[clang] [WIP][Safe Buffers] Serialize unsafe_buffer_usage pragmas (PR #92031)

[Artem Dergachev via cfe-commits]

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@@ -1551,6 +1567,58 @@ bool Preprocessor::isPPInSafeBufferOptOutRegion(SourceLocation &StartLoc) {
   return InSafeBufferOptOutRegion;
 }
 
+SmallVector<SourceLocation, 64>
+Preprocessor::serializeSafeBufferOptOutMap() const {
+  assert(!InSafeBufferOptOutRegion &&
+         "Attempt to serialize safe buffer opt-out regions before file being "
+         "completely preprocessed");
+
+  SmallVector<SourceLocation, 64> SrcSeq;
+
+  for (const auto &[begin, end] : SafeBufferOptOutMap) {
+    SrcSeq.push_back(begin);
+    SrcSeq.push_back(end);
+  }
+  // Only `SafeBufferOptOutMap` gets serialized. No need to serialize
+  // `LoadedSafeBufferOptOutMap` because if this TU loads a pch/module, every
+  // pch/module in the pch-chain/module-DAG will be loaded one by one in order.
+  // It means that for each loading pch/module m, it just needs to load m's own
+  // `SafeBufferOptOutMap`.
+  return SrcSeq;
+}
+
+void Preprocessor::setDeserializedSafeBufferOptOutMap(
+    const SmallVectorImpl<SourceLocation> &SourceLocations) {
+  auto It = SourceLocations.begin();
+
+  assert(SourceLocations.size() % 2 == 0 &&
+         "ill-formed SourceLocation sequence");
+  while (It != SourceLocations.end()) {
+    SourceLocation begin = *It++;
+    SourceLocation end = *It++;
+    SourceLocation FileLoc = SourceMgr.getFileLoc(begin);
+    FileID FID = SourceMgr.getDecomposedLoc(FileLoc).first;
+
+    if (FID.isInvalid()) {
+      // I suppose this should not happen:
+      assert(false && "Attempted to read a safe buffer opt-out region whose "
+                      "begin location is associated to an invalid File ID.");
+      break;
+    }
+    assert(!SourceMgr.isLocalFileID(FID) && "Expected a pch/module file");
+    // Here we assume that
+    // `SourceMgr.getFileLoc(begin) == SourceMgr.getFileLoc(end)`.
+    // Though it may not hold in very rare and strange cases, i.e., a pair of
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haoNoQ wrote:

If it may happen it shouldn't be an assert. If we really don't support this scenario it should probably be a compilation error, even if it only says "we don't support this yet sorry". (Can we emit compilation errors from here?)

https://github.com/llvm/llvm-project/pull/92031