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//===- GenericDomTree.h - Generic dominator trees for graphs ----*- 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
//
//===----------------------------------------------------------------------===//
/// \file
///
/// This file defines a set of templates that efficiently compute a dominator
/// tree over a generic graph. This is used typically in LLVM for fast
/// dominance queries on the CFG, but is fully generic w.r.t. the underlying
/// graph types.
///
/// Unlike ADT/* graph algorithms, generic dominator tree has more requirements
/// on the graph's NodeRef. The NodeRef should be a pointer and,
/// either NodeRef->getParent() must return the parent node that is also a
/// pointer or DomTreeNodeTraits needs to be specialized.
///
/// FIXME: Maybe GenericDomTree needs a TreeTraits, instead of GraphTraits.
///
//===----------------------------------------------------------------------===//
#ifndef LLVM_SUPPORT_GENERICDOMTREE_H
#define LLVM_SUPPORT_GENERICDOMTREE_H
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/GraphTraits.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Support/CFGDiff.h"
#include "llvm/Support/CFGUpdate.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cassert>
#include <cstddef>
#include <iterator>
#include <memory>
#include <type_traits>
#include <utility>
namespace llvm {
template <typename NodeT, bool IsPostDom>
class DominatorTreeBase;
namespace DomTreeBuilder {
template <typename DomTreeT>
struct SemiNCAInfo;
} // namespace DomTreeBuilder
/// Base class for the actual dominator tree node.
template <class NodeT> class DomTreeNodeBase {
friend class PostDominatorTree;
friend class DominatorTreeBase<NodeT, false>;
friend class DominatorTreeBase<NodeT, true>;
friend struct DomTreeBuilder::SemiNCAInfo<DominatorTreeBase<NodeT, false>>;
friend struct DomTreeBuilder::SemiNCAInfo<DominatorTreeBase<NodeT, true>>;
NodeT *TheBB;
DomTreeNodeBase *IDom;
unsigned Level;
SmallVector<DomTreeNodeBase *, 4> Children;
mutable unsigned DFSNumIn = ~0;
mutable unsigned DFSNumOut = ~0;
public:
DomTreeNodeBase(NodeT *BB, DomTreeNodeBase *iDom)
: TheBB(BB), IDom(iDom), Level(IDom ? IDom->Level + 1 : 0) {}
using iterator = typename SmallVector<DomTreeNodeBase *, 4>::iterator;
using const_iterator =
typename SmallVector<DomTreeNodeBase *, 4>::const_iterator;
iterator begin() { return Children.begin(); }
iterator end() { return Children.end(); }
const_iterator begin() const { return Children.begin(); }
const_iterator end() const { return Children.end(); }
DomTreeNodeBase *const &back() const { return Children.back(); }
DomTreeNodeBase *&back() { return Children.back(); }
iterator_range<iterator> children() { return make_range(begin(), end()); }
iterator_range<const_iterator> children() const {
return make_range(begin(), end());
}
NodeT *getBlock() const { return TheBB; }
DomTreeNodeBase *getIDom() const { return IDom; }
unsigned getLevel() const { return Level; }
std::unique_ptr<DomTreeNodeBase> addChild(
std::unique_ptr<DomTreeNodeBase> C) {
Children.push_back(C.get());
return C;
}
bool isLeaf() const { return Children.empty(); }
size_t getNumChildren() const { return Children.size(); }
void clearAllChildren() { Children.clear(); }
bool compare(const DomTreeNodeBase *Other) const {
if (getNumChildren() != Other->getNumChildren())
return true;
if (Level != Other->Level) return true;
SmallPtrSet<const NodeT *, 4> OtherChildren;
for (const DomTreeNodeBase *I : *Other) {
const NodeT *Nd = I->getBlock();
OtherChildren.insert(Nd);
}
for (const DomTreeNodeBase *I : *this) {
const NodeT *N = I->getBlock();
if (OtherChildren.count(N) == 0)
return true;
}
return false;
}
void setIDom(DomTreeNodeBase *NewIDom) {
assert(IDom && "No immediate dominator?");
if (IDom == NewIDom) return;
auto I = find(IDom->Children, this);
assert(I != IDom->Children.end() &&
"Not in immediate dominator children set!");
// I am no longer your child...
