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llvm-mirror/lib/CodeGen/TwoAddressInstructionPass.cpp
Bob Wilson 10465d5aa9 Overhaul the TwoAddressInstructionPass to simplify the logic, especially 
for the complicated case where one register is tied to multiple destinations.
This avoids the extra scan of instruction operands that was introduced by
my recent change.  I also pulled some code out into a separate
TryInstructionTransform method, added more comments, and renamed some
variables.

Besides all those changes, this takes care of a FIXME in the code regarding
an assumption about there being a single tied use of a register when
converting to a 3-address form.  I'm not aware of cases where that assumption
is violated, but the code now only attempts to transform an instruction,
either by commuting its operands or by converting to a 3-address form,
for the simple case where there is a single pair of tied operands.

llvm-svn: 80945
2009-09-03 20:58:42 +00:00

1115 lines
41 KiB
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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/LiveVariables.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.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(NumReMats, "Number of instructions re-materialized");
STATISTIC(NumDeletes, "Number of dead instructions deleted");
namespace {
class VISIBILITY_HIDDEN TwoAddressInstructionPass
: public MachineFunctionPass {
const TargetInstrInfo *TII;
const TargetRegisterInfo *TRI;
MachineRegisterInfo *MRI;
LiveVariables *LV;
// 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;
bool Sink3AddrInstruction(MachineBasicBlock *MBB, MachineInstr *MI,
unsigned Reg,
MachineBasicBlock::iterator OldPos);
bool isProfitableToReMat(unsigned Reg, const TargetRegisterClass *RC,
MachineInstr *MI, MachineInstr *DefMI,
MachineBasicBlock *MBB, unsigned Loc);
bool NoUseAfterLastDef(unsigned Reg, MachineBasicBlock *MBB, unsigned Dist,
unsigned &LastDef);
MachineInstr *FindLastUseInMBB(unsigned Reg, MachineBasicBlock *MBB,
unsigned Dist);
bool isProfitableToCommute(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);
bool ConvertInstTo3Addr(MachineBasicBlock::iterator &mi,
MachineBasicBlock::iterator &nmi,
MachineFunction::iterator &mbbi,
unsigned RegB, unsigned Dist);
typedef std::pair<std::pair<unsigned, bool>, MachineInstr*> NewKill;
bool canUpdateDeletedKills(SmallVector<unsigned, 4> &Kills,
SmallVector<NewKill, 4> &NewKills,
MachineBasicBlock *MBB, unsigned Dist);
bool DeleteUnusedInstr(MachineBasicBlock::iterator &mi,
MachineBasicBlock::iterator &nmi,
MachineFunction::iterator &mbbi,
unsigned regB, unsigned regBIdx, unsigned Dist);
bool TryInstructionTransform(MachineBasicBlock::iterator &mi,
MachineBasicBlock::iterator &nmi,
MachineFunction::iterator &mbbi,
unsigned SrcIdx, unsigned DstIdx,
unsigned Dist);
void ProcessCopy(MachineInstr *MI, MachineBasicBlock *MBB,
SmallPtrSet<MachineInstr*, 8> &Processed);
public:
static char ID; // Pass identification, replacement for typeid
TwoAddressInstructionPass() : MachineFunctionPass(&ID) {}
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
AU.addPreserved<LiveVariables>();
AU.addPreservedID(MachineLoopInfoID);
AU.addPreservedID(MachineDominatorsID);
if (StrongPHIElim)
AU.addPreservedID(StrongPHIEliminationID);
else
AU.addPreservedID(PHIEliminationID);
MachineFunctionPass::getAnalysisUsage(AU);
}
/// runOnMachineFunction - Pass entry point.
bool runOnMachineFunction(MachineFunction&);
};
}
char TwoAddressInstructionPass::ID = 0;
static RegisterPass<TwoAddressInstructionPass>
X("twoaddressinstruction", "Two-Address instruction pass");
const PassInfo *const llvm::TwoAddressInstructionPassID = &X;
/// 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) {
// Check if it's safe to move this instruction.
bool SeenStore = true; // Be conservative.
