lib/Target/X86/X86ExpandPseudo.cpp

   1 //===------- X86ExpandPseudo.cpp - Expand pseudo instructions -------------===//
   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 // This file contains a pass that expands pseudo instructions into target
  10 // instructions to allow proper scheduling, if-conversion, other late
  11 // optimizations, or simply the encoding of the instructions.
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #include "X86.h"
  16 #include "X86FrameLowering.h"
  17 #include "X86InstrBuilder.h"
  18 #include "X86InstrInfo.h"
  19 #include "X86MachineFunctionInfo.h"
  20 #include "X86Subtarget.h"
  21 #include "llvm/Analysis/EHPersonalities.h"
  22 #include "llvm/CodeGen/MachineFunctionPass.h"
  23 #include "llvm/CodeGen/MachineInstrBuilder.h"
  24 #include "llvm/CodeGen/Passes.h" // For IDs of passes that are preserved.
  25 #include "llvm/IR/GlobalValue.h"
  26 using namespace llvm;
  27
  28 #define DEBUG_TYPE "x86-pseudo"
  29 #define X86_EXPAND_PSEUDO_NAME "X86 pseudo instruction expansion pass"
  30
  31 namespace {
  32 class X86ExpandPseudo : public MachineFunctionPass {
  33 public:
  34   static char ID;
  35   X86ExpandPseudo() : MachineFunctionPass(ID) {}
  36
  37   void getAnalysisUsage(AnalysisUsage &AU) const override {
  38     AU.setPreservesCFG();
  39     AU.addPreservedID(MachineLoopInfoID);
  40     AU.addPreservedID(MachineDominatorsID);
  41     MachineFunctionPass::getAnalysisUsage(AU);
  42   }
  43
  44   const X86Subtarget *STI;
  45   const X86InstrInfo *TII;
  46   const X86RegisterInfo *TRI;
  47   const X86MachineFunctionInfo *X86FI;
  48   const X86FrameLowering *X86FL;
  49
  50   bool runOnMachineFunction(MachineFunction &Fn) override;
  51
  52   MachineFunctionProperties getRequiredProperties() const override {
  53     return MachineFunctionProperties().set(
  54         MachineFunctionProperties::Property::NoVRegs);
  55   }
  56
  57   StringRef getPassName() const override {
  58     return "X86 pseudo instruction expansion pass";
  59   }
  60
  61 private:
  62   void ExpandICallBranchFunnel(MachineBasicBlock *MBB,
  63                                MachineBasicBlock::iterator MBBI);
  64
  65   bool ExpandMI(MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI);
  66   bool ExpandMBB(MachineBasicBlock &MBB);
  67 };
  68 char X86ExpandPseudo::ID = 0;
  69
  70 } // End anonymous namespace.
  71
  72 INITIALIZE_PASS(X86ExpandPseudo, DEBUG_TYPE, X86_EXPAND_PSEUDO_NAME, false,
  73                 false)
  74
  75 void X86ExpandPseudo::ExpandICallBranchFunnel(
  76     MachineBasicBlock *MBB, MachineBasicBlock::iterator MBBI) {
  77   MachineBasicBlock *JTMBB = MBB;
  78   MachineInstr *JTInst = &*MBBI;
  79   MachineFunction *MF = MBB->getParent();
  80   const BasicBlock *BB = MBB->getBasicBlock();
  81   auto InsPt = MachineFunction::iterator(MBB);
  82   ++InsPt;
  83
  84   std::vector<std::pair<MachineBasicBlock *, unsigned>> TargetMBBs;
  85   DebugLoc DL = JTInst->getDebugLoc();
  86   MachineOperand Selector = JTInst->getOperand(0);
  87   const GlobalValue *CombinedGlobal = JTInst->getOperand(1).getGlobal();
  88
