RFR: 8282182: Document algorithm used to encode aarch64 logical immediate operands. [v2]

[Andrew Dinn]

On Mon, 21 Feb 2022 11:13:50 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Andrew Dinn has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - more logical flow to explanation
>>  - address initial reviewer feedback
>
> src/hotspot/cpu/aarch64/immediate_aarch64.cpp line 216:
> 
>> 214: // ensures that an all 0s or all 1s bit pattern is never generated.
>> 215: //
>> 216: // bit field construction:
> 
> The flow in this section is odd. I think the text should flow as: "This is what we intend to do; this is how we construct it is done; this is the example of the generated output; given all above; here are the invariants that are enforced".

Yeah, I agree, only I found it tricky to describe the algorithm without describing the constraints that determine how it proceeds. I have pushed a revised version to address that.

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PR: https://git.openjdk.java.net/jdk/pull/7536