[PATCH] Remove copies of MCSubtargetInfo from MCRelaxableFragment

[Duncan P. N. Exon Smith]

r241947
> On 2015-Jul-10, at 06:27, Rafael Espíndola <rafael.espindola at gmail.com> wrote:
> 
> Patch 1 LGTM.
> 
> 
> On 8 July 2015 at 20:30, Duncan P. N. Exon Smith <dexonsmith at apple.com> wrote:
>> Last I checked my `-g -flto` workload, `MCRelaxableFragment` was taking
>> up 4.7% of the heap during LTO.  Since these aren't debug info related,
>> the relative cost is even higher without `-g` (I figure 10% or so?).
>> The struct layout contained a shock: over half of
>> `sizeof(MCRelaxableFragment)` comes from a local copy (!?) of
>> `MCSubtargetInfo`.
>> 
>> It was more roundabout than I expected to fix, but this patch series
>> does it.  0001 removes the copy of `MCSchedModel` from
>> `MCSubtargetInfo`, 0002-0004 change the `MCSubtargetInfo` API to prove
>> that only the feature bits get mutated, and 0005 moves the copies of
>> `MCSubtargetInfo` to a cache in `MCContext`.
>> 
>> I'd love a pre-commit sanity check from someone for two of these:
>>  - 0001 (the object for `MCSchedModel::GetDefaultMCSubtarget()` doesn't
>>    need to be defined in the header for some reason, does it?) and
>>  - 0003 (I'm touching *all* the targets...)
>> 
>> and I've provided the rest of the series (and a combined all.patch) for
>> context.
>> 
>>