Re: [PATCH][RFC] Enable -fstrict-overflow by default

[Jeff Law <law@redhat.com>]

On 04/25/2017 09:09 AM, Richard Biener wrote:
> On April 25, 2017 4:39:49 PM GMT+02:00, Jeff Law <law@redhat.com> wrote:
>> On 04/24/2017 05:25 AM, Richard Biener wrote:
>>>
>>> The following makes signed overflow undefined for all
>> (non-)optimization
>>> levels.  The intent is to remove -fno-strict-overflow signed overflow
>>> behavior as that is not a sensible option to the user (it ends up
>>> with the worst of both -fwrapv and -fno-wrapv).  The implementation
>>> details need to be preserved for the forseeable future to not wreck
>>> UBSAN with either associating (-fwrapv behavior) or optimizing
>>> (-fno-wrapv behavior).
>>>
>>> The other choice would be to make -fwrapv the default for -O[01].
>>>
>>> A second patch in this series would unify -f[no-]wrapv, -f[no-]trapv
>>> and -f[no-]strict-overflow with a
>>> -fsigned-integer-overflow={undefined,wrapping,trapping[,sanitized]}
>>> option, making conflicts amongst the options explicit (and reduce
>>> the number of flag_ variables).  'sanitized' would essentially map
>>> to todays flag_strict_overflow = 0.  There's another sole user
>>> of flag_strict_overflow, POINTER_TYPE_OVERFLOW_UNDEFINED - not sure
>>> what to do about that, apart from exposing it as different flag
>>> alltogether.
>>>
>>> Further patches in the series would remove -Wstrict-overflow (and
>>> cleanup VRP for example).
>>>
>>> Anyway, most controversical part(?) below.
>>>
>>> Any comments on this particular patch (and the overall proposal)?
>>>
>>> Cleaning up the options is probably a no-brainer anyways.
>>>
>>> Thanks,
>>> Richard.
>>>
>>> 2017-04-24  Richard Biener  <rguenther@suse.de>
>>>
>>> 	* common.opt (fstrict-overflow): Enable by default.
>>> 	* opts.c (default_options_table): Remove OPT_fstrict_overflow entry.
>> Presumably when this work is complete -fno-strict-overflow will give
>> some kind of reasonable error message to the user directing them to the
>>
>> new option that most likely does what they were looking for?
> 
> No, it will simply map to -fwrapv.
That's fine as well.  As long as we do something sane ;-)

jeff