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llvm-mirror/lib/CodeGen/VirtRegRewriter.cpp
Jakob Stoklund Olesen 03dea01d94 Add <imp-def> and <imp-kill> operands when replacing virtual sub-register defs and kills. 
An instruction like this:

  %reg1097:1<def> = VMOVSR %R3<kill>, 14, %reg0

Must be replaced with this when substituting physical registers:

  %S0<def> = VMOVSR %R3<kill>, 14, %reg0, %D0<imp-def>

llvm-svn: 92812
2010-01-06 00:29:28 +00:00

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//===-- llvm/CodeGen/Rewriter.cpp - Rewriter -----------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "virtregrewriter"
#include "VirtRegRewriter.h"
#include "llvm/Function.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/Statistic.h"
#include <algorithm>
using namespace llvm;
STATISTIC(NumDSE , "Number of dead stores elided");
STATISTIC(NumDSS , "Number of dead spill slots removed");
STATISTIC(NumCommutes, "Number of instructions commuted");
STATISTIC(NumDRM , "Number of re-materializable defs elided");
STATISTIC(NumStores , "Number of stores added");
STATISTIC(NumPSpills , "Number of physical register spills");
STATISTIC(NumOmitted , "Number of reloads omited");
STATISTIC(NumAvoided , "Number of reloads deemed unnecessary");
STATISTIC(NumCopified, "Number of available reloads turned into copies");
STATISTIC(NumReMats , "Number of re-materialization");
STATISTIC(NumLoads , "Number of loads added");
STATISTIC(NumReused , "Number of values reused");
STATISTIC(NumDCE , "Number of copies elided");
STATISTIC(NumSUnfold , "Number of stores unfolded");
STATISTIC(NumModRefUnfold, "Number of modref unfolded");
namespace {
enum RewriterName { local, trivial };
}
static cl::opt<RewriterName>
RewriterOpt("rewriter",
cl::desc("Rewriter to use: (default: local)"),
cl::Prefix,
cl::values(clEnumVal(local, "local rewriter"),
clEnumVal(trivial, "trivial rewriter"),
clEnumValEnd),
cl::init(local));
static cl::opt<bool>
ScheduleSpills("schedule-spills",
cl::desc("Schedule spill code"),
cl::init(false));
VirtRegRewriter::~VirtRegRewriter() {}
/// substitutePhysReg - Replace virtual register in MachineOperand with a
/// physical register. Do the right thing with the sub-register index.
static void substitutePhysReg(MachineOperand &MO, unsigned Reg,
const TargetRegisterInfo &TRI) {
if (unsigned SubIdx = MO.getSubReg()) {
// Insert the physical subreg and reset the subreg field.
MO.setReg(TRI.getSubReg(Reg, SubIdx));
MO.setSubReg(0);
// Any def, dead, and kill flags apply to the full virtual register, so they
// also apply to the full physical register. Add imp-def/dead and imp-kill
// as needed.
MachineInstr &MI = *MO.getParent();
if (MO.isDef())
if (MO.isDead())
MI.addRegisterDead(Reg, &TRI, /*AddIfNotFound=*/ true);
else
MI.addRegisterDefined(Reg, &TRI);
else if (!MO.isUndef() &&
(MO.isKill() ||
MI.isRegTiedToDefOperand(&MO-&MI.getOperand(0))))
MI.addRegisterKilled(Reg, &TRI, /*AddIfNotFound=*/ true);
} else {
MO.setReg(Reg);
}
}
namespace {
/// This class is intended for use with the new spilling framework only. It
/// rewrites vreg def/uses to use the assigned preg, but does not insert any
/// spill code.
struct TrivialRewriter : public VirtRegRewriter {
bool runOnMachineFunction(MachineFunction &MF, VirtRegMap &VRM,
LiveIntervals* LIs) {
DEBUG(dbgs() << "********** REWRITE MACHINE CODE **********\n");
DEBUG(dbgs() << "********** Function: "
<< MF.getFunction()->getName() << '\n');
DEBUG(dbgs() << "**** Machine Instrs"
<< "(NOTE! Does not include spills and reloads!) ****\n");
DEBUG(MF.dump());
MachineRegisterInfo *mri = &MF.getRegInfo();
const TargetRegisterInfo *tri = MF.getTarget().getRegisterInfo();
bool changed = false;
for (LiveIntervals::iterator liItr = LIs->begin(), liEnd = LIs->end();
liItr != liEnd; ++liItr) {
const LiveInterval *li = liItr->second;
unsigned reg = li->reg;
if (TargetRegisterInfo::isPhysicalRegister(reg)) {
if (!li->empty())
mri->setPhysRegUsed(reg);
}
else {
if (!VRM.hasPhys(reg))
continue;
unsigned pReg = VRM.getPhys(reg);
mri->setPhysRegUsed(pReg);
for (MachineRegisterInfo::reg_iterator regItr = mri->reg_begin(reg),
regEnd = mri->reg_end(); regItr != regEnd;) {
MachineOperand &mop = regItr.getOperand();
assert(mop.isReg() && mop.getReg() == reg && "reg_iterator broken?");
++regItr;
substitutePhysReg(mop, pReg, *tri);
changed = true;
}
}
}
DEBUG(dbgs() << "**** Post Machine Instrs ****\n");
DEBUG(MF.dump());
return changed;
}
};
}
// ************************************************************************ //
namespace {
/// AvailableSpills - As the local rewriter is scanning and rewriting an MBB
/// from top down, keep track of which spill slots or remat are available in
/// each register.
///
/// Note that not all physregs are created equal here. In particular, some
/// physregs are reloads that we are allowed to clobber or ignore at any time.
/// Other physregs are values that the register allocated program is using
/// that we cannot CHANGE, but we can read if we like. We keep track of this
/// on a per-stack-slot / remat id basis as the low bit in the value of the
/// SpillSlotsAvailable entries. The predicate 'canClobberPhysReg()' checks
/// this bit and addAvailable sets it if.
class AvailableSpills {
const TargetRegisterInfo *TRI;
const TargetInstrInfo *TII;
// SpillSlotsOrReMatsAvailable - This map keeps track of all of the spilled
// or remat'ed virtual register values that are still available, due to
// being loaded or stored to, but not invalidated yet.
std::map<int, unsigned> SpillSlotsOrReMatsAvailable;
// PhysRegsAvailable - This is the inverse of SpillSlotsOrReMatsAvailable,
// indicating which stack slot values are currently held by a physreg. This
// is used to invalidate entries in SpillSlotsOrReMatsAvailable when a
// physreg is modified.
std::multimap<unsigned, int> PhysRegsAvailable;
void disallowClobberPhysRegOnly(unsigned PhysReg);
void ClobberPhysRegOnly(unsigned PhysReg);
public:
AvailableSpills(const TargetRegisterInfo *tri, const TargetInstrInfo *tii)
: TRI(tri), TII(tii) {
}
/// clear - Reset the state.
void clear() {
SpillSlotsOrReMatsAvailable.clear();
PhysRegsAvailable.clear();
}
const TargetRegisterInfo *getRegInfo() const { return TRI; }
/// getSpillSlotOrReMatPhysReg - If the specified stack slot or remat is
/// available in a physical register, return that PhysReg, otherwise
/// return 0.
unsigned getSpillSlotOrReMatPhysReg(int Slot) const {
std::map<int, unsigned>::const_iterator I =
SpillSlotsOrReMatsAvailable.find(Slot);
if (I != SpillSlotsOrReMatsAvailable.end()) {
return I->second >> 1; // Remove the CanClobber bit.
}
return 0;
}
/// addAvailable - Mark that the specified stack slot / remat is available
/// in the specified physreg. If CanClobber is true, the physreg can be
/// modified at any time without changing the semantics of the program.
void addAvailable(int SlotOrReMat, unsigned Reg, bool CanClobber = true) {
// If this stack slot is thought to be available in some other physreg,
// remove its record.
ModifyStackSlotOrReMat(SlotOrReMat);
PhysRegsAvailable.insert(std::make_pair(Reg, SlotOrReMat));
SpillSlotsOrReMatsAvailable[SlotOrReMat]= (Reg << 1) |
(unsigned)CanClobber;
if (SlotOrReMat > VirtRegMap::MAX_STACK_SLOT)
DEBUG(dbgs() << "Remembering RM#"
<< SlotOrReMat-VirtRegMap::MAX_STACK_SLOT-1);
else
DEBUG(dbgs() << "Remembering SS#" << SlotOrReMat);
DEBUG(dbgs() << " in physreg " << TRI->getName(Reg) << "\n");
}
/// canClobberPhysRegForSS - Return true if the spiller is allowed to change
/// the value of the specified stackslot register if it desires. The
/// specified stack slot must be available in a physreg for this query to
/// make sense.
bool canClobberPhysRegForSS(int SlotOrReMat) const {
assert(SpillSlotsOrReMatsAvailable.count(SlotOrReMat) &&
"Value not available!");
return SpillSlotsOrReMatsAvailable.find(SlotOrReMat)->second & 1;
}
/// canClobberPhysReg - Return true if the spiller is allowed to clobber the
/// physical register where values for some stack slot(s) might be
/// available.
bool canClobberPhysReg(unsigned PhysReg) const {
std::multimap<unsigned, int>::const_iterator I =
PhysRegsAvailable.lower_bound(PhysReg);
while (I != PhysRegsAvailable.end() && I->first == PhysReg) {
int SlotOrReMat = I->second;
I++;
if (!canClobberPhysRegForSS(SlotOrReMat))
return false;
}
return true;
}
/// disallowClobberPhysReg - Unset the CanClobber bit of the specified
/// stackslot register. The register is still available but is no longer
/// allowed to be modifed.
void disallowClobberPhysReg(unsigned PhysReg);
/// ClobberPhysReg - This is called when the specified physreg changes
/// value. We use this to invalidate any info about stuff that lives in
/// it and any of its aliases.
void ClobberPhysReg(unsigned PhysReg);
/// ModifyStackSlotOrReMat - This method is called when the value in a stack
/// slot changes. This removes information about which register the
/// previous value for this slot lives in (as the previous value is dead
/// now).
void ModifyStackSlotOrReMat(int SlotOrReMat);
/// AddAvailableRegsToLiveIn - Availability information is being kept coming
/// into the specified MBB. Add available physical registers as potential
/// live-in's. If they are reused in the MBB, they will be added to the
/// live-in set to make register scavenger and post-allocation scheduler.
void AddAvailableRegsToLiveIn(MachineBasicBlock &MBB, BitVector &RegKills,
std::vector<MachineOperand*> &KillOps);
};
}
// ************************************************************************ //
// Given a location where a reload of a spilled register or a remat of
// a constant is to be inserted, attempt to find a safe location to
// insert the load at an earlier point in the basic-block, to hide
// latency of the load and to avoid address-generation interlock
// issues.
static MachineBasicBlock::iterator
ComputeReloadLoc(MachineBasicBlock::iterator const InsertLoc,
MachineBasicBlock::iterator const Begin,
unsigned PhysReg,
const TargetRegisterInfo *TRI,
bool DoReMat,
int SSorRMId,
const TargetInstrInfo *TII,
const MachineFunction &MF)
{
if (!ScheduleSpills)
return InsertLoc;
// Spill backscheduling is of primary interest to addresses, so
// don't do anything if the register isn't in the register class
// used for pointers.
const TargetLowering *TL = MF.getTarget().getTargetLowering();
if (!TL->isTypeLegal(TL->getPointerTy()))
// Believe it or not, this is true on PIC16.
return InsertLoc;
const TargetRegisterClass *ptrRegClass =
TL->getRegClassFor(TL->getPointerTy());
if (!ptrRegClass->contains(PhysReg))
return InsertLoc;
// Scan upwards through the preceding instructions. If an instruction doesn't
// reference the stack slot or the register we're loading, we can
// backschedule the reload up past it.