if (!MI->isSafeToMove(TII, 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_iterator UI = MRI->use_begin(SavedReg),
UE = MRI->use_end(); UI != UE; ++UI) {
MachineOperand &UseMO = UI.getOperand();
if (!UseMO.isKill())
continue;
KillMI = UseMO.getParent();
break;
}
if (!KillMI || KillMI->getParent() != MBB || KillMI == MI)
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 = next(OldPos); I != KillPos; ++I) {
MachineInstr *OtherMI = I;
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;
}
}
}
// 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);
++Num3AddrSunk;
return true;
}
/// isTwoAddrUse - Return true if the specified MI is using the specified
/// register as a two-address operand.
static bool isTwoAddrUse(MachineInstr *UseMI, unsigned Reg) {
const TargetInstrDesc &TID = UseMI->getDesc();
for (unsigned i = 0, e = TID.getNumOperands(); i != e; ++i) {
MachineOperand &MO = UseMI->getOperand(i);
if (MO.isReg() && MO.getReg() == Reg &&
(MO.isDef() || UseMI->isRegTiedToDefOperand(i)))
// Earlier use is a two-address one.
return true;
}
return false;
}
/// isProfitableToReMat - Return true if the heuristics determines it is likely
/// to be profitable to re-materialize the definition of Reg rather than copy
/// the register.
bool
TwoAddressInstructionPass::isProfitableToReMat(unsigned Reg,
const TargetRegisterClass *RC,
MachineInstr *MI, MachineInstr *DefMI,
MachineBasicBlock *MBB, unsigned Loc) {
bool OtherUse = false;
for (MachineRegisterInfo::use_iterator UI = MRI->use_begin(Reg),
UE = MRI->use_end(); UI != UE; ++UI) {
MachineOperand &UseMO = UI.getOperand();
MachineInstr *UseMI = UseMO.getParent();
MachineBasicBlock *UseMBB = UseMI->getParent();
if (UseMBB == MBB) {
DenseMap<MachineInstr*, unsigned>::iterator DI = DistanceMap.find(UseMI);
if (DI != DistanceMap.end() && DI->second == Loc)
continue; // Current use.
OtherUse = true;
// There is at least one other use in the MBB that will clobber the
// register.
if (isTwoAddrUse(UseMI, Reg))
return true;
}
}
// If other uses in MBB are not two-address uses, then don't remat.
if (OtherUse)
return false;
// No other uses in the same block, remat if it's defined in the same
// block so it does not unnecessarily extend the live range.
return MBB == DefMI->getParent();
}
/// 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)
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);
}
MachineInstr *TwoAddressInstructionPass::FindLastUseInMBB(unsigned Reg,
MachineBasicBlock *MBB,
unsigned Dist) {
unsigned LastUseDist = 0;
MachineInstr *LastUse = 0;
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)
continue;
DenseMap<MachineInstr*, unsigned>::iterator DI = DistanceMap.find(MI);
if (DI == DistanceMap.end())
continue;
if (DI->second >= Dist)
continue;
if (MO.isUse() && DI->second > LastUseDist) {
LastUse = DI->first;
LastUseDist = DI->second;
}
}
return LastUse;
}
/// 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;
unsigned SrcSubIdx, DstSubIdx;
if (!TII->isMoveInstr(MI, SrcReg, DstReg, SrcSubIdx, DstSubIdx)) {
if (MI.getOpcode() == TargetInstrInfo::EXTRACT_SUBREG) {
DstReg = MI.getOperand(0).getReg();
SrcReg = MI.getOperand(1).getReg();
} else if (MI.getOpcode() == TargetInstrInfo::INSERT_SUBREG) {
DstReg = MI.getOperand(0).getReg();
SrcReg = MI.getOperand(2).getReg();
} else if (MI.getOpcode() == TargetInstrInfo::SUBREG_TO_REG) {
DstReg = MI.getOperand(0).getReg();
SrcReg = MI.getOperand(2).getReg();
}
}
if (DstReg) {
IsSrcPhys = TargetRegisterInfo::isPhysicalRegister(SrcReg);
IsDstPhys = TargetRegisterInfo::isPhysicalRegister(DstReg);
return true;
}
return false;
}
/// 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 (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 TargetInstrDesc &TID = MI.getDesc();
unsigned NumOps = (MI.getOpcode() == TargetInstrInfo::INLINEASM)
? MI.getNumOperands() : TID.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) {
MachineRegisterInfo::use_iterator UI = MRI->use_begin(Reg);
if (UI == MRI->use_end())
return 0;
MachineInstr &UseMI = *UI;
if (++UI != MRI->use_end())
// More than one use.
