RFR: 8243470: [macos] bring back O2 opt level for unsafe.cpp

[Magnus Ihse Bursie]

Thanks for cc:ing us.

This is not the correct way to check for compiler versions. Nor is it 
the correct place.

I don't have time for a full reply tonight, but will return with a 
better reply tomorrow.

/Magnus

On 2020-06-03 19:47, Daniel D. Daugherty wrote:
> Adding build-dev at ... since this is a build system change.
>
> As for the right HotSpot team, I'm not sure who should be making
> the call on changing the way unsafe.cpp is built for macOSX. My guess
> when I moved the bug to hotspot/runtime was that someone on the Runtime
> team would know, but...
>
> Dan
>
>
>
> On 6/3/20 1:38 PM, Vladimir Kempik wrote:
>> Hello
>>
>> Can somebody please review this simple change ?
>>
>> Thanks
>>
>>> 6 мая 2020 г., в 12:43, Vladimir Kempik <vkempik at azul.com> написал(а):
>>>
>>> Adding hotspot-runtime-dev
>>>
>>>> 23 апр. 2020 г., в 18:26, Vladimir Kempik <vkempik at azul.com> 
>>>> написал(а):
>>>>
>>>>
>>>> Hello
>>>> Please review a fix for JDK-8243470
>>>>
>>>> Long time ago as part of JEP284: New HotSpot Build System this fix 
>>>> was applied to jdk9 https://bugs.openjdk.java.net/browse/JDK-8152666
>>>> At that time it was decided to lower optimisation level for 
>>>> unsafe.cpp from O2 to O1 only for clang on Macosx.
>>>>
>>>> I suppose it was done due to issues in Set/Get<Object> helper 
>>>> functions where too optimistic optimisations were eliminating some 
>>>> null pointer checks. it was probably a clang bug.
>>>> That issue could be checked with test 
>>>> jdk/test/sun/misc/CopyMemory.java.
>>>>
>>>> I believe that workaround (going from O2 to O1) produced this issue 
>>>> - https://bugs.openjdk.java.net/browse/JDK-8234963 
>>>> (Thread.getStackTrace is slow with clang).
>>>> JDK-8234963 can only be seen on mac with libjvm compiled by clang.
>>>>
>>>> Here I propose the patch which eliminates that workaround for clang 
>>>> 8+.
>>>>
>>>> I have tested clang versions 8/9/9.1/10, all of them showed good 
>>>> results:
>>>> 1) CopyMemory test passes fine on 11/14/15.
>>>> 2) jdk11/jdk14 passed tck. Regression testing were good as well. 
>>>> jdk15: no new failures in tck.
>>>> 3) The testRandom "benchmark" from 8234963 shows great improvements 
>>>> on my machine, going down from ~200 seconds to ~150 seconds (the 
>>>> newer clang the better result). For comparision, gcc built libjvm 
>>>> for jdk11 shows ~130 seconds on my machine.
>>>>
>>>> The webrev: http://cr.openjdk.java.net/~vkempik/8243470/webrev.00/
>>>>
>>>> getStackTrace benchmark: 
>>>> http://cr.openjdk.java.net/~vkempik/8243470/TestRandom.java
>>>>
>>>> The bug: https://bugs.openjdk.java.net/browse/JDK-8243470
>>>>
>>>> Thanks, Vladimir
>