[clangd] Cache FS stat() calls when building preamble.linaro-local/ci/tcwg-llvm-kernel-baseline-armv8l-release-stablelinaro-local/ci/tcwg-llvm-kernel-baseline-armv8l-release-nextlinaro-local/ci/tcwg-llvm-kernel-baseline-armv8l-release-ltslinaro-local/ci/tcwg-llvm-kernel-baseline-aarch64-release-nextlinaro-local/ci/llvm-kernel-armv8l-baselinelinaro-local/ci/llvm-kernel-aarch64-baseline

Summary:
The file stats can be reused when preamble is reused (e.g. code
completion). It's safe to assume that cached status is not outdated as we
assume preamble files to remain unchanged.

On real file system, this made code completion ~20% faster on a measured file
(with big preamble). The preamble build time doesn't change much.

Reviewers: sammccall, ilya-biryukov

Reviewed By: sammccall

Subscribers: mgorny, MaskRay, jkorous, arphaman, kadircet, cfe-commits

Differential Revision: https://reviews.llvm.org/D52419

1 files changed, 46 insertions, 0 deletions

diff --git a/clang-tools-extra/unittests/clangd/FSTests.cpp b/clang-tools-extra/unittests/clangd/FSTests.cpp
new file mode 100644
index 00000000000..3b028426016
--- /dev/null
+++ b/clang-tools-extra/unittests/clangd/FSTests.cpp
@@ -0,0 +1,46 @@
+//===-- FSTests.cpp - File system related tests -----------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "FS.h"
+#include "TestFS.h"
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+
+namespace clang {
+namespace clangd {
+namespace {
+
+TEST(FSTests, PreambleStatusCache) {
+  llvm::StringMap<std::string> Files;
+  Files["x"] = "";
+  Files["y"] = "";
+  auto FS = buildTestFS(Files);
+  FS->setCurrentWorkingDirectory(testRoot());
+
+  PreambleFileStatusCache StatCache;
+  auto ProduceFS = StatCache.getProducingFS(FS);
+  EXPECT_TRUE(ProduceFS->openFileForRead("x"));
+  EXPECT_TRUE(ProduceFS->status("y"));
+
+  EXPECT_TRUE(StatCache.lookup(testPath("x")).hasValue());
+  EXPECT_TRUE(StatCache.lookup(testPath("y")).hasValue());
+
+  vfs::Status S("fake", llvm::sys::fs::UniqueID(0, 0),
+                std::chrono::system_clock::now(), 0, 0, 1024,
+                llvm::sys::fs::file_type::regular_file, llvm::sys::fs::all_all);
+  StatCache.update(*FS, S);
+  auto ConsumeFS = StatCache.getConsumingFS(FS);
+  auto Cached = ConsumeFS->status(testPath("fake"));
+  EXPECT_TRUE(Cached);
+  EXPECT_EQ(Cached->getName(), S.getName());
+}
+
+} // namespace
+} // namespace clangd
+} // namespace clang