[libclang] Allow to suspend a translation unit.

A suspended translation unit uses significantly less memory but on the
other side does not support any other calls than
clang_reparseTranslationUnit to resume it or
clang_disposeTranslationUnit to dispose it completely.

This helps IDEs to reduce the memory footprint. The data that is freed
by a call to clang_suspendTranslationUnit will be re-generated on the
next (re)parse anyway. Used with a preamble, this allows pretty fast
resumption of the translation unit for further use (compared to disposal
of the translation unit and a parse from scratch).

Patch by Nikolai Kosjar!

llvm-svn: 304212

1 files changed, 16 insertions, 11 deletions

diff --git a/clang/lib/Frontend/ASTUnit.cpp b/clang/lib/Frontend/ASTUnit.cpp
index d968882174f..01f7ca8aba9 100644
--- a/clang/lib/Frontend/ASTUnit.cpp
+++ b/clang/lib/Frontend/ASTUnit.cpp
@@ -1036,8 +1036,6 @@ static void checkAndSanitizeDiags(SmallVectorImpl<StoredDiagnostic> &
 bool ASTUnit::Parse(std::shared_ptr<PCHContainerOperations> PCHContainerOps,
                     std::unique_ptr<llvm::MemoryBuffer> OverrideMainBuffer,
                     IntrusiveRefCntPtr<vfs::FileSystem> VFS) {
-  SavedMainFileBuffer.reset();
-
   if (!Invocation)
     return true;
 
@@ -1090,17 +1088,11 @@ bool ASTUnit::Parse(std::shared_ptr<PCHContainerOperations> PCHContainerOps,
     Clang->createFileManager();
     FileMgr = &Clang->getFileManager();
   }
-  SourceMgr = new SourceManager(getDiagnostics(), *FileMgr,
-                                UserFilesAreVolatile);
-  TheSema.reset();
-  Ctx = nullptr;
-  PP = nullptr;
-  Reader = nullptr;
 
-  // Clear out old caches and data.
-  TopLevelDecls.clear();
-  clearFileLevelDecls();
+  ResetForParse();
 
+  SourceMgr = new SourceManager(getDiagnostics(), *FileMgr,
+                                UserFilesAreVolatile);
   if (!OverrideMainBuffer) {
     checkAndRemoveNonDriverDiags(StoredDiagnostics);
     TopLevelDeclsInPreamble.clear();
@@ -2116,6 +2108,19 @@ bool ASTUnit::Reparse(std::shared_ptr<PCHContainerOperations> PCHContainerOps,
   return Result;
 }
 
+void ASTUnit::ResetForParse() {
+  SavedMainFileBuffer.reset();
+
+  SourceMgr.reset();
+  TheSema.reset();
+  Ctx.reset();
+  PP.reset();
+  Reader.reset();
+
+  TopLevelDecls.clear();
+  clearFileLevelDecls();
+}
+
 //----------------------------------------------------------------------------//
 // Code completion
 //----------------------------------------------------------------------------//