On Mon, Oct 12, 2020 at 6:57 PM Aldy Hernandez via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Division by zero should return VARYING, otherwise we propagate undefine all
> over the
> ranger and cause bad things to happen :)
So we never should propagate UNDEFINED?
>. This fixes MOD 0 to also return VARYING.
>
> This is Andrew's patch. I forgot to use --author for proper patch
> attribution.
>
> Tested on x86-64 Linux.
>
> Pushed to trunk.
>
> gcc/ChangeLog:
>
> PR tree-optimization/97378
> * range-op.cc (operator_trunc_mod::wi_fold): Return VARYING for mod
> by zero.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.dg/pr97378.c: New test.
> ---
> gcc/range-op.cc | 6 +++---
> gcc/testsuite/gcc.dg/pr97378.c | 15 +++++++++++++++
> 2 files changed, 18 insertions(+), 3 deletions(-)
> create mode 100644 gcc/testsuite/gcc.dg/pr97378.c
>
> diff --git a/gcc/range-op.cc b/gcc/range-op.cc
> index ce6ae2de20c..6108de367ad 100644
> --- a/gcc/range-op.cc
> +++ b/gcc/range-op.cc
> @@ -1359,7 +1359,7 @@ operator_div::wi_fold (irange &r, tree type,
> // If we're definitely dividing by zero, there's nothing to do.
> if (wi_zero_p (type, divisor_min, divisor_max))
> {
> - r.set_undefined ();
> + r.set_varying (type);
> return;
> }
>
> @@ -2624,10 +2624,10 @@ operator_trunc_mod::wi_fold (irange &r, tree type,
> signop sign = TYPE_SIGN (type);
> unsigned prec = TYPE_PRECISION (type);
>
> - // Mod 0 is undefined. Return undefined.
> + // Mod 0 is undefined.
> if (wi_zero_p (type, rh_lb, rh_ub))
> {
> - r.set_undefined ();
> + r.set_varying (type);
> return;
> }
>
> diff --git a/gcc/testsuite/gcc.dg/pr97378.c b/gcc/testsuite/gcc.dg/pr97378.c
> new file mode 100644
> index 00000000000..27e4a1f4321
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/pr97378.c
> @@ -0,0 +1,15 @@
> +// { dg-do compile }
> +// { dg-options "-O2" }
> +
> +int a, b, c;
> +void d() {
> +e : {
> + long f;
> + long *g = &f;
> + if ((a != 0) - (b = 0))
> + ;
> + else
> + a &= (*g %= a *= c) >= (*g || f);
> + goto e;
> +}
> +}
> --
> 2.26.2
>
