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llvm-project/llvm/lib/CodeGen/TwoAddressInstructionPass.cpp

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//===-- TwoAddressInstructionPass.cpp - Two-Address instruction pass ------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the TwoAddress instruction pass which is used
// by most register allocators. Two-Address instructions are rewritten
// from:
//
// A = B op C
//
// to:
//
// A = B
// A op= C
//
// Note that if a register allocator chooses to use this pass, that it
// has to be capable of handling the non-SSA nature of these rewritten
// virtual registers.
//
// It is also worth noting that the duplicate operand of the two
// address instruction is removed.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "twoaddrinstr"
#include "llvm/CodeGen/Passes.h"
#include "llvm/Function.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/LiveVariables.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/MC/MCInstrItineraries.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
using namespace llvm;
STATISTIC(NumTwoAddressInstrs, "Number of two-address instructions");
STATISTIC(NumCommuted , "Number of instructions commuted to coalesce");
STATISTIC(NumAggrCommuted , "Number of instructions aggressively commuted");
STATISTIC(NumConvertedTo3Addr, "Number of instructions promoted to 3-address");
STATISTIC(Num3AddrSunk, "Number of 3-address instructions sunk");
STATISTIC(NumReSchedUps, "Number of instructions re-scheduled up");
STATISTIC(NumReSchedDowns, "Number of instructions re-scheduled down");
namespace {
class TwoAddressInstructionPass : public MachineFunctionPass {
MachineFunction *MF;
const TargetInstrInfo *TII;
const TargetRegisterInfo *TRI;
const InstrItineraryData *InstrItins;
MachineRegisterInfo *MRI;
LiveVariables *LV;
SlotIndexes *Indexes;
LiveIntervals *LIS;
AliasAnalysis *AA;
CodeGenOpt::Level OptLevel;
// DistanceMap - Keep track the distance of a MI from the start of the
// current basic block.
DenseMap<MachineInstr*, unsigned> DistanceMap;
// SrcRegMap - A map from virtual registers to physical registers which
// are likely targets to be coalesced to due to copies from physical
// registers to virtual registers. e.g. v1024 = move r0.
DenseMap<unsigned, unsigned> SrcRegMap;
// DstRegMap - A map from virtual registers to physical registers which
// are likely targets to be coalesced to due to copies to physical
// registers from virtual registers. e.g. r1 = move v1024.
DenseMap<unsigned, unsigned> DstRegMap;
/// RegSequences - Keep track the list of REG_SEQUENCE instructions seen
/// during the initial walk of the machine function.
SmallVector<MachineInstr*, 16> RegSequences;
bool Sink3AddrInstruction(MachineBasicBlock *MBB, MachineInstr *MI,
unsigned Reg,
MachineBasicBlock::iterator OldPos);
bool NoUseAfterLastDef(unsigned Reg, MachineBasicBlock *MBB, unsigned Dist,
unsigned &LastDef);
bool isProfitableToCommute(unsigned regA, unsigned regB, unsigned regC,
MachineInstr *MI, MachineBasicBlock *MBB,
unsigned Dist);
bool CommuteInstruction(MachineBasicBlock::iterator &mi,
MachineFunction::iterator &mbbi,
unsigned RegB, unsigned RegC, unsigned Dist);
bool isProfitableToConv3Addr(unsigned RegA, unsigned RegB);
bool ConvertInstTo3Addr(MachineBasicBlock::iterator &mi,
MachineBasicBlock::iterator &nmi,
MachineFunction::iterator &mbbi,
unsigned RegA, unsigned RegB, unsigned Dist);
bool isDefTooClose(unsigned Reg, unsigned Dist,
MachineInstr *MI, MachineBasicBlock *MBB);
bool RescheduleMIBelowKill(MachineBasicBlock *MBB,
MachineBasicBlock::iterator &mi,
MachineBasicBlock::iterator &nmi,
unsigned Reg);
bool RescheduleKillAboveMI(MachineBasicBlock *MBB,
MachineBasicBlock::iterator &mi,
MachineBasicBlock::iterator &nmi,
unsigned Reg);
bool TryInstructionTransform(MachineBasicBlock::iterator &mi,
MachineBasicBlock::iterator &nmi,
MachineFunction::iterator &mbbi,
unsigned SrcIdx, unsigned DstIdx,
unsigned Dist,
SmallPtrSet<MachineInstr*, 8> &Processed);
void ScanUses(unsigned DstReg, MachineBasicBlock *MBB,
SmallPtrSet<MachineInstr*, 8> &Processed);
void ProcessCopy(MachineInstr *MI, MachineBasicBlock *MBB,
SmallPtrSet<MachineInstr*, 8> &Processed);
typedef SmallVector<std::pair<unsigned, unsigned>, 4> TiedPairList;
typedef SmallDenseMap<unsigned, TiedPairList> TiedOperandMap;
bool collectTiedOperands(MachineInstr *MI, TiedOperandMap&);
void processTiedPairs(MachineInstr *MI, TiedPairList&, unsigned &Dist);
void CoalesceExtSubRegs(SmallVector<unsigned,4> &Srcs, unsigned DstReg);
/// EliminateRegSequences - Eliminate REG_SEQUENCE instructions as part
/// of the de-ssa process. This replaces sources of REG_SEQUENCE as
/// sub-register references of the register defined by REG_SEQUENCE.
bool EliminateRegSequences();
public:
static char ID; // Pass identification, replacement for typeid
TwoAddressInstructionPass() : MachineFunctionPass(ID) {
initializeTwoAddressInstructionPassPass(*PassRegistry::getPassRegistry());
}
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
AU.addRequired<AliasAnalysis>();
AU.addPreserved<LiveVariables>();
AU.addPreserved<SlotIndexes>();
AU.addPreserved<LiveIntervals>();
AU.addPreservedID(MachineLoopInfoID);
AU.addPreservedID(MachineDominatorsID);
MachineFunctionPass::getAnalysisUsage(AU);
}
/// runOnMachineFunction - Pass entry point.
bool runOnMachineFunction(MachineFunction&);
};
}
char TwoAddressInstructionPass::ID = 0;
INITIALIZE_PASS_BEGIN(TwoAddressInstructionPass, "twoaddressinstruction",
"Two-Address instruction pass", false, false)
INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
INITIALIZE_PASS_END(TwoAddressInstructionPass, "twoaddressinstruction",
"Two-Address instruction pass", false, false)
char &llvm::TwoAddressInstructionPassID = TwoAddressInstructionPass::ID;
/// Sink3AddrInstruction - A two-address instruction has been converted to a
/// three-address instruction to avoid clobbering a register. Try to sink it
/// past the instruction that would kill the above mentioned register to reduce
/// register pressure.
bool TwoAddressInstructionPass::Sink3AddrInstruction(MachineBasicBlock *MBB,
MachineInstr *MI, unsigned SavedReg,
MachineBasicBlock::iterator OldPos) {
// FIXME: Shouldn't we be trying to do this before we three-addressify the
// instruction? After this transformation is done, we no longer need
// the instruction to be in three-address form.
// Check if it's safe to move this instruction.
bool SeenStore = true; // Be conservative.
if (!MI->isSafeToMove(TII, AA, SeenStore))
return false;
unsigned DefReg = 0;
SmallSet<unsigned, 4> UseRegs;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg())
continue;
unsigned MOReg = MO.getReg();
if (!MOReg)
continue;
if (MO.isUse() && MOReg != SavedReg)
UseRegs.insert(MO.getReg());
if (!MO.isDef())
continue;
if (MO.isImplicit())
// Don't try to move it if it implicitly defines a register.
return false;
if (DefReg)
// For now, don't move any instructions that define multiple registers.
return false;
DefReg = MO.getReg();
}
// Find the instruction that kills SavedReg.
MachineInstr *KillMI = NULL;
for (MachineRegisterInfo::use_nodbg_iterator
UI = MRI->use_nodbg_begin(SavedReg),
UE = MRI->use_nodbg_end(); UI != UE; ++UI) {
MachineOperand &UseMO = UI.getOperand();
if (!UseMO.isKill())
continue;
KillMI = UseMO.getParent();
break;
}
// If we find the instruction that kills SavedReg, and it is in an
// appropriate location, we can try to sink the current instruction
// past it.
if (!KillMI || KillMI->getParent() != MBB || KillMI == MI ||
KillMI == OldPos || KillMI->isTerminator())
return false;
// If any of the definitions are used by another instruction between the
// position and the kill use, then it's not safe to sink it.
