[PATCH] D48942: [PCH] Add an option to not write comments into PCH

[Ilya Biryukov via Phabricator via cfe-commits]

ilya-biryukov created this revision.
ilya-biryukov added a reviewer: sammccall.
Herald added a subscriber: ioeric.

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.


Repository:
  rC Clang

https://reviews.llvm.org/D48942

Files:
  include/clang/Lex/PreprocessorOptions.h
  lib/Serialization/ASTWriter.cpp


Index: lib/Serialization/ASTWriter.cpp
===================================================================
--- lib/Serialization/ASTWriter.cpp
+++ lib/Serialization/ASTWriter.cpp
@@ -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::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 @@
     Record.push_back(I->isAlmostTrailingComment());
     Stream.EmitRecord(COMMENTS_RAW_COMMENT, Record);
   }
-  Stream.ExitBlock();
 }
 
 //===----------------------------------------------------------------------===//
Index: include/clang/Lex/PreprocessorOptions.h
===================================================================
--- include/clang/Lex/PreprocessorOptions.h
+++ include/clang/Lex/PreprocessorOptions.h
@@ -88,6 +88,11 @@
   /// 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;


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