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llvm-mirror/lib/CodeGen/TwoAddressInstructionPass.cpp
Taewook Oh 7e3c6fd16c Remove redundant copy in recurrences 
Summary:
If there is a chain of instructions formulating a recurrence, commuting operands can help removing a redundant copy. In the following example code,

```
BB#1: ; Loop Header
  %vreg0<def> = COPY %vreg13<kill>; GR32:%vreg0,%vreg13
  ...

BB#6: ; Loop Latch
  %vreg2<def> = COPY %vreg15<kill>; GR32:%vreg2,%vreg15
  %vreg10<def,tied1> = ADD32rr %vreg1<kill,tied0>, %vreg0<kill>, %EFLAGS<imp-def,dead>; GR32:%vreg10,%vreg1,%vreg0
  %vreg3<def,tied1> = ADD32rr %vreg2<kill,tied0>, %vreg10<kill>, %EFLAGS<imp-def,dead>; GR32:%vreg3,%vreg2,%vreg10
  CMP32ri8 %vreg3, 10, %EFLAGS<imp-def>; GR32:%vreg3
  %vreg13<def> = COPY %vreg3<kill>; GR32:%vreg13,%vreg3
  JL_1 <BB#1>, %EFLAGS<imp-use,kill>
```

Existing two-address generation pass generates following code:

```
BB#1:
  %vreg0<def> = COPY %vreg13<kill>; GR32:%vreg0,%vreg13
  ...

BB#6:
    Predecessors according to CFG: BB#5 BB#4
  %vreg2<def> = COPY %vreg15<kill>; GR32:%vreg2,%vreg15
  %vreg10<def> = COPY %vreg1<kill>; GR32:%vreg10,%vreg1
  %vreg10<def,tied1> = ADD32rr %vreg10<tied0>, %vreg0<kill>, %EFLAGS<imp-def,dead>; GR32:%vreg10,%vreg0
  %vreg3<def> = COPY %vreg10<kill>; GR32:%vreg3,%vreg10
  %vreg3<def,tied1> = ADD32rr %vreg3<tied0>, %vreg2<kill>, %EFLAGS<imp-def,dead>; GR32:%vreg3,%vreg2
  CMP32ri8 %vreg3, 10, %EFLAGS<imp-def>; GR32:%vreg3
  %vreg13<def> = COPY %vreg3<kill>; GR32:%vreg13,%vreg3
  JL_1 <BB#1>, %EFLAGS<imp-use,kill>
  JMP_1 <BB#7>
```

This is suboptimal because the assembly code generated has a redundant copy at the end of #BB6 to feed %vreg13 to BB#1:

```
.LBB0_6:
  addl  %esi, %edi
  addl  %ebx, %edi
  cmpl  $10, %edi
  movl  %edi, %esi
  jl  .LBB0_1
```

This redundant copy can be elimiated by making instructions in the recurrence chain to compute the value "into" the register that actually holds the feedback value. In this example, this can be achieved by commuting %vreg0 and %vreg1 to compute %vreg10. With that change, code after two-address generation becomes

```
BB#1:
  %vreg0<def> = COPY %vreg13<kill>; GR32:%vreg0,%vreg13
  ...

BB#6: derived from LLVM BB %bb7
    Predecessors according to CFG: BB#5 BB#4
  %vreg2<def> = COPY %vreg15<kill>; GR32:%vreg2,%vreg15
  %vreg10<def> = COPY %vreg0<kill>; GR32:%vreg10,%vreg0
  %vreg10<def,tied1> = ADD32rr %vreg10<tied0>, %vreg1<kill>, %EFLAGS<imp-def,dead>; GR32:%vreg10,%vreg1
  %vreg3<def> = COPY %vreg10<kill>; GR32:%vreg3,%vreg10
  %vreg3<def,tied1> = ADD32rr %vreg3<tied0>, %vreg2<kill>, %EFLAGS<imp-def,dead>; GR32:%vreg3,%vreg2
  CMP32ri8 %vreg3, 10, %EFLAGS<imp-def>; GR32:%vreg3
  %vreg13<def> = COPY %vreg3<kill>; GR32:%vreg13,%vreg3
  JL_1 <BB#1>, %EFLAGS<imp-use,kill>
  JMP_1 <BB#7>
```

and the final assembly does not have redundant copy:

```
.LBB0_6:
  addl  %edi, %eax
  addl  %ebx, %eax
  cmpl  $10, %eax
  jl  .LBB0_1
```

Reviewers: qcolombet, MatzeB, wmi

Reviewed By: wmi

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D31821

llvm-svn: 306758
2017-06-29 23:11:24 +00:00

1833 lines
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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.
