On Mon, Oct 26, 2015 at 12:32 PM, Markus Trippelsdorf
<mar...@trippelsdorf.de> wrote:
> Hi,
>
> the patch below fixes PR68087, an ICE caused by referring to a negative
> constexpr array element.
>
> Bootstrapped and tested on ppc64le.
> OK for trunk?
>
> gcc-5 also needs a slightly different fix. I'll post that as a
> follow-up, once this one gets approved.
>
> PR c++/68087
> * constexpr.c (cxx_eval_array_reference): Guard call to
> tree_to_shwi().
>
> diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
> index ebca411b3eb4..0828a90b0e75 100644
> --- a/gcc/cp/constexpr.c
> +++ b/gcc/cp/constexpr.c
> @@ -1782,8 +1782,7 @@ cxx_eval_array_reference (const constexpr_ctx *ctx,
> tree t,
> gcc_unreachable ();
> }
>
> - i = tree_to_shwi (index);
> - if (i < 0)
> + if (!tree_fits_shwi_p (index) || tree_to_shwi (index) < 0)
> {
Err, but that also catches very large positive constants. Why not use
wi::lt (index, 0)?
Or is index to be interpreted as signed? Then use wi::lts (index, 0).
> if (!ctx->quiet)
> error ("negative array subscript");
> @@ -1792,6 +1791,7 @@ cxx_eval_array_reference (const constexpr_ctx *ctx,
> tree t,
> }
>
> bool found;
> + i = tree_to_shwi (index);
> if (TREE_CODE (ary) == CONSTRUCTOR)
> {
> HOST_WIDE_INT ix = find_array_ctor_elt (ary, index);
> diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-array13.C
> b/gcc/testsuite/g++.dg/cpp0x/constexpr-array13.C
> new file mode 100644
> index 000000000000..ef18a60f3038
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-array13.C
> @@ -0,0 +1,7 @@
> +// PR c++/68087
> +// { dg-do compile { target c++11 } }
> +
> +constexpr char c[] = "hello";
> +constexpr const char *p = c;
> +
> +static_assert(*(p - 1) == 'h', ""); // { dg-error "non-constant|negative" }
> --
> Markus