IDom->Children.erase(I);
// Switch to new dominator
IDom = NewIDom;
IDom->Children.push_back(this);
UpdateLevel();
}
/// getDFSNumIn/getDFSNumOut - These return the DFS visitation order for nodes
/// in the dominator tree. They are only guaranteed valid if
/// updateDFSNumbers() has been called.
unsigned getDFSNumIn() const { return DFSNumIn; }
unsigned getDFSNumOut() const { return DFSNumOut; }
private:
// Return true if this node is dominated by other. Use this only if DFS info
// is valid.
bool DominatedBy(const DomTreeNodeBase *other) const {
return this->DFSNumIn >= other->DFSNumIn &&
this->DFSNumOut <= other->DFSNumOut;
}
void UpdateLevel() {
assert(IDom);
if (Level == IDom->Level + 1) return;
SmallVector<DomTreeNodeBase *, 64> WorkStack = {this};
while (!WorkStack.empty()) {
DomTreeNodeBase *Current = WorkStack.pop_back_val();
Current->Level = Current->IDom->Level + 1;
for (DomTreeNodeBase *C : *Current) {
assert(C->IDom);
if (C->Level != C->IDom->Level + 1) WorkStack.push_back(C);
}
}
}
};
template <class NodeT>
raw_ostream &operator<<(raw_ostream &O, const DomTreeNodeBase<NodeT> *Node) {
if (Node->getBlock())
Node->getBlock()->printAsOperand(O, false);
else
O << " <<exit node>>";
O << " {" << Node->getDFSNumIn() << "," << Node->getDFSNumOut() << "} ["
<< Node->getLevel() << "]\n";
return O;
}
template <class NodeT>
void PrintDomTree(const DomTreeNodeBase<NodeT> *N, raw_ostream &O,
unsigned Lev) {
O.indent(2 * Lev) << "[" << Lev << "] " << N;
for (const auto &I : *N)
PrintDomTree<NodeT>(I, O, Lev + 1);
}
namespace DomTreeBuilder {
// The routines below are provided in a separate header but referenced here.
template <typename DomTreeT>
void Calculate(DomTreeT &DT);
template <typename DomTreeT>
void CalculateWithUpdates(DomTreeT &DT,
ArrayRef<typename DomTreeT::UpdateType> Updates);
template <typename DomTreeT>
void InsertEdge(DomTreeT &DT, typename DomTreeT::NodePtr From,
typename DomTreeT::NodePtr To);
template <typename DomTreeT>
void DeleteEdge(DomTreeT &DT, typename DomTreeT::NodePtr From,
typename DomTreeT::NodePtr To);
template <typename DomTreeT>
void ApplyUpdates(DomTreeT &DT,
GraphDiff<typename DomTreeT::NodePtr,
DomTreeT::IsPostDominator> &PreViewCFG,
GraphDiff<typename DomTreeT::NodePtr,
DomTreeT::IsPostDominator> *PostViewCFG);
template <typename DomTreeT>
bool Verify(const DomTreeT &DT, typename DomTreeT::VerificationLevel VL);
} // namespace DomTreeBuilder
/// Default DomTreeNode traits for NodeT. The default implementation assume a
/// Function-like NodeT. Can be specialized to support different node types.
template <typename NodeT> struct DomTreeNodeTraits {
using NodeType = NodeT;
using NodePtr = NodeT *;
using ParentPtr = decltype(std::declval<NodePtr>()->getParent());
static_assert(std::is_pointer_v<ParentPtr>,
"Currently NodeT's parent must be a pointer type");
using ParentType = std::remove_pointer_t<ParentPtr>;
static NodeT *getEntryNode(ParentPtr Parent) { return &Parent->front(); }
static ParentPtr getParent(NodePtr BB) { return BB->getParent(); }
};
/// Core dominator tree base class.
///
/// This class is a generic template over graph nodes. It is instantiated for
/// various graphs in the LLVM IR or in the code generator.
template <typename NodeT, bool IsPostDom>
class DominatorTreeBase {
public:
static_assert(std::is_pointer_v<typename GraphTraits<NodeT *>::NodeRef>,
"Currently DominatorTreeBase supports only pointer nodes");
using NodeTrait = DomTreeNodeTraits<NodeT>;
using NodeType = typename NodeTrait::NodeType;
using NodePtr = typename NodeTrait::NodePtr;
using ParentPtr = typename NodeTrait::ParentPtr;
static_assert(std::is_pointer_v<ParentPtr>,
"Currently NodeT's parent must be a pointer type");
using ParentType = std::remove_pointer_t<ParentPtr>;
static constexpr bool IsPostDominator = IsPostDom;
using UpdateType = cfg::Update<NodePtr>;
using UpdateKind = cfg::UpdateKind;
static constexpr UpdateKind Insert = UpdateKind::Insert;
static constexpr UpdateKind Delete = UpdateKind::Delete;
enum class VerificationLevel { Fast, Basic, Full };
protected:
// Dominators always have a single root, postdominators can have more.
