Re: GCC 2.95.3 bug

[Sebastian Redl <sebastian dot redl at getdesigned dot at>]

Balogh, Ray wrote:
> Dear GCC folks:
>
> I'm having a problem with GCC 2.95.3 that appears to be a compiler bug.  It seems to be optimizing out inlined function code with side effects, and is related to binding a non-const pointer to a const pointer reference function parameter.  The problem only happens with optimization on, and goes away with -O0.
>
> inline unsigned unpack2 (const byte *&data)
> {
>     unsigned val = data[0] << 8 | data[1];
>     data += 2;
>     return val;
> }
> inline unsigned unpack2 (const byte *&data, unsigned &count)
> {
>     unsigned val = data[0] << 8 | data[1];
>     data += 2;
>     count -= 2;
>     return val;
> }
>
> void extractInfo (byte *&data, unsigned &datalen,
>                        unsigned &f1, unsigned &f2)
> {
>     cout << "data = " << data << ", datalen = " << datalen << endl;
>     f1 = unpack2 (data, datalen);
>     cout << "data = " << data << ", datalen = " << datalen << endl;
>
>     byte *peek = data;
>     //const byte *peek = data;  // **** Adding "const" works around the compiler problem ****
>                                 // Another work-around is to uncomment the non-const f1 of unpack2() above
>
>     unsigned tmp = datalen;
>     cout << "peek = " << peek << ", tmp = " << tmp << endl;
>     (void) unpack2 (peek, tmp);    // skip over irrelevant field
>     cout << "peek = " << peek << ", tmp = " << tmp << endl;
>     (void) unpack2 (peek, tmp);    // skip over irrelevant field
>     cout << "peek = " << peek << ", tmp = " << tmp << endl;
>
>     unsigned xlen = unpack2 (peek, tmp);
>     cout << "peek = " << peek << ", tmp = " << tmp << endl;
>
>     f2 = xlen;
> }
>   
In my opinion, the bug is that this even compiles. It's invalid to write
char *pc;
const char **ppc = &pc;

Why should it be valid to write
char *pc;
const char *&rpc = pc;
?

Sebastian