lib/Target/Mips/MipsDelaySlotFiller.cpp

   1 //===- MipsDelaySlotFiller.cpp - Mips Delay Slot Filler -------------------===//
   2 //
   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
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // Simple pass to fill delay slots with useful instructions.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "MCTargetDesc/MipsMCNaCl.h"
  14 #include "Mips.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"
  45 #include <algorithm>
  46 #include <cassert>
  47 #include <iterator>
  48 #include <memory>
  49 #include <utility>
  50
  51 using namespace llvm;
  52
  53 #define DEBUG_TYPE "mips-delay-slot-filler"
  54
  55 STATISTIC(FilledSlots, "Number of delay slots filled");
  56 STATISTIC(UsefulSlots, "Number of delay slots filled with instructions that"
  57                        " are not NOP.");
  58
  59 static cl::opt<bool> DisableDelaySlotFiller(
  60   "disable-mips-delay-filler",
  61   cl::init(false),
  62   cl::desc("Fill all delay slots with NOPs."),
  63   cl::Hidden);
  64
  65 static cl::opt<bool> DisableForwardSearch(
  66   "disable-mips-df-forward-search",
  67   cl::init(true),
  68   cl::desc("Disallow MIPS delay filler to search forward."),
  69   cl::Hidden);
  70
  71 static cl::opt<bool> DisableSuccBBSearch(
  72   "disable-mips-df-succbb-search",
  73   cl::init(true),
  74   cl::desc("Disallow MIPS delay filler to search successor basic blocks."),
  75   cl::Hidden);
  76
  77 static cl::opt<bool> DisableBackwardSearch(
  78   "disable-mips-df-backward-search",
  79   cl::init(false),
  80   cl::desc("Disallow MIPS delay filler to search backward."),
  81   cl::Hidden);
  82
  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.
  91 };
  92
  93 static cl::opt<CompactBranchPolicy> MipsCompactBranchPolicy(
  94   "mips-compact-branches",cl::Optional,
  95   cl::init(CB_Optimal),
  96   cl::desc("MIPS Specific: Compact branch policy."),
  97   cl::values(
  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.")
 101   )
 102 );
 103
 104 namespace {
 105
 106   using Iter = MachineBasicBlock::iterator;
 107   using ReverseIter = MachineBasicBlock::reverse_iterator;
 108   using BB2BrMap = SmallDenseMap<MachineBasicBlock *, MachineInstr *, 2>;
 109
 110   class RegDefsUses {
 111   public:
 112     RegDefsUses(const TargetRegisterInfo &TRI);
 113
 114     void init(const MachineInstr &MI);
 115
 116     /// This function sets all caller-saved registers in Defs.
 117     void setCallerSaved(const MachineInstr &MI);
 118
 119     /// This function sets all unallocatable registers in Defs.
 120     void setUnallocatableRegs(const MachineFunction &MF);
 121
 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);
 126
 127     bool update(const MachineInstr &MI, unsigned Begin, unsigned End);
 128
 129   private:
 130     bool checkRegDefsUses(BitVector &NewDefs, BitVector &NewUses, unsigned Reg,
 131                           bool IsDef) const;
 132
 133     /// Returns true if Reg or its alias is in RegSet.
 134     bool isRegInSet(const BitVector &RegSet, unsigned Reg) const;
 135
 136     const TargetRegisterInfo &TRI;
 137     BitVector Defs, Uses;
 138   };
 139
 140   /// Base class for inspecting loads and stores.
 141   class InspectMemInstr {
 142   public:
 143     InspectMemInstr(bool ForbidMemInstr_) : ForbidMemInstr(ForbidMemInstr_) {}
 144     virtual ~InspectMemInstr() = default;
 145
 146     /// Return true if MI cannot be moved to delay slot.
 147     bool hasHazard(const MachineInstr &MI);
 148
 149   protected:
 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;
 155
 156     /// Memory instructions are not allowed to move to delay slot if this flag
 157     /// is true.
 158     bool ForbidMemInstr;
 159
 160   private:
 161     virtual bool hasHazard_(const MachineInstr &MI) = 0;
 162   };
 163
 164   /// This subclass rejects any memory instructions.
