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

[Andrew Haley]

On 04/09/17 11:26, Erik Österlund wrote:
> 1) I want evidence for this claim. Can you get leading and trailing dmb 
> sy (rather than dmb ish) for atomic operations on ARMv7?

I hope not.  There is no reason for us to want such a thing in HotSpot.
But even if we did want such a thing, we could crop down to asm: the
point is the usual cases, not weird corner cases.

> 2) Even if you could and the compiler happens to generate that - we can 
> not rely on it because there is no contract to the compiler what fence 
> instructions it elects to use. The only contract the compiler needs to 
> abide to is how atomic C++ operations interact with other C++ 
> operations. And we do not want the underlying fencing to silently change 
> when performing compiler upgrades.

There is no way that GCC writers would break ABI compatibility in such a
fundamental way.  There would be a firestorm.  I know this because even
if no-one else started the fire, I would.  I am a GCC author.

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