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//===- DeltaTree.cpp - B-Tree for Rewrite Delta tracking ------------------===//
// 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 implements the DeltaTree and related classes.
#include "clang/Rewrite/Core/DeltaTree.h"
#include "clang/Basic/LLVM.h"
#include "llvm/Support/Casting.h"
#include <cassert>
#include <cstring>
using namespace clang;
/// The DeltaTree class is a multiway search tree (BTree) structure with some
/// fancy features. B-Trees are generally more memory and cache efficient
/// than binary trees, because they store multiple keys/values in each node.
/// DeltaTree implements a key/value mapping from FileIndex to Delta, allowing
/// fast lookup by FileIndex. However, an added (important) bonus is that it
/// can also efficiently tell us the full accumulated delta for a specific
/// file offset as well, without traversing the whole tree.
/// The nodes of the tree are made up of instances of two classes:
/// DeltaTreeNode and DeltaTreeInteriorNode. The later subclasses the
/// former and adds children pointers. Each node knows the full delta of all
/// entries (recursively) contained inside of it, which allows us to get the
/// full delta implied by a whole subtree in constant time.
namespace {
/// SourceDelta - As code in the original input buffer is added and deleted,
/// SourceDelta records are used to keep track of how the input SourceLocation
/// object is mapped into the output buffer.
struct SourceDelta {
unsigned FileLoc;
int Delta;
static SourceDelta get(unsigned Loc, int D) {
SourceDelta Delta;
Delta.FileLoc = Loc;
Delta.Delta = D;
return Delta;
/// DeltaTreeNode - The common part of all nodes.
class DeltaTreeNode {
struct InsertResult {
DeltaTreeNode *LHS, *RHS;
SourceDelta Split;
friend class DeltaTreeInteriorNode;
/// WidthFactor - This controls the number of K/V slots held in the BTree:
/// how wide it is. Each level of the BTree is guaranteed to have at least
/// WidthFactor-1 K/V pairs (except the root) and may have at most
/// 2*WidthFactor-1 K/V pairs.
enum { WidthFactor = 8 };
/// Values - This tracks the SourceDelta's currently in this node.
SourceDelta Values[2*WidthFactor-1];
/// NumValuesUsed - This tracks the number of values this node currently
/// holds.
unsigned char NumValuesUsed = 0;
/// IsLeaf - This is true if this is a leaf of the btree. If false, this is
/// an interior node, and is actually an instance of DeltaTreeInteriorNode.
bool IsLeaf;
/// FullDelta - This is the full delta of all the values in this node and
/// all children nodes.
int FullDelta = 0;
DeltaTreeNode(bool isLeaf = true) : IsLeaf(isLeaf) {}
bool isLeaf() const { return IsLeaf; }
int getFullDelta() const { return FullDelta; }
bool isFull() const { return NumValuesUsed == 2*WidthFactor-1; }
unsigned getNumValuesUsed() const { return NumValuesUsed; }
const SourceDelta &getValue(unsigned i) const {
assert(i < NumValuesUsed && "Invalid value #");
return Values[i];
SourceDelta &getValue(unsigned i) {
assert(i < NumValuesUsed && "Invalid value #");
return Values[i];
/// DoInsertion - Do an insertion of the specified FileIndex/Delta pair into
/// this node. If insertion is easy, do it and return false. Otherwise,
/// split the node, populate InsertRes with info about the split, and return
/// true.
bool DoInsertion(unsigned FileIndex, int Delta, InsertResult *InsertRes);
void DoSplit(InsertResult &InsertRes);
/// RecomputeFullDeltaLocally - Recompute the FullDelta field by doing a
/// local walk over our contained deltas.
void RecomputeFullDeltaLocally();
void Destroy();
/// DeltaTreeInteriorNode - When isLeaf = false, a node has child pointers.