  89   auto CmpTarget = [&](unsigned Target) {
  90     if (Selector.isReg())
  91       MBB->addLiveIn(Selector.getReg());
  92     BuildMI(*MBB, MBBI, DL, TII->get(X86::LEA64r), X86::R11)
  93         .addReg(X86::RIP)
  94         .addImm(1)
  95         .addReg(0)
  96         .addGlobalAddress(CombinedGlobal,
  97                           JTInst->getOperand(2 + 2 * Target).getImm())
  98         .addReg(0);
  99     BuildMI(*MBB, MBBI, DL, TII->get(X86::CMP64rr))
 100         .add(Selector)
 101         .addReg(X86::R11);
 102   };
 103
 104   auto CreateMBB = [&]() {
 105     auto *NewMBB = MF->CreateMachineBasicBlock(BB);
 106     MBB->addSuccessor(NewMBB);
 107     if (!MBB->isLiveIn(X86::EFLAGS))
 108       MBB->addLiveIn(X86::EFLAGS);
 109     return NewMBB;
 110   };
 111
 112   auto EmitCondJump = [&](unsigned CC, MachineBasicBlock *ThenMBB) {
 113     BuildMI(*MBB, MBBI, DL, TII->get(X86::JCC_1)).addMBB(ThenMBB).addImm(CC);
 114
 115     auto *ElseMBB = CreateMBB();
 116     MF->insert(InsPt, ElseMBB);
 117     MBB = ElseMBB;
 118     MBBI = MBB->end();
 119   };
 120
 121   auto EmitCondJumpTarget = [&](unsigned CC, unsigned Target) {
 122     auto *ThenMBB = CreateMBB();
 123     TargetMBBs.push_back({ThenMBB, Target});
 124     EmitCondJump(CC, ThenMBB);
 125   };
 126
 127   auto EmitTailCall = [&](unsigned Target) {
 128     BuildMI(*MBB, MBBI, DL, TII->get(X86::TAILJMPd64))
 129         .add(JTInst->getOperand(3 + 2 * Target));
 130   };
 131
 132   std::function<void(unsigned, unsigned)> EmitBranchFunnel =
 133       [&](unsigned FirstTarget, unsigned NumTargets) {
 134     if (NumTargets == 1) {
 135       EmitTailCall(FirstTarget);
 136       return;
 137     }
 138
 139     if (NumTargets == 2) {
 140       CmpTarget(FirstTarget + 1);
 141       EmitCondJumpTarget(X86::COND_B, FirstTarget);
 142       EmitTailCall(FirstTarget + 1);
 143       return;
 144     }
 145
 146     if (NumTargets < 6) {
 147       CmpTarget(FirstTarget + 1);
 148       EmitCondJumpTarget(X86::COND_B, FirstTarget);
 149       EmitCondJumpTarget(X86::COND_E, FirstTarget + 1);
 150       EmitBranchFunnel(FirstTarget + 2, NumTargets - 2);
 151       return;
 152     }
 153
 154     auto *ThenMBB = CreateMBB();
 155     CmpTarget(FirstTarget + (NumTargets / 2));
 156     EmitCondJump(X86::COND_B, ThenMBB);
 157     EmitCondJumpTarget(X86::COND_E, FirstTarget + (NumTargets / 2));
 158     EmitBranchFunnel(FirstTarget + (NumTargets / 2) + 1,
 159                   NumTargets - (NumTargets / 2) - 1);
 160
 161     MF->insert(InsPt, ThenMBB);
 162     MBB = ThenMBB;
 163     MBBI = MBB->end();
 164     EmitBranchFunnel(FirstTarget, NumTargets / 2);
 165   };
 166
 167   EmitBranchFunnel(0, (JTInst->getNumOperands() - 2) / 2);
 168   for (auto P : TargetMBBs) {
 169     MF->insert(InsPt, P.first);
 170     BuildMI(P.first, DL, TII->get(X86::TAILJMPd64))
 171         .add(JTInst->getOperand(3 + 2 * P.second));
 172   }
 173   JTMBB->erase(JTInst);
 174 }
 175
 176 /// If \p MBBI is a pseudo instruction, this method expands
 177 /// it to the corresponding (sequence of) actual instruction(s).
 178 /// \returns true if \p MBBI has been expanded.
