RFR: JDK-8287288: Fix some typos in C1

[Dean Long]

On Thu, 26 May 2022 03:36:11 GMT, Zhuojun Miao <zmiao at openjdk.org> wrote:

>> I was reading:
>> 
>> enum OprBits {
>>       pointer_bits   = 1
>>     , kind_bits      = 3
>>     , type_bits      = 4
>>     , size_bits      = 2
>>     , destroys_bits  = 1
>> 
>> as a bitfield description so 1 pointer bit followed by 3 kind bits, followed by 4 type bits etc. But I agree the later mask value only does a shift of 3 not 4.
>> 
>> Also the code indicates there are a lot more non-data bits before we get to the data so the diagram is incomplete in other ways.
>
> I don't think `pointer_bits` should be added to `non_data_bits`:
> 
> 
>     , non_data_bits  = pointer_bits + kind_bits + type_bits + size_bits + destroys_bits + virtual_bits
>                        + is_xmm_bits + last_use_bits + is_fpu_stack_offset_bits
>     , data_bits      = BitsPerInt - non_data_bits
>     , reg_bits       = data_bits / 2      // for two registers in one value encoding

I agree.  This was changed as part of JDK-8261235.
@chhagedorn, I think there must be a different issue with vreg_max in JDK-8261235.  I wounder if it should be using reg_bits instead of data_bits.

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PR: https://git.openjdk.java.net/jdk/pull/8880