[Bug c/17665] wrong code with -O2

["davids at webmaster dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From davids at webmaster dot com  2004-09-25 17:35 -------
(In reply to comment #4)

> The problematic object types in your code are "void *" and "char *" 
> (accessed by dereferencing "void **" and "char **" pointers), not "void" 
> and "char".

This is legal C and C++. The *only* use for 'void *' is to alias something. If 
it was 'char *' and 'int *', I'd 100% agree with you. However, you are 
specifically permitted to alias 'void *'.

Other than returning NULL or using it in a union, there is nothing you can do 
with 'void *' other than to use it to hold the same thing as some other type.

A pointer to a void is not actually a pointer to a void, it's a generic pointer 
type. Its typical use, defined by the standard, is to cast other types through 
it.

Unless you can explain how my use of 'void *' differs from the types 
specifically permitted by the standard, calling this bug report invalid is 
equivalent to saying you can't use 'void *' without defining -fno-strict-
aliasing.

Basically, what I'm saying is that because the standard specifically allows 
(and precisely defined the affects of) casting other pointer types to 'void *', 
the compiler should not assume that a 'void *' isn't an alias of another type, 
thought it is entirely justified in doing so for other types.

DS


-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |UNCONFIRMED
         Resolution|INVALID                     |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17665