1 //===- MipsDelaySlotFiller.cpp - Mips Delay Slot Filler -------------------===//
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7 //===----------------------------------------------------------------------===//
9 // Simple pass to fill delay slots with useful instructions.
11 //===----------------------------------------------------------------------===//
13 #include "MCTargetDesc/MipsMCNaCl.h"
15 #include "MipsInstrInfo.h"
16 #include "MipsRegisterInfo.h"
17 #include "MipsSubtarget.h"
18 #include "llvm/ADT/BitVector.h"
19 #include "llvm/ADT/DenseMap.h"
20 #include "llvm/ADT/PointerUnion.h"
21 #include "llvm/ADT/SmallPtrSet.h"
22 #include "llvm/ADT/SmallVector.h"
23 #include "llvm/ADT/Statistic.h"
24 #include "llvm/ADT/StringRef.h"
25 #include "llvm/Analysis/AliasAnalysis.h"
26 #include "llvm/Analysis/ValueTracking.h"
27 #include "llvm/CodeGen/MachineBasicBlock.h"
28 #include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
29 #include "llvm/CodeGen/MachineFunction.h"
30 #include "llvm/CodeGen/MachineFunctionPass.h"
31 #include "llvm/CodeGen/MachineInstr.h"
32 #include "llvm/CodeGen/MachineInstrBuilder.h"
33 #include "llvm/CodeGen/MachineOperand.h"
34 #include "llvm/CodeGen/MachineRegisterInfo.h"
35 #include "llvm/CodeGen/PseudoSourceValue.h"
36 #include "llvm/CodeGen/TargetRegisterInfo.h"
37 #include "llvm/CodeGen/TargetSubtargetInfo.h"
38 #include "llvm/MC/MCInstrDesc.h"
39 #include "llvm/MC/MCRegisterInfo.h"
40 #include "llvm/Support/Casting.h"
41 #include "llvm/Support/CodeGen.h"
42 #include "llvm/Support/CommandLine.h"
43 #include "llvm/Support/ErrorHandling.h"
44 #include "llvm/Target/TargetMachine.h"
53 #define DEBUG_TYPE "mips-delay-slot-filler"
55 STATISTIC(FilledSlots, "Number of delay slots filled");
56 STATISTIC(UsefulSlots, "Number of delay slots filled with instructions that"
59 static cl::opt<bool> DisableDelaySlotFiller(
60 "disable-mips-delay-filler",
62 cl::desc("Fill all delay slots with NOPs."),
65 static cl::opt<bool> DisableForwardSearch(
66 "disable-mips-df-forward-search",
68 cl::desc("Disallow MIPS delay filler to search forward."),
71 static cl::opt<bool> DisableSuccBBSearch(
72 "disable-mips-df-succbb-search",
74 cl::desc("Disallow MIPS delay filler to search successor basic blocks."),
77 static cl::opt<bool> DisableBackwardSearch(
78 "disable-mips-df-backward-search",
80 cl::desc("Disallow MIPS delay filler to search backward."),
83 enum CompactBranchPolicy {
84 CB_Never, ///< The policy 'never' may in some circumstances or for some
85 ///< ISAs not be absolutely adhered to.
86 CB_Optimal, ///< Optimal is the default and will produce compact branches
87 ///< when delay slots cannot be filled.
88 CB_Always ///< 'always' may in some circumstances may not be
89 ///< absolutely adhered to there may not be a corresponding
90 ///< compact form of a branch.
93 static cl::opt<CompactBranchPolicy> MipsCompactBranchPolicy(
94 "mips-compact-branches",cl::Optional,
96 cl::desc("MIPS Specific: Compact branch policy."),
98 clEnumValN(CB_Never, "never", "Do not use compact branches if possible."),
99 clEnumValN(CB_Optimal, "optimal", "Use compact branches where appropiate (default)."),
100 clEnumValN(CB_Always, "always", "Always use compact branches if possible.")
106 using Iter = MachineBasicBlock::iterator;
107 using ReverseIter = MachineBasicBlock::reverse_iterator;
108 using BB2BrMap = SmallDenseMap<MachineBasicBlock *, MachineInstr *, 2>;
112 RegDefsUses(const TargetRegisterInfo &TRI);
114 void init(const MachineInstr &MI);
116 /// This function sets all caller-saved registers in Defs.
