[ccache] Why not cache link commands?

[Mike Frysinger]

On Tuesday 18 September 2012 08:44:29 Andrew Stubbs wrote:
> 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.

or just re-use build-id ...

> The linker does not use any libraries not listed with "gcc '-###' whatever".

mmm different gcc flags can implicitly expand into -l### or different crt 
objects, so you can't cache linking at the compiler driver level w/out re-
implementing much of the guts of gcc, and even then you'd break with 
moderately patched gcc versions.

> 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.

gold should already support incremental linking (ala build-id), so i don't 
think that's already a fixed problem
-mike
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