RFR: 8186838: Generalize Atomic::inc/dec with templates

[Andrew Haley]

On 01/09/17 15:15, Erik Österlund wrote:
> It is not the simplest solution I can think of. The simplest solution I 
> can think of is to remove all specialized versions of Atomic::inc/dec 
> and just have it call Atomic::add directly. That would remove the 
> optimizations we have today, for whatever reason we have them. It would 
> lead to slightly more conservative fencing on PPC/S390,

I see.  Can you say what instructions would be different?

> and would lead to slightly less optimal machine encoding on x86
> (without immediate values in the instructions). But it would be
> simpler for sure. I did not put any judgement into whether our
> existing optimizations are worthwhile or not. But if you want to
> prioritize simplicity, removing those optimizations is one possible
> solution. Would you prefer that?

Is this really about optimization?  If we cared about getting this
stuff as optimized as possible we'd use intrinsics on GCC/x86 targets.
These have been supported for a long time.  But it seems we're
determined to preserve the legacy assembly-language implementations
and use them everywhere, even where they are not necessary.

-- 
Andrew Haley
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
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