llvm/lib/Transforms/IPO/BarrierNoopPass.cpp

   1 //===- BarrierNoopPass.cpp - A barrier pass for the pass manager ----------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // NOTE: DO NOT USE THIS IF AVOIDABLE
  10 //
  11 // This pass is a nonce pass intended to allow manipulation of the implicitly
  12 // nesting pass manager. For example, it can be used to cause a CGSCC pass
  13 // manager to be closed prior to running a new collection of function passes.
  14 //
  15 // FIXME: This is a huge HACK. This should be removed when the pass manager's
  16 // nesting is made explicit instead of implicit.
  17 //
  18 //===----------------------------------------------------------------------===//
  19
  20 #include "llvm/InitializePasses.h"
  21 #include "llvm/Pass.h"
  22 #include "llvm/Transforms/IPO.h"
  23 using namespace llvm;
  24
  25 namespace {
  26 /// 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.
  31 class BarrierNoop : public ModulePass {
  32 public:
  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
  43 ModulePass *llvm::createBarrierNoopPass() { return new BarrierNoop(); }
  44
  45 char BarrierNoop::ID = 0;
  46 INITIALIZE_PASS(BarrierNoop, "barrier", "A No-Op Barrier Pass",
  47                 false, false)