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

[Dean Michael Berris via llvm-dev]

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?
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