[ccache] Why not cache link commands?

[Andrew Stubbs]

On 18/09/12 16:37, Justin Lebar wrote:
> ldcache would hash object files and spit out linked files.  It would
> use an entirely separate cache.  Its handling of command-line options
> would be entirely different.  Its processing of input files would be
> entirely different.  ISTM that very little would be shared.

It takes multiple input files and returns a single output file, plus 
stderr. This much is the same.

An input object file is just as hashable as an input header file, you 
just find them a different way. I think the manifest file would need 
little or no modification.

Similarly, the output file is just as cacheable. There's probably no 
need to even use a different suffix in the cache.

I've yet to get into the precise details, but I think the file discovery 
mechanism would need to be abstracted out a little, but that's the 
biggest change.

The command line parsing would need a once over, of course. The biggest 
change there is that it's more normal to list multiple input files on 
the command line, and there's no "language" to determine.

> Since this is targeting a niche use-case and is a large change to
> ccache, I'd be hesitant to take this change upstream, if I were Joel.

Right, as little churn as possible, and no extra overhead in the most 
common cases.

Andrew