BarrierNoopPass.cpp revision 36b56886974eae4f9c5ebc96befd3e7bfe5de338 
1//===- BarrierNoopPass.cpp - A barrier pass for the pass manager ----------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// NOTE: DO NOT USE THIS IF AVOIDABLE
11//
12// This pass is a nonce pass intended to allow manipulation of the implicitly
13// nesting pass manager. For example, it can be used to cause a CGSCC pass
14// manager to be closed prior to running a new collection of function passes.
15//
16// FIXME: This is a huge HACK. This should be removed when the pass manager's
17// nesting is made explicit instead of implicit.
18//
19//===----------------------------------------------------------------------===//
20
21#include "llvm/Pass.h"
22#include "llvm/Transforms/IPO.h"
23using namespace llvm;
24
25namespace {
26/// \brief A nonce module pass used to place a barrier in a pass manager.
27///
28/// There is no mechanism for ending a CGSCC pass manager once one is started.
29/// This prevents extension points from having clear deterministic ordering
30/// when they are phrased as non-module passes.
31class BarrierNoop : public ModulePass {
32public:
33  static char ID; // Pass identification.
34
35  BarrierNoop() : ModulePass(ID) {
36    initializeBarrierNoopPass(*PassRegistry::getPassRegistry());
37  }
38
39  bool runOnModule(Module &M) override { return false; }
40};
41}
42
43ModulePass *llvm::createBarrierNoopPass() { return new BarrierNoop(); }
44
45char BarrierNoop::ID = 0;
46INITIALIZE_PASS(BarrierNoop, "barrier", "A No-Op Barrier Pass",
47                false, false)
48