117 void setCallerSaved(const MachineInstr &MI);
119 /// This function sets all unallocatable registers in Defs.
120 void setUnallocatableRegs(const MachineFunction &MF);
122 /// Set bits in Uses corresponding to MBB's live-out registers except for
123 /// the registers that are live-in to SuccBB.
124 void addLiveOut(const MachineBasicBlock &MBB,
125 const MachineBasicBlock &SuccBB);
127 bool update(const MachineInstr &MI, unsigned Begin, unsigned End);
130 bool checkRegDefsUses(BitVector &NewDefs, BitVector &NewUses, unsigned Reg,
133 /// Returns true if Reg or its alias is in RegSet.
134 bool isRegInSet(const BitVector &RegSet, unsigned Reg) const;
136 const TargetRegisterInfo &TRI;
137 BitVector Defs, Uses;
140 /// Base class for inspecting loads and stores.
141 class InspectMemInstr {
143 InspectMemInstr(bool ForbidMemInstr_) : ForbidMemInstr(ForbidMemInstr_) {}
144 virtual ~InspectMemInstr() = default;
146 /// Return true if MI cannot be moved to delay slot.
147 bool hasHazard(const MachineInstr &MI);
150 /// Flags indicating whether loads or stores have been seen.
151 bool OrigSeenLoad = false;
152 bool OrigSeenStore = false;
153 bool SeenLoad = false;
154 bool SeenStore = false;
156 /// Memory instructions are not allowed to move to delay slot if this flag
161 virtual bool hasHazard_(const MachineInstr &MI) = 0;
164 /// This subclass rejects any memory instructions.
165 class NoMemInstr : public InspectMemInstr {
167 NoMemInstr() : InspectMemInstr(true) {}
170 bool hasHazard_(const MachineInstr &MI) override { return true; }
173 /// This subclass accepts loads from stacks and constant loads.
174 class LoadFromStackOrConst : public InspectMemInstr {
176 LoadFromStackOrConst() : InspectMemInstr(false) {}
179 bool hasHazard_(const MachineInstr &MI) override;
182 /// This subclass uses memory dependence information to determine whether a
183 /// memory instruction can be moved to a delay slot.
184 class MemDefsUses : public InspectMemInstr {
186 MemDefsUses(const DataLayout &DL, const MachineFrameInfo *MFI);
189 using ValueType = PointerUnion<const Value *, const PseudoSourceValue *>;
191 bool hasHazard_(const MachineInstr &MI) override;
193 /// Update Defs and Uses. Return true if there exist dependences that
194 /// disqualify the delay slot candidate between V and values in Uses and
196 bool updateDefsUses(ValueType V, bool MayStore);
198 /// Get the list of underlying objects of MI's memory operand.
199 bool getUnderlyingObjects(const MachineInstr &MI,
200 SmallVectorImpl<ValueType> &Objects) const;
202 const MachineFrameInfo *MFI;
203 SmallPtrSet<ValueType, 4> Uses, Defs;
204 const DataLayout &DL;
206 /// Flags indicating whether loads or stores with no underlying objects have
208 bool SeenNoObjLoad = false;
209 bool SeenNoObjStore = false;
212 class MipsDelaySlotFiller : public MachineFunctionPass {
214 MipsDelaySlotFiller() : MachineFunctionPass(ID) {
215 initializeMipsDelaySlotFillerPass(*PassRegistry::getPassRegistry());
218 StringRef getPassName() const override { return "Mips Delay Slot Filler"; }
220 bool runOnMachineFunction(MachineFunction &F) override {
222 bool Changed = false;
223 for (MachineFunction::iterator FI = F.begin(), FE = F.end();
225 Changed |= runOnMachineBasicBlock(*FI);
227 // This pass invalidates liveness information when it reorders
228 // instructions to fill delay slot. Without this, -verify-machineinstrs
231 F.getRegInfo().invalidateLiveness();
236 MachineFunctionProperties getRequiredProperties() const override {
237 return MachineFunctionProperties().set(
238 MachineFunctionProperties::Property::NoVRegs);
241 void getAnalysisUsage(AnalysisUsage &AU) const override {
242 AU.addRequired<MachineBranchProbabilityInfo>();
243 MachineFunctionPass::getAnalysisUsage(AU);
249 bool runOnMachineBasicBlock(MachineBasicBlock &MBB);
251 Iter replaceWithCompactBranch(MachineBasicBlock &MBB, Iter Branch,
254 /// This function checks if it is valid to move Candidate to the delay slot
255 /// and returns true if it isn't. It also updates memory and register
256 /// dependence information.