 165   class NoMemInstr : public InspectMemInstr {
 166   public:
 167     NoMemInstr() : InspectMemInstr(true) {}
 168
 169   private:
 170     bool hasHazard_(const MachineInstr &MI) override { return true; }
 171   };
 172
 173   /// This subclass accepts loads from stacks and constant loads.
 174   class LoadFromStackOrConst : public InspectMemInstr {
 175   public:
 176     LoadFromStackOrConst() : InspectMemInstr(false) {}
 177
 178   private:
 179     bool hasHazard_(const MachineInstr &MI) override;
 180   };
 181
 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 {
 185   public:
 186     MemDefsUses(const DataLayout &DL, const MachineFrameInfo *MFI);
 187
 188   private:
 189     using ValueType = PointerUnion<const Value *, const PseudoSourceValue *>;
 190
 191     bool hasHazard_(const MachineInstr &MI) override;
 192
 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
 195     /// Defs.
 196     bool updateDefsUses(ValueType V, bool MayStore);
 197
 198     /// Get the list of underlying objects of MI's memory operand.
 199     bool getUnderlyingObjects(const MachineInstr &MI,
 200                               SmallVectorImpl<ValueType> &Objects) const;
 201
 202     const MachineFrameInfo *MFI;
 203     SmallPtrSet<ValueType, 4> Uses, Defs;
 204     const DataLayout &DL;
 205
 206     /// Flags indicating whether loads or stores with no underlying objects have
 207     /// been seen.
 208     bool SeenNoObjLoad = false;
 209     bool SeenNoObjStore = false;
 210   };
 211
 212   class MipsDelaySlotFiller : public MachineFunctionPass {
 213   public:
 214     MipsDelaySlotFiller() : MachineFunctionPass(ID) {
 215       initializeMipsDelaySlotFillerPass(*PassRegistry::getPassRegistry());
 216     }
 217
 218     StringRef getPassName() const override { return "Mips Delay Slot Filler"; }
 219
 220     bool runOnMachineFunction(MachineFunction &F) override {
 221       TM = &F.getTarget();
 222       bool Changed = false;
 223       for (MachineFunction::iterator FI = F.begin(), FE = F.end();
 224            FI != FE; ++FI)
 225         Changed |= runOnMachineBasicBlock(*FI);
 226
 227       // This pass invalidates liveness information when it reorders
 228       // instructions to fill delay slot. Without this, -verify-machineinstrs
 229       // will fail.
 230       if (Changed)
 231         F.getRegInfo().invalidateLiveness();
 232
 233       return Changed;
 234     }
 235
 236     MachineFunctionProperties getRequiredProperties() const override {
 237       return MachineFunctionProperties().set(
 238           MachineFunctionProperties::Property::NoVRegs);
 239     }
 240
 241     void getAnalysisUsage(AnalysisUsage &AU) const override {
 242       AU.addRequired<MachineBranchProbabilityInfo>();
 243       MachineFunctionPass::getAnalysisUsage(AU);
 244     }
 245
 246     static char ID;
 247
 248   private:
 249     bool runOnMachineBasicBlock(MachineBasicBlock &MBB);
 250
 251     Iter replaceWithCompactBranch(MachineBasicBlock &MBB, Iter Branch,
 252                                   const DebugLoc &DL);
 253
 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;
 259
 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;
 266
 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;
 270
 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;
 274
 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;
 279
 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;
 283
 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;
 288
 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;
 294
 295     bool terminateSearch(const MachineInstr &Candidate) const;
 296
 297     const TargetMachine *TM = nullptr;
 298   };
 299
 300 } // end anonymous namespace
 301
 302 char MipsDelaySlotFiller::ID = 0;
 303
 304 static bool hasUnoccupiedSlot(const MachineInstr *MI) {
 305   return MI->hasDelaySlot() && !MI->isBundledWithSucc();
 306 }
 307
 308 INITIALIZE_PASS(MipsDelaySlotFiller, DEBUG_TYPE,
 309                 "Fill delay slot for MIPS", false, false)
 310
 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();
 314
 315   for (BB2BrMap::const_iterator I = BrMap.begin(); I != BrMap.end(); ++I) {
 316     if (I->second) {
 317       MIBundleBuilder(I->second).append(MF->CloneMachineInstr(&*Filler));
 318       ++UsefulSlots;
 319     } else {
 320       I->first->insert(I->first->end(), MF->CloneMachineInstr(&*Filler));
 321     }
 322   }
 323 }
 324
 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);
 329     unsigned R;
 330
 331     if (!MO.isReg() || !MO.isDef() || !(R = MO.getReg()))
 332       continue;
 333
 334 #ifndef NDEBUG
 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.");
 339 #endif
 340
 341     if (!MBB.isLiveIn(R))
 342       MBB.addLiveIn(R);
 343   }
 344 }
 345
 346 RegDefsUses::RegDefsUses(const TargetRegisterInfo &TRI)
 347     : TRI(TRI), Defs(TRI.getNumRegs(), false), Uses(TRI.getNumRegs(), false) {}
 348
 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());
 352
 353   // If MI is a call, add RA to Defs to prevent users of RA from going into
 354   // delay slot.
