[LLVMdev] [cfe-dev] RFC: Another go at a cross compiler config file.

Richard Pennington
2014-09-08T22:33:54Z

On 09/08/2014 01:26 PM, Joerg Sonnenberger wrote:
> On Mon, Sep 08, 2014 at 10:59:17AM -0700, Bob Wilson wrote:
>>> On Sep 8, 2014, at 10:14 AM, Joerg Sonnenberger <joerg at
britannica.bec.de> wrote:
>>>
>>> On Fri, Sep 05, 2014 at 09:23:34PM -0500, Richard Pennington wrote:
>>>> Right now it only handles replacing a "-target foo"
option
>>>> with the options defined in the file foo in the resource/config
>>>> directory, but I think it has potential for doing quite a bit
more.
>>> Please don't overload the -target option like that, but make it
a
>>> separate option.
>> I disagree. One of the problems with clang’s driver now is that we have
>> such a long list of built-in targets. From the user’s point of view,
>> whether the target settings come from a yaml file or from hardcoded
>> logic in the driver should be an implementation detail. It would be
>> great if we could default to specify _all_ targets like this, and then
>> choose which targets to build into the driver based solely on
>> performance.
> Whether it is reasonably possible for such a transistion has to be seen.
> If you look at the target logic in the driver, you will seen that
> estimated 70% of the complexity is related to Linux, maybe 10% each to
> Darwinish systems and Windows and the rest for all other targets
> together. So while this can greatly simplify the maintainance cost and
> overall code size for Linux, it createse a complexity regression for
> other systems. That's a good enough reason for my request to keep it
> optional. I'm not against this feature -- if it is well done, it can
> improve the status quo. But I am against forced overhead for systems
> where we don't need it.
I agree that all drivers should not have to pay the overhead of reading
a file for each compilation. I've updated my blog post with a bit more
information ( http://ellcc.org/blog/?p=11877). Here's the gist of it:

I use the -target argument, or the prefix on the compiler name, to try
to open the config file. If a file of that name isn't found, the -target
argument passes through unscathed and works as it does now. I use YAMLIO
to read the configuration into a structure...
...After some good discussion on the LLVM mailing list, I realized that
with a simple registration process, statically initialized info
structures could be registered by pre-existing drivers. This would
obviously eliminate the need to read the config file for every compilation.

Thanks for the input!

-Rich

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