Re: [PATCH] AArch64: Optimize ADD relocations that resolve to zero

On Fri, Aug 14, 2026 at 10:12:39AM +0200, Jan Beulich wrote:
> On 13.08.2026 19:12, Alice Carlotti wrote:
> > On Fri, Jul 24, 2026 at 09:58:59AM +0000, Sivan Shani wrote:
> >> The "ELF for the Arm 64-bit Architecture" specification, section 5.7.9,
> >> recommends that linkers optimize ADD instructions whose immediate
> >> becomes zero after relocation.  In particular:
> >>
> >>    ADD x0, x1, 0
> >>    ADD x2, x2, 0
> >>
> >> may be replaced with:
> >>
> >>    MOV x0, x1
> >>    NOP
> >>
> >> Apply this optimization to all supported relocations that set an ADD
> >> immediate field.
> > 
> > 
> > I think this optimization is invalid if we're still emitting relocations,
> > because it breaks idempotency, so we probably need to add a check for that.
> > 
> > I'm not particularly familiar with this generic part of the linker, so I'd
> > appreciate any clarification from other maintainers on how to check this.
> 
> Do you perhaps refer to the bfd_link_relocatable() predicate?
> 
> Jan

I guessed that was at least part of it.  Some places (e.g.
bfd/elfnn-aarch64.c-8727) also check info->emitrelocations - do we need to
check both of these values, or should bfd_link_relocatable() suffice?

Thanks,
Alice