1 //===-- TwoAddressInstructionPass.cpp - Two-Address instruction pass ------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the TwoAddress instruction pass which is used
11 // by most register allocators. Two-Address instructions are rewritten
21 // Note that if a register allocator chooses to use this pass, that it
22 // has to be capable of handling the non-SSA nature of these rewritten
25 // It is also worth noting that the duplicate operand of the two
26 // address instruction is removed.
28 //===----------------------------------------------------------------------===//
30 #define DEBUG_TYPE "twoaddrinstr"
31 #include "llvm/CodeGen/Passes.h"
32 #include "llvm/Function.h"
33 #include "llvm/CodeGen/LiveVariables.h"
34 #include "llvm/CodeGen/MachineFunctionPass.h"
35 #include "llvm/CodeGen/MachineInstr.h"
36 #include "llvm/CodeGen/MachineInstrBuilder.h"
37 #include "llvm/CodeGen/MachineRegisterInfo.h"
38 #include "llvm/Analysis/AliasAnalysis.h"
39 #include "llvm/MC/MCInstrItineraries.h"
40 #include "llvm/Target/TargetRegisterInfo.h"
41 #include "llvm/Target/TargetInstrInfo.h"
42 #include "llvm/Target/TargetMachine.h"
43 #include "llvm/Target/TargetOptions.h"
44 #include "llvm/Support/Debug.h"
45 #include "llvm/Support/ErrorHandling.h"
46 #include "llvm/ADT/BitVector.h"
47 #include "llvm/ADT/DenseMap.h"
48 #include "llvm/ADT/SmallSet.h"
49 #include "llvm/ADT/Statistic.h"
50 #include "llvm/ADT/STLExtras.h"
53 STATISTIC(NumTwoAddressInstrs, "Number of two-address instructions");
54 STATISTIC(NumCommuted , "Number of instructions commuted to coalesce");
55 STATISTIC(NumAggrCommuted , "Number of instructions aggressively commuted");
56 STATISTIC(NumConvertedTo3Addr, "Number of instructions promoted to 3-address");
57 STATISTIC(Num3AddrSunk, "Number of 3-address instructions sunk");
58 STATISTIC(NumReMats, "Number of instructions re-materialized");
59 STATISTIC(NumDeletes, "Number of dead instructions deleted");
60 STATISTIC(NumReSchedUps, "Number of instructions re-scheduled up");
61 STATISTIC(NumReSchedDowns, "Number of instructions re-scheduled down");
64 class TwoAddressInstructionPass : public MachineFunctionPass {
65 const TargetInstrInfo *TII;
66 const TargetRegisterInfo *TRI;
67 const InstrItineraryData *InstrItins;
68 MachineRegisterInfo *MRI;
71 CodeGenOpt::Level OptLevel;
73 // DistanceMap - Keep track the distance of a MI from the start of the
74 // current basic block.
75 DenseMap<MachineInstr*, unsigned> DistanceMap;
77 // SrcRegMap - A map from virtual registers to physical registers which
78 // are likely targets to be coalesced to due to copies from physical
79 // registers to virtual registers. e.g. v1024 = move r0.
80 DenseMap<unsigned, unsigned> SrcRegMap;
82 // DstRegMap - A map from virtual registers to physical registers which
83 // are likely targets to be coalesced to due to copies to physical
84 // registers from virtual registers. e.g. r1 = move v1024.
85 DenseMap<unsigned, unsigned> DstRegMap;
87 /// RegSequences - Keep track the list of REG_SEQUENCE instructions seen
88 /// during the initial walk of the machine function.
89 SmallVector<MachineInstr*, 16> RegSequences;
91 bool Sink3AddrInstruction(MachineBasicBlock *MBB, MachineInstr *MI,
93 MachineBasicBlock::iterator OldPos);
95 bool isProfitableToReMat(unsigned Reg, const TargetRegisterClass *RC,
96 MachineInstr *MI, MachineInstr *DefMI,
97 MachineBasicBlock *MBB, unsigned Loc);
99 bool NoUseAfterLastDef(unsigned Reg, MachineBasicBlock *MBB, unsigned Dist,
102 MachineInstr *FindLastUseInMBB(unsigned Reg, MachineBasicBlock *MBB,
105 bool isProfitableToCommute(unsigned regA, unsigned regB, unsigned regC,
106 MachineInstr *MI, MachineBasicBlock *MBB,
109 bool CommuteInstruction(MachineBasicBlock::iterator &mi,
110 MachineFunction::iterator &mbbi,
111 unsigned RegB, unsigned RegC, unsigned Dist);
113 bool isProfitableToConv3Addr(unsigned RegA, unsigned RegB);
115 bool ConvertInstTo3Addr(MachineBasicBlock::iterator &mi,
116 MachineBasicBlock::iterator &nmi,
117 MachineFunction::iterator &mbbi,
118 unsigned RegA, unsigned RegB, unsigned Dist);
120 typedef std::pair<std::pair<unsigned, bool>, MachineInstr*> NewKill;
121 bool canUpdateDeletedKills(SmallVector<unsigned, 4> &Kills,
122 SmallVector<NewKill, 4> &NewKills,
123 MachineBasicBlock *MBB, unsigned Dist);
124 bool DeleteUnusedInstr(MachineBasicBlock::iterator &mi,
125 MachineBasicBlock::iterator &nmi,
126 MachineFunction::iterator &mbbi, unsigned Dist);
128 bool isDefTooClose(unsigned Reg, unsigned Dist,
129 MachineInstr *MI, MachineBasicBlock *MBB);
131 bool RescheduleMIBelowKill(MachineBasicBlock *MBB,
132 MachineBasicBlock::iterator &mi,
133 MachineBasicBlock::iterator &nmi,
135 bool RescheduleKillAboveMI(MachineBasicBlock *MBB,
136 MachineBasicBlock::iterator &mi,
137 MachineBasicBlock::iterator &nmi,
140 bool TryInstructionTransform(MachineBasicBlock::iterator &mi,
141 MachineBasicBlock::iterator &nmi,
142 MachineFunction::iterator &mbbi,
143 unsigned SrcIdx, unsigned DstIdx,
145 SmallPtrSet<MachineInstr*, 8> &Processed);
147 void ScanUses(unsigned DstReg, MachineBasicBlock *MBB,
148 SmallPtrSet<MachineInstr*, 8> &Processed);
150 void ProcessCopy(MachineInstr *MI, MachineBasicBlock *MBB,
151 SmallPtrSet<MachineInstr*, 8> &Processed);
153 void CoalesceExtSubRegs(SmallVector<unsigned,4> &Srcs, unsigned DstReg);
155 /// EliminateRegSequences - Eliminate REG_SEQUENCE instructions as part
156 /// of the de-ssa process. This replaces sources of REG_SEQUENCE as
157 /// sub-register references of the register defined by REG_SEQUENCE.
158 bool EliminateRegSequences();
161 static char ID; // Pass identification, replacement for typeid
162 TwoAddressInstructionPass() : MachineFunctionPass(ID) {
163 initializeTwoAddressInstructionPassPass(*PassRegistry::getPassRegistry());
166 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
167 AU.setPreservesCFG();
168 AU.addRequired<AliasAnalysis>();
169 AU.addPreserved<LiveVariables>();
170 AU.addPreservedID(MachineLoopInfoID);
171 AU.addPreservedID(MachineDominatorsID);
172 MachineFunctionPass::getAnalysisUsage(AU);
175 /// runOnMachineFunction - Pass entry point.
176 bool runOnMachineFunction(MachineFunction&);
180 char TwoAddressInstructionPass::ID = 0;
181 INITIALIZE_PASS_BEGIN(TwoAddressInstructionPass, "twoaddressinstruction",
182 "Two-Address instruction pass", false, false)
183 INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
184 INITIALIZE_PASS_END(TwoAddressInstructionPass, "twoaddressinstruction",
185 "Two-Address instruction pass", false, false)
187 char &llvm::TwoAddressInstructionPassID = TwoAddressInstructionPass::ID;
189 /// Sink3AddrInstruction - A two-address instruction has been converted to a
190 /// three-address instruction to avoid clobbering a register. Try to sink it
191 /// past the instruction that would kill the above mentioned register to reduce
192 /// register pressure.
193 bool TwoAddressInstructionPass::Sink3AddrInstruction(MachineBasicBlock *MBB,
194 MachineInstr *MI, unsigned SavedReg,
195 MachineBasicBlock::iterator OldPos) {
196 // FIXME: Shouldn't we be trying to do this before we three-addressify the
197 // instruction? After this transformation is done, we no longer need
198 // the instruction to be in three-address form.
200 // Check if it's safe to move this instruction.
201 bool SeenStore = true; // Be conservative.
202 if (!MI->isSafeToMove(TII, AA, SeenStore))
206 SmallSet<unsigned, 4> UseRegs;
208 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
209 const MachineOperand &MO = MI->getOperand(i);
212 unsigned MOReg = MO.getReg();
215 if (MO.isUse() && MOReg != SavedReg)
216 UseRegs.insert(MO.getReg());
220 // Don't try to move it if it implicitly defines a register.
223 // For now, don't move any instructions that define multiple registers.
225 DefReg = MO.getReg();
228 // Find the instruction that kills SavedReg.
