[PATCH] D49991: [clangd] Do not build AST if no diagnostics were requested

Ilya Biryukov via Phabricator via cfe-commits cfe-commits at lists.llvm.org
Mon Jul 30 08:40:02 PDT 2018

ilya-biryukov created this revision.
ilya-biryukov added a reviewer: ioeric.
Herald added subscribers: arphaman, jkorous, MaskRay, javed.absar.

It can be washed out from the cache before first access anyway, so
building it can just be a waste of time.

  rCTE Clang Tools Extra



Index: clangd/TUScheduler.cpp
--- clangd/TUScheduler.cpp
+++ clangd/TUScheduler.cpp
@@ -383,6 +383,14 @@
     // Remove the old AST if it's still in cache.
+    if (WantDiags == WantDiagnostics::No) {
+      // If no diagnostics were requested, building it in advance might be a
+      // waste if it will be removed from the cache before it is first accessed.
+      // So we choose to avoid building it in the first place, the rebuild will
+      // happen on first access instead.
+      return;
+    }
     // Build the AST for diagnostics.
     llvm::Optional<ParsedAST> AST =
         buildAST(FileName, std::move(Invocation), Inputs, NewPreamble, PCHs);

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