//
//===----------------------------------------------------------------------===//
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.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/CodeGen/Passes.h"
#include "llvm/IR/Function.h"
#include "llvm/MC/MCInstrItineraries.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetSubtargetInfo.h"
using namespace llvm;
#define DEBUG_TYPE "twoaddressinstruction"
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");
// Temporary flag to disable rescheduling.
static cl::opt<bool>
EnableRescheduling("twoaddr-reschedule",
cl::desc("Coalesce copies by rescheduling (default=true)"),
cl::init(true), cl::Hidden);
// Limit the number of dataflow edges to traverse when evaluating the benefit
// of commuting operands.
static cl::opt<unsigned> MaxDataFlowEdge(
"dataflow-edge-limit", cl::Hidden, cl::init(3),
cl::desc("Maximum number of dataflow edges to traverse when evaluating "
"the benefit of commuting operands"));
namespace {
class TwoAddressInstructionPass : public MachineFunctionPass {
MachineFunction *MF;
const TargetInstrInfo *TII;
const TargetRegisterInfo *TRI;
const InstrItineraryData *InstrItins;
MachineRegisterInfo *MRI;
LiveVariables *LV;
LiveIntervals *LIS;
AliasAnalysis *AA;
CodeGenOpt::Level OptLevel;
// The current basic block being processed.
MachineBasicBlock *MBB;
// Keep track the distance of a MI from the start of the current basic block.
DenseMap<MachineInstr*, unsigned> DistanceMap;
// Set of already processed instructions in the current block.
SmallPtrSet<MachineInstr*, 8> Processed;
// 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;
// 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(MachineInstr *MI, unsigned Reg,
MachineBasicBlock::iterator OldPos);
bool isRevCopyChain(unsigned FromReg, unsigned ToReg, int Maxlen);
bool noUseAfterLastDef(unsigned Reg, unsigned Dist, unsigned &LastDef);
bool isProfitableToCommute(unsigned regA, unsigned regB, unsigned regC,
MachineInstr *MI, unsigned Dist);
bool commuteInstruction(MachineInstr *MI, unsigned DstIdx,
unsigned RegBIdx, unsigned RegCIdx, unsigned Dist);
bool isProfitableToConv3Addr(unsigned RegA, unsigned RegB);
bool convertInstTo3Addr(MachineBasicBlock::iterator &mi,
MachineBasicBlock::iterator &nmi,
unsigned RegA, unsigned RegB, unsigned Dist);
bool isDefTooClose(unsigned Reg, unsigned Dist, MachineInstr *MI);
bool rescheduleMIBelowKill(MachineBasicBlock::iterator &mi,
MachineBasicBlock::iterator &nmi,
unsigned Reg);
bool rescheduleKillAboveMI(MachineBasicBlock::iterator &mi,
MachineBasicBlock::iterator &nmi,
unsigned Reg);
bool tryInstructionTransform(MachineBasicBlock::iterator &mi,
MachineBasicBlock::iterator &nmi,
unsigned SrcIdx, unsigned DstIdx,
unsigned Dist, bool shouldOnlyCommute);
bool tryInstructionCommute(MachineInstr *MI,
unsigned DstOpIdx,
unsigned BaseOpIdx,
bool BaseOpKilled,
unsigned Dist);
void scanUses(unsigned DstReg);
void processCopy(MachineInstr *MI);
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 eliminateRegSequence(MachineBasicBlock::iterator&);
public:
static char ID; // Pass identification, replacement for typeid
TwoAddressInstructionPass() : MachineFunctionPass(ID) {
initializeTwoAddressInstructionPassPass(*PassRegistry::getPassRegistry());
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
AU.addUsedIfAvailable<AAResultsWrapperPass>();
AU.addUsedIfAvailable<LiveVariables>();
AU.addPreserved<LiveVariables>();
AU.addPreserved<SlotIndexes>();
AU.addPreserved<LiveIntervals>();
AU.addPreservedID(MachineLoopInfoID);
AU.addPreservedID(MachineDominatorsID);
MachineFunctionPass::getAnalysisUsage(AU);
}
/// Pass entry point.
bool runOnMachineFunction(MachineFunction&) override;
};
} // end anonymous namespace
char TwoAddressInstructionPass::ID = 0;
INITIALIZE_PASS_BEGIN(TwoAddressInstructionPass, DEBUG_TYPE,
"Two-Address instruction pass", false, false)
INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
INITIALIZE_PASS_END(TwoAddressInstructionPass, DEBUG_TYPE,
"Two-Address instruction pass", false, false)
char &llvm::TwoAddressInstructionPassID = TwoAddressInstructionPass::ID;
static bool isPlainlyKilled(MachineInstr *MI, unsigned Reg, LiveIntervals *LIS);
/// 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(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(AA, SeenStore))
return false;
unsigned DefReg = 0;
SmallSet<unsigned, 4> UseRegs;
for (const MachineOperand &MO : MI->operands()) {
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 = nullptr;
if (LIS) {
LiveInterval &LI = LIS->getInterval(SavedReg);
assert(LI.end() != LI.begin() &&
"Reg should not have empty live interval.");
SlotIndex MBBEndIdx = LIS->getMBBEndIdx(MBB).getPrevSlot();
LiveInterval::const_iterator I = LI.find(MBBEndIdx);
if (I != LI.end() && I->start < MBBEndIdx)
return false;
--I;
KillMI = LIS->getInstructionFromIndex(I->end);
}
if (!KillMI) {
for (MachineOperand &UseMO : MRI->use_nodbg_operands(SavedReg)) {
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 ||
MachineBasicBlock::iterator(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 = nullptr;
MachineBasicBlock::iterator KillPos = KillMI;
++KillPos;
unsigned NumVisited = 0;
for (MachineInstr &OtherMI : llvm::make_range(std::next(OldPos), KillPos)) {
// 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() || (LIS && isPlainlyKilled(&OtherMI, MOReg, LIS))) {
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");
if (!LIS) {
// 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;
}
/// Return the MachineInstr* if it is the single def of the Reg in current BB.