SmallVector<NodeT *, IsPostDom ? 4 : 1> Roots;
using DomTreeNodeMapType =
DenseMap<NodeT *, std::unique_ptr<DomTreeNodeBase<NodeT>>>;
DomTreeNodeMapType DomTreeNodes;
DomTreeNodeBase<NodeT> *RootNode = nullptr;
ParentPtr Parent = nullptr;
mutable bool DFSInfoValid = false;
mutable unsigned int SlowQueries = 0;
friend struct DomTreeBuilder::SemiNCAInfo<DominatorTreeBase>;
public:
DominatorTreeBase() = default;
DominatorTreeBase(DominatorTreeBase &&Arg)
: Roots(std::move(Arg.Roots)),
DomTreeNodes(std::move(Arg.DomTreeNodes)),
RootNode(Arg.RootNode),
Parent(Arg.Parent),
DFSInfoValid(Arg.DFSInfoValid),
SlowQueries(Arg.SlowQueries) {
Arg.wipe();
}
DominatorTreeBase &operator=(DominatorTreeBase &&RHS) {
Roots = std::move(RHS.Roots);
DomTreeNodes = std::move(RHS.DomTreeNodes);
RootNode = RHS.RootNode;
Parent = RHS.Parent;
DFSInfoValid = RHS.DFSInfoValid;
SlowQueries = RHS.SlowQueries;
RHS.wipe();
return *this;
}
DominatorTreeBase(const DominatorTreeBase &) = delete;
DominatorTreeBase &operator=(const DominatorTreeBase &) = delete;
/// Iteration over roots.
///
/// This may include multiple blocks if we are computing post dominators.
/// For forward dominators, this will always be a single block (the entry
/// block).
using root_iterator = typename SmallVectorImpl<NodeT *>::iterator;
using const_root_iterator = typename SmallVectorImpl<NodeT *>::const_iterator;
root_iterator root_begin() { return Roots.begin(); }
const_root_iterator root_begin() const { return Roots.begin(); }
root_iterator root_end() { return Roots.end(); }
const_root_iterator root_end() const { return Roots.end(); }
size_t root_size() const { return Roots.size(); }
iterator_range<root_iterator> roots() {
return make_range(root_begin(), root_end());
}
iterator_range<const_root_iterator> roots() const {
return make_range(root_begin(), root_end());
}
/// isPostDominator - Returns true if analysis based of postdoms
///
bool isPostDominator() const { return IsPostDominator; }
/// compare - Return false if the other dominator tree base matches this
/// dominator tree base. Otherwise return true.
bool compare(const DominatorTreeBase &Other) const {
if (Parent != Other.Parent) return true;
if (Roots.size() != Other.Roots.size())
return true;
if (!std::is_permutation(Roots.begin(), Roots.end(), Other.Roots.begin()))
return true;
const DomTreeNodeMapType &OtherDomTreeNodes = Other.DomTreeNodes;
if (DomTreeNodes.size() != OtherDomTreeNodes.size())
return true;
for (const auto &DomTreeNode : DomTreeNodes) {
NodeT *BB = DomTreeNode.first;
typename DomTreeNodeMapType::const_iterator OI =
OtherDomTreeNodes.find(BB);
if (OI == OtherDomTreeNodes.end())
return true;
DomTreeNodeBase<NodeT> &MyNd = *DomTreeNode.second;
DomTreeNodeBase<NodeT> &OtherNd = *OI->second;
if (MyNd.compare(&OtherNd))
return true;
}
return false;
}
/// getNode - return the (Post)DominatorTree node for the specified basic
/// block. This is the same as using operator[] on this class. The result
/// may (but is not required to) be null for a forward (backwards)
/// statically unreachable block.
DomTreeNodeBase<NodeT> *getNode(const NodeT *BB) const {
auto I = DomTreeNodes.find(BB);
if (I != DomTreeNodes.end())
return I->second.get();
return nullptr;
}
/// See getNode.