229 MachineInstr *KillMI = NULL;
230 for (MachineRegisterInfo::use_nodbg_iterator
231 UI = MRI->use_nodbg_begin(SavedReg),
232 UE = MRI->use_nodbg_end(); UI != UE; ++UI) {
233 MachineOperand &UseMO = UI.getOperand();
236 KillMI = UseMO.getParent();
240 // If we find the instruction that kills SavedReg, and it is in an
241 // appropriate location, we can try to sink the current instruction
243 if (!KillMI || KillMI->getParent() != MBB || KillMI == MI ||
244 KillMI->isTerminator())
247 // If any of the definitions are used by another instruction between the
248 // position and the kill use, then it's not safe to sink it.
250 // FIXME: This can be sped up if there is an easy way to query whether an
251 // instruction is before or after another instruction. Then we can use
252 // MachineRegisterInfo def / use instead.
253 MachineOperand *KillMO = NULL;
254 MachineBasicBlock::iterator KillPos = KillMI;
257 unsigned NumVisited = 0;
258 for (MachineBasicBlock::iterator I = llvm::next(OldPos); I != KillPos; ++I) {
259 MachineInstr *OtherMI = I;
260 // DBG_VALUE cannot be counted against the limit.
261 if (OtherMI->isDebugValue())
263 if (NumVisited > 30) // FIXME: Arbitrary limit to reduce compile time cost.
266 for (unsigned i = 0, e = OtherMI->getNumOperands(); i != e; ++i) {
267 MachineOperand &MO = OtherMI->getOperand(i);
270 unsigned MOReg = MO.getReg();
277 if (OtherMI == KillMI && MOReg == SavedReg)
278 // Save the operand that kills the register. We want to unset the kill
279 // marker if we can sink MI past it.
281 else if (UseRegs.count(MOReg))
282 // One of the uses is killed before the destination.
288 // Update kill and LV information.
289 KillMO->setIsKill(false);
290 KillMO = MI->findRegisterUseOperand(SavedReg, false, TRI);
291 KillMO->setIsKill(true);
294 LV->replaceKillInstruction(SavedReg, KillMI, MI);
296 // Move instruction to its destination.
298 MBB->insert(KillPos, MI);
304 /// isTwoAddrUse - Return true if the specified MI is using the specified
305 /// register as a two-address operand.
306 static bool isTwoAddrUse(MachineInstr *UseMI, unsigned Reg) {
307 const MCInstrDesc &MCID = UseMI->getDesc();
308 for (unsigned i = 0, e = MCID.getNumOperands(); i != e; ++i) {
309 MachineOperand &MO = UseMI->getOperand(i);
310 if (MO.isReg() && MO.getReg() == Reg &&
311 (MO.isDef() || UseMI->isRegTiedToDefOperand(i)))
312 // Earlier use is a two-address one.
318 /// isProfitableToReMat - Return true if the heuristics determines it is likely
319 /// to be profitable to re-materialize the definition of Reg rather than copy
322 TwoAddressInstructionPass::isProfitableToReMat(unsigned Reg,
323 const TargetRegisterClass *RC,
324 MachineInstr *MI, MachineInstr *DefMI,
325 MachineBasicBlock *MBB, unsigned Loc) {
326 bool OtherUse = false;
327 for (MachineRegisterInfo::use_nodbg_iterator UI = MRI->use_nodbg_begin(Reg),
328 UE = MRI->use_nodbg_end(); UI != UE; ++UI) {
329 MachineOperand &UseMO = UI.getOperand();
330 MachineInstr *UseMI = UseMO.getParent();
331 MachineBasicBlock *UseMBB = UseMI->getParent();
333 DenseMap<MachineInstr*, unsigned>::iterator DI = DistanceMap.find(UseMI);
334 if (DI != DistanceMap.end() && DI->second == Loc)
335 continue; // Current use.
337 // There is at least one other use in the MBB that will clobber the
339 if (isTwoAddrUse(UseMI, Reg))
344 // If other uses in MBB are not two-address uses, then don't remat.
348 // No other uses in the same block, remat if it's defined in the same
349 // block so it does not unnecessarily extend the live range.
350 return MBB == DefMI->getParent();
353 /// NoUseAfterLastDef - Return true if there are no intervening uses between the
354 /// last instruction in the MBB that defines the specified register and the
355 /// two-address instruction which is being processed. It also returns the last
356 /// def location by reference
357 bool TwoAddressInstructionPass::NoUseAfterLastDef(unsigned Reg,
358 MachineBasicBlock *MBB, unsigned Dist,
361 unsigned LastUse = Dist;
362 for (MachineRegisterInfo::reg_iterator I = MRI->reg_begin(Reg),
363 E = MRI->reg_end(); I != E; ++I) {
364 MachineOperand &MO = I.getOperand();
365 MachineInstr *MI = MO.getParent();
366 if (MI->getParent() != MBB || MI->isDebugValue())
368 DenseMap<MachineInstr*, unsigned>::iterator DI = DistanceMap.find(MI);
369 if (DI == DistanceMap.end())
371 if (MO.isUse() && DI->second < LastUse)
372 LastUse = DI->second;
373 if (MO.isDef() && DI->second > LastDef)
374 LastDef = DI->second;
377 return !(LastUse > LastDef && LastUse < Dist);
380 MachineInstr *TwoAddressInstructionPass::FindLastUseInMBB(unsigned Reg,
381 MachineBasicBlock *MBB,
383 unsigned LastUseDist = 0;
384 MachineInstr *LastUse = 0;
385 for (MachineRegisterInfo::reg_iterator I = MRI->reg_begin(Reg),
386 E = MRI->reg_end(); I != E; ++I) {
387 MachineOperand &MO = I.getOperand();
388 MachineInstr *MI = MO.getParent();
389 if (MI->getParent() != MBB || MI->isDebugValue())
391 DenseMap<MachineInstr*, unsigned>::iterator DI = DistanceMap.find(MI);
392 if (DI == DistanceMap.end())
394 if (DI->second >= Dist)
397 if (MO.isUse() && DI->second > LastUseDist) {
399 LastUseDist = DI->second;
405 /// isCopyToReg - Return true if the specified MI is a copy instruction or
406 /// a extract_subreg instruction. It also returns the source and destination
407 /// registers and whether they are physical registers by reference.
408 static bool isCopyToReg(MachineInstr &MI, const TargetInstrInfo *TII,
409 unsigned &SrcReg, unsigned &DstReg,
410 bool &IsSrcPhys, bool &IsDstPhys) {
414 DstReg = MI.getOperand(0).getReg();
415 SrcReg = MI.getOperand(1).getReg();
416 } else if (MI.isInsertSubreg() || MI.isSubregToReg()) {
417 DstReg = MI.getOperand(0).getReg();
418 SrcReg = MI.getOperand(2).getReg();
422 IsSrcPhys = TargetRegisterInfo::isPhysicalRegister(SrcReg);
423 IsDstPhys = TargetRegisterInfo::isPhysicalRegister(DstReg);
427 /// isKilled - Test if the given register value, which is used by the given
428 /// instruction, is killed by the given instruction. This looks through
429 /// coalescable copies to see if the original value is potentially not killed.
431 /// For example, in this code:
433 /// %reg1034 = copy %reg1024
434 /// %reg1035 = copy %reg1025<kill>
435 /// %reg1036 = add %reg1034<kill>, %reg1035<kill>
437 /// %reg1034 is not considered to be killed, since it is copied from a
438 /// register which is not killed. Treating it as not killed lets the
439 /// normal heuristics commute the (two-address) add, which lets
440 /// coalescing eliminate the extra copy.
442 static bool isKilled(MachineInstr &MI, unsigned Reg,
443 const MachineRegisterInfo *MRI,
444 const TargetInstrInfo *TII) {
445 MachineInstr *DefMI = &MI;
447 if (!DefMI->killsRegister(Reg))
449 if (TargetRegisterInfo::isPhysicalRegister(Reg))
451 MachineRegisterInfo::def_iterator Begin = MRI->def_begin(Reg);
452 // If there are multiple defs, we can't do a simple analysis, so just
453 // go with what the kill flag says.
454 if (llvm::next(Begin) != MRI->def_end())
457 bool IsSrcPhys, IsDstPhys;
458 unsigned SrcReg, DstReg;
459 // If the def is something other than a copy, then it isn't going to
460 // be coalesced, so follow the kill flag.
461 if (!isCopyToReg(*DefMI, TII, SrcReg, DstReg, IsSrcPhys, IsDstPhys))
467 /// isTwoAddrUse - Return true if the specified MI uses the specified register
468 /// as a two-address use. If so, return the destination register by reference.
469 static bool isTwoAddrUse(MachineInstr &MI, unsigned Reg, unsigned &DstReg) {
470 const MCInstrDesc &MCID = MI.getDesc();
471 unsigned NumOps = MI.isInlineAsm()
472 ? MI.getNumOperands() : MCID.getNumOperands();
473 for (unsigned i = 0; i != NumOps; ++i) {
474 const MachineOperand &MO = MI.getOperand(i);
475 if (!MO.isReg() || !MO.isUse() || MO.getReg() != Reg)
478 if (MI.isRegTiedToDefOperand(i, &ti)) {
479 DstReg = MI.getOperand(ti).getReg();
486 /// findOnlyInterestingUse - Given a register, if has a single in-basic block
487 /// use, return the use instruction if it's a copy or a two-address use.
489 MachineInstr *findOnlyInterestingUse(unsigned Reg, MachineBasicBlock *MBB,
490 MachineRegisterInfo *MRI,
491 const TargetInstrInfo *TII,
493 unsigned &DstReg, bool &IsDstPhys) {
494 if (!MRI->hasOneNonDBGUse(Reg))
495 // None or more than one use.