 355   if (MI.isCall())
 356     Defs.set(Mips::RA);
 357
 358   // Add all implicit register operands of branch instructions except
 359   // register AT.
 360   if (MI.isBranch()) {
 361     update(MI, MI.getDesc().getNumOperands(), MI.getNumOperands());
 362     Defs.reset(Mips::AT);
 363   }
 364 }
 365
 366 void RegDefsUses::setCallerSaved(const MachineInstr &MI) {
 367   assert(MI.isCall());
 368
 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)) {
 373     Defs.set(Mips::RA);
 374     Defs.set(Mips::RA_64);
 375   }
 376
 377   // If MI is a call, add all caller-saved registers to Defs.
 378   BitVector CallerSavedRegs(TRI.getNumRegs(), true);
 379
 380   CallerSavedRegs.reset(Mips::ZERO);
 381   CallerSavedRegs.reset(Mips::ZERO_64);
 382
 383   for (const MCPhysReg *R = TRI.getCalleeSavedRegs(MI.getParent()->getParent());
 384        *R; ++R)
 385     for (MCRegAliasIterator AI(*R, &TRI, true); AI.isValid(); ++AI)
 386       CallerSavedRegs.reset(*AI);
 387
 388   Defs |= CallerSavedRegs;
 389 }
 390
 391 void RegDefsUses::setUnallocatableRegs(const MachineFunction &MF) {
 392   BitVector AllocSet = TRI.getAllocatableSet(MF);
 393
 394   for (unsigned R : AllocSet.set_bits())
 395     for (MCRegAliasIterator AI(R, &TRI, false); AI.isValid(); ++AI)
 396       AllocSet.set(*AI);
 397
 398   AllocSet.set(Mips::ZERO);
 399   AllocSet.set(Mips::ZERO_64);
 400
 401   Defs |= AllocSet.flip();
 402 }
 403
 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)
 408     if (*SI != &SuccBB)
 409       for (const auto &LI : (*SI)->liveins())
 410         Uses.set(LI.PhysReg);
 411 }
 412
 413 bool RegDefsUses::update(const MachineInstr &MI, unsigned Begin, unsigned End) {
 414   BitVector NewDefs(TRI.getNumRegs()), NewUses(TRI.getNumRegs());
 415   bool HasHazard = false;
 416
 417   for (unsigned I = Begin; I != End; ++I) {
 418     const MachineOperand &MO = MI.getOperand(I);
 419
 420     if (MO.isReg() && MO.getReg())
 421       HasHazard |= checkRegDefsUses(NewDefs, NewUses, MO.getReg(), MO.isDef());
 422   }
 423
 424   Defs |= NewDefs;
 425   Uses |= NewUses;
 426
 427   return HasHazard;
 428 }
 429
 430 bool RegDefsUses::checkRegDefsUses(BitVector &NewDefs, BitVector &NewUses,
 431                                    unsigned Reg, bool IsDef) const {
 432   if (IsDef) {
 433     NewDefs.set(Reg);
 434     // check whether Reg has already been defined or used.
 435     return (isRegInSet(Defs, Reg) || isRegInSet(Uses, Reg));
 436   }
 437
 438   NewUses.set(Reg);
 439   // check whether Reg has already been defined.