DomTreeNodeBase<NodeT> *operator[](const NodeT *BB) const {
return getNode(BB);
}
/// getRootNode - This returns the entry node for the CFG of the function. If
/// this tree represents the post-dominance relations for a function, however,
/// this root may be a node with the block == NULL. This is the case when
/// there are multiple exit nodes from a particular function. Consumers of
/// post-dominance information must be capable of dealing with this
/// possibility.
///
DomTreeNodeBase<NodeT> *getRootNode() { return RootNode; }
const DomTreeNodeBase<NodeT> *getRootNode() const { return RootNode; }
/// Get all nodes dominated by R, including R itself.
void getDescendants(NodeT *R, SmallVectorImpl<NodeT *> &Result) const {
Result.clear();
const DomTreeNodeBase<NodeT> *RN = getNode(R);
if (!RN)
return; // If R is unreachable, it will not be present in the DOM tree.
SmallVector<const DomTreeNodeBase<NodeT> *, 8> WL;
WL.push_back(RN);
while (!WL.empty()) {
const DomTreeNodeBase<NodeT> *N = WL.pop_back_val();
Result.push_back(N->getBlock());
WL.append(N->begin(), N->end());
}
}
/// properlyDominates - Returns true iff A dominates B and A != B.
/// Note that this is not a constant time operation!
///
bool properlyDominates(const DomTreeNodeBase<NodeT> *A,
const DomTreeNodeBase<NodeT> *B) const {
if (!A || !B)
return false;
if (A == B)
return false;
return dominates(A, B);
}
bool properlyDominates(const NodeT *A, const NodeT *B) const;
/// isReachableFromEntry - Return true if A is dominated by the entry
/// block of the function containing it.
bool isReachableFromEntry(const NodeT *A) const {
assert(!this->isPostDominator() &&
"This is not implemented for post dominators");
return isReachableFromEntry(getNode(const_cast<NodeT *>(A)));
}
bool isReachableFromEntry(const DomTreeNodeBase<NodeT> *A) const { return A; }
/// dominates - Returns true iff A dominates B. Note that this is not a
/// constant time operation!
///
bool dominates(const DomTreeNodeBase<NodeT> *A,
const DomTreeNodeBase<NodeT> *B) const {
// A node trivially dominates itself.
if (B == A)
return true;
// An unreachable node is dominated by anything.
if (!isReachableFromEntry(B))
return true;
// And dominates nothing.
if (!isReachableFromEntry(A))
return false;
if (B->getIDom() == A) return true;
if (A->getIDom() == B) return false;
// A can only dominate B if it is higher in the tree.
if (A->getLevel() >= B->getLevel()) return false;
// Compare the result of the tree walk and the dfs numbers, if expensive
// checks are enabled.
#ifdef EXPENSIVE_CHECKS
assert((!DFSInfoValid ||
(dominatedBySlowTreeWalk(A, B) == B->DominatedBy(A))) &&
"Tree walk disagrees with dfs numbers!");
#endif
if (DFSInfoValid)
return B->DominatedBy(A);
// If we end up with too many slow queries, just update the
// DFS numbers on the theory that we are going to keep querying.
SlowQueries++;
if (SlowQueries > 32) {
updateDFSNumbers();
return B->DominatedBy(A);
}
return dominatedBySlowTreeWalk(A, B);
}
bool dominates(const NodeT *A, const NodeT *B) const;
NodeT *getRoot() const {
assert(this->Roots.size() == 1 && "Should always have entry node!");
return this->Roots[0];
}
/// Find nearest common dominator basic block for basic block A and B. A and B
/// must have tree nodes.
NodeT *findNearestCommonDominator(NodeT *A, NodeT *B) const {
assert(A && B && "Pointers are not valid");
assert(NodeTrait::getParent(A) == NodeTrait::getParent(B) &&
"Two blocks are not in same function");
// If either A or B is a entry block then it is nearest common dominator
// (for forward-dominators).
if (!isPostDominator()) {
NodeT &Entry =
*DomTreeNodeTraits<NodeT>::getEntryNode(NodeTrait::getParent(A));
if (A == &Entry || B == &Entry)
return &Entry;
}
DomTreeNodeBase<NodeT> *NodeA = getNode(A);
DomTreeNodeBase<NodeT> *NodeB = getNode(B);
assert(NodeA && "A must be in the tree");
assert(NodeB && "B must be in the tree");
// Use level information to go up the tree until the levels match. Then
// continue going up til we arrive at the same node.