static MachineInstr *getSingleDef(unsigned Reg, MachineBasicBlock *BB,
const MachineRegisterInfo *MRI) {
MachineInstr *Ret = nullptr;
for (MachineInstr &DefMI : MRI->def_instructions(Reg)) {
if (DefMI.getParent() != BB || DefMI.isDebugValue())
continue;
if (!Ret)
Ret = &DefMI;
else if (Ret != &DefMI)
return nullptr;
}
return Ret;
}
/// Check if there is a reversed copy chain from FromReg to ToReg:
/// %Tmp1 = copy %Tmp2;
/// %FromReg = copy %Tmp1;
/// %ToReg = add %FromReg ...
/// %Tmp2 = copy %ToReg;
/// MaxLen specifies the maximum length of the copy chain the func
/// can walk through.
bool TwoAddressInstructionPass::isRevCopyChain(unsigned FromReg, unsigned ToReg,
int Maxlen) {
unsigned TmpReg = FromReg;
for (int i = 0; i < Maxlen; i++) {
MachineInstr *Def = getSingleDef(TmpReg, MBB, MRI);
if (!Def || !Def->isCopy())
return false;
TmpReg = Def->getOperand(1).getReg();
if (TmpReg == ToReg)
return true;
}
return false;
}
/// 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, unsigned Dist,
unsigned &LastDef) {
LastDef = 0;
unsigned LastUse = Dist;
for (MachineOperand &MO : MRI->reg_operands(Reg)) {
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);
}
/// Return true if the specified MI is a copy instruction or an 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;
}
/// Test if the given register value, which is used by the
/// given instruction, is killed by the given instruction.
static bool isPlainlyKilled(MachineInstr *MI, unsigned Reg,
LiveIntervals *LIS) {
if (LIS && TargetRegisterInfo::isVirtualRegister(Reg) &&
!LIS->isNotInMIMap(*MI)) {
// FIXME: Sometimes tryInstructionTransform() will add instructions and
// test whether they can be folded before keeping them. In this case it
// sets a kill before recursively calling tryInstructionTransform() again.
// If there is no interval available, we assume that this instruction is
// one of those. A kill flag is manually inserted on the operand so the
// check below will handle it.
LiveInterval &LI = LIS->getInterval(Reg);
// This is to match the kill flag version where undefs don't have kill
// flags.
if (!LI.hasAtLeastOneValue())
return false;
SlotIndex useIdx = LIS->getInstructionIndex(*MI);
LiveInterval::const_iterator I = LI.find(useIdx);
assert(I != LI.end() && "Reg must be live-in to use.");
return !I->end.isBlock() && SlotIndex::isSameInstr(I->end, useIdx);
}
return MI->killsRegister(Reg);
}
/// 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.
///
/// If allowFalsePositives is true then likely kills are treated as kills even
/// if it can't be proven that they are kills.
static bool isKilled(MachineInstr &MI, unsigned Reg,
const MachineRegisterInfo *MRI,
const TargetInstrInfo *TII,
LiveIntervals *LIS,
bool allowFalsePositives) {
MachineInstr *DefMI = &MI;
for (;;) {
// All uses of physical registers are likely to be kills.
if (TargetRegisterInfo::isPhysicalRegister(Reg) &&
(allowFalsePositives || MRI->hasOneUse(Reg)))
return true;
if (!isPlainlyKilled(DefMI, Reg, LIS))
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 (std::next(Begin) != MRI->def_end())
return true;
DefMI = Begin->getParent();
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;
}
}
/// 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) {
for (unsigned i = 0, NumOps = MI.getNumOperands(); 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;
}
/// 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 nullptr;
MachineInstr &UseMI = *MRI->use_instr_nodbg_begin(Reg);
if (UseMI.getParent() != MBB)
return nullptr;
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 nullptr;
}
/// 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;
}
/// 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);
}
// Returns true if Reg is equal or aliased to at least one register in Set.
static bool regOverlapsSet(const SmallVectorImpl<unsigned> &Set, unsigned Reg,
const TargetRegisterInfo *TRI) {
for (unsigned R : Set)
if (TRI->regsOverlap(R, Reg))
return true;
return false;
}
/// 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, 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 (!isPlainlyKilled(MI, regC, LIS))
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 CompB = FromRegB && regsAreCompatible(FromRegB, ToRegA, TRI);
bool CompC = FromRegC && regsAreCompatible(FromRegC, ToRegA, TRI);
// Compute if any of the following are true:
// -RegB is not tied to a register and RegC is compatible with RegA.
