HexagonPeephole.cpp

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//===-- HexagonPeephole.cpp - Hexagon Peephole Optimizations --------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
// This peephole pass optimizes in the following cases.
// 1. Optimizes redundant sign extends for the following case
//    Transform the following pattern
//    %170 = SXTW %166
//    ...
//    %176 = COPY %170:isub_lo
//
//    Into
//    %176 = COPY %166
//
//  2. Optimizes redundant negation of predicates.
//     %15 = CMPGTrr %6, %2
//     ...
//     %16 = NOT_p killed %15
//     ...
//     JMP_c killed %16, <%bb.1>, implicit dead %pc
//
//     Into
//     %15 = CMPGTrr %6, %2;
//     ...
//     JMP_cNot killed %15, <%bb.1>, implicit dead %pc;
//
// 3. Fuse the A2_vminub/C2_cmpgtup intrinsic pair, which share inputs, into the
//    dual-output A6_vminub_RdP hardware instruction.
//    %1 = A2_vminub %a, %b
//    %2 = C2_cmpgtup %a, %b
// turning it into
//    %3, %4 = A6_vminub_RdP %a, %b
// (Hexagon has no multi-output intrinsics, so the two results are produced by
// separate intrinsics that this pass recombines.)
//
// Note: The first two transformations make instructions like
// %170 = SXTW %166 or %16 = NOT_p killed %15
// redundant. A dead-instruction removal pass, such as DCE or DIE, eliminates
// them.
 
//===----------------------------------------------------------------------===//
 
#include "Hexagon.h"
#include "HexagonTargetMachine.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Target/TargetMachine.h"
 
using namespace llvm;
 
#define DEBUG_TYPE "hexagon-peephole"
 
static cl::opt<bool>
    DisableHexagonPeephole("disable-hexagon-peephole", cl::Hidden,
                           cl::desc("Disable Peephole Optimization"));
 
static cl::opt<bool> DisablePNotP("disable-hexagon-pnotp", cl::Hidden,
                                  cl::desc("Disable Optimization of PNotP"));
 
static cl::opt<bool>
    DisableOptSZExt("disable-hexagon-optszext", cl::Hidden, cl::init(true),
                    cl::desc("Disable Optimization of Sign/Zero Extends"));
 
static cl::opt<bool>
    DisableOptExtTo64("disable-hexagon-opt-ext-to-64", cl::Hidden,
                      cl::init(true),
                      cl::desc("Disable Optimization of extensions to i64."));
 
static cl::opt<bool>
    FuseIntrinsicVMinUB("hexagon-fuse-intrinsic-vminub", cl::Hidden,
                        cl::init(true),
                        cl::desc("Fuse A2_vminub/C2_cmpgtup into "
                                 "A6_vminub_RdP."));
 
namespace {
  struct HexagonPeephole : public MachineFunctionPass {
    const HexagonInstrInfo *QII;
    MachineRegisterInfo *MRI;
 
  public:
    static char ID;
    HexagonPeephole() : MachineFunctionPass(ID) {}
 
    bool runOnMachineFunction(MachineFunction &MF) override;
    bool fuseIntrinsicVMinUB(MachineFunction &MF);
 
    StringRef getPassName() const override {
      return "Hexagon optimize redundant zero and size extends";
    }
 
    void getAnalysisUsage(AnalysisUsage &AU) const override {
      MachineFunctionPass::getAnalysisUsage(AU);
    }
  };
}
 
char HexagonPeephole::ID = 0;
 
INITIALIZE_PASS(HexagonPeephole, "hexagon-peephole", "Hexagon Peephole",
                false, false)
 
bool HexagonPeephole::runOnMachineFunction(MachineFunction &MF) {
  if (skipFunction(MF.getFunction()))
    return false;
 
  bool Changed = false;
 
  QII = static_cast<const HexagonInstrInfo *>(MF.getSubtarget().getInstrInfo());
  MRI = &MF.getRegInfo();
 
  DenseMap<unsigned, unsigned> PeepholeMap;
  DenseMap<unsigned, std::pair<unsigned, unsigned> > PeepholeDoubleRegsMap;
 
  if (DisableHexagonPeephole) return false;
 
  // Loop over all of the basic blocks.
  for (MachineBasicBlock &MBB : MF) {
    PeepholeMap.clear();
    PeepholeDoubleRegsMap.clear();
 
    // Traverse the basic block.
    for (MachineInstr &MI : llvm::make_early_inc_range(MBB)) {
      // Look for sign extends:
      // %170 = SXTW %166
      if (!DisableOptSZExt && MI.getOpcode() == Hexagon::A2_sxtw) {
        assert(MI.getNumOperands() == 2);
        MachineOperand &Dst = MI.getOperand(0);
        MachineOperand &Src = MI.getOperand(1);
        Register DstReg = Dst.getReg();
        Register SrcReg = Src.getReg();
        // Just handle virtual registers.
        if (DstReg.isVirtual() && SrcReg.isVirtual()) {
          // Map the following:
          // %170 = SXTW %166
          // PeepholeMap[170] = %166
          PeepholeMap[DstReg] = SrcReg;
        }
      }
 