MachineBasicBlock::iterator NewInsertLoc = InsertLoc;
while (NewInsertLoc != Begin) {
MachineBasicBlock::iterator Prev = prior(NewInsertLoc);
for (unsigned i = 0; i < Prev->getNumOperands(); ++i) {
MachineOperand &Op = Prev->getOperand(i);
if (!DoReMat && Op.isFI() && Op.getIndex() == SSorRMId)
goto stop;
}
if (Prev->findRegisterUseOperandIdx(PhysReg) != -1 ||
Prev->findRegisterDefOperand(PhysReg))
goto stop;
for (const unsigned *Alias = TRI->getAliasSet(PhysReg); *Alias; ++Alias)
if (Prev->findRegisterUseOperandIdx(*Alias) != -1 ||
Prev->findRegisterDefOperand(*Alias))
goto stop;
NewInsertLoc = Prev;
}
stop:;
// If we made it to the beginning of the block, turn around and move back
// down just past any existing reloads. They're likely to be reloads/remats
// for instructions earlier than what our current reload/remat is for, so
// they should be scheduled earlier.
if (NewInsertLoc == Begin) {
int FrameIdx;
while (InsertLoc != NewInsertLoc &&
(TII->isLoadFromStackSlot(NewInsertLoc, FrameIdx) ||
TII->isTriviallyReMaterializable(NewInsertLoc)))
++NewInsertLoc;
}
return NewInsertLoc;
}
namespace {
// ReusedOp - For each reused operand, we keep track of a bit of information,
// in case we need to rollback upon processing a new operand. See comments
// below.
struct ReusedOp {
// The MachineInstr operand that reused an available value.
unsigned Operand;
// StackSlotOrReMat - The spill slot or remat id of the value being reused.
unsigned StackSlotOrReMat;
// PhysRegReused - The physical register the value was available in.
unsigned PhysRegReused;
// AssignedPhysReg - The physreg that was assigned for use by the reload.
unsigned AssignedPhysReg;
// VirtReg - The virtual register itself.
unsigned VirtReg;
ReusedOp(unsigned o, unsigned ss, unsigned prr, unsigned apr,
unsigned vreg)
: Operand(o), StackSlotOrReMat(ss), PhysRegReused(prr),
AssignedPhysReg(apr), VirtReg(vreg) {}
};
/// ReuseInfo - This maintains a collection of ReuseOp's for each operand that
/// is reused instead of reloaded.
class ReuseInfo {
MachineInstr &MI;
std::vector<ReusedOp> Reuses;
BitVector PhysRegsClobbered;
public:
ReuseInfo(MachineInstr &mi, const TargetRegisterInfo *tri) : MI(mi) {
PhysRegsClobbered.resize(tri->getNumRegs());
}
bool hasReuses() const {
return !Reuses.empty();
}
/// addReuse - If we choose to reuse a virtual register that is already
/// available instead of reloading it, remember that we did so.
void addReuse(unsigned OpNo, unsigned StackSlotOrReMat,
unsigned PhysRegReused, unsigned AssignedPhysReg,
unsigned VirtReg) {
// If the reload is to the assigned register anyway, no undo will be
// required.
if (PhysRegReused == AssignedPhysReg) return;
// Otherwise, remember this.
Reuses.push_back(ReusedOp(OpNo, StackSlotOrReMat, PhysRegReused,
AssignedPhysReg, VirtReg));
}
void markClobbered(unsigned PhysReg) {
PhysRegsClobbered.set(PhysReg);
}
bool isClobbered(unsigned PhysReg) const {
return PhysRegsClobbered.test(PhysReg);
}
/// GetRegForReload - We are about to emit a reload into PhysReg. If there
/// is some other operand that is using the specified register, either pick
/// a new register to use, or evict the previous reload and use this reg.
unsigned GetRegForReload(const TargetRegisterClass *RC, unsigned PhysReg,
MachineFunction &MF, MachineInstr *MI,
AvailableSpills &Spills,
std::vector<MachineInstr*> &MaybeDeadStores,
SmallSet<unsigned, 8> &Rejected,
BitVector &RegKills,
std::vector<MachineOperand*> &KillOps,
VirtRegMap &VRM);
/// GetRegForReload - Helper for the above GetRegForReload(). Add a
/// 'Rejected' set to remember which registers have been considered and
/// rejected for the reload. This avoids infinite looping in case like
/// this:
/// t1 := op t2, t3
/// t2 <- assigned r0 for use by the reload but ended up reuse r1
/// t3 <- assigned r1 for use by the reload but ended up reuse r0
/// t1 <- desires r1
/// sees r1 is taken by t2, tries t2's reload register r0
/// sees r0 is taken by t3, tries t3's reload register r1
/// sees r1 is taken by t2, tries t2's reload register r0 ...
unsigned GetRegForReload(unsigned VirtReg, unsigned PhysReg, MachineInstr *MI,
AvailableSpills &Spills,
std::vector<MachineInstr*> &MaybeDeadStores,
BitVector &RegKills,
std::vector<MachineOperand*> &KillOps,
VirtRegMap &VRM) {
SmallSet<unsigned, 8> Rejected;
MachineFunction &MF = *MI->getParent()->getParent();
const TargetRegisterClass* RC = MF.getRegInfo().getRegClass(VirtReg);
return GetRegForReload(RC, PhysReg, MF, MI, Spills, MaybeDeadStores,
Rejected, RegKills, KillOps, VRM);
}
};
}
// ****************** //
// Utility Functions //
// ****************** //
/// findSinglePredSuccessor - Return via reference a vector of machine basic
/// blocks each of which is a successor of the specified BB and has no other
/// predecessor.
static void findSinglePredSuccessor(MachineBasicBlock *MBB,
SmallVectorImpl<MachineBasicBlock *> &Succs) {
for (MachineBasicBlock::succ_iterator SI = MBB->succ_begin(),
SE = MBB->succ_end(); SI != SE; ++SI) {
MachineBasicBlock *SuccMBB = *SI;
if (SuccMBB->pred_size() == 1)
Succs.push_back(SuccMBB);
}
}
/// InvalidateKill - Invalidate register kill information for a specific
/// register. This also unsets the kills marker on the last kill operand.
static void InvalidateKill(unsigned Reg,
const TargetRegisterInfo* TRI,
BitVector &RegKills,
std::vector<MachineOperand*> &KillOps) {
if (RegKills[Reg]) {
KillOps[Reg]->setIsKill(false);
// KillOps[Reg] might be a def of a super-register.
unsigned KReg = KillOps[Reg]->getReg();
KillOps[KReg] = NULL;
RegKills.reset(KReg);
for (const unsigned *SR = TRI->getSubRegisters(KReg); *SR; ++SR) {
if (RegKills[*SR]) {
KillOps[*SR]->setIsKill(false);
KillOps[*SR] = NULL;
RegKills.reset(*SR);
}
}
}
}
/// InvalidateKills - MI is going to be deleted. If any of its operands are
/// marked kill, then invalidate the information.
static void InvalidateKills(MachineInstr &MI,
const TargetRegisterInfo* TRI,
BitVector &RegKills,
std::vector<MachineOperand*> &KillOps,
SmallVector<unsigned, 2> *KillRegs = NULL) {
for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI.getOperand(i);
if (!MO.isReg() || !MO.isUse() || !MO.isKill() || MO.isUndef())
continue;
unsigned Reg = MO.getReg();
if (TargetRegisterInfo::isVirtualRegister(Reg))
continue;
if (KillRegs)
KillRegs->push_back(Reg);
assert(Reg < KillOps.size());
if (KillOps[Reg] == &MO) {
KillOps[Reg] = NULL;
RegKills.reset(Reg);
for (const unsigned *SR = TRI->getSubRegisters(Reg); *SR; ++SR) {
if (RegKills[*SR]) {
KillOps[*SR] = NULL;
RegKills.reset(*SR);
}
}
}
}
}
/// InvalidateRegDef - If the def operand of the specified def MI is now dead
/// (since its spill instruction is removed), mark it isDead. Also checks if
/// the def MI has other definition operands that are not dead. Returns it by
/// reference.
static bool InvalidateRegDef(MachineBasicBlock::iterator I,
MachineInstr &NewDef, unsigned Reg,
bool &HasLiveDef,
const TargetRegisterInfo *TRI) {
// Due to remat, it's possible this reg isn't being reused. That is,
// the def of this reg (by prev MI) is now dead.
MachineInstr *DefMI = I;
MachineOperand *DefOp = NULL;
for (unsigned i = 0, e = DefMI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = DefMI->getOperand(i);
if (!MO.isReg() || !MO.isDef() || !MO.isKill() || MO.isUndef())
continue;
if (MO.getReg() == Reg)
DefOp = &MO;
else if (!MO.isDead())
HasLiveDef = true;
}
if (!DefOp)
return false;
bool FoundUse = false, Done = false;
MachineBasicBlock::iterator E = &NewDef;
++I; ++E;
for (; !Done && I != E; ++I) {
MachineInstr *NMI = I;
for (unsigned j = 0, ee = NMI->getNumOperands(); j != ee; ++j) {
MachineOperand &MO = NMI->getOperand(j);
if (!MO.isReg() || MO.getReg() == 0 ||
(MO.getReg() != Reg && !TRI->isSubRegister(Reg, MO.getReg())))
continue;
if (MO.isUse())
FoundUse = true;
Done = true; // Stop after scanning all the operands of this MI.
}
}
if (!FoundUse) {
// Def is dead!
DefOp->setIsDead();
return true;
}
return false;
}
/// UpdateKills - Track and update kill info. If a MI reads a register that is
/// marked kill, then it must be due to register reuse. Transfer the kill info
/// over.
static void UpdateKills(MachineInstr &MI, const TargetRegisterInfo* TRI,
BitVector &RegKills,
std::vector<MachineOperand*> &KillOps) {
for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI.getOperand(i);
if (!MO.isReg() || !MO.isUse() || MO.isUndef())
continue;
unsigned Reg = MO.getReg();
if (Reg == 0)
continue;
if (RegKills[Reg] && KillOps[Reg]->getParent() != &MI) {
// That can't be right. Register is killed but not re-defined and it's
// being reused. Let's fix that.
KillOps[Reg]->setIsKill(false);
// KillOps[Reg] might be a def of a super-register.
unsigned KReg = KillOps[Reg]->getReg();
KillOps[KReg] = NULL;
RegKills.reset(KReg);
// Must be a def of a super-register. Its other sub-regsters are no
// longer killed as well.
for (const unsigned *SR = TRI->getSubRegisters(KReg); *SR; ++SR) {
KillOps[*SR] = NULL;
RegKills.reset(*SR);
}
} else {
// Check for subreg kills as well.
// d4 =
// store d4, fi#0
// ...
// = s8<kill>
// ...
// = d4 <avoiding reload>
for (const unsigned *SR = TRI->getSubRegisters(Reg); *SR; ++SR) {
unsigned SReg = *SR;
if (RegKills[SReg] && KillOps[SReg]->getParent() != &MI) {
KillOps[SReg]->setIsKill(false);
unsigned KReg = KillOps[SReg]->getReg();
KillOps[KReg] = NULL;
RegKills.reset(KReg);
for (const unsigned *SSR = TRI->getSubRegisters(KReg); *SSR; ++SSR) {
KillOps[*SSR] = NULL;
RegKills.reset(*SSR);
}
}
}
}
if (MO.isKill()) {
RegKills.set(Reg);
KillOps[Reg] = &MO;
for (const unsigned *SR = TRI->getSubRegisters(Reg); *SR; ++SR) {
RegKills.set(*SR);
KillOps[*SR] = &MO;
}
}
}
for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI.getOperand(i);
if (!MO.isReg() || !MO.getReg() || !MO.isDef())
continue;
unsigned Reg = MO.getReg();
RegKills.reset(Reg);
KillOps[Reg] = NULL;
// It also defines (or partially define) aliases.
for (const unsigned *SR = TRI->getSubRegisters(Reg); *SR; ++SR) {
RegKills.reset(*SR);
KillOps[*SR] = NULL;
}
for (const unsigned *SR = TRI->getSuperRegisters(Reg); *SR; ++SR) {
RegKills.reset(*SR);
KillOps[*SR] = NULL;
}
}
}
/// ReMaterialize - Re-materialize definition for Reg targetting DestReg.