 440   return isRegInSet(Defs, Reg);
 441 }
 442
 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))
 447       return true;
 448   return false;
 449 }
 450
 451 bool InspectMemInstr::hasHazard(const MachineInstr &MI) {
 452   if (!MI.mayStore() && !MI.mayLoad())
 453     return false;
 454
 455   if (ForbidMemInstr)
 456     return true;
 457
 458   OrigSeenLoad = SeenLoad;
 459   OrigSeenStore = SeenStore;
 460   SeenLoad |= MI.mayLoad();
 461   SeenStore |= MI.mayStore();
 462
 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;
 467     return true;
 468   }
 469
 470   return hasHazard_(MI);
 471 }
 472
 473 bool LoadFromStackOrConst::hasHazard_(const MachineInstr &MI) {
 474   if (MI.mayStore())
 475     return true;
 476
 477   if (!MI.hasOneMemOperand() || !(*MI.memoperands_begin())->getPseudoValue())
 478     return true;
 479
 480   if (const PseudoSourceValue *PSV =
 481       (*MI.memoperands_begin())->getPseudoValue()) {
 482     if (isa<FixedStackPseudoSourceValue>(PSV))
 483       return false;
 484     return !PSV->isConstant(nullptr) && !PSV->isStack();
 485   }
 486
 487   return true;
 488 }
 489
 490 MemDefsUses::MemDefsUses(const DataLayout &DL, const MachineFrameInfo *MFI_)
 491     : InspectMemInstr(false), MFI(MFI_), DL(DL) {}
 492
 493 bool MemDefsUses::hasHazard_(const MachineInstr &MI) {
 494   bool HasHazard = false;
 495   SmallVector<ValueType, 4> Objs;
 496
 497   // Check underlying object list.
 498   if (getUnderlyingObjects(MI, Objs)) {
 499     for (SmallVectorImpl<ValueType>::const_iterator I = Objs.begin();
 500          I != Objs.end(); ++I)
 501       HasHazard |= updateDefsUses(*I, MI.mayStore());
 502
 503     return HasHazard;
 504   }
 505
 506   // No underlying objects found.
 507   HasHazard = MI.mayStore() && (OrigSeenLoad || OrigSeenStore);
 508   HasHazard |= MI.mayLoad() || OrigSeenStore;
 509
 510   SeenNoObjLoad |= MI.mayLoad();
 511   SeenNoObjStore |= MI.mayStore();
 512
 513   return HasHazard;
 514 }
 515
 516 bool MemDefsUses::updateDefsUses(ValueType V, bool MayStore) {
 517   if (MayStore)
 518     return !Defs.insert(V).second || Uses.count(V) || SeenNoObjStore ||
 519            SeenNoObjLoad;
 520
 521   Uses.insert(V);
 522   return Defs.count(V) || SeenNoObjStore;
 523 }
 524
 525 bool MemDefsUses::
 526 getUnderlyingObjects(const MachineInstr &MI,
 527                      SmallVectorImpl<ValueType> &Objects) const {
 528   if (!MI.hasOneMemOperand() ||
 529       (!(*MI.memoperands_begin())->getValue() &&
 530        !(*MI.memoperands_begin())->getPseudoValue()))
 531     return false;
 532
 533   if (const PseudoSourceValue *PSV =
 534       (*MI.memoperands_begin())->getPseudoValue()) {
 535     if (!PSV->isAliased(MFI))
 536       return false;
 537     Objects.push_back(PSV);
 538     return true;
 539   }
 540
 541   const Value *V = (*MI.memoperands_begin())->getValue();
 542
 543   SmallVector<Value *, 4> Objs;
 544   GetUnderlyingObjects(const_cast<Value *>(V), Objs, DL);
 545
 546   for (SmallVectorImpl<Value *>::iterator I = Objs.begin(), E = Objs.end();
 547        I != E; ++I) {
 548     if (!isIdentifiedObject(V))
 549       return false;
 550
 551     Objects.push_back(*I);
 552   }
 553
 554   return true;
 555 }
 556
 557 // Replace Branch with the compact branch instruction.
 558 Iter MipsDelaySlotFiller::replaceWithCompactBranch(MachineBasicBlock &MBB,
 559                                                    Iter Branch,
 560                                                    const DebugLoc &DL) {
 561   const MipsSubtarget &STI = MBB.getParent()->getSubtarget<MipsSubtarget>();
 562   const MipsInstrInfo *TII = STI.getInstrInfo();
 563
 564   unsigned NewOpcode = TII->getEquivalentCompactForm(Branch);
 565   Branch = TII->genInstrWithNewOpc(NewOpcode, Branch);
 566
 567   std::next(Branch)->eraseFromParent();
 568   return Branch;
 569 }
 570
 571 // For given opcode returns opcode of corresponding instruction with short
 572 // delay slot.