// -RegB is tied to the wrong physical register, but RegC is.
// -RegB is tied to the wrong physical register, and RegC isn't tied.
if ((!FromRegB && CompC) || (FromRegB && !CompB && (!FromRegC || CompC)))
return true;
// Don't compute if any of the following are true:
// -RegC is not tied to a register and RegB is compatible with RegA.
// -RegC is tied to the wrong physical register, but RegB is.
// -RegC is tied to the wrong physical register, and RegB isn't tied.
if ((!FromRegC && CompB) || (FromRegC && !CompC && (!FromRegB || CompB)))
return false;
}
// 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, 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, Dist, LastDefB))
return true;
// Look for situation like this:
// %reg101 = MOV %reg100
// %reg102 = ...
// %reg103 = ADD %reg102, %reg101
// ... = %reg103 ...
// %reg100 = MOV %reg103
// If there is a reversed copy chain from reg101 to reg103, commute the ADD
// to eliminate an otherwise unavoidable copy.
// FIXME:
// We can extend the logic further: If an pair of operands in an insn has
// been merged, the insn could be regarded as a virtual copy, and the virtual
// copy could also be used to construct a copy chain.
// To more generally minimize register copies, ideally the logic of two addr
// instruction pass should be integrated with register allocation pass where
// interference graph is available.
if (isRevCopyChain(regC, regA, MaxDataFlowEdge))
return true;
if (isRevCopyChain(regB, regA, MaxDataFlowEdge))
return false;
// 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;
}
/// 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(MachineInstr *MI,
unsigned DstIdx,
unsigned RegBIdx,
unsigned RegCIdx,
unsigned Dist) {
unsigned RegC = MI->getOperand(RegCIdx).getReg();
DEBUG(dbgs() << "2addr: COMMUTING : " << *MI);
MachineInstr *NewMI = TII->commuteInstruction(*MI, false, RegBIdx, RegCIdx);
if (NewMI == nullptr) {
DEBUG(dbgs() << "2addr: COMMUTING FAILED!\n");
return false;
}
DEBUG(dbgs() << "2addr: COMMUTED TO: " << *NewMI);
assert(NewMI == MI &&
"TargetInstrInfo::commuteInstruction() should not return a new "
"instruction unless it was requested.");
// Update source register map.
unsigned FromRegC = getMappedReg(RegC, SrcRegMap);
if (FromRegC) {
unsigned RegA = MI->getOperand(DstIdx).getReg();
SrcRegMap[RegA] = FromRegC;
}
return true;
}
/// 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));
}
/// 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,
unsigned RegA, unsigned RegB,
unsigned Dist) {
// FIXME: Why does convertToThreeAddress() need an iterator reference?
MachineFunction::iterator MFI = MBB->getIterator();
MachineInstr *NewMI = TII->convertToThreeAddress(MFI, *mi, LV);
assert(MBB->getIterator() == MFI &&
"convertToThreeAddress changed iterator reference");
if (!NewMI)
return false;
DEBUG(dbgs() << "2addr: CONVERTING 2-ADDR: " << *mi);
DEBUG(dbgs() << "2addr: TO 3-ADDR: " << *NewMI);
bool Sunk = false;
if (LIS)
LIS->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(NewMI, RegB, mi);
MBB->erase(mi); // Nuke the old inst.
if (!Sunk) {
DistanceMap.insert(std::make_pair(NewMI, Dist));
mi = NewMI;
nmi = std::next(mi);
}
// Update source and destination register maps.
SrcRegMap.erase(RegA);
DstRegMap.erase(RegB);
return true;
}
/// Scan forward recursively for only uses, update maps if the use is a copy or
/// a two-address instruction.
void
TwoAddressInstructionPass::scanUses(unsigned DstReg) {
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).second)
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!");
}
}
/// 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) {
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);
}
Processed.insert(MI);
}
/// 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::iterator &mi,
MachineBasicBlock::iterator &nmi,
unsigned Reg) {
// Bail immediately if we don't have LV or LIS available. We use them to find
// kills efficiently.
if (!LV && !LIS)
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 = nullptr;
if (LIS) {
LiveInterval &LI = LIS->getInterval(Reg);
assert(LI.end() != LI.begin() &&
"Reg should not have empty live interval.");
SlotIndex MBBEndIdx = LIS->getMBBEndIdx(MBB).getPrevSlot();
LiveInterval::const_iterator I = LI.find(MBBEndIdx);
if (I != LI.end() && I->start < MBBEndIdx)
return false;
--I;
KillMI = LIS->getInstructionFromIndex(I->end);
} else {
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(AA, SeenStore))
return false;
if (TII->getInstrLatency(InstrItins, *MI) > 1)
// FIXME: Needs more sophisticated heuristics.
return false;
SmallVector<unsigned, 2> Uses;
SmallVector<unsigned, 2> Kills;
SmallVector<unsigned, 2> Defs;
for (const MachineOperand &MO : MI->operands()) {
if (!MO.isReg())
continue;
unsigned MOReg = MO.getReg();
if (!MOReg)
continue;
if (MO.isDef())
Defs.push_back(MOReg);
else {
Uses.push_back(MOReg);
if (MOReg != Reg && (MO.isKill() ||
(LIS && isPlainlyKilled(MI, MOReg, LIS))))
Kills.push_back(MOReg);
}
}
// Move the copies connected to MI down as well.
