Fix a regression I introduced back in r178147.

We don't want cast and dyn_cast to work on temporaries. They don't extend
lifetime like a direct bind to a reference would, so they can introduce
hard to find bugs.

I added tests to make sure we don't regress this. Thanks to Eli Friedman for
noticing this and for his suggestions on how to test it.

llvm-svn: 186559

llvm/include/llvm/Support/Casting.h

@@ -206,7 +206,10 @@ template<class To, class FromTy> struct cast_convert_val<To,FromTy,FromTy> {
   }
 };
 
-
+template <class X> struct is_simple_type {
+  static const bool value =
+      is_same<X, typename simplify_type<X>::SimpleType>::value;
+};
 
 // cast<X> - Return the argument parameter cast to the specified type.  This
 // casting operator asserts that the type is correct, so it does not return null
@@ -216,10 +219,12 @@ template<class To, class FromTy> struct cast_convert_val<To,FromTy,FromTy> {
 //  cast<Instruction>(myVal)->getParent()
 //
 template <class X, class Y>
-inline typename cast_retty<X, const Y>::ret_type cast(const Y &Val) {
+inline typename enable_if_c<!is_simple_type<Y>::value,
+                            typename cast_retty<X, const Y>::ret_type>::type
+cast(const Y &Val) {
   assert(isa<X>(Val) && "cast<Ty>() argument of incompatible type!");
-  return cast_convert_val<X, const Y,
-                        typename simplify_type<const Y>::SimpleType>::doit(Val);
+  return cast_convert_val<
+      X, const Y, typename simplify_type<const Y>::SimpleType>::doit(Val);
 }
 
 template <class X, class Y>
@@ -230,10 +235,7 @@ inline typename cast_retty<X, Y>::ret_type cast(Y &Val) {
 }
 
 template <class X, class Y>
-inline typename enable_if<
-  is_same<Y, typename simplify_type<Y>::SimpleType>,
-  typename cast_retty<X, Y*>::ret_type
->::type cast(Y *Val) {
+inline typename cast_retty<X, Y *>::ret_type cast(Y *Val) {
   assert(isa<X>(Val) && "cast<Ty>() argument of incompatible type!");
   return cast_convert_val<X, Y*,
                           typename simplify_type<Y*>::SimpleType>::doit(Val);
@@ -259,7 +261,9 @@ inline typename cast_retty<X, Y*>::ret_type cast_or_null(Y *Val) {
 //
 
 template <class X, class Y>
-inline typename cast_retty<X, const Y>::ret_type dyn_cast(const Y &Val) {
+inline typename enable_if_c<!is_simple_type<Y>::value,
+                            typename cast_retty<X, const Y>::ret_type>::type
+dyn_cast(const Y &Val) {
   return isa<X>(Val) ? cast<X>(Val) : 0;
 }
 
@@ -269,10 +273,7 @@ inline typename cast_retty<X, Y>::ret_type dyn_cast(Y &Val) {
 }
 
 template <class X, class Y>
-inline typename enable_if<
-  is_same<Y, typename simplify_type<Y>::SimpleType>,
-  typename cast_retty<X, Y*>::ret_type
->::type dyn_cast(Y *Val) {
+inline typename cast_retty<X, Y *>::ret_type dyn_cast(Y *Val) {
   return isa<X>(Val) ? cast<X>(Val) : 0;
 }
 

llvm/unittests/Support/Casting.cpp

@@ -10,10 +10,15 @@
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm/IR/User.h"
 #include "gtest/gtest.h"
 #include <cstdlib>
 
 namespace llvm {
+// Used to test illegal cast. If a cast doesn't match any of the "real" ones,
+// it will match this one.
+struct IllegalCast;
+template <typename T> IllegalCast *cast(...) { return 0; }
 
 // set up two example classes
 // with conversion facility
@@ -60,10 +65,25 @@ foo *bar::naz() {
 
 
 bar *fub();
+
+template <> struct simplify_type<foo> {
+  typedef int SimpleType;
+  static SimpleType getSimplifiedValue(foo &Val) { return 0; }
+};
+
 } // End llvm namespace
 
 using namespace llvm;
 
+
+// Test the peculiar behavior of Use in simplify_type.
+int Check1[is_same<simplify_type<Use>::SimpleType, Value *>::value ? 1 : -1];
+int Check2[is_same<simplify_type<Use *>::SimpleType, Value *>::value ? 1 : -1];
+
+// Test that a regular class behaves as expected.
+int Check3[is_same<simplify_type<foo>::SimpleType, int>::value ? 1 : -1];
+int Check4[is_same<simplify_type<foo *>::SimpleType, foo *>::value ? 1 : -1];
+
 namespace {
 
 const foo *null_foo = NULL;
@@ -203,3 +223,8 @@ TEST(CastingTest, InferredUpcastTakesPrecedence) {
 
 } // end namespace inferred_upcasting
 } // end anonymous namespace
+// Test that we reject casts of temporaries (and so the illegal cast gets used).
+namespace TemporaryCast {
+struct pod {};
+IllegalCast *testIllegalCast() { return cast<foo>(pod()); }
+}