llvm-mirror/lib/Transforms/IPO/BarrierNoopPass.cpp

//===- BarrierNoopPass.cpp - A barrier pass for the pass manager ----------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// NOTE: DO NOT USE THIS IF AVOIDABLE
//
// This pass is a nonce pass intended to allow manipulation of the implicitly
// nesting pass manager. For example, it can be used to cause a CGSCC pass
// manager to be closed prior to running a new collection of function passes.
//
// FIXME: This is a huge HACK. This should be removed when the pass manager's
// nesting is made explicit instead of implicit.
//
//===----------------------------------------------------------------------===//

#include "llvm/Pass.h"
#include "llvm/Transforms/IPO.h"
using namespace llvm;

namespace {
/// \brief A nonce module pass used to place a barrier in a pass manager.
///
/// There is no mechanism for ending a CGSCC pass manager once one is started.
/// This prevents extension points from having clear deterministic ordering
/// when they are phrased as non-module passes.
class BarrierNoop : public ModulePass {
public:
  static char ID; // Pass identification.

  BarrierNoop() : ModulePass(ID) {
    initializeBarrierNoopPass(*PassRegistry::getPassRegistry());
  }

  bool runOnModule(Module &M) override { return false; }
};
}

ModulePass *llvm::createBarrierNoopPass() { return new BarrierNoop(); }

char BarrierNoop::ID = 0;
INITIALIZE_PASS(BarrierNoop, "barrier", "A No-Op Barrier Pass",
                false, false)