[FileManager] Do not call 'real_path' in getFile().

Summary:
This partially rolls back the change in D48903:
https://github.com/llvm-mirror/clang/commit/89aa7f45a1f728144935289d4ce69d8522999de0#diff-0025af005307891b5429b6a834823d5eR318

`real_path` can be very expensive on real file systems, and calling it on each
opened file can slow down the compilation. This also slows down deserialized
ASTs for which real paths need to be recalculated for each input files again.

For clangd code completion latency (using preamble):
Before
{F7039629}
After
{F7039630}

Reviewers: ilya-biryukov, simark

Reviewed By: ilya-biryukov

Subscribers: kadircet, cfe-commits

Differential Revision: https://reviews.llvm.org/D51159

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@340598 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Basic/FileManager.cpp b/lib/Basic/FileManager.cpp
index 5f783a7c0bca55ce921d7ebcb6ecc861c40a34be..060d3a687a9c8a2f40d51fda7ca7b4b47b4e8ec3 100644 (file)
--- a/lib/Basic/FileManager.cpp
+++ b/lib/Basic/FileManager.cpp
@@ -316,10 +316,14 @@ const FileEntry *FileManager::getFile(StringRef Filename, bool openFile,
   UFE.File = std::move(F);
   UFE.IsValid = true;
 
-  SmallString<128> RealPathName;
-  if (!FS->getRealPath(InterndFileName, RealPathName))
-    UFE.RealPathName = RealPathName.str();
-
+  llvm::SmallString<128> AbsPath(InterndFileName);
+  // This is not the same as `VFS::getRealPath()`, which resolves symlinks but
+  // can be very expensive on real file systems.
+  // FIXME: the semantic of RealPathName is unclear, and the name might be
+  // misleading. We need to clean up the interface here.
+  makeAbsolutePath(AbsPath);
+  llvm::sys::path::remove_dots(AbsPath, /*remove_dot_dot=*/true);
+  UFE.RealPathName = AbsPath.str();
   return &UFE;
 }