Reland "[clang][modules] Move `UNHASHED_CONTROL_BLOCK` up in the AST file"

This reverts commit b6ba804f7775f89f230ee1e62526a2f8225c7966, effectively relanding commit 7d1565727dad3acb54fe76a908630843835d7bc8.

The original commit incorrectly called `ASTWriter::writeUnhashedControlBlock()` before `ASTWriter::collectNonAffectingInputFiles()`, causing SourceLocations/FileIDs in the pragma diagnostic mappings block to be invalid. This is now tested by `clang/test/Modules/diag-mappings-affecting.c`.

1 files changed, 6 insertions, 3 deletions

diff --git a/clang/lib/Serialization/GlobalModuleIndex.cpp b/clang/lib/Serialization/GlobalModuleIndex.cpp
index d57f4ce..92417c7 100644
--- a/clang/lib/Serialization/GlobalModuleIndex.cpp
+++ b/clang/lib/Serialization/GlobalModuleIndex.cpp
@@ -697,9 +697,12 @@ llvm::Error GlobalModuleIndexBuilder::loadModuleFile(const FileEntry *File) {
     }
 
     // Get Signature.
-    if (State == DiagnosticOptionsBlock && Code == SIGNATURE)
-      getModuleFileInfo(File).Signature = ASTFileSignature::create(
-          Record.begin(), Record.begin() + ASTFileSignature::size);
+    if (State == DiagnosticOptionsBlock && Code == SIGNATURE) {
+      auto Signature = ASTFileSignature::create(Blob.begin(), Blob.end());
+      assert(Signature != ASTFileSignature::createDummy() &&
+             "Dummy AST file signature not backpatched in ASTWriter.");
+      getModuleFileInfo(File).Signature = Signature;
+    }
 
     // We don't care about this record.
   }