[15] RFR (S): 8238696: x86: Enumerate all detected CPU features in VM_Version feature string

[Vladimir Ivanov]

> Now I'm wondering about using the dot as a terminator. Doesn't the 
> return value from jio_snprintf tell you whether you exceeded the buffer?

Yes, very good point. How about the following?

   http://cr.openjdk.java.net/~vlivanov/8238696/webrev.03

Considering some tests have hard-coded feature names, I decided to 
enhance the new test and check that all reported features are known (at 
least, on x86).

Best regards,
Vladimir Ivanov

>> On 10.02.2020 17:12, Vladimir Ivanov wrote:
>>> Thanks for taking a look, David.
>>>
>>> Updated webrev:
>>>    http://cr.openjdk.java.net/~vlivanov/8238696/webrev.01/
>>>
>>>>> http://cr.openjdk.java.net/~vlivanov/8238696/webrev.00/
>>>>> https://bugs.openjdk.java.net/browse/JDK-8238696
>>>>>
>>>>> Abstract_VM_Version::features_string() doesn't contain all the CPU 
>>>>> features detected by the JVM on x86 (for example, for AVX-512 only 
>>>>> AVX-512F is included as "evex").
>>>>>
>>>>> The fix adds missing features to the list [1].
>>>>
>>>> The function naming that you have changed for 
>>>> supports_avx512_vpclmulqdq was explicitly requested by Vladimir K.:
>>>>
>>>> http://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2019-December/036326.html 
>>>>
>>>>
>>>> If anything I would suggest supports_vpopcntdq() should have the 
>>>> avx512 part added.
>>>
>>> Makes sense. Also, decided to rename VNNI, VAES, and VBMI2. They are 
>>> listed in the manual as part of AVX512.
>>>
>>>> The actual expansion of the feature string seems okay. It does make 
>>>> me wonder why these items have been left out previously.
>>>
>>> I believe it was just overlooked. Added a comment near cpu feature 
>>> constant declarations.
>>>
>>> Also, introduced a check to ensure the temporary on-stack buffer is 
>>> large enough.
>>>
>>> Best regards,
>>> Vladimir Ivanov
>>>>
>>>> Thanks,
>>>> David
>>>>
>>>>> Testing: manual (-Xlog:os+cpu=trace output on different hardware),
>>>>>           hs-precheckin-comp, hs-tier1, hs-tier2
>>>>>
>>>>> Best regards,
>>>>> Vladimir Ivanov
>>>>>
>>>>> [1] $ java -Xlog:os+cpu=trace -XX:UseAVX=3 -version
>>>>>
>>>>> ...
>>>>> [0.010s][info][os,cpu] UseSSE=4  UseAVX=3  UseAES=1  MaxVectorSize=64
>>>>> ...
>>>>> [0.011s][info][os,cpu] CPU:total 8 (initial active 8) (4 cores per 
>>>>> cpu, 2 threads per core) family 6 model 85 stepping 4, cmov, cx8, 
>>>>> fxsr, mmx, sse, sse2, sse3, ssse3, sse4.1, sse4.2, popcnt, 
>>>>> vzeroupper, avx, avx2, aes, clmul, erms, rtm, 3dnowpref, lzcnt, ht, 
>>>>> tsc, bmi1, bmi2, adx, avx512f, avx512dq, avx512cd, avx512bw, 
>>>>> avx512vl, fma, clflush, clflushopt, clwb
>>>>> ...
>>>>> [0.011s][info][os,cpu] flags        : fpu vme de pse tsc msr pae 
>>>>> mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse 
>>>>> sse2 ss ht syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon 
>>>>> rep_good nopl xtopology cpuid tsc_known_freq pni pclmulqdq vmx 
>>>>> ssse3 fma cx16 pcid sse4_1 sse4_2 x2apic movbe popcnt 
>>>>> tsc_deadline_timer aes xsave avx f16c rdrand hypervisor lahf_lm abm 
>>>>> 3dnowprefetch cpuid_fault invpcid_single pti ssbd ibrs ibpb stibp 
>>>>> tpr_shadow vnmi flexpriority ept vpid fsgsbase tsc_adjust bmi1 hle 
>>>>> avx2 smep bmi2 erms invpcid rtm mpx avx512f avx512dq rdseed adx 
>>>>> smap clflushopt clwb avx512cd avx512bw avx512vl xsaveopt xsavec 
>>>>> xgetbv1 xsaves arat umip pku ospke md_clear
>>>>> ...