Hi,
I am working on how to improve "restrict". I noticed
that my changes lead to failure of pr38212. After looking
at its code, I think the test may not be valid according
to c99 standard.
C99 standard 6.7.3.1:
EXAMPLE 4 The rule limiting assignments between restricted pointers does not
distinguish between a
function call and an equivalent nested block. With one exception, only
''outer-to-inner'' assignments
between restricted pointers declared in nested blocks have defined behavior.
{
int * restrict p1;
int * restrict q1;
p1 = q1; // undefined behavior
{
int * restrict p2 = p1; // valid
int * restrict q2 = q1; // valid
p1 = q2; // undefined behavior
p2 = q2; // undefined behavior
}
}
pr38212.c
int __attribute__((noinline))
foo (int *__restrict p, int i)
{
int *__restrict q;
int *__restrict r;
int v, w;
q = p + 1;
r = q - i;
v = *r;
*p = 1;
w = *r;
return v + w;
}
extern void abort (void);
int main()
{
int i = 0;
if (foo (&i, 1) != 1)
abort ();
return 0;
}
Isn't that "r = q - i" undefined? "q = p + 1" may be also undefined,
depending whether we regard parameter p from outer or inner block.
Cheers,
Bingfeng