497 MachineInstr &UseMI = *MRI->use_nodbg_begin(Reg);
498 if (UseMI.getParent() != MBB)
502 if (isCopyToReg(UseMI, TII, SrcReg, DstReg, IsSrcPhys, IsDstPhys)) {
507 if (isTwoAddrUse(UseMI, Reg, DstReg)) {
508 IsDstPhys = TargetRegisterInfo::isPhysicalRegister(DstReg);
514 /// getMappedReg - Return the physical register the specified virtual register
515 /// might be mapped to.
517 getMappedReg(unsigned Reg, DenseMap<unsigned, unsigned> &RegMap) {
518 while (TargetRegisterInfo::isVirtualRegister(Reg)) {
519 DenseMap<unsigned, unsigned>::iterator SI = RegMap.find(Reg);
520 if (SI == RegMap.end())
524 if (TargetRegisterInfo::isPhysicalRegister(Reg))
529 /// regsAreCompatible - Return true if the two registers are equal or aliased.
532 regsAreCompatible(unsigned RegA, unsigned RegB, const TargetRegisterInfo *TRI) {
537 return TRI->regsOverlap(RegA, RegB);
541 /// isProfitableToReMat - Return true if it's potentially profitable to commute
542 /// the two-address instruction that's being processed.
544 TwoAddressInstructionPass::isProfitableToCommute(unsigned regA, unsigned regB,
546 MachineInstr *MI, MachineBasicBlock *MBB,
548 if (OptLevel == CodeGenOpt::None)
551 // Determine if it's profitable to commute this two address instruction. In
552 // general, we want no uses between this instruction and the definition of
553 // the two-address register.
555 // %reg1028<def> = EXTRACT_SUBREG %reg1027<kill>, 1
556 // %reg1029<def> = MOV8rr %reg1028
557 // %reg1029<def> = SHR8ri %reg1029, 7, %EFLAGS<imp-def,dead>
558 // insert => %reg1030<def> = MOV8rr %reg1028
559 // %reg1030<def> = ADD8rr %reg1028<kill>, %reg1029<kill>, %EFLAGS<imp-def,dead>
560 // In this case, it might not be possible to coalesce the second MOV8rr
561 // instruction if the first one is coalesced. So it would be profitable to
563 // %reg1028<def> = EXTRACT_SUBREG %reg1027<kill>, 1
564 // %reg1029<def> = MOV8rr %reg1028
565 // %reg1029<def> = SHR8ri %reg1029, 7, %EFLAGS<imp-def,dead>
566 // insert => %reg1030<def> = MOV8rr %reg1029
567 // %reg1030<def> = ADD8rr %reg1029<kill>, %reg1028<kill>, %EFLAGS<imp-def,dead>
569 if (!MI->killsRegister(regC))
572 // Ok, we have something like:
573 // %reg1030<def> = ADD8rr %reg1028<kill>, %reg1029<kill>, %EFLAGS<imp-def,dead>
574 // let's see if it's worth commuting it.
576 // Look for situations like this:
577 // %reg1024<def> = MOV r1
578 // %reg1025<def> = MOV r0
579 // %reg1026<def> = ADD %reg1024, %reg1025
581 // Commute the ADD to hopefully eliminate an otherwise unavoidable copy.
582 unsigned ToRegA = getMappedReg(regA, DstRegMap);
584 unsigned FromRegB = getMappedReg(regB, SrcRegMap);
585 unsigned FromRegC = getMappedReg(regC, SrcRegMap);
586 bool BComp = !FromRegB || regsAreCompatible(FromRegB, ToRegA, TRI);
587 bool CComp = !FromRegC || regsAreCompatible(FromRegC, ToRegA, TRI);
589 return !BComp && CComp;
592 // If there is a use of regC between its last def (could be livein) and this
593 // instruction, then bail.
594 unsigned LastDefC = 0;
595 if (!NoUseAfterLastDef(regC, MBB, Dist, LastDefC))
598 // If there is a use of regB between its last def (could be livein) and this
599 // instruction, then go ahead and make this transformation.
600 unsigned LastDefB = 0;
601 if (!NoUseAfterLastDef(regB, MBB, Dist, LastDefB))
604 // Since there are no intervening uses for both registers, then commute
605 // if the def of regC is closer. Its live interval is shorter.
606 return LastDefB && LastDefC && LastDefC > LastDefB;
609 /// CommuteInstruction - Commute a two-address instruction and update the basic
610 /// block, distance map, and live variables if needed. Return true if it is
613 TwoAddressInstructionPass::CommuteInstruction(MachineBasicBlock::iterator &mi,
614 MachineFunction::iterator &mbbi,
615 unsigned RegB, unsigned RegC, unsigned Dist) {
616 MachineInstr *MI = mi;
617 DEBUG(dbgs() << "2addr: COMMUTING : " << *MI);
618 MachineInstr *NewMI = TII->commuteInstruction(MI);
621 DEBUG(dbgs() << "2addr: COMMUTING FAILED!\n");
625 DEBUG(dbgs() << "2addr: COMMUTED TO: " << *NewMI);
626 // If the instruction changed to commute it, update livevar.
629 // Update live variables
630 LV->replaceKillInstruction(RegC, MI, NewMI);
632 mbbi->insert(mi, NewMI); // Insert the new inst
633 mbbi->erase(mi); // Nuke the old inst.
635 DistanceMap.insert(std::make_pair(NewMI, Dist));
638 // Update source register map.
639 unsigned FromRegC = getMappedReg(RegC, SrcRegMap);
641 unsigned RegA = MI->getOperand(0).getReg();
642 SrcRegMap[RegA] = FromRegC;
648 /// isProfitableToConv3Addr - Return true if it is profitable to convert the
649 /// given 2-address instruction to a 3-address one.
651 TwoAddressInstructionPass::isProfitableToConv3Addr(unsigned RegA,unsigned RegB){
652 // Look for situations like this:
653 // %reg1024<def> = MOV r1
654 // %reg1025<def> = MOV r0
655 // %reg1026<def> = ADD %reg1024, %reg1025
657 // Turn ADD into a 3-address instruction to avoid a copy.
658 unsigned FromRegB = getMappedReg(RegB, SrcRegMap);
661 unsigned ToRegA = getMappedReg(RegA, DstRegMap);
662 return (ToRegA && !regsAreCompatible(FromRegB, ToRegA, TRI));
665 /// ConvertInstTo3Addr - Convert the specified two-address instruction into a
666 /// three address one. Return true if this transformation was successful.
668 TwoAddressInstructionPass::ConvertInstTo3Addr(MachineBasicBlock::iterator &mi,
669 MachineBasicBlock::iterator &nmi,
670 MachineFunction::iterator &mbbi,
671 unsigned RegA, unsigned RegB,
673 MachineInstr *NewMI = TII->convertToThreeAddress(mbbi, mi, LV);
675 DEBUG(dbgs() << "2addr: CONVERTING 2-ADDR: " << *mi);
676 DEBUG(dbgs() << "2addr: TO 3-ADDR: " << *NewMI);
679 if (NewMI->findRegisterUseOperand(RegB, false, TRI))
680 // FIXME: Temporary workaround. If the new instruction doesn't
681 // uses RegB, convertToThreeAddress must have created more
682 // then one instruction.
683 Sunk = Sink3AddrInstruction(mbbi, NewMI, RegB, mi);
685 mbbi->erase(mi); // Nuke the old inst.
688 DistanceMap.insert(std::make_pair(NewMI, Dist));
690 nmi = llvm::next(mi);
693 // Update source and destination register maps.
694 SrcRegMap.erase(RegA);
695 DstRegMap.erase(RegB);
702 /// ScanUses - Scan forward recursively for only uses, update maps if the use
703 /// is a copy or a two-address instruction.
705 TwoAddressInstructionPass::ScanUses(unsigned DstReg, MachineBasicBlock *MBB,
706 SmallPtrSet<MachineInstr*, 8> &Processed) {
707 SmallVector<unsigned, 4> VirtRegPairs;
711 unsigned Reg = DstReg;
712 while (MachineInstr *UseMI = findOnlyInterestingUse(Reg, MBB, MRI, TII,IsCopy,
713 NewReg, IsDstPhys)) {
714 if (IsCopy && !Processed.insert(UseMI))
717 DenseMap<MachineInstr*, unsigned>::iterator DI = DistanceMap.find(UseMI);
718 if (DI != DistanceMap.end())
719 // Earlier in the same MBB.Reached via a back edge.
723 VirtRegPairs.push_back(NewReg);
726 bool isNew = SrcRegMap.insert(std::make_pair(NewReg, Reg)).second;
728 assert(SrcRegMap[NewReg] == Reg && "Can't map to two src registers!");
729 VirtRegPairs.push_back(NewReg);
733 if (!VirtRegPairs.empty()) {
734 unsigned ToReg = VirtRegPairs.back();
735 VirtRegPairs.pop_back();
736 while (!VirtRegPairs.empty()) {
737 unsigned FromReg = VirtRegPairs.back();
738 VirtRegPairs.pop_back();
739 bool isNew = DstRegMap.insert(std::make_pair(FromReg, ToReg)).second;
741 assert(DstRegMap[FromReg] == ToReg &&"Can't map to two dst registers!");
744 bool isNew = DstRegMap.insert(std::make_pair(DstReg, ToReg)).second;
746 assert(DstRegMap[DstReg] == ToReg && "Can't map to two dst registers!");
750 /// ProcessCopy - If the specified instruction is not yet processed, process it
751 /// if it's a copy. For a copy instruction, we find the physical registers the
752 /// source and destination registers might be mapped to. These are kept in
753 /// point-to maps used to determine future optimizations. e.g.
