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Diffstat (limited to 'llvm/lib/Analysis/DomTreeUpdater.cpp')
| -rw-r--r-- | llvm/lib/Analysis/DomTreeUpdater.cpp | 533 |
1 files changed, 533 insertions, 0 deletions
diff --git a/llvm/lib/Analysis/DomTreeUpdater.cpp b/llvm/lib/Analysis/DomTreeUpdater.cpp new file mode 100644 index 000000000000..49215889cfd6 --- /dev/null +++ b/llvm/lib/Analysis/DomTreeUpdater.cpp @@ -0,0 +1,533 @@ +//===- DomTreeUpdater.cpp - DomTree/Post DomTree Updater --------*- C++ -*-===// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +//===----------------------------------------------------------------------===// +// +// This file implements the DomTreeUpdater class, which provides a uniform way +// to update dominator tree related data structures. +// +//===----------------------------------------------------------------------===// + +#include "llvm/Analysis/DomTreeUpdater.h" +#include "llvm/ADT/SmallSet.h" +#include "llvm/Analysis/PostDominators.h" +#include "llvm/IR/Dominators.h" +#include "llvm/Support/GenericDomTree.h" +#include <algorithm> +#include <functional> +#include <utility> + +namespace llvm { + +bool DomTreeUpdater::isUpdateValid( + const DominatorTree::UpdateType Update) const { + const auto *From = Update.getFrom(); + const auto *To = Update.getTo(); + const auto Kind = Update.getKind(); + + // Discard updates by inspecting the current state of successors of From. + // Since isUpdateValid() must be called *after* the Terminator of From is + // altered we can determine if the update is unnecessary for batch updates + // or invalid for a single update. + const bool HasEdge = llvm::any_of( + successors(From), [To](const BasicBlock *B) { return B == To; }); + + // If the IR does not match the update, + // 1. In batch updates, this update is unnecessary. + // 2. When called by insertEdge*()/deleteEdge*(), this update is invalid. + // Edge does not exist in IR. + if (Kind == DominatorTree::Insert && !HasEdge) + return false; + + // Edge exists in IR. + if (Kind == DominatorTree::Delete && HasEdge) + return false; + + return true; +} + +bool DomTreeUpdater::isSelfDominance( + const DominatorTree::UpdateType Update) const { + // Won't affect DomTree and PostDomTree. + return Update.getFrom() == Update.getTo(); +} + +void DomTreeUpdater::applyDomTreeUpdates() { + // No pending DomTreeUpdates. + if (Strategy != UpdateStrategy::Lazy || !DT) + return; + + // Only apply updates not are applied by DomTree. + if (hasPendingDomTreeUpdates()) { + const auto I = PendUpdates.begin() + PendDTUpdateIndex; + const auto E = PendUpdates.end(); + assert(I < E && "Iterator range invalid; there should be DomTree updates."); + DT->applyUpdates(ArrayRef<DominatorTree::UpdateType>(I, E)); + PendDTUpdateIndex = PendUpdates.size(); + } +} + +void DomTreeUpdater::flush() { + applyDomTreeUpdates(); + applyPostDomTreeUpdates(); + dropOutOfDateUpdates(); +} + +void DomTreeUpdater::applyPostDomTreeUpdates() { + // No pending PostDomTreeUpdates. + if (Strategy != UpdateStrategy::Lazy || !PDT) + return; + + // Only apply updates not are applied by PostDomTree. + if (hasPendingPostDomTreeUpdates()) { + const auto I = PendUpdates.begin() + PendPDTUpdateIndex; + const auto E = PendUpdates.end(); + assert(I < E && + "Iterator range invalid; there should be PostDomTree updates."); + PDT->applyUpdates(ArrayRef<DominatorTree::UpdateType>(I, E)); + PendPDTUpdateIndex = PendUpdates.size(); + } +} + +void DomTreeUpdater::tryFlushDeletedBB() { + if (!hasPendingUpdates()) + forceFlushDeletedBB(); +} + +bool DomTreeUpdater::forceFlushDeletedBB() { + if (DeletedBBs.empty()) + return false; + + for (auto *BB : DeletedBBs) { + // After calling deleteBB or callbackDeleteBB under Lazy UpdateStrategy, + // validateDeleteBB() removes all instructions of