[PATCH][match.pd] PR middle-end/66915 Restrict A - B -> A + (-B) to non-fixed-point types

[Kyrill Tkachov]

On 21/07/15 11:11, Richard Biener wrote:
> On Tue, 21 Jul 2015, Kyrill Tkachov wrote:
>
>> On 21/07/15 08:24, Richard Biener wrote:
>>> On Mon, 20 Jul 2015, Kyrill Tkachov wrote:
>>>
>>>> Hi all,
>>>>
>>>> This patch fixes the PR in question which is a miscompilation of
>>>> gcc.dg/fixed-point/unary.c on arm.
>>>> It just restricts the A - B -> A + (-B) transformation when the type is
>>>> fixed-point.
>>>>
>>>> This fixes the testcase for me.
>>>> Is this the right approach?
>>>>
>>>> Bootstrap and test on arm and x86 running.
>>>>
>>>> Ok if testing is clean?
>>> Ok, but I think the fold-const.c code has the same issue, no:
>>>
>>>         /* A - B -> A + (-B) if B is easily negatable.  */
>>>         if (negate_expr_p (arg1)
>>>             && !TYPE_OVERFLOW_SANITIZED (type)
>>>             && ((FLOAT_TYPE_P (type)
>>>                  /* Avoid this transformation if B is a positive REAL_CST.
>>> */
>>>                  && (TREE_CODE (arg1) != REAL_CST
>>>                      ||  REAL_VALUE_NEGATIVE (TREE_REAL_CST (arg1))))
>>>                 || INTEGRAL_TYPE_P (type)))
>>>           return fold_build2_loc (loc, PLUS_EXPR, type,
>>>                               fold_convert_loc (loc, type, arg0),
>>>                               fold_convert_loc (loc, type,
>>>                                                 negate_expr (arg1)));
>>>
>>> ah, no.  The above only applies to float-type and integral-types.
>>>
>>> Thus yes, your patch is ok.  Can you double-check the other pattern,
>>>
>>> /* -(A + B) -> (-B) - A.  */
>>> (simplify
>>>    (negate (plus:c @0 negate_expr_p@1))
>>>    (if (!HONOR_SIGN_DEPENDENT_ROUNDING (element_mode (type))
>>>         && !HONOR_SIGNED_ZEROS (element_mode (type)))
>>>     (minus (negate @1) @0)))
>>>
>>> ?
>> Thanks, committed with r226028.
>> I can add (FLOAT_TYPE_P (type) || INTEGRAL_TYPE_P (type)) to the condition.
>> That would more closely mirror the original logic, right?
>> That passes x86_64 bootstrap and aarch64 testing looks ok.
> Yeah, that works for me, too.

How about this patch then?
Bootstrapped and tested on x86_64 and aarch64.

Thanks,
Kyrill

2015-07-23  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>

     * match.pd (-(A + B) -> (-B) - A): Restrict to floating point
     and integral types.


>
> Thanks,
> Richard.
>

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