756 /// v1026 = add v1024, v1025
758 /// If 'add' is a two-address instruction, v1024, v1026 are both potentially
759 /// coalesced to r0 (from the input side). v1025 is mapped to r1. v1026 is
760 /// potentially joined with r1 on the output side. It's worthwhile to commute
761 /// 'add' to eliminate a copy.
762 void TwoAddressInstructionPass::ProcessCopy(MachineInstr *MI,
763 MachineBasicBlock *MBB,
764 SmallPtrSet<MachineInstr*, 8> &Processed) {
765 if (Processed.count(MI))
768 bool IsSrcPhys, IsDstPhys;
769 unsigned SrcReg, DstReg;
770 if (!isCopyToReg(*MI, TII, SrcReg, DstReg, IsSrcPhys, IsDstPhys))
773 if (IsDstPhys && !IsSrcPhys)
774 DstRegMap.insert(std::make_pair(SrcReg, DstReg));
775 else if (!IsDstPhys && IsSrcPhys) {
776 bool isNew = SrcRegMap.insert(std::make_pair(DstReg, SrcReg)).second;
778 assert(SrcRegMap[DstReg] == SrcReg &&
779 "Can't map to two src physical registers!");
781 ScanUses(DstReg, MBB, Processed);
784 Processed.insert(MI);
788 /// isSafeToDelete - If the specified instruction does not produce any side
789 /// effects and all of its defs are dead, then it's safe to delete.
790 static bool isSafeToDelete(MachineInstr *MI,
791 const TargetInstrInfo *TII,
792 SmallVector<unsigned, 4> &Kills) {
793 if (MI->mayStore() || MI->isCall())
795 if (MI->isTerminator() || MI->hasUnmodeledSideEffects())
798 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
799 MachineOperand &MO = MI->getOperand(i);
802 if (MO.isDef() && !MO.isDead())
804 if (MO.isUse() && MO.isKill())
805 Kills.push_back(MO.getReg());
810 /// canUpdateDeletedKills - Check if all the registers listed in Kills are
811 /// killed by instructions in MBB preceding the current instruction at
812 /// position Dist. If so, return true and record information about the
813 /// preceding kills in NewKills.
814 bool TwoAddressInstructionPass::
815 canUpdateDeletedKills(SmallVector<unsigned, 4> &Kills,
816 SmallVector<NewKill, 4> &NewKills,
817 MachineBasicBlock *MBB, unsigned Dist) {
818 while (!Kills.empty()) {
819 unsigned Kill = Kills.back();
821 if (TargetRegisterInfo::isPhysicalRegister(Kill))
824 MachineInstr *LastKill = FindLastUseInMBB(Kill, MBB, Dist);
828 bool isModRef = LastKill->definesRegister(Kill);
829 NewKills.push_back(std::make_pair(std::make_pair(Kill, isModRef),
835 /// DeleteUnusedInstr - If an instruction with a tied register operand can
836 /// be safely deleted, just delete it.
838 TwoAddressInstructionPass::DeleteUnusedInstr(MachineBasicBlock::iterator &mi,
839 MachineBasicBlock::iterator &nmi,
840 MachineFunction::iterator &mbbi,
842 // Check if the instruction has no side effects and if all its defs are dead.
843 SmallVector<unsigned, 4> Kills;
844 if (!isSafeToDelete(mi, TII, Kills))
847 // If this instruction kills some virtual registers, we need to
848 // update the kill information. If it's not possible to do so,
850 SmallVector<NewKill, 4> NewKills;
851 if (!canUpdateDeletedKills(Kills, NewKills, &*mbbi, Dist))
855 while (!NewKills.empty()) {
856 MachineInstr *NewKill = NewKills.back().second;
857 unsigned Kill = NewKills.back().first.first;
858 bool isDead = NewKills.back().first.second;
860 if (LV->removeVirtualRegisterKilled(Kill, mi)) {
862 LV->addVirtualRegisterDead(Kill, NewKill);
864 LV->addVirtualRegisterKilled(Kill, NewKill);
869 mbbi->erase(mi); // Nuke the old inst.
874 /// RescheduleMIBelowKill - If there is one more local instruction that reads
875 /// 'Reg' and it kills 'Reg, consider moving the instruction below the kill
876 /// instruction in order to eliminate the need for the copy.
878 TwoAddressInstructionPass::RescheduleMIBelowKill(MachineBasicBlock *MBB,
879 MachineBasicBlock::iterator &mi,
880 MachineBasicBlock::iterator &nmi,
882 // Bail immediately if we don't have LV available. We use it to find kills
887 MachineInstr *MI = &*mi;
888 DenseMap<MachineInstr*, unsigned>::iterator DI = DistanceMap.find(MI);
889 if (DI == DistanceMap.end())
890 // Must be created from unfolded load. Don't waste time trying this.
893 MachineInstr *KillMI = LV->getVarInfo(Reg).findKill(MBB);
894 if (!KillMI || MI == KillMI || KillMI->isCopy() || KillMI->isCopyLike())
895 // Don't mess with copies, they may be coalesced later.
898 if (KillMI->hasUnmodeledSideEffects() || KillMI->isCall() ||
899 KillMI->isBranch() || KillMI->isTerminator())
900 // Don't move pass calls, etc.
904 if (isTwoAddrUse(*KillMI, Reg, DstReg))
907 bool SeenStore = true;
908 if (!MI->isSafeToMove(TII, AA, SeenStore))
911 if (TII->getInstrLatency(InstrItins, MI) > 1)
912 // FIXME: Needs more sophisticated heuristics.
915 SmallSet<unsigned, 2> Uses;
916 SmallSet<unsigned, 2> Kills;
917 SmallSet<unsigned, 2> Defs;
918 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
919 const MachineOperand &MO = MI->getOperand(i);
922 unsigned MOReg = MO.getReg();
929 if (MO.isKill() && MOReg != Reg)
934 // Move the copies connected to MI down as well.
935 MachineBasicBlock::iterator From = MI;
936 MachineBasicBlock::iterator To = llvm::next(From);
937 while (To->isCopy() && Defs.count(To->getOperand(1).getReg())) {
938 Defs.insert(To->getOperand(0).getReg());
942 // Check if the reschedule will not break depedencies.
943 unsigned NumVisited = 0;
944 MachineBasicBlock::iterator KillPos = KillMI;
946 for (MachineBasicBlock::iterator I = To; I != KillPos; ++I) {
947 MachineInstr *OtherMI = I;
948 // DBG_VALUE cannot be counted against the limit.
949 if (OtherMI->isDebugValue())
951 if (NumVisited > 10) // FIXME: Arbitrary limit to reduce compile time cost.
954 if (OtherMI->hasUnmodeledSideEffects() || OtherMI->isCall() ||
955 OtherMI->isBranch() || OtherMI->isTerminator())
956 // Don't move pass calls, etc.
958 for (unsigned i = 0, e = OtherMI->getNumOperands(); i != e; ++i) {
959 const MachineOperand &MO = OtherMI->getOperand(i);
962 unsigned MOReg = MO.getReg();
966 if (Uses.count(MOReg))
967 // Physical register use would be clobbered.
969 if (!MO.isDead() && Defs.count(MOReg))
970 // May clobber a physical register def.
971 // FIXME: This may be too conservative. It's ok if the instruction
972 // is sunken completely below the use.
975 if (Defs.count(MOReg))
978 ((MO.isKill() && Uses.count(MOReg)) || Kills.count(MOReg)))
979 // Don't want to extend other live ranges and update kills.
981 if (MOReg == Reg && !MO.isKill())
982 // We can't schedule across a use of the register in question.
984 // Ensure that if this is register in question, its the kill we expect.
985 assert((MOReg != Reg || OtherMI == KillMI) &&
986 "Found multiple kills of a register in a basic block");
991 // Move debug info as well.
992 while (From != MBB->begin() && llvm::prior(From)->isDebugValue())
995 // Copies following MI may have been moved as well.
997 MBB->splice(KillPos, MBB, From, To);
998 DistanceMap.erase(DI);
1000 // Update live variables
1001 LV->removeVirtualRegisterKilled(Reg, KillMI);
1002 LV->addVirtualRegisterKilled(Reg, MI);
1007 /// isDefTooClose - Return true if the re-scheduling will put the given
1008 /// instruction too close to the defs of its register dependencies.
1009 bool TwoAddressInstructionPass::isDefTooClose(unsigned Reg, unsigned Dist,
1011 MachineBasicBlock *MBB) {
1012 for (MachineRegisterInfo::def_iterator DI = MRI->def_begin(Reg),
1013 DE = MRI->def_end(); DI != DE; ++DI) {
1014 MachineInstr *DefMI = &*DI;
1015 if (DefMI->getParent() != MBB || DefMI->isCopy() || DefMI->isCopyLike())
1018 return true; // MI is defining something KillMI uses
1019 DenseMap<MachineInstr*, unsigned>::iterator DDI = DistanceMap.find(DefMI);
1020 if (DDI == DistanceMap.end())
1021 return true; // Below MI
1022 unsigned DefDist = DDI->second;
1023 assert(Dist > DefDist && "Visited def already?");
1024 if (TII->getInstrLatency(InstrItins, DefMI) > (Dist - DefDist))
1030 /// RescheduleKillAboveMI - If there is one more local instruction that reads
1031 /// 'Reg' and it kills 'Reg, consider moving the kill instruction above the
1032 /// current two-address instruction in order to eliminate the need for the
1035 TwoAddressInstructionPass::RescheduleKillAboveMI(MachineBasicBlock *MBB,
1036 MachineBasicBlock::iterator &mi,
1037 MachineBasicBlock::iterator &nmi,
1039 // Bail immediately if we don't have LV available. We use it to find kills
1044 MachineInstr *MI = &*mi;
1045 DenseMap<MachineInstr*, unsigned>::iterator DI = DistanceMap.find(MI);
1046 if (DI == DistanceMap.end())
1047 // Must be created from unfolded load. Don't waste time trying this.
