[clangd] Drop usage of PreambleStatCache in scanPreamble

Summary: It was used inside buildCompilerInvocation to speed up stats. But
preambleStatCache doesn't contain stat information performed while
building compiler invocation. So it was an unnecessary optimization.

Furthermore, buildCompilerInvocation in scanPreamble doesn't need to
find gcc installation, include paths and such, as it is only trying to
lex directives. Hence we are passing an empty FS to get rid of any
redundant IO.

Reviewers: sammccall

Subscribers: ilya-biryukov, javed.absar, MaskRay, jkorous, arphaman, usaxena95, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D81719

diff --git a/clang-tools-extra/clangd/Preamble.cpp b/clang-tools-extra/clangd/Preamble.cpp
index 8652f35..ca0a76d 100644 (file)
--- a/clang-tools-extra/clangd/Preamble.cpp
+++ b/clang-tools-extra/clangd/Preamble.cpp
@@ -224,35 +224,22 @@ struct ScannedPreamble {
 
 /// Scans the preprocessor directives in the preamble section of the file by
 /// running preprocessor over \p Contents. Returned includes do not contain
-/// resolved paths. \p VFS and \p Cmd is used to build the compiler invocation,
-/// which might stat/read files.
+/// resolved paths. \p Cmd is used to build the compiler invocation, which might
+/// stat/read files.
 llvm::Expected<ScannedPreamble>
-scanPreamble(llvm::StringRef Contents,
-             llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS,
-             const tooling::CompileCommand &Cmd) {
-  // FIXME: Change PreambleStatCache to operate on FileSystemProvider rather
-  // than vfs::FileSystem, that way we can just use ParseInputs without this
-  // hack.
-  auto GetFSProvider = [](llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> FS) {
-    class VFSProvider : public ThreadsafeFS {
-    public:
-      VFSProvider(llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> FS)
-          : VFS(std::move(FS)) {}
-      llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem>
-      view(llvm::NoneType) const override {
-        return VFS;
-      }
-
-    private:
-      const llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS;
-    };
-    return std::make_unique<VFSProvider>(std::move(FS));
+scanPreamble(llvm::StringRef Contents, const tooling::CompileCommand &Cmd) {
+  class EmptyFS : public ThreadsafeFS {
+  public:
+    llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem>
+    view(llvm::NoneType) const override {
+      return new llvm::vfs::InMemoryFileSystem;
+    }
   };
-  auto FSProvider = GetFSProvider(std::move(VFS));
+  EmptyFS FS;
   // Build and run Preprocessor over the preamble.
   ParseInputs PI;
   PI.Contents = Contents.str();
-  PI.TFS = FSProvider.get();
+  PI.TFS = &FS;
   PI.CompileCommand = Cmd;
   IgnoringDiagConsumer IgnoreDiags;
   auto CI = buildCompilerInvocation(PI, IgnoreDiags);
@@ -272,7 +259,7 @@ scanPreamble(llvm::StringRef Contents,
       std::move(CI), nullptr, std::move(PreambleContents),
       // Provide an empty FS to prevent preprocessor from performing IO. This
       // also implies missing resolved paths for includes.
-      new llvm::vfs::InMemoryFileSystem, IgnoreDiags);
+      FS.view(llvm::None), IgnoreDiags);
   if (Clang->getFrontendOpts().Inputs.empty())
     return llvm::createStringError(llvm::inconvertibleErrorCode(),
                                    "compiler instance had no inputs");
@@ -422,8 +409,6 @@ PreamblePatch PreamblePatch::create(llvm::StringRef FileName,
   trace::Span Tracer("CreatePreamblePatch");
   SPAN_ATTACH(Tracer, "File", FileName);
   assert(llvm::sys::path::is_absolute(FileName) && "relative FileName!");
-  auto VFS = Baseline.StatCache->getConsumingFS(
-      Modified.TFS->view(/*CWD=*/llvm::None));
   // First scan preprocessor directives in Baseline and Modified. These will be
   // used to figure out newly added directives in Modified. Scanning can fail,
   // the code just bails out and creates an empty patch in such cases, as:
@@ -434,14 +419,13 @@ PreamblePatch PreamblePatch::create(llvm::StringRef FileName,
   //   there's nothing to do but generate an empty patch.
   auto BaselineScan = scanPreamble(
       // Contents needs to be null-terminated.
-      Baseline.Preamble.getContents().str(), VFS, Modified.CompileCommand);
+      Baseline.Preamble.getContents().str(), Modified.CompileCommand);
   if (!BaselineScan) {
     elog("Failed to scan baseline of {0}: {1}", FileName,
          BaselineScan.takeError());
     return PreamblePatch::unmodified(Baseline);
   }
-  auto ModifiedScan =
-      scanPreamble(Modified.Contents, std::move(VFS), Modified.CompileCommand);
+  auto ModifiedScan = scanPreamble(Modified.Contents, Modified.CompileCommand);
   if (!ModifiedScan) {
     elog("Failed to scan modified contents of {0}: {1}", FileName,
          ModifiedScan.takeError());