RFR: 8294729: [s390] Implement nmethod entry barriers

[Tyler Steele]

On Mon, 10 Oct 2022 09:18:47 GMT, Lutz Schmidt <lucy at openjdk.org> wrote:

>> I changed to the preferred test instruction. However, it seems like z_brnz won't work in this situation because the branch address is in a register and not a label.
>> 
>> Side note it too me a second to realize that I am using bcr and brnz is an alias for brc. It seems odd that there isn't a "speaking" alias for bcr (or maybe I'm just not finding it).
>
> You are right. There are no "speaking" aliases for brc. "Branch on Condition" is not used frequently in VM code. Therefore, nobody felt enough pain so far to define the aliases.
> May I please request you use the condition `Assembler::bcondNotZero`? `LTR` compares the register value against zero.

I'm happy to change bcondNotEqual -> bcondNotZero, especially since it seems to more clearly represent the intent. Thanks for the suggestion.

Out of curiosity: How are they different? You mentioned above that there are semantic differences between not equal and not zero, but in assembler_s390.hpp, it looks like bcondNotZero is actually an alias for bcondNotEqual.

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PR: https://git.openjdk.org/jdk/pull/10558