while (NodeA != NodeB) {
if (NodeA->getLevel() < NodeB->getLevel()) std::swap(NodeA, NodeB);
NodeA = NodeA->IDom;
}
return NodeA->getBlock();
}
const NodeT *findNearestCommonDominator(const NodeT *A,
const NodeT *B) const {
// Cast away the const qualifiers here. This is ok since
// const is re-introduced on the return type.
return findNearestCommonDominator(const_cast<NodeT *>(A),
const_cast<NodeT *>(B));
}
bool isVirtualRoot(const DomTreeNodeBase<NodeT> *A) const {
return isPostDominator() && !A->getBlock();
}
//===--------------------------------------------------------------------===//
// API to update (Post)DominatorTree information based on modifications to
// the CFG...
/// Inform the dominator tree about a sequence of CFG edge insertions and
/// deletions and perform a batch update on the tree.
///
/// This function should be used when there were multiple CFG updates after
/// the last dominator tree update. It takes care of performing the updates
/// in sync with the CFG and optimizes away the redundant operations that
/// cancel each other.
/// The functions expects the sequence of updates to be balanced. Eg.:
/// - {{Insert, A, B}, {Delete, A, B}, {Insert, A, B}} is fine, because
/// logically it results in a single insertions.
/// - {{Insert, A, B}, {Insert, A, B}} is invalid, because it doesn't make
/// sense to insert the same edge twice.
///
/// What's more, the functions assumes that it's safe to ask every node in the
/// CFG about its children and inverse children. This implies that deletions
/// of CFG edges must not delete the CFG nodes before calling this function.
///
/// The applyUpdates function can reorder the updates and remove redundant
/// ones internally (as long as it is done in a deterministic fashion). The
/// batch updater is also able to detect sequences of zero and exactly one
/// update -- it's optimized to do less work in these cases.
///
/// Note that for postdominators it automatically takes care of applying
/// updates on reverse edges internally (so there's no need to swap the
/// From and To pointers when constructing DominatorTree::UpdateType).
/// The type of updates is the same for DomTreeBase<T> and PostDomTreeBase<T>
/// with the same template parameter T.
///
/// \param Updates An ordered sequence of updates to perform. The current CFG
/// and the reverse of these updates provides the pre-view of the CFG.
///
void applyUpdates(ArrayRef<UpdateType> Updates) {
GraphDiff<NodePtr, IsPostDominator> PreViewCFG(
Updates, /*ReverseApplyUpdates=*/true);
DomTreeBuilder::ApplyUpdates(*this, PreViewCFG, nullptr);
}
/// \param Updates An ordered sequence of updates to perform. The current CFG
/// and the reverse of these updates provides the pre-view of the CFG.
/// \param PostViewUpdates An ordered sequence of update to perform in order
/// to obtain a post-view of the CFG. The DT will be updated assuming the
/// obtained PostViewCFG is the desired end state.
void applyUpdates(ArrayRef<UpdateType> Updates,
ArrayRef<UpdateType> PostViewUpdates) {
if (Updates.empty()) {
GraphDiff<NodePtr, IsPostDom> PostViewCFG(PostViewUpdates);
DomTreeBuilder::ApplyUpdates(*this, PostViewCFG, &PostViewCFG);
} else {
// PreViewCFG needs to merge Updates and PostViewCFG. The updates in
// Updates need to be reversed, and match the direction in PostViewCFG.
// The PostViewCFG is created with updates reversed (equivalent to changes
// made to the CFG), so the PreViewCFG needs all the updates reverse
// applied.
SmallVector<UpdateType> AllUpdates(Updates.begin(), Updates.end());
append_range(AllUpdates, PostViewUpdates);
GraphDiff<NodePtr, IsPostDom> PreViewCFG(AllUpdates,
/*ReverseApplyUpdates=*/true);
GraphDiff<NodePtr, IsPostDom> PostViewCFG(PostViewUpdates);
DomTreeBuilder::ApplyUpdates(*this, PreViewCFG, &PostViewCFG);
}
}
/// Inform the dominator tree about a CFG edge insertion and update the tree.
