[ccache] Why not cache link commands?

[Justin Lebar]

> So, again, before I waste my time implementing this feature, are there any
> other fundamental gotchas that would prevent it ever working or ever being
> useful?

On a large project with many inputs to ld, you'd have to hash a /lot/
of object files, increasing the overhead of ccache substantially.  I
understand that this isn't your particular use-case, but it's the
common one.

If you're on Linux, have you tried the gold linker?

-Justin

On Tue, Sep 18, 2012 at 8:44 AM, Andrew Stubbs <ams at codesourcery.com> wrote:
> Hi all, again,
>
> I've just posted about improving compile speed by caching compiler failures,
> and in the same vein I'd like to consider caching called-for-link compile
> tasks.
>
> This is partly interesting for the many small autoconf tests, but is also
> increasingly interesting for real compilations, now that
> whole-program-optimization and link-time-optimization is more available in
> GCC. Even without all this link-time compilation activity, there are some
> link operations that simply take forever, mostly due to large file sizes.
>
> Clearly there are some technical challenges in doing this: we'd have to hash
> all the object files and libraries (a la direct mode), but those problems
> are surmountable, I think. The linker does not use any libraries not listed
> with "gcc '-###' whatever".
>
> I'm also aware that it's not that interesting for many incremental builds,
> where the final link will always be different, but my use case is
> accelerating rebuilds of projects that my have many outputs, most of which
> are likely to be unaffected by small code changes. It's also worth noting
> that incremental builds are not the target use case for ccache in general.
>
> So, again, before I waste my time implementing this feature, are there any
> other fundamental gotchas that would prevent it ever working or ever being
> useful?
>
> Has anybody else ever tried to do this? Is anybody trying to do it now?
>
> Thanks
>
> Andrew
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