///
static void ReMaterialize(MachineBasicBlock &MBB,
MachineBasicBlock::iterator &MII,
unsigned DestReg, unsigned Reg,
const TargetInstrInfo *TII,
const TargetRegisterInfo *TRI,
VirtRegMap &VRM) {
MachineInstr *ReMatDefMI = VRM.getReMaterializedMI(Reg);
#ifndef NDEBUG
const TargetInstrDesc &TID = ReMatDefMI->getDesc();
assert(TID.getNumDefs() == 1 &&
"Don't know how to remat instructions that define > 1 values!");
#endif
TII->reMaterialize(MBB, MII, DestReg,
ReMatDefMI->getOperand(0).getSubReg(), ReMatDefMI, TRI);
MachineInstr *NewMI = prior(MII);
for (unsigned i = 0, e = NewMI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = NewMI->getOperand(i);
if (!MO.isReg() || MO.getReg() == 0)
continue;
unsigned VirtReg = MO.getReg();
if (TargetRegisterInfo::isPhysicalRegister(VirtReg))
continue;
assert(MO.isUse());
unsigned Phys = VRM.getPhys(VirtReg);
assert(Phys && "Virtual register is not assigned a register?");
substitutePhysReg(MO, Phys, *TRI);
}
++NumReMats;
}
/// findSuperReg - Find the SubReg's super-register of given register class
/// where its SubIdx sub-register is SubReg.
static unsigned findSuperReg(const TargetRegisterClass *RC, unsigned SubReg,
unsigned SubIdx, const TargetRegisterInfo *TRI) {
for (TargetRegisterClass::iterator I = RC->begin(), E = RC->end();
I != E; ++I) {
unsigned Reg = *I;
if (TRI->getSubReg(Reg, SubIdx) == SubReg)
return Reg;
}
return 0;
}
// ******************************** //
// Available Spills Implementation //
// ******************************** //
/// disallowClobberPhysRegOnly - Unset the CanClobber bit of the specified
/// stackslot register. The register is still available but is no longer
/// allowed to be modifed.
void AvailableSpills::disallowClobberPhysRegOnly(unsigned PhysReg) {
std::multimap<unsigned, int>::iterator I =
PhysRegsAvailable.lower_bound(PhysReg);
while (I != PhysRegsAvailable.end() && I->first == PhysReg) {
int SlotOrReMat = I->second;
I++;
assert((SpillSlotsOrReMatsAvailable[SlotOrReMat] >> 1) == PhysReg &&
"Bidirectional map mismatch!");
SpillSlotsOrReMatsAvailable[SlotOrReMat] &= ~1;
DEBUG(dbgs() << "PhysReg " << TRI->getName(PhysReg)
<< " copied, it is available for use but can no longer be modified\n");
}
}
/// disallowClobberPhysReg - Unset the CanClobber bit of the specified
/// stackslot register and its aliases. The register and its aliases may
/// still available but is no longer allowed to be modifed.
void AvailableSpills::disallowClobberPhysReg(unsigned PhysReg) {
for (const unsigned *AS = TRI->getAliasSet(PhysReg); *AS; ++AS)
disallowClobberPhysRegOnly(*AS);
disallowClobberPhysRegOnly(PhysReg);
}
/// ClobberPhysRegOnly - This is called when the specified physreg changes
/// value. We use this to invalidate any info about stuff we thing lives in it.
void AvailableSpills::ClobberPhysRegOnly(unsigned PhysReg) {
std::multimap<unsigned, int>::iterator I =
PhysRegsAvailable.lower_bound(PhysReg);
while (I != PhysRegsAvailable.end() && I->first == PhysReg) {
int SlotOrReMat = I->second;
PhysRegsAvailable.erase(I++);
assert((SpillSlotsOrReMatsAvailable[SlotOrReMat] >> 1) == PhysReg &&
"Bidirectional map mismatch!");
SpillSlotsOrReMatsAvailable.erase(SlotOrReMat);
DEBUG(dbgs() << "PhysReg " << TRI->getName(PhysReg)
<< " clobbered, invalidating ");
if (SlotOrReMat > VirtRegMap::MAX_STACK_SLOT)
DEBUG(dbgs() << "RM#" << SlotOrReMat-VirtRegMap::MAX_STACK_SLOT-1 <<"\n");
else
DEBUG(dbgs() << "SS#" << SlotOrReMat << "\n");
}
}
/// ClobberPhysReg - This is called when the specified physreg changes
/// value. We use this to invalidate any info about stuff we thing lives in
/// it and any of its aliases.
void AvailableSpills::ClobberPhysReg(unsigned PhysReg) {
for (const unsigned *AS = TRI->getAliasSet(PhysReg); *AS; ++AS)
ClobberPhysRegOnly(*AS);
ClobberPhysRegOnly(PhysReg);
}
/// AddAvailableRegsToLiveIn - Availability information is being kept coming
/// into the specified MBB. Add available physical registers as potential
/// live-in's. If they are reused in the MBB, they will be added to the
/// live-in set to make register scavenger and post-allocation scheduler.
void AvailableSpills::AddAvailableRegsToLiveIn(MachineBasicBlock &MBB,
BitVector &RegKills,
std::vector<MachineOperand*> &KillOps) {
std::set<unsigned> NotAvailable;
for (std::multimap<unsigned, int>::iterator
I = PhysRegsAvailable.begin(), E = PhysRegsAvailable.end();
I != E; ++I) {
unsigned Reg = I->first;
const TargetRegisterClass* RC = TRI->getPhysicalRegisterRegClass(Reg);
// FIXME: A temporary workaround. We can't reuse available value if it's
// not safe to move the def of the virtual register's class. e.g.
// X86::RFP* register classes. Do not add it as a live-in.
if (!TII->isSafeToMoveRegClassDefs(RC))
// This is no longer available.
NotAvailable.insert(Reg);
else {
MBB.addLiveIn(Reg);
InvalidateKill(Reg, TRI, RegKills, KillOps);
}
// Skip over the same register.
std::multimap<unsigned, int>::iterator NI = llvm::next(I);
while (NI != E && NI->first == Reg) {
++I;
++NI;
}
}
for (std::set<unsigned>::iterator I = NotAvailable.begin(),
E = NotAvailable.end(); I != E; ++I) {
ClobberPhysReg(*I);
for (const unsigned *SubRegs = TRI->getSubRegisters(*I);
*SubRegs; ++SubRegs)
ClobberPhysReg(*SubRegs);
}
}
/// ModifyStackSlotOrReMat - This method is called when the value in a stack
/// slot changes. This removes information about which register the previous
/// value for this slot lives in (as the previous value is dead now).
void AvailableSpills::ModifyStackSlotOrReMat(int SlotOrReMat) {
std::map<int, unsigned>::iterator It =
SpillSlotsOrReMatsAvailable.find(SlotOrReMat);
if (It == SpillSlotsOrReMatsAvailable.end()) return;
unsigned Reg = It->second >> 1;
SpillSlotsOrReMatsAvailable.erase(It);
// This register may hold the value of multiple stack slots, only remove this
// stack slot from the set of values the register contains.
std::multimap<unsigned, int>::iterator I = PhysRegsAvailable.lower_bound(Reg);
for (; ; ++I) {
assert(I != PhysRegsAvailable.end() && I->first == Reg &&
"Map inverse broken!");
if (I->second == SlotOrReMat) break;
}
PhysRegsAvailable.erase(I);
}
// ************************** //
// Reuse Info Implementation //
// ************************** //
/// GetRegForReload - We are about to emit a reload into PhysReg. If there
/// is some other operand that is using the specified register, either pick
/// a new register to use, or evict the previous reload and use this reg.
unsigned ReuseInfo::GetRegForReload(const TargetRegisterClass *RC,
unsigned PhysReg,
MachineFunction &MF,
MachineInstr *MI, AvailableSpills &Spills,
std::vector<MachineInstr*> &MaybeDeadStores,
SmallSet<unsigned, 8> &Rejected,
BitVector &RegKills,
std::vector<MachineOperand*> &KillOps,
VirtRegMap &VRM) {
const TargetInstrInfo* TII = MF.getTarget().getInstrInfo();
const TargetRegisterInfo *TRI = Spills.getRegInfo();
if (Reuses.empty()) return PhysReg; // This is most often empty.
for (unsigned ro = 0, e = Reuses.size(); ro != e; ++ro) {
ReusedOp &Op = Reuses[ro];
// If we find some other reuse that was supposed to use this register
// exactly for its reload, we can change this reload to use ITS reload
// register. That is, unless its reload register has already been
// considered and subsequently rejected because it has also been reused
// by another operand.
if (Op.PhysRegReused == PhysReg &&
Rejected.count(Op.AssignedPhysReg) == 0 &&
RC->contains(Op.AssignedPhysReg)) {
// Yup, use the reload register that we didn't use before.
unsigned NewReg = Op.AssignedPhysReg;
Rejected.insert(PhysReg);
return GetRegForReload(RC, NewReg, MF, MI, Spills, MaybeDeadStores, Rejected,
RegKills, KillOps, VRM);
} else {
// Otherwise, we might also have a problem if a previously reused
// value aliases the new register. If so, codegen the previous reload
// and use this one.
unsigned PRRU = Op.PhysRegReused;
if (TRI->regsOverlap(PRRU, PhysReg)) {
// Okay, we found out that an alias of a reused register
// was used. This isn't good because it means we have
// to undo a previous reuse.
MachineBasicBlock *MBB = MI->getParent();
const TargetRegisterClass *AliasRC =
MBB->getParent()->getRegInfo().getRegClass(Op.VirtReg);
// Copy Op out of the vector and remove it, we're going to insert an
// explicit load for it.
ReusedOp NewOp = Op;
Reuses.erase(Reuses.begin()+ro);
// MI may be using only a sub-register of PhysRegUsed.
unsigned RealPhysRegUsed = MI->getOperand(NewOp.Operand).getReg();
unsigned SubIdx = 0;
assert(TargetRegisterInfo::isPhysicalRegister(RealPhysRegUsed) &&
"A reuse cannot be a virtual register");
if (PRRU != RealPhysRegUsed) {
// What was the sub-register index?
SubIdx = TRI->getSubRegIndex(PRRU, RealPhysRegUsed);
assert(SubIdx &&
"Operand physreg is not a sub-register of PhysRegUsed");
}
// Ok, we're going to try to reload the assigned physreg into the
// slot that we were supposed to in the first place. However, that
// register could hold a reuse. Check to see if it conflicts or
// would prefer us to use a different register.
unsigned NewPhysReg = GetRegForReload(RC, NewOp.AssignedPhysReg,
MF, MI, Spills, MaybeDeadStores,
Rejected, RegKills, KillOps, VRM);
bool DoReMat = NewOp.StackSlotOrReMat > VirtRegMap::MAX_STACK_SLOT;
int SSorRMId = DoReMat
? VRM.getReMatId(NewOp.VirtReg) : NewOp.StackSlotOrReMat;
// Back-schedule reloads and remats.
MachineBasicBlock::iterator InsertLoc =
ComputeReloadLoc(MI, MBB->begin(), PhysReg, TRI,
DoReMat, SSorRMId, TII, MF);
if (DoReMat) {
ReMaterialize(*MBB, InsertLoc, NewPhysReg, NewOp.VirtReg, TII,
TRI, VRM);
} else {
TII->loadRegFromStackSlot(*MBB, InsertLoc, NewPhysReg,
NewOp.StackSlotOrReMat, AliasRC);
MachineInstr *LoadMI = prior(InsertLoc);
VRM.addSpillSlotUse(NewOp.StackSlotOrReMat, LoadMI);
// Any stores to this stack slot are not dead anymore.
