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