DelBB and adds an + // UnreachableInst as its terminator. So we check whether the BasicBlock to + // delete only has an UnreachableInst inside. + assert(BB->getInstList().size() == 1 && + isa<UnreachableInst>(BB->getTerminator()) && + "DelBB has been modified while awaiting deletion."); + BB->removeFromParent(); + eraseDelBBNode(BB); + delete BB; + } + DeletedBBs.clear(); + Callbacks.clear(); + return true; +} + +void DomTreeUpdater::recalculate(Function &F) { + + if (Strategy == UpdateStrategy::Eager) { + if (DT) + DT->recalculate(F); + if (PDT) + PDT->recalculate(F); + return; + } + + // There is little performance gain if we pend the recalculation under + // Lazy UpdateStrategy so we recalculate available trees immediately. + + // Prevent forceFlushDeletedBB() from erasing DomTree or PostDomTree nodes. + IsRecalculatingDomTree = IsRecalculatingPostDomTree = true; + + // Because all trees are going to be up-to-date after recalculation, + // flush awaiting deleted BasicBlocks. + forceFlushDeletedBB(); + if (DT) + DT->recalculate(F); + if (PDT) + PDT->recalculate(F); + + // Resume forceFlushDeletedBB() to erase DomTree or PostDomTree nodes. + IsRecalculatingDomTree = IsRecalculatingPostDomTree = false; + PendDTUpdateIndex = PendPDTUpdateIndex = PendUpdates.size(); + dropOutOfDateUpdates(); +} + +bool DomTreeUpdater::hasPendingUpdates() const { + return hasPendingDomTreeUpdates() || hasPendingPostDomTreeUpdates(); +} + +bool DomTreeUpdater::hasPendingDomTreeUpdates() const { + if (!DT) + return false; + return PendUpdates.size() != PendDTUpdateIndex; +} + +bool DomTreeUpdater::hasPendingPostDomTreeUpdates() const { + if (!PDT) + return false; + return PendUpdates.size() != PendPDTUpdateIndex; +} + +bool DomTreeUpdater::isBBPendingDeletion(llvm::BasicBlock *DelBB) const { + if (Strategy == UpdateStrategy::Eager || DeletedBBs.empty()) + return false; + return DeletedBBs.count(DelBB) != 0; +} + +// The DT and PDT require the nodes related to updates +// are not deleted when update functions are called. +// So BasicBlock deletions must be pended when the +// UpdateStrategy is Lazy. When the UpdateStrategy is +// Eager, the BasicBlock will be deleted immediately. +void DomTreeUpdater::deleteBB(BasicBlock *DelBB) { + validateDeleteBB(DelBB); + if (Strategy == UpdateStrategy::Lazy) { + DeletedBBs.insert(DelBB); + return; + } + + DelBB->removeFromParent(); + eraseDelBBNode(DelBB); + delete DelBB; +} + +void DomTreeUpdater::callbackDeleteBB( + BasicBlock *DelBB, std::function<void(BasicBlock *)> Callback) { + validateDeleteBB(DelBB); + if (Strategy == UpdateStrategy::Lazy) { + Callbacks.push_back(CallBackOnDeletion(DelBB, Callback)); + DeletedBBs.insert(DelBB); + return; + } + + DelBB->removeFromParent(); + eraseDelBBNode(DelBB); + Callback(DelBB); + delete DelBB; +} + +void DomTreeUpdater::eraseDelBBNode(BasicBlock *DelBB) { + if (DT && !IsRecalculatingDomTree) + if (DT->getNode(DelBB)) + DT->eraseNode(DelBB); + + if (PDT && !IsRecalculatingPostDomTree) + if (PDT->getNode(DelBB)) + PDT->eraseNode(DelBB); +} + +void DomTreeUpdater::validateDeleteBB(BasicBlock *DelBB) { + assert(DelBB && "Invalid push_back of nullptr DelBB."); + assert(pred_empty(DelBB) && "DelBB has one or more predecessors."); + // DelBB is unreachable and all its instructions are dead. + while (!DelBB->empty()) { + Instruction &I = DelBB->back(); + // Replace used instructions with an arbitrary value (undef). + if (!I.use_empty()) + I.replaceAllUsesWith(llvm::UndefValue::get(I.getType())); + DelBB->getInstList().pop_back(); + } + // Make sure DelBB has a valid terminator instruction. As long as DelBB is a + // Child of Function F it must contain valid IR. + new UnreachableInst(DelBB->getContext(), DelBB); +} + +void DomTreeUpdater::applyUpdates(ArrayRef<DominatorTree::UpdateType> Updates) { + if (!DT && !PDT) + return; + + if (Strategy == UpdateStrategy::Lazy) { + for (const auto U : Updates) + if (!isSelfDominance(U)) + PendUpdates.push_back(U); + + return; + } + + if (DT) + DT->applyUpdates(Updates); + if (PDT) + PDT->applyUpdates(Updates); +} + +void DomTreeUpdater::applyUpdatesPermissive( + ArrayRef<DominatorTree::UpdateType> Updates) { + if (!DT && !PDT) + return; + + SmallSet<std::pair<BasicBlock *, BasicBlock *>, 8> Seen; + SmallVector<DominatorTree::UpdateType, 8> DeduplicatedUpdates; + for (const auto U : Updates) { + auto Edge = std::make_pair(U.getFrom(), U.getTo()); + // Because it is illegal to submit updates that have already been applied + // and updates to an edge need to be strictly ordered, + // it is safe to infer the existence of an edge from the first update + // to this edge. + // If the first update to an edge is "Delete", it means that the edge + // existed before. If the first update to an edge is "Insert", it means + // that the edge didn't exist before. + // + // For example, if the user submits {{Delete, A, B}, {Insert, A, B}}, + // because + // 1. it is illegal to submit updates that have already been applied, + // i.e., user cannot delete an nonexistent edge, + // 2. updates to an edge need to be strictly ordered, + // So, initially edge A -> B existed. + // We can then safely ignore future updates to this edge and directly + // inspect the current CFG: + // a. If the edge still exists, because the user cannot insert an existent + // edge, so both {Delete, A, B}, {Insert, A, B} actually happened and + // resulted in a no-op. DTU won't submit any update in this case. + // b. If the edge doesn't exist, we can then infer that {Delete, A, B} + // actually happened but {Insert, A, B} was an invalid update which never + // happened. DTU will submit {Delete, A, B} in this case. + if (!isSelfDominance(U) && Seen.count(Edge) == 0) { + Seen.insert(Edge); + // If the update doesn't appear in the CFG, it means that + // either the change isn't made or relevant operations + // result in a no-op. + if (isUpdateValid(U)) { + if (isLazy()) + PendUpdates.push_back(U); + else + DeduplicatedUpdates.push_back(U); + } + } + } + + if (Strategy == UpdateStrategy::Lazy) + return; + + if (DT) + DT->applyUpdates(DeduplicatedUpdates); + if (PDT) + PDT->applyUpdates(DeduplicatedUpdates); +} + +DominatorTree &DomTreeUpdater::getDomTree() { + assert(DT && "Invalid acquisition of a null DomTree"); + applyDomTreeUpdates(); + dropOutOfDateUpdates(); + return *DT; +} + +PostDominatorTree &DomTreeUpdater::getPostDomTree() { + assert(PDT && "Invalid acquisition of a null PostDomTree"); + applyPostDomTreeUpdates(); + dropOutOfDateUpdates(); + return *PDT; +} + +void DomTreeUpdater::insertEdge(BasicBlock *From, BasicBlock *To) { + +#ifndef NDEBUG + assert(isUpdateValid({DominatorTree::Insert, From, To}) && + "Inserted edge does not appear in the CFG"); +#endif + + if (!DT && !PDT) + return; + + // Won't affect DomTree and PostDomTree; discard update. + if (From == To) + return; + + if (Strategy == UpdateStrategy::Eager) { + if (DT) + DT->insertEdge(From, To); + if (PDT) + PDT->insertEdge(From, To); + return; + } + + PendUpdates.push_back({DominatorTree::Insert, From, To}); +} + +void DomTreeUpdater::insertEdgeRelaxed(BasicBlock *From, BasicBlock *To) { + if (From == To) + return; + + if (!DT && !PDT) + return; + + if (!isUpdateValid({DominatorTree::Insert, From, To})) + return; + + if (Strategy == UpdateStrategy::Eager) { + if (DT) + DT->insertEdge(From, To); + if (PDT) + PDT->insertEdge(From, To); + return; + } + + PendUpdates.push_back({DominatorTree::Insert, From, To}); +} + +void DomTreeUpdater::deleteEdge(BasicBlock *From, BasicBlock *To) { + +#ifndef NDEBUG + assert(isUpdateValid({DominatorTree::Delete, From, To}) && + "Deleted