RFR: Add support of lzcnt and tzcnt

[Gilles Duboscq]

Hello Igor,

I tried integrating your changes but there is a dependency problem:
In AMD64Guards, which is an amd64-specific project, you are trying to
access HotSpotGraalRuntime which lives in a hotspot-specific project.
That's not possible. It shouldn't even have built.
How did you build it?

I suppose you'd need a better substitution guard system, which could
provide you with the Architecture object.

-Gilles

On Sun, Nov 16, 2014 at 9:56 AM, Igor Veresov <igor.veresov at oracle.com> wrote:
> Hi Gilles,
>
> Thanks for the review!
> Please find the replies inline.
>
>> On Nov 15, 2014, at 4:06 AM, Gilles Duboscq <duboscq at ssw.jku.at> wrote:
>>
>> Hi Igor,
>>
>> -BitScanForwardNode.inferStamp:
>> looks like firstMaybeSetBit and min can now be set outside of the if/else
>
> Good point. Fixed.
>
>> -BitOpsTest:
>> You could have used UnsafeAccess
>>
> Aha, thanks for pointing that out. I grepped for something like it but didn’t notice UnsafeAccess. Fixed.
>
>> The rest looks good to me. Thanks.
>
> Updated webrev: http://cr.openjdk.java.net/~iveresov/lztzcnt/webrev.01/
>
>>
>> Overall, it looks like we should rather use the Count*ZerosNode at the
>> high level regardless of the platform and lower them in a
>> platform-dependent way. On AMD64 without lzcnt/tzcnt we would then
>> introduce the BitScan* nodes only during platform-dependent lowering.
>> We should put that on the todo-list if we introduce a proper
>> platform-specific lowering phase before LIR.
>
> It’s a possible approach, I liked substitution guards though. They are fairly expressive.  May be we can allow a form of substitution specialization, in which there is a generic implementation and then we can define a specialized version for some platform that will automatically replace it. I guess it may be achieved, for example, by prioritizing replacement providers.

Yes, my thinking was that the Cound*ZerosNode are in general more
high-level and simpler to reason about.

>
> igor
>
>
>>
>> -Gilles
>>
>> On Sat, Nov 15, 2014 at 8:30 AM, Igor Veresov <igor.veresov at oracle.com> wrote:
>>> The change adds the following:
>>> - support of lzcnt and tzcnt instructions,
>>> - unit tests for lzcnt/tzcnt,
>>> - ability to emit bsf/bsr in case lzcnt/tzcnt were turned off from the command line,
>>> - tightening the stamps produced by ScanBitForward/ReverseNode nodes.
>>>
>>>
>>> Webrev: http://cr.openjdk.java.net/~iveresov/lztzcnt/webrev.00/
>>>
>>> Thanks!
>>> igor
>