On Wed, Nov 1, 2023 at 3:56 AM Daniil Frolov <exactl...@ispras.ru> wrote:
>
> Hi!
>
> When investigating bit shifts I got an incomprehensible moment with
> the following example:
>
> int f(int x, int k)
> {
> int tmp = x >> k;
> return (tmp & 1) << 10;
> }
>
> If we would like to take a look into GIMPLE then we'll get:
>
> int f (int x, int k)
> {
> int tmp;
> int D.2746;
> int _1;
> int _5;
>
> <bb 2> :
> tmp_4 = x_2(D) >> k_3(D);
> _1 = tmp_4 << 10;
> _5 = _1 & 1024;
>
> <bb 3> :
> <L0>:
> return _5;
>
> }
>
> Is the expression '_1 = tmp_4 << 10' considered legal in GIMPLE? Given
> the
> semantics of C bit shifts, this statement could modify the sign bit,
> potentially leading to overflow.
Except it was not undefined in C90.
Thanks,
Andrew
>
> ---
> With best regards,
> Daniil