      // Look for  %170 = COMBINE_ir_V4 (0, %169)
      // %170:DoublRegs, %169:IntRegs
      if (!DisableOptExtTo64 && MI.getOpcode() == Hexagon::A4_combineir) {
        assert(MI.getNumOperands() == 3);
        MachineOperand &Dst = MI.getOperand(0);
        MachineOperand &Src1 = MI.getOperand(1);
        MachineOperand &Src2 = MI.getOperand(2);
        if (Src1.getImm() != 0)
          continue;
        Register DstReg = Dst.getReg();
        Register SrcReg = Src2.getReg();
        PeepholeMap[DstReg] = SrcReg;
      }
 
      // Look for this sequence below
      // %DoubleReg1 = LSRd_ri %DoubleReg0, 32
      // %IntReg = COPY %DoubleReg1:isub_lo.
      // and convert into
      // %IntReg = COPY %DoubleReg0:isub_hi.
      if (MI.getOpcode() == Hexagon::S2_lsr_i_p) {
        assert(MI.getNumOperands() == 3);
        MachineOperand &Dst = MI.getOperand(0);
        MachineOperand &Src1 = MI.getOperand(1);
        MachineOperand &Src2 = MI.getOperand(2);
        if (Src2.getImm() != 32)
          continue;
        Register DstReg = Dst.getReg();
        Register SrcReg = Src1.getReg();
        PeepholeDoubleRegsMap[DstReg] =
          std::make_pair(*&SrcReg, Hexagon::isub_hi);
      }
 
      // Look for P=NOT(P).
      if (!DisablePNotP && MI.getOpcode() == Hexagon::C2_not) {
        assert(MI.getNumOperands() == 2);
        MachineOperand &Dst = MI.getOperand(0);
        MachineOperand &Src = MI.getOperand(1);
        Register DstReg = Dst.getReg();
        Register SrcReg = Src.getReg();
        // Just handle virtual registers.
        if (DstReg.isVirtual() && SrcReg.isVirtual()) {
          // Map the following:
          // %170 = NOT_xx %166
          // PeepholeMap[170] = %166
          PeepholeMap[DstReg] = SrcReg;
        }
      }
 
      // Look for copy:
      // %176 = COPY %170:isub_lo
      if (!DisableOptSZExt && MI.isCopy()) {
        assert(MI.getNumOperands() == 2);
        MachineOperand &Dst = MI.getOperand(0);
        MachineOperand &Src = MI.getOperand(1);
 
        // Make sure we are copying the lower 32 bits.
        if (Src.getSubReg() != Hexagon::isub_lo)
          continue;
 
        Register DstReg = Dst.getReg();
        Register SrcReg = Src.getReg();
        if (DstReg.isVirtual() && SrcReg.isVirtual()) {
          // Try to find in the map.
          if (unsigned PeepholeSrc = PeepholeMap.lookup(SrcReg)) {
            // Change the 1st operand.
            MI.removeOperand(1);
            MI.addOperand(MachineOperand::CreateReg(PeepholeSrc, false));
            Changed = true;
          } else  {
            DenseMap<unsigned, std::pair<unsigned, unsigned> >::iterator DI =
              PeepholeDoubleRegsMap.find(SrcReg);
            if (DI != PeepholeDoubleRegsMap.end()) {
              std::pair<unsigned,unsigned> PeepholeSrc = DI->second;
              MI.removeOperand(1);
              MI.addOperand(MachineOperand::CreateReg(
                  PeepholeSrc.first, false /*isDef*/, false /*isImp*/,
                  false /*isKill*/, false /*isDead*/, false /*isUndef*/,
                  false /*isEarlyClobber*/, PeepholeSrc.second));
              Changed = true;
            }
          }
        }
      }
 
      // Look for Predicated instructions.
      if (!DisablePNotP) {
        bool Done = false;
        if (QII->isPredicated(MI)) {
          MachineOperand &Op0 = MI.getOperand(0);
          Register Reg0 = Op0.getReg();
          const TargetRegisterClass *RC0 = MRI->getRegClass(Reg0);
          if (RC0->getID() == Hexagon::PredRegsRegClassID) {
            // Handle instructions that have a prediate register in op0
            // (most cases of predicable instructions).
            if (Reg0.isVirtual()) {
              // Try to find in the map.
              if (unsigned PeepholeSrc = PeepholeMap.lookup(Reg0)) {
                // Change the 1st operand and, flip the opcode.
                MI.getOperand(0).setReg(PeepholeSrc);
                MRI->clearKillFlags(PeepholeSrc);
                int NewOp = QII->getInvertedPredicatedOpcode(MI.getOpcode());
                MI.setDesc(QII->get(NewOp));
                Changed = true;
                Done = true;
              }
            }
          }
        }
 
        if (!Done) {
          // Handle special instructions.
          unsigned Op = MI.getOpcode();
          unsigned NewOp = 0;
          unsigned PR = 1, S1 = 2, S2 = 3;   // Operand indices.
 
