Re: FIXNUM_OVERFLOW_P on amd64

[Francesco Potorti`]

>
>> gcc -c -D_BSD_SOURCE   -Demacs -DHAVE_CONFIG_H   -I. 
>> -I/home/pot/gnu/emacs-22.0.91/src -D_BSD_SOURCE  -g -O2 -Wno-pointer-sign  
>> editfns.c
>> editfns.c: In function 'Fuser_uid':
>> editfns.c:1317: warning: comparison is always false due to limited range of 
>> data type
>> editfns.c:1317: warning: comparison is always false due to limited range of 
>> data type
>[...]
>> So the problem apparently is that gcc realises that taking geteuid(),
>> stretching it to long and then comparing it with something bigger that
>> what geteuid() possibly can be is a no-op.  This is what is intended, in
>> fact.  To remove the warning, I tried to change the definition of
>> FIXNUM_OVERFLOW_P in lisp.h by adding a precondition like this:
>
>This warning is clearly wrong.  The same problem happens at various places
>with SINGLE_BYTE_P which is sometimes called from a macro at spots where we
>happen to always know that the char is < 256 (for example).

I also have many others.  Most of them are related to the same macro in lisp.h.

>The problem is that such constant expressions are sometimes an indication of
>a programming bug, but they can also be the result of very good coding
>practices, where you want to let the compiler do the optimization.

Yes.  Can we do anything for preventing gcc from emitting those warnings?