RFR: 8283726: x86_64 intrinsics for compareUnsigned method in Integer and Long [v3]

[Jatin Bhateja]

On Tue, 28 Jun 2022 12:42:57 GMT, Quan Anh Mai <duke at openjdk.org> wrote:

>> src/hotspot/cpu/x86/x86_64.ad line 13043:
>> 
>>> 13041:     __ cmpl($src1$$Register, $src2$$Register);
>>> 13042:     __ movl($dst$$Register, -1);
>>> 13043:     __ jccb(Assembler::below, done);
>> 
>> By placing compare adjacent to conditional jump in-order frontend can trigger macro-fusion. 
>> Kindly refer section 3.4.2.2 of Intel's optimization manual.
>
> I realised that by swapping the `mov` and the `cmp` instruction, the rule needs to have `dst` different from `src1` and `src2`, which increases register pressure.

I do not follow your comment, allocation decisions purely based on LRGs interferences and data flow attributes attached to operands and is agnostic to encoding block contents.

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PR: https://git.openjdk.org/jdk/pull/9068