return 0;
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);
}
/// isProfitableToReMat - Return true if it's potentially profitable to commute
/// the two-address instruction that's being processed.
bool
TwoAddressInstructionPass::isProfitableToCommute(unsigned regB, unsigned regC,
MachineInstr *MI, MachineBasicBlock *MBB,
unsigned Dist) {
// 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 FromRegB = getMappedReg(regB, SrcRegMap);
unsigned FromRegC = getMappedReg(regC, SrcRegMap);
unsigned ToRegB = getMappedReg(regB, DstRegMap);
unsigned ToRegC = getMappedReg(regC, DstRegMap);
if (!regsAreCompatible(FromRegB, ToRegB, TRI) &&
(regsAreCompatible(FromRegB, ToRegC, TRI) ||
regsAreCompatible(FromRegC, ToRegB, TRI)))
return true;
// 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(errs() << "2addr: COMMUTING : " << *MI);
MachineInstr *NewMI = TII->commuteInstruction(MI);
if (NewMI == 0) {
DEBUG(errs() << "2addr: COMMUTING FAILED!\n");
return false;
}
DEBUG(errs() << "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);
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) {
// 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 FromRegA = getMappedReg(RegA, SrcRegMap);
unsigned ToRegA = getMappedReg(RegA, DstRegMap);
return (FromRegA && ToRegA && !regsAreCompatible(FromRegA, 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 RegB, unsigned Dist) {
MachineInstr *NewMI = TII->convertToThreeAddress(mbbi, mi, LV);
if (NewMI) {
DEBUG(errs() << "2addr: CONVERTING 2-ADDR: " << *mi);
DEBUG(errs() << "2addr: TO 3-ADDR: " << *NewMI);
bool Sunk = false;
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 = next(mi);
}
return true;
}
return false;
}
/// 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!");
SmallVector<unsigned, 4> VirtRegPairs;
bool IsCopy = false;
unsigned NewReg = 0;
while (MachineInstr *UseMI = findOnlyInterestingUse(DstReg, MBB, MRI,TII,
IsCopy, NewReg, IsDstPhys)) {
if (IsCopy) {
if (!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, DstReg)).second;
if (!isNew)
assert(SrcRegMap[NewReg] == DstReg &&
"Can't map to two src physical registers!");
VirtRegPairs.push_back(NewReg);
DstReg = 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 physical registers!");
ToReg = FromReg;
}
}
}
Processed.insert(MI);
}
/// isSafeToDelete - If the specified instruction does not produce any side
/// effects and all of its defs are dead, then it's safe to delete.
static bool isSafeToDelete(MachineInstr *MI, unsigned Reg,
const TargetInstrInfo *TII,
SmallVector<unsigned, 4> &Kills) {
const TargetInstrDesc &TID = MI->getDesc();
if (TID.mayStore() || TID.isCall())
return false;
if (TID.isTerminator() || TID.hasUnmodeledSideEffects())
return false;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg())
continue;
if (MO.isDef() && !MO.isDead())
return false;
if (MO.isUse() && MO.getReg() != Reg && MO.isKill())
Kills.push_back(MO.getReg());
}
return true;
}
/// canUpdateDeletedKills - Check if all the registers listed in Kills are
/// killed by instructions in MBB preceding the current instruction at
/// position Dist. If so, return true and record information about the
/// preceding kills in NewKills.
bool TwoAddressInstructionPass::
canUpdateDeletedKills(SmallVector<unsigned, 4> &Kills,
SmallVector<NewKill, 4> &NewKills,
MachineBasicBlock *MBB, unsigned Dist) {
while (!Kills.empty()) {
unsigned Kill = Kills.back();
Kills.pop_back();
if (TargetRegisterInfo::isPhysicalRegister(Kill))
return false;
MachineInstr *LastKill = FindLastUseInMBB(Kill, MBB, Dist);
if (!LastKill)
return false;
bool isModRef = LastKill->modifiesRegister(Kill);
NewKills.push_back(std::make_pair(std::make_pair(Kill, isModRef),
LastKill));
}
return true;
}
/// DeleteUnusedInstr - If an instruction with a tied register operand can
/// be safely deleted, just delete it.
bool
TwoAddressInstructionPass::DeleteUnusedInstr(MachineBasicBlock::iterator &mi,
MachineBasicBlock::iterator &nmi,
MachineFunction::iterator &mbbi,
unsigned regB, unsigned regBIdx,
unsigned Dist) {
// Check if the instruction has no side effects and if all its defs are dead.
