//===-- X86LowerTileCopy.cpp - Expand Tile Copy Instructions---------------===//
//
// 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 file defines the pass which lower AMX tile copy instructions. Since
// there is no tile copy instruction, we need store tile register to stack
// and load from stack to another tile register. We need extra GR to hold
// the stride, and we need stack slot to hold the tile data register.
// We would run this pass after copy propagation, so that we don't miss copy
// optimization. And we would run this pass before prolog/epilog insertion,
// so that we can allocate stack slot.
//
//===----------------------------------------------------------------------===//

#include "X86.h"
#include "X86InstrBuilder.h"
#include "X86InstrInfo.h"
#include "X86Subtarget.h"
#include "llvm/CodeGen/LiveRegUnits.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/InitializePasses.h"
#include "llvm/Support/Debug.h"

using namespace llvm;

#define DEBUG_TYPE "x86-lower-tile-copy"

namespace {

class X86LowerTileCopy : public MachineFunctionPass {
public:
  static char ID;

  X86LowerTileCopy() : MachineFunctionPass(ID) {}

  void getAnalysisUsage(AnalysisUsage &AU) const override;

  bool runOnMachineFunction(MachineFunction &MF) override;

  StringRef getPassName() const override { return "X86 Lower Tile Copy"; }
};

} // namespace

char X86LowerTileCopy::ID = 0;

INITIALIZE_PASS_BEGIN(X86LowerTileCopy, "lowertilecopy", "Tile Copy Lowering",
                      false, false)
INITIALIZE_PASS_END(X86LowerTileCopy, "lowertilecopy", "Tile Copy Lowering",
                    false, false)

void X86LowerTileCopy::getAnalysisUsage(AnalysisUsage &AU) const {
  AU.setPreservesAll();
  MachineFunctionPass::getAnalysisUsage(AU);
}

FunctionPass *llvm::createX86LowerTileCopyPass() {
  return new X86LowerTileCopy();
}

bool X86LowerTileCopy::runOnMachineFunction(MachineFunction &MF) {
  const X86Subtarget &ST = MF.getSubtarget<X86Subtarget>();
  const X86InstrInfo *TII = ST.getInstrInfo();
  const TargetRegisterInfo *TRI = ST.getRegisterInfo();
  BitVector GR64Regs =
      TRI->getAllocatableSet(MF, TRI->getRegClass(X86::GR64RegClassID));
  BitVector TILERegs =
      TRI->getAllocatableSet(MF, TRI->getRegClass(X86::TILERegClassID));
  bool Changed = false;

  for (MachineBasicBlock &MBB : MF) {
    // There won't be a tile copy if no tile register live in.
    bool HasTileCopy = false;
    for (const auto &LI : MBB.liveins()) {
      if (TILERegs.test(LI.PhysReg)) {
        HasTileCopy = true;
        break;
      }
    }
    if (!HasTileCopy)
      continue;
    LiveRegUnits UsedRegs(*TRI);
    UsedRegs.addLiveOuts(MBB);
    for (MachineInstr &MI : llvm::make_early_inc_range(reverse(MBB))) {
      UsedRegs.stepBackward(MI);
      if (!MI.isCopy())
        continue;
      MachineOperand &DstMO = MI.getOperand(0);
      MachineOperand &SrcMO = MI.getOperand(1);
      Register SrcReg = SrcMO.getReg();
      Register DstReg = DstMO.getReg();
      if (!X86::TILERegClass.contains(DstReg, SrcReg))
        continue;

      // Allocate stack slot for tile register
      unsigned Size = TRI->getSpillSize(X86::TILERegClass);
      Align Alignment = TRI->getSpillAlign(X86::TILERegClass);
      int TileSS = MF.getFrameInfo().CreateSpillStackObject(Size, Alignment);

      int StrideSS = 0;

      // Pick a killed register to avoid a save/reload.
      Register GR64Cand = X86::NoRegister;
      for (auto RegT : GR64Regs.set_bits()) {
        if (UsedRegs.available(RegT)) {
          GR64Cand = RegT;
          break;
        }
      }

      const DebugLoc &DL = MI.getDebugLoc();
      if (GR64Cand) {
        // mov 64 %reg
        BuildMI(MBB, MI, DL, TII->get(X86::MOV64ri), GR64Cand).addImm(64);
      } else {
        // No available register? Save RAX and reload it after use.

        // Allocate stack slot for stride register
        Size = TRI->getSpillSize(X86::GR64RegClass);
        Alignment = TRI->getSpillAlign(X86::GR64RegClass);
        StrideSS = MF.getFrameInfo().CreateSpillStackObject(Size, Alignment);

        // mov %reg (%sp)
        addFrameReference(BuildMI(MBB, MI, DL, TII->get(X86::MOV64mr)),
                          StrideSS)
            .addReg(X86::RAX);
        // mov 64 %reg
        BuildMI(MBB, MI, DL, TII->get(X86::MOV64ri), X86::RAX).addImm(64);
      }
      // tilestored %tmm, (%sp, %idx)
#define GET_EGPR_IF_ENABLED(OPC) (ST.hasEGPR() ? OPC##_EVEX : OPC)
      unsigned Opc = GET_EGPR_IF_ENABLED(X86::TILESTORED);
      MachineInstr *NewMI =
          addFrameReference(BuildMI(MBB, MI, DL, TII->get(Opc)), TileSS)
              .addReg(SrcReg, getKillRegState(SrcMO.isKill()));
      MachineOperand &MO = NewMI->getOperand(2);
      MO.setReg(GR64Cand ? GR64Cand : X86::RAX);
      MO.setIsKill(true);
      // tileloadd (%sp, %idx), %tmm
      Opc = GET_EGPR_IF_ENABLED(X86::TILELOADD);
#undef GET_EGPR_IF_ENABLED
      NewMI = addFrameReference(BuildMI(MBB, MI, DL, TII->get(Opc), DstReg),
                                TileSS);
      if (!GR64Cand) {
        // restore %rax
        // mov (%sp) %rax
        addFrameReference(
            BuildMI(MBB, MI, DL, TII->get(X86::MOV64rm), X86::RAX), StrideSS);
      }
      MI.eraseFromParent();
      Changed = true;
    }
  }
  return Changed;
}