//
// FIXME: This can be sped up if there is an easy way to query whether an
// instruction is before or after another instruction. Then we can use
// MachineRegisterInfo def / use instead.
MachineOperand *KillMO = NULL;
MachineBasicBlock::iterator KillPos = KillMI;
++KillPos;
unsigned NumVisited = 0;
for (MachineBasicBlock::iterator I = llvm::next(OldPos); I != KillPos; ++I) {
MachineInstr *OtherMI = I;
// DBG_VALUE cannot be counted against the limit.
if (OtherMI->isDebugValue())
continue;
if (NumVisited > 30) // FIXME: Arbitrary limit to reduce compile time cost.
return false;
++NumVisited;
for (unsigned i = 0, e = OtherMI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = OtherMI->getOperand(i);
if (!MO.isReg())
continue;
unsigned MOReg = MO.getReg();
if (!MOReg)
continue;
if (DefReg == MOReg)
return false;
if (MO.isKill()) {
if (OtherMI == KillMI && MOReg == SavedReg)
// Save the operand that kills the register. We want to unset the kill
// marker if we can sink MI past it.
KillMO = &MO;
else if (UseRegs.count(MOReg))
// One of the uses is killed before the destination.
return false;
}
}
}
assert(KillMO && "Didn't find kill");
// Update kill and LV information.
KillMO->setIsKill(false);
KillMO = MI->findRegisterUseOperand(SavedReg, false, TRI);
KillMO->setIsKill(true);
if (LV)
LV->replaceKillInstruction(SavedReg, KillMI, MI);
// Move instruction to its destination.
MBB->remove(MI);
MBB->insert(KillPos, MI);
if (LIS)
LIS->handleMove(MI);
++Num3AddrSunk;
return true;
}
/// NoUseAfterLastDef - Return true if there are no intervening uses between the
/// last instruction in the MBB that defines the specified register and the
/// two-address instruction which is being processed. It also returns the last
/// def location by reference
bool TwoAddressInstructionPass::NoUseAfterLastDef(unsigned Reg,
MachineBasicBlock *MBB, unsigned Dist,
unsigned &LastDef) {
LastDef = 0;
unsigned LastUse = Dist;
for (MachineRegisterInfo::reg_iterator I = MRI->reg_begin(Reg),
E = MRI->reg_end(); I != E; ++I) {
MachineOperand &MO = I.getOperand();
MachineInstr *MI = MO.getParent();
if (MI->getParent() != MBB || MI->isDebugValue())
continue;
DenseMap<MachineInstr*, unsigned>::iterator DI = DistanceMap.find(MI);
if (DI == DistanceMap.end())
continue;
if (MO.isUse() && DI->second < LastUse)
LastUse = DI->second;
if (MO.isDef() && DI->second > LastDef)
LastDef = DI->second;
}
return !(LastUse > LastDef && LastUse < Dist);
}
/// isCopyToReg - Return true if the specified MI is a copy instruction or
/// a extract_subreg instruction. It also returns the source and destination
/// registers and whether they are physical registers by reference.
static bool isCopyToReg(MachineInstr &MI, const TargetInstrInfo *TII,
unsigned &SrcReg, unsigned &DstReg,
bool &IsSrcPhys, bool &IsDstPhys) {
SrcReg = 0;
DstReg = 0;
if (MI.isCopy()) {
DstReg = MI.getOperand(0).getReg();
SrcReg = MI.getOperand(1).getReg();
} else if (MI.isInsertSubreg() || MI.isSubregToReg()) {
DstReg = MI.getOperand(0).getReg();
SrcReg = MI.getOperand(2).getReg();
} else
return false;
IsSrcPhys = TargetRegisterInfo::isPhysicalRegister(SrcReg);
IsDstPhys = TargetRegisterInfo::isPhysicalRegister(DstReg);
return true;
}
/// isKilled - Test if the given register value, which is used by the given
/// instruction, is killed by the given instruction. This looks through
/// coalescable copies to see if the original value is potentially not killed.
///
/// For example, in this code:
///
/// %reg1034 = copy %reg1024
/// %reg1035 = copy %reg1025<kill>
/// %reg1036 = add %reg1034<kill>, %reg1035<kill>
///
/// %reg1034 is not considered to be killed, since it is copied from a
/// register which is not killed. Treating it as not killed lets the
/// normal heuristics commute the (two-address) add, which lets
/// coalescing eliminate the extra copy.
///
static bool isKilled(MachineInstr &MI, unsigned Reg,
const MachineRegisterInfo *MRI,
const TargetInstrInfo *TII) {
MachineInstr *DefMI = &MI;
for (;;) {
if (!DefMI->killsRegister(Reg))
return false;
if (TargetRegisterInfo::isPhysicalRegister(Reg))
return true;
MachineRegisterInfo::def_iterator Begin = MRI->def_begin(Reg);
// If there are multiple defs, we can't do a simple analysis, so just
// go with what the kill flag says.
if (llvm::next(Begin) != MRI->def_end())
return true;
DefMI = &*Begin;
bool IsSrcPhys, IsDstPhys;
unsigned SrcReg, DstReg;
// If the def is something other than a copy, then it isn't going to
// be coalesced, so follow the kill flag.
if (!isCopyToReg(*DefMI, TII, SrcReg, DstReg, IsSrcPhys, IsDstPhys))
return true;
Reg = SrcReg;
}
}
/// isTwoAddrUse - Return true if the specified MI uses the specified register
/// as a two-address use. If so, return the destination register by reference.
static bool isTwoAddrUse(MachineInstr &MI, unsigned Reg, unsigned &DstReg) {
const MCInstrDesc &MCID = MI.getDesc();
unsigned NumOps = MI.isInlineAsm()
? MI.getNumOperands() : MCID.getNumOperands();
for (unsigned i = 0; i != NumOps; ++i) {
const MachineOperand &MO = MI.getOperand(i);
if (!MO.isReg() || !MO.isUse() || MO.getReg() != Reg)
continue;
unsigned ti;
if (MI.isRegTiedToDefOperand(i, &ti)) {
DstReg = MI.getOperand(ti).getReg();
return true;
}
}
return false;
}
/// findOnlyInterestingUse - Given a register, if has a single in-basic block
/// use, return the use instruction if it's a copy or a two-address use.
static
MachineInstr *findOnlyInterestingUse(unsigned Reg, MachineBasicBlock *MBB,
MachineRegisterInfo *MRI,
const TargetInstrInfo *TII,
bool &IsCopy,
unsigned &DstReg, bool &IsDstPhys) {
if (!MRI->hasOneNonDBGUse(Reg))
// None or more than one use.
return 0;
MachineInstr &UseMI = *MRI->use_nodbg_begin(Reg);
if (UseMI.getParent() != MBB)
return 0;
unsigned SrcReg;
bool IsSrcPhys;
if (isCopyToReg(UseMI, TII, SrcReg, DstReg, IsSrcPhys, IsDstPhys)) {
IsCopy = true;
return &UseMI;
}
IsDstPhys = false;
if (isTwoAddrUse(UseMI, Reg, DstReg)) {
IsDstPhys = TargetRegisterInfo::isPhysicalRegister(DstReg);
return &UseMI;
}
return 0;
}
/// getMappedReg - Return the physical register the specified virtual register
/// might be mapped to.
static unsigned
getMappedReg(unsigned Reg, DenseMap<unsigned, unsigned> &RegMap) {
while (TargetRegisterInfo::isVirtualRegister(Reg)) {
DenseMap<unsigned, unsigned>::iterator SI = RegMap.find(Reg);
if (SI == RegMap.end())
return 0;
Reg = SI->second;
}
if (TargetRegisterInfo::isPhysicalRegister(Reg))
return Reg;
return 0;
}
/// regsAreCompatible - Return true if the two registers are equal or aliased.
///
static bool
regsAreCompatible(unsigned RegA, unsigned RegB, const TargetRegisterInfo *TRI) {
if (RegA == RegB)
return true;
if (!RegA || !RegB)
return false;
return TRI->regsOverlap(RegA, RegB);
}
/// isProfitableToCommute - Return true if it's potentially profitable to commute
/// the two-address instruction that's being processed.
bool
TwoAddressInstructionPass::isProfitableToCommute(unsigned regA, unsigned regB,
unsigned regC,
MachineInstr *MI, MachineBasicBlock *MBB,
unsigned Dist) {
if (OptLevel == CodeGenOpt::None)
return false;
// Determine if it's profitable to commute this two address instruction. In
// general, we want no uses between this instruction and the definition of
// the two-address register.