257 bool delayHasHazard(const MachineInstr &Candidate, RegDefsUses &RegDU,
258 InspectMemInstr &IM) const;
260 /// This function searches range [Begin, End) for an instruction that can be
261 /// moved to the delay slot. Returns true on success.
262 template<typename IterTy>
263 bool searchRange(MachineBasicBlock &MBB, IterTy Begin, IterTy End,
264 RegDefsUses &RegDU, InspectMemInstr &IM, Iter Slot,
265 IterTy &Filler) const;
267 /// This function searches in the backward direction for an instruction that
268 /// can be moved to the delay slot. Returns true on success.
269 bool searchBackward(MachineBasicBlock &MBB, MachineInstr &Slot) const;
271 /// This function searches MBB in the forward direction for an instruction
272 /// that can be moved to the delay slot. Returns true on success.
273 bool searchForward(MachineBasicBlock &MBB, Iter Slot) const;
275 /// This function searches one of MBB's successor blocks for an instruction
276 /// that can be moved to the delay slot and inserts clones of the
277 /// instruction into the successor's predecessor blocks.
278 bool searchSuccBBs(MachineBasicBlock &MBB, Iter Slot) const;
280 /// Pick a successor block of MBB. Return NULL if MBB doesn't have a
281 /// successor block that is not a landing pad.
282 MachineBasicBlock *selectSuccBB(MachineBasicBlock &B) const;
284 /// This function analyzes MBB and returns an instruction with an unoccupied
285 /// slot that branches to Dst.
286 std::pair<MipsInstrInfo::BranchType, MachineInstr *>
287 getBranch(MachineBasicBlock &MBB, const MachineBasicBlock &Dst) const;
289 /// Examine Pred and see if it is possible to insert an instruction into
290 /// one of its branches delay slot or its end.
291 bool examinePred(MachineBasicBlock &Pred, const MachineBasicBlock &Succ,
292 RegDefsUses &RegDU, bool &HasMultipleSuccs,
293 BB2BrMap &BrMap) const;
295 bool terminateSearch(const MachineInstr &Candidate) const;
297 const TargetMachine *TM = nullptr;
300 } // end anonymous namespace
302 char MipsDelaySlotFiller::ID = 0;
304 static bool hasUnoccupiedSlot(const MachineInstr *MI) {
305 return MI->hasDelaySlot() && !MI->isBundledWithSucc();
308 INITIALIZE_PASS(MipsDelaySlotFiller, DEBUG_TYPE,
309 "Fill delay slot for MIPS", false, false)
311 /// This function inserts clones of Filler into predecessor blocks.
312 static void insertDelayFiller(Iter Filler, const BB2BrMap &BrMap) {
313 MachineFunction *MF = Filler->getParent()->getParent();
315 for (BB2BrMap::const_iterator I = BrMap.begin(); I != BrMap.end(); ++I) {
317 MIBundleBuilder(I->second).append(MF->CloneMachineInstr(&*Filler));
320 I->first->insert(I->first->end(), MF->CloneMachineInstr(&*Filler));
325 /// This function adds registers Filler defines to MBB's live-in register list.
326 static void addLiveInRegs(Iter Filler, MachineBasicBlock &MBB) {
327 for (unsigned I = 0, E = Filler->getNumOperands(); I != E; ++I) {
328 const MachineOperand &MO = Filler->getOperand(I);
331 if (!MO.isReg() || !MO.isDef() || !(R = MO.getReg()))
335 const MachineFunction &MF = *MBB.getParent();
336 assert(MF.getSubtarget().getRegisterInfo()->getAllocatableSet(MF).test(R) &&
337 "Shouldn't move an instruction with unallocatable registers across "
338 "basic block boundaries.");
341 if (!MBB.isLiveIn(R))
346 RegDefsUses::RegDefsUses(const TargetRegisterInfo &TRI)
347 : TRI(TRI), Defs(TRI.getNumRegs(), false), Uses(TRI.getNumRegs(), false) {}
349 void RegDefsUses::init(const MachineInstr &MI) {
350 // Add all register operands which are explicit and non-variadic.