 179 bool X86ExpandPseudo::ExpandMI(MachineBasicBlock &MBB,
 180                                MachineBasicBlock::iterator MBBI) {
 181   MachineInstr &MI = *MBBI;
 182   unsigned Opcode = MI.getOpcode();
 183   DebugLoc DL = MBBI->getDebugLoc();
 184   switch (Opcode) {
 185   default:
 186     return false;
 187   case X86::TCRETURNdi:
 188   case X86::TCRETURNdicc:
 189   case X86::TCRETURNri:
 190   case X86::TCRETURNmi:
 191   case X86::TCRETURNdi64:
 192   case X86::TCRETURNdi64cc:
 193   case X86::TCRETURNri64:
 194   case X86::TCRETURNmi64: {
 195     bool isMem = Opcode == X86::TCRETURNmi || Opcode == X86::TCRETURNmi64;
 196     MachineOperand &JumpTarget = MBBI->getOperand(0);
 197     MachineOperand &StackAdjust = MBBI->getOperand(isMem ? X86::AddrNumOperands
 198                                                          : 1);
 199     assert(StackAdjust.isImm() && "Expecting immediate value.");
 200
 201     // Adjust stack pointer.
 202     int StackAdj = StackAdjust.getImm();
 203     int MaxTCDelta = X86FI->getTCReturnAddrDelta();
 204     int Offset = 0;
 205     assert(MaxTCDelta <= 0 && "MaxTCDelta should never be positive");
 206
 207     // Incoporate the retaddr area.
 208     Offset = StackAdj - MaxTCDelta;
 209     assert(Offset >= 0 && "Offset should never be negative");
 210
 211     if (Opcode == X86::TCRETURNdicc || Opcode == X86::TCRETURNdi64cc) {
 212       assert(Offset == 0 && "Conditional tail call cannot adjust the stack.");
 213     }
 214
 215     if (Offset) {
 216       // Check for possible merge with preceding ADD instruction.
 217       Offset += X86FL->mergeSPUpdates(MBB, MBBI, true);
 218       X86FL->emitSPUpdate(MBB, MBBI, DL, Offset, /*InEpilogue=*/true);
 219     }
 220
 221     // Jump to label or value in register.
 222     bool IsWin64 = STI->isTargetWin64();
 223     if (Opcode == X86::TCRETURNdi || Opcode == X86::TCRETURNdicc ||
 224         Opcode == X86::TCRETURNdi64 || Opcode == X86::TCRETURNdi64cc) {
 225       unsigned Op;
 226       switch (Opcode) {
 227       case X86::TCRETURNdi:
 228         Op = X86::TAILJMPd;
 229         break;
 230       case X86::TCRETURNdicc:
 231         Op = X86::TAILJMPd_CC;
 232         break;
 233       case X86::TCRETURNdi64cc:
 234         assert(!MBB.getParent()->hasWinCFI() &&
 235                "Conditional tail calls confuse "
 236                "the Win64 unwinder.");
 237         Op = X86::TAILJMPd64_CC;
 238         break;
 239       default:
 240         // Note: Win64 uses REX prefixes indirect jumps out of functions, but
 241         // not direct ones.