MaybeDeadStores[NewOp.StackSlotOrReMat] = NULL;
++NumLoads;
}
Spills.ClobberPhysReg(NewPhysReg);
Spills.ClobberPhysReg(NewOp.PhysRegReused);
unsigned RReg = SubIdx ? TRI->getSubReg(NewPhysReg, SubIdx) :NewPhysReg;
MI->getOperand(NewOp.Operand).setReg(RReg);
MI->getOperand(NewOp.Operand).setSubReg(0);
Spills.addAvailable(NewOp.StackSlotOrReMat, NewPhysReg);
UpdateKills(*prior(InsertLoc), TRI, RegKills, KillOps);
DEBUG(dbgs() << '\t' << *prior(InsertLoc));
DEBUG(dbgs() << "Reuse undone!\n");
--NumReused;
// Finally, PhysReg is now available, go ahead and use it.
return PhysReg;
}
}
}
return PhysReg;
}
// ************************************************************************ //
/// FoldsStackSlotModRef - Return true if the specified MI folds the specified
/// stack slot mod/ref. It also checks if it's possible to unfold the
/// instruction by having it define a specified physical register instead.
static bool FoldsStackSlotModRef(MachineInstr &MI, int SS, unsigned PhysReg,
const TargetInstrInfo *TII,
const TargetRegisterInfo *TRI,
VirtRegMap &VRM) {
if (VRM.hasEmergencySpills(&MI) || VRM.isSpillPt(&MI))
return false;
bool Found = false;
VirtRegMap::MI2VirtMapTy::const_iterator I, End;
for (tie(I, End) = VRM.getFoldedVirts(&MI); I != End; ++I) {
unsigned VirtReg = I->second.first;
VirtRegMap::ModRef MR = I->second.second;
if (MR & VirtRegMap::isModRef)
if (VRM.getStackSlot(VirtReg) == SS) {
Found= TII->getOpcodeAfterMemoryUnfold(MI.getOpcode(), true, true) != 0;
break;
}
}
if (!Found)
return false;
// Does the instruction uses a register that overlaps the scratch register?
for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI.getOperand(i);
if (!MO.isReg() || MO.getReg() == 0)
continue;
unsigned Reg = MO.getReg();
if (TargetRegisterInfo::isVirtualRegister(Reg)) {
if (!VRM.hasPhys(Reg))
continue;
Reg = VRM.getPhys(Reg);
}
if (TRI->regsOverlap(PhysReg, Reg))
return false;
}
return true;
}
/// FindFreeRegister - Find a free register of a given register class by looking
/// at (at most) the last two machine instructions.
static unsigned FindFreeRegister(MachineBasicBlock::iterator MII,
MachineBasicBlock &MBB,
const TargetRegisterClass *RC,
const TargetRegisterInfo *TRI,
BitVector &AllocatableRegs) {
BitVector Defs(TRI->getNumRegs());
BitVector Uses(TRI->getNumRegs());
SmallVector<unsigned, 4> LocalUses;
SmallVector<unsigned, 4> Kills;
// Take a look at 2 instructions at most.
for (unsigned Count = 0; Count < 2; ++Count) {
if (MII == MBB.begin())
break;
MachineInstr *PrevMI = prior(MII);
for (unsigned i = 0, e = PrevMI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = PrevMI->getOperand(i);
if (!MO.isReg() || MO.getReg() == 0)
continue;
unsigned Reg = MO.getReg();
if (MO.isDef()) {
Defs.set(Reg);
for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS)
Defs.set(*AS);
} else {
LocalUses.push_back(Reg);
if (MO.isKill() && AllocatableRegs[Reg])
Kills.push_back(Reg);
}
}
for (unsigned i = 0, e = Kills.size(); i != e; ++i) {
unsigned Kill = Kills[i];
if (!Defs[Kill] && !Uses[Kill] &&
TRI->getPhysicalRegisterRegClass(Kill) == RC)
return Kill;
}
for (unsigned i = 0, e = LocalUses.size(); i != e; ++i) {
unsigned Reg = LocalUses[i];
Uses.set(Reg);
for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS)
Uses.set(*AS);
}
MII = PrevMI;
}
return 0;
}
static
void AssignPhysToVirtReg(MachineInstr *MI, unsigned VirtReg, unsigned PhysReg,
const TargetRegisterInfo &TRI) {
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (MO.isReg() && MO.getReg() == VirtReg)
substitutePhysReg(MO, PhysReg, TRI);
}
}
namespace {
struct RefSorter {
bool operator()(const std::pair<MachineInstr*, int> &A,
const std::pair<MachineInstr*, int> &B) {
return A.second < B.second;
}
};
}
// ***************************** //
// Local Spiller Implementation //
// ***************************** //
namespace {
class LocalRewriter : public VirtRegRewriter {
MachineRegisterInfo *RegInfo;
const TargetRegisterInfo *TRI;
const TargetInstrInfo *TII;
BitVector AllocatableRegs;
DenseMap<MachineInstr*, unsigned> DistanceMap;
public:
bool runOnMachineFunction(MachineFunction &MF, VirtRegMap &VRM,
LiveIntervals* LIs) {
RegInfo = &MF.getRegInfo();
TRI = MF.getTarget().getRegisterInfo();
TII = MF.getTarget().getInstrInfo();
AllocatableRegs = TRI->getAllocatableSet(MF);
DEBUG(dbgs() << "\n**** Local spiller rewriting function '"
<< MF.getFunction()->getName() << "':\n");
DEBUG(dbgs() << "**** Machine Instrs (NOTE! Does not include spills and"
" reloads!) ****\n");
DEBUG(MF.dump());
// Spills - Keep track of which spilled values are available in physregs
// so that we can choose to reuse the physregs instead of emitting
// reloads. This is usually refreshed per basic block.
AvailableSpills Spills(TRI, TII);
// Keep track of kill information.
BitVector RegKills(TRI->getNumRegs());
std::vector<MachineOperand*> KillOps;
KillOps.resize(TRI->getNumRegs(), NULL);
// SingleEntrySuccs - Successor blocks which have a single predecessor.
SmallVector<MachineBasicBlock*, 4> SinglePredSuccs;
SmallPtrSet<MachineBasicBlock*,16> EarlyVisited;
// Traverse the basic blocks depth first.
MachineBasicBlock *Entry = MF.begin();
SmallPtrSet<MachineBasicBlock*,16> Visited;
for (df_ext_iterator<MachineBasicBlock*,
SmallPtrSet<MachineBasicBlock*,16> >
DFI = df_ext_begin(Entry, Visited), E = df_ext_end(Entry, Visited);
DFI != E; ++DFI) {
MachineBasicBlock *MBB = *DFI;
if (!EarlyVisited.count(MBB))
RewriteMBB(*MBB, VRM, LIs, Spills, RegKills, KillOps);
// If this MBB is the only predecessor of a successor. Keep the
// availability information and visit it next.
do {
// Keep visiting single predecessor successor as long as possible.
SinglePredSuccs.clear();
findSinglePredSuccessor(MBB, SinglePredSuccs);
if (SinglePredSuccs.empty())
MBB = 0;
else {
// FIXME: More than one successors, each of which has MBB has
// the only predecessor.
MBB = SinglePredSuccs[0];
if (!Visited.count(MBB) && EarlyVisited.insert(MBB)) {
Spills.AddAvailableRegsToLiveIn(*MBB, RegKills, KillOps);
RewriteMBB(*MBB, VRM, LIs, Spills, RegKills, KillOps);
}
}
} while (MBB);
// Clear the availability info.
Spills.clear();
}
DEBUG(dbgs() << "**** Post Machine Instrs ****\n");
DEBUG(MF.dump());
// Mark unused spill slots.
MachineFrameInfo *MFI = MF.getFrameInfo();
int SS = VRM.getLowSpillSlot();
if (SS != VirtRegMap::NO_STACK_SLOT)
for (int e = VRM.getHighSpillSlot(); SS <= e; ++SS)
if (!VRM.isSpillSlotUsed(SS)) {
MFI->RemoveStackObject(SS);
++NumDSS;
}
return true;
}
private:
/// OptimizeByUnfold2 - Unfold a series of load / store folding instructions if
/// a scratch register is available.
/// xorq %r12<kill>, %r13
/// addq %rax, -184(%rbp)
/// addq %r13, -184(%rbp)
/// ==>
/// xorq %r12<kill>, %r13
/// movq -184(%rbp), %r12
/// addq %rax, %r12
/// addq %r13, %r12
/// movq %r12, -184(%rbp)
bool OptimizeByUnfold2(unsigned VirtReg, int SS,
MachineBasicBlock &MBB,
MachineBasicBlock::iterator &MII,
std::vector<MachineInstr*> &MaybeDeadStores,
AvailableSpills &Spills,
BitVector &RegKills,
std::vector<MachineOperand*> &KillOps,
VirtRegMap &VRM) {
MachineBasicBlock::iterator NextMII = llvm::next(MII);
if (NextMII == MBB.end())
return false;
if (TII->getOpcodeAfterMemoryUnfold(MII->getOpcode(), true, true) == 0)
return false;
// Now let's see if the last couple of instructions happens to have freed up
// a register.
const TargetRegisterClass* RC = RegInfo->getRegClass(VirtReg);
unsigned PhysReg = FindFreeRegister(MII, MBB, RC, TRI, AllocatableRegs);
if (!PhysReg)
return false;
MachineFunction &MF = *MBB.getParent();
TRI = MF.getTarget().getRegisterInfo();
MachineInstr &MI = *MII;
if (!FoldsStackSlotModRef(MI, SS, PhysReg, TII, TRI, VRM))
return false;
// If the next instruction also folds the same SS modref and can be unfoled,
// then it's worthwhile to issue a load from SS into the free register and
// then unfold these instructions.
if (!FoldsStackSlotModRef(*NextMII, SS, PhysReg, TII, TRI, VRM))
return false;
// Back-schedule reloads and remats.
ComputeReloadLoc(MII, MBB.begin(), PhysReg, TRI, false, SS, TII, MF);
// Load from SS to the spare physical register.
TII->loadRegFromStackSlot(MBB, MII, PhysReg, SS, RC);
// This invalidates Phys.
Spills.ClobberPhysReg(PhysReg);
// Remember it's available.
Spills.addAvailable(SS, PhysReg);
MaybeDeadStores[SS] = NULL;
// Unfold current MI.
SmallVector<MachineInstr*, 4> NewMIs;
if (!TII->unfoldMemoryOperand(MF, &MI, VirtReg, false, false, NewMIs))
llvm_unreachable("Unable unfold the load / store folding instruction!");
assert(NewMIs.size() == 1);
AssignPhysToVirtReg(NewMIs[0], VirtReg, PhysReg, *TRI);
VRM.transferRestorePts(&MI, NewMIs[0]);
MII = MBB.insert(MII, NewMIs[0]);
InvalidateKills(MI, TRI, RegKills, KillOps);
VRM.RemoveMachineInstrFromMaps(&MI);
MBB.erase(&MI);
++NumModRefUnfold;
// Unfold next instructions that fold the same SS.
do {
MachineInstr &NextMI = *NextMII;
NextMII = llvm::next(NextMII);
NewMIs.clear();
if (!TII->unfoldMemoryOperand(MF, &NextMI, VirtReg, false, false, NewMIs))
llvm_unreachable("Unable unfold the load / store folding instruction!");
assert(NewMIs.size() == 1);
AssignPhysToVirtReg(NewMIs[0], VirtReg, PhysReg, *TRI);
VRM.transferRestorePts(&NextMI, NewMIs[0]);
MBB.insert(NextMII, NewMIs[0]);
InvalidateKills(NextMI, TRI, RegKills, KillOps);
VRM.RemoveMachineInstrFromMaps(&NextMI);
MBB.erase(&NextMI);
++NumModRefUnfold;
if (NextMII == MBB.end())
break;
} while (FoldsStackSlotModRef(*NextMII, SS, PhysReg, TII, TRI, VRM));
// Store the value back into SS.
TII->storeRegToStackSlot(MBB, NextMII, PhysReg, true, SS, RC);
MachineInstr *StoreMI = prior(NextMII);
VRM.addSpillSlotUse(SS, StoreMI);
VRM.virtFolded(VirtReg, StoreMI, VirtRegMap::isMod);
return true;
}
/// OptimizeByUnfold - Turn a store folding instruction into a load folding
/// instruction. e.g.
/// xorl %edi, %eax
/// movl %eax, -32(%ebp)
/// movl -36(%ebp), %eax
/// orl %eax, -32(%ebp)
/// ==>
/// xorl %edi, %eax
/// orl -36(%ebp), %eax
/// mov %eax, -32(%ebp)
/// This enables unfolding optimization for a subsequent instruction which will
/// also eliminate the newly introduced store instruction.
bool OptimizeByUnfold(MachineBasicBlock &MBB,
MachineBasicBlock::iterator &MII,
std::vector<MachineInstr*> &MaybeDeadStores,
AvailableSpills &Spills,
BitVector &RegKills,
std::vector<MachineOperand*> &KillOps,
VirtRegMap &VRM) {
MachineFunction &MF = *MBB.getParent();
MachineInstr &MI = *MII;
unsigned UnfoldedOpc = 0;
unsigned UnfoldPR = 0;
unsigned UnfoldVR = 0;
int FoldedSS = VirtRegMap::NO_STACK_SLOT;
VirtRegMap::MI2VirtMapTy::const_iterator I, End;
for (tie(I, End) = VRM.getFoldedVirts(&MI); I != End; ) {
// Only transform a MI that folds a single register.
if (UnfoldedOpc)
return false;
UnfoldVR = I->second.first;
VirtRegMap::ModRef MR = I->second.second;
// MI2VirtMap be can updated which invalidate the iterator.
