kbobyrev created this revision.
kbobyrev added reviewers: ioeric, sammccall, ilya-biryukov.
kbobyrev added a project: clang-tools-extra.
Herald added subscribers: kadircet, arphaman, jkorous, MaskRay.
Use min-heap invariant for OR iterator's children. This helps to avoid
iterating through all children in `reachedEnd()`, `peek()` and allows
early-stopping in `consume()` and `advance()`.
This optimization results in ~8-9% of performance boost on benchmark with ~4300
real queries to LLVM static index.
benchmark's `compare.py` output:
benchmark Time CPU Time Old Time New
CPU Old CPU New
---------------------------------------------------------------------------------------------------------
DexQueries -0.0706 -0.0706 4719149241 4385985920
4719100956 4385946455
https://reviews.llvm.org/D52083
Files:
clang-tools-extra/clangd/index/dex/Iterator.cpp
clang-tools-extra/unittests/clangd/DexTests.cpp
Index: clang-tools-extra/unittests/clangd/DexTests.cpp
===================================================================
--- clang-tools-extra/unittests/clangd/DexTests.cpp
+++ clang-tools-extra/unittests/clangd/DexTests.cpp
@@ -255,20 +255,20 @@
}
TEST(DexIterators, StringRepresentation) {
- const PostingList L0({4, 7, 8, 20, 42, 100});
+ const PostingList L0({0, 1, 8, 20, 42, 100});
const PostingList L1({1, 3, 5, 8, 9});
const PostingList L2({1, 5, 7, 9});
- const PostingList L3({0, 5});
+ const PostingList L3({0, 1});
const PostingList L4({0, 1, 5});
const PostingList L5({});
- EXPECT_EQ(llvm::to_string(*(L0.iterator())), "[4]");
+ EXPECT_EQ(llvm::to_string(*(L0.iterator())), "[0]");
- auto Nested =
- createAnd(createAnd(L1.iterator(), L2.iterator()),
- createOr(L3.iterator(), L4.iterator(), L5.iterator()));
+ auto Nested = createAnd(
+ createAnd(L1.iterator(), L2.iterator(), L4.iterator(), L0.iterator()),
+ createOr(L3.iterator(), L5.iterator()));
- EXPECT_EQ(llvm::to_string(*Nested), "(& (| [5] [1] [END]) (& [1] [1]))");
+ EXPECT_EQ(llvm::to_string(*Nested), "(& (| [1] [END]) (& [1] [1] [1] [1]))");
}
TEST(DexIterators, Limit) {
Index: clang-tools-extra/clangd/index/dex/Iterator.cpp
===================================================================
--- clang-tools-extra/clangd/index/dex/Iterator.cpp
+++ clang-tools-extra/clangd/index/dex/Iterator.cpp
@@ -125,69 +125,80 @@
bool ReachedEnd = false;
};
+// Return LHS > RHS.
+auto Compare = [](const std::unique_ptr<Iterator> &LHS,
+ const std::unique_ptr<Iterator> &RHS) {
+ if (LHS->reachedEnd())
+ return true;
+ if (RHS->reachedEnd())
+ return false;
+ return LHS->peek() > RHS->peek();
+};
+
/// Implements Iterator over the union of other iterators.
///
/// OrIterator iterates through all items which can be pointed to by at least
/// one child. To preserve the sorted order, this iterator always advances the
/// child with smallest Child->peek() value. OrIterator becomes exhausted as
/// soon as all of its children are exhausted.
+///
+/// Invariant: Children are always stored in a min-heap which puts iterators
+/// with the smallest DocID to the front.
class OrIterator : public Iterator {
public:
explicit OrIterator(std::vector<std::unique_ptr<Iterator>> AllChildren)
: Children(std::move(AllChildren)) {
assert(!Children.empty() && "OR iterator should have at least one child.");
+ // Initialize invariant.
+ std::make_heap(begin(Children), end(Children), Compare);
}
- /// Returns true if all children are exhausted.
- bool reachedEnd() const override {
- return std::all_of(begin(Children), end(Children),
- [](const std::unique_ptr<Iterator> &Child) {
- return Child->reachedEnd();
- });
- }
+ /// Returns true if all children are exhausted. Due to the invariant, if the
+ /// first child has reached the end, all of them have reached the end.
+ bool reachedEnd() const override { return Children.front()->reachedEnd(); }
/// Moves each child pointing to the smallest DocID to the next item.
void advance() override {
assert(!reachedEnd() && "OR iterator can't advance() at the end.");
const auto SmallestID = peek();
- for (const auto &Child : Children)
- if (!Child->reachedEnd() && Child->peek() == SmallestID)
- Child->advance();
+ // The first element always contains Child with the smallest DocID.
+ while (!Children.front()->reachedEnd() &&
+ Children.front()->peek() == SmallestID) {
+ Children.front()->advance();
+ // Restore invariant.
+ std::pop_heap(begin(Children), end(Children), Compare);
+ std::push_heap(begin(Children), end(Children), Compare);
+ }
}
/// Advances each child to the next existing element with DocumentID >= ID.
void advanceTo(DocID ID) override {
assert(!reachedEnd() && "OR iterator can't advanceTo() at the end.");
for (const auto &Child : Children)
- if (!Child->reachedEnd())
- Child->advanceTo(ID);
+ Child->advanceTo(ID);
+ // Restore invariant.
+ std::make_heap(begin(Children), end(Children), Compare);
}
/// Returns the element under cursor of the child with smallest Child->peek()
/// value.
DocID peek() const override {
assert(!reachedEnd() && "OR iterator can't peek() at the end.");
- DocID Result = std::numeric_limits<DocID>::max();
-
- for (const auto &Child : Children)
- if (!Child->reachedEnd())
- Result = std::min(Result, Child->peek());
-
- return Result;
+ return Children.front()->peek();
}
// Returns the maximum boosting score among all Children when iterator is not
// exhausted and points to the given ID, DEFAULT_BOOST_SCORE otherwise.
float consume() override {
assert(!reachedEnd() && "OR iterator can't consume() at the end.");
const DocID ID = peek();
- return std::accumulate(
- begin(Children), end(Children), DEFAULT_BOOST_SCORE,
- [&](float Boost, const std::unique_ptr<Iterator> &Child) {
- return (!Child->reachedEnd() && Child->peek() == ID)
- ? std::max(Boost, Child->consume())
- : Boost;
- });
+ float Boost = DEFAULT_BOOST_SCORE;
+ for (const auto &Child : Children) {
+ if (Child->peek() != ID)
+ break;
+ Boost = std::max(Child->consume(), Boost);
+ }
+ return Boost;
}
size_t estimateSize() const override {
@@ -210,7 +221,6 @@
return OS;
}
- // FIXME(kbobyrev): Would storing Children in min-heap be faster?
std::vector<std::unique_ptr<Iterator>> Children;
};
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