/// This class tracks them.
class DeltaTreeInteriorNode : public DeltaTreeNode {
friend class DeltaTreeNode;
DeltaTreeNode *Children[2*WidthFactor];
~DeltaTreeInteriorNode() {
for (unsigned i = 0, e = NumValuesUsed+1; i != e; ++i)
DeltaTreeInteriorNode() : DeltaTreeNode(false /*nonleaf*/) {}
DeltaTreeInteriorNode(const InsertResult &IR)
: DeltaTreeNode(false /*nonleaf*/) {
Children[0] = IR.LHS;
Children[1] = IR.RHS;
Values[0] = IR.Split;
FullDelta = IR.LHS->getFullDelta()+IR.RHS->getFullDelta()+IR.Split.Delta;
NumValuesUsed = 1;
const DeltaTreeNode *getChild(unsigned i) const {
assert(i < getNumValuesUsed()+1 && "Invalid child");
return Children[i];
DeltaTreeNode *getChild(unsigned i) {
assert(i < getNumValuesUsed()+1 && "Invalid child");
return Children[i];
static bool classof(const DeltaTreeNode *N) { return !N->isLeaf(); }
} // namespace
/// Destroy - A 'virtual' destructor.
void DeltaTreeNode::Destroy() {
if (isLeaf())
delete this;
delete cast<DeltaTreeInteriorNode>(this);
/// RecomputeFullDeltaLocally - Recompute the FullDelta field by doing a
/// local walk over our contained deltas.
void DeltaTreeNode::RecomputeFullDeltaLocally() {
int NewFullDelta = 0;
for (unsigned i = 0, e = getNumValuesUsed(); i != e; ++i)
NewFullDelta += Values[i].Delta;
if (auto *IN = dyn_cast<DeltaTreeInteriorNode>(this))
for (unsigned i = 0, e = getNumValuesUsed()+1; i != e; ++i)
NewFullDelta += IN->getChild(i)->getFullDelta();
FullDelta = NewFullDelta;
/// DoInsertion - Do an insertion of the specified FileIndex/Delta pair into
/// this node. If insertion is easy, do it and return false. Otherwise,
/// split the node, populate InsertRes with info about the split, and return
/// true.
bool DeltaTreeNode::DoInsertion(unsigned FileIndex, int Delta,
InsertResult *InsertRes) {
// Maintain full delta for this node.
FullDelta += Delta;
// Find the insertion point, the first delta whose index is >= FileIndex.
unsigned i = 0, e = getNumValuesUsed();
while (i != e && FileIndex > getValue(i).FileLoc)
// If we found an a record for exactly this file index, just merge this
// value into the pre-existing record and finish early.
if (i != e && getValue(i).FileLoc == FileIndex) {
// NOTE: Delta could drop to zero here. This means that the delta entry is
// useless and could be removed. Supporting erases is more complex than
// leaving an entry with Delta=0, so we just leave an entry with Delta=0 in
// the tree.
Values[i].Delta += Delta;
return false;
// Otherwise, we found an insertion point, and we know that the value at the
// specified index is > FileIndex. Handle the leaf case first.
if (isLeaf()) {
if (!isFull()) {
// For an insertion into a non-full leaf node, just insert the value in
// its sorted position. This requires moving later values over.
if (i != e)
memmove(&Values[i+1], &Values[i], sizeof(Values[0])*(e-i));
Values[i] = SourceDelta::get(FileIndex, Delta);
return false;
// Otherwise, if this is leaf is full, split the node at its median, insert
// the value into one of the children, and return the result.
assert(InsertRes && "No result location specified");
if (InsertRes->Split.FileLoc > FileIndex)
InsertRes->LHS->DoInsertion(FileIndex, Delta, nullptr /*can't fail*/);
InsertRes->RHS->DoInsertion(FileIndex, Delta, nullptr /*can't fail*/);
return true;
// Otherwise, this is an interior node. Send the request down the tree.
auto *IN = cast<DeltaTreeInteriorNode>(this);
if (!IN->Children[i]->DoInsertion(FileIndex, Delta, InsertRes))
return false; // If there was space in the child, just return.