// e.g.
// %reg1028<def> = EXTRACT_SUBREG %reg1027<kill>, 1
// %reg1029<def> = MOV8rr %reg1028
// %reg1029<def> = SHR8ri %reg1029, 7, %EFLAGS<imp-def,dead>
// insert => %reg1030<def> = MOV8rr %reg1028
// %reg1030<def> = ADD8rr %reg1028<kill>, %reg1029<kill>, %EFLAGS<imp-def,dead>
// In this case, it might not be possible to coalesce the second MOV8rr
// instruction if the first one is coalesced. So it would be profitable to
// commute it:
// %reg1028<def> = EXTRACT_SUBREG %reg1027<kill>, 1
// %reg1029<def> = MOV8rr %reg1028
// %reg1029<def> = SHR8ri %reg1029, 7, %EFLAGS<imp-def,dead>
// insert => %reg1030<def> = MOV8rr %reg1029
// %reg1030<def> = ADD8rr %reg1029<kill>, %reg1028<kill>, %EFLAGS<imp-def,dead>
if (!MI->killsRegister(regC))
return false;
// Ok, we have something like:
// %reg1030<def> = ADD8rr %reg1028<kill>, %reg1029<kill>, %EFLAGS<imp-def,dead>
// let's see if it's worth commuting it.
// Look for situations like this:
// %reg1024<def> = MOV r1
// %reg1025<def> = MOV r0
// %reg1026<def> = ADD %reg1024, %reg1025
// r0 = MOV %reg1026
// Commute the ADD to hopefully eliminate an otherwise unavoidable copy.
unsigned ToRegA = getMappedReg(regA, DstRegMap);
if (ToRegA) {
unsigned FromRegB = getMappedReg(regB, SrcRegMap);
unsigned FromRegC = getMappedReg(regC, SrcRegMap);
bool BComp = !FromRegB || regsAreCompatible(FromRegB, ToRegA, TRI);
bool CComp = !FromRegC || regsAreCompatible(FromRegC, ToRegA, TRI);
if (BComp != CComp)
return !BComp && CComp;
}
// If there is a use of regC between its last def (could be livein) and this
// instruction, then bail.
unsigned LastDefC = 0;
if (!NoUseAfterLastDef(regC, MBB, Dist, LastDefC))
return false;
// If there is a use of regB between its last def (could be livein) and this
// instruction, then go ahead and make this transformation.
unsigned LastDefB = 0;
if (!NoUseAfterLastDef(regB, MBB, Dist, LastDefB))
return true;
// Since there are no intervening uses for both registers, then commute
// if the def of regC is closer. Its live interval is shorter.
return LastDefB && LastDefC && LastDefC > LastDefB;
}
/// CommuteInstruction - Commute a two-address instruction and update the basic
/// block, distance map, and live variables if needed. Return true if it is
/// successful.
bool
TwoAddressInstructionPass::CommuteInstruction(MachineBasicBlock::iterator &mi,
MachineFunction::iterator &mbbi,
unsigned RegB, unsigned RegC, unsigned Dist) {
MachineInstr *MI = mi;
DEBUG(dbgs() << "2addr: COMMUTING : " << *MI);
MachineInstr *NewMI = TII->commuteInstruction(MI);
if (NewMI == 0) {
DEBUG(dbgs() << "2addr: COMMUTING FAILED!\n");
return false;
}
DEBUG(dbgs() << "2addr: COMMUTED TO: " << *NewMI);
// If the instruction changed to commute it, update livevar.
if (NewMI != MI) {
if (LV)
// Update live variables
LV->replaceKillInstruction(RegC, MI, NewMI);
if (Indexes)
Indexes->replaceMachineInstrInMaps(MI, NewMI);
mbbi->insert(mi, NewMI); // Insert the new inst
mbbi->erase(mi); // Nuke the old inst.
mi = NewMI;
DistanceMap.insert(std::make_pair(NewMI, Dist));
}
// Update source register map.
unsigned FromRegC = getMappedReg(RegC, SrcRegMap);
if (FromRegC) {
unsigned RegA = MI->getOperand(0).getReg();
SrcRegMap[RegA] = FromRegC;
}
return true;
}
/// isProfitableToConv3Addr - Return true if it is profitable to convert the
/// given 2-address instruction to a 3-address one.
bool
TwoAddressInstructionPass::isProfitableToConv3Addr(unsigned RegA,unsigned RegB){
// Look for situations like this:
// %reg1024<def> = MOV r1
// %reg1025<def> = MOV r0
// %reg1026<def> = ADD %reg1024, %reg1025
// r2 = MOV %reg1026
// Turn ADD into a 3-address instruction to avoid a copy.
unsigned FromRegB = getMappedReg(RegB, SrcRegMap);
if (!FromRegB)
return false;
unsigned ToRegA = getMappedReg(RegA, DstRegMap);
return (ToRegA && !regsAreCompatible(FromRegB, ToRegA, TRI));
}
/// ConvertInstTo3Addr - Convert the specified two-address instruction into a
/// three address one. Return true if this transformation was successful.
bool
TwoAddressInstructionPass::ConvertInstTo3Addr(MachineBasicBlock::iterator &mi,
MachineBasicBlock::iterator &nmi,
MachineFunction::iterator &mbbi,
unsigned RegA, unsigned RegB,
unsigned Dist) {
MachineInstr *NewMI = TII->convertToThreeAddress(mbbi, mi, LV);
if (NewMI) {
DEBUG(dbgs() << "2addr: CONVERTING 2-ADDR: " << *mi);
DEBUG(dbgs() << "2addr: TO 3-ADDR: " << *NewMI);
bool Sunk = false;
if (Indexes)
Indexes->replaceMachineInstrInMaps(mi, NewMI);
if (NewMI->findRegisterUseOperand(RegB, false, TRI))
// FIXME: Temporary workaround. If the new instruction doesn't
// uses RegB, convertToThreeAddress must have created more
// then one instruction.
Sunk = Sink3AddrInstruction(mbbi, NewMI, RegB, mi);
mbbi->erase(mi); // Nuke the old inst.
if (!Sunk) {
DistanceMap.insert(std::make_pair(NewMI, Dist));
mi = NewMI;
nmi = llvm::next(mi);
}
// Update source and destination register maps.
SrcRegMap.erase(RegA);
DstRegMap.erase(RegB);
return true;
}
return false;
}
/// ScanUses - Scan forward recursively for only uses, update maps if the use
/// is a copy or a two-address instruction.
void
TwoAddressInstructionPass::ScanUses(unsigned DstReg, MachineBasicBlock *MBB,
SmallPtrSet<MachineInstr*, 8> &Processed) {
SmallVector<unsigned, 4> VirtRegPairs;
bool IsDstPhys;
bool IsCopy = false;
unsigned NewReg = 0;
unsigned Reg = DstReg;
while (MachineInstr *UseMI = findOnlyInterestingUse(Reg, MBB, MRI, TII,IsCopy,
NewReg, IsDstPhys)) {
if (IsCopy && !Processed.insert(UseMI))
break;
DenseMap<MachineInstr*, unsigned>::iterator DI = DistanceMap.find(UseMI);
if (DI != DistanceMap.end())
// Earlier in the same MBB.Reached via a back edge.
break;
if (IsDstPhys) {
VirtRegPairs.push_back(NewReg);
break;
}
bool isNew = SrcRegMap.insert(std::make_pair(NewReg, Reg)).second;
if (!isNew)
assert(SrcRegMap[NewReg] == Reg && "Can't map to two src registers!");
VirtRegPairs.push_back(NewReg);
Reg = NewReg;
}
if (!VirtRegPairs.empty()) {
unsigned ToReg = VirtRegPairs.back();
VirtRegPairs.pop_back();
while (!VirtRegPairs.empty()) {
unsigned FromReg = VirtRegPairs.back();
VirtRegPairs.pop_back();
bool isNew = DstRegMap.insert(std::make_pair(FromReg, ToReg)).second;
if (!isNew)
assert(DstRegMap[FromReg] == ToReg &&"Can't map to two dst registers!");
ToReg = FromReg;
}
bool isNew = DstRegMap.insert(std::make_pair(DstReg, ToReg)).second;
if (!isNew)
assert(DstRegMap[DstReg] == ToReg && "Can't map to two dst registers!");
}
}
/// ProcessCopy - If the specified instruction is not yet processed, process it
/// if it's a copy. For a copy instruction, we find the physical registers the
/// source and destination registers might be mapped to. These are kept in
/// point-to maps used to determine future optimizations. e.g.
