[clang] [clang][modules] Only serialize info for locally-included headers (PR #113718)

[Jan Svoboda via cfe-commits]

https://github.com/jansvoboda11 created https://github.com/llvm/llvm-project/pull/113718

I noticed that some PCM files contain `HeaderFileInfo` for headers only included in a dependent PCM file, which is wasteful.

This patch changes the logic to only write headers that are included locally. This makes the PCM files smaller and saves some superfluous deserialization of `HeaderFileInfo` triggered by `Preprocessor::alreadyIncluded()`.

>From 78d2aaf70db682d1ef7f630df1612d1ce803d498 Mon Sep 17 00:00:00 2001
From: Jan Svoboda <jan_svoboda at apple.com>
Date: Fri, 25 Oct 2024 10:53:38 -0700
Subject: [PATCH] [clang][modules] Only serialize info for locally-included
 headers

I noticed that some PCM files contain `HeaderFileInfo` for headers only included in a dependent PCM file, which is wasteful.

This patch changes the logic to only write headers that are included locally. This makes the PCM files smaller and saves some superfluous deserialization of `HeaderFileInfo` triggered by `Preprocessor::alreadyIncluded()`.
---
 clang/include/clang/Lex/Preprocessor.h | 2 +-
 clang/lib/Lex/HeaderSearch.cpp         | 1 -
 clang/lib/Serialization/ASTWriter.cpp  | 6 +++---
 3 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/clang/include/clang/Lex/Preprocessor.h b/clang/include/clang/Lex/Preprocessor.h
index f3f4de044fc41a..38a527d2324ffe 100644
--- a/clang/include/clang/Lex/Preprocessor.h
+++ b/clang/include/clang/Lex/Preprocessor.h
@@ -1490,7 +1490,7 @@ class Preprocessor {
   /// Mark the file as included.
   /// Returns true if this is the first time the file was included.
   bool markIncluded(FileEntryRef File) {
-    HeaderInfo.getFileInfo(File);
+    HeaderInfo.getFileInfo(File).IsLocallyIncluded = true;
     return IncludedFiles.insert(File).second;
   }
 
diff --git a/clang/lib/Lex/HeaderSearch.cpp b/clang/lib/Lex/HeaderSearch.cpp
index 8826ab449df493..052be1395161d4 100644
--- a/clang/lib/Lex/HeaderSearch.cpp
+++ b/clang/lib/Lex/HeaderSearch.cpp
@@ -1582,7 +1582,6 @@ bool HeaderSearch::ShouldEnterIncludeFile(Preprocessor &PP,
     }
   }
 
-  FileInfo.IsLocallyIncluded = true;
   IsFirstIncludeOfFile = PP.markIncluded(File);
   return true;
 }
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index 494890284d2f2c..612fdf499fa750 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -2163,8 +2163,8 @@ void ASTWriter::WriteHeaderSearch(const HeaderSearch &HS) {
       continue; // We have no information on this being a header file.
     if (!HFI->isCompilingModuleHeader && HFI->isModuleHeader)
       continue; // Header file info is tracked by the owning module file.
-    if (!HFI->isCompilingModuleHeader && !PP->alreadyIncluded(*File))
-      continue; // Non-modular header not included is not needed.
+    if (!HFI->isCompilingModuleHeader && !HFI->IsLocallyIncluded)
+      continue; // Header file info is tracked by the including module file.
 
     // Massage the file path into an appropriate form.
     StringRef Filename = File->getName();
@@ -2176,7 +2176,7 @@ void ASTWriter::WriteHeaderSearch(const HeaderSearch &HS) {
       SavedStrings.push_back(Filename.data());
     }
 
-    bool Included = PP->alreadyIncluded(*File);
+    bool Included = HFI->IsLocallyIncluded || PP->alreadyIncluded(*File);
 
     HeaderFileInfoTrait::key_type Key = {
       Filename, File->getSize(), getTimestampForOutput(*File)