RFR: 8281375: Accelerate bitCount operation for AVX2 and AVX512 target. [v2]

[Jatin Bhateja]

On Thu, 10 Feb 2022 06:19:52 GMT, Quan Anh Mai <duke at openjdk.java.net> wrote:

> We recently have [JDK-8278947](https://bugs.openjdk.java.net/browse/JDK-8278947) for this. With some adjustment you can ask for alignment of the constant, too. Thanks.

- Emitting 64 byte constants may prove to be costly, given that code-size of a native method used while taking in-lining decisions takes constant table size into consideration,  also X86 instructions are variable sized (1-15 bytes) hence rematerializing constants using couple of instructions may be efficient in terms of both code size and latency. Given that loading a 64 byte constant not aligned to 64 byte address boundary may  span across multiple cache lines.
- But we can evaluate and consider extensions done by your patch separately.

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PR: https://git.openjdk.java.net/jdk/pull/7373