351 update(MI, 0, MI.getDesc().getNumOperands());
353 // If MI is a call, add RA to Defs to prevent users of RA from going into
358 // Add all implicit register operands of branch instructions except
361 update(MI, MI.getDesc().getNumOperands(), MI.getNumOperands());
362 Defs.reset(Mips::AT);
366 void RegDefsUses::setCallerSaved(const MachineInstr &MI) {
369 // Add RA/RA_64 to Defs to prevent users of RA/RA_64 from going into
370 // the delay slot. The reason is that RA/RA_64 must not be changed
371 // in the delay slot so that the callee can return to the caller.
372 if (MI.definesRegister(Mips::RA) || MI.definesRegister(Mips::RA_64)) {
374 Defs.set(Mips::RA_64);
377 // If MI is a call, add all caller-saved registers to Defs.
378 BitVector CallerSavedRegs(TRI.getNumRegs(), true);
380 CallerSavedRegs.reset(Mips::ZERO);
381 CallerSavedRegs.reset(Mips::ZERO_64);
383 for (const MCPhysReg *R = TRI.getCalleeSavedRegs(MI.getParent()->getParent());
385 for (MCRegAliasIterator AI(*R, &TRI, true); AI.isValid(); ++AI)
386 CallerSavedRegs.reset(*AI);
388 Defs |= CallerSavedRegs;
391 void RegDefsUses::setUnallocatableRegs(const MachineFunction &MF) {
392 BitVector AllocSet = TRI.getAllocatableSet(MF);
394 for (unsigned R : AllocSet.set_bits())
395 for (MCRegAliasIterator AI(R, &TRI, false); AI.isValid(); ++AI)
398 AllocSet.set(Mips::ZERO);
399 AllocSet.set(Mips::ZERO_64);
401 Defs |= AllocSet.flip();
404 void RegDefsUses::addLiveOut(const MachineBasicBlock &MBB,
405 const MachineBasicBlock &SuccBB) {
406 for (MachineBasicBlock::const_succ_iterator SI = MBB.succ_begin(),
407 SE = MBB.succ_end(); SI != SE; ++SI)
409 for (const auto &LI : (*SI)->liveins())
410 Uses.set(LI.PhysReg);
413 bool RegDefsUses::update(const MachineInstr &MI, unsigned Begin, unsigned End) {
414 BitVector NewDefs(TRI.getNumRegs()), NewUses(TRI.getNumRegs());
415 bool HasHazard = false;
417 for (unsigned I = Begin; I != End; ++I) {
418 const MachineOperand &MO = MI.getOperand(I);
420 if (MO.isReg() && MO.getReg())
421 HasHazard |= checkRegDefsUses(NewDefs, NewUses, MO.getReg(), MO.isDef());
430 bool RegDefsUses::checkRegDefsUses(BitVector &NewDefs, BitVector &NewUses,
431 unsigned Reg, bool IsDef) const {
434 // check whether Reg has already been defined or used.
435 return (isRegInSet(Defs, Reg) || isRegInSet(Uses, Reg));
439 // check whether Reg has already been defined.
440 return isRegInSet(Defs, Reg);
443 bool RegDefsUses::isRegInSet(const BitVector &RegSet, unsigned Reg) const {
444 // Check Reg and all aliased Registers.
445 for (MCRegAliasIterator AI(Reg, &TRI, true); AI.isValid(); ++AI)
446 if (RegSet.test(*AI))
451 bool InspectMemInstr::hasHazard(const MachineInstr &MI) {
452 if (!MI.mayStore() && !MI.mayLoad())
458 OrigSeenLoad = SeenLoad;
459 OrigSeenStore = SeenStore;
460 SeenLoad |= MI.mayLoad();
461 SeenStore |= MI.mayStore();
463 // If MI is an ordered or volatile memory reference, disallow moving
464 // subsequent loads and stores to delay slot.
