[clang][dataflow] Copy only the fields present in the current derived…

clang/include/clang/Analysis/FlowSensitive/StorageLocation.h

@@ -144,6 +144,17 @@ class RecordStorageLocation final : public StorageLocation {
   /// The synthetic field must exist.
   StorageLocation &getSyntheticField(llvm::StringRef Name) const {
     StorageLocation *Loc = SyntheticFields.lookup(Name);
+    LLVM_DEBUG({
+      if (Loc == nullptr) {
+        llvm::dbgs() << "Couldn't find synthetic field " << Name
+                     << " on StorageLocation " << this << " of type "
+                     << getType() << "\n";
+        llvm::dbgs() << "Existing synthetic fields:\n";
+        for ([[maybe_unused]] const auto &[Name, Loc] : SyntheticFields) {
+          llvm::dbgs() << Name << "\n";
+        }
+      }
+    });
     assert(Loc != nullptr);
     return *Loc;
   }

clang/lib/Analysis/FlowSensitive/RecordOps.cpp

@@ -14,6 +14,9 @@
 #include "clang/AST/Decl.h"
 #include "clang/AST/DeclCXX.h"
 #include "clang/AST/Type.h"
+#include "clang/Analysis/FlowSensitive/ASTOps.h"
+#include "clang/Basic/LLVM.h"
+#include "llvm/ADT/StringMap.h"
 
 #define DEBUG_TYPE "dataflow"
 
@@ -79,18 +82,41 @@ void copyRecord(RecordStorageLocation &Src, RecordStorageLocation &Dst,
 
   if (SrcType == DstType || (SrcDecl != nullptr && DstDecl != nullptr &&
                              SrcDecl->isDerivedFrom(DstDecl))) {
+    // Dst may have children modeled from other derived types than SrcType, e.g.
+    // after casts of Dst to other types derived from DstType. Only copy the
+    // children and synthetic fields present in both Dst and SrcType.
+    const FieldSet FieldsInSrcType =
+        Env.getDataflowAnalysisContext().getModeledFields(SrcType);
     for (auto [Field, DstFieldLoc] : Dst.children())
-      copyField(*Field, Src.getChild(*Field), DstFieldLoc, Dst, Env);
+      if (const auto *FieldAsFieldDecl = dyn_cast<FieldDecl>(Field);
+          FieldAsFieldDecl && FieldsInSrcType.contains(FieldAsFieldDecl))
+        copyField(*Field, Src.getChild(*Field), DstFieldLoc, Dst, Env);
+    const llvm::StringMap<QualType> SyntheticFieldsForSrcType =
+        Env.getDataflowAnalysisContext().getSyntheticFields(SrcType);
     for (const auto &[Name, DstFieldLoc] : Dst.synthetic_fields())
-      copySyntheticField(DstFieldLoc->getType(), Src.getSyntheticField(Name),
-                         *DstFieldLoc, Env);
+      if (SyntheticFieldsForSrcType.contains(Name))
+        copySyntheticField(DstFieldLoc->getType(), Src.getSyntheticField(Name),
+                           *DstFieldLoc, Env);
   } else if (SrcDecl != nullptr && DstDecl != nullptr &&
              DstDecl->isDerivedFrom(SrcDecl)) {
-    for (auto [Field, SrcFieldLoc] : Src.children())
-      copyField(*Field, SrcFieldLoc, Dst.getChild(*Field), Dst, Env);
-    for (const auto &[Name, SrcFieldLoc] : Src.synthetic_fields())
-      copySyntheticField(SrcFieldLoc->getType(), *SrcFieldLoc,
-                         Dst.getSyntheticField(Name), Env);
+    // Src may have children modeled from other derived types than DstType, e.g.
+    // after other casts of Src to those types (likely in different branches,
+    // but without flow-condition-dependent field modeling). Only copy the
+    // children and synthetic fields of Src that are present in DstType.
+    const FieldSet FieldsInDstType =
+        Env.getDataflowAnalysisContext().getModeledFields(DstType);
+    for (auto [Field, SrcFieldLoc] : Src.children()) {
+      if (const auto *FieldAsFieldDecl = dyn_cast<FieldDecl>(Field);
+          FieldAsFieldDecl && FieldsInDstType.contains(FieldAsFieldDecl))
+        copyField(*Field, SrcFieldLoc, Dst.getChild(*Field), Dst, Env);
+    }
+    const llvm::StringMap<QualType> SyntheticFieldsForDstType =
+        Env.getDataflowAnalysisContext().getSyntheticFields(DstType);
+    for (const auto &[Name, SrcFieldLoc] : Src.synthetic_fields()) {
+      if (SyntheticFieldsForDstType.contains(Name))
+        copySyntheticField(SrcFieldLoc->getType(), *SrcFieldLoc,
+                           Dst.getSyntheticField(Name), Env);
+    }
   } else {
     for (const FieldDecl *Field :
          Env.getDataflowAnalysisContext().getModeledFields(TypeToCopy)) {

