From f2f108254546136b476af5dcfe77fa8120adc5bc Mon Sep 17 00:00:00 2001
From: Matthew Bentham <matthew.bentham@arm.com>
Date: Wed, 30 Jun 2021 12:00:05 +0100
Subject: Fix undefined behaviour in PolymorphicDowncast

In the assertion part of PolymorphicDowncast (and PolymorphicPointerDowncast)
there was an unnecessary static_cast of the source pointer to the destination
type. This is unnecessary because the implicit conversion of the result pointer
back to the base type is sufficient to check for correctness of the downcast,
and potentially harmful because if the downcast is actually incorrect the
behaviour of static_cast is undefined (not actually known to be a problem
in any tested implementation).

Fixes warnings detected by ubsan.

Signed-off-by: Matthew Bentham <matthew.bentham@arm.com>
Change-Id: I9126288cbb06564009f94e57f6ca4688fc3b53c4
---
 include/armnn/utility/PolymorphicDowncast.hpp | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/include/armnn/utility/PolymorphicDowncast.hpp b/include/armnn/utility/PolymorphicDowncast.hpp
index 8f052370e5..76b00fa888 100644
--- a/include/armnn/utility/PolymorphicDowncast.hpp
+++ b/include/armnn/utility/PolymorphicDowncast.hpp
@@ -48,14 +48,14 @@ std::shared_ptr<T1> DynamicPointerCast (const std::shared_ptr<T2>& sp)
 
 // static_pointer_cast overload for raw pointers
 template<class T1, class T2>
-inline T1* StaticPointerCast(T2 *ptr)
+inline T1* StaticPointerCast(T2* ptr)
 {
     return static_cast<T1*>(ptr);
 }
 
 // dynamic_pointer_cast overload for raw pointers
 template<class T1, class T2>
-inline T1* DynamicPointerCast(T2 *ptr)
+inline T1* DynamicPointerCast(T2* ptr)
 {
     return dynamic_cast<T1*>(ptr);
 }
@@ -71,13 +71,12 @@ inline T1* DynamicPointerCast(T2 *ptr)
 /// \param value        Pointer to the source object
 /// \return             Pointer of type DestType (Pointer of type child)
 template<typename DestType, typename SourceType>
-DestType PolymorphicDowncast(SourceType value)
+DestType PolymorphicDowncast(SourceType* value)
 {
-    static_assert(std::is_pointer<SourceType>::value &&
-                  std::is_pointer<DestType>::value,
+    static_assert(std::is_pointer<DestType>::value,
                   "PolymorphicDowncast only works with pointer types.");
 
-    ARMNN_POLYMORPHIC_CAST_CHECK(dynamic_cast<DestType>(value) == static_cast<DestType>(value));
+    ARMNN_POLYMORPHIC_CAST_CHECK(dynamic_cast<DestType>(value) == value);
     return static_cast<DestType>(value);
 }
 
@@ -94,8 +93,8 @@ template<typename DestType, typename SourceType>
 auto PolymorphicPointerDowncast(const SourceType& value)
 {
     ARMNN_POLYMORPHIC_CAST_CHECK(utility::DynamicPointerCast<DestType>(value)
-                                 == utility::StaticPointerCast<DestType>(value));
+                                 == value);
     return utility::StaticPointerCast<DestType>(value);
 }
 
-} //namespace armnn
\ No newline at end of file
+} //namespace armnn
-- 
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