[OE-core] [PATCH] ARMv8-A: Add tune for AArch32 state and AArch64 state

[Khem Raj]

> On Mar 30, 2016, at 3:46 PM, Phil Blundell <pb at pbcl.net> wrote:
> 
> On Wed, 2016-03-30 at 11:53 -0700, Andre McCurdy wrote:
>> Either way it shouldn't be a concern for the CPU tuning files.
>> Building Thumb2 for an armv8a CPU is really just an extension of
>> "optimise for size" and we don't include -Os, -O2, etc options in the
>> CPU tuning files.
> 
> Yes, agreed.  In principle there's no reason that the compiler couldn't
> choose between A32 and T32 instruction sets dynamically for each
> compilation unit (or each function) according to which it thinks would
> give the better result.  And from the user's point of view, the outcome
> should be equivalent apart from minor performance differences.

yes I think thumb2 on aarch32 may be controlled via a global configuration metadata
like distro feature or some such.

> 
>>>> For most cores from Cortex A9 onwards NEON and VFP are optional, so
>>>> hardcoded assumptions won't work.
> 
>> Nothing very concrete. The ARM Cortex-A Series Programmer’s Guide for
>> ARMv8-A mentions:
>> 
>> "Both floating-point and NEON are required in all standard ARMv8
>> implementations. However, implementations targeting specialized
>> markets may support the following combinations:
>> 
>> - No NEON or floating-point.
>> - Full floating-point and SIMD support with exception trapping.
>> - Full floating-point and SIMD support without exception trapping.
> 
> Is there any evidence that anyone is actually building ARMv8-A (as
> opposed to -R or -M) cores that lack VFP and/or NEON?  Unless there is a
> fairly clear indication that such cores do exist and are likely to be
> used with OE, I think we should not complicate the tuning files with
> support for such things.  Anybody who wants them can always add
> appropriate tunes later, either in oe-core or in their own layer.
> 

agreed.

> p.
> 
> 

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