[clangd] Use Builder for symbol slabs, and use sorted-vector for storage

Summary:
This improves a few things:
 - the insert -> freeze -> read sequence is now enforced/communicated by the
   type system
 - SymbolSlab::const_iterator iterates over symbols, not over id-symbol pairs
 - we avoid permanently storing a second copy of the IDs, and the
   string map's hashtable

The slab size is now down to 21.8MB for the LLVM project.
Of this only 2.7MB is strings, the rest is #symbols * `sizeof(Symbol)`.
`sizeof(Symbol)` is currently 96, which seems too big - I think
SymbolInfo isn't efficiently packed. That's a topic for another patch!

Also added simple API to see the memory usage/#symbols of a slab, since
it seems likely we will continue to care about this.

Reviewers: ilya-biryukov

Subscribers: klimek, mgrang, cfe-commits

Differential Revision: https://reviews.llvm.org/D41506

llvm-svn: 321412

1 files changed, 29 insertions, 11 deletions

diff --git a/clang-tools-extra/unittests/clangd/IndexTests.cpp b/clang-tools-extra/unittests/clangd/IndexTests.cpp
index 0a4f31a7f1b..fac2895ec63 100644
--- a/clang-tools-extra/unittests/clangd/IndexTests.cpp
+++ b/clang-tools-extra/unittests/clangd/IndexTests.cpp
@@ -13,10 +13,10 @@
 #include "gtest/gtest.h"
 
 using testing::UnorderedElementsAre;
+using testing::Pointee;
 
 namespace clang {
 namespace clangd {
-
 namespace {
 
 Symbol symbol(llvm::StringRef QName) {
@@ -33,6 +33,24 @@ Symbol symbol(llvm::StringRef QName) {
   return Sym;
 }
 
+MATCHER_P(Named, N, "") { return arg.Name == N; }
+
+TEST(SymbolSlab, FindAndIterate) {
+  SymbolSlab::Builder B;
+  B.insert(symbol("Z"));
+  B.insert(symbol("Y"));
+  B.insert(symbol("X"));
+  EXPECT_EQ(nullptr, B.find(SymbolID("W")));
+  for (const char *Sym : {"X", "Y", "Z"})
+    EXPECT_THAT(B.find(SymbolID(Sym)), Pointee(Named(Sym)));
+
+  SymbolSlab S = std::move(B).build();
+  EXPECT_THAT(S, UnorderedElementsAre(Named("X"), Named("Y"), Named("Z")));
+  EXPECT_EQ(S.end(), S.find(SymbolID("W")));
+  for (const char *Sym : {"X", "Y", "Z"})
+    EXPECT_THAT(*S.find(SymbolID(Sym)), Named(Sym));
+}
+
 struct SlabAndPointers {
   SymbolSlab Slab;
   std::vector<const Symbol *> Pointers;
@@ -45,18 +63,18 @@ struct SlabAndPointers {
 std::shared_ptr<std::vector<const Symbol *>>
 generateSymbols(std::vector<std::string> QualifiedNames,
                 std::weak_ptr<SlabAndPointers> *WeakSymbols = nullptr) {
-  auto Slab = std::make_shared<SlabAndPointers>();
-  if (WeakSymbols)
-    *WeakSymbols = Slab;
-
+  SymbolSlab::Builder Slab;
   for (llvm::StringRef QName : QualifiedNames)
-    Slab->Slab.insert(symbol(QName));
-
-  for (const auto &Sym : Slab->Slab)
-    Slab->Pointers.push_back(&Sym.second);
+    Slab.insert(symbol(QName));
 
-  auto *Pointers = &Slab->Pointers;
-  return {std::move(Slab), Pointers};
+  auto Storage = std::make_shared<SlabAndPointers>();
+  Storage->Slab = std::move(Slab).build();
+  for (const auto &Sym : Storage->Slab)
+    Storage->Pointers.push_back(&Sym);
+  if (WeakSymbols)
+    *WeakSymbols = Storage;
+  auto *Pointers = &Storage->Pointers;
+  return {std::move(Storage), Pointers};
 }
 
 // Create a slab of symbols with IDs and names [Begin, End], otherwise identical