r336539 - [PCH] Add an option to not write comments into PCH

[Ilya Biryukov via cfe-commits]

Author: ibiryukov
Date: Mon Jul  9 04:33:23 2018
New Revision: 336539

URL: http://llvm.org/viewvc/llvm-project?rev=336539&view=rev
Log:
[PCH] Add an option to not write comments into PCH

Summary:
Will be used in clangd, see the follow-up change.
Clangd does not use comments read from PCH to avoid crashes due to
changed contents of the file. However, reading them considerably slows
down code completion on files with large preambles.

Reviewers: sammccall

Reviewed By: sammccall

Subscribers: ioeric, cfe-commits

Differential Revision: https://reviews.llvm.org/D48942

Modified:
    cfe/trunk/include/clang/Lex/PreprocessorOptions.h
    cfe/trunk/lib/Serialization/ASTWriter.cpp

Modified: cfe/trunk/include/clang/Lex/PreprocessorOptions.h
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Lex/PreprocessorOptions.h?rev=336539&r1=336538&r2=336539&view=diff
==============================================================================
--- cfe/trunk/include/clang/Lex/PreprocessorOptions.h (original)
+++ cfe/trunk/include/clang/Lex/PreprocessorOptions.h Mon Jul  9 04:33:23 2018
@@ -95,6 +95,11 @@ public:
   /// processing the rest of the file.
   bool GeneratePreamble = false;
 
+  /// Whether to write comment locations into the PCH when building it.
+  /// Reading the comments from the PCH can be a performance hit even if the
+  /// clients don't use them.
+  bool WriteCommentListToPCH = true;
+
   /// The implicit PTH input included at the start of the translation unit, or
   /// empty.
   std::string ImplicitPTHInclude;

Modified: cfe/trunk/lib/Serialization/ASTWriter.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Serialization/ASTWriter.cpp?rev=336539&r1=336538&r2=336539&view=diff
==============================================================================
--- cfe/trunk/lib/Serialization/ASTWriter.cpp (original)
+++ cfe/trunk/lib/Serialization/ASTWriter.cpp Mon Jul  9 04:33:23 2018
@@ -78,6 +78,7 @@
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/PointerIntPair.h"
 #include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/ScopeExit.h"
 #include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/SmallVector.h"
@@ -3252,6 +3253,9 @@ void ASTWriter::WriteFileDeclIDsMap() {
 
 void ASTWriter::WriteComments() {
   Stream.EnterSubblock(COMMENTS_BLOCK_ID, 3);
+  auto _ = llvm::make_scope_exit([this] { Stream.ExitBlock(); });
+  if (!PP->getPreprocessorOpts().WriteCommentListToPCH)
+    return;
   ArrayRef<RawComment *> RawComments = Context->Comments.getComments();
   RecordData Record;
   for (const auto *I : RawComments) {
@@ -3262,7 +3266,6 @@ void ASTWriter::WriteComments() {
     Record.push_back(I->isAlmostTrailingComment());
     Stream.EmitRecord(COMMENTS_RAW_COMMENT, Record);
   }
-  Stream.ExitBlock();
 }
 
 //===----------------------------------------------------------------------===//