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

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