From: Ilya Biryukov <ibiryukov@google.com>
Date: Mon, 9 Jul 2018 11:33:23 +0000 (+0000)
Subject: [PCH] Add an option to not write comments into PCH
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=b5784f85be57b6010e656f881e64ac3d2ad25f6a;p=clang

[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

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@336539 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/include/clang/Lex/PreprocessorOptions.h b/include/clang/Lex/PreprocessorOptions.h
index f4ec2f27c4..3d7e5ab4a8 100644
--- a/include/clang/Lex/PreprocessorOptions.h
+++ b/include/clang/Lex/PreprocessorOptions.h
@@ -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;
diff --git a/lib/Serialization/ASTWriter.cpp b/lib/Serialization/ASTWriter.cpp
index 279960a129..bc569d17f2 100644
--- a/lib/Serialization/ASTWriter.cpp
+++ b/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::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();
 }
 
 //===----------------------------------------------------------------------===//