465 if (MI.hasOrderedMemoryRef() && (OrigSeenLoad || OrigSeenStore)) {
466 ForbidMemInstr = true;
470 return hasHazard_(MI);
473 bool LoadFromStackOrConst::hasHazard_(const MachineInstr &MI) {
477 if (!MI.hasOneMemOperand() || !(*MI.memoperands_begin())->getPseudoValue())
480 if (const PseudoSourceValue *PSV =
481 (*MI.memoperands_begin())->getPseudoValue()) {
482 if (isa<FixedStackPseudoSourceValue>(PSV))
484 return !PSV->isConstant(nullptr) && !PSV->isStack();
490 MemDefsUses::MemDefsUses(const DataLayout &DL, const MachineFrameInfo *MFI_)
491 : InspectMemInstr(false), MFI(MFI_), DL(DL) {}
493 bool MemDefsUses::hasHazard_(const MachineInstr &MI) {
494 bool HasHazard = false;
496 // Check underlying object list.
497 SmallVector<ValueType, 4> Objs;
498 if (getUnderlyingObjects(MI, Objs)) {
499 for (ValueType VT : Objs)
500 HasHazard |= updateDefsUses(VT, MI.mayStore());
504 // No underlying objects found.
505 HasHazard = MI.mayStore() && (OrigSeenLoad || OrigSeenStore);
506 HasHazard |= MI.mayLoad() || OrigSeenStore;
508 SeenNoObjLoad |= MI.mayLoad();
509 SeenNoObjStore |= MI.mayStore();
514 bool MemDefsUses::updateDefsUses(ValueType V, bool MayStore) {
516 return !Defs.insert(V).second || Uses.count(V) || SeenNoObjStore ||
520 return Defs.count(V) || SeenNoObjStore;
524 getUnderlyingObjects(const MachineInstr &MI,
525 SmallVectorImpl<ValueType> &Objects) const {
526 if (!MI.hasOneMemOperand())
529 auto & MMO = **MI.memoperands_begin();
531 if (const PseudoSourceValue *PSV = MMO.getPseudoValue()) {
532 if (!PSV->isAliased(MFI))
534 Objects.push_back(PSV);
538 if (const Value *V = MMO.getValue()) {
539 SmallVector<const Value *, 4> Objs;
540 GetUnderlyingObjects(V, Objs, DL);
542 for (const Value *UValue : Objs) {
543 if (!isIdentifiedObject(V))
546 Objects.push_back(UValue);
554 // Replace Branch with the compact branch instruction.
555 Iter MipsDelaySlotFiller::replaceWithCompactBranch(MachineBasicBlock &MBB,
557 const DebugLoc &DL) {
558 const MipsSubtarget &STI = MBB.getParent()->getSubtarget<MipsSubtarget>();
559 const MipsInstrInfo *TII = STI.getInstrInfo();
561 unsigned NewOpcode = TII->getEquivalentCompactForm(Branch);
562 Branch = TII->genInstrWithNewOpc(NewOpcode, Branch);
564 std::next(Branch)->eraseFromParent();
568 // For given opcode returns opcode of corresponding instruction with short
570 // For the pseudo TAILCALL*_MM instructions return the short delay slot
571 // form. Unfortunately, TAILCALL<->b16 is denied as b16 has a limited range
572 // that is too short to make use of for tail calls.
573 static int getEquivalentCallShort(int Opcode) {
576 return Mips::BGEZALS_MM;
578 return Mips::BLTZALS_MM;
581 return Mips::JALS_MM;
583 return Mips::JALRS_MM;
584 case Mips::JALR16_MM:
585 return Mips::JALRS16_MM;
586 case Mips::TAILCALL_MM:
587 llvm_unreachable("Attempting to shorten the TAILCALL_MM pseudo!");
588 case Mips::TAILCALLREG:
589 return Mips::JR16_MM;
591 llvm_unreachable("Unexpected call instruction for microMIPS.");
595 /// runOnMachineBasicBlock - Fill in delay slots for the given basic block.
596 /// We assume there is only one delay slot per delayed instruction.
