//===-- WebAssemblyRegNumbering.cpp - Register Numbering ------------------===//

//

// 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

//

//===----------------------------------------------------------------------===//

///

/// \file

/// This file implements a pass which assigns WebAssembly register

/// numbers for CodeGen virtual registers.

///

//===----------------------------------------------------------------------===//

#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"

#include "WebAssembly.h"

#include "WebAssemblyMachineFunctionInfo.h"

#include "WebAssemblySubtarget.h"

#include "WebAssemblyUtilities.h"

#include "llvm/ADT/SCCIterator.h"

#include "llvm/CodeGen/MachineFrameInfo.h"

#include "llvm/CodeGen/MachineFunction.h"

#include "llvm/CodeGen/MachineInstrBuilder.h"

#include "llvm/CodeGen/MachineLoopInfo.h"

#include "llvm/CodeGen/MachineRegisterInfo.h"

#include "llvm/CodeGen/Passes.h"

#include "llvm/Support/Debug.h"

#include "llvm/Support/raw_ostream.h"

using namespace llvm;

#define DEBUG_TYPE "wasm-reg-numbering"

namespace {

class WebAssemblyRegNumbering final : public MachineFunctionPass {

  StringRef getPassName() const override {

    return "WebAssembly Register Numbering";

  }

  void getAnalysisUsage(AnalysisUsage &AU) const override {

    AU.setPreservesCFG();

    MachineFunctionPass::getAnalysisUsage(AU);

  }

  bool runOnMachineFunction(MachineFunction &MF) override;

public:

  static char ID; // Pass identification, replacement for typeid

  WebAssemblyRegNumbering() : MachineFunctionPass(ID) {}

};

} // end anonymous namespace

char WebAssemblyRegNumbering::ID = 0;

INITIALIZE_PASS(WebAssemblyRegNumbering, DEBUG_TYPE,

                "Assigns WebAssembly register numbers for virtual registers",

                false, false)

FunctionPass *llvm::createWebAssemblyRegNumbering() {

  return new WebAssemblyRegNumbering();

}

bool WebAssemblyRegNumbering::runOnMachineFunction(MachineFunction &MF) {

  LLVM_DEBUG(dbgs() << "********** Register Numbering **********\n"

                       "********** Function: "

                    << MF.getName() << '\n');

  WebAssemblyFunctionInfo &MFI = *MF.getInfo<WebAssemblyFunctionInfo>();

  MachineRegisterInfo &MRI = MF.getRegInfo();

  MFI.initWARegs(MRI);

  // WebAssembly argument registers are in the same index space as local

  // variables. Assign the numbers for them first.

  MachineBasicBlock &EntryMBB = MF.front();

  for (MachineInstr &MI : EntryMBB) {

    if (!WebAssembly::isArgument(MI.getOpcode()))

      break;

    int64_t Imm = MI.getOperand(1).getImm();

    LLVM_DEBUG(dbgs() << "Arg VReg " << MI.getOperand(0).getReg()

                      << " -> WAReg " << Imm << "\n");

    MFI.setWAReg(MI.getOperand(0).getReg(), Imm);

  }

  // Then assign regular WebAssembly registers for all remaining used

  // virtual registers. TODO: Consider sorting the registers by frequency of

  // use, to maximize usage of small immediate fields.

  unsigned NumVRegs = MF.getRegInfo().getNumVirtRegs();

  unsigned NumStackRegs = 0;

  // Start the numbering for locals after the arg regs

  unsigned CurReg = MFI.getParams().size();

  for (unsigned VRegIdx = 0; VRegIdx < NumVRegs; ++VRegIdx) {

    Register VReg = Register::index2VirtReg(VRegIdx);

    // Skip unused registers.

    if (MRI.use_empty(VReg))

      continue;

    // Handle stackified registers.

    if (MFI.isVRegStackified(VReg)) {

      LLVM_DEBUG(dbgs() << "VReg " << VReg << " -> WAReg "

                        << (INT32_MIN | NumStackRegs) << "\n");

      MFI.setWAReg(VReg, INT32_MIN | NumStackRegs++);

      continue;

    }

    if (MFI.getWAReg(VReg) == WebAssembly::UnusedReg) {

      LLVM_DEBUG(dbgs() << "VReg " << VReg << " -> WAReg " << CurReg << "\n");

      MFI.setWAReg(VReg, CurReg++);

    }

  }

  return true;

}