SmallVector<unsigned, 4> Kills;
if (!isSafeToDelete(mi, regB, TII, Kills))
return false;
// If this instruction kills some virtual registers, we need to
// update the kill information. If it's not possible to do so,
// then bail out.
SmallVector<NewKill, 4> NewKills;
if (!canUpdateDeletedKills(Kills, NewKills, &*mbbi, Dist))
return false;
if (LV) {
while (!NewKills.empty()) {
MachineInstr *NewKill = NewKills.back().second;
unsigned Kill = NewKills.back().first.first;
bool isDead = NewKills.back().first.second;
NewKills.pop_back();
if (LV->removeVirtualRegisterKilled(Kill, mi)) {
if (isDead)
LV->addVirtualRegisterDead(Kill, NewKill);
else
LV->addVirtualRegisterKilled(Kill, NewKill);
}
}
// If regB was marked as a kill, update its Kills list.
if (mi->getOperand(regBIdx).isKill())
LV->removeVirtualRegisterKilled(regB, mi);
}
mbbi->erase(mi); // Nuke the old inst.
mi = nmi;
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 the tied operands
/// are eliminated altogether.
bool TwoAddressInstructionPass::
TryInstructionTransform(MachineBasicBlock::iterator &mi,
MachineBasicBlock::iterator &nmi,
MachineFunction::iterator &mbbi,
unsigned SrcIdx, unsigned DstIdx, unsigned Dist) {
const TargetInstrDesc &TID = mi->getDesc();
unsigned regA = mi->getOperand(DstIdx).getReg();
unsigned regB = mi->getOperand(SrcIdx).getReg();
assert(TargetRegisterInfo::isVirtualRegister(regB) &&
"cannot make instruction into two-address form");
// If regA is dead and the instruction can be deleted, just delete
// it so it doesn't clobber regB.
bool regBKilled = isKilled(*mi, regB, MRI, TII);
if (!regBKilled && mi->getOperand(DstIdx).isDead() &&
DeleteUnusedInstr(mi, nmi, mbbi, regB, SrcIdx, Dist)) {
++NumDeletes;
return true; // Done with this instruction.
}
// 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 (TID.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(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 (TID.isConvertibleTo3Addr()) {
// This instruction is potentially convertible to a true
// three-address instruction. Check if it is profitable.
if (!regBKilled || isProfitableToConv3Addr(regA)) {
// Try to convert it.
if (ConvertInstTo3Addr(mi, nmi, mbbi, regB, Dist)) {
++NumConvertedTo3Addr;
return true; // Done with this instruction.
}
}
}
return false;
}
/// runOnMachineFunction - Reduce two-address instructions to two operands.
///
bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) {
DEBUG(errs() << "Machine Function\n");
const TargetMachine &TM = MF.getTarget();
MRI = &MF.getRegInfo();
TII = TM.getInstrInfo();
TRI = TM.getRegisterInfo();
LV = getAnalysisIfAvailable<LiveVariables>();
bool MadeChange = false;
DEBUG(errs() << "********** REWRITING TWO-ADDR INSTRS **********\n");
DEBUG(errs() << "********** Function: "
<< MF.getFunction()->getName() << '\n');
// ReMatRegs - Keep track of the registers whose def's are remat'ed.
