[15] RFR (M): 8239008: C2: Simplify Replicate support for sub-word types on x86

[Vladimir Kozlov]

Thank you for all testing.

I agree with your changes.

Thanks,
Vladimir K

On 2/18/20 1:08 AM, Vladimir Ivanov wrote:
> 
>>>> I would like to see test compiler/codegen/Test*Vect.java which verify these instructions in 
>>>> different CPU configurations.
>>>
>>> Can you elaborate, please? compiler/codegen/Test*Vect.java and 
>>> compiler/c2/cr6340864/Test*Vect.java tests do exercise Repl* AD instructions and I saw them 
>>> catching bugs while working on the patch.
>>
>> For example, you can run Test*Vect.java tests with your changes on machines which have or don't 
>> avx512. Or run with -XX:UseAVX=1, -XX:UseAVX=2 on AVX512 machine.
> 
> I ran aforementioned tests on a SKL host in the following modes:
>    * -XX:UseAVX=3
>    * -XX:UseAVX=3, but BW/DQ/VL are disabled (mimics KNL)
>    * -XX:UseAVX=2
>    * -XX:UseAVX=1
>    * -XX:UseAVX=0
>    * -XX:UseAVX=0 -XX:UseSSE=2
> 
> Test results are clean.
> 
> Additionally, I explicitly disabled AVX512VL and observed different assertion failures. All of the 
> failures (except one) are not related to the changes being proposed. So, that particular 
> configuration (+F/+BW/+DQ/.../-VL) is already broken. Filed JDK-8239331 [1].
> 
> Considering there's no such hardware exist (SKL and beyond all have VL and KNL doesn't have BW/DQ), 
> it hasn't been tested before.
> 
> I propose to proceed with the patch as it is now and do the cleanup (JDK-8239331) later.
> 
> Best regards,
> Vladimir Ivanov
> 
> [1] https://bugs.openjdk.java.net/browse/JDK-8239331
> 
>>>
>>> Best regards,
>>> Vladimir Ivanov
>>>
>>> [1]
>>> VEX.128.66.0F38.W0 78 /r
>>> VPBROADCASTB xmm1, xmm2/m8
>>> AVX2
>>>
>>> VEX.256.66.0F38.W0 78 /r
>>> VPBROADCASTB ymm1, xmm2/m8
>>> AVX2
>>>
>>> EVEX.128.66.0F38.W0 78 /r
>>> VPBROADCASTB xmm1{k1}{z}, xmm2/m8
>>> AVX512VL AVX512BW
>>>
>>> EVEX.256.66.0F38.W0 78 /r
>>> VPBROADCASTB ymm1{k1}{z}, xmm2/m8
>>> AVX512VL AVX512BW
>>>
>>> EVEX.512.66.0F38.W0 78 /r
>>> VPBROADCASTB zmm1{k1}{z}, xmm2/m8
>>> AVX512BW
>>>
>>> [2] http://hg.openjdk.java.net/jdk/jdk/file/tip/src/hotspot/cpu/x86/assembler_x86.cpp#l7881
>>>
>>> [3] http://hg.openjdk.java.net/jdk/jdk/file/tip/src/hotspot/cpu/x86/assembler_x86.cpp#l7078
>>>
>>>> On 2/13/20 7:55 AM, Vladimir Ivanov wrote:
>>>>> http://cr.openjdk.java.net/~vlivanov/8239008/webrev.00/
>>>>> https://bugs.openjdk.java.net/browse/JDK-8239008
>>>>>
>>>>> Simplify Replicate support for sub-word types on x86 based on the following observations:
>>>>>    * 512-bit vectors of sub-word element types are supported only on AVX512BW-capable hardware 
>>>>> [1];
>>>>>    * VBROADCASTS[SD]/VPBROADCAST[BWDQ] are available since AVX/AVX2.
>>>>>
>>>>> Also, fixed asserts in VBROADCASTS[SD] according to the manual:
>>>>>    * reg-to-reg variants are part of AVX2 (while mem-to-reg are introduced in AVX);
>>>>>    * VBROADCASTSD doesn't have 128-bit variant.
>>>>>
>>>>> Testing: hs-precheckin-comp,hs-tier1,hs-tier2
>>>>>
>>>>> Thanks!
>>>>>
>>>>> Best regards,
>>>>> Vladimir Ivanov
>>>>>
>>>>> [1] http://hg.openjdk.java.net/jdk/jdk/file/tip/src/hotspot/cpu/x86/x86.ad#l1524
>>>>>
>>>>> const int Matcher::vector_width_in_bytes(BasicType bt) {
>>>>> ...
>>>>>    if (UseAVX > 2 && (bt == T_BYTE || bt == T_SHORT || bt == T_CHAR))
>>>>>      size = (VM_Version::supports_avx512bw()) ? 64 : 32;