//===- MetaRenamer.cpp - Rename everything with metasyntatic names --------===//
//
// 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 pass renames everything with metasyntatic names. The intent is to use
// this pass after bugpoint reduction to conceal the nature of the original
// program.
//
//===----------------------------------------------------------------------===//

#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/Twine.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/IR/Argument.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GlobalAlias.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/TypeFinder.h"
#include "llvm/Pass.h"
#include "llvm/Transforms/Utils.h"

using namespace llvm;

static const char *const metaNames[] = {
  // See http://en.wikipedia.org/wiki/Metasyntactic_variable
  "foo", "bar", "baz", "quux", "barney", "snork", "zot", "blam", "hoge",
  "wibble", "wobble", "widget", "wombat", "ham", "eggs", "pluto", "spam"
};

namespace {

  // This PRNG is from the ISO C spec. It is intentionally simple and
  // unsuitable for cryptographic use. We're just looking for enough
  // variety to surprise and delight users.
  struct PRNG {
    unsigned long next;

    void srand(unsigned int seed) {
      next = seed;
    }

    int rand() {
      next = next * 1103515245 + 12345;
      return (unsigned int)(next / 65536) % 32768;
    }
  };

  struct Renamer {
    Renamer(unsigned int seed) {
      prng.srand(seed);
    }

    const char *newName() {
      return metaNames[prng.rand() % array_lengthof(metaNames)];
    }

    PRNG prng;
  };

  struct MetaRenamer : public ModulePass {
    // Pass identification, replacement for typeid
    static char ID;

    MetaRenamer() : ModulePass(ID) {
      initializeMetaRenamerPass(*PassRegistry::getPassRegistry());
    }

    void getAnalysisUsage(AnalysisUsage &AU) const override {
      AU.addRequired<TargetLibraryInfoWrapperPass>();
      AU.setPreservesAll();
    }

    bool runOnModule(Module &M) override {
      // Seed our PRNG with simple additive sum of ModuleID. We're looking to
      // simply avoid always having the same function names, and we need to
      // remain deterministic.
      unsigned int randSeed = 0;
      for (auto C : M.getModuleIdentifier())
        randSeed += C;

      Renamer renamer(randSeed);

      // Rename all aliases
      for (auto AI = M.alias_begin(), AE = M.alias_end(); AI != AE; ++AI) {
        StringRef Name = AI->getName();
        if (Name.startswith("llvm.") || (!Name.empty() && Name[0] == 1))
          continue;

        AI->setName("alias");
      }

      // Rename all global variables
      for (auto GI = M.global_begin(), GE = M.global_end(); GI != GE; ++GI) {
        StringRef Name = GI->getName();
        if (Name.startswith("llvm.") || (!Name.empty() && Name[0] == 1))
          continue;

        GI->setName("global");
      }

      // Rename all struct types
      TypeFinder StructTypes;
      StructTypes.run(M, true);
      for (StructType *STy : StructTypes) {
        if (STy->isLiteral() || STy->getName().empty()) continue;

        SmallString<128> NameStorage;
        STy->setName((Twine("struct.") +
          renamer.newName()).toStringRef(NameStorage));
      }

      // Rename all functions
      const TargetLibraryInfo &TLI =
          getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
      for (auto &F : M) {
        StringRef Name = F.getName();
        LibFunc Tmp;
        // Leave library functions alone because their presence or absence could
        // affect the behavior of other passes.
        if (Name.startswith("llvm.") || (!Name.empty() && Name[0] == 1) ||
            TLI.getLibFunc(F, Tmp))
          continue;

        // Leave @main alone. The output of -metarenamer might be passed to
        // lli for execution and the latter needs a main entry point.
        if (Name != "main")
          F.setName(renamer.newName());

        runOnFunction(F);
      }
      return true;
    }

    bool runOnFunction(Function &F) {
      for (auto AI = F.arg_begin(), AE = F.arg_end(); AI != AE; ++AI)
        if (!AI->getType()->isVoidTy())
          AI->setName("arg");

      for (auto &BB : F) {
        BB.setName("bb");

        for (auto &I : BB)
          if (!I.getType()->isVoidTy())
            I.setName("tmp");
      }
      return true;
    }
  };

} // end anonymous namespace

char MetaRenamer::ID = 0;

INITIALIZE_PASS_BEGIN(MetaRenamer, "metarenamer",
                      "Assign new names to everything", false, false)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
INITIALIZE_PASS_END(MetaRenamer, "metarenamer",
                    "Assign new names to everything", false, false)

//===----------------------------------------------------------------------===//
//
// MetaRenamer - Rename everything with metasyntactic names.
//
ModulePass *llvm::createMetaRenamerPass() {
  return new MetaRenamer();
}