[PATCH] Sema: Fix CheckReturnStackAddr when RetValExp is an explicit cast

[Chongyu Zhu]

I have found that `Sema::CheckReturnStackAddr` failed to generate warnings
for `diag::warn_ret_stack_ref` and `diag::warn_ret_local_temp_ref` when the
return value expression is an explicit cast.

Provided the following code,

> const int &test1()
> {
>   return 0;
> }
> 
> const int &test2()
> {
>   int val = 0;
>   return val;
> }
> 
> const int &test3()
> {
>   return static_cast<const int &>(0);
> }
> 
> const int &test4()
> {
>   int val = 0;
>   return static_cast<const int &>(val);
> }

Clang (as of r194251) generates warnings for `test1` and `test2`, however,
no warnings are given for `test3` and `test4`.

GCC (4.8.1) is able to successfully generate warnings for all of the above.

http://llvm-reviews.chandlerc.com/D2132

Files:
  lib/Sema/SemaChecking.cpp

Index: lib/Sema/SemaChecking.cpp
===================================================================
--- lib/Sema/SemaChecking.cpp
+++ lib/Sema/SemaChecking.cpp
@@ -4192,10 +4192,17 @@
 
   E = E->IgnoreParens();
   switch (E->getStmtClass()) {
-  case Stmt::ImplicitCastExprClass: {
-    ImplicitCastExpr *IE = cast<ImplicitCastExpr>(E);
-    if (IE->getValueKind() == VK_LValue) {
-      E = IE->getSubExpr();
+  case Stmt::ImplicitCastExprClass:
+  case Stmt::CStyleCastExprClass:
+  case Stmt::CXXStaticCastExprClass:
+  case Stmt::CXXDynamicCastExprClass:
+  case Stmt::CXXReinterpretCastExprClass:
+  case Stmt::CXXConstCastExprClass:
+  case Stmt::CXXFunctionalCastExprClass:
+  case Stmt::ObjCBridgedCastExprClass: {
+    CastExpr *CE = cast<CastExpr>(E);
+    if (CE->getValueKind() == VK_LValue) {
+      E = CE->getSubExpr();
       continue;
     }
     return NULL;
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