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Re: [PATCH] Use flag_general_regs_only with -mgeneral-regs-only


On Tue, May 24, 2016 at 6:22 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Tue, May 24, 2016 at 8:52 AM, Uros Bizjak <ubizjak@gmail.com> wrote:
>> On Tue, May 24, 2016 at 5:40 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>
>>>> No, this is a flag, not a variable. Let's figure out how to extend
>>>> target flags to more than 63 flags first.
>>>
>>> Extending target flags to more than 63 bits requires replacing
>>> HOST_WIDE_INT with a bit vector.  Since target flags is used in
>>> TARGET_SUBTARGET_DEFAULT, change it to a bit vector is a
>>> non-trivial change.  On the other hand, -mgeneral-regs-only is a
>>> command-line option which doesn't require support for
>>> TARGET_SUBTARGET_DEFAULT, similar to other -m options like
>>> -mmitigate-rop.  Using flag_general_regs_only is an option.
>>
>> I have been informed that Intel people are looking into how to extend
>> target flags to accommodate additional ISA flags. There is no point to
>> hurry with an unoptimal solution. Perhaps you can coordinate your
>> patch with their efforts?
>
> iISA flags use x86_isa_flags, not target_flags.  -mgeneral-regs-only
> shouldn't use x86_isa_flags.  It was my oversight to use target_flags
> with -mgeneral-regs-only to begin with.   I don't think using
> flag_general_regs_only is not an optimal solution, which I should have
> used in the first place.  The x86 change for interrupt handler depends
> on -mgeneral-regs-only.

Oh, target_flags is only a 32bit integer :(. Is there a reason it
can't be extended to HOST_WIDE_INT, as is the case with
ix86_isa_flags?

Uros.


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