///
/// This function has to be called just before or just after making the update
/// on the actual CFG. There cannot be any other updates that the dominator
/// tree doesn't know about.
///
/// Note that for postdominators it automatically takes care of inserting
/// a reverse edge internally (so there's no need to swap the parameters).
///
void insertEdge(NodeT *From, NodeT *To) {
assert(From);
assert(To);
assert(NodeTrait::getParent(From) == Parent);
assert(NodeTrait::getParent(To) == Parent);
DomTreeBuilder::InsertEdge(*this, From, To);
}
/// Inform the dominator tree about a CFG edge deletion and update the tree.
///
/// This function has to be called just after making the update on the actual
/// CFG. An internal functions checks if the edge doesn't exist in the CFG in
/// DEBUG mode. There cannot be any other updates that the
/// dominator tree doesn't know about.
///
/// Note that for postdominators it automatically takes care of deleting
/// a reverse edge internally (so there's no need to swap the parameters).
///
void deleteEdge(NodeT *From, NodeT *To) {
assert(From);
assert(To);
assert(NodeTrait::getParent(From) == Parent);
assert(NodeTrait::getParent(To) == Parent);
DomTreeBuilder::DeleteEdge(*this, From, To);
}
/// Add a new node to the dominator tree information.
///
/// This creates a new node as a child of DomBB dominator node, linking it
/// into the children list of the immediate dominator.
///
/// \param BB New node in CFG.
/// \param DomBB CFG node that is dominator for BB.
/// \returns New dominator tree node that represents new CFG node.
///
DomTreeNodeBase<NodeT> *addNewBlock(NodeT *BB, NodeT *DomBB) {
assert(getNode(BB) == nullptr && "Block already in dominator tree!");
DomTreeNodeBase<NodeT> *IDomNode = getNode(DomBB);
assert(IDomNode && "Not immediate dominator specified for block!");
DFSInfoValid = false;
return createChild(BB, IDomNode);
}
/// Add a new node to the forward dominator tree and make it a new root.
///
/// \param BB New node in CFG.
/// \returns New dominator tree node that represents new CFG node.
///
DomTreeNodeBase<NodeT> *setNewRoot(NodeT *BB) {
assert(getNode(BB) == nullptr && "Block already in dominator tree!");
assert(!this->isPostDominator() &&
"Cannot change root of post-dominator tree");
DFSInfoValid = false;
DomTreeNodeBase<NodeT> *NewNode = createNode(BB);
if (Roots.empty()) {
addRoot(BB);
} else {
assert(Roots.size() == 1);
NodeT *OldRoot = Roots.front();
auto &OldNode = DomTreeNodes[OldRoot];
OldNode = NewNode->addChild(std::move(DomTreeNodes[OldRoot]));
OldNode->IDom = NewNode;
OldNode->UpdateLevel();
Roots[0] = BB;
}
return RootNode = NewNode;
}
/// changeImmediateDominator - This method is used to update the dominator
/// tree information when a node's immediate dominator changes.
///
void changeImmediateDominator(DomTreeNodeBase<NodeT> *N,
DomTreeNodeBase<NodeT> *NewIDom) {
assert(N && NewIDom && "Cannot change null node pointers!");
DFSInfoValid = false;
N->setIDom(NewIDom);
}
void changeImmediateDominator(NodeT *BB, NodeT *NewBB) {
changeImmediateDominator(getNode(BB), getNode(NewBB));
}
/// eraseNode - Removes a node from the dominator tree. Block must not
/// dominate any other blocks. Removes node from its immediate dominator's
/// children list. Deletes dominator node associated with basic block BB.
void eraseNode(NodeT *BB) {
DomTreeNodeBase<NodeT> *Node = getNode(BB);
assert(Node && "Removing node that isn't in dominator tree.");
assert(Node->isLeaf() && "Node is not a leaf node.");
DFSInfoValid = false;
// Remove node from immediate dominator's children list.
DomTreeNodeBase<NodeT> *IDom = Node->getIDom();
if (IDom) {
const auto I = find(IDom->Children, Node);
assert(I != IDom->Children.end() &&
"Not in immediate dominator children set!");
// I am no longer your child...