1050 MachineInstr *KillMI = LV->getVarInfo(Reg).findKill(MBB);
1051 if (!KillMI || MI == KillMI || KillMI->isCopy() || KillMI->isCopyLike())
1052 // Don't mess with copies, they may be coalesced later.
1056 if (isTwoAddrUse(*KillMI, Reg, DstReg))
1059 bool SeenStore = true;
1060 if (!KillMI->isSafeToMove(TII, AA, SeenStore))
1063 SmallSet<unsigned, 2> Uses;
1064 SmallSet<unsigned, 2> Kills;
1065 SmallSet<unsigned, 2> Defs;
1066 SmallSet<unsigned, 2> LiveDefs;
1067 for (unsigned i = 0, e = KillMI->getNumOperands(); i != e; ++i) {
1068 const MachineOperand &MO = KillMI->getOperand(i);
1071 unsigned MOReg = MO.getReg();
1075 if (isDefTooClose(MOReg, DI->second, MI, MBB))
1077 if (MOReg == Reg && !MO.isKill())
1080 if (MO.isKill() && MOReg != Reg)
1081 Kills.insert(MOReg);
1082 } else if (TargetRegisterInfo::isPhysicalRegister(MOReg)) {
1085 LiveDefs.insert(MOReg);
1089 // Check if the reschedule will not break depedencies.
1090 unsigned NumVisited = 0;
1091 MachineBasicBlock::iterator KillPos = KillMI;
1092 for (MachineBasicBlock::iterator I = mi; I != KillPos; ++I) {
1093 MachineInstr *OtherMI = I;
1094 // DBG_VALUE cannot be counted against the limit.
1095 if (OtherMI->isDebugValue())
1097 if (NumVisited > 10) // FIXME: Arbitrary limit to reduce compile time cost.
1100 if (OtherMI->hasUnmodeledSideEffects() || OtherMI->isCall() ||
1101 OtherMI->isBranch() || OtherMI->isTerminator())
1102 // Don't move pass calls, etc.
1104 SmallVector<unsigned, 2> OtherDefs;
1105 for (unsigned i = 0, e = OtherMI->getNumOperands(); i != e; ++i) {
1106 const MachineOperand &MO = OtherMI->getOperand(i);
1109 unsigned MOReg = MO.getReg();
1113 if (Defs.count(MOReg))
1114 // Moving KillMI can clobber the physical register if the def has
1117 if (Kills.count(MOReg))
1118 // Don't want to extend other live ranges and update kills.
1120 if (OtherMI != MI && MOReg == Reg && !MO.isKill())
1121 // We can't schedule across a use of the register in question.
1124 OtherDefs.push_back(MOReg);
1128 for (unsigned i = 0, e = OtherDefs.size(); i != e; ++i) {
1129 unsigned MOReg = OtherDefs[i];
1130 if (Uses.count(MOReg))
1132 if (TargetRegisterInfo::isPhysicalRegister(MOReg) &&
1133 LiveDefs.count(MOReg))
1135 // Physical register def is seen.
1140 // Move the old kill above MI, don't forget to move debug info as well.
1141 MachineBasicBlock::iterator InsertPos = mi;
1142 while (InsertPos != MBB->begin() && llvm::prior(InsertPos)->isDebugValue())
1144 MachineBasicBlock::iterator From = KillMI;
1145 MachineBasicBlock::iterator To = llvm::next(From);
1146 while (llvm::prior(From)->isDebugValue())
1148 MBB->splice(InsertPos, MBB, From, To);
1150 nmi = llvm::prior(InsertPos); // Backtrack so we process the moved instr.
1151 DistanceMap.erase(DI);
1153 // Update live variables
1154 LV->removeVirtualRegisterKilled(Reg, KillMI);
1155 LV->addVirtualRegisterKilled(Reg, MI);
1160 /// TryInstructionTransform - For the case where an instruction has a single
1161 /// pair of tied register operands, attempt some transformations that may
1162 /// either eliminate the tied operands or improve the opportunities for
1163 /// coalescing away the register copy. Returns true if no copy needs to be
1164 /// inserted to untie mi's operands (either because they were untied, or
1165 /// because mi was rescheduled, and will be visited again later).
1166 bool TwoAddressInstructionPass::
1167 TryInstructionTransform(MachineBasicBlock::iterator &mi,
1168 MachineBasicBlock::iterator &nmi,
1169 MachineFunction::iterator &mbbi,
1170 unsigned SrcIdx, unsigned DstIdx, unsigned Dist,
1171 SmallPtrSet<MachineInstr*, 8> &Processed) {
1172 if (OptLevel == CodeGenOpt::None)
1175 MachineInstr &MI = *mi;
1176 unsigned regA = MI.getOperand(DstIdx).getReg();
1177 unsigned regB = MI.getOperand(SrcIdx).getReg();
1179 assert(TargetRegisterInfo::isVirtualRegister(regB) &&
1180 "cannot make instruction into two-address form");
1182 // If regA is dead and the instruction can be deleted, just delete
1183 // it so it doesn't clobber regB.
1184 bool regBKilled = isKilled(MI, regB, MRI, TII);
1185 if (!regBKilled && MI.getOperand(DstIdx).isDead() &&
1186 DeleteUnusedInstr(mi, nmi, mbbi, Dist)) {
1188 return true; // Done with this instruction.
1191 if (TargetRegisterInfo::isVirtualRegister(regA))
1192 ScanUses(regA, &*mbbi, Processed);
1194 // Check if it is profitable to commute the operands.
1195 unsigned SrcOp1, SrcOp2;
1197 unsigned regCIdx = ~0U;
1198 bool TryCommute = false;
1199 bool AggressiveCommute = false;
1200 if (MI.isCommutable() && MI.getNumOperands() >= 3 &&
1201 TII->findCommutedOpIndices(&MI, SrcOp1, SrcOp2)) {
1202 if (SrcIdx == SrcOp1)
1204 else if (SrcIdx == SrcOp2)
1207 if (regCIdx != ~0U) {
1208 regC = MI.getOperand(regCIdx).getReg();
1209 if (!regBKilled && isKilled(MI, regC, MRI, TII))
1210 // If C dies but B does not, swap the B and C operands.
1211 // This makes the live ranges of A and C joinable.
1213 else if (isProfitableToCommute(regA, regB, regC, &MI, mbbi, Dist)) {
1215 AggressiveCommute = true;
1220 // If it's profitable to commute, try to do so.
1221 if (TryCommute && CommuteInstruction(mi, mbbi, regB, regC, Dist)) {
1223 if (AggressiveCommute)
1228 // If there is one more use of regB later in the same MBB, consider
1229 // re-schedule this MI below it.
1230 if (RescheduleMIBelowKill(mbbi, mi, nmi, regB)) {
1235 if (MI.isConvertibleTo3Addr()) {
1236 // This instruction is potentially convertible to a true
1237 // three-address instruction. Check if it is profitable.
1238 if (!regBKilled || isProfitableToConv3Addr(regA, regB)) {
1239 // Try to convert it.
1240 if (ConvertInstTo3Addr(mi, nmi, mbbi, regA, regB, Dist)) {
1241 ++NumConvertedTo3Addr;
1242 return true; // Done with this instruction.
1247 // If there is one more use of regB later in the same MBB, consider
1248 // re-schedule it before this MI if it's legal.
1249 if (RescheduleKillAboveMI(mbbi, mi, nmi, regB)) {
1254 // If this is an instruction with a load folded into it, try unfolding
1255 // the load, e.g. avoid this:
1257 // addq (%rax), %rcx
1258 // in favor of this:
1259 // movq (%rax), %rcx
1261 // because it's preferable to schedule a load than a register copy.
1262 if (MI.mayLoad() && !regBKilled) {
1263 // Determine if a load can be unfolded.
1264 unsigned LoadRegIndex;
1266 TII->getOpcodeAfterMemoryUnfold(MI.getOpcode(),
1267 /*UnfoldLoad=*/true,
1268 /*UnfoldStore=*/false,
1271 const MCInstrDesc &UnfoldMCID = TII->get(NewOpc);
1272 if (UnfoldMCID.getNumDefs() == 1) {
1273 MachineFunction &MF = *mbbi->getParent();
1276 DEBUG(dbgs() << "2addr: UNFOLDING: " << MI);
1277 const TargetRegisterClass *RC =
1278 TRI->getAllocatableClass(
1279 TII->getRegClass(UnfoldMCID, LoadRegIndex, TRI, MF));
1280 unsigned Reg = MRI->createVirtualRegister(RC);
1281 SmallVector<MachineInstr *, 2> NewMIs;
1282 if (!TII->unfoldMemoryOperand(MF, &MI, Reg,
1283 /*UnfoldLoad=*/true,/*UnfoldStore=*/false,
1285 DEBUG(dbgs() << "2addr: ABANDONING UNFOLD\n");
1288 assert(NewMIs.size() == 2 &&
1289 "Unfolded a load into multiple instructions!");
1290 // The load was previously folded, so this is the only use.
