Function generateWhileSwitchAround

src/compiler/cbs/SubCfgFormation.cpp:1198–1226

create the actual while loop around the subcfgs and the switch instruction to select the next subCFG based on the value in \a LastBarrierIdStorage

// create the actual while loop around the subcfgs and the switch instruction to
// select the next subCFG based on the value in \a LastBarrierIdStorage
llvm::BasicBlock *generateWhileSwitchAround(llvm::BasicBlock *PreHeader, llvm::BasicBlock *OldEntry,
                                            llvm::BasicBlock *Exit,
                                            llvm::AllocaInst *LastBarrierIdStorage,
                                            std::vector<SubCFG> &SubCFGs) {
  auto &F = *PreHeader->getParent();
  auto &M = *F.getParent();
  const auto &DL = M.getDataLayout();

  auto *WhileHeader = llvm::BasicBlock::Create(PreHeader->getContext(), "cbs.while.header",
                                               PreHeader->getParent(), OldEntry);
  llvm::IRBuilder Builder{WhileHeader, WhileHeader->getFirstInsertionPt()};
  auto *LastID = Builder.CreateLoad(LastBarrierIdStorage->getAllocatedType(), LastBarrierIdStorage,
                                    "cbs.while.last_barr.load");
  auto *Switch = Builder.CreateSwitch(LastID, createUnreachableBlock(F), SubCFGs.size());
  for (auto &Cfg : SubCFGs) {
    Switch->addCase(Builder.getIntN(DL.getLargestLegalIntTypeSizeInBits(), Cfg.getEntryId()),
                    Cfg.getEntry());
    Cfg.getEntry()->replacePhiUsesWith(PreHeader, WhileHeader);
    Cfg.getExit()->getTerminator()->replaceSuccessorWith(Exit, WhileHeader);
  }
  Switch->addCase(Builder.getIntN(DL.getLargestLegalIntTypeSizeInBits(), ExitBarrierId), Exit);

  Builder.SetInsertPoint(PreHeader->getTerminator());
  Builder.CreateStore(
      llvm::ConstantInt::get(LastBarrierIdStorage->getAllocatedType(), EntryBarrierId),
      LastBarrierIdStorage);
  PreHeader->getTerminator()->replaceSuccessorWith(OldEntry, WhileHeader);
  return WhileHeader;
}

// drops all lifetime intrinsics - they are misinforming ASAN otherwise (and are
// not really fixable at the right scope..)