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//===- CFGDiff.h - Define a CFG snapshot. -----------------------*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file defines specializations of GraphTraits that allows generic
// algorithms to see a different snapshot of a CFG.
#include "llvm/ADT/GraphTraits.h"
#include "llvm/ADT/iterator.h"
#include "llvm/ADT/iterator_range.h"
#include "llvm/Support/CFGUpdate.h"
#include "llvm/Support/type_traits.h"
#include <cassert>
#include <cstddef>
#include <iterator>
// Two booleans are used to define orders in graphs:
// InverseGraph defines when we need to reverse the whole graph and is as such
// also equivalent to applying updates in reverse.
// InverseEdge defines whether we want to change the edges direction. E.g., for
// a non-inversed graph, the children are naturally the successors when
// InverseEdge is false and the predecessors when InverseEdge is true.
namespace llvm {
namespace detail {
template <typename Range>
auto reverse_if_helper(Range &&R, std::integral_constant<bool, false>) {
return std::forward<Range>(R);
template <typename Range>
auto reverse_if_helper(Range &&R, std::integral_constant<bool, true>) {
return llvm::reverse(std::forward<Range>(R));
template <bool B, typename Range> auto reverse_if(Range &&R) {
return reverse_if_helper(std::forward<Range>(R),
std::integral_constant<bool, B>{});
} // namespace detail
// GraphDiff defines a CFG snapshot: given a set of Update<NodePtr>, provides
// a getChildren method to get a Node's children based on the additional updates
// in the snapshot. The current diff treats the CFG as a graph rather than a
// multigraph. Added edges are pruned to be unique, and deleted edges will
// remove all existing edges between two blocks.
template <typename NodePtr, bool InverseGraph = false> class GraphDiff {
struct DeletesInserts {
SmallVector<NodePtr, 2> DI[2];
using UpdateMapType = SmallDenseMap<NodePtr, DeletesInserts>;
UpdateMapType Succ;
UpdateMapType Pred;
// By default, it is assumed that, given a CFG and a set of updates, we wish
// to apply these updates as given. If UpdatedAreReverseApplied is set, the
// updates will be applied in reverse: deleted edges are considered re-added
// and inserted edges are considered deleted when returning children.
bool UpdatedAreReverseApplied;
// Keep the list of legalized updates for a deterministic order of updates
// when using a GraphDiff for incremental updates in the DominatorTree.
// The list is kept in reverse to allow popping from end.
SmallVector<cfg::Update<NodePtr>, 4> LegalizedUpdates;
void printMap(raw_ostream &OS, const UpdateMapType &M) const {
StringRef DIText[2] = {"Delete", "Insert"};
for (auto Pair : M) {
for (unsigned IsInsert = 0; IsInsert <= 1; ++IsInsert) {
OS << DIText[IsInsert] << " edges: \n";
for (auto Child : Pair.second.DI[IsInsert]) {
OS << "(";
Pair.first->printAsOperand(OS, false);
OS << ", ";
Child->printAsOperand(OS, false);
OS << ") ";
OS << "\n";
GraphDiff() : UpdatedAreReverseApplied(false) {}
GraphDiff(ArrayRef<cfg::Update<NodePtr>> Updates,
bool ReverseApplyUpdates = false) {
cfg::LegalizeUpdates<NodePtr>(Updates, LegalizedUpdates, InverseGraph);
for (auto U : LegalizedUpdates) {
unsigned IsInsert =
(U.getKind() == cfg::UpdateKind::Insert) == !ReverseApplyUpdates;
UpdatedAreReverseApplied = ReverseApplyUpdates;
auto getLegalizedUpdates() const {
return make_range(LegalizedUpdates.begin(), LegalizedUpdates.end());
unsigned getNumLegalizedUpdates() const { return LegalizedUpdates.size(); }
cfg::Update<NodePtr> popUpdateForIncrementalUpdates() {
assert(!LegalizedUpdates.empty() && "No updates to apply!");
auto U = LegalizedUpdates.pop_back_val();
unsigned IsInsert =
(U.getKind() == cfg::UpdateKind::Insert) == !UpdatedAreReverseApplied;
auto &SuccDIList = Succ[U.getFrom()];
auto &SuccList = SuccDIList.DI[IsInsert];
assert(SuccList.back() == U.getTo());
if (SuccList.empty() && SuccDIList.DI[!IsInsert].empty())
auto &PredDIList = Pred[U.getTo()];
auto &PredList = PredDIList.DI[IsInsert];
assert(PredList.back() == U.getFrom());
if (PredList.empty() && PredDIList.DI[!IsInsert].empty())
return U;
using VectRet = SmallVector<NodePtr, 8>;
template <bool InverseEdge> VectRet getChildren(NodePtr N) const {
using DirectedNodeT =
std::conditional_t<InverseEdge, Inverse<NodePtr>, NodePtr>;
auto R = children<DirectedNodeT>(N);
VectRet Res = VectRet(detail::reverse_if<!InverseEdge>(R));
// Remove nullptr children for clang.
llvm::erase_value(Res, nullptr);
auto &Children = (InverseEdge != InverseGraph) ? Pred : Succ;
auto It = Children.find(N);
if (It == Children.end())
return Res;
// Remove children present in the CFG but not in the snapshot.
for (auto *Child : It->second.DI[0])
llvm::erase_value(Res, Child);
// Add children present in the snapshot for not in the real CFG.
auto &AddedChildren = It->second.DI[1];
llvm::append_range(Res, AddedChildren);
return Res;
void print(raw_ostream &OS) const {
OS << "===== GraphDiff: CFG edge changes to create a CFG snapshot. \n"
"===== (Note: notion of children/inverse_children depends on "
"the direction of edges and the graph.)\n";
OS << "Children to delete/insert:\n\t";
printMap(OS, Succ);
OS << "Inverse_children to delete/insert:\n\t";
printMap(OS, Pred);
OS << "\n";
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
LLVM_DUMP_METHOD void dump() const { print(dbgs()); }
} // end namespace llvm