//===-- ResetMachineFunctionPass.cpp - Reset Machine Function ----*- C++ -*-==//
//
// 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 that will conditionally reset a machine
/// function as if it was just created. This is used to provide a fallback
/// mechanism when GlobalISel fails, thus the condition for the reset to
/// happen is that the MachineFunction has the FailedISel property.
//===----------------------------------------------------------------------===//

#include "llvm/CodeGen/ResetMachineFunctionPass.h"
#include "llvm/ADT/ScopeExit.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/StackProtector.h"
#include "llvm/IR/DiagnosticInfo.h"
#include "llvm/InitializePasses.h"
#include "llvm/Support/Debug.h"
#include "llvm/Target/TargetMachine.h"
using namespace llvm;

#define DEBUG_TYPE "reset-machine-function"

STATISTIC(NumFunctionsReset, "Number of functions reset");
STATISTIC(NumFunctionsVisited, "Number of functions visited");

static bool runImpl(MachineFunction &MF, bool EmitFallbackDiag,
                    bool AbortOnFailedISel) {
  ++NumFunctionsVisited;
  // No matter what happened, whether we successfully selected the function
  // or not, nothing is going to use the vreg types after us. Make sure they
  // disappear.
  llvm::scope_exit ClearVRegTypesOnReturn(
      [&MF]() { MF.getRegInfo().clearVirtRegTypes(); });

  if (!MF.getProperties().hasFailedISel())
    return false;

  if (AbortOnFailedISel)
    report_fatal_error("Instruction selection failed");

  LLVM_DEBUG(dbgs() << "Resetting: " << MF.getName() << '\n');
  ++NumFunctionsReset;

  if (MF.empty()) {
    // Nothing was materialized in the MachineFunction, so avoid the cost of
    // tearing down and rebuilding all of the per-function state. Just clear
    // the FailedISel bit so the SelectionDAG pipeline can proceed.
    auto &Props = MF.getProperties();
    Props.resetToInitial();
  } else {
    MF.reset();
    MF.initTargetMachineFunctionInfo(MF.getSubtarget());

    const TargetMachine &TM = MF.getTarget();
    // MRI callback for target specific initializations.
    TM.registerMachineRegisterInfoCallback(MF);
  }

  if (EmitFallbackDiag) {
    const Function &F = MF.getFunction();
    DiagnosticInfoISelFallback DiagFallback(F);
    F.getContext().diagnose(DiagFallback);
  }
  return true;
}

namespace {
class ResetMachineFunctionLegacy : public MachineFunctionPass {
  /// Tells whether or not this pass should emit a fallback
  /// diagnostic when it resets a function.
  bool EmitFallbackDiag;
  /// Whether we should abort immediately instead of resetting the function.
  bool AbortOnFailedISel;

public:
  static char ID; // Pass identification, replacement for typeid
  ResetMachineFunctionLegacy(bool EmitFallbackDiag = false,
                             bool AbortOnFailedISel = false)
      : MachineFunctionPass(ID), EmitFallbackDiag(EmitFallbackDiag),
        AbortOnFailedISel(AbortOnFailedISel) {}

  StringRef getPassName() const override { return "ResetMachineFunction"; }

  void getAnalysisUsage(AnalysisUsage &AU) const override {
    AU.addPreserved<StackProtector>();
    MachineFunctionPass::getAnalysisUsage(AU);
  }

  bool runOnMachineFunction(MachineFunction &MF) override {
    return runImpl(MF, EmitFallbackDiag, AbortOnFailedISel);
  }
};
} // end anonymous namespace

char ResetMachineFunctionLegacy::ID = 0;
INITIALIZE_PASS(ResetMachineFunctionLegacy, DEBUG_TYPE,
                "Reset machine function if ISel failed", false, false)

MachineFunctionPass *
llvm::createResetMachineFunctionLegacyPass(bool EmitFallbackDiag = false,
                                           bool AbortOnFailedISel = false) {
  return new ResetMachineFunctionLegacy(EmitFallbackDiag, AbortOnFailedISel);
}

PreservedAnalyses
ResetMachineFunctionPass::run(MachineFunction &MF,
                              MachineFunctionAnalysisManager &) {
  if (runImpl(MF, EmitFallbackDiag, AbortOnFailedISel))
    return getMachineFunctionPassPreservedAnalyses();
  return PreservedAnalyses::all();
}