Re: [PATCH][optabs][ifcvt][1/3] Define negcc, notcc optabs

[Kyrill Tkachov <kyrylo.tkachov@arm.com>]

On 09/09/15 22:51, Jeff Law wrote:
> On 09/02/2015 07:43 AM, Kyrill Tkachov wrote:
>
>>>> +  rtx_code code; +  if (val_a == -val_b)
>>> Do we have to worry about signed overflow here?  I'm thinking
>>> specifically when val_b is the smallest possible integer
>>> representable by a HOST_WIDE_INT.  I suspect you may be able to
>>> avoid these problems with judicious use of the hwi interfaces.
>> I understand the issue, but am not sure what hwi interfaces to use
>> here. Seems that the problem will be if val_b is HOST_WIDE_INT_MIN.
> Right.  When val_b is HOST_WIDE_INT_MIN, negating it will overflow.
>
>> Looking at the definition of abs_hwi in hwint.h before it negates
>> it's argument it asserts that it's not HOST_WIDE_INT_MIN. I think
>> that's to avoid this exact issue? If so, I've added a check for
>> HOST_WIDE_INT_MIN which should cover the undefined case when negating
>> a HOST_WIDE_INT, unless there's something else I'm missing.
> That should be sufficient.
>
> 2015-09-02  Kyrylo Tkachov <kyrylo.tkachov@arm.com>
>
>        * ifcvt.c (noce_try_inverse_constants): New function.
>        (noce_process_if_block): Call it.
>        * optabs.h (emit_conditional_neg_or_complement): Declare prototype.
>        * optabs.def (negcc_optab, notcc_optab): Declare.
>        * optabs.c (emit_conditional_neg_or_complement): New function.
>        * doc/tm.texi (Standard Names): Document negcc, notcc names.
>
> OK for the trunk.

Thanks for the review.
I'll commit it if/when the aarch64 and arm implementations of the hooks
in patches 2/3 and 3/3 are approved.

Kyrill

>
> Thanks for your patience.
>
> Jeff
>