[PATCH 0/4] RISCV: Improve linker time complexity

[Palmer Dabbelt]

On Tue, 12 Apr 2022 22:12:22 PDT (-0700), binutils@sourceware.org wrote:
> On Wed, Apr 13, 2022 at 08:58:38AM +0800, Kito Cheng via Binutils wrote:
>> And I have a suggestion here is - does it possible to let co-exist with current
>> implementation and having a command line option to select the linker
>> relaxation, of course we
>> could default to using the new implementation, but that gives us an
>> emergency fallback option to use the old implementation :)
>
> You already have an emergency fallback, use an older binutils or
> revert the patchset.  IMO you do not want two implementations of any
> given feature.   Doing so just makes it more likely that neither
> implementation is good.

IMO a key point here is that the hueristics are subtly different, the 
linear-time algorithm will fail at both forwards and backwards targets 
where relaxation enables relaxation (as opposed to just failing at the 
forwards targets, like the old one did).  The theory is that there 
aren't any pathological cases in the wild, but it's hard to know for 
sure.  I think it should just be a few lines of code to match the old 
behavior (ie, just eagerly delete instead of deferring it to after all 
relocations are processed), but I'm not sure -- the change around 
alignment handling is tripping me up, as that was unexpected on my end.

That said, there's certainly enough complexity here so I don't think 
it's a big deal to just only support the new flavor.