/// v1024 = mov r0
/// v1025 = mov r1
/// v1026 = add v1024, v1025
/// r1 = mov r1026
/// If 'add' is a two-address instruction, v1024, v1026 are both potentially
/// coalesced to r0 (from the input side). v1025 is mapped to r1. v1026 is
/// potentially joined with r1 on the output side. It's worthwhile to commute
/// 'add' to eliminate a copy.
void TwoAddressInstructionPass::ProcessCopy(MachineInstr *MI,
MachineBasicBlock *MBB,
SmallPtrSet<MachineInstr*, 8> &Processed) {
if (Processed.count(MI))
return;
bool IsSrcPhys, IsDstPhys;
unsigned SrcReg, DstReg;
if (!isCopyToReg(*MI, TII, SrcReg, DstReg, IsSrcPhys, IsDstPhys))
return;
if (IsDstPhys && !IsSrcPhys)
DstRegMap.insert(std::make_pair(SrcReg, DstReg));
else if (!IsDstPhys && IsSrcPhys) {
bool isNew = SrcRegMap.insert(std::make_pair(DstReg, SrcReg)).second;
if (!isNew)
assert(SrcRegMap[DstReg] == SrcReg &&
"Can't map to two src physical registers!");
ScanUses(DstReg, MBB, Processed);
}
Processed.insert(MI);
return;
}
/// RescheduleMIBelowKill - If there is one more local instruction that reads
/// 'Reg' and it kills 'Reg, consider moving the instruction below the kill
/// instruction in order to eliminate the need for the copy.
bool
TwoAddressInstructionPass::RescheduleMIBelowKill(MachineBasicBlock *MBB,
MachineBasicBlock::iterator &mi,
MachineBasicBlock::iterator &nmi,
unsigned Reg) {
// Bail immediately if we don't have LV available. We use it to find kills
// efficiently.
if (!LV)
return false;
MachineInstr *MI = &*mi;
DenseMap<MachineInstr*, unsigned>::iterator DI = DistanceMap.find(MI);
if (DI == DistanceMap.end())
// Must be created from unfolded load. Don't waste time trying this.
return false;
MachineInstr *KillMI = LV->getVarInfo(Reg).findKill(MBB);
if (!KillMI || MI == KillMI || KillMI->isCopy() || KillMI->isCopyLike())
// Don't mess with copies, they may be coalesced later.
return false;
if (KillMI->hasUnmodeledSideEffects() || KillMI->isCall() ||
KillMI->isBranch() || KillMI->isTerminator())
// Don't move pass calls, etc.
return false;
unsigned DstReg;
if (isTwoAddrUse(*KillMI, Reg, DstReg))
return false;
bool SeenStore = true;
if (!MI->isSafeToMove(TII, AA, SeenStore))
return false;
if (TII->getInstrLatency(InstrItins, MI) > 1)
// FIXME: Needs more sophisticated heuristics.
return false;
SmallSet<unsigned, 2> Uses;
SmallSet<unsigned, 2> Kills;
SmallSet<unsigned, 2> Defs;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg())
continue;
unsigned MOReg = MO.getReg();
if (!MOReg)
continue;
if (MO.isDef())
Defs.insert(MOReg);
else {
Uses.insert(MOReg);
if (MO.isKill() && MOReg != Reg)
Kills.insert(MOReg);
}
}
// Move the copies connected to MI down as well.
MachineBasicBlock::iterator From = MI;
MachineBasicBlock::iterator To = llvm::next(From);
while (To->isCopy() && Defs.count(To->getOperand(1).getReg())) {
Defs.insert(To->getOperand(0).getReg());
++To;
}
// Check if the reschedule will not break depedencies.
unsigned NumVisited = 0;
MachineBasicBlock::iterator KillPos = KillMI;
++KillPos;
for (MachineBasicBlock::iterator I = To; I != KillPos; ++I) {
MachineInstr *OtherMI = I;
// DBG_VALUE cannot be counted against the limit.
if (OtherMI->isDebugValue())
continue;
if (NumVisited > 10) // FIXME: Arbitrary limit to reduce compile time cost.
return false;
++NumVisited;
if (OtherMI->hasUnmodeledSideEffects() || OtherMI->isCall() ||
OtherMI->isBranch() || OtherMI->isTerminator())
// Don't move pass calls, etc.
return false;
for (unsigned i = 0, e = OtherMI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = OtherMI->getOperand(i);
if (!MO.isReg())
continue;
unsigned MOReg = MO.getReg();
if (!MOReg)
continue;
if (MO.isDef()) {
if (Uses.count(MOReg))
// Physical register use would be clobbered.
return false;
if (!MO.isDead() && Defs.count(MOReg))
// May clobber a physical register def.
// FIXME: This may be too conservative. It's ok if the instruction
// is sunken completely below the use.
return false;
} else {
if (Defs.count(MOReg))
return false;
if (MOReg != Reg &&
((MO.isKill() && Uses.count(MOReg)) || Kills.count(MOReg)))
// Don't want to extend other live ranges and update kills.
return false;
if (MOReg == Reg && !MO.isKill())
// We can't schedule across a use of the register in question.
return false;
// Ensure that if this is register in question, its the kill we expect.
assert((MOReg != Reg || OtherMI == KillMI) &&
"Found multiple kills of a register in a basic block");
}
}
}
// Move debug info as well.
while (From != MBB->begin() && llvm::prior(From)->isDebugValue())
--From;
// Copies following MI may have been moved as well.
nmi = To;
MBB->splice(KillPos, MBB, From, To);
DistanceMap.erase(DI);
// Update live variables
LV->removeVirtualRegisterKilled(Reg, KillMI);
LV->addVirtualRegisterKilled(Reg, MI);
if (LIS)
LIS->handleMove(MI);
DEBUG(dbgs() << "\trescheduled below kill: " << *KillMI);
return true;
}
/// isDefTooClose - Return true if the re-scheduling will put the given
/// instruction too close to the defs of its register dependencies.
bool TwoAddressInstructionPass::isDefTooClose(unsigned Reg, unsigned Dist,
MachineInstr *MI,
MachineBasicBlock *MBB) {
for (MachineRegisterInfo::def_iterator DI = MRI->def_begin(Reg),
DE = MRI->def_end(); DI != DE; ++DI) {
MachineInstr *DefMI = &*DI;
if (DefMI->getParent() != MBB || DefMI->isCopy() || DefMI->isCopyLike())
continue;
if (DefMI == MI)
return true; // MI is defining something KillMI uses
DenseMap<MachineInstr*, unsigned>::iterator DDI = DistanceMap.find(DefMI);
if (DDI == DistanceMap.end())
return true; // Below MI
unsigned DefDist = DDI->second;
assert(Dist > DefDist && "Visited def already?");
if (TII->getInstrLatency(InstrItins, DefMI) > (Dist - DefDist))
return true;
}
return false;
}
/// RescheduleKillAboveMI - If there is one more local instruction that reads
/// 'Reg' and it kills 'Reg, consider moving the kill instruction above the
/// current two-address instruction in order to eliminate the need for the
/// copy.
bool
TwoAddressInstructionPass::RescheduleKillAboveMI(MachineBasicBlock *MBB,
MachineBasicBlock::iterator &mi,
MachineBasicBlock::iterator &nmi,
unsigned Reg) {
// Bail immediately if we don't have LV available. We use it to find kills
// efficiently.
if (!LV)
return false;
MachineInstr *MI = &*mi;
DenseMap<MachineInstr*, unsigned>::iterator DI = DistanceMap.find(MI);
if (DI == DistanceMap.end())
// Must be created from unfolded load. Don't waste time trying this.
return false;
MachineInstr *KillMI = LV->getVarInfo(Reg).findKill(MBB);
if (!KillMI || MI == KillMI || KillMI->isCopy() || KillMI->isCopyLike())
// Don't mess with copies, they may be coalesced later.
return false;
unsigned DstReg;
if (isTwoAddrUse(*KillMI, Reg, DstReg))
return false;
bool SeenStore = true;
if (!KillMI->isSafeToMove(TII, AA, SeenStore))
return false;
SmallSet<unsigned, 2> Uses;
SmallSet<unsigned, 2> Kills;
SmallSet<unsigned, 2> Defs;
SmallSet<unsigned, 2> LiveDefs;
for (unsigned i = 0, e = KillMI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = KillMI->getOperand(i);
if (!MO.isReg())
continue;
unsigned MOReg = MO.getReg();
if (MO.isUse()) {
if (!MOReg)
continue;
if (isDefTooClose(MOReg, DI->second, MI, MBB))
return false;
if (MOReg == Reg && !MO.isKill())
return false;
Uses.insert(MOReg);
if (MO.isKill() && MOReg != Reg)
Kills.insert(MOReg);
} else if (TargetRegisterInfo::isPhysicalRegister(MOReg)) {
Defs.insert(MOReg);
if (!MO.isDead())
LiveDefs.insert(MOReg);
}
}
// Check if the reschedule will not break depedencies.
