReg());
unsigned R = MO.getReg();
MachineInstr *DI = defWithImmediate(R);
assert(DI && "Need an immediate operand");
// All currently supported "define-with-immediate" instructions have the
// actual immediate value in the operand(1).
int64_t v = DI->getOperand(1).getImm();
return v;
}
void HexagonHardwareLoops::setImmediate(MachineOperand &MO, int64_t Val) {
if (MO.isImm()) {
MO.setImm(Val);
return;
}
assert(MO.isReg());
unsigned R = MO.getReg();
MachineInstr *DI = defWithImmediate(R);
if (MRI->hasOneNonDBGUse(R)) {
// If R has only one use, then just change its defining instruction to
// the new immediate value.
DI->getOperand(1).setImm(Val);
return;
}
const TargetRegisterClass *RC = MRI->getRegClass(R);
unsigned NewR = MRI->createVirtualRegister(RC);
MachineBasicBlock &B = *DI->getParent();
DebugLoc DL = DI->getDebugLoc();
BuildMI(B, DI, DL, TII->get(DI->getOpcode()), NewR)
.addImm(Val);
MO.setReg(NewR);
}
bool HexagonHardwareLoops::fixupInductionVariable(MachineLoop *L) {
MachineBasicBlock *Header = L->getHeader();
MachineBasicBlock *Preheader = L->getLoopPreheader();
MachineBasicBlock *Latch = L->getLoopLatch();
if (!Header || !Preheader || !Latch)
return false;
// These data structures follow the same concept as the corresponding
// ones in findInductionRegister (where some comments are).
typedef std::pair<unsigned,int64_t> RegisterBump;
typedef std::pair<unsigned,RegisterBump> RegisterInduction;
typedef std::set<RegisterInduction> RegisterInductionSet;
// Register candidates for induction variables, with their associated bumps.
RegisterInductionSet IndRegs;
// Look for induction patterns:
// vreg1 = PHI ..., [ latch, vreg2 ]
// vreg2 = ADD vreg1, imm
typedef MachineBasicBlock::instr_iterator instr_iterator;
for (instr_iterator I = Header->instr_begin(), E = Header->instr_end();
I != E && I->isPHI(); ++I) {
MachineInstr *Phi = &*I;
// Have a PHI instruction.
for (unsigned i = 1, n = Phi->getNumOperands(); i < n; i += 2) {
if (Phi->getOperand(i+1).getMBB() != Latch)
continue;
unsigned PhiReg = Phi->getOperand(i).getReg();
MachineInstr *DI = MRI->getVRegDef(PhiReg);
unsigned UpdOpc = DI->getOpcode();
bool isAdd = (UpdOpc == Hexagon::A2_addi);
if (isAdd) {
// If the register operand to the add/sub is the PHI we are looking
// at, this meets the induction pattern.
unsigned IndReg = DI->getOperand(1).getReg();
if (MRI->getVRegDef(IndReg) == Phi) {
unsigned UpdReg = DI->getOperand(0).getReg();
int64_t V = DI->getOperand(2).getImm();
IndRegs.insert(std::make_pair(UpdReg, std::make_pair(IndReg, V)));
}
}
} // for (i)
} // for (instr)
if (IndRegs.empty())
return false;
MachineBasicBlock *TB = nullptr, *FB = nullptr;
SmallVector<MachineOperand,2> Cond;
// AnalyzeBranch returns true if it fails to analyze branch.
bool NotAnalyzed = TII->AnalyzeBranch(*Latch, TB, FB, Cond, false);
if (NotAnalyzed)
return false;
// Check if the latch branch is unconditional.
if (Cond.empty())
return false;
if (TB != Header && FB != Header)
// The latch does not go back to the header. Not a latch we know and love.
return false;
// Expecting a predicate register as a condition. It won't be a hardware
// predicate register at this point yet, just a vreg.