 242         Op = X86::TAILJMPd64;
 243         break;
 244       }
 245       MachineInstrBuilder MIB = BuildMI(MBB, MBBI, DL, TII->get(Op));
 246       if (JumpTarget.isGlobal()) {
 247         MIB.addGlobalAddress(JumpTarget.getGlobal(), JumpTarget.getOffset(),
 248                              JumpTarget.getTargetFlags());
 249       } else {
 250         assert(JumpTarget.isSymbol());
 251         MIB.addExternalSymbol(JumpTarget.getSymbolName(),
 252                               JumpTarget.getTargetFlags());
 253       }
 254       if (Op == X86::TAILJMPd_CC || Op == X86::TAILJMPd64_CC) {
 255         MIB.addImm(MBBI->getOperand(2).getImm());
 256       }
 257
 258     } else if (Opcode == X86::TCRETURNmi || Opcode == X86::TCRETURNmi64) {
 259       unsigned Op = (Opcode == X86::TCRETURNmi)
 260                         ? X86::TAILJMPm
 261                         : (IsWin64 ? X86::TAILJMPm64_REX : X86::TAILJMPm64);
 262       MachineInstrBuilder MIB = BuildMI(MBB, MBBI, DL, TII->get(Op));
 263       for (unsigned i = 0; i != X86::AddrNumOperands; ++i)
 264         MIB.add(MBBI->getOperand(i));
 265     } else if (Opcode == X86::TCRETURNri64) {
 266       JumpTarget.setIsKill();
 267       BuildMI(MBB, MBBI, DL,
 268               TII->get(IsWin64 ? X86::TAILJMPr64_REX : X86::TAILJMPr64))
 269           .add(JumpTarget);
 270     } else {
 271       JumpTarget.setIsKill();
 272       BuildMI(MBB, MBBI, DL, TII->get(X86::TAILJMPr))
 273           .add(JumpTarget);
 274     }
 275
 276     MachineInstr &NewMI = *std::prev(MBBI);
 277     NewMI.copyImplicitOps(*MBBI->getParent()->getParent(), *MBBI);
 278     MBB.getParent()->moveCallSiteInfo(&*MBBI, &NewMI);
 279
 280     // Delete the pseudo instruction TCRETURN.
 281     MBB.erase(MBBI);
 282
 283     return true;
 284   }
 285   case X86::EH_RETURN:
 286   case X86::EH_RETURN64: {
 287     MachineOperand &DestAddr = MBBI->getOperand(0);
 288     assert(DestAddr.isReg() && "Offset should be in register!");
 289     const bool Uses64BitFramePtr =
 290         STI->isTarget64BitLP64() || STI->isTargetNaCl64();
 291     Register StackPtr = TRI->getStackRegister();
 292     BuildMI(MBB, MBBI, DL,
 293             TII->get(Uses64BitFramePtr ? X86::MOV64rr : X86::MOV32rr), StackPtr)
 294         .addReg(DestAddr.getReg());
 295     // The EH_RETURN pseudo is really removed during the MC Lowering.
 296     return true;
 297   }
 298   case X86::IRET: {
 299     // Adjust stack to erase error code
 300     int64_t StackAdj = MBBI->getOperand(0).getImm();
 301     X86FL->emitSPUpdate(MBB, MBBI, DL, StackAdj, true);
 302     // Replace pseudo with machine iret
 303     BuildMI(MBB, MBBI, DL,
 304             TII->get(STI->is64Bit() ? X86::IRET64 : X86::IRET32));
 305     MBB.erase(MBBI);
 306     return true;
 307   }
 308   case X86::RET: {
 309     // Adjust stack to erase error code
 310     int64_t StackAdj = MBBI->getOperand(0).getImm();
 311     MachineInstrBuilder MIB;
 312     if (StackAdj == 0) {
 313       MIB = BuildMI(MBB, MBBI, DL,
 314                     TII->get(STI->is64Bit() ? X86::RETQ : X86::RETL));
 315     } else if (isUInt<16>(StackAdj)) {
 316       MIB = BuildMI(MBB, MBBI, DL,
 317                     TII->get(STI->is64Bit() ? X86::RETIQ : X86::RETIL))
 318                 .addImm(StackAdj);
 319     } else {
 320       assert(!STI->is64Bit() &&
 321              "shouldn't need to do this for x86_64 targets!");
 322       // A ret can only handle immediates as big as 2**16-1.  If we need to pop
 323       // off bytes before the return address, we must do it manually.
 324       BuildMI(MBB, MBBI, DL, TII->get(X86::POP32r)).addReg(X86::ECX, RegState::Define);
 325       X86FL->emitSPUpdate(MBB, MBBI, DL, StackAdj, /*InEpilogue=*/true);
 326       BuildMI(MBB, MBBI, DL, TII->get(X86::PUSH32r)).addReg(X86::ECX);
 327       MIB = BuildMI(MBB, MBBI, DL, TII->get(X86::RETL));
 328     }
 329     for (unsigned I = 1, E = MBBI->getNumOperands(); I != E; ++I)
 330       MIB.add(MBBI->getOperand(I));
 331     MBB.erase(MBBI);
 332     return true;
 333   }
 334   case X86::EH_RESTORE: {
 335     // Restore ESP and EBP, and optionally ESI if required.
