[clang][dataflow] Eliminate duplication between `AggregateStorageLocation` and `StructValue`.

After this change, `StructValue` is just a wrapper for an `AggregateStorageLocation`. For the wider context, see https://discourse.llvm.org/t/70086.

## How to review

- Start by looking at the comments added / changed in Value.h, StorageLocation.h,
  and DataflowEnvironment.h. This will give you a good overview of the semantic
  changes.

- Look at the corresponding .cpp files that implement the semantic changes.

- Transfer.cpp, TypeErasedDataflowAnalysis.cpp, and RecordOps.cpp show how the
  core of the framework is affected by the semantic changes.

- UncheckedOptionalAccessModel.cpp shows how this complex model is affected by
  the changes.

- Many of the changes in the rest of the patch are mechanical in nature.

Reviewed By: ymandel, xazax.hun

Differential Revision: https://reviews.llvm.org/D155446

1 files changed, 5 insertions, 1 deletions

diff --git a/clang/lib/Analysis/FlowSensitive/DataflowAnalysisContext.cpp b/clang/lib/Analysis/FlowSensitive/DataflowAnalysisContext.cpp
index bb1c2c7..9f72dc8 100644
--- a/clang/lib/Analysis/FlowSensitive/DataflowAnalysisContext.cpp
+++ b/clang/lib/Analysis/FlowSensitive/DataflowAnalysisContext.cpp
@@ -62,7 +62,11 @@ StorageLocation &DataflowAnalysisContext::createStorageLocation(QualType Type) {
   if (!Type.isNull() && Type->isRecordType()) {
     llvm::DenseMap<const ValueDecl *, StorageLocation *> FieldLocs;
     for (const FieldDecl *Field : getModeledFields(Type))
-      FieldLocs.insert({Field, &createStorageLocation(Field->getType())});
+      if (Field->getType()->isReferenceType())
+        FieldLocs.insert({Field, nullptr});
+      else
+        FieldLocs.insert({Field, &createStorageLocation(
+                                     Field->getType().getNonReferenceType())});
     return arena().create<AggregateStorageLocation>(Type, std::move(FieldLocs));
   }
   return arena().create<ScalarStorageLocation>(Type);