RFR: 8328998: Encoding support for Intel APX extended general-purpose registers [v2]

[Vladimir Kozlov]

On Wed, 17 Apr 2024 00:44:09 GMT, Steve Dohrmann <duke at openjdk.org> wrote:

>> Got it - it is for few registers check now. What is common between rsp, r12, r20, r28 registers (except encoding)?
>> R12 is used for heap base in compressed oops  and RSP is RSP. What are r20 and r28? Why they can't be used in this addressing mode?
>> 
>> Please add comments for all lines where you replaced checks for `r*->encoding()` to say for which registers you do a check and why.
>
> The reason registers 12, 20, and 28 are asserted out of that else at line 668 is they are handled earlier in an else around line 646.
> 
> `    } else if ((base_enc & 0x7) == 4) {
>       // [rsp + disp]
> `
> 
> I added a comment to this effect and have also added comments in the 3 other places in the function where the replacement was done, indicating the registers involved.

Good.

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

PR Review Comment: https://git.openjdk.org/jdk/pull/18476#discussion_r1568121201