IDom->Children.erase(I);
}
DomTreeNodes.erase(BB);
if (!IsPostDom) return;
// Remember to update PostDominatorTree roots.
auto RIt = llvm::find(Roots, BB);
if (RIt != Roots.end()) {
std::swap(*RIt, Roots.back());
Roots.pop_back();
}
}
/// splitBlock - BB is split and now it has one successor. Update dominator
/// tree to reflect this change.
void splitBlock(NodeT *NewBB) {
if (IsPostDominator)
Split<Inverse<NodeT *>>(NewBB);
else
Split<NodeT *>(NewBB);
}
/// print - Convert to human readable form
///
void print(raw_ostream &O) const {
O << "=============================--------------------------------\n";
if (IsPostDominator)
O << "Inorder PostDominator Tree: ";
else
O << "Inorder Dominator Tree: ";
if (!DFSInfoValid)
O << "DFSNumbers invalid: " << SlowQueries << " slow queries.";
O << "\n";
// The postdom tree can have a null root if there are no returns.
if (getRootNode()) PrintDomTree<NodeT>(getRootNode(), O, 1);
O << "Roots: ";
for (const NodePtr Block : Roots) {
Block->printAsOperand(O, false);
O << " ";
}
O << "\n";
}
public:
/// updateDFSNumbers - Assign In and Out numbers to the nodes while walking
/// dominator tree in dfs order.
void updateDFSNumbers() const {
if (DFSInfoValid) {
SlowQueries = 0;
return;
}
SmallVector<std::pair<const DomTreeNodeBase<NodeT> *,
typename DomTreeNodeBase<NodeT>::const_iterator>,
32> WorkStack;
const DomTreeNodeBase<NodeT> *ThisRoot = getRootNode();
assert((!Parent || ThisRoot) && "Empty constructed DomTree");
if (!ThisRoot)
return;
// Both dominators and postdominators have a single root node. In the case
// case of PostDominatorTree, this node is a virtual root.
WorkStack.push_back({ThisRoot, ThisRoot->begin()});
unsigned DFSNum = 0;
ThisRoot->DFSNumIn = DFSNum++;
while (!WorkStack.empty()) {
const DomTreeNodeBase<NodeT> *Node = WorkStack.back().first;
const auto ChildIt = WorkStack.back().second;
// If we visited all of the children of this node, "recurse" back up the
// stack setting the DFOutNum.
if (ChildIt == Node->end()) {
Node->DFSNumOut = DFSNum++;
WorkStack.pop_back();
} else {
// Otherwise, recursively visit this child.
const DomTreeNodeBase<NodeT> *Child = *ChildIt;
++WorkStack.back().second;
WorkStack.push_back({Child, Child->begin()});
Child->DFSNumIn = DFSNum++;
}
}
SlowQueries = 0;
DFSInfoValid = true;
}
/// recalculate - compute a dominator tree for the given function
void recalculate(ParentType &Func) {
Parent = &Func;
DomTreeBuilder::Calculate(*this);
}
void recalculate(ParentType &Func, ArrayRef<UpdateType> Updates) {
Parent = &Func;
DomTreeBuilder::CalculateWithUpdates(*this, Updates);
}
/// verify - checks if the tree is correct. There are 3 level of verification:
/// - Full -- verifies if the tree is correct by making sure all the
/// properties (including the parent and the sibling property)
/// hold.
/// Takes O(N^3) time.
///
/// - Basic -- checks if the tree is correct, but compares it to a freshly
/// constructed tree instead of checking the sibling property.
/// Takes O(N^2) time.
///
/// - Fast -- checks basic tree structure and compares it with a freshly
/// constructed tree.
/// Takes O(N^2) time worst case, but is faster in practise (same
/// as tree construction).
bool verify(VerificationLevel VL = VerificationLevel::Full) const {
return DomTreeBuilder::Verify(*this, VL);
}
void reset() {
DomTreeNodes.clear();
Roots.clear();
RootNode = nullptr;
Parent = nullptr;
DFSInfoValid = false;
SlowQueries = 0;
}
protected:
void addRoot(NodeT *BB) { this->Roots.push_back(BB); }
DomTreeNodeBase<NodeT> *createChild(NodeT *BB, DomTreeNodeBase<NodeT> *IDom) {
return (DomTreeNodes[BB] = IDom->addChild(
std::make_unique<DomTreeNodeBase<NodeT>>(BB, IDom)))
.get();
}
DomTreeNodeBase<NodeT> *createNode(NodeT *BB) {
return (DomTreeNodes[BB] =
std::make_unique<DomTreeNodeBase<NodeT>>(BB, nullptr))
.get();
}
// NewBB is split and now it has one successor. Update dominator tree to
// reflect this change.