// HexagonInstrInfo::AnalyzeBranch for negated branches inserts imm(0)
// into Cond, followed by the predicate register. For non-negated branches
// it's just the register.
unsigned CSz = Cond.size();
if (CSz != 1 && CSz != 2)
return false;
unsigned P = Cond[CSz-1].getReg();
MachineInstr *PredDef = MRI->getVRegDef(P);
if (!PredDef->isCompare())
return false;
SmallSet<unsigned,2> CmpRegs;
MachineOperand *CmpImmOp = nullptr;
// Go over all operands to the compare and look for immediate and register
// operands. Assume that if the compare has a single register use and a
// single immediate operand, then the register is being compared with the
// immediate value.
for (unsigned i = 0, n = PredDef->getNumOperands(); i < n; ++i) {
MachineOperand &MO = PredDef->getOperand(i);
if (MO.isReg()) {
// Skip all implicit references. In one case there was:
// %vreg140<def> = FCMPUGT32_rr %vreg138, %vreg139, %USR<imp-use>
if (MO.isImplicit())
continue;
if (MO.isUse()) {
unsigned R = MO.getReg();
if (!defWithImmediate(R)) {
CmpRegs.insert(MO.getReg());
continue;
}
// Consider the register to be the "immediate" operand.
if (CmpImmOp)
return false;
CmpImmOp = &MO;
}
} else if (MO.isImm()) {
if (CmpImmOp) // A second immediate argument? Confusing. Bail out.
return false;
CmpImmOp = &MO;
}
}
if (CmpRegs.empty())
return false;
// Check if the compared register follows the order we want. Fix if needed.
for (RegisterInductionSet::iterator I = IndRegs.begin(), E = IndRegs.end();
I != E; ++I) {
// This is a success. If the register used in the comparison is one that
// we have identified as a bumped (updated) induction register, there is
// nothing to do.
if (CmpRegs.count(I->first))
return true;
// Otherwise, if the register being compared comes out of a PHI node,
// and has been recognized as following the induction pattern, and is
// compared against an immediate, we can fix it.
const RegisterBump &RB = I->second;
if (CmpRegs.count(RB.first)) {
if (!CmpImmOp)
return false;
int64_t CmpImm = getImmediate(*CmpImmOp);
int64_t V = RB.second;
if (V > 0 && CmpImm+V < CmpImm) // Overflow (64-bit).
return false;
if (V < 0 && CmpImm+V > CmpImm) // Overflow (64-bit).
return false;
CmpImm += V;
// Some forms of cmp-immediate allow u9 and s10. Assume the worst case
// scenario, i.e. an 8-bit value.
if (CmpImmOp->isImm() && !isInt<8>(CmpImm))
return false;
// Make sure that the compare happens after the bump. Otherwise,
// after the fixup, the compare would use a yet-undefined register.
MachineInstr *BumpI = MRI->getVRegDef(I->first);
bool Order = orderBumpCompare(BumpI, PredDef);
if (!Order)
return false;
// Finally, fix the compare instruction.
setImmediate(*CmpImmOp, CmpImm);
for (unsigned i = 0, n = PredDef->getNumOperands(); i < n; ++i) {
MachineOperand &MO = PredDef->getOperand(i);
if (MO.isReg() && MO.getReg() == RB.first) {
MO.setReg(I->first);
return true;
}
}
}
}
return false;
}
/// \brief Create a preheader for a given loop.
MachineBasicBlock *HexagonHardwareLoops::createPreheaderForLoop(
MachineLoop *L) {
if (MachineBasicBlock *TmpPH = L->getLoopPreheader())
return TmpPH;
MachineBasicBlock *Header = L->getHeader();
MachineBasicBlock *Latch = L->getLoopLatch();
MachineFunction *MF = Header->getParent();
DebugLoc DL;
if (!Latch || Header->hasAddressTaken())
return nullptr;
typedef MachineBasicBlock::instr_iterator instr_iterator;
// Verify that all existing predecessors have analyzable branches
// (or no branches at all).
typedef std::vector<MachineBasicBlock*> MBBVector;
MBBVector Preds(Header->pred_begin(), Header->pred_end());
SmallVector<MachineOperand,2> Tmp1;
MachineBasicBlock *TB = nullptr, *FB = nullptr;
if (TII->AnalyzeBranch(*Latch, TB, FB, Tmp1, false))
return nullptr;
for (MBBVector::iterator I = Preds.begin(), E = Preds.end(); I != E; ++I) {
MachineBasicBlock *PB = *I;
if (PB != Latch) {
bool NotAnalyzed = TII->AnalyzeBranch(*PB, TB, FB, Tmp1, false);
if (NotAnalyzed)
return nullptr;
}
}
MachineBasicBlock *NewPH = MF->CreateMachineBasicBlock();
MF->insert(Header, NewPH);
if (Header->pred_size() > 2) {
// Ensure that the header has only two predecessors: the preheader and
// the loop latch. Any additional predecessors of the header should
// join at the newly created preheader. Inspect all PHI nodes from the
// header and create appropriate corresponding PHI nodes in the preheader.