 573 // For the pseudo TAILCALL*_MM instructions return the short delay slot
 574 // form. Unfortunately, TAILCALL<->b16 is denied as b16 has a limited range
 575 // that is too short to make use of for tail calls.
 576 static int getEquivalentCallShort(int Opcode) {
 577   switch (Opcode) {
 578   case Mips::BGEZAL:
 579     return Mips::BGEZALS_MM;
 580   case Mips::BLTZAL:
 581     return Mips::BLTZALS_MM;
 582   case Mips::JAL:
 583   case Mips::JAL_MM:
 584     return Mips::JALS_MM;
 585   case Mips::JALR:
 586     return Mips::JALRS_MM;
 587   case Mips::JALR16_MM:
 588     return Mips::JALRS16_MM;
 589   case Mips::TAILCALL_MM:
 590     llvm_unreachable("Attempting to shorten the TAILCALL_MM pseudo!");
 591   case Mips::TAILCALLREG:
 592     return Mips::JR16_MM;
 593   default:
 594     llvm_unreachable("Unexpected call instruction for microMIPS.");
 595   }
 596 }
 597
 598 /// runOnMachineBasicBlock - Fill in delay slots for the given basic block.
 599 /// We assume there is only one delay slot per delayed instruction.
 600 bool MipsDelaySlotFiller::runOnMachineBasicBlock(MachineBasicBlock &MBB) {
 601   bool Changed = false;
 602   const MipsSubtarget &STI = MBB.getParent()->getSubtarget<MipsSubtarget>();
 603   bool InMicroMipsMode = STI.inMicroMipsMode();
 604   const MipsInstrInfo *TII = STI.getInstrInfo();
 605
 606   for (Iter I = MBB.begin(); I != MBB.end(); ++I) {
 607     if (!hasUnoccupiedSlot(&*I))
 608       continue;
 609
 610     // Delay slot filling is disabled at -O0, or in microMIPS32R6.
 611     if (!DisableDelaySlotFiller && (TM->getOptLevel() != CodeGenOpt::None) &&
 612         !(InMicroMipsMode && STI.hasMips32r6())) {
 613
 614       bool Filled = false;
 615
 616       if (MipsCompactBranchPolicy.getValue() != CB_Always ||
 617            !TII->getEquivalentCompactForm(I)) {
 618         if (searchBackward(MBB, *I)) {
 619           Filled = true;
 620         } else if (I->isTerminator()) {
 621           if (searchSuccBBs(MBB, I)) {
 622             Filled = true;
 623           }
 624         } else if (searchForward(MBB, I)) {
 625           Filled = true;
 626         }
 627       }
 628
 629       if (Filled) {
 630         // Get instruction with delay slot.
 631         MachineBasicBlock::instr_iterator DSI = I.getInstrIterator();
 632
 633         if (InMicroMipsMode && TII->getInstSizeInBytes(*std::next(DSI)) == 2 &&
 634             DSI->isCall()) {
 635           // If instruction in delay slot is 16b change opcode to
 636           // corresponding instruction with short delay slot.
 637
 638           // TODO: Implement an instruction mapping table of 16bit opcodes to
 639           // 32bit opcodes so that an instruction can be expanded. This would
 640           // save 16 bits as a TAILCALL_MM pseudo requires a fullsized nop.
 641           // TODO: Permit b16 when branching backwards to the same function
 642           // if it is in range.
 643           DSI->setDesc(TII->get(getEquivalentCallShort(DSI->getOpcode())));
 644         }
 645         ++FilledSlots;
 646         Changed = true;
 647         continue;
 648       }
 649     }
 650
 651     // For microMIPS if instruction is BEQ or BNE with one ZERO register, then
 652     // instead of adding NOP replace this instruction with the corresponding
 653     // compact branch instruction, i.e. BEQZC or BNEZC. Additionally
 654     // PseudoReturn and PseudoIndirectBranch are expanded to JR_MM, so they can
 655     // be replaced with JRC16_MM.
