Use the new LLVM_LVALUE_FUNCTION to ban two getAs() calls on rvalues.

If 'x' is a temporary, x.getAs<Foo>() may not be safe if the result is
supposed to persist (if its address is stored somewhere). Since getAs()
can return a null value, the result is almost always stored into a
variable, which of course is not safe when the original value dies.

This has caused several bugs with GCC's "Temporaries May Vanish Sooner Than
You Expect" optimization; in C++11 builds, at least, we'll be able to catch
these problems now.

I would suggest applying these to other getAs() and get*As() methods
(castAs is "better" because sometimes the result is used directly, which
means the temporary will still be live), but these two have both caused
trouble in the analyzer in the past.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@168967 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 14 insertions, 5 deletions

diff --git a/include/clang/Analysis/CFG.h b/include/clang/Analysis/CFG.h
index 8cc5d814e8..5fcd64c76c 100644
--- a/include/clang/Analysis/CFG.h
+++ b/include/clang/Analysis/CFG.h
@@ -83,11 +83,13 @@ public:
 
   operator bool() const { return isValid(); }
 
-  template<class ElemTy> const ElemTy *getAs() const {
-    if (llvm::isa<ElemTy>(this))
-      return static_cast<const ElemTy*>(this);
-    return 0;
+  template<class ElemTy> const ElemTy *getAs() const LLVM_LVALUE_FUNCTION {
+    return dyn_cast<ElemTy>(this);
   }
+
+#if LLVM_USE_RVALUE_REFERENCES
+  template<class ElemTy> void getAs() && LLVM_DELETED_FUNCTION;
+#endif
 };
 
 class CFGStmt : public CFGElement {
diff --git a/include/clang/StaticAnalyzer/Core/PathSensitive/ExplodedGraph.h b/include/clang/StaticAnalyzer/Core/PathSensitive/ExplodedGraph.h
index b112e66d30..ebdb02dd22 100644
--- a/include/clang/StaticAnalyzer/Core/PathSensitive/ExplodedGraph.h
+++ b/include/clang/StaticAnalyzer/Core/PathSensitive/ExplodedGraph.h
@@ -155,7 +155,14 @@ public:
   ProgramStateRef getState() const { return State; }
 
   template <typename T>
-  const T* getLocationAs() const { return llvm::dyn_cast<T>(&Location); }
+  const T* getLocationAs() const LLVM_LVALUE_FUNCTION {
+    return dyn_cast<T>(&Location);
+  }
+
+#if LLVM_USE_RVALUE_REFERENCES
+  template <typename T>
+  void getLocationAs() && LLVM_DELETED_FUNCTION;
+#endif
 
   static void Profile(llvm::FoldingSetNodeID &ID,
                       const ProgramPoint &Loc,