RFR: 8279282: [vectorapi] Matcher::supports_vector_comparison_unsigned is not needed on x86 [v3]

[Sandhya Viswanathan]

On Sun, 9 Jan 2022 01:48:04 GMT, Quan Anh Mai <duke at openjdk.java.net> wrote:

>> Hi,
>> 
>> Currently, unsigned comparison on AVX is implemented by zero extending elements and comparing the results. This leads to unnecessary complexity. This patch changes the implementation to use the identity existing in `Integer/Long.compareUnsigned`, that is `compareUnsigned(x, y) == compare(x ^ min_value, y ^ min_value)`.
>> 
>> Thank you very much.
>
> Quan Anh Mai has updated the pull request incrementally with one additional commit since the last revision:
> 
>   use movddup for 128-bit vectors

@merykitty Very good work. I have only one comment above.

src/hotspot/cpu/x86/macroAssembler_x86.cpp line 3254:

> 3252:     vpcmpCC(dst, nds, src, eq_cond_enc, width, vector_len);
> 3253:     vallones(xtmp, vector_len);
> 3254:     vpxor(dst, xtmp, dst, vector_len);

This would add extra overhead of doing vallones every time versus what we had before.

-------------

PR: https://git.openjdk.java.net/jdk/pull/6966