//===- ReduceSpecialGlobals.cpp - Specialized Delta Pass ------------------===//
//
// 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 implements a function which calls the Generic Delta pass in order
// to reduce special globals, like @llvm.used, in the provided Module.
//
// For more details about special globals, see
// https://llvm.org/docs/LangRef.html#intrinsic-global-variables
//
//===----------------------------------------------------------------------===//

#include "ReduceSpecialGlobals.h"
#include "Delta.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/GlobalValue.h"

using namespace llvm;

static StringRef SpecialGlobalNames[] = {"llvm.used", "llvm.compiler.used"};

/// Removes all special globals aren't inside any of the
/// desired Chunks.
static void
extractSpecialGlobalsFromModule(const std::vector<Chunk> &ChunksToKeep,
                                Module *Program) {
  Oracle O(ChunksToKeep);

  for (StringRef Name : SpecialGlobalNames) {
    if (auto *Used = Program->getNamedGlobal(Name)) {
      Used->replaceAllUsesWith(UndefValue::get(Used->getType()));
      Used->eraseFromParent();
    }
  }
}

/// Counts the amount of special globals and prints their
/// respective name & index
static int countSpecialGlobals(Module *Program) {
  // TODO: Silence index with --quiet flag
  errs() << "----------------------------\n";
  errs() << "Special Globals Index Reference:\n";
  int Count = 0;
  for (StringRef Name : SpecialGlobalNames) {
    if (auto *Used = Program->getNamedGlobal(Name))
      errs() << "\t" << ++Count << ": " << Used->getName() << "\n";
  }
  errs() << "----------------------------\n";
  return Count;
}

void llvm::reduceSpecialGlobalsDeltaPass(TestRunner &Test) {
  errs() << "*** Reducing Special Globals ...\n";
  int Functions = countSpecialGlobals(Test.getProgram());
  runDeltaPass(Test, Functions, extractSpecialGlobalsFromModule);
  errs() << "----------------------------\n";
}