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Date: Wed, 21 Oct 2015 09:56:00 -0000
Message-ID: <CAFiYyc3Ne8pLSYoOm6=8paXv6MUur8M0rdaUt4p8+-RkU+nw3Q@mail.gmail.com>
Subject: Re: [patch] Fix failure of ACATS c45503c at -O2
From: Richard Biener <richard.guenther@gmail.com>
To: Eric Botcazou <ebotcazou@adacore.com>
Cc: Jeff Law <law@redhat.com>, GCC Patches <gcc-patches@gcc.gnu.org>, 	Joseph Myers <joseph@codesourcery.com>
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On Wed, Oct 21, 2015 at 9:24 AM, Eric Botcazou <ebotcazou@adacore.com> wrote:
>> So the only question is whether or not the CEIL_MOD_EXPR and
>> ROUND_MOD_EXPR bits are right.  I'm confident the change to
>> FLOOR_MOD_EXPR is right.
>
> OK.
>
>> Do we have any reasonable way to test CEIL_MOD_EXPR & ROUND_MOD_EXPR?
>
> Note that the patch makes the function punt on those 2 so it can do no harm.
> The sign of CEIL_MOD_EXPR is predictable (opposite of that of the divisor) but
> you cannot use that in the context; and finally the sign of ROUND_MOD_EXPR
> isn't predictable.
>
> I can add a few more comments:

Maybe add the comments to tree.def instead.

> Index: fold-const.c
> ===================================================================
> --- fold-const.c        (revision 229022)
> +++ fold-const.c        (working copy)
> @@ -12982,11 +12982,18 @@ tree_binary_nonnegative_warnv_p (enum tr
>        return RECURSE (op0) && RECURSE (op1);
>
>      case TRUNC_MOD_EXPR:
> -    case CEIL_MOD_EXPR:
> -    case FLOOR_MOD_EXPR:
> -    case ROUND_MOD_EXPR:
> +      /* The sign of the remainder is that of the dividend.  */
>        return RECURSE (op0);
>
> +    case FLOOR_MOD_EXPR:
> +      /* The sign of the remainder is that of the divisor.  */
> +      return RECURSE (op1);
> +
> +    case CEIL_MOD_EXPR:
> +       /* The sign of the remainder is the opposite of that of the divisor,
> +         but this cannot be used in this context.  */
> +    case ROUND_MOD_EXPR:
> +      /* The sign of the remainder is not predictable.  */
>      default:
>        return tree_simple_nonnegative_warnv_p (code, type);
>      }
>
>
> --
> Eric Botcazou