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Minor optimization:

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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.

llvm-svn: 65752
This commit is contained in:
Evan Cheng 2009-03-01 02:03:43 +00:00
parent 50be1d46f2
commit 276f9b02c5
3 changed files with 253 additions and 30 deletions
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266
lib/CodeGen/TwoAddressInstructionPass.cpp
View File

@ -63,28 +63,41 @@ namespace {
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,
DenseMap<MachineInstr*, unsigned> &DistanceMap);
MachineBasicBlock *MBB, unsigned Loc);
bool NoUseAfterLastDef(unsigned Reg, MachineBasicBlock *MBB, unsigned Dist,
DenseMap<MachineInstr*, unsigned> &DistanceMap,
unsigned &LastDef);
bool isProfitableToCommute(unsigned regB, unsigned regC,
MachineInstr *MI, MachineBasicBlock *MBB,
unsigned Dist,
DenseMap<MachineInstr*, unsigned> &DistanceMap);
unsigned Dist);
bool CommuteInstruction(MachineBasicBlock::iterator &mi,
MachineFunction::iterator &mbbi,
unsigned RegC, unsigned Dist,
DenseMap<MachineInstr*, unsigned> &DistanceMap);
unsigned RegB, unsigned RegC, unsigned Dist);
void ProcessCopy(MachineInstr *MI, MachineBasicBlock *MBB,
SmallPtrSet<MachineInstr*, 8> &Processed);
public:
static char ID; // Pass identification, replacement for typeid
TwoAddressInstructionPass() : MachineFunctionPass(&ID) {}
@ -233,10 +246,9 @@ static bool isTwoAddrUse(MachineInstr *UseMI, unsigned Reg) {
/// the register.
bool
TwoAddressInstructionPass::isProfitableToReMat(unsigned Reg,
const TargetRegisterClass *RC,
MachineInstr *MI, MachineInstr *DefMI,
MachineBasicBlock *MBB, unsigned Loc,
DenseMap<MachineInstr*, unsigned> &DistanceMap){
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) {
@ -269,9 +281,8 @@ TwoAddressInstructionPass::isProfitableToReMat(unsigned Reg,
/// 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,
DenseMap<MachineInstr*, unsigned> &DistanceMap,
unsigned &LastDef) {
MachineBasicBlock *MBB, unsigned Dist,
unsigned &LastDef) {
LastDef = 0;
unsigned LastUse = Dist;
for (MachineRegisterInfo::reg_iterator I = MRI->reg_begin(Reg),
@ -292,12 +303,110 @@ bool TwoAddressInstructionPass::NoUseAfterLastDef(unsigned Reg,
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;
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();
}
}
if (DstReg) {
IsSrcPhys = TargetRegisterInfo::isPhysicalRegister(SrcReg);
IsDstPhys = TargetRegisterInfo::isPhysicalRegister(DstReg);
return true;
}
return false;
}
/// 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();
for (unsigned i = 0, e = TID.getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI.getOperand(i);
if (!MO.isReg() || !MO.isUse() || MO.getReg() != Reg)
continue;
int ti = TID.getOperandConstraint(i, TOI::TIED_TO);
if (ti != -1) {
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))
return &UseMI;
IsDstPhys = false;
if (isTwoAddrUse(UseMI, Reg, 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, DenseMap<MachineInstr*, unsigned> &DistanceMap) {
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.
@ -323,16 +432,31 @@ TwoAddressInstructionPass::isProfitableToCommute(unsigned regB, unsigned regC,
// %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, DistanceMap, LastDefC))
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, DistanceMap, LastDefB))
if (!NoUseAfterLastDef(regB, MBB, Dist, LastDefB))
return true;
// Since there are no intervening uses for both registers, then commute
@ -345,9 +469,8 @@ TwoAddressInstructionPass::isProfitableToCommute(unsigned regB, unsigned regC,
/// successful.
bool
TwoAddressInstructionPass::CommuteInstruction(MachineBasicBlock::iterator &mi,
MachineFunction::iterator &mbbi,
unsigned RegC, unsigned Dist,
DenseMap<MachineInstr*, unsigned> &DistanceMap) {
MachineFunction::iterator &mbbi,
unsigned RegB, unsigned RegC, unsigned Dist) {
MachineInstr *MI = mi;
DOUT << "2addr: COMMUTING : " << *MI;
MachineInstr *NewMI = TII->commuteInstruction(MI);
@ -369,9 +492,91 @@ TwoAddressInstructionPass::CommuteInstruction(MachineBasicBlock::iterator &mi,
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;
}
/// 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;
isNew = isNew; // Silence compiler warning.
assert(isNew && "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;
isNew = isNew; // Silence compiler warning.
assert(isNew && "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;
isNew = isNew; // Silence compiler warning.
assert(isNew && "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, const TargetInstrInfo *TII) {
@ -411,14 +616,14 @@ bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) {
BitVector ReMatRegs;
ReMatRegs.resize(MRI->getLastVirtReg()+1);
// DistanceMap - Keep track the distance of a MI from the start of the
// current basic block.
DenseMap<MachineInstr*, unsigned> DistanceMap;
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);
@ -426,6 +631,9 @@ bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) {
bool FirstTied = true;
DistanceMap.insert(std::make_pair(mi, ++Dist));
ProcessCopy(&*mi, &*mbbi, Processed);
for (unsigned si = 1, e = TID.getNumOperands(); si < e; ++si) {
int ti = TID.getOperandConstraint(si, TOI::TIED_TO);
if (ti == -1)
@ -489,7 +697,7 @@ bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) {
"Not a proper commutative instruction!");
unsigned regC = mi->getOperand(3-si).getReg();
if (mi->killsRegister(regC)) {
if (CommuteInstruction(mi, mbbi, regC, Dist, DistanceMap)) {
if (CommuteInstruction(mi, mbbi, regB, regC, Dist)) {
++NumCommuted;
regB = regC;
goto InstructionRearranged;
@ -536,8 +744,8 @@ bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) {
// If it's profitable to commute the instruction, do so.
if (TID.isCommutable() && mi->getNumOperands() >= 3) {
unsigned regC = mi->getOperand(3-si).getReg();
if (isProfitableToCommute(regB, regC, mi, mbbi, Dist, DistanceMap))
if (CommuteInstruction(mi, mbbi, regC, Dist, DistanceMap)) {
if (isProfitableToCommute(regB, regC, mi, mbbi, Dist))
if (CommuteInstruction(mi, mbbi, regB, regC, Dist)) {
++NumAggrCommuted;
++NumCommuted;
regB = regC;
@ -552,7 +760,7 @@ bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) {
if (DefMI &&
DefMI->getDesc().isAsCheapAsAMove() &&
DefMI->isSafeToReMat(TII, regB) &&
isProfitableToReMat(regB, rc, mi, DefMI, mbbi, Dist,DistanceMap)){
isProfitableToReMat(regB, rc, mi, DefMI, mbbi, Dist)){
DEBUG(cerr << "2addr: REMATTING : " << *DefMI << "\n");
TII->reMaterialize(*mbbi, mi, regA, DefMI);
ReMatRegs.set(regB);

