r211420 - Driver: enhance MSC version compatibility

[Reid Kleckner]

On Sat, Jun 21, 2014 at 11:32 AM, Alp Toker <alp at nuanti.com> wrote:

> Please split out and name the new dotted form something like
> "-msc-full-version" to avoid ambiguity.


I was inclinded to overload the option because it means we don't have to
diagnose this case: -fmsc-version -fmsc-full-version=17.00.0.  We just do
the obvious thing of "last one always wins".  Diagnosing the conflict isn't
too hard, though, so let's just split the options and do exactly that in
the driver.


>  Due to
>> bitwidth limitations of the option, it is currently not possible to
>> define a
>> revision value.
>>
>
> What would be the practical burden of encoding this as 64-bits, or two
> 32-bit fields (one representing _MSC_BUILD and another for the rest)?
>
> Or is there a different plan to resolve the 32-bit encoding FIXMEs
> introduced in the commit? I suspect that getting the representation right
> will simplify computations below for free.


LangOptions are defined as unsigned bitfields, so we can't widen the full
version number to 64 bits without some disruptive changes.  Lots of
LangOpts shouldn't even be bitfields, for example.  If we supported that,
we could easily make the full version a 64-bit int.  Failing that, we could
split the build number into it's own option.
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