597 bool MipsDelaySlotFiller::runOnMachineBasicBlock(MachineBasicBlock &MBB) {
598 bool Changed = false;
599 const MipsSubtarget &STI = MBB.getParent()->getSubtarget<MipsSubtarget>();
600 bool InMicroMipsMode = STI.inMicroMipsMode();
601 const MipsInstrInfo *TII = STI.getInstrInfo();
603 for (Iter I = MBB.begin(); I != MBB.end(); ++I) {
604 if (!hasUnoccupiedSlot(&*I))
607 // Delay slot filling is disabled at -O0, or in microMIPS32R6.
608 if (!DisableDelaySlotFiller && (TM->getOptLevel() != CodeGenOpt::None) &&
609 !(InMicroMipsMode && STI.hasMips32r6())) {
613 if (MipsCompactBranchPolicy.getValue() != CB_Always ||
614 !TII->getEquivalentCompactForm(I)) {
615 if (searchBackward(MBB, *I)) {
617 } else if (I->isTerminator()) {
618 if (searchSuccBBs(MBB, I)) {
621 } else if (searchForward(MBB, I)) {
627 // Get instruction with delay slot.
628 MachineBasicBlock::instr_iterator DSI = I.getInstrIterator();
630 if (InMicroMipsMode && TII->getInstSizeInBytes(*std::next(DSI)) == 2 &&
632 // If instruction in delay slot is 16b change opcode to
633 // corresponding instruction with short delay slot.
635 // TODO: Implement an instruction mapping table of 16bit opcodes to
636 // 32bit opcodes so that an instruction can be expanded. This would
637 // save 16 bits as a TAILCALL_MM pseudo requires a fullsized nop.
638 // TODO: Permit b16 when branching backwards to the same function
639 // if it is in range.
640 DSI->setDesc(TII->get(getEquivalentCallShort(DSI->getOpcode())));
648 // For microMIPS if instruction is BEQ or BNE with one ZERO register, then
649 // instead of adding NOP replace this instruction with the corresponding
650 // compact branch instruction, i.e. BEQZC or BNEZC. Additionally
651 // PseudoReturn and PseudoIndirectBranch are expanded to JR_MM, so they can
652 // be replaced with JRC16_MM.
654 // For MIPSR6 attempt to produce the corresponding compact (no delay slot)
655 // form of the CTI. For indirect jumps this will not require inserting a
656 // NOP and for branches will hopefully avoid requiring a NOP.
657 if ((InMicroMipsMode ||
658 (STI.hasMips32r6() && MipsCompactBranchPolicy != CB_Never)) &&
659 TII->getEquivalentCompactForm(I)) {
660 I = replaceWithCompactBranch(MBB, I, I->getDebugLoc());
665 // Bundle the NOP to the instruction with the delay slot.
666 BuildMI(MBB, std::next(I), I->getDebugLoc(), TII->get(Mips::NOP));
667 MIBundleBuilder(MBB, I, std::next(I, 2));
675 template <typename IterTy>
676 bool MipsDelaySlotFiller::searchRange(MachineBasicBlock &MBB, IterTy Begin,
677 IterTy End, RegDefsUses &RegDU,
678 InspectMemInstr &IM, Iter Slot,
679 IterTy &Filler) const {
680 for (IterTy I = Begin; I != End;) {
685 if (CurrI->isDebugInstr())
688 if (terminateSearch(*CurrI))
691 assert((!CurrI->isCall() && !CurrI->isReturn() && !CurrI->isBranch()) &&
692 "Cannot put calls, returns or branches in delay slot.");
694 if (CurrI->isKill()) {
695 CurrI->eraseFromParent();
699 if (delayHasHazard(*CurrI, RegDU, IM))
702 const MipsSubtarget &STI = MBB.getParent()->getSubtarget<MipsSubtarget>();
703 if (STI.isTargetNaCl()) {
704 // In NaCl, instructions that must be masked are forbidden in delay slots.
705 // We only check for loads, stores and SP changes. Calls, returns and
706 // branches are not checked because non-NaCl targets never put them in
709 if ((isBasePlusOffsetMemoryAccess(CurrI->getOpcode(), &AddrIdx) &&
710 baseRegNeedsLoadStoreMask(CurrI->getOperand(AddrIdx).getReg())) ||
711 CurrI->modifiesRegister(Mips::SP, STI.getRegisterInfo()))
715 bool InMicroMipsMode = STI.inMicroMipsMode();
716 const MipsInstrInfo *TII = STI.getInstrInfo();
717 unsigned Opcode = (*Slot).getOpcode();
718 // This is complicated by the tail call optimization. For non-PIC code
719 // there is only a 32bit sized unconditional branch which can be assumed
720 // to be able to reach the target. b16 only has a range of +/- 1 KB.