unsigned NumVisited = 0;
MachineBasicBlock::iterator KillPos = KillMI;
for (MachineBasicBlock::iterator I = mi; I != KillPos; ++I) {
MachineInstr *OtherMI = I;
// DBG_VALUE cannot be counted against the limit.
if (OtherMI->isDebugValue())
continue;
if (NumVisited > 10) // FIXME: Arbitrary limit to reduce compile time cost.
return false;
++NumVisited;
if (OtherMI->hasUnmodeledSideEffects() || OtherMI->isCall() ||
OtherMI->isBranch() || OtherMI->isTerminator())
// Don't move pass calls, etc.
return false;
SmallVector<unsigned, 2> OtherDefs;
for (unsigned i = 0, e = OtherMI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = OtherMI->getOperand(i);
if (!MO.isReg())
continue;
unsigned MOReg = MO.getReg();
if (!MOReg)
continue;
if (MO.isUse()) {
if (Defs.count(MOReg))
// Moving KillMI can clobber the physical register if the def has
// not been seen.
return false;
if (Kills.count(MOReg))
// Don't want to extend other live ranges and update kills.
return false;
if (OtherMI != MI && MOReg == Reg && !MO.isKill())
// We can't schedule across a use of the register in question.
return false;
} else {
OtherDefs.push_back(MOReg);
}
}
for (unsigned i = 0, e = OtherDefs.size(); i != e; ++i) {
unsigned MOReg = OtherDefs[i];
if (Uses.count(MOReg))
return false;
if (TargetRegisterInfo::isPhysicalRegister(MOReg) &&
LiveDefs.count(MOReg))
return false;
// Physical register def is seen.
Defs.erase(MOReg);
}
}
// Move the old kill above MI, don't forget to move debug info as well.
MachineBasicBlock::iterator InsertPos = mi;
while (InsertPos != MBB->begin() && llvm::prior(InsertPos)->isDebugValue())
--InsertPos;
MachineBasicBlock::iterator From = KillMI;
MachineBasicBlock::iterator To = llvm::next(From);
while (llvm::prior(From)->isDebugValue())
--From;
MBB->splice(InsertPos, MBB, From, To);
nmi = llvm::prior(InsertPos); // Backtrack so we process the moved instr.
DistanceMap.erase(DI);
// Update live variables
LV->removeVirtualRegisterKilled(Reg, KillMI);
LV->addVirtualRegisterKilled(Reg, MI);
if (LIS)
LIS->handleMove(KillMI);
DEBUG(dbgs() << "\trescheduled kill: " << *KillMI);
return true;
}
/// TryInstructionTransform - For the case where an instruction has a single
/// pair of tied register operands, attempt some transformations that may
/// either eliminate the tied operands or improve the opportunities for
/// coalescing away the register copy. Returns true if no copy needs to be
/// inserted to untie mi's operands (either because they were untied, or
/// because mi was rescheduled, and will be visited again later).
bool TwoAddressInstructionPass::
TryInstructionTransform(MachineBasicBlock::iterator &mi,
MachineBasicBlock::iterator &nmi,
MachineFunction::iterator &mbbi,
unsigned SrcIdx, unsigned DstIdx, unsigned Dist,
SmallPtrSet<MachineInstr*, 8> &Processed) {
if (OptLevel == CodeGenOpt::None)
return false;
MachineInstr &MI = *mi;
unsigned regA = MI.getOperand(DstIdx).getReg();
unsigned regB = MI.getOperand(SrcIdx).getReg();
assert(TargetRegisterInfo::isVirtualRegister(regB) &&
"cannot make instruction into two-address form");
bool regBKilled = isKilled(MI, regB, MRI, TII);
if (TargetRegisterInfo::isVirtualRegister(regA))
ScanUses(regA, &*mbbi, Processed);
// Check if it is profitable to commute the operands.
unsigned SrcOp1, SrcOp2;
unsigned regC = 0;
unsigned regCIdx = ~0U;
bool TryCommute = false;
bool AggressiveCommute = false;
if (MI.isCommutable() && MI.getNumOperands() >= 3 &&
TII->findCommutedOpIndices(&MI, SrcOp1, SrcOp2)) {
if (SrcIdx == SrcOp1)
regCIdx = SrcOp2;
else if (SrcIdx == SrcOp2)
regCIdx = SrcOp1;
if (regCIdx != ~0U) {
regC = MI.getOperand(regCIdx).getReg();
if (!regBKilled && isKilled(MI, regC, MRI, TII))
// If C dies but B does not, swap the B and C operands.
// This makes the live ranges of A and C joinable.
TryCommute = true;
else if (isProfitableToCommute(regA, regB, regC, &MI, mbbi, Dist)) {
TryCommute = true;
AggressiveCommute = true;
}
}
}
// If it's profitable to commute, try to do so.
if (TryCommute && CommuteInstruction(mi, mbbi, regB, regC, Dist)) {
++NumCommuted;
if (AggressiveCommute)
++NumAggrCommuted;
return false;
}
// If there is one more use of regB later in the same MBB, consider
// re-schedule this MI below it.
if (RescheduleMIBelowKill(mbbi, mi, nmi, regB)) {
++NumReSchedDowns;
return true;
}
if (MI.isConvertibleTo3Addr()) {
// This instruction is potentially convertible to a true
// three-address instruction. Check if it is profitable.
if (!regBKilled || isProfitableToConv3Addr(regA, regB)) {
// Try to convert it.
if (ConvertInstTo3Addr(mi, nmi, mbbi, regA, regB, Dist)) {
++NumConvertedTo3Addr;
return true; // Done with this instruction.
}
}
}
// If there is one more use of regB later in the same MBB, consider
// re-schedule it before this MI if it's legal.
if (RescheduleKillAboveMI(mbbi, mi, nmi, regB)) {
++NumReSchedUps;
return true;
}
// If this is an instruction with a load folded into it, try unfolding
// the load, e.g. avoid this:
// movq %rdx, %rcx
// addq (%rax), %rcx
// in favor of this:
// movq (%rax), %rcx
// addq %rdx, %rcx
// because it's preferable to schedule a load than a register copy.
if (MI.mayLoad() && !regBKilled) {
// Determine if a load can be unfolded.
unsigned LoadRegIndex;
unsigned NewOpc =
TII->getOpcodeAfterMemoryUnfold(MI.getOpcode(),
/*UnfoldLoad=*/true,
/*UnfoldStore=*/false,
&LoadRegIndex);
if (NewOpc != 0) {
const MCInstrDesc &UnfoldMCID = TII->get(NewOpc);
if (UnfoldMCID.getNumDefs() == 1) {
// Unfold the load.
DEBUG(dbgs() << "2addr: UNFOLDING: " << MI);
const TargetRegisterClass *RC =
TRI->getAllocatableClass(
TII->getRegClass(UnfoldMCID, LoadRegIndex, TRI, *MF));
unsigned Reg = MRI->createVirtualRegister(RC);
SmallVector<MachineInstr *, 2> NewMIs;
if (!TII->unfoldMemoryOperand(*MF, &MI, Reg,
/*UnfoldLoad=*/true,/*UnfoldStore=*/false,
NewMIs)) {
DEBUG(dbgs() << "2addr: ABANDONING UNFOLD\n");
return false;
}
assert(NewMIs.size() == 2 &&
"Unfolded a load into multiple instructions!");
// The load was previously folded, so this is the only use.