// Increment the iterator first.
++I;
if (VRM.isAssignedReg(UnfoldVR))
continue;
// If this reference is not a use, any previous store is now dead.
// Otherwise, the store to this stack slot is not dead anymore.
FoldedSS = VRM.getStackSlot(UnfoldVR);
MachineInstr* DeadStore = MaybeDeadStores[FoldedSS];
if (DeadStore && (MR & VirtRegMap::isModRef)) {
unsigned PhysReg = Spills.getSpillSlotOrReMatPhysReg(FoldedSS);
if (!PhysReg || !DeadStore->readsRegister(PhysReg))
continue;
UnfoldPR = PhysReg;
UnfoldedOpc = TII->getOpcodeAfterMemoryUnfold(MI.getOpcode(),
false, true);
}
}
if (!UnfoldedOpc) {
if (!UnfoldVR)
return false;
// Look for other unfolding opportunities.
return OptimizeByUnfold2(UnfoldVR, FoldedSS, MBB, MII,
MaybeDeadStores, Spills, RegKills, KillOps, VRM);
}
for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI.getOperand(i);
if (!MO.isReg() || MO.getReg() == 0 || !MO.isUse())
continue;
unsigned VirtReg = MO.getReg();
if (TargetRegisterInfo::isPhysicalRegister(VirtReg) || MO.getSubReg())
continue;
if (VRM.isAssignedReg(VirtReg)) {
unsigned PhysReg = VRM.getPhys(VirtReg);
if (PhysReg && TRI->regsOverlap(PhysReg, UnfoldPR))
return false;
} else if (VRM.isReMaterialized(VirtReg))
continue;
int SS = VRM.getStackSlot(VirtReg);
unsigned PhysReg = Spills.getSpillSlotOrReMatPhysReg(SS);
if (PhysReg) {
if (TRI->regsOverlap(PhysReg, UnfoldPR))
return false;
continue;
}
if (VRM.hasPhys(VirtReg)) {
PhysReg = VRM.getPhys(VirtReg);
if (!TRI->regsOverlap(PhysReg, UnfoldPR))
continue;
}
// Ok, we'll need to reload the value into a register which makes
// it impossible to perform the store unfolding optimization later.
// Let's see if it is possible to fold the load if the store is
// unfolded. This allows us to perform the store unfolding
// optimization.
SmallVector<MachineInstr*, 4> NewMIs;
if (TII->unfoldMemoryOperand(MF, &MI, UnfoldVR, false, false, NewMIs)) {
assert(NewMIs.size() == 1);
MachineInstr *NewMI = NewMIs.back();
NewMIs.clear();
int Idx = NewMI->findRegisterUseOperandIdx(VirtReg, false);
assert(Idx != -1);
SmallVector<unsigned, 1> Ops;
Ops.push_back(Idx);
MachineInstr *FoldedMI = TII->foldMemoryOperand(MF, NewMI, Ops, SS);
if (FoldedMI) {
VRM.addSpillSlotUse(SS, FoldedMI);
if (!VRM.hasPhys(UnfoldVR))
VRM.assignVirt2Phys(UnfoldVR, UnfoldPR);
VRM.virtFolded(VirtReg, FoldedMI, VirtRegMap::isRef);
MII = MBB.insert(MII, FoldedMI);
InvalidateKills(MI, TRI, RegKills, KillOps);
VRM.RemoveMachineInstrFromMaps(&MI);
MBB.erase(&MI);
MF.DeleteMachineInstr(NewMI);
return true;
}
MF.DeleteMachineInstr(NewMI);
}
}
return false;
}
/// CommuteChangesDestination - We are looking for r0 = op r1, r2 and
/// where SrcReg is r1 and it is tied to r0. Return true if after
/// commuting this instruction it will be r0 = op r2, r1.
static bool CommuteChangesDestination(MachineInstr *DefMI,
const TargetInstrDesc &TID,
unsigned SrcReg,
const TargetInstrInfo *TII,
unsigned &DstIdx) {
if (TID.getNumDefs() != 1 && TID.getNumOperands() != 3)
return false;
if (!DefMI->getOperand(1).isReg() ||
DefMI->getOperand(1).getReg() != SrcReg)
return false;
unsigned DefIdx;
if (!DefMI->isRegTiedToDefOperand(1, &DefIdx) || DefIdx != 0)
return false;
unsigned SrcIdx1, SrcIdx2;
if (!TII->findCommutedOpIndices(DefMI, SrcIdx1, SrcIdx2))
return false;
if (SrcIdx1 == 1 && SrcIdx2 == 2) {
DstIdx = 2;
return true;
}
return false;
}
/// CommuteToFoldReload -
/// Look for
/// r1 = load fi#1
/// r1 = op r1, r2<kill>
/// store r1, fi#1
///
/// If op is commutable and r2 is killed, then we can xform these to
/// r2 = op r2, fi#1
/// store r2, fi#1
bool CommuteToFoldReload(MachineBasicBlock &MBB,
MachineBasicBlock::iterator &MII,
unsigned VirtReg, unsigned SrcReg, int SS,
AvailableSpills &Spills,
BitVector &RegKills,
std::vector<MachineOperand*> &KillOps,
const TargetRegisterInfo *TRI,
VirtRegMap &VRM) {
if (MII == MBB.begin() || !MII->killsRegister(SrcReg))
return false;
MachineFunction &MF = *MBB.getParent();
MachineInstr &MI = *MII;
MachineBasicBlock::iterator DefMII = prior(MII);
MachineInstr *DefMI = DefMII;
const TargetInstrDesc &TID = DefMI->getDesc();
unsigned NewDstIdx;
if (DefMII != MBB.begin() &&
TID.isCommutable() &&
CommuteChangesDestination(DefMI, TID, SrcReg, TII, NewDstIdx)) {
MachineOperand &NewDstMO = DefMI->getOperand(NewDstIdx);
unsigned NewReg = NewDstMO.getReg();
if (!NewDstMO.isKill() || TRI->regsOverlap(NewReg, SrcReg))
return false;
MachineInstr *ReloadMI = prior(DefMII);
int FrameIdx;
unsigned DestReg = TII->isLoadFromStackSlot(ReloadMI, FrameIdx);
if (DestReg != SrcReg || FrameIdx != SS)
return false;
int UseIdx = DefMI->findRegisterUseOperandIdx(DestReg, false);
if (UseIdx == -1)
return false;
unsigned DefIdx;
if (!MI.isRegTiedToDefOperand(UseIdx, &DefIdx))
return false;
assert(DefMI->getOperand(DefIdx).isReg() &&
DefMI->getOperand(DefIdx).getReg() == SrcReg);
// Now commute def instruction.
MachineInstr *CommutedMI = TII->commuteInstruction(DefMI, true);
if (!CommutedMI)
return false;
SmallVector<unsigned, 1> Ops;
Ops.push_back(NewDstIdx);
MachineInstr *FoldedMI = TII->foldMemoryOperand(MF, CommutedMI, Ops, SS);
// Not needed since foldMemoryOperand returns new MI.
MF.DeleteMachineInstr(CommutedMI);
if (!FoldedMI)
return false;
VRM.addSpillSlotUse(SS, FoldedMI);
VRM.virtFolded(VirtReg, FoldedMI, VirtRegMap::isRef);
// Insert new def MI and spill MI.
const TargetRegisterClass* RC = RegInfo->getRegClass(VirtReg);
TII->storeRegToStackSlot(MBB, &MI, NewReg, true, SS, RC);
MII = prior(MII);
MachineInstr *StoreMI = MII;
VRM.addSpillSlotUse(SS, StoreMI);
VRM.virtFolded(VirtReg, StoreMI, VirtRegMap::isMod);
MII = MBB.insert(MII, FoldedMI); // Update MII to backtrack.
// Delete all 3 old instructions.
InvalidateKills(*ReloadMI, TRI, RegKills, KillOps);
VRM.RemoveMachineInstrFromMaps(ReloadMI);
MBB.erase(ReloadMI);
InvalidateKills(*DefMI, TRI, RegKills, KillOps);
VRM.RemoveMachineInstrFromMaps(DefMI);
MBB.erase(DefMI);
InvalidateKills(MI, TRI, RegKills, KillOps);
VRM.RemoveMachineInstrFromMaps(&MI);
MBB.erase(&MI);
// If NewReg was previously holding value of some SS, it's now clobbered.
// This has to be done now because it's a physical register. When this
// instruction is re-visited, it's ignored.
Spills.ClobberPhysReg(NewReg);
++NumCommutes;
return true;
}
return false;
}
/// SpillRegToStackSlot - Spill a register to a specified stack slot. Check if
/// the last store to the same slot is now dead. If so, remove the last store.
void SpillRegToStackSlot(MachineBasicBlock &MBB,
MachineBasicBlock::iterator &MII,
int Idx, unsigned PhysReg, int StackSlot,
const TargetRegisterClass *RC,
bool isAvailable, MachineInstr *&LastStore,
AvailableSpills &Spills,
SmallSet<MachineInstr*, 4> &ReMatDefs,
BitVector &RegKills,
std::vector<MachineOperand*> &KillOps,
VirtRegMap &VRM) {
MachineBasicBlock::iterator oldNextMII = llvm::next(MII);
TII->storeRegToStackSlot(MBB, llvm::next(MII), PhysReg, true, StackSlot, RC);
MachineInstr *StoreMI = prior(oldNextMII);
VRM.addSpillSlotUse(StackSlot, StoreMI);
DEBUG(dbgs() << "Store:\t" << *StoreMI);
// If there is a dead store to this stack slot, nuke it now.
if (LastStore) {
DEBUG(dbgs() << "Removed dead store:\t" << *LastStore);
++NumDSE;
SmallVector<unsigned, 2> KillRegs;
InvalidateKills(*LastStore, TRI, RegKills, KillOps, &KillRegs);
MachineBasicBlock::iterator PrevMII = LastStore;
bool CheckDef = PrevMII != MBB.begin();
if (CheckDef)
--PrevMII;
VRM.RemoveMachineInstrFromMaps(LastStore);
MBB.erase(LastStore);
if (CheckDef) {
// Look at defs of killed registers on the store. Mark the defs
// as dead since the store has been deleted and they aren't
// being reused.
for (unsigned j = 0, ee = KillRegs.size(); j != ee; ++j) {
bool HasOtherDef = false;
if (InvalidateRegDef(PrevMII, *MII, KillRegs[j], HasOtherDef, TRI)) {
MachineInstr *DeadDef = PrevMII;
if (ReMatDefs.count(DeadDef) && !HasOtherDef) {
// FIXME: This assumes a remat def does not have side effects.
VRM.RemoveMachineInstrFromMaps(DeadDef);
MBB.erase(DeadDef);
++NumDRM;
}
}
}
}
}
// Allow for multi-instruction spill sequences, as on PPC Altivec. Presume
// the last of multiple instructions is the actual store.
LastStore = prior(oldNextMII);
// If the stack slot value was previously available in some other
// register, change it now. Otherwise, make the register available,
// in PhysReg.
Spills.ModifyStackSlotOrReMat(StackSlot);
Spills.ClobberPhysReg(PhysReg);
Spills.addAvailable(StackSlot, PhysReg, isAvailable);
++NumStores;
}
/// isSafeToDelete - Return true if this instruction doesn't produce any side
/// effect and all of its defs are dead.
static bool isSafeToDelete(MachineInstr &MI) {
const TargetInstrDesc &TID = MI.getDesc();
if (TID.mayLoad() || TID.mayStore() || TID.isCall() || TID.isTerminator() ||
TID.isCall() || TID.isBarrier() || TID.isReturn() ||
TID.hasUnmodeledSideEffects())
return false;
for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI.getOperand(i);
if (!MO.isReg() || !MO.getReg())
continue;
if (MO.isDef() && !MO.isDead())
return false;
if (MO.isUse() && MO.isKill())
// FIXME: We can't remove kill markers or else the scavenger will assert.