// Okay, this split the subtree, producing a new value and two children to
// insert here. If this node is non-full, we can just insert it directly.
if (!isFull()) {
// Now that we have two nodes and a new element, insert the perclated value
// into ourself by moving all the later values/children down, then inserting
// the new one.
if (i != e)
memmove(&IN->Children[i+2], &IN->Children[i+1],
IN->Children[i] = InsertRes->LHS;
IN->Children[i+1] = InsertRes->RHS;
if (e != i)
memmove(&Values[i+1], &Values[i], (e-i)*sizeof(Values[0]));
Values[i] = InsertRes->Split;
return false;
// Finally, if this interior node was full and a node is percolated up, split
// ourself and return that up the chain. Start by saving all our info to
// avoid having the split clobber it.
IN->Children[i] = InsertRes->LHS;
DeltaTreeNode *SubRHS = InsertRes->RHS;
SourceDelta SubSplit = InsertRes->Split;
// Do the split.
// Figure out where to insert SubRHS/NewSplit.
DeltaTreeInteriorNode *InsertSide;
if (SubSplit.FileLoc < InsertRes->Split.FileLoc)
InsertSide = cast<DeltaTreeInteriorNode>(InsertRes->LHS);
InsertSide = cast<DeltaTreeInteriorNode>(InsertRes->RHS);
// We now have a non-empty interior node 'InsertSide' to insert
// SubRHS/SubSplit into. Find out where to insert SubSplit.
// Find the insertion point, the first delta whose index is >SubSplit.FileLoc.
i = 0; e = InsertSide->getNumValuesUsed();
while (i != e && SubSplit.FileLoc > InsertSide->getValue(i).FileLoc)
// Now we know that i is the place to insert the split value into. Insert it
// and the child right after it.
if (i != e)
memmove(&InsertSide->Children[i+2], &InsertSide->Children[i+1],
InsertSide->Children[i+1] = SubRHS;
if (e != i)
memmove(&InsertSide->Values[i+1], &InsertSide->Values[i],
InsertSide->Values[i] = SubSplit;
InsertSide->FullDelta += SubSplit.Delta + SubRHS->getFullDelta();
return true;
/// DoSplit - Split the currently full node (which has 2*WidthFactor-1 values)
/// into two subtrees each with "WidthFactor-1" values and a pivot value.
/// Return the pieces in InsertRes.
void DeltaTreeNode::DoSplit(InsertResult &InsertRes) {
assert(isFull() && "Why split a non-full node?");
// Since this node is full, it contains 2*WidthFactor-1 values. We move
// the first 'WidthFactor-1' values to the LHS child (which we leave in this
// node), propagate one value up, and move the last 'WidthFactor-1' values
// into the RHS child.
// Create the new child node.
DeltaTreeNode *NewNode;
if (auto *IN = dyn_cast<DeltaTreeInteriorNode>(this)) {
// If this is an interior node, also move over 'WidthFactor' children
// into the new node.
DeltaTreeInteriorNode *New = new DeltaTreeInteriorNode();
memcpy(&New->Children[0], &IN->Children[WidthFactor],
NewNode = New;
} else {
// Just create the new leaf node.
NewNode = new DeltaTreeNode();
// Move over the last 'WidthFactor-1' values from here to NewNode.
memcpy(&NewNode->Values[0], &Values[WidthFactor],
// Decrease the number of values in the two nodes.
NewNode->NumValuesUsed = NumValuesUsed = WidthFactor-1;
// Recompute the two nodes' full delta.