NewMIs[1]->addRegisterKilled(Reg, TRI);
// Tentatively insert the instructions into the block so that they
// look "normal" to the transformation logic.
mbbi->insert(mi, NewMIs[0]);
mbbi->insert(mi, NewMIs[1]);
DEBUG(dbgs() << "2addr: NEW LOAD: " << *NewMIs[0]
<< "2addr: NEW INST: " << *NewMIs[1]);
// Transform the instruction, now that it no longer has a load.
unsigned NewDstIdx = NewMIs[1]->findRegisterDefOperandIdx(regA);
unsigned NewSrcIdx = NewMIs[1]->findRegisterUseOperandIdx(regB);
MachineBasicBlock::iterator NewMI = NewMIs[1];
bool TransformSuccess =
TryInstructionTransform(NewMI, mi, mbbi,
NewSrcIdx, NewDstIdx, Dist, Processed);
if (TransformSuccess ||
NewMIs[1]->getOperand(NewSrcIdx).isKill()) {
// Success, or at least we made an improvement. Keep the unfolded
// instructions and discard the original.
if (LV) {
for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI.getOperand(i);
if (MO.isReg() &&
TargetRegisterInfo::isVirtualRegister(MO.getReg())) {
if (MO.isUse()) {
if (MO.isKill()) {
if (NewMIs[0]->killsRegister(MO.getReg()))
LV->replaceKillInstruction(MO.getReg(), &MI, NewMIs[0]);
else {
assert(NewMIs[1]->killsRegister(MO.getReg()) &&
"Kill missing after load unfold!");
LV->replaceKillInstruction(MO.getReg(), &MI, NewMIs[1]);
}
}
} else if (LV->removeVirtualRegisterDead(MO.getReg(), &MI)) {
if (NewMIs[1]->registerDefIsDead(MO.getReg()))
LV->addVirtualRegisterDead(MO.getReg(), NewMIs[1]);
else {
assert(NewMIs[0]->registerDefIsDead(MO.getReg()) &&
"Dead flag missing after load unfold!");
LV->addVirtualRegisterDead(MO.getReg(), NewMIs[0]);
}
}
}
}
LV->addVirtualRegisterKilled(Reg, NewMIs[1]);
}
MI.eraseFromParent();
mi = NewMIs[1];
if (TransformSuccess)
return true;
} else {
// Transforming didn't eliminate the tie and didn't lead to an
// improvement. Clean up the unfolded instructions and keep the
// original.
DEBUG(dbgs() << "2addr: ABANDONING UNFOLD\n");
NewMIs[0]->eraseFromParent();
NewMIs[1]->eraseFromParent();
}
}
}
}
return false;
}
// Collect tied operands of MI that need to be handled.
// Rewrite trivial cases immediately.
// Return true if any tied operands where found, including the trivial ones.
bool TwoAddressInstructionPass::
collectTiedOperands(MachineInstr *MI, TiedOperandMap &TiedOperands) {
const MCInstrDesc &MCID = MI->getDesc();
bool AnyOps = false;
unsigned NumOps = MI->getNumOperands();
for (unsigned SrcIdx = 0; SrcIdx < NumOps; ++SrcIdx) {
unsigned DstIdx = 0;
if (!MI->isRegTiedToDefOperand(SrcIdx, &DstIdx))
continue;
AnyOps = true;
MachineOperand &SrcMO = MI->getOperand(SrcIdx);
MachineOperand &DstMO = MI->getOperand(DstIdx);
unsigned SrcReg = SrcMO.getReg();
unsigned DstReg = DstMO.getReg();
// Tied constraint already satisfied?
if (SrcReg == DstReg)
continue;
assert(SrcReg && SrcMO.isUse() && "two address instruction invalid");
// Deal with <undef> uses immediately - simply rewrite the src operand.
if (SrcMO.isUndef()) {
// Constrain the DstReg register class if required.
if (TargetRegisterInfo::isVirtualRegister(DstReg))
if (const TargetRegisterClass *RC = TII->getRegClass(MCID, SrcIdx,
TRI, *MF))
MRI->constrainRegClass(DstReg, RC);
SrcMO.setReg(DstReg);
DEBUG(dbgs() << "\t\trewrite undef:\t" << *MI);
continue;
}
TiedOperands[SrcReg].push_back(std::make_pair(SrcIdx, DstIdx));
}
return AnyOps;
}
// Process a list of tied MI operands that all use the same source register.
// The tied pairs are of the form (SrcIdx, DstIdx).
void
TwoAddressInstructionPass::processTiedPairs(MachineInstr *MI,
TiedPairList &TiedPairs,
unsigned &Dist) {
bool IsEarlyClobber = false;
bool RemovedKillFlag = false;
bool AllUsesCopied = true;
unsigned LastCopiedReg = 0;
unsigned RegB = 0;
for (unsigned tpi = 0, tpe = TiedPairs.size(); tpi != tpe; ++tpi) {
unsigned SrcIdx = TiedPairs[tpi].first;
unsigned DstIdx = TiedPairs[tpi].second;
const MachineOperand &DstMO = MI->getOperand(DstIdx);
unsigned RegA = DstMO.getReg();
IsEarlyClobber |= DstMO.isEarlyClobber();
// Grab RegB from the instruction because it may have changed if the
// instruction was commuted.
RegB = MI->getOperand(SrcIdx).getReg();
if (RegA == RegB) {
// The register is tied to multiple destinations (or else we would
// not have continued this far), but this use of the register
// already matches the tied destination. Leave it.
AllUsesCopied = false;
continue;
}
LastCopiedReg = RegA;
assert(TargetRegisterInfo::isVirtualRegister(RegB) &&
"cannot make instruction into two-address form");
#ifndef NDEBUG
// First, verify that we don't have a use of "a" in the instruction
// (a = b + a for example) because our transformation will not
// work. This should never occur because we are in SSA form.
for (unsigned i = 0; i != MI->getNumOperands(); ++i)
assert(i == DstIdx ||
!MI->getOperand(i).isReg() ||
MI->getOperand(i).getReg() != RegA);
#endif
// Emit a copy.
BuildMI(*MI->getParent(), MI, MI->getDebugLoc(),
TII->get(TargetOpcode::COPY), RegA).addReg(RegB);
// Update DistanceMap.
MachineBasicBlock::iterator PrevMI = MI;
--PrevMI;
DistanceMap.insert(std::make_pair(PrevMI, Dist));
DistanceMap[MI] = ++Dist;
SlotIndex CopyIdx;
if (Indexes)
CopyIdx = Indexes->insertMachineInstrInMaps(PrevMI).getRegSlot();
DEBUG(dbgs() << "\t\tprepend:\t" << *PrevMI);
MachineOperand &MO = MI->getOperand(SrcIdx);
assert(MO.isReg() && MO.getReg() == RegB && MO.isUse() &&
"inconsistent operand info for 2-reg pass");
if (MO.isKill()) {
MO.setIsKill(false);
RemovedKillFlag = true;
}
// Make sure regA is a legal regclass for the SrcIdx operand.
if (TargetRegisterInfo::isVirtualRegister(RegA) &&
TargetRegisterInfo::isVirtualRegister(RegB))
MRI->constrainRegClass(RegA, MRI->getRegClass(RegB));
MO.setReg(RegA);
// Propagate SrcRegMap.
SrcRegMap[RegA] = RegB;
}
if (AllUsesCopied) {
if (!IsEarlyClobber) {
// Replace other (un-tied) uses of regB with LastCopiedReg.
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (MO.isReg() && MO.getReg() == RegB && MO.isUse()) {
if (MO.isKill()) {
MO.setIsKill(false);
RemovedKillFlag = true;
}
MO.setReg(LastCopiedReg);
}
}
}
// Update live variables for regB.
if (RemovedKillFlag && LV && LV->getVarInfo(RegB).removeKill(MI)) {
MachineBasicBlock::iterator PrevMI = MI;
--PrevMI;
LV->addVirtualRegisterKilled(RegB, PrevMI);
}
} else if (RemovedKillFlag) {
// Some tied uses of regB matched their destination registers, so
// regB is still used in this instruction, but a kill flag was
// removed from a different tied use of regB, so now we need to add
// a kill flag to one of the remaining uses of regB.
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (MO.isReg() && MO.getReg() == RegB && MO.isUse()) {
MO.setIsKill(true);
break;
}
}
}
}
/// runOnMachineFunction - Reduce two-address instructions to two operands.
///
bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &Func) {
MF = &Func;
const TargetMachine &TM = MF->getTarget();
MRI = &MF->getRegInfo();
TII = TM.getInstrInfo();
TRI = TM.getRegisterInfo();
InstrItins = TM.getInstrItineraryData();
Indexes = getAnalysisIfAvailable<SlotIndexes>();
LV = getAnalysisIfAvailable<LiveVariables>();
LIS = getAnalysisIfAvailable<LiveIntervals>();
AA = &getAnalysis<AliasAnalysis>();
OptLevel = TM.getOptLevel();
bool MadeChange = false;
DEBUG(dbgs() << "********** REWRITING TWO-ADDR INSTRS **********\n");
DEBUG(dbgs() << "********** Function: "
<< MF->getName() << '\n');
// This pass takes the function out of SSA form.
