llvm/lib/Analysis/DomTreeUpdater.cpp

   1 //===- DomTreeUpdater.cpp - DomTree/Post DomTree Updater --------*- C++ -*-===//
   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 // This file implements the DomTreeUpdater class, which provides a uniform way
  10 // to update dominator tree related data structures.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "llvm/Analysis/DomTreeUpdater.h"
  15 #include "llvm/Analysis/GenericDomTreeUpdaterImpl.h"
  16 #include "llvm/Analysis/PostDominators.h"
  17 #include "llvm/IR/Constants.h"
  18 #include "llvm/IR/Instructions.h"
  19 #include "llvm/Support/GenericDomTree.h"
  20 #include <functional>
  21
  22 namespace llvm {
  23
  24 template class GenericDomTreeUpdater<DomTreeUpdater, DominatorTree,
  25                                      PostDominatorTree>;
  26
  27 template void
  28 GenericDomTreeUpdater<DomTreeUpdater, DominatorTree,
  29                       PostDominatorTree>::recalculate(Function &F);
  30
  31 template void
  32 GenericDomTreeUpdater<DomTreeUpdater, DominatorTree, PostDominatorTree>::
  33     applyUpdatesImpl</*IsForward=*/true>();
  34 template void
  35 GenericDomTreeUpdater<DomTreeUpdater, DominatorTree, PostDominatorTree>::
  36     applyUpdatesImpl</*IsForward=*/false>();
  37
  38 bool DomTreeUpdater::forceFlushDeletedBB() {
  39   if (DeletedBBs.empty())
  40     return false;
  41
  42   for (auto *BB : DeletedBBs) {
  43     // After calling deleteBB or callbackDeleteBB under Lazy UpdateStrategy,
  44     // validateDeleteBB() removes all instructions of DelBB and adds an
  45     // UnreachableInst as its terminator. So we check whether the BasicBlock to
  46     // delete only has an UnreachableInst inside.
  47     assert(BB->size() == 1 && isa<UnreachableInst>(BB->getTerminator()) &&
  48            "DelBB has been modified while awaiting deletion.");
  49     eraseDelBBNode(BB);
  50     BB->eraseFromParent();
  51   }
  52   DeletedBBs.clear();
  53   Callbacks.clear();
  54   return true;
  55 }
  56
  57 // The DT and PDT require the nodes related to updates
  58 // are not deleted when update functions are called.
  59 // So BasicBlock deletions must be pended when the
  60 // UpdateStrategy is Lazy. When the UpdateStrategy is
  61 // Eager, the BasicBlock will be deleted immediately.
  62 void DomTreeUpdater::deleteBB(BasicBlock *DelBB) {
  63   validateDeleteBB(DelBB);
  64   if (Strategy == UpdateStrategy::Lazy) {
  65     DeletedBBs.insert(DelBB);
  66     return;
  67   }
  68
  69   eraseDelBBNode(DelBB);
  70   DelBB->eraseFromParent();
  71 }
  72
  73 void DomTreeUpdater::callbackDeleteBB(
  74     BasicBlock *DelBB, std::function<void(BasicBlock *)> Callback) {
  75   validateDeleteBB(DelBB);
  76   if (Strategy == UpdateStrategy::Lazy) {
  77     Callbacks.push_back(CallBackOnDeletion(DelBB, Callback));
  78     DeletedBBs.insert(DelBB);
  79     return;
  80   }
  81
  82   eraseDelBBNode(DelBB);
  83   DelBB->removeFromParent();
  84   Callback(DelBB);
  85   delete DelBB;
  86 }
  87
  88 void DomTreeUpdater::validateDeleteBB(BasicBlock *DelBB) {
  89   assert(DelBB && "Invalid push_back of nullptr DelBB.");
  90   assert(pred_empty(DelBB) && "DelBB has one or more predecessors.");
  91   // DelBB is unreachable and all its instructions are dead.
  92   while (!DelBB->empty()) {
  93     Instruction &I = DelBB->back();
  94     // Replace used instructions with an arbitrary value (poison).
  95     if (!I.use_empty())
  96       I.replaceAllUsesWith(PoisonValue::get(I.getType()));
  97     DelBB->back().eraseFromParent();
  98   }
  99   // Make sure DelBB has a valid terminator instruction. As long as DelBB is a
 100   // Child of Function F it must contain valid IR.
 101   new UnreachableInst(DelBB->getContext(), DelBB);
 102 }
 103
 104 LLVM_DUMP_METHOD
 105 void DomTreeUpdater::dump() const {
 106   Base::dump();
 107 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
 108   raw_ostream &OS = dbgs();
 109   OS << "Pending Callbacks:\n";
 110   int Index = 0;
 111   for (const auto &BB : Callbacks) {
 112     OS << "  " << Index << " : ";
 113     ++Index;
 114     if (BB->hasName())
 115       OS << BB->getName() << "(";
 116     else
 117       OS << "(no_name)(";
 118     OS << BB << ")\n";
 119   }
 120 #endif
 121 }
 122
 123 } // namespace llvm