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 BarrierNoop()35 BarrierNoop() : ModulePass(ID) { 36 initializeBarrierNoopPass(*PassRegistry::getPassRegistry()); 37 } 38 runOnModule(Module & M)39 bool runOnModule(Module &M) override { return false; } 40 }; 41 } 42 createBarrierNoopPass()43ModulePass *llvm::createBarrierNoopPass() { return new BarrierNoop(); } 44 45 char BarrierNoop::ID = 0; 46 INITIALIZE_PASS(BarrierNoop, "barrier", "A No-Op Barrier Pass", 47 false, false) 48