gcc-3.4.4-20050211: maybe a danger behaviour

gcc-3.4.4-20050211: maybe a danger behaviour

[Denis Zaitsev]

Consider the following example:


enum w {
//    c=-1,
    a,
    b
};
whattodo (
    char option
) {
    static
    struct todo {
        enum w what;
        char option;
    } todos[]= {
        {a,'a'},
        {b,'b'},
        {-1}
    };
    struct todo *p= todos;
    do if (
        (option && !option)
    ) break;
    while ((++p)->what >= 0);
    return p->what;
}


Compiling with -O[>0] and -Wall for x86 we have that code for
whattodo:


whattodo:
.L2:
	jmp	.L2


a) Formally, the code is correct.  As p->what can never be < 0
according to its type.

b) GCC _silently_ allows the {-1} initialization for that type, even
with -Wall.

Uncommenting the c= -1 member of enum, or explicit casting p->what to
int solves the problem, of course.  But maybe some warning would be
appropriate in such a situation?  It takes some time for me to
recognize what leads me to that cool .L2: jmp .L2 from seemengly
harmless C code...  Or maybe I don't know some healthy compiler
option?