// An alternative is to add a ADD pseudo instruction to replace kill
// markers.
return false;
}
return true;
}
/// TransferDeadness - A identity copy definition is dead and it's being
/// removed. Find the last def or use and mark it as dead / kill.
void TransferDeadness(MachineBasicBlock *MBB, unsigned CurDist,
unsigned Reg, BitVector &RegKills,
std::vector<MachineOperand*> &KillOps,
VirtRegMap &VRM) {
SmallPtrSet<MachineInstr*, 4> Seens;
SmallVector<std::pair<MachineInstr*, int>,8> Refs;
for (MachineRegisterInfo::reg_iterator RI = RegInfo->reg_begin(Reg),
RE = RegInfo->reg_end(); RI != RE; ++RI) {
MachineInstr *UDMI = &*RI;
if (UDMI->getParent() != MBB)
continue;
DenseMap<MachineInstr*, unsigned>::iterator DI = DistanceMap.find(UDMI);
if (DI == DistanceMap.end() || DI->second > CurDist)
continue;
if (Seens.insert(UDMI))
Refs.push_back(std::make_pair(UDMI, DI->second));
}
if (Refs.empty())
return;
std::sort(Refs.begin(), Refs.end(), RefSorter());
while (!Refs.empty()) {
MachineInstr *LastUDMI = Refs.back().first;
Refs.pop_back();
MachineOperand *LastUD = NULL;
for (unsigned i = 0, e = LastUDMI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = LastUDMI->getOperand(i);
if (!MO.isReg() || MO.getReg() != Reg)
continue;
if (!LastUD || (LastUD->isUse() && MO.isDef()))
LastUD = &MO;
if (LastUDMI->isRegTiedToDefOperand(i))
break;
}
if (LastUD->isDef()) {
// If the instruction has no side effect, delete it and propagate
// backward further. Otherwise, mark is dead and we are done.
if (!isSafeToDelete(*LastUDMI)) {
LastUD->setIsDead();
break;
}
VRM.RemoveMachineInstrFromMaps(LastUDMI);
MBB->erase(LastUDMI);
} else {
LastUD->setIsKill();
RegKills.set(Reg);
KillOps[Reg] = LastUD;
break;
}
}
}
/// rewriteMBB - Keep track of which spills are available even after the
/// register allocator is done with them. If possible, avid reloading vregs.
void RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM,
LiveIntervals *LIs,
AvailableSpills &Spills, BitVector &RegKills,
std::vector<MachineOperand*> &KillOps) {
DEBUG(dbgs() << "\n**** Local spiller rewriting MBB '"
<< MBB.getName() << "':\n");
MachineFunction &MF = *MBB.getParent();
// MaybeDeadStores - When we need to write a value back into a stack slot,
// keep track of the inserted store. If the stack slot value is never read
// (because the value was used from some available register, for example), and
// subsequently stored to, the original store is dead. This map keeps track
// of inserted stores that are not used. If we see a subsequent store to the
// same stack slot, the original store is deleted.
std::vector<MachineInstr*> MaybeDeadStores;
MaybeDeadStores.resize(MF.getFrameInfo()->getObjectIndexEnd(), NULL);
// ReMatDefs - These are rematerializable def MIs which are not deleted.
SmallSet<MachineInstr*, 4> ReMatDefs;
// Clear kill info.
SmallSet<unsigned, 2> KilledMIRegs;
RegKills.reset();
KillOps.clear();
KillOps.resize(TRI->getNumRegs(), NULL);
unsigned Dist = 0;
DistanceMap.clear();
for (MachineBasicBlock::iterator MII = MBB.begin(), E = MBB.end();
MII != E; ) {
MachineBasicBlock::iterator NextMII = llvm::next(MII);
VirtRegMap::MI2VirtMapTy::const_iterator I, End;
bool Erased = false;
bool BackTracked = false;
if (OptimizeByUnfold(MBB, MII,
MaybeDeadStores, Spills, RegKills, KillOps, VRM))
NextMII = llvm::next(MII);
MachineInstr &MI = *MII;
if (VRM.hasEmergencySpills(&MI)) {
// Spill physical register(s) in the rare case the allocator has run out
// of registers to allocate.
SmallSet<int, 4> UsedSS;
std::vector<unsigned> &EmSpills = VRM.getEmergencySpills(&MI);
for (unsigned i = 0, e = EmSpills.size(); i != e; ++i) {
unsigned PhysReg = EmSpills[i];
const TargetRegisterClass *RC =
TRI->getPhysicalRegisterRegClass(PhysReg);
assert(RC && "Unable to determine register class!");
int SS = VRM.getEmergencySpillSlot(RC);
if (UsedSS.count(SS))
llvm_unreachable("Need to spill more than one physical registers!");
UsedSS.insert(SS);
TII->storeRegToStackSlot(MBB, MII, PhysReg, true, SS, RC);
MachineInstr *StoreMI = prior(MII);
VRM.addSpillSlotUse(SS, StoreMI);
// Back-schedule reloads and remats.
MachineBasicBlock::iterator InsertLoc =
ComputeReloadLoc(llvm::next(MII), MBB.begin(), PhysReg, TRI, false,
SS, TII, MF);
TII->loadRegFromStackSlot(MBB, InsertLoc, PhysReg, SS, RC);
MachineInstr *LoadMI = prior(InsertLoc);
VRM.addSpillSlotUse(SS, LoadMI);
++NumPSpills;
DistanceMap.insert(std::make_pair(LoadMI, Dist++));
}
NextMII = llvm::next(MII);
}
// Insert restores here if asked to.
if (VRM.isRestorePt(&MI)) {
std::vector<unsigned> &RestoreRegs = VRM.getRestorePtRestores(&MI);
for (unsigned i = 0, e = RestoreRegs.size(); i != e; ++i) {
unsigned VirtReg = RestoreRegs[e-i-1]; // Reverse order.
if (!VRM.getPreSplitReg(VirtReg))
continue; // Split interval spilled again.
unsigned Phys = VRM.getPhys(VirtReg);
RegInfo->setPhysRegUsed(Phys);
// Check if the value being restored if available. If so, it must be
// from a predecessor BB that fallthrough into this BB. We do not
// expect:
// BB1:
// r1 = load fi#1
// ...
// = r1<kill>
// ... # r1 not clobbered
// ...
// = load fi#1
bool DoReMat = VRM.isReMaterialized(VirtReg);
int SSorRMId = DoReMat
? VRM.getReMatId(VirtReg) : VRM.getStackSlot(VirtReg);
const TargetRegisterClass* RC = RegInfo->getRegClass(VirtReg);
unsigned InReg = Spills.getSpillSlotOrReMatPhysReg(SSorRMId);
if (InReg == Phys) {
// If the value is already available in the expected register, save
// a reload / remat.
if (SSorRMId)
DEBUG(dbgs() << "Reusing RM#"
<< SSorRMId-VirtRegMap::MAX_STACK_SLOT-1);
else
DEBUG(dbgs() << "Reusing SS#" << SSorRMId);
DEBUG(dbgs() << " from physreg "
<< TRI->getName(InReg) << " for vreg"
<< VirtReg <<" instead of reloading into physreg "
<< TRI->getName(Phys) << '\n');
++NumOmitted;
continue;
} else if (InReg && InReg != Phys) {
if (SSorRMId)
DEBUG(dbgs() << "Reusing RM#"
<< SSorRMId-VirtRegMap::MAX_STACK_SLOT-1);
else
DEBUG(dbgs() << "Reusing SS#" << SSorRMId);
DEBUG(dbgs() << " from physreg "
<< TRI->getName(InReg) << " for vreg"
<< VirtReg <<" by copying it into physreg "
<< TRI->getName(Phys) << '\n');
// If the reloaded / remat value is available in another register,
// copy it to the desired register.
// Back-schedule reloads and remats.
MachineBasicBlock::iterator InsertLoc =
ComputeReloadLoc(MII, MBB.begin(), Phys, TRI, DoReMat,
SSorRMId, TII, MF);
TII->copyRegToReg(MBB, InsertLoc, Phys, InReg, RC, RC);
// This invalidates Phys.
Spills.ClobberPhysReg(Phys);
// Remember it's available.
Spills.addAvailable(SSorRMId, Phys);
// Mark is killed.
MachineInstr *CopyMI = prior(InsertLoc);
CopyMI->setAsmPrinterFlag(AsmPrinter::ReloadReuse);
MachineOperand *KillOpnd = CopyMI->findRegisterUseOperand(InReg);
KillOpnd->setIsKill();
UpdateKills(*CopyMI, TRI, RegKills, KillOps);
DEBUG(dbgs() << '\t' << *CopyMI);
++NumCopified;
continue;
}
// Back-schedule reloads and remats.
MachineBasicBlock::iterator InsertLoc =
ComputeReloadLoc(MII, MBB.begin(), Phys, TRI, DoReMat,
SSorRMId, TII, MF);
if (VRM.isReMaterialized(VirtReg)) {
ReMaterialize(MBB, InsertLoc, Phys, VirtReg, TII, TRI, VRM);
} else {
const TargetRegisterClass* RC = RegInfo->getRegClass(VirtReg);
TII->loadRegFromStackSlot(MBB, InsertLoc, Phys, SSorRMId, RC);
MachineInstr *LoadMI = prior(InsertLoc);
VRM.addSpillSlotUse(SSorRMId, LoadMI);
++NumLoads;
DistanceMap.insert(std::make_pair(LoadMI, Dist++));
}
// This invalidates Phys.
Spills.ClobberPhysReg(Phys);
// Remember it's available.
Spills.addAvailable(SSorRMId, Phys);
UpdateKills(*prior(InsertLoc), TRI, RegKills, KillOps);
DEBUG(dbgs() << '\t' << *prior(MII));
}
}
// Insert spills here if asked to.
if (VRM.isSpillPt(&MI)) {
std::vector<std::pair<unsigned,bool> > &SpillRegs =
VRM.getSpillPtSpills(&MI);
for (unsigned i = 0, e = SpillRegs.size(); i != e; ++i) {
unsigned VirtReg = SpillRegs[i].first;
bool isKill = SpillRegs[i].second;
if (!VRM.getPreSplitReg(VirtReg))
continue; // Split interval spilled again.
const TargetRegisterClass *RC = RegInfo->getRegClass(VirtReg);
unsigned Phys = VRM.getPhys(VirtReg);
int StackSlot = VRM.getStackSlot(VirtReg);
MachineBasicBlock::iterator oldNextMII = llvm::next(MII);
TII->storeRegToStackSlot(MBB, llvm::next(MII), Phys, isKill, StackSlot, RC);
MachineInstr *StoreMI = prior(oldNextMII);
VRM.addSpillSlotUse(StackSlot, StoreMI);
DEBUG(dbgs() << "Store:\t" << *StoreMI);
VRM.virtFolded(VirtReg, StoreMI, VirtRegMap::isMod);
}
NextMII = llvm::next(MII);
}
/// ReusedOperands - Keep track of operand reuse in case we need to undo
/// reuse.
ReuseInfo ReusedOperands(MI, TRI);
SmallVector<unsigned, 4> VirtUseOps;
for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI.getOperand(i);
if (!MO.isReg() || MO.getReg() == 0)
continue; // Ignore non-register operands.
unsigned VirtReg = MO.getReg();
if (TargetRegisterInfo::isPhysicalRegister(VirtReg)) {
// Ignore physregs for spilling, but remember that it is used by this
// function.
RegInfo->setPhysRegUsed(VirtReg);
continue;
}
// We want to process implicit virtual register uses first.
if (MO.isImplicit())
// If the virtual register is implicitly defined, emit a implicit_def
// before so scavenger knows it's "defined".
// FIXME: This is a horrible hack done the by register allocator to
// remat a definition with virtual register operand.
VirtUseOps.insert(VirtUseOps.begin(), i);
else
VirtUseOps.push_back(i);
}
// Process all of the spilled uses and all non spilled reg references.
SmallVector<int, 2> PotentialDeadStoreSlots;
KilledMIRegs.clear();
for (unsigned j = 0, e = VirtUseOps.size(); j != e; ++j) {
unsigned i = VirtUseOps[j];
MachineOperand &MO = MI.getOperand(i);
unsigned VirtReg = MO.getReg();
assert(TargetRegisterInfo::isVirtualRegister(VirtReg) &&
"Not a virtual register?");
unsigned SubIdx = MO.getSubReg();
if (VRM.isAssignedReg(VirtReg)) {
// This virtual register was assigned a physreg!
unsigned Phys = VRM.getPhys(VirtReg);
RegInfo->setPhysRegUsed(Phys);
if (MO.isDef())
ReusedOperands.markClobbered(Phys);
substitutePhysReg(MO, Phys, *TRI);
if (VRM.isImplicitlyDefined(VirtReg))
// FIXME: Is this needed?