1291 NewMIs[1]->addRegisterKilled(Reg, TRI);
1293 // Tentatively insert the instructions into the block so that they
1294 // look "normal" to the transformation logic.
1295 mbbi->insert(mi, NewMIs[0]);
1296 mbbi->insert(mi, NewMIs[1]);
1298 DEBUG(dbgs() << "2addr: NEW LOAD: " << *NewMIs[0]
1299 << "2addr: NEW INST: " << *NewMIs[1]);
1301 // Transform the instruction, now that it no longer has a load.
1302 unsigned NewDstIdx = NewMIs[1]->findRegisterDefOperandIdx(regA);
1303 unsigned NewSrcIdx = NewMIs[1]->findRegisterUseOperandIdx(regB);
1304 MachineBasicBlock::iterator NewMI = NewMIs[1];
1305 bool TransformSuccess =
1306 TryInstructionTransform(NewMI, mi, mbbi,
1307 NewSrcIdx, NewDstIdx, Dist, Processed);
1308 if (TransformSuccess ||
1309 NewMIs[1]->getOperand(NewSrcIdx).isKill()) {
1310 // Success, or at least we made an improvement. Keep the unfolded
1311 // instructions and discard the original.
1313 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
1314 MachineOperand &MO = MI.getOperand(i);
1316 TargetRegisterInfo::isVirtualRegister(MO.getReg())) {
1319 if (NewMIs[0]->killsRegister(MO.getReg()))
1320 LV->replaceKillInstruction(MO.getReg(), &MI, NewMIs[0]);
1322 assert(NewMIs[1]->killsRegister(MO.getReg()) &&
1323 "Kill missing after load unfold!");
1324 LV->replaceKillInstruction(MO.getReg(), &MI, NewMIs[1]);
1327 } else if (LV->removeVirtualRegisterDead(MO.getReg(), &MI)) {
1328 if (NewMIs[1]->registerDefIsDead(MO.getReg()))
1329 LV->addVirtualRegisterDead(MO.getReg(), NewMIs[1]);
1331 assert(NewMIs[0]->registerDefIsDead(MO.getReg()) &&
1332 "Dead flag missing after load unfold!");
1333 LV->addVirtualRegisterDead(MO.getReg(), NewMIs[0]);
1338 LV->addVirtualRegisterKilled(Reg, NewMIs[1]);
1340 MI.eraseFromParent();
1342 if (TransformSuccess)
1345 // Transforming didn't eliminate the tie and didn't lead to an
1346 // improvement. Clean up the unfolded instructions and keep the
1348 DEBUG(dbgs() << "2addr: ABANDONING UNFOLD\n");
1349 NewMIs[0]->eraseFromParent();
1350 NewMIs[1]->eraseFromParent();
1359 /// runOnMachineFunction - Reduce two-address instructions to two operands.
1361 bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) {
1362 const TargetMachine &TM = MF.getTarget();
1363 MRI = &MF.getRegInfo();
1364 TII = TM.getInstrInfo();
1365 TRI = TM.getRegisterInfo();
1366 InstrItins = TM.getInstrItineraryData();
1367 LV = getAnalysisIfAvailable<LiveVariables>();
1368 AA = &getAnalysis<AliasAnalysis>();
1369 OptLevel = TM.getOptLevel();
1371 bool MadeChange = false;
1373 DEBUG(dbgs() << "********** REWRITING TWO-ADDR INSTRS **********\n");
1374 DEBUG(dbgs() << "********** Function: "
1375 << MF.getFunction()->getName() << '\n');
1377 // This pass takes the function out of SSA form.
1380 // ReMatRegs - Keep track of the registers whose def's are remat'ed.
1381 BitVector ReMatRegs(MRI->getNumVirtRegs());
1383 typedef DenseMap<unsigned, SmallVector<std::pair<unsigned, unsigned>, 4> >
1385 TiedOperandMap TiedOperands(4);
1387 SmallPtrSet<MachineInstr*, 8> Processed;
1388 for (MachineFunction::iterator mbbi = MF.begin(), mbbe = MF.end();
1389 mbbi != mbbe; ++mbbi) {
1391 DistanceMap.clear();
1395 for (MachineBasicBlock::iterator mi = mbbi->begin(), me = mbbi->end();
1397 MachineBasicBlock::iterator nmi = llvm::next(mi);
1398 if (mi->isDebugValue()) {
1403 // Remember REG_SEQUENCE instructions, we'll deal with them later.
1404 if (mi->isRegSequence())
1405 RegSequences.push_back(&*mi);
1407 const MCInstrDesc &MCID = mi->getDesc();
1408 bool FirstTied = true;
1410 DistanceMap.insert(std::make_pair(mi, ++Dist));
1412 ProcessCopy(&*mi, &*mbbi, Processed);
1414 // First scan through all the tied register uses in this instruction
1415 // and record a list of pairs of tied operands for each register.
1416 unsigned NumOps = mi->isInlineAsm()
1417 ? mi->getNumOperands() : MCID.getNumOperands();
1418 for (unsigned SrcIdx = 0; SrcIdx < NumOps; ++SrcIdx) {
1419 unsigned DstIdx = 0;
1420 if (!mi->isRegTiedToDefOperand(SrcIdx, &DstIdx))
1425 ++NumTwoAddressInstrs;
1426 DEBUG(dbgs() << '\t' << *mi);
1429 assert(mi->getOperand(SrcIdx).isReg() &&
1430 mi->getOperand(SrcIdx).getReg() &&
1431 mi->getOperand(SrcIdx).isUse() &&
1432 "two address instruction invalid");
1434 unsigned regB = mi->getOperand(SrcIdx).getReg();
1436 // Deal with <undef> uses immediately - simply rewrite the src operand.
1437 if (mi->getOperand(SrcIdx).isUndef()) {
1438 unsigned DstReg = mi->getOperand(DstIdx).getReg();
1439 // Constrain the DstReg register class if required.
1440 if (TargetRegisterInfo::isVirtualRegister(DstReg))
1441 if (const TargetRegisterClass *RC = TII->getRegClass(MCID, SrcIdx,
1443 MRI->constrainRegClass(DstReg, RC);
1444 mi->getOperand(SrcIdx).setReg(DstReg);
1445 DEBUG(dbgs() << "\t\trewrite undef:\t" << *mi);
1448 TiedOperands[regB].push_back(std::make_pair(SrcIdx, DstIdx));
1451 // Now iterate over the information collected above.
1452 for (TiedOperandMap::iterator OI = TiedOperands.begin(),
1453 OE = TiedOperands.end(); OI != OE; ++OI) {
1454 SmallVector<std::pair<unsigned, unsigned>, 4> &TiedPairs = OI->second;
1456 // If the instruction has a single pair of tied operands, try some
1457 // transformations that may either eliminate the tied operands or
1458 // improve the opportunities for coalescing away the register copy.
1459 if (TiedOperands.size() == 1 && TiedPairs.size() == 1) {
1460 unsigned SrcIdx = TiedPairs[0].first;
1461 unsigned DstIdx = TiedPairs[0].second;
1463 // If the registers are already equal, nothing needs to be done.
1464 if (mi->getOperand(SrcIdx).getReg() ==
1465 mi->getOperand(DstIdx).getReg())
1466 break; // Done with this instruction.
1468 if (TryInstructionTransform(mi, nmi, mbbi, SrcIdx, DstIdx, Dist,
1470 break; // The tied operands have been eliminated.
1473 bool IsEarlyClobber = false;
1474 bool RemovedKillFlag = false;
1475 bool AllUsesCopied = true;
1476 unsigned LastCopiedReg = 0;
1477 unsigned regB = OI->first;
1478 for (unsigned tpi = 0, tpe = TiedPairs.size(); tpi != tpe; ++tpi) {
1479 unsigned SrcIdx = TiedPairs[tpi].first;
1480 unsigned DstIdx = TiedPairs[tpi].second;
1482 const MachineOperand &DstMO = mi->getOperand(DstIdx);
1483 unsigned regA = DstMO.getReg();
1484 IsEarlyClobber |= DstMO.isEarlyClobber();
1486 // Grab regB from the instruction because it may have changed if the
1487 // instruction was commuted.
1488 regB = mi->getOperand(SrcIdx).getReg();
1491 // The register is tied to multiple destinations (or else we would
1492 // not have continued this far), but this use of the register
1493 // already matches the tied destination. Leave it.
1494 AllUsesCopied = false;
1497 LastCopiedReg = regA;
1499 assert(TargetRegisterInfo::isVirtualRegister(regB) &&
1500 "cannot make instruction into two-address form");
1503 // First, verify that we don't have a use of "a" in the instruction
1504 // (a = b + a for example) because our transformation will not
1505 // work. This should never occur because we are in SSA form.
1506 for (unsigned i = 0; i != mi->getNumOperands(); ++i)
1507 assert(i == DstIdx ||
1508 !mi->getOperand(i).isReg() ||
1509 mi->getOperand(i).getReg() != regA);
1512 // Emit a copy or rematerialize the definition.
