[cfe-dev] warnings in clang

[Argiris Kirtzidis]

Mike Stump wrote:
> On Nov 14, 2008, at 2:55 PM, Argiris Kirtzidis wrote:
>> Mike Stump wrote:
>>> Here are the warnings from a recent build of clang (-r59324):
>>>
>>> DeclSerialization.cpp: In member function 'void  
>>> clang::ScopedDecl::ReadInRec(llvm::Deserializer&, clang::ASTContext&)':
>>> DeclSerialization.cpp:170: warning: dereferencing type-punned 
>>> pointer  will break strict-aliasing rules
>>> DeclSerialization.cpp:171: warning: dereferencing type-punned 
>>> pointer  will break strict-aliasing rules
>>
>> I'm the one to blame for these. Care to explain more about what is 
>> wrong and how to fix it ?
>
> Hum, depends upon your background.  I'd assume you're new to the 
> wording in the standards that says that you can only play with a type 
> as the type (plus a few other obscure cases).  If you change your code 
> to always play with variables of type X, as type X, you can never get 
> this error.
>
>> D.ReadUIntPtr(reinterpret_cast<uintptr_t&>(MDC->SemanticDC), 
>> SemaDCPtrID);
>>
>> where 'MDC->SemanticDC' is a pointer (DeclContext*).
>
> reinterpret_cast<uintptr_t&>?  Never use reinterpret_cast.

Here's a similar case, doesn't gcc has a problem with this ?

  template <typename T>
  void ReadPtr(T*& PtrRef, const SerializedPtrID& PtrID,
               bool AllowBackpatch = true) {
    ReadUIntPtr(reinterpret_cast<uintptr_t&>(PtrRef), PtrID, 
AllowBackpatch);
  }