RFR (S) : 8014362 : Need to expose some processor features via Unsafe interface

[David Chase]

I believe I was doing monkey-see-monkey-do.
Other not-always-present machine features options seemed to be coded that way, so I copied it.
Till we know it's a modern processor, it's not safe (I can verify that it does indeed crash if you try new instructions on an old chip).

David

On 2013-05-21, at 12:49 AM, David Holmes <david.holmes at oracle.com> wrote:

> David,
> 
> I don't quite understand the handling of UseCLMUL. Why do you set it to false initially:
> 
>  99   product(bool, UseCLMUL, false,           \
> 100           "Control whether CLMUL instructions can be used on x86/x64")      \
> 
> then force it to true if supported:
> 
> 493   // Use CLMUL instructions if available.
> 494   if (supports_clmul()) {
> 495     if (FLAG_IS_DEFAULT(UseCLMUL)) {
> 496       UseCLMUL = true;
> 497     }
> 498   } else if (UseCLMUL) {
> 
> I would expect it to be true by default and set to false if not supported. That way the value in globals_x86.hpp really is the default value.
> 
> That said we seem to handle a number of these flags in what I would consider an odd way.
> 
> David
> -----
> 
> 
> 
> On 18/05/2013 7:28 AM, David Chase wrote:
>> There was a spacing change that did not get reverted.
>> This time, for sure.
>> Note that this sets a property that won't get reset without a companion change in the JDK.
>> (And the companion change is getting a bit of a pushback, though I hope to find, once I digest
>> all the benchmarks I ran this afternoon, that it's not as scary as feared.)
>> 
>> http://cr.openjdk.java.net/~drchase/8014362/webrev.04
>> 
>> On 2013-05-17, at 4:30 PM, Vladimir Kozlov <vladimir.kozlov at oracle.com> wrote:
>> 
>>> Somehow globals.hpp showed up in the webrev. Otherwise changes are good.
>>> 
>>> Vladimir
>>> 
>>> On 5/17/13 1:28 PM, David Chase wrote:
>>>> New webrev:
>>>> 
>>>> http://cr.openjdk.java.net/~drchase/8014362/webrev.03/
>>>> 
>>>> It compiles (and runs) on both x86 and Sparc.
>>>> 
>>>> David
>>>> 
>>>> On 2013-05-16, at 11:32 PM, Vladimir Kozlov <vladimir.kozlov at oracle.com> wrote:
>>>> 
>>>>> Okay, I agree with X86_ONLY().
>>>>> 
>>>>> Vladimir
>>>> 
>>