edge still exists in the CFG!"); +#endif + + if (!DT && !PDT) + return; + + // Won't affect DomTree and PostDomTree; discard update. + if (From == To) + return; + + if (Strategy == UpdateStrategy::Eager) { + if (DT) + DT->deleteEdge(From, To); + if (PDT) + PDT->deleteEdge(From, To); + return; + } + + PendUpdates.push_back({DominatorTree::Delete, From, To}); +} + +void DomTreeUpdater::deleteEdgeRelaxed(BasicBlock *From, BasicBlock *To) { + if (From == To) + return; + + if (!DT && !PDT) + return; + + if (!isUpdateValid({DominatorTree::Delete, From, To})) + return; + + if (Strategy == UpdateStrategy::Eager) { + if (DT) + DT->deleteEdge(From, To); + if (PDT) + PDT->deleteEdge(From, To); + return; + } + + PendUpdates.push_back({DominatorTree::Delete, From, To}); +} + +void DomTreeUpdater::dropOutOfDateUpdates() { + if (Strategy == DomTreeUpdater::UpdateStrategy::Eager) + return; + + tryFlushDeletedBB(); + + // Drop all updates applied by both trees. + if (!DT) + PendDTUpdateIndex = PendUpdates.size(); + if (!PDT) + PendPDTUpdateIndex = PendUpdates.size(); + + const size_t dropIndex = std::min(PendDTUpdateIndex, PendPDTUpdateIndex); + const auto B = PendUpdates.begin(); + const auto E = PendUpdates.begin() + dropIndex; + assert(B <= E && "Iterator out of range."); + PendUpdates.erase(B, E); + // Calculate current index. + PendDTUpdateIndex -= dropIndex; + PendPDTUpdateIndex -= dropIndex; +} + +#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) +LLVM_DUMP_METHOD void DomTreeUpdater::dump() const { + raw_ostream &OS = llvm::dbgs(); + + OS << "Available Trees: "; + if (DT || PDT) { + if (DT) + OS << "DomTree "; + if (PDT) + OS << "PostDomTree "; + OS << "\n"; + } else + OS << "None\n"; + + OS << "UpdateStrategy: "; + if (Strategy == UpdateStrategy::Eager) { + OS << "Eager\n"; + return; + } else + OS << "Lazy\n"; + int Index = 0; + + auto printUpdates = + [&](ArrayRef<DominatorTree::UpdateType>::const_iterator begin, + ArrayRef<DominatorTree::UpdateType>::const_iterator end) { + if (begin == end) + OS << " None\n"; + Index = 0; + for (auto It = begin, ItEnd = end; It != ItEnd; ++It) { + auto U = *It; + OS << " " << Index << " : "; + ++Index; + if (U.getKind() == DominatorTree::Insert) + OS << "Insert, "; + else + OS << "Delete, "; + BasicBlock *From = U.getFrom(); + if (From) { + auto S = From->getName(); + if (!From->hasName()) + S = "(no name)"; + OS << S << "(" << From << "), "; + } else { + OS << "(badref), "; + } + BasicBlock *To = U.getTo(); + if (To) { + auto S = To->getName(); + if (!To->hasName()) + S = "(no_name)"; + OS << S << "(" << To << ")\n"; + } else { + OS << "(badref)\n"; + } + } + }; + + if (DT) { + const auto I = PendUpdates.begin() + PendDTUpdateIndex; + assert(PendUpdates.begin() <= I && I <= PendUpdates.end() && + "Iterator out of range."); + OS << "Applied but not cleared DomTreeUpdates:\n"; + printUpdates(PendUpdates.begin(), I); + OS << "Pending DomTreeUpdates:\n"; + printUpdates(I, PendUpdates.end()); + } + + if (PDT) { + const auto I = PendUpdates.begin() + PendPDTUpdateIndex; + assert(PendUpdates.begin() <= I && I <= PendUpdates.end() && + "Iterator out of range."); + OS << "Applied but not cleared PostDomTreeUpdates:\n"; + printUpdates(PendUpdates.begin(), I); + OS << "Pending PostDomTreeUpdates:\n"; + printUpdates(I, PendUpdates.end()); + } + + OS << "Pending DeletedBBs:\n"; + Index = 0; + for (auto BB : DeletedBBs) { + OS << " " << Index << " : "; + ++Index; + if (BB->hasName()) + OS << BB->getName() << "("; + else + OS << "(no_name)("; + OS << BB << ")\n"; + } + + OS << "Pending Callbacks:\n"; + Index = 0; + for (auto BB : Callbacks) { + OS << " " << Index << " : "; + ++Index; + if (BB->hasName()) + OS << BB->getName() << "("; + else + OS << "(no_name)("; + OS << BB << ")\n"; + } +} +#endif +} // namespace llvm |