MachineBasicBlock::iterator Begin = MI;
MachineBasicBlock::iterator AfterMI = std::next(Begin);
MachineBasicBlock::iterator End = AfterMI;
while (End->isCopy() &&
regOverlapsSet(Defs, End->getOperand(1).getReg(), TRI)) {
Defs.push_back(End->getOperand(0).getReg());
++End;
}
// Check if the reschedule will not break dependencies.
unsigned NumVisited = 0;
MachineBasicBlock::iterator KillPos = KillMI;
++KillPos;
for (MachineInstr &OtherMI : llvm::make_range(End, KillPos)) {
// 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 (const MachineOperand &MO : OtherMI.operands()) {
if (!MO.isReg())
continue;
unsigned MOReg = MO.getReg();
if (!MOReg)
continue;
if (MO.isDef()) {
if (regOverlapsSet(Uses, MOReg, TRI))
// Physical register use would be clobbered.
return false;
if (!MO.isDead() && regOverlapsSet(Defs, MOReg, TRI))
// 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 (regOverlapsSet(Defs, MOReg, TRI))
return false;
bool isKill =
MO.isKill() || (LIS && isPlainlyKilled(&OtherMI, MOReg, LIS));
if (MOReg != Reg && ((isKill && regOverlapsSet(Uses, MOReg, TRI)) ||
regOverlapsSet(Kills, MOReg, TRI)))
// Don't want to extend other live ranges and update kills.
return false;
if (MOReg == Reg && !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 (Begin != MBB->begin() && std::prev(Begin)->isDebugValue())
--Begin;
nmi = End;
MachineBasicBlock::iterator InsertPos = KillPos;
if (LIS) {
// We have to move the copies first so that the MBB is still well-formed
// when calling handleMove().
for (MachineBasicBlock::iterator MBBI = AfterMI; MBBI != End;) {
auto CopyMI = MBBI++;
MBB->splice(InsertPos, MBB, CopyMI);
LIS->handleMove(*CopyMI);
InsertPos = CopyMI;
}
End = std::next(MachineBasicBlock::iterator(MI));
}
// Copies following MI may have been moved as well.
MBB->splice(InsertPos, MBB, Begin, End);
DistanceMap.erase(DI);
// Update live variables
if (LIS) {
LIS->handleMove(*MI);
} else {
LV->removeVirtualRegisterKilled(Reg, *KillMI);
LV->addVirtualRegisterKilled(Reg, *MI);
}
DEBUG(dbgs() << "\trescheduled below kill: " << *KillMI);
return true;
}
/// 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) {
for (MachineInstr &DefMI : MRI->def_instructions(Reg)) {
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;
}
/// 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::iterator &mi,
MachineBasicBlock::iterator &nmi,
unsigned Reg) {
// Bail immediately if we don't have LV or LIS available. We use them to find
// kills efficiently.
if (!LV && !LIS)
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 = nullptr;
if (LIS) {
LiveInterval &LI = LIS->getInterval(Reg);
assert(LI.end() != LI.begin() &&
"Reg should not have empty live interval.");
SlotIndex MBBEndIdx = LIS->getMBBEndIdx(MBB).getPrevSlot();
LiveInterval::const_iterator I = LI.find(MBBEndIdx);
if (I != LI.end() && I->start < MBBEndIdx)
return false;
--I;
KillMI = LIS->getInstructionFromIndex(I->end);
} else {
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(AA, SeenStore))
return false;
SmallSet<unsigned, 2> Uses;
SmallSet<unsigned, 2> Kills;
SmallSet<unsigned, 2> Defs;
SmallSet<unsigned, 2> LiveDefs;
for (const MachineOperand &MO : KillMI->operands()) {
if (!MO.isReg())
continue;
unsigned MOReg = MO.getReg();
if (MO.isUse()) {
if (!MOReg)
continue;
if (isDefTooClose(MOReg, DI->second, MI))
return false;
bool isKill = MO.isKill() || (LIS && isPlainlyKilled(KillMI, MOReg, LIS));
if (MOReg == Reg && !isKill)
return false;
Uses.insert(MOReg);
if (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;
for (MachineInstr &OtherMI :
llvm::make_range(mi, MachineBasicBlock::iterator(KillMI))) {
// 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 (const MachineOperand &MO : OtherMI.operands()) {
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() || (LIS && isPlainlyKilled(&OtherMI, MOReg, LIS))))
// 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() && std::prev(InsertPos)->isDebugValue())
--InsertPos;
MachineBasicBlock::iterator From = KillMI;
MachineBasicBlock::iterator To = std::next(From);
while (std::prev(From)->isDebugValue())
--From;
MBB->splice(InsertPos, MBB, From, To);
nmi = std::prev(InsertPos); // Backtrack so we process the moved instr.