          switch (Op) {
            case Hexagon::C2_mux:
            case Hexagon::C2_muxii:
              NewOp = Op;
              break;
            case Hexagon::C2_muxri:
              NewOp = Hexagon::C2_muxir;
              break;
            case Hexagon::C2_muxir:
              NewOp = Hexagon::C2_muxri;
              break;
          }
          if (NewOp) {
            Register PSrc = MI.getOperand(PR).getReg();
            if (unsigned POrig = PeepholeMap.lookup(PSrc)) {
              BuildMI(MBB, MI.getIterator(), MI.getDebugLoc(), QII->get(NewOp),
                      MI.getOperand(0).getReg())
                  .addReg(POrig)
                  .add(MI.getOperand(S2))
                  .add(MI.getOperand(S1));
              MRI->clearKillFlags(POrig);
              MI.eraseFromParent();
              Changed = true;
            }
          } // if (NewOp)
        } // if (!Done)
 
      } // if (!DisablePNotP)
 
    } // Instruction
  } // Basic Block
 
  if (FuseIntrinsicVMinUB)
    Changed |= fuseIntrinsicVMinUB(MF);
 
  return Changed;
}
 
// Return true if both instructions have identical input operands in order.
static bool hasCommonInputOps(const MachineInstr &I1, const MachineInstr &I2) {
  auto I1Uses = I1.explicit_uses();
  auto I2Uses = I2.explicit_uses();
  unsigned I1NumUses = I1.getNumExplicitOperands() - I1.getNumExplicitDefs();
  unsigned I2NumUses = I2.getNumExplicitOperands() - I2.getNumExplicitDefs();
  if (!I1NumUses || I1NumUses != I2NumUses)
    return false;
 
  auto I2Use = I2Uses.begin();
  for (const MachineOperand &I1Use : I1Uses)
    if (!I1Use.isIdenticalTo(*I2Use++))
      return false;
  return true;
}
 
static bool modifiesPhysicalInput(ArrayRef<Register> Inputs,
                                  const MachineInstr &Between,
                                  const TargetRegisterInfo *TRI) {
  for (Register Input : Inputs)
    if (Between.modifiesRegister(Input, TRI))
      return true;
  return false;
}
 
bool HexagonPeephole::fuseIntrinsicVMinUB(MachineFunction &MF) {
  bool Changed = false;
  const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
 
  for (MachineBasicBlock &MBB : MF) {
    SmallPtrSet<MachineInstr *, 8> DeadMIs;
 
    for (MachineInstr &MI : MBB) {
      unsigned Opc = MI.getOpcode();
      if ((Opc != Hexagon::A2_vminub && Opc != Hexagon::C2_cmpgtup) ||
          DeadMIs.count(&MI))
        continue;
 
      unsigned SiblingOpc =
          Opc == Hexagon::A2_vminub ? Hexagon::C2_cmpgtup : Hexagon::A2_vminub;
      SmallVector<Register, 2> PhysicalInputs;
      for (const MachineOperand &MO : MI.operands())
        if (MO.isReg() && !MO.isDef() && MO.getReg().isPhysical())
          PhysicalInputs.push_back(MO.getReg());
      MachineInstr *Sibling = nullptr;
      auto It = MI.getIterator();
      for (++It; It != MBB.end(); ++It) {
        if (!DeadMIs.count(&*It) && It->getOpcode() == SiblingOpc &&
            hasCommonInputOps(MI, *It)) {
          Sibling = &*It;
          break;
        }
        if (modifiesPhysicalInput(PhysicalInputs, *It, TRI))
          break;
      }
      if (!Sibling)
        continue;
 
      MachineInstr *VMin = Opc == Hexagon::A2_vminub ? &MI : Sibling;
      MachineInstr *Cmp = Opc == Hexagon::A2_vminub ? Sibling : &MI;
      Register VMinReg =
          MRI->createVirtualRegister(&Hexagon::DoubleRegsRegClass);
      Register CmpReg = MRI->createVirtualRegister(&Hexagon::PredRegsRegClass);
 
      BuildMI(MBB, MI.getIterator(), MI.getDebugLoc(),
              QII->get(Hexagon::A6_vminub_RdP), VMinReg)
          .addReg(CmpReg, RegState::Define)
          .add(VMin->getOperand(1))
          .add(VMin->getOperand(2));
 
      Register VMinDef = VMin->getOperand(0).getReg();
      Register CmpDef = Cmp->getOperand(0).getReg();
      assert(VMinDef.isVirtual() && CmpDef.isVirtual() &&
             "vminub fusion requires virtual result registers");
      MRI->replaceRegWith(VMinDef, VMinReg);
      VMin->getOperand(0).setReg(VMinDef);
      MRI->replaceRegWith(CmpDef, CmpReg);
      Cmp->getOperand(0).setReg(CmpDef);
 
      DeadMIs.insert(&MI);
      DeadMIs.insert(Sibling);
      Changed = true;
    }
 
    for (MachineInstr *MI : DeadMIs)
      MI->eraseFromParent();
  }
 
  return Changed;
}
 
FunctionPass *llvm::createHexagonPeephole() {
  return new HexagonPeephole();
}