Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."

[Bernd Schmidt <bernds_cb1 at t-online dot de>]

Eric Blake wrote:

> /* The maximum and minimum values for the integer type T.  These
>    macros have undefined behavior if T is signed and has padding bits.
>    If this is a problem for you, please let us know how to fix it for
>    your host.  */
> #define TYPE_MINIMUM(t) \
>   ((t) (! TYPE_SIGNED (t) \
> 	? (t) 0 \
> 	: TYPE_SIGNED_MAGNITUDE (t) \
> 	? ~ (t) 0 \
> 	: ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1)))
> #define TYPE_MAXIMUM(t) \
>   ((t) (! TYPE_SIGNED (t) \
> 	? (t) -1 \
> 	: ~ (~ (t) 0 << (sizeof (t) * CHAR_BIT - 1))))

I must admit I don't know what an integer with padding bits would look 
like.  Can someone check what the C standard has to say about the 
bit-not operator?  According to what GCC currently does, there is no 
integer overflow anywhere in this code: bit-not expressions never 
overflow, and a integer shift of -1 by (sizeof - 1) bits does not change 
the sign, and therefore doesn't overflow.

Even with -Woverflow, GCC does not warn when these macros are used for 
type "int".


Bernd