diff --git a/lld/ELF/CallGraphSort.cpp b/lld/ELF/CallGraphSort.cpp index 12f89e4f5d34..459aa3c01b5c 100644 --- a/lld/ELF/CallGraphSort.cpp +++ b/lld/ELF/CallGraphSort.cpp @@ -45,6 +45,8 @@ #include "SymbolTable.h" #include "Symbols.h" +#include + using namespace llvm; using namespace lld; using namespace lld::elf; @@ -56,7 +58,7 @@ struct Edge { }; 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 @@ struct Cluster { return double(weight) / double(size); } - std::vector sections; + int next; + int prev; size_t size = 0; uint64_t weight = 0; uint64_t initialWeight = 0; @@ -80,8 +83,6 @@ public: private: std::vector clusters; std::vector sections; - - void groupClusters(); }; // Maximum ammount the combined cluster density can be worse than the original @@ -103,7 +104,7 @@ CallGraphSort::CallGraphSort() { DenseMap 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 @@ static bool isNewDensityBad(Cluster &a, Cluster &b) { 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 &leaders, int v) { + while (leaders[v] != v) { + leaders[v] = leaders[leaders[v]]; + v = leaders[v]; + } + return v; +} + +static void mergeClusters(std::vector &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 sortedSecs(clusters.size()); - std::vector secToCluster(clusters.size()); +DenseMap CallGraphSort::run() { + std::vector sorted(clusters.size()); + std::vector 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 CallGraphSort::run() { - groupClusters(); - - // Generate order. DenseMap 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 @@ DenseMap CallGraphSort::run() { // 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(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;