BuildMI(MBB, &MI, MI.getDebugLoc(),
TII->get(TargetInstrInfo::IMPLICIT_DEF), Phys);
continue;
}
// This virtual register is now known to be a spilled value.
if (!MO.isUse())
continue; // Handle defs in the loop below (handle use&def here though)
bool AvoidReload = MO.isUndef();
// Check if it is defined by an implicit def. It should not be spilled.
// Note, this is for correctness reason. e.g.
// 8 %reg1024<def> = IMPLICIT_DEF
// 12 %reg1024<def> = INSERT_SUBREG %reg1024<kill>, %reg1025, 2
// The live range [12, 14) are not part of the r1024 live interval since
// it's defined by an implicit def. It will not conflicts with live
// interval of r1025. Now suppose both registers are spilled, you can
// easily see a situation where both registers are reloaded before
// the INSERT_SUBREG and both target registers that would overlap.
bool DoReMat = VRM.isReMaterialized(VirtReg);
int SSorRMId = DoReMat
? VRM.getReMatId(VirtReg) : VRM.getStackSlot(VirtReg);
int ReuseSlot = SSorRMId;
// Check to see if this stack slot is available.
unsigned PhysReg = Spills.getSpillSlotOrReMatPhysReg(SSorRMId);
// If this is a sub-register use, make sure the reuse register is in the
// right register class. For example, for x86 not all of the 32-bit
// registers have accessible sub-registers.
// Similarly so for EXTRACT_SUBREG. Consider this:
// EDI = op
// MOV32_mr fi#1, EDI
// ...
// = EXTRACT_SUBREG fi#1
// fi#1 is available in EDI, but it cannot be reused because it's not in
// the right register file.
if (PhysReg && !AvoidReload &&
(SubIdx || MI.getOpcode() == TargetInstrInfo::EXTRACT_SUBREG)) {
const TargetRegisterClass* RC = RegInfo->getRegClass(VirtReg);
if (!RC->contains(PhysReg))
PhysReg = 0;
}
if (PhysReg && !AvoidReload) {
// This spilled operand might be part of a two-address operand. If this
// is the case, then changing it will necessarily require changing the
// def part of the instruction as well. However, in some cases, we
// aren't allowed to modify the reused register. If none of these cases
// apply, reuse it.
bool CanReuse = true;
bool isTied = MI.isRegTiedToDefOperand(i);
if (isTied) {
// Okay, we have a two address operand. We can reuse this physreg as
// long as we are allowed to clobber the value and there isn't an
// earlier def that has already clobbered the physreg.
CanReuse = !ReusedOperands.isClobbered(PhysReg) &&
Spills.canClobberPhysReg(PhysReg);
}
if (CanReuse) {
// If this stack slot value is already available, reuse it!
if (ReuseSlot > VirtRegMap::MAX_STACK_SLOT)
DEBUG(dbgs() << "Reusing RM#"
<< ReuseSlot-VirtRegMap::MAX_STACK_SLOT-1);
else
DEBUG(dbgs() << "Reusing SS#" << ReuseSlot);
DEBUG(dbgs() << " from physreg "
<< TRI->getName(PhysReg) << " for vreg"
<< VirtReg <<" instead of reloading into physreg "
<< TRI->getName(VRM.getPhys(VirtReg)) << '\n');
unsigned RReg = SubIdx ? TRI->getSubReg(PhysReg, SubIdx) : PhysReg;
MI.getOperand(i).setReg(RReg);
MI.getOperand(i).setSubReg(0);
// The only technical detail we have is that we don't know that
// PhysReg won't be clobbered by a reloaded stack slot that occurs
// later in the instruction. In particular, consider 'op V1, V2'.
// If V1 is available in physreg R0, we would choose to reuse it
// here, instead of reloading it into the register the allocator
// indicated (say R1). However, V2 might have to be reloaded
// later, and it might indicate that it needs to live in R0. When
// this occurs, we need to have information available that
// indicates it is safe to use R1 for the reload instead of R0.
//
// To further complicate matters, we might conflict with an alias,
// or R0 and R1 might not be compatible with each other. In this
// case, we actually insert a reload for V1 in R1, ensuring that
// we can get at R0 or its alias.
ReusedOperands.addReuse(i, ReuseSlot, PhysReg,
VRM.getPhys(VirtReg), VirtReg);
if (isTied)
// Only mark it clobbered if this is a use&def operand.
ReusedOperands.markClobbered(PhysReg);
++NumReused;
if (MI.getOperand(i).isKill() &&
ReuseSlot <= VirtRegMap::MAX_STACK_SLOT) {
// The store of this spilled value is potentially dead, but we
// won't know for certain until we've confirmed that the re-use
// above is valid, which means waiting until the other operands
// are processed. For now we just track the spill slot, we'll
// remove it after the other operands are processed if valid.
PotentialDeadStoreSlots.push_back(ReuseSlot);
}
// Mark is isKill if it's there no other uses of the same virtual
// register and it's not a two-address operand. IsKill will be
// unset if reg is reused.
if (!isTied && KilledMIRegs.count(VirtReg) == 0) {
MI.getOperand(i).setIsKill();
KilledMIRegs.insert(VirtReg);
}
continue;
} // CanReuse
// Otherwise we have a situation where we have a two-address instruction
// whose mod/ref operand needs to be reloaded. This reload is already
// available in some register "PhysReg", but if we used PhysReg as the
// operand to our 2-addr instruction, the instruction would modify
// PhysReg. This isn't cool if something later uses PhysReg and expects
// to get its initial value.
//
// To avoid this problem, and to avoid doing a load right after a store,
// we emit a copy from PhysReg into the designated register for this
// operand.
unsigned DesignatedReg = VRM.getPhys(VirtReg);
assert(DesignatedReg && "Must map virtreg to physreg!");
// Note that, if we reused a register for a previous operand, the
// register we want to reload into might not actually be
// available. If this occurs, use the register indicated by the
// reuser.
if (ReusedOperands.hasReuses())
DesignatedReg = ReusedOperands.GetRegForReload(VirtReg,
DesignatedReg, &MI,
Spills, MaybeDeadStores, RegKills, KillOps, VRM);
// If the mapped designated register is actually the physreg we have
// incoming, we don't need to inserted a dead copy.
if (DesignatedReg == PhysReg) {
// If this stack slot value is already available, reuse it!
if (ReuseSlot > VirtRegMap::MAX_STACK_SLOT)
DEBUG(dbgs() << "Reusing RM#"
<< ReuseSlot-VirtRegMap::MAX_STACK_SLOT-1);
else
DEBUG(dbgs() << "Reusing SS#" << ReuseSlot);
DEBUG(dbgs() << " from physreg " << TRI->getName(PhysReg)
<< " for vreg" << VirtReg
<< " instead of reloading into same physreg.\n");
unsigned RReg = SubIdx ? TRI->getSubReg(PhysReg, SubIdx) : PhysReg;
MI.getOperand(i).setReg(RReg);
MI.getOperand(i).setSubReg(0);
ReusedOperands.markClobbered(RReg);
++NumReused;
continue;
}
const TargetRegisterClass* RC = RegInfo->getRegClass(VirtReg);
RegInfo->setPhysRegUsed(DesignatedReg);
ReusedOperands.markClobbered(DesignatedReg);
// Back-schedule reloads and remats.
MachineBasicBlock::iterator InsertLoc =
ComputeReloadLoc(&MI, MBB.begin(), PhysReg, TRI, DoReMat,
SSorRMId, TII, MF);
TII->copyRegToReg(MBB, InsertLoc, DesignatedReg, PhysReg, RC, RC);
MachineInstr *CopyMI = prior(InsertLoc);
CopyMI->setAsmPrinterFlag(AsmPrinter::ReloadReuse);
UpdateKills(*CopyMI, TRI, RegKills, KillOps);
// This invalidates DesignatedReg.
Spills.ClobberPhysReg(DesignatedReg);
Spills.addAvailable(ReuseSlot, DesignatedReg);
unsigned RReg =
SubIdx ? TRI->getSubReg(DesignatedReg, SubIdx) : DesignatedReg;
MI.getOperand(i).setReg(RReg);
MI.getOperand(i).setSubReg(0);
DEBUG(dbgs() << '\t' << *prior(MII));
++NumReused;
continue;
} // if (PhysReg)
// Otherwise, reload it and remember that we have it.
PhysReg = VRM.getPhys(VirtReg);
assert(PhysReg && "Must map virtreg to physreg!");
// Note that, if we reused a register for a previous operand, the
// register we want to reload into might not actually be
// available. If this occurs, use the register indicated by the
// reuser.
if (ReusedOperands.hasReuses())
PhysReg = ReusedOperands.GetRegForReload(VirtReg, PhysReg, &MI,
Spills, MaybeDeadStores, RegKills, KillOps, VRM);
RegInfo->setPhysRegUsed(PhysReg);
ReusedOperands.markClobbered(PhysReg);
if (AvoidReload)
++NumAvoided;
else {
// Back-schedule reloads and remats.
MachineBasicBlock::iterator InsertLoc =
ComputeReloadLoc(MII, MBB.begin(), PhysReg, TRI, DoReMat,
SSorRMId, TII, MF);
if (DoReMat) {
ReMaterialize(MBB, InsertLoc, PhysReg, VirtReg, TII, TRI, VRM);
} else {
const TargetRegisterClass* RC = RegInfo->getRegClass(VirtReg);
TII->loadRegFromStackSlot(MBB, InsertLoc, PhysReg, SSorRMId, RC);
MachineInstr *LoadMI = prior(InsertLoc);
VRM.addSpillSlotUse(SSorRMId, LoadMI);
++NumLoads;
DistanceMap.insert(std::make_pair(LoadMI, Dist++));
}
// This invalidates PhysReg.
Spills.ClobberPhysReg(PhysReg);
// Any stores to this stack slot are not dead anymore.
if (!DoReMat)
MaybeDeadStores[SSorRMId] = NULL;
Spills.addAvailable(SSorRMId, PhysReg);
// Assumes this is the last use. IsKill will be unset if reg is reused
// unless it's a two-address operand.
if (!MI.isRegTiedToDefOperand(i) &&
KilledMIRegs.count(VirtReg) == 0) {
MI.getOperand(i).setIsKill();
KilledMIRegs.insert(VirtReg);
}
UpdateKills(*prior(InsertLoc), TRI, RegKills, KillOps);
DEBUG(dbgs() << '\t' << *prior(InsertLoc));
}
unsigned RReg = SubIdx ? TRI->getSubReg(PhysReg, SubIdx) : PhysReg;
MI.getOperand(i).setReg(RReg);
MI.getOperand(i).setSubReg(0);
}
// Ok - now we can remove stores that have been confirmed dead.
for (unsigned j = 0, e = PotentialDeadStoreSlots.size(); j != e; ++j) {
// This was the last use and the spilled value is still available
// for reuse. That means the spill was unnecessary!
int PDSSlot = PotentialDeadStoreSlots[j];
MachineInstr* DeadStore = MaybeDeadStores[PDSSlot];
if (DeadStore) {
DEBUG(dbgs() << "Removed dead store:\t" << *DeadStore);
InvalidateKills(*DeadStore, TRI, RegKills, KillOps);
VRM.RemoveMachineInstrFromMaps(DeadStore);
MBB.erase(DeadStore);
MaybeDeadStores[PDSSlot] = NULL;
++NumDSE;
}
}
DEBUG(dbgs() << '\t' << MI);
// If we have folded references to memory operands, make sure we clear all
// physical registers that may contain the value of the spilled virtual
// register
SmallSet<int, 2> FoldedSS;
for (tie(I, End) = VRM.getFoldedVirts(&MI); I != End; ) {
unsigned VirtReg = I->second.first;
VirtRegMap::ModRef MR = I->second.second;
DEBUG(dbgs() << "Folded vreg: " << VirtReg << " MR: " << MR);
// MI2VirtMap be can updated which invalidate the iterator.
// Increment the iterator first.
