[analyzer] Fix a crash on casting symbolic pointers to derived classes.

Commit r340984 causes a crash when a pointer to a completely unrelated type
UnrelatedT (eg., opaque struct pattern) is being casted from base class BaseT to
derived class DerivedT, which results in an ill-formed region
Derived{SymRegion{$<UnrelatedT x>}, DerivedT}.

Differential Revision: https://reviews.llvm.org/D52189

llvm-svn: 343051

1 files changed, 11 insertions, 1 deletions

diff --git a/clang/lib/StaticAnalyzer/Core/Store.cpp b/clang/lib/StaticAnalyzer/Core/Store.cpp
index c3b706d90f6..cc9939a68dc 100644
--- a/clang/lib/StaticAnalyzer/Core/Store.cpp
+++ b/clang/lib/StaticAnalyzer/Core/Store.cpp
@@ -375,8 +375,18 @@ SVal StoreManager::attemptDownCast(SVal Base, QualType TargetType,
     MR = Uncasted;
   }
 
+  // If we're casting a symbolic base pointer to a derived class, use
+  // CXXDerivedObjectRegion to represent the cast. If it's a pointer to an
+  // unrelated type, it must be a weird reinterpret_cast and we have to
+  // be fine with ElementRegion. TODO: Should we instead make
+  // Derived{TargetClass, Element{SourceClass, SR}}?
   if (const auto *SR = dyn_cast<SymbolicRegion>(MR)) {
-    return loc::MemRegionVal(MRMgr.getCXXDerivedObjectRegion(TargetClass, SR));
+    QualType T = SR->getSymbol()->getType();
+    const CXXRecordDecl *SourceClass = T->getPointeeCXXRecordDecl();
+    if (TargetClass && SourceClass && TargetClass->isDerivedFrom(SourceClass))
+      return loc::MemRegionVal(
+          MRMgr.getCXXDerivedObjectRegion(TargetClass, SR));
+    return loc::MemRegionVal(GetElementZeroRegion(SR, TargetType));
   }
 
   // We failed if the region we ended up with has perfect type info.