MRI->leaveSSA();
TiedOperandMap TiedOperands;
SmallPtrSet<MachineInstr*, 8> Processed;
for (MachineFunction::iterator mbbi = MF->begin(), mbbe = MF->end();
mbbi != mbbe; ++mbbi) {
unsigned Dist = 0;
DistanceMap.clear();
SrcRegMap.clear();
DstRegMap.clear();
Processed.clear();
for (MachineBasicBlock::iterator mi = mbbi->begin(), me = mbbi->end();
mi != me; ) {
MachineBasicBlock::iterator nmi = llvm::next(mi);
if (mi->isDebugValue()) {
mi = nmi;
continue;
}
// Remember REG_SEQUENCE instructions, we'll deal with them later.
if (mi->isRegSequence())
RegSequences.push_back(&*mi);
DistanceMap.insert(std::make_pair(mi, ++Dist));
ProcessCopy(&*mi, &*mbbi, Processed);
// First scan through all the tied register uses in this instruction
// and record a list of pairs of tied operands for each register.
if (!collectTiedOperands(mi, TiedOperands)) {
mi = nmi;
continue;
}
++NumTwoAddressInstrs;
MadeChange = true;
DEBUG(dbgs() << '\t' << *mi);
// If the instruction has a single pair of tied operands, try some
// transformations that may either eliminate the tied operands or
// improve the opportunities for coalescing away the register copy.
if (TiedOperands.size() == 1) {
SmallVector<std::pair<unsigned, unsigned>, 4> &TiedPairs
= TiedOperands.begin()->second;
if (TiedPairs.size() == 1) {
unsigned SrcIdx = TiedPairs[0].first;
unsigned DstIdx = TiedPairs[0].second;
unsigned SrcReg = mi->getOperand(SrcIdx).getReg();
unsigned DstReg = mi->getOperand(DstIdx).getReg();
if (SrcReg != DstReg &&
TryInstructionTransform(mi, nmi, mbbi, SrcIdx, DstIdx, Dist,
Processed)) {
// The tied operands have been eliminated or shifted further down the
// block to ease elimination. Continue processing with 'nmi'.
TiedOperands.clear();
mi = nmi;
continue;
}
}
}
// Now iterate over the information collected above.
for (TiedOperandMap::iterator OI = TiedOperands.begin(),
OE = TiedOperands.end(); OI != OE; ++OI) {
processTiedPairs(mi, OI->second, Dist);
DEBUG(dbgs() << "\t\trewrite to:\t" << *mi);
}
// Rewrite INSERT_SUBREG as COPY now that we no longer need SSA form.
if (mi->isInsertSubreg()) {
// From %reg = INSERT_SUBREG %reg, %subreg, subidx
// To %reg:subidx = COPY %subreg
unsigned SubIdx = mi->getOperand(3).getImm();
mi->RemoveOperand(3);
assert(mi->getOperand(0).getSubReg() == 0 && "Unexpected subreg idx");
mi->getOperand(0).setSubReg(SubIdx);
mi->getOperand(0).setIsUndef(mi->getOperand(1).isUndef());
mi->RemoveOperand(1);
mi->setDesc(TII->get(TargetOpcode::COPY));
DEBUG(dbgs() << "\t\tconvert to:\t" << *mi);
}
// Clear TiedOperands here instead of at the top of the loop
// since most instructions do not have tied operands.
TiedOperands.clear();
mi = nmi;
}
}
// Eliminate REG_SEQUENCE instructions. Their whole purpose was to preseve
// SSA form. It's now safe to de-SSA.
MadeChange |= EliminateRegSequences();
return MadeChange;
}
static void UpdateRegSequenceSrcs(unsigned SrcReg,
unsigned DstReg, unsigned SubIdx,
MachineRegisterInfo *MRI,
const TargetRegisterInfo &TRI) {
for (MachineRegisterInfo::reg_iterator RI = MRI->reg_begin(SrcReg),
RE = MRI->reg_end(); RI != RE; ) {
MachineOperand &MO = RI.getOperand();
++RI;
MO.substVirtReg(DstReg, SubIdx, TRI);
}
}
// Find the first def of Reg, assuming they are all in the same basic block.
static MachineInstr *findFirstDef(unsigned Reg, MachineRegisterInfo *MRI) {
SmallPtrSet<MachineInstr*, 8> Defs;
MachineInstr *First = 0;
for (MachineRegisterInfo::def_iterator RI = MRI->def_begin(Reg);
MachineInstr *MI = RI.skipInstruction(); Defs.insert(MI))
First = MI;
if (!First)
return 0;
MachineBasicBlock *MBB = First->getParent();
MachineBasicBlock::iterator A = First, B = First;
bool Moving;
do {
Moving = false;
if (A != MBB->begin()) {
Moving = true;
--A;
if (Defs.erase(A)) First = A;
}
if (B != MBB->end()) {
Defs.erase(B);
++B;
Moving = true;
}
} while (Moving && !Defs.empty());
assert(Defs.empty() && "Instructions outside basic block!");
return First;
}
/// CoalesceExtSubRegs - If a number of sources of the REG_SEQUENCE are
/// EXTRACT_SUBREG from the same register and to the same virtual register
/// with different sub-register indices, attempt to combine the
/// EXTRACT_SUBREGs and pre-coalesce them. e.g.
/// %reg1026<def> = VLDMQ %reg1025<kill>, 260, pred:14, pred:%reg0
/// %reg1029:6<def> = EXTRACT_SUBREG %reg1026, 6
/// %reg1029:5<def> = EXTRACT_SUBREG %reg1026<kill>, 5
/// Since D subregs 5, 6 can combine to a Q register, we can coalesce
/// reg1026 to reg1029.
void
TwoAddressInstructionPass::CoalesceExtSubRegs(SmallVector<unsigned,4> &Srcs,
unsigned DstReg) {
SmallSet<unsigned, 4> Seen;
for (unsigned i = 0, e = Srcs.size(); i != e; ++i) {
unsigned SrcReg = Srcs[i];
if (!Seen.insert(SrcReg))
continue;
// Check that the instructions are all in the same basic block.
MachineInstr *SrcDefMI = MRI->getUniqueVRegDef(SrcReg);
MachineInstr *DstDefMI = MRI->getUniqueVRegDef(DstReg);
if (!SrcDefMI || !DstDefMI ||
SrcDefMI->getParent() != DstDefMI->getParent())
continue;
// If there are no other uses than copies which feed into
// the reg_sequence, then we might be able to coalesce them.
bool CanCoalesce = true;
SmallVector<unsigned, 4> SrcSubIndices, DstSubIndices;
for (MachineRegisterInfo::use_nodbg_iterator
UI = MRI->use_nodbg_begin(SrcReg),
UE = MRI->use_nodbg_end(); UI != UE; ++UI) {
MachineInstr *UseMI = &*UI;
if (!UseMI->isCopy() || UseMI->getOperand(0).getReg() != DstReg) {
CanCoalesce = false;
break;
}
SrcSubIndices.push_back(UseMI->getOperand(1).getSubReg());
DstSubIndices.push_back(UseMI->getOperand(0).getSubReg());
}
if (!CanCoalesce || SrcSubIndices.size() < 2)
continue;
// Check that the source subregisters can be combined.
std::sort(SrcSubIndices.begin(), SrcSubIndices.end());
unsigned NewSrcSubIdx = 0;
if (!TRI->canCombineSubRegIndices(MRI->getRegClass(SrcReg), SrcSubIndices,
NewSrcSubIdx))
continue;
// Check that the destination subregisters can also be combined.
std::sort(DstSubIndices.begin(), DstSubIndices.end());
unsigned NewDstSubIdx = 0;
if (!TRI->canCombineSubRegIndices(MRI->getRegClass(DstReg), DstSubIndices,
NewDstSubIdx))
continue;
// If neither source nor destination can be combined to the full register,
// just give up. This could be improved if it ever matters.
if (NewSrcSubIdx != 0 && NewDstSubIdx != 0)
continue;
// Now that we know that all the uses are extract_subregs and that those
// subregs can somehow be combined, scan all the extract_subregs again to
// make sure the subregs are in the right order and can be composed.
