RFR(S): Vector popcount support

[Vladimir Kozlov]

Hi Razvan,

In general changes are good. Do you plans to add vpopcntb,w too?

Use 'supports' with 's' in name as in other support functions names:
supports_avx512_vpopcntdq()

Also why use avx512 in function name? I know it is CPUID bit name. But 
do you have other vpopcntdq instructions, not avx512?

In assembler_x86.cpp and other places you don't need to check UseAVX, 
support_avx512_vpopcntdq() is enough. You can clear feature bit in 
vm_version_x86.cpp when AVX < 3:

   if (UseAVX < 3) {
     _features &= ~CPU_AVX512F;
     _features &= ~CPU_AVX512DQ;
     _features &= ~CPU_AVX512CD;
     _features &= ~CPU_AVX512BW;
     _features &= ~CPU_AVX512VL;
+   _features &= ~CPU_AVX512_VPOPCNTDQ;
   }

In x86.ad you forgot to add length check in predicate() like next:

instruct vadd2I_reg(vecD dst, vecD src1, vecD src2) %{
   predicate(UseAVX > 0 && n->as_Vector()->length() == 2);

And, please, add code generation test to 
test/hotspot/jtreg/compiler/vectorization/ tests to verify correctness 
of vector operations.

Thanks,
Vladimir

On 3/9/18 2:54 PM, Lupusoru, Razvan A wrote:
> Hi everyone,
> 
> As per “Intel Architecture Instruction Set Extensions and Future 
> Features Programming Reference” manual [1], vector popcount instruction 
> will be supported in future Intel ISA. I have updated the superword 
> vectorizer to take advantage of this instruction. I have tested with 
> Intel SDE [2] to confirm encoding and semantics are correctly 
> implemented. Please take a look and let me know if you have any 
> questions or comments.
> 
> http://cr.openjdk.java.net/~rlupusoru/jdk_hs/webrev_vpopcount_01/index.html
> 
> Thanks,
> 
> Razvan
> 
> [1] 
> https://software.intel.com/sites/default/files/managed/c5/15/architecture-instruction-set-extensions-programming-reference.pdf
> 
> [2] 
> https://software.intel.com/en-us/articles/intel-software-development-emulator
> 
> [3] https://bugs.openjdk.java.net/browse/JDK-8199421
>