[clang][modules] NFCI: Avoid unnecessary serialization logic for non-…

…affecting files

This patch delays some `ASTWriter` logic until after we've checked whether the source location entry we're serializing as an affecting file or not.

Depends on D137214.

Reviewed By: dexonsmith

Differential Revision: https://reviews.llvm.org/D137216

clang/lib/Serialization/ASTWriter.cpp

@@ -2047,7 +2047,6 @@ void ASTWriter::WriteSourceManagerBlock(SourceManager &SourceMgr,
     // Record the offset of this source-location entry.
     uint64_t Offset = Stream.GetCurrentBitNo() - SLocEntryOffsetsBase;
     assert((Offset >> 32) == 0 && "SLocEntry offset too large");
-    SLocEntryOffsets.push_back(Offset);
 
     // Figure out which record code to use.
     unsigned Code;
@@ -2062,8 +2061,6 @@ void ASTWriter::WriteSourceManagerBlock(SourceManager &SourceMgr,
     Record.clear();
     Record.push_back(Code);
 
-    // Starting offset of this entry within this module, so skip the dummy.
-    Record.push_back(getAdjustedOffset(SLoc->getOffset()) - 2);
     if (SLoc->isFile()) {
       const SrcMgr::FileInfo &File = SLoc->getFile();
       const SrcMgr::ContentCache *Content = &File.getContentCache();
@@ -2073,6 +2070,9 @@ void ASTWriter::WriteSourceManagerBlock(SourceManager &SourceMgr,
         // Do not emit files that were not listed as inputs.
         continue;
       }
+      SLocEntryOffsets.push_back(Offset);
+      // Starting offset of this entry within this module, so skip the dummy.
+      Record.push_back(getAdjustedOffset(SLoc->getOffset()) - 2);
       AddSourceLocation(File.getIncludeLoc(), Record);
       Record.push_back(File.getFileCharacteristic()); // FIXME: stable encoding
       Record.push_back(File.hasLineDirectives());
@@ -2133,6 +2133,9 @@ void ASTWriter::WriteSourceManagerBlock(SourceManager &SourceMgr,
     } else {
       // The source location entry is a macro expansion.
       const SrcMgr::ExpansionInfo &Expansion = SLoc->getExpansion();
+      SLocEntryOffsets.push_back(Offset);
+      // Starting offset of this entry within this module, so skip the dummy.
+      Record.push_back(getAdjustedOffset(SLoc->getOffset()) - 2);
       LocSeq::State Seq;
       AddSourceLocation(Expansion.getSpellingLoc(), Record, Seq);
       AddSourceLocation(Expansion.getExpansionLocStart(), Record, Seq);