721 // It's entirely possible that the target function is reachable with b16
722 // but we don't have enough information to make that decision.
723 if (InMicroMipsMode && TII->getInstSizeInBytes(*CurrI) == 2 &&
724 (Opcode == Mips::JR || Opcode == Mips::PseudoIndirectBranch ||
725 Opcode == Mips::PseudoIndirectBranch_MM ||
726 Opcode == Mips::PseudoReturn || Opcode == Mips::TAILCALL))
728 // Instructions LWP/SWP and MOVEP should not be in a delay slot as that
729 // results in unpredictable behaviour
730 if (InMicroMipsMode && (Opcode == Mips::LWP_MM || Opcode == Mips::SWP_MM ||
731 Opcode == Mips::MOVEP_MM))
741 bool MipsDelaySlotFiller::searchBackward(MachineBasicBlock &MBB,
742 MachineInstr &Slot) const {
743 if (DisableBackwardSearch)
746 auto *Fn = MBB.getParent();
747 RegDefsUses RegDU(*Fn->getSubtarget().getRegisterInfo());
748 MemDefsUses MemDU(Fn->getDataLayout(), &Fn->getFrameInfo());
753 MachineBasicBlock::iterator SlotI = Slot;
754 if (!searchRange(MBB, ++SlotI.getReverse(), MBB.rend(), RegDU, MemDU, Slot,
758 MBB.splice(std::next(SlotI), &MBB, Filler.getReverse());
759 MIBundleBuilder(MBB, SlotI, std::next(SlotI, 2));
764 bool MipsDelaySlotFiller::searchForward(MachineBasicBlock &MBB,
766 // Can handle only calls.
767 if (DisableForwardSearch || !Slot->isCall())
770 RegDefsUses RegDU(*MBB.getParent()->getSubtarget().getRegisterInfo());
774 RegDU.setCallerSaved(*Slot);
776 if (!searchRange(MBB, std::next(Slot), MBB.end(), RegDU, NM, Slot, Filler))
779 MBB.splice(std::next(Slot), &MBB, Filler);
780 MIBundleBuilder(MBB, Slot, std::next(Slot, 2));
785 bool MipsDelaySlotFiller::searchSuccBBs(MachineBasicBlock &MBB,
787 if (DisableSuccBBSearch)
790 MachineBasicBlock *SuccBB = selectSuccBB(MBB);
795 RegDefsUses RegDU(*MBB.getParent()->getSubtarget().getRegisterInfo());
796 bool HasMultipleSuccs = false;
798 std::unique_ptr<InspectMemInstr> IM;
800 auto *Fn = MBB.getParent();
802 // Iterate over SuccBB's predecessor list.
803 for (MachineBasicBlock::pred_iterator PI = SuccBB->pred_begin(),
804 PE = SuccBB->pred_end(); PI != PE; ++PI)
805 if (!examinePred(**PI, *SuccBB, RegDU, HasMultipleSuccs, BrMap))
808 // Do not allow moving instructions which have unallocatable register operands
809 // across basic block boundaries.
810 RegDU.setUnallocatableRegs(*Fn);
812 // Only allow moving loads from stack or constants if any of the SuccBB's
813 // predecessors have multiple successors.
814 if (HasMultipleSuccs) {
815 IM.reset(new LoadFromStackOrConst());
817 const MachineFrameInfo &MFI = Fn->getFrameInfo();
818 IM.reset(new MemDefsUses(Fn->getDataLayout(), &MFI));
821 if (!searchRange(MBB, SuccBB->begin(), SuccBB->end(), RegDU, *IM, Slot,
825 insertDelayFiller(Filler, BrMap);
826 addLiveInRegs(Filler, *SuccBB);
827 Filler->eraseFromParent();
833 MipsDelaySlotFiller::selectSuccBB(MachineBasicBlock &B) const {
837 // Select the successor with the larget edge weight.
