Cleanup the simplify_type implementation.

As far as simplify_type is concerned, there are 3 kinds of smart pointers:

* const correct: A 'const MyPtr<int> &' produces a 'const int*'. A
'MyPtr<int> &' produces a 'int *'.
* always const: Even a 'MyPtr<int> &' produces a 'const int*'.
* no const: Even a 'const MyPtr<int> &' produces a 'int*'.

This patch then does the following:

* Removes the unused specializations. Since they are unused, it is hard
to know which kind should be implemented.
* Make sure we don't drop const.
* Fix the default forwarding so that const correct pointer only need
one specialization.
* Simplifies the existing specializations.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178147 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Support/Casting.h

@@ -36,9 +36,13 @@ template<typename From> struct simplify_type {
 };
 
 template<typename From> struct simplify_type<const From> {
-  typedef const From SimpleType;
-  static SimpleType &getSimplifiedValue(const From &Val) {
-    return simplify_type<From>::getSimplifiedValue(static_cast<From&>(Val));
+  typedef typename simplify_type<From>::SimpleType NonConstSimpleType;
+  typedef typename add_const_past_pointer<NonConstSimpleType>::type
+    SimpleType;
+  typedef typename add_lvalue_reference_if_not_pointer<SimpleType>::type
+    RetType;
+  static RetType getSimplifiedValue(const From& Val) {
+    return simplify_type<From>::getSimplifiedValue(const_cast<From&>(Val));
   }
 };
 
@@ -81,6 +85,13 @@ template <typename To, typename From> struct isa_impl_cl<To, From*> {
   }
 };
 
+template <typename To, typename From> struct isa_impl_cl<To, From*const> {
+  static inline bool doit(const From *Val) {
+    assert(Val && "isa<> used on a null pointer");
+    return isa_impl<To, From>::doit(*Val);
+  }
+};
+
 template <typename To, typename From> struct isa_impl_cl<To, const From*> {
   static inline bool doit(const From *Val) {
     assert(Val && "isa<> used on a null pointer");
@@ -102,7 +113,7 @@ struct isa_impl_wrap {
   static bool doit(const From &Val) {
     return isa_impl_wrap<To, SimpleFrom,
       typename simplify_type<SimpleFrom>::SimpleType>::doit(
-                          simplify_type<From>::getSimplifiedValue(Val));
+                          simplify_type<const From>::getSimplifiedValue(Val));
   }
 };
 
@@ -121,7 +132,8 @@ struct isa_impl_wrap<To, FromTy, FromTy> {
 //
 template <class X, class Y>
 inline bool isa(const Y &Val) {
-  return isa_impl_wrap<X, Y, typename simplify_type<Y>::SimpleType>::doit(Val);
+  return isa_impl_wrap<X, const Y,
+                       typename simplify_type<const Y>::SimpleType>::doit(Val);
 }
 
 //===----------------------------------------------------------------------===//
@@ -178,7 +190,7 @@ struct cast_retty {
 //
 template<class To, class From, class SimpleFrom> struct cast_convert_val {
   // This is not a simple type, use the template to simplify it...
-  static typename cast_retty<To, From>::ret_type doit(const From &Val) {
+  static typename cast_retty<To, From>::ret_type doit(From &Val) {
     return cast_convert_val<To, SimpleFrom,
       typename simplify_type<SimpleFrom>::SimpleType>::doit(
                           simplify_type<From>::getSimplifiedValue(Val));
@@ -204,20 +216,14 @@ template<class To, class FromTy> struct cast_convert_val<To,FromTy,FromTy> {
 //  cast<Instruction>(myVal)->getParent()
 //
 template <class X, class Y>
-inline typename enable_if_c<
-  !is_same<Y, typename simplify_type<Y>::SimpleType>::value,
-  typename cast_retty<X, Y>::ret_type
->::type cast(const Y &Val) {
+inline typename cast_retty<X, const Y>::ret_type cast(const 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);
+  return cast_convert_val<X, const Y,
+                        typename simplify_type<const Y>::SimpleType>::doit(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);
@@ -253,18 +259,12 @@ inline typename cast_retty<X, Y*>::ret_type cast_or_null(Y *Val) {
 //
 
 template <class X, class Y>
-inline typename enable_if_c<
-  !is_same<Y, typename simplify_type<Y>::SimpleType>::value,
-  typename cast_retty<X, Y>::ret_type
->::type dyn_cast(const Y &Val) {
+inline typename cast_retty<X, const Y>::ret_type dyn_cast(const Y &Val) {
   return isa<X>(Val) ? cast<X>(Val) : 0;
 }
 