15
test/CodeGen/X86/twoaddr-coalesce-2.ll Normal file
View File

@ -0,0 +1,15 @@
; RUN: llvm-as < %s | llc -march=x86 -mattr=+sse2 -stats |& \
; RUN: grep {twoaddrinstr} | grep {Number of instructions aggressively commuted}
; rdar://6480363
target triple = "i386-apple-darwin9.6"
define <2 x double> @t(<2 x double> %A, <2 x double> %B, <2 x double> %C) nounwind readnone {
entry:
%tmp.i3 = bitcast <2 x double> %B to <2 x i64> ; <<2 x i64>> [#uses=1]
%tmp2.i = or <2 x i64> %tmp.i3, <i64 4607632778762754458, i64 4607632778762754458> ; <<2 x i64>> [#uses=1]
%tmp3.i = bitcast <2 x i64> %tmp2.i to <2 x double> ; <<2 x double>> [#uses=1]
%tmp.i2 = add <2 x double> %tmp3.i, %A ; <<2 x double>> [#uses=1]
%tmp.i = add <2 x double> %tmp.i2, %C ; <<2 x double>> [#uses=1]
ret <2 x double> %tmp.i
}

2
test/CodeGen/X86/twoaddr-coalesce.ll
View File

@ -1,4 +1,4 @@
; RUN: llvm-as < %s | llc -march=x86 -join-cross-class-copies -stats |& \
; RUN: llvm-as < %s | llc -march=x86 -stats |& \
; RUN: grep {twoaddrinstr} | grep {Number of instructions aggressively commuted}
; rdar://6523745