[clang] [clang][dataflow] Add support for serialization and deserialization. (PR #152487)

[Yitzhak Mandelbaum via cfe-commits]

================
@@ -140,6 +140,15 @@ class DataflowAnalysisContext {
   /// Adds `Constraint` to the flow condition identified by `Token`.
   void addFlowConditionConstraint(Atom Token, const Formula &Constraint);
 
+  /// Adds `Deps` to the dependencies of the flow condition identified by
+  /// `Token`. Intended for use in deserializing contexts. The formula alone
+  /// doesn't have enough information to indicate its deps.
+  void addFlowConditionDeps(Atom Token, const llvm::DenseSet<Atom> &Deps) {
----------------
ymand wrote:

Here is deserialization:

```
static llvm::Error loadTokenDefinitions(
    const proto2::Map<uint32_t, FormulaProto> &AtomDefs,
    DataflowAnalysisContext &AC, dataflow::Arena &Arena,
    llvm::DenseMap<unsigned, dataflow::Atom> &AtomMap) {
  for (const auto &[AtomData, Proto] : AtomDefs) {
    auto DeserializedOrErr =
        Formula::deserialize(Proto.serialized(), Arena, AtomMap);
    if (!DeserializedOrErr) return DeserializedOrErr.takeError();
    auto [It, Inserted] = AtomMap.try_emplace(AtomData, dataflow::Atom());
    if (Inserted) It->second = Arena.makeAtom();
    AC.addFlowConditionConstraint(It->second, **DeserializedOrErr);
  }
  return llvm::Error::success();
}

static llvm::Error loadLogicalContext(
    const LogicalContext &LC, DataflowAnalysisContext &AC,
    dataflow::Arena &Arena, llvm::DenseMap<unsigned, dataflow::Atom> &AtomMap) {
  if (LC.has_ground_truth()) {
    auto GroundTruth =
        Formula::deserialize(LC.ground_truth().serialized(), Arena, AtomMap);
    if (!GroundTruth) return GroundTruth.takeError();
    AC.addInvariant(**GroundTruth);
  }

 for (const auto &[AtomData, DepSet] : LC.atom_deps()) {
    auto [It, Inserted] = AtomMap.try_emplace(AtomData, dataflow::Atom());
    if (Inserted) It->second = Arena.makeAtom();
    llvm::DenseSet<dataflow::Atom> Deps;
    for (uint32_t DepAtomData : DepSet.atoms()) {
      auto [DepIt, DepInserted] =
          AtomMap.try_emplace(DepAtomData, dataflow::Atom());
      if (DepInserted) DepIt->second = Arena.makeAtom();
      Deps.insert(DepIt->second);
    }
    AC.addFlowConditionDeps(It->second, Deps);
  }

  return loadTokenDefinitions(LC.atom_defs(), AC, Arena, AtomMap);
}
```

https://github.com/llvm/llvm-project/pull/152487