 656
 657     // For MIPSR6 attempt to produce the corresponding compact (no delay slot)
 658     // form of the CTI. For indirect jumps this will not require inserting a
 659     // NOP and for branches will hopefully avoid requiring a NOP.
 660     if ((InMicroMipsMode ||
 661          (STI.hasMips32r6() && MipsCompactBranchPolicy != CB_Never)) &&
 662         TII->getEquivalentCompactForm(I)) {
 663       I = replaceWithCompactBranch(MBB, I, I->getDebugLoc());
 664       Changed = true;
 665       continue;
 666     }
 667
 668     // Bundle the NOP to the instruction with the delay slot.
 669     BuildMI(MBB, std::next(I), I->getDebugLoc(), TII->get(Mips::NOP));
 670     MIBundleBuilder(MBB, I, std::next(I, 2));
 671     ++FilledSlots;
 672     Changed = true;
 673   }
 674
 675   return Changed;
 676 }
 677
 678 template <typename IterTy>
 679 bool MipsDelaySlotFiller::searchRange(MachineBasicBlock &MBB, IterTy Begin,
 680                                       IterTy End, RegDefsUses &RegDU,
 681                                       InspectMemInstr &IM, Iter Slot,
 682                                       IterTy &Filler) const {
 683   for (IterTy I = Begin; I != End;) {
 684     IterTy CurrI = I;
 685     ++I;
 686
 687     // skip debug value
 688     if (CurrI->isDebugInstr())
 689       continue;
 690
 691     if (terminateSearch(*CurrI))
 692       break;
 693
 694     assert((!CurrI->isCall() && !CurrI->isReturn() && !CurrI->isBranch()) &&
 695            "Cannot put calls, returns or branches in delay slot.");
 696
 697     if (CurrI->isKill()) {
 698       CurrI->eraseFromParent();
 699       continue;
 700     }
 701
 702     if (delayHasHazard(*CurrI, RegDU, IM))
 703       continue;
 704
 705     const MipsSubtarget &STI = MBB.getParent()->getSubtarget<MipsSubtarget>();
 706     if (STI.isTargetNaCl()) {
 707       // In NaCl, instructions that must be masked are forbidden in delay slots.
 708       // We only check for loads, stores and SP changes.  Calls, returns and
 709       // branches are not checked because non-NaCl targets never put them in
 710       // delay slots.
 711       unsigned AddrIdx;
 712       if ((isBasePlusOffsetMemoryAccess(CurrI->getOpcode(), &AddrIdx) &&
 713            baseRegNeedsLoadStoreMask(CurrI->getOperand(AddrIdx).getReg())) ||
 714           CurrI->modifiesRegister(Mips::SP, STI.getRegisterInfo()))
 715         continue;
 716     }
 717
 718     bool InMicroMipsMode = STI.inMicroMipsMode();
 719     const MipsInstrInfo *TII = STI.getInstrInfo();
 720     unsigned Opcode = (*Slot).getOpcode();
 721     // This is complicated by the tail call optimization. For non-PIC code
 722     // there is only a 32bit sized unconditional branch which can be assumed
 723     // to be able to reach the target. b16 only has a range of +/- 1 KB.
 724     // It's entirely possible that the target function is reachable with b16
 725     // but we don't have enough information to make that decision.
 726      if (InMicroMipsMode && TII->getInstSizeInBytes(*CurrI) == 2 &&
 727         (Opcode == Mips::JR || Opcode == Mips::PseudoIndirectBranch ||
 728          Opcode == Mips::PseudoReturn || Opcode == Mips::TAILCALL))
 729       continue;
 730      // Instructions LWP/SWP and MOVEP should not be in a delay slot as that
 731      // results in unpredictable behaviour
 732      if (InMicroMipsMode && (Opcode == Mips::LWP_MM || Opcode == Mips::SWP_MM ||
 733                              Opcode == Mips::MOVEP_MM))
 734        continue;
 735
 736     Filler = CurrI;
 737     return true;
 738   }
 739
 740   return false;
 741 }
 742
 743 bool MipsDelaySlotFiller::searchBackward(MachineBasicBlock &MBB,
 744                                          MachineInstr &Slot) const {
 745   if (DisableBackwardSearch)
 746     return false;
 747
 748   auto *Fn = MBB.getParent();
 749   RegDefsUses RegDU(*Fn->getSubtarget().getRegisterInfo());
 750   MemDefsUses MemDU(Fn->getDataLayout(), &Fn->getFrameInfo());
 751   ReverseIter Filler;
 752
 753   RegDU.init(Slot);
 754
 755   MachineBasicBlock::iterator SlotI = Slot;
 756   if (!searchRange(MBB, ++SlotI.getReverse(), MBB.rend(), RegDU, MemDU, Slot,
 757                    Filler))
 758     return false;
 759
 760   MBB.splice(std::next(SlotI), &MBB, Filler.getReverse());
 761   MIBundleBuilder(MBB, SlotI, std::next(SlotI, 2));
 762   ++UsefulSlots;
 763   return true;
 764 }
 765
 766 bool MipsDelaySlotFiller::searchForward(MachineBasicBlock &MBB,
 767                                         Iter Slot) const {
 768   // Can handle only calls.
