[llvm-dev] x86: How to Force 2-byte `jmp` instruction in lowering

[Rafael Espíndola via llvm-dev]

On 29 June 2016 at 02:49, Dean Michael Berris <dberris at google.com> wrote:
> On Wed, Jun 29, 2016 at 12:17 PM Rafael Espíndola
> <rafael.espindola at gmail.com> wrote:
>>
>> On 28 June 2016 at 22:14, Dean Michael Berris <dberris at google.com> wrote:
>> > On Wed, Jun 29, 2016 at 12:06 PM Rafael Espíndola
>> > <rafael.espindola at gmail.com> wrote:
>> >>
>> >> On 22 June 2016 at 16:36, Dean Michael Berris via llvm-dev
>> >> <llvm-dev at lists.llvm.org> wrote:
>> >> > Peter suggested just writing out '.byte 0xeb, 0x09' and that allowed
>> >> > the
>> >> > jump instruction to bypass the relaxation, so that fixes my immediate
>> >> > problem. The question still stands though whether it should be
>> >> > possible
>> >> > to
>> >> > do through the instruction builder interface.
>> >> >
>> >>
>> >> I don't think so. When the relax-all flag is on MC will relax all
>> >> instructions.
>> >>
>> >
>> > I see.
>> >
>> > So the question becomes what's the advantage (if any) of Clang passing
>> > the
>> > 'relax-all' flag down to MC? Is there a good reason for this behaviour
>> > at
>> > all?
>>
>> Speed, but it has probably been years since anyone benchmarked that.
>>
>
> Okay. Any objections to just removing that from the clang side?


Depends on what the benchmarks show.

Cheers,
Rafael