template <class N>
void Split(typename GraphTraits<N>::NodeRef NewBB) {
using GraphT = GraphTraits<N>;
using NodeRef = typename GraphT::NodeRef;
assert(llvm::hasSingleElement(children<N>(NewBB)) &&
"NewBB should have a single successor!");
NodeRef NewBBSucc = *GraphT::child_begin(NewBB);
SmallVector<NodeRef, 4> PredBlocks(inverse_children<N>(NewBB));
assert(!PredBlocks.empty() && "No predblocks?");
bool NewBBDominatesNewBBSucc = true;
for (auto *Pred : inverse_children<N>(NewBBSucc)) {
if (Pred != NewBB && !dominates(NewBBSucc, Pred) &&
isReachableFromEntry(Pred)) {
NewBBDominatesNewBBSucc = false;
break;
}
}
// Find NewBB's immediate dominator and create new dominator tree node for
// NewBB.
NodeT *NewBBIDom = nullptr;
unsigned i = 0;
for (i = 0; i < PredBlocks.size(); ++i)
if (isReachableFromEntry(PredBlocks[i])) {
NewBBIDom = PredBlocks[i];
break;
}
// It's possible that none of the predecessors of NewBB are reachable;
// in that case, NewBB itself is unreachable, so nothing needs to be
// changed.
if (!NewBBIDom) return;
for (i = i + 1; i < PredBlocks.size(); ++i) {
if (isReachableFromEntry(PredBlocks[i]))
NewBBIDom = findNearestCommonDominator(NewBBIDom, PredBlocks[i]);
}
// Create the new dominator tree node... and set the idom of NewBB.
DomTreeNodeBase<NodeT> *NewBBNode = addNewBlock(NewBB, NewBBIDom);
// If NewBB strictly dominates other blocks, then it is now the immediate
// dominator of NewBBSucc. Update the dominator tree as appropriate.
if (NewBBDominatesNewBBSucc) {
DomTreeNodeBase<NodeT> *NewBBSuccNode = getNode(NewBBSucc);
changeImmediateDominator(NewBBSuccNode, NewBBNode);
}
}
private:
bool dominatedBySlowTreeWalk(const DomTreeNodeBase<NodeT> *A,
const DomTreeNodeBase<NodeT> *B) const {
assert(A != B);
assert(isReachableFromEntry(B));
assert(isReachableFromEntry(A));
const unsigned ALevel = A->getLevel();
const DomTreeNodeBase<NodeT> *IDom;
// Don't walk nodes above A's subtree. When we reach A's level, we must
// either find A or be in some other subtree not dominated by A.
while ((IDom = B->getIDom()) != nullptr && IDom->getLevel() >= ALevel)
B = IDom; // Walk up the tree
return B == A;
}
/// Wipe this tree's state without releasing any resources.
///
/// This is essentially a post-move helper only. It leaves the object in an
/// assignable and destroyable state, but otherwise invalid.
void wipe() {
DomTreeNodes.clear();
RootNode = nullptr;
Parent = nullptr;
}
};
template <typename T>
using DomTreeBase = DominatorTreeBase<T, false>;
template <typename T>
using PostDomTreeBase = DominatorTreeBase<T, true>;
// These two functions are declared out of line as a workaround for building
// with old (< r147295) versions of clang because of pr11642.
template <typename NodeT, bool IsPostDom>
bool DominatorTreeBase<NodeT, IsPostDom>::dominates(const NodeT *A,
const NodeT *B) const {
if (A == B)
return true;
// Cast away the const qualifiers here. This is ok since
// this function doesn't actually return the values returned
// from getNode.
return dominates(getNode(const_cast<NodeT *>(A)),
getNode(const_cast<NodeT *>(B)));
}
template <typename NodeT, bool IsPostDom>
bool DominatorTreeBase<NodeT, IsPostDom>::properlyDominates(
const NodeT *A, const NodeT *B) const {
if (A == B)
return false;
// Cast away the const qualifiers here. This is ok since
// this function doesn't actually return the values returned
// from getNode.
return dominates(getNode(const_cast<NodeT *>(A)),
getNode(const_cast<NodeT *>(B)));
}
} // end namespace llvm
#endif // LLVM_SUPPORT_GENERICDOMTREE_H
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