"Udo A. Steinberg" <us15@xxxxxxxxxxxxxxxxxxxx> writes:
> gcc now complains about the following code snippet, saying...
> warning: assuming pointer wraparound does not occur when comparing
> P +- C1 with P +- C2
Presumably only when you use -Wstrict-overflow=N where N >= 3. At
that level false positives are likely.
> char const x[] = "deadbeef";
> int main (void)
> {
> for (char const *ptr = x; ptr < x + 4; ptr++)
> putc (*ptr, stdout);
>
> return 0;
> }
> In the first snippet ptr never points outside x[], so the compiler shouldn't
> warn. What am I missing here?
Nothing. The compiler could be smarter here. pointer_may_wrap_p in
fold-const.c could handle TREE_CODE (TREE_TYPE (base)) == ARRAY_TYPE.
By the way, the compiler doesn't warn here:
> char const *x = "deadbeef";
> int main (void)
> {
> for (char const *ptr = x; ptr < x + 4; ptr++)
> putc (*ptr, stdout);
>
> return 0;
> }
because it doesn't know that putc doesn't change x, so it can't
optimize away the comparison.
Ian
