OK.
On Tue, Feb 21, 2017 at 8:42 AM, Jakub Jelinek <ja...@redhat.com> wrote:
> Hi!
>
> The following patch fixes ICE where we try to store a[-1]. The problem
> is that we don't check the bounds first and then later on we assert it
> is not negative.
>
> Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux, ok for
> trunk?
>
> 2017-02-21 Jakub Jelinek <ja...@redhat.com>
>
> PR c++/79655
> * constexpr.c (cxx_eval_array_reference): Diagnose negative subscript.
>
> * g++.dg/cpp1y/constexpr-79655.C: New test.
>
> --- gcc/cp/constexpr.c.jj 2017-02-17 18:29:21.000000000 +0100
> +++ gcc/cp/constexpr.c 2017-02-21 13:49:06.530261975 +0100
> @@ -2263,9 +2263,10 @@ cxx_eval_array_reference (const constexp
> nelts = cxx_eval_constant_expression (ctx, nelts, false, non_constant_p,
> overflow_p);
> VERIFY_CONSTANT (nelts);
> - if (lval
> - ? !tree_int_cst_le (index, nelts)
> - : !tree_int_cst_lt (index, nelts))
> + if ((lval
> + ? !tree_int_cst_le (index, nelts)
> + : !tree_int_cst_lt (index, nelts))
> + || tree_int_cst_sgn (index) < 0)
> {
> diag_array_subscript (ctx, ary, index);
> *non_constant_p = true;
> --- gcc/testsuite/g++.dg/cpp1y/constexpr-79655.C.jj 2017-02-21
> 14:14:37.245395108 +0100
> +++ gcc/testsuite/g++.dg/cpp1y/constexpr-79655.C 2017-02-21
> 14:14:07.000000000 +0100
> @@ -0,0 +1,18 @@
> +// PR c++/79655
> +// { dg-do compile { target c++14 } }
> +
> +constexpr int
> +foo (int x, int y)
> +{
> + int a[6] = { 1, 2, 3, 4, 5, 6 };
> + a[x] = 0;
> + return a[y];
> +}
> +
> +constexpr int b = foo (0, -1); // { dg-error "is outside the bounds" }
> +constexpr int c = foo (0, 6); // { dg-error "is outside the bounds" }
> +constexpr int d = foo (6, 0); // { dg-error "is outside the bounds" }
> +constexpr int e = foo (-1, 0); // { dg-error "is outside the bounds" }
> +static_assert (foo (5, 5) == 0, "");
> +static_assert (foo (4, 5) == 6, "");
> +static_assert (foo (5, 4) == 5, "");
>
> Jakub