InsertRes.LHS = this;
InsertRes.RHS = NewNode;
InsertRes.Split = Values[WidthFactor-1];
// DeltaTree Implementation
//#define VERIFY_TREE
/// VerifyTree - Walk the btree performing assertions on various properties to
/// verify consistency. This is useful for debugging new changes to the tree.
static void VerifyTree(const DeltaTreeNode *N) {
const auto *IN = dyn_cast<DeltaTreeInteriorNode>(N);
if (IN == 0) {
// Verify leaves, just ensure that FullDelta matches up and the elements
// are in proper order.
int FullDelta = 0;
for (unsigned i = 0, e = N->getNumValuesUsed(); i != e; ++i) {
if (i)
assert(N->getValue(i-1).FileLoc < N->getValue(i).FileLoc);
FullDelta += N->getValue(i).Delta;
assert(FullDelta == N->getFullDelta());
// Verify interior nodes: Ensure that FullDelta matches up and the
// elements are in proper order and the children are in proper order.
int FullDelta = 0;
for (unsigned i = 0, e = IN->getNumValuesUsed(); i != e; ++i) {
const SourceDelta &IVal = N->getValue(i);
const DeltaTreeNode *IChild = IN->getChild(i);
if (i)
assert(IN->getValue(i-1).FileLoc < IVal.FileLoc);
FullDelta += IVal.Delta;
FullDelta += IChild->getFullDelta();
// The largest value in child #i should be smaller than FileLoc.
assert(IChild->getValue(IChild->getNumValuesUsed()-1).FileLoc <
// The smallest value in child #i+1 should be larger than FileLoc.
assert(IN->getChild(i+1)->getValue(0).FileLoc > IVal.FileLoc);
FullDelta += IN->getChild(IN->getNumValuesUsed())->getFullDelta();
assert(FullDelta == N->getFullDelta());
#endif // VERIFY_TREE
static DeltaTreeNode *getRoot(void *Root) {
return (DeltaTreeNode*)Root;
DeltaTree::DeltaTree() {
Root = new DeltaTreeNode();
DeltaTree::DeltaTree(const DeltaTree &RHS) {
// Currently we only support copying when the RHS is empty.
assert(getRoot(RHS.Root)->getNumValuesUsed() == 0 &&
"Can only copy empty tree");
Root = new DeltaTreeNode();
DeltaTree::~DeltaTree() {
/// getDeltaAt - Return the accumulated delta at the specified file offset.
/// This includes all insertions or delections that occurred *before* the
/// specified file index.
int DeltaTree::getDeltaAt(unsigned FileIndex) const {
const DeltaTreeNode *Node = getRoot(Root);
int Result = 0;
// Walk down the tree.
while (true) {
// For all nodes, include any local deltas before the specified file
// index by summing them up directly. Keep track of how many were
// included.
unsigned NumValsGreater = 0;
for (unsigned e = Node->getNumValuesUsed(); NumValsGreater != e;
++NumValsGreater) {
const SourceDelta &Val = Node->getValue(NumValsGreater);
if (Val.FileLoc >= FileIndex)
Result += Val.Delta;
// If we have an interior node, include information about children and
// recurse. Otherwise, if we have a leaf, we're done.
const auto *IN = dyn_cast<DeltaTreeInteriorNode>(Node);
if (!IN) return Result;
// Include any children to the left of the values we skipped, all of
// their deltas should be included as well.
for (unsigned i = 0; i != NumValsGreater; ++i)
Result += IN->getChild(i)->getFullDelta();
// If we found exactly the value we were looking for, break off the
// search early. There is no need to search the RHS of the value for
// partial results.
if (NumValsGreater != Node->getNumValuesUsed() &&
Node->getValue(NumValsGreater).FileLoc == FileIndex)
return Result+IN->getChild(NumValsGreater)->getFullDelta();
// Otherwise, traverse down the tree. The selected subtree may be
// partially included in the range.
Node = IN->getChild(NumValsGreater);
/// AddDelta - When a change is made that shifts around the text buffer,
/// this method is used to record that info. It inserts a delta of 'Delta'
/// into the current DeltaTree at offset FileIndex.
void DeltaTree::AddDelta(unsigned FileIndex, int Delta) {
assert(Delta && "Adding a noop?");
DeltaTreeNode *MyRoot = getRoot(Root);
DeltaTreeNode::InsertResult InsertRes;
if (MyRoot->DoInsertion(FileIndex, Delta, &InsertRes)) {
Root = MyRoot = new DeltaTreeInteriorNode(InsertRes);