 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;
 }
 

include/llvm/Support/ValueHandle.h

@@ -20,6 +20,7 @@
 
 namespace llvm {
 class ValueHandleBase;
+template<typename From> struct simplify_type;
 
 // ValueHandleBase** is only 4-byte aligned.
 template<>
@@ -162,14 +163,12 @@ public:
 
 // Specialize simplify_type to allow WeakVH to participate in
 // dyn_cast, isa, etc.
-template<typename From> struct simplify_type;
-template<> struct simplify_type<const WeakVH> {
+template<> struct simplify_type<WeakVH> {
   typedef Value* SimpleType;
-  static SimpleType getSimplifiedValue(const WeakVH &WVH) {
-    return static_cast<Value *>(WVH);
+  static SimpleType getSimplifiedValue(WeakVH &WVH) {
+    return WVH;
   }
 };
-template<> struct simplify_type<WeakVH> : public simplify_type<const WeakVH> {};
 
 /// AssertingVH - This is a Value Handle that points to a value and asserts out
 /// if the value is destroyed while the handle is still live.  This is very
@@ -236,18 +235,6 @@ public:
   ValueTy &operator*() const { return *getValPtr(); }
 };
 
-// Specialize simplify_type to allow AssertingVH to participate in
-// dyn_cast, isa, etc.
-template<typename From> struct simplify_type;
-template<> struct simplify_type<const AssertingVH<Value> > {
-  typedef Value* SimpleType;
-  static SimpleType getSimplifiedValue(const AssertingVH<Value> &AVH) {
-    return static_cast<Value *>(AVH);
-  }
-};
-template<> struct simplify_type<AssertingVH<Value> >
-  : public simplify_type<const AssertingVH<Value> > {};
-
 // Specialize DenseMapInfo to allow AssertingVH to participate in DenseMap.
 template<typename T>
 struct DenseMapInfo<AssertingVH<T> > {
@@ -345,18 +332,6 @@ public:
   ValueTy &operator*() const { return *getValPtr(); }
 };
 
-// Specialize simplify_type to allow TrackingVH to participate in
-// dyn_cast, isa, etc.
-template<typename From> struct simplify_type;
-template<> struct simplify_type<const TrackingVH<Value> > {
-  typedef Value* SimpleType;
-  static SimpleType getSimplifiedValue(const TrackingVH<Value> &AVH) {
-    return static_cast<Value *>(AVH);
-  }
-};
-template<> struct simplify_type<TrackingVH<Value> >
-  : public simplify_type<const TrackingVH<Value> > {};
-
 /// CallbackVH - This is a value handle that allows subclasses to define
 /// callbacks that run when the underlying Value has RAUW called on it or is
 /// destroyed.  This class can be used as the key of a map, as long as the user
@@ -399,18 +374,6 @@ public:
   virtual void allUsesReplacedWith(Value *);
 };
 
-// Specialize simplify_type to allow CallbackVH to participate in
-// dyn_cast, isa, etc.
-template<typename From> struct simplify_type;
-template<> struct simplify_type<const CallbackVH> {
-  typedef Value* SimpleType;
-  static SimpleType getSimplifiedValue(const CallbackVH &CVH) {
-    return static_cast<Value *>(CVH);
-  }
-};
-template<> struct simplify_type<CallbackVH>
-  : public simplify_type<const CallbackVH> {};
-
 } // End llvm namespace
 
 #endif

include/llvm/Support/type_traits.h

@@ -209,6 +209,26 @@ template <typename T> struct remove_pointer<T*volatile> { typedef T type; };
 template <typename T> struct remove_pointer<T*const volatile> {
     typedef T type; };
 
+// If T is a pointer, just return it. If it is not, return T&.
+template<typename T, typename Enable = void>
+struct add_lvalue_reference_if_not_pointer { typedef T &type; };
+
+template<typename T>
+struct add_lvalue_reference_if_not_pointer<T,
+                                     typename enable_if<is_pointer<T> >::type> {
+  typedef T type;
+};
+
+// If T is a pointer to X, return a pointer to const X. If it is not, return
+// const T.
+template<typename T, typename Enable = void>
+struct add_const_past_pointer { typedef const T type; };
+
+template<typename T>
+struct add_const_past_pointer<T, typename enable_if<is_pointer<T> >::type> {
+  typedef const typename remove_pointer<T>::type *type;
+};
+
 template <bool, typename T, typename F>
 struct conditional { typedef T type; };