Re: Some wide-int review comments

[Richard Biener <richard dot guenther at gmail dot com>]

On Tue, Nov 26, 2013 at 5:33 PM, Kenneth Zadeck
<zadeck@naturalbridge.com> wrote:
> Richi,
>
> patch ping

Ok.

Thanks,
Richard.

> also two more pieces of information.    With further testing, this seems to
> fix
>
> Tests that now work, but didn't before:
> ===============
> ext/random/hypergeometric_distribution/operators/values.cc (test for excess
> errors)
>
> New tests that PASS:
>
> ext/random/hypergeometric_distribution/operators/values.cc execution test
> ================
>
> also, the corresponding frag for fold-const.c on the wide-int branch will
> look like
> ================
> Index: gcc/fold-const.c
> ===================================================================
> --- gcc/fold-const.c    (revision 205224)
> +++ gcc/fold-const.c    (working copy)
> @@ -1030,51 +1030,51 @@ int_const_binop_1 (enum tree_code code,
>
>      case TRUNC_DIV_EXPR:
>      case EXACT_DIV_EXPR:
> -      res = wi::div_trunc (arg1, arg2, sign, &overflow);
> -      if (overflow)
> +      if (arg2 == 0)
>      return NULL_TREE;
> +      res = wi::div_trunc (arg1, arg2, sign, &overflow);
>        break;
>
>      case FLOOR_DIV_EXPR:
> -      res = wi::div_floor (arg1, arg2, sign, &overflow);
> -      if (overflow)
> +      if (arg2 == 0)
>      return NULL_TREE;
> +      res = wi::div_floor (arg1, arg2, sign, &overflow);
>        break;
>
>      case CEIL_DIV_EXPR:
> -      res = wi::div_ceil (arg1, arg2, sign, &overflow);
> -      if (overflow)
> +      if (arg2 == 0)
>      return NULL_TREE;
> +      res = wi::div_ceil (arg1, arg2, sign, &overflow);
>        break;
>
>      case ROUND_DIV_EXPR:
> -      res = wi::div_round (arg1, arg2, sign, &overflow);
> -      if (overflow)
> +      if (arg2 == 0)
>      return NULL_TREE;
> +      res = wi::div_round (arg1, arg2, sign, &overflow);
>        break;
>
>      case TRUNC_MOD_EXPR:
> -      res = wi::mod_trunc (arg1, arg2, sign, &overflow);
> -      if (overflow)
> +      if (arg2 == 0)
>      return NULL_TREE;
> +      res = wi::mod_trunc (arg1, arg2, sign, &overflow);
>        break;
>
>      case FLOOR_MOD_EXPR:
> -      res = wi::mod_floor (arg1, arg2, sign, &overflow);
> -      if (overflow)
> +      if (arg2 == 0)
>      return NULL_TREE;
> +      res = wi::mod_floor (arg1, arg2, sign, &overflow);
>        break;
>
>      case CEIL_MOD_EXPR:
> -      res = wi::mod_ceil (arg1, arg2, sign, &overflow);
> -      if (overflow)
> +      if (arg2 == 0)
>      return NULL_TREE;
> +      res = wi::mod_ceil (arg1, arg2, sign, &overflow);
>        break;
>
>      case ROUND_MOD_EXPR:
> -      res = wi::mod_round (arg1, arg2, sign, &overflow);
> -      if (overflow)
> +      if (arg2 == 0)
>      return NULL_TREE;
> +      res = wi::mod_round (arg1, arg2, sign, &overflow);
>        break;
>
>      case MIN_EXPR:
>
> ================
>
> On 11/20/2013 06:31 PM, Kenneth Zadeck wrote:
>>
>> On 11/13/2013 04:59 AM, Richard Biener wrote:
>>>
>>> On Tue, Nov 12, 2013 at 5:43 PM, Kenneth Zadeck
>>> <zadeck@naturalbridge.com> wrote:
>>>>
>>>> On 11/12/2013 11:27 AM, Joseph S. Myers wrote:
>>>>>
>>>>> On Tue, 12 Nov 2013, Kenneth Zadeck wrote:
>>>>>
>>>>>> Richi,
>>>>>>
>>>>>> i am having a little trouble putting this back the way that you want.
>>>>>> The
>>>>>> issue is rem.
>>>>>> what is supposed to happen for INT_MIN % -1?
>>>>>>
>>>>>> I would assume because i am failing the last case of
>>>>>> gcc.dg/c90-const-expr-8.c
>>>>>> that INT_MIN %-1 should not overflow even if INT_MIN / -1 does.
>>>>>> however,
>>>>>
>>>>> Given the conclusion in C11 that a%b should be considered undefined if
>>>>> a/b
>>>>> is not representable, I think it's reasonable to say INT_MIN % -1
>>>>> *should*
>>>>> be considered to overflow (for all C standard versions) (and bug 30484
>>>>> is
>>>>> only a bug for -fwrapv).
>>>>>
>>>> however, my local question is what do we want the api to be
>>>> int-const-binop-1?    The existing behavior seems to be that at least
>>>> for
>>>> common modes this function silently returns 0 and it is up to the front
>>>> ends
>>>> to put their own spin on it.
>>>
>>> For wide-int you create 1:1 the behavior of current trunk (if a change of
>>> behavior in TImode is not tested in the testsuite then you can ignore
>>> that).
>>> Whatever change you do to semantics of functions you do separately
>>> from wide-int (preferably first on trunk, or at your choice after the
>>> wide-int
>>> merge).
>>>
>>> For this case in question I'd say a % -1 should return 0, but for
>>> INT_MIN % -1 that 0 should have TREE_OVERFLOW set (and
>>> thus you need to adjust that c90-const-expr-8.c testcase).
>>>
>>> Richard.
>>>
>>>> kenny
>>
>> richi,
>> I have done this exactly as you suggested.   bootstrapped and regression
>> tested on x86-64.
>>
>> 2013-11-20  Kenneth Zadeck  <zadeck@naturalbridge.com>
>>
>>     * fold-const.c
>>     (int_const_binop_1): Make INT_MIN % -1 return 0 with the overflow
>>     bit set.
>>
>>
>> 2013-11-20  Kenneth Zadeck  <zadeck@naturalbridge.com>
>>
>>     * gcc.dg/c90-const-expr-8.c: Look for overflow on INT_MIN % -1.
>>     * gcc.dg/c99-const-expr-8.c: Look for overflow on INT_MIN % -1.
>>
>> ok to commit?
>>
>> kenny
>>
>