 769   if (DisableForwardSearch || !Slot->isCall())
 770     return false;
 771
 772   RegDefsUses RegDU(*MBB.getParent()->getSubtarget().getRegisterInfo());
 773   NoMemInstr NM;
 774   Iter Filler;
 775
 776   RegDU.setCallerSaved(*Slot);
 777
 778   if (!searchRange(MBB, std::next(Slot), MBB.end(), RegDU, NM, Slot, Filler))
 779     return false;
 780
 781   MBB.splice(std::next(Slot), &MBB, Filler);
 782   MIBundleBuilder(MBB, Slot, std::next(Slot, 2));
 783   ++UsefulSlots;
 784   return true;
 785 }
 786
 787 bool MipsDelaySlotFiller::searchSuccBBs(MachineBasicBlock &MBB,
 788                                         Iter Slot) const {
 789   if (DisableSuccBBSearch)
 790     return false;
 791
 792   MachineBasicBlock *SuccBB = selectSuccBB(MBB);
 793
 794   if (!SuccBB)
 795     return false;
 796
 797   RegDefsUses RegDU(*MBB.getParent()->getSubtarget().getRegisterInfo());
 798   bool HasMultipleSuccs = false;
 799   BB2BrMap BrMap;
 800   std::unique_ptr<InspectMemInstr> IM;
 801   Iter Filler;
 802   auto *Fn = MBB.getParent();
 803
 804   // Iterate over SuccBB's predecessor list.
 805   for (MachineBasicBlock::pred_iterator PI = SuccBB->pred_begin(),
 806        PE = SuccBB->pred_end(); PI != PE; ++PI)
 807     if (!examinePred(**PI, *SuccBB, RegDU, HasMultipleSuccs, BrMap))
 808       return false;
 809
 810   // Do not allow moving instructions which have unallocatable register operands
 811   // across basic block boundaries.
 812   RegDU.setUnallocatableRegs(*Fn);
 813
 814   // Only allow moving loads from stack or constants if any of the SuccBB's
 815   // predecessors have multiple successors.
 816   if (HasMultipleSuccs) {
 817     IM.reset(new LoadFromStackOrConst());
 818   } else {
 819     const MachineFrameInfo &MFI = Fn->getFrameInfo();
 820     IM.reset(new MemDefsUses(Fn->getDataLayout(), &MFI));
 821   }
 822
 823   if (!searchRange(MBB, SuccBB->begin(), SuccBB->end(), RegDU, *IM, Slot,
 824                    Filler))
 825     return false;
 826
 827   insertDelayFiller(Filler, BrMap);
 828   addLiveInRegs(Filler, *SuccBB);
 829   Filler->eraseFromParent();
 830
 831   return true;
 832 }
 833
 834 MachineBasicBlock *
 835 MipsDelaySlotFiller::selectSuccBB(MachineBasicBlock &B) const {
 836   if (B.succ_empty())
 837     return nullptr;
 838
 839   // Select the successor with the larget edge weight.