for (instr_iterator I = Header->instr_begin(), E = Header->instr_end();
I != E && I->isPHI(); ++I) {
MachineInstr *PN = &*I;
const MCInstrDesc &PD = TII->get(TargetOpcode::PHI);
MachineInstr *NewPN = MF->CreateMachineInstr(PD, DL);
NewPH->insert(NewPH->end(), NewPN);
unsigned PR = PN->getOperand(0).getReg();
const TargetRegisterClass *RC = MRI->getRegClass(PR);
unsigned NewPR = MRI->createVirtualRegister(RC);
NewPN->addOperand(MachineOperand::CreateReg(NewPR, true));
// Copy all non-latch operands of a header's PHI node to the newly
// created PHI node in the preheader.
for (unsigned i = 1, n = PN->getNumOperands(); i < n; i += 2) {
unsigned PredR = PN->getOperand(i).getReg();
MachineBasicBlock *PredB = PN->getOperand(i+1).getMBB();
if (PredB == Latch)
continue;
NewPN->addOperand(MachineOperand::CreateReg(PredR, false));
NewPN->addOperand(MachineOperand::CreateMBB(PredB));
}
// Remove copied operands from the old PHI node and add the value
// coming from the preheader's PHI.
for (int i = PN->getNumOperands()-2; i > 0; i -= 2) {
MachineBasicBlock *PredB = PN->getOperand(i+1).getMBB();
if (PredB != Latch) {
PN->RemoveOperand(i+1);
PN->RemoveOperand(i);
}
}
PN->addOperand(MachineOperand::CreateReg(NewPR, false));
PN->addOperand(MachineOperand::CreateMBB(NewPH));
}
} else {
assert(Header->pred_size() == 2);
// The header has only two predecessors, but the non-latch predecessor
// is not a preheader (e.g. it has other successors, etc.)
// In such a case we don't need any extra PHI nodes in the new preheader,
// all we need is to adjust existing PHIs in the header to now refer to
// the new preheader.
for (instr_iterator I = Header->instr_begin(), E = Header->instr_end();
I != E && I->isPHI(); ++I) {
MachineInstr *PN = &*I;
for (unsigned i = 1, n = PN->getNumOperands(); i < n; i += 2) {
MachineOperand &MO = PN->getOperand(i+1);
if (MO.getMBB() != Latch)
MO.setMBB(NewPH);
}
}
}
// "Reroute" the CFG edges to link in the new preheader.
// If any of the predecessors falls through to the header, insert a branch
// to the new preheader in that place.
SmallVector<MachineOperand,1> Tmp2;
SmallVector<MachineOperand,1> EmptyCond;
TB = FB = nullptr;
for (MBBVector::iterator I = Preds.begin(), E = Preds.end(); I != E; ++I) {
MachineBasicBlock *PB = *I;
if (PB != Latch) {
Tmp2.clear();
bool NotAnalyzed = TII->AnalyzeBranch(*PB, TB, FB, Tmp2, false);
(void)NotAnalyzed; // suppress compiler warning
assert (!NotAnalyzed && "Should be analyzable!");
if (TB != Header && (Tmp2.empty() || FB != Header))
TII->InsertBranch(*PB, NewPH, nullptr, EmptyCond, DL);
PB->ReplaceUsesOfBlockWith(Header, NewPH);
}
}
// It can happen that the latch block will fall through into the header.
// Insert an unconditional branch to the header.
TB = FB = nullptr;
bool LatchNotAnalyzed = TII->AnalyzeBranch(*Latch, TB, FB, Tmp2, false);
(void)LatchNotAnalyzed; // suppress compiler warning
assert (!LatchNotAnalyzed && "Should be analyzable!");
if (!TB && !FB)
TII->InsertBranch(*Latch, Header, nullptr, EmptyCond, DL);
// Finally, the branch from the preheader to the header.
TII->InsertBranch(*NewPH, Header, nullptr, EmptyCond, DL);
NewPH->addSuccessor(Header);
return NewPH;
}