[PATCH] D49783: [clangd] Do not rebuild AST if inputs have not changed

[Ilya Biryukov via Phabricator via cfe-commits]

ilya-biryukov added inline comments.


================
Comment at: clangd/TUScheduler.cpp:357
+
+    bool CanReuseAST = InputsAreTheSame && OldPreamble == NewPreamble;
     {
----------------
ioeric wrote:
> nit: `(OldPreamble == NewPreamble)`
> 
> Do you intend to compare the shared pointer instead of the values?
Yes, this is intentional. `buildPreamble` will either return the old one, if it can be reused, or build the new one.


================
Comment at: clangd/TUScheduler.cpp:360
       std::lock_guard<std::mutex> Lock(Mutex);
+      OldPreamble.reset();
       if (NewPreamble)
----------------
ioeric wrote:
> Why reset?
We don't need the old preamble at this point, so we give it a chance to die (if there are no more references).
Note that there's an expensive operation that follows (building the AST), so removing the preamble before it seems like a win


================
Comment at: clangd/TUScheduler.cpp:373
+      // FIXME(ibiryukov): the AST could actually change if non-preamble
+      // includes changed, but we choose to ignore it.
+      // FIXME(ibiryukov): should we refresh the cache in IdleASTs for the
----------------
ioeric wrote:
> Do we choose to ignore this because it's rare? What are non-preamble #includes?
Exactly, we don't have the code to track and check for all accessed files.
This should be rare, hopefully won't show up in practice.


================
Comment at: test/clangd/extra-flags.test:26
 ---
-{"jsonrpc":"2.0","method":"textDocument/didChange","params":{"textDocument":{"uri":"test:///foo.c","version":2},"contentChanges":[{"text":"int main() { int i; return i; }"}]}}
+{"jsonrpc":"2.0","method":"textDocument/didChange","params":{"textDocument":{"uri":"test:///foo.c","version":2},"contentChanges":[{"text":"int main() { int i; return i+1; }"}]}}
 #      CHECK:  "method": "textDocument/publishDiagnostics",
----------------
ioeric wrote:
> Why this change?
The test expects two publishDiagnostics, but it won't get the second one since if the contents of the file are the same :-)
So I altered the contents a bit to make sure we get the second result too


Repository:
  rCTE Clang Tools Extra

https://reviews.llvm.org/D49783