DistanceMap.erase(DI);
// Update live variables
if (LIS) {
LIS->handleMove(*KillMI);
} else {
LV->removeVirtualRegisterKilled(Reg, *KillMI);
LV->addVirtualRegisterKilled(Reg, *MI);
}
DEBUG(dbgs() << "\trescheduled kill: " << *KillMI);
return true;
}
/// Tries to commute the operand 'BaseOpIdx' and some other operand in the
/// given machine instruction to improve opportunities for coalescing and
/// elimination of a register to register copy.
///
/// 'DstOpIdx' specifies the index of MI def operand.
/// 'BaseOpKilled' specifies if the register associated with 'BaseOpIdx'
/// operand is killed by the given instruction.
/// The 'Dist' arguments provides the distance of MI from the start of the
/// current basic block and it is used to determine if it is profitable
/// to commute operands in the instruction.
///
/// Returns true if the transformation happened. Otherwise, returns false.
bool TwoAddressInstructionPass::tryInstructionCommute(MachineInstr *MI,
unsigned DstOpIdx,
unsigned BaseOpIdx,
bool BaseOpKilled,
unsigned Dist) {
if (!MI->isCommutable())
return false;
unsigned DstOpReg = MI->getOperand(DstOpIdx).getReg();
unsigned BaseOpReg = MI->getOperand(BaseOpIdx).getReg();
unsigned OpsNum = MI->getDesc().getNumOperands();
unsigned OtherOpIdx = MI->getDesc().getNumDefs();
for (; OtherOpIdx < OpsNum; OtherOpIdx++) {
// The call of findCommutedOpIndices below only checks if BaseOpIdx
// and OtherOpIdx are commutable, it does not really search for
// other commutable operands and does not change the values of passed
// variables.
if (OtherOpIdx == BaseOpIdx || !MI->getOperand(OtherOpIdx).isReg() ||
!TII->findCommutedOpIndices(*MI, BaseOpIdx, OtherOpIdx))
continue;
unsigned OtherOpReg = MI->getOperand(OtherOpIdx).getReg();
bool AggressiveCommute = false;
// If OtherOp dies but BaseOp does not, swap the OtherOp and BaseOp
// operands. This makes the live ranges of DstOp and OtherOp joinable.
bool DoCommute =
!BaseOpKilled && isKilled(*MI, OtherOpReg, MRI, TII, LIS, false);
if (!DoCommute &&
isProfitableToCommute(DstOpReg, BaseOpReg, OtherOpReg, MI, Dist)) {
DoCommute = true;
AggressiveCommute = true;
}
// If it's profitable to commute, try to do so.
if (DoCommute && commuteInstruction(MI, DstOpIdx, BaseOpIdx, OtherOpIdx,
Dist)) {
++NumCommuted;
if (AggressiveCommute)
++NumAggrCommuted;
return true;
}
}
return false;
}
/// 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). If the shouldOnlyCommute flag is true, only
/// instruction commutation is attempted.
bool TwoAddressInstructionPass::
tryInstructionTransform(MachineBasicBlock::iterator &mi,
MachineBasicBlock::iterator &nmi,
unsigned SrcIdx, unsigned DstIdx,
unsigned Dist, bool shouldOnlyCommute) {
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, LIS, true);
if (TargetRegisterInfo::isVirtualRegister(regA))
scanUses(regA);
bool Commuted = tryInstructionCommute(&MI, DstIdx, SrcIdx, regBKilled, Dist);
// If the instruction is convertible to 3 Addr, instead
// of returning try 3 Addr transformation aggresively and
// use this variable to check later. Because it might be better.
// For example, we can just use `leal (%rsi,%rdi), %eax` and `ret`
// instead of the following code.
// addl %esi, %edi
// movl %edi, %eax
// ret
if (Commuted && !MI.isConvertibleTo3Addr())
return false;
if (shouldOnlyCommute)
return false;
// If there is one more use of regB later in the same MBB, consider
// re-schedule this MI below it.
if (!Commuted && EnableRescheduling && rescheduleMIBelowKill(mi, nmi, regB)) {
++NumReSchedDowns;
return true;
}
// If we commuted, regB may have changed so we should re-sample it to avoid
// confusing the three address conversion below.
if (Commuted) {
regB = MI.getOperand(SrcIdx).getReg();
regBKilled = isKilled(MI, regB, MRI, TII, LIS, 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, regA, regB, Dist)) {
++NumConvertedTo3Addr;
return true; // Done with this instruction.
