revng-revng/lib/RemoveCpuLoopStore/RemoveCpuLoopStorePass.cpp

//
// Copyright rev.ng Srls. See LICENSE.md for details.
//

#include "llvm/ADT/SmallVector.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Module.h"

#include "revng/Model/LoadModelPass.h"
#include "revng/Support/FunctionTags.h"
#include "revng/Support/IRHelpers.h"

#include "revng-c/RemoveCpuLoopStore/RemoveCpuLoopStorePass.h"

using namespace llvm;

char RemoveCpuLoopStorePass::ID = 0;
using Reg = RegisterPass<RemoveCpuLoopStorePass>;
static Reg X("remove-cpu-loop-store", "Removes store to cpu_loop", true, true);

void RemoveCpuLoopStorePass::getAnalysisUsage(llvm::AnalysisUsage &AU) const {
  AU.addRequired<LoadModelWrapperPass>();
}

bool RemoveCpuLoopStorePass::runOnFunction(Function &F) {

  // Skip non-isolated functions
  auto FTags = FunctionTags::TagsSet::from(&F);
  if (not FTags.contains(FunctionTags::Lifted))
    return false;

  // Retrieve the global variable `cpu_loop_exiting`
  Module *M = F.getParent();
  GlobalVariable *CpuLoop = M->getGlobalVariable("cpu_loop_exiting");

  // Remove in bulk all the users of the global variable.
  SmallVector<LoadInst *, 8> Loads;
  SmallVector<StoreInst *, 8> Stores;
  for (User *U : CpuLoop->users()) {
    Instruction *I = cast<Instruction>(U);

    // Check only translated functions.
    if (I->getParent()->getParent() != &F)
      continue;

    if (auto *Store = dyn_cast<StoreInst>(U))
      Stores.push_back(Store);
    else if (auto *Load = dyn_cast<LoadInst>(U))
      Loads.push_back(Load);
    else
      revng_abort("Unexpected use of cpu_loop_exiting");
  }

  // Remove in bulk all the store found before.
  bool Changed = not Loads.empty() or not Stores.empty();
  for (Instruction *I : Stores)
    eraseFromParent(I);

  for (LoadInst *L : Loads) {
    // Replace all uses of loads with "false"
    L->replaceAllUsesWith(llvm::Constant::getNullValue(L->getType()));
    eraseFromParent(L);
  }

  return Changed;
}