[PATCH] add the -mrecip driver flag and process its options

Sanjay Patel spatel at rotateright.com
Mon May 18 14:27:39 PDT 2015

In http://reviews.llvm.org/D8989#174000, @hfinkel wrote:

> Yes, it is worth it. There is no reason to force users to remember which compiler uses which minor syntactic differences. Users end up quoting lots of stuff, and turning off these reciprocal estimates in modes where they are otherwise on is likely to be rare, so I'm not particularly bothered by the quoting.
> That having been said, I'm not enamored with GCC's syntax, plus, as you know, what GCC accepts is actually different depending on the target (x86 vs. PPC, etc.) I think we should either accept this logicak superset with the same syntax as GCC, or just break with GCC completely and use a different option name (maybe -mrecip-est=..., or something like that, which I think is clearer anyway).

Thanks for the explanation, Hal. I'm not sure which is the greater inconvenience for users (incompatiblity or hostile syntax). Given that we've come this far without supporting -mrecip at all, I agree that it's not worth worrying about too much.

I've gone ahead with the '!' syntax here and in http://reviews.llvm.org/D8982. If we can find a clear preference from users, I assume we can change the interface before this makes it into a clang release. I've tried to make the code changes needed for that as obvious and minimal as possible.



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