MachineInstr *SomeMI = 0;
CanCoalesce = true;
for (MachineRegisterInfo::use_nodbg_iterator
UI = MRI->use_nodbg_begin(SrcReg),
UE = MRI->use_nodbg_end(); UI != UE; ++UI) {
MachineInstr *UseMI = &*UI;
assert(UseMI->isCopy());
unsigned DstSubIdx = UseMI->getOperand(0).getSubReg();
unsigned SrcSubIdx = UseMI->getOperand(1).getSubReg();
assert(DstSubIdx != 0 && "missing subreg from RegSequence elimination");
if ((NewDstSubIdx == 0 &&
TRI->composeSubRegIndices(NewSrcSubIdx, DstSubIdx) != SrcSubIdx) ||
(NewSrcSubIdx == 0 &&
TRI->composeSubRegIndices(NewDstSubIdx, SrcSubIdx) != DstSubIdx)) {
CanCoalesce = false;
break;
}
// Keep track of one of the uses. Preferably the first one which has a
// <def,undef> flag.
if (!SomeMI || UseMI->getOperand(0).isUndef())
SomeMI = UseMI;
}
if (!CanCoalesce)
continue;
// Insert a copy to replace the original.
MachineInstr *CopyMI = BuildMI(*SomeMI->getParent(), SomeMI,
SomeMI->getDebugLoc(),
TII->get(TargetOpcode::COPY))
.addReg(DstReg, RegState::Define |
getUndefRegState(SomeMI->getOperand(0).isUndef()),
NewDstSubIdx)
.addReg(SrcReg, 0, NewSrcSubIdx);
// Remove all the old extract instructions.
for (MachineRegisterInfo::use_nodbg_iterator
UI = MRI->use_nodbg_begin(SrcReg),
UE = MRI->use_nodbg_end(); UI != UE; ) {
MachineInstr *UseMI = &*UI;
++UI;
if (UseMI == CopyMI)
continue;
assert(UseMI->isCopy());
// Move any kills to the new copy or extract instruction.
if (UseMI->getOperand(1).isKill()) {
CopyMI->getOperand(1).setIsKill();
if (LV)
// Update live variables
LV->replaceKillInstruction(SrcReg, UseMI, &*CopyMI);
}
UseMI->eraseFromParent();
}
}
}
static bool HasOtherRegSequenceUses(unsigned Reg, MachineInstr *RegSeq,
MachineRegisterInfo *MRI) {
for (MachineRegisterInfo::use_iterator UI = MRI->use_begin(Reg),
UE = MRI->use_end(); UI != UE; ++UI) {
MachineInstr *UseMI = &*UI;
if (UseMI != RegSeq && UseMI->isRegSequence())
return true;
}
return false;
}
/// EliminateRegSequences - Eliminate REG_SEQUENCE instructions as part
/// of the de-ssa process. This replaces sources of REG_SEQUENCE as
/// sub-register references of the register defined by REG_SEQUENCE. e.g.
///
/// %reg1029<def>, %reg1030<def> = VLD1q16 %reg1024<kill>, ...
/// %reg1031<def> = REG_SEQUENCE %reg1029<kill>, 5, %reg1030<kill>, 6
/// =>
/// %reg1031:5<def>, %reg1031:6<def> = VLD1q16 %reg1024<kill>, ...
bool TwoAddressInstructionPass::EliminateRegSequences() {
if (RegSequences.empty())
return false;
for (unsigned i = 0, e = RegSequences.size(); i != e; ++i) {
MachineInstr *MI = RegSequences[i];
unsigned DstReg = MI->getOperand(0).getReg();
if (MI->getOperand(0).getSubReg() ||
TargetRegisterInfo::isPhysicalRegister(DstReg) ||
!(MI->getNumOperands() & 1)) {
DEBUG(dbgs() << "Illegal REG_SEQUENCE instruction:" << *MI);
llvm_unreachable(0);
}
bool IsImpDef = true;
SmallVector<unsigned, 4> RealSrcs;
SmallSet<unsigned, 4> Seen;
for (unsigned i = 1, e = MI->getNumOperands(); i < e; i += 2) {
// Nothing needs to be inserted for <undef> operands.
if (MI->getOperand(i).isUndef()) {
MI->getOperand(i).setReg(0);
continue;
}
unsigned SrcReg = MI->getOperand(i).getReg();
unsigned SrcSubIdx = MI->getOperand(i).getSubReg();
unsigned SubIdx = MI->getOperand(i+1).getImm();
// DefMI of NULL means the value does not have a vreg in this block
// i.e., its a physical register or a subreg.
// In either case we force a copy to be generated.
MachineInstr *DefMI = NULL;
if (!MI->getOperand(i).getSubReg() &&
!TargetRegisterInfo::isPhysicalRegister(SrcReg)) {
DefMI = MRI->getUniqueVRegDef(SrcReg);
}
if (DefMI && DefMI->isImplicitDef()) {
DefMI->eraseFromParent();
continue;
}
IsImpDef = false;
// Remember COPY sources. These might be candidate for coalescing.
if (DefMI && DefMI->isCopy() && DefMI->getOperand(1).getSubReg())
RealSrcs.push_back(DefMI->getOperand(1).getReg());
bool isKill = MI->getOperand(i).isKill();
if (!DefMI || !Seen.insert(SrcReg) ||
MI->getParent() != DefMI->getParent() ||
!isKill || HasOtherRegSequenceUses(SrcReg, MI, MRI) ||
!TRI->getMatchingSuperRegClass(MRI->getRegClass(DstReg),
MRI->getRegClass(SrcReg), SubIdx)) {
// REG_SEQUENCE cannot have duplicated operands, add a copy.
// Also add an copy if the source is live-in the block. We don't want
// to end up with a partial-redef of a livein, e.g.
// BB0:
// reg1051:10<def> =
// ...
// BB1:
// ... = reg1051:10
// BB2:
// reg1051:9<def> =
// LiveIntervalAnalysis won't like it.
//
// If the REG_SEQUENCE doesn't kill its source, keeping live variables
// correctly up to date becomes very difficult. Insert a copy.
// Defer any kill flag to the last operand using SrcReg. Otherwise, we
// might insert a COPY that uses SrcReg after is was killed.
if (isKill)
for (unsigned j = i + 2; j < e; j += 2)
if (MI->getOperand(j).getReg() == SrcReg) {
MI->getOperand(j).setIsKill();
isKill = false;
break;
}
MachineBasicBlock::iterator InsertLoc = MI;
MachineInstr *CopyMI = BuildMI(*MI->getParent(), InsertLoc,
MI->getDebugLoc(), TII->get(TargetOpcode::COPY))
.addReg(DstReg, RegState::Define, SubIdx)
.addReg(SrcReg, getKillRegState(isKill), SrcSubIdx);
MI->getOperand(i).setReg(0);
if (LV && isKill && !TargetRegisterInfo::isPhysicalRegister(SrcReg))
LV->replaceKillInstruction(SrcReg, MI, CopyMI);
DEBUG(dbgs() << "Inserted: " << *CopyMI);
}
}
for (unsigned i = 1, e = MI->getNumOperands(); i < e; i += 2) {
unsigned SrcReg = MI->getOperand(i).getReg();
if (!SrcReg) continue;
unsigned SubIdx = MI->getOperand(i+1).getImm();
UpdateRegSequenceSrcs(SrcReg, DstReg, SubIdx, MRI, *TRI);
}
// Set <def,undef> flags on the first DstReg def in the basic block.
// It marks the beginning of the live range. All the other defs are
// read-modify-write.
if (MachineInstr *Def = findFirstDef(DstReg, MRI)) {
for (unsigned i = 0, e = Def->getNumOperands(); i != e; ++i) {
MachineOperand &MO = Def->getOperand(i);
if (MO.isReg() && MO.isDef() && MO.getReg() == DstReg)
MO.setIsUndef();
}
DEBUG(dbgs() << "First def: " << *Def);
}
if (IsImpDef) {
DEBUG(dbgs() << "Turned: " << *MI << " into an IMPLICIT_DEF");
MI->setDesc(TII->get(TargetOpcode::IMPLICIT_DEF));
for (int j = MI->getNumOperands() - 1, ee = 0; j > ee; --j)
MI->RemoveOperand(j);
} else {
DEBUG(dbgs() << "Eliminated: " << *MI);
MI->eraseFromParent();
}
// Try coalescing some EXTRACT_SUBREG instructions. This can create
// INSERT_SUBREG instructions that must have <undef> flags added by
// LiveIntervalAnalysis, so only run it when LiveVariables is available.
if (LV)
CoalesceExtSubRegs(RealSrcs, DstReg);
}
RegSequences.clear();
return true;
}
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