BitVector ReMatRegs;
ReMatRegs.resize(MRI->getLastVirtReg()+1);
typedef DenseMap<unsigned, SmallVector<std::pair<unsigned, unsigned>, 4> >
TiedOperandMap;
TiedOperandMap TiedOperands(4);
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 = next(mi);
const TargetInstrDesc &TID = mi->getDesc();
bool FirstTied = true;
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.
unsigned NumOps = (mi->getOpcode() == TargetInstrInfo::INLINEASM)
? mi->getNumOperands() : TID.getNumOperands();
for (unsigned SrcIdx = 0; SrcIdx < NumOps; ++SrcIdx) {
unsigned DstIdx = 0;
if (!mi->isRegTiedToDefOperand(SrcIdx, &DstIdx))
continue;
if (FirstTied) {
FirstTied = false;
++NumTwoAddressInstrs;
DEBUG(errs() << '\t' << *mi);
}
assert(mi->getOperand(SrcIdx).isReg() &&
mi->getOperand(SrcIdx).getReg() &&
mi->getOperand(SrcIdx).isUse() &&
"two address instruction invalid");
unsigned regB = mi->getOperand(SrcIdx).getReg();
TiedOperandMap::iterator OI = TiedOperands.find(regB);
if (OI == TiedOperands.end()) {
SmallVector<std::pair<unsigned, unsigned>, 4> TiedPair;
OI = TiedOperands.insert(std::make_pair(regB, TiedPair)).first;
}
OI->second.push_back(std::make_pair(SrcIdx, DstIdx));
}
// Now iterate over the information collected above.
for (TiedOperandMap::iterator OI = TiedOperands.begin(),
OE = TiedOperands.end(); OI != OE; ++OI) {
SmallVector<std::pair<unsigned, unsigned>, 4> &TiedPairs = OI->second;
// 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 && TiedPairs.size() == 1) {
unsigned SrcIdx = TiedPairs[0].first;
unsigned DstIdx = TiedPairs[0].second;
// If the registers are already equal, nothing needs to be done.
if (mi->getOperand(SrcIdx).getReg() ==
mi->getOperand(DstIdx).getReg())
break; // Done with this instruction.
if (TryInstructionTransform(mi, nmi, mbbi, SrcIdx, DstIdx, Dist))
break; // The tied operands have been eliminated.
}
bool RemovedKillFlag = false;
bool AllUsesCopied = true;
unsigned LastCopiedReg = 0;
unsigned regB = OI->first;
for (unsigned tpi = 0, tpe = TiedPairs.size(); tpi != tpe; ++tpi) {
unsigned SrcIdx = TiedPairs[tpi].first;
unsigned DstIdx = TiedPairs[tpi].second;
unsigned regA = mi->getOperand(DstIdx).getReg();
// 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 or rematerialize the definition.
const TargetRegisterClass *rc = MRI->getRegClass(regB);
MachineInstr *DefMI = MRI->getVRegDef(regB);
// If it's safe and profitable, remat the definition instead of
// copying it.
if (DefMI &&
DefMI->getDesc().isAsCheapAsAMove() &&
DefMI->isSafeToReMat(TII, regB) &&
isProfitableToReMat(regB, rc, mi, DefMI, mbbi, Dist)){
DEBUG(errs() << "2addr: REMATTING : " << *DefMI << "\n");
unsigned regASubIdx = mi->getOperand(DstIdx).getSubReg();
TII->reMaterialize(*mbbi, mi, regA, regASubIdx, DefMI);
ReMatRegs.set(regB);
++NumReMats;
} else {
bool Emitted = TII->copyRegToReg(*mbbi, mi, regA, regB, rc, rc);
(void)Emitted;
assert(Emitted && "Unable to issue a copy instruction!\n");
}
MachineBasicBlock::iterator prevMI = prior(mi);
// Update DistanceMap.
DistanceMap.insert(std::make_pair(prevMI, Dist));
DistanceMap[mi] = ++Dist;
DEBUG(errs() << "\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;
}
MO.setReg(regA);
}
if (AllUsesCopied) {
// 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))
LV->addVirtualRegisterKilled(regB, prior(mi));
} 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;
}
}
}
MadeChange = true;
DEBUG(errs() << "\t\trewrite 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;
}
}
// Some remat'ed instructions are dead.
int VReg = ReMatRegs.find_first();
while (VReg != -1) {
if (MRI->use_empty(VReg)) {
MachineInstr *DefMI = MRI->getVRegDef(VReg);
DefMI->eraseFromParent();
}
VReg = ReMatRegs.find_next(VReg);
}
return MadeChange;
}
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