1513 bool isCopy = false;
1514 const TargetRegisterClass *rc = MRI->getRegClass(regB);
1515 MachineInstr *DefMI = MRI->getUniqueVRegDef(regB);
1516 // If it's safe and profitable, remat the definition instead of
1519 DefMI->isAsCheapAsAMove() &&
1520 DefMI->isSafeToReMat(TII, AA, regB) &&
1521 isProfitableToReMat(regB, rc, mi, DefMI, mbbi, Dist)){
1522 DEBUG(dbgs() << "2addr: REMATTING : " << *DefMI << "\n");
1523 unsigned regASubIdx = mi->getOperand(DstIdx).getSubReg();
1524 TII->reMaterialize(*mbbi, mi, regA, regASubIdx, DefMI, *TRI);
1525 ReMatRegs.set(TargetRegisterInfo::virtReg2Index(regB));
1528 BuildMI(*mbbi, mi, mi->getDebugLoc(), TII->get(TargetOpcode::COPY),
1533 // Update DistanceMap.
1534 MachineBasicBlock::iterator prevMI = prior(mi);
1535 DistanceMap.insert(std::make_pair(prevMI, Dist));
1536 DistanceMap[mi] = ++Dist;
1538 DEBUG(dbgs() << "\t\tprepend:\t" << *prevMI);
1540 MachineOperand &MO = mi->getOperand(SrcIdx);
1541 assert(MO.isReg() && MO.getReg() == regB && MO.isUse() &&
1542 "inconsistent operand info for 2-reg pass");
1544 MO.setIsKill(false);
1545 RemovedKillFlag = true;
1548 // Make sure regA is a legal regclass for the SrcIdx operand.
1549 if (TargetRegisterInfo::isVirtualRegister(regA) &&
1550 TargetRegisterInfo::isVirtualRegister(regB))
1551 MRI->constrainRegClass(regA, MRI->getRegClass(regB));
1556 // Propagate SrcRegMap.
1557 SrcRegMap[regA] = regB;
1560 if (AllUsesCopied) {
1561 if (!IsEarlyClobber) {
1562 // Replace other (un-tied) uses of regB with LastCopiedReg.
1563 for (unsigned i = 0, e = mi->getNumOperands(); i != e; ++i) {
1564 MachineOperand &MO = mi->getOperand(i);
1565 if (MO.isReg() && MO.getReg() == regB && MO.isUse()) {
1567 MO.setIsKill(false);
1568 RemovedKillFlag = true;
1570 MO.setReg(LastCopiedReg);
1575 // Update live variables for regB.
1576 if (RemovedKillFlag && LV && LV->getVarInfo(regB).removeKill(mi))
1577 LV->addVirtualRegisterKilled(regB, prior(mi));
1579 } else if (RemovedKillFlag) {
1580 // Some tied uses of regB matched their destination registers, so
1581 // regB is still used in this instruction, but a kill flag was
1582 // removed from a different tied use of regB, so now we need to add
1583 // a kill flag to one of the remaining uses of regB.
1584 for (unsigned i = 0, e = mi->getNumOperands(); i != e; ++i) {
1585 MachineOperand &MO = mi->getOperand(i);
1586 if (MO.isReg() && MO.getReg() == regB && MO.isUse()) {
1593 // Schedule the source copy / remat inserted to form two-address
1594 // instruction. FIXME: Does it matter the distance map may not be
1595 // accurate after it's scheduled?
1596 TII->scheduleTwoAddrSource(prior(mi), mi, *TRI);
1600 DEBUG(dbgs() << "\t\trewrite to:\t" << *mi);
1603 // Rewrite INSERT_SUBREG as COPY now that we no longer need SSA form.
1604 if (mi->isInsertSubreg()) {
1605 // From %reg = INSERT_SUBREG %reg, %subreg, subidx
1606 // To %reg:subidx = COPY %subreg
1607 unsigned SubIdx = mi->getOperand(3).getImm();
1608 mi->RemoveOperand(3);
1609 assert(mi->getOperand(0).getSubReg() == 0 && "Unexpected subreg idx");
1610 mi->getOperand(0).setSubReg(SubIdx);
1611 mi->getOperand(0).setIsUndef(mi->getOperand(1).isUndef());
1612 mi->RemoveOperand(1);
1613 mi->setDesc(TII->get(TargetOpcode::COPY));
1614 DEBUG(dbgs() << "\t\tconvert to:\t" << *mi);
1617 // Clear TiedOperands here instead of at the top of the loop
1618 // since most instructions do not have tied operands.
1619 TiedOperands.clear();
1624 // Some remat'ed instructions are dead.
1625 for (int i = ReMatRegs.find_first(); i != -1; i = ReMatRegs.find_next(i)) {
1626 unsigned VReg = TargetRegisterInfo::index2VirtReg(i);
1627 if (MRI->use_nodbg_empty(VReg)) {
1628 MachineInstr *DefMI = MRI->getVRegDef(VReg);
1629 DefMI->eraseFromParent();
1633 // Eliminate REG_SEQUENCE instructions. Their whole purpose was to preseve
1634 // SSA form. It's now safe to de-SSA.
1635 MadeChange |= EliminateRegSequences();
1640 static void UpdateRegSequenceSrcs(unsigned SrcReg,
1641 unsigned DstReg, unsigned SubIdx,
1642 MachineRegisterInfo *MRI,
1643 const TargetRegisterInfo &TRI) {
1644 for (MachineRegisterInfo::reg_iterator RI = MRI->reg_begin(SrcReg),
1645 RE = MRI->reg_end(); RI != RE; ) {
1646 MachineOperand &MO = RI.getOperand();
1648 MO.substVirtReg(DstReg, SubIdx, TRI);
1652 // Find the first def of Reg, assuming they are all in the same basic block.
1653 static MachineInstr *findFirstDef(unsigned Reg, MachineRegisterInfo *MRI) {
1654 SmallPtrSet<MachineInstr*, 8> Defs;
1655 MachineInstr *First = 0;
1656 for (MachineRegisterInfo::def_iterator RI = MRI->def_begin(Reg);
1657 MachineInstr *MI = RI.skipInstruction(); Defs.insert(MI))
1662 MachineBasicBlock *MBB = First->getParent();
1663 MachineBasicBlock::iterator A = First, B = First;
1667 if (A != MBB->begin()) {
1670 if (Defs.erase(A)) First = A;
1672 if (B != MBB->end()) {
1677 } while (Moving && !Defs.empty());
1678 assert(Defs.empty() && "Instructions outside basic block!");
1682 /// CoalesceExtSubRegs - If a number of sources of the REG_SEQUENCE are
1683 /// EXTRACT_SUBREG from the same register and to the same virtual register
1684 /// with different sub-register indices, attempt to combine the
1685 /// EXTRACT_SUBREGs and pre-coalesce them. e.g.
1686 /// %reg1026<def> = VLDMQ %reg1025<kill>, 260, pred:14, pred:%reg0
1687 /// %reg1029:6<def> = EXTRACT_SUBREG %reg1026, 6
1688 /// %reg1029:5<def> = EXTRACT_SUBREG %reg1026<kill>, 5
1689 /// Since D subregs 5, 6 can combine to a Q register, we can coalesce
1690 /// reg1026 to reg1029.
1692 TwoAddressInstructionPass::CoalesceExtSubRegs(SmallVector<unsigned,4> &Srcs,
1694 SmallSet<unsigned, 4> Seen;
1695 for (unsigned i = 0, e = Srcs.size(); i != e; ++i) {
1696 unsigned SrcReg = Srcs[i];
1697 if (!Seen.insert(SrcReg))
1700 // Check that the instructions are all in the same basic block.
1701 MachineInstr *SrcDefMI = MRI->getUniqueVRegDef(SrcReg);
1702 MachineInstr *DstDefMI = MRI->getUniqueVRegDef(DstReg);
1703 if (!SrcDefMI || !DstDefMI ||
1704 SrcDefMI->getParent() != DstDefMI->getParent())
1707 // If there are no other uses than copies which feed into
1708 // the reg_sequence, then we might be able to coalesce them.
1709 bool CanCoalesce = true;
1710 SmallVector<unsigned, 4> SrcSubIndices, DstSubIndices;
1711 for (MachineRegisterInfo::use_nodbg_iterator
1712 UI = MRI->use_nodbg_begin(SrcReg),
1713 UE = MRI->use_nodbg_end(); UI != UE; ++UI) {
1714 MachineInstr *UseMI = &*UI;
1715 if (!UseMI->isCopy() || UseMI->getOperand(0).getReg() != DstReg) {
1716 CanCoalesce = false;
1719 SrcSubIndices.push_back(UseMI->getOperand(1).getSubReg());
1720 DstSubIndices.push_back(UseMI->getOperand(0).getSubReg());
1723 if (!CanCoalesce || SrcSubIndices.size() < 2)
1726 // Check that the source subregisters can be combined.
1727 std::sort(SrcSubIndices.begin(), SrcSubIndices.end());
1728 unsigned NewSrcSubIdx = 0;
1729 if (!TRI->canCombineSubRegIndices(MRI->getRegClass(SrcReg), SrcSubIndices,
1733 // Check that the destination subregisters can also be combined.
1734 std::sort(DstSubIndices.begin(), DstSubIndices.end());
1735 unsigned NewDstSubIdx = 0;
1736 if (!TRI->canCombineSubRegIndices(MRI->getRegClass(DstReg), DstSubIndices,
1740 // If neither source nor destination can be combined to the full register,
1741 // just give up. This could be improved if it ever matters.
