[ELF] Use union-find set and doubly linked list in Call-Chain Clustering (C³) heuristic
Before, SecToClusters[*] was used to track the belonged cluster.
During a merge (From -> Into), every element of From has to be updated.
Use a union-find set to speed up this use case.
Also, replace `std::vector<int> Sections;` with a doubly-linked
pointers: int Next, Prev;
Reviewed By: Bigcheese
Differential Revision: https://reviews.llvm.org/D46228
git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@373708 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/ELF/CallGraphSort.cpp b/ELF/CallGraphSort.cpp
index 12f89e4..459aa3c 100644
--- a/ELF/CallGraphSort.cpp
+++ b/ELF/CallGraphSort.cpp
@@ -45,6 +45,8 @@
#include "SymbolTable.h"
#include "Symbols.h"
+#include <numeric>
+
using namespace llvm;
using namespace lld;
using namespace lld::elf;
@@ -56,7 +58,7 @@
};
struct Cluster {
- Cluster(int sec, size_t s) : sections{sec}, size(s) {}
+ Cluster(int sec, size_t s) : next(sec), prev(sec), size(s) {}
double getDensity() const {
if (size == 0)
@@ -64,7 +66,8 @@
return double(weight) / double(size);
}
- std::vector<int> sections;
+ int next;
+ int prev;
size_t size = 0;
uint64_t weight = 0;
uint64_t initialWeight = 0;
@@ -80,8 +83,6 @@
private:
std::vector<Cluster> clusters;
std::vector<const InputSectionBase *> sections;
-
- void groupClusters();
};
// Maximum ammount the combined cluster density can be worse than the original
@@ -103,7 +104,7 @@
DenseMap<const InputSectionBase *, int> secToCluster;
auto getOrCreateNode = [&](const InputSectionBase *isec) -> int {
- auto res = secToCluster.insert(std::make_pair(isec, clusters.size()));
+ auto res = secToCluster.try_emplace(isec, clusters.size());
if (res.second) {
sections.push_back(isec);
clusters.emplace_back(clusters.size(), isec->getSize());
@@ -151,79 +152,84 @@
return newDensity < a.getDensity() / MAX_DENSITY_DEGRADATION;
}
-static void mergeClusters(Cluster &into, Cluster &from) {
- into.sections.insert(into.sections.end(), from.sections.begin(),
- from.sections.end());
+// Find the leader of V's belonged cluster (represented as an equivalence
+// class). We apply union-find path-halving technique (simple to implement) in
+// the meantime as it decreases depths and the time complexity.
+static int getLeader(std::vector<int> &leaders, int v) {
+ while (leaders[v] != v) {
+ leaders[v] = leaders[leaders[v]];
+ v = leaders[v];
+ }
+ return v;
+}
+
+static void mergeClusters(std::vector<Cluster> &cs, Cluster &into, int intoIdx,
+ Cluster &from, int fromIdx) {
+ int tail1 = into.prev, tail2 = from.prev;
+ into.prev = tail2;
+ cs[tail2].next = intoIdx;
+ from.prev = tail1;
+ cs[tail1].next = fromIdx;
into.size += from.size;
into.weight += from.weight;
- from.sections.clear();
from.size = 0;
from.weight = 0;
}
// Group InputSections into clusters using the Call-Chain Clustering heuristic
// then sort the clusters by density.
-void CallGraphSort::groupClusters() {
- std::vector<int> sortedSecs(clusters.size());
- std::vector<Cluster *> secToCluster(clusters.size());
+DenseMap<const InputSectionBase *, int> CallGraphSort::run() {
+ std::vector<int> sorted(clusters.size());
+ std::vector<int> leaders(clusters.size());
- for (size_t i = 0; i < clusters.size(); ++i) {
- sortedSecs[i] = i;
- secToCluster[i] = &clusters[i];
- }
-
- llvm::stable_sort(sortedSecs, [&](int a, int b) {
+ std::iota(leaders.begin(), leaders.end(), 0);
+ std::iota(sorted.begin(), sorted.end(), 0);
+ llvm::stable_sort(sorted, [&](int a, int b) {
return clusters[a].getDensity() > clusters[b].getDensity();
});
- for (int si : sortedSecs) {
- // clusters[si] is the same as secToClusters[si] here because it has not
- // been merged into another cluster yet.
- Cluster &c = clusters[si];
+ for (int l : sorted) {
+ // The cluster index is the same as the index of its leader here because
+ // clusters[L] has not been merged into another cluster yet.
+ Cluster &c = clusters[l];
// Don't consider merging if the edge is unlikely.
if (c.bestPred.from == -1 || c.bestPred.weight * 10 <= c.initialWeight)
continue;
- Cluster *predC = secToCluster[c.bestPred.from];
- if (predC == &c)
+ int predL = getLeader(leaders, c.bestPred.from);
+ if (l == predL)
continue;
+ Cluster *predC = &clusters[predL];
if (c.size + predC->size > MAX_CLUSTER_SIZE)
continue;
if (isNewDensityBad(*predC, c))
continue;
- // NOTE: Consider using a disjoint-set to track section -> cluster mapping
- // if this is ever slow.
- for (int si : c.sections)
- secToCluster[si] = predC;
-
- mergeClusters(*predC, c);
+ leaders[l] = predL;
+ mergeClusters(clusters, *predC, predL, c, l);
}
- // Remove empty or dead nodes. Invalidates all cluster indices.
- llvm::erase_if(clusters, [](const Cluster &c) {
- return c.size == 0 || c.sections.empty();
+ // Sort remaining non-empty clusters by density.
+ sorted.clear();
+ for (int i = 0, e = (int)clusters.size(); i != e; ++i)
+ if (clusters[i].size > 0)
+ sorted.push_back(i);
+ llvm::stable_sort(sorted, [&](int a, int b) {
+ return clusters[a].getDensity() > clusters[b].getDensity();
});
- // Sort by density.
- llvm::stable_sort(clusters, [](const Cluster &a, const Cluster &b) {
- return a.getDensity() > b.getDensity();
- });
-}
-
-DenseMap<const InputSectionBase *, int> CallGraphSort::run() {
- groupClusters();
-
- // Generate order.
DenseMap<const InputSectionBase *, int> orderMap;
- ssize_t curOrder = 1;
-
- for (const Cluster &c : clusters)
- for (int secIndex : c.sections)
- orderMap[sections[secIndex]] = curOrder++;
+ int curOrder = 1;
+ for (int leader : sorted)
+ for (int i = leader;;) {
+ orderMap[sections[i]] = curOrder++;
+ i = clusters[i].next;
+ if (i == leader)
+ break;
+ }
if (!config->printSymbolOrder.empty()) {
std::error_code ec;
@@ -235,15 +241,19 @@
// Print the symbols ordered by C3, in the order of increasing curOrder
// Instead of sorting all the orderMap, just repeat the loops above.
- for (const Cluster &c : clusters)
- for (int secIndex : c.sections)
+ for (int leader : sorted)
+ for (int i = leader;;) {
// Search all the symbols in the file of the section
// and find out a Defined symbol with name that is within the section.
- for (Symbol *sym: sections[secIndex]->file->getSymbols())
+ for (Symbol *sym : sections[i]->file->getSymbols())
if (!sym->isSection()) // Filter out section-type symbols here.
if (auto *d = dyn_cast<Defined>(sym))
- if (sections[secIndex] == d->section)
+ if (sections[i] == d->section)
os << sym->getName() << "\n";
+ i = clusters[i].next;
+ if (i == leader)
+ break;
+ }
}
return orderMap;
