macho: speed up the linker by embracing multi-threaded approach

[kubkon]

At the time of writing, comparison in linking #138 (./new is zld after rewrite, ./old is current master, ./ld is Apple's new linker, ./ld_classic is Apple's old linker, and ./lld is LLVM's stock linker):

Also, just for completeness, speed up in -r relocatable mode between old and new zld:

[mlugg]

On par with LLD, that's what we like to see! So... what shenanigans are Apple up to to make ld so fast?

[kubkon]

On par with LLD, that's what we like to see! So... what shenanigans are Apple up to to make ld so fast?

Sadly I don't have access to ld's sources - they haven't released them yet, if ever. Anyhow, we still have room for improvement - we don't mmap the output file yet, or any file in fact.

[kubkon]

Oh, and also, bear in mind we do more work since we don't generate the latest MachO binary format. What I mean by this is that the latest dyld doesn't need dyld opcodes which are fairly expensive to generate. Also, I am sure there are places in zld codebase that could be improved further from the algorithmic perspective.

[mlugg]

Sadly I don't have access to ld's sources - they haven't released them yet, if ever.

That just means it's reverse-engineering time ;-) /hj

I am sure there are places in the zld codebase that could be improved further from the algorithmic perspective.

If there are any particularly hot bits of code which you think ought to be looked at, I'd be happy to see if I can think of any improvements!