1742 if (NewSrcSubIdx != 0 && NewDstSubIdx != 0)
1745 // Now that we know that all the uses are extract_subregs and that those
1746 // subregs can somehow be combined, scan all the extract_subregs again to
1747 // make sure the subregs are in the right order and can be composed.
1748 MachineInstr *SomeMI = 0;
1750 for (MachineRegisterInfo::use_nodbg_iterator
1751 UI = MRI->use_nodbg_begin(SrcReg),
1752 UE = MRI->use_nodbg_end(); UI != UE; ++UI) {
1753 MachineInstr *UseMI = &*UI;
1754 assert(UseMI->isCopy());
1755 unsigned DstSubIdx = UseMI->getOperand(0).getSubReg();
1756 unsigned SrcSubIdx = UseMI->getOperand(1).getSubReg();
1757 assert(DstSubIdx != 0 && "missing subreg from RegSequence elimination");
1758 if ((NewDstSubIdx == 0 &&
1759 TRI->composeSubRegIndices(NewSrcSubIdx, DstSubIdx) != SrcSubIdx) ||
1760 (NewSrcSubIdx == 0 &&
1761 TRI->composeSubRegIndices(NewDstSubIdx, SrcSubIdx) != DstSubIdx)) {
1762 CanCoalesce = false;
1765 // Keep track of one of the uses. Preferably the first one which has a
1766 // <def,undef> flag.
1767 if (!SomeMI || UseMI->getOperand(0).isUndef())
1773 // Insert a copy to replace the original.
1774 MachineInstr *CopyMI = BuildMI(*SomeMI->getParent(), SomeMI,
1775 SomeMI->getDebugLoc(),
1776 TII->get(TargetOpcode::COPY))
1777 .addReg(DstReg, RegState::Define |
1778 getUndefRegState(SomeMI->getOperand(0).isUndef()),
1780 .addReg(SrcReg, 0, NewSrcSubIdx);
1782 // Remove all the old extract instructions.
1783 for (MachineRegisterInfo::use_nodbg_iterator
1784 UI = MRI->use_nodbg_begin(SrcReg),
1785 UE = MRI->use_nodbg_end(); UI != UE; ) {
1786 MachineInstr *UseMI = &*UI;
1788 if (UseMI == CopyMI)
1790 assert(UseMI->isCopy());
1791 // Move any kills to the new copy or extract instruction.
1792 if (UseMI->getOperand(1).isKill()) {
1793 CopyMI->getOperand(1).setIsKill();
1795 // Update live variables
1796 LV->replaceKillInstruction(SrcReg, UseMI, &*CopyMI);
1798 UseMI->eraseFromParent();
1803 static bool HasOtherRegSequenceUses(unsigned Reg, MachineInstr *RegSeq,
1804 MachineRegisterInfo *MRI) {
1805 for (MachineRegisterInfo::use_iterator UI = MRI->use_begin(Reg),
1806 UE = MRI->use_end(); UI != UE; ++UI) {
1807 MachineInstr *UseMI = &*UI;
1808 if (UseMI != RegSeq && UseMI->isRegSequence())
1814 /// EliminateRegSequences - Eliminate REG_SEQUENCE instructions as part
1815 /// of the de-ssa process. This replaces sources of REG_SEQUENCE as
1816 /// sub-register references of the register defined by REG_SEQUENCE. e.g.
1818 /// %reg1029<def>, %reg1030<def> = VLD1q16 %reg1024<kill>, ...
1819 /// %reg1031<def> = REG_SEQUENCE %reg1029<kill>, 5, %reg1030<kill>, 6
1821 /// %reg1031:5<def>, %reg1031:6<def> = VLD1q16 %reg1024<kill>, ...
1822 bool TwoAddressInstructionPass::EliminateRegSequences() {
1823 if (RegSequences.empty())
1826 for (unsigned i = 0, e = RegSequences.size(); i != e; ++i) {
1827 MachineInstr *MI = RegSequences[i];
1828 unsigned DstReg = MI->getOperand(0).getReg();
1829 if (MI->getOperand(0).getSubReg() ||
1830 TargetRegisterInfo::isPhysicalRegister(DstReg) ||
1831 !(MI->getNumOperands() & 1)) {
1832 DEBUG(dbgs() << "Illegal REG_SEQUENCE instruction:" << *MI);
1833 llvm_unreachable(0);
1836 bool IsImpDef = true;
1837 SmallVector<unsigned, 4> RealSrcs;
1838 SmallSet<unsigned, 4> Seen;
1839 for (unsigned i = 1, e = MI->getNumOperands(); i < e; i += 2) {
1840 // Nothing needs to be inserted for <undef> operands.
1841 if (MI->getOperand(i).isUndef()) {
1842 MI->getOperand(i).setReg(0);
1845 unsigned SrcReg = MI->getOperand(i).getReg();
1846 unsigned SrcSubIdx = MI->getOperand(i).getSubReg();
1847 unsigned SubIdx = MI->getOperand(i+1).getImm();
1848 // DefMI of NULL means the value does not have a vreg in this block
1849 // i.e., its a physical register or a subreg.
1850 // In either case we force a copy to be generated.
1851 MachineInstr *DefMI = NULL;
1852 if (!MI->getOperand(i).getSubReg() &&
1853 !TargetRegisterInfo::isPhysicalRegister(SrcReg)) {
1854 DefMI = MRI->getUniqueVRegDef(SrcReg);
1857 if (DefMI && DefMI->isImplicitDef()) {
1858 DefMI->eraseFromParent();
1863 // Remember COPY sources. These might be candidate for coalescing.
1864 if (DefMI && DefMI->isCopy() && DefMI->getOperand(1).getSubReg())
1865 RealSrcs.push_back(DefMI->getOperand(1).getReg());
1867 bool isKill = MI->getOperand(i).isKill();
1868 if (!DefMI || !Seen.insert(SrcReg) ||
1869 MI->getParent() != DefMI->getParent() ||
1870 !isKill || HasOtherRegSequenceUses(SrcReg, MI, MRI) ||
1871 !TRI->getMatchingSuperRegClass(MRI->getRegClass(DstReg),
1872 MRI->getRegClass(SrcReg), SubIdx)) {
1873 // REG_SEQUENCE cannot have duplicated operands, add a copy.
1874 // Also add an copy if the source is live-in the block. We don't want
1875 // to end up with a partial-redef of a livein, e.g.
1877 // reg1051:10<def> =
1883 // LiveIntervalAnalysis won't like it.
1885 // If the REG_SEQUENCE doesn't kill its source, keeping live variables
1886 // correctly up to date becomes very difficult. Insert a copy.
1888 // Defer any kill flag to the last operand using SrcReg. Otherwise, we
1889 // might insert a COPY that uses SrcReg after is was killed.
1891 for (unsigned j = i + 2; j < e; j += 2)
1892 if (MI->getOperand(j).getReg() == SrcReg) {
1893 MI->getOperand(j).setIsKill();
1898 MachineBasicBlock::iterator InsertLoc = MI;
1899 MachineInstr *CopyMI = BuildMI(*MI->getParent(), InsertLoc,
1900 MI->getDebugLoc(), TII->get(TargetOpcode::COPY))
1901 .addReg(DstReg, RegState::Define, SubIdx)
1902 .addReg(SrcReg, getKillRegState(isKill), SrcSubIdx);
1903 MI->getOperand(i).setReg(0);
1904 if (LV && isKill && !TargetRegisterInfo::isPhysicalRegister(SrcReg))
1905 LV->replaceKillInstruction(SrcReg, MI, CopyMI);
1906 DEBUG(dbgs() << "Inserted: " << *CopyMI);
1910 for (unsigned i = 1, e = MI->getNumOperands(); i < e; i += 2) {
1911 unsigned SrcReg = MI->getOperand(i).getReg();
1912 if (!SrcReg) continue;
1913 unsigned SubIdx = MI->getOperand(i+1).getImm();
1914 UpdateRegSequenceSrcs(SrcReg, DstReg, SubIdx, MRI, *TRI);
1917 // Set <def,undef> flags on the first DstReg def in the basic block.
1918 // It marks the beginning of the live range. All the other defs are
1919 // read-modify-write.
1920 if (MachineInstr *Def = findFirstDef(DstReg, MRI)) {
1921 for (unsigned i = 0, e = Def->getNumOperands(); i != e; ++i) {
1922 MachineOperand &MO = Def->getOperand(i);
1923 if (MO.isReg() && MO.isDef() && MO.getReg() == DstReg)
1926 // Make sure there is a full non-subreg imp-def operand on the
1927 // instruction. This shouldn't be necessary, but it seems that at least
1928 // RAFast requires it.
1929 Def->addRegisterDefined(DstReg, TRI);
1930 DEBUG(dbgs() << "First def: " << *Def);
1934 DEBUG(dbgs() << "Turned: " << *MI << " into an IMPLICIT_DEF");
1935 MI->setDesc(TII->get(TargetOpcode::IMPLICIT_DEF));
1936 for (int j = MI->getNumOperands() - 1, ee = 0; j > ee; --j)
1937 MI->RemoveOperand(j);
1939 DEBUG(dbgs() << "Eliminated: " << *MI);
1940 MI->eraseFromParent();
1943 // Try coalescing some EXTRACT_SUBREG instructions. This can create
1944 // INSERT_SUBREG instructions that must have <undef> flags added by
1945 // LiveIntervalAnalysis, so only run it when LiveVariables is available.
1947 CoalesceExtSubRegs(RealSrcs, DstReg);
1950 RegSequences.clear();