Re: [PATCH, i386] Fix -mpreferred-stack-boundary

[Uros Bizjak <ubizjak at gmail dot com>]

On Fri, Nov 15, 2013 at 10:58 AM, Bernd Edlinger
<bernd.edlinger@hotmail.de> wrote:

>>>> Well, this way it could be fixed too.
>>>>
>>>> But opts->x_ix86_preferred_stack_bounary_arg is not dependent on any
>>>> pragma or target attribute. Correct me if that is wrong.
>>>
>>> That seems correct.
>>>
>>>>
>>>> And this code
>>>>
>>>> if (opts_set->x_ix86_preferred_stack_boundary_arg)
>>>> {
>>>> int min = (TARGET_64BIT_P (opts->x_ix86_isa_flags)
>>>> ? (TARGET_SSE_P (opts->x_ix86_isa_flags) ? 4 : 3) : 2);
>>>> int max = (TARGET_SEH ? 4 : 12);
>>>>
>>>> if (opts->x_ix86_preferred_stack_boundary_arg < min
>>>> || opts->x_ix86_preferred_stack_boundary_arg> max)
>>>>
>>>> checks func_options against global_options_set:
>>>>
>>>> new_target = ix86_valid_target_attribute_tree (args, &func_options,
>>>> &global_options_set);
>>>>
>>>> So this code as it is will fail if this option was ever made target specific.
>>>
>>> This is correct. But, right now global_options_set is capturing only
>>> the command line options that are set and does not seem to be
>>> modified. If this option were to be made target specific we should not
>>> access this field off global_options_set. We should add a MASK to
>>> target flags and get it from there just like any other target flag
>>> that is function specific does it.
>>>
>>>> There is still a reason why this check needs to be executed each time
>>>> the opts->x_ix86_isa_flags changes.
>>>>
>>>> Because of this I still would prefer my second attempt of fixing this issue,
>>>> because it is simple and it removes the different handling between
>>>> -mpreferred-stack-boundary and -mincoming-stack-boundary.
>>>
>>> I understand your problem better now. I still do not think we should
>>> make ix86_option_override_internal should read global_options flags
>>> directly. That is overriding opts passed in as a parameter. I am fine
>>> with Patch 1 which is explicitly copying global_options
>>> preferred_stack_boundary_arg fields onto func_options. FYI, I cannot
>>> approve any patches and you still have to get it approved by the
>>> maintainers. I will sweep these copies and save it into
>>> cl_target_option as a cleanup if more of these emerge.
>>
>> I'd prefer the proposed general solution. It seems to me that Patch 1
>> is somehow a hack that will "solve" only one particular option out of
>> many similar.
>>
>> Thanks,
>> Uros.
>
> I agree, if you want, I can apply patch #2 today, (which at least does not
> look so hacky as my first approach), to buy us some time.
>
> And I think Sriram should prepare a followup-patch that removes
> this dependencies on global_options_set or makes that data structure
> also target specific.

Do we have a pressing issue here that needs immediate, but incomplete fix?

If this is not the case, I'd rather wait for a correct fix.

Thanks,
Uros.