[clang][Tooling] Try to avoid file system access if there is no record for the file in compile_commads.json

Summary:
If there is no record in compile_commands.json, we try to find suitable record with `MatchTrie.findEquivalent()` call.
This is very expensive operation with a lot of `llvm::sys::fs::equivalent()` calls in some cases.

This patch disables file symlinks for performance reasons.

Example scenario without this patch:
- compile_commands.json generated at clangd build (contains ~3000 files).
- it tooks more than 1 second to get compile command for newly created file in the root folder of LLVM project.
- we wait for 1 second every time when clangd requests compile command for this file (at file change).

Reviewers: sammccall, kadircet, hokein

Reviewed By: sammccall

Subscribers: chandlerc, djasper, klimek, ilya-biryukov, kadircet, usaxena95, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D83621

1 files changed, 9 insertions, 0 deletions

diff --git a/clang/unittests/Tooling/CompilationDatabaseTest.cpp b/clang/unittests/Tooling/CompilationDatabaseTest.cpp
index cc948b8..3bfb0ec 100644
--- a/clang/unittests/Tooling/CompilationDatabaseTest.cpp
+++ b/clang/unittests/Tooling/CompilationDatabaseTest.cpp
@@ -281,6 +281,15 @@ TEST_F(FileMatchTrieTest, CannotResolveRelativePath) {
   EXPECT_EQ("Cannot resolve relative paths", Error);
 }
 
+TEST_F(FileMatchTrieTest, SingleFile) {
+  Trie.insert("/root/RootFile.cc");
+  EXPECT_EQ("", find("/root/rootfile.cc"));
+  // Add subpath to avoid `if (Children.empty())` special case
+  // which we hit at previous `find()`.
+  Trie.insert("/root/otherpath/OtherFile.cc");
+  EXPECT_EQ("", find("/root/rootfile.cc"));
+}
+
 TEST(findCompileArgsInJsonDatabase, FindsNothingIfEmpty) {
   std::string ErrorMessage;
   CompileCommand NotFound = findCompileArgsInJsonDatabase(