clang/unittests/Analysis/FlowSensitive/RecordOpsTest.cpp

@@ -64,7 +64,8 @@ TEST(RecordOpsTest, CopyRecord) {
   runDataflow(
       Code,
       [](QualType Ty) -> llvm::StringMap<QualType> {
-        if (Ty.getAsString() != "S")
+        std::string TypeAsString = Ty.getAsString();
+        if (TypeAsString != "S" && TypeAsString != "struct S")
           return {};
         QualType IntTy =
             getFieldNamed(Ty->getAsRecordDecl(), "outer_int")->getType();
@@ -123,7 +124,8 @@ TEST(RecordOpsTest, RecordsEqual) {
   runDataflow(
       Code,
       [](QualType Ty) -> llvm::StringMap<QualType> {
-        if (Ty.getAsString() != "S")
+        std::string TypeAsString = Ty.getAsString();
+        if (TypeAsString != "S" && TypeAsString != "struct S")
           return {};
         QualType IntTy =
             getFieldNamed(Ty->getAsRecordDecl(), "outer_int")->getType();
@@ -213,9 +215,10 @@ TEST(RecordOpsTest, CopyRecordBetweenDerivedAndBase) {
   )";
   auto SyntheticFieldCallback = [](QualType Ty) -> llvm::StringMap<QualType> {
     CXXRecordDecl *ADecl = nullptr;
-    if (Ty.getAsString() == "A")
+    std::string TypeAsString = Ty.getAsString();
+    if (TypeAsString == "A" || TypeAsString == "struct A")
       ADecl = Ty->getAsCXXRecordDecl();
-    else if (Ty.getAsString() == "B")
+    else if (TypeAsString == "B" || TypeAsString == "struct B")
       ADecl = Ty->getAsCXXRecordDecl()
                   ->bases_begin()
                   ->getType()

clang/unittests/Analysis/FlowSensitive/TransferTest.cpp

@@ -3709,6 +3709,80 @@ TEST(TransferTest, StaticCastBaseToDerived) {
       });
 }
 
+TEST(TransferTest, MultipleConstructionsFromStaticCastsBaseToDerived) {
+  std::string Code = R"cc(
+ struct Base {};
+
+struct DerivedOne : public Base {
+  // Need a field in one of the derived siblings that the other doesn't have.
+  int I;
+};
+
+struct DerivedTwo : public Base {};
+
+int getInt();
+
+void target(Base* B) {
+  // Need something to cause modeling of I.
+  DerivedOne D1;
+  (void)D1.I;
+
+  // Switch cases are a reasonable pattern where the same variable might be
+  // safely cast to two different derived types within the same function
+  // without resetting the value of the variable. getInt is a stand-in for what
+  // is usually a function indicating the dynamic derived type.
+  switch (getInt()) {
+    case 1:
+      // Need a CXXConstructExpr or copy/move CXXOperatorCallExpr from each of
+      // the casts to derived types, cast from the same base variable, to
+      // trigger the copyRecord behavior.
+      (void)new DerivedOne(*static_cast<DerivedOne*>(B));
+      break;
+    case 2:
+      (void)new DerivedTwo(*static_cast<DerivedTwo*>(B));
+      break;
+  };
+}
+)cc";
+  runDataflow(
+      Code,
+      [](const llvm::StringMap<DataflowAnalysisState<NoopLattice>> &Results,
+         ASTContext &ASTCtx) {
+        // This is a crash repro. We used to crash when transferring the
+        // construction of DerivedTwo because B's StorageLocation had a child
+        // for the field I, but DerivedTwo doesn't. Now, we should only copy the
+        // fields from B that are present in DerivedTwo.
+      });
+}
+
+TEST(TransferTest, CopyConstructionOfBaseAfterStaticCastsBaseToDerived) {
+  std::string Code = R"cc(
+ struct Base {};
+
+struct Derived : public Base {
+// Need a field in Derived that is not in Base.
+  char C;
+};
+
+void target(Base* B, Base* OtherB) {
+  Derived* D = static_cast<Derived*>(B);
+  *B = *OtherB;
+  // Need something to cause modeling of C.
+  (void)D->C;
+}
+
+)cc";
+  runDataflow(
+      Code,
+      [](const llvm::StringMap<DataflowAnalysisState<NoopLattice>> &Results,
+         ASTContext &ASTCtx) {
+        // This is a crash repro. We used to crash when transferring the
+        // copy construction of B from OtherB because B's StorageLocation had a
+        // child for the field C, but Base doesn't. Now, we should only copy the
+        // fields from B that are present in Base.
+      });
+}
+
 TEST(TransferTest, ExplicitDerivedToBaseCast) {
   std::string Code = R"cc(
     struct Base {};