[analyzer] Fix assertion in SVals.h

Fix assertion in SVals.h apparently caused by
https://reviews.llvm.org/D89055.

clang:clang/include/clang/StaticAnalyzer/Core/PathSensitive/SVals.h:596:
clang::ento::loc::MemRegionVal::MemRegionVal(const clang::ento::MemRegion *):
  Assertion `r' failed.

Backtrace:
...
     clang/include/clang/StaticAnalyzer/Core/PathSensitive/SVals.h:597:3
     clang::QualType, clang::QualType)
     clang/lib/StaticAnalyzer/Core/SValBuilder.cpp:773:18
     clang::QualType, clang::QualType)
     clang/lib/StaticAnalyzer/Core/SValBuilder.cpp:612:12
     clang::QualType) clang/lib/StaticAnalyzer/Core/SValBuilder.cpp:587:12
     namespace)::RegionBindingsRef const&, clang::ento::Loc, clang::QualType)
     clang/lib/StaticAnalyzer/Core/RegionStore.cpp:1510:24
...

Reviewed By: ASDenysPetrov

Differential Revision: https://reviews.llvm.org/D101635

clang/lib/StaticAnalyzer/Core/SValBuilder.cpp

@@ -761,8 +761,8 @@ SVal SValBuilder::evalCastSubKind(loc::MemRegionVal V, QualType CastTy,
       // Next fixes pointer dereference using type different from its initial
       // one. See PR37503 and PR49007 for details.
       if (const auto *ER = dyn_cast<ElementRegion>(R)) {
-        R = StateMgr.getStoreManager().castRegion(ER, CastTy);
-        return loc::MemRegionVal(R);
+        if ((R = StateMgr.getStoreManager().castRegion(ER, CastTy)))
+          return loc::MemRegionVal(R);
       }
 
       return V;

clang/test/Analysis/casts.c

@@ -250,3 +250,19 @@ void no_crash_reinterpret_char_as_uchar(char ***a, int *b) {
   if (**a == 0) // no-crash
     ;
 }
+
+// See PR50179.
+// Just don't crash.
+typedef struct taskS {
+  void *pJob;
+} taskS;
+
+typedef struct workS {
+  taskS *pTaskList;
+} workS;
+
+void *getTaskJob(unsigned jobId, workS *pWork, unsigned taskId) {
+  const taskS *pTask = pWork->pTaskList + taskId;
+  taskS task = *pTask;
+  return task.pJob;
+}