[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 It's safe to assume that cached status is not outdated as we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, 17 insertions, 9 deletions

diff --git a/clang-tools-extra/clangd/ClangdUnit.cpp b/clang-tools-extra/clangd/ClangdUnit.cpp
index 6c184ff06b0..2ad6dc69cc8 100644
--- a/clang-tools-extra/clangd/ClangdUnit.cpp
+++ b/clang-tools-extra/clangd/ClangdUnit.cpp
@@ -246,9 +246,10 @@ const IncludeStructure &ParsedAST::getIncludeStructure() const {
 }
 
 PreambleData::PreambleData(PrecompiledPreamble Preamble,
-                           std::vector<Diag> Diags, IncludeStructure Includes)
+                           std::vector<Diag> Diags, IncludeStructure Includes,
+                           std::unique_ptr<PreambleFileStatusCache> StatCache)
     : Preamble(std::move(Preamble)), Diags(std::move(Diags)),
-      Includes(std::move(Includes)) {}
+      Includes(std::move(Includes)), StatCache(std::move(StatCache)) {}
 
 ParsedAST::ParsedAST(std::shared_ptr<const PreambleData> Preamble,
                      std::unique_ptr<CompilerInstance> Clang,
@@ -334,9 +335,12 @@ std::shared_ptr<const PreambleData> clangd::buildPreamble(
     // We proceed anyway, our lit-tests rely on results for non-existing working
     // dirs.
   }
+
+  auto StatCache = llvm::make_unique<PreambleFileStatusCache>();
   auto BuiltPreamble = PrecompiledPreamble::Build(
-      CI, ContentsBuffer.get(), Bounds, *PreambleDiagsEngine, Inputs.FS, PCHs,
-      StoreInMemory, SerializedDeclsCollector);
+      CI, ContentsBuffer.get(), Bounds, *PreambleDiagsEngine,
+      StatCache->getProducingFS(Inputs.FS), PCHs, StoreInMemory,
+      SerializedDeclsCollector);
 
   // When building the AST for the main file, we do want the function
   // bodies.
@@ -347,7 +351,7 @@ std::shared_ptr<const PreambleData> clangd::buildPreamble(
          FileName);
     return std::make_shared<PreambleData>(
         std::move(*BuiltPreamble), PreambleDiagnostics.take(),
-        SerializedDeclsCollector.takeIncludes());
+        SerializedDeclsCollector.takeIncludes(), std::move(StatCache));
   } else {
     elog("Could not build a preamble for file {0}", FileName);
     return nullptr;
@@ -361,15 +365,19 @@ llvm::Optional<ParsedAST> clangd::buildAST(
   trace::Span Tracer("BuildAST");
   SPAN_ATTACH(Tracer, "File", FileName);
 
-  if (Inputs.FS->setCurrentWorkingDirectory(Inputs.CompileCommand.Directory)) {
+  auto VFS = Inputs.FS;
+  if (Preamble && Preamble->StatCache)
+    VFS = Preamble->StatCache->getConsumingFS(std::move(VFS));
+  if (VFS->setCurrentWorkingDirectory(Inputs.CompileCommand.Directory)) {
     log("Couldn't set working directory when building the preamble.");
     // We proceed anyway, our lit-tests rely on results for non-existing working
     // dirs.
   }
 
-  return ParsedAST::build(
-      llvm::make_unique<CompilerInvocation>(*Invocation), Preamble,
-      llvm::MemoryBuffer::getMemBufferCopy(Inputs.Contents), PCHs, Inputs.FS);
+  return ParsedAST::build(llvm::make_unique<CompilerInvocation>(*Invocation),
+                          Preamble,
+                          llvm::MemoryBuffer::getMemBufferCopy(Inputs.Contents),
+                          PCHs, std::move(VFS));
 }
 
 SourceLocation clangd::getBeginningOfIdentifier(ParsedAST &Unit,