 840   auto &Prob = getAnalysis<MachineBranchProbabilityInfo>();
 841   MachineBasicBlock *S = *std::max_element(
 842       B.succ_begin(), B.succ_end(),
 843       [&](const MachineBasicBlock *Dst0, const MachineBasicBlock *Dst1) {
 844         return Prob.getEdgeProbability(&B, Dst0) <
 845                Prob.getEdgeProbability(&B, Dst1);
 846       });
 847   return S->isEHPad() ? nullptr : S;
 848 }
 849
 850 std::pair<MipsInstrInfo::BranchType, MachineInstr *>
 851 MipsDelaySlotFiller::getBranch(MachineBasicBlock &MBB,
 852                                const MachineBasicBlock &Dst) const {
 853   const MipsInstrInfo *TII =
 854       MBB.getParent()->getSubtarget<MipsSubtarget>().getInstrInfo();
 855   MachineBasicBlock *TrueBB = nullptr, *FalseBB = nullptr;
 856   SmallVector<MachineInstr*, 2> BranchInstrs;
 857   SmallVector<MachineOperand, 2> Cond;
 858
 859   MipsInstrInfo::BranchType R =
 860       TII->analyzeBranch(MBB, TrueBB, FalseBB, Cond, false, BranchInstrs);
 861
 862   if ((R == MipsInstrInfo::BT_None) || (R == MipsInstrInfo::BT_NoBranch))
 863     return std::make_pair(R, nullptr);
 864
 865   if (R != MipsInstrInfo::BT_CondUncond) {
 866     if (!hasUnoccupiedSlot(BranchInstrs[0]))
 867       return std::make_pair(MipsInstrInfo::BT_None, nullptr);
 868
 869     assert(((R != MipsInstrInfo::BT_Uncond) || (TrueBB == &Dst)));
 870
 871     return std::make_pair(R, BranchInstrs[0]);
 872   }
 873
 874   assert((TrueBB == &Dst) || (FalseBB == &Dst));
 875
 876   // Examine the conditional branch. See if its slot is occupied.
 877   if (hasUnoccupiedSlot(BranchInstrs[0]))
 878     return std::make_pair(MipsInstrInfo::BT_Cond, BranchInstrs[0]);
 879
 880   // If that fails, try the unconditional branch.
 881   if (hasUnoccupiedSlot(BranchInstrs[1]) && (FalseBB == &Dst))
 882     return std::make_pair(MipsInstrInfo::BT_Uncond, BranchInstrs[1]);
 883
 884   return std::make_pair(MipsInstrInfo::BT_None, nullptr);
 885 }
 886
 887 bool MipsDelaySlotFiller::examinePred(MachineBasicBlock &Pred,
 888                                       const MachineBasicBlock &Succ,
 889                                       RegDefsUses &RegDU,
 890                                       bool &HasMultipleSuccs,
 891                                       BB2BrMap &BrMap) const {
 892   std::pair<MipsInstrInfo::BranchType, MachineInstr *> P =
 893       getBranch(Pred, Succ);
 894
 895   // Return if either getBranch wasn't able to analyze the branches or there
 896   // were no branches with unoccupied slots.
 897   if (P.first == MipsInstrInfo::BT_None)
 898     return false;
 899
 900   if ((P.first != MipsInstrInfo::BT_Uncond) &&
 901       (P.first != MipsInstrInfo::BT_NoBranch)) {
 902     HasMultipleSuccs = true;
 903     RegDU.addLiveOut(Pred, Succ);
 904   }
 905
 906   BrMap[&Pred] = P.second;
 907   return true;
 908 }
 909
 910 bool MipsDelaySlotFiller::delayHasHazard(const MachineInstr &Candidate,
 911                                          RegDefsUses &RegDU,
 912                                          InspectMemInstr &IM) const {
 913   assert(!Candidate.isKill() &&
 914          "KILL instructions should have been eliminated at this point.");
 915
 916   bool HasHazard = Candidate.isImplicitDef();
 917
 918   HasHazard |= IM.hasHazard(Candidate);
 919   HasHazard |= RegDU.update(Candidate, 0, Candidate.getNumOperands());
 920
 921   return HasHazard;
 922 }
 923
 924 bool MipsDelaySlotFiller::terminateSearch(const MachineInstr &Candidate) const {
 925   return (Candidate.isTerminator() || Candidate.isCall() ||
 926           Candidate.isPosition() || Candidate.isInlineAsm() ||
 927           Candidate.hasUnmodeledSideEffects());
 928 }
 929
 930 /// createMipsDelaySlotFillerPass - Returns a pass that fills in delay
 931 /// slots in Mips MachineFunctions
 932 FunctionPass *llvm::createMipsDelaySlotFillerPass() { return new MipsDelaySlotFiller(); }