 336     bool IsSEH = isAsynchronousEHPersonality(classifyEHPersonality(
 337         MBB.getParent()->getFunction().getPersonalityFn()));
 338     X86FL->restoreWin32EHStackPointers(MBB, MBBI, DL, /*RestoreSP=*/IsSEH);
 339     MBBI->eraseFromParent();
 340     return true;
 341   }
 342   case X86::LCMPXCHG8B_SAVE_EBX:
 343   case X86::LCMPXCHG16B_SAVE_RBX: {
 344     // Perform the following transformation.
 345     // SaveRbx = pseudocmpxchg Addr, <4 opds for the address>, InArg, SaveRbx
 346     // =>
 347     // [E|R]BX = InArg
 348     // actualcmpxchg Addr
 349     // [E|R]BX = SaveRbx
 350     const MachineOperand &InArg = MBBI->getOperand(6);
 351     Register SaveRbx = MBBI->getOperand(7).getReg();
 352
 353     unsigned ActualInArg =
 354         Opcode == X86::LCMPXCHG8B_SAVE_EBX ? X86::EBX : X86::RBX;
 355     // Copy the input argument of the pseudo into the argument of the
 356     // actual instruction.
 357     TII->copyPhysReg(MBB, MBBI, DL, ActualInArg, InArg.getReg(),
 358                      InArg.isKill());
 359     // Create the actual instruction.
 360     unsigned ActualOpc =
 361         Opcode == X86::LCMPXCHG8B_SAVE_EBX ? X86::LCMPXCHG8B : X86::LCMPXCHG16B;
 362     MachineInstr *NewInstr = BuildMI(MBB, MBBI, DL, TII->get(ActualOpc));
 363     // Copy the operands related to the address.
 364     for (unsigned Idx = 1; Idx < 6; ++Idx)
 365       NewInstr->addOperand(MBBI->getOperand(Idx));
 366     // Finally, restore the value of RBX.
 367     TII->copyPhysReg(MBB, MBBI, DL, ActualInArg, SaveRbx,
 368                      /*SrcIsKill*/ true);
 369
 370     // Delete the pseudo.
 371     MBBI->eraseFromParent();
 372     return true;
 373   }
 374   case TargetOpcode::ICALL_BRANCH_FUNNEL:
 375     ExpandICallBranchFunnel(&MBB, MBBI);
 376     return true;
 377   }
 378   llvm_unreachable("Previous switch has a fallthrough?");
 379 }
 380
 381 /// Expand all pseudo instructions contained in \p MBB.
 382 /// \returns true if any expansion occurred for \p MBB.
 383 bool X86ExpandPseudo::ExpandMBB(MachineBasicBlock &MBB) {
 384   bool Modified = false;
 385
 386   // MBBI may be invalidated by the expansion.
 387   MachineBasicBlock::iterator MBBI = MBB.begin(), E = MBB.end();
 388   while (MBBI != E) {
 389     MachineBasicBlock::iterator NMBBI = std::next(MBBI);
 390     Modified |= ExpandMI(MBB, MBBI);
 391     MBBI = NMBBI;
 392   }
 393
 394   return Modified;
 395 }
 396
 397 bool X86ExpandPseudo::runOnMachineFunction(MachineFunction &MF) {
 398   STI = &static_cast<const X86Subtarget &>(MF.getSubtarget());
 399   TII = STI->getInstrInfo();
 400   TRI = STI->getRegisterInfo();
 401   X86FI = MF.getInfo<X86MachineFunctionInfo>();
 402   X86FL = STI->getFrameLowering();
 403
 404   bool Modified = false;
 405   for (MachineBasicBlock &MBB : MF)
 406     Modified |= ExpandMBB(MBB);
 407   return Modified;
 408 }
 409
 410 /// Returns an instance of the pseudo instruction expansion pass.
 411 FunctionPass *llvm::createX86ExpandPseudoPass() {
 412   return new X86ExpandPseudo();
 413 }