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

[Vladimir Ivanov]

>>> 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;