}
}
}
// Return if it is commuted but 3 addr conversion is failed.
if (Commuted)
return false;
// 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 (EnableRescheduling && rescheduleKillAboveMI(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.
MBB->insert(mi, NewMIs[0]);
MBB->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 TransformResult =
tryInstructionTransform(NewMI, mi, NewSrcIdx, NewDstIdx, Dist, true);
(void)TransformResult;
assert(!TransformResult &&
"tryInstructionTransform() should return false.");
if (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]);
}
SmallVector<unsigned, 4> OrigRegs;
if (LIS) {
for (const MachineOperand &MO : MI.operands()) {
if (MO.isReg())
OrigRegs.push_back(MO.getReg());
}
}
MI.eraseFromParent();
// Update LiveIntervals.
if (LIS) {
MachineBasicBlock::iterator Begin(NewMIs[0]);
MachineBasicBlock::iterator End(NewMIs[1]);
LIS->repairIntervalsInRange(MBB, Begin, End, OrigRegs);
}
mi = NewMIs[1];
} 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() && !DstMO.getSubReg()) {
// 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);
SrcMO.setSubReg(0);
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;
for (unsigned tpi = 0, tpe = TiedPairs.size(); tpi != tpe; ++tpi) {
const MachineOperand &DstMO = MI->getOperand(TiedPairs[tpi].second);
IsEarlyClobber |= DstMO.isEarlyClobber();
}
bool RemovedKillFlag = false;
bool AllUsesCopied = true;
unsigned LastCopiedReg = 0;
SlotIndex LastCopyIdx;
unsigned RegB = 0;
unsigned SubRegB = 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();
// Grab RegB from the instruction because it may have changed if the
// instruction was commuted.
RegB = MI->getOperand(SrcIdx).getReg();
SubRegB = MI->getOperand(SrcIdx).getSubReg();
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.
MachineInstrBuilder MIB = BuildMI(*MI->getParent(), MI, MI->getDebugLoc(),
TII->get(TargetOpcode::COPY), RegA);
// If this operand is folding a truncation, the truncation now moves to the
// copy so that the register classes remain valid for the operands.
MIB.addReg(RegB, 0, SubRegB);
const TargetRegisterClass *RC = MRI->getRegClass(RegB);
if (SubRegB) {
if (TargetRegisterInfo::isVirtualRegister(RegA)) {
assert(TRI->getMatchingSuperRegClass(RC, MRI->getRegClass(RegA),
SubRegB) &&
"tied subregister must be a truncation");
// The superreg class will not be used to constrain the subreg class.
RC = nullptr;
}
else {
assert(TRI->getMatchingSuperReg(RegA, SubRegB, MRI->getRegClass(RegB))
&& "tied subregister must be a truncation");
}
}
// Update DistanceMap.
MachineBasicBlock::iterator PrevMI = MI;
--PrevMI;
DistanceMap.insert(std::make_pair(&*PrevMI, Dist));
DistanceMap[MI] = ++Dist;
if (LIS) {
LastCopyIdx = LIS->InsertMachineInstrInMaps(*PrevMI).getRegSlot();
if (TargetRegisterInfo::isVirtualRegister(RegA)) {
LiveInterval &LI = LIS->getInterval(RegA);
VNInfo *VNI = LI.getNextValue(LastCopyIdx, LIS->getVNInfoAllocator());
SlotIndex endIdx =
LIS->getInstructionIndex(*MI).getRegSlot(IsEarlyClobber);
LI.addSegment(LiveInterval::Segment(LastCopyIdx, endIdx, VNI));
}
}
DEBUG(dbgs() << "\t\tprepend:\t" << *MIB);
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, RC);
MO.setReg(RegA);
// The getMatchingSuper asserts guarantee that the register class projected
// by SubRegB is compatible with RegA with no subregister. So regardless of
// whether the dest oper writes a subreg, the source oper should not.
MO.setSubReg(0);
// Propagate SrcRegMap.
SrcRegMap[RegA] = RegB;
}
if (AllUsesCopied) {
if (!IsEarlyClobber) {
// Replace other (un-tied) uses of regB with LastCopiedReg.
for (MachineOperand &MO : MI->operands()) {
if (MO.isReg() && MO.getReg() == RegB &&
MO.isUse()) {
if (MO.isKill()) {
MO.setIsKill(false);
RemovedKillFlag = true;
}
MO.setReg(LastCopiedReg);
MO.setSubReg(MO.getSubReg());
}
}
}
// Update live variables for regB.
if (RemovedKillFlag && LV && LV->getVarInfo(RegB).removeKill(*MI)) {
MachineBasicBlock::iterator PrevMI = MI;
--PrevMI;
LV->addVirtualRegisterKilled(RegB, *PrevMI);
}
// Update LiveIntervals.