838 auto &Prob = getAnalysis<MachineBranchProbabilityInfo>();
839 MachineBasicBlock *S = *std::max_element(
840 B.succ_begin(), B.succ_end(),
841 [&](const MachineBasicBlock *Dst0, const MachineBasicBlock *Dst1) {
842 return Prob.getEdgeProbability(&B, Dst0) <
843 Prob.getEdgeProbability(&B, Dst1);
845 return S->isEHPad() ? nullptr : S;
848 std::pair<MipsInstrInfo::BranchType, MachineInstr *>
849 MipsDelaySlotFiller::getBranch(MachineBasicBlock &MBB,
850 const MachineBasicBlock &Dst) const {
851 const MipsInstrInfo *TII =
852 MBB.getParent()->getSubtarget<MipsSubtarget>().getInstrInfo();
853 MachineBasicBlock *TrueBB = nullptr, *FalseBB = nullptr;
854 SmallVector<MachineInstr*, 2> BranchInstrs;
855 SmallVector<MachineOperand, 2> Cond;
857 MipsInstrInfo::BranchType R =
858 TII->analyzeBranch(MBB, TrueBB, FalseBB, Cond, false, BranchInstrs);
860 if ((R == MipsInstrInfo::BT_None) || (R == MipsInstrInfo::BT_NoBranch))
861 return std::make_pair(R, nullptr);
863 if (R != MipsInstrInfo::BT_CondUncond) {
864 if (!hasUnoccupiedSlot(BranchInstrs[0]))
865 return std::make_pair(MipsInstrInfo::BT_None, nullptr);
867 assert(((R != MipsInstrInfo::BT_Uncond) || (TrueBB == &Dst)));
869 return std::make_pair(R, BranchInstrs[0]);
872 assert((TrueBB == &Dst) || (FalseBB == &Dst));
874 // Examine the conditional branch. See if its slot is occupied.
875 if (hasUnoccupiedSlot(BranchInstrs[0]))
876 return std::make_pair(MipsInstrInfo::BT_Cond, BranchInstrs[0]);
878 // If that fails, try the unconditional branch.
879 if (hasUnoccupiedSlot(BranchInstrs[1]) && (FalseBB == &Dst))
880 return std::make_pair(MipsInstrInfo::BT_Uncond, BranchInstrs[1]);
882 return std::make_pair(MipsInstrInfo::BT_None, nullptr);
885 bool MipsDelaySlotFiller::examinePred(MachineBasicBlock &Pred,
886 const MachineBasicBlock &Succ,
888 bool &HasMultipleSuccs,
889 BB2BrMap &BrMap) const {
890 std::pair<MipsInstrInfo::BranchType, MachineInstr *> P =
891 getBranch(Pred, Succ);
893 // Return if either getBranch wasn't able to analyze the branches or there
894 // were no branches with unoccupied slots.
895 if (P.first == MipsInstrInfo::BT_None)
898 if ((P.first != MipsInstrInfo::BT_Uncond) &&
899 (P.first != MipsInstrInfo::BT_NoBranch)) {
900 HasMultipleSuccs = true;
901 RegDU.addLiveOut(Pred, Succ);
904 BrMap[&Pred] = P.second;
908 bool MipsDelaySlotFiller::delayHasHazard(const MachineInstr &Candidate,
910 InspectMemInstr &IM) const {
911 assert(!Candidate.isKill() &&
912 "KILL instructions should have been eliminated at this point.");
914 bool HasHazard = Candidate.isImplicitDef();
916 HasHazard |= IM.hasHazard(Candidate);
917 HasHazard |= RegDU.update(Candidate, 0, Candidate.getNumOperands());
922 bool MipsDelaySlotFiller::terminateSearch(const MachineInstr &Candidate) const {
923 return (Candidate.isTerminator() || Candidate.isCall() ||
924 Candidate.isPosition() || Candidate.isInlineAsm() ||
925 Candidate.hasUnmodeledSideEffects());
928 /// createMipsDelaySlotFillerPass - Returns a pass that fills in delay
929 /// slots in Mips MachineFunctions
930 FunctionPass *llvm::createMipsDelaySlotFillerPass() { return new MipsDelaySlotFiller(); }