++I;
int SS = VRM.getStackSlot(VirtReg);
if (SS == VirtRegMap::NO_STACK_SLOT)
continue;
FoldedSS.insert(SS);
DEBUG(dbgs() << " - StackSlot: " << SS << "\n");
// If this folded instruction is just a use, check to see if it's a
// straight load from the virt reg slot.
if ((MR & VirtRegMap::isRef) && !(MR & VirtRegMap::isMod)) {
int FrameIdx;
unsigned DestReg = TII->isLoadFromStackSlot(&MI, FrameIdx);
if (DestReg && FrameIdx == SS) {
// If this spill slot is available, turn it into a copy (or nothing)
// instead of leaving it as a load!
if (unsigned InReg = Spills.getSpillSlotOrReMatPhysReg(SS)) {
DEBUG(dbgs() << "Promoted Load To Copy: " << MI);
if (DestReg != InReg) {
const TargetRegisterClass *RC = RegInfo->getRegClass(VirtReg);
TII->copyRegToReg(MBB, &MI, DestReg, InReg, RC, RC);
MachineOperand *DefMO = MI.findRegisterDefOperand(DestReg);
unsigned SubIdx = DefMO->getSubReg();
// Revisit the copy so we make sure to notice the effects of the
// operation on the destreg (either needing to RA it if it's
// virtual or needing to clobber any values if it's physical).
NextMII = &MI;
--NextMII; // backtrack to the copy.
NextMII->setAsmPrinterFlag(AsmPrinter::ReloadReuse);
// Propagate the sub-register index over.
if (SubIdx) {
DefMO = NextMII->findRegisterDefOperand(DestReg);
DefMO->setSubReg(SubIdx);
}
// Mark is killed.
MachineOperand *KillOpnd = NextMII->findRegisterUseOperand(InReg);
KillOpnd->setIsKill();
BackTracked = true;
} else {
DEBUG(dbgs() << "Removing now-noop copy: " << MI);
// Unset last kill since it's being reused.
InvalidateKill(InReg, TRI, RegKills, KillOps);
Spills.disallowClobberPhysReg(InReg);
}
InvalidateKills(MI, TRI, RegKills, KillOps);
VRM.RemoveMachineInstrFromMaps(&MI);
MBB.erase(&MI);
Erased = true;
goto ProcessNextInst;
}
} else {
unsigned PhysReg = Spills.getSpillSlotOrReMatPhysReg(SS);
SmallVector<MachineInstr*, 4> NewMIs;
if (PhysReg &&
TII->unfoldMemoryOperand(MF, &MI, PhysReg, false, false, NewMIs)) {
MBB.insert(MII, NewMIs[0]);
InvalidateKills(MI, TRI, RegKills, KillOps);
VRM.RemoveMachineInstrFromMaps(&MI);
MBB.erase(&MI);
Erased = true;
--NextMII; // backtrack to the unfolded instruction.
BackTracked = true;
goto ProcessNextInst;
}
}
}
// If this reference is not a use, any previous store is now dead.
// Otherwise, the store to this stack slot is not dead anymore.
MachineInstr* DeadStore = MaybeDeadStores[SS];
if (DeadStore) {
bool isDead = !(MR & VirtRegMap::isRef);
MachineInstr *NewStore = NULL;
if (MR & VirtRegMap::isModRef) {
unsigned PhysReg = Spills.getSpillSlotOrReMatPhysReg(SS);
SmallVector<MachineInstr*, 4> NewMIs;
// We can reuse this physreg as long as we are allowed to clobber
// the value and there isn't an earlier def that has already clobbered
// the physreg.
if (PhysReg &&
!ReusedOperands.isClobbered(PhysReg) &&
Spills.canClobberPhysReg(PhysReg) &&
!TII->isStoreToStackSlot(&MI, SS)) { // Not profitable!
MachineOperand *KillOpnd =
DeadStore->findRegisterUseOperand(PhysReg, true);
// Note, if the store is storing a sub-register, it's possible the
// super-register is needed below.
if (KillOpnd && !KillOpnd->getSubReg() &&
TII->unfoldMemoryOperand(MF, &MI, PhysReg, false, true,NewMIs)){
MBB.insert(MII, NewMIs[0]);
NewStore = NewMIs[1];
MBB.insert(MII, NewStore);
VRM.addSpillSlotUse(SS, NewStore);
InvalidateKills(MI, TRI, RegKills, KillOps);
VRM.RemoveMachineInstrFromMaps(&MI);
MBB.erase(&MI);
Erased = true;
--NextMII;
--NextMII; // backtrack to the unfolded instruction.
BackTracked = true;
isDead = true;
++NumSUnfold;
}
}
}
if (isDead) { // Previous store is dead.
// If we get here, the store is dead, nuke it now.
DEBUG(dbgs() << "Removed dead store:\t" << *DeadStore);
InvalidateKills(*DeadStore, TRI, RegKills, KillOps);
VRM.RemoveMachineInstrFromMaps(DeadStore);
MBB.erase(DeadStore);
if (!NewStore)
++NumDSE;
}
MaybeDeadStores[SS] = NULL;
if (NewStore) {
// Treat this store as a spill merged into a copy. That makes the
// stack slot value available.
VRM.virtFolded(VirtReg, NewStore, VirtRegMap::isMod);
goto ProcessNextInst;
}
}
// If the spill slot value is available, and this is a new definition of
// the value, the value is not available anymore.
if (MR & VirtRegMap::isMod) {
// Notice that the value in this stack slot has been modified.
Spills.ModifyStackSlotOrReMat(SS);
// If this is *just* a mod of the value, check to see if this is just a
// store to the spill slot (i.e. the spill got merged into the copy). If
// so, realize that the vreg is available now, and add the store to the
// MaybeDeadStore info.
int StackSlot;
if (!(MR & VirtRegMap::isRef)) {
if (unsigned SrcReg = TII->isStoreToStackSlot(&MI, StackSlot)) {
assert(TargetRegisterInfo::isPhysicalRegister(SrcReg) &&
"Src hasn't been allocated yet?");
if (CommuteToFoldReload(MBB, MII, VirtReg, SrcReg, StackSlot,
Spills, RegKills, KillOps, TRI, VRM)) {
NextMII = llvm::next(MII);
BackTracked = true;
goto ProcessNextInst;
}
// Okay, this is certainly a store of SrcReg to [StackSlot]. Mark
// this as a potentially dead store in case there is a subsequent
// store into the stack slot without a read from it.
MaybeDeadStores[StackSlot] = &MI;
// If the stack slot value was previously available in some other
// register, change it now. Otherwise, make the register
// available in PhysReg.
Spills.addAvailable(StackSlot, SrcReg, MI.killsRegister(SrcReg));
}
}
}
}
// Process all of the spilled defs.
for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI.getOperand(i);
if (!(MO.isReg() && MO.getReg() && MO.isDef()))
continue;
unsigned VirtReg = MO.getReg();
if (!TargetRegisterInfo::isVirtualRegister(VirtReg)) {
// Check to see if this is a noop copy. If so, eliminate the
// instruction before considering the dest reg to be changed.
// Also check if it's copying from an "undef", if so, we can't
// eliminate this or else the undef marker is lost and it will
// confuses the scavenger. This is extremely rare.
unsigned Src, Dst, SrcSR, DstSR;
if (TII->isMoveInstr(MI, Src, Dst, SrcSR, DstSR) && Src == Dst &&
!MI.findRegisterUseOperand(Src)->isUndef()) {
++NumDCE;
DEBUG(dbgs() << "Removing now-noop copy: " << MI);
SmallVector<unsigned, 2> KillRegs;
InvalidateKills(MI, TRI, RegKills, KillOps, &KillRegs);
if (MO.isDead() && !KillRegs.empty()) {
// Source register or an implicit super/sub-register use is killed.
assert(KillRegs[0] == Dst ||
TRI->isSubRegister(KillRegs[0], Dst) ||
TRI->isSuperRegister(KillRegs[0], Dst));
// Last def is now dead.
TransferDeadness(&MBB, Dist, Src, RegKills, KillOps, VRM);
}
VRM.RemoveMachineInstrFromMaps(&MI);
MBB.erase(&MI);
Erased = true;
Spills.disallowClobberPhysReg(VirtReg);
goto ProcessNextInst;
}
// If it's not a no-op copy, it clobbers the value in the destreg.
Spills.ClobberPhysReg(VirtReg);
ReusedOperands.markClobbered(VirtReg);
// Check to see if this instruction is a load from a stack slot into
// a register. If so, this provides the stack slot value in the reg.
int FrameIdx;
if (unsigned DestReg = TII->isLoadFromStackSlot(&MI, FrameIdx)) {
assert(DestReg == VirtReg && "Unknown load situation!");
// If it is a folded reference, then it's not safe to clobber.
bool Folded = FoldedSS.count(FrameIdx);
// Otherwise, if it wasn't available, remember that it is now!
Spills.addAvailable(FrameIdx, DestReg, !Folded);
goto ProcessNextInst;
}
continue;
}
unsigned SubIdx = MO.getSubReg();
bool DoReMat = VRM.isReMaterialized(VirtReg);
if (DoReMat)
ReMatDefs.insert(&MI);
// The only vregs left are stack slot definitions.
int StackSlot = VRM.getStackSlot(VirtReg);
const TargetRegisterClass *RC = RegInfo->getRegClass(VirtReg);
// If this def is part of a two-address operand, make sure to execute
// the store from the correct physical register.
unsigned PhysReg;
unsigned TiedOp;
if (MI.isRegTiedToUseOperand(i, &TiedOp)) {
PhysReg = MI.getOperand(TiedOp).getReg();
if (SubIdx) {
unsigned SuperReg = findSuperReg(RC, PhysReg, SubIdx, TRI);
assert(SuperReg && TRI->getSubReg(SuperReg, SubIdx) == PhysReg &&
"Can't find corresponding super-register!");
PhysReg = SuperReg;
}
} else {
PhysReg = VRM.getPhys(VirtReg);
if (ReusedOperands.isClobbered(PhysReg)) {
// Another def has taken the assigned physreg. It must have been a
// use&def which got it due to reuse. Undo the reuse!
PhysReg = ReusedOperands.GetRegForReload(VirtReg, PhysReg, &MI,
Spills, MaybeDeadStores, RegKills, KillOps, VRM);
}
}
assert(PhysReg && "VR not assigned a physical register?");
RegInfo->setPhysRegUsed(PhysReg);
unsigned RReg = SubIdx ? TRI->getSubReg(PhysReg, SubIdx) : PhysReg;
ReusedOperands.markClobbered(RReg);
MI.getOperand(i).setReg(RReg);
MI.getOperand(i).setSubReg(0);
if (!MO.isDead()) {
MachineInstr *&LastStore = MaybeDeadStores[StackSlot];
SpillRegToStackSlot(MBB, MII, -1, PhysReg, StackSlot, RC, true,
LastStore, Spills, ReMatDefs, RegKills, KillOps, VRM);
NextMII = llvm::next(MII);
// Check to see if this is a noop copy. If so, eliminate the
// instruction before considering the dest reg to be changed.
{
unsigned Src, Dst, SrcSR, DstSR;
if (TII->isMoveInstr(MI, Src, Dst, SrcSR, DstSR) && Src == Dst) {
++NumDCE;
DEBUG(dbgs() << "Removing now-noop copy: " << MI);
InvalidateKills(MI, TRI, RegKills, KillOps);
VRM.RemoveMachineInstrFromMaps(&MI);
MBB.erase(&MI);
Erased = true;
UpdateKills(*LastStore, TRI, RegKills, KillOps);
goto ProcessNextInst;
}
}
}
}
ProcessNextInst:
// Delete dead instructions without side effects.
if (!Erased && !BackTracked && isSafeToDelete(MI)) {
InvalidateKills(MI, TRI, RegKills, KillOps);
VRM.RemoveMachineInstrFromMaps(&MI);
MBB.erase(&MI);
Erased = true;
}
if (!Erased)
DistanceMap.insert(std::make_pair(&MI, Dist++));
if (!Erased && !BackTracked) {
for (MachineBasicBlock::iterator II = &MI; II != NextMII; ++II)
UpdateKills(*II, TRI, RegKills, KillOps);
}
MII = NextMII;
}
}
};
}
llvm::VirtRegRewriter* llvm::createVirtRegRewriter() {
switch (RewriterOpt) {
default: llvm_unreachable("Unreachable!");
case local:
return new LocalRewriter();
case trivial:
return new TrivialRewriter();
}
}
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