if (LIS) {
LiveInterval &LI = LIS->getInterval(RegB);
SlotIndex MIIdx = LIS->getInstructionIndex(*MI);
LiveInterval::const_iterator I = LI.find(MIIdx);
assert(I != LI.end() && "RegB must be live-in to use.");
SlotIndex UseIdx = MIIdx.getRegSlot(IsEarlyClobber);
if (I->end == UseIdx)
LI.removeSegment(LastCopyIdx, UseIdx);
}
} 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 (MachineOperand &MO : MI->operands()) {
if (MO.isReg() && MO.getReg() == RegB && MO.isUse()) {
MO.setIsKill(true);
break;
}
}
}
}
/// Reduce two-address instructions to two operands.
bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &Func) {
MF = &Func;
const TargetMachine &TM = MF->getTarget();
MRI = &MF->getRegInfo();
TII = MF->getSubtarget().getInstrInfo();
TRI = MF->getSubtarget().getRegisterInfo();
InstrItins = MF->getSubtarget().getInstrItineraryData();
LV = getAnalysisIfAvailable<LiveVariables>();
LIS = getAnalysisIfAvailable<LiveIntervals>();
if (auto *AAPass = getAnalysisIfAvailable<AAResultsWrapperPass>())
AA = &AAPass->getAAResults();
else
AA = nullptr;
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;
for (MachineFunction::iterator MBBI = MF->begin(), MBBE = MF->end();
MBBI != MBBE; ++MBBI) {
MBB = &*MBBI;
unsigned Dist = 0;
DistanceMap.clear();
SrcRegMap.clear();
DstRegMap.clear();
Processed.clear();
for (MachineBasicBlock::iterator mi = MBB->begin(), me = MBB->end();
mi != me; ) {
MachineBasicBlock::iterator nmi = std::next(mi);
if (mi->isDebugValue()) {
mi = nmi;
continue;
}
// Expand REG_SEQUENCE instructions. This will position mi at the first
// expanded instruction.
if (mi->isRegSequence())
eliminateRegSequence(mi);
DistanceMap.insert(std::make_pair(&*mi, ++Dist));
processCopy(&*mi);
// 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) {
SmallVectorImpl<std::pair<unsigned, unsigned> > &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, SrcIdx, DstIdx, Dist, false)) {
// 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 (auto &TO : TiedOperands) {
processTiedPairs(&*mi, TO.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;
}
}
if (LIS)
MF->verify(this, "After two-address instruction pass");
return MadeChange;
}
/// Eliminate a REG_SEQUENCE instruction as part of the de-ssa process.
///
/// The instruction is turned into a sequence of sub-register copies:
///
/// %dst = REG_SEQUENCE %v1, ssub0, %v2, ssub1
///
/// Becomes:
///
/// %dst:ssub0<def,undef> = COPY %v1
/// %dst:ssub1<def> = COPY %v2
///
void TwoAddressInstructionPass::
eliminateRegSequence(MachineBasicBlock::iterator &MBBI) {
MachineInstr &MI = *MBBI;
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(nullptr);
}
SmallVector<unsigned, 4> OrigRegs;
if (LIS) {
OrigRegs.push_back(MI.getOperand(0).getReg());
for (unsigned i = 1, e = MI.getNumOperands(); i < e; i += 2)
OrigRegs.push_back(MI.getOperand(i).getReg());
}
bool DefEmitted = false;
for (unsigned i = 1, e = MI.getNumOperands(); i < e; i += 2) {
MachineOperand &UseMO = MI.getOperand(i);
unsigned SrcReg = UseMO.getReg();
unsigned SubIdx = MI.getOperand(i+1).getImm();
// Nothing needs to be inserted for <undef> operands.
if (UseMO.isUndef())
continue;
// Defer any kill flag to the last operand using SrcReg. Otherwise, we
// might insert a COPY that uses SrcReg after is was killed.
bool isKill = UseMO.isKill();
if (isKill)
for (unsigned j = i + 2; j < e; j += 2)
if (MI.getOperand(j).getReg() == SrcReg) {
MI.getOperand(j).setIsKill();
UseMO.setIsKill(false);
isKill = false;
break;
}
// Insert the sub-register copy.
MachineInstr *CopyMI = BuildMI(*MI.getParent(), MI, MI.getDebugLoc(),
TII->get(TargetOpcode::COPY))
.addReg(DstReg, RegState::Define, SubIdx)
.add(UseMO);
// The first def needs an <undef> flag because there is no live register
// before it.
if (!DefEmitted) {
CopyMI->getOperand(0).setIsUndef(true);
// Return an iterator pointing to the first inserted instr.
MBBI = CopyMI;
}
DefEmitted = true;
// Update LiveVariables' kill info.
if (LV && isKill && !TargetRegisterInfo::isPhysicalRegister(SrcReg))
LV->replaceKillInstruction(SrcReg, MI, *CopyMI);
DEBUG(dbgs() << "Inserted: " << *CopyMI);
}
MachineBasicBlock::iterator EndMBBI =
std::next(MachineBasicBlock::iterator(MI));
if (!DefEmitted) {
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();
}
// Udpate LiveIntervals.
if (LIS)
LIS->repairIntervalsInRange(MBB, MBBI, EndMBBI, OrigRegs);
}
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