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

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//===- TwoAddressInstructionPass.cpp - Two-Address instruction pass -------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the TwoAddress instruction pass which is used
// by most register allocators. Two-Address instructions are rewritten
// from:
//
// A = B op C
//
// to:
//
// A = B
// A op= C
//
// Note that if a register allocator chooses to use this pass, that it
// has to be capable of handling the non-SSA nature of these rewritten
// virtual registers.
//
// It is also worth noting that the duplicate operand of the two
// address instruction is removed.
//
//===----------------------------------------------------------------------===//
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/iterator_range.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/CodeGen/LiveInterval.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/LiveVariables.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/SlotIndexes.h"
#include "llvm/MC/MCInstrDesc.h"
#include "llvm/MC/MCInstrItineraries.h"
#include "llvm/Pass.h"
#include "llvm/Support/CodeGen.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/TargetOpcodes.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetSubtargetInfo.h"
#include <cassert>
#include <iterator>
#include <utility>
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);
using TiedPairList = SmallVector<std::pair<unsigned, unsigned>, 4>;
using TiedOperandMap = SmallDenseMap<unsigned, TiedPairList>;
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;
char &llvm::TwoAddressInstructionPassID = TwoAddressInstructionPass::ID;
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)
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 : 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;
while (true) {
// 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 : 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 :
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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